Plasma was developed over a hundred years ago, but extensive work with materials other than industrial high temperature metallurgical applications did not occur until work was needed to simulate re-entry temperatures on the heat shield of re-entry vehicles in the late 50’s and 60’s. Recently, this technology has begun to emerge as a commercial tool in several industries, i.e., steel making, metallurgy, precious metal recovery, and waste disposal.

Most of the research and testing with plasma was done with a plasma torch. A plasma torch is a device that converts electrical energy into thermal energy (Camacho, 1998, 1991).  Plasma is an ionized gas that is conditioned to respond to electromagnetic forces.  The plasma arc is created when a voltage is established between two points.  The plasma acts as a resistive heating element and as a resistive heating element it presents a distinct advantage over any solid heating element as plasma is a gas and cannot melt or fail. 

The plasma arc creates a “flame” that has temperatures ranging from 4,000 to 7,000 ºC, which is hotter than the surface of the sun.  Thus, plasma torches operate at much higher temperatures, higher enthalpies, and at efficiencies much greater than those of fossil fuel burners.  In addition, plasma torches require only about 5 percent of the gas necessary for fossil fuel burners; therefore, waste effluent gases are greatly reduced.  Because of this factor, reactor systems can be built that are much more compact than traditional furnaces, at correspondingly reduced capital costs.

Several plasma arc torch and/or solid electrode systems and processes for the destruction of a variety of waste materials have been developed, successfully tested and implemented.  The very high temperatures and energy densities, in conjunction with the ionized and reactive medium, have fully demonstrated the potential of plasma arc technology to eliminate many waste materials in an environmentally safe and cost-effective manner.  Materials vitrified in atmospherically controlled reactors with Plasma Technology readily pass all standard EPA leaching tests.

The process of utilizing plasma generators to thermally dissociate waste materials and convert these materials into re-usable products is distinctly different from combustion (incineration) in that it uses energy from plasma to thermally convert organic waste from a solid or liquid to a gas through a process called controlled pyrolysis or controlled gasification.  The constant high operating temperatures ensure the complete destruction of all complex organic compounds, and the process control minimizes the possibility of reformation of a complex pollutants and hazardous gases.  The escape of volatile metals and acid gases is also minimized to levels that have met the most stringent air emission standards.

The key elements in the destruction process are the ATONN Plasma Gasifier Feed System and the Controlled Atmosphere Reactor.  Both proprietary systems ensure the complete control of the pyrolytic process beginning with the precisely controlled introduction of feedstock into the reactor.  The ATONN processes is essentially  endothermic.

Municipal Waste Destruction and Production of Electricity:

The ATONN Plasma Conversion System exploits the unique capabilities of plasma generating systems by integrating them with associated technologies to realize the latent value assets in the municipal solid waste stream.  Plasma Generating Systems have, at their core, the capacity to dissociate compounds into elemental atoms.  Once the atoms are feed to move independently, simple chemistry is applied to reassemble the atoms into usable, commercially viable products.

S.A.A. brings a number of proprietary technologies involving thermal plasma that through their unique application provide the most efficient method of generating synthesis gas.  The important difference between the ATONN Plasma Conversion System and other plasma designs is our ability to deliver municipal solid waste into the reaction chamber not only without air, but also in a continuous, controlled supply at controlled density and in a large volumes (2000, 3000 or 4000 tons per day).  This ability results in a superior synthesis gas product with higher Btu energy value but also makes the process economically feasible because solid municipal waste disposal requires the ability to process not pounds but tons per hours.

The organic content of average municipal solid waste will dissociate or thermally depolymerise into 30,000 to 33,000 cubic feet of synthesis gas per ton, having an energy value of 300 Btu per standard cubic foot of gas.  The heat rate for ATONN combined cycle power generating system is expected to be about 7.277 or lower, generating 1,360 kW per ton of municipal solid waste that is processed.  The processing of 1000 tons of municipal solid waste per day or 41 tons per hour will release 1,353,000 cubic feet of synthesis gas per hour with a total Btu value of 405,900,000 Btu/hr.  At a heat rate of 7,277 the ATONN combined cycle gas turbine system will generate a gross of 55.76 Megawatts of electricity per hour, twenty‑four hours a day.  When we deduct 26 Megawatts of this electric current to maintain the plasma arc and for other plant requirements, we are left with 29.76 Megawatts per hour (714.24 Megawatts per day) available to supply the grid.

Description of the ATONN  Plasma Conversion System for MSW:

Dual Graphite Electrode Technology (patent applied for):

ATONN brings proprietary plasma generation technology consisting of a rugged, outer shroud for pressure containment,  the electrodes, a vortex generator, and insulators.  The typical shroud has an outer diameter of approximately 20 feet and is constructed of carbon steel with an internal insulation and refractory lining resistant to the environment of the process vessel.  Each gasifier will include one or two plasma arc assemblies, each sized to provide the required power to achieve the maximum energy required for materials dissociation. Electrodes are fabricated from carbon graphite materials providing improved electrode life. ATONN’s graphite electrode technology has been successfully proven over many years of commercial operation in the metallurgical industry and typically has an availability rate of greater than 90 percent.

Plasma Gasifier Feed Systems (patent applied for):

ATONN brings a proprietary feed system, one for municipal solid wastes and conventional carbonaceous wastes and one possibly consisting of a pressure compensation feeder for medical wastes.  The system ensures the highest efficiency in the feed rate and is designed and engineered to prevent the introduction of extraneous air into the gasification chamber (a very important element of the plasma gasification process).  The system consists of a compactor/extruder integrated with waste feed containers and a conveyor system that will introduce the waste feedstock into the gasifier.

The following example illustrates how municipal solid waste would be processed in our plasma conversion system.

The waste feedstock is delivered and discharged by truck or other means to the “tipping floor”. A pre-crusher compacts and densifies the waste into a specially designed compaction container.  Once filled, the container is provided with a metallic door that will be closed, thus preventing problems with rodents and foul odours.  An overhead crane or conveyor system then moves the filled containers into the gasifier area.  This will allow efficient control of the process and will ensure that there is no chance that a filled container can be “forgotten” (a major cause of rodent and odour problems in MSW facilities).

Once the container reaches the gasifier, a small crane will place the container into the gasifier‑feeding platform (after removing the empty container previously fed into the system).  The empty container is placed in a second conveyor that will return it to the container area.  The feeding platform is an articulated tilting “table” where the container door is opened.  Once the door is opened, the articulated “table” is inclined approximately 60 degrees directly over the compactor/extruder, which then feeds the MSW into the gasifier.  The compactor/extruder that is provided, in conjunction with the storage container, provides a unique advantage that maximizes the unique benefits of plasma gasification of MSW.  Firstly, the system feeds the waste feedstock into the gasifier after having extruded a significant portion of the entrained air in the waste feedstock (the most important aspect to ensure the production of the highest quality synthesis gas). 

Finally, the feed rate can be adjusted and controlled in essentially an infinite manner thus allowing their feed rate to equal the rate of dissociation and gasification within the gasifier chamber.

The graphite electrode Plasma Gasification system brought by the ATONN technical team builds upon the extensive and very successful commercial experience of graphite arc technology used in the metallurgical industry.  The ATONN system is particularly effective for the conversion of high volumes of carbonaceous wastes particularly MSW, but also tires, pet coke and ASR.  The system briefly summarized above is powered by an electric arc Plasma generated by two or more graphite electrodes that introduce the electric arc through a “slag molten bath” of the waste being processed, i.e. molten slag, [It should be noted that plasma fields can also be generated by DC or AC powered “plasma torches”, however, the use of graphite technology has been extensively used worldwide in a wide range of applications and can provide much larger throughputs than can be achieved with the plasma torch method of generating plasma fields.]

Concurrent with, or independent of, the controlled pyrolysis of organic materials, the ATONN plasma gasification system can melt inorganic materials (glass, soil, metals, and ash) if present.  These components, common in many waste streams, are melted and typically recovered as a glassy slag.  The glass layer serves as a medium for chemically binding many metals in a non‑leachable manner through vitrification.  If large amounts of ferrous and non –ferrous metals are present, the molten material will separate as one or more layers, a glassy layer over a metal alloy layer.  Waste streams that are predominantly metal can usually be processed to promote metal recovery.  This is an important and unique benefit, particularly when processing MSW, but also beneficial when processing tires or ASR.

The processing chamber is heated to the desired temperature (1100 to 1300ºC) before the waste materials are fed into the reactor.  Waste is fed into the processing chamber on a continuous basis.  Organic materials rapidly dissociate into elemental constituents, mainly hydrogen, carbon, oxygen, and depending on the halogenated compounds in the feed stock, small amounts of acid gases.  The elements will form simple gases that are stable at the operating temperatures, primarily diatomic hydrogen, carbon monoxide and hydrogen chloride.  To prevent the remaining carbon from re-associating into a solid, a limited source of oxygen (usually in the form of steam) is introduced through an exact, computer controlled metering system at which time it will form carbon monoxide. 

The result is a pyrolysis gas (“Syngas”) composed mainly of dissociation of the organic elements.  Small amounts of other gases will be present, including nitrogen.  Within the strongly reducing environment of the pyrolysis chamber, most NO_x is either not formed or quickly reduced to gaseous elemental nitrogen.

The process is not “incineration” as combustion of the material is not occurring inside the gasifier.  Recognition as “not an incinerator” often becomes an issue when a government which bans or puts a moratorium on incinerators cannot accept an application for a permit to construct and operate an incinerator.  Furthermore, the ATONN systems status as “non-incinerator” offers a significant advantage in terms of public acceptance of the technology. 

The position that the ATONN process is not incineration is based on two premises.  One, the process in the chamber that destroys the waste does not fit the definition of combustion, but is instead, pyrolysis.  Two, the by-products of pyrolysis (hydrogen, carbon and carbon monoxide) are different from the products of combustion (carbon dioxide and water) and offers options for chemical energy recovery that combustion and incineration do not.

DESCRIPTION OF PLASMA TECHNOLOGIES

Plasma technologies include the following:

“Table Top” plasma gasifier built by Georgia Tech Plasma Lab

In-situ Plasma Arc Vitrification System – A technology developed by Dr. Louis Circeo, the patent holder.  In-situ remediation of sites (including landfills) contaminated with hazardous and/or radioactive wastes.  The technology has been successfully proven (and validated by the US Department of Energy) to completely (and in-situ) remediate highly contaminated sites, vitrifying the soil and the contaminants into a totally inert glass matrix (the most stable waste form – in fact a waste form utilized for the permanent immobilization of high-level nuclear wastes).  This method offers unique cost and personnel safety advantages and can provide clients with a unique, cost effective and fast method to remediate contaminated sites.   The in-situ process achieves a major reduction in volume of the materials processed and the formation of very stable soil structures for future construction at the site.

Graphite electrode systems – This is a variation of the standard arc furnaces used in the steel and specialty metals industry for years whereby the system is converted to a true plasma arc system in lieu of being a conventional Joule heater.  The advantage is in the ability to handle large volumes in a safe and very cost effective manner.

Plasma Gasifier Feed Systems  – S.A.A. brings a number of proprietary feed system designs for plasma reactors where the feeder allows for the control introduction of materials into the reactor while maintaining control on the environment inside the reactor.  One of these feeders allows for the homogeneous densification of waste and controlled feeding to maintain ideal operating reactor parameters.

INTRODUCTION TO PLASMA GASIFICATION

Several of the technologies employed in ATONN plasma gasification/waste destruction and metals recovery projects have been fully permitted for construction and approved for operation in a number of states in the United States.

Why Plasma Gasification will NOT produce Dioxins and Furans:

           5)     A temperature range between 250 C to 450 C

In order to prevent the formation of dioxins throughout ANY portion of the gasification system, the synthetic gas produced will be cleaned or filtered at temperatures exceeding 450 C.  The filters will remove particulate matter (#3) (and therefore the binding “surfaces”).  At the same time, the filters will remove metals that can act as catalysts (#4). 

In summary, the ATONN design PREVENTS the formation of dioxins or furans throughout ANY portion of the gasification process by:

Minimizing the presence of Chlorine in the syngas stream by the addition of lime into the reactor such that the Chlorine will combine with the Calcium and thus be trapped in the silicate slag.

HCl in the gas stream is removed by the scrubber forming a benign salt through the addition of NaOH with the feedstock.

Removal of particulates in the gas stream through filtration

Results from measurements taken in conventional gasifiers confirm that, in general, VOC’s such as benzene, toluene and xylene, when detected, were present in the parts per billion levels.  SVOC’s, including PAH’s, were also detected in the syngas and/or turbine exhaust.  SVOC’s were typically present at extremely low levels: on the order of parts per trillion.

Gasification tests using chlorinated feedstocks have also been conducted to measure the DRE for organic compounds such as chlorobenzene and hexachlorobenzene.  DRE’s greater than 99.99% were demonstrated for both compounds.

Dioxin and Furan compounds (PCDD/PCDF’s) are not expected to be present in the syngas from gasification systems for two major reasons: (1) the ultra-high temperatures in the gasification process effectively destroy PCDD/PCDF compounds or precursors in the feed and (2) the lack of oxygen in the reduced gas environment will preclude the formation of the free Chlorine from HCl, thus limiting the chlorination of any precursors in the syngas. 

Measurements of PCDD/PCDF compounds in gasification systems confirm these principles.