China proposed a target to reach maximum CO2 emissions before 2030 and attain carbon neutrality by 2060 in 2020. As a system highly relying on fossil fuel, and at the same time, with the rapid growth of renewable energy, the power system in China has to face the challenges both from carbon emission reduction and stability of electric grid. It can be predicted that the future coal fired power plants has to frequently work in partial load conditions to contribute flexibility to the grid, and moreover, to recover its carbon emission through adopting CO2 capture technology. However, the partial load operation of power generation system will undoubtedly influence the CO2 capture unit, which may lead to the variation of CO2 capture ratio (CCR). Through investigating the interaction between power generation system and CO2 capture unit under partial load conditions, the aim of this paper is to evaluate the potential of CO2 emission reduction of a variable load power plant. The model of a coal-fired power plants with post-combustion CO2 capture had been setup via EBSILON and Aspen. The performance of MEA CO2 separation unit had been simulated. By quantitatively analyzing the performance of a typical coal fired power plants in partial load operation and further combining the CO2 capture unit with the power generation system, the operating characteristics of the CO2 capture unit in partial load operation are explored. The results indicate several factors including the pressure of extracted steam for reboiler, the CO2 concentration in the flue gas and the flow rate of flue gas, will impose the possible impact on CO2 capture unit. The extraction steam temperature and pressure of the power generation unit also decrease as the power load decreases. When the load depth falls below 50%, the pressure drops to a certain level that could not meet the requirements for the operation of the CO2 capture unit, the capture unit will cease operation. The opening of the steam extraction valves remains unchanged, and the operating parameters of the capture unit are not adjusted under power load variation conditions. As the power load decreases, the mass flow of flue gas decreases from 1148.72 kg/s at 100% load to 521.63 kg/s at 30% load, while the CO2 mass fraction in the flue gas decreases from 17.8% to 13.9%. These changes will undoubtedly affect the CO2 load in solvent. The three factors together reduced the CCR for treated gas from 90% at 100% load to 50.42% at 30% load. The practical CCR for a power generation unit in a period of real operation conditions is lower than design CCR for treated gas, which is 90% at 100% load. Conclusively, the factors influencing capture ratio on the power generation side, such as flue gas and steam parameters, are important factors in CCR changing.
Keywords carbon capture ratio, coal-fired power plant, partial load, carbon neutrality