Study On Combustion Characteristics Of Coal Blends At Constant Temperatures

Coal blending is an effective measure to realize the safe and economicoperation of power plant, reduce emissions and impove the coal flexibility. Gradualheated TGA is the most commonly used method to study thermal gravimetric measuresof coal blends, but this method do not coincide with practical industrial application inwhich pulverized coal is suddenly exposed to high temperature circumstances.In this work, the combustion characteristics of coal blends were studied by means ofa customized isothermal thermo-gravimetric experiment system, which is designed tosimulate the real combustion conditions with high heating rate, synchronously NO andSO2formation characteristics were measured. Besides, the effects of water vapor on thecombustion characteristics of coal char were investigated, because a large number ofmoisture is added when blending the low rank coal. In the end, a new mothod ofprediction the ash fusion temperatures was put forward, on the base of mineralconversion of coal-ash in fusing process, which studied by XRD on the ash of single andblended coals made at different temperatures. The results show that:Pulverized coals blended with Indonesian lignite lead to the average rate of weightloss increasing, the burn-out time reducing, and the influence degree enhancing with thecoalification higher. Morever, it is suggested that the combustion performance of coalblends, such as the average rates of weight loss in entire process and initial stage, displaythe additive effect of parent coals, while the burning time and average rate of weight lossin main reaction stage are nonlinear.At low oxygen concentration, water vapor has an significant effect on the coal charweight loss characteristics, Since the gasification reaction of water vapor and coal charhappens. Moreover, the effect of water vapor on the combustion characteristics of coalchar increases with the rise in temperature. Additionally, the effects of water vapor on thecombustion characteristics of coal char reduce with the increase of coal rank, in otherwords, water vapor can significantly affect combustion characteristics of the coal charwith higher reactivity.Both single coal and coal blends, NO emissions are mainly concentrated in the firsthalf of the reaction and SO2emissions are mainly concentrated in pulverized coal heating stage of ignition. Due to the interactions between the single coal, NO and SO2emissioncharacteristics of coal blends display the nonadditive effect of single coals, and thecumulative emissions are different levels of less than that of the weighted value. Besides,the NO cumulative emissions of coal blends fall in between those of single coals, andwhen the Indonesia lignite blends less than1/2, the coal blends not including Yuanquancoal blends, SO2cumulative emissions are lower than that of each single coals.Tashan coal has a higher ash fusion temperatures, because the mullite may beproduced in the coal-ash fusing process. The ash of Xinjiang coal contains a plenty ofCaO, MgO and Na2O, these substances can be formed a large number of feldsparminerals, leading to a lower fusion temperatures. In addtion, the fusion temperatures ofcoal blends ash is far lower than that of the weighted value, due to the low temperatureeutectic may be formed by the calcium minerals, such as anorthite, gehlenite and so on.The new model of prediction the ash fusion temperatures based on the mineralconversion of coal-ash in fusing process has a good stability and high accuracy. This mayprovide a new way to resolve slag issue of boiler in power plant.