高温下煤灰热膨胀行为研究

为了更好地了解硅铝比在煤炭燃烧和气化过程中对炉体结渣和堵渣产生的影响,选取硅铝比不同的A、B、C三种煤样,在弱还原性气氛下,利用自主研制高温熔融装置,考察三种煤灰样在高温熔融炉中的形变情况,探究煤灰热膨胀行为。针对A煤样,将其灰化后分别添加SiO2和Al2O3,添加量为煤基的1%~5%,研究其高温下XRD物相变化、熔渣流动现象和熔渣表观形貌。结果表明:不同硅铝比的煤灰热膨胀行为存在差异,B、C煤灰产生明显热膨胀现象,A煤灰未出现此现象;添加SiO2的A煤灰产生明显热膨胀现象,而添加Al2O3却未出现膨胀过程。添加SiO2后的煤灰在高温下灰粘度会增加,气体较难透过粘稠液体相,造成煤灰在高温下会出现明显膨胀现象,进而会导致煤炭在燃烧和气化过程中出现炉体内壁的结渣和出渣口堵渣等问题。通过考察弱还原性气氛下,研究不同硅铝比对煤灰高温熔融过程形变的影响,为解决实际生产中气化炉结渣和堵渣问题提供理论依据。     

Determination of fouling characteristics of various coals under gasification condition

In a coal gasifier and heat exchanger, adhered and deposited fouling inhibits heat transfer making the stable operation of the gasifier difficult. Since heat-transfer performance of the heat exchanger directly affects the output of Integrated Coal Gasification Combined Cycle plants, it is important to understand the effect of fouling on the characteristics of adhesion and deposition on the heat exchanger tube beforehand. But very few studies have been conducted about concerning the relationship between fouling property and adherability, which depend on the reducing condition on the gasifier system.The main purpose of the present investigation is to determine the low temperature ash deposition behavior under coal gasification condition by using drop tube furnace (DTF), in which behavior of coal particle in actual gasification condition can be simulated experimentally. Nine pulverized coal samples which are in the range of bituminous and sub-bituminous are injected into DTF under gasification condition. The ash particles are deposited onto sample collector by impacting and agglomerating actions; deposit samples of ash are collected, quantitative analyses are performed by EDX and weight measurements. Experiment results illustrated that mineral components are generally considered as a dominant parameter to determine behavior of ash deposition at low temperature among various physical and chemical properties of coal. It is also found that the alkaline earth mineral in coal ash such as MgO and CaO compounds leads to fouling deposition under the gasification condition.     

灰熔聚流化床粉煤气化技术加压大型化研发新进展

灰熔聚流化床粉煤气化技术历经20余年的研发和工程化放大,低压气化技术已日趋成熟,并用于氮肥企业原料气改造和新建甲醇合成厂。该气化技术可使用不同灰含量和灰熔融性温度的煤,过程效率也较高,符合我国资源特点。为此在山西省发展和改革委员会的支持下,中科院山西煤化所和山西晋煤集团合作成立的“山西省粉煤气化工程研究中心”正在建设3.0MPa加压灰熔聚流化床粉煤气化中试平台,2006年年底已建成,预计于2007年3月进行加压气化试验,2007年完成加压灰熔聚流化床煤气化工业装置设计软件包的编制,形成具有我国自主知识产权、适应中国煤炭特点的大规模加压灰熔聚流化床粉煤气化技术。本文介绍了灰熔聚流化床粉煤气化过程,指出它的优点、缺点、适用范围、技术现状和发展方向,并对加压灰熔聚气化中试技术进行了简介。     

中国高灰、高硫、高灰熔融性温度煤的灰熔聚流化床气化

煤气化将会在未来中国可持续发展中占有相当重要的位置。对目前的煤气化技术和中国的煤种特性进行了描述和分析,介绍了中国科学院山西煤炭化学研究所灰熔聚流化床的研究与开发现状以及一些煤种的实验结果。结果表明:灰熔聚流化床煤气化技术适合中国高灰、高硫、高灰熔融性温度煤的气化。     

煤制氢技术的初步方案及性能分析

构造了煤制氢新工艺系统,对新工艺气化过程热效应进行了分析,结果表明降低压力和提高温度在热力学上有利于气化反应的进行。根据热力学分析结果,对系统中气化炉热效应和整个系统的热效率进行了模拟计算,得出：该工艺可以提高单位原料煤的产气量,煤气中有效成分含量高,有效的利用了煤炭资源,系统的热效率可以达到90．65％。     

恩德炉入炉煤的加工和管理

恩德炉煤种和煤质对气化反应至关重要。因此,必须加强进厂煤管理和入炉煤加工管理及入炉煤质管理。特别是煤的粒度、水分、灰分、活性、粘性对粉煤气化的影响最大。     

Coal fouling characteristic to deposit probe with different temperatures under the gasification condition

Coal gasification was carried out to verify the coal fouling characteristic in a drop tube furnace (DTF). Four pulverized coal samples, in the range of bituminous and sub-bituminous, were used. To analyze the fouling characteristic by different temperature of deposit probe, a two-stage deposit probe was used in the experiment. Ash deposition rate was at upper deposit probe higher than at lower one. The X-ray fluorescence (XRF) results indicated that coal fouling included acid minerals such as SiO₂ and Al₂O₃ at upper deposit probe more than that at lower deposit probe. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that the fouling particles at high deposit temperature were agglomerated more than those at low deposit temperature. And the convective heat transfer efficiency was reduced by ash deposition on probe. Especially, the convective heat transfer coefficient substantially declined with small particle size of fouling and Fe₂O₃, CaO, and MgO.     

Large-scale laboratory study on the evolution law of temperature fields in the context of underground coal gasification

This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions. The results show that in the cultivation stage of oxidation zone, the main direction of the temperature field expansion is consistent with the crack direction of the coal seam. In the gasification stabilization stage, the main direction of the temperature field expansion is along the channel. The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature, and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface. However, temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface. The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction. Moreover, some degree of thermal dispersion is observed in the vertical direction near the outlet. The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.     

煤气化工序中气化炉系统的节能分析与计算

煤气化工序消耗大量的原料煤,所以必然要作为一个重点能耗单元来进行细致分析、核算。文章通过煤气化工序中气化炉系统的节能分析与计算,利用实例对气化炉系统的物料平衡和热平衡计算评估过程做了阐述,介绍了节能分析与计算在实际操作中的应用。     

Fine ash formation during combustion of pulverised coal-coal property impacts

In many countries, legislation has been enacted to set guidelines for ambient concentrations and to limit the emission of fine particulates with an aerodynamic diameter less than 10 μm (PM₁₀) and less than 2.5 μm (PM_2.5). Ash particles are formed during the combustion of coal in pf boilers and fine ash particulates may potentially pass collection devices. The ash size fractions of legislative interest formed during coal combustion are the result of several ash formation mechanisms; however, the contribution of each of the mechanisms to the fine ash remains unclear. This study provides insight into the mechanisms and coal characteristics responsible for the formation of fine ash. Five well characterized Australian bituminous coals have been burned in a laminar flow drop tube furnace in two oxygen environments to determine the amount and composition of the fine ash (PM₁₀, PM_2.5 and PM₁) formed. Coal characteristics have been identified that correlate with the formation of fine ash during coal combustion. The results indicate that coal selection based on (1) char characterization and (2) ash fusion temperature could play an important role in the minimization of the fine ash formed. The implications of these findings for coal selection for use in pf-fired boilers are discussed.     

新型煤气化炉内温度场影响因素研究

采用电热还原的方法将固体煤转化为可燃气体（煤气），为煤的气化提供了一条新思路．通过研究煤新型气化炉内温度场的成因以及各因素对温度场的影响，获取了不同高度空间温度场的主控因素．实验结果表明，气化功率、煤的种类、集气罩材料和排气速率等对气化炉内温度场均有较大影响；气化炉内的炉表近区域温度场主要由辐射场控制，集气罩近区域温度场受对流场控制．研究成果为煤新型气化温度场控制和气化炉经济密封高度的选择提供了依据．     

Behaviour of calcium-containing minerals in the mechanism towards in situ CO2 capture during gasification

Mineral matter transformation and the behavior of mineral matter in the coal during gasification, provide more information on the suitability of a specific coal source for combustion or gasification purposes. Therefore, the chemistry and mineral interactions have to be understood in order to determine the suitability for fixed bed gasification purposes with regards to mineral matter transformations and slagging properties.Although a suite of minerals important for the gasification process were identified [Van Dyk JC, Melzer S, Sobiecki A. Mineral matter transformations during Sasol-Lurgi fixed bed dry bottom gasification - utilization of HT-XRD and FactSage modelling. Minerals Engineering 2006; 19: 1126-35], some of the minerals, i.e. anorthite and calcite, with a specific behavior at different concentrations in the mineral structure and the transformation thereof was not studied and highlighted in detail. A number of other researchers [Reifenstein AP, Kahraman H, Coin CDA, Calos NJ, Miller G, Uwins P. Behavior of selected minerals in an improved ash fusion test: quartz, potassium feldspar, sodium feldspar, kaolinite, illite, calcite, dolomite, siderite, pyrite and apatite. Fuel 1999; 78: 1449-61], [Kondratiev A, Jaks E. Predicting coal ash slag flow characteristics (viscosity model for the Al₂O₃-CaO-‘FeO’-SiO₂ system). Fuel 2001; 80: 1989-2000] and [Kondratiev A, Jak E. Applications of the coal ash slag viscosity model for the slagging gasification technologies (viscosity model in the Al₂O₃-CaO-‘FeO’-SiO₂ system), 18th Pittsburgh Coal Conference, Newcastle, Australia, December 2001]) also did not investigate these gasification changes and mineralogical deformation during specific gasification conditions in detail.The principle aim of this paper is to identify the role of Ca-containing mineral species towards the in situ capture of CO₂ during gasification, as well as understanding the chemistry and interpret the mechanism of CO₂ capture by means of high temperature X-ray diffraction (HT-XRD), in combination with FactSage modeling. The CaO content of a South African and another coal source investigated in the present study, were 6 mass% and 30 mass% respectively. The basic components present in the coal, or specifically CaO, only act as a fluxing component up to a specific percentage, where after the ash fusion temperature starts to increase again. At this turning point the (Si+Al):Ca molar mass ratio is 2.75, which implies that after the turning point, the formation of anorthite is maximized and can thereafter only remain at the same level.The anorthite formation, when the Ca content increases, follows the inverse trend of the ash flow temperature prediction curve with the coal containing 6% CaO. The decrease in anorthite formation, with increasing Ca content, after the turning point in the graph, can be explained by the fact that more of the crystalline phase becomes a liquid (slag), and thus also the increase in the amount CaO in the slag will be observed. At the turning point, it is also interesting to note the stabilisation of the amount of other Ca-containing species. These are the minerals that are responsible and available for the mechanism where CO₂ can be captured on Ca to form CaCO₃. The formation of CaCO₃ can also be observed from the turning point where the (Si+Al):Ca molar mass ratio is <2.75, which corresponds with the formation of other Ca-containing species.Thermodynamic modeling with FactSage results indicated that anorthite can only form to the point where the (Si+Al):Ca molar mass ratio is >2.75. Anorthite (CaSi₂Al₂O₈) forms within the gasification zone and all non-reacted Ca react with CO₂ to form CaCO₃ further down in the combustion zone.     

Coal gasification in a jet-spouted bed

Coal gasification has been studied for the production of synthesis gas by use of a laboratory-scale, two-stage, jet-spouted bed reactor. Tests were conducted in the dry ash mode with oxygen-steam mixtures. The effects of operating conditions on the gasification performance were investigated at atmospheric pressure and temperatures up to 1150°C. Carbon conversions of 75% to 97% and cold gas thermal efficiencies of 62 to 78% were obtained for Taiheiyo coal. Both the carbon conversion and thermal efficiency were mainly affected by the oxygen/coal ratio. The product gases contained 36-41% hydrogen and 30-43% carbon monoxide.     

秸秆灰对煤焦气化反应性的影响

钾、钙对煤焦气化反应性具有重要影响,秸秆灰中含有丰富的钾、钙。以神木煤为制焦原料,通过STA409PC同步热分析仪研究了秸秆灰对煤焦气化反应性的影响,并通过测定煤焦的碘吸附值对其比表面积及孔隙结构进行了分析。结果表明：煤与玉米秸秆共焦化所得煤焦的气化反应性明显优于单独煤焦,且与玉米秸秆的添加比例有关;采用脱灰玉米秸秆与煤共焦化所得煤焦的气化反应性与单纯煤焦相近;将与玉米秸秆等效的秸秆灰添加到煤焦中,煤焦的气化效果明显优于等效玉米秸秆与煤共焦化所得煤焦。煤焦碘吸附值测定结果表明,脱灰秸秆与煤共焦化所得煤焦的碘吸附值最大,单纯煤焦的碘吸附值最小,说明玉米秸秆及秸秆灰对煤焦的比表面积及孔隙结构具有重要的影响,与煤焦的气化反应性评价结果基本一致。     

Multilateral approaches for investigation of particle stickiness of coal ash at low temperature fouling conditions

Particle stickiness is a key parameter for increasing ash deposition in gasification process. We conducted multilateral investigations to evaluate particle stickiness of coal ash at low temperature fouling conditions through Watt and Fereday’s viscosity model, dilatometry (DIL) and laser flash apparatus (LFA) technique. Seventeen coals were employed for ash deposition experiments under gasification condition through drop tube furnace (DTF). The low viscosity not only led to increasing ash deposition behavior, but also increasing the particle size of deposited ash. From DIL analysis, the ash sintering behavior increased with increasing temperature due to increase of particle stickiness. The high amount of Fe₂O₃, CaO and MgO components resulted in low sintering temperature and high reduction of physical length. Through LFA analysis, the thermal conductivity increased with increasing temperature, because of increasing particle stickiness. In addition, its value was correlated with the propensity of common fouling indices.     

添加剂对催化气化工艺中煤灰结渣性及气化性能影响研究

煤催化气化工艺中碱金属催化剂的引入加剧了气化炉的结渣，直接影响了流化床气化炉的正常操作。煤灰的烧结特性是流化床气化炉结渣的主要影响因素之一。通过自制的压差法烧结温度测定实验装置，并结合XRD 等分析表征及Factsage热力学软件模拟计算，考察了不同添加剂对煤灰烧结特性及气化性能的影响，并从矿物学角度探讨了添加剂对煤灰结渣特性及气化工艺的影响。结果表明，添加硅铝系添加剂可提高煤灰的烧结温度；相比硅系添加剂，添加高铝系添加剂对改善煤灰的烧结温度效果更明显；高铝系添加剂可作为一种高效的阻熔剂，但因在气化过程中容易同催化剂反应，导致催化剂催化性能降低，对煤的气化活性及催化剂回收率产生不利影响；添加氧化钙添加剂，煤的灰熔温度及烧结温度均增加，随氧化钙含量增加，灰熔点及烧结温度均升高，且对气化活性及催化剂回收率有良性作用；氧化钙可作为改善煤种结渣性的添加剂用于催化气化工艺中，需根据煤种性质及工艺特点确定适宜的添加量。     

高温下煤焦气化反应特性(Ⅰ)灰分熔融对煤焦气化反应的影响

在900～1500℃灰分的熔融温度范围内和常压下,研究了煤焦与二氧化碳的气化反应。实验研究发现,活化能随气化过程而变化,除反应初期外,气化反应严重受内扩散过程的影响。高温下的煤焦气化存在一个特性温度,在该温度下,反应中、后期气化速率显著降低,其影响范围在特性温度上下约200～300℃。特性温度与煤种及灰分性质等因素有关,一般低于其相应灰分的软化点温度。     

高效能两段组合式煤气化过程热态试验

针对现有气流床气化技术在显热回收方面的不足,华东理工大学洁净煤技术研究所创新性开发煤基两段组合式气化工艺。在所建立的两段组合式煤气化炉热态试验装置上,考察了二段处理煤量和一段出口煤气组成对出口煤气热值、有效气浓度、二段碳转化率、水蒸气和二氧化碳转化率的影响。试验结果表明此气化工艺能有效利用一段炉煤气中的显热,提高气化炉出口煤气热值;二段适宜加入褐煤量为1400g,是一段处理量的10%;二段加煤量过多会降低二段煤层反应温度和促使焦油的生成;随着一段气化炉出口煤气所含水蒸气、CO2等气化剂浓度的增加,其对显热回收的作用就更明显;该工艺能减少CO2排放,具有良好的环境效益。     

现代煤气化技术及其煤种的适应性分析

结合国内外煤气化技术发展现状与趋势,讨论了煤质特性对气化过程的影响及其在不同气化炉型中的适应性。分析表明,煤种的多样性及气化工艺的选择促进了煤气化技术的快速发展,气流床和流化床代替固定床是煤气化技术发展的必然所趋。在充分认识各类煤气化技术优缺点的基础上,应发挥优势,针对煤种选用炉型,开发具有单炉生产能力高、煤种适应性强、气体成分可调等优势的加压气化技术以及可有效利用煤气高温显热的两段或多段式气化技术。     

In situ diagnostics of Victorian brown coal combustion in O2/N2 and O2/CO2 mixtures in drop-tube furnace

Experimental investigation of the combustion of an air-dried Victorian brown coal in O₂/N₂ and O₂/CO₂ mixtures was conducted in a lab-scale drop-tube furnace (DTF). In situ diagnostics of coal burning transient phenomena were carried out with the use of high-speed camera and two-colour pyrometer for photographic observation and particle temperature measurement, respectively. The results indicate that the use of CO₂ in place of N₂ affected brown coal combustion behaviour through both its physical influence and chemical interaction with char. Distinct changes in coal pyrolysis behaviour, ignition extent, and the temperatures of volatile flame and burning char particles were observed. The large specific heat capacity of CO₂ relative to N₂ is the principal factor affecting brown coal combustion, which greatly quenched the ignition of individual coal particles. As a result, a high O₂ fraction of at least 30% in CO₂ is required to match air. Moreover, due to the accumulation of unburnt volatiles in the coal particle vicinity, coal ignition in O₂/CO₂ occurred as a form of volatile cloud rather than individual particles that occurred in air. The temperatures of volatile flame and char particles were reduced by CO₂ quenching throughout coal oxidation. Nevertheless, this negative factor was greatly offset by char-CO₂ gasification reaction which even occurred rapidly during coal pyrolysis. Up to 25% of the nascent char may undergo gasification to yield extra CO to improve the reactivity of local fuel/O₂ mixture. The subsequent homogeneous oxidation of CO released extra heat for the oxidation of both volatiles and char. As a result, the optical intensity of volatile flame in ∼27% O₂ in CO₂ was raised to a level twice that in air at the furnace temperature of 1273 K. Similar temperatures were achieved for burning char particles in 27% O₂/73% CO₂ and air. As this O₂/CO₂ ratio is lower than that for bituminous coal, 30-35%, a low consumption of O₂ is desirable for the oxy-firing of Victorian brown coal. Nevertheless, the distinct emission of volatile cloud and formation of strong reducing gas environment on char surface may affect radiative heat transfer and ash formation, which should be cautioned during the oxy-fuel combustion of Victorian brown coal.