Plasma gasification

Last updated
Plasma Arc gasification
Process typeChemical
Industrial sector(s)Waste management
Energy
Main technologies or sub-processesPlasma arc
Plasma electrolysis
FeedstockMunicipal and industrial waste
Biomass
Solid hydrocarbons
Product(s) Syngas
Slag
Separated metal scrap

Plasma gasification is an extreme thermal process using plasma which converts organic matter into a syngas (synthesis gas) which is primarily made up of hydrogen and carbon monoxide. A plasma torch powered by an electric arc is used to ionize gas and catalyze organic matter into syngas, with slag [1] [2] [3] remaining as a byproduct. It is used commercially as a form of waste treatment, and has been tested for the gasification of refuse-derived fuel, biomass, industrial waste, hazardous waste, and solid hydrocarbons, such as coal, oil sands, petcoke and oil shale. [2]

Contents

Process

Small plasma torches typically use an inert gas such as argon where larger torches require nitrogen. The electrodes vary from copper or tungsten to hafnium or zirconium, along with various other alloys. A strong electric current under high voltage passes between the two electrodes as an electric arc. Pressurized inert gas is ionized passing through the plasma created by the arc. The torch's temperature ranges from 2,000 to 14,000 °C (3,600 to 25,200 °F). [4] The temperature of the plasma reaction determines the structure of the plasma and forming gas. [5]

The waste is heated, melted and finally vaporized. Only at these extreme conditions can molecular dissociation occur by breaking apart molecular bonds. Complex molecules are separated into individual atoms. The resulting elemental components are in a gaseous phase (syngas). Molecular dissociation using plasma is referred to as "plasma pyrolysis." [6]

Feedstocks

The feedstock for plasma waste treatment is most often refuse-derived fuel, biomass waste, or both. Feedstocks may also include biomedical waste and hazardous materials. Content and consistency of the waste directly impacts performance of a plasma facility. Pre-sorting to extract treatable material for the gasification provides consistency. Too much inorganic material such as metal and construction waste increases slag production, which in turn decreases syngas production. However, a benefit is that the slag itself is chemically inert and safe to handle (certain materials may affect the content of the gas produced, however [7] ). Shredding waste to small uniform particles before entering the main chamber is generally required. This creates an efficient transfer of energy which enable sufficient breakdown of the materials. [7]

Steam is sometimes added into gasification processes to increase the generation of hydrogen (steam reforming).

Yields

Pure highly calorific synthesis gas consists predominantly of carbon monoxide (CO) and hydrogen (H2). [8] Inorganic compounds in the waste stream are not broken down but melted, which includes glass, ceramics, and various metals.

The high temperature and lack of oxygen prevents the formation of many toxic compounds such as furans, dioxins, nitrogen oxides, or sulfur dioxide in the flame itself. However, dioxins are formed during cooling of the syngas.

Metals resulting from plasma pyrolysis can be recovered from the slag and eventually sold as a commodity. Inert slag produced from some processes is granulated and can be used in construction. A portion of the syngas produced feeds on-site turbines, which power the plasma torches and thus support the feed system. [8]

Equipment

Some plasma gasification reactors operate at negative pressure, [1] but most attempt to recover [9] gaseous and/or solid resources.

Advantages

The main advantages of plasma torch technologies for waste treatment are:

Disadvantages

Main disadvantages of plasma torch technologies for waste treatment are:

Commercialization

Plasma torch gasification is used commercially for waste disposal [30] at a total of five sites worldwide with a combined design capacity of 200 tonnes of waste per day, half of which is biomass waste.

Energy recovery from waste streams using plasma gasification is currently implemented in a total of one (possibly two) installation representing a treatment capacity of 25-30 tonnes per day of waste.

Military use

The US Navy is employing Plasma Arc Waste Destruction System (PAWDS) on its latest generation Gerald R. Ford-class aircraft carrier. The compact system being used will treat all combustible solid waste generated on board the ship. After having completed factory acceptance testing in Montreal, the system is scheduled to be shipped to the Huntington Ingalls shipyard for installation on the carrier. [31]

See also

Related Research Articles

Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.

<span class="mw-page-title-main">Waste management</span> Activities and actions required to manage waste from its source to its final disposal

Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment, and disposal of waste, together with monitoring and regulation of the waste management process and waste-related laws, technologies, and economic mechanisms.

Thermal depolymerization (TDP) is the process of converting a polymer into a monomer or a mixture of monomers, by predominantly thermal means. It may be catalysed or un-catalysed and is distinct from other forms of depolymerisation which may rely on the use of chemicals or biological action. This process is associated with an increase in entropy.

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

The pyrolysis process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. The word is coined from the Greek-derived elements pyro "fire", "heat", "fever" and lysis "separating".

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

<span class="mw-page-title-main">Plasma torch</span> Device for generating a directed flow of plasma

A plasma torch is a device for generating a directed flow of plasma.

<span class="mw-page-title-main">Waste-to-energy plant</span> Building that incinerates unusable garbage

A waste-to-energy plant is a waste management facility that combusts wastes to produce electricity. This type of power plant is sometimes called a trash-to-energy, municipal waste incineration, energy recovery, or resource recovery plant.

<span class="mw-page-title-main">Municipal solid waste</span> Type of waste consisting of everyday items discarded by the public

Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste, as in a garbage disposal; the two are sometimes collected separately. In the European Union, the semantic definition is 'mixed municipal waste,' given waste code 20 03 01 in the European Waste Catalog. Although the waste may originate from a number of sources that has nothing to do with a municipality, the traditional role of municipalities in collecting and managing these kinds of waste have produced the particular etymology 'municipal.'

<span class="mw-page-title-main">Synthetic fuel</span> Fuel from carbon monoxide and hydrogen

Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by reforming of natural gas.

<span class="mw-page-title-main">Refuse-derived fuel</span> Extracted combustible fraction of municipal and other solid waste

Refuse-derived fuel (RDF) is a fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste.

<span class="mw-page-title-main">Waste-to-energy</span> Process of generating energy from the primary treatment of waste

Waste-to-energy (WtE) or energy-from-waste (EfW) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source. WtE is a form of energy recovery. Most WtE processes generate electricity and/or heat directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels, often derived from the product syngas.

Pyrolysis oil, sometimes also known as bio-crude or bio-oil, is a synthetic fuel under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500 °C (900 °F) with subsequent cooling. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non-volatility, corrosiveness, immiscibility with fossil fuels, thermal instability, and a tendency to polymerize when exposed to air. As such, it is distinctly different from petroleum products. Removing oxygen from bio-oil or nitrogen from algal bio-oil is known as upgrading.

There are a number of different waste treatment technologies for the disposal, recycling, storage, or energy recovery from different waste types. Each type has its own associated methods of waste management.

Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.

The Isle of Wight gasification facility is a municipal waste treatment plant in southern England. It entered the commissioning phase in autumn 2008, and will be replaced by a new moving grate incinerator in 2019

<span class="mw-page-title-main">Waste converter</span>

A waste converter is a machine used for the treatment and recycling of solid and liquid refuse material. A converter is a self-contained system capable of performing the following functions: pasteurization of organic waste; sterilization of pathogenic or biohazard waste; grinding and pulverization of refuse into unrecognizable output; trash compaction; dehydration. Because of the wide variety of functions available on converters, this technology has found application in diverse waste-producing industrial segments. Hospitals, clinics, municipal waste facilities, farms, slaughterhouses, supermarkets, ports, sea vessels, and airports are the primary beneficiaries of on-site waste conversion.

<span class="mw-page-title-main">Ze-gen</span>

Ze-gen, Inc. was a renewable energy company developing advanced gasification technology to convert waste into synthesis gas. Founded in 2004, Ze-gen was a venture-backed company based in Boston, Massachusetts.

Plasma gasification is in commercial use as a waste-to-energy system that converts municipal solid waste, tires, hazardous waste, and sewage sludge into synthesis gas (syngas) containing hydrogen and carbon monoxide that can be used to generate power. Municipal-scale waste disposal plasma arc facilities have been in operation in Japan and China since 2002. No commercial implementations in Europe and North America have succeeded so far. The technology is characterized by the potential of very high level of destruction of the incoming waste, but low or negative net energy production and high operational costs.

Syngas to gasoline plus (STG+) is a thermochemical process to convert natural gas, other gaseous hydrocarbons or gasified biomass into drop-in fuels, such as gasoline, diesel fuel or jet fuel, and organic solvents.

References

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