Tradeoff between the efficiency penalty and load depth in a coal-fired power plant with CO2 capture under partial load conditions

Abstract

With the penetration of renewable energy increasing rapidly in the power system, flexible operation of coal-fired power plants with CO2 capture is expected to play a key role in grid peak-regulating in China. However, studies on the interactions between power generation and CO2 separation units under partial load are still limited. Accordingly, in this paper, the factors that affect the system performance were investigated based on a 1000-MW post-combustion power plant under partial load. The results indicate that minimizing the difference between the quality of the steam extracted from the turbine and the minimum steam quality required for the reboiler, meanwhile resulting in no extra work losses, is the essential target for system integration. Under the IP-LP-PMV (Pressure Maintaining Valve) scheme, the irreversible loss caused by PMV led to an extra system efficiency penalty of 3.31% points under 30% load. However, for the IP-interstage-PMV scheme, the system efficiency could be improved by 0.7% and 1% points under loads of 30% and 40%, respectively, because the work losses caused by splitting and throttling under low load conditions could be reduced by adjusting the extraction location. Therefore, the system performance could be improved by altering the extraction position under partial load operation. By investigating the optimal extraction location under variable loads, it is disclosed that the IP-interstage-PMV scheme and the IP-LP-PMV scheme are the most efficient steam extraction schemes under 40% or 70% loads respectively. Therefore, the theoretical optimal steam extraction position varied under the different loads, and the extraction position should be selected based on the average operating load from the perspective of all the working conditions. This integration principle provides the highest performance improvement potential of 2% points for partial load operation. This study will be helpful to promoting the further deployment of large-scale post-combustion capture projects.