Experimental And Theoretical Study On CFB Gas/Heat/Power Cogeneration System

Coal is the primary energy source of China. Most of the coal consumed is usually used through a single way that often brings on high cost and complex technology to gain the high carbon conversion efficiency. The cogeneration technology combines multi-different processes based on coal as one system, and enhances the coal utilization efficiency on the whole. Then the problem of environment and resource faced at present will be better solved.The investigation status about the cogeneration technology that mainly has three types based on pyrolysis, partial gasification and gasification respectively is summarized and commented in the paper.To know the reaction features of coal in different conversion stage which include pyrolysis,gasification and combustion and analyze the relation of the reaction rate with the physical factors, for example concentration, temperature, pressure and catalyzer etc, the experiment was carried out on coal pyrolysis, gasification, combustion and char combustion with TGA. The reaction character of coal in the different conversion stage achieved will help to the next step experiment, industry design and operation.For making the experimental investigation, a 1MW pilot plant test facility that consists of a fluidized bed gasifier, a CFB combustor, flue gas and fuel gas clean and cool system, data acquisition and control system has been erected. Experiments on coal partial gasification with air, and recycle gas have been made on the 1 MW pilot plant test facility. The results achieved at long time steady operation status of the facility show that, with air as gasification agent, the system can produce 4-5MJ/Nm3 low heating value gas and the carbon conversion efficiency increases with the bed temperature in the gasifier.The system can produce 12-14MJ/Nm3 middle heating value gas by using high temperature circulation solid as heat carrier and recycle gas or steam as gasification media, but the fuel conversion efficiency is lower in the gasifier and most of fuel energy is converted in the combustor.The tar does much harm to gas produce and traffic processes. Experiments on tar produce and CaCO₃ effecting on tar cracking have been made on the 1 MW pilot plant test facility. The results show that CaCO₃ has an obvious effect on tar cracking and H₂S removal. And the tar oxidation thermal cracking experimental facility was designed to decrease the amount of tar in the gas from the gasifier. The tar oxidation thermal cracking experiment was made. The results show that amount of tar in the gas reduces obviously with the tar oxidation thermal cracking temperature increasing.Combining with the experimental results on the 1 MW pilot plant test facility, an overall mathematical model of CFB gas/heat/power cogeneration system is developed on the basis of the previous research work. The model includes hydrodynamic, coal pyrolysis gasification, H2S and NH3 removal, tar cracking, cyclone, particle attrition and being carried out, heat transfer in CFB, mass balance and energy balance about CFB and gasifier.The overall mathematical model was applied to the simulation of 1 MW pilot plant...