Exergy Analysis And Optimization Of An Integrated Split Ammonia-based Carbon Capture And Methanol Synthesis Process

The world attaches great importance to global warming,and CO₂ emissions are the root cause of this phenomenon.In order to solve the problem of CO₂ emissions from coal-fired power plants,effective CO₂ emission reduction measures must be taken.At present,the purpose of carbon emission reduction can be achieved by using carbon capture and utilization technology to capture CO₂ and convert it into other products.The post-combustion carbon capture technology with ammonia as the absorbent has the characteristics of strong absorption capacity,low corrosion,low absorbent cost and less change to the original process,which is very suitable for the carbon emission reduction work of power plants.As a basic organic chemical raw material,methanol has high use value as a synthetic product of CO₂.Based on the above,this thesis uses carbon capture technology to capture CO₂ in flue gas and convert CO₂ into methanol.This thesis focuses on the optimization of an integrated ammonia-based carbon capture and methanol synthesis process,which is conducive to the implementation and application of the process,and has certain guiding significance for promoting carbon emission reduction.At present,there are two main problems in the integrated ammonia-based carbon capture and methanol synthesis process:First,the regeneration duty is high,which is not conducive to process operation;secondly,the limitation of raw material H₂ is large,and only pure H₂ can be used for synthesis reaction.In order to solve the above problems,the conventional process is improved in this thesis.The solvent split technology is used to reduce the regeneration duty at the cost of losing part of the carbon capture capacity.At the same time,in order to make up for the carbon capture capacity,the double tower absorption technology with intermediate cooling is used to improve the carbon capture capacity and effectively reduce the ammonia loss.In the conventional methanol synthesis process,CO₂ and pure H₂ are used to synthesize methanol.By replacing the flash evaporator in the separation process with a stripper,the process can use wet hydrogen as a synthetic raw material.Based on the above improvement methods,this thesis constructs an integrated split ammonia-based carbon capture and methanol synthesis process.In order to make the integrated split ammonia-based carbon capture and methanol synthesis process operate effectively,the process parameters are optimized.The effects of NH₃concentration,temperature,flow rate and split ratio on CO₂ absorption rate,NH₃ loss rate,condenser duty and reboiler duty were studied.After parameter optimization,the carbon capture rate of the process is 90%,the reboiler duty is reduced from 13.39MJ/kg _CO2 to 12.04MJ/kg _CO2,saving 10.08%,and the condenser duty is reduced from 0.88MJ/kg _CO2 to 0.79MJ/kg _CO2,saving10.23%.For methanol synthesis process,the effects of H₂ and CO₂ feed molar ratio,reaction temperature,reaction pressure and catalyst loading mass on methanol synthesis rate are studied.After optimization,the methanol synthesis rate reaches 25.49%,and the methanol yield is59.45kg/h.In order to maximize the energy utilization of the process,the exergy analysis method is used in the integrated split ammonia-based carbon capture and methanol synthesis process.The entropy and enthalpy of the logistics are calculated,and then the physical exergy and chemical exergy are calculated.The exergy loss of each equipment is calculated by combining the equilibrium equation,and then the process is optimized by the heat exchange network optimization method.After optimization,the total exergy loss of the heat exchanger decreased from 70.02k W to 40.45k W,the exergy loss of the desorption tower decreased from 209.29k W to180.91k W,and the total exergy loss of the process decreased from 437.24k W to 372.68k W,which decreased by 14.8%.