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PLASMA TECHNOLOGY
FOR
WASTE TREATMENT
ABSTRACT
In Nature there is no such thing as "waste." If it were not for the "waste" oxygen that plants produce, we would not have oxygen to breathe Part of the plan for "re-using" material from living things is to have it "decompose"(treat) so that it can be assimilated by another life form. These ideas opened the doors for the evolution of a technique called Plasma technology.
Plasma technology is not a new technology but its application for waste treatment, electricity generation and processing is new. This technique has started its service since 1900â„¢s as a producer of fuel from natural gas for the industries. During latter part of the century NASA, have refined and improved the Plasma Arc technology in both efficiency and expanding user applications, including all sorts of Municipal Waste like Contaminated Soils, Medical wastes, Hazardous wastes, including polychlorinated biphenyl (PCB), Municipal waste, Oxidant with hydrocarbon, Small Arms Ammunition, Coal ash, Waste with suspended Volatile Metals, Thermal batteries and Low-level Radioactive wastes
In this technique, Plasma Arc Heaters use electricity as a source of energy and convert it into a clean, low mass heat which in turn is converted into plasma which produces electricity. The standard module size for normal municipal solid waste is 300 tons per day can be used. It provides specific size, cost, operability and operational advantages over other state-of-the-art technologies in addition, to the cleaner environmental emission characteristics.
EXTRACTION OF ENERGY FROM
MUNICIPALITY WASTE
INTRODUCTION:
Waste:
Generally the term waste refer to not useful or necessary thing which are generally logged on, but with the advancement in science and as per law of conservation of energy Energy can neither be created or destroyed but can be transferred form one form to another paid the way for the birth of waste treatment technology there by making a right usage of energy trapped in them.
What Is Waste Treatment?
Waste treatment techniques are used to change the physical, chemical, or biological character of the waste, to reduce its volume and/or toxicity, and to make the waste safer for disposal and for further usage, there by preventing the pollutions caused and helping in maintaining a clean and green earth. There are several waste treatment methods currently available. Among them Plasma Technology holds the highest precedence due to its efficiency and expanding user applications.
Plasma Waste Treatment Technology:
Plasma technologies for environmental cleanup and waste management are rapidly emerging. Plasma technology utilizes the intense heat of an electric arc to treat the most difficult waste such as nuclear waste, military waste, and chemical waste. In particular, this technology has proven effective in encapsulating inorganic compounds in a non-leachable, glass-like slag while also destroying organic compounds by the extreme heat of the process.
Utilizing this Plasma technology, scientists who previously worked for NASA, have refined and improved the Plasma Arc technology in both efficiency and expanding user applications of waste treatment, including Municipal Solid Waste, all toxic & hazardous waste streams, medical waste, Low Level Radioactive waste, etc.
Principle of Plasma Technology in Waste Treatment:
Plasma Arc Heaters use electricity as a source of energy and convert it into a clean, low mass heat. Low mass heat means that very little gas is used to generate the "Plasma", the 4th state of matter (after the other states, e.g., 1st-solid, 2nd-liquid, 3rd-gas). The Plasma conducts electricity like a metal wire and, like a metal wire, Plasma resists the flow of electrical current. The resistance to the flow of electrical current is the mechanism for converting electricity into heat. This heat is used to generate electricity which is usually more than the electricity supplied to it.
However, unlike metal wires and other standard heating techniques that have melting temperature limitations, the Plasma conductor has NO TEMPERATURE LIMITATION. This unique ability of the Plasma Arc Column (i.e., to continue to exist at high temperatures and not melt) makes it possible to generate sustained heat at temperatures much higher than is possible by combustion heaters or metallic resistance heaters. The sustained high temperatures that are achievable only by Plasma heaters qualify this novel heat source for the specific and stringent heating demands of our waste management systems.
Plasma arcs are generated by the electrical discharge in the gas, usually between high voltage electrodes. The pressure of the gas involved determines the temperature and transport properties of each Plasma, allowing us to tailor its destructive capacity to meet the demands of various waste materials. With core temperatures of up to 14,000 degrees Centigrade, Plasma can break down toxic compounds within MILLISECONDS in a very -safe way.
Plasma Gasification Basic Process Description:
Plasma gasification is a non-incineration thermal process which uses extremely high temperatures in an oxygen-starved environment to completely decompose input material into very simple molecules. The extreme heat and lack of oxygen results in pyrolysis of the input waste material. Pyrolysis is the decomposition of matter in the absence of oxygen. Incineration is merely the burning of waste material in the presence of oxygen, and incinerators have significant air emission control problems.
The byproducts of pyrolysis are: (1) combustible gas, which can be used to generate electricity, and (2) inert slag, which is a vitrified glassy rock, primarily composed of silicon which can be directly drawn off and make wool insulation. The heat source is a plasma arc torch, a device which produces a very high temperature plasma gas. Plasma gas is the hottest sustainable heat source available. The plasma arc centerline temperature can be as high as 50,000 degrees Centigrade, and the resulting plasma gas has a temperature profile between 3,000 and 8,000 degrees Centigrade.
A plasma gasification system is designed specifically for the type, size and quantity of waste material which must be processed. The refractory-lined reactor vessel is preheated to a minimum of approximately 1,100 degrees Centigrade before any processing commences. The very high temperature profile of the plasma gas then provides an optimal processing zone with the reactor vessel through which all input waste material is forced to pass. The reactor vessel operates at atmospheric pressure.
Pyrolysis provides for virtually complete gasification of all volatiles in the source material, while non-combustible material, including glass and metal, is reduced to an inert slag. With municipal solid waste as the input waste material, the product gas and slag have very distinct characteristics. The product gas is high in hydrogen and carbon monoxide with traces of methane, acetylene and ethylene; therefore, it can be combusted very efficiently resulting in carbon dioxide, nitrogen and water vapor as the only gaseous exhaust to the atmosphere. The carbon dioxide can be recovered through use of special membrane filters. The slag is a homogeneous, silicometallic monolith with leachate toxicity several orders of magnitude lower than those specified in current landfill regulations. This slag could also be converted into brick and very high quality tiles or into wool insulation.
The product gas and slag from the plasma gasification of municipal solid waste both have commercial value. The product gas has a heating value approximately 1/4 to 1/3 the heating value of natural gas; therefore, it can be used as an efficient fuel source for industrial processes, including the generation of electricity, and the production of methanol and ethanol. The slag can be used in the construction industry, wool insulation or for road paving. All other byproducts, such as scrubber water and cyclone catch material, can be recycled into the process for reprocessing to alleviate disposal requirements. Plasma gasification has no byproducts which must be disposed of as waste; therefore, it can be viewed as a totally closed treatment system and the ultimate recycling process. This is a viable process for using low grade coal as fuelstock to generate electricity.
Other types of waste will generate different product gas and slag characteristics. The chemical composition of different input waste materials will result in differing gas and slag characteristics. Input waste materials with a high carbon content and a high percentage of non-volatile material will produce results very similar to those with municipal solid waste. Other waste materials, such as biomass, liquid wastes and organic wastes, will not produce hardly any slag since virtually all of the waste is gasifiable.
Types of Material Which Can Be Processed:
Plasma gasification is a generic type process which can accommodate virtually any input waste material in as-received condition, including liquids, gases and solids in any form, combination or packaging. Moisture content is not a problem.
Liquids, gases and small particle size waste materials are very easily and efficiently processed. Bulky items, such as household appliances, tires and bedsprings, can also be readily accommodated without loss of destruction efficiency. The reactor vessel and waste feed mechanism are designed for the physical characteristics of the input waste stream.
Even waste materials such as low-level radioactive waste can be processed to reduce the bulk and encapsulate the radioactive constituents to reduce leachability.
Handling Capabilities and Versatility:
Plasma gasification systems can be implemented in virtually any size capacity. They are modular which provides operability and maintainability advantages. Modularity also provides for future growth at minimal incremental cost.
The standard module size for normal municipal solid waste is 300 tons per day. Such a module is comprised of one or two individual plasma heating sources per vessel which would permit efficient operation through a wide range of waste throughput. The following types of waste could be treated using the Plasma technologies:
Contaminated Soils, Medical wastes, Hazardous wastes, including polychlorinated biphenyl (PCB),Municipal waste,Oxidant with hydrocarbon,Small Arms Ammunition,Coal ash,Waste with suspended Volatile Metals,Thermal batteries and Low-level Radioactive wastes
Maintenance Requirements:
Plasma systems are very reliable since no moving parts are involved. An annual inspection of the refractory can easily achieve a very high availability, with an up-time of 340 days plus per year.
Configuration Variability:
Plasma technology allows the formation of a Fuel to Energy facility of different configuration depending on the end user requirements. Plasma gasification systems are highly modular, which provides tremendous versatility and configuration flexibility to
handle wide variations in the type and quantity of input waste loads. Since the heat source is completely independent of the existing infrastructure, full flexibility is realized to implement any configuration to best meet the needs of the waste type and quantity.
Plasma gasification systems can be implemented as an adjunct to existing processes, such as incinerators or coal-fired power plants. The plasma system can process the bottom and fly ashes, as well as flue gases directly from the incinerator or coal-fired power plants.
Mobile/transportable plasma systems are under development to provide waste disposal services to locations which do not have sufficient waste quantities to justify a permanent installation.
If needed, plasma gasification systems can be installed largely underground for aesthetic purposes. Such installations require only a single floor above ground to house administrative offices and provide an area for waste haulers.
Environmental Emissions Superiority:
The consistently low environmental emission characteristics exhibited by plasma gasification indicate that it can be used as a waste treatment and coal-fired power station alternative to other technologies with significantly lower air emissions than competing technologies.
The extremely tight physical and chemical bonds within the slag results in consistently low leachate characteristics.
Technology Advantages:
Plasma gasification is not a new technology but its application for waste treatment, electricity generation and processing is new. The technology addresses those concerns which other technologies could not address. It provides specific size, cost, operability and operational advantages over other state-of-the-art technologies. In addition, to the cleaner environmental emission characteristics, plasma gasification offers the following unique advantages:
1. Can handle any waste material in any form without loss of destruction efficiency; therefore, there is no need for additional treatment or disposal of the solid constituents of many waste materials, such as contaminated steel drums.
2. Requires an extremely small space compared to other disposal technologies. Install within an existing superstructure, underground for a pleasing aesthetic appearance increasing public acceptance.
3. The unit is modular and thus provides much operational flexibility. Initial capacity can be geared to the initial requirement and the modularity feature can provide the desired growth when required, at a minimal cost.
4. Produces a combustible gas as a discrete byproduct. This gas can be used immediately, stored for future use or piped to a remote location for use. On the other hand an incinerator automatically produces steam regardless of steam demand.
5. The plasma torch is an independent heat source providing temperature controllability, heat transfer rate and process variability benefits. Optimal operating characteristics can be set and maintained.
6. Process is independent of input moisture content; therefore, there is no loss of destruction efficiency if the moisture content varies.
7. Provides for the complete removal of all carbon from the input material. This destruction efficiency is in marked contrast to incineration which can leave as much as 30 percent unprocessed material in the ash ! Process provides an immense volume reduction ratio of input material to slag. This figure is in excess of 250:1 for as-received municipal waste (99.6 percent reduction) and 400:1 reduction for boxed biomedical waste (99.7 percent reduction). Other technologies such as incineration offer only 5:1 (80 percent reduction).
8. The Plasma Gasification Process requires no presorting of waste, negating the need for saving on labor and machinery.
9. No post process treatment of the waste is required. Profits will not be diminished through secondary hauling and/or disposal fees.
10. The amount of land required for USP's Plasma Gasification system is significantly less than for landfill or incineration disposal methods.
11. The Plasma Gasification Process creates two revenue-generating byproducts.
(a) An energy rich gas that can be used to create electricity, and
(b) A slag that has many and varied commercial uses.
12. A Plasma Gasification Operator can offer its clients freedom from downstream liability because the processed waste is chemically non-recognizable.
Increased Efficiency:
Current coal fired power plant technology is only 35-40% efficient. The waste gasses and fly ash can fed into a plasma plant and reclaim what would normally be waste and converted into electricity. This results in a about a 90% efficiency for the coal fired plant. These coal fired power stations can be closed down once there useful life has expired and totally use this plasma process.
Regulatory:
With the advent of new, more stringent EPA and World Bank regulations for particulate matter and ozone, industrial sources and infrastructure, projects will be required to meet more stringent emission limitations by 2004. Investment in the plasma gasification technology will ensure that an infrastructure facility is in compliance with current and future air emission limitations.
Summary:
Environmental standards invariably become more stringent and improved standards are achieved when new technologies demonstrate they can reliably meet more stringent limits. The plasma gasification process effectively produces no associated air, soil, groundwater or surface water contamination. The plasma gasification process is in full commercialization Plasma gasification processes the waste problems produced by society and creates useful commercial byproducts.