Geochemical aspects of Amynteon lignites, Northern Greece

Several lignite samples were collected from Amynteon lignite mine, Northern Greece. Chemical analysis for major and trace elements was conducted with the help of X-ray fluorescence and inductively coupled plasma-atomic emission spectroscopy methods. Trace element concentrations of Amynteon lignites have equal or slightly higher values when compared to other worldwide coals. Boron content implies that the lowest lignite beds raised in a middle brackish environment, while the upper lignite beds had a fresh water environment of deposition. Correlation and cluster analysis revealed an inorganic affinity for the elements Al, Si, Ti, Fe, Mg, K, Na, Ni, Cu, Ba, Mo and Sr, while Ca, Cr, Mn, Zn, P, Cd, Sb, Pb, S, B, Co and W, and only F showed an organic affinity. The calculated slagging and fouling indices indicate medium to high slagging and high to severe fouling propensity.     

Selection of IGCC candidate coals by pilot-scale gasifier operation

Nine imported coal samples were tested to make the guidelines for IGCC (Integrated Gasification Combined Cycle) candidate coals — the guidelines that are applicable in future commercial IGCC plants in Korea. Entrained-bed slagging gasifier whose maximum capacity is 3 ton/day has been operated under pressure ranges of 10–29 bar. The factors considered were conversion efficiencies, moisture content, sulfur content, ash content, ash melting temperature, slag viscosity, slag characteristics, and coal reactivity. The best coal type for IGCC applications appears to be the one that contains low ash content with low-enough slag viscosity and high reactivity in coal. However, coal that exhibits high fluidity at the gasifier exit resulted in higher probability in plugging by fly-slag, so that the coal of ash fluid temperature lower than 1260 °C would require precaution for utilizing the feedstock in the entrained-bed gasifier. Conventional ash fusion measurement data might disagree with slag viscosity results in estimating the optimal operation temperature, and thus actual viscosity tests on slag would be necessary.     

中国煤的燃烧和NOx排放特性研究

Seven Chinese coals ranking from anthracite to sub-bituminous from the Shanxi province were selected for study to forecast the combustion and NOx emission behavior.Three UK,one Indonesia and one South Africa coal was included in the study for reference.A flat flame-turbulent jet apparatus was employed to assess flame stability,ignition performance and NOx emission behavior for the initial stage of devolatilization and combustion. This apparatus can simulate particle heating rates,maximum temperatures and the influence of the turbulent fluid interactionson the fate of volatiles.To simulate processes occurring over longer residence time, additional devolatilization experiments were performed in a drop tube furnace.Char reactivity was studied through thermogravimetric analysis.Finally,fouling propensity was studied with the aid of a purpose-built laboratory combustor that enabled the characteristics of the ash deposit to be assessed empirically.The results show that Chinese coals do not appear to possess unusual features in respect of NOx formation,flame stability and ignition,char burnout and ash slagging.The range of coals available in China appears sufficiently broad that suits all requirements.In particular,Shenfu coal,with its initial fast devolatilization and nitrogen release rates and its low initial nitrogen content and high char reactivity,will perform well when fired in industrial boilers as far as NOx emission,flame stability and combustion efficiency are concerned.Pingshuo coal exhibits high char reactivity and an attractive slagging performance suggesting that this fuel represents a good compromise between NOx emission and overall plant efficiency.     

An advanced ash fusion study on the melting behaviour of coal,oil shale and blends under gasification conditions using picture analysis andgraphing method

This study investigates the potential of solid fuel blending as an effective approach to manipulate ash melting behaviour to alleviate ash-related problems during gasification, thus improving design, operabil-ity and safety. The ash fusion characteristics of Qinghai bituminous coal together with Fushun, Xinghua and Laoheishan oil shales (and their respective blends) were quantified using a novel picture analysis and graphing method, which incorporates conventional ash fusion study, dilatometry and sintering strength test, in a CO/CO2 atmosphere. This image-based characterisation method was used to monitor and quan-tify the complete melting behaviour of ash samples from room temperature to 1520 ℃. The impacts of blending on compositional changes during heating were determined experimentally via X-ray diffraction and validated computationally using FactSage. Results showed that the melting point of Qinghai coal ash to be the lowest at 1116 ℃, but would increase up to 1208 ℃, 1161 ℃ and 1160 ℃ with the addition of 30％–50％ of Laoheishan, Fushun, and Xinghua oil shales, respectively. The formation of high-melting anorthite and mullite structures inhibits the formation of low-melting hercynite. However, the sintering point of Qinghai coal ash was seen to decrease from 1005 ℃ to 855 ℃, 834 ℃, and 819 ℃ in the same blends due to the formation of low-melting aluminosilicate. Results also showed that blending directly influences the sintering strength during the various stages of melting. The key finding from this study is that it is possible to mitigate against the severe ash slagging and fouling issue arising from high calcium and iron coals by co-gasification with a high silica-alumina oil shale. Moreover, blending coals with oil shales can also modify the ash melting behaviour of fuels to create the optimal ash chemistry that meets the design specification of the gasifier, without adversely affecting thermal performance.     

锅炉全烧准东煤沾污结渣特性分析

针对燃烧新疆准东煤存在结渣、沾污等问题,在新疆宜化150 t/h锅炉全烧准东煤进行实炉测试试验。在全烧准东煤期间,对锅炉炉膛水冷壁、过热器、低温受热面、底渣的结渣形态观测,对以上各部位渣样取样分析。结果显示,锅炉全部燃烧准东煤时存在严重的结渣与沾污问题。结合实验室试验研究及本次实炉测试试验,认为结渣、沾污主要原因是由于煤中钠的氯化物、氧化物、单质气化后形式挥发到烟气中冷凝在高温管壁,与烟气SO_2、Fe_2O_3等化合生成硫酸盐沉积,煤中铁矿石分解后与CaO、Al_2O_3等形成低温共融化合物,降低灰熔融性温度,增加准东煤灰结渣、沉积倾向,煤中高钙、高水分加速了烟气低温段的积灰。     

Coal blend combustion: fusibility ranking from mineral matter composition☆

Although coal blends are increasingly utilized at power plants, ash slagging propensity is a non-additive property of the pure coals and hence difficult to predict. Coal ash tendency to slag is related to its bulk chemistry and ash fusion temperatures, and the present study aims to compare the results obtained from thermodynamic simulation with characterization of samples obtained as outcomes of plant-based coal-blend combustion trials at three utilities located in the Centre and North of Chile. Pulverized coal and plant residues samples from five families of binary blends tested in an experimental program were characterized for chemistry, mineralogy and maceral composition. The slagging was evaluated by determination of fusion curves using the MTDATA software and NPLOX3 database for the main coal ash oxides. The ranking obtained was approximately the same as obtained from carbon in the fly ashes and from plant residues observations. The thermodynamic modeling was a valid option to predict the fusibility during the combustion of blends.     

Total chlorine in coal seam profiles from the South Staffordshire (Cannock) coalfield

In a coalfield of noted high-chlorine coals, seam profiles were taken from two collieries. Three seam profiles from each colliery were analysed for total chlorine to try to correlate chlorine level with position in the seam. Moisture contents and ash yields were determined for four of the seams. Total chlorine is highest in the coals, reaching 1 wt%, and low in the mudrocks, down to 0.08 wt%. Intermediate chlorine values are associated with dirty coals and carbonaceous mudrocks. Water centrifuged from an intraseam dirt band showed that the moisture held the total chlorine content. Similar element ratios were achieved from water centrifuged from coal. These results, together with National Coal Board groundwater data, suggest that the majority of chlorine in coal has been introduced by chloride-rich groundwaters which evolved during diagenesis, as has been suggested for Illinois and Nottinghamshire coals. There is a very significant positive correlation between coal moisture and total chlorine contents. Total chlorine levels are thus thought to be controlled by groundwater concentration levels and coal porosity, hence the positive relationship between organic carbon and chlorine concentrations. Total chlorine levels vary through the seams, but there is not a consistent change with position in the seam. There exists a correlation between coal type and total chlorine content. Bright coals hold significantly more chlorine than dull coals, owing to different porosities of the coal macerals. Departures from this relationship with coal type may be explained by mineral matter dilution or the ingress of recent groundwaters, overriding the original coal type-chlorine relationship.     

神华石炭-侏罗纪煤掺烧的结渣性能

神华侏罗纪煤具有易燃、低硫、低灰等优点,但存在易结渣等不足之处;神华石炭纪煤结渣特性则明显优于前者;侏罗纪煤与石炭煤掺烧,可充分利用石炭煤灰的高熔融温度特性以降低混煤的结渣倾向,并保持侏罗纪煤的易燃特性以提高混煤的火焰稳定性,具有低硫、低灰、较高热值、较低钙含量、低结渣、易燃烧等优点,保证了神华配煤在以非神华煤设计的锅炉中不会带来运行上的困难。笔者通过试验提出的神华两类煤掺烧结渣趋势变化图可为神华配煤方案的设计提供依据。     

Reducing fly ash deposition by pretreatment of brown coal: Effect of aluminium on ash character

The effect of pretreatment on the structure and the related fouling/slagging behaviour of fly ash from brown coal has been investigated. Condensable sodium salts and low melting sodium silicates are known as fouling and slagging materials. Experimental proof is given that less of such components were formed after treatment of Loy Yang brown coal with water and, particularly, with Al compounds.For the range of temperatures applied (1000–1400°C) in a drop tube furnace, the quantity of condensable salts generated was found to depend only on the amount of sodium in Loy Yang coal. Aluminium had the effect of reducing the sodium level by ion exchange and thus the formation of fouling ash components. The stickiness of sodium silicates from this coal was also shown to be reduced by aluminium.     

Ash fusibility and compositional data of solid recovered fuels

Several approaches are established to analyse the fouling and slagging propensities of coal ashes, but the same cannot be said of solid recovered fuel (SRF) ashes. This work has been conducted by using some fouling and slagging indicators, which are commonly applicable to coal ashes, on SRF ashes to ascertain their applicability.In this work, laboratory prepared ashes derived from municipal solid waste (MSW), sewage sludge, demolition wood, shredded rubber tyres, and plastic/paper fluff are analysed for their fusibility leading to fouling and slagging using three approaches; the ash fusibility temperatures (AFT), ternary phase diagrams, and fouling/slagging indices. The results from each approach are examined to determine the inclination of the ashes toward fouling and slagging. A subsequent inter-comparison of the methods was conducted to validate the methods which are in agreement and are applicable to SRF ashes. The study showed that ternary equilibrium phase diagram SiO₂-CaO-Al₂O₃, various fouling and slagging indices, and AFT can be used to complement each other to predict ash fusion properties, fouling and slagging propensities of SRF ashes.     

Analysis of pulverized coal particles (10–100 μm) for Fe, S, Ca, Si and Al on a particle-by-particle basis

A computer controlled scanning electron microscope fitted with soft X-ray fluorescence analysed thousands of pulverized coal particles in the size range 10 to 100 μm for amounts of Al, Si, Ca, S and Fe in each of the particles. Two coals were used, namely, subbituminous C, Comanche-Wyoming and subbituminous B, Rosebud-Montana. In pulverized coal combustion Rosebud coal has a bad slagging record not predictable from conventional slagging indices based on the elemental analyses of the total coal ash. The coal particles were placed into one of four groups: little mineral matter; low melting point inorganic composition; high melting point compositions; and large amounts of iron or pyrite. On this basis, Rosebud coal had 47% of its mineral matter in groups likely to cause slagging compared with 12% for Comanche coal, in agreement with the slagging record. It is concluded that although the particle-by-particle analysis technique used here is in a crude state of development, it can give a correct indication of the possible slagging behaviour of a pulverized coal in cases where conventional slagging indices based on the analysis of the total mean coal ash fail to give the correct indication.     

用于混煤燃烧控制砷排放模型研究

混煤掺烧是控制燃煤砷排放的有效方式,但由于缺乏相关的配煤模型,限制了该技术的应用。根据燃煤过程中砷的挥发释放机制,提出一种采用砷的释放指数P表征煤燃烧过程砷的释放特性的配煤模型。该模型综合考虑煤的灰分、灰中主要矿物元素含量、各矿物元素对砷的固定系数以及煤中砷含量等因素。研究结果表明,随着煤灰固定系数由23.12增至50.90,煤灰的气相砷吸附量由3.39 mg/g增至6.14 mg/g;随着释放指数P增大,砷的固定率减小,且随着温度升高,两者相关性由900℃的0.67增至1 300℃的0.86。根据P值筛选煤种进行掺烧,当掺混煤种P值差异较大时,掺烧低P值煤种不仅可降低混煤中的砷含量,还能促进高P值煤的砷在灰中富集,促进率达77.14%;掺混煤种P值差异较小时,掺烧低P值煤种会促进砷的释放。本模型可较好地筛选煤种,为混煤掺烧控制砷等痕量元素的排放提供了新的思路。     

Mineral matter and elemental concentrations in selected western canadian coals

Major and trace element analyses were performed on coals from various locations in western Canada, and on low-temperature (150 °C) and high-temperature (1000 °C) coal ash produced from these coals. Elemental analyses were carried out by X-ray fluorescence spectroscopy and intense neutron activation analyses. Based on their trace elements, the coals in this study fall into two groups: 1. low-rank coals (lignite-subbituminous) of late Cretaceous and Tertiary age; and 2. high-rank coal (bituminous-semianthracite) of Jurassic-Cretaceous age. The elemental analyses of the coals and coal ash indicate that the local conditions had considerable influence on the concentrations of certain trace elements.Antimony and selenium in coals are the only elements which are enriched relative to concentrations in the earth's crust; arsenic is concentrated in lignite to subbituminous coal, but is depleted in bituminous-anthracite coals; as expected the ash of these coals showed many more instances of enrichment.     

高钠煤灰烧结特性研究进展

中国新疆准东煤具有储量巨大、开采成本低、挥发分高、硫含量低等特点,是优质的动力用煤。但准东煤钠含量高,燃烧利用时易在受热面上形成烧结性积灰,产生严重的结渣,极大限制了高钠煤的开发利用。因此,要实现高钠煤的清洁高效利用,需充分认识高钠煤灰的烧结特性。总结了高钠煤积灰结渣机理,概述了高钠煤灰烧结机制,探讨了二者之间的内在关联。高钠煤在燃烧过程中,煤中碱金属(主要为钠)释放并以Na_2SO_4、NaCl及Na的形式存在于烟气中,与受热面接触并于其上冷凝形成黏性内白层,内白层捕获飞灰颗粒后反应生成低熔点化合物,其烧结温度降低,使锅炉受热面上发生沾污增强型的"沾污烧结"过程。高钠煤灰的烧结过程包含固相烧结、液相烧结和气相烧结3种方式,对煤灰烧结过程的影响因素包括反应温度、化学组成、煤灰粒径、反应气氛、添加剂种类、锅炉设计和锅炉运行工况等。其中添加剂按氧化物种类可分为碱性氧化物和酸性氧化物,一般情况下碱性氧化物可以降低煤灰烧结温度,酸性氧化物可提高煤灰烧结温度。未来对于提高高钠煤灰烧结温度的研究方向可从新型添加剂出发,找到既能固定烟气中的钠,又能与灰渣中的低熔点含钠矿物质反应生成高熔点化合物的单一或混合成分的添加剂。同时,关于钠蒸气对积灰结渣在微观层面上的动态特性的影响机制也需进一步研究。概述了煤灰烧结温度的测量方法,热导率分析法、压力测量法、热机械分析法、筛分法和压降法,其中压降法是目前为止测量烧结温度较为准确的方法。介绍了上海理工大学碳基燃料洁净转化实验室在高钠煤灰烧结特性方面的研究方向,以期为解决燃用高钠煤锅炉积灰结渣问题提供参考。     

Solvent-refined coal from high-ash non-coking coals and washery middlings for use in metallurgical coke making Part 1. Production,testing and characterisation

This paper presents studies on the preparation of a potential coking additive, solvent-refined coal (SRC), from typical high-ash Indian non-coking bituminous coals, tertiary Assam coal with a high sulphur content and washery middlings in a bench-scale unit (10 kg h⁻¹ coal throughput capacity) under hydrogen pressure. The extraction of the coal samples was conducted under moderate reaction conditions of temperature, pressure and residence time. No external catalyst was used in the process. Pre-beneficiated coal was used as the feed material and anthracene oil with a boiling range of 270–360°C was used as the solvent. Rigorous solid separation from the extract slurry by filtration was avoided by centrifugation in a super-decanter centrifuge to produce SRC with an ash content of 6–7%. The yield of SRC from non-coking Samla seam coal of the Raniganj coalfield was found to be 85% while its caking index was 44. Substantial improvement in the quality of blast furnace-grade coke was achieved by co-carbonisation of coking blends by mixing only 10% of the SRC prepared from Assam coal. The hydrogen requirement was low (1.5% wt/wt of d.a.f. coal) and recovery was of the order of 96% of the solvent used for the preparation of the coal-oil slurry. The yield of SRC and its quality as a coking agent are reported, along with the quality of the coke produced using SRC obtained from typical coal.     

Remediation of ash problems in pulverised coal-fired boilers

This paper reports the control methods for mitigating fouling and slagging in brown coal-fired power utilities. Two control methods were investigated, i.e. wet pretreatment of coal and the use of mineral additives. By the first technique, samples of brown coal were treated with aluminium solutions to adjust the levels of Na, Al and Cl. The effect of cleaning was tested under closely controlled conditions in the range of 1000–1400°C. At a gas temperature of 1250°C, the deposition behaviour of treated and raw coals were compared using a deposition probe maintained at temperatures of 500, 600, 700 and 800°C. The second technique involved experiments with mixtures of candidate mineral additives and sodium compounds at temperatures ranging from 1000 to 1400°C.

Experiments showed that both the methods were effective in reducing ash-related problems. Between 1000 and 1400°C, the quantity of condensable salts generated was found to depend only on the amount of sodium in coal. With the wet method, aluminium reduces the sodium level and thus fouling by ion exchange. The stickiness of sodium silicates from this coal was also shown to be reduced by aluminium. Deposition model calculations based on sticking probability also indicated that Al-treated coals result in less ash deposition on boiler surfaces. Experiments with mineral additives showed that sodium could be captured by clay minerals, particularly kaolin. For Victorian brown coal-based power station boilers, 10–20 μm kaolin making up 2–3 wt.% of the feed was estimated to effectively reduce the ash problems.     

Correlation relations between mineralogical components in ash from Kaa-Khem coals

Regression analysis was used to study correlation relations between the mineral components of coals. Regularities in the variability of the concentrations of individual ash-forming elements with changing ash contents of coals and changing seam depth were found. The X-ray diffraction characteristics of coal ashes and the qualitative composition of their mineralogical components are presented.     

神东矿区侏罗纪2-2#煤煤质特征研究

根据煤岩学、煤化学与扫描电镜分析结果 ,研究了神东矿区 2 -2 # 煤的煤岩特征及主要性质 ,探讨了神东煤变质程度、显微组成 (包括矿物组成 )对其性质的影响 ,认为高含量的丝质组影响了其液化性能 ,而煤中相对含量较高的次生方解石影响了其煤灰熔融性 ,动力配煤和煤岩分选技术是进一步改善神东煤利用性能的两种有用技术     

Ash deposition behavior of cynara-coal blends in a PF pilot furnace

Biomass is nowadays considered as a very interesting option to substitute conventional fossil fuels. Although biomass could be burnt alone, it can also be co-fired together with coal in existing power plants, at a lower cost. One of the main problems related with biomass used in thermal applications is its propensity to form ash deposits. Slagging and fouling caused by ash may derive in heat transfer losses, corrosion in the tubes or even boiler shutdown. A deposition probe has been designed and proved to study this phenomenon. Several combustion tests have been performed in a 500 kW_th PF pilot test rig burning cynara blended with two coals at different shares in energy basis. Different analyses have been performed to those ash samples collected during the tests. From the results, it is observed that the quantity of collected ash in the deposition probe did not increase noticeably when increasing the biomass share up to 15% in energy basis. However, the opposite was detected in Spanish coal tests, due to its higher ash content. Major components of ash samples were aluminosilicates coming from coal clays. These components may act as protective ash coal compounds, but inorganic elements such as calcium or potassium also appeared and their presence increased with the biomass share. Although chlorine content in cynara was high, no important presence of this element was encountered in none of the ash samples collected. Experimental results agree with other experimental studies showing that aluminosilicates from coals may act as protective ash compounds, preventing chlorine deposition on heat transfer surfaces. The beneficial effect is also detected at pulverized fuel conditions.     

Energy utilisation of biowaste — Sunflower-seed hulls for co-firing with coal

Sunflower-seed hulls (SSH) represent a source of combustible biomass characterised by high contents of potassium and phosphorus and a low silica content. The relatively high net calorific value of 20 MJ/kg d.m. is mainly influenced by the lignin content. Potassium and phosphorus are very important elements in biomass combustion for fuel, influencing slagging and fouling problems. Mixtures with different ratios of brown coal and sunflower-seed hulls (0-22% SSH) were co-fired in the Olomouc power plant. The behaviour of elements in the fly ash and the bottom ash (SiO₂, Al₂O₃, K₂O, P₂O₅, Zn, Cu and Cd) varied in relation to the amount of SSH added to the coal. The fly ash from the co-firing of 20% SSH with coal had a high content of water-leachable sulphates and total dissolved solids. The utilisation of fly ash in civil engineering (land reclamation) should fulfil criteria established by the Council Decision 2003/33/EC for non-hazardous waste. To ensure that the required water-leachable sulphate concentrations are within regulatory limits the fuel may contain a maximum of 14% SSH.