Research On Combustion Characteristics And Optimum Ratio Of Coal-based Fuel Blends

Because of the shortage of coal resources and transport capability and the policy of low-quality coal combustion in power plants in China, the coal-fired power plants cannot burn the design coal. More and more power plants began to use the blended coal for the sake of cutting down cost and fulfilling the contamination emission regulation of the govenment.The combustion of blended coal is an extraordinary complex physical chemistry process. During the combustion of blended coal,the component of different coals affect each other,so the blended coals exhibit different combustion characteristics from the single coal. The variety of coal brings many new problems which influent the security of boiler operation, such as low stability of combustion,slagging easily,raising of contamination release and so on. Therefore, it's necessary to study the combustion characteristics of blended coals in order to solve problems and fully display the advantage of blended coals. Understanding the combustion behaviour of blended coals is very important to the designing of boilers and controling of the combustion process.We can get many related parameters from industry analysis, elemental analysis, thermogravimetric experiments and ash fusion experiment of two typical coal-based fuels which mixed Pingdingshan bituminous coal with Youxian anthracite and mixed Youxian anthracite with Xiangtan rice straw.Then we got the optimal ratio by calculation and analysis relating to the weight and grey theory.By industry analysis, we found that the volatile content of coal increased with the increase of the proportion of Pingdingshan bituminous coal, those account that the addition of anthracite coal can improve the fuel characteristics of blended coal. Anthracite mxied with straw can increase the volatile content and decrease the ash content, which indicated that the rice straw can improve the fuel characteristics of anthracite significantly.The ignition temperature, burn-out temperature, maximum weight loss rate and the corresponding temperature of the coal-based fuel are studied in thermogravimetric experiments and the DT,ST,HT,FT are studied in ash fusion experiments.We verify the advantages and disadvantages of different proportions integrated coal-based fuel by the flammability index and stability index and study the variation law of different mixing ratio of coal-based fuel's combustion characteristics. Experimental results show that combustion ignition temperature and comprehensive index of mixed coal decreased with the increase content of bituminous coal and burnout characteristics and slagging characteristics of anthracite got close to Youxian anthracite.By mixing rice straw in anthracite the ignition temperature decreased, the comprehensive combustion index increased and the ash melting temperature got close to the Youxian anthracite.From arrhenius law,we found the activation energy and frequency factors with coats-redfern-integration by calculating the combustion parameters.The conclusion is that Pingdingshan bituminous coal:Youxian anthracite=3:7 and Youxian anthracite:Xiangtan rice straw=1:1 are best. These provided important data for the software which was used in optimizing coal-based fuel mixture ratio.Based on the experimental data and empirical formula, we set the economy as the objective function, coal-based fuel mixed fuel characteristics and combustion characteristics as the constraints, and use VC language as a tool to develop the optimal ratio systems of coal-based mixed fuel, and to verify and modify it.