Flue gas stack at GRES-2 Power Station in Ekibastusz, Kazakhstan is the tallest in the world (420 meters)^[1]

A flue gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. The GRES-2 Power Station (or Power Station Ekibastuz) is a power generating station in Ekibastuz Ekibastuz ( Екібастұз) is a town in Pavlodar Province, northeastern Kazakhstan. Kazakhstan, also Kazakstan ( Қазақстан, Qazaqstan, qɑzɑqˈstɑn Казахстан, Kazakhstán,) officially the A chimney is a system for venting hot Flue gases or Smoke from a Boiler, Stove, Furnace or Fireplace to the outside Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of 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 oven Furnace, Boiler Flue gases are 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 device. An oil is a substance that is in a viscous Liquid state ( "oily") at ambient temperatures or slightly warmer and is Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of A furnace is a device used for Heating The name derives from Latin fornax, Oven. A power station (also referred to as generating station, power plant or powerhouse) is an industrial facility for the generation of A boiler is a closed vessel in which Water or other Fluid is heated Flue gas is usually composed of carbon dioxide (CO₂) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the It also contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. The term nitrogen oxide typically refers to any Binary compound of Oxygen and Nitrogen, or to a mixture of such compounds Nitric The flue gas stacks are often quite tall, up to 400 meters (1300 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 policy and environmental regulation. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance

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.

History

The first industrial chimneys were built in the mid-17th century when it was first understood how they could improve the combustion of a furnace by increasing the draft (draught) of air into the combustion zone. A furnace is a device used for Heating The name derives from Latin fornax, Oven. Stack effect is the movement of air into and out of buildings Chimneys, Flue gas stacks, or other containers and is driven by Buoyancy. ^[2] As such, they played an important part in the development of reverberatory furnaces and a coal-based metallurgical industry, one of the key sectors of the early Industrial Revolution. A reverberatory furnace is a metallurgical or process Furnace that isolates the material being processed from contact with the Fuel, but not from contact The Industrial Revolution was a period in the late 18th and early 19th centuries when major changes in agriculture manufacturing and transportation had a profound effect on the Most 18th century industrial chimneys (now commonly referred to as flue gas stacks) were built into the walls of the furnace much like a domestic chimney. The first free-standing industrial chimneys were probably those erected at the end of the long condensing flues associated with smelting lead. A flue is a duct, Pipe, or Chimney for conveying Exhaust gases from a Fireplace, Furnace, Water heater, Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly

The powerful association between industrial chimneys and the characteristic smoke-filled landscapes of the industrial revolution was due the universal application of the steam engine for most manufacturing processes. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. The chimney is part of a steam-generating boiler, and its evolution is closely linked to increases in the power of the steam engine. A boiler is a closed vessel in which Water or other Fluid is heated The chimneys of Thomas Newcomen’s steam engine were incorporated into the walls of the engine house. Thomas Newcomen (born shortly before 24 February 1664; died 5 August 1729) was an Ironmonger by trade and a Baptist The taller, free-standing industrial chimneys that appeared in the early 19th century were related to the changes in boiler design associated with James Watt’s "double-powered" engines, and they continued to grow in stature throughout the Victorian period. James Watt ( 19 January 1736 &ndash 25 August 1819 Boulton proved to be an excellent businessman and both men eventually made fortunes Decorative embellishments are a feature of many industrial chimneys from the 1860s, with over-sailing caps and patterned brickwork.

The invention of fan-assisted forced draft (draught) in the early 20th century removed the industrial chimney's original function, that of drawing air into the steam-generating boilers or other furnaces. With the replacement of the steam engine as a prime mover, first by diesel engines and then by electric motors, the early industrial chimneys began to disappear from the industrial landscape. Building materials changed from stone and brick to steel and later reinforced concrete, and the height of the industrial chimney was determined by the need to disperse combustion flue gases to comply with governmental air pollution control regulations. Air pollution is the human introduction into the atmosphere of Chemicals Particulate matter, or Biological materials that cause harm or discomfort

Flue gas stack draft (or draught)

The stack effect in chimneys: the gauges represent absolute air pressure and the airflow is indicated with light grey arrows. The gauge dials move clockwise with increasing pressure.

Main article: Stack effect

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. Stack effect is the movement of air into and out of buildings Chimneys, Flue gas stacks, or other containers and is driven by Buoyancy. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 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. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface 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". HVAC (pronounced either "H-V-A-C" or occasionally " H-vak " is an Initialism or Acronym that stands for " Heating Stack effect is the movement of air into and out of buildings Chimneys, Flue gas stacks, or other containers and is driven by Buoyancy. The taller the stack, the more draft (or draught) is created.

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:^[3][4]

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. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) Both assumptions are fairly good but not exactly accurate.

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:^[5]

Designing chimneys and stacks to provide the correct amount of natural draft involves a great many factors such as:

• The height and diameter of the stack. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic
• 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 density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different
• 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.

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).

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. Flue gas desulfurization (FGD is the technology used for removing Sulfur dioxide (SO2 from the exhaust flue gases in power plants that The term nitrogen oxide typically refers to any Binary compound of Oxygen and Nitrogen, or to a mixture of such compounds Nitric e, selective catalytic reduction, exhaust gas recirculation, thermal deNOx, or low NOx burners). Selective catalytic reduction ( SCR) is a means of converting nitrogen oxides, also referred to as {{chem|NO|x}} with the aid of a Catalyst into At such power plants, it is possible to use a cooling tower as a flue gas stack. Cooling towers are heat removal devices used to transfer process waste heat to the Atmosphere. Examples can be seen in Germany at the Power Station Staudinger Grosskrotzenburg and at the Rostock Power Station. Grosskrotzenburg Power Station (Grosskrotzenburg Staudinger Power Station is a modern Coal -fired thermal Power station in Grosskrotzenburg, Hesse Rostock Power Station is a Bituminous coal -fired combined heat and power plant operated by Kraftwerks- und Netzgesellschaft mbH (KNG located in Rostock Power plants without flue gas purification, would experience serious corrosion in such cooling towers.

In the United States and a number of other countries, atmospheric dispersion modeling^[6] studies are required to determine the flue gas stack height needed to comply with the local air pollution regulations. Atmospheric dispersion modeling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. Air pollution is the human introduction into the atmosphere of Chemicals Particulate matter, or Biological materials that cause harm or discomfort The United States also limits the maximum height of a flue gas stack to what is known as the "Good Engineering Practice (GEP)" stack height. ^[7][8] In the case of existing flue gas stacks that exceed the GEP stack height, any air pollution dispersion modeling studies for such stacks must use the GEP stack height rather than the actual stack height.

See also

• Chimney
• Flue gas
• Flue gas desulfurization
• Flue gas emissions from fossil fuel combustion
• Incineration
• Stack effect

References

1. ^ Diagram of 25 tallest flue gas stacks worldwide
2. ^ Douet, James (1988). A chimney is a system for venting hot Flue gases or Smoke from a Boiler, Stove, Furnace or Fireplace to the outside 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 oven Furnace, Boiler Flue gas desulfurization (FGD is the technology used for removing Sulfur dioxide (SO2 from the exhaust flue gases in power plants that Flue gas emissions from fossil fuel combustion refers to the Combustion product gas resulting from the burning of Fossil fuels. Incineration is a waste treatment technology that involves the Combustion of organic materials and/or substances Stack effect is the movement of air into and out of buildings Chimneys, Flue gas stacks, or other containers and is driven by Buoyancy. Going up in Smoke:The History of the Industrial Chimney, Victorian Society, London, England. Victorian Society Casework Reports
3. ^ Natural Ventilation Lecture 2
4. ^ Perry, R. H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook, 6th Edition (page 9-72), McGraw-Hill Book Company. ISBN 0-07-049479-7.  
5. ^ Natural Ventilation Lecture 3
6. ^ Beychok, Milton R. (2005). Fundamentals Of Stack Gas Dispersion, 4th Edition, author-published. Fundamentals Of Stack Gas Dispersion is a book devoted to the basic fundamentals of Air pollution dispersion modeling of continuous buoyant pollution plumes ISBN 0-9644588-0-2.   www.air-dispersion.com
7. ^ Guideline for Determination of Good Engineering Practice Stack Height (Technical Support Document for the Stack Height Regulations), Revised (1985), EPA Publication No. EPA–450/4–80–023R, U. S. Environmental Protection Agency (NTIS No. PB 85–225241)
8. ^ Lawson, Jr. , R. E. and W. H. Snyder (1983). Determination of Good Engineering Practice Stack Height: A Demonstration Study for a Power Plant, EPA Publication No. EPA–600/3–83–024. U. S. Environmental Protection Agency (NTIS No. PB 83–207407)

External links

• ASHRAE's Fundamentals Handbook is available here from ASHRAE
• ASME Codes and Standards available from ASME
• Diagram of 25 tallest flue gas stacks worldwide