Drying and gas or vapor contact with solids – Apparatus – Stationary receptacle or tube with agitator or conveyor
Patent
1996-09-30
1999-01-12
Bennett, Henry A.
Drying and gas or vapor contact with solids
Apparatus
Stationary receptacle or tube with agitator or conveyor
366288, F26B 1112
Patent
active
058572643
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a dryer, particularly for granular or powdered products, which includes: chamber for the aforesaid products and the outer and inner walls of which define between them an interspace for the circulation of a diathermic fluid, and about its own axis, at least one blade being securely fixed to the shaft and operable, on rotation of the latter, to exert a mixing action on the products and to detach them from the inner wall of the casing.
In prior art dryers of the above type the shaft is mounted so that it projects into the drying chamber with its axis coincident with that of the chamber.
Since the blades fixed to the shaft must extend close to the inner wall of the casing to carry out an effective scraping action, the overall diameter of the rotary members is substantially the same as the inner diameter of the drying chamber.
Hence, if the latter is rather large, the rotary members must be large and heavy, thus placing limitations on the performance of the dryer which, in some cases, are quite considerable.
For example, the speed of rotation of the shaft must not exceed certain values in order to avoid causing excessive twisting and bending stresses, thus limiting the effectiveness of the mixing.
In addition, significant clearance must be maintained between the facing surfaces of the distal ends of the blades and the inner wall of the chamber to prevent the machine from seizing up as a result of heat expansion or deformation caused by mechanical stress on the rotary members.
As a result, a significant layer of the material to be dried builds up on the inner wall of the chamber as the blades are unable to detach it and this behaves like a layer of insulation towards the diathermic fluid circulating in the interspace, thereby compromising the efficiency of the heat exchange in the dryer to a certain extent.
SUMMARY OF THE INVENTION
In order to overcome the above disadvantages, the present invention provides a dryer of the above type, characterised in that the shaft is mounted eccentrically of the longitudinal axis of the chamber and has means for enabling it to rotate about the longitudinal axis of the chamber.
According to the invention, the overall diameter of the rotary members is therefore considerably smaller than that of the drying chamber, for example, of the order of about one half, thereby considerably reducing their moments of inertia and mass compared with those of rotary members of prior art dryers with diameters substantially the same as that of the drying chambers.
The shaft of the dryer of the invention thus offers the advantage of being able to rotate at a far higher angular velocity, even an order of magnitude higher, than that of the shafts of the prior art dryers described above, thereby improving the mixing of the products in the drying chamber.
In addition, the reduction in heat expansion and deformation due to mechanical stress resulting from the reduced diameter of the rotary members enables the necessary clearances between the ends of the blades and the inner wall of the drying chamber to be reduced, thus ensuring efficient scraping and improving the heat exchange between the diathermic fluid and the inside of the chamber.
Furthermore, in any operating condition, only one region of the outer circumference of each cross-section of the rotary members of the dryer of the invention is adjacent the inner wall of the drying chamber, with the advantages that the operations required to mount and dismantle the rotary members are simplified considerably and it is almost impossible for them to jam against the inner wall of the chamber.
In a preferred embodiment of the dryer of the invention, the means for enabling the shaft to rotate about the axis of the chamber and about its own axis are independent of each other.
This means that, when, for example, the dryer is started up, it is possible to rotate the shaft about its own axis only, it being held in the upper portion of the chamber so that it is only partly immersed in the material t
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patent: 2552360 (1951-05-01), Zichis
patent: 2732186 (1956-06-01), Ivarsson
patent: 3855404 (1974-12-01), Rotaru
patent: 4183673 (1980-01-01), Kimmel
patent: 4506838 (1985-03-01), Riniker et al.
patent: 4882851 (1989-11-01), Wennerstrum et al.
patent: 5150968 (1992-09-01), Inoue
Bennett Henry A.
Drake Malik N.
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