煤岩显微组分的气化反应性及其影响因素分析

煤的岩相特性是决定煤质的关键因素,在煤的加工利用中具有重要的影响。笔者对煤的主要有机显微组分的气化反应性及其主要影响因素进行了分析概述,归纳和比较了镜质组、惰质组和壳质组3种基本有机显微组分的反应性,对煤阶、反应压力和温度、升温速率、矿物质、显微组分的结构及其交互作用在显微组分气化中的影响作了探讨,并对气化过程中注重煤岩显微组分的作用提出了看法。     

Behaviour of coal mineral matter in sintering and slagging of ash during the gasification process

The mineral matter in typical feed coals used in South African gasification processes and the ash derived from gasifying such coals have been investigated using a variety of mineralogical, chemical and electron microscope techniques. The mineral matter in the feed coals consists mainly of kaolinite, with minor proportions of quartz, illite, dolomite, calcite and pyrite plus traces of rutile and phosphate minerals. The calcite and dolomite occur in veins within the vitrinite macerals, and are concentrated in the floats fraction after density separation. Some Ca and Ti also appear to be present as inorganic elements associated with the organic matter.Electron microscope studies show that the gasification ash is typically made up of partly altered fragments of non-coal rock, bonded together by a slag-like material containing anorthite and mullite crystals and iron oxide particles, with interstitial vesicular glass of calcic to iron-rich composition. Ash formation and characteristics thus appear to be controlled by reactions at the particle scale, allowing the different types of particles within the feed coal to interact with each other in a manner controlled mainly by the modes of mineral occurrence. Integration of such techniques provides an improved basis for evaluating ash-forming processes, based on quantitative phase identification, bulk and particle chemistry, and the geometric forms in which the different phases occur.     

The CO2-gasification and kinetics of Shenmu maceral chars with and without catalyst

The CO₂ gasification of maceral chars was performed using CAHN TG-151 pressurized thermobalance under different conditions. The effect of mineral in macerals and catalyst on the gasification reactivity of maceral chars and the gasification kinetics were systematically investigated. The results showed that the apparent gasification rate of maceral chars depends on the temperature, pressure, BET surface area of chars and the gasification extent. With increasing temperature and pressure, the gasification rate of maceral chars all increase. After demineralization, the gasification reactivity of maceral chars all decrease. The gasification reactivity of maceral chars greatly increases with loading catalyst. And the loading method of catalyst has great effect on the gasification reactivity. The maceral chars loaded with catalyst by ultrasonic treatment have higher gasification reactivity than that by impregnation. The comparison of gasification reactivity of maceral charas demineralized maceral chars and maceral chars with and without catalyst showed that vitrinite chars always have higher gasification reactivity than inertinite chars. The kinetic results by distributed activation energy model showed that inertinite char has higher activation energy than vitrinite char, and the addition of catalyst greatly minimizes the activation energy and enhances the gasification rate.     

Influences of minerals transformation on the reactivity of high temperature char gasification

Two Chinese coals were used in this study and coal chars were prepared at different temperatures. High temperature gasification of coal chars with CO₂ was investigated in a bench scale fixed-bed reactor and the transformations of minerals from these two coals were also studied from 1100 to 1500 °C. Mineral matters produced at different temperature and ash generated after gasification were collected and analyzed by XRD and FTIR. It was found that the iron oxides were only catalytic mineral matters existing at high temperature. And gasification behaviors above ash melting temperature were different for different mineral composition, especially the content and form of iron oxide, which not only accelerates the gasification reaction, but also reduces the influence caused by melting minerals.     

Maceral and rank influences on the morphology of coal char

Concentrates of vitrinite and inertinite macerals have been pyrolysed in a flame under conditions representative of the initial stages of pulverized coal combustion. Char was distinguished from soot by size analysis and the char yield correlated with the proximate analysis. The char morphology was studied by optical microscopy and quantitative measurements of porosity and pore size were made using image analysis. Vitrinite and inertinite produce chars of characteristic morphology. The softening behaviour of inertinite varies with coal rank and can be related to the optical reflectance. The porosity of vitrinite chars approaches that of inertinite chars at high rank.     

Effects of alkaline metal on coal gasification at pyrolysis and gasification phases

A Chinese high-rank coal was acid-washed and ion-exchanged with Na and K to prepare the H-form, Na-form and K-form coals. After pyrolysis, H-form, Na-form and K-form chars and two additional H-form chars (acid washed Na-form and K-form chars) were prepared to investigate the effects of alkaline metal (AM) on coal gasification at the pyrolysis and gasification phases. The H-form char had the highest pryolysis rate; the H-form char had a relative low gasification rate. The AM loaded coals exhibited relative low pyrolysis rate, while the corresponding chars had high gasification reactivity. Acid-washing reduced the reactivities of Na-form and K-form chars. AM inhibited the progress of graphitization of the base carbon resulting in a more reactive char of less ordered crystalline carbon structure. A kinetic model incorporating AM-catalyzed gasification and non-catalytic gasification was developed to describe the gasification rate changes in the char conversion for AM-catalyzed gasification of chars.     

煤岩显微组分分离富集物热化学反应特性

依据煤中不同类型有机质性质差异对其进行分离，进而分质利用是实现煤炭清洁高效利用的有效手段。论文利用重选法将一种低变质烟煤分质得到镜质组较原煤48.25%增加至76.02%的富镜样，惰质组较原煤43.96%增加至63.98%的富惰样，以及矿物质含量高于61.99%的富矿样。利用热重-质谱分析仪，考察了分离富集物的热解反应特性及气体逸出规律，及其燃烧和气化反应特性。结果表明，分离所得富镜样热解反应失重量及热解过程中逸出的小分子挥发分的量及组成与富惰样和富矿样均有明显差异，表明分质实现了煤中不同类型官能团的分离富集。而由分离所得富镜样、富惰样和原煤热解失重峰温基本一致则表明分质所得煤的主体官能团结构仍较为接近，但含量有明显差距。富镜、富惰与原煤的燃烧曲线整体趋势较为类似，燃烧活性差别不大。以气化反应峰值温度高低判断，富镜样气化反应活性最低，富惰样与原煤气化反应活性较为接近，富矿样气化反应活性最高。将原煤在对应热反应时的理论反应曲线与实验曲线进行对比，发现煤分质过程及煤中镜质组、惰质组和矿物质的分离与否对热解过程挥发分的逸出影响较小，但导致了其燃烧和气化反应活性有所降低。     

Reactivities of 34 coals under steam gasification

The reactivities of 34 coal chars of varying rank with H₂O have been determined to examine the effect of coal rank on the gasification rate of coal char. The reactivities of chars derived from caking coals and anthracites (carbon content > 78 wt%, daf) were very small compared with those from non-caking (lower-rank) coals. The reactivities of low-rank chars do not correlate with the carbon content of the parent coals. To clarify which factor is more important in determining the reactivity, the evolution of CO and CO₂ from char, the moisture content of char and the amount of exchangeable cations were determined for these low-rank coals or their chars. These values were considered to represent the amount of active carbon sties, the porosity and the catalysis by inherent mineral matters, respectively. It was concluded that the amount of surface active sites and/or the amount of exchangeable Ca and Na control the reactivity of low-rank chars in H₂O.     

宁夏庆华煤镜质组和惰质组显微组分的分子结构及对比分析

使用密度梯度离心法对宁夏庆华煤的显微组分进行分离,获得煤的镜质组和惰质组。通过元素分析、X射线光电子能谱（XPS）、固体¹³C核磁共振（¹³C NMR）技术、傅里叶变换红外光谱（FTIR）和X射线衍射（XRD）技术等表征手段对不同显微组分进行物性表征。进一步基于统计平均的分子结构近似结合分子模拟计算,确定庆华煤镜质组和惰质组显微组分的分子结构可分别表示为C₂₆₉H₁₉₆N₄O₁₃S和C₂₅₅H₁₇₉N₃O₁₄S。通过FTIR光谱与¹³C NMR光谱验证,从而实现了不同显微组分的分子结构描述。对两种显微组分的分子模型和结构参数进行了系统对比分析,发现镜质组的芳碳百分数为51.95,惰质组的芳碳百分数为62.16。镜质组模型中芳碳结构数目较少,脂肪碳结构丰富,不饱和度较小,还原度最大。惰质组模型中芳碳结构数量最大,脂肪碳结构数目少,不饱和度最大,煤化程度高。镜质组在原煤中含量高,是原煤的主要组成。惰质组的含量少且大分子结构缩合度高,分布在镜质组构成的基体中。     

Fourier transform infrared study of high-purity maceral types

A suite of density-differentiated macerals from several coals was analysed by Fourier transform infrared spectroscopy to obtain information on the nature and magnitude of the variations exhibited by the various maceral fractions. The most characteristic change between maceral groups was the variation in aliphatic hydrogen content, with exinite ? vitrinite ? inertinite. Since the separation technique (density gradient centrifugation) generally provided a number of fractions within a maceral group region, some of these were also analysed. In a series of density fractions from a low rank vitrinite, it was found that the aliphatic hydrogen content decreased as the density increased. The inertinites also exhibited a decrease in aliphatic hydrogen. The inertinite C—O bands had extinction coefficients different from those of vitrinites or exinites. The data suggest that quite profound variations in organic structure as determined by FT-i.r. spectroscopy can exist within a maceral group, so that for the most critical work on coals it is necessary to take this into account.     

Influence of coal characteristics on CO2 gasification

The rate of CO₂ gasification of a coke is one of the most important qualities of metallurgical coke. Many workers are trying to estimate the rate of CO₂ gasification of coke by studying properties of coal, such as the reflectance of vitrinite and the amounts of inertinite and ash in coal. The specific-gravity separation method is used to prepare coals which possess almost the same reflectance, but contain different amounts of inertinite and ash. The relation between the rate of gasification and the properties of coal is quantitatively explained.     

Formation of HCN and NH3 during coal macerals pyrolysis and gasification with CO2

Three coal macerals with high purities were separated from Pingshuo gas coal. The formation rules of HCN and NH₃ during macerals pyrolysis and gasification were investigated. Experiments were carried out in a tubular quartz reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a prespecified period of time at a peak temperature. The amount of HCN and NH₃ were quantified by ion chromatography. The influence of temperature and macerals type on the formation rules of HCN and NH₃ was discussed. Results showed that the formation of HCN was mainly due to the thermal cracking of volatile, and NH₃ formed both from the thermal cracking of volatile and the cracking of nascent char. The HCN yield increased with an increase in pyrolysis temperature. For three coal macerals (liptinite, vitrinite and inertinite), the yield of HCN depended not only on their volatile contents but also nitrogen-containing functional groups, in which more pyrrole-type nitrogens would form more amount of HCN at lower temperature. The yield of NH₃ depended on the ability of forming ‘H’ radical. Under the experiment condition in this study, inertinite could convert more nitrogen into NH₃ than vitrinite and liptinite. The yield of HCN during gasification was almost the same as that during pyrolysis, the yield of NH₃ during gasification was little higher than that during pyrolysis.     

Transformation of alkali and alkaline earth metals in low rank coal during gasification

Transformation of alkali and alkaline earth metals (AAEM) in low rank coals during gasification was examined by combining computer-controlled scanning electron microscopy (CCSEM) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Two sub-bituminous coals were pyrolyzed at 1500 °C using a drop tube furnace, and the resultant chars were then gasified in CO₂ atmosphere at the same temperature. Total amounts of AAEM species in the raw coals and the chars were determined by ICP-AES. Minerals in the raw coals and ash particles in the chars were analyzed by CCSEM.AAEM species were mainly present in the raw coals as dispersed species, organically associated cations or fine mineral particles (<1 μm), which cannot be quantified by CCSEM. It was found that the dispersed Ca species were first converted into fine ash particles upon the devolatilization and then most of the particles interacted with inherent clay minerals to form complex aluminosilicates. In the case of Na and K, the dispersed species mostly vaporized and the interaction with inherent minerals was not observed.     

Exploring the possibilities of using Brazilian subbituminous coals for blast furnace pulverized fuel injection

The current study investigates the combustion and blast furnace injection performance of three Brazilian subbituminous coals (Mina do Recreio) and their beneficiation products using laboratory scale combustion tests. The coals have relative high ash yields (up to 40 wt%) that were reduced stepwise to levels as low as 12 wt%, dry basis. The reduction of ash yields is paralleled by a significant decrease in sulphur and inertinite contents.The combustion tests were performed in a drop tube reactor operating at 1300 °C using two different atmospheres (2.5 and 5% O₂). The chars exhibited preferentially rounded shapes with thick walls and abundant secondary porosity for the 2.5% O₂ chars, whereas the 5% O₂ chars showed very thin walls as a consequence of extensive burnout. The intrinsic reactivities of both set of chars were similar. The differences in conversion between the two working atmospheres were 24-37% and roughly tend to increase with increasing mineral matter content. Conversions as high as 76-81% were reached operating under 5% O₂ indicating that the coals are easy to burn. The small differences in burnout among the coals and their beneficiation products cannot be clearly attributed neither to mineral matter or inertinite content. A rough inverse relationship was found between the intrinsic reactivity of the chars and the inertinite content of the parent coal indicating that the char material derived from inertinite was intrinsically less reactive than that derived from vitrinite. These differences were no longer relevant at high temperature.Blast furnace injection performance was studied through thermobalance experiments using CO₂ atmosphere and 1050 °C temperature. It is apparent that the beneficiation process has no effect on the reactivity of the coals from Recreio Mine. The only exception is the low ash coal-2-LabB (11.5 wt%), for which a higher reactivity is indicated. The reactivity tests show also that the coals have adequate properties to be used together with imported coal blends in pulverized coal injection in the blast furnace (PCI).     

Influence of coal preoxidation and the relation between char structure and gasification potential

A study was carried out to ascertain the effects of coal preoxidation and carbonization conditions on the structure and relative gasification potential of a series of bituminous coal chars. Chars were prepared from two freshly mined bituminous coals and preoxidized samples derived from them. Carbonization conditions included a wide range of heating rate (0.2–10000K s^?1), temperature (1073–1273 K) and time (0.25–3600 s). Char properties were characterized in terms of analysis of char morphology, surface area, elemental composition, and gasification reactivity in air. Over the range of conditions used, preoxidation substantially reduced coal fluid behaviour and influenced macroscopic char properties (char morphology). Following slow heating (0.2 K s^?1), preoxidized coals yielded chars having higher total surface areas and higher reactivities toward gasification in air than did similar chars prepared from fresh coal. Following rapid heating (10000 K s^?1) and short residence times (0.25 s), chars prepared from preoxidized and fresh coals exhibited similar microstructural and chemical properties (surface area, $\text{C}\text{H}$ ratios, gasification rates). Carbonization time and temperature were found to be the critical parameters influencing char structure and gasification potential.     

The variation of structural characteristics of macerals during pyrolysis

Vitrinite and inertinite were separated by DGC from Chinese Shenmu bituminous coal and the structural characteristics of the macerals, before and after pyrolysis, were analyzed by ultimate analysis, FTIR and ¹³C NMR. The results showed that vitrinite chars always had higher H and lower C content than inertinite char at the same pyrolysis temperature. The FTIR and ¹³C NMR indicated that vitrinite had more aliphatic C-H, hydrogen bonding and lower aromaticity. With increasing temperature, the aliphatic C-H decreased, aromatic C-H, aromaticity and H_ar/H_al ratio increased. At the same temperature, inertinite always had higher H_ar/H_al ratio than vitrinite, which is consistent with that inertinite had higher aromaticity than vitrinite. And the H_ar/H_al ratio was also related to the remainder volatile matter. With increasing H_ar/H_al ratio, the remainder volatile matter in vitrinite and inertinite decreased. The higher aromaticity and H_ar/H_al ratio and lower H content of the inertinite in all temperature range were correlated with its higher thermal stability and lower volatile yield than vitrinite.     

Optically anisotropic fragments in a Western Canadian subbituminous coal

Large Isotropic and anisotropic, angular and rounded fragments of inertinite were found in a Canadian subbituminous coal (%R oil = 0.50). The istropic fragments included pyrofusinite, macrinite and pseudovitrinite with pre-oxidized, heat-treated fragments showing oxidation rims. The anisotropic fragments include the heat-treated residue of liptinite, e.g. resinite showing granular anisotropy, pyrolytic carbon and fragments of vitrinite showing basic anisotropy. The morphology of inertinite fragments is described and an attempt is made to correlate these particles with heat-affected coal macerals. The occurrence of pyrolytic carbon with a reflectance of 3.11% and of liptinite showing anisotropy in a coal matrix with a reflectance of 0.50% is unusual. It indicates the detrital nature of the pyrolytic carbon. The formation of isotropic and anisotropic inertinite was possibly due to a thermal event, perhaps a wood or swamp fire. The pseudovitrinite found in these coals may have been formed by heat-treatment of fossil oxidized vitrinite fragments. The anisotropic fragments in the coals (e.g. pyrolytic carbon and anisotropic vitrinite), are detrital and are grouped with inertodetrinite.