Fuel and related compositions – Consolidated solids – Vegetation or refuse
Reexamination Certificate
2001-04-11
2004-02-17
Toomer, Cephia D. (Department: 1714)
Fuel and related compositions
Consolidated solids
Vegetation or refuse
C044S590000, C044S593000, C044S595000, C044S605000, C044S606000, C044S634000, C044S635000, C428S002000
Reexamination Certificate
active
06692544
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of waste disposal. In particular, this invention relates to the field of municipal waste disposal, including disposal of municipal solid waste (MSW), refuse derived fuel (RDF), biomass, discarded tires, and sewage sludge. Briquettes which may be produced according to the present invention may be used as landfill or as alternative fuel sources.
BACKGROUND OF THE INVENTION
The disposal of municipal waste, including both solid waste, or “garbage”, and sanitary waste, or “sewage” is clearly a major economic concern for western society in the 21st century. Conflicting demands of technique, regulation, and politics create a rich field for invention and innovation. A waste stream emanating from a major urban center may include both municipal solid waste (MSW) and sewage sludge—a semi-solid residual fraction resulting from chemical and physical treatment of septic human wastes in sewage or water pollution control plants requiring eventual disposal in landfill or by deep water dumping. The waste stream may also include pre-separated sub-streams, including for example refuse derived fuel (RDF) and biomass. RDF is a partially separated or processed fraction of solid waste containing a higher proportion of waste paper, wood chips and other combustible materials, and substantially free from metals and inorganics, and thereby suitable for use as a fuel. Biomass comprises disposed plant material, often yard waste or such material cleared from land as a fire preventative measure, and is primarily cellulosic, and often has a high moisture content.
Aims in the disposal of municipal solid waste are, as always, economic, and the various objective to which an economic value may be attached are: reduction in landfill airspace volume used; reduction in landfill leachate or run off; reduction in landfill effluent gasses; production of useable energy from waste; recovery of useable waste fractions from the waste stream; and reduction in air pollution resulting from waste combustion. A “traditional” method of waste disposal may be characterized as dumping of an undifferentiated waste stream in an open location, which, in a slightly modified form, becomes creation of so-called sanitary landfill, with some effort at ground water protection, compaction, and covering. A traditional method of waste disposal is being phased out in most locations, including the developing world, where large waste reclamation and control projects are being undertaken; albeit a large fraction of global waste is still disposed of in an approximately traditional manner, modified by informal recycling efforts, or “garbage picking”
In moving from a traditional system to one meeting one or several of the above listed objectives, one encounters the characteristic economic problem of tradeoffs, or conflicting objectives. Notwithstanding, multiple objectives may be simultaneously advanced beyond a level of undifferentiated open disposal of waste, with an optimal mix determined by local conditions, and available technology.
Municipal waste buried in landfill is subject to slow degradation under microbial action, producing effluent gases, as well as objectionable odors. Chief among landfill effluent gasses is methane, which is thought to be a contributor to global warming and ozone destruction. Methane can be collected by post-fitting existing landfill with gas collection systems, and may be evolved in usable quantities over a 50 year period following waste disposal. Burned as fuel, the methane is effectively substituted by carbon dioxide as an effluent, which may still contribute to global warming. It is estimated that only about one quarter of the potentially useable energy of a waste pile can be recovered this way, however, relative to methods employing direct burn, or burn after processing. Gas production does have an advantage of yielding a clean burning fuel; heavy metals and problem compounds are left behind in the ground, in the dump, rather than possibly being injected into the atmosphere on combustion, and requiring scrubbing technology to partially ameliorate.
Conventional waste disposal landfill has a disadvantage of dimensional instability, which, coupled with gas evolution, make such a site unsuitable for reclamation for other use for a period of at least 50 years.
Compared to landfill gasification, a more rapid production of fuel gas from waste is possible by placing the waste in specially designed reactors for the acceleration of bio-fermentation.
A production of pellets and briquettes from solid waste streams and sewage sludge is known in the art, with numerous recipes reciting a mixing of the waste stream with coal or other binders. Existing patents concentrate on a evaluation or characterization of physical-mechanical properties of the resulting briquettes and pellets, and on an ability of these briquettes to undergo waste-to-energy transformation, in particular for production of electric power.
A use of pellets and briquettes as a fuel stuff in a waste-to-energy or refuse-derived fuel (RDF) fired plant was introduced by Schulz in U.S. Pat. No. 4,225,457. Briquettes of specified geometry and composition are produced to serve as feed material or burden in a moving-burden gasifier for a synthesis of fuel gas from organic solid waste materials and coal. The briquettes are formed from a mixture of shredded organic solid wastes, including especially municipal solid waste (MSW) or biomass, and crushed caking coal, including coal fines. A binder may or may not be required, depending on a ratio of Coal/MSW, and compaction pressure employed. Briquettes may be extruded, stamped, or pressed, employing compaction pressures in excess of 1000 psi, and preferably in the range of 2000 to 10,000 psi. A ratio of caking coal to shredded municipal solid waste is selected so that each part of a predominately cellulosic organic solid waste will be blended with 0.5 to 3.0 parts of crushed coal. Suitable binder material include dewatered sewage sludge, “black liquor” rich in lignin derivatives, black strap molasses, waste oil and starch; when used, a binder concentration is preferably in a range of 2 to 6 percent.
In U.S. Pat. No. 4,426,042, entitled “Method of Shredding Solid Waste”, an improved method of shredding MSW or garbage is disclosed, which maintains the moisture content of the waste. The shredded waste is then available for efficient disposal or further processing. In U.S. Pat. No. 4,934,285, entitled “Method for Treating Waste Materials”, there is described a method for treating waste materials which divides the waste material into a compost fraction and a refuse-derived fuel fraction, wherein the compost fraction is exposed to a biological treatment to produce a gaseous fuel. The refuse-derived fuel is burned at high temperature, and the exhaust gases are routed into an after-burning chamber, along with the gaseous fuel from the biologically decomposed compost.
In U.S. Pat. No. 4,227,653, entitled “Method of Processing Waste Materials”, moist municipal waste is subjected to a preliminary comminuting action to reduce particle size, and the larger heavy particles are segregated from lighter particles which include relatively small fibrous particles and relatively large additional lighter particles. The relatively large additional lighter particles are then segregated from the relatively small fibrous particles and subjected to a severing action to reduce their size to a size not exceeding that of the small fibrous particles. The fibrous particles are then mixed with the severed additional particles, the mixture is dried and ozonized, and portions thereof are used for the manufacture of shaped articles.
In U.S. Pat. No. 4,540,467 entitled “Method of Fragmenting Municipal Solid Waste”, a method and apparatus is disclosed for the removal of mold core material from metal castings and for fragmentation of municipal waste materials, e.g. paper products. The method involves heating and hydrating the materials within a pressure vessel. In U.S. Pat. No. 4,540,495 entitled “Process
Agris Cheryl H.
Ecosystems Projects, LLC
Toomer Cephia D.
LandOfFree
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