SUPERHEATERS

A household furnace is a major appliance that is permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam or hot water. The most common fuel source for modern furnaces in the United States is natural gas; other common fuel sources include LPG (Liquefied petroleum gas), fuel oil, coal, or wood. In some cases electrical resistance heating is used as the source of heat, especially where the cost of electricity is low.

Combustion furnaces always need to be vented to the outside. Traditionally, this was through a chimney, which tends to expel heat along with the exhaust. Modern high-efficiency furnaces can be 98% efficient and operate without a chimney. The small amount of waste gas and heat are mechanically ventilated through a small tube through the side or roof of the house.

Modern household furnaces are classified as condensing or non-condensing based on their efficiency in extracting heat from the exhaust gases. Furnaces with efficiencies greater than approximately 89% extract so much heat from the exhaust that water vapor in the exhaust condenses; they are referred to as condensing furnaces. Such furnaces must be designed to avoid the corrosion that this highly acidic condensate might cause and may need to include a condensate pump to remove the accumulated water. Condensing furnaces can typically deliver heating savings of 20% - 35% assuming the old furnace was in the 60% Annual Fuel Utilization Efficiency (AFUE) range.

SUPERHEATERS

Tuning- in

Task 1

List the main parts of the boiler. Combine your list with others in your group and say your opinion about a superheater function in a steam boiler system.

Wordlist

The following words help you understand the text. Try to remember the pronunciation and meanings of these words.

Saturated steam- насыщенный пар

Specific volume удельный объем

Enthalpy теплосодержание, энтальпия

Fluid friction трение жидкости

Wet steam влажный пар

High- efficiency steam turbine паровая турбина с высоким К.П.Д.

Convection superheater конвективный пароперегреватель

Radiant superheater радиационный пароперегреватель

To absorb heat поглощать тепло

Header водяная камера, водяной коллектор

Inlet header входной коллектор

Gain увеличение

Output производительность

Circulator циркуляционный насос, циркулятор

Outlet header выходной коллектор

To adhere прилипать

Sticky липкий, клейкий

Thereby в связи с этим, вследствие этого

Due to из-за, благодаря, вследствие, в результате

Pronunciation.

Task 2

Read the following words and remember their pronunciation

Header [ 'hedq ]

Temperature ['temprICq ]

Advantage [qd' vRntIdZ ]

Considerable [kqn'sId(q)rqbl ]

Enthalpy [ en'TxlpI ]

Surroundings [sq'rQundINz ]

Moisture [' mOIsCq ]

Sufficiently [sq'fISqntlI]

Actual ['xkCuql ]

Compare [kqm'pFq]

Efficiency [ IfIS(q)nsI ]

Diameter [daI'xmItq]

Adhere [qd'hIq]

Reading

Task 3

Read the text below to find the answers to these questions.

1.What is the main component of a boiler?

2. What is the function of a superheater?

3. How is superheated steam produced?

4. How can a superheater maximum work be obtained?

5. What advatages has superheated steam in comparison with saturated one?

6. What types of superheaters do you know?

7. Why the products of combustion must be cooled?

A superheater is a very important component of a boiler, therefore, designing an efficient superheater contributes to the boiler efficiency. Normally, superheaters are located at the highest temperature region in the boiler where the highest heat transfer needs to take place. The main function of a superheater is to raise the temperature of a slightly superheated steam coming from the steam drum to higher temperatures to reach a desired superheat levels.

Superheated steam is produced by causing saturated steam from a boiler to flow through a heated tube or superheater, thereby increasing the temperature, enthalpy, the specific volume of the steam.

It should be noted that in actual superheater there will be a decrease in steam pressure due to fluid friction in the superheater tubing. Maximum work is obtained when a fluid expands without friction and without heat transfer to the sorroundings.

In addition to the gain in output due to the increased temperature of superheated steam as compared to saturated steam, the increase of temperature of superheated steam has considerable advantages to the use of superheated steam in turbines. The first law of thermodynamics states that all the work done by the turbine comes from the energy in the steam flowing through the turbine. Each per cent of moisture in the steam reduces the efficiency of that part of the turbine in which the wet steam is expanded. It is necessary; therefore, that high- efficiency steam turbines be supplied with superheated steam.

Superheaters may be classified as convection or radiant superheaters. Convection superheaters are those which receive heat by direct contact with the hot products of combustion flowing around the tubes. Radiant superheaters are located in furnace walls where they “see“ the flame and absorb heat by radiation with a minimum of contact with hot gases.

In a typical superheater of the convection type saturated steam from the boiler is supplied to the upper or inlet header of the superheater by a single pipe or by a group of circulator tubes. Steam flows at high velolocity from the inlet to the outlet header through a large number of parallel tubes or elements of small diameter.

The amount of surface required in the superheater depends upon the final temperature to which the steam is to be superheated, the amount of steam to be superheated, the quantity of hot gas flowing around the superheater, and the temperature of the gas. In order to keep the surface to a minimum and thus reduce the cost of the superheater, it should be located where high-temperature gases will flow around the tubes. On the other hand, the products of combustion must be cooled sufficiently before they enter the superheater tubes so that any ash that may be present has been cooled to a temperature at which it is no longer sticky or plastic and will not adhere to the superheater tubes.

Word- building

Task 4

Look through the text and find the words corresponding to the given ones. Fill in the table.

Vocabulary

Task 5

Match the words from the right column with the words in the left one.

1. steam 1. advantage

2. fluid 2. velocity

3. convection 3. steam

4. considerable 4. superheater

5. high 5. volume

6. wet 6. boiler

7. combustion 7. friction

8. inlet 8. header

9. superheater 9. cost

10. increased 10. heat

11. specific 11. temperature

12. absorb 12. products

Task6

Find in the text English equivalents to the following groups of words.

Таким образом увеличивая температуру, передача тепла, понижение давления пара из-за трения жидкости, влажность понижает эффективность, поэтому необходимо обеспечивать, насыщенный пар подается к коллектору, его следует расположить там ,где газы …, перед тем как они поступят в трубы пароперегревателя, она больше не липкая.

Task 7

Date: 2014-12-29; view: 1511