Furnaces – Process – Treating fuel constituent or combustion product
Patent
1999-06-21
2000-08-22
Ferensic, Denise L.
Furnaces
Process
Treating fuel constituent or combustion product
110165A, 422173, 422175, 422178, F23J 300, F23J 100, F01N 310, B01D 5000
Patent
active
061055174
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
This invention relates to the treatment of fly ash and other ash of a fine particulate nature, and in particular to its detoxification and/or re-use. The invention provides novel apparatus and methods for such treatment.
An object of the present invention is to treat toxic fly ash from incinerators, which ash is particulate, and other ash of particulate nature which can be retrieved, for example, from bottom ash of incinerators, and to convert such ash into a material which can be used, for example, in the construction industry. Throughout this specification, reference is made to fly ash, but this term is to be understood to include ash of fine particulate nature from any source of an incinerator, including bottom ash. In the UK the total toxic fly ash which is produced is approximately 200,000 tonnes/year from municipal incinerators alone. There is a major problem in the disposal of the fly ash/grit from an incinerator since it contains toxic, leachable heavy metals and organic materials such as dioxins. It is becoming more difficult and expensive to find landfill sites in which it is permitted to bury such material.
It has been proposed to heat fly ash to its fusion temperature in an arc furnace to form a fused slag which can be used for road making or for construction material purposes. Such processes, however, require a great deal of energy and are relatively inefficient.
GB-A-942620 discloses pelletising fly ash with a binder and then sintering the fly ash pellets on a moving grate. Nevertheless, this method requires a great deal of energy as well, not just to drive off the water binding the pellets together, but also to heat the inside of the pellets to effect internal sintering of the pellet ash. EP-A-0034389 discloses a similar process, as does JP-A-62256746. JP-A-3247541 appears to suggest settling fly ash on a moving grate and sintering it there.
JP-A-6351965 discloses a cyclone the inside of which is coated with sintered Titanium Dioxide.
SUMMARY
According to the present invention there is provided a process for treating toxic particulate ash from an incinerator which comprises providing a flow of combustible gas, burning the gas, suspending the particulate ash in the moving gas to heat the ash while in suspension to a temperature at which sintering of the fly ash takes place, separating the ash while still at sintering temperature and forming the ash to produce a frit or sintered pellets of ash.
The present invention also provides apparatus for treating toxic particulate ash from incinerators, which comprises means for producing a flow of a combustible gas, means to ignite the gas so that it burns, means to introduce the ash into the gas so that it is suspended in the flow of gas and heated by the gas so that the temperature of the fly ash is raised to at least a temperature at which sintering of the fly ash takes place, means to separate hot ash from the gas, and means to form pellets or frit of sintered ash.
It has been found that, in the process of the present invention, sintering of the fly ash can result in substantial destruction of its toxic organic components and also fixation of its heavy metal content to form a substantially unleachable material which can be used, for example in applications such as building roads and foundations.
In order to sinter the fly ash material, its temperature must be raised to the softening point. This occurs at a temperature of about 850.degree. C., which is significantly lower than its melting point at about 1300.degree. C. A preferred sintering temperature is in the range of from about 750.degree. C. to 1000.degree. C.
For many purposes it will be sufficient to raise the temperature of the fly ash particles to the sintering temperature. The invention does not, however, exclude the possibility that the fly ash particles can be heated to their fusion temperature in order to produce an unleachable slag or frit.
Preferably, the fly ash is caused to reach sintering temperature within a cyclone. The fly ash is introduced into the cyclone simulta
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patent: 5297495 (1994-03-01), Weber
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Ferensic Denise L.
Rinehart Kenneth B.
University of Sheffield
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