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Text 3. Cyclone Furnace (Crushed Coal)
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Do the following tasks:
1) Write out specific terms used in the texts and translate them into Russian.
2) Speak about the types of furnaces.
Cyclone Furnace (Crushed Coal)
The cyclone furnace is a water-cooled horizontal cylinder (5 to 10 ft in diameter) into which coal is introduced.
As the coal moves from front to rear, combustion air is introduced tangentially at high velocity and about 35-in water gage pressure. This causes a whirling or centrifugal action, with the solid fuel particles moving to the periphery of the combustion chamber where their movement is retarded by molten slag that covers its walls. Although the finer fuel particles burn in suspension, the cyclone method of combustion is primarily a surface-burning process. The solid fuel particles in the liquid ash coating on the walls are scrubbed by the incoming air stream, providing intimate coal and air mixing. Combustion in the cyclone furnace is complete and has practically no carbon loss.
The cyclone furnace is water-cooled as an adjunct to the boiler circulation system. It is attached to the steam generating unit, which may have either of two types of secondary furnace: 1) the water screen type, in which a water screen of tubes divides the furnace into lower and upper section; and 2) the open furnace type. In the water screen furnace, the fly-ash loading of the flue gases will be about 10 percent of the total ash fired. In the open furnace, the loading will be about 15 percent. This refuse may be collected and returned for reinjection.
Some stations find the cyclone furnace advantageous and there are definite sales trends in its favour. As it is not necessary to pulverize the coal, a considerable saving is obtained in both initial investment and also in operating expense.
This furnace has been proved to be suitable for a wide range of coals and for firing gas or oil either in combination with coal or as stand-by or substitute fuel. The cyclone furnace is also capable of burning waste or by-product fuels such as wood, chars, and cokes.
Text 4. Pulverized coal furnace
Do the following tasks:
1) Write out specific terms used in the texts and translate them into Russian.
2) Describe the operational principle of the pulverized coal furnace.
3) Make up questions to each paragraph of the text.
4) Give the Russian variant of the following expressions: steam generators, coal-fired boilers, ash-fusion temperature, ultimate design, flame shape, furnace height, tangential firing, tube wastage, excess air.
5) Make up the sentences with the words above.
Pulverized coal furnace
Coal may be fired as a finely powdered fuel that is injected into the furnace. The coal is pulverized to a fineness of 70 percent or more through a 200 mesh sieve. It is then transported by hot primary air (which also dries the coal) to the furnace.
The majority of all central steam generators operating at 200,000-lb steam per hr and over are fired by pulverized coal. The number of pulverizers are determined by pulverizer capacity and stand-by requirements. Larger installations have two, three or four pulverizers. Provision for three pulverizers, one for each row of burners plus one for stand-by is not unusual. Pulverized coal-fired boilers may be either the dry bottom or slag-tap type. Vertical, horizontal, opposed, or tangential firing methods may be employed.
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The size of the unit, its pressure and temperature, available space, fuel characteristics, ash-fusion temperature, type of burner, and ash removal method determine the volume of the furnace, the extent of water cooling, and the ultimate design of the entire steam-generating unit.
Pulverized coal furnaces are usually convertible to firing with oil or gas. Units near oil refineries may utilize fluid coke. Pulverized coal firing removes a limitation on the amount of fuel that can be burned in a boiler (with stoker firing there is a definite limit).
The type and multiplicity of burners, their arrangement and the flame shape will determine the furnace width and depth dimensions. The furnace height is a function of the required furnace volume. The exit temperature of the gases should be below the ash-fusion temperature of the lowest quality fuel to be used. Thus, coal with a large percentage of low-fusion ash will require larger waterwall surfaces, which in turn make a larger furnace volume necessary.
All pulverized coal-fired furnaces constructed to-day are partially or completely water-cooled. If tangential firing is used, the furnace must be completely water-cooled, because there is considerable flame impingement. It is desirable to eliminate, as much as possible, blasting of flames against the furnace walls. Molten ash particles stick to and dissolve most refractories. Heat and high sulphur content may induce a slow attack or tube wastage of the water-cooled walls. Flame length varies with coal particle size (the length is by uniformly fine puliverization), the percentage and composition of the volatile constituent, turbulence, furnace temperature, and excess air.
Text 4. Pulverized coal furnace
Do the following task:
1) Give a written translation of the text into English.
Печи
На современном крупном промышленном предприятии используются высокотемпературные теплотехнологические установки, которые можно разделить на следующие группы:
а) обжиговые печи, в которых термическая обработка исходного материала, связанная с физико-химическим его преобразованием, происходит без изменения его агрегатного состояния;
б) плавильные печи, в которых процессы предварительного нагрева и обжига исходного материала сочетаются с процессами плавления, восстановления или окисления перерабатываемого расплава (то есть сопровождаются изменением агрегатного состояния материала);
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в) чисто нагревательные печи, в которых осуществляется только тепловая обработка материала.
Unit 3
Memorize the words
transfer-передача; перенос, перемещение
fluid-жидкость, жидкий, текучий
steam-пар; подвергать действию пара, пропаривать
fan- вентилятор
blower- воздуходувка; компрессор; продувочный
viscosity-вязкость; тягучесть; липкость; клейкость; внутреннее трение
piston pump-поршневой насос
centrifugal-центробежный
impellent-движущаяся сила, побуждающий, двигающий
impeller-рабочее колесо, крыльчатка
impeller rim-обод рабочего колеса
shaft-стол; вал, стержень; ось; рукоятка, ручка
vane-лопатка; лопасть; крыло (вентилятора), лопастный, крыльчатый
radial-радиальный; лучевой, звездообразный двигатель, двигатель с радиально расположенными цилиндрами
volute casing-спиральная турбинная камера, улитка
adiabatic-адиабатическая, теплонепроницаемая
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