Flue-gas emissions from fossil-fuel combustion

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Before flue-gas desulfurization was installed, emissions from Four Corners Generating Station, New Mexico contained excessive amounts of sulfur dioxide. Air pollution by industrial chimneys.jpg
Before flue-gas desulfurization was installed, emissions from Four Corners Generating Station, New Mexico contained excessive amounts of sulfur dioxide.

Flue-gas emissions from fossil-fuel combustion refers to the combustion-product gas resulting from the burning of fossil fuels. [1] Most fossil fuels are combusted with ambient air (as differentiated from combustion with pure oxygen). Since ambient air contains about 79 volume percent gaseous nitrogen (N2), [2] which is essentially non-combustible, the largest part of the flue gas from most fossil-fuel combustion is uncombusted nitrogen. Carbon dioxide (CO2), the next largest part of flue gas, can be as much as 10−25 volume percent or more of the flue gas. This is closely followed in volume by water vapor (H2O) created by the combustion of the hydrogen in the fuel with atmospheric oxygen. Much of the 'smoke' seen pouring from flue gas stacks is this water vapor forming a cloud as it contacts cool air.

Combustion high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized in a mixture termed as smoke

Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242 kJ/mol of heat and reduces the enthalpy accordingly :

Fossil fuel fuel formed by natural processes such as anaerobic decomposition of buried dead organisms

A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing energy originating in ancient photosynthesis. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years. Fossil fuels contain high percentages of carbon and include petroleum, coal, and natural gas. Other commonly used derivatives include kerosene and propane. Fossil fuels range from volatile materials with low carbon to hydrogen ratios like methane, to liquids like petroleum, to nonvolatile materials composed of almost pure carbon, like anthracite coal. Methane can be found in hydrocarbon fields either alone, associated with oil, or in the form of methane clathrates.

Oxygen Chemical element with atomic number 8

Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.

Contents

A typical flue gas from the combustion of fossil fuels contains very small amounts of nitrogen oxides (NOx), sulfur dioxide (SO2) and particulate matter. [1] The nitrogen oxides are derived from the nitrogen in the ambient air as well as from any nitrogen-containing compounds in the fossil fuel. The sulfur dioxide is derived from any sulfur-containing compounds in the fuels. The particulate matter is composed of very small particles of solid materials and very small liquid droplets which give flue gases their smoky appearance.

Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:

Sulfur dioxide chemical compound

Sulfur dioxide is the chemical compound with the formula SO
2. It is a toxic gas with a burnt match smell. It is released naturally by volcanic activity and is produced as a by-product of the burning of fossil fuels contaminated with sulfur compounds and copper extraction.

The steam generators in large power plants and the process furnaces in large refineries, petrochemical and chemical plants, and incinerators burn considerable amounts of fossil fuels and therefore emit large amounts of flue gas to the ambient atmosphere. The table below presents the total amounts of flue gas typically generated by the burning of fossil fuels such as natural gas, fuel oil and coal. The data were obtained by stoichiometric [3] calculations. [4]

Furnace device used for heating in industry

A furnace is a device used for high-temperature heating. The name derives from Latin word fornax, which means oven. The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces.

Oil refinery industrial process plant where crude oil is processed and refined into more useful products

Oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into more useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel and fuel oils. Petrochemicals feed stock like ethylene and propylene can also be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha.

Petrochemical chemical product derived from petroleum

Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn, palm fruit or sugar cane.

It is of interest to note that the total amount of wet flue gas generated by coal combustion is only 10 percent higher than the flue gas generated by natural-gas combustion (the ratio for dry flue gas is higher).

Exhaust flue gas generated by combustion of fossil fuels
(In SI metric units and in US customary units)
Combustion data Fuel gas Fuel oil Coal
Fuel properties:
Gross caloric value, MJ/m343.01
Gross heating value, Btu/scf1,093
Gross caloric value, MJ/kg43.50
Gross heating value, Btu/gal[ vague ]150,000
Gross caloric value, MJ/kg25.92
Gross heating value, Btu/lb11,150
Molecular weight 18
Specific gravity 0.9626
Gravity, °API15.5
Carbon/hydrogen ratio by weight8.1
weight % carbon61.2
weight % hydrogen4.3
weight % oxygen 7.4
weight % sulfur3.9
weight % nitrogen1.2
weight % ash 12.0
weight % moisture 10.0
Combustion air:
Excess combustion air, %121520
Wet exhaust flue gas:
Amount of wet exhaust gas, m3/GJ of fuel294.8303.1323.1
Amount of wet exhaust gas, scf/106 Btu of fuel11,60011,93012,714
CO2 in wet exhaust gas, volume %8.812.413.7
O2 in wet exhaust gas, volume %2.02.63.4
Molecular weight of wet exhaust gas27.729.029.5
Dry exhaust flue gas:
Amount of dry exhaust gas, m3/GJ of fuel241.6269.3293.6
Amount of dry exhaust gas, scf/106 Btu of fuel9,51010,60011,554
CO2 in dry exhaust gas, volume %10.814.015.0
O2 in dry exhaust gas, volume %2.52.93.7
Molecular weight of dry exhaust gas29.930.430.7
Note:  m3 are standard cubic meters at 0 °C and 101.325 kPa, and scf is standard cubic feet at 60 °F and 14.696 psia.

See also

<i>AP 42 Compilation of Air Pollutant Emission Factors</i>

The AP 42 Compilation of Air Pollutant Emission Factors is a compilation of the US Environmental Protection Agency (EPA)'s emission factor information on air pollution, first published in 1968. As of 2018, the last edition is the 5th from 2010.

Emission standard legal requirements governing air pollutants released into the atmosphere; set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes

Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. They are generally designed to achieve air quality standards and to protect human life.

Flue-gas stack

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. 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. 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. It also contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides. The flue gas stacks are often quite tall, up to 400 metres (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.

Related Research Articles

Acid rain rain that is unusually acidic

Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions. It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Some governments have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes, and sulfur dioxide is produced by volcanic eruptions. Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms, causing paint to peel, corrosion of steel structures such as bridges, and weathering of stone buildings and statues as well as having impacts on human health.

Smoke mass of airborne particulates and gases

Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires, but may also be used for pest control (fumigation), communication, defensive and offensive capabilities in the military, cooking, or smoking. It is used in rituals where incense, sage, or resin is burned to produce a smell for spiritual purposes. Smoke is sometimes used as a flavoring agent, and preservative for various foodstuffs. Smoke is also a component of internal combustion engine exhaust gas, particularly diesel exhaust.

Fluidized bed combustion

Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels.

Alternative fuel

Alternative fuels, known as non-conventional and advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels like; fossil fuels, as well as nuclear materials such as uranium and thorium, as well as artificial radioisotope fuels that are made in nuclear reactors.

Exhaust gas emitted as a result of the combustion of fuels such as natural gas, gasoline, petrol, biodiesel blends, diesel fuel, fuel oil, or coal

Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline, petrol, biodiesel blends, diesel fuel, fuel oil, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.

Flue-gas desulfurization

Flue-gas desulfurization (FGD) is a set of technologies used to remove sulfur dioxide from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulfur oxide emitting processes

Fossil fuel power station Facility that burns fossil fuels to produce electricity

A fossil fuel power station is a thermal power station which burns a fossil fuel such as coal, natural gas, or petroleum to produce electricity. Central station fossil fuel power plants are designed on a large scale for continuous operation. In many countries, such plants provide most of the electrical energy used. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating internal combustion engine. All plants use the energy extracted from expanding gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have efficiency limited by the Carnot efficiency and therefore produce waste heat.

Flue gas gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator

Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants. Its composition depends on what is being burned, but it will usually consist of mostly nitrogen derived from the combustion of air, carbon dioxide, and water vapor as well as excess oxygen. It further contains a small percentage of a number of pollutants, such as particulate matter, carbon monoxide, nitrogen oxides, and sulfur oxides.

Scrubber systems are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. The first air scrubber was designed to remove carbon dioxide from the air of an early submarine, the Ictineo I, a role for which they continue to be used today. Traditionally, the term "scrubber" has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream. Recently, the term has also been used to describe systems that inject a dry reagent or slurry into a dirty exhaust stream to "wash out" acid gases. Scrubbers are one of the primary devices that control gaseous emissions, especially acid gases. Scrubbers can also be used for heat recovery from hot gases by flue-gas condensation. They are also used for the high flows in solar, PV, or LED processes.

Coal pollution mitigation

Coal pollution mitigation, often called clean coal, is a series of systems and technologies that seek to mitigate the pollution and other environmental effects normally associated with the burning of coal, which is widely regarded as the dirtiest of the common fuels for industrial processes and power generation.

LO-NOx burner type of burner

A LO NOx burner is a type of burner that is typically used in utility boilers to produce steam and electricity.

Clean coal technology is a collection of technologies being developed in attempts to lessen the negative environmental impact of coal energy generation and to mitigate worldwide climate change. When coal is used as a fuel source, the gaseous emissions generated by the thermal decomposition of the coal include sulfur dioxide (SO2), nitrogen oxides (NOx), mercury, and other chemical byproducts that vary depending on the type of the coal being used. These emissions have been established to have a negative impact on the environment and human health, contributing to acid rain, lung cancer and cardiovascular disease. As a result, clean coal technologies are being developed to remove or reduce pollutant emissions to the atmosphere. Some of the techniques that would be used to accomplish this include chemically washing minerals and impurities from the coal, gasification (see also IGCC), improved technology for treating flue gases to remove pollutants to increasingly stringent levels and at higher efficiency, carbon capture and storage technologies to capture the carbon dioxide from the flue gas and dewatering lower rank coals (brown coals) to improve the calorific value, and thus the efficiency of the conversion into electricity. Concerns exist regarding the economic viability of these technologies and the timeframe of delivery, potentially high hidden economic costs in terms of social and environmental damage, and the costs and viability of disposing of removed carbon and other toxic matter.

An emission inventory is an accounting of the amount of pollutants discharged into the atmosphere. An emission inventory usually contains the total emissions for one or more specific greenhouse gases or air pollutants, originating from all source categories in a certain geographical area and within a specified time span, usually a specific year.

Oxy-fuel combustion process

Oxy-fuel combustion is the process of burning a fuel using pure oxygen instead of air as the primary oxidant. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame.

Continuous emission monitoring systems (CEMS) were historically used as a tool to monitor flue gas for oxygen, carbon monoxide and carbon dioxide to provide information for combustion control in industrial settings. They are currently used as a means to comply with air emission standards such as the United States Environmental Protection Agency's (EPA) Acid Rain Program, other federal emission programs, or state permitted emission standards. Facilities employ the use of CEMS to continuously collect, record and report the required emissions data.

F. B. Culley Generating Station

F. B. Culley Generating Station is a 369 megawatt (MW) coal power plant located southeast of Newburgh in Warrick County, Indiana. It sits on the north bank of Ohio River, immediately adjacent and upstream of the Warrick Power Plant, and is owned and operated by Vectren.

The SNOX process is a process which removes sulfur dioxide, nitrogen oxides and particulates from flue gases. The sulfur is recovered as concentrated sulfuric acid and the nitrogen oxides are reduced to free nitrogen. The process is based on the well-known WSA process, a process for recovering sulfur from various process gasses in the form of commercial quality sulfuric acid (H2SO4).

References

  1. 1 2 Compilation of Air Pollutant Emission Factors
  2. ↑ Perry, R.H. and Green, D.W. (Editors) (1997). Perry's Chemical Engineers' Handbook (7th ed.). McGraw Hill. ISBN   0-07-049841-5.CS1 maint: Multiple names: authors list (link) CS1 maint: Extra text: authors list (link)
  3. ↑ Zumdahl, Steven S. (2005). Chemical Principles (5th ed.). Houghton Mifflin College Division. ISBN   0-618-37206-7.
  4. ↑ Air Dispersion Modeling Conversions and Formulas
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