Flue gas stack at GRES-2 Power Plant in Ekibastus, Kazachstan is 420 meters tall

Flue gas stacks are large vertical pipes, channels or similar structures through which combustion product gases (called flue gases) produced when coal, oil, natural gas, wood or any other fuel is combusted in an industrial furnace, a power plant's steam-generating boiler, or other large combustion equipment are exhausted to the outside air. The composition of the flue gas will usually consist of mostly carbon dioxide (CO2) and water vapor as well as nitrogen and excess oxygen (derived from the combustion air). It also contains a small percentage of pollutants such particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides. The flue gas stacks are often quite tall, up to 400 meters (1312 feet) or more, so as to disperse the exhaust pollutants over a greater area and thereby reduce the concentration of the pollutants to the levels required by governmental environmental policies and regulations. Flue gas is gas that exits to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, furnace, boiler or generator. ... Coal (previously referred to as pitcoal or seacoal) is a fossil fuel extracted from the ground by underground mining or open-pit mining (surface mining). ... Natural olive oil Synthetic motor oil Oil, in a general sense, is a chemical compound that is not miscible with water, and is in a liquid state at ambient temperatures. ... Many stoves use natural gas. ... A tree trunk as found at the Veluwe, The Netherlands Wood derives from woody plants, notably trees but also shrubs. ... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... A furnace is a device for heating air or any other fluid. ... Oil power plant in Iraq A power station or power plant is a facility for the generation of electric power. ... A boiler is a closed vessel in which water or other fluid is heated under pressure. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Particulates, alternately referred to as Particulate Matter (PM) , aerosols or fine particles are tiny particles of solid or liquid suspended in the air. ... Carbon monoxide, chemical formula CO, is a colorless, odorless, tasteless, flammable and highly toxic gas. ... Nitrogen has six different oxides: Nitric oxide (NO) Nitrous oxide (N2O) Nitrogen dioxide (NO2) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen pentoxide (N2O5) The term nitrogen oxide is imprecise and can be used to refer to any of these or to a mixture of them. ... Sulfur oxide refers to one or more of the following: Sulfur monoxide (SO) Sulfur dioxide (SO2) Sulfur trioxide (SO3) This is a disambiguation page: a list of articles associated with the same title. ... In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. ... Environmental Policy refers to the laws, regulations, and other policy mechanisms concerning environmental issues. ...

When the flue gases are exhausted from stoves, ovens, fireplaces, or other small sources within residential abodes, restaurants, hotels, or other public buildings and small commercial enterprises, their flue gas stacks are referred to as chimneys.

Chimney stacks on a Newcastle upon Tyne building A chimney is a system for venting hot gases and smoke from a stove, furnace or fireplace to the outside atmosphere. ...

History

(still being worked on)

Flue gas stack draft (or draught)

The combustion flue gases inside the flue gas stacks are much hotter than the ambient outside air and therefore less dense than the ambient air. That causes the bottom of the vertical column of hot flue gas to have a lower pressure than the pressure at the bottom of a corresponding column of outside air. That higher pressure outside the chimney is the driving force that moves the required combustion air into the combustion zone and also moves the flue gas up and out of the chimney. That movement or flow of combustion air and flue gas is called "natural draft (or draught)", "natural ventilation", "chimney effect", or "stack effect". The taller the stack, the more draft (or draught) is created. Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface. ... HVAC (pronounced either H-V-A-C or, occasionally, H-VAK) is an initialism/acronym that stands for heating, ventilation and air-conditioning. This is sometimes referred to as climate control. ... Stack effect is the ventilation in buildings and chimneys that results from thermal differences between indoor and outside temperature. ...

The equation below provides an approximation of the pressure difference, ΔP, (between the bottom and the top of the flue gas stack) that is created by the draft:^[1][2]

where:
ΔP	= available pressure difference, in Pa
C	= 0.0342
a	= atmospheric pressure, in Pa
h	= height of the flue gas stack, in m
To	= absolute outside air temperature, in K
Ti	= absolute average temperature of the flue gas inside the stack, in K

The above equation is an approximation because it assumes that the molar mass of the flue gas and the outside air are equal and that the pressure drop through the flue gas stack is quite small. Both assumptions are fairly good but not exactly accurate. The pascal (symbol: Pa) is the SI unit of pressure. ... metre or meter, see meter (disambiguation) The metre is the basic unit of length in the International System of Units. ... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ...

The flue gas flow rate induced by the draft

As a "first guess" approximation, the following equation can be used to estimate the flue gas flow rate induced by the draft of a flue gas stack. The equation assumes that the molar mass of the flue gas and the outside air are equal and that the frictional resistance and heat losses are negligible:^[3]

It has been suggested that Frictional force be merged into this article or section. ...

Designing chimneys and stacks to provide the correct amount of natural draft involves a great many factors such as: The cubic meter (symbol m³) is the SI derived unit of volume. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The gravity denoted g (also gee, g-force or g-load) is a non-SI unit of acceleration defined as exactly 9. ... metre or meter, see meter (disambiguation) The metre (in the U.S., chiefly meter) is a measure of length, approximately equal to 3. ... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ...

• The height and diameter of the stack.
• The desired amount of excess combustion air needed to assure complete combustion.
• The temperature of the flue gases leaving the combustion zone.
• The composition of the combustion flue gas, which determines the flue gas density.
• The frictional resistance to the flow of the flue gases through the chimney or stack, which will vary with the materials used to construct the chimney or stack.
• The heat loss from the flue gases as they flow through the chimney or stack.
• The local atmospheric pressure of the ambient air, which is determined by the local elevation above sea level.

The calculation of many of the above design factors requires trial-and-error reiterative methods. Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ...

Governmental agencies in most countries have specific codes which govern how such design calculations must be performed. Many non-governmental organizations also have codes governing the design of chimneys and stacks (notably, the ASME codes). The American Society of Mechanical Engineers (ASME) is a professional body, specifically an engineering society, focused on mechanical engineering. ...

Other items of interest

It should be noted that not all fuel-burning industrial equipment rely upon natural draft. Many such equipment items use large fans or blowers to accomplish the same objectives, namely: the flow of combustion air into the combustion chamber and the flow of the hot flue gas out of the chimney or stack.

A great many power plants are equipped with facilities for the removal of sulfur dioxide (i.e., flue gas desulfurization) and nitrogen oxides (i.e, selective catalytic reduction, exhaust gas recirculation, thermal deNOx, or low NOx burners). At such power plants, it is possible to use a cooling tower as a flue gas stack. Examples can be seen in Germany at the Power Station Staudinger Grosskrotzenburg and at the Power Station Rostock. Power plants without flue gas purification, would experience serious corrosion in such cooling towers. Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... Flue gas desulfurization is technology that employs a sorbent, usually lime or limestone, to remove sulfur dioxide(SO2) from the gases produced by burning fossil fuels. ... Nitrogen has six different oxides: Nitric oxide (NO) Nitrous oxide (N2O) Nitrogen dioxide (NO2) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen pentoxide (N2O5) The term nitrogen oxide is imprecise and can be used to refer to any of these or to a mixture of them. ... Selective Catalytic Reduction (SCR): Gaseous or liquid ammonia is added to the flue gas stream and is absorbed onto a catalyst. ... Exhaust gas recirculation (EGR) is an NOx (Nitrogen oxide and Nitrogen Dioxide) reduction technique used in most Gasoline and Diesel engines. ... Cooling towers are structures for cooling water or other working medium to near-ambient temperature. ... The power station Staudinger Grosskrotzenburg is a modern hard coal-beaconed thermal power station at Grosskrotzenburg. ... the power station and net company ltd. ...

See also

• Chimneys
• Flue gas
• Flue gas desulfurization
• Flue gas emissions from fossil fuel combustion
• HVAC
• Stack effect

Chimney stacks on a Newcastle upon Tyne building A chimney is a system for venting hot gases and smoke from a stove, furnace or fireplace to the outside atmosphere. ... Flue gas is gas that exits to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, furnace, boiler or generator. ... Flue gas desulfurization is technology that employs a sorbent, usually lime or limestone, to remove sulfur dioxide(SO2) from the gases produced by burning fossil fuels. ... The combustion product gas resulting from the burning of fossil fuels (or any other combustible fuel) is called flue gas. ... HVAC (pronounced either H-V-A-C or, occasionally, H-VAK) is an initialism/acronym that stands for heating, ventilation and air-conditioning. This is sometimes referred to as climate control. ... Stack effect is the ventilation in buildings and chimneys that results from thermal differences between indoor and outside temperature. ...

References

1. ^ Natural Ventilation Lecture 2
2. ^ Perry, R.H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook, 6th Edition (page 9-72), McGraw-Hill Book Company. ISBN 0070494797.
3. ^ Natural Ventilation Lecture 3

External links

• ASHRAE's Fundamentals Handbook is available here from ASHRAE
• ASME's codes for steel flue gas stacks are available here from ASME