Study On The Dynamic Features And Control Strategy Of Chemical Absorption Carbon Capture In Biomass Thermal Power Plants

The"14th Five-Year Plan"is the key period and window period for China to achieve"carbon peak",and the emission reduction is crucial to achieve"carbon peak and carbon neutral".《The"14th Five-Year Plan"Comprehensive Work Plan for Energy Conservation and Emission Reduction》was published by the State Council of the People’s Republic of China in Jan 24,2022.Which pointed out that,the growth of coal consumption should be strictly and reasonably controlled according to China’s current status,i.e.coal-based primary energy consumption.The goal is towards"carbon neutral"rather than"zero carbon".Therefore,the carbon negative emission technologies（NETs）will play an important role in achieving China’s climate target of reaching the peak emission by 2030 and realizing carbon neutrality by 2060.Among NETs,biomass energy conversion with carbon capture and storage（BECCS）is considered as the most potential solution.Biomass is commonly used as fuel for combustion,in particular in biomass combined heat and power plants（Bio-CHP）,which contribute more than 70%of the world’s power generation from biomass.So,there exists a big potential to integrate CO₂ capture with Bio-CHP.The amine-based chemical absorption carbon capture system（MEA-CC）has been commercialized.However,the integration of MEA-CC with biomass combustion still faces many challenges,such as how to improve the operation efficiency and how to regulate the operation to reduce the energy consumption and maximize the amount of CO₂ capture,which requires an in-depth understanding of the dynamic features of the MEA-CC.And the design of MEA-CC control strategies should be combined with the operational requirements of MEA-CC.However,most of the current research on BECCS is about the steady-state,which provides limited knowledge on the dynamic operation of MEA-CC integration with Bio-CHP.At the same time,most of the research on the dynamic features and control strategies of MEA-CC has focused on CO₂ capture from coal-fired power plants.Different from coal-fired power plants,the diversity and seasonality of biomass affect the operating conditions of the biomass boiler significantly,which in turn affects the dynamic performance of the MEA-CC.In addition,since bio-CHP primarily focuses on supplying heat,the available heat that can be used for CO₂ capture varies from time to time.This also brings huge challenges to the efficient operation of MEA-CC.Therefore,this work aims to explore the dynamic features of capture CO₂ from Bio-CHP by using MEA-CC,and finds a suitable control strategy to improve the performance of MEA-CC.In addition,an artificial intelligence（AI）model is also developed for dynamic modelling MEA-CC,which can be used to replace the physical model for control purpose.The main findings of this work are as follows:（1）When the flue gas flowrate or the CO₂ concentration in the flue gas increases（decreases）can lead to decreases（increases）of the CO₂ capture rate and energy penalty,and an increase（decrease）in reboiler duty.When the flue gas flow rate and the CO₂ concentration in the flue gas change in opposite ways,the changes of the CO₂ flowrate in the flue gas would determine the changes of CO₂ capture rate,energy penalty and reboiler duty.（2）Compared to the flue gas,the reboiler duty has a more significant effect on the CO₂capture rate.In the shutdown process of MEA-CC,some captured CO₂ will stay in the MEA solution.during the start-up of MEA-CC,preheating the desorber is suggested to desorb CO2,which can shorten the start-up time of MEA-CC.Compared to the start-ups from room temperature,the start-up time can be shortened to 106mins form 151mins by preheating reboiler temperature to 353K.（3）When using the traditional distributed control strategy for reboiler duty regulation,there is a time delay between the regulation of reboiler duty and the changes of the flue gas.Which resulting in severe fluctuation of CO₂ capture rate and reboiler temperature.The influences of external disturbance on the CO₂ capture rate and reboiler temperature can be effectively reduced by adding an outer loop control strategy with the CO₂ capture rate as the controlled variable（control strategy B）or adding a feedforward compensation with the rich solution flowrate fluctuation as the input（control strategy C）.Compared to the control strategy A,the control strategy B and C can shorten the settling time from 71 mins to 32.25mins and 17 mins,respectively.However,even though control strategy B can reduce the average energy penalty by 0.3%,the total amount of captured CO₂ also decreases by 0.13%.the control strategy C reduces the average energy penalty by 0.14%with an increase in the total amount of captured CO₂ by 0.35%.（4）For MEA-CC,the AI model developed based the Informer model can accurately predict CO₂ capture rate,energy penalty and reboiler temperature,based on flue gas flowrate,CO₂ concentrations in flue gas,lean solution flowrate and reboiler duty（MAPE:0.08-6.25%,R~2:0.84-0.991）.