Drying and gas or vapor contact with solids – Process – With contacting of material treated with solid or liquid agent
Reexamination Certificate
1999-04-23
2001-03-06
Wilson, Pamela (Department: 3794)
Drying and gas or vapor contact with solids
Process
With contacting of material treated with solid or liquid agent
C034S345000, C034S355000, C034S401000, C034S071000, C034S095000, C034S217000, C034S236000, C426S640000, C426S468000, C426S518000, C426S520000
Reexamination Certificate
active
06195908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for thermal drying of a solid product in small pieces, whereby a layer of the product in small pieces is brought between a first gas permeable conveyor and a second gas permeable conveyor which both are in contact with the layer which is heated by supplying hot air.
2. Related Art
The invention particularly relates to a method for drying food products such as meals, vegetables, meat or fish, pharmaceutical products, minerals and so on, as far as they are in small pieces and preferably are somewhat deformable
These products can be cut into pieces beforehand, but they can also naturally have the shape of small pieces, such as, for example, peas.
In known methods for thermal drying, the so-called conveyor drying, a stream of rather hot air is supplied over the products on a conveyor. These known methods, however, are relatively slow, whereas the applied high temperatures exert a disadvantageous influence upon the quality of the products.
A method of this kind is disclosed in DE-C-508.308. According to this method, plant materials are fed in a relatively thick layer between two endless perforated conveyors and heated by means of hot air. Hot air may be sucked from one side to the other along the layer. No pressure is exerted by the conveyors.
Another method of this kind, but for drying a filter cake, is disclosed in EP-A-0.651.218. A suspension is fed to an endless perforated conveyor. After filtering, the filter cake is dried by contact with heating elements inside a chamber heated by a gas. In one form the of embodiment, a pressure is exerted on the filter cake by perforated boxes provided with a supplemental heating element inside, which boxes do not move with the conveyor. In other embodiments the filter cake is brought between two perforated conveyors, but then no pressure is exerted. The temperature of the heating gas is as high as possible.
Although thermal drying always is preferred in respect to freeze-drying, as it is cheaper, it, anyhow, requires a lot of energy and has a low thermal efficiency.
SUMMARY OF THE INVENTION
The invention aims at a method for thermal drying of a product in small pieces, whereby these and other disadvantages are excluded and which is relatively fast and economical providing dried products of a good quality.
According to the invention, this aim is achieved by the fact that a layer with a thickness of 15 mm at the most is brought between the conveyors, a pressure between 1 g/cm
2
and 36 g/cm
2
is exerted onto the layer and the hot air has a temperature below 70° C.
Preferably, the small pieces are brought in a single layer between the two conveyors.
In a particular form of the embodiment, the drying by means of heat and pressure is exerted by the conveyors is preceded by a freezing of the small pieces.
The invention also relates to a device which is particularly suitable for the application of the method according to one of the preceding embodiments.
The invention thus relates to a device for the thermal drying of a product in small pieces, comprising two gas-permeable conveyors situated one above the other, between which a layer of small pieces can be brought into contact with these two conveyors, and further comprising means for creating a stream of hot air over the layer, characterized in that it contains means for exerting a pressure on the layer by the intermediary of at least one of the conveyors, and a freezing device preceding the conveyors.
The device may comprise means for bringing the small pieces in a single layer onto one of the conveyors.
REFERENCES:
patent: 2207278 (1940-07-01), Albrecht
patent: 2230197 (1941-01-01), Currie
patent: 4464844 (1984-08-01), Dickey et al.
patent: 4464847 (1984-08-01), Dickey et al.
Bacon & Thomas PLLC
D.S.P. N.V.
Wilson Pamela
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