Study On Microwave Assisted Gasification Performances Of Rice Husk/Silicon Carbide In Fluidized Bed Reactors

Since entering the new century,the rapid growth of the global economy has brought great pressure to the supply of energy.The depletion of fossil energy has gradually become a key factor restricting the sustainable development of economy.Gaining more control over energy plays an important role in improving China’s international status and ensuring sustainable economic development.The development and utilization of renewable energy has brought dawn to the supply of energy.Biomass energy has gradually occupied an important pos ition in the utilization of renewable energy because of its wide sources and convenient access.The application of microwave heating technology provides a new direction for the efficient transformation and utilization of biomass energy.Rice husk is a typical biomass in China,this paper explored the microwave gasification characteristics of rice husk/silicon carbide under the irraction of microwave in the fluidized bed reactor,and investigated the methods to improve the gasification index,which has important theoretical and practical significance.The cold co-fluidization performance of rice husk and silicon carbide in fluidized bed was investigated by building a rice husk/silicon carbide cold fluidization test-bed system.The specific objective is to obtain the co fluidization characteristics of rice husk and silicon carbide particles in a fluidized bed reactor（fluidization performance,bed expansion and pressure drop）,and explore the effects of fluidization speed,silicon carbide particle size and sili con carbide/rice husk mass ratio on co-fluidization performance.The experimental results show ed that when the fluidization wind speed was 0.30 m/s,the bed developed stably and the rice husk and silicon carbide particles were mixed evenly,which was the best value of fluidization wind speed.If the silicon carbide particle size was too small,it would fly out of the reactor,and the excessive particle size of silicon carbide le d to obvious stratification with rice husk.When the particle size of silicon carbide was in the range of 0.20-0.25 mm,the mixing of rice husk and silicon carbide was the best.With the decrease of rice husk/silicon carbide mass ratio,the mixing of rice husk and silicon carbide particles gradually became worse,and the phenomena of stratified fluidization and gully flow appeared.When the mass ratio of rice husk to silicon carbide was 1:5,the rice husk and silicon carbide particles were mixed evenly and the bed developed well,which was the best mass ratio.By designing and building a microwave heating test-bed,the heating experiment of silicon carbide under microwave was carried out,and the energy conversion characteristics of silicon carbide under microwave were obtained.Subsequently,a microwave gasification test-bed was designed and built,and a comprehensive hot state experiment of microwave gasification of rice husk/silicon carbide was carried out.The experimental data of the components of gasification products and syngas under different factors were obtained,and the gasification characteristics of rice husk biomass under microwave were obtained.Through further analysis,the energy conversion characteristics of biomass in the gasification process were clarified.The results showed that when the silicon carbide loading,microwave power and reactor volume changed,the average heating rate of silicon carbide particles changed in the range of 0.36-7.08℃/s,and the energy absorption efficiency changed in the range of 1.49%-37.38%.With the change of gasification temperature,air equivalent ratio and silicon carbide loading,the proportion of syngas in gasification products varied from 48.45%to 78.15%,and the heating value of syngas also varied from 2.98 MJ/Nm³ to 6.33 MJ/Nm³.The proportions of combustible gases H₂,CO,CH₄,C₂H₄ and C₂H₆ in syngas varied in the range of2.32%-11.89%,12.38%-19.38%,1.28%-4.58%,0.79%-1.17%and 0.83%-0.98%,respectively.A new CFD biomass microwave gasification model was developed to simulate the process of rice husk/silicon carbide microwave air gasification.Combined with the experimental and analytical results of rice husk/silicon carbide microwave gasification in Chapter 3,the energy source term under microwave radiation was coupled in the model to describe the influence of microwave power.The rapid and transient control characteristics of microwave heating were loaded into the gasification reaction model through UDF compilation function,Combined with the Euler Euler method in the commercial software ANSYS fluent,the microwave gasification model of rice husk/silicon carbide was constructed.The microwave gasification products of rice husk/silicon carbide were simulated by the model,and the errors between the simulation results and the experimental results in Chapter 3were compared and analyzed.The results showed that for the composition of simulated and experimental syngas（CO,CO₂,H₂,CH₄,C₂H₄ and N₂）,the relative error（7.84%-19.34%）of most（94.44%）was within 20%,and for the heating value of simulated and experimental syngas（HHV and LHV）,their relative error was between 3.44%-8.62%.Therefore,the model established in this thesis is reliable and can be used to simulate biomass microwave-assisted air gasification.Based on the experimental results of rice husk/silicon carbide microwave gasification,combined with the response surface method,the multi-objective optimization of rice husk/silicon carbide microwave gasification process in fluidized bed was carried out.Four experimental variables,which significantly affect the gasification process,including gasification temperature,silicon carbide particle size,air equivalence ratio and silicon carbide loading,were selected as the operation factors,and the hydrogen content,gas production rate and cold air efficiency were set as the optimization objectives of the gasification process.The results showed that for the microwave air gasification process of rice husk/silicon carbide in fluidized bed reactor,the gasification temperature is an important factor affecting the calorific value of syngas and gasification gas production rate,and the loading of silicon carbide is the key condition affecting the c old air efficiency of rice husk gasification.Based on the experimental research on the co-fluidization performances of rice husk/silicon carbide mixture,this study completed the design of fluidized bed reactor for microwave assisted air gasification of rice husk,and carried out relevant experiments to explore the microwave assisted gasification characteristics of ric e husk/silicon carbide.Meanwhile,a CFD model which can be applied to the numerical calculation of rice husk/silicon carbide microwave gasification was developed,and the accuracy of the model was verified and the accuracy of the original model was improved according to the experimental data.Finally,the response surface of rice husk/silicon carbide microwave gasification process was optimized according to the experimental results,and the key factors affecting the relevant objectives were detailed.In this study,the microwave gasification performances of rice husk/silicon carbide in fluidized bed were investigated through relevant experiments and simulation methods.