Turbine by-pass system.pdf
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Transcript of Turbine by-pass system.pdf
Overview
Over the years, turbine-bypass technology has advanced along with that of the power
industry. F turbine-bypass systems have grown in sophistication to enhance
operational flexibility and to protect power plant components during a variety of transient
modes. With more than 1500 bypass valves supplied over the last 40 years and a strong
worldwide service network, our leadership has been proven time and time again.
Turbine-bypass systems are not only essential for the flexible operation of large coal-
fired power plants but play an equally important role in advanced combined-cycle
power plants. Turbine-bypass systems permit operation of the steam-generator independently
of the turbine during start-up, commissioning, shutdown and load disturbances. This enhances
operational flexibility during transient operating conditions. As a result, startup and reloading
times are reduced. In addition, equipment life and overall plant availability are increased.
To achieve the desired results, turbine-bypass systems must be adequately sized to meet
the needs of transient operating modes. F can effectively support plant designers
and plant operators in selecting and integrating a bypass system into an overall plant
design. In addition to providing original-equipment, we have extensive experience in
integrating bypass systems into existing plants and in retrofitting existing bypass valves that
have failed in service. Our worldwide sales and service organization and local engineering
centers are ready to support customers in their evaluation and engineering efforts.
F turbine-bypass systems meet the requirements of all governing boiler and valve
codes, including ANSI, ASME, TRD and many others.
Examples of CCI/Sulzer Bypass Systems:
1967 RWE Frimmersdorf, Germany(combined bypass and safety function)
1975 TEAS, Elbistan A, Turkey(once through boiler)
1982 Chubu Electric, Kawagoe 1&2, Japan(ultra-supercritical plant)
1988 HIPDC Shidongku, China(supercritical power plant)
1991 Korea Electric Power Corp., Korea(twenty supercritical units, Poryong, Taean,Hadong & others)
1993 Shanghai Municipal Electric Power Bureau,WaiGaoQiao 1-4, China
1993 China Light and Power, Black Point, China(eight combined cycle plants)
1993 Kansai Electric, Himeji Units 1-5/1-6, Japan(combined cycle units)
1995 Shell Australia Ltd., Geolong Refinery, Australia(system redesign and valve replacement)
1996 VEAG, Schwarze Pumpe, Germany(supercritical, combined bypass and safetyfunction)
1965-98 Various plants, Japan(over 40 bypass systems)
1971-98 Neyvilly Lignite 1-3, NTPC Rihand STPP, NTPC Talcher,CESC Budge Budge and other plants, India(over 100 bypass systems)
1972-98 Various plants, China(over 130 bypass systems with all utilities)
1981-98 EGAT, Mae Moh 4-13, Rayong, Ratchaburi, Thailand(drum, combined cycle, and supercritical plants)
1988 Pacific Gas & Electric, Moss Landing, USA(supercritical, cyclic operation)
1990 New England Power Service Co., Brayton Point, USA(supercritical, cyclic operation)
WaiGaoQiao Power Plant, China
Heat RecoverySteam Generator
Deaerator
Steam Turbine
HP-Bypass
Gas Turbine
LP-Bypass
IP-Bypass
HP-SystemIP-System
LP-System
GT GIP LPHP
Typical combined cycle power plant schematic
Purpose
Faster Start-up and Minimized Thermal Stress
A good turbine-bypass system reduces start-up time under cold, warm, and hot conditions. The turbine-
bypass system provides continuous flow through the superheater and the reheater, and allows for higher
firing rates which result in quicker boiler warm-up. It also controls superheater and reheater pressure during
the entire startup, keeping thermal transients in the boiler to a minimum. Operating experience shows that
power plants equipped with F turbine-bypass systems experience reduced start-up times and
much less solid particle erosion of the turbine blades, reducing the need for expensive repair and replacement.
Temperature Matching
A F turbine-bypass system allows optimum steam to metal temperature matching for all start-
up modes. The boiler load can be selected to reach the desired superheater and reheater conditions
for turbine start. This results in reduced start-up time and extented life for main turbine components.
“F turbine-bypass systems are recognized aroundstartup, preventing needless energy loss, lengthening
Avoid Boiler Trip after Load Rejections
A fast-acting F turbine-bypass system allows boiler operation to continue at an optimal
standby load while demand for turbine load is re-established after a load rejection. The turbine
can cover house load requirements. Pressure and temperature transients invariably associated
with boiler trip and restart are avoided.
Eliminate HP-Safety Valves
A F HP-bypass valve sized for 100% MCR capacity can serve as an HP-safety valve
when equipped with the necessary safe opening devices. This eliminates the need for separate
spring-loaded HP-Safety valves, associated piping, and silencers and can save millions of dollars
in equipment and maintenance costs. Our engineering staff is qualified to review applicable codes
and system designs.
Preventing Energy and Feedwater Loss
Even when regulations require spring-loaded safety valves, a large capacity F turbine-
bypass system with fast acting actuators can avoid lifting of the safety valves and the resulting
energy and water losses under almost all upset conditions.
Typical coal fired supercritical plant schematic
Steam Turbine
RH-Safety Valve
DeaeratorPreheaterEconomizer
Evaporator
Superheater
Reheater
HP-Bypass
Condenser
LP-Bypass
p
p
p
T
T
SafetySystem
SafetySystem
HP-BypassController
HP IP LP G
LP-BypassController
SafetySystem
the world as the best turbine-bypass systems for fastertrouble-free plant life and increasing plant reliability.”
Sizing of the F Turbine-Bypass System
Turbine-bypass system sizing considerations must take into account all plant operating
conditions such as the number of warm starts, hot starts and requirements for house load
operation. Later in plant life, cyclic operation may become common. Sizing of low pressure
turbine-bypass valves must take into account the desired reheater pressure for turbine
start as well as condenser capacity.
F turbine-bypass systems are custom designed to meet the specific capacity
requirements of the individual plant. Capacity can range up to 100 percent of the maximum
continuous rating (MCR) boiler steam flow for the HP-bypass as well as for the LP-bypass.
Integrating Turbine-Bypass Systems
F turbine-bypass systems can be supplied for any type of fossil-fired power plant.
The schematics on pages 4-5 show the integration of a turbine-bypass system into a
combined-cycle power plant (CCPP) and a 500 MW fossil-fuel-fired supercritical plant.
The chart to the right shows a typical hot-startup characteristic for a supercritical, fossil-
fuel-fired, 500 MW unit using a F turbine bypass system. Forty minutes after
lighting the steam generator, the steam temperature is matched to the turbine metal
temperature. The bypass system flow rate equals the difference between steam-
generator and turbine flows. In this case it is 22 percent of full flow. The corresponding
steam-generator pressure is 30 percent of full-load pressure (80 bar [1160 psig] at 40
minutes compared to 260 bar [3800 psig] at full load).
The result is a required turbine bypass system capacity of approximately 70 percent
MCR at full load (percent-steam-flow divided by percent-pressure). Because of the
large bypass system designed into this particular plant, coal firing can be initiated
earlier, thus reducing the amount and cost of oil necessary in the start-up cycle.
minutes
%
100
100
50
50
0
Full LoadSynchr.
Pulverizers
Light up
0
˚C
500
400
300
200
100
0
barflowtemp press
S t e a m
Start-Up Time
300
200
100
4.2
4.1
3.1
2.42.3
2.22.1
1.1
1.1 Firing Rate2.1 Feedwater Flow2.2 Waterwall Flow2.3 Steam Flow (Superheater)2.4 Steam Flow (Turbine)
3.2
3.1 Superheater Pressure3.2 Reheater Pressure4.1 Superheater Temperature4.2 Reheater Temperature
Hot start of a supercritical 500 MW unit
“F has developed a wide range of technologies for
supplier of turbine-bypass systems, F supplies researched
Valves
Duty of a Turbine-Bypass System
The primary job of any turbine-bypass system is steam conditioning — high-pressure throttling
integrated with desuperheating. Bypass valves must be able to perform these functions
and achieve the desired pressures and temperatures without undue noise and vibration
and without destructive valve-trim wear. In addition, bypass valves must perform these
functions under severe temperature cycling.
Depending upon plant design, bypass systems must also perform additional functions
such as safe HP-bypass opening and LP-bypass closing for condenser protection during
transient operating periods.
F offers the advanced valve technology to meet these severe service
requirements. With its distinctive body design, F is recognized as the lasting
turbine bypass valve technology around the world.
Lower Noise and Vibration
Excessive vibration in a turbine bypass valve can break pipe hangers and shake
accessories off actuators, resulting in high maintenance costs and unscheduled downtime.
Using wave-principle theory, F developed the unique WING-type stem with
contoured cage design for use in high pressure bypass systems. Unlike conventional plug
designs, the WING-type stem has a specially contoured profile to produce wave
interference. This effectively “cancels out” some of the aerodynamic effects as they impact
valve parts. This design incorporates specially engineered channels that divide the steam
flow into discrete paths and increase generated noise frequency. This higher frequency
noise is more easily absorbed by the adjacent piping and results in noise-level reduction
of more than 10 dBA as compared to conventional designs.
F WING-type trim
valves, desuperheating, actuators and controls. As the original
and proven solutions to suit the needs of any type of plant.”
In addition, the WING-type stem with contoured cage creates a highly turbulent zone
immediately down-stream of the valve seat in drum and supercritical plants. This turbulent
zone is ideally suited for the in-body injection of desuperheating spraywater. Also, noise is
attenuated by water injection inside the valve. This valve design ensures that this turbulent
zone is removed from any valve surface to eliminate a source of vibration.
For installations requiring strict noise control, F offers a low noise DRAG® solution.
DRAG® solutions provide the lowest noise for any turbine-bypass available in the industry.
Noise generated by the valve can be kept to below 85 dBA throughout the entire operating
range without the use of back pressure diffusers and acoustic insulation.
CCI DRAG® Disk Stack
With their distinctive body design, F are recognized as the benchmark of
turbine bypass systems — Distinctive, Complete, Proud, Swiss — F
Thermographic analysis of a bypass valve during start-up showingcomplete water atomisation inside a F DRE valve
Thermally Efficient Design
F turbine bypass systems feature unique thermally efficient bodies designed to
eliminate the stresses from thermal transients associated with cycling duty. The body designs
incorporate thin-walled spherical sections to produce compact, strong valves that are
easily recognized as the distinctive F style.
Isolation Valves
Specifications often call for steam-isolation valves upstream of the LP-bypass valve
for condenser protection. F supplies LP-bypass valves which combine the
control function with a safe-closing function. However, if the specification requires a
bypass system with separate control and isolation valves for reasons of a different
plant safety philosophy, we an also supply steam isolation valves.
Reheater Safety Valves
F has developed many different
technologies for desuperheating. The
primary job for any type of desuperheater
is the complete evaporation of the
injected water — this must be
accomplished without any water droplets
hitting the pressure boundary walls of the
valve or downstream piping. Key factors
affecting desuperheater performance are
the degree of atomisation of the injected
water and the mixing with the steam, and
second, quick evaporation with proper
location and direction of the spray water
jet. Complete evaporation must be
attained before the first pipe bend to
prevent any erosion caused by high-speed
droplets contacting the pipe walls.
The degree of spraywater atomization
attained is determined by the relative
speed of steam flow to that of injection
water flow. Full atomisation is the result of
high water injection speed and injection
of the desuperheating water into a zone
of turbulent, high-speed steam flow. In
addition, factors such as accuracy of
controls, flow range and piping
arrangement can affect the quality of
atomisation. Finally, good atomisation can
only be achieved when the proper
spraywater valve is selected. A good
spraywater valve will have multi-stage
pressure letdown to eliminate cavitation
and trim erosion in order to maintain fine
temperature control at all steam flows.
F experience and technology
ensures the optimal solution of complete
atomisation every time.
In-Body Desuperheating
For HP bypass applications in a drum or
supercritical power plant, Frecommends in-body desuperheating.
In-body desuperheating makes the best
use of the principle of water injection into
a zone of high steam-flow turbulence. The
spraywater is fully atomised before the
steam exits the valve body, thereby
providing the shortest evaporation length.
In-body desuperheating provides the
best atomisation available.
Desuperheating
“The desuperheating function in a F turbine-bypass
and quick evaporation of the injected water without
Steam conditioning valve type DREusing inbody desuperheating technology
Proper design of in-body desuperheating
requires a detailed understanding of the
flow pattern inside the valve at all load
conditions. F has done extensive
research into these flow patterns, including
spraywater injection and atomisation with
the help of dynamic numerical calculations.
Optimum arrangement of the injection
nozzles, material selection, and shape
and hole pattern of the cage around
the injection zone is the result of this
extensive research.
F is the only turbine bypass
system supplier that has perfected in-body
desuperheating technology to provide
long lasting, fully integrated steam-
conditioning within the valve body. With
this technology, we recommend only a
very short straight length of piping
downstream of the valve. In addition,
piping material downstream of the valve
may be switched to carbon steel instead
of alloy material.
must provide for excellent steam and spraywater mixing
creating thermal stress that can cause system damage.”
Steam conditioning valve type NBSEusing spring loaded spray nozzles
Spring-Loaded Injection Nozzles
Spring-loaded nozzles are typically used for LP
bypass applications, but can be used in all
types of combined cycle power plant
applications. The atomizing principle of spring-
loaded injection nozzles is based on high-
speed injection. Due to the design of the
spring-loaded nozzles, a sufficient injection
pressure and injection speed exists at minimum
load. The injection speed results not only in good
atomisation but also in a sufficient penetration
of the spraywater into the steam flow.
In addition, the F spring-loaded
nozzle incorporates a unique swirl pattern
which provides rotational energy to the
spraywater over the entire range of flow
conditions. This insures an even distribution
which produces good mixing of steam and
spraywater with extremely good rangeability.
Ring-Type Desuperheater
For LP bypass applications, Frecommends separate desuperheating
downstream of pressure reduction. In a ring-
type desuperheater, which is used primarily in
drum and supercritical power plants, steam
turbulence is created by the shape of the
steam-flow. The steam velocity is increased by
a contraction of the flow path, and the
injection takes place where the flow path
abruptly expands. Mixing takes place in this
region of turbulence to produce the shortest
distance required for atomisation.
Ring type desuperheater EK
F DRAG® steam conditioning valve
using steam assisted STEAMJET desuperheating technology.
The desuperheater is also available as a separate
downstream component.
Steam-Assisted Desuperheaters
F has developed the STEAMJET
desuperheater for steam conditioning
applications requir ing the best possible
atomisation outside of the body. The
STEAMJET provides significantly better
atomisation than the ring-type and spring-
loaded nozzle desuperheaters currently
available in the industry. The design is
based on a combination of high-speed
water injection into a high-velocity , venturi
steam flow. The "compound swirl" nozzle
provides high injection speed while the
atomising steam provides a velocity which
is virtually independent of the main steam
flow. The spray pattern is centered in the
piping to produce even temperature
distribution at all flow conditions.
F STEAMJET produces the shortest
distance required for atomisation of all
downstream desuperheaters.
Sparger Tubes
F provides custom-engineered
condenser sparger (dump) tubes for the
introduction of steam from the bypass valves
to the condenser. These optional sparger
tubes are custom designed to meet the space
constraints of the specific condenser and to
protect the internals of the condenser.
As required, we will engineer the sparger tubes
to meet low-noise requirements.
Pneumatic actuator
Hydraulic power unit for a bypass system
Actuators and Controls
Reliable system operation is based on the proper
select ion and design of al l of the system
components . Using advanced technology
developed by F over years of testing and
experience, our expertise has produced the best
pneumatic and hydraulic actuation technology
in the industry.
Pneumatic Actuators
F pneumatic actuators feature a double-
acting piston designed to meet the application
requirements for stroke, speed, actuating force, and
positional accuracy. The actuator is equipped with
quick acting components to achieve stroke speeds
for bypass applications of one second.
F is the only supplier in the industry to provide
high speed pneumatic actuation with stable control.
Hydraulic Actuators
Hydraulic actuators are well suited for applications
requiring high force and high stroking speeds with
precise control. F provides the complete
system consisting of hydraulic cylinders, control devices,
positioners and hydraulic power units. The hydraulic
power units meet all safety requirements and consist
of a fluid tank, pumps, filters, accumulators, and the
necessary monitoring and controls.
“Turbine-bypass valves and their actuators and controls
must be matched for optimum system performance.”
Hydraulic actuator
F AV6 series bypass controller
Our hydraulic actuation systems and controls are
recognized as the original, long-lasting technology
for hydraulic actuation.
Safety Systems for HP Bypass valves
In countries where regulations allow the use of HP-
bypass valves as safety valves against superheater
overpressure, F can provide bypass valves,
actuators , and the necessary safety control
equipment. Safe trip devices can be easily mounted
on hydraulic actuators permitting the use of bypass
systems in place of safety valves. The complete safety
system has a type approval according to the
German TRD421 code.
F Turbine-bypass Controller
A well-designed bypass controller is important for
smooth plant operation, especially during plant
start-up, shut down, and load disturbances. We
have more than 25 years’ experience in designing
and supplying turbine-bypass controllers.
Our latest AV6 series turbine-bypass controller uses
advanced control strategies. The state controller
with observer (SCO) provides more precise control
than standard systems, thereby producing less thermal
cycling stresses on valves and pipings.
The AV6 series controllers can easily interface to any
boiler and turbine control system.
CCI World HeadquartersTelephone: (949) 858-1877Fax: (949) 858-187822591 Avenida EmpresaRancho Santa MargaritaCalifornia 92688 USA
CCI Switzerlandformerly SULZER THERMTECTelephone: 41 52 262 11 66Fax: 41 52 262 01 65P.O. Box Hegifeldstrasse 10CH-8404 Winterthur, Switzerland
CCI JapanTelephone: 81 726 41 7197Fax: 81 726 41 7198194-2, ShukunoshoIbaraki-City, Osaka 567Japan
CCI KoreaTelephone: 82 341 85 9430Fax: 82 341 85 055226-17, Pungmu-RiKimpo-Eup, Kimpo GunKyunggi-Do, South Korea
CCI UK Technology CentreNorth EuropeSharp StreetWorsley, ManchesterM2B 3NA, England
MC-310-10/98 310
“We Solve Control Valve Problems”Sales & Service Locations Throughout The WorldE-Mail: [email protected] Site: http://www.ccivalve.com
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