O2/CO2粉煤燃烧技术的过程分析及烟气排放控制Q

目前减少CO2排放潜力较大、可行性较好的CCS、IGCC都离不开CO2的捕集技术。新型O2/CO2粉煤燃烧技术可以将排放烟气中的CO2浓度提高到95%,并使高温烟气回流,减少热量损失,同时又减少SO2、NOx等污染物的排放。与传统的O2/N2煤燃烧技术相比,O2/CO2粉煤燃烧技术增加了空气分离装置和烟气循环回流工艺。燃烧反应器中的主要反应包括有机物的燃烧反应、矿物质的氧化反应、脱硫剂的硫化反应等。高温烟气循环代替空气参与煤的燃烧反应能够减少能量损失,但减少的部分并不等于原有工艺排放的高温N2所带走的热损失,模型求解为Q=QA-QB。O2/CO2粉煤燃烧技术的主要优势体现在CO2高浓度捕集和液化储存环节,液化电耗约只有3%的下降,而传统技术液化电耗则可下降约27.8%左右,再加上减少的热损失,其经济性更加明显。O2/CO2粉煤燃烧技术可以对O2流量进行控制,使得不同质量的煤都得到充分燃烧。同时能够根据要求控制反应过程中排放的CO2、SO2、NOx中任意单个污染物的摩尔百分含量,通过求解目标函数f=f（XCO2,XSO2,XNOx,XCO,XH2O,…）,使其达到最优值。     

旋流煤粉燃烧技术的发展

文中回顾了国内外旋流煤粉燃烧技术的发展,根据二次风的供入方式,一次风粉混合物煤粉浓度的不同将此类技术分为三类：普通型、分级燃烧型、浓缩型、浓缩型又分为高浓度型及浓淡型,总结了各种类型燃烧器在火焰稳定性、燃烧效率、ＮＯｘ排放、结渣、高温腐蚀、调节性能等方面的特点,指出浓淡型旋流煤粉燃烧器是我国旋流煤粉燃烧技术的发展方向。     

Combustion technology developments in power generation in response to environmental challenges

Combustion system development in power generation is discussed ranging from the pre-environmental era in which the objectives were complete combustion with a minimum of excess air and the capability of scale up to increased boiler unit performances, through the environmental era (1970–), in which reduction of combustion generated pollution was gaining increasing importance, to the present and near future in which a combination of clean combustion and high thermodynamic efficiency is considered to be necessary to satisfy demands for CO₂ emissions mitigation.

From the 1970s on, attention has increasingly turned towards emission control technologies for the reduction of oxides of nitrogen and sulfur, the so-called acid rain precursors. By a better understanding of the NO_x formation and destruction mechanisms in flames, it has become possible to reduce significantly their emissions via combustion process modifications, e.g. by maintaining sequentially fuel-rich and fuel-lean combustion zones in a burner flame or in the combustion chamber, or by injecting a hydrocarbon rich fuel into the NO_x bearing combustion products of a primary fuel such as coal.

Sulfur capture in the combustion process proved to be more difficult because calcium sulfate, the reaction product of SO₂ and additive lime, is unstable at the high temperature of pulverized coal combustion. It is possible to retain sulfur by the application of fluidized combustion in which coal burns at much reduced combustion temperatures. Fluidized bed combustion is, however, primarily intended for the utilization of low grade, low volatile coals in smaller capacity units, which leaves the task of sulfur capture for the majority of coal fired boilers to flue gas desulfurization.

During the last decade, several new factors emerged which influenced the development of combustion for power generation. CO₂ emission control is gaining increasing acceptance as a result of the international greenhouse gas debate. This is adding the task of raising the thermodynamic efficiency of the power generating cycle to the existing demands for reduced pollutant emission. Reassessments of the long-term availability of natural gas, and the development of low NO_x and highly efficient gas turbine–steam combined cycles made this mode of power generation greatly attractive also for base load operation.

However, the real prize and challenge of power generation R&D remains to be the development of highly efficient and clean coal-fired systems. The most promising of these include pulverized coal combustion in a supercritical steam boiler, pressurized fluid bed combustion without or with topping combustion, air heater gas turbine-steam combined cycle, and integrated gasification combined cycle. In the longer term, catalytic combustion in gas turbines and coal gasification-fuel cell systems hold out promise for even lower emissions and higher thermodynamic cycle efficiency. The present state of these advanced power-generating cycles together with their potential for application in the near future is discussed, and the key role of combustion science and technology as a guide in their continuing development highlighted.     

炉内煤粉燃烧一维数学模型及其仿真

为了准确计算炉内煤粉的燃尽率,从研究煤粉粒子的燃烧机理入手,以炉膛内最复杂的燃烧器区域的煤粉燃烧过程为研究对象,通过合理简化煤粉中挥发分和焦炭的燃烧过程,建立了炉内煤粉燃烧沿高度方向上的一维宏观模型,在模型中考虑了煤粉燃烧过程中氧含量的变化,以单个煤粉颗粒燃烧的等密度模型为基础,通过多种煤粉粒径的燃烧过程反映煤粉燃烧的整体过程,推导出计算炉内煤粉燃尽率的显示公式,满足了实时仿真计算的要求。计算结果与实测数据和现有的文献相符,并对结果进行了分析。     

Full-scale co-firing trial tests of sawdust and bio-waste in pulverized coal-fired 230 t/h steam boiler

Co-firing trial tests of sawdust and bio-waste coming from cereal production with hard coal were carried out at Skawina Power Plant in Poland (1532 MW in fuel, currently belonging to CEZ Group). Skawina Power Plant is a tangentially-fired pulverized coal unit with nine boilers (4 boilers of 210 t/h and five boilers of 230 t/h live steam respectively) that produces 590 MW electricity and 618 MW of heat (district heating and process steam).The paper presents an analysis of energy and ecological effects of sawdust and bio-waste co-firing in the existing pulverized hard coal boiler. The mixture of coal and biomass was blended in the coal yard, and fed into the boiler through the coal mills. During the tests, combustion of mixtures composed of hard coal and sawdust (with mass share of 9.5%) and hard coal – bio-waste (6.6% mass basis) were examined. The co-firing tests were successful. Based on the analysis of the test results, the influence of biomass co-firing on specific components of energy balance (e.g. stack losses and boiler thermal efficiency) was discussed, in comparison to combustion of coal alone. The emission indices during coal combustion were calculated and compared to the emission indices for biomass co-firing. It was proved that co-firing of both biomass sorts leads to a decrease of CO and SO₂ emissions. Due to the possibility of considering the part of the energy generated during biomass co-firing as renewable energy, the procedure for biomass based renewable energy share determination is presented and illustrated with an example.     

煤粉预热燃烧原理分析与实验研究

针对我国电站用煤品质下降和煤质多变的现状,提出了煤粉预热燃烧的新型技术理念。该技术的核心是快速预热煤粉气流并保持恰当的风/粉比例,通过自动控制装置调节预燃室中的负压程度使得一次风粉射流卷吸适量高温烟气来预热煤粉气流帮助燃烧。     

锅炉低NOx排放煤粉分级燃烧的优化

燃料分级燃烧是目前广泛采用的降低ＮＯｘ排放的有效方法之一。本文通过数值计算对优化煤粉分级燃烧进行了研究，以保证锅炉ＮＯｘ低水平的排放，并确定了煤粉４级燃烧的组织原则。     

空气深度分级对低挥发分煤燃烧过程影响的研究

通过数值模拟研究了在一维燃烧炉上燃用低挥发分煤的条件下,空气深度分级和煤粉细度变化对煤粉燃尽过程和NO_x排放的影响,得到了沿炉膛轴线方向上的温度、氧浓度和NO_x的分布,表明空气深度分级后燃烧后期的氧量增加,炉膛温度水平提高,而煤粉细度的提高使得上述效果更加明显,因而燃烧效率提高和NO_x排放降低,并通过实际燃烧试验验证了数值模拟结果.研究结果表明,对燃用低挥发分煤,采用空气深度分级技术和提高煤粉细度的措施,可以同时取得高效低NO_x排放的效果.     

分级燃烧降低燃煤锅炉NOx排放的机理及影响因素分析

再燃燃料在还原性气氛下对主燃区煤粉燃烧生成的氮氧化物的还原反应中 ,再燃燃料中产生的中间产物氰基、氨基和烃根等起到分解氮氧化物的作用。同一再燃燃料中烃类物质在富燃料和贫燃料气氛中所起作用截然不同。实际应用中应使再燃区内各处处于弱还原性气氛下以保证再燃降低NOx 排放的效果 ,并尽量采用气体燃料作为再燃燃料 ,同时在获取所需NOx 排放水平前提下尽量选取较高的空气过量系数(化学当量比 ) ,以同时降低飞灰中的含碳量、减轻高温腐蚀的程度。     

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.     

中心大速差射流浓缩煤粉方法的研究

本文提出了一种新的煤粉浓缩方法－位于一次风出口处的中心大速差射流方法，并对中心大速差射流的冷态工况进行了实验研究和数值模拟，实验和计算表明，该方法有明显的浓缩煤粉的效果，因此它不仅可以改善煤粉锅炉的燃烧稳定性及降低ＮＯｘ，而且有可能解决当前煤粉浓缩燃烧技术难以解决的煤粉浓度难以控制，后期混合不好，煤粉管易堵塞和磨损以及引发炉内结焦等一系列问题。     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

低挥发分煤低NO_X燃烧技术研究与开发

我国排放的氮氧化物中,燃煤电站产生的氮氧化物(NOX)占排放总量的比例逐年在增加,控制燃煤电站NOX排放至关重要。本文介绍目前国内燃煤电站主要采用的低NOX燃烧技术,重点通过低挥发分贫煤燃烧过程NOX释放特性的实验研究,提出新一代立体分级低氮燃烧技术,可以有效降低燃贫煤锅炉NOX排放。     

Meeting emission standards with high-sulfur coals

The economics of strategies for meeting sulfur oxides (SO_x) emission standards from furnaces fueled with high-sulfur coals has been assessed based on published data. The strategy of SO_x control depends on how the coal is utilized. For large power plants, flue-gas desulfurization (FGD) is preferable to conversion of coal to clean fuel. In comparison with coal conversion, the total capital and operating costs for FGD are almost an order of magnitude lower, thermal efficiencies are higher, and utility requirements are lower. Even with possible breakthroughs in coal-conversion technologies, it appears that FGD will remain the economically preferred route to desulfurization. FGD has been in commercial operation since 1968, and the reliability of the process has reached an acceptable level. For industrial furnaces, direct combustion is preferred to gasification because gasification is inherently expensive. Fluidized-bed combustion is the only viable option for clean direct combustion of coal in small industrial furnaces. Fluidized-bed combustion has reached commercial status and is economically competitive in many parts of the world. For furnaces requiring gaseous or liquid fuels, gasification to medium-Btu gas is preferred. For domestic and commercial uses, coal can be gasified to clean, low-Btu gas. This is an old process and might be amenable to cost reduction through application of new technologies. The only other economically viable approach involves the production of clean solid fuel by compounding coal with additives such as limestone and manganese nodules.     

超细化煤粉的投入量对再燃效果影响的实验研究

目前我国燃煤电厂NOx排放的控制任务相当艰巨和繁重,急需开发适合我国国情的降低NOx排放的技术。超细化煤粉再燃是一种降低燃煤锅炉NOx排放的技术,本文通过在热态燃烧试验装置上进行的试验研究,论述了超细化煤粉的投入量对锅炉N0x排放、结渣状况及机械不完全燃烧损失的影响。通过试验得知,加入再燃煤粉后,炉膛火焰中心的位置变化不大;NOx的脱除率能够达到50％以上;结渣状况有所减轻;机械不完全燃烧损失增加。     

不同煤种燃烧生成多环芳烃的研究

燃煤过程产生的多环芳烃类有机污染物烃具有强烈的致癌、致突变、致畸变等作用 ,日益受到广泛的重视。本文进行了不同煤种燃烧时多环芳烃的生成研究 ,比较了燃煤排放和原煤中含有的多环芳烃之间关系 ,研究了煤的固定碳、挥发份、灰份等组分对燃煤过程中多环芳烃排放的影响     

一种用于携带流反应器试验台的煤粉燃烧器的优化设计

为了优化一种用于携带流反应器系统的煤粉燃烧器结构参数,降低氮氧化物排放,本文利用计算流体动力学软件FLUENT对该煤粉燃烧器结构参数的优化过程进行了数值模拟研究,并与试验结果进行了对比验证。结果表明,燃烧器一次风喷口采用扩口结构以及对冲二次风的引入均能有效的促进二次风与一次风煤粉的混合,增强煤粉着火及燃烧的稳定性。适当增加二次风喷口与一次风喷口的间距可以加速煤粉的燃尽。采用优化后的结构参数可以获得更低的氮氧化物排放,为基于携带流反应器系统的燃煤污染物减排研究提供了坚实的基础。     

玉米秸秆与煤掺烧锅炉运行性能分析

基于ASPEN PLUS软件,对玉米秸秆与煤的掺烧过程进行建模与模拟,研究在不同的生物质掺混比例及含水率下,锅炉运行性能以及污染物排放的变化规律。结果表明:与单独燃烧煤粉相比,随着掺烧比例的增大,生成的理论烟气量和烟气热损失增大,锅炉效率有所降低,气体污染物NO及SO2减少;随着生物质含水率的增大,NO的排放量减少,而SO2的排放量增加。     

Efficiency enhancement of pressurized oxy‐coal power plant with heat integration

The oxy‐coal combustion with carbon dioxide capture and sequestration is among the promising clean coal technologies for reducing CO₂ emissions. Because most of oxy‐coal power plants need to cope with energy penalties from air separation and CO₂ compressor units, the pressurized combustion is added to reduce the electricity demand for the CCS system, and the waste heat of the pressurized flue gas is recovered by the heat integration technique to increase the power generation from steam turbines. Finally, the efficiency enhancement of a 100 MW_e‐scale power plant is successfully validated by Aspen Plus simulation. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of pressure on coal char combustion

A two-dimensional, two-phase combustion model of pulverized coal char at elevated pressures is presented in this paper. This is often encountered in furnaces used for power generation, industrial heating and steam production, and for conversion of solids to gas and liquid products. In pressurized circulating fluidized bed boilers, the effect of pressure on char combustion is significant. Of particular importance is to reveal the relative significance of the diffusion and chemical reaction, as controlling mechanisms, and to evaluate the effect of total pressure on the performance of the combustion chamber. The partial differential equations of conservation of mass, momentum and energy are solved taking into consideration turbulent flow, interphase mass- and heat-transfer, radiation and varying operational conditions (e.g. feed of coal and primary and secondary air). The equations are integrated with the finite volume method and are solved for the flow field, temperature field in the gaseous and solid phases and the concentration of reactants and products. The results show that both chemical reaction and diffusion mechanisms control the combustion at elevated pressure. Moreover, the effect of pressure on the reaction kinetics proves to be significant.