高碱煤热化学转化过程中碱金属迁移转化特性研究

发布时间：2017-12-31 07:13

本文关键词：高碱煤热化学转化过程中碱金属迁移转化特性研究　出处：《中国科学院工程热物理研究所》2017年博士论文　论文类型：学位论文

【摘要】：准东高碱煤田是我国近年来发现的最大整装煤田。准东高碱煤具有高挥发分、低灰分、反应活性好、储量丰富、开采成本低等特点,适宜用作动力燃料和气化用煤。但由于准东高碱煤中碱金属含量高,在电厂煤粉锅炉直接燃用过程中出现了炉内燃烧器区结渣严重,锅炉炉膛出口烟温升高,高温换热面沾污严重,低温受热面积灰严重,部分过热器发生超温爆管等问题。目前准东高碱煤在现役机组上无法直接利用。为有效解决准东高碱煤利用过程中出现的结渣、沾污和腐蚀问题,本研究将循环流化床技术应用于准东高碱煤利用,开展高碱煤循环流化床热化学转化过程中碱金属迁移转化特性的研究,为高碱煤的大规模利用提供新的思路和工艺路线。本研究采用实验研究和理论分析相结合的方法,以化学反应动力学和热力学等基础理论为指导,采用管式炉、循环流化床并结合化学热力学计算软件,利用1C、XRD、XRF及SEM-EDX等先进的分析手段,对准东高碱煤热化学转化过程中碱金属的迁移转化规律及烟气冷却过程中碱金属的析出特性进行研究。获得的主要结论如下:(1)准东高碱煤的基本物理化学特性与我国常规动力用煤显著不同。煤中C1含量随矿区不同而具有较大差异。煤灰中Na_2O含量较高,大于2%,属于结渣煤种。具有良好的着火特性和燃尽特性。准东高碱煤中碱金属钠主要以水溶态形式存在,而碱金属钾元素与钠元素不同,主要以不溶态形式存在。(2)预处理方法对准东高碱煤以及高碱煤气化灰中碱金属含量测定的准确性具有重要影响。为了准确获得准东高碱煤及气化灰样品中的碱金属含量,建议采用氧弹燃烧法进行煤中碱金属含量的测定。另外,对于碱金属钠含量的测定,萃取法也可以相对准确的反映煤中碱金属钠的含量,同时获得煤中碱金属的赋存形态。(3)由于不同准东高碱煤中碱金属含量不同,赋存形态不同,在煤气化过程中的转化途径不同,其运行特性也有所不同。煤灰中Na_2O含量较高的天池木垒煤(灰中Na_2O含量7.28%)在循环流化床煤气化运行过程中易于发生失流现象,而煤中Cl含量高的沙尔湖煤(煤中C1含量1.13%)则易于发生金属换热面的腐蚀。试验结果及热力学平衡计算结果表明,提高反应温度和降低反应压力可促进碱金属的气相析出。(4)反应气氛对高碱煤热化学转化过程中碱金属钠的迁移转化特性具有重要影响。随着当量空气系数的增加,气相碱金属钠增加,固相碱金属钠减小。灰中未反应碳对碱金属钠具有固留作用。增加气化剂氧气浓度和水蒸气浓度,可促进灰中碱金属钠由水溶态钠向不溶态钠转化。在低当量空气系数还原性气氛和高当量空气系数氧化性气氛下,提升管内的结渣问题和尾部换热面的沾污问题尤为严重。在热化学转化初期,煤颗粒中水溶态碱金属钠一部分将会以气相钠的形式析出。在氧化性气氛条件下,气相钠将会发生硫酸化反应生成硫酸钠,而在还原性气氛条件下,气相钠将保持原析出形态不变。另一部分水溶态碱金属钠则在高温作用下向盐酸溶态钠及不溶态钠形式转化。(5)基于吉布斯自由能最小理论的化学热力学平衡计算结果显示,不同反应条件对不同煤种中碱金属平衡分布的影响作用不同。升高反应温度可促进碱金属钠的挥发及熔融。反应压力主要影响碱金属的气相与固相平衡,升高反应压力会抑制碱金属的气相析出,增加碱金属的固相固留率。相较于氧化性气氛,还原性气氛下熔融态钠的含量更高,表明在高碱煤实际热化学转化过程中,还原性气氛下,更易于发生结渣。在富氧水蒸气气氛条件下大量碱金属钠被固留于固相中,气相碱金属较少且未有熔融态物质生成,计算结果与试验结果基本一致。富氧水蒸气气化技术是解决准东高碱煤热化学转化过程中结渣沾污问题的极具发展前景的技术。
[Abstract]:The high alkali is the largest integrated coalfield coalfield discovered in China in recent years. The high alkali coal with high volatile, low ash content, good reaction activity, abundant reserves, low cost mining, suitable for use as fuel and coal gasification. But due to the high base of coal in Zhundong high content of alkali metals in pulverized coal fired boiler in power plant the direct use of appeared in the process of the burner slagging serious, boiler furnace outlet Wen Shenggao, high temperature heat transfer surface contamination is serious, low temperature heated area ash is serious, part of the superheater tube burst occurred. The problems at present in the existing high alkali Zhundong coal unit cannot be used directly. To solve the problem of high alkali Zhundong coal the use of slag in the process of contamination and corrosion problems, this study apply circular fluidized bed technology in Zhundong coal using high alkali, carry out coal in circulating fluidized bed thermochemical conversion process of high alkali alkali metal transfer characteristics The research, to provide ideas and new process route for the large-scale use of high alkali coal. This research adopts experimental research methods combined with theoretical analysis, with chemical reaction kinetics and thermodynamics theory, a tube furnace, the circulating fluidized bed combined with chemical thermodynamics calculation software, using 1C, XRD analysis method advanced XRF and SEM-EDX, studied the precipitation characteristics of alkali metal of high alkali coal conversion Zhundong thermochemical process of alkali metal migration and flue gas cooling process. The main conclusions are as follows: (1) the basic physical and chemical properties of Zhun Donggao base and China's conventional coal power coal is significantly different. The content of C1 in the coal mining area with different and have great difference. Higher Na_2O content of fly ash is more than 2%, which belongs to the slagging coal. With the ignition and burnout characteristics of good alkali metal sodium. High alkali coal mainly in Zhundong water In soluble form, and alkali metal potassium and sodium, mainly in insoluble form. (2) has an important influence on the accuracy of the determination of high alkali and high alkali Zhundong coal gasification ash alkali metal content in pretreatment method. In order to obtain the accurate content of alkali metal and alkali coal gasification ash Zhundong high in the sample determination suggested by oxygen bomb combustion method for alkali metal in coal content. In addition, for the determination of alkali metal sodium content, also can accurately reflect the relative content of sodium alkali metal in coal extraction, and speciation of alkali metal in coal. (3) due to the different high alkali Zhundong coal the alkali content in different, different forms, different ways of transforming the coal gasification process and its operation characteristics are also different. Higher Na_2O content in coal ash Tianchi Mulei coal (7.28% Na_2O ash content) in a circulating fluidized bed gasification process Easy to lose flow phenomenon, and the high Cl content in coal schallsee coal (1.13% C1 content in coal) is prone to the heat transfer surface of metal corrosion. The experimental results and thermodynamic equilibrium calculation results show that the higher reaction temperature and lower reaction pressure can promote the alkali metal vapor precipitation (4) has an important influence. The migration and transformation characteristics of reaction atmosphere transformation process of alkali metal sodium in high alkali coal. With the increase of air equivalent thermal coefficient, vapor of alkali metal sodium increased, solid alkali metal sodium decreased. Ash unreacted carbon has a retention effect on alkali metal sodium. The increase of gasification agent concentration of oxygen and water vapor concentration, can promote ash alkali metal sodium by water soluble sodium into insoluble sodium. The reducing atmosphere and the high equivalent coefficient of air oxidizing atmosphere in the low equivalent air coefficient, the riser slagging problem and the tail of the heat transfer surface contamination problem is particularly serious In the early form of thermochemical conversion, precipitation of coal particles in water soluble alkali metal sodium vapor will be a part of sodium. In the oxidizing atmosphere conditions, gas phase reaction of sodium sulfate will occur with sodium sulfate, and in reductive conditions, sodium vapor will remain unchanged. Another form of primary precipitation part of the water soluble alkali metal sodium under high temperature to the hydrochloric acid soluble and insoluble sodium sodium form. (5) the Gibbs free energy of chemical thermodynamic equilibrium theory of the minimum calculation results show that based on the different reaction conditions of different kinds of coal in different alkali metal equilibrium distribution effect. The reaction temperature can promote the volatile and molten alkali metal sodium. The main effect of reaction pressure alkali metal gas phase and solid phase equilibrium, increasing the reaction pressure will inhibit alkali metal vapor phase precipitation, solid alkali metal retention rate. Compared to the oxidizing atmosphere, but also the original Atmosphere in molten sodium higher, showed that the conversion in high alkali coal actual thermochemical process, reducing atmosphere, more prone to slagging. In the oxygen rich water vapor atmosphere under the condition of a large number of alkali metal sodium is retention in the solid phase, gas phase and no less alkali metal molten material formation the calculation results are consistent with the experimental results. The oxygen rich steam gasification technology is very promising to solve the contamination problem node transformation process of slag in high alkali coal chemical Zhundong technology.

【学位授予单位】：中国科学院工程热物理研究所
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ530.2

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