Advanced Ultra-Supercritical Turbine Cycle

Steam temperature currently used for Ultra-Supercritical turbine cycle is 600 oC(1100 oF).   

Japanese manufacturers dominate 1000 MW class coal fired thermal power plant market in Asia including Korea in these days.  Manufacturers of USA and Europe are also constructing similar class Ultra-Supercritical coal fired thermal power plants, but their activities are not so vivid, because of strict environmental regulation in the region.

Meanwhile, manufacturers of USA, Europe and Japan are now studying Advanced Ultra-Supercritical thermal power plants applying + 700 oC (+ 1300 oF) steam temperature.   The purpose of applying higher temperature is to improve cycle efficiency and to reduce emissions per unit power generated.

Critical thing to apply + 700 oC steam temperature is to secure commercial alloy steel sustainable at the temperature.  Commercial means that the alloy steel should be available at industrial working environment, not at laboratory environment, and further accepted by national or international design codes.

Reference Document [1] is the technical paper for Advanced Ultra-Supercritical Power Plant (700 to 760 oC) Design, presented at Power Gen Asia in 2012, by Babcock & Wilcox U.S.A. and Toshiba Corp. Japan.   

ENGSOFT Lab studied the turbine cycle presented in the paper by ES_Rankine, and found that the final feed water temperature used in the paper is optimum, but the reheat pressure used in the paper has some room to improve.   It is found that the most optimum reheat pressure is 76 bara, while the paper uses 60 bara.

The following are results of the study.

 

Advanced Ultra-Supercritical Turbine Cycle Design Data

Major design data of turbine cycle used in the advanced ultra-supercritical power plant of Reference Document [1].

Output

: 840 MW Gross

HP Steam

:

- Pressure

: 300 bara (4350 psia)

- Temperature

: 700 oC (1292 oF)

Reheat Steam

 (Single Reheat)

- Pressure

: 60 bara (870 psia)

- Temperature

: 730 oC (1346 oF)

Condenser Pressure

: 3 inch Hg abs.

Final Feed Water Temp.

: 330 oC (626 oF)

No. of FW Heaters

: 9 (4 HP Heaters, 1 Deaerator, 4 LP Heaters, 1 or 2 De-superheaters)

LP Turbine

: 1 x Double Flows

Last Stage Blade

: 48 inch, 3000 rpm

Thermal Efficiency

: 6% Improvement comparing with 600 oC Class Ultra-Supercritical Turbine Cycle

 

Comparison between Ultra-Supercritical and Advanced Ultra-Supercritical

Simulation results of ES_Rankine for 850 MW class Ultra-Supercritical and Advanced Ultra-Supercritical turbine cycle are as below.

Description

850 MW Ultra-Supercritical

850 MW Advanced Ultra-Supercritical

HP Steam

 

 

- Pressure, bara

246

300

- Temperature, oC

600

700

Reheat Steam

(Single Reheat)

(Single Reheat)

- Pressure, bara

46

60

- Temperature, oC

600

730

Condenser Pressure, in Hg abs.

1.5

1.5

Final Feed Water Temperature, oC

294

330

No. of FW Heaters, each

8 (3 HP Heaters, 1 Deaerator, 4 LP Heaters

9 (4 HP Heaters, 1 Deaerator, 4 LP Heaters

LP Turbine

2 x Double Flows

2 x Double Flows

Last Stage Blade

48 inch, 3600 rpm

48 inch, 3000 rpm

Turbine Wheel Efficiency, %

HP : 89.5, Reheat : 92

HP : 89.5, Reheat : 92

Gross Heat Rate, kJ/kWh

7415.6 (48.55 % Eff.)

7060.6 (50.99 % Eff.)

Thermal Efficiency

Base

4.8% Improvement

 * Reference Document [1] describes that thermal efficiency improvement by Advanced Ultra-Supercritical over Ultra-Supercritical power plant is about 6%.   But, according to ES_Rankine's simulation, the improvement is 4.8%.   Since the paper did not describe design conditions of Ultra-Supercritical power plant compared, both may be correct.

 

Optimization of Advanced Ultra-Supercritical

By using the "Optimum Enthalpy Rise Run" and "Smart Run" functions of ES_Rankine, ENGSOFT Lab studied the turbine cycle presented in the Reference Document [1] and got the following results.

ES_Rankine shows that the final feed water temperature used by the paper is nearly optimum, i.e the least heat rate, but the reheat pressure used by the paper is not.   If the reheat pressure is changed to 76 bara instead of 60 bara, turbine cycle efficiency is improved by 0.1%.    0.1% efficiency should be evaluated by Users depending on their economics.

ES_Rankine shows also that 340 oC and 77 bara is the maximum to use.   More than those makes cycle efficiency worse.   Therefore, User must not use figures above those.

Description

Reference Doc. [1] Basis

Optimized by ES_Rankine

HP Steam

 

 

- Pressure, bara

300

300

- Temperature, oC

700

700

Reheat Steam

(Single Reheat)

(Single Reheat)

- Pressure, bara

60

76

- Temperature, oC

730

730

Condenser Pressure, in Hg abs.

1.5

1.5

Final Feed Water Temperature, oC

330

340

No. of FW Heaters, each

9 (4 HP Heaters, 1 Deaerator, 4 LP Heaters

9 (4 HP Heaters, 1 Deaerator, 4 LP Heaters

LP Turbine

2 x Double Flows

2 x Double Flows

Last Stage Blade

48 inch, 3000 rpm

48 inch, 3000 rpm

Turbine Wheel Efficiency, %

HP : 89.5, Reheat : 92

HP : 89.5, Reheat : 92

Gross Heat Rate, kJ/kWh

7060.6 (50.99 % Eff.)

7054.2 (51.03 % Eff.)

Thermal Efficiency

Base

0.1% Improvement

 

Optimum Enthalpy Rise Run Data of ES_Rankine

The following picture is Chart output of Optimum Enthalpy Rise Run of ES_Rankine studied for "Reference Document [1] Basis" described in the table above.   It shows that the maximum efficiency is achieved at 338.78 oC final feed water temperature.

 

Smart Run Data of ES_Rankine

The following picture is Text output of Smart Run of ES_Rankine studied for "Reference Document [1] Basis" described in the table above.   It shows that the maximum efficiency is achieved at 340 oC final feed water temperature and 76 bara reheat pressure.

Please note that the Reheating AEEP Level for the maximum efficiency is 30.57%.   Theoretically, the best efficiency of reheat cycle is achieved at around 30% reheating AEEP level.

 

Design Heat Balance Diagram of 850MW Advanced Ultra-Supercritical

 

Design Heat Balance Diagram of Optimized 850MW Advanced Ultra-Supercritical

 

Design Heat Balance Diagram of 850MW Ultra-Supercritical

 

Reference Document :

1. BR-1884, Advanced Ultra-Supercritical Power Plant (700 to 760 oC) Design for Indian Coal, Technical Paper presented at Power-Gen Asia held in Bangkok, Thailand dated October 3-5, 2012, by P.S. Weitzel, J.M. Tanzosh, B. Boring of Babcock & Wilcox U.S.A. and N. Okita, T. Takahashi, N. Ishikawa of Toshiba Corp. Japan


Copyright (c) 2013 ENGSoft Inc., Seoul, Korea, All right reserved / www.engsoft.co.kr