Process Design And System Analysis Of Coal-based Chemicals And Power Poly-generation With Low Energy Consumption For CO₂ Capture

China is rich in coal resources,and the coal chemical industry develops rapidly in recent years.However,the development of coal chemical industry is still facing the problems of large amount of carbon emissions and high energy consumption.Previous research shows that the low concentration of CO₂ is the key reason for the energy consumption and high cost of CO₂ capture.In the single coal chemicals production processes,due to the restriction of chemicals synthesis to the ratio of hydrogen to carbon monoxide,the mixing of shifted syngas and unshifted syngas in water gas shift unit makes the concentration of CO₂ lower before capture,and the energy consumption of CO₂ capture is increased.On the other hand,in order to improve the chemicals yields,the recycle of unreacted gas makes the production energy consumption high.Based on the integrated principle of energy conversion and CO₂ capture,coal based methanol and power polygeneration process is taken as a study case,a new polygeneration process with low energy consumption for CO₂ capture is proposed.In this process,the CO₂capture unit is transferred to the place ahead of mixing of the syngas,this adjustment improves the concentration before CO₂ capture and reduces the energy consumption.The hydrogen rich gas obtained after the capture is partly mixed with the unshifted syngas to adjust the hydrogen to carbon monoxide ratio to 2.0-2.1 for methanol synthesis.The unreacted gas of methanol synthesis is moderately recycled,and the unrecycled syngas enters the combined cycle for power generation.The Aspen Plus simulation software is used to simulate the polygeneration process,and the input and output material and the energy balance data at key points are obtained.The polygeneration process is analyzed from two aspects of unit operation and system structure.The results show that the energy consumption of CO₂ capture in the new co production process is 0.7GJ/t,which is reduced by 40.6%compared to the original process,presenting the advantage of CO₂ capture.The energy consumption for CO₂ capture of SNG and power polygeneration process with the same process unit and system structure is decreased by 35%.The lower hydrogen to carbon monoxide ratio of chemicals synthesis unit,the more obvious the energy saving effect was.The technical and economic advantages of the process are analyzed by using the energy saving ratio and the cost saving ratio indicators.The calculation results show that the energy saving ratio and the cost saving ratio of the polygeneration process are 16.5%and 13.2%at optimal splitting ratio.The improvement of the technical and economic performance of the process comes from decrease in the energy consumption for CO₂ capture,moderate recycle of unreacted syngas and cascade utilization of energy.