Lesson 1  Lesson 2  Lesson 3  Lesson 4  Lesson 5  Lesson 6  Lesson 7  Lesson 8  Lesson 9  Lesson 10

Thermal Engineering |Теплоэнергетика

Lesson 1

Read the text: Boilers and combustion chambers

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.

Construction of boilers is mainly limited to carbon steel, stainless steel, and cast iron. In live steam toys, brass is often used.

The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Electric boilers use resistance or immersion type heating elements. Nuclear fission is also used as a heat source for generating steam. Heat recovery steam generators (HRSGs) use the heat rejected from other processes such as gas turbines.

Boilers can be classified into the following configurations:

"Pot boiler" or "Haycock boiler": a primitive "kettle" where a fire heats a partially-filled water container from below. 18th Century Haycock boilers generally produced and stored large volumes of very low-pressure steam, often hardly above that of the atmosphere. These could burn wood or most often, coal. Efficiency was very low.

Fire-tube boiler. Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam (steam space). The heat source is inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating surface just below boiling point. The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating surface which can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple tubes (two-pass or return flue boiler); alternatively the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In the case of a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increase the heating surface compared to a single tube and further improve heat transfer. Fire-tube boilers usually have a comparatively low rate of steam production, but high steam storage capacity. Fire-tube boilers mostly burn solid fuels, but are readily adaptable to those of the liquid or gas variety.

Diagram of a water-tube boiler.In this type,the water tubes are arranged inside a furnace in a number of possible configurations:

often the water tubes connect large drums, the lower ones containing water and the upper ones, steam; in other cases, such as a mono-tube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage capacity than the above. Water tube boilers can be designed to exploit any heat source including nuclear fission and are generally preferred in high pressure applications since the high pressure water/steam is contained within narrow pipes which can withstand the pressure with a thinner wall.

Fire-tube boiler with Water-tube firebox. Sometimes the two above types have been combined in the following manner: the firebox contains an assembly of water tubes, the gases then pass through a conventional fire tube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success in other countries.

1. Match the left part with the right:

1. The source of heat for a boiler is                    a) the heat rejected from other processes such as gas turbines.

2. Electric boilers use                                     b) combustion of any of several fuels.

3. Nuclear fission is also used                          c) resistance or immersion type heating elements.

4. Heat recovery steam generators (HRSGs) use   d) as a heat source for generating steam.

2. Complete the sentences with the suggested words:

within; preferred; withstand; designed; source

Water tube boilers can be ________ to exploit any heat ________ including nuclear fission and are generally ________ in high pressure applications since the high pressure water/steam is contained ________ narrow pipes which can ________ the pressure with a thinner wall.