Drying and gas or vapor contact with solids – Apparatus – With fluid current conveying of treated material
Reexamination Certificate
2000-02-01
2002-04-09
Lu, Jiping (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
With fluid current conveying of treated material
C034S588000, C034S168000, C034S169000, C034S237000, C432S058000
Reexamination Certificate
active
06367165
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for treating particulate product having a process chamber for receiving and treating the product, a bottom of the process chamber being constructed from baffle plates, that overlap each other, with slots formed between the latter through which the process air can be introduced into the process chamber with a substantially horizontal component of motion.
A device of this kind is known from EP 0 370 167 A1.
Devices of this kind are used to dry, granulate or coat particulate products.
A gaseous agent, known as process air, is introduced into the process chamber through the bottom, entering the process chamber through the numerous slots between the overlapping baffle plates in substantially horizontal direction.
In the case of the before-mentioned device the bottom consists of a ring of radially extending guide plates, that overlap each other, with the slots extending in radial direction. The product to be treated, placed on the bottom, is whirled up by the process air to form a toroidally rotating band. The bottom is annular in shape, i.e. comprises a centrally arranged displacement body. Due to its initial horizontally directed component of motion, the toroidally rotating band moves on a process air cushion. For spraying a desired agent on to the particulate product to be treated, nozzles may be arranged in the bottom between the baffle plates.
This technology is based on the principle that the process air must be introduced into the process chamber initially with a substantially horizontal component.
In a further device for treating particulate product, known from EP 0 436 787 A1, the process air is guided in such a way that it is imparted a substantially bottom-up, i.e. a substantially vertical flow direction already as it enters the process chamber. In the process chamber, there are provided longitudinally extending hollow lances which generally extend in cross-wise direction to the gas flow and which are provided with upwardly directed nozzles so that both the process air and the spraying direction of the nozzles follow a substantially vertical line of movement from the bottom toward the top. A device of that kind serves in particular for coating relatively coarse-grained products, for example pellets, in the pharmaceutical area.
The spectrum of particulate products to be treated is much broader in the case of the before-mentioned device according to EP 0 370 167 A1 than the spectrum of products that can be treated wit h the last-mentioned device.
Especially in applications in the fields of chemistry and pharmaceutical technology, the following essential criteria must be considered in connection with devices of that kind.
In order to meet the demands placed on hygiene, agreeable to contact and easy to clean surfaces should be provided.
The processes in the process chamber should be reproducible, which means that any functional contingencies must be excluded by suitable means.
A very e essential criterion is to be seen in what is known as “scaling-up”, i.e. the ability to enlarge the scale linearly while maintaining the specific process functions, such as the continuous recirculation and movement of the product according to an exactly defined pattern. Reverting to the rotating toroidal band produced in the device described first, this means that any scaling-up should only have the result to produce a rotating band of larger diameter, while the flow, particle and motion conditions prevailing in the band as such per volume unit should remain unchanged.
Further criteria are the best possible function of the device, achieved by giving the components a formal design adapted to the particularities of the product to be treated, in combination with the aerodynamic and thermodynamic aspects to be taken into consideration. In addition, an optimum design is to be achieved by suitable configuration both of the entire unit and of its details, in order to ensure agreeable handling, where form is function and function is form.
In the case of the device mentioned first, the product placed on the bottom can be lifted off the latter by the process air entering the system in horizontal direction and can be expanded to sort of an air bed.
However, the process air must of course eventually exit the rotating toroidal band, which ideally should occur without any outbursts or sort of volcanic eruptions of gas from the toroidal band. But finally there do not exist any defined breaking-up points for the moving product and/or any defined points of exit for the process air from the product. In order to achieve the best possible degree of uniformity in the drying process of the particulate product, especially in cases where a liquid sprayed from nozzles is to be applied as uniformly as possible on the product, that has been whirled up in the toroidal band, the nozzles must be distributed, statistically, in such a way that all breaking-up points, that may arise in statistical distribution, will be uniformly covered in statistical average.
A further considerable problem with respect to the design of the radial slots arises in connection with the scaling-up aspect. Viewed from the top, the different overlapping baffle plates are substantially trapezoidal in shape. Now, when the diameter of the bottom is very much enlarged for scaling-up purposes, the distance at the periphery between two slots following each other in the direction of flow is much smaller in the radially inner region than in the radially outer region. To say it in other words: A particle of the product circulating in the radially inner region is accelerated and whirled up by the process air, that enters through the next following slot, after a much shorter travel than a particle circulating in a radially outer region. In order to ensure improved uniformity of the conditions it is, therefore, necessary to impart to a particle, that revolves in a radially outer region, a higher circumferential speed in order to guarantee that it will be surrounded, accelerated and whirled up by new process air at the same point in time as a radially inner particle. This is effected by making the height of the air exit slots greater toward the outside so that more process air can enter through the slots in the radial outer region. But this necessarily has the effect that the baffle plates rise a little in radial direction toward the outside and that the outer edge, consequently, presents a mechanical obstacle to the revolving floating band. It is, however, desired to have the product band float on an air cushion in non-contact fashion. In order to form a closed ring, the individual baffle plates are obliquely inclined. This inclination, and the arrangement of the baffle plates in the form of a ring where each baffle plate overlaps the next following baffle plate, lead to a structure that exhibits relatively large openings in the area of the slots through which product may drop, which is undesirable.
In view of the criteria mentioned before and the disadvantages of the device described first, as regards the undefined breaking-up points and the difficulties in connection with the scaling-up aspect, it is the object of the present invention to overcome these advantages and to provide a device that allows a broad spectrum of particulate product to be optimally treated.
SUMMARY OF THE INVENTION
This object is achieved according to the invention by the fact that the slots are arranged in such a way that two opposite flows of incoming process air, being directed one toward the other and along a substantially horizontal path, meet along a breaking-up zone and are then deflected to form an upwardly directed, substantially vertical flow.
As the process air is introduced through the bottom with a substantially horizontal motion component, it is possible to initially build up an air cushion carrying the product that has been whirled up in the process chamber. By providing two substantially horizontal, opposite flows, directed one toward the other, a zone is created where the two flows meet and are forcedly defl
Lu Jiping
St. Onge Steward Johnston & Reens LLC
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