Effects of biomass co-firing with coal on ash properties. Part I: Characterisation and PSD

The alterations of ash quality and utilisation aspects when co-firing coal with biomass were investigated. Co-combustion tests were performed in lab and semi-industrial scale facilities, using several coal-biomass blends. The collected ash samples were analysed for major elements and heavy metals content, loss on ignition (LOI), free CaO content and grain size distribution. Since a variety of co-combustion residues were tested, important implications concerning the ash composition and, consequently, its further use in potential applications came up. Results showed that properties of co-combustion residues are directly connected to the combustion conditions and the individual blend components. Biomass exploitation as secondary fuel in co-combustion processes is technically and economically feasible up to 20% w/w and the produced ash could be further utilised without any major treatment.     

Co-combustion of coal and meat and bone meal

Feeding meat and bone meal (MBM) to cattle, sheep or other animals has been banned within the EU since 1 of July 1994. The quantities to be eliminated are measured in millions of tons. Disposal to landfill is not an option, as simply burying the material cannot destroy any potential bovine spongiform encephalopathy (BSE) pathogens. One disposal option is the co-combustion of coal and MBM, to ensure that any living organism is totally thermally destroyed and at the same time valorising its energetic potential. Fluidised bed co-combustion of MBM is considered a viable technological option as it has the flexibility to burn coal with different materials in an efficient way, at relatively low temperatures (750-850 °C) with lower environmental impact. For this purpose, co-combustion tests of coal and MBM were carried out on a pilot scale FBC, to investigate the implications of the results. This involved the determination of the emissions of pollutants like NO_x, N₂O, VOC, CO₂, as well as the composition and the valorisation of the ashes produced. The ashes from the bed, the cyclones and the stack were collected and analyzed for biological activity, ecotoxicity, heavy metal concentration and leachability. The results obtained suggest that the ashes were suitable to be deposited in municipal landfills.     

Ash transformation during co-firing coal and straw

Co-firing straw with coal in pulverized fuel boilers can cause problems related to fly ash utilization, deposit formation, corrosion and SCR catalyst deactivation due to the high contents of Cl and K in the ash. To investigate the interaction between coal and straw ash and the effect of coal quality on fly ash and deposit properties, straw was co-fired with three kinds of coal in an entrained flow reactor. The compositions of the produced ashes were compared to the available literature data to find suitable scaling parameters that can be used to predict the composition of ash from straw and coal co-firing. Reasonable agreement in fly ash compositions regarding total K and fraction of water soluble K was obtained between co-firing in an entrained flow reactor and full-scale plants. Capture of potassium and subsequent release of HCl can be achieved by sulphation with SO₂ and more importantly, by reaction with Al and Si in the fly ash. About 70–80% K in the fly ash appears as alumina silicates while the remainder K is mainly present as sulphate. Lignite/straw co-firing produces fly ash with relatively high Cl content. This is probably because of the high content of calcium and magnesium in lignite reacts with silica so it is not available for reaction with potassium chloride. Reduction of Cl and increase of S in the deposits compared to the fly ashes could be attributed to sulphation of the deposits.     

Direct modification of solid residues during co-firing of coal sludge and coal

In order to utilize the solid residues simultaneously with clean and high-combustion efficiency when firing high sulfur and ash coal sludge generated in coal washing process in China, the mineral composition and usability of combustion solid products were investigated when injecting compound additives into series of coals or coals blended with sludges. In this study, a single burner furnace was used for combustion test and the solid residues were analyzed by means of X-ray powder diffraction method. The influences of temperature, residence time, and compound additives on mineral characteristics of the residues have been discussed. The results indicate that, the compositions of solid products are principally free oxides and a small amount of gehlenite, dicalcium silicate, etc. below 1000 °C; when the firing temperature increases above 1100 °C, the major minerals are gehlenite and dicalcium silicate. Also it can be found that several seconds is not enough for mineral complete reaction, and suitable calcium oxide content and particles fineness are recommended. The result of combustion test shows that there is no evident effect on ignition and combustion when the additive/coal (a/c) ratio is below 30% by weight; and the normal stable combustion with ignition delay can be achieved when the a/c ratio is ranging between 30 and 50%; but the a/c ratio exceeding 50% will damage combustion and even result in fire extinction. Industrial test results indicated that the solid residues was composed of silicate mineral rich in belite by adopting compound additives, but the comprehensive reaction mechanism needs further studies as well as the effect of additives on combustion should be concerned.     

Co-gasification behavior of meat and bone meal char and coal char

The co-gasification behavior of meat and bone meal (MBM) char and two types of coal (Jincheng anthracite (JC) and Huolinhe lignite (HLH)) char was investigated using a thermogravimetric analyzer (TGA). The effects of coal type, mineral matter in MBM, gasification temperatures and contacting conditions between MBM char and coal char on the gasification behavior were studied. The results show that the gasification behavior of MBM char and HLH char can be well described by ash diffusion controlled shrinking core model, while that of JC char can be described by chemical reaction controlled shrinking core model. The co-gasification rate of MBM/JC chars at 950 °C is approximately 1.5 times faster than that calculated from independent behavior. The mineral matter in MBM may play as a catalyst during co-gasification. However, the analogous effect observed in the blends of HLH/MBM chars is smaller, suggesting that the coal types play a great role. Furthermore, as the gasification temperature increased from 850 to 1000 °C, the maximum synergistic effect is observed at 900 °C. The lower temperature is not conducive to transferring the mineral matters of MBM to the coal char, while the higher temperature makes Na and Ca react with minerals of coal, leading to a loss of catalytic activity.     

CMS煤磨选粉机在风扫煤磨系统中的应用

为降低熟料煅烧成本,国内各回转窑水泥厂纷纷采用无烟煤或贫煤代替烟煤。为此,我们开发出了 CMS煤磨选粉机。首批 2台 CMS－30煤磨选粉机在广州石井水泥公司 2台 DTM2500/3900风扫磨系统中应用,并于 2000年上半年投产,取得满意的效果。之后,湖南金磊水泥集团有限公司、郑州金龙水泥股份有限公司和郑州长城铝业公司水泥厂先后选用 CMS－30和 CMS－15煤磨选粉机分别用在 DTM2500/3900、Φ 2. 4m× 4. 75m和Φ 1. 7m× 2. 5m风扫煤磨系统上。 1结构和分级原理 CMS煤磨选粉机的结构如图 1所示。 图 1 CMS煤磨选粉机结构示意 从…     

煤泥—煤矸石混烧技术在沸腾床锅炉上的应用

依据洗煤泥—煤矸石的混合特性 ,在沸腾床锅炉上进行了混合燃烧试验 ,探讨了沸腾床锅炉燃烧洗煤泥—煤矸石的机理 ,确定了沸腾床锅炉掺烧洗煤泥改造的最佳方式及应采取的有效措施 ,指出了煤泥—煤矸石混烧过程中存在的问题     

HP磨煤机磨制高水分印尼煤选型

根据高水分印尼煤的煤质特点,分析了HP磨煤机磨制高水分印尼煤时的技术特点,从研磨出力和干燥出力角度出发,详细论述了HP磨煤机的选型方法。通过实际工程HP磨煤机选型实践,得出HP磨煤机可以磨制收到基水分高达40%的印尼煤,研磨出力和干燥出力均能满足设计要求。     

Impact of co-firing coal and biomass on flame characteristics and stability

This paper presents the use of vision-based measurement techniques for the on-line monitoring and characterisation of coal-biomass co-firing flames on an industrial-scale combustion test facility. The characteristic parameters of the flame, including ignition points, brightness, temperature and oscillation frequency, are measured using a vision-based flame monitoring system in an on-line continuous mode. A common type of pulverised coal was fired with five different types of biomass for different proportions ranging from 0% to 20% by weight. Various combustion conditions were created during the test runs, including variations in excess air and the method of biomass injection. The relationships between the flame characteristics and the primary combustion process data are analysed. The results suggest that, due to the varying physical and chemical properties of the biomass fuels, the biomass additions impact on the characteristics of the flame, particularly the flame ignition points and brightness. However, in all cases studied, the flame stability has been found to be little affected by the amount of biomass added provided that the addition is no more than 20%.     

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.     

Characterisation of large solid recovered fuel particles for direct co-firing in large PF power plants

Solid Recovered Fuels (SRF) are solid fuels prepared from high calorific fractions of non-hazardous waste materials intended to be co-fired in coal power plants and industrial furnaces (CEN/TC 343, Solid Recovered Fuels, 2003). They are composed of variety of materials of which some, although recyclable in theory, may have become in forms that made their recycling an unsound option. The SRF with an equivalent median diameter D₅₀ of 6.8 mm are to be directly co-fired in an existing pulverised coal power plant. In comparison to pulverised coal, the particle size distribution of the SRF is of several magnitudes higher, resulting in a different burnout behaviour. Size reduction of the SRF to a fraction similar to coal is not economically feasible. As such, the idea is to co-fire SRF without any further size reduction, and of course this proceeding bears the risk of incomplete combustion.Accordingly, the prediction of the burner levels at which the SRF should be injected and whether or not a complete combustion will be achieved under full and part load conditions are the primary objectives of this paper. In this work, laboratory experiments have been conducted to forecast the success of co-firing the SRF in a commercial pulverised coal power plant. It involves the analyses of the fuel and its intermediate chars, generated at conditions comparable to boiler conditions, to determine some characteristic parameters, namely the burnout time, the aerodynamic lift velocity (ALV), and the apparent densities. The information gathered from the lab experiments are correlated to boiler conditions to determine the possible distances they are likely to travel under various regimes, full load and part load, before they are completely consumed. Different scenarios are examined, and based on the results, the optimal boiler injection points are predicted.     

CMS煤磨选粉机的应用

在广州石井水泥公司的煤磨系统的改造中，CMS煤磨选粉机表现出选粉效率高，生产能力大，细度易控制，体积小，安全可靠等特点。     

Co-gasification of meat and bone meal with coal in a fluidised bed reactor

After the Bovine Spongiform Encephalopathy illness appeared, the meat and bone meat (MBM) produced from animal residues became an important waste. In spite of being a possible fuel due to its heating value (around 21.4 MJ/kg), an important fraction of the meat and bone meal is being sent to landfills. The aim of this work is to evaluate the co-gasification of low percentages of meat and bone meal with coal in a fluidised bed reactor as a potential waste management alternative. The effect of the bed temperature (800-900 °C), the equivalence ratio (0.25-0.35) and the percentage of MBM in the solid fed (0-1 wt.%) on the co-gasification product yields and properties is evaluated. The results show the addition of 1 wt.% of MBM in a coal gasification process increases the gas and the liquid yield and decreases the solid yield at 900 °C and 0.35 of temperature and equivalence ratio operational conditions. At operational conditions of 900 °C and equivalence ratio of 0.35, the specific yield to gas (y_gas) increases from 3.18 m³(STP)/kg to 4.47 m³(STP)/kg. The gas energy yield decreased 24.1% and the lower heating value of the gas decreases from 3.36 MJ/m³(STP) to 2.16 MJ/m³(STP). The concentration of the main gas components (H₂, CO and CO₂) hardly varies with the addition of MBM, however the light hydrocarbon concentrations decrease and the H₂S concentration increases at the higher temperature (900 °C).     

Characterisation of biomass and coal co-firing on a 3 MWth Combustion Test Facility using flame imaging and gas/ash sampling techniques

Co-firing of biomass with pulverised coal at existing coal power stations remains a practical option available to power plant operators and is being widely adopted as one of the main technologies for reducing greenhouse gas emissions. However, there is a range of technological problems that are not well understood. This paper presents experimental investigations into the co-firing of pulverised coal directly co-milled with 5–20% biomass on a 3 MWth Combustion Test Facility. A number of combustion parameters, including flame temperature and oscillation frequency and particle size distribution, were measured under a range of co-firing conditions. The gas species within the flame and fly ash in flue gas were also sampled and analysed. The experimental data collected are used to study the impact of biomass additions to pulverised coal on the combustion characteristics of the co-firing process. The relationships between the flame characteristics, gas species and ash deposition of the furnace are investigated. The results suggest that, due to the varying physical and chemical properties of the biomass fuels, the biomass additions have impact on the combustion characteristics in a very complicated way. It has been found that the biomass addition to coal would improve the combustion efficiency because of the lower CO concentrations and higher char burnout level in co-firing. In addition, NO_x emission has been found closely linked to the flame stability, and SO_x emission reduced in general for all co-firing cases.     

The effect of coal sulfur on the behavior of alkali metals during co-firing biomass and coal

Biomass contains high amounts of volatile alkali metals and chlorine, which can cause deposition, corrosion and agglomeration during combustion. Meanwhile coal contains a certain amount of sulfur that produces serious environmental pollution following combustion. To investigate the effects of sulfur on the migration of alkali metals during biomass and coal co-combustion, thermodynamic equilibrium calculations were applied and experiments were performed in a laboratory scale reactor combining with a scanning electron microscope (SEM), X-ray powder diffraction (XRD) and other analytical approaches. The results indicate that inorganic sulfur FeS₂ addition significantly enhanced the formation of potassium sulfate when the S/K molar ratio was less than 2. Meanwhile increasing FeS₂ dosage reduced the formation of KCl(g) and KOH(g) and increased the release of HCl(g). In addition potassium sulfate can react with silica and aluminum to form potassium aluminosilicates and release HCl at the S/K molar ratio above 4.     

工业煤粉锅炉煤粉制备中磨煤机的选型及发展

磨煤机是工业煤粉锅炉煤粉制备系统中的核心设备。我国煤炭种类的多样性决定了磨煤机类型的多样化,磨煤机的正确选型在煤粉制备系统中至关重要。详细介绍了低速、中速和高速三大类别中各类型磨煤机各自的发展历程、工作原理、结构特点以及优缺点,分析了各类型磨煤机对煤种的适用性,说明中速磨煤机最适宜应用于目前工业煤粉锅炉煤粉制备系统,指出随着工业煤粉锅炉的快速发展,磨煤机不仅要适应性强,粉磨效果好、产量高、质量硬,还要在降耗及环境方面有所突破。     

用于煤和焦炭粉磨的新一代EM磨

论述了用于煤和焦炭粉磨的新一代EM磨(盘—球磨)。详细地介绍了磨机的结构、工作原理及其应用条件。特别指出了有关该磨机技术维护及粉磨元件更换的一些技术问题。同时还对装有PRECOM计量器的煤屑供给及其精确定量系统作了研究。全套设备均按防爆型要求制造。     

提高煤磨出口温度对煤磨和煅烧系统的影响

我公司提能改造后,窑的日产量有了很大的提高,但很难稳定在目标值（4800t／d）,一般在4500—4600t／d之间。从2004年9月份开始,我们将煤磨出口温度由75℃提高到90℃控制,发现煤磨产质量有了明显的提高,窑的煅烧状况也有了明显的改善,窑产量可稳定在4900t／d。现在,我们将该温度提高到97℃控制,窑产量可以提高到5000t／d以上。     

循环流化床锅炉掺烧煤泥发电技术及其应用

煤泥掺烧发电是煤泥综合利用的最重要方式;循环流化床锅炉燃烧技术与高压管道输送技术成功解决了工业化燃用煤泥过程面临的难题。通过分析CFB机组煤泥掺烧关键环节,及其掺烧煤泥对机组运行工况的影响,并且对比了多台机组煤泥掺烧前后的经济性差异,证实CFB机组掺烧煤泥技术可行,经济效益好。     

煤磨烘干热风管取风位置的技术改造

本文介绍了某5 000 t/d生产线余热发电系统,入AQC锅炉的热风来自篦冷机一段高温热风和二段中温热风,煤磨烘干热风设在篦冷机中温热风管路上。由于两者互相抢风,影响余热发电量,为此,通过对煤磨烘干热风取风位置进行技术改造,解决了上述问题,同时充分利用了篦冷机回收余热,提高了发电量。