Supply the proper preposition.

1. Exhaust gas heat exchanger is mounted … the main engine uptake.

2. The exhaust gases are sent to the funnel … lower temperatures.

3. The exhaust gas boiler is equipped … an economizer and a superheater.

4. Thermal energy contained in the exhaust gases of diesel engines is superior … 30% of the total heating value … the fuel.

5. The temperatures of the exhaust gases vary … 270°C … 320°C for slow two- stroke engines.

6. This residual energy is recovered … using exhaust gas boilers.

UNIT 3

TEXT A

WATER-TUBE BOILER DESIGN

One of the most commonly used types of marine boilers is a water-tube boiler. In the water-tube boiler the gases pass around a number of small diameter tubes through which steam-water mixture circulates.

In a modern water-tube boiler burners are located in front of the furnace.

The furnace is the place where air and fuel are mixed for the combustion that heats the water in the drums, tubes and headers. It is line the floor and walls with refractory material which prevents the heat loss due to radiation.

The furnace is surrounded onall sides by tubes. These tubes are connected either to upper and lower headers or a lower header and thes team drum.

Between the steam drum and the smaller water drum below, large numbers of smaller-diameter generating tubes are fitted. They provide the main heat transfer surfaces for steam generation. Large-bore pipes or downcomers are fitted between the steam and water drum to ensure go odnatural circulation of the water.

Superheaters are essentially a bank of tubes used to heat the steam above the saturation temperature. Superheater tubing is used to further cool the gases; as gases are cooled, the steam is superheated.

Economizers are heat exchangers which are fitted in a boiler to increase the efficiency of the boiler. This is done by extracting the heat from the gases and using it to heat the feed water entering the boiler.

Air heaters are used to heat combustion air and to recover more of the heat energy from the exhaust gases before they are sent to the stack.

There are two types of water-tube boilers – main boilers and auxiliary boilers.

The circulation in water-tube boilers is either natural or forced.

According to the pressure they are classed as low, intermediate and high pressure boilers. The boilers generating steam under the pressure up to 15 atm. are called low pressure boilers, up to 28 atm. intermediate pressure boilers, and those generating steam under the pressure higher than 28 atm. may be called high pressure marine water-tube boilers. As to more detailed classification of water-tube boilers they may be classed:

а) according to the number of drums as single-drum, two-drum and three-drum boilers;

b) according to the tube inclination as horizontal – those having tube inclination up to 30°, and vertical – with tube inclination of 45-90°;

c) according to the superheater location as horizontal and vertical;

d) according to the arrangement of gas flow as single-flow and double flow.

Vocabulary

mixture, n смесь

front of the boiler фронт (передняя часть) котла

header, n коллектор

line (with), v облицовывать; футеровать; выкладывать

floor, n под (топки)

refractory, adj огнеупорный; жаростойкий

due to radiation из-за излучения

generating tubes водогрейные (испарительные) трубы котла

provide, v обеспечивать

heat transfer surface теплопередающая поверхность

steam generation парообразование

large-bore pipes трубы с большим (внутренним) диаметром

superheater, n пароперегреватель

bank of tubes пучок труб

saturation temperature температура насыщения

economizer, n экономайзер

heat exchanger теплообменник

efficiency, n производительность; КПД

extract, v извлекать

recover, v утилизировать

stack, n дымовая труба

intermediate pressure среднее (промежуточное) давление

single-drum однобарабанный

inclination, n наклон

arrangement of gas flow способ течения газа

single-flow однопроточный (одноходовой)

E X E R C I S E S

1. Give English equivalents:

Наиболее распространенный тип; пароводяная смесь; трубы маленького диаметра; циркулировать по трубам; смешивать; предотвращать; потеря тепла; окружать; соединять; естественная циркуляция; воздухоподогреватель, выхлопные газы, котел низкого давления, котел высокого давления, до 15 атмосфер, свыше 28 атмосфер, двухпроточный.

2. Answer the questions according to the models:

Model A. Does the boiling occur in the economizer? No, it doesn’t. Do the gases pass from the furnace to the stack? Yes, they do.

1. Do the gases pass through a number of tubes in the water-tube boiler?

2. Does steam-water mixture circulate through tubes in the water-tube boiler?

3. Does the combustion heat the water only in the drums?

4. Do downcomers provide good natural circulation of the water?

5. Do superheaters heat the steam below the saturation temperature?

6. Does a horizontal water-tube boiler have an inclination more than 45º?

Model B. Is superheater tubing used to heat the gases? No, it isn’t. Are burners located in front of the furnace? Yes, they are.

1. Is the furnace surrounded on all sides by the tubes?

2. Is superheater tubing used to heat the gases?

3. Are the gases cooled in the economizer?

4. Is the circulation in the water-tube boiler only natural?

5. Are air heaters provided to heat combustion air?

6. Are the exhaust gases sent to the stack?

Ask for details:

Model C. Burners are located in the boiler front. Where are the burners located?

1. Heat energy is contained in the steam.

2. The heated water is fed to the boiler.

3. Air and fuel are mixed in the furnace.

4. Downcomers are located between the steam and water drums.

5. The furnace is lined with refractory material on the floor and walls.

6. Generating tubes are fitted between the steam and water drums.

3. Match the type of the boiler with its principle of classification:

Boilers may be classified into:

single-drum, two-drum and three-drum boilers by the pressure

main and auxiliary boilers by the number of drums

vertical and horizontal boilers by the tube inclination

single-flow and double flow boilers by their purpose

natural and forces circulation boilers by the superheater location

vertical and horizontal boilers by the arrangement of gas flow

low, intermediate and high pressure boilers by the principle of water and

steam mixture motion.

4. Self-assessment questions:

1. Which is one of the most widely used types of marine boilers?

2. Where do the gases pass in the water-tube boiler?

3. What does the steam-water mixture circulate through?

4. Where are burners installed in a modern water-tube boiler?

5. What is the function of the furnace?

6. What is the furnace lined with?

7. What is the function of superheater tubing?

8. What are air heaters used for?

9. What is the boiler classification according to the pressure?

10. How are water-tube boilers classed according to the number of drums?

11. What do we call boilers with tube inclination of 45-90°?

12. How can the superheater be located in the boiler?

13. How are water-tube boilers classed according to the gas flow arrangement?

5.Translate into English:

1. В водотрубном котле вода циркулирует в трубках.

2. Форсунки расположены на фронте котла.

3. Пароперегреватель подогревает пар, а экономайзер – питательную воду.

4. Циркуляция в котле может быть естественной и принудительной.

5. Котлы подразделяются на котлы низкого, среднего и высокого давления.

6. Котлы могут быть одно-, двух- и трехбарабанные.

7. Наклон котельных трубок может быть от 30° до 90°.

8. Пароперегреватель располагается вертикально или горизонтально.

9. Водотрубные котлы бывают однопроточными и двухпроточными.

TEXT B

WATER-TUBE BOILERS

The water-tube boiler is used to generate steam having high pressure and temperature. It is a type of the boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes.

The heated water then rises into the steam drum. Here, saturated steam is drawn off from the top of the drum. The steam enters the furnace through a superheater to become superheated. Superheated steam is steam that is heated above the boiling point at a given pressure. Superheated steam is a dry gas and therefore used to drive turbines, since water droplets can severely damage turbine blades.

Cool water at the bottom of the steam drum returns to the water drum through large-bore downcomer tubes.

Water-tube boilers are the most widely used boilers. They have replaced many boilers, including the fire-tube type, mainly because of the follow in reasons:

· The weigh to the water-tube boiler is much less than any type of boiler of equivalent size.

· Steam rais in gand steam generation process is much faster.

· The design can include any kind of modifications.

· It has very high efficiency than the rest of the boilers.

· The design facilitates good natural circulation of the feed water.

E X E R C I S E S

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