| Coal is the main constitution of energy consumption in China. And more than half of coal consumption are used in coal-fired utility boilers and industrial boilers burning. However, the national energy policy required that the quality of power coal should be bad. These power coal contain relatively higher sulfur and ash. In consequence, they are easy to result in fouling, slagging, erosion and abrasion ash related problems in the heat transfer surface in boiler. The fouling and slagging ash related problems plagued the operation of coal-fired power palnts long time, which greatly reduces the reliability and safety of the boiler, meanwhile reducing the efficiency of the boiler and increasing the operating cost of power plant. Additionally, ash sintering and melting are one of the important properties of ash depostion, it directly affects the growth of ash depositon on heat transfer surface in boiler. In order to study the inferior coal ash deposition characteristics, this paper used one-dimensional flame furnace, ash deposition probe system and digital image processing system which are designed by ourself. Meanwhlie, the thermodynamic software FactSage, scanning electron microscope, energy dispersive fluorescence analyzer and X-ray diffraction analyzer were used to investigate the chemical equilibrium calculation, the micro structure, chemical composition and mineral phase of ash deposits. This paper conducted the online thickness and thermal conductivity measurement of ash deposition. At the same time, this research evaluated the effect of furnace temperature and probe surface temperature on the growth of ash deposition. In addition, in order to study the sintering characteristic of ash under oxy-fuel combustion atmosphere, a horizontal sintering furnace system with atmosphere variable is developed. The system contains the horizontal sintering furnace, a CCD camera system, sintering probe system, and automatic retreat device. The research simulated coal ash and mixed fuel ash sintering on water wall tube in oxy-fuel combustion atmosphere. The following is the main research work:Firstly, an oil-cooled ash deposition probe system and digital image processing system were developed. They contained ash depostion probe, CCD image system, ash deposit thickness on-line monitoring software. Using this system to investigate the slagging characteristic of Shanxi coal in a one-dimensional flame furnace. The real-time on-line thickness of the ash deposit and the heat flux through the probe are obtained.Sencondly, applying the principle of two color method of temperature measurement and combining digital image technique processing system to obtain the measurement method of average effective conductivity of ash deposition. Using the above method to conduct the research of slagging characteristic of Zhundong coal characterized by high sodium in one-dimensional flame furnace. The experiments obtained the relationship between the thermal conductivity of ash deposit and its thicknesss.Thirdly, using the digital image technology to investigate the effect of furnace temperature on the slagging characteristic of Shanxi coal in one-dimensional flame furnace. During the experiments, the furnace tempeataures were set to 1573 K,1523 K,1473 K, respectively. Furthermore, the research analyzed the growth characteristic of ash deposits and their corresponding mircrostrture in different cases. Meanwhile, using the improved Urbain model and combining FactSage software to study relationship between the viscosity of ash deposit and temperature.Fourth, this paper applied digital image processing system to evaluate the influence of ash deposition surface temperature on the growth characteristic of fouling in a one-dimensional flame furnace. In addition, combining X-ray diffraction analyzer, scanning electron microscopic and energy dispersive fluorescence analyzer to analyze ash mineral distribution, microstructure and chemical composition.Fifth, the digital image technology processing system was used to study the effect of ash deposition surface temperature on the slagging characteristic of Zhundong coal in one-dimensional furnace. At the same time, the microstructureof ash deposit, and corresponding chemical composition and mineral distribution are discussed in this paper.Sixth, use the horizontal sintering furnace of with atmosphere variable was developed to investigate the Zhundong coal ash sintering characteristic under oxy-fuel combustion atmosphere. The experiments obtained the height shrinkage rate and area shrinkage rate of ash sample in different sintering temperatures. At the same time, the microstructure, chemical composition and mineral distribution of the sintered ash samples are analyzed.Finally, the above horizontal sintering furnace was used to investigate sintering behavior of the shenhua coal ash blending with wood ash in oxy-fuel combustion atmosphere. The experiments obtained the height shrinkage rate and area shrinkage rate of ash samples under different blending proportion. In addition, the crystalline phase distribution and microstructure of the ash samples are analyzed. |
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