District heating

District heating is a system for distributing heat generated in a centralised location for residential and commercial space heating and water heating. The heat is obtained from a heat boiler station or cogeneration plant (combined heat and power) by burning fossil fuels but, more often, biomass; geothermal heating and central solar heating as well as nuclear power are also used. District heating plants or cogeneration plants can provide higher efficiency and better pollution control than local boiler stations. The difference between the two systems is that in a cogeneration plant, heat and electricity are generated simultaneously, and in a heat boiler station, only heat is generated.

After generation, the heat is distributed to the customer via a network of pipes. Usually the pipes are installed underground but there are also systems with overground pipes. The common medium for heat distribution is water or steam.

District heating has various advantages compared to individual heating systems. District heating is more energy efficient. The larger combustion units have a more advanced flue gas cleaning than single boiler systems. District heating systems use waste heat energy from industries and are environment friendly. But they require high financing. They are attractive only for areas with large buildings.

What are the advantages and disadvantages of district heating systems?

UNIT VIII

Exercise I. Make sure you pronounce the following words correctly:

Cylinder, shell, corrugated furnace, chamber, circumferential, collapse, hazard.

Fire-tube boilers

A fire-tube or Scotch boiler is a boiler in which the water is outside the tube and the hot gases pass through the tube.

Fire-tube boilers generally consist of a cylindrical shell; they are internally fired, and are fitted with corrugated furnaces and return-tube fire tubes. These boilers are both single- and double-end type, usually having two or more furnaces in each end, either with one combustion chamber for each furnace or with a single combustion chamber serving several furnaces.

Furnaces are cylindrical shells with circumferential corrugations to afford strength against collapse and to provide for expansion. With oil fuel, burners are applied by means of a suitable furnace behind which refractory is placed. If coal fuel is used, grates are placed approximately on the horizontal centre of the furnace. To direct air through the fuel bed a wall is erected at the rear of the grates.

The purpose of the combustion chamber is to allow combustion to be completed and to distribute the flue gases to the tubes.

The advantages of a fire-tube boiler are easy maintenance and repair, ability to use feed water of doubtful quality, and adaptability to practically any fuel. As for disadvantages, they require large quantities of boiler water, are heavy and bulky, cannot raise steam quickly, and are extremely hazardous, if damaged, due to the large quantities of water and steam contained in the shells.

Exercise II. Translate the following attributive groups into Russian:

Return-tube fire tubes, double-end type boiler, single combustion chamber, combustion chamber work, flue gases distribution, oil fuel burner application, maintenance and repair expenses.

Exercise III. Form nouns from the following words. Find them in the text.

a) strong b) able c) to adapt d) to expand e) to maintain f) to repair g) to collapse

Exercise IV. Complete the sentences according to the text:

1) Fire-tube boilers consist of … 2) Double-end type boilers have two or more … 3) Furnaces are cylindrical shells with … 4) The purpose of the combustion chamber is …

Exercise V. Complete the sentences inserting the “-ed” or “-ing” form of the verbs in brackets:

1) Fire-tube boilers are easily … (maintain). 2) Fire-tube boilers can be extremely dangerous because of large quantities of water and steam …in the shells. (contain) 3) The tubes …water are usually installed underground. (contain)

4) This type of boilers is fitted with …furnaces. (corrugate) 5) District … plants can provide greater efficiency. (heat) 6) The water … up to 100ºC evaporates. (heat) 7) In a cogeneration plant, heat and electricity are ……. simultaneously. (generate)

Exercise VI. Make questions about fire-tube boilers to which the following sentences are the answers. Model: … … … ? – Hot gases. (What is inside the boiler tubes?)

1) … … … ? - A cylindrical shell, corrugated furnaces, fire tubes and combustion chambers. 2) … … … ? - Circumferential corrugation is necessary to afford strength against collapse and to provide for expansion.

3) … … … ? - At the rear of the grates.

4) … … … ? - To distribute the flue gases to the tubes.

5) … … … ? - Easy maintenance and adaptability to any water quality and any fuel.

Exercise VII. Working in pairs, role-play a conversation in which an engineer explains the advantages and disadvantages of a fire-tube boiler.

Exercise VIII. Read the following text without a dictionary and speak about the development of heating systems in the world.