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连续升温条件下高硫煤还原磷石膏产物特性研究
【作者】 张慧娜；
【导师】 宁平；
【作者基本信息】 昆明理工大学 ， 环境工程， 2009， 硕士
【摘要】 磷石膏在我国已被定性为危险固体废物,其危害严重影响了环境的持续发展。用磷石膏生产硫酸联产水泥是大量消耗磷石膏的途径之一。同时又能节约经济成本,造福环境。以往的生产工艺主要是用焦炭还原磷石膏,而且产生的SO2尾气浓度较低。用高硫煤还原分解磷石膏可利用煤中S含量较高的特点,提高烟气中SO2的浓度。本文实验中采用连续升温的加热方式,对不同反应温度、C/S03比、高硫煤粒径、高硫煤种条件下,高硫煤还原分解磷石膏的气体产物SO2的浓度、磷石膏的分解率、脱硫率,以及固体产物品质及变化规律进行研究。并结合热重-差热分析(TG-DTA)、X射线衍射(XRD)物相分析和SEM扫描电镜分析手段,对高硫煤还原磷石膏的反应机理进行初步研究。主要研究成果如下：(1)利用同步热重-差热分析(TG-DTA)技术,对高硫煤还原分解磷石膏在不同条件下的热失重、热效应、热稳定性进行分析研究。实验结果表明：不同条件下的热分析曲线都有两个失重阶段。磷石膏DTA曲线在1100℃处出现吸热峰,说明此时的磷石膏已开始发生熔化与分解反应。在1230-1300℃失重率达到24.541%,为强烈分解的放热反应阶段。加入高硫煤作还原剂的磷石膏热重分析曲线,在1018-1101.5℃失重率为29.758%,吸热峰温度为1060.64℃,说明用高硫煤作为还原剂,能降低磷石膏的分解温度。对不同高硫煤粒径条件下的热分析曲线进行比较,发现高硫煤粒径较小时,吸热温度区间缩短,出现吸热峰的温度降低,但失重率差别不大。在一定升温速率范围内,失重率随升温速率的增大而增大,反应的起始温度和终止温度也相应地向高温方向移动。(2)高硫煤还原分解磷石膏气体产物品质研究对不同反应温度、C/S03比、高硫煤粒径、高硫煤种条件下所得的S02浓度、磷石膏的分解率及脱硫率进行研究。实验结果表明：用高硫煤还原磷石膏可以提高S02浓度。在700-800℃和1000-1100℃,SO2浓度出现了两个峰值。当反应温度小于800℃时,较强的还原气氛有利于SO2的生成；当反应温度大于800℃时,较弱的还原气氛有利于S02的生成。在700-800℃时,高硫煤粒径对S02浓度的影响作用最显著,S02浓度最大相差15%左右。SO2浓度随着粒径的逐渐减小,呈先减小后增大的趋势。不同高硫煤种作还原剂时产生的SO2浓度变化趋势基本一致,但出现高浓度和低浓度SO2的温度范围有所不同。磷石膏的分解率、脱硫率都是随反应温度升高先缓慢后加速增长。反应气氛对分解率的影响较明显,而对脱硫率的影响不大。高硫煤粒径对分解率、脱硫率的影响变化规律不是很明显。(3)对高硫煤还原分解磷石膏所得固体产物中的CaO、总F、总P含量进行测定,作为衡量是否达到水泥原料标准的主要指标。实验结果表明：CaO含量随温度的不断升高而缓慢增大。而反应温度较低时,总F、总P含量也相对较小。不同C/S03比条件下所得的CaO含量,基本达到了水泥原料的标准。在各种反应条件下所得的总F含量,均能满足制水泥熟料的要求。强还原气氛中,不同高硫煤种对总F、总P含量的变化无显著影响。不同高硫煤粒径条件下的CaO含量随分解率、脱硫率的相互影响而变化。高硫煤粒径较大时,总F、总P含量较小。(4)采用X射线衍射(XRD)物相分析、SEM扫描电镜分析手段,结合前述实验分析结果,对高硫煤还原分解磷石膏的固体产物进行表征和分析。结果发现,1100℃时固体产物中已有C3A存在。
【Abstract】 Phosphogypsum is defined as a kind of dangerous solid waste, it impacts on the Environmental sustainability. Producting sulfuric acid integrated with cement by phosphogypsum, it is a good way to consume lots of phosphogypsum. At the same time, ecomomic cost savings and good for the environment. The reduction reaction of Phosphogypsum used to by coke, and the SO2 concentration was low. Now, the reduction and decomposition of phosphogypsum by high-sulphur coal can make the SO2 concentration higher, it characterizes by the high-sulphur coal in that sulphur content is higher.In this paper, study on the trend of SO2 concentration and quality of the solid production, which in continuous heating, different reaction temperature, different C/SO3 ratio, different particle size of high-sulphur coal and kinds of high-sulphur coal condition.At the same time, TG-DTA, XRD and SEM are used for studying the reaction mechanism of the reduction reaction of phosphogypsum by high-sulphur coal. Main research conclusions are as follows:(1) Thermogravimetric analysis was used for the study on weight loss, enthalpy and stability of the reduction and decompositon of phosphogypsum by high-sulphur coal in different conditions. The result indicates that thermal analysis curves all have two weight loss stages. At 1100℃, there is a heat absorption peak in the DTA curves of phosphogypsum, which shows the phosphogypsum has beginning to melt and decompose. When the temperature is from 1230℃to 1300℃, it is the stage of heat releasing of phosphogypsum intensely decompose, while the weight loss is 24.541%. The thermogravimetric analysis curve of the reduction and decompositon of phosphogypsum by high-sulphur coal, at 1018-1101.5℃, the weight loss is 29.758%, and the heat absorption peak is 1060.64℃. It indicates that the high-sulphur coal can lower the reaction temperature of decomposing phosphogypsum. Comparing with the thermogravimetric analysis curves in different particle size of high-sulphur coal conditions, it can find that when the particle size of high-sulphur coal is smaller, the heat absorption temperature interval is shorten, and the temperature of heat absorption peak is lower, but the weight loss rate is not very different. In some temperature interval, the weight loss rate increases when the heating rate increases. The initial and termination temperature of the reaction are corresponding to the high-temperature direction.(2) Study on the concentration of SO2, decompose rate and desulphurization rate of phosphogypsum in different reaction temperature, different C/SO3 ratio, different particle size of high-sulphur coal and kinds of high-sulphur coal condition. It shows that decomposition of phosphogypsum by high-sulphur coal can increase the SO2 concentration greatly,at the 700～800℃and 1000～1100℃, there are two peaks of SO2 concentration. When the temperature less than 800℃, undering the stronger reducing atmospheres are good for produing SO2, the situation is opposite when the temperature more than 800℃. At 700～800℃, the particle size of high-sulphur coal is affected SO2 concentration most obviously, there is about 15% at most. The smaller the particle size of high-sulphur coal is, the lower the SO2 concentration is produced firstly, and then is more and more. The trends of SO2 concentration are almost as same as in different kinds of high-sulphur coal, just the temperature intervals of high SO2 concentration and low SO2 concentration are different. The decompose rate and desulphurization rate of phosphogypsum become lower firstly and then higher when the temperature is continuously rising. In different C/SO3 ratio conditions, decompose rate of phosphogypsum changes obviously, but not for the desulphurization rate. And in different the particle size of high-sulphur coal condition, the decompose rate and desulphurization rate of phosphogypsum do not change obviously.(3) Study on the CaO content, the total fluorine content and the total phosphor content of the solid product, and take those as the indexs of cement raw material. The experimental results show that the CaO content grows slowly with temperature rising. When the reaction temperature is low, the total fluorine and the total phosphorus content are smaller. In different C/SO3 ratio condition, the CaO content can basically meet the standard of cement raw material, while the total fluorine content can meet the requirements in any reaction conditions. At the Strong reduction atmosphere, the total fluorine and the total phosphorus content do not change significantly in different kinds of high-sulfur coal condition. In different particle size of high-sulphur coal condition, the CaO content change with the decomposition rate and the desulfurization rate. When the high-sulfur coal particle size is larger, the total fluorine and the total phosphorus content are less.(4) Combinating of the foregoing experimental analysis results, it characterizes and analyzes the solid products of decomposing phosphogypsum by high-sulphur coal by XRD and SEM. The result shows that, there is some C3A in the solid product at 1100℃.