| Biomass gasification technology is an emerging biomass energy utilization technologies of clean energy conversion. Biomass gas have its own excellence of easy to store, convenient transportation and high calorific value and so on, while solve the air pollution caused by biomass burning. It has become the focus of development in this field. And also broad market prospects. With advantages of stable calorific value, less ash, easy to operate and control, Fixed-bed downdraft biomass gasifier has been used frequently in biomass gasification. However, as unstable working condition this gasification technology may appear poor conditions of low efficiency, poor quality and high tar content. So this can't play full superiority of biomass gasification technology.Gasifying condition is the biomass gasification condition that under a particular environment, also a expression of the relationship between gasification parameters. Method of gasification agent supply, gasification pressure and temperature are the conditions that have obvious effect, with interaction between each gasification parameters, alter one of the parameters of gasification process may achieve the purpose of system control, in order to improve the gas quality and gasification results. The research on gasifying condition start late in the world, only examined one of gasification parameter that influence the quality of product gas. Ignore the interaction between working conditions.In order to research the affection of temperature, pressure and air distribution rate on different gasification stage. This project targets on the affection of 3 parameters, study in-depth by theoretical and experimental research. Test the parameters affection on reaction kinetics while in gasification. Provide the theoretical function for gasification condition research. Compared the change of bed pressure field through air distribution choice, find out the most reasonable way of air distribution, following the experimental results, build the gasification temperature, pressure mathematic model. Overall understanding the whole bed pressure and flow field through the gasifier simulation. Provide the basis of application for gasifier air distribution design, reduce the cost of biomass gasification and biomass gasification project.Kinetics of thermal decomposition is the basis for studying the effect of gasification condition, and TGA is the most effective methods of dynamics experiment. Research the gasification characteristics of biomass material in different gasification conditions by isothermal TGA and pressure TGA, investigate the effect on biomass conversion rate in the condition of different temperature, gasification agent flux and operating pressure. Calculated influence on activation energy and pre-exponential factor. The results have shown that, carbon conversion rate has been exceeded with the increase of temperature, the external diffusion of gasifying agent can be eliminated after air flow rate greater than 60ml/min. the gasification reaction rate will accelerate by the improving pressure, also the carbon conversion rate has increased, the increasing relationship in the same reaction time was not linear, the reduction reaction was less impact by the high pressure, the changing discipline of pre-exponential factor and activation energy were no different, show that they were all decrease first and then increase with the pressure increased. this phenomenon indicates that the increase of pressure can increase the activation of reactant molecules in the collision frequency, so increased the reaction activity at last. However, the gasification reaction would be inhibited when the pressure become much high.According to the results of pyrolysis experiment, the affection of working condition on biomass materials pyrolysis process are almost the same, rice husk as the bed material in biomass gasification reaction, studied the temperature, pressure and gas composition changes in 3 air distribution condition of single layer, double layer and central tube, through the active air distribution experiment. Obtain the best condition of air distribution, established the temperature and pressure relationship model in gasifier. The results shown that the pressure distribution of gasifier bed is most reasonable and bed temperature highest in the condition of centre air distribution, in this condition, the relationship of each reaction layer's temperature and pressure had a high applicability, the CO, H2 in gas composition decreased with the pressure increased, the change of CH4, did not changed significantly with pressure. the heating value appears an upward trend. Analyze the results by collision theory and Arrhenius theorem in pyrolysis process, proved that inprove the gasification pressure could accelerate the gasification reaction rate, promote the quality of biomass gas.Based on the results of gasifier temperature and pressure test, established a mathematical model of binary number according to least squares theory that reflected the relationship of each reaction layer temperature and pressure. Obtain the reasonable equation by test verification and error analysis. Provide the foundation of gasifier depth research.With the limitations of multi-point test which could not expression the whole gasifier pressure, take the active air distribution downdraft biomass gasifier as the research object, used the method of CFD to simulate the bed pressure and flow field through 3 gasification agent distribution conditions. Build gasifier bed model based on porous media, analysis gasifier flow field characteristics by Euler Lagrangian algorithm, comparative analysis the bed pressure field result of simulation and experimental results, then calculate the error, verify the feasibility of model, analyze the reason of gasifier pressure field distribution according to Bernoulli's equation, derived the relationship between reaction rate and gasification pressure by the combination theory of kinetic and combustion, Further revealed the influence of pressure distribution by kinetic reaction rate.This project systematic study the influence of gasification process parameters on biomass gasification by combination method of theoretical, experimental and simulation method, has an important meaning and effect on deeply research in the field of biomass energy conversion and utilization. |
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