US3838523A

US3838523A - Multi-stage drying apparatus and method

Info

Publication number: US3838523A
Application number: US00339469A
Authority: US
Inventors: S Hurd
Original assignee: Motch and Merryweather Machinery Co
Current assignee: Motch and Merryweather Machinery Co
Priority date: 1973-03-08
Filing date: 1973-03-08
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01
Also published as: FR2220298A1; DE2409843A1; IT1008397B; JPS5030154A; JPS5434280Y2; JPS53153269U

Abstract

Disclosed is a primary dryer and a pre-dryer. The drum dryer includes an elongated cylindrical drum having a plurality of slots through its wall in communication with a plenum containing gas under pressure whereby gas flows through the slots and forms gas jets. The gas jets entrain the wetted material within the drum for transport from its inlet end to its outlet end. The predryer includes a horizontal deck which overlies a plenum and has a plurality of slots in communication with the plenum whereby gas under pressure issues through the slots in a direction moving material disposed above the deck toward the inlet of the drum dryer. The pre-dryer includes a booster jet which, in conjunction with the gas jets issuing through the slots, prevents contact between the deck and the wetted material. The pre-dryer reduces the wetted content of the material, prior to its introduction to the drum dryer, to a level such that the material does not stick or adhere to the interior surface of the drum dryer or otherwise interfere with the primary drying in the drum.

Description

United States Patent Hurd MULTl-STAGE DRYlNG APPARATUS AND METHOD Primary Examiner-William F. ODea Assistant ExaminerWilliam C. Anderson Attorney, Agent, or FirmPatrick J. Walsh [57] ABSTRACT Disclosed is a primary dryer and a pre-dryer. The drum dryer includes an elongated cylindrical drum having a plurality of slots through its wall in communication with a plenum containing gas under pressure whereby gas flows through the slots and forms gas jets. The gas jets entrain the wetted material within the drum for transport from its inlet end to its outlet end. The pre-dryer includes a horizontal deck which overlies a plenum and has a plurality of slots in communication with the plenum whereby gas under pres sure issues through the slots in a direction moving material disposed above the deck toward the inlet of the drum dryer. The pre-dryer includes a booster jet which, in conjunction with the gas jets issuing through the slots, prevents contact between the deck and the wetted material. The pre-dryer reduces the wetted content of the material, prior to its introduction to the drum dryer, to a level such that the material does not stick or adhere to the interior surface of the drum dryer or otherwise interfere with the primary drying in the drum.

13 Claims, 4 Drawing Figures MULTl-STAGE DRYING APPARATUS AND METHOD The present invention relates to apparatus for and method of treating heavily wetted material and particularly relates to two-stage drying apparatus and method wherein a pre-dryer reduces the wetted content of wet material to a level whch permits the primary drum-type dryer to function efficiently and without the material clogging or otherwise inhibiting the primary dryer. While the present invention is herein described in part with particular reference to heated air used to remove moisture from material, it will be appreciated that the invention is also applicable to other gaseous treatments of materials which have a tendency to adhere or stick to the surfaces of a primary gas-treating device of the drum type due to the wetted nature of the materials tending to cause them to stick or adhere to the surface of the treatment device. The term wetted is therefore used herein to include water and non-aqueous liquids.

Drum-type apparatus for treating materials have been proposed and constructed in the past. For example, in US. Pat. No. 3,418,724 of common assignee herewith, there is disclosed a horizontally disposed closed cylindrical drum having a plurality of openings spaced along an extent of its cylindrical surface in communication with a plenum. The drum has inlet and outlet openings at its opposite ends for respectively receiving material to be treated and discharging treated material. Gas from the plenum and issuing through the openings into the drum forms gas jets which entrain the material and move it circumferentially about the walls of the drum whereby the gas treats the material as desired. The material and gas progress axially in a generally helical path from the inlet toward the outlet end of the drum where treated material is discharged.

However satisfactory units of this type have proved for treating materials, there is a tendency in treating materials having a high wetness content for such materials to stick or adhere to the surface of the drum. As a result, the heavily wetted material tends to clog and jam the gas slots as well as the inlet and outlet ports precluding slots as well as the inlet and outlet ports precluding effective treatment of the material received within the drum. That is, a treatment unit of the drum type as herein disclosed is only effective for material having a wetted content below a predetermined level. For example, when tomato pomace is dried in a drum dryer, the first couple of feet of the drum adjacent its inlet develops a build-up of residue which eventually plugs or clogs the gas slots. A normal drying requirement for tomato pomace would be to dry it from 57-60 percent water down to about 4-6 percent water. It has been found that when tomato pomace obtains a moisture content lower than about 52 percent, there is no longer any tendency for the residue to build up and clog the dryer. Consequently, to employ a drum-dryer for tomato pomace, it is necessary to pre-dry the tomato pomace to a moisture level at or below 50-52 percent in order that the drum dryer can be utilized effectvely.

A further example of the foregoing is the drying of cellulose fibers mixed with water and isopropanol. Generally, this mixture is about 50 percent solids and 50 percent volatiles. In this range, the material is quite sticky and quickly forms a build-up when introduced to the drum dryer. In actual tests, this build-up does not occur if the wetted level is reduced to about percent or below prior to introducing the material to the drum dryer. Consequently, it is likewise necessary to pre-dry this material prior to its introduction into the drum dryer. It is noted that it is very desirable to utilize a drum-type dryer because of its high heat transfer efficiency and the long residence time obtained during the drying process.

The present invention minimizes and/or eliminates the above-identified problems associated with drumtype treatment units and provides a novel and improved multi-stage treatment unit having various advantages in construction, mode of operation and result over such prior units. Particularly, the present invention provides a drum-type unit for treating material with a gas and a pre-dryer unit for reducing the wetted content of the material to a level at or below which the material will not stick or adhere to the surfaces of the drum unit or generally clog orjam the unit. The present invention provides a pre-dryer unit comprised of horizontally disposed deck overlying a plenum and a plurality of openings through the deck such that gas issuing through the openings forms gas jets directed against the material for conveying it in a direction toward the inlet of the drum unit. The gas issuing through the openings predries the material as it is conveyed. The pre-dryer also includes a horizontally disposed high velocity booster jet which, in combination with an inclined feed chute and the gas jets issuing from the openings in the conveyor deck. carry the material in a gaseous layer precluding its contact with and hence adherence to the deck. Consequently, material having an initial wetted level above which will produce clogging or jamming of the primary treatment drum unit if introduced directly into such unit. is pre-dried to a wetted level below which the material will not jam or clog the primary treatment unit before the material is introduced into such unit. Referring to the first above-noted example, the pre-dryer unit reduces the wetted level of the tomato pomace from the 60 percent range down to about percent prior to introducing the pomace into the drum dryer. With respect to the cellulose fibers, the pre-dryer reduces the wetted level to about 45 percent prior to introducing the fibers into the drum dryer. It is again noted that a drum-type dryer unit is very desirable for drying this type of materials as it is considerably more efficient and effective as a dryer than most known dryers. While drying sections of the type herein employed as a pre-dryer have been per se utilized in the past, it is not itself suitable for heavily wetted material because of the long path necessary to achieve the required residence time and its relatively poor heat transfer qualities. Thus, the present invention provides a multi-stage gas treatment unit combining the advantages of both a horizontally disposed dryer and a drumtype dryer.

Accordingly, it is the primary object of the present invention to provide a novel and improved multi-stage apparatus and method for treating materials with a gas.

It is another object of the present invention to pro vide a novel and improved multi-stage drying unit formed particularly to eliminate material residue buildup within the unit due to the adherence or sticking of wetted material to its surfaces.

It is still another object of the present invention to provide a novel apparatus and method for drying wetted material.

It is a further object of the present invention to provide a multi-stage dryer for wetted material having no moving parts in contact with the material.

It is a still further object of the present invention to provide a novel method and apparatus for drying wetted material which is readily. easily and inexpensively constructed and which combines the advantages of both horizontal and drum-type drying units.

These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings wherein:

FIG. 1 is a plan view of a multi-stage drying apparatus constructed in accordance with the present invention and illustrated with parts broken out and in crosssection;

FIG. 2 is a cross-sectional view thereof taken about on line 22 in FIG. 1;

FIG. 3 is an enlarged fragmentary cross-sectional view of the openings formed in the deck of the predryer unit; and

FIG. 4 is a perspective view of the cylindrical drum dryer unit illustrating the location of the gas openings about the cylindrical surface thereof.

Referring now to the drawings, particularly to FIGS. 1 and 2, there is illustrated a drum dryer unit generally indicated and a pre-dryer unit generally indicated 12. The drum dryer unit 10 comprises a plenum 14 defined by oppositely disposed

side walls

16 and 18, a lower wall 20 and end walls. Disposed within and coextensive with the plenum is an elongated cylindrical drum 22 having, as best illustrated in FIGS. 2 and 4, a plurality of openings 24 formed through a lower wall portion defining the drum 22 and distributed throughout its full length. Particularly, the openings 24 are arranged in a plurality of rows extending circumferentially about the drum over a limited circumferential extent thereof, the circumferentially extending rows being longitudinally spaced one from the other substantially as described in [1.8. Pat. No. 3,418,724 especially FIGS. 8-10 thereof. As illustrated in FIG. 4, openings 24 extend circumferentially about the lower part of the drum through an arc of about 90. Each opening 24, as best illustrated in FIG. 2, is comprised of an incision formed in the wall of the drum with a portion 26 depressed outwardly from the arcuate surface of the drum into the underlying plenum chamber 14. Accordingly, aswill be appreciated from the ensuing description, the depressed portions 24 thus form slots for directing air under pressure from plenum 14 for issuance into the drum as gas jets having flow components predominantly in a generally circumferential direction about the interior of drum 22. Drum 22 has an inlet opening and partially overlies plenum 14. Deck 40 is connected with and. in effect, forms a horizontal tangential continuation of the cylindrical surface of drum 22. Deck 40 also forms the bottom wall of a passage defined by spaced side walls 42 and an upper wall 44 which connect with the cylindrical surface of drum 22 about inlet opening 28.

Pre-dryer unit 12 also includes a plenum 46 underlying deck 40. the plenum 46 being defined by a lower wall 48, opposite end walls 50 and 51 and the lower continuations of the side walls 42. An inclined wall 52 depends from the upper end of end wall 50 and. with the edge of upper wall 44, defines a chute 54 for introducing material into pre-dryer unit 12. As best illustrated in FIG. 1, there is disclosed a blower unit 56 in communication with the plenum 46 via a conduit 58 and also in communication with plenum 14 via conduit 60. Blower unit 56 also has a heating element 57. A gate valve 62 is provided in conduit 60 whereby a higher pressure air may be introduced in plenum 46 than in plenum 14.

Deck 40 of pre-dryer unit 12 is provided with slots 64 similarly configured as slots 24. Particularly, slots 64 each comprise an incision formed in the plate 40 with a portion 66 depressed from the plane of plate 40 downstream from the incision. Depressed portion 66 thus forms a baffle for directing air from plenum 46 through slots 64 for issuance along the upper side of deck 40 as air jets having both vertical and horizontal flow components. These air jets serve to move the material from inlet chute 54 along the passage defined by side walls 42, top wall 44 and deck 40, through inlet opening 28, and into drum dryer 22. The lower end of inclined chute 52 is spaced above deck 40 and defines a longitudinally extending slot 68 in communication with plenum 46. Slot 68 defines a high velocity booster jet having substantially horizontally extending flow components in a direction toward inlet opening 28.

In use, the wetted material is introduced to the drying apparatus through chute 54. The high velocity booster air jet issuing through slot 68 in combination with the inclined feed chute 52 and the air jets issuing through the slots 64 of deck 40 carry the material in an air layer from chute 54 through inlet opening 28 in such a manner that the material is prevented from contacting deck 40. The air provided by blower 56 is heated and accordingly the material introduced to the pre-dryer unit 12 is dried as it is conveyed horizontally toward the drum dryer inlet opening 28. As will be appreciated from the foregoing, this pre-drying action occurs throughout the length of travel of the material along passage 55. The velocity of the air issuing through the openings 64 and slot 68 as well as the length of the plate 40 are predetermined such that the wetted material introduced into pre-drying unit 12 is dried sufficiently prior to its introduction through inlet opening 28 to drum 22 such that its wetted content is below the wetted content at which the material would adhere or stick to the surfaces of drum dryer unit 22. In the example of tomato pomace previously described, the predryer plate 40 extends for about 10 feet.

Upon introduction of the predried material into the drum dryer 22, the material is entrained by the air jets issuing through the slots 24 and circulated circumferentially about drum 22. Due to the pressure differential between the inlet and outlet ends of the drum, the material and air circumscribe helical paths as they progress from inlet 28 in an axial direction along the chamber toward outlet 32 at the opposite end of the drum. Alternatively, the slots 24 can be configured to have axial flow components for transporting the material to the outlet 32. It will be apparent that the heated air provided the drum from the plenum l4 dries the material within the drum to the desired predetermined level prior to discharge from the drum through outlet 32.

It will thus be appreciated that the objects of the present invention are fully accomplished by the foregoing apparatus. Particularly, wetted material is predried in the pre-dryer unit 12 to the extent that it obtains a wetted content upon introduction into the drum dryer 22 at or below the level of wetness which would cause the material to stick or adhere to the drum surfaces. Moreover, the efficiencies and advantages of a drumtype drying unit are retained in the present invention and the capability of such drum-type unit is extended to the handling of wetted materials which would otherwise cause the drum dryer unit to clog, jam and be rendered ineffective.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. Apparatus for treating material with a gas comprismg:

first and second treatment devices, said first device having an inlet for receiving the material and a generally horizontally disposed conveyor deck having a plurality of openings,

means for supplying a gas under pressure for passage through said openings for treating the material, said openings being configured such that the gas issuing therethrough forms jets having horizontal flow components for conveying the material from said inlet in a direction generally parallel to said deck to said second treatment device, said second device including a generally cylindrical drum defining a chamber, said drum having an inlet to said chamber adjacent one end thereof for receiving the material from said first device and an outlet from said chamber adjacent its opposite end for discharging the material, said drum having a plurality of openings through at least a portion of the cylindrical wall defining the same, said conveyor deck forming a substantially tangential extension of the drum wall at its inlet, means for supplying a gas under pressure for passage through said openings into said chamber for treatment of the material therein, each of said latter openings being configured such that the gas issuing therethrough forms jets having flow components for conveying the material in a generally circumferential direction about said chamber, and means for conveying the material in an axial direction along said drum for discharge through said outlet.

2. Apparatus according to claim 1 including means adjacent the inlet of said first device for forming a gas jet having flow components predominantly parallel to and adjacent said deck wherein, in conjunction with the gas jets issuing through the openings in said deck, the material against which the gas jets impinge is adapted for conveyance in spaced relation to said deck.

3. Apparatus according to claim 1 including first and second plenums underlying said deck and said drum, said inlet to said first conveyor including a chute having an inclined wall spaced from said deck and defining a slot therewith, said slot lying in communication with the gas under pressure in said first plenum and being configured to form a high velocity gas jet having flow components predominantly parallel to and adjacent said deck.

4. Apparatus according to claim 1 including means for supplying heated gas for passage through the openings in each of said deck and said drum.

5. Apparatus according to claim 1 including first and second plenums underlying said deck and said drum, said inlet to said first device including a chute having an inclined wall spaced for said deck and defining a slot therewith, said slot lying in communication with said first plenum and being configured to form a gas jet having flow components predominantly parallel to and adjacent said deck, said deck forming a generally horizontal and tangential extension of the wall defining a portion of said drum. the gas issuing through said slot and the openings in said deck being adapted to maintain the material in spaced relation to said deck, and means for supplying heated gas for passage through said slot and the openings in said decks.

6. Apparatus for drying wetted material comprising; a predryer, a primary dryer, said predryer including a generally horizontally disposed deck having a plurality of openings and an inlet adjacent one end of said deck for receiving the wetted material, a plenum underlying said deck. a source of heated air under pressure in communication with said plenum for supplying heated air through said openings, said openings being configured such that the air issuing therethrough dries the wetted material and forms jets having horizontal flow components for conveying the wetted material from said inlet in a direction generally parallel to said deck to said primary dryer, said primary dryer including a generally cylindrical drum defining a chamber having an inlet and an outlet adjacent opposite ends of said chamber, for respectively receiving the material from said predryer and discharging the material, said drum having a plurality of openings through at least a portion of the cylindrical wall defining the same, said conveyor deck forming a substantially tangential extension of the drum wall at its inlet, a second plenum surrounding at least the portion of the drum containing said openings, means for communicating the heated air from said source to said second plenum for issuance through said drum openings into said chamber, said drum openings being configured such that the air issuing therethrough dries the wetted material received from said predryer and forms jets having circumferential flow components for conveying the wetted material in a generally circumferential direction about said chamber, and means-for conveying the material in an axial direction along said drum for discharge through said outlet.

7. Apparatus according to claim 6 wherein the inlet to said pre-dryer includes a chute having an inclined wall, the lower end of said wall being spaced above said deck to define a slot therewith in communication with the plenum underlying said deck. said slot being configured to form an air jet having flow components predominantly parallel to and adjacent said deck whereby, in conjunction with said inclined wall and the air jets issuing through the openings in said deck. the material is adapted to conveyance along said deck in spaced relation thereto.

8. Apparatus according to claim 6 wherein the inlet to said pre-dryer includes a chute having an inclined wall, the lower end of said wall being spaced above said deck to define a slot therewith in communication with the plenum underlying said deck, said slot being configured to form an air jet having flow components predominantly parallel to and adjacent said deck whereby, in conjunction with said inclined wall and the air jets issuing through the openings in said deck, the material is adapted for conveyance along said deck in spaced relation thereto, the opposite end of said deck from its inlet end forming a substantially tangential extension of the wall defining a portion of said drum at its inlet, the

openings in the wall of said drum being distributed in a wall portion of said drum which extends circumferentially from said deck and in a predetermined circumferential extent of the drum wall for the full distance between the drum inlet and drum outlet.

9. Apparatus according to claim 6 wherein the plurality of openings in the wall of said drum are provided at least in a wall portion of said drum which extends circumferentially from said deck.

10. A two-stage method of drying wetted material utilizing a predryer comprised on a conveyor deck having a plurality of openings and a primary dryer comprised of a drum having a plurality of openings through a predetermined area of the cylindrical wall defining said drum comprising the steps of delivering the wetted material to the predryer, passing heated air through the openings in said deck for drying the wetted material and conveying it toward said primary dryer. delivering the predried wetted material to said primary dryer. in a direction substantially tangential to said cylindrical wall. passing heated air through the openings in said primary dryer drum for imparting circumferential movement to said material about said chamber and for drying the material and conveying the air and material axially along said drum to discharge the dried material at the outlet to said drum.

1!. The method according to claim 10 wherein the material has an initial wetted content above a predetermined wetted level at which the material will clog or otherwise impair the efficiency of the primary dryer including the step of predrying the material in said predryer such that the wetted level of the material delivered to the primary dryer is below the predetermined level.

12. The method according to claim 11 including the step of providing an air jet along said deck in the direction of movement of the material whereby the air jet and the air issuing through the openings entrains the material in a cushion of air flowing above the deck.

13. The method according to claim 12 including the step of delivering the wetted material into said predreyer along an inclined chute.

Claims

1. Apparatus for treating material with a gas comprising: first and second treatment devices, said first device having an inlet for receiving the material and a generally horizontally disposed conveyor deck having a plurality of openings, means for supplying a gas under pressure for passage through said openings for treating the material, said openings being configured such that the gas issuing therethrough forms jets having horizontal flow components for conveying the material from said inlet in a direction generally parallel to said deck to said second treatment device, said second device including a generally cylindrical drum defining a chamber, said drum having an inlet to said chamber adjacent one end thereof for receiving the material from said first device and an outlet from said chamber adjacent its opposite end for discharging the material, said drum having a plurality of openings through at least a portion of the cylindrical wall defining the same, said conveyor deck forming a substantially tangential extension of the drum wall at its inlet, means for supplying a gas under pressure for passage through said openings into said chamber for treatment of the material therein, each of said latter openings being configured such that the gas issuing therethrough forms jets having flow components for conveying the material in a generally circumferential direction about said chamber, and means for conveying the material in an axial direction along said drum for discharge through said outlet.

5. Apparatus according to claim 1 including first and second plenums underlying said deck and said drum, said inlet to said first device including a chute having an inclined wall spaced for said deck and defining a slot therewith, said slot lying in communication with said first plenum and being configured to form a gas jet having flow components predominantly parallel to and adjacent said deck, said deck forming a generally Horizontal and tangential extension of the wall defining a portion of said drum, the gas issuing through said slot and the openings in said deck being adapted to maintain the material in spaced relation to said deck, and means for supplying heated gas for passage through said slot and the openings in said decks.

6. Apparatus for drying wetted material comprising; a predryer, a primary dryer, said predryer including a generally horizontally disposed deck having a plurality of openings and an inlet adjacent one end of said deck for receiving the wetted material, a plenum underlying said deck, a source of heated air under pressure in communication with said plenum for supplying heated air through said openings, said openings being configured such that the air issuing therethrough dries the wetted material and forms jets having horizontal flow components for conveying the wetted material from said inlet in a direction generally parallel to said deck to said primary dryer, said primary dryer including a generally cylindrical drum defining a chamber having an inlet and an outlet adjacent opposite ends of said chamber, for respectively receiving the material from said predryer and discharging the material, said drum having a plurality of openings through at least a portion of the cylindrical wall defining the same, said conveyor deck forming a substantially tangential extension of the drum wall at its inlet, a second plenum surrounding at least the portion of the drum containing said openings, means for communicating the heated air from said source to said second plenum for issuance through said drum openings into said chamber, said drum openings being configured such that the air issuing therethrough dries the wetted material received from said predryer and forms jets having circumferential flow components for conveying the wetted material in a generally circumferential direction about said chamber, and means for conveying the material in an axial direction along said drum for discharge through said outlet.

7. Apparatus according to claim 6 wherein the inlet to said pre-dryer includes a chute having an inclined wall, the lower end of said wall being spaced above said deck to define a slot therewith in communication with the plenum underlying said deck, said slot being configured to form an air jet having flow components predominantly parallel to and adjacent said deck whereby, in conjunction with said inclined wall and the air jets issuing through the openings in said deck, the material is adapted to conveyance along said deck in spaced relation thereto.

8. Apparatus according to claim 6 wherein the inlet to said pre-dryer includes a chute having an inclined wall, the lower end of said wall being spaced above said deck to define a slot therewith in communication with the plenum underlying said deck, said slot being configured to form an air jet having flow components predominantly parallel to and adjacent said deck whereby, in conjunction with said inclined wall and the air jets issuing through the openings in said deck, the material is adapted for conveyance along said deck in spaced relation thereto, the opposite end of said deck from its inlet end forming a substantially tangential extension of the wall defining a portion of said drum at its inlet, the openings in the wall of said drum being distributed in a wall portion of said drum which extends circumferentially from said deck and in a predetermined circumferential extent of the drum wall for the full distance between the drum inlet and drum outlet.

10. A two-stage method of drying wetted material utilizing a predryer comprised on a conveyor deck having a plurality of openings and a primary dryer comprised of a drum having a plurality of openings through a predetermined area of the cylindrical wall defining said drum comprisinG the steps of delivering the wetted material to the predryer, passing heated air through the openings in said deck for drying the wetted material and conveying it toward said primary dryer, delivering the predried wetted material to said primary dryer, in a direction substantially tangential to said cylindrical wall, passing heated air through the openings in said primary dryer drum for imparting circumferential movement to said material about said chamber and for drying the material and conveying the air and material axially along said drum to discharge the dried material at the outlet to said drum.

11. The method according to claim 10 wherein the material has an initial wetted content above a predetermined wetted level at which the material will clog or otherwise impair the efficiency of the primary dryer including the step of predrying the material in said pre-dryer such that the wetted level of the material delivered to the primary dryer is below the predetermined level.

13. The method according to claim 12 including the step of delivering the wetted material into said pre-dreyer along an inclined chute.