Study On Microwave Pyrolysis Of Low Rank Coal

With the development of economy, the shortage of energy resources isincreasingly aggravated, and the economic value of low rank coal and its upgradingtechnology has received more and more attentions. Pyrolysis has been considered asone of the effective motheds to upgrading of LRC, which can convert LRC to cleanfeedstock of power generation, in the meaning time, liquid and gas fuel, and othervaluable chemicals can be obtained. Comparing to traditional pyrolysis, microwaveheating shows several advantages such as selective material heating, volumetricheating, easy to control, which is a promsing method of the fast pyrolysis of coal.In this thesis, three low rank coals were pyrolyzed by microwave heating.According to the temperature rise characteristics of some dielectric materials,thesemicoke produced the pyrolysis or LRC itself was choosen for microwave absorbermicrowave pyrolysis. The influences of semicoke amount, microwave power, pyrolysistemperature, residence time, and particle size of raw material, moisture and minerals inthe raw material on LRC pyrolysis by microwave were discussed also. These worksfound as follows:(1) Semicoke which final pyrolysis temperature is greater than650℃is ideal formicrowave absorbent for coal microwave pyrolysis. The effects of particle size of theabsorbent on the temperature rise characteristics are negligible.(2) With the increase of microwave power, the heating rate speed up, theconversion of coal pyrolysis improved. With microwave power increasing, the tar yieldraised. With the increase of pyrolysis retention time，the conversion rate of coal raised,the tar yield reaches a maximum at20min that stays in final temperature. With thepyrolysis temperature increased, the conversion rate of coal raised, the tar yield reachesmaximum at650℃. After microwave pyrolysis, the LRC is upgraded, its calorificvalue increases obviously, spontaneous combustion has been suppressed and waterreabsorption decreases greatly.(3) The effects of coal particle size on the temperature rise characteristics arefound negligible during microwave pyrolysis. The liquid yield increased with theincrease of particle size, and semicoke yield decreases gradually. In microwave field, the moisture content of coal samples impact in the heating rate under200℃. The effectof minerals in coal on microwave pyrolysis is determined by the kinds of mineralitself.(4) The comparison of pyrolysis by use of microwave and conventional found that,under the same pyrolysis temperature, coal conversion and tar yield of microwavepyrolysis of coal is higher than that of conventional pyrolysis. The content of CO, H2produced by microwave is higher than that of conventional pyrolysis. In theexperiment temperature, the content of CH4in the conventional pyrolysis is higherthan that of microwave pyrolysis. During the microwave pyrolysis process CH4contentdecreased with increasing temperature, after600℃, CH4content roughly constant.