Energy Integration In Carbon Capture Process By Chemical Absorption Method

In recent decades,CO₂-based greenhouse gas emissions have far exceeded human imagination,and various rare disasters have arrived.Reducing carbon emissions is a top priority now.The demand for electric power in modern civilization is self-evident.Therefore,the task of CO₂ capture for power plants is imminent.The traditional carbon capture process has the following problems:1.The carbon capture process will use low-pressure steam to regenerate the absorbent,which will cause a large decrease in the power output of the power plant.2.The CO₂ concentration in flue gas of natural gas combined power station（NGCC）is low and the difficulty of capture is increased.3.NGCC power plant raw gas（LNG）cold energy,power plant flue gas waste heat,and steam extraction waste heat are wasted.Aiming at the problems existing in the above NGCC power plants,in order to improve the power output of the power plant with carbon capture process and reduce the efficiency penalty,this paper proposes research ideas for energy integration,and it is mainly studied from two aspects:increasing the concentration of flue gas in the gas power station system and utilizing the energy cascade of the power station.Firstly,the gas power station with 393 MW power output is determined as the research object,and a multi-system hysys integration model with the Brayton cycle and the three-stage evaporative water steam Rankine cycle as the main body is constructed.A mathematical model of the counter-current purge membrane was constructed,and a component separator was used to simulate the counter-current purge membrane to achieve an accurate and selective recirculation process of CO₂ in the flue gas,the comparison gap between the data of each model was less than 1%.Secondly,it is difficult for NGCC power plants to utilize a large amount of low-temperature waste heat due to the low temperature.This paper proposes a scheme to integrate LNG cold energy with NGCC power plants using the PCC process.For a 391 MW NGCC power plant with a PCC system based on MEA,the impact of the exhaust gas recirculation（EGR）process was first considered,and the basic situation of 35%EGR was obtained.Then,the internal energy integration of the NGCC+PCC+EGR system indicates that there are a large number of waste heat sources at different temperatures in the system,and then the dual-pressure ORC is integrated into the system for energy integration.Finally,in order to integrate the unused low-temperature waste heat and recover the cold energy of LNG,the two-stage condensation Rankine cycle were integrated with NGCC+PCC+EGR+TI+ORC.The net power output of the LNG cold energy integration process is 17.55MW higher than that of the NGCC+PCC+EGR system,the total efficiency is increased by2.51%,and the efficiency penalty is reduced to 7.9%.Finally,aiming at the low CO₂ concentration in flue gas of NGCC power station with EGR process,the NGCC、NGCC+S-EGR process-based cycle is studied under non-design conditions.On this basis,taking the O2 concentration in the feed air≥16%as the lower limit,considering the influence of the EGR ratio on the power station,the final determination of the EGR ratio in the mixed carbon capture process is 20%.Under non-design conditions,the internal energy integration process improves the power generation efficiency of each configured power station by about 0.5%.Among them,the total efficiency of NGCC+S-EGR+20%EGR is the largest,being 50.47%.The external energy integration process has been greatly improved.On the basis of internal energy integration,the overall efficiency of the power station has increased by about 1.8%.The total efficiency of the NGCC+S-EGR+20%EGR system is still the highest,52.28%,and the power penalty of the power plant is reduced to 6.47%.