Experimental Study On Dual Circulating Fluidized Beds Gasification And Oxygen-Enriched Gasification

In China, due to the deficient oil, lean gas, and rich coal energy structure which will remain for a long time, many downstream processes need liquid and gaseous fuel without dust. Natural gas is a kind of premium fuel, which is too expensive. Fixed bed gasifiers are widely used for coal gasification in gas industry in China. However, there are some disadvantages of the gasifiers, such as small scale and pollutant problems. The technology demand for the industrial gas market can be satisfied by the coal gasification process with better fuel economy and less environmental pollution.Based on the circulating fluidized bed gasification technology, research on the dual fluidized beds gasification and oxygen enriched gasification were carried out to raise the gas heating value. The operating ranges of the main parameters were determined through the fundamental experiments. On the test rig with a coal feeding rate of 10 kg/h, the characteristics of the produced gas and the system efficiency of the two types of gasification technology under different operating conditions were studied. And the results are analyzed in detail, which are useful for industrial application.The influence of temperature and heat carrier particles on char structure, char gasification reactivity, and the primary pyrolysis products were investigated on the devices including an electrical heating vertical tube furnace, a thermogravimetric analyzer and a modified bubbling bed, respectively. Through the experiments, the temperature range and the operation mode of the pyrolyzer were determined.On the dual fluidized beds gasification device, experiments under different air/coal ratios and steam/coal ratios were conducted with Shenmu bituminous coal, Datong bituminous coal, Gangkou lignitous coal and Xinjiang char, respectively. The results show that the gas heating value and the cold gas efficiency reach the highest value when the air/ratio is 2.1 m3/kg, but there is some tar remained in gas. Tar is completely cracked as the air/coal ratio increases to 2.4 m3/kg. No tar is detected in gas and the gas heating value reaches 3.58 MJ/m3 when steam/coal ratio is 0.1 kg/kg. The final product gas heating value can increase with a higher pyrolysis temperature. Char gasification and tar cracking reactions in the dilute zone of the gasifier are also useful to improve the heating value of the product gas.The experiments of Shenmu coal under different oxygen concentrations, equivalent ratios and gasification intensities were carried out on the oxygen enriched circulating fluidized bed. The results reveal that, the gas heating value, the cold gas efficiency and the carbon conversion all increase as the oxygen concentration increases. The heating value of the gas with the oxygen concentration of 40% is 1.84 times of that of air gasification. Gas production rate decreases from 2.35 m3/kg to 2.13 m3/kg. When the equivalent ratio increases from 0.20 to 0.29, the gas production rate increases from 1.94 m3/kg to 2.29 m3/kg, the cold gas efficiency increases and then decreases, but the gas heating value decreases continuously. H2 and CO concentration reduces after the gasification intensity increases, and the carbon conversion and the cold gasification efficiency are also lower. According to the results of different oxygen concentration, a method of estimating the changes between income and expenditure is proposed. The changes are classified into three types, which can provide a basis for choosing oxygen enriched circulating fluidized bed gasification technology.