Process for minimizing dioxin formation during waste and biomass utilization
Inactive Publication Date: 2014-04-24
COGEN DESIGNS
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Benefits of technology
The patent text describes a process for creating synthetic coal from biomass or waste. The process involves sorting the material, shredding it, and then pyrolyzing it at a high temperature using viscous shear heating. The resulting material is then used to produce mechanical work. The process results in a granulated synthetic char coal with low moisture content. The invention aims to provide a sustainable and cost-effective solution for the production of energy from biomass and waste.
Problems solved by technology
However, landfilling has become less of a solution to waste disposal and more of a means of storing waste until an effective means of disposal or utilization can be developed.
Each program brings some benefit, but does not represent a full solution for the waste problem.
Effective recycling requires economic justification, and most components of the waste stream do not have sufficient economic value to offset their cost of separation and recovery.
Composting is effective on some parts of the waste stream, but the majority of the waste is not amenable to compost production.
However, the high moisture content, variability of composition and physical characteristics of urban waste have made incineration systems expensive, inefficient, high maintenance, and unpopular with the general public.
Worse still, the incomplete combustion of waste and biomass produces toxic dioxins.
However, waste pyrolysis oils are not readily compatible with petroleum-based liquid fuels, and therefore require extensive and expensive upgrading to achieve that compatibility.
However, the pyrolysis gases are not compatible with today's natural gas pipeline systems, and must be used on-site.
These processes are often characterized by high energy consumption, that is, low thermal efficiency, high reaction temperature, low product yield, long processing time and batch processing.
This avenue also requires expensive upgrading, as the char from most pyrolysis processes using urban waste does not have the porosity, surface area and high chemical reactivity desired by the activated carbon market.
However, these processes have little temperature control, and produce a wide spectrum of byproducts ranging from tars and heavy oils to light combustible gases, all diluted by the products of partial combustion.
While the transfer of heat to the feed material is efficient, the handling of the byproducts is often difficult.
These designs suffer from several limitations.
Dioxins may be present in some waste products, and can be emitted to the environment if the combustion of those wastes is incomplete, and insufficiently high in temperature to destroy these dioxins.
), PAH's are destroyed by combustion, but conventional waste incineration technology does not reach the temperatures needed for their complete destruction.
The result is the formation of de novo dioxins prevalent in waste and biomass combustion.
However, because of the limitations in internal heat transfer and product mixing present in his vertical moving bed reactor, it was necessary to add alkali agents such as sodium hydroxide or sodium bicarbonate, and to operate the reactor at temperatures above 680° F.
These researchers were proceding with the intent to then wash the alkali-chloride salts from the char, but were unsuccessful in doing so, as the char particles had very limited porosity.
Below this, the liberation of chlorine is not effective, while above it chlorine capture by alkali is blocked by ash silicates.
If heating and temperature are not uniform, and the material is not well stirred during the reaction process, some portions of the biomass will be subject to higher temperatures and some to lower temperatures, resulting in less than complete dioxin destruction, less alkali capture, and the potential for formation of de novo dioxin precursors.
Thus pyrolysis heating systems that rely on contacting the feedstock with hot circulating solids, partial oxidation, heat conduction through external reactor wall surfaces, or radiation to feedstock particle surfaces cannot achieve the degree of temperature and concentration uniformity required to maximize dioxin control.
These other systems inevitably result in the need for catalyst and / or alkali addition, long residence times, and limited dioxin destruction efficiency.
In addition, the fuel should limit the availability of free chlorine in the combustion products.
In addition, this fuel would be lower in primary pollutants such as sulfur and mercury, would limit the availability of free chlorine in the combustion products, and reduce the net greenhouse gas emissions of the plant burning it, not just by substitution of “renewable carbon” for “fossil fuel carbon,” but in real tons of total CO2 emitted.
Heat transfer is limited to the surface of the tube, and, the solids must be in contact with it to be heated.
Method used
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[0089]Initially, 2000 pounds of urban waste are sorted to remove foreign material, FIG. 4, and shredded to produce approximately 1500 pounds of organic matter equivalent to Refuse Derived Fuel (RDF). The shredded waste material is fed by metered conveyor to the feed port 8 of the pyrolysis reactor, See FIG. 5, where it is conveyed and compacted by the internal reactor augers 15, which deliver it to the first mixing zone 9. Here intense mixing converts mechanical work into direct in-situ heating of the waste materials through viscous shear forces within the feedstock itself. During the short period in which the waste is maintained within the first mixing zone, the temperature of the waste is increased to approximately 260° F., liberating moisture in the form of water vapor. The waste leaves the mixing zone, passing into an area without compaction, which permits the vapors and solids to separate, with the water vapor leaving the reactor from a vent 12 on its top surface, at a temperat...
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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.
Description
FIELD OF USE[0001]The present invention relates to an improved process for producing a synthetic coal of superior quality from biomass or urban waste, and in the process dramatically reduces the potential for dioxin formation that is prevalent in conventional biomass combustion, incineration and waste-to-energy technologies.BACKGROUND OF THE INVENTION[0002]The disposal of urban waste has been traditionally handled by landfilling. However, landfilling has become less of a solution to waste disposal and more of a means of storing waste until an effective means of disposal or utilization can be developed. The desire to reduce the amount of waste volume landfilled, and to avoid some of the issues associated with less than perfect waste containment in landfills, has led to programs for recycling, composting and incineration of urban waste materials. Each program brings some benefit, but does not represent a full solution for the waste problem. Effective recycling requires economic justif...
Claims
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Login to View More IPC IPC(8): C10L5/44
CPCC10L5/44Y02E50/10Y02E50/30C10L5/46C10L9/083C10B7/10C10B53/02
InventorJONES, FRED L.
OwnerCOGEN DESIGNS