Drying and gas or vapor contact with solids – Apparatus – Gravity flow type
Patent
1993-01-05
1994-03-01
Bennet, Henry A.
Drying and gas or vapor contact with solids
Apparatus
Gravity flow type
34177, B26B 1712
Patent
active
052896439
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for drying a moist particulate material having a non-uniform particle size with superheated steam, the apparatus including a lower cylindrical part having a number of parallel, substantially vertical elongated chambers located in ring form, one or more of the chambers having a closed bottom and the remaining chambers having a steam-permeable bottom, the adjacent chambers being interconnected through openings in the chamber walls at the lower ends of the chambers, and an upper conical part which is also divided into chambers, which at its lower end is connected to the chambers of the cylindrical part of the apparatus and which at the top is connected to a transfer zone, the chambers of the conical part of the apparatus being divided into smaller chambers by means of inclined guide plates, means for supplying moist particulate material to a chamber having a steam-permeable bottom, means for discharging dried material from a chamber having a closed bottom, means for supplying superheated steam to the area below the steam- permeable chamber bottoms, means for discharging steam from the transfer zone, and means for reheating the discharged steam and recirculating it to the area below the steam-permeable chamber bottoms.
2. The Prior Art
An apparatus of the type mentioned above is known from Zuckerind. 114 (1989) No. 12, pp. 964-70 and EP-A-0153704. This prior art apparatus is particularly suitable for drying beet pulp formed by extracting sugar from sugar beet slices with water, but the apparatus is also suitable for removing liquid, including liquids other than water, from a number of sensitive organic materials.
The prior art apparatus presents the advantage that the particulate material is dried without the access of air, thereby making it possible to avoid oxidation of the material during drying. Another important advantage of the apparatus is that it is environmentally highly acceptable as the drying takes place in a substantially closed system. Furthermore, the excess amount of steam, which, e.g., is generated when drying beet pulp, is very pure and consequently it can be used for the concentration of sugar juice, and the condensate thus formed does not cause odour nuisances as compared to the emission products formed by, e.g., drum-drying beet pulp.
In practical use of the drying apparatus mentioned above it has been found that partially dried particulate material tends to adhere to the oblique guide panels and in particular to the upper sides of these panels and that a gradually increasing coating is formed on the guide plates.
SUMMARY OF THE INVENTION
The object of the invention is to avoid this drawback and according to the invention this object is obtained with an apparatus of the type mentioned above, which apparatus is characterized in that at least part of the oblique guide plates in the conical part of the apparatus is provided with means for heating the plates.
Thus, the invention is based on the discovery that by heating the guide plates mentioned above it is possible to eliminate or at least considerably reduce the tendency of the particulate material to adhere to the upper side of the guide plates. The reason why such an adherence is avoided is unknown but it is assumed that contact with the warm guide plates makes the liquid-containing particles "dance" on the plates in the same manner as water drops on a hot-plate or that a zone of relative hot steam is formed close to the surfaces of the plates, the steam causing the surfaces of the particles to dry.
The oblique guide plates according to the invention are preferably hollow and the interior of the guide plates are connected with means for supplying steam thereto. However, the guide plates may also be heated otherwise, e.g., they may comprise electric heating members.
During use of the apparatus according to the invention the surface temperature of the guide plates is preferably maintained at a value which is 20.degree.-80.degree. C. highe
Bennet Henry A.
Niro A/S
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