| Biomass gasification process is one of the effective ways of producing gas or hydrogen-rich synga, and have marked meaning in pollution reduction and sustainable development. It is still in the primary stage. Due to differences of the types of gasifier, the gasifying agent and the operating conditions, many researchers had performed experimental studies in biomass gasification but obtained different results. In order to deal with the problem, a technical way for fluidized bed biomass gasification based on induction heating was presented and a small-scale experiment system of biomass gasification based on induction heating was designed and constructed, performing tests of reactor temperature rise properties and feed rate of biomass. The reactor in the system provided heat for pyrolysis and gasification processes of the fluidized biomass pellets, realizing accurate temperature control in the whole gasification process.In the experiments of producing high calorific value fuel gas, rice husk was applied as fuel and steam was used as gasifying agent. What’s more, the simulation and exergy analysis of the biomass gasification process were also carried out. The main experimental results and conclusions are as follows in this dissertation:Steam and air gasification studies were carried out. The effects of reactor temperature, steam-to-biomass ratio (S/B), and equivalence ratio (ER) on gas composition and hydrogen yield were investigated. According to the experimental results, we could find that when the reactor temperature was800℃, the hydrogen content increased with the increase of S/B or the decrease of ER, hydrogen yield reached its maximum at the S/B of1.5or at the ER of2.2. The highest hydrogen content (35.47%) and the highest hydrogen yield (78.22g hydrogen/kg biomass), was achieved simultaneously at a reactor temperature of950℃, ER of0.22, and S/B of1.5. The product gas had great potential for further enhancing the hydrogen content and yield by promoting the shift reaction.The orthogonal test design was used in the sensitivity analysis of the three principal factors and their interactive influences for the lower heating value of gas. The range analysis and variance analysis were applied to analyze the results, and the best resultant of factor lever and the significance relation of key factor influencing the lower heating value was obtained. The results showed that in the range of experimental parameters, the order from master to minor was equivalence ratio> gasification temperature> steam/biomass mass ratio> interactive influences of steam/biomass mass ratio and equivalence ratio> interactive influences of gasification temperature and steam/biomass mass ratio> interactive influences of gasification temperature and equivalence ratio. Equivalence ratio, gasification temperature and steam/biomass mass ratio had a notable effect on the lower heating value of gas. The best application conditions were obtained by interactive analysis, when the gasification temperature was750℃, the steam/biomass mass ratio was0.75, and the equivalence ratio was0.25, the lower heating value of gas reaches its maximum of6.530MJ/m3.In view of the multiple factors and their interactive influences affecting the hydrogen concentration of biomass gasification, biomass gasification for hydrogen-rich gas tests were performed, the effects of gasification temperature, steam/biomass mass ratio, and equivalence ratio on the hydrogen concentration were investigated with the methods of interactive orthoplan, range analysis and variance analysis were applied to analyze the sensitivity of these factors and their interactive influences. The results achieved by both analysis were same. The study indicated that gasification temperature, steam/biomass mass ratio, and equivalence ratio had a notable effect on the hydrogen concentration, and so did the interactive influences of gasification temperature and steam/biomass mass ratio. The best application conditions were obtained by interactive analysis, when the gasification temperature was800℃, the steam/biomass mass ratio was2.5and the equivalence ratio was0.22, hydrogen concentration reached its maximum of38.27%.The simulation of hydrogen generation from biomass gasification was carried out, using ASPEN PLUS software to establish gasification model. The gasification parameters included reactor temperature, steam-to-biomass ratio and equivalence ratio, and their effects on the indexes of gasification were discussed. The results showed that in the range of750to950℃, with the increase of gasification temperature, there appeared increase in the concentration of H2and the product gas yield, as well as the hydrogen yield and steam decomposition rate. Meanwhile, it also enabled the reduction of CO and the heating value of the product gas. Besides, with the increase of S/B in the range of1.6to2.4, there increased the concentration of H2, the product gas rate and steam decomposition rate, which also reduced the concentration of CO, CH4and CO2and the heating value of the product gas. Furthermore, with the increase of S/B in the range of0.2to0.28, there appeared decrease in the concentration of CO, H2and CH4and combustible components of product gas, and increase in the concentration of CO2, the product gas yield and non-combustible components of product gas. Besides, the simulation of the steam decomposition rate increased first and then decreased, indicating that there was a peak. In this paper, simulation results indicated that the established model could reveal the rule of hydrogen production deeply. The establishment of such a model provided theoretical instruction for designing, debugging and operation of experiment system.In this section, lots of studies were carried out, including establishment of the exergy gasification process flow diagram of the induction heating gasification reactor, calculation of the exergy of various reactant among the gasification process and analysis of the effects of the operating conditions on the product gas, which containing the effects on exergy distribution, exergetic efficiency and gasification efficiency. And the studies above showed that, when the gasification temperature increased from750℃to950℃, the exergy value of gas would tend to increase and there would also have promotions to the gasification efficiency of the gasification process and exergetic efficiency. The exergy value of product gas tended to increase with increase in S/B from1.6to2.4and so did the gasification efficiency. However, exergetic efficiency increased first and then decreased, indicating the presence of an optimum value among S/B. When the ER varied from0.2to0.28, the total exergy value of product gas increased first and then decreased. With the increase of ER, the exergy value of gas would reach the peak at0.26. Meanwhile, gasification efficiency and exergy efficiency tended to first increase and then decrease, which also both reached the peak when ER was0.26at the same time. This indicated that there was an optimum value of S/B, from the perspective of the rational use of energy considerations. Among the exergy values of product gas, H2and CO accounted for a large proportion and also made a greater contribution to the total exergy values of product gas. A lot of irreversible processes accompany with the gasification process would result in a decrease in the quality of energy and lead to exergy efficiency being less efficient than gasification thermal efficiency. |
PDF Full Text Request