PowerPlantSim 2013 Conference

Fossil Track January 28-30, 2013

Presented by: Robert Lancaster Simulation Program Director – GP Strategies 970.290.1754 rlancaster@gpstrategies.com www.gpworldwide.com

Using a High Fidelity Simulator to Study and Mitigate the

Effects of Frequent Cycling and Extended Unit Shutdown on

Large Coal Fired Units

Background

• With the changing electrical needs throughout the country and the construction of gas fired combined cycle units, some base loaded plants today are more often becoming load following units.

• With load following comes the need for different operational profiles for unit operation.

EPRI Project

• Develop and conduct a survey for both drum and once-through supercritical coal-fired units identifying the following: – Current problems and constraints – Operating experience – Problems to overcome – Significant problems or obstacles – Areas needing additional resolution

EPRI Project

• Develop a test strategy using: – Survey results – Best engineering practices

EPRI Project

• Outcome of Testing: – Strategies to minimize thermal fatigue during

frequent cycling – Establish methods to maximize unit turndown

optimizing unit operational flexibility

EPRI Project

• Testing Should Address: – Necessary boiler and turbine instruments – Possible modification to boiler process and

procedures – Mill configuration, firing rates, combustion

stability and heat distribution – Use of boiler vents and drains – Secondary air flow setting – Steam temperature control

EPRI Project

• Testing Should Address (cont’d): – Sootblowing strategies – Use of startup fuels – Water chemistry – Coal type – Air pollution control equipment performance

impact

EPRI Project

• Testing Should Address (cont’d): – Steam turbine process and procedure

modification including: • Expanded sliding pressure operation • Modified transfer point from partial to full arc

admission – Startup and Shutdown consideration – Operating limitations for boiler, turbine, and

emission control equipment

Simulator Selection Criteria

• Must be an EPRI Member • Simulator must:

– Be for a large coal fired unit – Contain the desired fidelity to perform low

power testing – Be portable to allow remote testing – Be fully emulated to limit the cost of third party

software

Other Factors

• Host utility must agree to allow use of their simulator models for the testing.

• Simulator vendor must agree to allow the simulator software to run on GP hardware.

• Host utility must be willing to provide plant specific data related to the simulated unit.

EPRI Requirements

• The simulator must be able to provide accurate data at all turbine extraction points to allow detailed turbine stress analysis using EPRI software.

• The simulator must accurately reflect boiler pressure and temperature conditions throughout the unit load range.

GP Involvement

• Provided the fidelity requirements needed on the simulator to perform the needed low power testing.

• Developed survey questions for the industry related to the need for low power testing and methods currently being used in the industry.

• Results from the survey would help provide the test criteria needed during the simulator testing.

Simulator Selection

• Progress Energy was willing to support the low power testing as an EPRI member and allow the use of one of their simulators for the testing.

• Roxboro Unit 2 simulator for a 670 MW Drum Coal Fired Unit was selected.

• Western Services Corporation (WSC) – The simulator vendor was willing to support the project.

Simulator Setup

• The WSC software was delivered to the GP office and installed on a single computer for initial testing and review.

• Additional computers were networked to the server to provide a more complete test environment.

Portable Simulator Setup

Initial Simulator Testing

• The unit simulated was of the following unit design: – CE Forced Circulation Drum Type Boiler – GE MHC Turbine Generator – Steam Driven Boiler Feed Pumps without a

DA between the Condensate and Feedwater System

General Simulator Comments

• Most Fossil Power Pant Simulators are designed as training simulators and not as engineering tools.

• Since the simulators are designed as training simulators, testing of simulator fidelity only considers its effectiveness as an operator training tool.

Simulator Limitations

• Since a GE MHC unit was simulated, the ability to shift between FA and PA during the testing was lost.

• Turbine valve losses and nozzle efficiencies were not simulated since the unit could only operate in a PA mode.

• Turbine windage effects at low load on the turbine were not accurately simulated.

Limitations Continued

• Since the temperature effects at the turbine first stage were not modeled for FA and PA operation, the effects of this concept could not be utilized.

• Since on an MHC unit, the turbine valve operation is limited to a fix cam rotation, all four control valves and their nozzles were not fully simulated.

Limitations Continued

• The metal mass in the main turbine was not fully modeled limiting the simulators response to the following: – Shell Expansion Rate – Rotor Expansion Rates – Differential Expansion Indications

General Simulator Limitations

• The combustion process inside the boiler is very complex and unpredictable for this reason the following limits are expected: – Flame stability prediction is difficult, especially

with the varying coal qualities used in firing a typical boiler.

– Boiler soot conditions and soot locations are almost impossible to predict and optimum soot conditions are assumed in the simulator.

Unit Sliding Pressure Testing

• Since the simulator models were not fully tested in a sliding pressure shutdown, testing was conducted to verify boiler responses during sliding pressure.

• Plant data was obtained for a plant shutdown for a boiler tube leak when pressure was dropped to 600 psig prior to coming off line.

Test Results

• The boiler model responded and followed plant data within expected tolerances including: – Boiler firing rates – Air flows – Mill configurations – Superheat and reheat attemperator rates – Burner tilt setting – Turbine valve positions

Test Results

• Certain boiler conditions could not be fully verified such as the soot conditions on the water walls, superheaters, reheaters and economizers.

• Assumptions were made that boiler soot blowing had been conducted prior to the shutdown since boiler work was required to repair boiler tube leaks.

Model Modification Made

• Turbine models were modified to add all four control valves and the nozzles associated with each steam admission point into the turbine first stage.

Model Modification Made

• Turbine models were modified to add all four control valves and the nozzles associated with each steam admission point into the turbine first stage.

• Model modifications were made to allow operation of the GE turbine as an Admission Mode Select (AMS) turbine design.

Model Modification Made

• Turbine models were modified to add all four control valves and the nozzles associated with each steam admission point into the turbine first stage.

• Model modifications were made to allow operation of the GE turbine as an Admission Mode Select (AMS) turbine design.

• Turbine models tuned to reflect the GE predicted curves for FA vs. PA operation throughout the turbine load range.

Model Modification Made

Model Modification Made

• Turbine models were modified to add all four control valves and the nozzles associated with each steam admission point into the turbine first stage.

• Model modifications were made to allow operation of the GE turbine as an Admission Mode Select (AMS) turbine design.

• Turbine models tuned to reflect the GE predicted curves for FA vs. PA operation throughout the turbine load range.

• Turbine first stage temperature was verified to follow the GE expected sliding pressure operating curves.

GE Predicted 1st Stage Steam

Turbine Testing

• After the turbine valve configuration modifications were made, the turbine and boiler operation during sliding pressure down to 600 psig were compared using plant data.

• Turbine extraction pressure and temperatures were also compared with heat balance drawing at full unit load and minimum load of 165MW.

Turbine Testing

• At the minimum load point of 165MW, the 2nd low pressure heater extraction point temperature was off by139°F. – Since all other LP heaters were within 0.5%

this was determined to be a plant instrument problem.

• The high pressure heater extraction temperatures were approximately 30°F lower than plant data. (approximately 5% lower).

Turbine Testing

• Comparison of the simulator data with the plant heat balance at the same load point indicated that all parameters were well within 0.5%.

• The difference indicated some drop in turbine efficiency for initial design data.

• It was decided that the turbine and boiler models were representative of a large coal fired unit and satisfactory to perform the needed testing.

Summary of Shutdown Testing

• Three cases were used in the low power testing: – Case 1 – Typical Load Drop

• Full Pressure Operation • Partial Arc Turbine Operation

– Case 2 – Sliding Pressure – Pre-Programmed Controls

• Slide Start at 425 MW dropping to 1500 Psig at 200 MW

• Full Arc Turbine Operation – Case 3 – Modified Sliding Pressure

• Slide pressure to maintain CV opening > 90% • Full Arc Turbine Operation

Maximum Turndown Test Results

• 185 MW Net – Normal SCR Operation – No Support Fuel Required

• 60 MW – Minimum Sustainable Load – Support Fuel Required – Below SCR ammonia flow limits

Case 1: Full Pressure 283 MW Net

2400 PSIG – Partial Arc - First Stage @ 773°F

Case 2: Programmed Sliding Pressure 185 MW

1500 PSIG – Full Arc - First Stage @ 890°F

Case 3: Modified Sliding Pressure 185 MW

870 PSIG – Full Arc - First Stage @ 911°F

Case 1: Full Pressure 60 MW Net

2400 PSIG – Partial Arc - First Stage @ 589°F

Case 2: Programmed Sliding Pressure 60 MW Net, 1500

PSIG – Full Arc – First Stage @ 863°F

Case 3: Modified Sliding Pressure 60 MW Net,

800 PSIG – Full Arc - First Stage @ 942°F

Summary of Turndown Test Results

• The following table represents the steam temperature, gas temperature and turbine temperatures during the three tests while at 60 MWs

Unit 8 Hours Into Shutdown

• Boiler bottled up at shutdown • Turbine vacuum at atmospheric with gland

seal steam removed • Drum level controlled using condensate

pumps

Case 1: After 8 Hour Shutdown 430 PSIG – First Stage @

506°F

Case 2: After 8 Hour Shutdown 186 PSIG – First Stage @

700°F

Case 3: After 8 Hour Shutdown 135 PSIG – First Stage @

775°F

Summary of Unit Cool Down

• The following table represents the first stage metal temperature, reheat bowl and crossover temperatures achieved by each test; after 1 hour, and after 8 hours shutdown

Parameter Case 1 at 1 HR on SD Case 2 at 1 HR on SD Case 3 at 1 HR on SD

1st Stage Metal 559 823 903

RH Bowl 783 850 865

Crossover 513 545 550

Parameter Case 1 at 8 HR on SD Case 2 at 8 HR on SD Case 3 at 8 HR on SD

1st Stage Metal 504 700 775

RH Bowl 734 730 755

Crossover 475 520 525

Boiler Startup Case 1 and 3

• Utilized lower mills associated with the warm-up guns on Roxboro Unit 2.

• Established turbine drains to prevent any possible turbine water induction.

• On start of second mill the tilts were used to limit the main steam and reheat temperature ramps.

• Gas flow bypass the economizer to bring the SCR temperatures up for establishing ammonia flow.

Factors Effecting Turbine Stress During Startup after 8 hours

• Turbine Metal Temperature at the startup • Boiler Steam Pressure and Temperature

(Enthalpy) during startup • Rate of unit startup • Turbine Valve Operation • Initially the HP and IP turbines cooldown

until the steam temperature at the respective turbine inlet are greater than metal temperatures.

Steam Pressure and Temperature Response on

Startup

Case 1: Restart Metal Temperatures

Case 3: Restart Metal Temperatures

Results From Testing

• Case 1: Normal Start – 4.5 Hours Required to Reach 300 MW – 2.75 Hours of Support Fuel (Light Oil)

Required

• Case 3: Normal Start – 2.5 Hours Required to Reach 300 MW – 1.25 Hours of Support Fuel (Light Oil)

Required

“SAFER” Software Program (Stress and Fracture Evaluation

of Rotors)

• Developed in 1976-1980 following burst of TVA Gallatin IP/LP rotor in 1974.

• Evaluates remaining life for the following type of cracks: – Near-Bore Cracking (Primary Use) – Periphery Groove Cracking – Low Temperature Shrunk-On Disk Bore/Keyway SCC – High Temperature Blade Attachment Creep

1. GEOMETRY DATA: a) Radial/Axial dimensions of rotor cross-section including bore profile. b) Total Rim load for each stage (or #Blades, weight, length and C.G.). c) Seal Clearance diagram: need seal Height, and Radial/Axial clearances

for each stage. 2. OPERATIONAL DATA

a) Steam inlet and outlet conditions (T, P) as a function of time during a typical cold start of the unit (i.e., from the time the turbine is taken off turning gear to full load).

b) Approximate rotor metal temperature at startup (when the turbine is rolled off turning gear).

c) Rotor RPM versus time during the typical cold start. d) Heat balance diagram for the unit at partial and full load conditions. e) Overspeed trip settings for the unit. f) Projections for future operation of the unit: Number of Hours and Starts

per year.

EPRI SAFER Code – Inputs Needed

EPRI SAFER Code – Inputs Needed (cont’d.)

3. ROTOR MATERIAL DATA: a) Chemical composition (Nominal) b) Yield & Ultimate strength c) Fracture Toughness: FATT, and, Charpy V-Notch (CVN)

impact energy data or fracture toughness (KIc) values (if available)

4. NDE DATA:

a) Bore visual inspection & magnetic particle inspection results b) Boresonic results: Bore Profile (Diameter versus axial position) c) Indication Location (R, Theta, Z), Size and Axial Reference for

NDE data (from coupling face).

EPRI SAFER Code – Geometry Module

• Uses geometry templates to quickly assemble components into 2D Axisymmetric FE model

0 5000 10000 150000

20

40

60

80

Time (Sec)

KIC

(ksi*

sqrt

(inch))

KIC

comparison with fracture toughness - ac =0.1 inch

Fracture toughness (Normal)

KIC

(Normal,504 degF metal temp)

Case 1: HP Normal Startup with 504 Deg F Metal Temperature – Stress Intensity

0 1000 2000 3000 4000 5000 6000 7000 80000

20

40

60

80

Time (Sec)

KIC

(ksi*

sqrt

(inch))

KIC

comparison with fracture toughness - ac =0.1 inch

Fracture toughness (Normal)

KIC

(Normal,765 degF metal temp)

Case 3: HP Normal Startup with 765 Deg F Metal Temperature – Stress Intensity

0 1000 2000 3000 4000 5000 6000 7000 8000-20

0

20

40

60

80

Time (Sec)

KIC

(ksi*

sqrt

(inch))

KIC

comparison with fracture toughness - ac =0.1 inch

Fracture toughness (normal)

KIC

(normal,815 degF metal temp)

Case 3: IP Normal Startup with 815 Deg F Metal Temperature – Stress Intensity

Case 1: HP Fast Startup with 504 Deg F Metal Temperature – Stress Intensity

0 1000 2000 3000 4000 5000 6000 7000 80000

20

40

60

80

Time (Sec)

KIC

(ksi*

sqrt

(inch))

KIC

comparison with fracture toughness - ac =0.1 inch

Fracture toughness (Fast)

KIC

(Fast,504 degF metal temp)

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Temperature Plot @ 100 Sec.

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Temperature Plot @ 4000 Sec.

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Temperature Plot @ 8000 Sec.

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Stress Plot @ 100 Sec.

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Stress Plot @ 3000 Sec.

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Stress Plot @ 5000 Sec.

Case 1: HP Fast Startup with 504 Deg F Metal Temperature - Stress Plot @ 8000 Sec.

0 1000 2000 3000 4000 5000 6000 7000 800010

20

30

40

50

60

70

80

Time (Sec)

KIC

(ksi*

sqrt

(inch))

KIC

comparison with fracture toughness - ac =0.1 inch

Fracture toughness (Fast)

KIC

(Fast,70 degF metal temp)

Failure occurs !!

Case 1: HP FAST Startup with 70 Deg F Metal Temperature – Stress Intensity

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Temperature Plot @ 100 Sec.

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Temperature Plot @ 4000 Sec.

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Temperature Plot @ 8000 Sec.

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Stress Plot @ 100 Sec.

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Stress Plot @ 1500 Sec.

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Stress Plot @ 2000 Sec.

Case 1: HP FAST Startup with 70 Deg F Metal Temperature - Stress Plot @ 8000 Sec.

Questions or Comments

Presented by: Robert Lancaster Simulation Program Director – GP Strategies 970.209.1754 rlancaster@gpstrategies.com www.gpstrategies.com