Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing single metal
Reexamination Certificate
2000-02-22
2002-04-30
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing single metal
C205S742000, C205S688000, C205S693000
Reexamination Certificate
active
06379527
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to apparatus and methods adapted for use in waste recycling and conversion, more especially in association with the recycling and conversion of municipal solid waste (MSW) derived for example from domestic and commercial refuse or garbage.
Known apparatus and methods of which the applicant is aware are not as efficient as is desired, and are used in association with land filling and incineration which can lead to problems of toxic or hazardous air emissions and land pollution.
The apparatus and methods of the invention are especially although not exclusively adapted for use in association with waste management procedures which avoid the problems associated with land filling and incineration, as all the products are marketable, and there are no toxic or hazardous air emissions nor is there release of land pollutants.
BRIEF SUMMARY OF THE INVENTION
In one aspect, the present invention provides a trommel for classifying municipal solid waste (MSW) comprising an inclined cylindrical drum driven to rotate about its axis and having perforations in its side wall through which fragments conforming to a predetermined size range may fall, means for introducing MSW at an upper end of the drum, and means for inducing flow of a stream of gas inwardly through the perforations in said side wall and outwardly through the lower end of the drum to retain and remove relatively less dense materials through the lower end of the drum.
The trommel may advantageously be used as part of an initial stage of treatment of MSW. Whereas known trommels of which applicant is aware serve to classify materials only as to size, the present trommel also serves to classify materials according to the density of the components of the waste. For example, the stream of gas referred to serves to retain within the trommel and separate out relatively light weight materials such as paper and plastics to provide an output stream which can be treated in conventional manner to separate paper and plastics to provide saleable outputs of recycled paper and plastics, respectively.
A further advantage of the arrangement of the invention is that it avoids the need for air classifiers in later stages of the treatment and this reduces the energy requirements for operation of the system.
In a further aspect, the invention provides a method of digestion of MSW comprising digestible organic material and lignin coated cellulose fiber, comprising: heating the MSW in the presence of moisture to yield a heated solid phase; compressing and explosively decompressing the heated solid phase to yield a treated solid phase comprising the fibers in ruptured condition exposing the cellulosic internal surfaces thereof; slurrying the treated solid phase in an aqueous phase and subjecting the slurry to anaerobic digestion; and recovering a solid residue. The starting material MSW may itself have undergone a primary stage of anaerobic digestion before being subjected to explosive decompression to expose cellulosic fibers. Mercury, if present in the MSW may be distilled off and collected as the MSW is heated.
In a preferred form, the MSW material treated in this method comprises material that has undergone treatment in a trommel as described above and has been treated to remove paper, plastics, ferrous materials and aluminum and other non-ferrous metals, and hence is a principally organic substrate.
In accordance with further aspects of the invention, the digestate moves in a substantially straight line path through the digesters, and temperatures of the various zones of the digester are controlled by supply to these zones of a mixture of heated and unheated recirculated compressed digester gas.
In a preferred form, where the MSW contains heavy metals, a portion of the aqueous phase containing dissolved heavy metals is removed from the digester before completion of the digestion, and heavy metals are removed from the aqueous phase. Various conventional treatments, for example application of reverse osmotic pressure membranes, separation membranes, chemical precipitation, or, more preferably, contacting the aqueous phase with a solid adsorbent may be used to remove the heavy metals. The resulting heavy metal poor aqueous phase may be discarded or may be utilized for slurrying solid phase digestible material that is fed to a digester.
Alternatively, or in a further heavy metals recovery step, heavy metals are recovered from anaerobically digested waste residue municipal solid waste containing lignin and heavy metals, by mixing the waste residue with mineral acid solution and obtaining a heavy metal salt solution containing heavy metal cations and lignin in solution and an insoluble residue; separating the solution from the insoluble residue; electrolyzing the separated solution, and causing electrodeposition of the heavy metal cations in the presence of the lignin to yield a heavy metal electrodeposit and recovering the electrodeposit. The presence of lignin, preferably obtained as a residue from an anaerobic digestion procedure as described above, increases the efficiency of the plating out of the heavy metals.
In a further aspect, plastics residues remaining in the anaerobic digested material are recovered in the acidification step, wherein the specific gravity of the acid solution is sufficient to cause the plastics and any undigested organics to float on the surface of the acid solution, whereby they may be separated, for example by skimming them off.
REFERENCES:
patent: 3884782 (1975-05-01), Pittman et al.
patent: 3953306 (1976-04-01), Lancy
patent: 4033763 (1977-07-01), Markels, Jr.
patent: 4395315 (1983-07-01), Zambrano
patent: 4557908 (1985-12-01), Laveyne et al.
Humus Chemistry, Genesis, Composition, Reactions, FJ. Stevenson, pp. 355-373. No date available.
Vogt Gregory M.
Vogt Hubert S.
Walter Herman K.
Eastern Power Limited
Gorgos Kathryn
Nicolas Wesley A.
Ridout & Maybee LLP
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