Study On VAM Preheating Direct Catalytic Oxidation Performance Under The Background Of Double Carbon

VAM gas has the characteristics of large air volume,low methane concentration and wide fluctuation range,so it is difficult for traditional burners to oxidize and utilize it.Under the background that "carbon neutralization and carbon peak" has become the consensus of our society,the study of low-carbon green energy utilization technology has become the first choice for the transformation and upgrading of the traditional energy industry.As a clean and green energy,the research and development of low concentration methane utilization technology has been paid more and more attention.Therefore,it is great significance to realize the double carbon goal to study how to make rational and efficient use of low concentration methane.On the basis of traditional thermal countercurrent oxidation technology and preheating catalytic oxidation technology,our research group developed the preheating direct catalytic oxidation technology,and carried out systematic research on this technology through theoretical analysis and numerical simulation:(1)Technical development: consult the literature and improve the existing equipment.The direct flow structure is adopted in the design,which avoids the commutation operation;by setting the top heating device,the exhaust air temperature and exhaust temperature entering the oxidation bed are controlled,the life of the device is prolonged,and the energy recovery efficiency is improved.(2)Built test bench: Designed and buit a test bench for the preheating direct catalytic oxidation system of VAM,including eight parts:gas source subsystem,measurement control subsystem,auxiliary electric heating subsystem,catalytic layer subsystem,preheating subsystem,safety alarm subsystem,flue gas heat load adjustment subsystem and smoke exhaust subsystem.Besedes,introducing the operation principle,technological process,composition of each subsystem and experimental operation process of the device.(3)Numerical simulation:Simulated the catalytic combustion performance of VAM in the catalytic layer of the device.Studied the variation of methane conversion efficiency of spent air with and without catalyst as a function of preheating temperature;The effects of preheating temperature,concentration,and flow rate for average temperature,conversion rate and effective reaction length of the catalytic layer cross-section were studied.The results show that when the concentration of exhaust methane is 1% and the flow rate is 1m/s,the preheating temperature corresponding to the effective reaction with catalyst is450℃,while the preheating temperature needed for effective reaction without catalyst is 700℃ under the same conditions.When the preheating temperature and flow rate keep constant,as the concentration of VAM methane increases,the overall temperature rise of the catalytic layer increases,the effective reaction length slightly shortens,and the methane conversion rate slightly increases;When the preheating temperature and concentration keep determined,increasing the VAM flow rate,increases the effective reaction length and reduction the methane conversion rate.(4)Theoretical calculations:The theoretical calculation of energy balance of the experimental device was carried out,and the values of catalytic oxidation heat release,electric heating power,surface heat loss and smoke exhaust heat loss were obtained,which verified the possibility of the device operating under the theoretical optimum operating state parameters,and calculated the abundant heat.(5)Optimization of the preheating system: Based on the laws of thermodynamics and the theory of(entransy)analysis,the heat conductivity model of heat exchanger network was established to study the influence of maximum operating temperature and circulating temperature difference on the heat exchanger network conductance.The results show that when the total thermal conductivity is greater than a certain value,the total thermal conductivity decreases significantly with the increase of the maximum operating temperature and the decrease of the cyclic temperature difference.When the total thermal conductivity is less than this value,the influence of parameter change on it is no longer obvious.In view of this,the concept of threshold optimization is put forward,compared with the original design value,when the threshold optimization value is used as the design parameter,the total thermal conductivity of the system heat exchanger network is reduced by20.2%,and the heat capacity flow is reduced by 23.9%.Threshold optimization can be combined with the actual operation requirements of the system to increase the total thermal conductivity by 12.5% in exchange for a heat capacity flow decrease of 39.1%.