Performance simulation on an integrated natural gas-, N2- and organic fluid-cycle thermal power plant

Abstract

Seeking for a low-cost carbon capture method and recovering waste heat of the flue gas are the effective ways to improve the thermal efficiency of power plants with carbon capture. A novel oxy-fuel combustion nature gas (NG) power plant integrated the gas turbine (GT), N2 Brayton cycle (NBC), Organic Rankine cycle (ORC), CO2 capture and cold energy utilization of liquefied natural gas (LNG) is proposed in this paper. NBC combined with GT to generate electricity can simplify heat transfer process and provide a utilization path of N2 to reduce the cost of air separation unit (ASU). ORC is used to recover low temperature waste heat of the sulfur-free flue gas with improving system efficiency. LNG cold energy is utilized to achieve low-cost carbon capture. O2/CO2 combustion and O2/H2O combustion are investigated to determine the suitable diluent. The result shows that GT and NBC have better performance in the O2/CO2 cycle compared to O2/H2O cycle, while ORC is more potential in the O2/H2O cycle. Taking into account the energy consumption of ASU and CO2 capture, the result shows that the liquid H2O is not suitable to be used to moderate the combustion temperature because the recycled H2O is vaporized in the combustor and consumes a large amount of heat. In the O2/CO2 atmosphere, the net power generation efficiency of integrated system can reach 56.57%.