Plasma gasification is a thermal process that converts organic matter into a syngas (synthesis gas) which is primarily made up of

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

and

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

. A plasma torch powered by an

electric arc An electric arc (or arc discharge) is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma ( ...

ionizes gas and transforms organic matter into syngas, producing slag as a byproduct. It is used commercially as a form of waste treatment. It has been tested for the gasification of refuse-derived fuel,

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

industrial waste Industrial waste is the waste produced by industrial activity which includes any material that is rendered useless during a manufacturing process such as that of factories, mills, and mining operations. Types of industrial waste include dirt and ...

hazardous waste Hazardous waste is waste that must be handled properly to avoid damaging human health or the environment. Waste can be hazardous because it is Toxicity, toxic, Chemical reaction, reacts violently with other chemicals, or is Corrosion, corrosive, ...

, and solid hydrocarbons, such as

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

, oil sands, petcoke, and

oil shale Oil shale is an organic-rich Granularity, fine-grained sedimentary rock containing kerogen (a solid mixture of Organic compound, organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general compos ...

Process

A plasma torch passes strong electric current under high voltage between two electrodes as an

. Pressurized gas is ionized passing through the plasma created by the arc. The torch's temperature ranges from . The temperature determines the structure of the plasma and forming gas. The waste is heated, melted and finally vaporized. At these conditions molecular dissociation occurs by breaking apart molecular bonds. Complex molecules are separated into individual

atoms Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other ...

. The resulting elemental components are in a gaseous phase ( syngas). Molecular dissociation using plasma is referred to as " plasma pyrolysis."

Materials

Smaller torches typically use an inert gas such as

argon Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

, while larger sizes require

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

Electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s vary from

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

or tungsten to hafnium or zirconium, along with other

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

Feedstocks

Feedstocks are most often refuse-derived fuel,

waste, both or biomedical waste and

hazardous materials Dangerous goods are substances that are a risk to health, safety, property or the Natural environment, environment during transport. Certain dangerous goods that pose risks even when not being transported are known as hazardous materials (syll ...

. The content and consistency of the waste directly impacts performance. Extracting treatable material improves consistency. Too much inorganic material such as metal and construction waste increases slag production, while decreasing syngas production. However, the slag is chemically inert and safe to handle. Shredding waste to create uniform particles is generally required. This creates an efficient transfer of energy which breaks down the material. Added steam supports steam reforming.

Yields

Pure synthesis gas consists predominantly of

(CO⁻) and

(H₂).

Inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

s in the waste stream melt, including glass, ceramics, and metals. The temperature and lack of oxygen prevents the formation of many toxic compounds such as furans, dioxins, nitrogen oxides, or

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

in the flame. However, dioxins form during cooling. Metals can be recovered from the slag and sold. Inert slag produced from some processes is granulated and can be used in construction. A portion of the syngas feeds on-site turbines, which powers the plasma torches and thus supports the feed system.

Equipment

Some plasma gasification reactors operate at negative pressure, although most attempt to recover gaseous and/or solid resources.

Advantages

The main advantages of plasma torch technologies for waste treatment are: * Preventing hazardous waste from reaching landfills * Some processes are designed to recover fly ash, bottom ash, and most other particulates, for 95% or better diversion from landfills, and no harmful emissions of toxic waste * Potential production of vitrified slag which could be used as construction material * Processing of

waste into combustible syngas for

electric power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...

and heat or for synthesis into fuels or chemicals. * Production of

value-added Value added is a term in economics for calculating the difference between market value of a product or service, and the sum value of its constituents. It is relatively expressed by the demand curve, supply-demand curve for specific units of sale. ...

products (metals) from slag * Safe means to destroy both

medical Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

and many other

s. * Gasification with starved combustion and rapid quenching of syngas from elevated temperatures can avoid the production of dioxins and furans that are common to incinerators * Air emissions can be cleaner than landfills and similar to that of incinerators.

Disadvantages

Main disadvantages of plasma torch technologies for waste treatment are: * Large initial investment costs relative to that of alternatives, including landfill and incineration. * Operational costs are high relative to that of incineration. * Wet feed stock reduces syngas production and increases energy consumption. * Little or negative net energy production when taking into account all energy inputs. * Frequent maintenance and limited plant availability.

Commercialization

Plasma torch gasification is used commercially for waste disposal at 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 used in one or two installations treating 25–30 tonnes per day.

Military use

The

US Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

employs the Plasma Arc Waste Destruction System (PAWDS) on its latest generation Gerald R. Ford-class aircraft carrier. The compact system treats all combustible solid waste.

References

External links

Department of Trade and Industry - Using thermal plasma technology to create a valuable product from hazardous waste
{{DEFAULTSORT:Plasma Arc Waste Disposal Sustainable technologies Plasma processing Thermal treatment