Progress in developments of dry coal beneficiation

China’s energy supply heavily relies on coal and China’s coal resource and water resource has a reverse distribution.The problem of water shortages restricts the applications of wet coal beneficiation technologies in drought regions.The present situation highlights the significance and urgency of developing dry beneficiation technologies of coal.Besides,other countries that produce large amounts of coal also encounter serious problem of lack of water for coal beneficiation,such as American,Australia,Canada,South Africa,Turkey and India.Thus,dry coal beneficiation becomes the research hot-points in the field of coal cleaning worldwide in recent years.This paper systematically reviewed the promising research efforts on dry coal beneficiation reported in literature in last 5 years and discussed the progress in developments of dry coal beneficiation worldwide.Finally,we also elaborated the prospects and the challenges of the development of dry coal beneficiation.

Modularized dry coal beneficiation technique based on gas-solid fluidized bed

A 40-60 t/h modularized dry coal beneficiation process with a novel method to control the bed was designed around a gas-solid fluidized bed separator. Furthermore,the hydrodynamics of medium-solids consisting of wide-size-range magnetite powder (0.3-0.06 mm) and <1 mm fine coal were numerically studied. The simulation results show that the fluidization performance of the wide-size-range medium-solid bed is good. The separation performance of the modularized system was then investigated in detail using a mixture of <0.3 mm magnetite powder (mass fraction of 0.3-0.06 mm particles is 91.38 %) and <1 mm fine coal as solid media. The experimental results show that at separation densities of 1.33 g/cm3 or 1.61 g/cm3,50-6 mm coal can be separated effectively with probable error,E,values of 0.05 g/cm3 and 0.06 g/cm3,respectively. This technique is beneficial for saving water resources and for the clean utilization of coal.

Change in Grain-Size Composition of Lignite under Cyclic Freezing-Thawing and Wetting-Drying

The paper presents the change in grain-size composition of lignite under cyclic freezing-thawing (FTC) and wetting-drying (WDC). The article shows that in the spring and autumn periods the lignites can be subjected to repeated freezing-thawing and wetting-drying, which determines the possibility of changing their grain-size composition and structure. Experimental studies in laboratory conditions on the influence of cyclic freezing-thawing (FTC) and wetting-drying (WDC) on the quality indicators of lignites have been carried out, their granulometric (fractional) composition has been studied. Freezing-thawing cycle conditions are as follows (FTC): minimum exposure temperature: -20°C;maximum: +5°C;relative humidity: 30%;number of processing cycles: 3. Wetting-drying cycles are as follows (WDC): drying temperatures are +20, +40, +60, +80°C, drying time 90 minutes, the coals are further subjected to rain (soaking) for a period of water saturation to humidity of 30% - 40% and dry again. The number of wetting-drying cycles is 3 times. The tests have revealed the destructive effects of FTC and WDC on the samples of lower metamorphic grade coal, and the cycles of wet-dry lead to the much higher yield of fine sizes (-6+0;-13+0 mm) than the cycles of freeze-thaw. Furthermore, it is found that the increase in the yield of fines depends on the heating temperature: coal disintegration proceeds more intensively at a higher temperature of drying.

Cleaning of South African coal using a compound dry cleaning apparatus

复合干燥清洗原则简短被描述。南非的煤上的 beneficiation 测试用模型混合物被进行干燥清洗仪器。优秀结果被获得，操作参数的最佳是坚定的。他们是：3.0 公里， 47.5 Hz 的马达频率， 50% 的空气体积， 7 掳的一个横向的角度，和一个纵的角度的一个振幅 ? 2 掳。这些条件产出包含 11% 灰和 75% 的煤生产的干净的煤。器官的效率，畏，是 95.86% 。这些结果证明南非的煤能被复合干燥清洗有效地分开，它将推广复合干燥清洗方法。

Dry Separation of Iron Minerals from Low-Grade Coal-series Kaolin

Dry separation of iron mineral from low-grade coal-series kaolin in Hubei Province of China was investigated. The structure and chemical composition of the kaolin ore were determined by X-ray diffraction(XRD) and X-ray Fluorescence(XRF) analyses. The narrow particle size range classification, dry magnetic separation and calcination were carried out to evaluate the particle size distribution, and the relation between the content of iron and the whiteness. Experimental results revealed that the highest content of iron(3.70%) in kaolin ore was in the particle size range from 60 to 74 μm, and pyrite was the main occurrence of iron in the kaolin ore. Dry magnetic separation showed that the removal rate of iron in kaolin ore could be increased obviously after calcination, and the rate of iron removal was 60% in the particle size range from 60 to 74 μm. As pyrite can be transformed into hematite through calcination, thermodynamic studies and XRD analysis showed that the maximum content of hematite was obtained at 900 ℃, which would be more beneficial to magnetic separation.

Combined Removal of Surface Moisture and Dust from Feed Coal for Coal Dry Cleaning with an Air-solid Fluidized Bed

A demonstration plant and a commercial plant employing coal dry cleaning technology with an air-solid fluidized bed were built in China. The operation practice of these two plants shows that the surface moisture and the fines or dust of feed coal must be well controlled as low as possible. For this purpose, a new process of combined removal of surface moisture and dust from feed coil using a vibrated fluidized bed dryer was investigated in a batch test apparatus and a pilot test system. A mathematical model on drying kinetics of coal surface moisture was developed and three empirical formulas of the model coefficient involving the main operating variables were determined based on the test results from the batch test apparatus. The mathematical model shows that the surface moisture retained in coal during drying decreases exponentially with drying time. According to this model, a new divisional heat supply mode, in which the inlet gas of higher temperature was introduced into the fore part of the dryer and the inlet gas of lower temperature into the rear part of the dryer, was employed in the pilot test system. The pilot tests show that 1) the new divisional heat supply mode is effective for lowering down the average temperature and reducing the total heat loss of the outlet gas off the dryer, 2) the moist coal of about 60 g/kg surface moisture contentcan be dried to about 10 g/kg, and simultaneously the fines (<1mm in diameter) adhering to the surface of coarse coal particles are completely washed off by the gas flow.

Motion analysis of waste rock in gas-solids fluidized bed in coal dry beneficiation

Through the analysis of forces acting on the waste rock in the gas solid fluidized bed, the waste rock velocity equations and displacement equations in the gas solids fluidized bed were achieved and the influential factors of the waste rock motion in the fluidized bed were studied in this paper. The conclusions show that the primary factors influencing the waste rock motion are the waste rock grain size and the scraper velocity according to the computer simulation. This has provided the theoretical foundation both for improving the separating effect and ascertaining the length of the separating cell.

DRY CLEANING OF COAL WITH AIR DENSE MEDIUM FLUIDIZED BED

This paper deals with the experimental study of dry cleaning of coal with air dense medium fluidized bed. This technique opens up an efficient way of coal separation for vast areas in the country where water resources are in short supply or coals tend to slime seriously in wet process. Tests show that it can separate any kind of coal (6--50mm) efficiently. The probable error E, can reach 0.05--0.08. The separating density can be adjusted in the range of 1.0--2.0 g/cm^3. This technique brings about enormous economic benifits.

Experiment research on two-stage dry-fed entrained flow coal gasifier

The process flow and the main devices of a new two-stage dry-fed coal gasification pilot plant with a throughout of 36 t/d are introduced in this paper. For comparison with the traditional one-stage gasifiers, the influences of the coal feed ratio between two stages on the performance of the gasifier are detailedly studied by a series of experiments. The results reveal that the two-stage gasification decreases the temperature of the syngas at the outlet of the gasifier, simplifies the gasification process, and reduces the size of the syngas cooler. Moreover, the cold gas efficiency of the gasifier can be improved by using the two-stage gasification. In our experiments, the efficiency is about 3%-6% higher than the existing one-stage gasifiers.

Construction of Dry Cover System for Prevention of Acid Mine Drainage at Mine Waste Dump in Open Cast Coal Mines, Indonesia

Acid Mine Drainage (AMD) which occurs when sulfide minerals are exposed to water and oxygen with an excavation is one of the serious environmental problems in the world. A dry cover system is generally constructed in waste dump for the prevention of AMD in Indonesia by virtue of low cost and availability of waste rocks for a cover layer. However, the failure of the system caused by the lack of information related to the construction of cover system in mines, which leads to AMD, has been reported recently in Indonesia. In this study, the field investigation was conducted in pit and waste dump in open cast coal mine in Indonesia with the aim of obtaining the information on the construction of a cover layer and backfilling conditions of waste rocks in the waste dump. The rock samples taken in two areas of the mine were analyzed by geochemical analysis and sequential extraction with acids. The results indicated that Net Acid Producing Potential (NAPP) of the rocks in the waste dump down to 100 cm depth in both areas was from 10 to 30 kg H2SO4/ton, suggesting that Potentially Acid Forming (PAF) was backfilled in a cover layer. The backfill of PAF was contrary to the concept of cover system, which caused the failure of constructing a cover layer. The cause of the failure was likely attributed to the shortage of cover rocks which are classified as Non Acid Forming (NAF) or the failure of proper placement of them by an operational problem in the areas. Moreover, the results of the extraction with acids suggested that the form of iron and sulfur has to be taken into account to discuss the occurrence of AMD.

Study on the removal of Hg^0 from flue gas by coal dry powder gasification coarse slag

The prevention and treatment of mercury in coal-fired power plants has always been the focus and difficulty.How to control the pollution of mercury to human body and ecological environment quickly and effectively is a hot research topic nowadays.As a low cost and potential adsorbent,there is a huge space for the development of coal dry powder gasification coarse slag.In this paper,Mercury osmotic tubes are heated by water bath tank as mercury source,and the scavenging effect of adsorbent on Mercury monomer under different influence conditions is explored.The adsorbent plays an important role in adsorption of mercury monomer because of its special active sites on the surface.The reason is that the adsorbent surface is rich in carboxyl group,hydroxyl functional group,combined with mercury to form complexes.This shows that chemical adsorption facilitates the adsorption process.

烟气干法熄焦在低阶煤热解工艺中的应用研究

以烟气为干法熄焦介质,可以回收半焦热量用于原煤的干燥,从而提高热解系统热效率。通过中试考察了烟气流量、停留时间对半焦温度的影响,分析了热解工业装置冷却段运行数据。结果表明,采用烟气干法熄焦,半焦显热回收率达到93.8%,影响冷却效果的主要因素是烟气流量,其次是半焦入口温度。

潮湿细粒煤复合式干法分选特性研究

为研究潮湿细粒煤复合式干法分选效率,对潮湿细粒煤进行了振动强度和气速的单因素试验,结合RSM-BBD预测模型获得了最优参数;并探索了不同水分的原煤在不同分选时间内的分选效果,同时分析了气流对潮湿细粒煤分选过程的影响,并评价了分选效果。结果表明:随着分选时长的增加,分选效果明显提高,最大灰分离析度可达12.05。试验煤样在气速为0.78 m/s,振动频率为25 Hz,振幅为3 mm时达到最佳分选效果,此时可能偏差E=0.135 g/cm^(3),且在此条件下分选产品有很好的脱水效果,复合式干法分选可实现潮湿煤炭的提质。该研究可以对细粒煤炭的干法分选工艺提供理论和技术支持。

干煤粉气化炉烧嘴偏置角度变化下的烧嘴罩性能优化研究

介绍了华能公司IGCC机组干煤粉气化工艺,针对干煤粉气化炉一段烧嘴水平偏置改造后,产渣量大幅提升,导致烧嘴罩发生漫渣、泄漏的问题,通过采取提高烧嘴罩探入深度、优化配煤方式控制气化炉产渣量、改造粉煤给料罐底锥稳定煤线波动等措施,进一步提升了烧嘴罩运行的稳定性,基本避免了烧嘴罩发生漫渣、泄漏现象。

干燥温度对磨煤机出力的影响

煤的可磨性指数表征的是破碎煤的难易程度,影响到制粉系统能耗。通过一组干燥试验,研究了干燥强度对大同烟煤和元宝山褐煤的哈氏可磨性指数的影响规律,归集出干燥强度对哈氏可磨性指数影响趋势线。干燥对可磨性指数的影响不仅体现在水分的变化,干燥过程中会使煤的结构变化,也影响着可磨性指数。研究结果可以指导火电厂磨煤机运行中,各干燥介质风量组成及一次风温度等参数的调整。通过煤的干燥强度的调整,可以有效降低制粉系统的能耗。

Negative-pressure pneumatic separator:a new solution for hard-coal beneficiation

Hard coal is an important source of energy worldwide.Owing to the imperfections of excavation technology,most run-of-mine coals must be processed before they can be utilised as fuel.In this study,tests on the dry separation process were performed with numerous different raw hard coal and coal waste material samples,using a newly designed and constructed negative-pressure pneumatic separator(NPPS).The experiments revealed the effects of the feed-material properties and material processing conditions.These experiments were preceded by additional tests for evaluating the influence of each device operating parameter on the process,to determine the optimal method of supplying the feed material.The calorific value of the processed materials was improved by 5%–40%,while a minimal output yield of products(60%–70%)was maintained.The trials indicated that in coal material processing,the developed NPPS can be used for not only raw coal enrichment but also coal recovery from materials stored at coal-waste dumps.The main advantages of the device are its mobility,low material processing cost,and lack of water consumption during operation.

干煤粉气化激冷流程工艺运行分析及优化措施

介绍了国能集团宁夏煤业有限责任公司400万t/a煤间接液化项目干煤粉气化激冷流程的工艺流程。针对气化炉激冷流程工艺系统运行时存在的合成气带水、带渣、带灰等问题,经分析认为主要原因是激冷室液位控制不当、合成气洗涤塔塔盘冲洗水水质差且塔盘结构设计不合理;为此,进行了相应的结构、材料、管线等方面的技改优化。运行效果表明:改造后合成气带水、带渣、带灰等问题得到了有效解决,合成气洗涤塔塔盘压差趋于平稳。

煤焦-Ni复合物催化甲烷干重整及其反应后形成碳材料的电化学性能研究

甲烷干重整(DRM)反应能够将CH_(4)和CO_(2)两种温室气体转化为合成气,具有突出的环境和经济效益。但DRM反应过程的高温条件和产出的积炭易造成Ni等金属催化剂的失活,限制了其在工业上的应用。中低温煤热解半焦(简称“煤焦”)具有作为高效Ni基催化剂载体的良好潜力。为了提升DRM反应性能并促进煤焦利用,设计并制备了一种煤焦-Ni复合物,以K_(2)CO_(3)为助剂,考察了DRM反应性能、煤焦-Ni复合物在反应后形成碳材料的表面结构特征及其用作超级电容器电极材料的性能。研究发现,当m(煤焦):m(K_(2)CO_(3)):m(Ni)=1.00:1.00:0.05、DRM反应温度为850℃时,CH_(4)和CO_(2)初始转化率分别达71%和72%。优化反应条件(催化剂的Ni负载量、反应温度和反应时间)后,以煤焦-Ni复合物在反应后形成的碳材料为超级电容器电极材料可表现出优良的电化学性能,其中,CC-2在扫描速率为5 mV/s时,比电容为136 F/g;在电流密度为1 A/g时,比电容为143 F/g。本研究为DRM和煤焦的协同转化利用、反应后碳材料(反应中作为催化剂或催化剂载体)的回收利用提供了潜在路径。

燃煤电站掺烧污泥热力学与经济性分析

我国污泥产量逐年增加,如何对其进行无害化、资源化处理成为亟待解决的问题,拟将燃煤电站与污泥干燥系统耦合,湿污泥干燥后进行掺烧。以某典型超临界660MW机组为研究对象,在THA工况下,通过对锅炉进行热力计算和对系统整体进行热力学分析及经济性分析,研究掺烧不同含水率(10%、20%、35%、50%、65%)不同掺烧量(2%、4%、6%、8%、10%)的干化污泥对排烟温度、锅炉效率、净发电效率、湿污泥发电折合净效率和干化污泥发电折合净效率等参数的影响。结果表明:当干化污泥含水率超过50%时会导致参数恶化且随掺烧量的增加变化趋势加剧;干化污泥的含水率应控制在50%及以下,若超过此值,掺烧量应小于4%;掺烧污泥导致系统的㶲效率降低,主要原因是锅炉和干燥设备的㶲损失增加;当掺烧含水率为20%,掺烧量为10%的干化污泥时,系统经济性最好,动态回收周期仅为4.02年。