Smouldering

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Smouldering combustion in glowing embers of barbecue coal briquettes Embers 01.JPG
Smouldering combustion in glowing embers of barbecue coal briquettes

Smouldering (British English) or smoldering (American English; see spelling differences) is the slow, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. [1] Many solid materials can sustain a smouldering reaction, including coal, cellulose, wood, cotton, tobacco, cannabis, peat, plant litter, humus, synthetic foams, charring polymers including polyurethane foam and some types of dust. Common examples of smouldering phenomena are the initiation of residential fires on upholstered furniture by weak heat sources (e.g., a cigarette, a short-circuited wire), and the persistent combustion of biomass behind the flaming front of wildfires. [2]

Contents

Fundamentals

A smouldering cigarette. Papierosa 1 ubt 0069.jpeg
A smouldering cigarette.

The fundamental difference between smouldering and flaming combustion is that smouldering occurs on the surface of the solid rather than in the gas phase. Smouldering is a surface phenomenon but can propagate to the interior of a porous fuel if it is permeable to flow. The characteristic temperature and heat released during smouldering are low compared to those in the flaming combustion. Smouldering propagates in a creeping fashion, around 0.1 mm/s (0.0039 in/s), which is about ten times slower than flames spread over a solid. In spite of its weak combustion characteristics, smouldering is a significant fire hazard. Smouldering emits toxic gases (e.g., carbon monoxide) at a higher yield than flaming fires and leaves behind a significant amount of solid residue. The emitted gases are flammable and could later be ignited in the gas phase, triggering the transition to flaming combustion. [3]

Smouldering materials

Polyurethane foam sample from the NASA smouldering experiments. Nasa Microgravity Smoldering Combustion experiments.jpg
Polyurethane foam sample from the NASA smouldering experiments.

Many materials can sustain a smouldering reaction, including coal, tobacco, decaying wood and sawdust, biomass fuels on the forest surface (duff) and subsurface (peat), cotton clothing and string, and polymeric foams (e.g., upholstery and bedding materials). Smouldering fuels are generally porous, permeable to flow and formed by aggregates (particulates, grains, fibres or of cellular structure). These aggregates facilitate the surface reaction with oxygen by allowing gas flow through the fuel and providing a large surface area per unit volume. They also act as thermal insulation, reducing heat losses. The most studied materials to date are cellulose and polyurethane foams.

Threats from smouldering

The characteristics of smouldering fires make them a threat of new dimensions, taking the form of colossal underground fires or silent fire safety risks, as summarized below.

Beneficial applications

Smouldering combustion has some beneficial applications.

See also

Related Research Articles

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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 does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. While activation energy must be supplied to initiate combustion, the heat from a flame may provide enough energy to make the reaction self-sustaining.

<span class="mw-page-title-main">Wood gas</span> Syngas fuel created by gasification of biomass

Wood gas is a fuel gas that can be used for furnaces, stoves, and vehicles. During the production process, biomass or related carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce a combustible mixture. In some gasifiers this process is preceded by pyrolysis, where the biomass or coal is first converted to char, releasing methane and tar rich in polycyclic aromatic hydrocarbons.

<span class="mw-page-title-main">Pyrolysis</span> Thermal decomposition of materials at elevated temperatures, often in an inert atmosphere

The pyrolysis process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere.

<span class="mw-page-title-main">Solid fuel</span> Solid material that can be burnt to release energy

Solid fuel refers to various forms of solid material that can be burnt to release energy, providing heat and light through the process of combustion. Solid fuels can be contrasted with liquid fuels and gaseous fuels. Common examples of solid fuels include wood, charcoal, peat, coal, hexamine fuel tablets, dry dung, wood pellets, corn, wheat, rice, rye, and other grains. Solid fuels are extensively used in rocketry as solid propellants. Solid fuels have been used throughout human history to create fire and solid fuel is still in widespread use throughout the world in the present day.

<span class="mw-page-title-main">Briquette</span> Compressed block of biomass used for fueling a fire

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<span class="mw-page-title-main">Bioenergy</span> Renewable energy made from biomass

Bioenergy is a type of renewable energy that is derived from plants and animal waste. The biomass that is used as input materials consists of recently living organisms, mainly plants. Thus, fossil fuels are not regarded as biomass under this definition. Types of biomass commonly used for bioenergy include wood, food crops such as corn, energy crops and waste from forests, yards, or farms.

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<span class="mw-page-title-main">Fire-retardant fabric</span> Flame retardant fabric

Fire-retardant fabrics are textiles that are more resistant to fire than others through chemical treatment of flame-retardant or manufactured fireproof fibers.

<span class="mw-page-title-main">Biochar</span> Lightweight black residue, made of carbon and ashes, after pyrolysis of biomass

Biochar is the lightweight black residue, made of carbon and ashes, remaining after the pyrolysis of biomass, and is a form of charcoal. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment". Biochar is a stable solid that is rich in pyrogenic carbon and can endure in soil for thousands of years.

<span class="mw-page-title-main">Biomass (energy)</span> Biological material used as a renewable energy source

Biomass, in the context of energy production, is matter from recently living organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues including straw, and organic waste from industry and households. Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo. The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.

<span class="mw-page-title-main">Biomass heating system</span>

Biomass heating systems generate heat from biomass. The systems may use direct combustion, gasification, combined heat and power (CHP), anaerobic digestion or aerobic digestion to produce heat. Biomass heating may be fully automated or semi-automated they may be pellet-fired, or they may be combined heat and power systems.

A landfill fire occurs when waste disposed of in a landfill ignites and spreads. Two types of landfills fires are generally recognized – surface fires and deep-seated fires. Surface fires typically occur in underdeveloped countries that lack capacity to properly cover waste with inert daily and intermediate cover. Modern examples of such fires include the Deonar and Ghazipur Landfills in India, Cerro Patacon Landfill in Panama and the New Providence Landfill in the Bahamas.

<span class="mw-page-title-main">Slash-and-char</span> Farming method for clearing vegetation

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<span class="mw-page-title-main">Carbon dioxide removal</span> Removal of atmospheric carbon dioxide through human activity

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<span class="mw-page-title-main">Charcoal</span> Lightweight black carbon residue

Charcoal is a lightweight black carbon residue produced by strongly heating wood in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, called charcoal burning, often by forming a charcoal kiln, the heat is supplied by burning part of the starting material itself, with a limited supply of oxygen. The material can also be heated in a closed retort. Modern "charcoal" briquettes used for outdoor cooking may contain many other additives, e.g. coal.

<span class="mw-page-title-main">Bioenergy with carbon capture and storage</span>

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. BECCS can theoretically be a "negative emissions technology" (NET), although its deployment at the scale considered by many governments and industries can "also pose major economic, technological, and social feasibility challenges; threaten food security and human rights; and risk overstepping multiple planetary boundaries, with potentially irreversible consequences". The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy ("bioenergy") is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods.

<span class="mw-page-title-main">Glossary of firelighting</span>

This is an alphabetized glossary of terms pertaining to lighting fires, along with their definitions. Firelighting is the process of starting a fire artificially. Fire was an essential tool in early human cultural development. The ignition of any fire, whether natural or artificial, requires completing the fire triangle, usually by initiating the combustion of a suitably flammable material.

<span class="mw-page-title-main">Climate-friendly gardening</span> Low greenhouse gases gardening

Climate-friendly gardening is a form of gardening that can reduce emissions of greenhouse gases from gardens and encourage the absorption of carbon dioxide by soils and plants in order to aid the reduction of global warming. To be a climate-friendly gardener means considering both what happens in a garden and the materials brought into it as well as the impact they have on land use and climate. It can also include garden features or activities in the garden that help to reduce greenhouse gas emissions through processes not directly related to gardening.

In fire and explosion prevention engineering, inerting refers to the introduction of an inert (non-combustible) gas into a closed system to make a flammable atmosphere oxygen deficient and non-ignitable.

References

  1. http://fire.nist.gov/bfrlpubs/fire02/art074.html "Smoldering Combustion" by T.J. Ohlemiller, SFPE Handbook of Fire Protection Engineering (3rd Edition), 2002
  2. G Rein, Smouldering Combustion Phenomena in Science and Technology, International Review of Chemical Engineering 1, pp. 3-18, 2009 http://hdl.handle.net/1842/2678
  3. http://fire.nist.gov/bfrlpubs/fire02/art074.html "Smoldering Combustion" by T.J. Ohlemiller, SFPE Handbook of Fire Protection Engineering (3rd Edition), 2002.
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