Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Microwave energy
Patent
1998-04-06
1999-11-09
Bennett, Henry
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Microwave energy
F26B 334
Patent
active
059790733
DESCRIPTION:
BRIEF SUMMARY
This Invention relates to a method of drying a porous body.
According to one aspect of the invention there is provided a method of drying a porous body having an external surface provided with pores in communication with interconnected pores or channels in its interior containing a liquid, the method comprising the steps of: electromagnetic radiation for an initial period to cause the body to undergo an average rate of temperature increase over the initial period of at least 2.degree. C./minute; and subsequent period to reduce the rate of temperature increase of the body to at most 1 .degree. C./minute.
The ratio of the initial period: subsequent period may be 1:10-10:1, preferably 1:4-4:1.
According to another aspect of the invention there is provided a method of drying a porous body having an external surface provided with pores in communication with interconnected pores or channels in its interior containing a liquid, the method comprising the steps of: electromagnetic radiation to cause the body to undergo an average rate of temperature increase of at least 2.degree. C./minute; and
Preferably the method of the present invention comprises both said step of reducing the rate of heat energy input, and said step of resisting heat energy loss. In this case there may be a ratio between the initial period and the subsequent period of 1:10-10:1, the method including resisting heat energy loss from the external surface of the body.
By drying is meant a reduction in the liquid content of the body to a desired value. Preferably, the drying is carried out to a degree where the body can be handled without causing any damage thereto or unacceptable deformation thereof. For bodies comprising consolidated particulate material of the type described hereunder, a dried body having lost about 2-5% of its wet mass during drying has been found to be sufficiently dry for handling purposes.
Resisting said heat energy loss may be by thermally insulating the body, eg by providing thermal insulation in contact with or in close proximity to the external surface of the body. The heat energy loss may, instead or in addition, be resisted by supplying heat to the external surface of the body from an external heat source, eg by heating walls defining a cavity around the body and/or by maintaining an ambient atmosphere surrounding the body at a predetermined temperature, eg by increasing the temperature of the ambient atmosphere around the body, and/or the temperature of said walls, during said temperature increase of the body. In particular, resisting heat energy loss from the exterior surface of the body may comprise heating the external surface of the body by means of radiant heat, radiated on to the external surface of the body from at least one radiant heat source, such as a radiant heating element. Preferably, the temperature of said walls, and/or the temperature of said ambient atmosphere, are kept as close as feasible or practicable to the temperature of the external surface of the body. In particular, resisting heat energy loss from the external surface of the body may be such as to keep the external surface of the body at substantially the same temperature as the interior of the body, so that no unacceptable temperature gradient exists in the body between any part of its interior which is hotter than the external surface, and the external surface, routine experimentation being employed to determine the reduction of heat loss required. As indicated above, the method may comprise heating the environment surrounding the body to cause its temperature to increase progressively as the temperature of the body increases, the environment being defined by a cavity having a wall or walls directed at the porous body and by the atmosphere in the cavity around the body, and the temperature difference between the external surface of the porous body and the wall surface temperature of the cavity preferably being restricted to an acceptably small value. If desired the surface of the thermally insulating material which faces the body may be he
REFERENCES:
patent: 5237755 (1993-08-01), Lowe
patent: 5306675 (1994-04-01), Wu et al.
patent: 5335425 (1994-08-01), Tomizawa et al.
patent: 5388345 (1995-02-01), Brundage et al.
Fuls Paul F
Le Roux Johann D
Bennett Henry
Gravini Steve
Implico B.V.
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