Electric heating – Inductive heating – With workpiece support
Patent
1994-04-22
1996-05-14
Leung, Philip
Electric heating
Inductive heating
With workpiece support
219619, 219651, 219654, 588234, 588237, H05B 610
Patent
active
055170048
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for removing one or more contaminations from dry solid bulk material, in which method the dry solid bulk material is fed into a treating chamber, said treating chamber being formed by a drum rotatable around a rotation axis, which drum comprises a casing containing an electrically conductive material, said dry solid bulk material is subjected to a temperature treatment under subatmospheric pressure during rotation of the drum by heating the container by means of electrical induction heating and said treated dry solid bulk material is discharged from said treating chamber.
2. Description of Related Art
The invention relates furthermore to an apparatus for carrying out the method according to the invention, said apparatus comprising a treating chamber for the treatment therein of contaminated dry solid bulk material, the treating chamber being a drum of which the casing contains an electrically conductive material, the apparatus comprising rotating means for rotating the drum around a rotational axis, feeding means for feeding the dry solid bulk material in the treating chamber, discharging means for discharging the treated dry solid bulk material from the treating chamber, heating means comprising an electrical induction means arranged around the drum for heating the dry solid bulk material in the treating chamber, and vacuum means for forming a subatmospheric pressure in the treating chamber.
A method as described in the opening paragraph is known from EP 0 423 039 A1. In this method the dry solid bulk material is fed in the drum through an opening after which the drum is activated to rotate. During rotation the dry solid bulk material is subjected to a temperature which is strictly lower than 500.degree. C. at a pressure which is in the order of 0.01 bar or more, for a period of three hours or more in order to remove contaminations. After this treatment the dry solid bulk material is discharged through the same opening.
It is one of the objects of the invention to provide a method for removing one or more contaminations from a dry solid bulk material with which a high removal yield can be achieved in an efficient way with no or at least a low risk to the environment.
It is another object of the invention to provide an apparatus for carrying out the inventive method.
SUMMARY OF THE INVENTION
For this purpose a method as described in the opening paragraph is, in accordance with the invention, characterized in that said drum is provided with at least one entrance and at least one separate exit, in that the dry solid bulk material is fed into the drum through said at least one entrance, in that the drum is rotated for continuously transporting said solid dry bulk material from said at least one entrance to said at least one exit, in that said dry solid bulk material is subjected to a subatmospheric pressure lower than 3 mbar, and in that said treated dry solid bulk material is discharged from the drum through said at least on exit.
The vacuum treatment of the bulk material has an important advantage, particularly by the formation of a high vacuum, i.e. a pressure lower than 3 mbar in the treating chamber, in that the vapour pressure and therefore also the boiling point of the contaminations is lowered, so that the contaminations can easily escape from the bulk material. By doing so contaminations containing heavy metals, such as cadmium or less volatile hydrocarbon compounds, such as insecticides, pesticides and PCB's can also be removed. Besides, the closed vacuum system reduces leakage of vapours to an absolute minimum. Apart from that, the absence of air in the treating chamber prevents the formation of dioxines and other environmentally hazardous substances formed by oxidization. As the quantity of combustion gases is very small, the follow-up treatment of the extracted vapours can take place more efficiently.
Furthermore, by continuously transporting the dry solid bulk material through the drum the length of stay
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patent: 4931610 (1990-06-01), Hughes et al.
patent: 5134260 (1992-07-01), Piehler et al.
Leung Philip
Recycling Nederland Holding B.V.
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