| Continuous increase of energy demand will result in raising the net oil&gas import dependency in China and underpin the coal-dominated energy structure of China in a long period. Thus the development of clean coal technology is the significant strategic choice of China’s energy adjustment.The substitution of coal for oil and gas is limited by the poor cleanness of flame and pollutant emission in coal combustion. Combined with the low ash and sulfur level of coal water slurry (CWS) and high slag captured rate of slag-tap cyclone furnace, a novel clean coal utilization technology is very promising. The high temperature product gas with low content of ash produced by the combustion of CWS in cyclone furnaces can serve as heat source for industrial production. For the first time, a series of investigation have been conducted to evaluate the key problems of the utilization of this technology.In this thesis, cold model experiments and numerical simulations have been systematically carried out for the design of the vertical-type slag-tap cyclone furnace using CWS as fuel. Results depict the flow characteristics and particle concentration distribution in the furnace, and the effect of burners, air distribution patterns, spray angles and the structure of slag coagulating pipes was also evaluated. Results provide sufficient information for the application in thermal test.Based on the results of cold modeling, the operation characteristics of the CWS cyclone furnace was evaluated by thermal tests and numerical simulations. The combustion of CWS in the cyclone furnace is well organized with the load adaptability between75%～100%at least, and the NOx emission can be effectively reduced by air staging. This technique can produce low ash content high-temperature product gas with sufficient heat and better effective radiation capacity. The content of fly ash in the product gas is reduced to a very low level due to the high average slag captured rate (>94%) of the system. Therefore, the feasibility for industrial application was validated.This study presented a novel diagnostics for the combustion of CWS in a slag-tap vertical cyclone furnace using flame images and three-dimensional temperature distributions reconstructed from these flame images through a two-step inverse radiation analysis. The accuracy of the reconstructed temperature was evaluated by infrared thermometer measurements, with a discrepancy of less than50K. The effects of air/fuel equivalence ratio, air distribution pattern, and furnace load on combustion performance were analyzed based on the reconstructed temperature profiles. Experimental and analytical results showed that flame stability was clearly represented by the variance of the image pixel values. The three-dimensional temperature profiles also effectively illustrated the combustion characteristics in the cyclone furnace under different air/fuel settings. By appropriately supplying air, the combustion efficiency of CWS can be maintained at>99%in the proposed cyclone furnace.The flow characteristics of high-temperature flue gas are important factors in the heat transfer of CWS combustion furnaces. By examining a250kg/h vertical-type slag tap cyclone furnace, this paper presents non-intrusive measurements of flow field by using a two-dimensional (2D) particle-image velocimetry (PIV) technique. The method was verified through experiments that directly used fly ash in high-temperature flue gas as tracer particles. The flow field of the flue gas was analyzed by using a time-averaged method, based on which the effects of excess air ratios and loads were discussed. The flue gas separated by a gas separator maintained good rigidity near the furnace wall rather than eroding the heating surface. The numerical simulation results validate the reliability of the PIV system under actual circumstances in the furnace. This study provides guidelines for the application of2D PIV system to represent the flue gas in thermal test boilers.The mechanism of high-chromia refractory failure in the oxidizing atmosphere of cyclone furnaces differs from the reducing atmosphere in gasifiers. In this paper, postmortem analysis was conducted to investigate the changes in the microstructures of exposed high-chromia refractory caused by its interaction with infiltrating coal slag under cyclone furnace conditions. The effects of the temperature level and viscosity of the molten slag were also investigated. Postmortem analysis confirmed that the form of Fe found in the slag in an oxidizing atmosphere was Fe2O3rather than FeO, the phase present in a reducing atmosphere of gasifiers. Furthermore, the higher melting temperature of Fe2O3weakened the slag penetration and chemical corrosion in an oxidizing atmosphere. As coal slag infiltrated a high-chromia refractory, Fe2O3in the slag reacted with Cr2O3until Fe2O3depleted in the penetrating slag. Cr2O3was dissolved in the slag because of the permeation of the slag in large pores of the refractory. The depth of the slag penetration increased as the temperature increased because of its lower viscosity at higher temperature. |
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