Drying apparatus for bulk materials

Details Drying apparatus for bulk materials Drying apparatus for bulk materials

1999-10-29

2001-03-13

Gravini, Stephen (Department: 3749)

Drying and gas or vapor contact with solids

Apparatus

With means to treat gas or vapor

C034S168000, C034S186000, C034S187000

Reexamination Certificate

active

06199294

ABSTRACT:

STATE OF THE ART
The invention relates to an apparatus for drying bulk materials, having an at least partially funnel-shaped container. The invention moreover relates to a drying apparatus for bulk materials, which has a device for dehumidifying the drying gas that is used.
Drying apparatus for drying bulk materials such as plastic granules, for example, are disclosed in DE 3234431 C2 among others. The granules to be dried are in a container which tapers downwardly with a hopper shape to a granule outfeed and is fed with the granules at the top. To dry the granules they are fed into a drying gas, especially heated air, which carries away the moisture adhering to the granules. To improve the drying results the drying air is previously passed through a dehumidifier.
Drying apparatus are generally designed for a particular throughput of bulk material. The plastic granules are fed after drying, especially to plastic fabricating machines. Previously they are often mixed with other components which constitute a substantially lower percentage in the desired raw material. Conventional dryers are suitable to only a limited extent for the preliminary treatment of additive granules which are used in only small amounts. If they are not completely filled, problems can arise in regard to the granule drying results, because the passage of the drying air through them does not take place in a uniform manner. On the other hand, it is not possible to fill the drying apparatus entirely with granules on account of the time-related degradation of the bulk material. The capacity of the drying apparatus therefore cannot be matched to the desired amount of the dried granular material. In particular, the drying air dehumidifier remains largely underutilized if the drying capacity is reduced, since it has to be designed for the full load capacity of the apparatus. To dehumidify the drying air, regeneratable cartridges containing moisture absorbing substances are often used, which are associated with the granular material dryers as an additional component.
The problem to which the invention is addressed consists in creating a drying apparatus for bulk materials which can be optimally adapted to the amount of the granular material to be dried, especially small amounts thereof, and will have great flexibility, especially with regard to the different places where it will be used.
This problem is solved by providing a granular material container with adjustable walls. Furthermore, a drying apparatus is provided which has a membrane dryer as dehumidifier.
ADVANTAGES OF THE INVENTION
The drying apparatus according to the invention has a funnel-shaped container into which the bulk material to be dried is placed and can be taken out. Furthermore, the passage of a drying gas through the container is possible such that the drying air flows through the bulk material. The container is characterized by a hopper wall whose angle of inclination can be adjusted at least partially, so that the capacity of the container is variable. This makes it possible to adjust the container to the desired amount of bulk material to be dried. This can be done either manually or, by means of a suitable actuator, automatically.
The adjustability of the angle of inclination of the hopper wall can have a positive influence on the discharge of the container contents. If the container is filled with a lesser amount there will be a steeper slope inside of the container. In the case of small amounts of bulk material, the steeper pitch of the hopper makes up for the lack of the weight of the granules in the upper area of the container pressing down on the granules being taken from the container. By means of the angular adjustment of the hopper walls the capacity of the container is simultaneously reduced. The smaller amount of bulk material therefore will have the same or a slightly lower level in the container than it will when the apparatus is used at full capacity. This brings it about that the drying air flows uniformly through the granules even when the volumetric flow is throttled, and it takes a path of defined length through the granules.
To change the angle of inclination and capacity of the container not all of the parts of the hopper wall need to be adjustable. Adjustable and fixed, substantially rigid wall parts can be used, which by their cooperation form the hopper. Just the same, however, it is conceivable to make the hopper out of an elastic material, whereby the capacity and slope of the hopper are achieved by an elastic deformation of the hopper.
An advantageous embodiment of the hopper provides for constructing it of a plurality of flat surfaces. At least one of them is to form an adjustable side of the hopper, so as thus to assure the adjustability of the hopper. An appropriate configuration of this variant is accomplished by providing a pyramidal hopper with four surfaces. Two opposite hopper surfaces are fixed, the other two being the adjustable sides. This keeps the expenditure on components for the bulk material container within limits and at the same time offers the possibility of adapting the hopper capacity and the angle of inclination of a sufficient portion of the hopper walls to the amount of bulk material. The stationary wall portions can be made steeper than the adjustable sides when in the position of maximum container capacity. Thus, even in the case of a low fill level in the container an optimal outfeed performance can be achieved. The stationary wall parts of the hopper can also be made at least partially also perpendicular.
In a practical embodiment of the idea of the invention the adjustable sides are hinged in the area of the outfeed opening. In this embodiment, by pivoting the adjustable sides, while keeping the size of the outfeed opening the same, the angle of the container walls as well as the capacity of the container can be varied. The means for fixing the adjustable sides in various angles of inclination can be provided, for example, on the stationary wall parts.
If the stationary wall parts are inclined, the result will be adjustable sides of a substantially trapezoidal shape. If the angle of inclination is varied, the result will be a different pitch at the lateral margins of the adjustable sides in the horizontal projection parallel to the stationary wall parts. This can be compensated by making the stationary wall parts of the container with an angle of inclination varying over the range of adjustment of the adjustable sides. This brings it about that a constant-size gap can be maintained between the outside margins of the adjustable sides and the stationary side parts throughout the range of adjustment of the adjustable sides. Additional sealers, such as rubber lips, for example, at the edges of the adjustable sides thus become superfluous.
In one of the stationary side walls a maintenance access opening can be disposed. This is easiest to achieve if this wall part is made perpendicular. The maintenance opening permits cleaning the container, for example, whenever other types of granular materials are to be dried with it.
The container can advantageously be double-walled, so that the drying air is carried through the hollow space thus formed, before reaching the bulk material. Thus the temperature loss in the container can be reduced, thereby reducing the thermal energy requirement. This measure is practical on account of the small amount of bulk material having an unfavorable ratio of volume to surface area.
The apparatus for drying bulk materials is an alternative solution for the purpose of permitting flexible use. This apparatus is supplemented by a dehumidifier, which can be integrated, especially also structurally, into the system unit of the drying container. This becomes possible by providing a membrane dryer for dehumidifying the drying air since, in comparison with the conventional dehumidifying apparatus referred to above, it is characterized by requiring little space. A cleansing gas inlet and a cleansing gas outlet are provided, which permit cleansing gas to pass through a clean

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