Analysis Of Co-combustion Characteristics Of Sludge In A Coal-Fired Boiler

With the rapid development of the urbanization and residents' living standard in China,the amount of urban sewage is increasing year by year.In the process of sewage treatment,a lot of sludge produces as unavoidable contaminants.Sludge is a floc containing a variety of organic and inorganic substances.The calorie value of semi-dry sludge is equal to lignite,which can combust and product electricity as auxiliary fuel.At the same time,the sludge contains a lot of toxic and hazardous substances,which may be harm to the human and environment if handled improperly.In view of immature reality of the co-disposal sludge in the coal-fired power plant,this paper carried out the following research areas.This paper studied combustion characteristics of sludge with diverse heating rates and particle sizes by using thermogravimetric analysis.The combustion characteristic parameters and dynamic characteristic parameters were solved.On the basis of these,the sludge and coal were mixed in different proportions,and the co-combustion characteristics of the two were studied.The results show that: larger heating rates and smaller particle sizes were beneficial to sludge combustion;It can be seen that the mixburning performace of sewage sludge with coal was generally expressing the joint action result.The flammability index,the stability burnability index and the comprehensive combustion property index changed slightly with less than 10% sludge added to coal.However,when the mixing ratio reached 10%,the combustion performance parameters were significantly reduced,affecting the combustion.Numerical simulations were carried out to evaluate the characteristics of co-combustion coal and sludge in a 330,MW tangentially fired utility boiler,and the characteristics of flow,combustion and NO_x emissions were studied.The results show that when the sludge moisture content was 40%,the co-combustion had little influence on characteristics of flow;The furnace temperature and the concentration of emissions were also change slightly when the blending ratio is less than 20%,yet the average temperature and maximum temperature of the combustion zone were significantly reduced when the blending ratio exceed 20%.The NO_x concentration emission was also greatly increased due to the large amount of fuel type NO_x.Take a sewage treatment plant as an example,the economy of sludge mixed with coal was calculated,the result show that nine 9 tons of sludge can get a profit of 722 yuan after drying and burning.Therefore,it is not only possible to clean the environment,but also bring some economic benefits.In this paper,through a number of studies on the mixed combustion characteristics,they are desirable to provide some scientific datas for the development of sludge incineration technology.