The Experimental Study Of Biomass Catalytic Gasification And Tar Cracking In Fluidized Bed Gasifier

Biomass energy is derived from solar energy through plant photosynthesis, which has been attracted increasing concern with many advantages: carbon dioxide zero emission, huge amount, renewable and versatile utilization technologies. Biomass gasification is one of the most promising technologies to convert biomass to energy, it is favorable for global environmental protection and energy utilization. However, high content of tar in the production gas limits its application widely. With the focus of decreasing tar amount and upgrade the quality of product gas, the gasification of local biomass samples was performed in Fluid bed gasifier. The influence of catalyst (dolomite, magnesite and olivine) and variant operting condition on tar cracking was studied in detail. A novel nickel-based catalyst was observed with ultrasonic radiation, it is efficient to reduce the coked amount coating on catalyst and prolong the operational life of catalyst. It is important for the utilization of catalyst. It is great for the development of biomass gasification technology.Firstly, the pyrolysis under CO2 condition of three different biomass samples was carried out in TGA with variant heating rates and final temperatures. It was observed that the pyrolysis of biomass was taken place in four stages. The optimum condition for biomass pyrolysis are : 10mg of biomass sample, 10-20℃/min for elevating temperature velocity with the final temperature 960℃. Then, the first-order pyrogenation kinetics parameters was calculated in the main pyrolysis range 200-450℃. It was showed that peanut shell has the lowest activation energy during emission of volatile and the best pyrolysis feature.The nickel based catalyst is one of the most widely used in the cracking reactor. However, the most popular problem is the coke coating on the surface of the nickel based catalyst, hence the catalysis was decreased, catalytic activity was reduced and the operational life was shorten. Here ultrasonic was applied in the preparation process of the nickel based catalyst. the influence of the ultrasonic radiation, additive La2O3, CeO2 and the calcined temperature on the coked amount of Ni/γ-Al2O3 catalyst was analyzed. It was observed that the impact order is: calcined temperature≈the ultrasonic radiation > CeO2 > La2O3. The influence of calcined temperature and ultrasonic radiation was obvious, and the influence of auxiliary CeO2 was also significant. Simultaneously, the influencing factor of ultrasonic radiation was studied in depth. The difference of the coke amount for three catalyst samples were analyzed with characteristic approaches (BET, XRD and SEM, etc), and thermogravimetric experiments. it can be found that ultrasonic radiation can make small pores in the carrier change into the middle ones. The diameter of middle pore is comparative to the size of active component particles, to make the active component dispersed in the middle pore more easily. Ultrasonic radiation can refrain the reaction of the active component and the carrier, and avoid producing NiAl2O4 crystalling phases and loss activity. Ultrasonic radiation can also reduce the coked amount of the catalyst greatly. The ultrasonic radiation in low power is more effective on reducing the coked amount in catalyst than the ultrasonic radiation in high power.Then, the gasification of three local biomass samples (saw-dust, peanut shell and straw) was carried out in fluidized bed gasifier system. the influence of catalyst addition (dolomite, magnesite and olivine), operation conditions (ER, temperature) on the production of biomass gasification and tar component was investigated in detail. The component of the gas products was determined by GC, and the species of collected tar was measured with GC/MS. it can be observed that the process of the biomass gasification can be optimized through changing the operating conditions according to target. Adding cheaper catalyst in the process of biomass gasification can reduce over half of tar amount in the final products, the conversion ratio of tar is 48.4-70.5%. Adjust the componente of tar and reducing the content of heavy tar are favorable for the downstream process.Finally, ASPEN PLUS, a computer program to simulate chemical industry process based on the principle of Gibbs free energy minimization was involved in to approach the behavior of biomass gasification. The model was approached based on mass, energy and chemical element constant. As the equilibrium state is impossible to arrive in the gasifier, a restricted equilibrium of RGIBBS reactor was introduced in according to the experiment result. It was observed that a good agreement was shown between simulation and experiment result. It is great for the understanding and development of biomass gasification.