热提质对低阶煤水分复吸与自燃特性影响研究

发布时间：2018-01-05 00:31

本文关键词：热提质对低阶煤水分复吸与自燃特性影响研究　出处：《中国矿业大学(北京)》2017年博士论文　论文类型：学位论文

更多相关文章： 热提质 水分复吸 机理 吸湿预氧化 自燃

【摘要】：低阶煤储量大,是我国重要的储备能源;其高效提质和清洁利用,具有重要的能源战略意义。但低阶煤热提质后极易复吸水分,导致生产效率降低、运输成本增加;储存过程遇到雨雪天气后的高湿环境,易诱发自燃,带来安全隐患。因而,热提质缺乏经济性和安全性,阻碍了技术的全面工业化和低阶煤的推广应用。针对低阶煤热提质后的水分复吸/自燃问题,本文强化基础规律研究,系统探究水分复吸差异、自燃特性差异及产生原因,明确热提质-水分复吸-自燃特性内在联系。论文的主要研究内容和结果包括:1.低阶煤热提质后的水分复吸规律研究选取两种代表性的低阶煤(褐煤和长焰煤),采用固定床反应器在105~900℃范围内进行热提质,通过恒温恒湿箱水分复吸实验,系统地研究了不同温、湿度贮存环境(10~40℃、15~98%RH)下提质低阶煤的水分复吸规律。结果表明,(1)相对湿度≤40%RH,提质温度越高,复吸水分含量越低;98%RH时,900℃提质样品的复吸水分含量明显提高至12%。环境温度高,复吸平衡所需时间缩短。不同温度提质褐煤的水分复吸行为差异比长焰煤明显。(2)环境湿度越大,平衡水分含量(EMC)越高。湿度≥60%RH,提质温度增加,EMC先减小后增大,600℃提质褐煤和400℃提质长焰煤的EMC分别最低。湿度80%RH,各温度提质褐煤的水分含量均大于燃煤电厂煤质指标8%。(3)样品粒度(3mm以下)和环境温度对EMC的影响较小。复吸水分含量高的样品,颗粒尺寸效应影响明显。(4)回转窑提质热碎样品的EMC比固定床同粒级样品低;与固定床不同,热碎使灰分在小粒度富集,粒度级减小,EMC越小。2.水分复吸的等温吸附/吸附动力学模型分析通过等温吸附和吸附动力学模型解析水分复吸过程,发现:(1)105/400℃提质样品广泛分布了结合水和自由水,而600/900℃提质样品的吸附势低于特征曲线拐点时,自由水分含量剧增。(2)原煤和105/400℃提质样品的吸附等温线符合Dent模型;600/900℃提质样品的吸附等温线符合DS2模型。提质温度增加,或煤阶增加(褐煤→长焰煤),第一位吸附量减少;600/900℃提质样品的第一位吸附量极低,复吸水分主要来自孔内填充。第二位吸附量先减小后增加,600℃提质褐煤和400℃提质长焰煤的第二位吸附量分别最小。(3)水分复吸经历快/慢两个阶段,4h超过EMC的85%,拟二级动力学模型拟合度均高于0.999。样品的初始水分含量低,初始吸附速率高,但400℃提质样品最低。EMC高的样品,亲水性吸附位浓度高或者孔结构发达,易快速形成水膜,吸附速率常数低。3.低阶煤热提质后结构性质变化及水分复吸机理研究采用多种测试表征手段(元素分析仪、马弗炉、扫描电子显微镜sem、氮吸附、傅里叶红外光谱ft-ir分峰拟合)分析煤质变化、亲水性官能团分解、孔隙结构破坏效应,明确了结构性质变化对水分复吸的影响,揭示了吸水可逆性差异的化学本质、与提质条件的内在联系,提出了水分复吸机理的描述模型。结果表明,(1)提质温度增加,o含量降低,最高平衡水分含量(mhc*)先减小后增加,223y12.470.60x0.16x1.3710x-(28)--(10)?两者符合关系式;o含量9%时,mhc*最小4.5%。vdaf与mhc*的相关性比ad显著。(2)提质温度增加,褐煤表面严重褶皱、塌陷;长焰煤表面呈收缩、裂隙。褐煤的孔体积和比表面积增加,900℃提质后孔体积增至134.19×10-3cm3/g;长焰煤先略微减小后增加,400℃提质后孔体积最小23.69×10-3cm3/g。热提质使褐煤20~50nm中孔增多,600/900℃提质后微孔急剧增加;提质长焰煤变化不如褐煤显著,2~10nm孔居多。(3)亲水性含氧官能团含量顺序为羟基羧基羰基。羟基含量高,对mhc*的影响最大。不同温度提质褐煤的亲水性官能团含量与mhc*的线性相关性0.82~0.95;提质长焰煤仅0.16~0.53。(4)水分复吸特性变化的主要机理:105~600℃提质褐煤的亲水性含氧官能团逐渐减少,吸附位数量降低,mhc*降低;600~900℃提质褐煤微孔增加,高湿环境下微孔填充自由水分,mhc*增加。但600℃提质褐煤表面被疏水性焦油覆盖,mhc*最小。提质长焰煤的亲水性含氧官能团比同温度提质褐煤少,mhc*受2~10nm的孔体积改变影响较大。400℃提质样品的孔体积最小,且具有特殊的表面亲疏水性相间结构,水分子难以稳定吸附形成水簇,mhc*最低。4.水分复吸和吸湿预氧化对自燃特性的影响研究将热提质后的新鲜样、及其水分复吸样/吸湿氧化样分别在程序升温装置中进行自燃测定,对比吸氧量、交叉点温度(cpt)、升温速率等参数差异和fcc判定的自燃倾向性,分析了热提质样品水分复吸/吸湿预氧化后的自燃特性变化。结果表明,(1)提质温度增加,新鲜样的自燃倾向性降低。但热提质后的水分复吸样临界温度吸氧量比新鲜样降低60%以上;加速氧化阶段吸氧量变化出现短暂“平台”期后消耗加速。200~500℃提质褐煤水分复吸样的hr(cpt附近升温速率)比新鲜样高;加速氧化阶段,瞬时升温速率增加更快;自燃倾向性比新鲜样明显增加,更易自燃。提质长焰煤的自燃倾向性低于提质褐煤,且水分复吸对其自燃特性影响小。(2)吸湿预氧化2天即使200~500oc提质褐煤的自燃倾向性(较其提质新鲜样)显著增加,400℃提质样品吸湿预氧化30天后自燃倾向性继续增加接近原煤。(3)105~300℃提质褐煤易复吸水分,水分复吸样对cpt的影响比吸湿氧化样显著,而吸氧量差异不明显。400/500℃提质样品不易复吸水分,但复吸少量水分,cpt显著增加、吸氧量显著降低。与吸湿氧化样相比,水分复吸样的水分含量增加值与fcc的增加值呈正比关系(5y0.23x9.2110-(28)-?)。5.热提质和吸湿预氧化对自燃特性的影响机理研究采用SEM、X射线能谱仪(EDS)、红外光谱仪、氮吸附仪、微量热仪等测定了各样品的表面化学结构变化、孔结构及吸湿性差异,利用X-band电子自旋共振波谱仪进行自由基动态原位分析,描述了不同样品的自燃历程,探究了热提质-亲水亲氧结构-水分复吸-吸湿预氧化-自燃特性的内在关系。结果表明,(1)热提质和吸湿预氧化导致结构性质变化是褐煤自燃倾向性改变的本质原因。105~500oC提质褐煤新鲜样在空气中发生预氧化,表面氧含量及内部氧化活性基团数量增加;脂肪侧链、含氧官能团和(提质后生成的)新自由基等氧化活性基团的存在,与比表面积的增大,共同强化了样品的预氧化和自燃。吸湿产生的润湿热促进热量聚集的同时,加深预氧化而间接影响自燃;吸湿程度大的样品,自燃倾向性增强显著。(2)热提质和吸湿预氧化利于自由基的形成。氧化温度升高,新鲜样和吸湿氧化样的自由基浓度相对增加率均先减小后增加,但吸湿氧化样的增加率更高。(3)氧化升温过程中,105℃提质新鲜样的部分活泼分子侧链断裂,持续产生活性自由基;而400℃提质新鲜样的小分子自由基被迅速消耗,交叉点温度后不能产生大量新自由基维持氧化反应,因而自燃倾向性降低。吸湿预氧化使活性自由基增加;水分使样品在加速氧化阶段后期,继续产生自由基,维持氧化自热升温,因而吸湿氧化样的自燃倾向性增加。本研究为低阶煤提质和分质利用的产业化发展提供了理论支持。
[Abstract]:Low rank coal reserves, is China's important energy reserves; its high quality and clean use of energy, has important strategic significance. But the low rank coal quality and easy to relapse after hot water, resulting in lower production efficiency, increased transportation costs; storage process encountered rain and snow after high humidity environment, easy to induce spontaneous combustion and bring security risks. Therefore, the heat quality and lack of safety and economy, hindered the popularization and application of comprehensive industrial technology and low rank coal. For the low rank coal hot water quality after relapse / the problem of spontaneous combustion, this paper studies the law basis to strengthen the system, explore moisture re adsorption differences and causes of differences in the characteristics of spontaneous combustion clear, hot - water - quality and relapse of spontaneous combustion characteristics of internal relationship. The main research contents and results include: 1. low rank coal heat after upgrading the moisture re adsorption of low rank coal law study selected two representative (brown coal and long flame coal mining). With a fixed bed reactor for thermally upgrading at 105~900 Deg. C, through constant temperature and humidity box moisture re adsorption experiment, systematically studied the different temperature and humidity storage environment (10~40 C 15~98%RH) under the upgrading of low rank coal moisture re adsorption law. The results show that (1) the relative humidity is less than 40%RH, and temperature the higher the relapse, the lower the moisture content; 98%RH, relapse moisture content was increased to 12%. ambient temperature of 900 DEG C higher quality samples, relapse balance shorter time. Different temperature of lignite moisture relapse behavior differences than the long flame coal obviously. (2) the environmental humidity is bigger, water balance the content of (EMC). The higher humidity is larger than 60%RH, and the increase of temperature, EMC decreased firstly and then increased, 600 DEG and 400 DEG C lignite long flame coal quality and EMC respectively. The lowest humidity 80%RH, the moisture content of each temperature of lignite were higher than coal-fired power plant coal quality index 8%. (3) sample size (3mm) The smaller and the influence of environmental temperature on EMC. The relapse samples with high moisture content, grain size effect is obvious. (4) the quality of rotary kiln thermal broken sample EMC than fixed bed with low grade samples; unlike fixed bed, the broken ash in the small heat accumulation, decreasing particle size, adsorption / the smaller the EMC.2. moisture re adsorption kinetic model through the analysis of the adsorption isotherm and kinetics model analysis of moisture re adsorption process, found that: (1) 105/400 samples are widely distributed in the C and bound water and free water, and the adsorption of 600/900 and the potential is lower than C sample characteristic curve inflection point, increasing the free moisture content (. 2) the adsorption isotherms of coal and 105/400 C quality and samples with the Dent model; adsorption isotherm of 600/900 C quality samples in accordance with the DS2 model. The quality and temperature increase, or increase the order of coal (lignite, long flame coal), the first adsorption amount decreased; 600/900 C quality The first adsorption capacity of samples is very low, relapse water mainly from hole filling. Second the adsorption capacity decreases first and then increases, the second adsorption capacity of 600 DEG and 400 DEG C and lignite long flame coal were minimal. (3) water fast / slow relapse experience two stages, 4H more than EMC 85%, the initial moisture content of two order kinetics model fitting degree is higher than that of 0.999. samples is low, the initial adsorption rate is high, but at 400.EMC high quality and lowest sample sample, hydrophilic adsorption sites of high concentration or developed pore structure, easy to form a water film, the adsorption rate constant low.3. low rank coal thermal structure after upgrading the nature of change and relapse mechanism of water using a variety of characterization means (element analyzer, muffle furnace, scanning electron microscopy SEM, nitrogen adsorption, Fourier transform infrared spectroscopy FT-IR peak fitting) analysis of coal quality variation, decomposition of hydrophilic functional groups, the destructive effect of pore structure, The influence of structure changes on the properties of moisture re adsorption, reveals the chemical nature of water absorption reversibility differences, internal relation and quality conditions, put forward the description model of moisture re adsorption mechanism. The results show that (1) the quality and temperature increased, O content decreased, the highest equilibrium moisture content (mhc*) decreased first and then increased, 223y12.470.60x0.16x1.3710x- (28) - (10)? The coincidence relation; the content of O 9%, mhc* 4.5%.vdaf and mhc* significant correlation between the minimum ratio ad. (2) and the increase of temperature, coal surface collapse; serious fold, long flame coal surface is contraction cracks. The pore volume of lignite and specific surface area increased. 900 C after upgrading the pore volume increased to 134.19 * 10-3cm3/g; long flame coal first slightly increased after 400 DEG C, after upgrading the pore volume of 23.69 * 10-3cm3/g. and the minimum heat 20~50nm mesoporous microporous lignite increased, increased sharply at 600/900 DEG C after upgrading; upgrading the long flame coal does not change Such as lignite significantly, the holes in the 2~10nm. (3) hydrophilic oxygen-containing functional groups in order. High content of hydroxyl carbonyl hydroxyl and carboxyl group, the greatest impact on mhc*. The linear correlation between 0.82~0.95 different temperature lignite hydrophilic group content and mhc*; and long flame coal only 0.16~ 0.53. (4) the main mechanism of water complex suction characteristic changes: 105~600 C lignite hydrophilic oxygen-containing functional groups gradually reduced, reducing the adsorption quantity of mhc* decreased; 600~900 C microporous lignite increased under high humidity environment, micropore filling free water, mhc* increased. But the 600 C lignite surface is hydrophobic tar coverage, mhc* minimum. The quality of long flame coal the hydrophilic oxygen-containing functional groups than the same temperature of lignite, the pore volume change of mhc* 2~10nm has a significant influence on the quality and sample.400 C minimum pore volume, and surface hydrophobicity and special structure, water molecules are difficult to The formation of stable adsorption water clusters, like fresh research and hygroscopic pre oxidation of mhc*.4. lowest moisture re adsorption effect on the spontaneous combustion characteristic of heat after upgrading, and its moisture re adsorption / absorption oxidation samples were measured in a temperature programmed combustion device, comparison of oxygen uptake, cross point temperature (CPT) temperature, spontaneous combustion tendency the parameters such as rate difference and FCC determination, analysis of the spontaneous combustion characteristic changes of heat moisture re adsorption / absorption and sample pre oxidation. The results showed that (1) and the increase of temperature, the spontaneous combustion tendency of fresh sample decreased. But the heat after upgrading the moisture re adsorption like critical temperature of oxygen consumption is more than 60% lower than the fresh sample the accelerated oxidation stage; oxygen consumption changes a short period after the "platform" consumption accelerated.200~500 C lignite moisture re adsorption kind of HR (near CPT heating rate) than the fresh sample; accelerated oxidation stage, the instantaneous heating up rate increases faster; spontaneous combustion Orientation was significantly higher than that of fresh samples, more prone to spontaneous combustion. And long flame coal spontaneous combustion tendency is lower than that of lignite, and the moisture re adsorption has little influence on the spontaneous combustion characteristics. (2) moisture pre oxidation even after 2 days of spontaneous combustion tendency of 200~500oc lignite (the quality than the fresh sample) was significantly increased at 400 and after 30 days of pre oxidation sample moisture to coal spontaneous combustion tendency continues to increase. (3) 105~300 C lignite easy relapse than water, moisture absorption oxidation effect of CPT kind of like water relapse, and oxygen consumption were not significantly different at.400/500 quality and the sample is not easy to relapse moisture, but relapse of a small amount of water, CPT increased oxygen consumption decreased significantly. Compared with moisture oxidation, moisture content moisture re adsorption kind of added value is proportional to the increasing value of FCC (5y0.23x9.2110- (28) -?).5. heat and moisture and oxidation on the influence mechanism of the spontaneous combustion characteristics by SEM, X Ray spectrometer (EDS), infrared spectroscopy, nitrogen adsorption instrument, surface chemical structure of each sample were measured microcalorimeter, pore structure and moisture absorption difference, analysis of free radicals in situ by X-band electron spin resonance, spontaneous combustion process of different samples are described, to explore the internal relationship between the heat the quality and structure of water - hydrophilic oxygen - relapse hygroscopic pre oxidation and spontaneous combustion characteristics. The results show that (1) thermal upgrading and moisture pre oxidation leads to structural changes in the nature of coal spontaneous combustion tendency of change is the essential reason of.105~500oC lignite fresh sample pre oxidation in air, the number of surface oxygen content and internal oxidation activity group increased; aliphatic side chains, oxygen containing functional group and (after upgrading generation) new free radical oxidation of active groups, with the increase of the surface area, to enhance the sample pretreatment and the moisture absorption of spontaneous combustion. Wetting heat and promote heat gathering at the same time, enhance the pre oxidation indirectly affect spontaneous combustion; degree of hygroscopicity large sample, spontaneous combustion tendency increased significantly. (2) the formation of heat and moisture and pre oxidation to free radicals. The oxidation temperature, moisture absorption and oxidation of fresh sample kind of free radical concentration relative increase rate decreases after the increase, but the increase rate of oxidation absorption higher. (3) oxidation during the heating process, some active molecule side chain cleavage 105 DEG C and fresh samples, continue to produce reactive free radicals and free radicals; 400 C quality of fresh sample was quickly consumed, the junction temperature can produce a large number of new to maintain the free radical oxidation reaction, thus reducing moisture. The spontaneous combustion tendency of pre oxidation activity of free radicals increased; water samples in accelerated oxidation stage to produce free radicals, maintain the oxidation temperature, and moisture like in spontaneous combustion oxidation This study provides a theoretical support for the industrialization of low order coal extraction and utilization.

【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ530

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