Effect of oxy-fuel combustion with steam addition on coal ignition and burnout in an entrained flow reactor

The ignition temperature and burnout of a semi-anthracite and a high-volatile bituminous coal were studied under oxy-fuel combustion conditions in an entrained flow reactor (EFR). The results obtained under oxy-fuel atmospheres (21%O₂-79%CO₂, 30%O₂-70% O₂ and 35%O₂-65%CO₂) were compared with those attained in air. The replacement of CO₂ by 5, 10 and 20% of steam in the oxy-fuel combustion atmospheres was also evaluated in order to study the wet recirculation of flue gas. For the 21%O₂-79%CO₂ atmosphere, the results indicated that the ignition temperature was higher and the coal burnout was lower than in air. However, when the O₂ concentration was increased to 30 and 35% in the oxy-fuel combustion atmosphere, the ignition temperature was lower and coal burnout was improved in comparison with air conditions. On the other hand, an increase in ignition temperature and a worsening of the coal burnout was observed when steam was added to the oxy-fuel combustion atmospheres though no relevant differences between the different steam concentrations were detected.     

Ash transformation and deposition characteristic during straw combustion

The main objective of this study was to determine ash transformation and deposition characteristic for three types of straw (corn straw, oat straw, and rice straw) combustion at temperatures between 500 and 1000°C. The collected deposits on the sampling probe were characterized with X-ray diffraction and scanning electron microscopy combined with energy dispersive X-ray analysis. The results indicated that the ash forming processes of straw were influenced by fuel composition and temperature. The quantity of corn straw ash collected from deposition probe was noticeably lower than that of oat straw and rice straw due to different contents of K, S, and Si in fuels. The deposition amounts of corn straw and oat straw followed a linear pattern at temperatures below 800°C, while rice straw followed a nonlinear pattern as a function of temperature. Corn straw was an ideal fuel compared to oat straw and rice straw from the points of deposition amounts and appearance. It also can be found that silicon, calcium, potassium, and sulfur were key points in the forming process of ash deposits.     

Combustion performance and slagging characteristics during co-combustion of Zhundong coal and sludge

Zhundong coal (ZDc) with a very large reserve is faced with severe problems of slagging and fouling during combustion in boilers because of the high-Na content. Sludge, the by-product of urban sewage treatment, is also faced with the problem in utilization. In this study, the co-combustion of ZDc and sludge was investigated in a laboratory-scale experimental apparatus before further studies in larger-scale setups. The experimental results confirm an interaction between ZDc and sludge during co-combustion, which was mainly caused by the Na catalytic action and improved the combustion performance of the co-fuels. The catalytic effect was particularly significant at low sludge mixing ratios. The reactions between Na-based compounds in ZDc and Si/Al/P-rich minerals in sludge, forming high-melting-point phosphates and aluminosilicates, not only increased Na retention in residual ash reducing the risk of fouling on tail-heating surfaces in boilers, but also raised the ash fusibility of the co-fuels avoiding low-temperature sintering. Even so, to prevent slagging, the high combustion temperature above 900 °C should be avoided during co-combustion because of the high Na retention in residual ash. Moreover, the high heavy metal retention in residual ash decreased the pollution caused by heavy metal volatilization during sludge combustion.     

Valuation of investments in natural resources using contingent-claim framework with application to bituminous coal developments in Korea

As Brennan and Schwartz [Brennan M, Schwartz E. Evaluating natural resource investment. Journal of Business 1985;58:135–57] point out in their pioneering work, the valuation of natural resources projects is particularly difficult due to the high degree of uncertainty in output prices of resources. In general, there are two competing procedures to evaluate risky projects in natural resources developments. One is decision analytic, based on traditional discounted cash flow and stochastic dynamic programming [Fleten SE, Maribu KM, Wangensteen I. Optimal investment strategies in decentralized renewable power generation under uncertainty. Energy 2007;32:803–15; Smith J, McCardle K. Valuing oil properties: integrating option pricing and decision analysis approaches. Operations Research 1998;46(2):198–217; Szklo AS, Carneiro JTG, Machado G. Break-even price for upstream activities in Brazil: evaluation of the opportunity cost of oil production delay in a non-mature sedimentary production region. Energy 2008;33:589–600], and the other is contingent claims analysis, based on the no-arbitrage theory of financial markets [Brennan M, Schwartz E. Evaluating natural resource investment. Journal of Business 1985;58:135–57; Emhjellen M, Alaouze CM. A comparison of discounted cash flow and modern asset pricing methods – project selection and policy implications. Energy Policy 2003;31:1213–20; Laughton D. The management of flexibility in the upstream petroleum industry. The Energy Journal 1998;19:83–114; Paddock L, Siegel D, Smith J. Option valuation of claims on real assets: the case of offshore petroleum leases. Quarterly Journal of Economics 1988;103(3):479–508; Schwartz ES. Valuing long-term commodity assets. Journal of Energy Finance and Development 1998;3(2):85–99; Sezgen O, Goldman CA, Krishnarao P. Option value of electricity demand response. Energy 2007;32:108–19]. In this paper, we use the second approach to develop a new model, and the main contributions are providing a tractable and realistic means of incorporating the option value and optimal timing into the investment decision in natural resources and presenting an example that shows option and timing considerations to be important. We demonstrated the validity of the model using both numerical analysis and real data.     

煤粉炉无油点火新技术-高能等离子体点火

高能等离子体直接点燃煤粉是一种很有发展前途的无油点火及低负荷稳燃新技术．本文较详细地论述和分析了该技术的现状、技术特性、经济特性和发展前景等,给出了适当的结论．通过全面的分析讨论,可以看到该技术具有良好的发展前景．     

Characteristics of co-combustion and kinetic study on hydrothermally treated municipal solid waste with different rank coals: A thermogravimetric analysis

This study presents an investigation on the influence of hydrothermally treated municipal solid waste (MSW) on the co-combustion characteristics with different rank coals, i.e. Indian, Indonesian and Australian coals. MSW blends of 10%, 20%, 30% and 50% (wt.%) with different rank coals were tested in a thermogravimetric analyser (TGA) in the temperature range from ambient to 700 °C under the heating rate of 10 °C/min. Combustion characteristics such as volatile release, ignition and burnout were studied for the blend fuel. Different ignition behavior was observed depending on the blends composition and the coal rank. The result of this work indicates that the blending of MSW improves devolatization properties of coal. But it was found that the co-combustion characteristics of MSW and coal blend cannot be predicted only from the pyrolytic and or devolatization phenomena as the other factors such as the coal quality also plays a vital role in deciding the blends co-combustion characteristics. The TGA combustion profiles showed that the combustion characteristics of blends followed those of parent fuels in both an additive and non-additive manners. These experimental results help to understand and predict the behavior of coal and MSW blends in practical applications.     

Comparison of bituminous coal and lignite during combustion: Combustion performance,coking and slagging characteristics

The combustion characteristics such as combustion performance, coking, and slagging—at high temperatures (700–1300 °C) of bituminous coal and lignite were investigated and compared. The results show that the ignition temperature and the activation energy of lignite are lower than those of bituminous coal, and the combustion index and the burnout index are less than those of bituminous coal. Lignite has almost no coking while bituminous coal tends to coke at high temperatures. The larger the content and reflectivity of the vitrinite, the more severe the degree of coking. In the range of 700–1300 °C, the increase of temperature has little influence on the coking characteristics of lignite and bituminous coal. The low-rank lignite has larger amounts of mineral content which tend to form low-fusion-temperature eutectics. Furthermore, there is a connection between the combustion performance, coking and slagging characteristics through the maceral compositions: the coal which is hard to ignite but easy to burn out is more likely to have strong coking ability. Meanwhile, coking tends to keep alkaline oxides stay in the char and reinforce slagging at high temperatures.     

The transition of heterogeneous–homogeneous ignitions of dispersed coal particle streams

This work is assessing a study of the collective ignition behaviors of dispersed coal particle streams, with ambience temperature from 1200 K to 1800 K and oxygen mole fractions in the range of 10–30%. The dispersed coal particles of 65–74 μm are injected into an optical Hencken flat-flame burner by a novel de-agglomeration feeder. Three kinds of pulverized coals from different ranks, Hulunbel lignite, high-ash-fusion bituminous and low-ash-fusion bituminous, are considered. The normalized visible light signal intensity, deleting the background noise, is established to characterize the ignition delay of coal particle streams. Firstly, the prevalent transition from heterogeneous ignition to hetero–homogeneous ignition due to ambience temperature is observed. The pure homogeneous ignition rarely occurs, with an exception under high temperature and low oxygen for high-volatile coal. By comparing time scales between pyrolysis and heating processes, the competition of the volatile evolution and heterogeneous surface reaction are discussed. Then, the effects of ambience temperature, oxygen mole fraction and coal rank on the characteristic ignition delay are examined. Finally, the transient mode is developed, which not only well interprets the observed ignition transition phenomena, but also approximately predicts a variation of heterogeneous ignition time as a function of oxygen fraction.     

Characteristics of co-combustion of anthracite with bituminous coal in a 200-MWe circulating fluidized bed boiler

The effect of co-combustion of Vietnamese anthracite with Australian bituminous coal on the performance of a commercial circulating fluidized bed boiler was observed in the Tonghae thermal power plant.The temperature in the cyclone exit of the boiler increased slightly, which caused a decrease in the desulfurization efficiency as the co-combustion ratio of the bituminous coal increased from 40 to 100%. The unburned carbon fraction also increased. Consequently, the fine particles of the bituminous coal had lower combustion reactivity than those of the anthracite.NO_x emissions decreased as the bituminous coal ratio increased, although the fraction of nitrogen in the bituminous coal was higher than that in the anthracite. However, the emission of dust was found to increase due to an increase in the amount of CaO and MgO in the fly ash, which could lower the efficiency of the electrostatic precipitator.From these results, we concluded that the complete switch from the anthracite to Australian bituminous coal was possible, although the efficiency and the operation stability became lower than before. Additionally, as a future study, it is necessary to monitor the instability of the temperature increase and its effect on the prolonged clinker formation in the boiler.     

中温烟气旁路技术在变煤种宽负荷脱硝工程运用

随着我国电煤市场变化和火电机组运行灵活性政策出台,许多烟煤锅炉开始燃用褐煤并参与深度调峰,如何适应新煤种并实现宽负荷脱硝成为亟需解决的问题。本文在制粉系统防爆技改基础上,提出了一种中温烟气加热SCR系统入口烟温的技术方案,并结合工程实际运用进行了介绍,为同类型机组参与深度调峰工作提供一定借鉴。     

可拓工程方法在火电厂煤粉着火及时性评价中的应用

考虑到煤粉能否及时着火对于电站锅炉安全经济运行的重要程度,提出基于物元概念和可拓集合理论的可拓物元评价方法.在建立评价等级指标和评价模型的基础上,通过计算与煤粉燃烧及时性有关的状态参数和各种评价等级之间的可拓关联度,由关联度的大小判断锅炉煤粉的着火状态是否及时.最后通过实例表明,此方法用于评价锅炉煤粉着火状态的有效性、准确性及工程实用性.     

单角试验炉煤粉射流着火可视化试验研究

本文通过一个图像采集与处理系统，将单角试验炉煤粉射流着火火焰锋面从背景中分离出来。将火焰锋面到燃烧器出口的最近距离定义为着火距离，对一种烟煤的试验研究结果表明，随着煤粉浓度的提高，其平均着火距离明显缩短。具有较高稳定性的钝体燃烧器的煤粉射流着火，倾向于在分离射流的外侧首先出现。     

甲醇发动机的点火正时和喷射正时优选的试验研究

缸内喷射、火花助燃甲醇发动机是在缸内形成一种层状分布的不均匀混合气，为获得优良的燃烧和排放性能，存在一个最佳的点火和喷射正时。此时着火延迟期最短，缸内混合气浓、稀分布最合理，平均火焰传播速度最快，热效率最高，效率和排放折衷最好。本文详细介绍了点火正时和喷射正时的优选过程及对缸内混合气浓度分布及燃烧过程的影响。     

着火促进剂作用机理的数值研究

在Ｓｈｅｌｌ着火模型的基础上，分析了着火促进剂的作用机理，将其纳入Ｓｈｅｌｌ模型中进行了数值计算，计算结果表明，着火促进缩短燃油着火前的冷焰诱导期，其效力受促进热解动力学参数的控制，并随春添加浓度的增加而增加。     

Isoconversional kinetic analysis of co-combustion of sewage sludge with straw and coal

In this paper, the co-combustion behaviour of sewage sludge with straw and coal were carried out in a thermogravimetric analyzer under different atmospheres and at different heating rates (10, 20 and 40 K min⁻¹) in the temperature range from ambient temperature to 1000 °C. TG and DTG curves were analysed. The Flynn–Wall–Ozawa’s (FWO) and Kissinger–Akahira–Sunose’s (KAS) isoconversional methods were used to yield dependency of the activation energy of reduction process on the degree of conversion. The values of E_α were obtained. The results indicate that: with the increase of heating rate, the maximum weight loss rate of samples increase obviously. The activation energy is practically constant in the 0.2 ? α ? 0.9 range, with the average values of E_α = 137.27 and 132.38 kJ mol⁻¹ calculated by FWO and KAS methods, respectively.