Simulation And Optimization Of TBCFB System For Pyrolysis-Gasification-Combustion Of Low Rank Coal And CO₂ Capture System

China’s coal resources are abundant,among which low-rank coal accounts for a large proportion,and its volatile content is equivalent to hundreds of billions of tons of oil and gas resources,and its high water content leads to low utilization efficiency.Therefore,coal multi-product utilization technology is adopted through the quality-based utilization of coal.It is of great significance to realize efficient and clean utilization of low-rank coal resources.The pyrolysis-gasification-combustion triple-bed combined circulating fluidized bed（TBCFB）technology that separates the gasification process from the pyrolysis process and avoids the influence of pyrolysis products on the gasification process.Compared to the traditional TBCFB system,a new process is proposed in this work,in which sand particles are replaced by char particles as the circulating heat-carried medium.In the process of realizing coal multi-generation and quality-based utilization,it is also accompanied by the production of CO₂.However,in the traditional chemical absorption CO₂ capture process,energy consumption is also a problem.The self-heat recuperation technology is a new type of energy-saving technology,can achieve significant energy-saving effects by using low-grade energy to upgrade to high-grade energy.Therefore,this work uses the process simulation software Aspen plus to complete the calculation and optimization of the low-rank coal pyrolysis-gasification-combustion TBCFB system and the self-heat recuperation technology CO₂ capture system.Mainly complete the following work.This work first established the TBCFB system simulation process.The system is based on the concept of low-rank coal quality-based utilization of the development of a novel process system,which includes a pyrolyzer,a gasifier and a combustor of the three main reactors.By reviewing the literature collection of downer pyrolysis and bubbling fluidized bed gasification data,an empirical correlation formula for pyrolysis product distribution and temperature was established,and on this the establishment and validation of the system simulation process was completed.In addition,compared to the traditional TBCFB system,a new process is proposed in this work,in which sand particles are replaced by char particles as the circulating heat-carried medium.In order to obtain the optimum operating conditions for material conversion and energy utilization between the three reactors,Aspen Plus is used to establish the simulation process of this new system.The results show that the combustion of only 39.92%coal-char can provide enough energy for both coal pyrolysis at 600℃and gasification of 60.08%coal-char at 800.9℃.The best ratio of circulation solid heat-carrier particles char,ash,sand to raw coal is 5.5,12 and 11,respectively.Compared with sand or high-temperature ash,the amount of heat-carried particles circulated in the system can be significantly reduced when char particles are used as the heat-carried particles due to its high heat capacity,and reduce the difficulty of operation.According to the comprehensive analysis of syngas composition,the cold gasification efficiency（CGE）and the lower heating value（LHV）,the optimal ratio of steam to coal-char（St/C）is 1.5 in gasification.The simulation results may possibly provide some indications on the industrial application of the TBCFB system with coal-char as the heat particles.Secondly,this work focuses on the capture of CO₂ from combustion in the TBCBF system.The work selected the most commonly used chemical absorption CO₂ capture by MEA technology in the industry as an object.On this basis,the traditional CO₂ capture by MEA simulation process was established using Aspen plus,and it was determined that the CO₂ capture rate was 85%and the product CO₂ concentration was captured to 98%.The number of plates required for absorption tower and desorption tower is 9 blocks and 7 blocks respectively.By analyzing the amount of lean MEA absorbent and the reboiler heat loading,and determined the lean MEA absorbent inlet temperature of the absorption column and loading were 40℃and 0.23,respectively.The minimum energy consumed of capture 1molCO₂ was 174.96 kJ.The CO₂ capture by MEA simulation process based on lean MEA heat pump technology have been completed.In this system,the energy-saving effect of two kinds of heat pumps with n-butane and trifluoro-dichloroethane as the working medium was analyzed.The results showed that the trifluoro-dichloroethane was used as the working medium,the energy-saving effect was better,and energy saving of 19.31 kJ·（molCO₂）^-1 can be achieved,save11.04%energy compared to traditional methods.And self-heat recuperation technology have been completed.In this system,the heat from the source of lean liquid,the heat released by the absorption reaction in the absorption tower,and the heat from the top stream of the desorption tower are recovered.The results show that energy savings of 53.21 k J·（molCO₂）^-1 can be realized by using self-heating regeneration technology,and the total energy consumption can be reduced by 30.46%.This technology can significantly reduce the energy consumption of CO₂ capture process.The establishment of the model provides a theoretical basis for the application of self-heat recuperation technology in CO₂ capture.