Advanced UltraSupercritical Turbine Cycle
Steam temperature currently used for UltraSupercritical 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 UltraSupercritical 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 UltraSupercritical 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 UltraSupercritical 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 UltraSupercritical Turbine Cycle Design Data
Major design data of turbine cycle used in the advanced ultrasupercritical 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 Desuperheaters) 
LP Turbine 
: 1 x Double Flows 
Last Stage Blade 
: 48 inch, 3000 rpm 
Thermal Efficiency 
: 6% Improvement comparing with 600 oC Class UltraSupercritical Turbine Cycle 
Comparison between UltraSupercritical and Advanced UltraSupercritical
Simulation results of ES_Rankine for 850 MW class UltraSupercritical and Advanced UltraSupercritical turbine cycle are as below.
Description 
850 MW UltraSupercritical 
850 MW Advanced UltraSupercritical 
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 UltraSupercritical over UltraSupercritical 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 UltraSupercritical power plant compared, both may be correct.
Optimization of Advanced UltraSupercritical
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 UltraSupercritical
Design Heat Balance Diagram of Optimized 850MW Advanced UltraSupercritical
Design Heat Balance Diagram of 850MW UltraSupercritical
Reference Document :
1. BR1884, Advanced UltraSupercritical Power Plant (700 to 760 oC) Design for Indian Coal, Technical Paper presented at PowerGen Asia held in Bangkok, Thailand dated October 35, 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
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