Chimney
A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas.
Chimneys are adjacent to large industrial refineries, fossil fuel combustion facilities or part of buildings, steam locomotives and ships.
[1][2] The height of a chimney influences its ability to transfer flue gases to the external environment via stack effect.
The dispersion of pollutants over a greater area can reduce their concentrations and facilitate compliance with regulatory limits.
Industrial chimney use dates to the Romans, who drew smoke from their bakeries with tubes embedded in the walls.
The earliest surviving example of an English chimney is at the keep of Conisbrough Castle in Yorkshire, which dates from 1185 AD,[3] but they did not become common in houses until the 16th and 17th centuries.
These were typically much wider than modern chimneys and started relatively high above the fire, meaning more heat could escape into the room.
[6] Industrial chimneys are commonly referred to as flue-gas stacks and are generally external structures, as opposed to those built into the wall of a building.
They are generally located adjacent to a steam-generating boiler or industrial furnace and the gases are carried to them with ductwork.
Today the use of reinforced concrete has almost entirely replaced brick as a structural element in the construction of industrial chimneys.
The 300 m (980 ft) high steam plant chimney at the Secunda CTL's synthetic fuel plant in Secunda, South Africa consists of a 26 m (85 ft) diameter windshield with four 4.6 metre diameter concrete flues which are lined with refractory bricks built on rings of corbels spaced at 10 metre intervals.
The height is to ensure the pollutants are dispersed over a wider area to meet legal or other safety requirements.
Stainless steel liners must have a cap and be insulated if they service solid fuel appliances, but following the manufacturer's instructions carefully.
Class B are uninsulated double wall pipes often called B-vent, and are only used to vent non-condensing gas appliances.
A metal wire mesh is often used as a spark arrestor to minimize burning debris from rising out of the chimney and making it onto the roof.
In the late Middle Ages in Western Europe the design of stepped gables arose to allow maintenance access to the chimney top, especially for tall structures such as castles and great manor houses.
Those gases are generally exhausted to the ambient outside air through chimneys or industrial flue-gas stacks (sometimes referred to as smokestacks).
This condition can result in poor drafting, and in the case of wood burning appliances, the cooling of the gases before emission can cause creosote to condense near the top of the chimney.
Gas fired appliances must have a draft hood to cool combustion products entering the chimney and prevent updrafts or downdrafts.
[8][9][10] A characteristic problem of chimneys is they develop deposits of creosote on the walls of the structure when used with wood as a fuel.
Disconnected or loose chimney fittings caused by corrosion over time can pose serious dangers for residents due to leakage of carbon monoxide into the home.
Bracing or strapping old masonry chimneys has not proven to be very effective in preventing damage or injury from earthquakes.
Although this use has the disadvantage that conductor ropes may corrode faster due to the exhaust gases, one can find such structures also sometimes in countries not influenced by the former Soviet Union.
Chimneys can carry antennas for radio relay services, cell phone transmissions, FM-radio and TV on their structure.
At some power stations, which are equipped with plants for the removal of sulfur dioxide and nitrogen oxides, it is possible to use the cooling tower as a chimney.
At power stations that are not equipped for removing sulfur dioxide, such usage of cooling towers could result in serious corrosion problems which are not easy to prevent.
