Experimental Research On Combustion Characteristics Of Residual Carbon Of Fly Ash From CFB Boiler

With the wide adaptation of fuel, high efficiency and low pollutant emission, circulating fluidized bed (CFB) boiler developed fast. However, the carbon content of fly ash is very high with using of low activity coal, such as anthracite coal, lean coal and coal gauge in China, hence, the combustion efficiency is quite low. Advanced technology of fly ash re-burning is attracted great concern with the point view of reducing the unburned carbon content, upgrading heat efficiency and low pollution. it is great for the development of environment friendly and high efficiency energy utilization technology. In the project, the combustion characteristic of residual carbon in fly ash from CFB boiler was investigated in depth.Firstly,the development of CFB boiler world widely was summarized. It pointed out the existence of CFB boiler fly ash with high carbon content in China. The possible factors were analyzed and introduced the main measures taken in present. Simultaneously, the limitation of the current measures used was discussed. It is necessary to research new method to reduce carbon content.The residual carbon involved was extracted from Kaifeng (440t / h), Gongyi (440t / h) and Fenyi (410t / h) CFB boiler fly ash by floating, which mitigated the influence of ash and minerals on the combustion behavior of residual carbon. High carbon content of residual carbon samples were gotten through Flotation election.Then, the combustion characteristic of three residual carbons and the original coal particles was analyzed using thermal analysis (TGA, STA409C, Netzsch, Germany). It was observed that the ignition temperature of the residual carbon is much higher than that of original coal sample. The combustion property of residual carbon reaction is not only dependent on original coal property, it also related to the operating condition.Simultaneously, the influence of oxygen content and heating rate was studied in TGA. The selected O2 content are 20%, 30%, 40% and 70% in O2/N2 mixture with the flow rate of 100ml/min. It was found that higher oxygen content is favor for the upgrading of combustion behavior of residual carbon, and oxygen-rich combustion of residual carbon can lower ignition temperature, accelerate the combustion rate. It can be derived that oxygen concentration of 40% is the optimal chose to improve combustion characteristics residual carbon best. With heating rate increasing, the ignition flame stability of residual carbon was enhanced greatly, and the combustion characteristics were good.Finally, Coats-Redfern method was introduced in to analysis the mechanism of residual carbon combustion, and the kinetics parameters (the activation energy and exponent factor) were calculated. Activation energy decreased with O2 content increasing and heating rate as well.It is great for the development of fly ash utilization technology; it is favorable for improving of efficiency of CFB boiler.