Chimney is a vertical duct which serves to guide the combustion gases or toxic to the upper atmosphere so as not to jeopardize the welfare of the population.

The chimneys can be:

1. When the building material.

1.1. Masonry

The chimneys are built: with a brick red rolled format radial and settlers from sand, lime and cement.
The stability of the structure is ensured by a spreadsheet based on the weight of materials that are part of the building.
It is built entirely without columns of reinforced concrete.
The great advantage of this construction is to not need the lining to temperatures up to 500 º C or higher in specific cases.
Today a height of 80 meters and the maximum economically feasible, provided that you do not need to be coated.

1.2. Concrete.

Are concrete towers built in wired circular section and coated internally to protect the concrete from the heat or corrosive gases.
These towers are built using forms sliding or climbing.
The advantage is speed of construction and achieve very high chimneys. There are already stacks of 600-feet tall.

1.2.1. Uni - tubular.

Are towers with a gas flow, ie, a pipeline that takes gas to the atmosphere.

1.2.2. Multi-tubular - (Multi Flue)

The tower serves as a support structure for multiple internal pipelines of various materials depending on the chemical composition and temperature of the gases that lead to the top. Very common in Pulp and Paper Mill and Oil Refineries.

1.3. Metallics

Chimneys are made of sheet steel or aluminum.
The steel construction allows varying formats in order to get more stability with less use of materials.
They must also be covered depending on the gases that pass through them.

2. As for the format:

2.1. Tapered.

It is most common, starts with a diameter that decreases as an angle that can range from 1% to 6% of the diameter in relation to height.

2.2. Tapered trunk.

For economy of material and because of the need to have a larger diameter at the base to receive the intake ducts, it is necessary to have a larger diameter at the foot of the chimney.
So to a certain height the chimney will then be tapered and cylindrical.

2.3. Cylindrical.

Foot to the top the chimney diameter is constant.

3. As to the operation or purpose:

3.1. Chimneys of Natural Circulation.

Are the chimneys that make the extraction of gases from furnaces or chemical processes without the need for electromechanical equipment such as exhaust fans or blowers.
It only works when the gases are at a higher temperature than the environment in order to generate a draft, or a vacuum in the chimney.

For the burning process is necessary if oxygen (air), combustion air enters the furnace because the chimney pulls the combustion gases and to replace the space left there is need for input from other gases and in the case of combustion air .

The hot gases inside the chimney creates an upward movement, creating a vacuum at the entrance that will pull the combustion gases. This phenomenon is called a draft. The higher the internal temperature and stack height, the greater the pull, ie the vacuum formed inside the bottom of the chimney.

The advantage of this process is energy saving and the disadvantage is that the velocity of the gases is low which reduces the efficiency of a boiler or a chemical process.

3.2. Forced Circulation chimney.

Chimneys are electromechanical devices that have to extract the gases from industrial process and blow them in the chimney.
The advantage of this type of fireplace is the largest of the gases throne speed the production process more effective.

3.3. Fireplace Dispersion

Direct the gases from industrial processes to the upper atmosphere so as not to jeopardize people's lives.
The higher the chimney more dispersed the particles arriving at ground level. If we play a handful of talcum powder than a meter high, the floor will turn white due to dust and if we play 50 feet high dust "disappear."