【作者】 左永飞；

【导师】 李凡；

【作者基本信息】 太原理工大学 ， 化学工艺， 2011， 硕士

【摘要】 随着国内一次能源供应的日益紧张,高灰熔融性温度(灰熔点)大于1500℃的劣质煤高效利用备受关注。目前,煤气化技术向着高温高压发展,液态排渣气化技术逐渐占据主导地位。气流床气化技术对煤种适应性强,拓宽了煤种的利用范围,特别是可以气化含灰量较高的煤种。但是为满足液态排渣气化技术对灰熔点的要求,一些具有高灰熔点温度的煤,必须先有效地降低其灰熔点。我国高灰点煤炭资源储量较大,其中灰熔点大于1500℃的煤占煤炭总资源的50%,若该资源能合理高效利用不仅能提高煤炭利用率,还能缓解我国能源紧张的局面。为解决上述需求,本研究以煤灰中主要氧化物为研究对象,通过CaO-Al2O3-SiO2三相图分析,模拟煤灰(不同硅铝比值混合物)实验等化学方法,得出助熔剂降低煤灰熔点的作用机理,联合XRD和TG-DSC表征手段得到和化学方法一致的规律。依据这一机理,添加相同助熔剂降低实际煤灰熔点和模拟煤灰熔点获得相同的规律,即降低煤灰熔融性温度的一般规律是通过调节煤灰中主要氧化物含量变化,促使体系形成三元或多元的低共熔点矿物。在降低煤灰熔点实验中,.也获得了两种使煤的灰熔点达到理想温度的高效助熔剂。为了考察加入助熔剂后煤的气化反应特性,利用耐弛同步热分析仪研究了两种高效助熔剂对煤焦气化反应性及煤气组成的影响规律。得到以下主要结论：1)XRD和TG-DSC联合表征探明,煤灰受热温度高于1.000℃时,偏高岭石等矿物质分解转化成石英和莫来石等高熔点矿物质是造成原煤灰熔点过高的主要原因。通过添加助熔剂与煤灰中矿物质反应生成三元或四元的低共熔体能有效降低煤的灰熔点。2)灰中硅铝比值在2.33时,通过添加助熔剂调节酸碱比值到0.82-1.50之间或添加生物质调节煤灰中的硅铝比值到2.15-2.60之间,煤灰熔融性温度均可降低至1350℃以下,完全达到液态排渣气化技术对灰熔点的要求。3)在煤灰和模拟煤灰中添加不同助熔剂降低煤灰熔点的规律一致,即在灰中添加碱性氧化物Na2O、CaO和Fe2O3任一单一助熔剂均能降低煤灰熔点,且助熔效果为Na2O>CaO>Fe2O3.另外不同比例的CaO和Fe2O3复合助熔剂也可以有效降低煤灰熔融性温度,CaO和Fe2O3之间存在协同效应,且最佳的复合比为3:1(质量比)。4)在相同气化温度下,具有较高变质程度的东山煤的气化反应活性显著高于中等变质程度的西山煤,钠基和复合助熔剂都对二者的煤气化反应起到催化作用,但钠基助熔剂的催化能力强于复合助熔剂。添加助熔剂后两个煤的气化反应活性大小与原煤的顺序一致,但是由于助熔剂的作用缩小了二种煤气化反应活性间的差异。5)东山和西山原煤及添加助熔剂后煤样的水蒸气气化研究发现,不同样品煤气中H2/CO比均随气化温度的升高呈现下降的趋势。适合高温气化的复合助熔剂和低温气化的钠基助熔剂,均在不同程度上提高了煤气中H2/CO的比值,特别是钠基助熔剂的引入使煤气中H2/CO的比值随温度变化更明显,可以满足不同化学品生成目的对合成气的需求。更多还原

【Abstract】 Great attentions have been focused on the high efficiency utilization of poor quality coal with high ash fusion temperature since the primary energy is now in a state of short supply. Recently coal gasification technology is developing towards thigh temperature and pressure, slag-tap gasification, which bring opportunities for the utilization of poor quality coal. The ash fusion temperature (AFT) of coal should be lower about 100℃than the operation temperature of the slag-tap gasification technology in order to make sure normal runing of the slagging system. The poor quality coal reserves which AFT is higher than 1500℃account for about 50% of the coal gross reserves and those coals are not suitable for slag-tap gasification. So it is important work to decrease the AFT of those coals to meet the demand of the slag-tap gasification technology. If this goal can be realized, lots poor quality of coal can feed in gasifier, not only increase the coal utilization efficiency but also alleviate the energy crisis in some extent.For the above purpose, the major oxides that exist in the coal ash were regarded as the research objects for the present study. The mechanism that the fluxing agents could decrease the AFT were obtained through the analysis of the ternary phase diagram of SiO2-Al2O3-CaO and the simulation ash experiment. Combined TG-DSC and XRD, the consistent mechanism of decreasing the AFT could be further explained. Based on the mentioned mechanism, the following conclusion, which was applicable in both simulation and real ash, could be drawn as a general rule to explain why the AFT was decreased when fluxing agents were added, the contents of the major oxides were adjusted and the ternary or quaternary mixture system which have low melting point were formed. In the simulation ash and real coal ash experimental process, two most effective fluxing agents which could guarantee the AFT in an idea temperature interval were got. In order to investigate the impacts that fluxing agents imposed on the coal char reactivity and the producer gas formation rule, the STA449 F3 simultaneous thermal analyzer was used in this experiment. Some significant results were obtained.1) Combinating XRD and TG-DSC analysis, it was found some high melting minerals such as quartz and mullite can be formed when the temperature was higher than 1000℃and lead to a high ash fusion temperature, And the low eutectic minerals are formed by adding fluxing agents during the coal ash heating process which was the reason the AFT of coal can be decreased remarkably.2) Adjusting acid-base ratio of coal ash to 0.82-1.50 by adding fluxing agent or silica-alumina ratio to 2.15-2.60 by blending biomass the AFT of coal can come down the required temperature of slag-tap gasification which was under 1350℃.3) The ash melting point of coal which is higher than 1500℃was decreased evidently by adding any one of the fluxing agents of Na2O, CaO or Fe2O3, and the fluxing effect was in the order of Na2O> CaO> Fe2O3. In addition, the AFT of coal was also decreased remarkably when both CaO and Fe2O3 added in the coal ash due to some synergy effects between each other and the optimum mass ratio of CaO and Fe2O3 is 3:1.4) It was found that coal char reactivity was enhanced after fluxing agent used to reduce the AFT of coal, and the catalytic effect of Na-based fluxing agent was superior to multi-fluxing agent containg CaO and Fe2O3 with a mass ratio of 3:1. In addition, the coal char reactivity of two coals order was not changed when multi-fluxing agent was added and Na-based fluxing agent had limited function in changing the reactivity of different rank coal. 5) It was found that the H2/CO molar ratio of gas all demonstrated downward trends with the gasification temperature increased for Dongshan and Xishan raw Coal as well as the two coals with fluxing agents. The composite fluxing agent was fit for high temperature gasification and Na-based fluxing agent did for low temperature gasification. And the two kinds fluxing agents all made the gas molar ratio of H2/CO change obviously with operation temperature up and the function of the latter one was more evident which could satisfy the synthetic requirements for different chemical products.更多还原