运行参数对锅炉煤粉着火燃烧和飞灰含碳量影响的数值研究

为了达到锅炉的优化运行以保证煤粉气流及时着火和充分燃尽，采用IPSA两相流动模型和煤粉燃烧综合模型，在不同的一次风率和煤粉细度的工况下，对1台350MW锅炉煤粉燃烧过程进行了数值模拟，得出了炉内燃烧器区域以及出口处烟气温度场和燃烧产物的组分浓度分布。分析了一次风率和煤粉细度对煤粉着火燃烧和飞灰含碳量的影响规律，并确定了优化的运行参数。结果表明：一次风率对煤粉气流的着火影响较大，而对出口处烟气温度、氧量以及飞灰含碳量影响较小。煤粉细度对煤粉气流的着火、燃烧以及燃尽均有较大影响。图8表2参9     

Investigation on ash deposition characteristics during Zhundong coal combustion

The reserves of Zhundong (ZD) coal in China are huge. However, the high content of Na and Ca induces serious slagging and fouling problems. In this study, the ZD coal was burned in a DTF (drop tube furnace), and the ashes collected at different gas temperature with non-cooling probe were analyzed to obtain the ash particle properties and their combination mode. The results showed that Na, Ca and Fe are the main elements leading to slagging when the gas temperature is about 1000 °C during ZD coal combustion, but their mechanisms are quite different. Some sodium silicates and aluminosilicates and calcium sulfate keep molten state in the ashes collected at 1000 °C. These molten ash particles may impact and adhere on the bare tube surface, and then solidified quickly. With the growth of slag thickness, the depositing surface temperature is increased. The molten ash particles might form a layer of molten film, which could capture the other high fusion temperature particles. The Fe₂O₃ sphere were captured by the formed molten slag and then they blended together to form a new molten slag with lower melting temperature.     

Comparison of nitrogen oxide emissions from boilers for a wide range of coal qualities

This paper presents the results of experimental researches on nitrogen oxide emissions from coal-fired boilers. Two Chinese lean coals have been fired in two full scale boilers (1 025 t · h ⁻¹ ) and in a pilot scale test furnace (Drop-Tube Furnace) to study the influence of nitrogen content in coal on nitrogen oxide emission. The nitrogen oxide emission was found to correlate well with the fuel nitrogen content. The test results of the drop-tube furnace and the single burner furnace with three Chinese coals show that the staged combustion can greatly reduce the nitrogen oxide emission. Identical trends in nitrogen oxide emission as a function of the volatile matter of the coals have been obtained under different combustion conditions. The principle of low nitrogen oxide emissions of the wide range burner (biased combustion or internal air staging) and the cases with over fired air port (furnace air staging) is introduced in this paper. In addition, the influence of excess oxygen content on nitrogen oxide emission has been tested in the utility boilers and test furnaces.     

Effect of rice husk co-combustion with coal on gaseous emissions and combustion efficiency

Investigation on co-combustion of Lakhra coal and rice husk blends was carried out in a drop tube furnace to measure its impact on flue gas emissions and carbon burnout. According to experimental results, the emissions of NO and SO₂ were higher in case of combustion of Lakhra coal compared to coal?–rice husk blends combustion. The emissions of CO decreased rapidly at higher furnace temperatures beyond 900°C. Minimum of CO emissions were nearly 45 ppm while SO₂ and NO emissions were found to be 554 and 120 ppm, respectively, for 15% biomass blending ratio and at exit furnace temperature of 1000°C. The unburnt carbon was found to be reduced significantly with an increase in furnace temperature and blending ratio. The study has shown that blending of rice husk would be a useful option to minimize SO₂ and NO emissions during combustion of Lakhra coal.     

Experimental study on ash deposition of Zhundong coal in oxy-fuel combustion

To facilitate the large-scale utilization of high-alkali and -alkaline earth metals (AAEMs) coals in power generation, the ash deposition behaviors of a typical Zhundong coal in oxy-fuel combustion were experimentally investigated using a drop tube furnace. A wall-temperature-controlled ash deposition probe by which the bulk gas temperature could be measured simultaneously was designed and employed in the experiments. The deposition tendencies, ash morphologies, chemical compositions of deposited ash particles were studied respectively under various oxygen concentrations, bulk gas temperatures, probe surface temperatures and probe exposure times. The experimental results revealed that the oxygen concentration had a significant influence on the deposition behavior during oxy-fuel combustion of high-alkali coal. Compared with air case, more fine ash particles were generated during the combustion of Zhundong coal in 21% O₂/79% CO₂ atmosphere but the deposition tendency was weaker. However, a higher oxygen concentration could aggravate the tendency of ash deposition. The high contents of iron (Fe), calcium (Ca), sulfur (S), and sodium (Na) in Zhundong coal could result in the generations of low-melting point compounds. Calcium in flue gas existed as CaO and was captured prior to SO₃ by the probe surface during the ash deposition process. At the initial 30 min of the ash deposition process, the dark spherical fine ash particles rich in Fe, Na, oxygen (O), and S were largely produced, while in the range of 60–90 min the light spherical fine ash particles with high contents of Ca, barium (Ba), O, and S were generated on the other hand. The deposition mechanisms at different stages were different and the melted CaO (BaO)/CaSO₄ (BaSO₄) would give rise to a fast growth rate of ash deposit.     

600 MW偏转二次风系统锅炉炉内结渣特性的数值模拟

偏转二次风系统已广泛应用于大型四角切圆燃烧锅炉，用以报制炉内结渣，防止水冷壁高温腐蚀等。为降低炉膛出口扭转残余，通常采和下部二次风大角度正切、上部二次风和OFA风反切的布置方式。本文对某台采用偏转二次风系统的600MW燃煤四角切圆燃烧锅炉的炉内结渣过程进行模拟，对炉内气固相流动、温度场、气固相燃烧、固相向水冷的输运过程和灰粒在水冷壁上的附生长过程进行了数值模拟，结果表明，偏转二次风系统具有较强的防结渣性能，这一点也被锅炉的实际运行所证实。     

On-Line Performance Model of the Convection Passes of a Pulverized Coal Boiler

This article describes an on-line heat transfer simulation for the convection passes of a typical pulverized coal boiler (PCB) power plant that accounts for fouling. Performance analysis of heat exchanger assemblies employed in pulverized coal boilers was characterized using the effectiveness–number of transfer units (NTU) method. The model calculates instantaneous heat rates in different sections of the boiler so as to determine a local cleanliness factor. The effects of changing plant load are fully accounted for in the model. Generally, a close correlation between calculated cleanliness factors and normalized strain gage measurements of pendant section weight variations due to accumulated fouling was obtained. Furnace exit gas temperatures calculated by the model agreed reasonably well with measurements available in the literature for a similar design of PCB power plant.     

W火焰锅炉制粉系统优化技术研究

为了满足W火焰锅炉在燃烧无烟煤过程中对煤粉细度的要求,几乎所有W火焰锅炉均采用了配备钢球磨煤机的制粉系统。控制磨煤机出口煤粉细度、一次风煤粉浓度,并使其维持在最佳值附近是保证锅炉燃烧效率的基础条件。研究了不同直径钢球装载比例对磨煤机煤粉细度特性的影响,通过优化磨煤机不同直径钢球装载比例、多点修正一次风流量测量偏差等技术,提高了磨煤机出口煤粉细度,减小了一次风流量测量偏差,从而改善了锅炉运行特性,提高了燃烧效率。     

Energy from municipal solid waste: A comparison with coal combustion technology

The conversion of municipal solid waste (MSW) to energy can conserve more valuable fuels and improve the environment by lessening the amount of waste that must be landfilled and by conserving energy and natural resources. The importance of utilizing MSW was recognized in the 1991 U.S. National Energy Strategy, which sought to “support the conversion of municipal solid waste to energy.” One route to utilizing the energy value of MSW is to burn it in a steam power plant to generate electricity. Coal has long been the predominant source of energy for electricity production in the U.S.; therefore, a considerable science and technology base related to coal combustion and emissions control can be, and has been, applied with substantial benefit to MSW combustion. This paper compares the combustion of coal and MSW in terms of fuel characteristics, combustion technology, emissions, and ash utilization/disposal. Co-combustion of coal and MSW is also discussed. MSW issues that can be addressed by research and development are provided.The major environmental issues that designers of MSW combustion systems have had to address are emissions of trace organic compounds, particularly polychlorinated dioxins and furans, and trace elements such as mercury, lead, and cadmium. Emission of trace organics is generally the result of a poorly designed and/or operated combustion system; modern MSW systems use good combustion practices that destroy organic compounds during the combustion process. Proper control of air/fuel mixing and temperature, and avoidance of “quench” zones in the furnace, help to ensure that potentially harmful organics are not emitted. Computer codes and other design and troubleshooting tools that were developed for coal combustion systems have been applied to improve the performance of waste-to-energy systems.Trace element emissions from both coal and MSW combustion result primarily from vaporization of elements during the combustion process. Most of the trace elements that are vaporized condense on fly ash as the combustion products cool downstream of the furnace and can be effectively controlled by using an efficient particulate removal device. However, volatile elements, particularly mercury, are emitted as a vapor. Several mechanisms are available to capture mercury vapor and some are in use. The development of satisfactory control technology for mercury is a topic currently of high interest in coal burning.The potential for leaching of trace elements and organics from MSW residues after disposal raises issues about the classification and management of ash. Results of laboratory leaching tests, especially for lead and cadmium, have not been consistently supported by field experience. Careful interpretation of the available test protocols is needed to make sure that residues are properly managed.Because of the large scale of coal-fired boilers for electricity production, co-firing of MSW with coal in such boilers could consume large quantities of waste. Several short-term demonstrations have shown that co-firing is feasible. The issues involved in co-firing are emissions of trace elements, trace organics, and acid gases; boiler slagging and fouling; and long-term effects, such as corrosion and erosion of boiler tubes.Areas where research and development has contributed to improved MSW combustion include (a) the formation mechanisms of polychlorinated dioxins/furans, especially low-temperature, catalytic mechanisms, (b) methods of combustion air distribution in incinerators that result in better combustion and reduced emission of organic compounds, (c) the use of gas reburning to control NOx and reduce emission of organic compounds, (d) practical methods for removing organic compounds and mercury from MSW flue gas, (e) the performance of electrostatic precipitators in removing MSW fly ash, particularly when co-firing MSW and coal in existing coal-fired boilers, and (f) burning MSW in fluidized beds or of pulverizing refuse-derived fuel and firing it in suspension-fired, pulverized coal boilers.     

四角切向燃烧锅炉煤粉射流逆向稳燃技术的研究开发

本文首次提出并分析了四角切向燃烧锅炉煤粉射流逆向稳燃技术的设计思想。根据炉内三维湍流流场的数值模拟，优化设计了本项技术应用于焦作电厂Ｎｏ．３炉的燃烧器改造方案。计算结果及现场应用证实，采用煤粉射流逆向稳燃技术能够大幅度延长一次风射流中煤粉颗粒在着火初期的停留时间，改善煤粉气流的着火条件，同时能够有效地削弱炉膛出口气流的残余旋转，从而减轻烟温偏差，并能改变煤粉颗粒的切圆运动轨迹，从而缓解了炉膛燃烧器区域水冷壁的结渣与高温腐蚀。     

能源动力系统除灰新技术的机理及应用

我国能源动力系统尤其是电站锅炉燃用大量高灰煤,致使系统尾部受热面严重积灰,影响锅炉的效率和出力,中国科学院力学研究所采用了可燃气体快速燃烧,产生燃气脉冲清除积灰的原理,研究发展了一种适用于我国大型电站锅炉的新一代除灰技术,目前,燃气脉冲除灰技术已在全国几十台125MW-600MW机组上获得成功应用。图9参4     

Combustion kinetics of coal chars in oxygen-enriched environments

Oxygen-enhanced and oxygen-fired pulverized coal combustion is actively being investigated to achieve emission reductions and reductions in flue gas cleanup costs, as well as for coal-bed methane and enhanced oil recovery applications. To fully understand the results of pilot scale tests and to accurately predict scale-up performance through CFD modeling, accurate rate expressions are needed to describe coal char combustion under these unconventional combustion conditions. In the work reported here, the combustion rates of two pulverized coal chars have been measured in both conventional and oxygen-enriched atmospheres. A combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometry diagnostic and a rapid-quench sampling probe has been used for this investigation. Highvale subbituminous coal and a high-volatile eastern United States bituminous coal have been investigated, over oxygen concentrations ranging from 6 to 36 mol% and gas temperatures of 1320-1800 K. The results from these experiments demonstrate that pulverized coal char particles burn under increasing kinetic control in elevated oxygen environments, despite their higher burning rates in these environments. Empirical fits to the data have been successfully performed over the entire range of oxygen concentrations using a single-film oxidation model. Both a simple nth-order Arrhenius expression and an nth-order Langmuir-Hinshelwood kinetic equation provide good fits to the data. Local fits of the nth-order Arrhenius expression to the oxygen-enriched and oxygen-depleted data produce lower residuals in comparison to fits of the entire dataset. These fits demonstrate that the apparent reaction order varies from 0.1 under near-diffusion-limit oxygen-depleted conditions to 0.5 under oxygen-enriched conditions. Burnout predictions show good agreement with measurements. Predicted char particle temperatures tend to be low for combustion in oxygen-depleted environments.     

燃高灰分劣质无烟煤角管式链条炉排锅炉技术改造

从工程实践的角度出发,针对高灰分劣质无烟煤的特点,对一台角管式链条炉排锅炉在燃用非设计煤种时,所产生的锅炉出力降低、受热面积灰严重的状况进行了研究和分析.通过对锅炉炉拱和炉内烟气流道的改造,以及二次风的运用,提高锅炉在燃用高灰分劣质无烟煤时的出力和运行效率,改善了炉内的严重积灰现象.改造突出了锅炉前、后拱在链条炉燃烧组织中极其重要的作用,可为其它在燃用非设计煤种时出力降低的锅炉技术改造提供借鉴.     

基于偏最小二乘回归法的电站锅炉炉膛出口烟温调整试验研究

针对某电厂的锅炉炉膛出口烟温进行了调整试验.通过数据预处理和偏最小二乘回归分析,建立了炉膛出口烟温的统计学模型.通过分析模型的影响因子,进行了运行参数的调节,给出了不同负荷下锅炉的合理运行工况.试验结果表明:通过调节炉膛出口烟温,可提高燃烧效率,减少煤耗.利用偏最小二乘回归方法分析试验数据,有助于调试人员掌握被调对象的运行特性,且便于寻找最佳工作点.     

燃油锅炉除垢剂的试验研究

针对炼油企业燃油锅炉结垢严重的问题 ,在燃油锅炉上进行了除垢剂工业试验 ,并对试验结果进行了分析。试验结果表明 ,采用向锅炉内部喷射除垢剂的方法是可行的 ,能达到除垢的目的 ,而且在其他条件不变的情况下可以提高锅炉处理量 ,降低炉膛及排烟温度 ,具有一定的经济效益     

Fundamentals of coal combustion during injection into a blast furnace

The efficiency of coal combustion is important for the blast furnace process. Incomplete combustion of coal does not reduce coke consumption as can be expected and decreases burden permeability which results in improper gas flow and temperature distribution. Consequently, this reduces the throughput of the blast furnace.

This paper describes combustion conditions and mechanisms of coal combustion in the blast furnace, and discusses factors affecting coal combustion such as injector location, coal type, injection rate, maceral composition, and air blast parameters. Also, mathematical models of coal and coal/coke combustion in the blast furnace are considered.     

Mineral transformation during combustion of coal blends

Mineral behaviour for two individual coals (I, J) and their two‐component coal blends and 800°C ash blends heating were studied. Ash samples were heated progressively from 800°C to IT (initial deformation temperature) at 100°C intervals under different conditions. Coal samples were heated from room temperature to the corresponding temperature. Mineral transformation at each temperature was determined by X‐ray diffraction and SEM measurements. The results show that Si, Al, Fe and Ca compounds have a great form variation during heating. Their forms at different temperatures depend on the chemical composition of the ash, the blending ratio and the atmosphere. For different coal ashes, the main mineral matters at 800°C were quartz, anhydrite, hematite, calcite and feldspar. As the temperature increased, oxidation, thermal decomposition, transformation and reaction occurred between the components. Comparing a 40% I+60% J ash blend with individual ashes, fayalite was formed at 1100°C for the blend; the reaction product existed in a glassy phase at 1300°C. For a coal blend having the same ash ratio as the ash blend, FeO reacted with amorphous SiO₂ or Al₂O₃ to form fayalite and hercynite at 1000°C. As the temperature increased to 1100°C, fayalite and hercynite increased obviously. At 1200°C, some iron inclusion compounds melted to become glassy phase matter. Compared with the ash blend, iron species undergo a different change during coal blend heating: fayalite and hercynite formed earlier, iron compounds melted to form a glassy phase at lower temperature. This may be caused by early combustion of the more reactive coal (J coal) in the blend inducing local variation in oxygen concentration gradients around the less reactive coal and consequently affecting the reaction atmosphere and Fe mineral behaviour and interaction. That is to say, for coal blends, the mineral transformation was affected by both the mineral species interaction and the combustion behaviour. The calculations were performed to examine the fate of mineral matter under different combustion conditions using a thermodynamic chemical equilibrium calculation program. Calculations from coal blends were comparable with experiments from ash blends, this is because the calculation program only considers the interaction among the mineral species but does not consider the combustion reaction. It indicates that combustion and the relative volatiles also affected the mineral behaviour and slagging during coal blend combustion. Meanwhile, the mineral species evaporations were measured at high temperature: the main evaporated species were Na, K pure species and compounds, Fe, FeO, SiO and SiO₂. The evaporation of Fe has an important effect on initial deposition. Calculations were comparable with the experiments. Copyright © 1999 John Wiley & Sons, Ltd.     

Emissions of organic hazardous air pollutants during Chinese coal combustion

This paper provides a general investigation of the emissions of organic hazardous air pollutants (HAPs) during the combustion of several typical Chinese coals. First, the distribution of four types of HAP, i.e., aliphatics, cyclic hydrocarbons, monoaromatic compounds and PAHs, in the CH₂Cl₂ extracts of six Chinese coals were studied and the influences of the extractive times and coal varieties were also evaluated. Second, the partitioning of these HAPs in the flue gas during coal combustion in a small-scale reactor were investigated, depending on oven temperatures (500 °C, 600 °C, 700 °C, 800 °C, 900 °C) and coal varieties. The behaviors of HAP in the combustion flue gas were compared with those in the CH₂Cl₂ extracts. Finally, combustion was conducted at given conditions in two laboratory-scale reactors: a fluidized bed and a fixed bed. Two coals (Shengmu bituminous coal and Xunhuan anthracite coal) and one coke were considered in this case. The HAP partitioning both in flue gases and in ashes were evaluated and compared between the two combustors.     

电站锅炉燃气脉冲除灰过程研究

中国电站锅炉燃用大量的未经洗选的劣质煤,导致严重的锅炉积灰。积灰不仅使锅炉热效率下降,而且堵塞烟气通道,影响了锅炉的正常运行。燃气脉冲除灰技术是中国科学院力学研究所燃烧实验室开发的,并在30多台大型电站锅炉应用,取得了很好的效果。本文工作研究了该项技术中燃烧室结构和燃料对火焰传播和压力脉冲的影响;用压力传感器测量燃气脉冲在出口外流场中的压力分布,观察燃气脉冲的作用强度和作用范围;用振动传感器测量积灰板的振动,以及在不同空间位置振动加速度的变化情况,由此推论了除灰作用的机理。     

高温空气燃烧技术的特点及其应用前景

高温空气燃烧技术（HTAC）是九十年代初在日本开发的一项新的燃烧技术,该项技术具有节约燃烧、低NOx排放、热利用率高和减设备尺寸等特点。分析了HTAC的火焰温度分布特征及其可降低NOx排放的原理。高炉煤气、焦炉煤气及94．5％高炉煤气与5．5％焦炉煤气的混合煤气应用于HTAC技术的理论计算结果表明,理论燃烧温度随着预热空气和燃气温度的升高而升高,因此HTAC技术可燃用传统燃烧方式不能使用的低热值燃气。此外,空气、燃气双预热可奖排烟温度将得更低,热利用率提高更高。最后,指出了在燃油、燃气锅炉及煤（或可燃固体废弃物）气化系统中采用HTAC技术的可能性。