Process for minimizing dioxin formation during waste and biomass utilization

Abstract

A process for the production of high quality synthetic coal from biomass or urban waste, while effectively reducing its potential for dioxin production. The feedstock is first sorted to remove recyclable inorganic materials. After size reduction, the feedstock is pyrolyzed at a temperature range of 500 to 600° F. (260-315° C.), in a high capacity, continuous mixer reactor, using in-situ viscous shear heating of the waste materials, to produce a highly uniform, granular synthetic fuel product similar in energy content, storage and handling characteristics to, but much cleaner burning than, natural coal. The process effectively destroys dioxins and other chlorinated hydrocarbons that may be present in the feedstock, while removing and sequestering chlorine as alkali salts.

What is claimed is: 
     
         1 . A process for the production of synthetic coal (char) from biomass or urban waste comprising:
 (a) sorting a material selected from the group consisting of
 i biomass, 
 ii waste, and 
 iii a combination of biomass and waste, to remove foreign materials; 
   (b) shredding said sorted material;   (c) pyrolyzing said sorted material at a temperature in the range of 500 to 600° F. by means of in-situ viscous shear heating; and   (d) utilizing the liquid and gaseous byproducts of pyrolysis for the production of mechanical work used to cause said pyrolysis to occur.   
     
     
         2 . The process according to  claim 1 , whereby said sorted material is both dried and pyrolized within a single reactor. 
     
     
         3 . The process according to  claim 1 , whereby said pyrolysis is conducted in a twin screw mixer, converting the mechanical shaft energy of mixing using viscous shear forces to produce in-situ heating of the sorted materials. 
     
     
         4 . The process according to  claim 1 , whereby unique mixing using a viscous shear heating method, combined with the process temperature range, maximizes the destruction of chlorinated hydrocarbons, including dioxins, within the sorted material. 
     
     
         5 . The process according to  claim 1 , whereby a unique heating method and temperature range combine to maximize the liberation and alkali sequestration of chlorine to minimize future formation of dioxins during combustion of the char product of said process. 
     
     
         6 . The process according to  claim 1 , whereby a unique heating method and temperature range combine to maximize the energy efficiency of sorted materials pyrolysis. 
     
     
         7 . The process according to  claim 1 , whereby the sorted materials are reduced to a uniform, hard granular solid fuel product by means of in-situ heating and mixing caused by said reactor. 
     
     
         8 . The process according to  claim 1 , whereby a solid fuel product of said process has significantly lower potential for de novo dioxin formation than its sorted material, due to product high reactivity and high combustion temperature. 
     
     
         9 . The process according to  claim 1 , whereby the solid fuel product of said reactor has significantly lower potential for de novo dioxin formation, due to the sequestration of chlorine by alkali salts present in any product ash. 
     
     
         10 . The process according to  claim 1 , whereby said solid fuel product of said reactor has a calorific value in the range of 9,000-10,500 Btu/pound. 
     
     
         11 . The process according to  claim 1 , whereby said solid fuel product of said reaction reactor is similar in handling, storage and burning characteristics to high volatile bituminous coal. 
     
     
         12 . The process according to  claim 1 , whereby said solid fuel product of this reactor is capable of reducing greenhouse gas emissions from combustion sources, compared to natural coal. 
     
     
         13 . The process according to  claim 1 , whereby said pyrolysis is conducted in a temperature range of 500 to 600° F. 
     
     
         14 . The process according to  claim 1 , whereby byproduct water vapor, oils and gases are removed from said pyrolysis reactor by separate vents. 
     
     
         15 . The process according to  claim 1 , whereby byproduct water vapor produced in a first mixing/drying zone of said reactor is used to remove any entrapped air from said sorted materials by way of a first gas vent, thereby reducing dioxin formation potential in subsequent pyrolysis zones in said reactor. 
     
     
         16 . The process according to  claim 1 , whereby byproduct oils, gases and sensible heat are utilized in a boiler to produce steam. 
     
     
         17 . A process according to  claim 1 , whereby the energy requirements of pyrolysis are met by the introduction of mechanical energy, which is converted to in-situ heating of the sorted materials within said reactor by the process of viscous shear during mixing. 
     
     
         18 . The process according to  claim 1 , whereby the use of in-situ heating within and throughout said reactor provides for rapid heating and conversion of said sorted materials without any limitations in reaction rate imposed by transfer of heat through reactor walls and other surfaces. 
     
     
         19 . A process according to  claim 1 , whereby the use of in-situ heating within and throughout said reactor provides for conversion of the sorted materials without any limitations in product uniformity imposed by delivery of heat by conduction through contact with reactor wall surfaces. 
     
     
         20 . A process according to  claim 1 , whereby the use of in-situ heating within and throughout the reactor provides for the scaling of said reactor capacity based on said reactor mixing zone volume rather than area of heated surface. 
     
     
         21 . A process according to  claim 1 , whereby the effective heating of sorted materials for said pyrolysis can be accomplished without risk of any ash softening and deposition on reactor walls and other surfaces. 
     
     
         22 . A process for the preparation of synthetic char coal fuel from a feedstock selected from the group consisting of
 i biomass,   ii waste, and,   iii a combination of biomass and waste, comprising:   (a) sorting said feedstock to remove foreign materials;   (b) reducing the size of non-foreign feedstock;   (c) pyrolyzing said feedstock at a temperature in the range of 500 to 600° F., using viscous shear in-situ heating, to produce a granulated synthetic coal char fuel having a moisture content of 3% or less;   (d) collecting and cooling said granulated synthetic coal char fuel, and,   (e) collecting and utilizing the byproduct oils and gases to produce mechanical energy to import into the pyrolysis reactor to accomplish in-situ heating of the sorted non-foreign materials.