modelling of combined cycle powerplants with ebsilon...

Modelling of Combined Cycle Powerplantswith EBSILON®Professional

Dr. Hans-Peter Wolf

AGH Letniej Szkoły Energetyki 2018

Modelling of Combined Cycle Power Plant with EBSILONProfessional 2

Stepwise introduction into modelling of gas turbine process and heat recovery boiler (HRSG)

• Gas turbine process using individual components

• HRSG 1-pressure

• HRSG 2-pressure

• HRSG 3-pressure

• Reheat

• Separation of superheat and reheat

• HRSG and steam turbine in Ts – diagram

• Superheat of IP and LP steam

• HRSG in QT - diagram

• Water injections

• Auxiliary burner

• VTU Gas turbine library for a particular gas turbine

• Alternative heat exchanger components

• EbsWizard



Exercise, Step 1 Modelling of Gasturbine

Modelling of gasturbine with Ebsilon-components

- compressor (comp. 24)

- Combustion chamber (comp. 22)

- Turbine (comp. 23)

(detailled Modelling using VTU Gasturbine library -> Exercise, Step 10)



Exercise, Step 2, Adding a HRSG (1-pressure)

Modelling of HRSG with components

- Heat exchanger (comp. 26) for superheater and economizer

- Evaporator with drum (comp. 70)AGH Letniej Szkoły Energetyki 2018


Exercise, Step 2, Explanations

The recommended procedure for configuration of components :

• Superheater :- Specification of steam outlet temperature (measurement)

- FTYPHX = „Superheater“- FSPECD = „both cold stream and one hot stream temperature“

• Evaporator (with drum) :- FSPECD = „specification of pinchpoint PINPN“

- PINPN = 5K (default value)

- FTAPPN = „by specification value TAPPN“

- TAPPN = 3K (default value)

• Economizer :- FTYPHX = „Economizer“

- FSPECD = „both cold stream and one hot stream temperature“



Exercise, Step 2, Explanations

Alternative Procedure for configuration of components(if no heater outlet temperatures and Terminal TemperatureDifferences are known):

• Superheater :- FSPECD = „Effectiveness Method“- EFF = 0.8 (default value)

• Evaporator (with drum) :- FSPECD = „Effectiveness given as EFF“

- EFF = 0.96 (recommended value)

- FTAPPN = „T1 given externally“

• Economizer :- FSPECD = „Effectiveness Method“- EFF = 0.8 (default value)



Exercise, Step 3, 2-pressure HRSG

- Splitting the turbine into HP and LP turbine

- LP drum supplies steam to LP turbine



Exercise, Step 4, 3-pressure HRSG

- Splitting the turbine into HP-, IP- and LP-turbine



Exercise, Step 4, 3-pressure HRSG in Ts-diagram

Challenge: steam quality at LP turbine outlet too small(same with 1- and 2- pressure HRSG at same steam parameters)

XX < 0.9



Exercise, Step 5, Reheat

- Steam leaving HP turbine is heated again

- As a consequence in Ts-diagram the turbine-expansion isshifted to the right (-> higher steam quality)



Exercise, Step 5, 3-pressure HRSG with Reheat in Ts-diagram

Challenge: Heat in fluegas after superheater not sufficient toreach desired reheat temperature

X ~0.9

T < 540 °C



Exercise, Step 6, Splitting the superheater and reheater

Splitting the superheater and reheater allows higher reheat steamtemperature (because superheater 2 takes less heat from fluegas) A splitting of superheaters and reheaters into additional heaters is possible



Exercise, Step 6, Splitting of Heaters in Ts-Diagram

The desired reheat temperature (540 °C) can be rreached.

When mixing steam into cold reheat and before LP-turbine, there are significant

temperature differences (-> exergy loss)

T = 540 °C



Exercise, Step 7, Superheat of IP and LP steam

By superheating IP and LP steam, exergy losses are reducedwhen mixing the steam



Exercise, Step 7, Superheat of IP/LP steam in Ts-Diagram

When mixing streams with similar temperature, the exergy losses are reduced



3-pressure HRSG in QT-Diagram

Significant difference in the „slope“ dT/dQbetween fluegas side and water/steam side(because of high fluegas mass flow)

But temperature differences(pinchpoints) are relatively small(compared to coal fired boilers)



Comparison to coal-fired boiler: coal fired boiler in QT-Diagram

In coal fired boilers (at same thermal power) significantly lower fluegas flow (because fluegastemperature is much higher)

Higher exergy losses in boiler becauseof larger temperature differences in heattransfer

Pinchpoint

(at „cold end“)



Comparison: 1-pressure HRSG in QT-diagram

In 1-pressure HRSG pinchpoint is located „in the middle“-> large difference between feedwater ínlet temperatureand fluegas outlet temperature

The location of the pinchpoint (-> evaporationpressure) determines the fluegas losses

Pinchpoint

(„in the middle“)

High fluegas outlet

temperature and

losss

Therefore: Evaporation at different pressure levels toreduce the fluegas outlet losses



Exercise, Step 8, Water injections into SH and RH

The injections should be very small in the Design case (0.001 kg/s).

The controllers should be active only in Off-Design

Both controllers control theinjection massflows so, thatthe target steam temperaturebehind the heaters ismaintained (i.e. not exceeded)



Exercise, Step 9, Auxiliary burner

The auxiliary burner should be deactivated in Design case

The controllers should be active only in Off-design

In Off-design the controller setsthe fuel flow to the auxiliaryburner so, that the desiredsteam temperature is reached



Exercise, Step 10, VTU GT-Lib for realistic GT data

Replace individual Ebsilon components of the GT with comp. 106,

Select a proper gas turbine (for example Siemens SGT5-3000E)AGH Letniej Szkoły Energetyki 2018


Exercise, Step 10, VTU GT-Lib for a particular gas turbine

Calculates realistic results using manufacturers data

New Gasturbine Data

Meanwhile (GT-Lib Version 5) more than 600 Turbinesfrom 13 manufacturers

(Alstom, Ansaldo, Capstone, Centrax, GE, Hitachi, Kawasaki, MAN, Mitsubishi, OPRA, Rolls-Royce, Siemens, Solar Turbines)

if required by the customer, datasets for additional turbines canbe created




Consistent

Reference Conditions




The maximum loadcase for the auxiliary burner is encountered at lowambient temperatures, because then the fluegas temperature is low

Correction curve for fluegas outlet temperature as function of ambient temperature for

Siemens „SGT5-3000E (41MAC) Oil“




Also in Off-design there is a drop in fluegas temperature

Correction curve for fluegas outlet temperature as function of ambient temperature for

Siemens „SGT5-3000E (41MAC) Oil“



Exercise, Step 11, Auxiliary burner and Design case

Because the fluegas massflow is increased (when operating theauxiliary burner), it is recommended to use the case with maximumfiring of the auxiliary burner as the Design case for the HRSG :

• Define the case with maximum firing of auxiliary burner as theDesign case for the complete plant



Exercise, Step 11, auxiliary firing in QT-diagram



Alternative heat-exchanger componentscomponent 20, drum

Comp. 20 : drum, for the separate modelling of evaporator anddrum



Alternative heat-exchanger componentscomp. 61, heat-exchanger with exponents

This heat-exchanger can be uses as alternative to comp.26

The specification values are the same like in comp. 26 with thefollowing additional options :

When specifying the Alpha-values of fluegas and water/steam side, the component allows to calculate the heat-transfer area A and theheat transfer coefficient k

For the Alpha-values of fluegas and water/steam side plausible valuesare recommended (-> Online help of comp.61)

The Off-Design performance is calculated like the following

• 1/k = 1/ αi+1/αa

• αi/ αiN = (M1/M1N)**EX12

• αa/αaN = (M3/M3N)**EX34 *(1.-0005*(T34-T34N))



Alternative heat-exchanger componentscomp. 62, Duplex-heatexchanger

Duplex-heatexchanger (as extension of comp.61) as combinationof 2 heat-exchangers



Alternative heat-exchanger componentscomp. 88 and 89, boiler heating surface

Instead of the aforementioned heat-exchanger components also theso-called „boiler components“ comp.88 („Boiler: fluegas zone“) andcomp.89 („Boiler: bundle heating surface“) can be used.

These components allow to calculate the heat-transfer taking intoacount geometry and material data.

The heat transfer coefficients (Alpha values) are calculated fromgeometry and material data according to VDI Wärmeatlas Mb4 (there is an English edition, the „VDI heat atlas“)

Also a heat-transfer by radiation between neighbouring heatingsurfaces is taken into account by these components

Remark: only since Ebsilon Rel.11 Patch 4 correct calculation according to VDI

Wärmeatlas. Earlier there were some simplified calculations



EbsWizardAssisted creation of complete model

The EbsWizard allows to create a model of a GT + HRSG + water/steam-cycle in very short time (5 minutes)

(prerequiste: VTU GT-Lib)



EbsWizardAssisted creation of complete model

Modifications of internal details of Macros is possible by editing the Macros


modelling of combined cycle powerplants with ebsilon...

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