Study Of CO₂ Methanation Process In Fluidized Bed Based On Nickel-based Catalyst

In recent years,China's renewable energy development has accelerated.However,renewable energy such as wind energy,solar energy and hydropower has the characteristic of volatility and randomness,so it can not meet the needs of all-weather power supply.In addition,China's power consumption is slowing down.These factors have led to the waste of renewable energy and dependence of fossil fuels.Power to gas technology(P2G)can be used to convert electric power to chemical energy(synthetic natural gas,SNG)for storage.SNG can be transported through the gas pipeline network or drive the gas turbine to generate electricity.Methanation is the core technology of P2G.The current commercial methanation reactors are fixed-bed reactors and are equipped with supporting catalysts,nevertheless,a large amount of heat will be released during the methanation process,and it is necessary to control the temperature rise by using appropriate methods such as increasing the gas circulation rate and connection multiple reactors in series which is complicated and energy intensive.The fluidized bed reactor has excellent heat and mass transfer performance and is suitable for strong exothermic reaction processes.Based on the above discussion,in this paper,a series of Ni-based methanation catalysts were supported on?-Al₂O₃ using impregnation method.The catalytic performance for CO₂ methanation was investigated in a micro-fixed-bed.The characteristic of the methanation reaction of the catalyst was investigated in micro-fixed-bed and fluidized bed.And based on the fluidized bed reactor,the technology of biomass gasification coupled P2G with biomass as carbon source was designed.The main results and conclusions are as follows:The effect of Ni,Mn loading on catalytic performance were investigated by CO₂ methanation.Catalysts with 12 wt.%and 16 wt.%Ni-loading showed better catalytic performance.Ni-loading was fixed at 12 wt.%,the addition of Mn,Ce and Mn-Ce promoters to Ni-based catalysts can improve the catalytic activity of the catalysts significantly,in addition,catalysts with different Mn-loading showed similar catalytic performance.The characterization analysis showed that the addition of promoters can reduce the interaction of Ni species with the carrier,increase the dispersion and surface area of the active metal,increase the number of adsorbed CO₂,lower the reaction temperature,and effectively inhibit the surface sintering and agglomeration of catalysts during methanation.Among them,the Mn-Ce promoter showed the best synergistic effect.The catalysts with Mn-Ce promoter have good heat resistance and reaction stability.Suitable weight hourly space velocity and high reaction pressures can improve the catalytic performance of the catalyst.The methanation characteristics of 2Mn-2Ce-Ni/Al₂O₃ catalyst were investigated in fluidized bed reactor.The results showed that the bed height had less influence on the catalytic performance of the catalyst,and the catalytic activity of CO₂ methanation was maximized at 350°C for all catalysts with different bed heights.The weight hourly space velocity and reaction pressure have an important influence on the methanation process,and the CO₂ conversion rate decreased with increasing weight hourly space velocity.Increasing the reaction pressure had a significant effect on improving the catalytic performance of the catalyst,and the pressure increases from 0.1 MPa to 0.75 MPa at 300°C and 6000 m L·g^-1·h^-1,the CO₂ conversion rate increased by 19%.The addition of methane is detrimental to the methanation process as it reduced CO₂conversion rate and CH₄ selectivity.Compared with fixed-bed reactors,fluidized bed reactors have good heat transfer performance and uniform bed temperature distribution,so the catalytic activity of CO₂ methanation of the catalyst at higher temperatures is higher than that of the fixed bed.The fluidized bed reactors can effectively inhibit the sintering and agglomeration of the active components on the surface of the catalyst and reduce carbon accumulation in the catalyst.Fluidized bed with good heat transfer capacity,is suitable for strong exothermic reaction of CO₂methanation.The simulation analysis of different fluidized bed methanation processes through Aspen software showed that the two-stage methanation process with interstage water removal can produce product gas that meets the pipeline gas standard at a lower operating pressure.Biomass gasification gas was coupled with a two-stage process.While producing qualified product gas,heat was efficiently used to produce by-product high-pressure superheated steam and medium-pressure saturated steam.When biomass gasification gas flow rate is 1000 kmol·h^-1,temperature is 800?,The process is capable of producing 307.85 kmol·h^-1 of qualifying product gas and by-production of 1099.06 kmol·h^-1 of superheated steam and 10.54 kmol·h^-1 of saturated steam.Using biomass as a carbon source,a process based on biomass gasification coupled with P2G was designed with five units:methanation,biomass gasification,hydrogen production from water electrolysis,gas genset,and heat utilization,and the process thermal efficiency was calculated to be 80.14%.