Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Reexamination Certificate
1999-08-30
2001-02-20
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
C106S284020, C588S256000
Reexamination Certificate
active
06190447
ABSTRACT:
The present invention relates to a method for the remediation of bottom ash from domestic waste incinerators and the production of an asphalt which is suitable for use in the construction of roads.
The ever-increasing volume of domestic waste has resulted in a considerable pressure on available landfill space. One process that has been developed to reduce this pressure is the incineration of the waste in high-temperature incinerators at combined heat and power facilities. In this process, domestic waste is incinerated at temperatures of 1000° C. or more, producing electricity, steam, fly ash and bottom ash (the latter is also known as domestic waste incinerator residue—D.I.R). The bottom ash and fly ash differ both in particle size and chemical composition. Some metals can be retrieved from this bottom ash (e.g. by electromagnetic and eddy current separation), but this still leaves a mass of material which until now has had no use and was simply disposed of in landfill sites. Even this disposal causes problems, because of high metal concentrations in leachate produced from the bottom ash. In particular, the levels of lead, copper, zinc and chromium are greater than the relevant environmental guidelines (drinking water and groundwater guidelines).
It would be highly desirable, therefore, to develop a process for the remediation of bottom ash from domestic waste incinerators to give a material whose leachate was more environmentally stable. Furthermore, it would be desirable for the remediation process to give a material with useful properties rather than simply disposing of it in landfill sites.
Asphalt stabilisation is a remediation technology that has been developed and applied for some considerable times. The process is designed to bind contaminated material in a stable product, reducing risks associated with dermal contact, ingestion and leaching of contaminants to groundwater and surface water. In addition, the process eliminates the need for landfill disposal of contaminated material and associated environmental problems that may arise.
Currently, technology of this type is used to recycle road plannings, reducing the demand for virgin aggregates and recycling the old road surface material. Two methods are used to process materials, hot mix bituminous concrete production and the cold mix method. In these processes an asphalt binder is mixed with soil/stone aggregate and blended to ensure each soil grain and stone aggregate is coated with a thin layer of asphalt. In order to mix the asphalt binder, which is a solid at room temperature, with the aggregate it must be in a liquefied form. Hot mix bituminous concrete production uses heat to liquefy the solid asphalt. The cold mix process, also known as Asphalt Emulsion Stabilisation (AES), uses a mixture of water and surfactants to get asphalt into a workable liquid form.
Asphalt stabilisation has not, however, previously been successfully applied to the remediation of bottom ash from domestic waste incinerators. It is an object of the present invention to provide a process of remediating bottom ash from domestic waste incinerators using asphalt stabilisation technology. It is a further object of the invention to provide a remediated product which is both environmentally stable and suitable for use in the construction of roads.
Thus, in a first aspect of the present invention there is provided a process for the remediation of bottom ash from domestic waste incinerators comprising hot mixing from 10 to 50% by weight of said bottom ash with from 4 to 6% by weight of bitumen having a penetration of from 50 to 200 pen, from 25 to 55% by weight of crushed rock having a particle size greater than 2 mm, from 10 to 35% by weight of crushed rock fines having a particle size less than 2 mm and from 0 to 3% by weight of a filler to give a hot mix asphalt product.
This process remediates the bottom ash to give an asphalt product which is more environmentally stable, particularly with regard to leachate levels of metals such as lead, copper and zinc, and which has similar properties to conventional hot mix asphalts obtained from virgin aggregate, making it suitable for use in the construction of roads.
In a further aspect of the present invention, there is provided a hot mix asphalt comprising from 10 to 50% by weight of bottom ash from a domestic waste incinerator, from 4 to 6% by weight of bitumen having a penetration of from 50 to 200 pen, from 25 to 55% by weight of crushed rock having a particle size of greater than 2 mm, from 10 to 35% by weight of crushed rock fines having a particle size of less than 2 mm and from 0 to 3% by weight of a filler.
The bitumen used in the present invention has a penetration of from 50 to 200 pen, as determined according to British Standard Specification (B.S.) 3690 (a test which is based on viscosity ranking test; 1 pen=0.1 mm). Preferably, from 4.7 to 5.5% by weight of bitumen is added to the hot mix.
The crushed rock used in the present invention is the coarse aggregate element and refers to the particles whose size exceeds 2 mm, as tested using the appropriate British Standard test sieve. It is obtained from the quarry process of blasting, crushing and screening of a mineral deposit. The crushed rock used can be any conventionally used in the production of hot mix asphalts e.g. limestone and granite. Preferably, from 29 to 52% by weight of crushed rock is added to the hot mix.
The crushed rock fines are particles whose size is less than 2 mm, as tested by the appropriate B.S. test sieve, and are obtained from the same quarry process on the crushed rock. Preferably, from 12.5 to 32% by weight of crushed rock fines are added to the hot mix.
The fillers used are those conventionally used in the production of hot mix asphalts. They are generally powders whose particle size is substantially less than 75 &mgr;m as tested by the appropriate British Standard test sieve. Examples of suitable fillers include the product of milling limestone aggregate. Preferably 2% by weight of filler is added.
In a preferred embodiment of the present invention, the bottom ash is subjected to electromagnetic and eddy current separation before the mixing process to remove substantially all of the ferrous metal and up to 60% of the non-ferrous metal. The bottom ash can also, preferably, be crushed and screened to reduce the average particle size before the mixing process.
The precise amounts of the different components can be varied according to the intended use for the asphalt product. Thus, for example, surface course material which complies with the requirements of 10 mm wearing coarse British Standard 4987 (in terms of gradation, binder content and temperature for mix and lay) is obtained by hot mixing the following components according to the process of the present invention.
Raw Materials
% Composition
Domestic Waste Incinerator Residue
10
20
50
Bitumen 50 pen, 100 pen, 200 pen
5.5
5.5
5.5
Crushed Rock
52
46
30
Crushed Rock fines
30.5
26.5
12.5
Limestone Filler
2
2
2
Basecourse asphalt which complies with the requirements of a 20 mm dense basecourse macadam British Standard 4987 (in terms of gradation, binder content and temperature of mix and lay) is obtained by hot mixing the following components according to the present invention.
% Composition
Raw Materials
Mix A
Mix B
Mix C
Domestic Waste Incinerator Residue
10
20
50
50 Pen Bitumen
5
5
5
Screened Crushed Rock
51
45
20
Crushed Rock Fines
32
28
14
Limestone Filler
2
2
2
The present invention can be further understood by consideration of the following examples, in which the reduction in leachate metal concentrations and the loading bearing properties of the hot mix asphalt of the present invention were tested.
Using a hot mix asphalt plant, the following materials were combined according to the present invention to give an asphalt which met the requirements of British Standard 4987 as a basecourse macadam.
%
Component
Source
by weight
Coarse Aggregate
Bardon Hill Quarry Hardstone aggregate
28.3
Fine Aggregate
Bardon Hill Quarry Hardstone aggregate
15.0
D.I.R.
So
Phillips Paul
Smart Malcolm
Aggregate Industries, Inc.
Brunsman David
Morrison & Foerster / LLP
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