Environmental consequences of the contemporary lifestyle in this country frequently result in dramatic problems in a number of areas of public concern. A major related concern is the need to increase the capacity for disposing of residential and industrial wastes.
One of the political topics which tends to generate the most public response is the topic of finding a location for a new landfill facility. Everyone generates waste, and yet no one wants to have a waste disposal site or a waste incinerator nearby. The reasons for this public dislike of waste disposal facilities ranges from toxic hazards, to leaching of dangerous chemicals into the groundwater, to unpleasant odors and to reduction in real estate values.
Despite this generally held dislike for landfills, the need for more waste disposal capacity keeps growing. We produce more waste each year and the existing landfills are rapidly approaching the point of being filled to capacity. The problem encompasses residential waste such as bio-degradable and non-biodegradable garbage and industrial waste including scrap, chemical residues, sludge, mill tailings, and other forms of waste, some of which may be industrial, hazardous, toxic or radioactive. Common municipal solid waste is being generated at the rate of over 200 million tons per year. Over ninety percent (90%) of this waste is deposited in landfills. At this rate, more than half the operating landfills in the country will reach their limit of capacity within the next few years. Efforts at recycling, while helpful, fall far short of coping with the problem.
A typical landfill contains a great variety of materials, only a small number of which will decompose naturally. A weight analysis of landfill components by category indicates paper products (41%), glass and metal (16.9%), plastics (6.5%), rubber and textiles (4.3%), yard waste (17.9%), wood (3.7%) and food (7.9%).
The process of incineration deals somewhat with the capacity problem, but it simultaneously creates other problems, such as pollution, odors, acid rain, depletion of fuels, etc. Incineration, by its nature, is a combustion process and, therefore, generates a number of gaseous products which range from unpleasant to dangerous.
Pyrolysis is a chemical decomposition of materials due to the action of heat. Pyrolysis is distinct from combustion in that oxygen is not present and, therefore, the resulting chemical products are different. When pyrolysis of materials is accomplished under sufficiently hot conditions, some gases (potentially useful as fuel) are generated due to decomposition of the organic compounds, and the residue from the waste materials is melted and solidified (vitrified), thus greatly reducing its volume. The chemical composition of the gases generated by pyrolysis can be controlled by the introduction of specific additives, such as steam.
The present invention recognizes that there exists a relatively new technology which may be employed in the pyrolysis and vitrification of waste materials by the application of quantities of very high temperature heat energy. The basic tool used in this technology is the plasma arc torch. Plasma arc torches can routinely operate at temperatures of 4000.degree. C. to 7000.degree. C. in the range of 85-93% electric to heat energy efficiency. The highest temperature attainable by fuel combustion sources is in the vicinity of 2700.degree. C.
A plasma arc torch operates by causing a high energy electric arc to form across a stream of plasma, or ionized gas, thus generating large amounts of heat energy. There are many types of plasma torches, but all torches generally fall into one of two basic categories according to the arc configuration relative to the torch electrodes, i.e., transferred arc type and non-transferred arc type. The arc of a transferred arc torch is formed by and jumps from a single electrode on the torch, through the plasma gas, and to an external electrode which is connected to an opposite electrical pole. The arc of a non-transferred arc torch is formed by and jumps from one electrode on the torch across the plasma gas to another electrode on the torch.
In a plasma arc torch, the heat energy produced is proportional to the length of the arc, assuming the type of plasma gas and flow of electrical current both remain constant.
Since the present invention makes use of a plasma arc torch, reference is next made to U.S. Pat. No. 4,067,390 granted to the present inventors for "Apparatus And Method For The Recovery Of Fuel Products From Subterranean Deposits Of Carbonaceous Matter Using A Plasma Arc" which teaches the use of a plasma arc torch to gasify or to liquify underground deposits of coal, oil, oil shale and other carbonaceous materials. The teachings of the '390 patent are incorporated herein by reference.