【正文】 d, 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℃ (800186。然而一些年來，沒有太多的天然氣可供電廠使用，并且人們沒有正視這樣的事實，即天然氣作為一種優(yōu)質(zhì)燃料將會重新得到大量應用。 Since coal firing requires some excess oxygen in the bustion zone to achieve total carbon burnout and nitrogen free coal is unavailable, NOx reduction has to be performed by boiler and burner design. 因為煤在燃燒區(qū)的燃燒需要一定的過量氧氣以便使所有的碳燃盡，且不含氮的煤是難以獲得的 ，因此 NOx 的減少必須依靠鍋爐和燃燒器的設計來完成。當煤進入爐膛其化學結構被破壞時，一些煤中的化合氮就作為揮發(fā)分被釋放出來。作為整個燃燒系統(tǒng)設計的性能參數(shù)，煤粉細度、 磨 煤機 出口溫度 、 空煤比 等都必須達到要求。在第三代鍋爐的設計中進行了進一步降低 NOx的 開拓 性試驗。同以前相比，在流動平衡上的設計成果現(xiàn)在已能使鍋爐在較低的過量空氣水平下運行，并在不增加飛灰含碳量水平的情況下提高了總的效率。 2910 Coal bustion 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. 煤燃燒系統(tǒng) 煤燃燒器的發(fā)展模式同油燃燒器類似，而且重點放在準確控制每只燃燒器煤和油的供給量。為保證鍋爐中每個燃燒器獲得同樣多的空氣也做了大量的工作。在 20 世紀 60 年代早期，人們對油燃燒器設計進行了深入研究和開發(fā)，目的在于解決燃油的排放問題。 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，要比一般的餾分油（柴油，汽油等）便宜，但又帶來一些問題：酸性污染物和粉塵的排放。一般地，燃油都是粘度在 3500 sec 到 6500sec 的殘渣燃料油。然而，在過去的二十多年中，為了將大氣排放和污染降到可行的最低程度，燃燒技術得到了很大程度的提高。這套系統(tǒng)目的在于確定煤的商業(yè)使用價值，并提供關于煤燃燒特性的基本信息。 The system used in the . 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 mercial uses of coals and provides basic information regarding bustion characteristics. 現(xiàn)在美國應用的煤分類標準是由美國材料試驗學會（ ASTM）建立的。這表現(xiàn)為煤化程度的大?。簭暮置旱截毭骸熋阂约盁o煙煤。中國煤的性質(zhì)如表 21 所示。雖然天然氣和燃油也許是未來化石燃料電廠的燃料選擇 ， 但對于 帶 基本負荷的新電站，煤仍將是主要的鍋爐燃料。這些包括泥煤、木材及木材廢棄物、麥稈、咖啡渣、玉米稈、煤礦廢棄物（煤屑）、煉鋼爐廢熱甚至太陽能。然而，在過去的幾十年里，至少在發(fā)電領域核能開始扮演一個主要角色。因此，在對蒸汽循環(huán)及機組容量進行較大改進的時期，必須和廠商在設計、制造領域，以及運行、維護技術領域密切合作，以保證經(jīng)濟利益的可靠。因此，需要平衡考慮由效率提高、投資成本減少等帶來的直接經(jīng)濟效益，與新設計機組可能產(chǎn)生的可靠性低和需要大的改進等風險。雖然一些新的特性可以在安裝前進行測試，但一個新設計鍋爐的真正測試是和汽輪發(fā)電機組配套 運行后 進行的。 A utility normally procures plant from specialist manufactures who have responsibility for design, manufacture, erection and missioning. 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 mercial 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. 電站設備一般向負責設計、制造、建設和調(diào)試的專業(yè)廠商購得。這一變化使再熱變得可行，而且隨著高溫鋼材297 可用性的提高，蒸汽參數(shù)不斷變化，達到了當前的 2400lbf/in2（ ）， 568℃ 和 568℃ 再熱的標準循環(huán)。這種布置反應了鍋爐的可用性低于汽輪機。蒸汽參數(shù)的提高，機組容量的增大及燃料燃燒特性改進都要求在材料、制造技術和運行程序上相應發(fā)展。 Development of Utility Boiler The modern 660MW coalfired boiler has some 6000 tons of pressure parts which include 500 km of tubing, km of integral piping and 30,000 tube butt welds. It is the culmination 教材 25 頁 of some fifty years development and while the basic concept of pulverized fuel firing into a furnace lined with evaporator tubes, with the bustion 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. 電站鍋爐的發(fā)展 現(xiàn)代 660MW 燃煤鍋爐有大約 6000 噸的壓力部件，其中包括 500 千米的受熱面管材， 千米連接管，和 30000 個管接頭焊口。 296 Blast furnace hood heat recovery generates steam using the waste heat from a blast furnace. 高爐排煙熱量回收：利用高爐余熱產(chǎn)生蒸汽。 Integrated Gasification Combined Cycle (IGCC) adds a coal gasifier to the CC to reduce fuel cost and minimize airborne emissions. 整體煤氣化聯(lián)合循環(huán)（ IGCC）：在 CC 基礎上增加煤氣化爐，以降低燃料費用并將污染排放降到最低。這些系統(tǒng)常常利用廉價或免費燃料，聯(lián)合動力循環(huán)和過程，以及余熱回收，