锅炉专业英语

Chapter 2 Boiler 第二章锅炉 Air heater 空预器Commissioning 试运行 Anchor 支座,固定Compressor 压缩机、压气机Anhydrous ammonia 无水氨Condenser 凝汽器 Anthracite 无烟煤Containment 反应堆安全壳Atomized 雾化Convection 对流 Austenitic 奥氏体钢Coolant 制冷剂 Auxialiary 辅助机械Coordinated 坐标,定位 Axis 轴Corten低合金耐腐蚀钢 Bagasse 甘蔗渣Counterflow 逆流(换热器) Bare tube 光管Creep strength 蠕变强度 Bark 树皮Criterion Beam 梁,横梁Critical pressure 临界压力Bituminous coal 烟煤Culm 煤屑 Blade 叶片Cyclone furnace 旋风炉 Blast 鼓风Debris 残骸、有机残留物Blowdown 排污Decane 癸烷 Boiler 锅炉Decay 分解 Bulk 大块的Deposited 沉积,沉淀的 Burner zone 燃烧器区域Deterioration 恶化 Butane 丁烷Diesel oil 柴油 Calcination 煅烧Differential 差动,微分 Capacity 出力Distillate 馏出物 Carbon steel 碳钢Distortion 变形 Cerium 铈Division wall 分隔墙,双面水冷壁Chromium 铬Drainage 疏水 Circulating fluidized bed CFB 循环流化 Drum 汽包 床锅炉 Coal char 煤焦Dwell time 保留时间Cogenerator 热电联产机组Economizer 省煤器 Combustion 燃烧Embrittlement 脆性,脆化Equalization 均衡,平衡Ingress进口,入口 Erosive 侵蚀的,腐蚀的In-line 顺列 Ethane 乙烷Inorganic 无机的 Evaluate 评估,Ion 离子 Evaporate 蒸发Jurisdiction 权限 Excess air 过量空气Lignite 褐煤 Extended surface 扩展受热面Lime 石灰 Fatigue 疲劳Limestone 石灰石 Feedwater 给谁Low alloy 低合金钢 Ferrite 铁素体Low-volatile 低挥发分的 Fin 鳍片,肋片Margin 裕量,安全系数Flange 法兰Matrix 矩阵 Flue gas 烟气Membrane 膜 Fouling 沾污Methane 甲烷 Furnace 炉膛Mill 磨煤机 Generator 发电机Molecule 分子 Geological 地质的Molten 熔化 Girth 环形Nitric oxide 氮氧化物 Govern 控制、调节Nonpressure 非承压的 Gravity 重力Nontoxic 无毒的 Header 联箱,集箱Organisms 有机体 Helical 螺旋状的Oxidation 氧化 Helium 氦Peat 泥煤 Heterogeneous 不均匀的Pendants superheat platen 悬吊式屏式过热器 Hopper 斗,料斗Pentane 戊烷 Husk 壳,外壳Petrochemical 石油化工制品Hydraulic 水力的,液压的Petroleum 石油制品 Ignite 点火Plasma spray coating 等离子喷涂Impurity 杂质Platen 屏 Inert 惰性Polymer 聚合物 Inferior 低级的,劣质的Pores 气孔,小孔 Ingredients 成分Porosity多空的 Potassium 钾Slurry 水煤浆 Prandtl numbers 普朗特数Sodium 钠 Prefabricated 预制的Solvents 溶剂 Premium fuel 优质燃料Sootblower 吹灰器 Pressure loss 压力损失Sour gas 含硫气体 Primary air 一次风Specification 规格 Propane 丙烷Stable ignition 稳定着火Proximate analysis 工业分析Stanton number 斯坦顿数 Pulp 纸浆Saturated 饱和的 Pyrites 黄铁矿Straw 稻草 Radius 半径,范围Steam line blowing 蒸汽管路吹灰Rare earth element 稀土元素Steams 茎,杆 Recuperator 间壁式换热器Stress corrosion 应力腐蚀Regenerator 回热器,蓄热器Structural formula 结构式Regulate 控制,调节Stud 双头螺栓 Repercussions 反应Subbituminous 贫煤,次烟煤Reservoirs 储气罐Suction 真空,负压 Residuale fuel oil 渣油Sulphur 硫 Resonant 共振Superheater 过热器 Retract缩回Swamp 沼泽 Reynolds number 雷诺数Sweet gas 无硫气 Rigid 刚性的,紧密地Switchgear 配电装置,开关装置Rollers 辊子Temperature-entropy 温熵图 Scale 水垢,Tenacious 黏的 Seal 密封Thermodynamics 热力学Sedimentary 沉积Tube bundles 管束 Serpentine tube 蛇形管Tubular 管状的 Shale 页岩Turbine 汽轮机 Silica 二氧化硅Velocity 速度 Silt 淤泥Vertical spidle mill 中速磨,立轴磨Single-phase 单相Vessel 容器 Skin casing 外护板Viscosity 黏度 Slag 结渣V olumetric expansion 体膨胀Vulnerable 易损的,薄弱的DEH 数字电液系统 Wear磨损DNB 偏离核态沸腾 Welded 焊接FDF 送风机 Wingwall屏式凝渣管FGD 烟气脱硫 Yttrim 釔FSSS 炉膛安全检测保护系统Abbreviations HRB 回热锅炉 AFBC 常压流化床燃烧IDF 引风机 AFCO 燃料自动切断IGCC 整体煤气化联合循环 AFWC 给水自动切断LMTD 对数平均温差 ASME 美国机械工程师协会MFT 主燃料切断 ATM 标准大气压MUF 锅炉补给水 BFP 锅炉给水泵NWL 正常水位 BUT 按钮OFA 火上风,燃尽风 BWC锅炉水浓度PFBC 增压流化床燃烧 BYP 旁路SSC 刮板除渣机 CFBB 循环流化床锅炉TGA 热重分析仪 MCR 最大连续蒸发量UBC 未燃烧 DAS 数据采集系统WFGD 湿法烟气脱硫 2.1 Introduction Boilers use heat to convert water into steam for a variety of applications. Primary among these are electric power generation and industrial process heating. Steam has become a key resource because of its wide availability, advantageous properties and non toxic nature. The steam flow rates and operating conditions can vary dramatically; from 1000lb/h (0.1kg/s) in one process use to more than 10 million lb/h (1260kg/s) in large electric power plant; from about 14.7 psi (1 bar) and 212oF in some heating applications to more than 4500 psi (310bar) and 1100oF (593℃) in advanced cycle power plant. 2.1 简介SSC 锅炉利用热量使水转变成蒸汽以进行各种利用。其中主要是发电和工业供热。由于蒸汽具有有利的参数和无毒特性,因此蒸汽作为一种关键的工质(资源)被广泛地应用。蒸汽流量和运行参数的变化很大:从某一过程里1000磅/小时(0.126kg/s)到大型电厂超过10×106磅/小时(1260kg/s),压力从一些加热应用的14.7磅/ in2(1.0135bar)212F(100℃)到先进循环电厂的4500磅/ in2(310bar)1100F(593℃)。 Modern boilers can be classified by various criteria. These include end use, firing method, operating pressure, fuel and circulation method. 现代锅炉可根据不同的标准分类。这些包括最终用途、燃烧方式、运行压力、燃料和循环方式。 Utility boilers are used primarily to generate electricity in large central power stations. They are designed to optimize overall thermodynamic efficiency at the highest possible availability. A key characteristic of newer units is the use of a reheater section to increase overall cycle efficiency. 大型中心电站的电站锅炉主要用来发电。它们经过优化设计,可达到最高的热效率。新机组的关键特性是利用再热器提高整个循环效率。 A variety of additional systems also produce steam for power and process applications. These systems usually take advantage of low cost or free fuels, a combination of power cycles and process, and recovery of waste heat in order to reduce overall costs, examples of these include: 各种附加的系统也产生蒸汽用于发电及其他过程应用。这些系统常常利用廉价或免费燃料,联合动力循环和过程,以及余热回收,以减少总费用。这些例子包括: Gas turbine combined cycle (CC) use advanced gas turbines with heat recovery steam generator as part of a base cycle to use waste heat recovery and increase thermal efficiency. 燃气轮机联合循环(CC):先进的燃气轮机,将余热锅炉作为基本循环的一部分,以利用余热并提高热效率。 Integrated Gasification Combined Cycle (IGCC) adds a coal gasifier to the CC to reduce fuel cost and minimize airborne emissions. 整体煤气化联合循环(IGCC):在CC基础上增加煤气化炉,以降低燃料费用并将污染排放降到最低。 Pressurized Fluidized-bed Combustion (PFBC) includes higher pressure combustion with gas cleaning and expansion of the combustion products through a gas turbine. 增压循环流化床燃烧(PFBC):在更高压力下燃烧,包括燃气净化,以及燃烧产物膨胀并通过燃气轮机做功。 Blast furnace hood heat recovery generates steam using the waste heat from a blast furnace. 高炉排烟热量回收:利用高炉余热产生蒸汽。 Solar steam generator uses concentrators to collect and concentrate solar radiation and generate steam. 太阳能蒸汽发生器:利用集热器收集太阳辐射热产生蒸汽。 2.2 Development of Utility Boiler The modern 660MW coal-fired boiler has some 6000 tons of pressure parts which include 500 km of tubing, 3.5 km of integral piping and 30,000 tube butt welds. It is the culmination of some fifty years development and while the basic concept of pulverized fuel firing into a furnace lined with evaporator tubes, with the combustion gases then passing over convection superheater and heat recovery surface, has remained unchanged, the advancement of steam conditions, increases in unit size and the properties of the fuel fired have required major changes in materials employed, fabrication techniques and operating procedures. 2.2 电站锅炉的发展 现代660MW燃煤锅炉有大约6000吨的压力部件,其中包括500千米的受热面管材, 3.5千米连接管,和30000个管接头焊口。这是经过大约50年发展的成果,并形成了至今未变的基本概念,即煤粉在布置有蒸发管束的炉膛内燃烧,然后烟气通过对流过热器和热回收表面。蒸汽参数的提高,机组容量的增大及燃料燃烧特性改进都要求在材料、制造技术和运行程序上相应发展。 In the years immediately following the second World War, is was customary to install in a power station, a greater number of boilers than turbines, the boilers feeding a range to which the turbines were connected. This arrangement reflected the inferior availability of boilers compared with turbines but increase in boiler availability in the late 1940s led to the acceptance of unitized boilers and turbines. The change to unitized boiler and turbine allowed reheat to become practical and, with the availability of high temperature steels, there followed a continuous advance in steaming conditions to the current standard cycle of 2400 lbf/in2(165.5bar), 568℃with reheat to 568℃. To take full advantage of the more advanced steam conditions and to obtain the economies of size, the next fifteen years also saw a twenty-fold increase in unit size. 二战后的一些年里,在电厂安装锅炉的数量多于汽轮机是很常见的,锅炉提供蒸汽到母管然后到汽机。这种布置反应了锅炉的可用性低于汽轮机。四十年代后期,随着锅炉可用性的提高,锅炉和汽机开始可以相互配套使用。这一变化使再热变得可行,而且随着高温钢材可用性的提高,蒸汽参数不断变化,达到了当前的2400lbf/in2(165.5bar),568℃和568℃再热的标准循环。为充分利用更高的蒸汽参数和获得更大的经济性,在接下来的15年,机组容量又增加了20倍。 A utility normally procures plant from specialist manufactures who have responsibility for design, manufacture, erection and commissioning. While the manufactures carry out development of manufacturing process and continuously update their design methods, and change in operation conditions and size necessarily results in a new plant being of a prototype nature. While some new features can be tested in advance of construction the only real test of a new boiler design is in operation and with its associated turbine and generator. The commercial success of a new design is proved over the whole projected life of power station and utility, therefore, has to balance the immediate economic advantages of a new design in terms of improved efficiency, reduced capital costs, etc. against the risk of poor availability, need for major modifications, etc., which might result from a new development. A utility normally purchases plant against generating needs and the repercussions of poor initial availability are not only being unable to meet load demand but also having to use costly plant to make up the shortfall. This period of major advance in steam cycle and unit size therefore required quite exceptional interaction with manufacturers in design and fabrication area and development of operation and maintenance techniques to ensure that the economic gains did not prove illusory. 电站设备一般向负责设计、制造、建设和调试的专业厂商购得。同时生产厂商实施生产过程的发展,不断修正设计方法,改变必要的运行参数和容量, 从而形成新电厂的原型。虽然一些新的特性可以在安装前进行测试,但一个新设计锅炉的真正测试是和汽轮发电机组配套运行后进行的。一个新的设计获得商业成功需要通过电站在整个设计寿命中的使用来证明。因此,需要平衡考虑由效率提高、投资成本减少等带来的直接经济效益,与新设计机组可能产生的可靠性低和需要大的改进等风险。公用事业公司一般依靠发电需求购买设备,并且最初可用性较低的影响不仅不能满足负荷需求,还需要使用昂贵设备以弥补不足。因此,在对蒸汽循环及机组容量进行较大改进的时期,必须和厂商在设计、制造领域,以及运行、维护技术领域密切合作,以保证经济利益的可靠。 2.3 Fuel and combustion The fuels used in most boilers are coal, natural gas and oil. However, during the past few decades, nuclear energy has also begun to play a major role in at least the electric power generation area. Also, an increasing variety of biomass materials and process byproducts have become heat sources for steam generation. These include peat, wood and wood wasters, straw, coffee ground, corn husks, coal mine wastes (culm)[煤屑], waste heat from steelmaking furnaces and even solar energy. 2.3 燃料及燃烧 大部分锅炉以煤、天然气和石油作为燃料。然而,在过去的几十年里,至少在发电领域核能开始扮演一个主要角色。同样,不断增加的各种生物质和工业副产品也成为生产蒸汽的热源。这些包括泥煤、木材及木材废弃物、麦秆、咖啡渣、玉米秆、煤矿废弃物(煤屑)、炼钢炉废热甚至太阳能。 The dominant fuel in modern U.S. central stations is coal, either bituminous, sub-bituminous or lignite. While natural gas or fuel oil may be the fuel of choice for selected future fossil fuel power plants, coal expected to continue its dominant role in supplying energy to new, base power utility power station boilers. 现代美国中心电站以煤作为主要燃料,使用烟煤、次烟煤或褐煤。虽然天然气和燃油也许是未来化石燃料电厂的燃料选择,但对于带基本负荷的新电站,煤仍将是主要的锅炉燃料。 2.3.1 Coal classification A coal classification system is needed because coal is a heterogeneous substance with a wide range of composition and properties. The properties of a typical China coal are showed in table 2-1. Coals are typically calssified by rank. This indicates the progressive alteration in the coalification process from lignite to subitiminous, bituminous and anthracite coals. The rank indicates a coal’s geological history and characteristics. 表2-1(27页) 2.3.1 煤的分类 由于煤是一种不均匀的物质,且其组成和特性变动很大,所以建立煤的分类系统是很必要的。中国煤的性质如表2-1所示。以煤阶进行煤的分类是典型的做法。这表现为煤化程度的大小:从褐煤到贫煤、烟煤以及无烟煤。煤阶表明了煤的地质历史和主要特性。 The system used in the U.S. for classifying coal by rank was established by the American Society for Testing and Materials (ASTM). ASTM classification is a system which uses the volatile matter and fixed carbon(FC) results from the proximate analysis and the heating value of the coal as ranking criteria. This system aids in identifying commercial uses of coals and provides basic information regarding combustion characteristics. 现在美国应用的煤分类标准是由美国材料试验学会(ASTM)建立的。其分类是通过煤的工业分析所确定的挥发分和固定碳的含量以及煤的发热量作为分类标准。这套系统目的在于确定煤的商业使用价值,并提供关于煤燃烧特性的基本信息。 2.3.2 Combustion systems The combustion of fossil fuels within a boiler for steam raising purposes has been practised for many years. However, within the past two decades combustion techniques have been considerably refined in order to reduce atmospheric emissions and pollution to practicable minimum. 2.3.2 燃烧系统 锅炉内化石燃料燃烧以产生蒸汽的技术已成熟多年。然而,在过去的二十多年中,为了将大气排放和污染降到可行的最低程度,燃烧技术得到了很大程度的提高。 Oil combustion systems Oil is burned in all utility boiler, in coal boiler to ignite the coal burners, to warm up the boiler and raise pressure before coal is admitted, and in oil fired boilers as the main load fuel. In general, the oil is residual Fuel Oil of 3500 sec. to 6500 sec. viscosity. In order to burn effectively this oil must be heated to 120-130℃and divided or atomized into very small droplets. 油燃烧系统 所有的电站锅炉都燃用油,在燃煤锅炉中点燃煤粉,在煤进入炉膛之前加热炉膛并升压,而在燃油锅炉中则作为主要负荷燃料。一般地,燃油都是粘度在3500 sec到6500sec的残渣燃料油。为了有效的燃烧,这些油必须被加热到120~130℃并被良好地分散或雾化成很小的微滴。 The use of this oil, cheaper than normal distillate (diesel/gas oil etc.) causes problems, amongst them, acid smuts and dust emissions. The smut problem is caused by the sulfur content of the oil, which may be up to 3%. In the early 1960s the utility undertook an intensive development program on oil burner design, which was aimed at removing the problems of oil fired emissions. This resulted in an oil burner, “the Standard Burner”which reduced emissions of carbon at very low excess air levels. Considerable work was also done in order to ensure that burner in a boiler received the same amount of air, and the current operating level for excess air in an oil fired unit is 2%. 燃用渣油,要比一般的馏分油(柴油,汽油等)便宜,但又带来一些问题:酸性污染物和粉尘的排放。酸性污染问题是由石油中的硫产生的,硫分的含量有时可高达3%。在20世纪60年代早期,人们对油燃烧器设计进行了深入研究和开发,目的在于解决燃油的排放问题。由此诞生了一种油燃烧器——“标准燃烧器”,它可以在非常低的过量空气系数下减少碳排放。为保证锅炉中每个燃烧器获得同样多的空气也做了大量的工作。目前油燃烧过量空气系数运行水平为2%。 Coal combustion systems Coal burners have been developed in a similar fashion to the oil burners, and considerable emphasis is placed upon feeding each burner with carefully regulated amounts of coal and oil. All coal fired boilers in the utility fire pulverized coal (produced by milling) which is very finely divided coal carried to the burner on a stream of air (primary air). The design effort directed at flow equalization has produced boilers which can be operated at lower excess air levels than previously, and thus have increased overall efficiency without increasing unburned carbon levels in the ash. 煤燃烧系统 煤燃烧器的发展模式同油燃烧器类似,而且重点放在准确控制每只燃烧器煤和油的供给量。实际中所有的燃煤锅炉都是燃烧煤粉(由磨煤机生产),这些煤粉经过很好的粉碎,然后由空气流(一次风)送入燃烧器。同以前相比,在流动平衡上的设计成果现在已能使锅炉在较低的过量空气水平下运行,并在不增加飞灰含碳量水平的情况下提高了总的效率。 This, when combined with the development of low NO x burners will result in reduced gaseous emission in line with EEC directives and is the main objective of two boiler conversions (both complete) to establish the level to which NO x maybe reduced in the exhaust from 500MW coal fired boilers. A NO x reduction development trial is proposed on a third boiler design, 这样,结合低NOx燃烧器的开发,就使气体排放达到欧共体的标准,这也是两代锅炉转换(已完成)的主要目的,即设定500MW燃煤锅炉可能达到的NOx排放水平。在第三代锅炉的设计中进行了进一步降低NOx的开拓性试验。 The arrangement of coal-fired system components must be determined according to economic factors as well as the attributes of the coal. The performance in terms of product fineness, mill outlet temperature, and air-coal ratio must all be determined as part of overall combustion system design. 煤燃烧系统部件的布置必须根据经济因素和煤的性质来确定。作为整个燃烧系统设计的 性能参数,煤粉细度、磨煤机出口温度、空煤比等都必须达到要求。 Low NO x combustion systems The factors affecting NO x are the proportion of nitrogen chemically combined with the fuel, peak flame temperature, the available oxygen in the flame and the residence time of the gases within the system. Some of the coal bound nitrogen is released as volatiles as the chemical structure of the coal breaks down on entering the furnace. Nitric oxide produced from atmospheric nitrogen as “thermal NO x”can be limited by minimizing residence times at high temperature, which limiting the amount of oxygen available to the fuel during the combustion stage results in the production of harmless nitrogen rather than NO x. 低NO X燃烧系统 影响NOx生成的因素包括燃料含氮量、火焰峰值温度、火焰中的可用氧量以及气流在锅炉系统中的停留时间。当煤进入炉膛其化学结构被破坏时,一些煤中的化合氮就作为挥发分被释放出来。由大气中的氮生成的一氧化氮即“热力型NOx”可以通过减少烟气在高温区域的停留时间而得到控制,这样就会控制燃烧阶段中可用氧量,最后生成的是无害氮而不是NOx。 Since coal firing requires some excess oxygen in the combustion zone to achieve total carbon burnout and nitrogen free coal is unavailable, NO x reduction has to be performed by boiler and burner design. 因为煤在燃烧区的燃烧需要一定的过量氧气以便使所有的碳燃尽,且不含氮的煤是难以获得的,因此NOx的减少必须依靠锅炉和燃烧器的设计来完成。 Gas combustion systems Natural gas has been fired at power stations for main load purposes. However, gas has not been available to the utility for some years now and it is not envisaged that, as a premium fuel, it will ever be available again in any quantity. Propane is widely used in igniters for the oil burners in both main oil and coal fired boilers. 天然气燃烧系统 天然气曾经作为电厂主要燃料。然而一些年来,没有太多的天然气可供电厂使用,并且人们没有正视这样的事实,即天然气作为一种优质燃料将会重新得到大量应用。 丙烷常常作为一种点火剂,广泛地应用于燃油锅炉和燃煤锅炉中的油燃烧器。 2.3.3 Fluidized-bed combustion A variation on PC combustion is fluidized bed combustion in which coal is burned with air in a fluid bed, typically a circulating fluidized bed (CFB). CFBs are best suited to low-cost waste fuels and low-quality or low heating value coals. Crushed coal and lime stone are fed into the bed, where the lime stone undergoes calcination to produce lime (CaO). The fluidized bed consist only of lime, with a few percent coal and recirculated coal char. The bed operates at significantly lower temperatures, about 427℃(800oF), which thermodynamically favors low NO x formation and SO2 capture by reaction with CaO to form CaSO4. The steam cycle can be subcritical and potentially supercritical, as with PC combustion, and generating efficiencies are similar. The primary advantage of CFB technology is its capacity to capture SO2 in the bed, and its flexibility to a wide range of coal properties, including coals with low heating value, high ash coals and low volatile coals, and changes in coal type during operation. Several lignite-burning CFB units have been constructed recently, and CFBs are well suited to co-firing biomass. 2.3.3 流化床燃烧 流化床燃烧是煤粉燃烧方式的一种,采用这种燃烧方式时煤在空气中的燃烧发生在流化床中,典型的是循环流化床。循环流化床最适合于燃烧低成本废弃燃料、低品质或低热量煤。将煤粒和石灰石投入到床中,石灰石在床内煅烧成石灰。流化床中主要是石灰和少量的煤,煤焦在其中循环。运行中的床温很低,只有427℃ (800℉),在这个温度下的热力学环境有利于减少NOx的形成和捕集SO2,使之与CaO 反应生成CaSO4。对于煤燃烧,蒸汽循环可以是亚临界,也可能是超临界,它们具有相近的发电效率。循环流化床技术的最大的优点是它在床中捕捉SO2的能力和它对煤质的广泛适应性,其中包括低热量煤、高灰分煤和低挥发分煤,并且在运行中可以改变煤种。循环流化床锅炉适合与生物质共燃,最近就新建了几台燃烧褐煤的循环流化床机组。 The most commonly used circulating fluidized bed combustor is shown in Fig. 2-1. Coal and coal char are burned while the coal, coal char, coal ash and sorbent are carried up through the furnace by combustion air. The solid materials are separated from the flue gas in 图2-1 循环流化床锅炉设计布置实例 教材29页 the cyclone and pass through a convective section where heat is transferred to boiler tubes generating high-pressure steam. Additional steam is generated by removing heat from the hot solids in the fluidized bed heat exchange section before they are returned to the furnace. There are no boiler tubes in the lower furnace because the rapid moving solids cause excessive erosion. NO x is managed through low temperature and staged injection of the combustion air. SO x emission is controlled via the lime sorbent in the bed. This saves significant capital for flue gas cleanup, but low SO x emission require low-sulfur coal, and NO x emissions are limited by combustion chemistry. Extremely low emissions levels would require the addition of flue gas clean-up units with the attendant cost increase. The largest CFB unit is 330MW e in China, and 600MW units have been designed, but no unit of this size has been built. 如图2-1所示,目前最常用的流化床技术是循环流化床燃烧技术。煤和煤焦燃烧的同时,空气携带煤、煤焦、煤灰和脱硫剂通过炉膛。固体材料通过旋风分离器从烟气中分离出来,然后通过对流烟道部分,烟气把热量传给炉管以产生高 压蒸汽。另一部分蒸汽是由流化床中的高温固体在返回炉膛前放出热量产生的。炉膛内固体快速运动会引起过量的磨损,因此炉膛底部不安装炉管。通过低燃烧温度和空气分级燃烧来控制NOx的生成。SOx排放通过床中石灰脱硫剂控制。这些为烟气净化节省了大笔的投资,但是低的SOx排放需要燃烧低硫分煤,并且NOx的排放受燃烧反应的限制。极低的排放需要额外的烟气净化设备,同时会增加相应的维护成本。在中国最大的流化床锅炉是330MWe,设计最大的锅炉是600 MWe,但是还没有投建。 2.4 Pulverizing System The development and growth of coal pulverization closely parallels the development of pulverized coal-firing technology. In order to achieve efficient combustion in the boiler furnace the coal leaving the burner must be sized so that it can burn rapidly and this means that it must be in the form of small particles that can quickly be heated up to ignition temperature and get ready access to the combustion air. The job of the pulverizers is to grind the feed coal down to a suitable size for the above purposes. Early systems used ball-and-tube pulverizers to grind coal and holding bins to temporarily store the coal before firing. Evolution of the technology to eliminate the bins and direct fire the coal pneumatically transported from the pulverizers required more responsive and reliable grinding equipment. Vertical air-swept pulverizers met this need. 2.4 制粉系统 煤粉制备与煤粉燃烧技术的发展是同步的。为了使煤在炉膛中有效燃烧,煤在离开燃烧器时必须被粉碎到一定的大小,这样才能迅速燃烧,这就意味着煤必须被加工成小颗粒,才能被迅速加热到着火温度并和空气良好混合。磨煤机的工作就是把煤磨碎到符合上述要求的合适的大小。较早的系统使用筒式球磨机磨煤粉,并且在燃烧前利用储仓暂时储存煤粉。如果对该技术进行改进,去掉中间储仓而将从磨煤机出来的煤粉直接送去燃烧,就会对磨煤机的可靠性有很高的要求。 On pressurized pulverizing systems the primary air fan which provides the pulverized fuel transport medium is situated before the pulverizer and there handle clean air and is not subject to erosive wear as is an exhaust fan. This is the chief advantage of the pulverizing system, however the pulverizer does need sealing air which is usually provided by a separate fan at a pressure higher than that of the pulverizer interior. 正压制粉系统中,提供煤粉输送介质的一次风机位于磨煤机前,因而它运送的是清洁空气,不会像排粉风机一样受到侵蚀磨损。这是正压磨煤系统的主要优点。然而,磨煤机需要由单独风机提供高于磨煤机内部压力的密封空气。 A disadvantage of the pressure type pulverizer is that it must be absolutely air tight in order to avoid pulverised fuel leakage to the atmosphere. Conversely the standard of sealing on a suction pulverizer need not be so high, but it must not be allowed to deteriorate too far as the inwards leakage, being cold air, will make it difficult to dry the wetter coals. This leakage air is also unmeasured as regards its quantity, and if excessive under certain conditions produces a high air/coal ratio which may be explosive should there be an ignition source. 正压磨煤机的一个缺点是它必须完全由空气密封以避免煤粉泄露到大气中。相对来说,负压磨煤机的密封标准并不需要这样高,但也不允许漏入过多空气,因为冷空气难以干燥湿煤。这种方式泄露的空气量也无法测量,如果达到高的空/煤比,遇到明火则可能发生爆炸。 2.4.1 Vertical air-swept pulverizers The roller passes over a layer of granular material, compressing it against a moving table. The movement of the roller causes motion between particles, while the roller pressure creates compressive loads between particles. Motion under applied pressure within the particle layer cause attrition (particle breakup by friction) which is the dominant size reduction mechanism. The compressed granular layer has a cushioning influence which reduces grinding effectiveness but also reduces the rate of roller wear dramatically. When working surfaces in a grinding zone are close together, near the dimensions of single product particles, wear is increased by three body contact (roller, particle and table). Wear rates can be three body contact has also been observed in operating mills when significant amounts of quarts bearing rock are present in sizes equal to or greater than the grinding layer thickness. 2.4.1 中速磨 磨辊在一层耐磨层上滚动,通过移动的磨盘把煤压碎。磨辊的运动引起煤粒间的相互运动同时磨辊的压力在煤粒间形成压力负荷。一定压力下在煤粒层上的运动引起摩擦(煤粒依靠摩擦力破碎),这就是磨煤机的工作原理。耐磨层具有缓冲作用,虽然降低了磨的效率,但也大大降低了磨辊的磨损。当磨煤区的工作面间距离很近时,比如到了一个颗粒大小,三个部件(磨辊,颗粒,磨盘)间的磨损就会大大增加,磨损速率会是正常磨煤机的100倍。当带有石英的石头尺寸等于或大于磨层厚度时,也会在运行中发生三部件接触的磨损。 As grinding proceeds, fine particles are removed from the process to prevent excessive grinding, power consumption and wear. Fig.2-2 presents a simplified MPS vertical pulverizer, showing the essential elements of a vertical air-swept design. A table is turned from below and rollers, called tires, rotate against the table. Raw coal is fed into the mill from above and passes between the rollers and the rotating table. Each passage of the particles under the rollers reduces the size of coal. The combined effects of centrifugal force and displacement of the coal layer by the rollers spills partly ground coal off the outside edge of the table. An upward flow of air fluidizes and entrains this coal. 随着磨煤的进行,为了防止过度磨制和降低能耗及磨损,磨好的煤粉从磨煤机中排出。图2-2是MPS型中速磨的示意图,显示了中速磨煤机的基本组成。在磨煤机下部有一个转动的台面,称为辊胎的辊子在台面上滚动。原煤由上部的磨煤机给入,然后在磨辊和转动的磨盘间经过,磨辊下的煤就被磨碎了。离心力加上磨辊对煤层的沉降力共同作用,将部分磨好的煤粉挤出磨盘边缘,由上升的空气流流化并携带这些煤粉。 图2-2 磨煤机内部的颗粒循环 The point where air is introduced is often called the air port ring, nozzle ring or throat. Rising air flow, mixed with the coal particles, creastes a fluidized particle bed just above the throat. The air velocity is low enough so that it entrains only the smaller particles and percolates with them through the bed. The air-solids flow leaving the bed forms the initial stage of size separation or classification. The preheated air stream also dries the coal to enhance the combustion process. 空气进入点一般称为进风环,喷嘴环或者喉部。上升的空气流与煤粒混合在进风环上面产生流化的颗粒床。空气的流速很低,以至于只能携带少部分的煤粒通过床层过滤。空气和煤粒离开流化床形成了第一步的分离。预热的空气同时干燥煤粉以保证煤粉的有效燃烧。 Vertical pulverizers are effective drying devices. Coal with moisture content up to 40% have been successfully handled in vertical mills. Higher moisture levels are possible, but the primary air temperature needed would required special structure materials and would increase the chance of pulverizer fires. A practical moisture limit is 40%, by weight, requiring air temperature to 750oF (398℃). 立式中速磨是有效的干燥装置。即使煤中水分到40%也能在中速磨中很好地得到干燥,干燥水分再高些的煤粉也是可能的,但是需要的一次风温度则要求使用特殊材料,并且增加了磨煤机着火的可能。实际运行的水分最大值是40%(质量),此时要求一次风温高达750℉。 As the air-solids mixture flows upward, the flow area increase and velocity decreases returning larger particles directly to the grinding zone. The final stage of size separation is provided by the classifier located at the top of the pulverizer. This device is a centrifugal separator. The coal-air mixture flows through openings angled to impart spin and induce centrifugal force. The coarser particles impact the perimeter, come out of suspension and fall back into the grinding zone. The finer particles remain suspended in the air mixture and exit to the fuel conduits. 空气煤粉向上流动时,由于流动面积增大使流动速度降低,大粒径的煤粒就会回落到磨盘上。最后的煤粉分离采用磨煤机上部的粗粉分离器,粗粉分离器是利用离心力的分离装置。风粉混合物以一定角度进入,从而发生旋转并产生离心力。粗一点的煤粉冲击到分离器的周边,不再保持悬浮状态而回落到磨盘上。风粉混合物中的细煤粉颗粒保持悬浮状态,并最终上升进入煤粉管。 2.4.2 Low speed pulverizers The oldest pulverizer design still in frequent use is the ball and tube mill. This is a horizontal cylinder, partly filled with small diameter balls (Fig.2-3). The cylinder is lined with wear resistant material contoured to enhance the action of the tumbling balls and the balls fill 25% to 30% of the cylinder volume. The rational speed is 80% of that at which centrifugal force would overcome gravity and cause the balls to cling to the shell wall. Grinding is caused by the tumbling action which traps coal particles between balls as they impact. 图2-3 典型的钢球磨制粉系统 2.4.2低速磨 筒式钢球磨是现在仍在使用的最早的磨煤机。它是一个卧式的筒体,里面装有小直径的钢球。筒体内衬耐磨材料以加强球的滚动,球占筒体总容积的25%到30%。转速取离心力可以克服重力时速度的80%,这样可以使钢球贴在筒体的内壁上。通过筒体转动时钢球的碰撞来实现煤粉的磨制。 Ball-and-tube mills may be either single or double ended. In the former, air and coal enter through one end and exit the opposite. Double ended mills are fed coal and air at each end and ground-dried coal is extracted from each end. In both types, classifiers are external to the mill and oversize material is injected back to the mill with the raw feed. Ball-and-tube mills do not develop the fluidized bed which is characteristic of vertical mills and the poor mixing of air and coal limits the drying capability. When coal with moisture over 20% must be ground in ball-and-tube mills, auxiliary equipment, usually crusher dryers, must be used. 筒式钢球磨有单进单出和双进双出两种。对于单进单出型,空气和煤从一端进入从另一端流出。双进双出型磨煤机是空气和原煤从两端进入,磨好的干燥的煤粉从两端流出。对于这两种类型,粗粉分离器布置于磨煤机的外部,粒径过大的粗粉被送回到磨煤机与原煤混合。筒式钢球磨不具有类似立式磨的流化床特点,同时由于空气和煤粉的混合不均匀限制了干燥能力。如果筒式钢球磨要磨的煤中水分高于20%,就必须使用辅助的干燥装置,比如破碎干燥机。 Ball-and-tube mills have largely been supplanted by vertical air-swept pulverizers for new boilers. They typically require larger building volume and higher specific power consumption than the vertical air-swept pulverizres. They are also more difficult to control and have higher metal wear rates. They are, however, well suited for grinding extremely abrasive, low moisture and difficult material such as petroleum coke. Their long time makes them effective for fine grinding. 对新建锅炉来说,中速磨已经大量的取代了筒式钢球磨。相对于中速磨,筒式钢球磨往往需要大的建筑空间和较高的能耗。同时,筒式钢球磨难于控制且有较高的磨损速度。但是,筒式钢球磨能很好的适应极具磨损作用的、低水分的难磨燃料,比如石油焦。煤在其中较长的停留时间可以实现有效的磨制。 2.4.3 Pulverizing systems Pulverizers are part of lager systems, normally classified as either direct-fired or storage. In direct firing, coal leaving each mill goes directly to the combustion process. The air, evaporated moisture and the thermal energy which entered the mill, along with the ground coal, all become part of the combustion process. Storage systems separate the ground coal from the air, evaporated moisture and the thermal energy prior to the combustion process. Stored ground coal is then injected with new transport air to the combustion process. Bin storage systems are seldom used in steam generation today, but are still used with special technologies such as coal gasification and blast furnace coal injection. Of the 1000 or so MPS pulverizers in service in the U.S. more than 90% are used in direct-fired systems. 2.4.3制粉系统 磨煤机只是庞大的制粉系统的一部分,制粉系统一般有直吹式和中储式两种。在直吹式系统中,从磨煤机出来的煤粉直接参与燃烧过程,同时参与的还有空气、水蒸汽和通入磨煤机的热能。中储式系统把煤粉从空气、水蒸汽和通入磨煤机的能量中分离开再去燃烧。储仓中的煤粉由新的一次风输送到燃烧设备。目前生产蒸汽的过程中很少采用中储式制粉系统,但是很多特殊的场合仍然需要,比如煤气化和高炉投煤。目前在美国运行的中速磨大约有1000台,其中99%以上的是直吹式系统。 The essential elements of a direct-fired system are: (1) A raw coal feeder that regulates the coal flow from a silo or bunker to the pulverizer. (2) A heat source that preheat the primary air for coal drying. (3) A pulverizer (primary air) fan that is typically located ahead of the mill (pressurized mill) as a blower, or after the mill (suction mill) as an exhauster. (4) A pulverizer, configured as either a pressurized or suction unit. (5) Piping that directs the coal and primary air from the pulverizer to the burners. (6) Burners which mix the coal and balance of combustion air, and (7) Control and regulating devices. 直吹式系统的主要部件有: (1) 给煤机,通过煤仓调节进入磨煤机的给煤量。 (2) 热源,用来预热干燥煤粉的一次风 (3) 一次风机,典型的情况是作为鼓风机布置于磨煤机之前(正压系统),或作为排粉风机 位于磨煤机之后(负压系统) (4) 磨煤机,作为正压系统或负压系统的主体部分。 (5) 管路,把煤和一次风从磨煤机输送到燃烧器 (6) 燃烧器,混合煤粉和平衡燃烧空气 (7) 控制和调节装置 These components can be arranged in several ways on project economics. With pressurized pulverizers, the choice must be made between hot primary air fans with a dedicated fan for each mill, or cold fans located ahead of a dedicated air heater and a hot air supply systems have a lower capital cost because a dedicated primary air heater is not required. Cold fan systems have lower operating costs which, on larger systems, may offset the higher initial cost. 根据工程的经济性,以上部件可以按照不同的形式布置。在正压系统中,需要做出选择,是采用热一次风风机(每个磨一个风机),还是采用冷风风机(布置在特定的空气加热器前面)。热风输送系统初始投资费用较低,因为不需要特定的空气加热器。对大型机组而言,冷风风机系统具有较低的运行费用,可以补偿较高的初始投资。 The terminology for air-swept pulverizers refers to the air introduced for drying and transport as primary air. Control of primary air is of vital importance to proper pulverizer system operation. For direct-fired or storage systems and hot fan and cold fan systems, common control elements are found. Primary air must be controlled for flow rate and pulverizer outlet temperature. This control is achieved by three interrelated damper s. 中速磨这个术语是指空气引入到磨煤机中作为一次风用来干燥和输送煤粉。一次风的控制对制粉系统的正常运行是非常重要的。不管是直吹式还是中储式制粉系统,也不管采用热风还是冷风风机系统都需要普遍的控制。必须控制一次风量和磨煤机出口温度,这个控制由三个相互联系的节气阀来实现。 Two of these, hot and cold air dampers, regulate air temperature to the mill and these dampers are usually linked so that as one opens, the other closes. The third damper is independent and controls air volume. Some manufacturers use only two dampers, but lack of stability or slow load change response can offset the cost advantages. 其中的两个是热和冷的节气阀,用来调节磨煤机的空气温度,这些节气阀通常是相互关联的,从而保证一个开启另一个则关闭。第三个节气阀是独立的,用来控制空气容积。一些生产商只采用两个节气阀,但是缺乏稳定性,而变负荷时的低反应能力抵消了初投资的减少带来的好处。 2.5 System Arrangement and Key Components. Modern boilers are a complex configuration of thermal-hydarulic (steam and water) sections which preheat and evaporate water, and superheat steam. These surfaces are arranged so that:1) the fuel can be burned completely and efficiently while minimizing emissions, 2) the steam is generated at the required flow rate, pressure and temperature, and 3) the maximum amount of energy is recovered. A relatively simple coal-fired utility boiler is illustrated in Fig.2-4. the major components in the steam generating and heat recovery system include: (1) Furnace and convection pass (2) Steam superheaters (primary and secondary) (3) Steam reheaters (4) Boiler or steam generating bank (industrial units only) (5) Economizer (6) Steam drum (7)Attemperator and steam temperature control system (8) Air heater 图2-4 燃煤锅炉(机组) 2.5 系统布置和主要部件 现代锅炉具有复杂的热力—水力(蒸汽和水)受热面结构,以预热和蒸发水,产生过热 蒸汽。这些受热面是这样布置的:(1)燃料在最小污染排放的情况下完全有效地燃烧;(2)按要求产生一定流量、压力和温度的蒸汽;(3)最大限度地回收能量。一个相对简单的燃煤电站锅炉如图2-4所示。产生蒸汽和热量回收系统中的主要部件有:(1)炉膛和对流烟道(2)蒸汽过热器(第一级和第二级)(3)蒸汽再热器(4)产生蒸汽的管组(仅仅存在于工业锅炉中)(5)省煤器(6)汽包(或锅筒)(7)减温器和蒸汽温度控制系统(8)空气预热器 2.5.1 Furnace The furnace is a large enclosed open space for fuel combustion and for cooling of the flue gas before it enters the convection pass. Excessive gas temperatures leaving the furnace and entering the tube bundles could cause particle accumulation on the tubes or excessive tube metal temperature. The specific geometry and dimensions of the furnace are highly influenced the fuel and type of combustion equipment. In this case, finely ground or pulverized coal is blown into the furnace where it burns in suspension. The products of combustion then rise through the upper furnace. The superheater, reheater and economizer surfaces are typically located in the horizontal and down-flow sections of the boiler enclosure (convection pass). 2.5.1炉膛 炉膛是一个四周封闭的开口大空间,燃料在其中燃烧,产生的烟气在进入对流烟道前得到冷却。离开炉膛进入管束的烟气温度过高则会导致烟尘微粒沉积在管壁上或使金属管壁超温。燃料和燃烧设备的类型对炉膛的几何形状和尺寸影响很大。在这种情况下,磨细的煤粉被送入炉膛悬浮燃烧。燃烧产物上升穿过炉膛上部。过热器、再热器和省煤器等受热面被特定布置于锅炉围墙内部的水平或垂直烟道内(对流烟道)。 In modern steam generators, the furnace and convection pass walls are composed of steam-or-water cooler carbon steel or low alloy tubes to maintain wall metal temperatures within acceptable limits. These tubes are connected at the top and bottom by headers, or manifolds. These headers distribute or collect the water, steam or steam-water mixture. The furnace wall tubes in most modern units also serve as key steam generating components or surfaces. The tubes are weld ed together with steel bars to provide membrane wall panels which are gas-tight, continuous and rigid. The tubes are usually prefabricated into shippable membrane panels with openings for burners, observation doors, sootblowers (boiler cleaning equipment) and gas injection ports. 在现代蒸汽发生器中,炉膛和对流烟道的炉墙是由碳钢或低合金钢的汽冷或水冷壁组成,以维持炉墙的金属温度在允许的范围内。这些管子在顶部和底部由联箱或母管连接在一起。这些联箱用来分配或收集水、蒸汽或汽水混合物。在最现代化的机组中,炉墙管道也作为主要的产生蒸汽的部件或受热面。这些管子用钢条(专业上叫鳍片)焊接在一起,组成气密的、连续的、刚性的膜式墙。这些管道通常预制成可装运的膜板,并且板上留有燃烧器口、观察孔、吹灰器口(锅炉清洁设备)和燃气喷入口。 2.5.2 Superheaters and reheaters Superheaters and reheaters are specially designed inline tube bundles that increase the temperature of saturated steam. In general terms, they are simple-phase heat exchangers with steam flowing inside the tubes and the flue gas passing outside, generally in cross flow. These critical components are manufacture d from steel alloy material because of their high operating temperature. They are typically configured to help control steam outlet temperatures, keep metal temperatures below acceptable and control steam flow pressure loss. 2.5.2 过热器和再热器 过热器和再热器被专门设计成顺列管束,用来提高饱和蒸汽的温度。一般形式下,它们是简单的单相换热器,蒸汽在管道内流动,烟气从外面经过,通常二者是交叉流动。由于其较高的运行温度,这些关键的部件一般用合金钢制造。典型的布置通常有利于控制出口蒸汽的温度,保持金属温度低于其可接受的极限和控制蒸汽流动的压力损失。 The main difference between superheaters and reheaters is the steam pressure. In a typical drum boiler, the superheater outlet pressure might be 2700 psi (186bar) while the reheater outlet might be only 580 psi (40bar). The physical design and location of the surfaces depends on the desired outlet temperatures, heat absorption, fuel ash characteristics and cleaning equipment. These surfaces can be either horizontal or vertical. The superheater and sometimes reheater are often divided into multiple sections to help control steam temperature and optimize heat recovery. 过热器和再热器的主要区别是蒸汽压力。在典型的汽包锅炉中,过热器的出口压力为2700psi(186bar),而再热器的出口压力为580psi(40bar)。受热面的结构设计和布置取决于所要求的出口温度、吸热量、燃料的灰分特性和清洁设备。这些受热面可以呈水平或垂直布置。过热器和有的再热器经常被分为几段以利于控制蒸汽温度和优化热量回收。 Superheater types Two basic types of superheaters are available depending on the mode of heat transfer from the flue gas. The original type was the convection superheate r, for gas temperatures where the portion of heat transfer by radiation from the flue gas is small. With a unit of this design, the steam temperature leaving the superheater increase with boiler output because of decreasing percentage of unit heat input that is absorbed in the furnace. This result in more heat available for superheater absorption. Because convection heat transfer rate are almost a direct function of gas flow rate and therefore boiler output, the total absorption in the superheater per pound of steam, and therefore steam temperature increase with boiler output (see Fig.2-5). This effect is increasingly pronounced the farther the superheater is located from the furnace and the lower the gas temperature entering the superheater. 过热器的类型 根据烟气侧的传热方式,过热器可分为两种基本类型。最初的一种是对流过热器,从烟气吸收的辐射热量很小。在这样的机组中,蒸汽温度随锅炉负荷的增加而升高,这是因为炉 膛吸收单位输入热量的百分比下降。这导致过热器吸收了更多的热量。因为对流传热速率几乎与烟气流率即锅炉负荷成直线关系,因此,过热器中每磅蒸汽的总吸热量以及蒸汽的温度都会随锅炉负荷而增长(见图2-5)。过热器布置得离炉膛越远,进入过热器的烟气温度越低,这种效果越明显。 A radiant superheater receives the energy primarily by thermal radiation from the furnace with little energy from convective heat transfer. It usually takes the form of widely spaced [24 in.(609.6mm) ] or large side spacing steam-cooled wingwalls or pendants superheat platens 图2-5 布置有对流和辐射过热器的在一定负荷范围内出口汽温基本均匀located in the furnace. It is some times incorporated into the furnace enclosure curtain walls. Because the heat absorption by furnace surfaces dose not increase as rapidly as boiler output, the radiant superheater outlet temperature declines with an increasing boiler output, as shown in Fig.2-5. 辐射式过热器主要吸收来自炉膛的辐射热,对流传热量很少。一般采用较大间距(24英寸或很大的侧边距)的屏式凝渣管或悬吊屏式过热器的型式布置于炉膛中。有时这种过热器和包墙管组合成一体。因为炉膛受热面吸热不如锅炉负荷增长快,所以随着锅炉负荷的增长辐射式过热汽温度反而下降,如图2-5所示。 In certain cases the two opposite sloping curves have been coordinated by the series combination of radiant and convectional superheaters to give a flat superheat curve over a wide load range, as indicated in Fig.2-5. A separately fired superheater can also be used to produce a flat superheat curve. 某些情况下,在较大的负荷范围内,这两条变化趋势相反的曲线可由一系列联合的辐射、对流过热器叠加为平缓的过热曲线,如图2-4所示。一个单独加热的过热器也能产生平缓的过热曲线。 The design of radiant and convective superheaters requires extra care to avoid steam and flue gas distribution difference which could lead to tube overheating. Superheaters generally have steam mass fluxes of 100,000 to 1,000,000 lb/h ft2[136 to 1356 kg/(m2·s)] or higher. These are set to provide adequate tube cooling while meeting allowable pressure drop limits. The mass flux selected depends upon the steam pressure and temperature as well as superheater thermal duty. In addition, the higher-pressure loss associated with higher velocities improves the steam side flow distribution. 辐射和对流式过热器的设计需要特别注意避免因蒸汽和烟气流量分配不均而造成的管子超温。一般过热器中有100,000到1,000,000lb/hft2(136到1356kg/m2s)或更多的蒸汽质量流量。这种设置是在允许压降的范围内对管子内部进行充分的冷却。质量流量的选择取决于蒸汽的压力和温度,还有过热器的热负荷。此外,高速下的高压损会改善蒸汽侧流场分布。 2.5.3 Economizers and heaters. Economizers and air heaters perform a key function in providing high overall boiler thermal efficiency by recovering the low level, i.e., low temperature, energy from the flue gas before it is exhausted to the atmosphere. For each 40oF (22℃) that the flue gas is cooled by economizer or air heater, the overall boiler efficiency increases by approximately 1%. Economizers recover the energy by heating the boiler feedwater while air heaters heat the combustion air. Air heating also enhances the combustion of many fuels and ensuring stable ignition. 2.5.3 省煤器和空气预热器 省煤器和空气预热器在提高锅炉总的热效率方面发挥着重要作用, 它们回收了排入大气前烟气中的低品位热量,也就是低温热量。烟气被省煤器或空气预热器冷却每40℉(22℃),总的锅炉效率就会被提高大约1%。省煤器吸热加热锅炉给水,空气预热器则是加热燃烧空气。热空气强化了多种燃料的燃烧,并保证了稳定的着火。 Economizers The economizer is a counterflow heat exchanger for recovering energy from the flue gas beyond the superheater and, if used, the reheater. It increases the temperature of the water entering the steam drum. The tube bundles are typically an arrangement of parallel horizontal serpentine tubes with the water flowing inside but in the opposite direction (counterflow) to the flue gas. Tube spacing is as tight as possible to promote heat transfer while still permitting adequate tube surface cleaning flue gas side pressure loss. By design, steam is usually not generated inside these tubes. 省煤器 省煤器是一种逆流布置的热交换器,在流过过热器或再热器(如果使用)的烟气中获取能量。它提高了汽包进水的温度。其管束布置是一种典型的平行水平蛇形管束,水在管内流动而烟气在外侧反方向(逆流)流动。管子间尽量紧密以强化传热,同时要求有足够的管子表面清洁空间和合理的烟气侧压损。根据设计,这些管子内一般不会产生蒸汽。 The most common and reliable economizer design is the bare tube, in-line, crossflow type. When coal is fired, the flyash creates a high fouling and erosive environment. The bare tube, in-line arrangement minimizes the likelihood of erosion and trapping the ash as compared to a staggered arrangement. It is also the easiest geometry to be kept clean by sootblowers. However, these benefits must be evaluated against the possible larger weight, volume and cost of this arrangement. 最普通、最可靠的省煤器设计就是光管、顺列、交叉流省煤器(如图2-6)。煤燃烧后,飞灰就会产生一种高污垢、侵蚀的环境。相对于如图2-6的错列布置,这些顺列布置的光管就会尽可能减少飞灰粘附、侵蚀的可能性。这也是通过吹灰器保持清洁的最简单的几何形状。然而,这种布置的好处必须要结合它大重量、大空间以及造价进行综合评估。 To reduce capital cost, most boiler manufacturers have built economizers with a variety of fin types top enhance the controlling gas side heat transfer rate. Fins are inexpensive nonpressure parts which can reduce the overall size and cost of an economizer. However, successful application is very sensitive to the flue gas environment. Surface clean ability is a key concern. 为减少投资,大多数锅炉省煤器应用了各种鳍片以强化烟气侧的传热效率。鳍片是廉价的非承压物件(相对的有受压件pressure parts),它可减少省煤器的总尺寸和造价。然而,成功的应用对于烟气环境是非常敏感的。表面的清洁能力是一关键因素。 Air heaters The air heater utilises the heat in the boiler flue gases leaving the economizer to heat the combustion air and provide hot air for drying coal. The air outlet temperature limit in coal fired plant is directed by the coal mill exit temperature and capacity of the tempering air system with the gas outlet temperature limited by considerations of fouling of the heat transfer surface and corrosion of downstream equipment. 空气预热器 空气预热器是利用经过省煤器的锅炉烟气携带的热量加热燃烧空气,并提供干燥煤粉的热空气。在燃煤电厂中,空气预热器的出口温度受限于磨煤机的出口温度和调温风系统容量,烟气出口温度则要考虑传热表面的污染和后面设备的腐蚀情况。 On older boiler tubular or plate recuperators [间壁式换热器]were generally used which were large, difficult to clean and did not lend themselves to easy replacement of damaged heating surface. On all modern boilers regenerators [回转式] are used. 在较老的锅炉中一般采用管式或板式空预器,体积大,很难清理,而且坏损的传热表面不易替换。现代锅炉都采用回转式。 The most significant feature of regenerative air heaters, is the marked saving in space compared with recuperative designs. This stems from the adoption of a closely packed heating surface matrix, which is permissible only if good soot-blowing facilities are available to keep it clean. 回转式空气预热器的最大特点是显著地节省了空间。回转式空预器采用紧密的受热面布置方式,必须采用性能良好的吹灰器使其保持清洁。 The heat transfer surface consists of steel or Corten plates pressed to specific profile. The plates are 0.5 mm to 0.8 mm thick and are generally compressed and packed into solid steel containers which are then placed into the supporting structure. The profile of the plates is optimized to give high thermal performance with the minimum of pressure loss within the constraint of being adequately cleaned by soot-blowing. 受热面由压制成特殊形状的钢板或考登钢板组成。这些板子厚0.5到0.8mm,一般被压紧并装进置于支撑结构上的钢制仓体。这些板子的形状经过优化,具有很高的传热效率,同时要在使用吹灰器充分保持清洁的情况下保证压损最小。 For a 660MW unit there are two air heaters, each 14.6 m in diameter and weighing some 500 tons each. The surface area of the heat transfer surface is some 100,000m2 in total. For coal-fired plant the typical temperatures would be a gas inlet of 535℃and outlet of 120℃with an air inlet of 32℃and outlet of 290℃. The performance of the air heater can be expressed in terms of the efficiency of heat transfer, pressure loss and air dimensional groups Reynolds, Prandtl and Stanton numbers. By carrying out laboratory scale rig test these relationships can be established for each type of air-heater element. This allows the possibility of optimizing designs, estimating the possible performance of newly developed element geometries and the effect of replacement element type which may be required because of fouling problems. 一台660MW的单元机组配有两台空气预热器,每台直径14.6m,重约500吨。传热元件的表面积总共约100,000平方米。燃煤电厂典型的温度应是烟气进口335℃,出口120℃,空气进口32℃,出口290℃。空气预热器的性能主要表现在传热效率、压损以及空气对烟气侧的泄漏上。前两项能被理想的表示为一组无量纲数:雷诺数、普朗特数和斯坦顿数的关系。通过实验室规模试验可以确立每种空气预热器组件的关系式。这就可以进行优化设计,估算新开发部件的几何性能,以及评估由于灰污问题而需使用替代部件的效果。 2.6 On-load Cleaning Boilers The effective utilization of fossil fuels for power generation depends on a great extent on the capability of the steam generating equipment to accommodate the inert residuals of combustion, commonly known as ash. Soot-blowers are provided to remove combustion deposits from the boiler surface and ensure effective heat transfer to the steam. Steam is used almost exclusively as a blowing medium on the Continent but many air installations are in use in the USA. 2.6 锅炉在线吹灰 是否高效的燃烧化石燃料来生产电力很大程度上取决于蒸汽产生设备对煤燃烧产物(煤灰)的适应性。吹灰器用来吹扫沉积在锅炉受热面上的积灰来保证有效地向蒸汽传热。在欧洲大陆吹灰介质大部分用蒸汽而在美国一般用空气。 Furnace Wall Blower Using Steam or Air As required the short lance rotates forward into the furnace and the air or steam is turned on as the blowers clear the wall tubes. The total travel is about 200~250mm. Dependent on the design the lance either turns between an arc of 120oor can make to several complete turns until a limit switch reserves the drive and reacts the lance. The cleaning radius is 1.5 m ~2.0m. (1) 应用蒸汽或空气的炉膛吹灰器 按照要求,短伸缩式吹灰器在吹扫炉膛壁面时向前旋转推进,同时打开空气或蒸汽。其总的行程大约200-250mm。根据设计要求,吹灰枪可以在120°范围内摆动或者在限位开关下做整圈的运动,直到吹灰枪缩回。这种吹灰器的吹扫半径为1.5-2m。 Furnace wall blowers can also use water but few are in service. They are used for cleaning tenacious or molten slag from furnace walls with a low velocity jet. A variable speed motor ensures that the water jet impinge with a uniform dwell time on the tube surfaces. 炉膛的吹扫介质也可以用水,但实际中很少应用。水通常用来在低速下清除炉膛内顽固的熔融的渣。用变速马达来保证喷水在受热面上有相同的停留时间。 Long Travel Blowers Long travel blowers are used to clean the superheater, reheater and sometimes the economizer surfaces. When the blower is initiated the lance moves forward and rotates simultaneously so that the oppose jets describe a helical motion. When the jets clear the boiler wall the blowing medium is turned on and passed to the jets. (2) 长伸缩式吹灰器 长伸缩式吹灰器用来吹扫过热器、再热器有时还有省煤器。当吹灰器启动时,吹灰枪向前移动,同时旋转来保证对冲的射流形成螺旋状的运动。当利用喷口吹扫炉墙时,就打开吹灰介质使其流向喷口。 When the lance is at full travel, it turns through 90othus tracing a helical path in the reverse direction which bisects the path in the forward direction. Unsupported lance lengths up to 16.75m are practical thus giving the boiler designer boiler widths up to 33.5m. 当吹灰枪行程达到最大时,吹灰枪旋转90度角,这样在返回时与进入的吹灰部分错开。没有支撑的吹灰枪长度可达16.75m,因此锅炉炉宽可以设计到33.5m。 Sonic soot blowers Sonic soot blowers are on trial in a variety of positions on utility boilers. The device is a low frequency (20Hz) sound generator driven by compressed air, and produces resonant frequency waves, which will clean enclosures up to 4900 m3. Results of trials have been mixed and it is too early to predict the extent to which sonic blowing will be used. (3) 声波吹灰器 声波吹灰器在电站锅炉不同位置进行了试验。这个装置是个压缩空气驱动的低频(20Hz)发声器,产生共振频率波,可以吹扫4900m3的空间。试验结果是个综合效果,因此预言声波吹灰器的应用范围还为时过早。 Until recently, steam was used exclusively for soot blowing. Air was first used in the USA. 目前为止,一直采用蒸汽吹灰,空气吹灰的首次应用是在美国。 Air has the following advantages: ●Effective soot blowing is available at all loads. ●Maintenance of soot blowing is considerably reduced due to the absence of condensate, thermal shock and erosion on mechanism, lance and nozzles. ●No warming through of air pipe work etc. is required and drainage of the pipe work is considerably reduced when compared to steam blowing. ●Insulation of the pipe work is not required. ●The incidence of boiler tube erosion leading to tube failure and boiler outage is reduced by 50% or more. ●Air heater plates give twice the effective life when air blown. ●Maintenance of the compressors and soot blowers is less extensive and less costly than maintenance of an equivalent steam system including the steam pressure reducing stations. 空气吹灰有以下优点: ?在任何负荷下都可以得到有效的吹灰。 ?由于没有凝结水、热冲击和对吹灰枪、喷嘴等部件的磨蚀,吹灰器的维护费用大大降低。 ?对空气管件不需要预热,并且相对于蒸汽吹灰,凝结水的排放大大减小。 ?管件不需要保温。 ?由于炉管磨蚀造成的故障和停炉减少了50%或更多。 ?空气吹灰可以使空气预热器的受热面寿命增加一倍。 ?相对于包括蒸汽减压站的蒸汽吹灰系统,空气压缩机(air compressors)和吹灰器及系统的维护费用大大降低。 To set against these considerable advantages is the additional capital cost of the compressors, motors, switchgear, cables and compressor house. However, operational data from 500MW boilers indicates that the energy consumption of equivalent steam and air systems are comparable. 抛开以上优点,空气吹灰也有其他的一些附加初始费用,如空压机、马达、开关设备、电缆和压缩机房。但是,从500MW锅炉的运行数据上来看,两种吹灰系统的能耗相当。 2.7 Energy balance In accordance with the first law of thermodynamics the energy balance around the steam generator envelope can be stated as: Energy entering the system – Energy leaving the system = Accumulation energy in the system. Since a steam generator should be tested under steady-stated conditions, such that accumulation is zero, the equation is: Energy entering the system = Energy leaving the system Energy entering the system is the energy associated with the entering mass flow streams and auxiliary equipment motive power. Energy leaving the system is the energy associated with the leaving mass flow streams and heat transfer to the environment from the steam generator surfaces. 2.7 能量守恒 由热力学第一定律,蒸汽发生器系统的能量平衡如下所述: 进入系统的能量- 离开系统的能量= 系统内部能量的积累 因为蒸汽发生器应在稳态下检测,这样积累的能量就为0,其方程为: 进入系统的能量 = 离开系统的能量 进入系统的能量就是进入系统的质量流所携带的能量,以及辅助设备的驱动能量。离开系统的能量就是离开系统的质量流所携带的能量,以及通过蒸汽发生器表面传递给环境的能量。 Efficiency is the ratio of energy output to energy input, expressed as a percentage: ,%100Input Output EF = (2-1) When input is defined as the total energy of combustion available from the fuel, the resulting efficiency is commonly referred to as fuel efficiency. 效率为输出能量和输入能量的比值,以百分数的形式表示: ,%100Input Output EF = (2-1) 当输入能量定义为燃料释放的所有能量时,所得的效率通常称为燃料效率。 2.7.1 Efficiency-energy balance method In the energy balance method, the energy closure losses and credits are used to calculate efficiency. The energy balance method is the preferred method for determining efficiency. It is usually more accurate than the input-output method because errors impact the losses and credits rather than the total energy. For example, if the total losses and credits are 10% of the total input, a 1% measurement error would result in only a 0.1% error in efficiency, where a 1% error in measuring fuel flow results in a 1% error in efficiency. Another major advantage to the energy balance method is that reasons for variations in efficiency from 教材39页 one test to the next can be identified. Also, it is readily possible to correct the efficiency to reference or contract conditions for deviations from test conditions such as the fuel analysis. 2.7.1 效率-能量平衡法(反平衡法) 在能量平衡法中,采用能量损失和外来热量来计算效率。能量平衡法是确定效率的首选方法。因为测量误差仅影响着各项损失而不影响总能量,所以它一般情况下比输入-输出法更精确。例如:如总损失占总输入能量的10%,则1%的测量误差仅会导致0.1%的效率误差,而在测量燃料流量中1%的误差将会导致效率的1%的误差。能量平衡法的另一个优点就是可以确认两次效率测试结果不同的原因,另外,对于诸如燃料分析数据等试验条件的变化,该方法可以容易的将效率修正到基准工况或保证工况。 2.7.2 Efficiency-Input-Output method Efficiency calculated by the input-output method is based upon measuring the fuel flow and steam generator fluid side conditions necessary to calculate output. The uncertainty of efficiency calculated by the input-output method is directly proportional to the uncertainty of determining the fuel flow, a respective fuel analysis, and steam generator output. Therefore, to obtain reliable results, extreme care must be taken to determine these items accurately. 教材40页(第2章结束) 2.7.2 效率-输入-输出法(正平衡法) 根据输入-输出法计算的效率是基于测定燃料量和计算输出能量所必需的锅炉汽水侧参数。该方法计算的效率的不确定度直接与燃料测量、样本燃料分析和锅炉输出能量求取等的不确定度成正比。所以,要获得可靠的结果,在精确测量上述各项时必须格外谨慎。