生物质热解焦油的热裂解与催化裂解

Experimental Study on Catalytic and Thermal Cracking of Tar from Biomass Pyrolysis

生物质气化过程中产生的焦油对气化系统和用气设备都有极大的危害.为了开发适合于商业应用的焦油缩减方法,探索达到最优焦油脱除效果的操作条件,在固定床反应器上,利用石灰石、白云石、高铝砖作为催化剂研究了生物质(稻秆、稻壳、木屑等)热解焦油的催化裂解反应,利用炭化硅作为热载体研究了焦油的热裂解反应,对热解煤气中焦油含量的变化以及热解煤气组成和热值的变化进行了比较,并对裂解温度、气相停留时间等因素对裂解效果的影响进行了探讨.实验发现,600～900℃范围内ηtar随裂解温度升高而升高,900℃时热裂解条件下可达60%,而催化裂解条件下可达90%以上.0.5～1s范围内,ηtar随停留时间增加而升高,幅度约7%～10%.相比于原始煤气,裂解后煤气组成出现了较大变化,热裂解后煤气热值增加,而催化裂解后煤气热值下降,且热裂解与催化裂解处理后煤气组成也有较大差异.

Tar from biomass gasification process is harmful to the gasification system and gas consuming equipment. For the development of tar removal method suitable to be applied in industrial use, it is necessary to seek out the optimal operating condition for tar cracking process. On a fixed-bed reactor, catalytic cracking of tar from pyrolysis of biomass, including rice straw, rice husk and wood chip, is investigated using limestone, dolomite and alumina brick as catalysts, and silicon carbide as an inert catalyst for thermal cracking. The effects of different catalysts on the variation of tar content in the gas, the gas composition and heating value, are investigated. Several factors that may influence the efficiency of the tar cracking process are studied for better catalytic effect. It reveals that tar removal efficiency rises with the cracking temperature from 600 to 900°C, reaching 60 percent in thermal cracking and above 90 percent in catalytic cracking at 900°C. When the gas residence time rises from 0.5 to 1 second, the tar removal efficiency increases about 7 to 10 percent. The gas composition changes greatly after the cracking process, with the gas heating value increases after thermal cracking and decreases after catalytic cracking.