Experimental Suty On Flash Pyrolysis Products Distribution Of Bituminous Coal In Coal Topping Process

Coal is the main energy source and resource in China and provides about 75% of China's total energy consumption. More than 80% of the coal is consumed as industrial and civilian fuel by direct combustion, which is of low efficiency and accounts for the major source of air pollution in China. Meanwhile, China is greatly short of petroleum and natural gas resources and depends on imports increasingly. To utilize coal with high efficiency and remedy the shortage of petroleum and natural gas, a oil-gas-heat-power co-generation technology, so-called "coal topping" process, was proposed by the Institute of Process Engineering, China Academy Sciences. The technology combines a downer pyrolysis reactor and a circulating fluidized bed combustor (CFBC). High temperature circulating solids from CFBC as heat carrier mix intensely with coal particles which are fed into the upper part of the downer. Coal particles undergo flash pyrolysis at atmospheric pressure and relatively low temperature(550～700℃) without catalysts or H2. The gaseous products are quickly separated from the solids at the exit of the downer and quenched quickly to minimize the secondary reactions for more medium hydrocarbons (light tars). The char produced in the downer is introduced into the CFBC for further combustion. The heat produced in the CFBC is used to generate steam and power. In this way, oil, gas, heat, and power co-generation can be realized.Both slow and flash pyrolysis process of bituminous coal were investigated in the present work, which was very important for optimizing the coal topping process and obtaining desirable valuable chemicals, such as light tars.Firstly, study on Hegang bituminous coal pyrolysis behavior was carried out by TG-FTIR with a heating rate of 30℃/s and the final temperature of 900℃. Gaseous products, including gaseous tar, were simultaneously detected by FTIR. The results indicated that Hegang bituminous coal experienced fierce pyrolysis reaction in the range of 430～650℃with evolution of a great deal of CH4, CO₂, CO, etc. CO2 and CO evolution continued above 700℃.Secondly, flash pyrolysis of Hegang bituminous coal were studied in a spouted-entrained bed reactor with a rapid heating rate in the order of 103 K/s and a feeding rate of 4 g/min. Effect of pyrolysis temperature on the distribution of products were investigated. The result showed that char yield decreased with the increase of temperature in the range of 550～700℃, but gas and liquid yields increased. Gaseous products consisted of inorganic gases such as H2, CO, CO2, and organic gases such as CH4, C2H6, C2H4 and C3-C5 hydrocarbons. At 700℃, liquid yield reached 22% (dry basis coal) and the ratio of the total volatiles (TVM) over the volatile matter of proximate analysis (PVM) was 1.14. A general trend of char combustion reactivity which was studied by TGA decreased with increasing temperature. A mathematical modeling of pyrolysis of coal in spouted-entrained bed was developed; the computational results showed that the average heating rate increased with the increase of bed temperature and that pyrolysis rate increased tremendously with the bed temperature, thus pyrolysis reaction time reduced with increasing the bed temperature.Finally, coal topping experiment of a bituminous coal was carried out in the downer pyrolysis reactor. Typical data of products distribution were obtained at the temperature of 558℃with a feeding rate of 1.5 kg/h, which would provide basic data for an industrial-scale experiment.