Vertical dryer with vertical particle removal plenum and method of use

Information

  • Patent Grant
  • 6311411
  • Patent Number
    6,311,411
  • Date Filed
    Wednesday, April 5, 2000
    24 years ago
  • Date Issued
    Tuesday, November 6, 2001
    23 years ago
Abstract
An vertical dryer (10) is provided having a plurality of individual dryer decks (12-18) including alternating fan and heater decks (14, 16), an air circulation assembly (11), and an upright, common plenum chamber (26) in communication with the decks (12-18). The assembly (11) is operable to create a continuous drying air stream which passes upwardly in countercurrent flow relationship to product on the decks (12-18). Also, the assembly (11) serves to pass the drying air stream into, through and out of the plenum (26) at the level of each heater deck (16); in the plenum (26), the air stream velocity is decreased, causing particulate fines to fall out of the stream for collection. The use of the common plenum (26) also allows independent control of the decks (12-18) in terms of air flows therethrough and recirculation characteristics.
Description




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.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic side view of a prior art vertical dryer wherein each drying zone includes an individual cyclone collector for fines removal;





FIG. 2

is a schematic side view of another prior art vertical dryer employing only a single exhaust air cyclone collector for fines removal;





FIG. 3

is a rear schematic view with parts broken away of the improved vertical dryer of the invention;





FIG. 4

is a vertical sectional side view taken along line


4





4


of FIG.


3


and showing air flows and air-directing structure associated with the preferred dryer decks and upright plenum of the invention;





FIG. 5

is a vertical sectional rear view taken along line


5





5


of FIG.


4


and illustrating the construction of the preferred upright plenum chamber;





FIG. 6

is a vertical sectional rear view taken along line


6





6


of FIG.


4


and depicting certain of the air-conveying passageways associated with the vertical dryer decks;





FIG. 7

is a vertical sectional central view taken along line


7





7


of FIG.


4


and illustrating other air-conveying passageways of the vertical dryer decks; and





FIG. 8

is a schematic side view of the improved vertical dryer of the invention, shown with exemplary air flows throughout the height of the dryer.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




Turning now to the drawings, and particularly

FIGS. 4-7

, a vertical dryer


10


in accordance with the invention is illustrated. The exemplary dryer


10


is made up of a total of eight superposed, vertically spaced apart decks (although a less or greater number of decks could be used), and a multiple-fan air circulation assembly broadly referred to by the numeral


11


associated with the dryer decks. The dryer


10


has an uppermost inlet deck


12


six alternating fan and heater decks


14


and


16


, and an optional lower cooling deck


18


. Each set of decks


14


,


16


provides a drying zone, and thus the depicted dryer


10


has three such zones. The inlet deck


12


is surmounted by a product inlet housing


20


having a product inlet


22


, while product collection hopper


24


is located beneath cooler deck


18


. The overall dryer


10


also includes an upright, vertically oriented, common plenum chamber


26


supported by and communicating with the decks


12


-


18


. The dryer


10


is designed to receive quantities of product through inlet


22


and to dry such product by successive passage of quantities thereof through the decks


12


-


18


for ultimate collection in hopper


24


and delivery to other downstream equipment (not shown).




Inasmuch as all of the fan decks


14


are identical to each other, a description of a single fan deck will suffice for all; likewise, given that all of the heater decks


16


are identical to each other, only a single description thereof is provided. Each fan deck


14


includes a substantially flat, air-pervious floor


28


(

FIG. 7

) as well as upright outboard sidewalls


30


,


32


, front wall


34


and rear wall


36


. In addition, a pair of upright inboard walls


38


and


40


are located adjacent the sidewalls


30


,


32


. As illustrated in

FIGS. 7

, the walls


38


,


40


extend from sidewall


34


for a majority of the length of the deck


14


, but are shortened to leave a rear space


41


which is important for purposes to be described. A depending wall


41




a


extends from the top of the deck downwardly and is affixed to the butt ends of the walls


20


,


32


and


38


,


40


. Each wall


38


,


40


includes a vertical segment


42


, an outwardly extending segment


44


, and a perforated inturned return segment


46


.




As best seen in

FIGS. 4 and 7

, the spaces between the walls


30


,


38


and


32


,


40


beneath the segments


44


houses a plurality of elongated arcuate vane members


48


,


50


,


52


. The vane members cooperatively define a total of four air passageways which are open along the bottom margin of the deck and at the rear ends thereof.




The floor


28


is made up of a plurality of elongated, side-by-side, pivotally moveable slats


54


. The floor


28


is selectively openable via a conventional drive


56


(

FIG. 4

) coupled with the floor slats


28


. When the floor


28


is in its closed position depicted in

FIG. 7

, it is operable to support a quantity of product


58


thereon but is nevertheless air-pervious. However, when the drive


56


is actuated the floor slats


54


are pivoted to an open position, thereby allowing the product


58


to descend under the influence of gravity onto the next lower deck.




In order to provide access to the internal components of the fan deck, front and rear access doors


60


,


62


are provided.




Referring next to

FIG. 6

, it will be seen that a double fan assembly


64


is housed within the space


41


. In particular, the assemble


64


includes a pair of powered fans


66


,


68


respectively mounted in the sidewalls


30


,


32


. A somewhat Y-shaped duct


70


extends from the base of deck


14


upwardly to the inlet sides of the fan


66


,


68


. The outlet sides of the fans in turn communicate with the passageways defined by the vanes


48


-


52


extending along each side of the deck.




Each heater deck


16


is in many respects similar to the fan decks


14


, and thus the same reference numerals are applied to like parts. Each fan deck


14


includes a floor


28


, outer sidewalls


30


,


32


, front wall


34


, rear wall


36


, inner sidewalls


38


,


40


, internal space


41


, short wall


41




a


, and vanes


48


-


52


. Moreover, the deck


28


is made up of slats


54


moveable via drive


56


. However, the heater decks


16


differ from the fan decks


14


(see

FIG. 6

) by provision of dampers


72


,


74


at the outlets of the air passageways, as well as box-like ducts


75


extending from the dampers


72


,


74


and communicating with outboard side openings


76


provided in rear wall


36


. In addition, the wall


36


includes a pair of inboard openings


78


. The deck


16


also includes a bifurcated duct


80


which includes a pair of lower, arcuate, converging segments


82


,


84


and side segments


86


,


88


. The duct


80


communicates with the inboard openings


78


and is open at the upper margin of the deck


16


. A heater


90


is situated within the duct


80


, and is typically gas fired. The heater


90


is coupled to a combustion air inlet conduit


92


which leads to atmosphere.




The inlet deck


12


is identical with each of the heater decks


16


, except that the inlet deck has no duct


80


or heater


90


. While this deck is equipped with the outboard openings


76


, it does not have the corresponding inboard openings


78


of the decks


16


.




The cooler deck


18


is identical with each of the fan decks


14


with the exception that the rear wall


36


thereof has a central fresh air inlet opening


94


formed therein. As noted previously, provision of a cooler deck is optional.




The product inlet housing


22


is located atop inlet deck


12


and is designed to house a conventional rake or other spreader device (not shown) serving to level incoming product delivered via inlet


22


. The housing


20


includes upright sidewalls


96


,


98


, front wall


100


, rear wall


102


and top wall


104


. In addition (see

FIG. 7

) a pair of inner walls


96




a


,


98




a


are provided adjacent corresponding sidewalls


96


,


98


. A pair of uppermost air inlet openings


106


are provided in rear wall


102


and communicate with the regions between the walls


96


,


96




a


and


98


,


98




a.






The plenum


26


is located adjacent the rear walls of the decks


12


and


14


-


16


. The plenum has rearwardly projecting sidewalls


108


,


110


(

FIG. 3

) as well as a rear wall


112


and top wall


113


, the latter having an outlet


113




a


formed therein. The rear wall


112


is equipped with a pair of access doors


114


at the level of each heater deck


16


. Moreover, the rear wall


112


has an elongated, central, vertically extending recess


116


therein allowing access to the central doors


62


associated with the fan decks


14


. Inwardly extending walls


118


define the recess


116


and are connected with plenum rear wall


112


and the rear walls


36


of the decks. A powered combustion air fan


120


is operatively coupled with each of the conduits


92


within.




The plenum


26


is equipped with a series of diverters


122


which are located adjacent each of the inboard openings


78


associated with the heater decks


16


. Referring to

FIG. 5

, it will be observed that each of the diverters includes an oblique segment


124


as well as a depending wall segment


126


.




Finally, the plenum


26


includes a lowermost collection hopper


128


presenting a fines outlet


130


as well as an elongated, axially rotatable fines conveying auger


132


.




The outlet


113




a


of the plenum


26


is coupled to a conventional exhaust fan


134


; if desired, an additional cyclone separator may be employed to insure the separation of any fines or dust entrained within the outlet air from the plenum.




In operation, product (e.g., pellets) are delivered to the dryer


10


via inlet


22


and are initially leveled on the floor of inlet deck


12


. During the drying process, individual quantities of the product are delivered to each of the decks in serial order so that, during continuous operation, individual quantities are supported on each of the decks


12


-


18


. This condition is illustrated in FIG.


7


.




Considering the operation of the dryer


10


during such continuous drying, it will be seen that fresh air is drawn into cooler deck


18


by the associated fans


66


,


68


, this air being directed by the vanes


48


-


50


to a point below the floor


28


. This air is then directed upwardly through the deck floor and the quantity of product situated thereon (see arrows


136


,


138


). When the fresh air passes through this product, it is drawn upwardly through the perforated return segments


46


of the deck


18


whereupon it enters the vane-defined passageways of the next above heater deck


16


(arrows


140


, FIG.


7


). This air is then drawn rearwardly by the fans


66


,


68


of the next above fan deck


14


through the dampers


72


,


74


, along the box ducts


75


and through the openings


76


to enter the plenum


26


(arrows


142


, FIG.


5


). Given that the plenum presents a much greater volume, the velocity of the air traversing the plenum is greatly reduced, thereby facilitating dropout of fines from the air stream. Moreover, the air from the openings


76


is forced to traverse a tortuous path owing to the presence of the diverters


122


. The air from the plenum chamber passes back into the deck


16


through the inboard openings


78


, where it is conveyed by the duct


80


through the heater


90


and, in a heated condition, to the duct


70


of the next-above fan deck


14


. Also, additional combustion air as needed is delivered by the fan


120


through conduit


92


into the heater


90


, which combustion air thus joins the air stream.




It will thus be appreciated that the continuous air stream created in the dryer


10


passes upwardly from deck-to-deck, being successively heated as required in the heater decks


16


and with supplemental combustion air being added. Air drawn into each deck as leakage through the deck structure is also added to the continuous air stream. At the upper end of the dryer


10


, at the level in inlet deck


12


, fresh inlet air is drawn through the openings


106


by the fans


66


,


68


of the highest fan deck


14


, such air passing downwardly through the product on the inlet deck. Also at the inlet deck


12


, the drying air stream passes through the uppermost outboard opening


76


into the plenum


26


for ultimate passage through outlet


113




a.






The described circulation of air through the dryer


10


creates a situation where air is drawn in opposite directions through adjacent decks. Thus, air is drawn upwardly through the cooler deck


18


, while air is draw downwardly through the next-above heater deck


16


. This alternating pattern continues throughout the full height of the vertical dryer


10


.




Attention is next directed to schematic

FIG. 8

which illustrates exemplary air flows during the operation of the dryer


10


. In this example, all air flows are in cubic meters per hour (m


3


/h). As shown, fresh air at the rate of 10,000 m


3


/h is draw into the bottom of the dryer


10


by the cooler deck fans; this air passes upwardly through the cooler deck to a point above the product thereon. The fan in the next higher fan deck


14


is set to draw air at the rate of 20,100 m


3


/h from the region above cooler deck


18


. This is to accommodate 100 m


3


/h leakage at the cooler deck, and also to achieve a 10,000 m


3


/h air flow downwardly through the next-above heater deck


16


. The 20,100 m


3


/h air flow then passes through the plenum


26


and thence through the heater


90


of the deck


16


. At this point, the needed combustion air, in this example 1,000 m


3


/h, is drawn by the fan


120


of the deck


16


into the heater.




Given that in this example the user wishes to maintain a 10,000 m


3


/h air flow through each of the decks, it is necessary for the fans


66


,


68


of the next-above deck


14


to deliver 20,000 m


3


/h, i.e., this air flow is split 10,000/10,000 m


3


/h between the two adjacent decks. This being the case, the fan is set to draw 19,000 m


3


/h of air from the plenum


26


, which with the 1,000 m


3


/h of combustion air provides the necessary 20,000 m


3


/h. The excess air (1,100 m


3


/h) simply passes upwardly through the plenum for ultimate exhaust through outlet


113




a.






This same pattern is thus repeated throughout each of the deck pairs throughout the height of the dryer


10


, so that, at each deck a 10,000 m


3


/h air flow is maintained and excess air is exhausted through the plenum outlet. This is an important advantage provided by the present invention. That is, by selective fan and/or damper control, it is possible to individually regulate the air flow and recirculation through respective decks. Such precise control has heretofore not been obtainable in vertical dryers. Moreover, the ability to economically remove fines and other particulates from the drying air stream also represents a significant advance in the art.




These important differences can best be understand by a consideration of the prior art designs depicted in

FIGS. 1 and 2

. In

FIG. 1

, a multiple-deck vertical dryer


144


is provided which has an individual cyclone dust collector assembly


146


,


148


and


150


associated with corresponding dryer decks. While this approach does remove fines at each deck level, it is disadvantage for a number of reasons. Provision of separate collectors greatly increases costs and requires more plant space. In addition, and again referring to the exemplary air flows given in

FIG. 1

, it will be seen that air flows generally increase from top to bottom, with a 10,000 m


3


/h air flow at lower levels and culminating in a 16,600 m


3


/h air flow at the dryer outlet. Thus, larger collection equipment is needed from bottom to top of the dryer because greater quantities of air are being handled at the upper decks.




In the

FIG. 2

prior art system, use of individual dust collection assemblies is avoided, there being only a single assembly


136


to treat the exhaust air from the dryer. While this design is less costly than that shown in

FIG. 1

, there is no fines removal at each deck, which may result in fines accumulation in internal components unless the system is carefully designed and maintained. Further, this system suffers from the same increasing air flow from bottom to top described in connection with the

FIG. 1

dryer.




It will thus be seen that the present invention provides cost and operational advantages which cannot be duplicated in prior art systems. These advantages are derived from the use of a multiple-deck vertical dryer having a common upright plenum and an air circulation assembly whereby the air circulation assembly operates to pass the continuous drying air stream into, through and out of the plenum chamber as the air stream passes between respective decks.



Claims
  • 1. In a vertical dryer including 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, and a drying air circulation assembly operable to generate and direct a continuous drying air stream through said decks and the product quantities thereon, the improvement which comprises an upright, common plenum chamber in communication with said decks, said air circulation assembly operable to pass said air stream into, through and out of said plenum chamber as the air stream passes between respective decks.
  • 2. The dryer of claim 1, said plenum chamber including a diverter for changing the direction of said air stream during passage of the air stream there-through.
  • 3. The dryer of claim 2, including a particle collector adjacent the lower end of said plenum chamber.
  • 4. The dryer of claim 1, said air circulation assembly including a plurality of individually controllable, vertically spaced apart fan units permitting independent control of the velocity of said air stream as the air stream passes through individual decks.
  • 5. The dryer of claim 4, each of said fan units comprising a fan and an associated, selectively openable and closeable damper.
  • 6. The dryer of claim 1, said plenum chamber having an exhaust air outlet adjacent the upper end thereof, said air circulation assembly constructed for passage of said air stream through said plenum outlet.
  • 7. The dryer of claim 6, including a dust collector operably coupled with said plenum outlet.
  • 8. The dryer of claim 1, said air circulation assembly operable to pass said air stream into, through, and out said plenum chamber at a plurality of vertically spaced locations along the height of the plenum chamber.
  • 9. In a method of drying product in a vertical dryer including a plurality of superposed, air-pervious drying decks which support quantities of products to be dried thereon, the method including the step of generating and directing a continuous drying air stream through said decks and the product quantities thereon, the improvement which comprises providing an upright, common plenum chamber in communication with said decks, and passing said air stream into, through and out of said plenum chamber as the air stream passes between respective decks.
  • 10. The method of claim 9, including the step of decreasing the velocity of said air stream during said passage of said air stream therethrough in order to cause suspended particles to drop out of the air stream within the plenum chamber.
  • 11. The method of claim 10, including the step of collecting particles adjacent the lower end of the plenum chamber.
  • 12. The method of claim 9, including the step of independently controlling the velocity of said air stream as the air stream passes through individual decks.
  • 13. The method of claim 12, said independent control step comprising the step of passing the air stream through respective dampers associated with corresponding individual decks.
  • 14. The method of claim 9, said plenum chamber comprising an exhaust outlet adjacent the upper end thereof, including the step of exhausting said air stream through said plenum outlet.
  • 15. The method of claim 9, including the step of passing said air stream into, through and out of said plenum chamber at a plurality of vertically spaced locations.
US Referenced Citations (7)
Number Name Date Kind
3896562 Zimmerman Jul 1975
4043051 Lussenden Aug 1977
4392310 Hohman et al. Jul 1983
4914834 Sime Apr 1990
5167081 Loyns Dec 1992
5243767 Stein Sep 1993
5893218 Hunter et al. Apr 1999
Non-Patent Literature Citations (1)
Entry
Wenger Bulletin “Wenger Cascade Dryer”, No. CD699 (1999), Wenger Manufacturing, Inc.