Study On Products Characteristics Of Wheat Straw By Microwave Pyrolysis

Biomass is a kind of rich and important renewable energy sources. The biomass resources, especially crop straws, are abundant in China. But the utilization ratio is low. It is significant for economy and society to develop biomass utilization technologies. Pyrolysis can produce activated carbon, bio-oil or gas, which can achieve the clean use of biomass. But the conventional pyrolysis of biomass requires deep pretreatment of raw materials. It increases equipment investment and energy consumption. Since microwave heating is rapid, uniform and highly efficient, microwave pyrolysis of biomass can greatly reduce the requirements on biomass pretreatment. Meanwhile, microwave pyrolysis can change the nature and composition of biomass pyrolysis products, it can enhance the use value of pyrolysis products.In order to increase the yield of the gas products (especially CO and H2), this paper design a set of microwave heating device. The raw material is wheat straw. The additives are pyrolysis char, K2CO3, Na2CO3, CuO and Fe3O4. The experiment is carried out using fixed bed to study the laws of biomass microwave pyrolysis. The solid products are collected and weighed. The functional groups, surface morphology and elemental composition of the solid products are also analyzed. Microwave power, additive type and add ratio are investigated, which affect the yield and components of gas, liquid and solid. The effects of the five additives to microwave pyrolysis are diffierent. CuO and Fe3O4 can effectively promote the pyrolysis of materials, only when the add ratio and power are large enough (20wt.%,800W). And most of the products are liquid, the yield is 52.92wt.% and 55.82wt.%. K2CO3 and Na2CO3 can significantly promote the pyrolysis of raw materials. When the power is 800W and the add ratio is 10wt.%, the yield of liquid is 48.73wt.% and 48.09wt.%. When the power is 800W and the add ratio is 20wt.%, the yield of gas is 48.95wt.% and 56.86wt.%. Meanwhile, K2CO3 and Na2CO3 can increase the production of H2, the yield of H2 can reach 47.4vol.% and 46vol.%. Pyrolysis char can promote the pyrolysis of raw materials and improve the yield of gas products. When the power is 800W and the add ratio is 20wt.%, the yield of gas is 60.94wt.%. The gas product of CO2 was decreased. The yield of CO is increased. And the yield of H2 is significantly increased. Pyrolysis char is the product of pyrolysis reaction. It can be easily obtained and can be repeatedly used. Therefore, pyrolysis char is most beneficial for the purpose of obtaining gas products.In order to investigate the effect of temperature, the experiments are carried out under the fixed temperature. The results show that the temperature is the main factor in the pyrolysis process. The volatile is released at 300～500℃. High temperature can enhance the yield of gas products and the ratio of fuel gas (especially H2). The yield of H2 can reach 43.7vol.% at 600℃. The bores are tiny and numerous at the high temperature. When the temperature goes up from 400℃to 600℃, the BET surface increase from 0.89m2/g to 9.81m2/g. The solid products can be made into active carbon, which can be used as adsorbent.