Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1996-02-21
1998-01-27
Bennett, Henry A.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 86, 34217, 34449, 34559, F26B 2106
Patent
active
057110867
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method and apparatus for continuous drying of moist materials in superheated steam.
BACKGROUND OF THE INVENTION
The expression "materials" is intended to include moist materials of all kinds which may require to be dried, including granular or friable raw materials, partly processed materials and products, finished materials and products, and residues. For example the invention is applicable to the drying of chemicals, pharmaceuticals, coal, timber, cloth, paper, towels, bed linen, garments, bricks, porcelain, sewage sludge and the residues produced by the recycling of paper.
It is known to dry moist materials .by the use of superheated steam. For example, British Patent Specification No. 2209383 describes a method and apparatus in which moist materials to be dried are introduced into an enclosure and the air or other gas which initially fills the enclosure is recirculated between a heat source and the material so as to produce steam from the moisture in the material. This steam increasingly displaces the initial gas from the enclosure and continues to be heated by recirculation past the heat source until it becomes superheated. A proportion of the steam is discharged from the enclosure through a vent and at least part of the thermal energy is recovered from the discharged steam by condensation.
Specification No. 2209383 discloses primarily a batch process in which a batch of material is introduced into the enclosure, is dried and is then removed. However for many commercial applications it is desirable for materials to be dried in a continuous process where the materials are continually passed through a drying location. In a batch method there is no difficulty in retaining the superheated steam in the enclosure while drying is taking place since the enclosure may simply be sealed in gas-tight manner after the batch of material has been introduced and opened again when it is necessary to remove the material after drying. In a continuous drying process, however, it is necessary to prevent the escape of the superheated steam from the enclosure, and the entry of air into the enclosure, during drying, while at the same time allowing the continual passage of materials into and out of the enclosure. It is therefore necessary to provide some sort of substantially gas-tight seal or barrier which will permit the passage of the materials into and out of the enclosure while at the same time preventing the escape of the superheated steam. In British Specification No. 2209383 a continuous drying arrangement is described where the inlet and outlet from the enclosure are each defined by a pair of cooperating rollers having flexibly resilient engaging outer surfaces. A conveyor, carrying the articles to be dried, passes through the nip of each pair of rollers and the resilient outer surfaces of the rollers press tightly against the conveyor and articles as they pass through, thus providing a substantially gas-tight seal to prevent the escape of superheated steam from the enclosure, or entry of air into the enclosure.
In the arrangement described in the earlier specification the articles are garments suspended from a conveyor and it is quite feasible for garments, at least of some kinds, to pass between flexible rollers in this manner. However, there are many other materials for which this form of barrier is unsuitable, either because the flexible rollers cannot provide an adequate gas-tight seal in view of the nature and shape of the materials, or because the materials might be damaged or altered by the pressure of the rollers. For example it is extremely difficult to arrange for bricks and similar solid articles to pass between resilient rollers in a substantially gas-tight manner, and comparatively delicate products, such as ceramics, are also likely to be damaged by the pressure of the rollers.
British Patent Specification No. 798291 describes a humpback drying apparatus for the continuous drying of charged accumulator plates. A water seal is provided at the lower e
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"Stoving Techniques for Mass Production", Mechanical World and Engineering Record, vol. 134, Oct. 1954, p. 449.
Bennett Henry A.
Doster Dinnatia
Heat-Win Limited
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