Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2000-04-05
2001-11-06
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S174000, C034S178000, C034S211000, C034S228000, C034S487000
Reexamination Certificate
active
06311411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with vertical, multiple-deck continuous batch dryers designed for drying of pellets and other similar products. More particularly, the invention pertains to such dryers and drying methods wherein the dryers have a series of superposed, air-pervious drying decks and an air circulation assembly operable to generate and direct a continuous drying air stream through the decks; a common upright plenum chamber is provided adjacent and in communication with the dryer decks, and the air circulation assembly is designed to pass the air stream into, through and out of the plenum chamber as the air stream passes through respective decks. This allows easy removal of entrained fines within the drying air stream and also permits the user to individually control both the air flow and the percentage of air recirculation through each deck, independently of the other decks.
2. Description of the Prior Art
Multiple-deck vertical continuous batch dryers have been used in the past for drying of pellets and other agricultural and food products. A vertical design allows product transfer between decks with good product separation. Moreover, a higher degree of moisture uniformity is achieved owing to multiple turning of the product as it passes between the vertically spaced decks. The countercurrent design of these dryers (product descends and air flows move upwardly) also gives higher energy efficiencies.
Several different design approaches have been tried in the past with vertical dryers. In one system, each deck assembly is provided with a separate fines collection unit in the form of a cyclone separator, fan and heater. This approach does have the virtue of removing fines at each deck level, thus minimizing the tendency for fines to accumulate on internal dryer components. However, this is a very expensive expedient, with the multiple fines collection units greatly increasing equipment costs and necessary plant space. In another system, only a single collection device is provided at the upper outlet of the dryer. This significantly reduces costs, but does not remove fines at each dryer stage. Thus, it is necessary to have increasing air velocities from bottom to top of the dryer in order to insure that the fines remain entrained in the drying air stream for ultimate separation at the final collector.
Furthermore, both of these prior art approaches suffer from the inability to effectively and efficiently control dryer operation at each deck, independently of the other decks. This means that the air flows (velocities) through each deck cannot be independently controlled, nor can the amount of air recirculation at each deck be controlled.
There is accordingly a real and unsatisfied need in the art for an improved vertical dryer which avoids the high costs associated with multiple collector type dryers, while at the same time giving the same or a better degree of staged fines removal. Also, there is a need for a vertical dryer wherein the individual decks thereof can be independently controlled in terms of airflow velocities and recirculation characteristics.
SUMMARY OF THE INVENTION
The present invention overcomes the problems outlined above, and provides an improved vertical dryer which comprises a plurality of superposed, air-pervious drying decks which support quantities of product to be dried thereon and which are selectively openable to allow the product quantities to descend from deck-to-deck during drying thereof. The dryer also includes an air circulation assembly operable to generate and direct a continuous drying air stream through the respective decks and the product quantities thereon. The vertical dryer of the invention also includes an upright, common plenum chamber adjacent and in communication with the drying decks, such air circulation assembly being operable to pass the continuous air stream into, through and out of the plenum chamber as the air stream passes between respective decks. Such traversal through the plenum chamber facilities fines removal and also allows independent deck control.
In preferred forms, the plenum chamber is sized so that when the drying air stream passes into and through the chamber it loses substantial velocity, which facilities dropout of suspended fines. Furthermore, a series of diverters are located within the plenum chamber for redirecting the air flow through the chamber. The plenum preferably has a particle collector adjacent the lower end thereof.
The air circulation assembly includes a plurality of individually controllable fan units which can be adjusted to provide independent control of the velocity of the drying air stream as the latter passes through individual decks. Such fan units typically comprise a fan and an adjacent, selectively openable and closeable damper. Alternately, variable speed fans can be employed.
REFERENCES:
patent: 3896562 (1975-07-01), Zimmerman
patent: 4043051 (1977-08-01), Lussenden
patent: 4392310 (1983-07-01), Hohman et al.
patent: 4914834 (1990-04-01), Sime
patent: 5167081 (1992-12-01), Loyns
patent: 5243767 (1993-09-01), Stein
patent: 5893218 (1999-04-01), Hunter et al.
Wenger Bulletin “Wenger Cascade Dryer”, No. CD699 (1999), Wenger Manufacturing, Inc.
Hovey Williams Timmons & Collins
Wenger Manufacturing Inc.
Wilson Pamela
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