干燥后褐煤水分复吸性的试验研究

在实验室条件下考察了深度干燥和轻度干燥后的褐煤在高湿度环境和自然环境中的水分复吸性。结果表明：干燥后褐煤由于自身特点,具有较大的吸水能力,但受环境条件的影响比较显著,深度干燥后的褐煤水分复吸性较强,当干燥后褐煤处于不同的湿度环境下,或复吸水分或复失水分,但最终将会趋于某一稳定水分值。建议工业化干燥过程中,干燥后褐煤的含水量略大于内含水量,当处于正常自然环境中,干燥后褐煤不会发生显著的水分复吸现象,过度干燥既不经济也无必要。     

强制干燥空气温度对木质家具用单组分水性封闭底漆的水分挥发规律的影响

在湿度恒定、温度变化的强制干燥条件下,为了探讨在重涂间隔时间内温度对水分挥发速度和挥发量的影响,本研究以枫木薄木贴面家具板件为基材,以单组分水性封闭底漆为涂料,在相对湿度恒定为50%、温度为15～35℃范围内强制干燥涂层,研究涂层的水分挥发规律。结果表明:随时间的推移,同一温度条件下,水性封闭底漆的水分挥发率不断增加,水分挥发速度逐渐降低;不同温度条件下,水分挥发率和挥发速度差异不明显;相同的时间段内,在15～25℃温度范围内水分挥发率的差异程度要小于25～35℃的干燥条件;随着时间的推移,水分挥发速度的差距越来越不明显。     

褐煤物化结构对水分复吸的影响

阐述了褐煤中水分的赋存形态及其在受热过程中的转化行为。分析了不同提质干燥过程中褐煤物化结构的变化,探讨了褐煤物化结构与水分脱除及复吸的关系。结果表明:褐煤表面丰富的孔结构和大量亲水性含氧官能团是其水分较高的主要原因。干燥提质过程中,孔结构坍塌和交联反应的剧烈程度对于抑制复吸非常重要。加热过程中褐煤表面活性含氧官能团的数量、形成和分解行为直接影响褐煤的持水和吸氧能力,含氧官能团的分解会使煤的疏水性增加,自燃倾向性降低。最后说明褐煤提质的关键是水分的高效安全脱除,脱水煤表面氧化和水分复吸的抑制,并提出了抑制提质褐煤复吸水分的可能途径是依据不同组成、结构褐煤的水分赋存和脱除行为,针对性地改善干燥操作条件,调节样品孔径分布、比表面积和表面含氧官能团的存在形态及数量。     

卫生瓷成型车间温湿度的调节

卫生瓷成型车间石膏模和坯体的干燥一般是在操作室内进行的。干燥的方法是加热蒸发,蒸发的速度一方面取决于模型、坯体的内在因素;另一方面取决于模型、坯体周围的空气温度、湿度和流动速度。无疑温度越高,湿度越少,空气流动的速度越快,水分蒸发的越快。但是,对于陶瓷坯体来说,由于坯泥的     

影响低阶煤热稳定性因素的实验研究

为了研究影响低阶煤热稳定性的因素,探讨其规律性,测定了新疆、河南等地低阶煤的内水、挥发分、灰分、全水及煤的显微组分,分析结果表明:低阶煤的热稳定性与煤的内水、灰分、挥发分关系密切,单因素的关联度为MadVadAad,煤的全水与煤的热稳定性关联度不高,无规律可循;煤的显微组分中壳质组越高,煤的热稳定性越低;同一煤层煤的镜质组含量越高,煤的热稳定性越低;6 mm~13 mm范围内煤的粒度越大,测定的热稳定性越高。根据实验数据,借助Spss软件,建立了煤的热稳定性与煤的内水、灰分、挥发分关系单因素及多因素的7个线性回归方程,可根据拟合度高的方程,通过煤的工业分析来预测煤的热稳定性。     

褐煤润湿性及水分复吸的量热法研究

利用量热法分别对褐煤、脱灰褐煤和常见矿物质的润湿热进行测定,考察水分复吸对褐煤润湿性的影响,并对干燥褐煤水分复吸动力学进行分析.结果表明:褐煤中有机质的润湿热远大于其矿物质的润湿热,是褐煤润湿放热的主体.褐煤中含氧官能团越多,润湿热值越大.酸洗脱灰降低了褐煤的亲水性.芒来褐煤脱灰后,润湿热由101.61J/g降至66.79J/g,褐煤矿物质中高岭石的润湿热高于方解石和石英的润湿热;干燥褐煤的水分复吸符合二级动力学模型,相关系数大于0.99;褐煤复吸水分越多,其润湿热越小,芒来褐煤复吸水分增加到28.76%(质量分数)时,其润湿热由101.61J/g降至5.04J/g.水分复吸过程中,在表面形成的单层吸附或团簇吸附是褐煤润湿热降低的主要影响因素,而孔隙吸附或毛细凝聚吸附对其润湿热影响较小.     

几种炼焦煤有效热扩散率的测算和影响因素的研究

本文采用传热微分方程的差分格式,计算了煤料的有效热扩散率。在100～400℃范围内,五种不同变质程度煤(R°=0.75～1.89％)的有效热扩散率都在1.5×10~(-7)m~2/s左右。在400～900℃范围内,煤的有效热扩散率随温度上升而增大;随煤的变质程度增高而减小。水分含量对煤的有效热扩散率的影响主要反映在100℃前,含适量水煤样的有效热扩散率明显大于干燥煤样的有效热扩散率。     

影响测定原煤一般分析试验水分的质量分数准确性因素的研究

通过对比分析不同原煤、不同的环境、不同的干燥温度、干燥时间、冷却时间、不同粒度等条件下制备一般分析试验煤样,测试其试验水分的质量分数,来研究影响测定原煤一般分析试验水分的质量分数准确性因素。结果表明,煤的品种品质、空气湿度温度、干燥温度、干燥时间、冷却时间、煤样粒度等均对一般分析试验水分的质量分数检测结果准确性有一定的影响。为了检测结果的准确性精密度,原煤制备一般分析试验煤样在环境温度中,达到大气湿度平衡为准;制备试样时要严格控制粒度;测定时间应尽量短（最多不超过7 d）。     

热风和微波干燥对煤泥品质的影响

采用热风和微波两种方式对煤泥进行干燥处理,从主要组分、燃烧特性和水分复吸特性等方面对煤泥干燥产品进行了分析。通过工业分析对比了干燥前后煤泥主要组分的变化,发现两种煤泥干燥过程中煤泥的挥发分、灰分和固定碳含量没有明显变化。采用热重分析研究了原煤泥和两种煤泥干燥产品的燃烧特性,发现除了失水阶段,3种煤泥样品的热重曲线没有较大差异,3种样品的燃烧特性指数十分接近。最后探究了两种干燥方式下煤泥干燥产品的水分复吸特性,发现环境湿度和煤泥含水率对水分复吸特性有显著影响,而干燥方式对水分复吸特性影响并不明显。     

褐煤腐植酸的抽提及其对褐煤吸水性能的影响

褐煤腐植酸含量高,腐植酸中含有多种活性基团,在工业、农业、畜牧业等领域有多种用途。褐煤直接燃烧利用率不大,因此在开发利用褐煤资源前对其进行腐植酸抽提是一种较好的提质方式。本文采用碱浸法对褐煤进行腐植酸的抽提,研究了煤样粒度、抽提条件等因素对腐植酸抽提率的影响,以及干燥的原煤、腐植酸抽提残煤和脱灰煤的水分复吸性能。结果表明:粒度在0.2mm以下的煤样,在超声波条件下抽提腐植酸效果较好;抽提残煤水分复吸率明显高于原煤,但将抽提残煤脱灰处理后,水分复吸率有明显下降,且与原煤脱灰后吸水性能相近,说明抽提残煤的吸水性与煤的孔隙率及表面的极性官能团有关,特别是碱浸法抽提腐植酸时生成的强吸水性羧酸盐类对抽提残煤吸水性有显著影响。     

褐煤深度脱水的实验研究

针对褐煤低温烟气干燥技术脱水幅度难以提高,发热量增加不多等问题,提出了低温干燥与深度脱水的联合工艺。研究了不同干燥温度、干燥时间和煤样粒度对褐煤深度脱水效果的影响,结果表明:褐煤深度脱水适宜的干燥温度为500～800℃,较为适宜的干燥时间为80 s左右,当粒度小于50 mm时,干燥产物发热量随粒度变化不大。最后提出了褐煤深度脱水最佳工艺条件和参数,即当预干燥煤的Mar约为18%,煤样粒度为-50 mm,干燥温度为700℃,干燥时间为80 s时,深度脱水产物的Mar为8%,Vdaf在46%左右,折算Qnet,ar约为21 kJ/g。褐煤深度脱水促进了褐煤发热量的进一步提高,实现了褐煤资源的增值,研究结果为褐煤低温干燥与深度脱水联合工艺技术方案的确定奠定了基础。     

Effect of mechanical thermal expression drying technology on lignite structure

Mechanical thermal expression (MTE) is a developing nonevaporative lignite dewatering technology. It has been proved to be effective to dewater high moisture content in low-rank coals via the application of mechanical force and thermal energy at elevated temperatures. In this paper, the dewatering behavior of the Xiaolongtang lignite in Yunnan province, China during the MTE process was studied with three process parameters: time, temperature, and pressure. Meanwhile, the mechanism was also explored of how variations in temperature and pressure during the MTE process affect the surface oxygen functional groups and pore structure, which was mainly conducted by means of Fourier transform-infrared spectrometer (FTIR) and mercury intrusion porosimetry (MIP). Increases in MTE temperature and pressure resulted in significant reductions in residual moisture content and moisture-holding capacity, along with the increase in fixed carbon content and content reductions of other elements, especially oxygen content, this could be largely attributed to the destruction of the surface oxygen functional groups and porosity in the lignite. Technologically, the optimal conditions for temperature and pressure are 150–220°C and 6–10?MPa. The residual moisture content of the lignite treated by MTE at 200°C, 10?MPa is lower than 8%; the dewatering rate reaches over 76% with the calorific value being approximately 22?MJ/kg. Carboxyl and hydroxyl groups break down at drying temperatures above 120°C and constant applied pressure 10?MPa; with the pore volume significantly reduced, only few pores (diameter?相似文献   

不同干燥程度胜利褐煤燃烧与自燃特性

为了探究高水分褐煤干燥后的燃烧与自燃特性变化,采用一维火焰炉、煤粉着火炉以及自燃试验台对不同干燥程度的胜利褐煤进行了试验研究。试验结果表明,试验样品的着火温度随着干燥程度的增加而降低,随着风煤比的增加而增加,煤粉细度同样会对着火温度产生影响。在燃用干燥褐煤过程中宜采用较高一次风率以提高制粉系统的安全性。胜利褐煤及其干燥褐煤均属于极易燃尽煤种,燃尽率均在99.4%以上,水分的变化对燃尽率影响不大。建议胜利褐煤与20%水分干燥褐煤的运行氧含量控制在3.5%左右。随着干燥程度的加深和粒径的减小,褐煤越容易自燃。胜利褐煤干燥到20%以下可能有自燃的风险。     

单颗粒褐煤高温烟气干燥过程数值模拟

褐煤干燥对于提高其品质具有重要意义。为了模拟高温烟气干燥这一高温差、变温差非稳态传热传质过程中褐煤内水分蒸发过程,采用有限体积法建立了一维球坐标系下蒸发界面向内迁移的单颗粒褐煤干燥数学模型,并利用该模型分析了初始烟气温度和颗粒粒径对单个褐煤颗粒干燥特性的影响。模型模拟结果与实验结果对比表明二者变化趋势一致,所建模型能较好地反映出高温烟气干燥过程中褐煤内水分蒸发过程。结果表明,初始烟气温度越高,颗粒粒径越小,蒸发界面向内迁移速度越快,水分脱除越快,干燥时间越短;蒸发界面平均迁移速度均与初始烟气温度和颗粒粒径呈线性关系;在初始烟气温度700℃下,较短的停留时间使得颗粒表面温度未达到挥发分析出温度,本研究中不同粒径褐煤颗粒在干燥过程中基本没有挥发分的析出。     

Drying behavior of lignite under microwave heating

Because of lignite’s high moisture content, it must be dried before most applications. Microwave radiation may be suitable for efficient drying because of its special heating properties. This study investigated the drying behavior of lignite samples from eastern Inner Mongolia by microwave thermogravimetric analysis. Three stages of microwave drying were observed: preheating, fast weight loss, and falling rate drying periods. Samples’ surface temperatures increased dramatically during preheating, dropped slightly in the second period, and rose again in the final period. The measured surface temperature was <95°C during microwave heating. The overall moisture content decreased more rapidly under higher microwave power. Fine lignite particles (diameter <0.2?mm) and lump samples (particle size 10?mm) dried better than granular lignite (particle size 1–2?mm). The samples also underwent slight natural drying (1–2% point reduction in moisture content) after microwave treatment. The critical moisture content of lignite (11–15% under experimental conditions) was redefined. Energy consumption was analyzed to evaluate the feasibility of the proposed drying process.     

内蒙古霍林河褐煤热力初步改质研究

针对褐煤水分高、易风化破碎、氧化自燃、利用率低等问题,采用热力脱水方法对内蒙古霍林河褐煤进行了实验室改质研究,分析了改质温度、停留时间、原煤粒径对褐煤改质效果的影响。结果表明:改质温度、停留时间对褐煤改质效果影响显著,原煤粒径对褐煤改质影响不明显,当处理温度为300℃,停留时间为20 min时,褐煤改质效果最好;此时,褐煤Mad降低了79.75%,H含量增加了153%,O含量降低了62.47%,C含量提高了72.46%,N含量增加了26.09%,Qgr,ad增加了108.50%,Qnet,M增加了161.86%;褐煤改质过程明显降低了煤中Mad和O含量,并使C含量和发热量大幅提高,改质效果明显,这将为褐煤热力改质的应用奠定基础。     

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

In order to improve the drying efficiency of lignite and restrain the moisture re-adsorption of dewatered coal, the drying characteristics of typical Chinese lignite, the re-adsorption performances of dewatered samples and the change in pore structure throughout the entire processes were investigated in this study. Lignite samples with four different particle size fractions were dried in a fixed-bed reactor in the temperature range 60–160°C. The re-adsorbing moisture behaviors of dewatered coal samples containing different water contents were investigated at temperatures of 20–40°C and humidities of 55–95%. The changes in the pore structure of raw coal and different dried samples were measured by mercury intrusion porosimetry (MIP) and the relations between their re-adsorption performance and change in pore structure were explored. The moisture removal yields of lignite increased with an increase in drying time and temperature and was close to 100% above 120°C and over 100% after holding 40 and 15 min at temperatures of 140 and 160°C due to the release of CO₂ from the decomposing carboxyl group in the coal matrix. The re-adsorbed moisture content in dewatered coal was influenced by drying temperature and coal particle size through varying pore structure. The temperature and relative humidity in the re-adsorbing process were the main factors that influenced the moisture re-adsorption capacity of dewatered lignite, in which the re-adsorbing temperature mainly operated by varying the bonding ability of water on the surface of dewatered coal, and the relative humidity was connected with the pore structure as well. The mesopore was the main factor that influenced the re-adsorption of dewatered coal and the re-adsorption of moisture in dewatered coal at 100°C was highest due to the narrow range of the pore radius and because the relative volume ratio of 5 to 50 nm mesopore (above 91%) was high. The water loss yield of lignite with smaller particle size was higher due to its larger pore volume and surface area, but its re-adsorption capacity was lower because of lower volume ratio of 5 to 50 nm mesopore volume in dewatered coal obtained from the smaller size lignite.     

Effect of Hydrodynamics During Crystallization on Mechanical Dewatering of Salicylic Acid

Mechanical cake dewatering is always desired to reduce the load on thermal dewatering (drying). Any change in the upstream process such as crystallization can have a significant influence on the filtration as well as cake dewatering characteristics. The present study deals with the effect of hydrodynamics (mixing intensity) during salicylic acid crystallization on the air dewatering characteristics in the subsequent pressure filtration. The mixing conditions during crystallization were varied by using three different types of agitators (anchor impeller [AI], curved blade turbine [CBT], and bar turbine [BT]) and by varying the speed of agitation. The effect of operating pressure and dewatering time on the final moisture content of the cake was also studied.

The crystal properties (crystal size and size distribution) were found to vary with the mixing intensity, which further influenced the cake dewatering kinetics as well as the residual moisture content. An AI, which is a laminar flow impeller, produced crystals with a wide size distribution and higher mean particle size, which resulted in cake with high porosity and hence higher moisture content. The high porosity (as well as high cake permeability) caused early air breakthrough, which resulted in ineffective dewatering of cake. Therefore, in this case the residual moisture in cake was found to be higher (27%) even at higher dewatering pressure (1.5 bar gauge) and longer dewatering time (90 s). A BT creates high turbulence during mixing and produced crystals with a relatively narrow size distribution and lower mean particle size, which provided low-porosity cakes. Such cakes could be efficiently dewatered and the final cake moisture content was found to decrease to about 15%, a significant improvement in the filterability of the cake. The dewatering data were modeled according to the correlation between irreducible cake saturation and capillary number for predicting the cake dewatering characteristics (residual moisture as well as dewatering kinetics) and the results were compared with the experimental data.     

Physico-chemical properties of Loy Yang lignite dewatered by mechanical thermal expression

Mechanical thermal expression (MTE) is a pressure dewatering process, which is carried out at elevated temperatures. The process is being investigated as a means of lowering greenhouse gas emissions from existing lignite fired power stations by reducing the moisture content of lignites. The investigation was carried out to identify how variations in temperature and pressure during the MTE process affect the physico-chemical properties of MTE treated Loy Yang lignites. Increases in MTE temperature (<250 °C) and pressure (<12.7 MPa) resulted in significant reductions in residual moisture content, moisture holding capacity and sodium levels, which have been largely attributed to the destruction of porosity in the lignite.