Development Of Carbonaceous Catalytic CH₄-CH₂Reforming Reactor And Simulation Research Of The Proccess

The primary greenhouse gases CO2and CH4are considered invaluable resources. With the advent of global warming, CO2emissions have received much attention from the global society. The double gas head of multi-generation systems that utilize gasification and coke oven gases as gas resource can produce energy and chemical products and can improve the energy conversion efficiency. Clean coal conversion systems of improving the energy conversion efficiency is important to lessen green-house gas emissions. The production of synthesis gas (syngas) by reforming coke oven gas (COG; CH4) and gasification gas (CO2) is considered the most critical technology in the conversion system. Obtaining an optimal design for the reforming reactor is the ultimate goal to realize industrialization. Therefore, developing the car-bon catalytic reactor for CO2-CH4reforming is the key point of this research. The main conclusion in this study was obtained by using the following methods:(1) on-line experimental study of small reforming reactors;(2) numerical simulation re-search on small reforming reactors;(3) The operation condition simulation provided credible foundation for process conditions optimization;(4) simulation research and development of pilot catalytic reforming reactors;(5) development of reforming reactors and reforming section for industrial application. The main conclusions are described below.1. Online experimental research of the small reactor shows that at constant oxygen flow, the effective components H2and CH4in the outlet gas decreases with increasing intake ratio of oxygen and COG volume flow; CO and CO2increases with increasing intake of O2/COG (volume ratio). The adjustable range of H2/CO is1.8to3.0. In the research range of the oxygen volume flow in the intake, the total mole fraction of (H2+CO) as effective component in the outlet gas reaches the maximum value when the flow rate of the oxygen volume intake is at1.2m3/h. By adjusting the O2/COG ratio in the small quartz pipe reactor, the optimal ratio of O2/COG in the COG and CO2carbon catalytic reforming reaction for syngas preparation is0.26. When the oxygen flow rate is1.4m3/h and when the O2/COG ratio is0.26, the methane conver-sion rate reaches up to97%or higher and the effective gas content in syngas reaches up to87%.2. A general turbulence model that can address all questions is not available. For the turbulence model, the Boussinesq hypothesis is generally used to relate the Reynolds stress and the average velocity gradient as follows:Boussinesq assumptions were used in the standard k-ε model; however, this type of approximation is not highly advantageous for computer requests. The standard k-ε model has two equations, of which the full turbulence model is the simplest, generat-ing two variables, namely, speed and length scale, in the solution. The constant used in this model is provided by the user. The advantage of the K-ε model is its more ac-curate predictions of flat and cylindrical jet divergence ratios. In comparison, the RNG k-ε model consumes10%to15%more CPU time and15%to20%higher memory than the standard k-ε model.The P1radiation model is the simplest PN model. When only the first four terms of the orthogonal spherical harmonic function are considered, the equation for the radiation heat flux qr is as follows:The-(?)qr expression can be directly inserted into the energy equation to obtain the heat sources (sinks) caused by radiation.The bases of the simplified assumptions of some series of the non premixed si-mulation method are the fluid transient thermal chemical state and a conserved quan-tity, namely, a mixture fraction f to being related. According to the atomic mass frac-tions, the mixed fractions can be expressed as By assuming the same spread rate, the component equation can be reduced to a single equation of the mixture fraction f. No reaction source term is included in the component equation. Therefore,f is a conserved quantity. The average mixed frac-tional equation is as follows: Simulation studies on the small reactor shows the simulation results of the main components under different reaction temperatures. The volume fraction of H? de-creased from66.17%to43.29%; CO decreased from23.25%to20.2%; CH4de-creased from8.705%to0.105%. The effective syngas (H2+CO) decreased from89.4%to63.5%, and H2/CO decreased from2.8to2.14. The simulated data agree with the experimental data, thus suggesting that the P1radiation heat transfer model and the non-premixed combustion model can satisfy the simulation requirements with the aim of choosing a suitable turbulence model.3. The operation condition simulation provided credible foundation for process con-ditions optimization. The mole fraction of H2+CO in all outlet gas reached90%when wall temperature was1100K and when the inlet O2/COG ratio was0.26. And the mole fraction of (H2+H2O) and (CO+CO2) remained constant no matter how the inlet O2/COG ratio changed. The influence of inlet gas flow on outlet gas mole fraction is little.4. To solve solid, porous carbon catalyst problems using simulations, the porous me-dia model should be applied. The simulation parameters and solution strategy for porous media of carbon catalysts were determined through research. In turbulent flow, the medium flow for filling may be simulated using permeability and internal loss coefficients.The method for deducing the appropriate constants includes the use of the Ergun equation, and the laminar flow simulation of the full medium uses the Blake-Kozeny equation: By comparing Darcy’s equation in the porous media with the internal loss coefficient equation, the permeability and internal loss coefficients for each direction can be de-fined asThe mechanism of the simulated chemical reaction was determined by CHEM-KIN. To produce the synthetic gas process in a high-temperature carbon system, the following chemical reactions are considered:(1) reformation reaction of CH4and CO2;(2) C and CO2gas-solid heterogeneous reaction;(3) methane decomposition reaction; and (4) water-gas shift reaction. The first reaction is the main one, while the remaining three are deputy reactions.The kinetic rate equation model for the reformation reaction is expressed as fol-lows: Simulation results of the pilot carbon catalytic CH4-CO2reforming reactor shows that at800℃to1300℃catalyst layer temperature, the optimum temperature for the carbon catalytic CH4-CO2reforming reaction is1200℃. The H2content increased from44%to56.6%; the CO content increased from23.2%to29.5%; the CO2content decreased from7.97%to1.4%; the CH4content dropped from14.71%to1.62%. The export of H2/CO ratio was around2.0. CH4and CO2were effectively converted into syngas (H2+CO) through carbon catalytic reforming. The structure of the pilot re-forming reactor exhibited the expected performance and can be used as design refer-ence for practical industrial carbon catalytic CH4-CO2reforming reactors.5. This paper introduces the design of the reforming conversion reactor. The material and heat balances were calculated and the resistance properties were studied on the basis of the parameters of the reforming reactor and related gas material data. The heat generated by CO and H2O in the reaction system of the reforming furnace is the main heat source; the heat quantity at1.553×106kJ/h accounts for71.03%of the system heat income. The endothermic reaction of CH4and CO2conversion reaction has heat absorption capacity of7.210×105kJ/h, which accounts for33%of the total heat expenditure. Gases consume a great amount of heat (1.163×106kJ/h) at high temperatures, which accounts for53.24%of the heat expenditure of the system. A heat release of2.953x105kJ/h accounts for13.51%of the heat expenditure of the system. The sieve grade composition of carbon particles is the main factor influen-cing the carbon catalyst bed layer resistance. When the particle size of the carbon cat-alyst increases, the unit thickness of the carbon catalyst-bed resistance decreases. Thus, the most effective way of reducing carbon catalyst bed layer resistance is to make carbon blocks with size ranging from25mm to35mm. The most suitable sieve grade compositions for optimum carbon catalyst-bed fluid resistance are approx-imately80%of the25mm to35mm particle size,15%of the15mm to25mm par-ticle size, and5%of the5mm to15mm particle size. The fluid resistance of the unit thickness carbon catalyst bed layer is AP=313.5Pa/m.6. The pressure drop in the sections of the reforming reaction system, such as oxygen buffer tank, heating furnace, oxygen pipeline OG101to OG104equipment, is large. The gas flow rate drops rapidly with the increase in pipe diameter. The pressure drop also decreases rapidly; however, when the pipe diameter exceeds a certain range, the pressure drop decrease trend levels off. Optimizing the equipment and pipeline size to reduce the gas flow rate can effectively reduce the reforming equipment and pipeline pressure drop in the system. The total pressure drop in the system decreased from 8260.6Pa to3289.9Pa after optimization. When the system inlet pressure is P1=40kPa, the system outlet pressure is P2=36.7kPa.