TECHNICAL FIELD

The present disclosure relates to solid fuel compositions formed from mixed solid wastes. More specifically, the present disclosure relates to solid fuel compositions that are substantially free of volatile organic compounds and are not pyrolyzed.

BACKGROUND

The management of solid wastes such as municipal wastes from residential, institutional, and commercial sources, agricultural wastes, and other wastes such as sewage sludge, remains a challenging issue with ever-evolving solutions. As landfills reach and exceed capacity worldwide, and as the solid waste industry and societies generally limit the use of landfills, alternative methods of managing solid wastes and have been developed that additionally process the solid wastes to reduce the volume introduced into landfills. Recycling of metals, plastics, and paper products, as well as composting organic matter are relatively common methods of reducing the overall volume of solid wastes going to landfills. Waste-to-Energy processes have also been developed to convert the energetic content of solid wastes into a more usable form such as electrical power.

A variety of Waste-to-Energy processes may use thermal treatments such as incineration, pyrolysis, or gasification to release the energy content of the solid waste stream, which is subsequently used to drive downstream electrical generators. Although pyrolysis and gasification afford many advantages over incineration in Waste-to-Energy processes, the effective use of pyrolysis or gasification is limited when municipal solid waste (MSW) or agricultural waste is used as the feedstock, due to the high water content, low density, and lack of homogeneity.

Efficient operation of a pyrolysis or a gasification chamber typically uses feedstock that is high density and of consistent composition with essentially no moisture. Because solid waste streams are inherently low density and variable in composition, most Waste-to-Energy plants incinerate the solid waste stream to liberate the energy of the solid waste stream. Enhanced pyrolysis mechanisms, such as advanced gasification, may overcome inefficiencies associated with the inherent inconsistency of solid waste composition, but these advanced mechanisms require significant investment in specialized equipment. Further, they are still limited by the quality of the feedstock.

Other processes use pelletizers to render the solid waste stream of the pyrolysis chamber more uniform in size. But the pelletized solid waste retains the variation in composition inherent in solid waste streams. Further, pelletizing the solid waste stream fails to transform the solid waste into a high density and low moisture fuel appropriate for the efficient operation of a pyrolysis (or gasification) chamber.

A need exists for a solid fuel composition and a process of producing a solid fuel composition from a solid waste stream that may include mixed solid wastes and other wastes to be used as a feedstock. Such a fuel would provide efficient operation of a pyrolysis (or gasification) chamber as part of a Waste-to-Energy process, without additional capital investment in advanced machinery. In addition, a need exists for a process that transforms a solid waste stream with variable composition into a solid fuel composition with a relatively consistent composition that is high density and low moisture, as this provides a better fuel composition. Further, a need exists for a process for forming a solid fuel composition from a solid waste stream that may further eliminate odors, bacteria, and other undesired properties of the solid waste stream used to produce the solid fuel composition. The solid fuel composition resulting from such a process may enable the use of high-efficiency pyrolysis or gasification methods as part of a Waste-to-Energy process by providing a homogenized, dry, dense, and energy rich fuel primed for pyrolysis or gasification.

BRIEF SUMMARY

The methods disclosed herein process solid waste mixtures without extensive presorting or predrying, as typically employed for producing an engineered fuel. Because the source material need not be dried or presorted (other than the optional removal non-combustibles of metal, glass, and hazardous materials), variations of content based on the site of origin, the season, or the weather do not substantially affect the process.

The process starts by obtaining a solid waste mixture which includes organic material, trash, and plastic. The system processes the solid waste mixture in a process vessel below atmospheric pressure, driving away excess moisture, volatile organic compounds (VOCs), chlorinated organics, and chlorine gas, which are sequestered without exposure of these gasses to the atmosphere. Then heat increases after removal of the water and VOCs to melt mixed plastics in the solid waste mixture. This process melts plastics content within the dried solid waste mixture, thereby distributing the plastic throughout the solid fuel composition and increasing the density of the solid fuel composition, in contrast to existing compositions. The finished product has not been pyrolyzed and includes organic compounds and plastic. The finished product is of a general uniform consistency, meaning that large pieces within the solid waste mixture are reduced to an average particle size equal to or less than other individual pieces within the solid waste mixture. The finished product also has low water content (<1% wt.), and is suitable for a variety of post process applications, including use as fuel for incineration, or as syngas feedstock, for example via pyrolysis or gasification.

Briefly, therefore, the present disclosure provides a solid fuel composition with an energy content between about 8,000 BTU/lb. and about 14,000 BTU/lb., and a density between about 30 lbs./ft3and about 80 lbs./ft3. The solid fuel composition is substantially free from volatile organic compounds and is not pyrolyzed, meaning that the solid fuel composition has not been thermally and chemically transformed into ash, char, synoil and syngas. The solid fuel composition comprises from about 40% wt. to about 80% wt. carbon, from about 5% wt. to about 20% wt. hydrogen, from about 5% wt. to about 20% wt. oxygen, less than about 2% wt. sulfur, less than about 2% wt. chlorine, and less than about 1% wt. water. The solid fuel composition is formed from a solid waste mixture without the formation of syngas by heating a solid waste mixture comprising between about 5% wt. and about 60% wt. mixed plastics within a process vessel to a temperature of about 90° C. to about 110° C. to separate the solid waste mixture into a dried solid waste mixture and vaporized compounds released from the heated solid waste mixtures. Syngas is a product of pyrolysis, which does not occur in the present process. The vaporized compounds are removed from the process vessel to form a dried solid waste mixture. The dried solid waste mixture is heated and mixed to at least 160° C. and below atmospheric pressure to form a heated solid waste mixture comprising melted mixed plastics. The heated solid waste mixture is extruded below about 200° C. to produce an extruded solid waste mixture. The extruded solid waste mixture is cooled to less than about 65° C. to form the solid fuel composition.

The solid waste mixture may comprise municipal solid waste and agricultural waste. The solid waste mixture may comprise a sorted municipal solid waste produced by removing plastics and non-combustible wastes from municipal solid waste; and the amount of mixed plastics in the solid waste mixture may be adjusted to between about 5% wt. and about 60% wt. The solid waste mixture is substantially free of non-combustible waste, such as non-combustible metallic waste.

The mixed plastics may comprise one or more plastics selected from the group consisting of polyester, polyethylene terephthalate, polyethylene, polyvinyl chloride, polyvinylidene chloride, polypropylene, polystyrene, polyamides, acrylonitrile butadiene styrene, polyethylene/acrylonitrile butadiene styrene, polycarbonate, polycarbonate/acrylonitrile butadiene styrene, polyurethanes, maleimide/bismaleimide, melamine formaldehyde, phenol formaldehydes, polyepoxide, polyetheretherketone, polyetherimide, polyimide, polylactic acid, polymethyl methacrylate, polytetrafluoroethylene, and urea-formaldehyde. The mixed plastics may comprise polyvinyl chloride, polyvinylidene chloride, and combinations thereof, and the dried solid waste may be heated to at least about 190° C. The solid waste mixture may comprise from about 5% wt. to about 35% wt. mixed plastics. The pressure maintained within the process vessel may be less than about 50 torr. Alternatively, the solid fuel composition may comprise less than 0.5% wt. water. The solid fuel composition may release per million BTUs when burned less than about 0.5 lb. alkali oxide, less than about 3 lb. ash, less than about 0.1 lb. SO2, and less than about 1.5 lb. of chlorine. The solid fuel composition may be essentially non-porous, essentially odor-free, and/or essentially sterile. Further, the solid fuel composition may be extruded in the form of rods with a maximum cross-sectional dimension of about two inches and a rod length of less than about 2 feet. The solid fuel composition may also be ground to a plurality of particles with a maximum particle dimension of less than about 3 mm.

The present disclosure further provides a solid fuel composition with an energy content between about 8,000 BTU/lb. and about 14,000 BTU/lb., and a density between about 30 lbs./ft3and about 80 lbs./ft3. The solid fuel composition is not pyrolyzed and is substantially free of volatile organic compounds and non-combustible waste. The solid fuel composition comprises from about 40% wt. to about 80% wt. carbon, from about 5% wt. to about 20% wt. hydrogen, from about 5% wt. to about 20% wt. oxygen, less than about 2% wt. sulfur, less than about 2% wt. chlorine, and less than about 1% wt. water. The solid fuel composition comprises between about 5% wt. and about 35% wt. mixed plastics. The solid fuel composition releases per million BTUs burned less than about 0.5 lb. alkali oxide, less than about 3 lb. ash, less than about 0.1 lb. SO2, and less than about 1.5 lb. of chlorine. The solid fuel composition is essentially non-porous, essentially odor-free, and essentially sterile. The solid fuel composition may be a non-waste, for example a non-waste produced from discarded non-hazardous secondary material.

The present disclosure also provides a solid waste mixture, comprising between about 5% wt. and about 60% wt. mixed plastics and less than about 1% wt. water, being substantially free of volatile organic compounds, at a temperature between about 160° C. and about 260° C. and at a pressure of less than about 50 torr.

While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosure. As will be realized, the invention is capable of modifications, all without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

