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1、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.,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。,Also, an increasing varie
2、ty of biomass materials and process byproducts have become heat sources for steam generation. These include peat, wood and wood wasters, straw, coffee grounds, corn husks, coal mine wastes (culm), waste heat from steelmaking furnaces and even solar energy.,同样，不断增加的各种生物质和过程副产品也成为蒸汽生产的热源。这些包括泥煤、木材及木材废
3、弃物、稻草、咖啡渣、稻谷壳、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, subbituminous or lignite.,现代美国中心电站用燃料主要是煤，或是烟煤、次烟煤或是褐煤。,Bituminous adj.含沥青的，烟煤的 Bituminous coal 烟煤 Subbituminous adj.亚烟煤的 Subbituminous coal 亚烟煤 Lignite n. 地 褐煤 Lean coal 贫煤 Anthracite n
4、. 无烟煤,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 loaded utility power station boilers.,虽然天然气和燃油也许是未来化石燃料电厂的燃料选择，但煤仍然是今后新的，基本负荷电站锅炉的主要燃料。,U.S net electricity generat
5、ion by energy source during 1990-2,835.3 billion kWh,Worldwide net electricity generation by energy source during 1988-10,537.6 billion kWh,2004年中国总发电量21，870亿千瓦时，火力占86%，水力占15%，核发电占2.3%，其它0.1%,2.3.1Coal classification,A coal classification system is needed because coal is a heterogeneous substance wi
6、th a wide range of composition and properties. The properties of a typical China coal are showed in Tab. 2-1. Coals are typically classified by rank. This indicates the progressive alteration in the coalification process from lignite to subbituminous, bituminous and anthracite coals. The rank indica
7、tes a coals geological history and broad characteristics.,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 (AS
8、TM). 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 characteri
9、stics.,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燃烧系统,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
10、 techniques have been considerably refined in order to reduce atmospheric emissions and pollution to a practicable minimum.,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油燃烧系统 Oil is burned in all utility boiler, in coal boilers to ignite the coal burn
11、ers, 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 3,500 sec. to 6,500 sec. viscosity. In order to burn effectively this oil must be heated to 120130 and finely divided or atomised into ve
12、ry small droplets.,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120130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 fuels (diesel/gas oil etc.) causes problems, amongst them, acid smuts and dust emissions. The smut
13、 problem is caused by the sulphur content of the oil, which may be up to 3%. In the early 1960s the utility undertook an intensive development programme 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 re
14、duced emissions of carbon at very low excess air levels. Considerable work was also done in order to ensure that each 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
15、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 burners have been developed in a similar fashion to the oil burners, and considerable emphasis is placed upon feeding each burner with carefu
16、lly regulated amounts of coal and oil. All coal fired boilers in the utility fire pulverised 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 equalisation 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
