Electrical resistors – Incased – embedded – or housed – With gaseous or vacuum spacing between element and casing or...
Patent
1989-06-21
1991-11-12
Evans, Geoffrey S.
Electrical resistors
Incased, embedded, or housed
With gaseous or vacuum spacing between element and casing or...
373134, H01C 1026
Patent
active
050651315
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to devices for electrically heating a medium by resistance, which devices are further commonly called immersion heaters, of the type comprising a substantially cylindrical elongate graphite heating element, surrounded by a refractory material sheath defining, about the heating element, a sealed chamber retaining a gas capable of protecting the graphite from oxidation.
It finds a particularly important, although not exclusive, application in the field of electric heating devices reaching, in furnaces where a corrosive or oxidizing atmosphere prevails, temperatures as high as those reached by the use of a fossil fuel.
2. Electric heating prior art devices of the above defined type are already known. In particular, in the patent application FR-A-84 02358, the applicant describes a device comprising a graphite heating element protected against oxidation by an atmosphere containing carbon monoxide formed from the heating element when the device is first put into use and surrounded by a corrosion resistant tubular refractory ceramic sheath. This solution solves numerous problems.
However, the use of a ceramic sheath, whose heat conductivity is low, limits the power which can be dissipated per unit of surface.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved electric heating device. It is a more particular object to provide a device which makes it possible to obtain a shape of sheath particularly favourable to the diffusion of the radiating heat coming from the graphite heating element, which was impossible with ceramic sheaths whose shape was limited to a cylinder of revolution or an oval, in that it overcomes the dangers of electric short circuits between the graphite heating element and the sheath, which dangers are caused by the movement and vibration of the device in its heated medium, in that it comprises means for fixing and centring the graphite heating element inside its sheath which considerably minimize the difficulties of fitting such a device and the problems met with during handling thereof, and in that it makes it possible to obtain a considerable life-span of the device through an inert gas supply system which is inexpensive, simple to use and easy to maintain, protecting the graphite element against oxidation.
To this end, the invention provides more particularly an electric heating device of the above defined type, characterized:
in that the sheath is made from refractory metal alloy sheeting resisting the corrosion of the medium or is coated with a substantially constant protective external metal layer,
in that said sheath has regular corrugations adapted so that all the points of the internal surface of the sheath see the heating element directly,
in that said heating element is provided with two solid blocks forming a first end portion of said element and connected respectively to the input and output terminals of the electric power supply,
and in that said graphite heating element comprises means for fixing and centring said heating element inside the sheath, said fixing and centring means comprising an insulating refractory material ring fixed on the second end portion of the graphite heating element and engaged in a cylindrical skirt fixed on the internal portion of the sheath, so that centring of the graphite element with respect to the sheath at the level of the second end portion of said element is provided, and a composite bed plate for fixing the graphite heating element and supplying it with electricity, which is removably fixed on the first end portion of said element and on which are fixed input and output bars for the electric power supply, said bed plate being formed by two metal portions forming respectively the electric input and output terminals of said graphite element, said metal portions being insulated electrically and fixed rigidly together by means of a ceramic insulating plate.
In an advantageous embodiment of the device applied to a heating element used in a vertica
REFERENCES:
patent: 4016403 (1977-04-01), Best
patent: 4215233 (1980-07-01), Kastilahn
patent: 4327281 (1982-04-01), Jager et al.
patent: 4862137 (1989-08-01), Jaume
Ducourroy Andre
Jaume Richard
Electricite de France (Service National
Evans Geoffrey S.
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