Plasma Arc Waste Disposal
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Plasma gasification is a thermal process that converts
organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...
into a
syngas 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 ...
(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 A plasma torch (also known as a plasma arc, plasma gun, plasma cutter, or plasmatron) is a device for generating a directed flow of plasma. The plasma jet can be used for applications including plasma cutting, plasma arc welding, plasma spray ...
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 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 ...
, producing
slag The general term slag may be a by-product or co-product of smelting (pyrometallurgical) ores and recycled metals depending on the type of material being produced. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be c ...
as a byproduct. It is used commercially as a form of waste treatment. It has been tested for the gasification of
refuse-derived fuel Refuse-derived fuel (RDF) is a Waste-to-energy, fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste. The World Business Council for Sustainable Development provides a definition: ' ...
,
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 In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic; their odor is usually faint, and may b ...
, 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 Oil sands are a type of unconventional petroleum deposit. They are either loose sands, or partially consolidated sandstone containing a naturally occurring mixture of sand, clay, and water, soaked with bitumen (a dense and extremely viscous ...
, 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
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 ( ...
. Pressurized gas is
ionized Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
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 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 ...
). Molecular dissociation using plasma is referred to as " plasma pyrolysis."


Materials

Smaller torches typically use an
inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. Though inert gases have a variety of applications, they are generally used to prevent u ...
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 Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
to
hafnium Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dm ...
or
zirconium Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...
, 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 ...
s.


Feedstocks

Feedstocks are most often
refuse-derived fuel Refuse-derived fuel (RDF) is a Waste-to-energy, fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste. The World Business Council for Sustainable Development provides a definition: ' ...
,
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 ...
waste, both or
biomedical waste Biomedical waste or hospital waste is any kind of waste containing Infection, infectious (or potentially infectious) materials generated during the treatment of humans or animals as well as during research involving biologics. It may also include ...
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 Construction waste or debris is any kind of debris from the construction process. Different government agencies have clear definitions. For example, the United States Environmental Protection Agency EPA defines construction and demolition mate ...
increases slag production, while decreasing
syngas 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 ...
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 Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly, natural gas is the feedstock. The main purpose of this technology is often hydrogen ...
.


Yields

Pure
synthesis gas 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 ...
consists predominantly of
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 ...
(CO) and
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 ...
(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
furan Furan is a Heterocyclic compound, heterocyclic organic compound, consisting of a five-membered aromatic Ring (chemistry), ring with four carbon Atom, atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as f ...
s, dioxins,
nitrogen oxides In atmospheric chemistry, is shorthand for nitric oxide () and nitrogen dioxide (), the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tr ...
, 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 Negative may refer to: Science and mathematics * Negative number * Minus sign (−), the mathematical symbol * Negative mass * Negative energy * Negative charge, one of the two types of electric charge * Negative (electrical polarity), ...
, 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 Toxic waste is any unwanted material in all forms that can cause harm (e.g. by being inhaled, swallowed, or absorbed through the skin). Mostly generated by industry, consumer products like televisions, computers, and phones contain toxic chemi ...
* Potential production of vitrified slag which could be used as construction material * Processing of
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 ...
waste into combustible
syngas 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 ...
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 Synthesis or synthesize may refer to: Science Chemistry and biochemistry *Chemical synthesis, the execution of chemical reactions to form a more complex molecule from chemical precursors **Organic synthesis, the chemical synthesis of organi ...
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
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, ...
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 Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...
. * 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.


See also

*
Gasification 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 (). This is achieved by reacting ...
* Staged reforming *
Waste management 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 monitor ...
* Waste to energy *
Northeast of England Process Industry Cluster The North East of England Process Industry Cluster (NEPIC) is an economic cluster developed in accordance with Michael Porter's theories and strategies regarding industrial clusters. The chemistry-using sectors in North East England, where mor ...
NEPIC


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