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Text 3. Классификация паротурбинных электрических станции
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Do the following tasks:
1) Read the text. Translate the underlined terms into English.
2) Make up sentences of your own with the terms used in the text. Let your neighbour translate their Russian versions into English, then change parts.
3) Find in the text following abbreviations and give their full version: HEPGS, SPP, CPS.
Классификация паротурбинных электрических станции
Паровые турбины составляют основное оборудование ТЭС. Кроме этих агрегатов, на электростанциях используются разнообразные машины и механизмы. Среди этих машин большой интерес в отношении преобразования энергии представляют машины, предназначенные для перемещения жидкостей по трубопроводам. К ним в основном относятся насосы,вентиляторы и компрессоры. В противоположность тепловым двигателям в этих машинах происходит не преобразование тепловой энергии в механическую, а наоборот – механическая (электрическая) энергия превращается в тепло.
Промышленные и коммунально-бытовые предприятия используют в основном энергию двух видов: электрическую и тепловую. Выработка этих двух видов энергии может производится раздельно, в двух технологических процессах, или совместно – в одном технологическом процессе. Таким образом паротурбинная электрическая станция классифицируется на КЭС и ТЭЦ. КЭС – конденсационные электрические станции вырабатывают только электрическую энергию. ТЭЦ – теплоэлектроцентраль вырабатывает тепловую и электрическую энергию одновременно.
Text 4. Теплоэлектроцентрали
Do the following tasks:
1) Read the text and find sentences where the following terms are used. Translate them: вентиляция, очистка, канализация, паропреобразователь, примеси, конденсат.
2) Look through the text. What information did you get about the heat and electric power generating station?
Теплоэлектроцентрали
Источниками тепла в системах централизованного теплоснабжения являются теплоэлектроцентрали (ТЭЦ). Теплоэлектроцентрали вырабатывают два вида продукции: электрическую и тепловую энергию. Теплоэлектроцентрали отпускают тепло двум основным потребителям: промышленным – в виде пара и горячей воды; коммунальным – в виде горячей воды для отопления, вентиляции, горячего водоснабжения. На теплоэлектроцентрали для целей теплофикации используется пар, частично отработавший в турбине.
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Если потребителю отпускается тепло в виде пара, то потребитель может возвращать на ТЭЦ конденсат отработавшего пара с помощью насоса обратного конденсата. Доля возвращаемого на ТЭЦ конденсата колеблется от 0 до 1. Если конденсат не загрязнен различными примесями, то возвращается в тепловую схему, в противном случае конденсат проходит очистку или сбрасывается в канализацию.
ТЭЦ отпускает внешнему потребителю тепло в виде:
- пара непосредственно из отбора или вторичного пара, полученного в специальном испарителе, называемом паропреобразователем;
- горячей воды, нагретой в теплообменниках, называемых сетевыми подогревателями или бойлерами.
Unit 2
Memorize the words
grate – колосниковая решетка
stoker – механическая топка, стокер
mesh – отверстие, ячейка; сеть, сетка; меш (число отверстие или ячеек по один линейный дюйм)
suspension – взвесь, взвешенное состояние
ashpit – зольник, поддувало
plunger – скальчатый поршень
fuse – плавить(ся); сплавлять(ся), расплавлять
heat transfer – теплопередача
turbulence – турбулентность, беспорядок
spall – дробить, разбивать, обтесывать
to fluctuate – быть неустойчивым, меняться, колебаться, колыхаться
to erode – разъедать, разрушать, вытравлять, выветривать, размывать, эродировать;
to adhere – прилипать, приставать, приклеиваться, прирастать, придерживаться;
slag – выгарки, окалина, шлаг
adjunct – принадлежности
char – легковоспламеняемый остаток ректификации угля; древесный уголь, обжечься, обуглиться, сгореть
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sieve- решетчатый фильтр, сетчатый фильтр; просеивающая машина, просеивать, грохот
refinery – очистительный завод.
Text 1. Burning equipment
Do the following the tasks:
1) Think of questions to the following sentences.
a) There are two general methods of firing fuel commonly employed
b) Coals may be broadly classified into 4 groups
c) A fuel of this group is satisfactorily burned on traveling gate or chain – gate stoker
d) A few coals of this class have a low ash-fusion temperature with a resulting tendency to fuse and jam the operating parts of the stoker
e) They have a tendency to disintegrate on the grate
2) Speak with your group mates about the types of fuel, their use, the operation of the burning equipment. Have a talk with your group mates.
Burning equipment
There are two general methods of firing fuel commonly employed: 1) on stationary grates, or 2) on stokers. Also coal may be pulverized to the consistency of 70 percent through a 200-mesh screen and burned in suspension. The types of solid fuel encountered in various parts of the world and the general conditions under which they must be burned are so variable that it is impossible to design one type of grate or stoker that is exactly suited to all fuels. The problem becomes one rather of suiting the equipment to the type of fuel to be handled.
To a certain extent, the design of the furnace must be considered coincidentally with the selection of fuel burning equipment, so that satisfactory ignition and heat release may be ensured. The choice of equipment for a given set of conditions is limited, and, although any stoker will burn any fuel only one design as a rule will give satisfactory results. Coals may be broadly classified as follows:
Group 1. This group includes the anthracites and semi-anthracites. Which should be burned without agitation of the fuel bed.
A fuel of this class is satisfactorily burned on traveling gate or chain-gate stokers, on which the coal is fed in a comparatively thin, uniform layer. As combustion progresses, the ash covers the surface of the stoker and acts as a protective blanket, the fuel being supplied with combustion air as it travels toward the ashpit.
Group 2. This group includes the bituminous coals of the caking type which require agitation of the fuel bed to break up the mass of coke as it forms as well as to resist the tendency of this fuel into a mat, or cake, that resists the passage of air and retards the process of combustion. Underfeed stokers of the multiple-retort type are designed to burn coals of this class, for the plungers have a characteristic forward and upward motion. By breaking up the surface of the fuel bed, more air passages are created, with a tendency to increase combustion rate. A few coals of this class have a low ash-fusion temperature with a resulting tendency to fuse and jam the operating parts of the stoker. These coals, particularly if high in sulphur, should be avoided as stoker fuels.
Group 3. This group includes Midwestern coals and most of the western bituminous coals. These do not tend to soften but form masses of coke, they require no agitation of the fuel bed and are burned to best advantages on chain-grate stokers.
Group 4. This group consist of most of sub bituminous coals and lignites which do not fuse when heated and do not require agitation. They have a tendency to disintegrate or slack on the grate as well as drift and sift through if disturbed. They have a tendency to avalanche on inclined grates and are most satisfactorily burned on chain or traveling grate stokers.
Text 2. Furnaces
Do the following tasks:
1) Make up 10 questions about the text and let your neighbour answer them, then change parts.
2) Make up a detailed plan of each part of the text: a) divide the text into several parts; b) give each part a heading. Retell each part of the text separately.
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3) Give a written translation of the text into Russian.
Furnaces
A furnace is a fairly gas tight and well insulated space in which gas, oil, pulverized coal, of the combustible gases from solid fuel beds may be burned with a minimum amount of excess air and with reasonably complete combustion. Near the exit from the furnace at which place most of the fuel has been burned, the furnace gases will consist of inert gases such as CO2, N2 and H2O vapor, together with some O2 and some combustible gases such as CO, H2, hydrocarbons, and particles of free carbon (soot). If combustion is to be complete, the combustible gases must be brought into intimate contact with the residual oxygen in a furnace atmosphere composed principally of inert gases. Also, the oxygen must be kept to a minimum if the loss due to heating the excess air from room temperature to chimney –gas temperature is to be low. Consequently, the major function of the furnace is to provide space in which the fuel may be burned with a minimum amount of excess air and with a minimum loss due to the escape of unburned fuel.
For each particular fossil fuel, there is a minimum temperature, known as the ignition temperature, below which the combustion of that fuel in the correct amount of air will not take place.
The ignition temperature of a fuel in air as reported by various investigators depend somewhat upon the methods used to determine it and, for some common gases, is as follows:
Hydrogen (H2) 1075-1995˚ F
Carbon monoxide (CO) 1190-1215˚ F
Methane (CH4) 1200-1380˚ F
Ethane (C2H6) 970-1165˚ F
If the combustion gases are cooled below the ignition temperature, they will not burn, regardless of the amount of oxygen present. A furnace must therefore be large enough and be maintained at a high enough temperature to permit the combustible gases to burn before they are cooled below ignition temperature. In other words, the relatively cool heat transfer surface must be so located that they do not cool the furnace gases below the ignition temperature until after combustion is reasonably complete.
Turbulence is essential if combustion is to be complete in a furnace of economized size. Violent mixing of oxygen with the combustible gases in a furnace increases the rate of combustion, shortens the flame, reduces the required furnace volume, and decreases the chance that combustible gases will escape from the furnace without coming into contact with the oxygen necessary for their combustion. The amount of excess oxygen or air required for combustion is decreased by effective mixing. Turbulence is obtained, in the case of oil, gas, and powdered coal, by using burners which introduce the fuel –air mixture into the furnace with a violent whirling action.
Since combustion is not instantaneous, time must be provided for the oxygen to find and react with the combustible gases in the furnace. In burning fuels such as gas, oil, or pulverized coal, the incoming fuel-air mixture must be heated above the ignition temperature by radiation from the flame or hot walls of the furnace. Since gaseous fuels are composed of molecules, they burn very rapidly when thoroughly mixed with oxygen at a temperature above the ignition temperature. However, the individual particles of pulverized coal or atomized oil are very large in comparison with the size of molecules, and many molecules of oxygen are necessary to burn one particle of coal or droplet of oil. Time is required for the oxygen molecules to diffuse through the blanket of inert products of combustion which surround a partially burned particle of fuel and to react with the unburned fuel. Consequently, oil and pulverized coal burn with a longer flame than gaseous fuels.
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The required furnace volume is dependent, therefore, upon the kind of fuel burned, the method of burning the fuel, the quantity of excess air in the furnace, and the effectiveness of furnace turbulence. The shape of the furnace depends upon the kind of fuel burned, the equipment employed to burn the fuel, and the type of boiler used to absorb the energy if the fuel is burned for steam generation.
Industrial furnaces in which the objective is to create and maintain a region at a high temperature and the furnaces of small steam boilers are constructed of fire brick, a brick that has been developed to withstand high temperatures without softening, to resist the erosive effect of furnace atmosphere and particles of ash, and to resist spalling when subjected to fluctuating temperatures. Low vertical walls may be constructed of fire brick in the conventional manner. High walls which are subject to considerable expansion, may be tied to and sectionally supported by an external steel frame.
When a boiler furnace is operated at high capacity, the temperature may be high enough to melt or fuse the ash which is carried in suspension by the furnace gases. Molten ash will chemically attack and erode the fire brick with which it comes into contact. Also, if the ash particles are not cooled below the temperature at which they are plastic or sticky before they are carried into the convection tube banks of the boiler, they will adhere to these surface, obstruct the gas passages, and force a shutdown of the unit. Moreover, the function of a boiler is to generate steam, and the most effective heat transfer surface is that which can see the high temperature flame and absorb radiant energy.
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