Optimization Of Coke Oven Gas Methanation Process Based On Exergy Analysis

With the rapid economy development and the steady advancement of urbanization in China,the demand for natural gas has risen sharply,and its proportion in the energy structure has gradually increased.However,China's natural gas consumption is far greater than production,resulting in the relationship between natural gas supply and demand is seriously imbalanced,and external dependence is rising year by year.Therefore,various synthetic natural gas technologies have attracted widespread attention.Compared with coal-based natural gas,coke oven gas methanation produces natural gas with low pollution,low cost and mature technology.It can not only achieve clean and efficient use of gas,alleviate the contradiction between supply and demand of natural gas,but also reduce harmful gas emissions,and play a positive role in promoting the construction of resource-saving and environment-friendly society.According to the characteristics of the coke oven gas methanation reaction system,the independent reaction of the reaction system was selected.The thermodynamic parameters such as Gibbs free energy,reaction enthalpy and equilibrium constant of methanation reaction under different reaction conditions were calculated.The results show that the low temperature is favorable for the methanation reaction,and the CO methanation reaction takes precedence over the CO₂ methanation reaction.The adiabatic equilibrium model of coke oven gas methanation reaction system was established.The effects of different temperature and pressure on the equilibrium temperature,equilibrium composition,CO and CO₂ equilibrium conversion rate of the reactor outlet were studied.It was found that the methanation process of coke oven gas was suitable.Operating conditions:The reactor inlet temperature is 300⁵00 K;the reaction pressure is about 3 MPa.Based on the analysis of methanation reaction mechanism and the steady-state simulation results of multi-stage adiabatic methanation process in the literature,the kinetic equation suitable for coke oven gas methanation reaction system was established.Based on Aspen Plus software to establish process simulation,in order to improve product quality,sensitivity analysis was used to investigate the effects of process conditions such as hydrogen-carbon ratio,cycle ratio,N₂ mole fraction in feed gas,operating pressure and feed amount on methanation reaction and product concentration.The results show that the optimum hydrogen-to-carbon ratio is 3.6³.7,and the optimal cycle ratio is 1.0.The increase of N₂ mole fraction in the feed gas will decrease the methane concentration in the product gas,and the pressure increase will be beneficial to the synthesis of methane.The optimum feed rate for furnace gas is 13,000 m³?STP?·h-1.According to the analysis results,some process parameters are optimized.Based on the Kameyama-Yoshida environmental state model,the standard molar chemical enthalpy of each component was calculated.The physical enthalpy,chemical enthalpy,mixed enthalpy and total enthalpy of each stream were calculated by extracting parameters such as entropy,enthalpy and logistics components in the simulation results of each stock of Aspen Plus software.Based on the exergy-balance principle,the enthalpy losses of different units are calculated,and the key unit of exergy loss is found as the heat exchange unit.The existing process was modified according to the principle of energy cascade utilization.After the original process was improved,the helium loss was reduced by 610.54 kW and the helium efficiency was increased by 0.9%.Using the pinch-exergy technology analysis,the logistics parameters were extracted from the Aspen Plus software,and the hot and cold composite temperature-enthalpy diagram was used to solve the heat transfer process of the system by the problem table method.The average pinch was 305??the heat flow pinch temperature was 310?,and the cold flow pinch temperature was 300??.According to the definition of exergy,the cold-heat composite temperature-enthalpy diagram is transformed into the heat-exchange system exergy composite curve.The calorific value is 3686.92 kW,the cooling capacity 337 is 3337.57 kW,and the heat recovery system exergy loss is 313.15 kW.Based on the thermodynamics and kinetics analysis of the coke oven gas methanation reaction system,the process simulation,sensitivity analysis and system in the coke oven gas methanation process?Lurgi three-stage adiabatic cycle methanation process?The analysis and exergy-pinch analysis were carried out to provide technical support and theoretical basis for the engineering analysis,process optimization,energy recovery and stable operation of the entire coke oven gas methanation process.