Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
1999-06-10
2002-06-18
Bennett, Henry (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S246000, C110S223000, C110S226000
Reexamination Certificate
active
06405663
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus methods of waste treatment.
BACKGROUND
This invention has particular but not exclusive application to apparatus and methods for the incinerative processing of waste with organic content such as municipal wastes, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as processing of industrial waste.
Waste disposal and particularly the disposal of bulk waste is an ongoing problem, with landfills being rapidly filled and polluting leachates therefrom being a frequent contaminant of waterways. Municipal and industrial wastes invariably contain or break down to form toxic products and polluting outgas. Such waste may include sub-micron particulates to liquids and gases and may contain substances of extreme human or environmental toxicity such as toxic metals, synthetic organic compounds and unnatural concentrations of normally innocuous substances such as hydrocarbons, refuse and sewage.
Highly toxic wastes of the organic type such as poly chlorinated aromatic hydrocarbons such as PCB's are presently disposed of by high temperature incineration. Often, the waste must be transported overseas to be destroyed either at foreign specialized facilities or at sea. Foreign treatment is extremely expensive, a cost which is added to the cost of manufactures at home.
Other less toxic wastes are disposed of by less intensive and more cost effective treatments such as by cementation and burial or dumping of the solid waste product. This method of disposal presents the problem of the disposal of the liquid supernatant of the cementation process as well as the disposal of an increased volume of often leachable solid material. Sewage waste solids are generally even more simply disposed of by settling and evaporation of primary treatment slurries followed by open-site dumping of the partially dewatered sludge.
Where hydrocarbon based waste such as condemned fuel and waste lubricants is to be destroyed, this has generally been by incineration. However, the energy values of such waste are generally wasted since contamination of the waste prevents its use as incinerator fuel.
Wherever incineration of waste is done, there remains a disposal problem in respect of leachable ash and scrubber sludges.
International Patent Specification WO 90/12251 discloses an improved method and apparatus for waste treatment including grinding bulk waste from a broad range of sources, mixing the waste material with a binder, pelletizing the mixture, coating the pellets with a refractory material and firing the mixture in a furnace at a temperature above 1300 degrees celsius. It was found that heating the waste pellets to a temperature above 1300 degrees celsius under oxidizing conditions provided a product clinker having reduced leachability and increased chemical and physical stability, and flue gases having no unpyrolysed content and a high oxidation state compared with prior art incineration processes.
The process disclosed has several disadvantages. One disadvantage is that the coating process essential to prevent agglomeration of the pellets, utilizing as it does aluminium silicate-rich clay dust, tends to result in an easily spalled coating to the pellets under processing and kiln conditions. This results in an unacceptably high agglomeration rate of the pellets in the kiln.
Accordingly it is an object of the present invention to provide an apparatus and method for treating a broad variety of waste, which apparatus and which will alleviate the deficiencies of the prior art and are reliable, economical and efficient in use. Other objects and advantages of this invention will hereinafter become apparent.
SUMMARY
With the foregoing and other objects in view, this invention in one aspect resides broadly in a method of treatment of waste material including the steps of:
mixing the waste material with a firable binder;
pelletizing the mixture;
coating the pellets with a coating comprising a refractory material selected to permit firing of the pellets substantially without pellet agglomeration, and a support material for said refractory, and
firing said coated pellets in a rotary kiln.
It has surprisingly been determined that the spalling problems associated with the use of refractory coating of the pellets prior to and during firing are substantially alleviated by the process of the present invention, whether or not the support material comprises a non agglomerating material under kiln and processing conditions.
The waster material may include any solid, liquid or mixed waste product including sewage sludges, oil sludges, common garbage or liquid toxic metal wastes, and including mixtures of waste materials. Preferably the waste material has a solid content and/or solids are added to the mixture before firing such that the mixture of the waste with the binder material is of a consistency suitable for pelletizing.
Preferably, the waste material has a combustible content and/or combustible materials are added to the mixture before firing such that the energy demand of the firing process is diminished. However, in the case of wastes having little or no inherent energy available from high temperature oxidation in air, it is envisaged that the entire energy requirement may be provided by an external source such as electricity, pulverized coal, gas or fuel oil.
The waste materials may be pumped or conveyed to a mixer where they may be blended with absorbent and earthen materials, and, if necessary, further water and other materials to produce a firm plastic type material. By example the composition of a typical processed galvanic sludge and toxic liquid waste prior to pelletising is, by weight:
Waste 46% (galvanic sludge & liquid waste)
Absorbent 9% (sawdust)
Clay 1%
Other 4% (lime and barium carbonate)
Typically the components of the mix prior to pelletizing lie within the band, by weight, of:
15-50%
waste as received
5-12%
absorbent (sawdust, newspaper, etc.)
40-60%
clay
0-15%
other material (lime, old glass, fluxing agents)
0-15%
water (as required)
The amount of waste that can be incorporated is dependent on the type of waste and the strength of the final pellet required. Alkali such as lime may be used to control the pH of the mix to a preferred slightly alkaline state as well as to give the desired ceramic characteristics of the finished pellet. Where the mixture is acidic, the lime, lime containing waste stream materials or other alkali or basic materials may be added to at least partially neutralize the mixture during firing to control outgassing, resulting in the production of closed-surfaced fired pellets. Outgassing tends to form voids in the pellets which may reach the surface to form pores. This phenomenon may be desirable where the pellets are to be recycled to the process with, for example, a liquid waste adsorbed into the pellets.
After mixing, the material may be pelletized by any suitable process such as sheet rolling and punching, extrusion, or the like. Preferably, the mixture is extruded through a die consisting of a plurality of holes of typically 10 mm diameter in a die plate, and the resultant extruded material cut off at typically about 15 mm length to form pellets.
After pelletizing, the pellets are coated. Preferably, the refractory coating is selected from the refractory clays such as those having a high aluminium silicate content, china clays, refractory compounds such as aluminium silicate per se, or other suitable refractory, non agglomerating material. By “refractory” in this context is meant those materials having sufficient resistance to melting at all temperatures below 1200° C. and a sufficient range above 1200° C. to enable pellets coated therewith to resist agglomeration under rotary kiln process conditions.
The support material may be selected from material compatible with the refractory materials, such as hydrated silicates, organic binders such as resins, or sticky clays such as ball clays. The support may be a
Bennett Henry
Plas, Ltd.
Rinehart K. B.
Schwegman Lundberg Woessner & Kluth P.A.
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