CO2 EE-00100-CO2-002

56
30621127-000-3BD-EE-00100-CO2 REV 002 1 of 56

Transcript of CO2 EE-00100-CO2-002

Page 1: CO2 EE-00100-CO2-002

30621127-000-3BD-EE-00100-CO2 REV 002

1 of 56

Page 2: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

DOCUMENT NO. EE-00100-CO2

QURAYYAH COMBINED CYCLE PLANT

CARBON DIOXIDE SYSTEM DESCRIPTION

Revision Date Purpose Prepared Reviewed Approved 000 14 May 10 Issued For Approval AJM KB PMK 001 21 Sep 10 Issued For Approval AJM KB PMK 002 25 Apr 11 Issued For Approval AJM KB SSG

30621127-000-3BD-EE-00100-CO2 REV 002

2 of 56

Page 3: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

1. CARBON DIOXIDE SYSTEM

1.1 System Function

The carbon dioxide system is required to supply carbon dioxide for the purging of air and hydrogen from the main generators prior to the filling of hydrogen and subsequent shutdown respectively. The Generator has a large open volume internally. This volume contains hydrogen during normal operation. It contains air during maintenance outages. An inert gas is put into the generator volume as an intermediate gas so that air and hydrogen do not mix inside the generator casing. Carbon dioxide gas is used as the inert gas because it has a substantially higher density and lower thermal conductivity compared to hydrogen or air. For detailed P&ID of Carbon dioxide (CO2 ) System refer to Dwg. No. EA-682813.

1.2 General Description

General

Purging of generator is carried out to remove the hydrogen gas prior to a maintenance activity. This results in effective inerting the generator. Prior to personnel working inside the generator, the CO2 gas must be purged with instrument air. The second instance a CO2 purge is performed after the generator has been opened up and maintenance has been completed. In this case CO2 is used to purge the generator cavity of air prior to refilling with hydrogen gas. The substantially different properties are used by the gas analyzer (inside the hydrogen cabinet) so that gas concentration during purging can be monitored. The carbon dioxide is supplied from a centralized carbon dioxide storage where carbon dioxide gas is stored in dip tube type cylinder. Open cycle loose carbon dioxide cylinder that are located in CO2 & N2 shelter of Project-B (Item no# 42 in site layout) will be relocated in centralized carbon dioxide gas storage shelter (Item#233 in Site layout) of Project-C. CO2 gas from centralized storage is supplied to both open cycle and combined cycle generators for purging.

Combined Cycle carbon dioxide cylinder manifolds are arranged in five groups with each group having dual redundant headers to facilitate removal and replacement of cylinders on one manifold whilst the other manifold is in use. CO2 cylinder are kept in racks with each rack consisting of 16 cylinders.

Open Cycle carbon dioxide bottles are also kept in racks with each rack consisting of 16 cylinders. Open cycle carbon dioxide cylinder manifolds are arranged in ten (10) groups with each group having dual redundant headers to facilitate removal and replacement of cylinders on one manifold whilst the other manifold is in use, similar to combined cycle.

002

30621127-000-3BD-EE-00100-CO2 REV 002

3 of 56

Page 4: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

The redundant header of each rack is connected to redundant main header (C00-025-QJK-011-Q0605,C00-025-QJK-012-Q0605) and these redundant main headers are connected to redundant streams each of them provided with a waterbath heater (C00-QJK-50-AC-001/002).Downstream of waterbath heater, redundant central pressure reduction station (CPRS) (C00-QJK-50-AA-081/082) are provided. From CPRS, CO2 gas is supplied to STG area pressure reducing stations (two STG PRS - one (C00-QJK-50-AA-084) for STG block#1,2,3 and other (C00-QJK-50-AA-083) for STG block 4,5 & 6 (future)) from where CO2 is supplied to Generator Gas Control Station of individual steam turbine generators at required pressure.

A low pressure side interconnection is provided from combined cycle header to open cycle enabling supply of CO2 gas supply to Open cycle Gas turbines. Interconnection is provided from downstream of central pressure reducing station (CPRS) and extended to GTG area. Pressure reducing stations (PRS) (C10/20/30/40/50-QJK-50-AA-081) are provided at GTG area (One PRS for each block GTGs) to supply CO2 gas to generator at required pressure. Each GTG area PRS has one orifice in bypass header .A spool pipe with a NRV is added at low pressure side of open cycle CO2 piping. before flow transmitter on pipeline connecting to GE terminal point LE002. QCPP interconnection pipe is connected to this spool pipe (after NRV).

At each main header a safety relief valve (C00-WJK-50-AA-195/196) is provided to protect the system from overpressure.

Carbon dioxide system consist of following major components /equipments

• Five (5) banks of QCCPP Carbon dioxide dip tube type cylinder for generator purging. Each bank consists of 40 cylinders.

• Two (2 x 100%) capacity waterbath heaters (C00-QJK-50-AC-001/002)

• One (1) redundant pressure reducing stream (C00-QJK-50-AA-081/082) to supply carbon dioxide gas to the generator terminal point at the pressure required for STG / GTG.

• Two (2) redundant pressure reducing station (C00-QJK-50-AA-083/084) for STG area is provided to supply CO2 to STG at required pressure. Each pressure reducing stream is having orifice (C00-QJK-50-BP-001/002 respectively) in bypass header.

• Five (5) Pressure Reducing station (C10/20/30/40/50-QJK-50-AA-081), one (1) for each block GTGs is provided to supply CO2 to GTG at required Pressure. Each pressure reducing stream is having orifice (C10/20/30/40/50-QJK-50-BP-001 respectively).

• Ten (10) banks of QCCPP Carbon dioxide dip tube type cylinder for generator purging. Nine (9) banks consist of 40 cylinders and One(1) bank consists of 30 cylinders.

002

002

30621127-000-3BD-EE-00100-CO2 REV 002

4 of 56

Page 5: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

1.2.1 Carbon dioxide cylinder and storage racks

Carbon dioxide cylinders of dip tube type will be stored in a storage rack. The cylinders are segregated in storage rack separately for STG purging & open cycle purging. Number of carbon dioxide cylinder is estimated considering three (3) air and three (3) hydrogen purging for each of the five (5) steam turbine generators. Additionally 5% margin is provided to cover leakages. Total 200 cylinders (40 per block) in are kept at central CO2 storage in racks consisting of 16 cylinders each. Total 390 Open cycle cylinders are relocated to central CO2 storage and are kept in racks of 16 cylinders each Number of QCPP cylinder racks - 13 Number of OCPP cylinder racks - 25 Carbon dioxide gas will be supplied from centralized storage shelter (item#233 in Site layout) with dual manifold arrangement to facilitate removal and replacement of cylinders on one manifold whilst the other manifold is in use.

1.2.2 Electrically heated waterbath type evaporators (C00-QJK-50-AC-001/002) with temperature gauges, alarms, thermostats and water level gauges.

1.2.3 Central Pressure reducing station, consisting of one self regulating pressure reducing valve (in each header) reduces the carbon dioxide gas pressure to required pressure suitable for distribution to the generator.

1.2.4 STG and GTG area pressure reducing station consist of one self regulating pressure reducing valve which reduces pressure to required pressure suitable for distribution to the generator. A ball valve along with orifice is provided in bypass line.

Carbon dioxide gas is supplied from storage at 74 barg and pressure is reduced to 11 barg at central pressure reduction stage. Further pressure is reduced to 8.62 barg (required pressure at Generator) at STG and GTG area PRV stations.

1.2.5 Relief valves are located downstream of pressure-regulating valves to protect the system from overpressure. Vents of relief valve will be routed to safe height approximately 1 m above the building/facility.

1.2.6 Piping is designed per ANSI/ASME B31.1, Power Piping.

1.2.7 Generator purging requirement and interconnecting piping between STG modules are as per STG Supplier recommendations.

Low pressure side interconnection is provided between combined cycle and open cycle.

30621127-000-3BD-EE-00100-CO2 REV 002

5 of 56

Page 6: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

pipe sizing of pipe line up to interconnection junction point is sized considering six(6) generator (5 STG+1GTG) simultaneously at any point of time.

CO2 Consumption data

Total Carbon Dioxide (CO2) gas required for air and hydrogen purge for each generator (at STP condition)

247 m3

The carbon dioxide gas is stored in cylinder at central storage area. From the storage unit, CO2 will be supplied to combined cycle steam generator terminal point and open cycle CO2 gas supply low pressure side (interconnection junction) at 8.62 barg.

See GE’s product literature (Attachment 1.11.2) for details of carbon dioxide operating pressure range for each generator design.

1.3 System Operation

Normal Operation

The operation of the system is manual and as required by the generator manufacturer’s operating instructions. Carbon dioxide gas flows from the centralized bulk storage through watebath heater and Pressure reducing station (PRS) for distribution to respective generators at required pressure, i.e., 8.62 barg

One local control panel will be supplied by Vendor for operation, control and monitoring of waterbath heaters.

30621127-000-3BD-EE-00100-CO2 REV 002

6 of 56

Page 7: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

Abnormal Operation

In case CO2 Gas is being supplied from bottles and sufficient pressure is not available downstream of CPRS, low pressure alarm is provided.

In case CO2 Gas is being supplied from bottles and high pressure is available downstream of CPRS, High pressure alarm is provided.

In case CO2 Gas is being supplied from bottles and sufficient pressure is not available downstream of STG pressure reducing station, low pressure alarm is provided.

In case CO2 Gas is being supplied from bottles and high pressure is available downstream of STG pressure reducing station,high pressure alarm is provided.

In case CO2 Gas is being supplied from bottles and sufficient pressure is not available at open cycle supply header, low pressure alarm is provided.

In case CO2 Gas is being supplied from bottles and high pressure is available at open cycle supply header, High pressure alarm is provided.

High and low temperature alarm provision is provided at downstream of CPRS.

Start-up Operation

None

Shutdown Operation

None

1.4 Interlock & Protection:

None 1.5 Major Controls

None

1.6 Instrumentation Description

Instrumentation & Measurement Process

Pressure Transmitter (C00-QJK-50-CP-013/014) at main header in CO2 shelter, is provided for indication of header pressure in the DCS .

Pressure Transmitter (C00-QJK-50-CP-001) downstream of waterbath heater and upstream of CPRS, is provided for indication of header pressure in the DCS .

30621127-000-3BD-EE-00100-CO2 REV 002

7 of 56

Page 8: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

Pressure Transmitter (C00-QJK-50-CP-007) downstream of CPRS, is provided for indication of header pressure in the DCS and high pressure alarm and low pressure alarm in the DCS.

Pressure Transmitter (C00-QJK-50-CP-010) downstream of CPRS at interconnection header, is provided for indication of header pressure in the DCS and high pressure alarm and low pressure alarm in the DCS.

Pressure Transmitter (C00-QJK-50-CP-011/012) downstream of STG PRS, is provided for indication of STG supply header pressure in the DCS and high and low pressure alarm in the DCS.

Temperature Element (C00-QJK-50-CT-004) downstream of CPRS, is provided for indication in the DCS and high and low temperature alarm in the DCS.

Temperature indicator (C00-QJK-50-CT-502) downstream of CPRS is provided

Local Pressure Gauges (C00-QJK-50-CP-508, C00-QJK-50-CP-509) at redundant main header (C00-025-QJK-012/011-Q0605 respectively)

Local Pressure Gauges (C00-QJK-50-CP-502, C00-QJK-50-CP-505) upstream of PRV-A, PRV-B respectively are provided.

Local Pressure Gauges (C00-QJK-50-CP-503, C00-QJK-50-CP-506) downstream of PRV-A, PRV-B respectively are provided.

Local Pressure Gauges (C11-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -1 of block-1

Local Pressure Gauges (C12-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -2 of block-1

Local Pressure Gauges (C13-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -3 of block-1

Local Pressure Gauges (C21-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -1 of block-2

Local Pressure Gauges (C22-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -2 of block-2

Local Pressure Gauges (C23-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -3 of block-2

Local Pressure Gauges (C31-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -1 of block-3

Local Pressure Gauges (C32-QJK-50-CP-501) at interconnection to OCPP CO2 system

30621127-000-3BD-EE-00100-CO2 REV 002

8 of 56

Page 9: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

low pressure side for generator -2 of block-3

Local Pressure Gauges (C33-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -3 of block-3

Local Pressure Gauges (C41-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -1 of block-4

Local Pressure Gauges (C42-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -2 of block-4

Local Pressure Gauges (C43-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -3 of block-4

Local Pressure Gauges (C51-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -1 of block-5

Local Pressure Gauges (C52-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -2 of block-5

Local Pressure Gauges (C53-QJK-50-CP-501) at interconnection to OCPP CO2 system low pressure side for generator -3 of block-5

Valves

Self regulating Pressure Reduction valves (C00-QJK-50-AA-081 and C00-QJK-50-AA-082) at central pressure reducing station to reduce the downstream pressure to 11 bar(g). Self regulating Pressure Reduction valves (C00-QJK-50-AA-083 and C00-QJK-50-AA-084) at STG area pressure reducing station to reduce the downstream pressure to 8.62 bar(g). Self regulating Pressure Reduction valves (C10-QJK-50-AA-081,C20-QJK-50-AA-082,C30-QJK-50-AA-083,C40-QJK-50-AA-084,C50-QJK-50-AA-085) at GTG area pressure reducing station to reduce the downstream pressure to 8.62 bar(g).

1.7 Design operating parameters

Design pressure & Design Temperature of Carbon Dioxide system piping is as follows,

Description Design Pressure (barg)

Design Temperature

(Deg C)

PDT

From Centralized Carbon Dioxide storage to waterbath heater

88.8 60 QCC 0605

From waterbath heater to centralized storage.

85.50 60 QCC 0605

30621127-000-3BD-EE-00100-CO2 REV 002

9 of 56

Page 10: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

Description Design Pressure

(barg) Design

Temperature (Deg C)

PDT

From Centralized Carbon Dioxide storage STG Pressure reducing station

13.20 60 QCC 0105

From STG Pressure Reducing Station to Generator Terminal Point

10.344 60 QCC 0105

From Centralized Carbon Dioxide storage GTG Pressure reducing station

13.20 60 QCC 0105

From GTG Pressure Reducing Station to OCPP low pressure side

10.344 60 QCC 0105

1.8 Technical Particulars

For Generator purging

Item No Description Units Particulars

1. Number of CO2 cylinders per generator

Number 40

2. Number of generator Number 5 3. Total number of CO2 cylinders for

generators Number 200

4. Capacity of CO2 dip tube type cylinder

Kg 45

5. Useable CO2 within dip tube type cylinder (80%)

kg 36.29

6. Gas pressure in CO2 dip tube type cylinder

barg 74

7. Design temperature Dec C 50

Waterbath Heaters

Item No Description Units Particulars

1. Number of waterbath heaters Number 2 2. Flow Capacity of waterbath heater Scfm 720 3. Maximum operating Temperature of Deg C 57.22

30621127-000-3BD-EE-00100-CO2 REV 002

10 of 56

Page 11: CO2 EE-00100-CO2-002

12620-001 QURAYYAH COMBINED CYCLE PLANT

Sargent & Lundy LLC SYSTEM DESCRIPTION DOCUMENT NO. EE-00100-CO2

carbon dioxide gas at the outlet of waterbath heater

4. Pressure Drop across waterbath heater

Bar 2.5

1.9 Standards

The standards listed below are the design codes used for design and construction of the Industrial gases system. American National Standards Institute (ANSI)

ANSI/ASME B31.1 Power Piping ANSI B16.5 Pipe Flanges and Flanged Fittings ANSI B16.9 Factory Made Wrought Steel Butt welding Fittings ANSI B16.11 Forged Fittings, Socket Welded and Threaded ANSI B16.34 Valves Flanged, Threaded, and Welding End ANSI B36.10 Welded and Seamless Wrought Steel Pipe

American Society for Testing Materials (ASTM)

ASTM A105 Forgings, Carbon Steel, for Piping Components ASTM A106 Seamless Carbon Steel Pipe for High Temperature Service ASTM A216 Steel Castings, Carbon Suitable for Fusion Welding for High

Temperature Service 1.10 Drawings

EA-682813 Piping & Instrumentation Diagram – Carbon Dioxide System EE-00045 Calculation for Carbon dioxide Plant Capacity EE-00037B Pipe Sizing Calculation for Carbon dioxide System EA-682700 General Arrangement Site Development EA-682909 General Arrangement STG CO2 Shelter GEK 103763d Hydrogen and Carbon dioxide Control System for Non

Packaged Units 357A2258 Generator Gas System Installation Design Specification EE-01655 Generator P&ID ED-680427 CO2 system logics

1.11 Attachment

1.11.1 Chemtron High Pressure CO2 purging system Drawing D54946

1.11.2 GEK 103763d - Hydrogen and Carbon dioxide Control System for Non Packaged Units.

30621127-000-3BD-EE-00100-CO2 REV 002

11 of 56

Page 12: CO2 EE-00100-CO2-002

Fire S

ystems

30621127-000-3BD-EE-00100-CO2 REV 002

12 of 56

DCAD12
Line
DCAD12
Line
DCAD12
Line
DCAD12
Text Box
Interconnection form CCPP CO2 System Low Pressure Side
AJMSNL
Text Box
Attachment 1.11.1
Page 13: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units

Operation and Maintenance Instructions

These instructions do not purport to cover all details or variations in equipment nor to provide for every possiblecontingency to be met in connection with installation, operation or maintenance. Should further information bedesired or should particular problems arise which are not covered suf�ciently for the purchaser’s purposes thematter should be referred to the GE Company.© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

GEK 103763dRevised August 2008

GE Energy

30621127-000-3BD-EE-00100-CO2 REV 002

13 of 56

AJMSNL
Text Box
ATTACHMENT 1.11.2
Page 14: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

The below will be found throughout this publication. It is important that the signi�cance of each is thoroughlyunderstood by those using this document. The de�nitions are as follows:

NOTE

Highlights an essential element of a procedure to assure correctness.

CAUTION

Indicates a potentially hazardous situation, which, if not avoided, could result inminor or moderate injury or equipment damage.

WARNING

INDICATES A POTENTIALLY HAZARDOUS SITUATION,WHICH, IF NOT AVOIDED, COULD RESULT IN DEATH ORSERIOUS INJURY

***DANGER***

INDICATES AN IMMINENTLY HAZARDOUS SITUA-TION, WHICH, IF NOT AVOIDED WILL RESULT INDEATH OR SERIOUS INJURY.

2 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

14 of 56

Page 15: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

TABLE OF CONTENTS

I. GENERAL DESCRIPTION ......................................................................................................... 5A. Why Hydrogen ......................................................................................................................... 5B. Explosion Hazard ..................................................................................................................... 5C. Inert Intermediate Gas.............................................................................................................. 5D. Essential Parts of the Gas Control System............................................................................... 5E. Gas Storage .............................................................................................................................. 8F. Gas Valve Station ..................................................................................................................... 8

II. WARNINGS CONCERNING THE USE OF HYDROGEN...................................................... 8A. General Rules for Safe Handling of Hydrogen ........................................................................ 8B. Unknown Contaminant is Assumed to be Air.......................................................................... 8C. Rules for Safe Handling of Hydrogen...................................................................................... 9D. Maintenance on Hydrogen Equipment..................................................................................... 9E. Hydrogen Zone......................................................................................................................... 9

III. GENERAL DESCRIPTION OF THE GAS CONTROL SYSTEM ......................................... 10A. The Rotor Fan .......................................................................................................................... 10B. CO2 as Intermediate Gas.......................................................................................................... 10C. Distribution Pipes..................................................................................................................... 10D. Gas Control Valves................................................................................................................... 10E. Casing Liquid Detector ............................................................................................................ 10F. Shaft Sealing ............................................................................................................................ 11G. Seal Oil Draining...................................................................................................................... 11H. Oil De�ectors ........................................................................................................................... 11I. Gas Flow Between Cavities ..................................................................................................... 11J. Scavenging to Retain H2 Purity in the End Cavities................................................................ 11K. Vacuum Seal Oil Systems ........................................................................................................ 16L. Gas Purity Monitoring.............................................................................................................. 16

IV. GAS CONTROL VALVE EQUIPMENT .................................................................................... 16A. Features of the Gas Control Valve Assembly .......................................................................... 16B. Features of Bottle Manifolds.................................................................................................... 19C. Features in the Gas System Piping........................................................................................... 19D. Features of the Liquid Detector Assembly............................................................................... 19

V. OPERATION.................................................................................................................................. 19A. Operator Activities Start Up / Shut Down ............................................................................... 19B. Generator Gas Purging and Normal Operation ........................................................................ 21C. Setting the Scavenging Flow Rates.......................................................................................... 27D. Operating the Generator at Full Speed with Air Inside............................................................ 28

VI. ALARM RESPONSES .................................................................................................................. 30A. Low-Low and Low Generator Gas Purity Alarms................................................................... 30B. Generator Gas Temperature High ............................................................................................ 31C. Generator Gas Pressure High ................................................................................................... 31D. Generator Gas Pressure Low.................................................................................................... 32E. Hydrogen Supply Pressure Low............................................................................................... 32F. Liquid Detection....................................................................................................................... 32

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 3

30621127-000-3BD-EE-00100-CO2 REV 002

15 of 56

Page 16: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

VII. MAINTENANCE........................................................................................................................... 34A. Leak Testing ............................................................................................................................. 34B. Regular Maintenance ............................................................................................................... 34C. Special Maintenance ................................................................................................................ 35D. If the Hydrogen Control Cabinet is Flooded with Oil or Water............................................... 36E. Materials and Design Conditions ............................................................................................. 36

VIII. OPERATION AND DESIGN REQUIREMENTS FOR THE H2 AND CO2 GAS SUP-PLIES .............................................................................................................................................. 37A. Requirements on Gas used in the Generator ............................................................................ 37B. Characteristics of Compressed Gas.......................................................................................... 38C. Carbon Dioxide in Pipes and Valves........................................................................................ 40D. Sizing the Carbon Dioxide Flow Ori�ce.................................................................................. 41E. The Hydrogen Flow Ori�ce ..................................................................................................... 42F. Sizing the Manifold Pressure Regulator Valves....................................................................... 42G. Calculating the Quantity of CO2 Bottles Required to Purge a Generator................................ 42H. Calculating the Quantity of H2 Bottles to Purge and Fill the Generator.................................. 43

LIST OF FIGURES

Figure 1. Represents a typical generator gas control system with all possible accessories .................... 7Figure 2. Gas Control Valve Assembly ................................................................................................... 13Figure 3. H2 or CO2 Bottle Manifold ...................................................................................................... 14Figure 4. Liquid Level Detector Assembly ............................................................................................. 15

LIST OF TABLES

Table 1. Purge Activity Parameters....................................................................................................... 23

4 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

16 of 56

Page 17: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

I. GENERAL DESCRIPTION

This manual provides operation and maintenance instructions for the H2/CO2 piping and other equipmentwhich is external to the generator. This manual applies to unpackaged generators. Such generators are allgenerators with water cooled stators, all 390H generators, all hydrogen cooled Leads Down generators, and324 Leads Up generators.

A. Why Hydrogen

The generator interior components are cooled by convection whereby a gas transports heat to the gen-erator gas/water heat exchanger. Generator windage losses are greatly reduced with hydrogen ratherthan air as the gas inside the generator because hydrogen has a lower density. In addition, compared toair, hydrogen has greater thermal conductivity and convection coef�cients. The generator gas thermalcapacity is further increased by the use of pressurized hydrogen. The sealed environment necessary tocontain hydrogen has the secondary bene�t of keeping the generator parts clean.

Also, hydrogen, rather than air, greatly reduces armature insulation deterioration caused by corona.

B. Explosion Hazard

Hydrogen must be handled carefully to prevent catastrophic oxidation. The gas control valves providea means for safely handling hydrogen.

C. Inert Intermediate Gas

An inert gas, carbon dioxide, is used as an intermediate gas so that air and hydrogen do not mix insidethe generator. The purging procedure for the generator has carbon dioxide introduced to displace theair, then hydrogen introduced to displace the carbon dioxide. The generator is then pressurized withhydrogen and the pressure is maintained automatically with a control valve. The generator may remainpressurized with hydrogen during short outages even if the shaft is not on turning gear. Prior to openingthe generator for maintenance, the hydrogen is depressurized, and then carbon dioxide is introduced todisplace the hydrogen. Air is then introduced to displace the carbon dioxide, and the end shields can beopened. During an emergency it is important to at least purge the generator of hydrogen by introducingcarbon dioxide.

Gas control during the purge operations is performed manually at the gas control valve station.

D. Essential Parts of the Gas Control System

The gas control system has these primary parts:

Generator, with gas piping connections

Gas Piping with Valving

Gas Control Valve Assembly

Hydrogen Control Cabinet, primarily for gas purity analysis

Hydrogen Gas Storage

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 5

30621127-000-3BD-EE-00100-CO2 REV 002

17 of 56

Page 18: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

Carbon Dioxide Gas Storage

Liquid Level Detectors

6 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

18 of 56

Page 19: CO2 EE-00100-CO2-002

Hydrogen

andC

arbonD

ioxideG

asC

ontrolSystemforN

onPackaged

Units

GEK

103763d

Fi gure1.R

epresentsatypicalgenerator

gascontrolsystemwith

allpossibleaccessories

©GeneralElectric

Company,2008.G

EProprietary

Information.A

llRightsR

eserved.7

30621127-000-3BD-EE-00100-CO2 REV 002

19 of 56

Page 20: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

E. Gas Storage

The source of the hydrogen or carbon dioxide is out of the scope of the equipment provided with thegenerator. Some power plants have bulk supply systems, some use bottle manifolds, other have acombination of the two systems. GE does offer bottle manifolds if requested by the customer, and forthose facilities which use those manifolds, instructions are provided in this document.

The bottle manifolds for CO2or for H2may or may not be located near the gas control valves, dependingon the design of the facility.

F. Gas Valve Station

The gas control valves are located in the gas control valve station of the power plant. It is good to placethe gas dryer (if there is one), liquid level detectors, seal oil drain �oat trap and other equipment inthe vicinity of the gas control valves to reduce the number of hydrogen zones in the power plant. Thehydrogen control cabinet, or a generator gas purity display, or other means of monitoring hydrogenpurity should be available at the gas control valve station.

II. WARNINGS CONCERNING THE USE OF HYDROGEN

Hydrogen and air form a highly explosive mixture if concentrations are between 4.1% and 74.2% hydrogenby volume in air.

When completely assembled and operated in the proper manner, the generator casing, which forms thehydrogen container, is a gas tight enclosure. In the very unlikely event of an explosion, the casing is strongenough to limit the destructive effect to the generator casing and the enclosed parts.

A. General Rules for Safe Handling of Hydrogen

Precautions must be taken to safeguard against a hydrogen explosion.

1. Never permit an explosive mixture to exist.

2. Eliminate any possible source of ignition.

B. Unknown Contaminant is Assumed to be Air

Any unknown contaminant in the hydrogen gas shall be assumed to be air. The exception is that ifthe hydrogen is supplied directly from a hydrogen generation device, which derives the hydrogen fromsplitting water to hydrogen and oxygen, then the policy may be to assume that any unknown con-taminant will be assumed to be pure oxygen. Hydrogen and oxygen form an explosive mixture withapproximately 96% hydrogen (4% oxygen) by volume.

During the carbon dioxide purge the contaminant is known to be carbon dioxide. If the seal oil is notbeing vacuum treated and the seal oil system is operating normally, the contaminant may be assumedto be air. At any other time, the contaminant is not known and shall be assumed to be air except asnoted immediately above.

8 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

20 of 56

Page 21: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

C. Rules for Safe Handling of Hydrogen

The procedure for purging the generator is designed to prevent explosivemixtures. The purging steps ofremoving spool pieces, disconnecting bottles, and disconnecting the air supply must be strictly adheredto. In addition

1. Do not have a permanent air supply connected to the generator, the hydrogen control cabinet, orany other device connected to the generator or gas piping. This practice prevents the possibility ofan explosive mixture inside the generator due to operator error or valve leakage.

2. The generator and all piping must be pressure tested with air or CO2 for leaks prior to pressurizingthe generator with hydrogen.

3. Hydrogen pressure inside the generator must always be higher than ambient to prevent air fromleaking in. If automatic controls are inoperative, the operator must manually maintain pressure.Additionally, the seal oil systems requires a casing pressure of 2 psig minimum to drain correctlyfrom the seal drain enlargement tank to the bearing drain enlargement tank. Please note that the�oat trap will have to be bypassed until a casing pressure of 15 psig has been attained.

4. No welding may be done on the gas system or seal oil system while there is hydrogen in the gen-erator.

5. The hydrogen is sealed at the shaft to casing interface by oil �lm seals. The operator must befamiliar with the shaft seal oil system prior to operating the generator gas system.

6. Avoid having high pressure hydrogen escape to the room because it can ignite itself due to selfgenerated static charges.

7. Hydrogen �ame is nearly invisible. If an operator suspects hydrogen is escaping into the work areaand desires to feel for a gas escape �ow, he should not use his hand or anything combustible, suchas clothing.

D. Maintenance on Hydrogen Equipment

Components of the gas control system, which are intended for maintenance while the generator is pres-surized, are listed in a later section. Prior to maintenance, the operator should use, if available, twovalves rather than only one to isolate the work area from high pressure hydrogen. Also, prior to openinga joint in a gas line, the operator should use, if available, a vent valve to depressurize the equipment.Some components might not have the vent valve or the second set of isolation valves close to the worksite.

E. Hydrogen Zone

Electrical equipment in the vicinity of joints in hydrogen piping should not be sources of ignition.The local or national codes pertaining to explosive atmospheres vary, and should be investigated ifthe operator is suspicious of potentially sparking electrical equipment located in the vicinity of thehydrogen equipment.

As a minimum, a Division 2 (or Zone 2) H2 atmosphere extends for 1.2 meters for 5 psig to 60 psig(35 to 414 kPa–g, 0.352 to 4.22 kg/cm2) piping and 1.8 meters for 75 psig to 150 psig (517 to 1034kPa–g, 5.27 to 10.55 kg/cm2) piping. It extends down 0.2 meters and up 4.2 meters. Potential small

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 9

30621127-000-3BD-EE-00100-CO2 REV 002

21 of 56

Page 22: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

leak sites are non–welded joints in piping, including �anges, valves, threaded joints, and O–rings andcompression �ttings. The extent of the explosive atmosphere does not penetrate walls or other similarbarriers. Each piece of electrical equipment in the explosive atmosphere should have one of the fol-lowing: explosion proof housing with conduit or cable sealing, intrinsically safe circuit, hermeticallysealed contacts, non–sparking components, non–incendive circuit, forced ventilation from a non–con-taminated air source, or purging with pressurization.

III. GENERAL DESCRIPTION OF THE GAS CONTROL SYSTEM

A. The Rotor Fan

The generator gas is circulated inside the generator by a fan on each end of the rotor. The fan cre-ates a differential pressure of several inches of water. The fan blown hydrogen cools the generatorrotor windings, armature windings (unless these are separately cooled by water), and armature magnetlaminates. The fan blown hydrogen also is forced through a cooler, where it loses the heat it pickedup from cooling the generator electro–magnetic components. The fan differential pressure is used byexternal gas system components, which require a small �ow rate and need to return the gas to the gener-ator. Examples of possible equipment are (not necessarily supplied with every generator): gas dryers,over–heating particle detectors, and gas analyzers.

B. CO2 as Intermediate Gas

The generator has a large open volume internally (1000 cubic feet (30 m3) or more). This volumecontains hydrogen during normal operation. It contains air during maintenance outages. An inert gasis put into the generator volume as an intermediate gas so that air and hydrogen do not mix inside thecasing. Carbon dioxide is used as the inert gas because it has a substantially higher density and lowerthermal conductivity compared to hydrogen or air. The substantially different properties are used by thegas analyzer (inside the hydrogen cabinet) so that gas concentrations during purging can be monitored.

C. Distribution Pipes

Along the top of the generator interior is a long pipe with holes, which acts as a manifold for admittinghydrogen. Similarly, along the bottom of the generator interior is a long pipe with holes for admittingcarbon dioxide. These are called the hydrogen distribution pipe and the carbon dioxide distributionpipe, respectively. During a purge operation, when gas enters the generator through one of the pipes,the gas, which is being displaced from the generator exits out the other pipe.

D. Gas Control Valves

The piping between the gas supply source and the generator typically has a set of valves, which theoperator uses for purging the generator. During this purge operation, the operator will look at thehydrogen control cabinet (or a remote display) so that he knows when the gas concentration is highenough to stop purging.

E. Casing Liquid Detector

Drain ports are located in the low points of the generator. Liquid that enters these ports is routed to thegenerator casing liquid detector.

10 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

22 of 56

Page 23: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

F. Shaft Sealing

The rotor of each generator extends beyond the generator casing at both the turbine end (TE) and thecollector end (CE). These two shaft to casing interfaces are sealed against hydrogen escape with oil�lm shaft seals. The shaft seals are located to the inside of the bearings. The shaft seals require acontinuous supply of clean cool oil as supplied by the seal oil system.

G. Seal Oil Draining

Used seal oil inside the generator will drain to seal oil drain enlargements (one on the CE and one on theTE) where hydrogen bubbles can come to the surface of the oil, and then to a common �oat trap valvewhich reduces the oil pressure from generator pressure down to bearing drain pressure and preventshydrogen from escaping with the oil.

H. Oil De�ectors

There are three gas cavities inside the generator, called:

1. The Turbine End Seal Cavity,

2. The Generator Casing (where the generator windings are), and

3. The Collector End Seal Cavity.

Seal oil is restricted to the end cavities. These cavities are separated from each other by oil de�ectors,which are extensions of the casing that have a small clearance between the static hardware and the rotor.

I. Gas Flow Between Cavities

Gas �ow into and out of the cavities is limited to:

1. New clean hydrogen being introduced to the generator casing.

2. Gas to the hydrogen cabinet, en route to the scavenging valves and the cell blocks, being takenfrom all three cavities but especially the end cavities because of the scavenging valves. (Vacuumtreatment seal oil system generators might not have a scavenging capability).

3. The end cavities are not connected to each other to the extent that gas cannot travel from one endto the other. Therefore gas �ow is limited to traveling from the generator casing to the end cavities.

J. Scavenging to Retain H2 Purity in the End Cavities

The end cavities include the seal oil drain enlargements. In these containers there is a net transfer ofair escaping solution from the oil and also hydrogen entering solution into the oil. The resulting effectis that the end cavities have a relatively high concentration of air.

For generators, which have non–vacuum treated seal oil, the hydrogen cabinet has scavenging valvesthrough which the contaminated hydrogen is slowly exhausted to a vent. New clean hydrogen fromanother part of the hydrogen system piping enters the generator casing to replace the scavenged gas.By this process, the air contamination in the end cavities remains at a safe low level to avoid the gasfrom being a combustible mixture. Also, the �ow of gas across the thin gap of the inner oil de�ector

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 11

30621127-000-3BD-EE-00100-CO2 REV 002

23 of 56

Page 24: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

retards the passage of the air contamination from entering the generator casing. Air contamination inthe generator casing region decreases generator performance.

12 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

24 of 56

Page 25: CO2 EE-00100-CO2-002

Hydrogen

andC

arbonD

ioxideG

asC

ontrolSystemforN

onPackaged

Units

GEK

103763d

Figure2.

Gas

ControlValve

Assem

bly

©GeneralElectric

Company,2008.G

EProprietary

Information.A

llRightsR

eserved.13

30621127-000-3BD-EE-00100-CO2 REV 002

25 of 56

Page 26: CO2 EE-00100-CO2-002

GEK

103763dH

ydrogenand

Carbon

Dioxide

Gas

ControlSystem

forNon

PackagedU

nits

Fi gure3.

H2or

CO2Bottle

Manifold

14©GeneralElectric

Company,2008.G

EProprietary

Information.A

llRightsR

eserved.

30621127-000-3BD-EE-00100-CO2 REV 002

26 of 56

Page 27: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

Figure 4. Liquid Level Detector Assembly

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 15

30621127-000-3BD-EE-00100-CO2 REV 002

27 of 56

Page 28: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

K. Vacuum Seal Oil Systems

Some generators have the seal oil treated in a vacuum chamber prior to the oil being exposed to thegenerator gas. These generators would not require the scavenging valves to be open except during theabnormal operation when the vacuum chamber does not have a vacuum or otherwise is not being used.The hydrogen control cabinets provided with these generators might not be connected to the seal oildrain enlargements.

L. Gas Purity Monitoring

The generator gas in the end cavities should be monitored in generators, which do not have vacuumtreated seal oil. If the seal oil is vacuum treated, then, it would be acceptable to monitor only thegenerator casing gas. During the purging operation, the gas purity of the venting gas (the gas exitingthe generator) should be monitored.

IV. GAS CONTROL VALVE EQUIPMENT

The gas control valves provide the operator with an ef�cient and safe means of handling hydrogen. Thegas control valves can be roughly placed into these categories:

H2 Gas Storage (perhaps nothing more than a bottle manifold)CO2 Gas Storage (perhaps nothing more than a bottle manifold and

�ow ori�ce)H2 Gas Control Valves (part of the gas control valve assembly)CO2 Gas Control Valves (part of the gas control valve assembly)Purging Gas Control Valves (part of the gas control valve assembly)Liquid DetectorsInterconnecting Piping and Valves

A. Features of the Gas Control Valve Assembly

The gas control valve assembly, Figure 2, is the operator’s control station during purging. There aretwo main runs where gas �ows from left to right. H2 is on the top run, and CO2 or air is on the bottomrun. There are two 3–way valves which operate in tandem. The top port of each 3–way valve connectsto the generator directly, the outside ports connect to H2 (on left) and CO2 (on right) and the insideports connect to the main vent. With the 3–way valve handles pointing down, the CO2 run will beconnected to the generator. With the 3–way handles pointing to the right, the H2 run will be connectedto the generator. Speci�c features on the gas control valve assembly are:

1. H2 Gas Control Valves

a. Hydrogen Inlet Pressure Relief Valve (PSV-2923). Pressure will be automatically relieved tothe piping design pressure if there is a pressure regulation malfunction, such as a leaky valveseat, in the hydrogen supply system upstream of the gas control valves.

b. Hydrogen Pressure Breaker Valve (HV-2925). The operator can de–pressurize the hydrogensupply system by opening this valve.

16 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

28 of 56

Page 29: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

c. Hydrogen Spool Piece. The operator is required by the equipment con�guration to remove thissegment of hydrogen pipe in order to connect an air supply to the generator.

d. Hydrogen Inlet Pressure Instrumentation (PI-2930). A gauge provides information to the op-erator that there is hydrogen pressure available for the generator. A low pressure switch willinform the operator that the supply system has insuf�cient pressure and that maintenance, suchas replacing hydrogen bottles, is required.

e. Connection for Hydrogen Cabinet Calibration (LE004). A port is provided on the gas valvesso that pure hydrogen can be supplied to the hydrogen cabinet for calibrating the gas analyzers.

f. Connection for Portable Gas Analyzer (LE033). A port for providing pure hydrogen for cali-brating an auxiliary gas analyzer is provided for customer convenience.

g. Generator Gas Flow Control Pipe Restriction. This ori�ce regulates the �ow rate of hydrogenduring the purging step that has hydrogen being admitted to the generator. It is manufacturedinside the piping to reduce the number of joints.

h. Generator Gas Pressure Regulator (PCV-2935). A pressure regulator is provided as an au-tomatic pressure control to replace small amount of generator internal gas used by the gasanalyzer, gas that has gone into solution with the draining seal oil, and gas which may slowleak out the casing joints. When carbon dioxide is being admitted into the generator an iso-lation valve in series with this regulator is closed. During purging, the gas goes through thisregulator, and it is full open because during purging generator gas pressure is well below theregulator set point.

i. Generator Gas Pressure Regulator Bypass Valve (HV-2935). The Generator Gas Pressure Reg-ulator is not used during the initial generator pressurization. During this operation the bypassvalve is open.

j. Hydrogen Secondary Block Valve (HV-2936). A second block valve is provided for redundanthydrogen isolation. It would be closed if the Generator Gas Pressure Regulator is removed formaintenance.

2. CO2Gas Control Valves

a. Carbon Dioxide Pressure Relief Valve (PSV-2940). Pressure will be automatically relieved tothe piping design pressure if there is a pressure regulation malfunction, such as a leaky valveseat, in the CO2 supply system upstream of the gas control valves.

b. Carbon Dioxide / Air Spool Piece. Prior to air being admitted to the generator, this spool piecewill have to be removed from the carbon dioxide line and placed into the air line. When inthe air line, it will be impossible for either hydrogen or carbon dioxide to be admitted to thegenerator.

c. Carbon Dioxide Supply Pressure Gauge (PI-2944). A gauge indicating carbon dioxide supplypressure is provided for the operator performing the purging operation.

d. Other Ports in the Carbon Dioxide Line. In the carbon dioxide line there are utility portswhich, might not be used: hydrogen cabinet gas analyzer calibration (LE055), gas dryer purge

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 17

30621127-000-3BD-EE-00100-CO2 REV 002

29 of 56

Page 30: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

(LE008), and one un–assigned. A port for portable gas analyzer calibration (LE013) is pro-vided for customer convenience.

e. Carbon Dioxide Shut Off Valve (HV-2946). The carbon dioxide shut off valve is closed exceptwhen carbon dioxide is admitted to the generator. If it is open during normal operation, carbondioxide may leak into the generator.

f. Air Shut Off Valve (HV-2947). The air shut off valve is closed except when air is admitted tothe generator.

g. Temporary Air Connection (LE009). A port is provided for clean dry air so that the generatorcan be �lled with air prior to opening a cover on the generator.

3. Purging Control Valves

a. Three–Way Valves (HV-2952/HV-2955). Each of the two three–way valve handles shouldalways be in the same position as the other. In one con�guration the hydrogen control valvesare connected to the generator and in the other con�guration the carbon dioxide control valvesare connected to the generator. In both con�gurations the generator is connected to the ventvalve.

b. Check Valves (CV-2950/CV-2940). There is a check valve in the supply line immediatelyadjacent to the three–way valves. The check valve prevents generator gas from back–�owingup the hydrogen or carbon dioxide supply lines.

c. Vent Valve (HV-2954). The main vent valve has 2 modes of operation: (a) Fully open todepressurize the generator, (b) Partially open during the purge operation to maintain generatorinternal pressure a few psi (several kPa, a fraction of a kg/cm2) above ambient.

d. Port in Vent Line for Gas Analyzer (LE056). The port in the vent line for the gas analyzer hasa projection into the vent line so that it senses total pressure (which equals pressure plus thekinetic energy of the gas �ow). It is ported to the hydrogen cabinet gas analyzer for use by theoperator during purging so that he knows when to stop purging.

e. Port in Vent Line for Portable Gas Analyzer (LE034). An additional port is placed in the ventline with a total pressure port for use with a portable gas analyzer. It is provided as a conve-nience to the customer.

f. Generator Gas Pressure Instrumentation (PI-2950/PT-2950/PSL-2950). A gauge and high/lowpressure switches for generator gas pressure are provided on the assembly.

g. Generator Gas Pressure Relief Valve (PSV-2950). A relief valve is provided so that duringnormal operation, generator casing pressure does not increase above the capability of the sealoil system. There is a �ow restriction upstream of it so that it has more �ow capability than afailed open generator gas pressure regulator, but not so much that the generator depressurizesrapidly if it itself fails open. The �ow restriction is inside the pipe so that the number of pipingjoints is reduced.

h. Vent Stack Drain Valve (HV-2943). A valve is provided on the bottom of the vent stack so thatcondensation can be removed. Water condensed in the pipes leading to the generator would

18 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

30 of 56

Page 31: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

also drain down to this valve during outage times. A slight bit of oil may be mixed with thewater.

B. Features of Bottle Manifolds

If a hydrogen gas bottle manifold is provided, it has these features. The carbon dioxide bottle manifoldhas the same features:

1. Pigtails, one for each hydrogen gas bottle. There is a check valve on the manifold end �tting ofeach pigtail.

2. Globe Valve, one for each hydrogen bottle.

3. Pressure Regulator Valve. These valves drops the pressure from the high bottle manifold pressuredown to approximately 125 psig (862 kPa–g, 8.79 kg/cm2) as required by the downstream �owregulation restriction. Gauges are provided on the regulator valve.

4. Pressure Regulator Bypass Valve. The bypass valve should be opened or closed completely andnot put into a partially open position.

C. Features in the Gas System Piping

1. CO2 Flow Regulation Ori�ce. The CO2piping upstream of the gas control valves should have a�ow regulation ori�ce to control �ow rate during the purge step which admits CO2into the gener-ator. Downstream of this ori�ce there should be a section of large diameter pipe where solid CO2precipitation can accumulate.

2. Drip Legs. Low points in pipe runs are provided with one or two valves. Accumulated liquid canbe drained. If there is only one valve, then either the pipe must be isolated or the generator degassedprior to draining the liquid. If there are two valves, then the liquid can be drained by alternatingthe valves between open and closed. Drip legs are placed in piping so that condensation and othercontamination is routed away from sensitive equipment.

3. Valves on the Underside of the Generator. There are several types of gas connections to the gener-ator: low point drains, gas feeds and vents, and pipes to gas sensing and gas processing equipment.Many of these have isolation valves at the generator connection to assist in maintenance.

4. Equipment Isolation Valves. Most pieces of equipment have isolation valves so that they may berepaired on line.

D. Features of the Liquid Detector Assembly

The liquid detector assembly has these features for each detector: isolation valve, drain valve, sightglass, �ll port for test, and the sensor.

V. OPERATION

A. Operator Activities Start Up / Shut Down

1. Pre-Start-Up

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 19

30621127-000-3BD-EE-00100-CO2 REV 002

31 of 56

Page 32: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

a. Read the warnings concerning the explosiveness and combustibility of hydrogen, which is inan earlier section of this document.

b. Ensure the piping to the cabinet and the piping of the gas valves used for gas control arecorrectly installed.

c. Ensure the external wiring of gas system electrical equipment is correctly installed.

d. Inspect the gas system equipment for damage. Drain out liquid, which may have accumulatedin the piping.

e. Be familiar with the operation of the seal oil system and the generator gas control system.

f. Be familiar with the use of the hydrogen control cabinet for gas purity monitoring.

g. Ensure there is enough CO2 available to purge out the air plus enough CO2 to purge outhydrogen should there be an emergency.

h. Ensure the gas valves are in the correct position for the admission of carbon dioxide.

i. Energize the hydrogen control cabinet and prepare it for use.

j. Energize all seal oil pump motors, including all AC and DC, and all primary, backup, andemergency pump motors.

2. Leak Test Piping.

After installation and prior to introducing hydrogen to the gas system equipment, all parts of thegas system should be air tested to ensure there is no leakage. A similar, perhaps coinciding, testshould be performed to the generator casing and end shields. The air test may be performed withCO2 after purging out the air if additional CO2 is available to be used to increase the pressure toa usable level for leak testing.

Leaks can be identi�ed by applying a soapy solution to the joints and welds. A typical solutionwould be liquid soap, glycerin and water. Bubbling will indicate leakage.

3. Start–Up.

The seal oil system should be started when the admission of carbon dioxide into the generatorcasing has raised the internal pressure to 2 psig. The pressure forces the seal oil to drain throughthe �oat trap valve �ow restriction. Initially, as pressure builds, seal oil may begin to �ood theseal oil drain enlargement. It is important that the seal oil not build up to the extent that it �oodsthe generator.

Therefore an operator should manually bypass the �oat trap temporarily until the generator casingpressure is 15 psig.

Start–Up Steps:

a. Manually open the �oat trap bypass valve. (See Section V. B. 5 Page 26 for further �oat trapbypass instruction details.)

20 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

32 of 56

Page 33: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

b. Start pressurizing the generator casing with CO2.

c. Turn on the seal oil supply system once the carbon dioxide pressure reaches 2 psig.

d. As the pressure inside the generator increases, the �oat trap bypass valve should be manuallyclosed, starting no earlier than 5 psig and reaching full closed position at 15 psig.

4. Purging and Other Normal Operations.

Please see below for other operator activities.

5. Shut–Down.

Prior to turning off the seal oil system, the generator should be purged so that hydrogen is notpresent in a dangerous concentration. If maintenance activity is required inside, beneath, or nearthe generator, or if the down time will be more than a few hours, then the carbon dioxide shouldbe purged out and replaced with air. After the purging steps are complete:

a. Reduce the Carbon Dioxide pressure by venting.

b. As the pressure inside the casing falls to 15 psig, begin to open manually the �oat trap bypassvalve. The valve should be completely open when the internal pressure reaches 5 psig.

c. Turn off the seal oil supply system when the internal pressure reaches 2 psig. This prevents�ooding of the generator or hydrogen control cabinet with oil.

d. Open the generator vent valve.

e. Do not open the generator end shields or other access covers until the operator is sure thatthere is no pressure inside the generator.

f. Use compressed air or large fans to blow CO2 out of low spots in the generator after openingthe generator.

B. Generator Gas Purging and Normal Operation

The generator is purged with gases before and after normal operation of the generator.

1. Purge Table

Perform the operations per the following chart. Please read the clarifying notes below.

2. General Information on Purging

Estimated Time of Purge = Volume of Generator *Amount of Gas / Flow Rate

Recommended Flow Rates of CO2 and H2. The recommended carbon dioxide �ow rate is 120 scfm(3.4 s m3/minute) for a 2800 ft3 (80 m3) generator internal volume. The recommended hydrogen�ow rate is 50 scfm (1.4 s m3/minute) for a 2800 ft3 (80 m3) generator internal volume.

* Please see comments concerning allowable gas speeds unders section B in paragraph 2.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 21

30621127-000-3BD-EE-00100-CO2 REV 002

33 of 56

Page 34: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

Please note that hydrogen is purging the carbon dioxide out of the machine in preparation for nor-mal operation. The gas speed in the feed piping shall be 300 feet per second maximum. Higherspeeds are permitted in the vents if compressible gas friction affects are considered. These �owrates are approximate, and for generator volumes greatly different from 2800 ft3 (80 m3), the rec-ommended �ow rate would change proportionally with generator volume (for example, twice the�ow rate if the generator is twice as large). Gas �ow rates during purging shall be slow enough totake advantage of the buoyancy effect of the gases inside the generator so that mixing is avoided.This will minimize the customer’s gas usage during the purge.

22 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

34 of 56

Page 35: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

Table 2. Purge Activity Parameters

Activity Air toCO2

CO2 toH2

H2 �ll Normal degas H2 toCO2

CO2toAir

Estimated Time(hrs)

0.5 2.0 1 N/A 0.5 1 N/A

Recommended FlowRate*(s m3/hr)(scfm)(minutes per bottle)

3.41203

1.4505

N/AN/AN/A

N/AN/AN/A

N/AN/AN/A

3.41203

N/AN/AN/A

Amount of Gas(x GeneratorVolume)

1 2 n N/A 0 2 >3

Hydrogen ControlCabinet Controls“Mode” Selection Purge Purge N/A Normal N/A Purge Purge“Function”Selection CO2 in

Air

H2inCO2

H2 in Air H2inAir

H2 inAir

H2inCO2

CO2in Air

Stop % 70%CO2

90% H2 N/A N/A N/A 5% H2 5%CO2

Gas Valve StationValve Positions3–Way Valves down right right right either down downMain Vent Valve partially

openpartiallyopen

closed closed fullopen

par-tiallyopen

par-tiallyopen

Generator PCVIsolation Valve

closed open open open closed closed closed

Generator PCVBypass Valve

closed closed open closed closed closed closed

CO2Shut–Off Valve open closed closed closed closed open closedAir Shut–Off Valve closed closed closed closed closed closed openH2 Spool Piece out H2 line H2 line H2 line H2

lineeitherposition

out

CO2Spool Piece CO2 line CO2line

CO2 line CO2 line CO2line

CO2line

airline

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 23

30621127-000-3BD-EE-00100-CO2 REV 002

35 of 56

Page 36: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

Automatic Flow Control of CO2 and H2 During Purging. The �ow rate during purging is automat-ically controlled by the size of �ow restrictions which are integral with the equipment.

Bottles May Be Discharged Simultaneously. Two bottles would decrease in pressure in about twicethe time, three bottles in about thrice the time, relative to the time given on the table above.

Manual Generator Pressure Control During Purging. Because of the gas strati�cation due to buoy-ancy, which occurs inside the generator, there will be very little if any change in gas mixture in theventing gas for the �rst 2/3 of the purge time. During the last 1/3 of the purge, the gas concentra-tions will change rapidly.

The generator vent valve (HV-2954) should be positioned and adjusted to hold between 2 and 5psig (13.8 to 34.5 kPa–g, 0.14 to 0.35 kg/cm2) inside the generator. The generator pressure willchange, and the valve may need adjusting, during the �nal 1/3 of the purge because during thattime the gas density may change dramatically.

Quantifying Gas Quantity. Because gas is compressible and buoyant it is dif�cult to measure andunnatural to perceive the concept of gas quantity. The mass of a sample of gas does not change, al-though its volume may change due to the interactions of pressure, temperature, and density. There-fore the best way to quantify gas quantity is by units ofmass. However, because gas has little weightand deforms and diffuses, the mass cannot be determined by measurement on a weight scale. Andunits of mass do not have direct importance because gas is used for its volume, not its mass, inmost applications in mechanics.

Therefore, it has become the industry standard to describe gas quantity in units of “standard” vol-ume. The “standard” means that pressure and temperature are assumed to be at 14.7 psia (1 at-mosphere at sea level, 101.4 kPa–a, 1.034 kg/cm2–a) and 77°F (25°C), respectively. Sometimesthe temperature standard is different, so it is important to know the speci�c standard pressure andtemperature, which are being used whenever a standard gas volume is given. The actual pressureor temperature of a gas sample may be substantially different from the “standard” conditions, how-ever, the mass of the gas sample can be quanti�ed by pretending it is at “standard conditions”.For example, a bottle of compressed gas may have only a few cubic feet of physical volume, buthave hundreds of cubic feet of “standard” volume worth of gas because the gas can expand to the“standard” pressure.

This measurement system works because there is only one gas density corresponding to a pres-sure/temperature combination for a particular type of gas. Therefore there is only one “standard”density for a type of gas. The “standard” volume of a particular gas can therefore be considered ameasurement of mass.

“scfm” means “standard cubic feet per minute”. “Standard” means the gas mass �ow is equivalentto the volumetric �ow if the gas were at 25° C (77°F) and 1 atmosphere (14.7 psia, 101.4 kPa–a,1.034 kg/cm2, which is 0 psig at sea level). The “s” in front of “m3/hr” also means “standard”.

3. Purging With CO2

Low Pressure Means Less Gas Used. During the purge process the generator gas pressure shouldbe between 2 and 5 psig (13.8 to 34.5 kPa–g, 0.14 to 0.35 kg/cm2), preferably 2 psig (13.8, kPa–g,0.14 kg/cm2) by throttling valve HV-2954. A lower generator gas pressure requires less purge gas.This is because purging is a gas displacement phenomena, which is volume driven, and higherpressure gasses have more mass (more gas) per a given volume. For example, a 2800 ft3 (80 m3)

24 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

36 of 56

Page 37: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

generator will require one additional CO2 bottle of gas to displace H2 for each psi (each 7 kPa,each 0.07 kg/cm2) additional gas pressure.

Low Flow Rate Means Less Gas Used. Flow rate during the purge is kept low to avoid mixing thegasses inside the generator. The gasses are naturally separated by buoyancy.

Nitrogen Content of Air. The 70% CO2 in Air concentration is acceptable because it results in onlyabout 6% O2, the remainder being the inert gases N2 and CO2

Purge Dead Cavities with CO2. After the generator is purged with carbon dioxide to 70% CO2in Air or 95% CO2 in H2, the generator gas pressure of a few psig (several kPa–g, a fraction ofa kg/cm2) should be used to purge the dead cavities of the generator. Most importantly, the sealoil drain enlargements should be purged by simultaneously opening the scavenging valves longenough to vent out 35 ft3 (1 m3) of gas. If there are volumes of air or H2 which cannot be purgedusing generator CO2 pressure, then a portable CO2 supply should be used.

Purge Out H2 after Rotor has Slowed Down. Prior to admitting CO2, it is necessary to wait untilthe rotor has decelerated to turning gear or stand still. A rotating shaft will mix the gasses insidethe generator. The mixing will destroy the buoyancy layering which keeps CO2 on the bottom andH2 on the top. If the generator is to be purged while the shaft is rotating, there should be suf�cientCO2 available to account for the mixing. This can be several times the normal amount of CO2required for a purge.

Water Vapor Fog Layer. During the purge where cold CO2 replaces ambient temperature air, alayer of condensed water vapor fog forms at the boundary of the two gasses. The optimum CO2�ow rate was originally calculated based on witnessing the movement of this fog layer.

4. Placing Air into Generator

The Removable Spool Pieces are designed to (a) inhibit the introduction of air while there is hy-drogen in the generator and (b) provide a means of absolutely preventing the in�ow of dangerousgas while personnel are inside the generator performing maintenance.

Air Can Have a High Flow Rate .Air is relatively inexpensive compared to H2 and CO2. Therefore,the generator and the purge procedure are not designed to minimize the quantity of air needed.

So that there is no chance of mixing H2 and air together, air is introduced into the generator throughthe CO2 distribution pipe on the bottom of the generator interior. Thus the lighter air is below theheavier CO2, and the gasses thoroughly mix during purging. Because mixing cannot be avoided,a very high �ow rate of air can be used.

Air Supply Must Be Typically Disconnected. All air connections to the generator should be dis-connected when CO2 is admitted, and especially when H2 is inside the generator.

Remove Bottles and Spool Pieces Prior to Admitting Air. Prior to admitting air into the generator,totally disable the CO2 and the H2 feed lines, which connect CO2 or H2 bottles to the generator, tothe hydrogen cabinet, and to all other equipment, such as a gas dryer. Closing valves is not suf�-cient. The bottles should be removed, or the piping disassembled at a spool piece or other �tting. Ifa workman is working on the generator, a dangerous situation can develop by gas leakage throughvalves. CO2 is poisonous at moderately low concentrations and H2 is explosive at concentrationsabove 4%.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 25

30621127-000-3BD-EE-00100-CO2 REV 002

37 of 56

Page 38: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

Blow out CO2 from Low Spots in Generator. After the generator is purged with air, some CO2 willremain in the generator low points. After the end shield, bushing box cover, or other access plateis removed, the generator should be blown free of CO2, either with a compressed air hose or largefans.

Control Condensation During an Outage. During a generator outage the valves in the piping shouldbe closed so that humid atmospheric air does not enter the piping. Humid air will cause conden-sation to form internal to the piping as ambient temperature �uctuates day to night. Speci�cally,the valves on the underside of the generator should be closed. This will prevent corrosion internalto the pipe and water build–up. Water which freezes could cause pipe rupture and a resulting gasleak. Alternatively, to route condensed water to the vent stack, the three way valve handles shouldbe to the right.

5. Turning On and Off the Seal Oil Supply

Turning on the Seal Oil System. The seal oil system should not be turned on prior to the generatorinternal pressure reaching 2 psig of CO2. At this low pressure, the �oat trap bypass valve must beopen to prevent �ooding of the generator or the hydrogen control cabinet. Then the seal oil systemmay be turned on for the purge. While the bypass is used, it is critical that the oil level not fallbelow the �oat trap. If this happens and there is hydrogen inside the generator, hydrogen couldenter the bearing area through the bearing drain enlargement. As the generator internal pressurerises above 5 psig, the bypass valve should be throttled, until it is fully closed when the generatorinternal pressure reaches 15 psig.

Shutting Down the Seal Oil System. Under no circumstance should the seal oil system be shutdown while there is hydrogen in the generator. This procedure refers to after the hydrogen hasbeen purged out with CO2.

As the air purge reduces the generator internal pressure to 15 psig, the �oat trap bypass valve shouldbe manually opened, such that it is completely open when the internal generator pressure drops to5 psig. The seal oil system should be shut off when the pressure inside the generator drops to 2psig. The seal oil system should not be kept operating if the pressure in the generator drops below2 psig because the �ow restriction of the �oat trap may cause �ooding of the generator with oil.

6. H2 Purging, Filling, Normal Operation, and degassing

CO2 Must Always Be Available. The CO2 feed system for the generator should be continuouslyoperational during the H2 purge and normal operation. It may be necessary to emergency purgeout the H2 at any time.

Pressurize the Generator with H2 to a Slightly Lower Pressure. The generator does not need tobe �lled to the full operating pressure, but rather about 10% low (relative to absolute pressure).The gas temperature shortly after the purge and �lling will be nearly ambient because of the hugethermal mass of the generator electrical components. During operation the generator gas is muchwarmer. By the perfect gas law, the pressure will increase as the temperature increases given aconstant volume for the gas. Therefore, the pressure at the end of a �ll should be per the tablebelow.

Pressure During Operation psig 15 30 45 60 75Pressure After H2 Fill psig 12 25.5 39 52.5 66

26 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

38 of 56

Page 39: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

Pressure During Operation kPa–g 103 207 310 414 517Pressure After H2 Fill kPa–g 83 176 268 361 454

Pressure During Operation kg/cm2 1.05 2.11 3.17 4.22 5.28

Pressure After H2 Fill kg/cm2 0.84 1.79 2.74 3.69 4.64

Close H2 Feed When De–Pressurizing the Generator. When the operator opens the vent valve todepressurize the generator, he should also close the hydrogen feed valve in the pipe leading to thegenerator.

7. Hydrogen Control Cabinet Use During Purge

Hydrogen Control Cabinet Settings. The hydrogen control cabinet is the device which monitorsgenerator gas purity. “Purge” selection will control valves such that the gas sample is taken fromthe generator vent. “Normal” selection will control valves such that the gas sample is taken fromthe generator itself.

CO2 Contamination of Filters. Be sure the “purge” setting and not the “normal” setting is appliedto all applicable gas sensors of the hydrogen control cabinet when purging. This will prevent CO2from entering the �lter dryers, which are molecular sieves. If CO2 enters the �lter dryers it willslowly bleed out over the �rst day of normal operation with H2 in the generator. If this happensthe reading will be inaccurate, in that it will indicate more air contamination in the generator gasthan is actually present during the �rst day of operation.

C. Setting the Scavenging Flow Rates

Generators which do not have vacuum treated seal oil should be provided with a means of continuouslybleeding out a small �ow of generator gas from each of the two seal oil drain enlargements. The seal oildrain enlargements are where air contamination will be introduced into the generator because air comesout of solution from the seal oil. The gas control valves will automatically introduce clean hydrogeninto the generator casing when gas is bled out, with the result of maintaining generator gas purity at anacceptable level.

The scavenge �ow rate visual meters and hand operated control valves are typically located on thehydrogen control cabinet. The �ow rates should be set so that the end cavity generator gas purity ismaintained substantially above the Upper Explosion Level for H2 in air, see Table 1 above. The exactvalue is dependent on the accuracy of the purity monitoring equipment and the operating philosophyof the power plant (Refer to the international standard IEC 842 for guidance if no philosophy exists).

1. Start–Up

Initially, before there is any data or precedence on which to base the actual �ow rate set point, thevalves should be set for removing about 1 scfh (472 ml/min) from each seal oil drain enlargement.After several hours, which is a long time duration to ensure the system has stabilized, the �ow ratecan be changed. Higher �ow rates will improve gas purity, lower �ow rates will degrade gas purity.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 27

30621127-000-3BD-EE-00100-CO2 REV 002

39 of 56

Page 40: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

A high �ow rate is not desired from an economic perspective because the scavenged gas is lost toa vent.

2. After a Low Purity Alarm

There are three settings for scavenged gas purity: Control Set Point, LowAlarm, Low–LowAlarm.The Low–Low Alarm point should not be below 80% H2 in Air by volume purity.

If the hydrogen purity in an end cavity drops to the low alarm, the operator should re–adjust thescavenging rates to achieve the control set point. It may happen that the �ow rate cannot be in-creased further, in which case the generator should be shut down and purged of hydrogen so thatthe cause of the problem can be �xed.

3. Trending

It is unusual to have a need to increase scavenging. Records should be kept and plotted so thatthe two end cavity scavenging rates can be trended over long periods of time. Generator shaft sealhealth, CO2 valve leaks, and other problems can be identi�ed in this way.

4. Jumpy Flow Gauge

If the �ow gauge for scavenging gas is jumpy, meaning the �ow indicator moves every second orso by itself, then the equipment can continue to operate until the next outage, at which time thecause for the jumpy reading can be investigated and corrected. The correct reading of �ow is theaverage of the jumpy readings. Jumpiness is caused by liquid in the lines (so all drip legs shouldbe drained), or light solid blockage that moves back and forth. Flow through thermister based gasanalyzers is also permitted to have some jumpiness.

D. Operating the Generator at Full Speed with Air Inside

During commissioning or another special circumstance, the generator may be required to operate atfull speed with air inside the casing. The shaft seals will need oil for lubrication during this operationmode, and therefore the seal oil system must be operating, with the �oat trap bypass valve manuallyopened. Without the valve opened, the seal oil, which drains to the generator side and out the �oat trap,may back up into and �ood the generator. Therefore, the generator should be pressurized with air to 2to 5 psig (13.8 to 34.5 kPa–g, 0.14 to 0.35 kg/cm2) and the �oat trap bypassed so that the oil will drainproperly. A higher pressure, about 15 psig (103.5 kPag), is necessary, if it is not possible to manuallymonitor the �oat trap performance.

NOTE

It may not be possible to produce any electrical power under these circumstances.Contact GE Power System Product Services to determine operational limits.

The generator fan differential pressure will increase proportional to gas density. Therefore it may be3, 4, maybe 8 times as high as during normal operation with hydrogen inside the generator. The gen-erator fan differential pressure gauge may not be designed for the high differential service, and may berequired to be isolated so that its mechanisms do not get damaged. In particular, if the fan differentialgauge is a manometer, it must be isolated so that the heavy bromine liquid does not get blown into thegenerator where it would cause corrosion.

28 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

40 of 56

Page 41: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

The greater fan differential pressuremay cause oil to be drawn into the generator unless: (a) the pressureis kept high and (b) the vent lines, typically used for scavenging, on the two seal oil drain enlargementsare slightly open such that air is being vented from out of the generator through them.

The air supply should be clean and dry. A �lter and an air dryer should be used. If a hydrogen gasdryer is provided with the generator, it should be isolated from the system and not used unless the gasdryer manufacturer speci�cally approves of its use as an air dryer.

VI. ALARM RESPONSES

Activation of any alarm requires prompt attention by the operator. Excessive delay in correcting an alarmcondition could result in damage to the generator and equipment, and possible injury to personnel.

Alarms in the hydrogen gas system are summarized below.

1. Operator Investigation: Further deterioration will not cause a generator load reduction nor an unsafecondition:

Small accumulation of liquid in drip legs

Indications concerning humidity or the gas dryer equipment (if part of the gas system)

2. Operator Investigation: Operator attention is necessary at the soonest convenience:

High Generator Gas Pressure

Low Hydrogen Supply Pressure

High Generator Casing Liquid Detection

3. Operator Investigation: A generator load reduction or an unsafe condition is possible with furtherdeterioration:

Low Generator Gas Pressure

Low Generator Gas Purity

High Generator Gas Temperature

High–High Generator Casing Liquid Detection

High Seal Oil Drain Enlargement Liquid Detection

Insulation Overheating Particle Detection Alarm (Not provided with all generators)

4. Manual Shutdown of Turbine–Generator

Low–Low Generator Gas Purity

5. Automatic Shutdown of Turbine–Generator:

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 29

30621127-000-3BD-EE-00100-CO2 REV 002

41 of 56

Page 42: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

None

6. Automatic Trip of Turbine–Generator

None

A. Low-Low and Low Generator Gas Purity Alarms

1. Assume Air is the Contaminant

Please read the warnings concerning hydrogen contamination as provided in the beginning of thisdocument. In particular, the contaminant is assumed to be air unless there is a reason to suspectpure oxygen may be introduced. A condition to suspect pure oxygen is if the hydrogen source is ahydrogen generation device.

2. Explosion Danger

Low purity is a concern primarily because of the hydrogen explosion danger.

3. Effect of Low Purity in Casing Gas

Low purity gas in the casing will slightly raise generator winding temperatures because air has arelatively low thermal conductivity (about a tenth that of hydrogen’s) and air forms larger boundarylayer thickness which reduces convection. Also, air in the generator casing increases windagelosses and noise. Most generators have fan differential pressure indicators, which will be readingnoticeably high if the generator casing gas purity is below 90%.

4. Gas Purity Reading has a Time Lag

There is a time lag between the generator gas purity change and the monitoring of that change dueto the volume of gas in the interconnecting piping and the �ow rate through that piping, as well ascontaminate diffusion which will occur in the piping. Given the �ow rate, pipe size and length, gaspressure ratioed to ambient, and a factor of 2 to account for diffusion, the operator can calculatethe time lag.

For example, a sensing line of 50 feet of pipe 0.5 inch diameter and a generator pressure of 60 psigwith a gas �ow rate of 2 scfh will have a time lag of

2 * 50 feet * (0.25 * pi * 0.5 * 0.5) in2 * (74.7 psia / 14.7 psia) * X / 2 scfh = 21 minutesX = unit conversion factors (therefore X = 1)For example, a sensing line of 15.24 meters of pipe 12.7 mm diameter and a generator pressureof 414 kPa–g (4.22 kg/cm2) with a gas �ow rate of 944 ml/minute will have a time lag of2 * 15.24 m * (0.25 * pi * 12.7 * 12.7) mm2 * (414 + 101.4 / 101.4) * X / 944 ml/min =21 minutesX = unit conversion factors (therefore X = 1)

Therefore, while troubleshooting, the operator should remember that the purity reading is not cur-rent.

30 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

42 of 56

Page 43: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

5. Non–Vacuum Treated Seal Oil Systems

If there is a purity–low–alarm in an end cavity (not the generator casing), the rate of scavengingshould be increased to reestablish the desired set point reading. If purity cannot be maintainedbetween the desired set point and the low–alarm and if scavenging is at a maximum, then the gen-erator should be shut–down and the source of the contamination identi�ed and corrected. Do notoperate the generator for more than a few minutes with purity less than the low–low–alarm point.

6. Vacuum Treated Seal Oil Systems

Systems with vacuum treated seal oil are not susceptible to contamination in the end cavities andtherefore do not require scavenging from the drain enlargements. It is possible that the gas puritymonitoring equipment will only sample gas from the generator casing. The desired set point of gen-erator casing gas will be very high, approximately 95-98% and will not be adjustable because thereis no scavenging. The low–alarm point initiates operator investigation and the low–low–alarmpoint would be used to advise the operator to shut down the generator.

If the vacuum treatment processing of the seal oil is being bypassed or is inoperative, then theoperator will have to scavenge gas from the seal oil drain enlargements. 35 standard cubic feet(1 m3) (about 1/6 of a bottle), (17.5 ft3 (0.5 m3) TE and 17.5 ft (0.5 m3) CE), of gas should bescavenged every hour.

7. Sources of Contamination

Possible sources of contamination of the end cavity gas are (a) excessive seal oil �ow, (b) poor sealoil draining, (c) insuf�cient scavenging, and (d) excessive air in the seal oil supply.

The low purity in the casing may be due to a leaky CO2 valve. CO2 valves often corrode due to aninteraction of CO2 with humidity causing an acid to form, and so are susceptible to internal leaks.

Moisture in the gas analyzer probe may cause erroneous readings. An alumina moisture indicatorshould be upstream of the gas analyzer probe, and will warn of moisture contamination.

Moisture is often removed from the gas sample by a molecular sieve �lter. This special type of�lter traps carbon dioxide and bleeds it out over a day or so. Therefore, if the carbon dioxide fromthe purge operation was inadvertently routed to the �lter, then the reading will erroneously showlow purity for about a day.

B. Generator Gas Temperature High

If the generator casing gas temperature is too high there is a possibility of damage to the windinginsulation. The generator casing gas temperature alarm is part of the generator equipment, and notpart of the hydrogen gas system. Typically the alarm point is 2°C (3.5°F) above normal operating gastemperature. After the alarm, cooling water �ow should be increased, or other action taken immediatelyto lower the gas temperature. If the cause cannot be immediately corrected, the load on the generatorshould be reduced until the normal gas temperature is obtained.

C. Generator Gas Pressure High

The generator gas pressure is maintained by a control valve in the gas control valve assembly. If thecontrol valve is found to be non–adjustable or otherwise malfunctioned, it can be isolated and repaired.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 31

30621127-000-3BD-EE-00100-CO2 REV 002

43 of 56

Page 44: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

The generator can continue to operate with hydrogen being periodically provided through the bypassvalve around the control valve. Alternatively, if a two–stage pressure regulator is provided on the bottlemanifold, that regulator can be adjusted and used to control generator gas pressure temporarily.

The primary concern with high generator gas pressure is that it will rise above the capability of the sealoil system. By system design, this situation is unlikely.

D. Generator Gas Pressure Low

A low generator gas pressure of only a few psi (several kPa, several hundredth’s of a kg/cm2) will causeseveral degrees C of elevated temperature in the rotor windings. Therefore it is important to reestablishnominal generator gas pressure or else reduce load after a low generator gas pressure alarm.

The generator pressure low alarm should be set within 2 psi (13.8 kPa, 0.14 kg/cm2) below nominalgenerator gas pressure.

The generator gas pressure is maintained by a control valve in the gas control valve assembly. If thecontrol valve is found to be non–adjustable or otherwise malfunctioned, it can be isolated and repaired.The generator can continue to operate with hydrogen being periodically provided through the bypassvalve around the control valve. Alternatively, if a two–stage pressure regulator is provided on the bottlemanifold, that regulator can be adjusted and used to control generator gas pressure temporarily.

The other likely cause of a gradual lowering of generator gas pressure is low hydrogen supply pressureor an extremely leaky vent valve.

If the pressure is dropping rapidly, the cause is possibly a failed open relief valve, a shaft seal failure,a casing or pipe failure, or a failed open �oat trap valve in the seal oil drain system. In case thereis a rupture of hydrogen containment, the generator should be shutdown immediately, and it shouldbe determined that the area is free of H2 or CO2 hazards before an operator approaches or enters theequipment. Generators with autopurge feature will put CO2 into the generator automatically. Theconcentrations of hydrogen in air, which are explosive, are between 5% and 75% hydrogen. Duringthis emergency period, while the generator is still charged with hydrogen, the seal oil system shouldbe operating, in spite of the fact it may be pumping oil into the generator. As the pressure drops below15 psig of CO2 or air, if it is possible to do so, the �oat trap bypass valve should be opened. As thepressure of CO2 or air drops below 2 psig, the seal oil system should be shut down.

E. Hydrogen Supply Pressure Low

An indication of low hydrogen supply pressure is provided so that the operator can be prompted toreplace depleted hydrogen bottles and avoid the more critical event of a low generator gas pressurealarm.

F. Liquid Detection

Liquid inside the generator indicates that there is an oil or water leak, or else the seal oil drain is backedup.

Liquid oil and oil vapor (which easily condenses) create a sticky surface on the generator internal sur-faces including the insulation. Dirt particles then have a tendency to cling to the insulation and mayeventually damage it. Liquid water on the insulation will degrade the quality of the insulation.

32 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

44 of 56

Page 45: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

A High Generator Liquid Detection Alarm may indicate a slow leak of liquid into the generator casingwhich should be investigated when convenient. A slow leak of oil is possible due to the interaction ofseal oil with rotor rotation while on turning gear.

A fast leak is evident if there is a High–High Generator Liquid Detection Alarm. The fast leak shouldbe immediately identi�ed and corrected, or else the generator should be shut down prior to generatorcasing �ooding.

A High Seal Oil Drain Enlargement Liquid Detection Alarm is provided so that the operator will knowthe reason for an impending High Generator Liquid Detection Alarm and can take proper correctiveaction.

1. Investigation

After an alarm, the liquid detection device can be drained to determine if the liquid is water or oil.

2. Water

There are two sources of water: The hydrogen coolers and the stator cooling water system (if thearmature bars are direct water cooled).

A recent abnormal requirement for make–up water for the stator cooling water system indicates apossible leak.

To determine if a hydrogen cooler is leaking, valves on the underside of the generator may beintermittently closed and opened. Also the operator could shut off the �ow of water to one coolerat a time if running at 80% of rated load capacity. If a cooler leak is severe, the defective coolermay be left out of service until repairs can be made. Generators are typically designed to operateat rated power factor at 80% rated load capacity with one hydrogen cooler out of service.

The hydrogen gas dryer, if provided, does not have the capability to dry the generator if there is agenerator internal water leak.

3. Oil

Oil may enter the generator from the shaft seals or else from �ooding of the hydrogen detrainingtank.

Do not shut down the seal oil supply until after H2 has been purged out of the generator with CO2.Oil may be �owing quickly into the detector during the purging process.

During the generator gas purge process, draining seal oil may have a tendency to back up in thedrain system if the generator pressure becomes abnormally low. A bypass valve is typically pro-vided so that an operator can increase the drain �ow rate.

Oil from the shaft seal area may be due to a leaky �ange, or an extremely large seal oil �ow, oranother problem. It can be isolated to be either the turbine end or the collector end by intermittentlyclosing the drain valves located near the end shield on either side of the underside of the generator.

Shaft seals may become unseated if there is a temporary reversal of pressure on the gas side sealring. This may occur during a transfer from one seal oil supply pump to another, either due to a

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 33

30621127-000-3BD-EE-00100-CO2 REV 002

45 of 56

Page 46: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

time lag between pump stop and start or due to a time lag in the pressure control valve response. Anunseated seal may cause an extremely large oil �ow, which might not drain through the generator’sinternal drains to the seal oil drain enlargement. This event is more typical when the shaft is notturning. Field experience has shown that the seals often re–seat after several minutes when theshaft is rotated at turning gear speed.

VII. MAINTENANCE

A. Leak Testing

After a joint has been adjusted or otherwise loosened or tightened, such as after a component is re-placed, the joint must be pressure tested to ensure it will not leak hydrogen. Testing may be performedwith air or CO2, typically at approximately 20 psig (14 kPa–g, 0.14 kg/cm2).

Leaks can be identi�ed by applying a soapy solution to the joints and welds. A typical solution wouldbe liquid soap, glycerin and water. Bubbling will indicate leakage.

B. Regular Maintenance

An operator should be available in the control room to receive alarms at all times.

Each mechanism in the gas control system should be inspected periodically to ensure it is functioningproperly.

1. Daily Inspections

Once a day the operator should review the transmitter signals from the gas system and comparethemwith standard values. The standard values will be established from previous operation experi-ence. Also the transmitter signals should be compared with the previous days’ readings to identifyany trends. The gas control system transmitter signals are:

Generator Gas Pressure

Generator Gas Purity

Core Monitor (Not provided with all generators)

Hygrometers (Not provided with all generators)

Once a day the operator should walk around the gas system equipment to look for anything abnor-mal. The gas control system features to be daily inspected are:

All valves should be in the proper position

Check the sight glass in the gas dryer (if a gas dryer is provided and it has a sight glass)

Compare the reading on all the pressure gauges with standard values

Hydrogen control cabinet settings and indicators should be normal.

Core monitor and pyrolysate collector should be operating normally (if provided with generator)

34 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

46 of 56

Page 47: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

Check the sight glass in both liquid detectors and the seal oil drain system �oat trap

Drain condensate or other liquid out of the main vent line

2. Weekly Inspections

Visually inspect the moisture indicators (MI-2971, MI-2972, and MI-2973). A blue medium indi-cates dry hydrogen, while a pink medium indicates excessive moisture in the hydrogen gas samplethat may affect the stability of the Generator Gas Analyzers (GGA). Replace or regenerate theMoisture Indicator and replace the Gas Puri�er if the medium is pink. Refer to Removal of Mois-ture Indicators and Gas Puri�ers. Blow down puri�ers by �rst removing cap at the base of theisolation valve and then open the valve itself. It is advisable to have a container available to collectany �uid contained within the puri�er. Please refer to the provided Hydrogen Control Panel Oper-ation and Maintenance manual for further details covering how to perform maintenance activities.

CAUTION

The Puri�ers May Contain Hydrogen Gas; Use Proper Safety Precautions

3. Inspections Every Six Months

Calibrate or otherwise perform maintenance on the hydrogen control cabinet as required.

Perform a Core Monitor system test. (Core Monitor is not provided with all generators).

Check the calibration and operation of all the alarm devices and contacts.

4. Inspections to be Done After Every Scheduled Purge with Carbon Dioxide

Check all drip legs and other drains for liquid accumulation. If the generator is purged with air,close isolation valves in piping at the generator and elsewhere to prevent humid atmospheric airfrom entering the piping.

5. Generator Maintenance Outage

Test all the relief valves for a possible leakage into the vent lines. All gauges should be calibratedevery three years minimum.

C. Special Maintenance

1. Gas System Components Designed for Maintenance Activity

Tag all valves, switches, or other devices, which are important to be in a particular state during themaintenance duration.

Do not disable the CO2 supply system at anytime for maintenance. CO2 must be continuouslyavailable for an emergency purge.

Read the warnings concerning hydrogen which are at the beginning of this document. The fol-lowing gas system �uid processing components have been designed for maintenance while thegenerator is operating normally:

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 35

30621127-000-3BD-EE-00100-CO2 REV 002

47 of 56

Page 48: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

Hydrogen supply pressure sensing devices

Generator gas pressure sensing devices

Pressure Regulating Valve

Pressure Relief Valves

Liquid Level Detectors

Core Monitor (Not provided with all generators)

Gas Dryer (if a gas dryer is provided)

Hygrometer Probes (if provided)

Hydrogen control cabinet (short duration only)

Because there are no compressed air sources permitted to be connected to the generator, it is un-likely that a fast air contamination of the generator gas can occur. Therefore the hydrogen controlcabinet can be isolated for a short duration for simple maintenance activity (for example, changingthe �lter cartridge).

D. If the Hydrogen Control Cabinet is Flooded with Oil or Water

If the generator is �ooded with oil or water, then there is the possibility that the hydrogen cabinet mayalso have been �ooded.

After a �ooding accident, all the tubing and components of the hydrogen cabinet should be cleanedand dried. Oil �ooding will require cleaning with alcohol or similar solvent (not methanol CH3OHbecause it deteriorates elastomeric seals). This will require some dis–assembly at tubing and NPTjoints. The �lter–dryer cartridges will have to be replaced. The silica–gel will have to be replaced if itwas contaminated with oil. The cell blocks will have to be removed and �ushed with alcohol to removeoil from inside the thermister chamber.

The cleaning should extend at least back to the last drip leg in the piping.

E. Materials and Design Conditions

The gas system piping and components are made of ASTM A105/A106 carbon steel, AISI304/304L/316/316L stainless steel, or bronze.

The design pressure of the piping and assemblies is 150 psig (1034 kPa–g, 10.55 kg/cm2). Bottlemanifolds are designed to a higher pressure.

VIII. OPERATION AND DESIGN REQUIREMENTS FOR THE H2 AND CO2 GAS SUPPLIES

The gas system equipment supplied with the generator does not include the H2 and CO2 gas storage equip-ment nor the piping to connect the gas storage equipment to the gas system gas control valves. This equip-ment is not provided because there are many alternative gas storage systems available to the power plantdesigners and they should choose one, which best �ts their needs.

36 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

48 of 56

Page 49: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

The following section gives instructions on the design of the gas storage equipment and piping. It alsoprovides instructions to operators on how to use equipment, which is designed to these requirements.

A. Requirements on Gas used in the Generator

The sources of gas should be able to provide gas to the gas control valves to the following requirements:

1. Carbon Dioxide

Phase: Vapor Phase. This includes the emergency event of a loss of AC power.

Purity: Commercially available purity grade.

Flow rate: 120 scfm (3.4 s m3/min) for a 2800 ft3 (80 m3) generator. Flow rate changes propor-tionally with generator volume.

Pressure: 125 psig +/-10 psig (861.8 kPa-g +/- 68.9 kPa-g or 8.79 kg/cm2 +/- 0.70 kg/cm2) (betweenthe pressure reducing valve and the CO2 �ow ori�ce). The CO2 pressure at customer connectionLE049 shall be approximately 2 psig (13.8 kPa–g, 0.14 kg/cm2) as determined by the generatorinternal pressure.

Temperature: Low temperatures are acceptable.

Gas Quantity: There should be enough carbon dioxide available for an operator to purge the gen-erator of hydrogen during an emergency. Bottles should be stored near the manifold.

The �ow rate and pressure requirements can be satis�ed by the use of an ori�ce when designed tothe design requirements given below. Please note ori�ce is already provided for CO2 gas �owingfrom the GE designed CO2 bottle manifold system.

2. Hydrogen

Purity: 99.9% or better.(note that hydrogen manufactured from some processes may contain mea-surable hydrogen sul�de and should not be utilized)

Humidity: maximum of 0.1 gram of water per cubic meter of gas (0.00007 lbm/ft3) (Gas shouldbe desiccant dried.)

Flow rate: 50 scfm (1.4 s m3/min) during purging for a 2800 ft3 (80 m3) generator. Higher �owrates are permitted during the generator �ll operation. The gas �ow rates in feed pipes shall belimited to 300 feet per second maximum.

Pressure: 125psig +/-10 psig (861.8 kPa-g +/- 68.9 kPa-g or 8.79 kg/cm2 +/- 0.70 kg/cm2) duringpurging and normal operation. During the generator �ll operation the gas control valves have no�ow restriction smaller than a 1 inch (25.4 mm) diameter pipe, so the pressure downstream ofPCV-2935 will be between 2 psig (13.8 kPa–g, 0.14 kg/cm2) and full generator gas pressure asdetermined by generator internal pressure.

Temperature: Low temperatures as experienced during the discharge of bottles are acceptable.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 37

30621127-000-3BD-EE-00100-CO2 REV 002

49 of 56

Page 50: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

3. Air

Humidity: Air should be desiccant dried.

Cleanliness: Air should be �ltered. No oil vapor is permitted.

Flow rate: No upper limit on �ow rate. Maximum �ow rate based on the pipe size restriction isexpected to be 150 scfm (4.2 m3 /min)

Pressure: Approximately 2 psig (13.8 kPa–g, 0.14 kg/cm2) as determined by generator pressure.The gas valve piping has no �ow restriction smaller than 1 inch (25.4 mm) diameter pipe.

Temperature: Should be between -20 and 120°F (-28.9 to 48.9°C).

Gas Quantity: Several generator volumes of gas will be necessary to purge the generator.

B. Characteristics of Compressed Gas

It is important that the operator become familiar with the behavior of compressed hydrogen and carbondioxide.

Compressed gas is dangerous. Be cautious when using compressed gas. Be alert to kinked �exiblepigtails, especially at the �ttings, and to over–stressed metal tubing–type pigtails. Replace damagedpigtails immediately. Be cautious of high pressure gauges by minimizing the amount of time an oper-ator stands in front of them. Read all warnings provided by the gas supplier.

1. Gas Bottles and Regulators

Regulators

Connecting Bottles: Prior to attaching a bottle, the dirt and dust in the valve outlet and in the pigtail�tting should be completely removed. Dirt in a pressure regulator will cause it to leak internallywhen it should have a tight shut off.

Slowly Open Valve. Bottle pressure should be applied to a pressure regulator by slowly openingthe bottle’s hand valve. This avoids damage to the regulator or a gauge by a pressure shock.

Replace Leaky Valve Seats. If the pressure downstream of the pressure regulator increases whenthere is no �ow, then the pressure regulator valve seat may leak. The seat should be replaced if itleaks. If the pressure at the gas control valve assembly is at the pressure relief valve setting, thenthe seat of the pressure regulator is likely leaking.

Low Flow Delivery Pressure. Single stage regulators (which have more �ow capacity than twostage regulators) have their delivery pressure set point established at a high �ow rate. During lowor no �ow, the delivery pressure set point is much higher. Therefore, if the gas system is designedso that a tight shut–off is necessary (ie, the manifold globe valves are open in a “ready” mode),then the low or no �ow delivery pressure should be deliberately set below the gas system reliefvalve setting. Otherwise, the gas from the bottles will seep out the relief valve and not be availablewhen needed.

38 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

50 of 56

Page 51: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

H2 Bottles

Hydrogen bottle size: 239 standard cubic feet (6.77 m3) per bottle (about 200 ft3 (5.7 m3) is usablebecause the pressure drops off during discharge). At 70° F (21°C) the pressure is 2400 psig (16.5MPa, 169 kg/cm2).

Minimize Number of Active H2 Bottles. For safety reasons, as few bottles of hydrogen as possibleshould be used during any one time during normal operation.

Do Not “Crack” Hydrogen Bottles: Unlike non–�ammable gasses, it is not recommended to“crack” hydrogen bottles prior to connecting them to a regulator of manifold since “self–ignition”of the released hydrogen is likely to occur.

CO2 Bottles

Use Gaseous CO2 Only. Only bottles which discharge the vapor phase of carbon dioxide should beused. Bottles which have a siphon tube so that they discharge liquid, or bottles with the dischargeport on the bottom so that they discharge liquid, are not to be used with the generator. Liquidcarbon dioxide is extremely cold and may adversely affect the welds in the piping. Also, it willeasily form solid carbon dioxide after dropping in pressure in a �ow restriction and potentiallyblock the piping.

Carbon dioxide bottle size: 50 lbm (50 pounds mass, 22.7 kg) of gas per bottle. At 70°F (21.1°C)the pressure is 850 psig (5.86 MPa, 59.8 kg/cm2) and the contents is about 45 lbm (20.4 kg) liquidand 5 lbm (2.3 kg) gas. At 110°F (43.3°C) a full CO2 bottle will have 1800 psig (12.4 MPa, 127kg/cm2) of pressure, at 140°F (60°C), 2600 psig (17.9 MPa, 183 kg/cm2). The pressure inside acarbon dioxide bottle decreases during discharge because the evaporating liquid cools the bottlecontents, thus lowering the vapor pressure.

Usable CO2 — Freezing. A 50 lbm (22.7 kg) bottle has 435 standard cubic feet (12.3 m3) of gas.However, the CO2 may freeze during the bottle discharge. A portion of the contents in a CO2 bottlewill be liquid for bottle pressures between approximately 60 psig (414 kPa–g, 4.22 kg/cm2) and1050 psig (7.24 MPa, 73.9 kg/cm2). During a bottle discharge, the �uid contents at 60 psig (414kPa, 4.22 kg/cm2) will be at approximately -56° C (-68.7°F). As gas continues to be depleted fromthe bottle, the liquid will transform into a solid.

Bottles initially at 30° F (-1°C) will discharge only 63% of their contents; bottles initially at 110°F(43.3°C) will discharge only 85% of their contents. The relationship between available % andinitial temperature is approximately linear (a mid point is 73% at 70° F (21°C)). Bottles which aredisconnected from the manifold will not continue to discharge their gas to the generator as theywarm up. Therefore, in systems with all the CO2 bottles connected to bottle manifold connections,the bottle freezing phenomena has less of an effect.

Bottles which are partially depleted will return to the full bottle pressure of 850 psig (5.86 MPa,59.8 kg/cm2) at 70°F (21° C) after they warm up if they have about 30% or more of the CO2 stillinside.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 39

30621127-000-3BD-EE-00100-CO2 REV 002

51 of 56

Page 52: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

C. Carbon Dioxide in Pipes and Valves

During the purge step of admitting CO2 to the generator, the carbon dioxide should go through twostages of pressure drop. The �rst is through a pressure regulator, the second is through an ori�ce. Thetwo could be combined into one ori�ce, but �ow rate would then vary considerably with bottle pressure.

CO2 Feed Piping Should Have a Region Where Solid CO2 Can Form. Carbon dioxide will form solidprecipitation as it goes through a �ow restriction (such as a valve or ori�ce) if the pressure on the dis-charge of the restriction is below approximately 60 psig (414 kPa, 4.22 kg/cm2) and the gas is cold,such as during the second half of a bottle discharge. Therefore the piping should be designed to accom-modate a build–up of solid carbon dioxide and operating procedures should be set up to periodicallyvaporize it by admitting warm CO2 or heat from another source.

The ori�ce which regulates carbon dioxide �ow rate should be designed so that the precipitation accu-mulates in a large diameter pipe. The large diameter pipe provides surface for heat transfer from theambient environment and will greatly extend the time before the solid carbon dioxide accumulationrestricts �ow rate. Precipitation should not be directed into a globe valve or small diameter pipe elbow.A well designed system will accommodate solid CO2 accumulation without forming a blockage if theoperators simultaneously open all the CO2 bottles which are connected to manifolds.

If there is a pressure regulator on the bottle manifold, then it should be designed to have a dischargepressure substantially higher than 60 psig (414 kPa–g, 4.22 kg/cm2), such as 100 psig (690 kPa–g, 7.0kg/cm2) or 125 psig (862 kPa–g, 8.79 kg/cm2). In addition, it should have a �ow rate capacity (inscfm’s) greater than the �ow rate expected through the ori�ce. If it does not have a high enough �owrate capacity, then it will not pass enough �ow to maintain the 100 psig (690 kPa–g, 7.0 kg/cm2) or125 psig (862 kPa–g, 8.79 kg/cm2), and there will be a possibility of solid CO2 accumulating in thesmall bore piping immediately downstream of the pressure regulator. More than one bottle manifoldpressure regulator can feed the ori�ce which regulates carbon dioxide �ow rate. See regulator sizinginstructions below.

Vaporizing Solid CO2 Blockage. If the operator experiences blockage due to solid carbon dioxidebuild–up in the piping, there are several methods of vaporizing it.

1. More Bottles Simultaneously to Avoid Rapid Boiling of CO2. Bottles which discharge too quicklywill have rapid boiling inside the bottle. The rapid boiling causes foam and splatter which willtransport liquid to the top of the bottle. If it is suspected that some liquid is being dischargedfrom the bottle, then more bottles should be discharged simultaneously. By having more bottlesdischarge simultaneously, they each will discharge more slowly, and the boiling will not be sorapid.

2. Less Bottles Simultaneously to Periodically Vaporize Solid CO2 Build–Up. If blockage is due tosolid carbon dioxide forming after a �ow restriction, then less bottles should be discharged simul-taneously. For example, if the blockage occurs during the last few minutes of �ve bottles beingdischarged, then there will be less blockage after four bottles are discharged. When the next fourbottles are initially discharged, the relatively warm carbon dioxide will vaporize the solid carbondioxide, which had accumulated.

3. Heating Pipes With Water. Water can be dripped onto pipes and valves to provide heat to vaporizesolid carbon dioxide.

40 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

52 of 56

Page 53: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

CO2 Heaters May Not Operate In An Emergency. Even if the carbon dioxide is being electricallyheated, the system and operating procedures should be designed to accommodate solid carbon dioxideprecipitation and the operators should be familiar with effects of solid carbon dioxide. The heater maynot be available during an emergency situation if the AC electrical power is lost.

Optimal CO2 Storage and Piping Design. The best carbon dioxide supply system is one where thereare enough carbon dioxide bottles connected for fully purging the generator. The advantages are that(a) the operator will not be busy removing and installing bottles in the event of an emergency purge,and (b) the full contents of the bottles are available because bottles which have had solid CO2 formwill eventually warm up and discharge their remaining gas. It would also be advantageous if the pipingis designed so that all the bottles can be opened simultaneously without the possibility of solid carbondioxide accumulating to the extent that it blocks the pipe to the generator.

D. Sizing the Carbon Dioxide Flow Ori�ce

The CO2 ori�ce should be sized to provide the optimum �ow rate of CO2 into the generator during thepurge process. A �ow rate, which is too high will waste CO2 because CO2 will mix with H2. A �owrate, which is too low will cause the process to outlast the DC seal oil pump battery life, assuming thepurge is being done because of an emergency after AC power is lost.

Optimum �ow rate is 120 scfm (4.2 m3/min) for a 2800 ft3 (80 m3) generator interior. The optimum�ow rate is approximately proportional to generator volume. The ori�ce will have an upstream pres-sure between 115 psig (792.9 kPa–g, 8.09 kg/cm2) and 135 psig (930.8 kPa–g, 9.5 kg/cm2) and adownstream pressure between 2 psig (13.8 kPa–g, 0.14 kg/cm2) and 5 psig (34.5 kPa–g, 0.35 kg/cm2).Therefore �ow through the ori�ce is choked (Mach Number = 1), greatly simplifying the calculation.

Use the �ow function relationship for choked �ow, which is:

mass �ow = area * (total pressure / sqrt (total temperature) ) * XX = sqrt ( k / R ) * sqrt ( ( 2 / ( k+1 ) ) ^ ( ( k+1 ) / ( k–1 ) ) )where R = 35.04 lbf*ft / lbm*R (0.1889 kJ/kgK) for CO2and k = 1.29 for CO2

Given average upstream conditions of 125 psig (862 kPa–g, 8.72 kg/cm2) and -10°F (-23.3°C) and adesired mass �ow rate of 120 scfm ( 4.2 s m3/min), the effective area of the ori�ce is 0.0536 in2 (35.0mm2). “The discharge co–ef�cient, Cd, for large pressure ratios such as this situation is 0.85 per “TheDynamics and Thermodynamics of Compressible Fluid Flow” by Ascher H. Shapiro (page 100).

Actual Area = Effective Area / Cd

The actual area of 0.063 in2 (42.5 mm2), the physical diameter of the �ow restriction should be between0.283 (7.2 mm). A standard manufacturing tolerance can be applied to the ori�ce diameter.

The calculation method is given so that generators with gas volumes substantially different from 2800ft3 (80 m3 can have their ori�ces custom sized. Note that area is proportional to �ow and inverselyproportional to pressure.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 41

30621127-000-3BD-EE-00100-CO2 REV 002

53 of 56

Page 54: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

E. The Hydrogen Flow Ori�ce

Because hydrogen does not form solid precipitation inside the pipe, the ori�ce may be in the vicinityof valves. Therefore it is included in the gas control valve assembly, and does not have to be providedby others.

F. Sizing the Manifold Pressure Regulator Valves

The pressure regulator valves have to be sized large enough to pass enough �ow so that the downstreamori�ce is the most restrictive component of the circuit, and therefore the ori�ce is the device whichcontrols the �ow rate. This is especially critical for the CO2 circuit. If the CO2 manifold pressureregulator valve is too restrictive, then the pressure immediately downstream of the regulator will bebelow 60 psig (414 kPa–g, 4.22 kg/cm2) and solid CO2 precipitation would form in the thin pipe afterthe bottled CO2 becomes cold.

A typical manifold regulator is the Victor SR–703–ME–996 (0780–0805). The Victor catalog provides2 data points for air with 125 psig (862 kPa–g, 8.79 kg/cm2) delivery pressure: (50 scfm at 200 psig)(1.4 s m3/min at 1.380 MPa, 14.07 kg/cm2) and (183 scfm at 2000 psig) (5.1 s m3/min at 13.8 MPa,140.7 kg/cm2). The conversion factors from the catalog are 0.81 for CO2 and 3.79 for H2. Therefore,for CO2, the �ow rates are (40 scfm at 200 psig) (1.1 s m3/min at 1.380 MPa, 14.07 kg/cm2) and (150scfm at 2000 psig) (4.2 s m3/min at 13.8 MPa, 140.7 kg/cm2).

Given 40 scfm at 200 psig (1.1 s m3/min at 1.380 MPa, 14.07 kg/cm2), there would have to be three(3) of this style regulator for 120 scfm (3.4 s m3min). Below 200 psig (1.380 MPa, 14.07 kg/cm2),some solid CO2 precipitation may form near the regulator. If only two (2) regulators are used, solidCO2 precipitation may form with bottle discharge pressures up closer to 400 psig (2.76 MPa, 28.15kg/cm2).

If there is one pressure regulator for each bottle manifold, then the operator should open bottles fromeach of the manifolds simultaneously, so that all the regulators are in use simultaneously.

G. Calculating the Quantity of CO2 Bottles Required to Purge a Generator

It is important to have enough gas immediately available for a carbon dioxide purge of the generatorof hydrogen. A typical CO2 bottle, when fully charged, has 50 pounds (22.7 kg) of carbon dioxide.When expanded and heated to ambient inside the generator, the typical bottle has 435 cubic feet (12.3m3) of gas. Of this gas, a fraction, x, is available prior to the bottle being removed from the manifold.If the bottle is not removed, x = 1. The fraction, x, may be less than 1 because of CO2 which freezesin the bottom of the bottle.

Because some mixing of gas will occur during purging, twice the generator worth of bottled CO2 isrequired to purge out hydrogen.

# bottles of CO2 = 2 * generator volume / ( x * volume of gas in a bottle)Example: Therefore, for a generator of 2800 ft3 (80 m3) and bottles originally at 32°F (0°C) forwhich x=0.64, 2*2800 / (0.64*435) = 21 number of bottles of CO2 are required to be availablein the event of an emergency purge.

42 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

54 of 56

Page 55: CO2 EE-00100-CO2-002

Hydrogen and Carbon Dioxide Gas Control System for NonPackaged Units GEK 103763d

H. Calculating the Quantity of H2 Bottles to Purge and Fill the Generator

The typical H2 bottle has about 200 cubic feet (5.7 m3) of usable hydrogen when warmed to ambienttemperature inside the generator. Because some mixing of gas will occur during purging, twice thegenerator worth of bottled H2 is required.

# bottles for purging = 2 * generator volume / volume of gas in a bottle

Additional bottles of hydrogen are required to pressurize the generator. Conservatively, this quantityis.

# bottles for �lling = n * generator volume / volume of gas in a bottle

where n is chosen from the chart below:

n �nal generatorpressure (psig)

(kPa–g) (kg/cm2)

1 15 100 12 30 200 23 45 300 34 60 400 45 75 500 5

The total number of hydrogen bottles which should be available prior to putting hydrogen into thegenerator is

# bottles of H2 = # bottles for purging + # bottles for �lling

Example: To purge and pressurize a generator of 2800 ft3 (80 m3) to 60 psig (about 400 kPa or 4kg/cm2), there should be 2*2800/200 + 4*2800/200 = 84 number of bottles available.

© General Electric Company, 2008. GE Proprietary Information. All Rights Reserved. 43

30621127-000-3BD-EE-00100-CO2 REV 002

55 of 56

Page 56: CO2 EE-00100-CO2-002

GEK 103763dHydrogen and Carbon Dioxide Gas Control System

for Non Packaged Units

GE Energy

General Electric Companywww.gepower.com

44 © General Electric Company, 2008. GE Proprietary Information. All Rights Reserved.

30621127-000-3BD-EE-00100-CO2 REV 002

56 of 56