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Furnaces
Coal is the product of vegetable matter that has beenvformed by Although coal is not a true mineral, its formation processes are According to the amount of carbon coals are classified into; Although carbon is the most important element in coal, as Lignite is intermediate in properties between peat and bitumi- Brown coal is harder than lignite, containing from 60 to 65 per As for the thickness, the beds of this kind of coal are not very Anthracite or "hard" coal has a brilliant lustre containing more
WRITING
Task 16 Write an abstract of the text “ Coal and Its Classification” according to the plan:
1. The classification of coal. 2. The characteristic of lignite, brown coal, anthracite 3. The largest deposits of coals in the world
WORDLIST
Furnaces
TUNING – IN Task 1 Name the principal function of the furnace
Task 2 Study the diagram below of a condensing furnace. Answer these questions using the diagram and your own knowledge of engineering.
1. What are the main parts of a condensing furnace? 2. What is the role of condensate drain hose? 3. What is the difference between condensing furnace and non-condensing one?
duct – канал, трубопровод humidifier – увлажнитель pleated filter - гофрированный (бумажный) фильтр intake pipe – впускная (подводящая) труба exhaust vent pipe – выпускная вентиляционная труба, труба для отбора пара hose – гибкая труба, шланг
WORDLIST
PRONUNCIATION
Task 3 Remember the pronunciation of the following words
WORD-BUILDING
Task 4 Fill in the table
READING
Task 5 Read the text and look for answers to these questions: 1. What is a furnace? 2. What does the design of the furnace depend upon? 3. What is the design of a satisfactory furnace based upon? 4. What is the ignition temperature? 5. What is turbulence? 6. What conditions is the required furnace volume dependent upon? 7. What kinds of furnaces do you know?
The design of the furnace depends considerably upon the fuel to be burned. On the other hand, it also depends upon the supplement equipment so that satisfactory ignition and heat release may be ensured. A furnace is a gas-tight and well-insulated space, in which gas, oil or pulverized coal may be burned. If combustion is to be complete, the combustible gases must be brought into close contact with oxygen. Also, the oxygen must be kept to a minimum and the excess air from room temperature to chimney-gas temperature also is to be low. The design of a satisfactory furnace is based upon the "three T's of combustion": temperature, turbulence, and time. 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. If the combustible 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 the ignition temperature. Thus, the principle function of the furnace is to provide space in which the fuel may be burnt with a minimum amount of excess air and with a minimum loss due to the escape of unburned fuel. Turbulence plays an important role in combustion. It is the turbulence that gives an effective combustion. 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. 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. The required furnace volume is dependent upon the kind of fuel burnt, 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 burnt, the supplement equipment, and the type of boiler used to absorb the energy if the fuel is burnt for steam generation. There are different kinds of furnaces, namely, cyclone furnaces (crushed coal), pulverized coal furnaces, spreader stokers and chain-and traveling - grade stokers.
Date: 2014-12-29; view: 2046
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