Investigating Exergy Analysis And Energy Conservation Of Coke Oven Gas To Methanol Process

Hundreds billion cubic meters of coke oven gas in China was produced every year,but were mostly discharged by the way of a torch,which not only polluted the atmospheric environment,but also resulted in high energy consumption.Thus,methanol production from coke oven gas is widely used by comparing with other utilization methods of coke oven gas.Since the methanol price is greatly fluctuated,energy saving and consumption reduction have become the focus of methanol enterprises.Therefore,we established the process model of methanol production from coke oven gas,and carried out systematic analysis and energy efficiency optimization of the process,which provided technical support for energy conservation and consumption reduction in methanol industrial production.Accordingly,the thesis mainly carried out the following work:The methanol synthesis reaction was analyzed from the perspective of thermodynamics and kinetics.Firstly,thermodynamic parameters such as reaction heat and reaction equilibrium constant were estimated,which indicted that too high temperature was not conducive to the reaction equilibrium.Then,the kinetic equation and kinetic parameters of methanol synthesis reaction were determined by analyzing the reaction mechanism and reported kinetic data of methanol synthesis.The simulation results of our process are in good agreement with the literature data,which indicated that the proposed model is correct and valid.Furtherly,the influence of different operating conditions on reforming conversion unit and synthesis unit was investigated.The results showed that the temperature of reforming reactor should be controlled above 930 ℃ and below 18 bar,the optimal steam / coke oven gas ratio was1.2～1.6,and the optimal carbon supplement amount was 110～125.In the methanol synthesis unit,the optimal coolant temperature is 225 ℃,the optimal reaction pressure is 65 bar,and the optimal value of unreacted gas circulation rate is 0.95.After optimization,the total carbon conversion rate is increased by 7% and the methanol yield is increased by 2%.By extracting the thermodynamic parameters of each flow in the proposed process,the physical,chemical,mixed and total energy were calculated according to the selected environmental state model.Then,the loss of different unit equipment was calculated based on the principle of equilibrium.The results shown that the exergy efficiency of the system is 75.17%,and the methanol synthesis and rectification unit is the main unit of the system which the exergy loss is 18.29 MW and 26.02 MW respectively.Pinch technology is proposed to optimize the energy efficiency of methanol synthesis and distillation unit.Based on above discussion,methanol synthesis and distillation unit were analyzed.It was found that the pinch temperature of cold and hot materials was 73.8 ℃ and83.8 ℃ respectively.According to the principle of thermodynamics,it is found that there is unreasonable energy consumption in the system such as cross pinch heat exchange.Therefore,a new energy efficiency optimization scheme is designed by using Aspen energy analyzer.The optimized heat exchange network scheme can save 7164 kw of heat utility and 13668 kw of cold utility.