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'''Flue gas''' is [[gas]] that exits to the atmosphere via a ''flue'' which may be a pipe, channel or chimney for conveying [[combustion]] product gases from a fireplace, oven, [[furnace]], [[boiler]] or [[steam generator]].
'''Entrainment''' as commonly used in various branches of [[science]] and [[engineering]] may be defined as the entrapment of one substance by another substance.<ref>{{cite book|author=Perry, R.H. and Green, D.W. (Editors)|title=[[Perry's Chemical Engineers' Handbook]]|edition=Sixth Edition|publisher=McGraw-Hill|year=1984|id=ISBN 0-07-049479-7}}</ref>


Flue gases are produced when [[coal]], [[fuel oil]], [[natural gas]], [[wood]] or any other fuel is [[combustion|combusted]] in an industrial [[furnace]] or [[boiler]], a [[steam-generator]] in a  [[fossil fuel]] [[power plant]] or other combustion sources.
== Types of entrainment ==


== Flue gas composition ==
Ther are a great many types of entrainment encountered in [[chemistry]], [[chemical engineering]], other [[engineering]] disciplines and in [[atmospheric science]]s. Here are a number of examples:


Flue gas is usually composed of [[carbon dioxide]] (CO<sub>2</sub>) and water vapor as well as [[nitrogen]] and excess [[oxygen]] remaining from the intake combustion air. It may also contain a small percentage of air pollutants such as [[particulate matter]], [[carbon monoxide]], [[nitrogen oxide]]s, [[sulfur oxide]]s and [[mercury]]. Typically, more than two-thirds of the flue gas is nitrogen.
* The entrapment of [[liquid]] entrapment in air or any other [[gas]] as in [aerosol]]s or [[fog]].
* The entrapment of liquid droplets and [[solid]] [[particulate matter]] in a flowing [[gas]], as in [[smoke]] entrapped in  [[combustion]] [[flue gas]]es.
* The entrapment of gas bubbles or solid particulates in a flowing liquid, as with [[aeration]].
* Given two mutually insoluble liquids, the [[emulsion]] of droplets of one liquid entrapped in the other liquid, as with [[margarine]].
* Given two gases, the entrapment of one gas into the other gas.
* The intentional entrapment of air bubbles in concrete.


Table 1 provides the amounts of flue gas (on a dry basis as well as a wet basis) that are generated by burning a typical flue gas or  fuel oil or coal. The flue gas amounts were obtained by [[stoichiometry|stoichiometric]] calculations using the indicated typical excess combustion air percentages: 
==References==


{| class="wikitable" align=center
{{reflist}}
|-
|+ Table 1: Flue gas generated by burning fossil fuels
! Combustion data!!Fuel gas!!Fuel oil!!Coal
|-
|'''Fuel properties:'''||&nbsp;||&nbsp;||&nbsp;
|-
|Gross [[heating value]], MJ/m³||align=center|43.01||&nbsp;||&nbsp;
|-
|Gross heating value, MJ/kg||&nbsp;||align=center|43.50||align=center|25.92
|-
|[[Molecular mass]]||align=center|18||&nbsp;||&nbsp;
|-
|[[Specific gravity]]||&nbsp;||align=center|0.9626||&nbsp;
|-
|[[Carbon]]/[[hydrogen]] ratio by weight||&nbsp;||align=center|8.1||&nbsp;
|-
|weight % carbon||&nbsp;||&nbsp;||align=center|61.2
|-
|weight % hydrogen||&nbsp;||&nbsp;||align=center|4.3
|-
|weight % oxygen||&nbsp;||&nbsp;||align=center|7.4
|-
|weight % [[sulfur]]||&nbsp;||&nbsp;||align=center|3.9
|-
|weight % nitrogen||&nbsp;||&nbsp;||align=center|1.2
|-
|weight % [[Coal assay|ash]]||&nbsp;||&nbsp;||align=center|12.0
|-
|weight % [[Coal assay|moisture]]||&nbsp;||&nbsp;||align=center|10.0
|-
|'''Combustion air:'''||&nbsp;||&nbsp;||&nbsp;
|-
|Excess combustion air, %||align=center|12||align=center|15|| align=center|20
|-
|'''Wet combustion flue gas:'''||&nbsp;||&nbsp;||&nbsp;
|-
|Wet combustion flue gas, m³/GJ of fuel|| align=center|294.8||align=center|303.1||align=center|323.1
|-
|Molecular mass of wet combustion gas||align=center|27.7 ||align=center|29.0||align=center|29.5
|-
|'''Dry combustion flue gas:'''||&nbsp;||&nbsp;||&nbsp;
|-
|Dry combustion flue gas, m³/GJ of fuel|| align=center|241.6||align=center|269.3||align=center|293.6
|-
|Molecular mass of dry combustion gas||align=center|29.9 ||align=center|30.4||align=center|30.7
|-
|'''Notes:'''<br>(1) Gas amounts (m³) are at 0 °C and 1 atm<br>(2) Heating value = caloric value ||&nbsp;||&nbsp;||&nbsp;
|}
 
Given the amount of gas, oil or coal fuel burned in a combustion device, then the flue gas generation data (i.e., m³/GJ of fuel) in Table 1 provides a basis for estimating the amount of flue gas generated.
 
== Flue gas treatment ==
 
At power plants, flue gas is often treated with a series of chemical processes and [[scrubber]]s, which remove  pollutants. [[Electrostatic Precipitator|Electrostatic precipitators]] or fabric filters remove particulate matter and [[flue gas desulfurization]] captures the [[sulfur]] dioxide produced by burning fossil fuels, particularly coal.
 
Nitrogen oxides emissions are reduced either by modifications to the combustion process to prevent their formation, or by catalytic reaction with ammonia or urea. In either case, the aim is to produce nitrogen gas, rather than nitrogen oxides.
 
In the United States, there is also a rapid deployment of technologies to remove mercury from flue gas - typically by adsorption on sorbents or by capture in inert solids as part of the flue gas desulfurization product.
 
Technologies for the removal and capture of carbon dioxide  from flue gases are now under active research  and development as a means of reducing the emissions of so-called ''greenhouse gas''.
 
==See also==
* [[Combustion]]
* [[Emission standard]]
* [[Exhaust gas]]
* [[Flue gas emissions from fossil fuel combustion]]
* [[Flue gas stacks]]
* [[Flue gas desulfurization]] (often referred to as FGD)
* [[Integrated Gasification Combined Cycle]] (often referred to as IGCC)
* [[Nitrogen oxide]]s emission (often referred to as NOx)

Revision as of 21:36, 19 June 2008

Entrainment as commonly used in various branches of science and engineering may be defined as the entrapment of one substance by another substance.[1]

Types of entrainment

Ther are a great many types of entrainment encountered in chemistry, chemical engineering, other engineering disciplines and in atmospheric sciences. Here are a number of examples:

  • The entrapment of liquid entrapment in air or any other gas as in [aerosol]]s or fog.
  • The entrapment of liquid droplets and solid particulate matter in a flowing gas, as in smoke entrapped in combustion flue gases.
  • The entrapment of gas bubbles or solid particulates in a flowing liquid, as with aeration.
  • Given two mutually insoluble liquids, the emulsion of droplets of one liquid entrapped in the other liquid, as with margarine.
  • Given two gases, the entrapment of one gas into the other gas.
  • The intentional entrapment of air bubbles in concrete.

References

  1. ↑ Perry, R.H. and Green, D.W. (Editors) (1984). Perry's Chemical Engineers' Handbook, Sixth Edition. McGraw-Hill. ISBN 0-07-049479-7. 
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