EP0031379A1

EP0031379A1 - Dehydration equipment

Info

Publication number: EP0031379A1
Application number: EP19800901554
Authority: EP
Inventors: Wilfried P. Duske; Lowell C. Frank
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-07-02
Filing date: 1981-01-26
Publication date: 1981-07-08
Also published as: CA1152317A; WO1981000146A1

Abstract

Un systeme de sechage rotatif pour un materiau particulaire comprend une secheuse rotative (1) du type a cylindres multiples avec un axe de rotation horizontal. Un four (2) est monte a une extremite et un separateur centrifuge dispose horizontalement (7) du type a volute est monte a l'autre extremite. Un petit separateur a cyclone (12) est accouple au separateur a volute et il est connecte dans un systeme a circuit ferme au separateur a volute pour le recyclage permanent de l'air au travers de ce dernier. La dimension verticale de la secheuse rotative etant essentiellement la plus grande, le profil du systeme est reduit au minimum. La secheuse rotative est formee avec un cylindre interieur (17) conique ayant une entree relativement petite et un diametre de passage augmentant progressivement jusqu'a une grande extremite de refoulement accouplee a un passage intermediaire entre le cylindre interieur et un cylindre intermediaire de diametre constant (16). La section du passage intermediaire s'agrandit continuellement jusqu'a un passage de decharge finale forme par un cylindre externe concentrique (15). Des plaques d'usure remplacables (53) supportent une extremite des cylindres intermediaire et interieur pour limiter leur mouvement relatif. Les passages sont proportionnes pour etablir une distribution volumetrique de sechage et de fuite de temperature optimum pour empecher la degradation du produit et assurer un sechage efficace.A rotary drying system for a particulate material comprises a rotary dryer (1) of the multi-cylinder type with a horizontal axis of rotation. A furnace (2) is mounted at one end and a horizontally arranged centrifugal separator (7) of the scroll type is mounted at the other end. A small cyclone separator (12) is coupled to the volute separator and it is connected in a closed circuit system to the volute separator for the permanent recycling of air through the latter. As the vertical dimension of the rotary dryer is essentially the largest, the profile of the system is reduced to a minimum. The rotary dryer is formed with a conical inner cylinder (17) having a relatively small inlet and a passage diameter progressively increasing until a large discharge end coupled with an intermediate passage between the internal cylinder and an intermediate cylinder of constant diameter ( 16). The section of the intermediate passage is continuously enlarged up to a final discharge passage formed by a concentric external cylinder (15). Replaceable wear plates (53) support one end of the intermediate and inner cylinders to limit their relative movement. The passages are proportional to establish a volumetric distribution of drying and optimum temperature leakage to prevent degradation of the product and ensure efficient drying.

Description

DEHYDRATION EQUIPMENT Background Of The Invention This invention relates to a dehydration appa¬ ratus in which particulate material is carried by a fluid medium through a rotary dryer.

Particulate matter which includes moisture or the other gaseous material may be passed through a ro¬ tary dryer for removal of the liquid or gaseous medium with subsequent separation of the particles from the fluid medium. Generally, in a rotary dryer system which is widely employed in industry and agricultural product drying and the like includes a gas or oil fired furnace or other heat source mounted to one end of a horizon¬ tally located and supported rotary dryer to supply hot air which is mixed with the product and through which particulate laden air is passed. The dryer includes a plurality of concentric cylinders or drums defining a central inlet passageway connected at one end to the hot air and connected in series by one or more intermediate passageways to an outermost discharge passageway. The particulate laden air moves through the multiple pass¬ ageways by suction created by a dryer discharge fan. The rotary cylinders include suitable surface vanes to con¬ tinuously circulate the particulate matter within the drums to the top portion and establish intimate mixing of the particles with the hot air or gases from the heat source. The air with the dried particle is fed to one or more cyclone separators, drop-out boxes or other suitable means for the separation of the dust particles from the hot gases. A cyclone separator generally in¬ cludes a large vertically oriented unit having a top cylindrical inlet portion with a conical bottom dis¬ charge portion as well as a central top air.exhaust duct member. The particulate laden air is fed into the unit with a centrifugal motion such as that as it moves down- wardly through the cylindrical portion the particles are concentrated in the outer layer, and continue to drop downwardly through the cone-shape portion for exiting from the bottom. The primary carrier air is drawn up- wardly through the center duct to the top of the cyclon¬ ic separator for further treatment or exhausting. For example, the air may be recirculated to the furnace. Alternately, a series of cyclonic separators may be pro¬ vided to further clean the carrier air if it is to be exhausted to the atmosphere. Such rotary dryers are widely employed in connection with many industrial and agricultural products. Generally appropriate housing of the system apparatus includes enclosure of the furnace and dryer with the cyclonic separator mounted on or in a support structure.

Such systems are well known and are furnished by various sources of manufacture. Generally, the prior art has followed a basic pattern for years in which three constant diameter concentric cylinders are interconnected to define a triple pass drying flow path..

Although they provide satisfactory results, they do not provide necessarily the proper degree of dry¬ ing which is often desired and/or required. Further, in various application scorching or excessive drying of particulate may occur. This is known to be particularly troublesome in connection with certain high sugar con¬ tent wood products where scorching occurs as well as products or the like where various sized particles are encountered and degradation of product quality may occur if proper drying is not provided. Although various sys¬ tems have been suggested a totally acceptable solution has not been found prior to the present invention. Summary Of The Present Invention The present invention is particularly directed to a rotary dryer system employing an improved rotary dryer construction which may produce a significantly im¬ proved quality product and operate with significantly improved efficiencies as well as providing a total oper¬ ating system which can eliminate the large bulky verti- cally oriented cyclonic separator.

Generally in accordance with the present in¬ vention, a multiple cylinder rotary dryer apparatus is formed with an inner tapered cylindrical wall means which preferably is of a substantially conical construc- tion and having a relatively small inlet diameter means. The inner cylindrical means progressively increases in diameter, preferably in the manner of a conical member to a relatively large discharge diameter means, which is coupled by a transfer passageway to a return passageway along the exterior of the cylindrical means and an in- ^"'termediate cylindrical means. The intermediate cylin¬ drical means may be a cylinder having a constant diam¬ eter, thus creating a relatively small inlet portion adjacent the discharge of the inner cylindrical wall means and a relatively large discharge end adjacent the discharge end of the intermediate cylindrical wall means. Thus, a second continuously expanding flow path is again created for the particulate laden gases. The several wall means are in accordance known practice pro- vided with suitable flights for carrying and recircula- tion of particulate material to the top portion of the cylinders from which the particulate tend to fall down¬ wardly through the ^'hot gases. A tapered construction with a smooth and progressively changing diameters has been found to provide a highly effective means of maxi¬ mizing the contact time particularly of the heavier moisture laden particles.

Further, the passageways are proportioned to establish the volumetric distribution which results in an optimum drying characteristic, and particularly ef- fective drying of the particulate material without scorching thereof or otherwise creating degradation of the quality of the dried materials. Generally, the in¬ termediate passageway is enlarged while the outer pass- ageway is reduced in volume. The resident time in the inner and intermediate passageways are optimized while the velocity in the final or discharge passageway is in¬ creased to minimize the problems heretofore resulting from excessive temperatures and particle-to-surface en- gagement, particularly at the area immediately adjacent the final discharge area from the rotary dryer. Thus, the present invention may employ a higher initial tem¬ perature than generally employed in comparable prior art systems, and in particular for drying of alfalfa and like material, initial inlet temperature may be 2100 ^'degrees Fahrenheit with a discharge temperature on the order of 24o degrees Fahrenheit or less.

In such multiple pass drums, the several cyl¬ inders or drums are interconnected to each other for simultaneous rotation. However, the temperature varia¬ tion from passageway to passageway is such that the cylinders tend to move relative to each other. Such movement has been accommodated by allowing one end of the cylinders to move relative to the adjacent cylinders. Although necessary, such structure has also resulted in periodic maintenance requirement as the result of sur¬ face wear at the relatively moving interfaces. The cylinders in the preferred embodiment of this invention include replaceable wear means which minimize the cost • of maintenance while producing an improved operational system.

Further, the present invention, which promotes the effective drying of the particles, has been used with scroll-type centrifugal separators rather than the standard or conventional cyclonic separator with sep- arate fan. For example, in a particular unique embodi¬ ment of the present invention, a horizontally disposed centrifugal separator of the scroll-type is used with a horizontal flow pattern. This permits a construction of 5 a dryer system in which the dryer drum has essentially the largest vertical dimension and therefore profile of the system minimized. This is particularly advantageous both from the standpoint of original cost and subsequent maintenance or service costs as well as appearance. The

10 minimized profile is also advantageous where the system is .housed in a conventional building as it avoids the necessity of the unusual building, height, or special roof openings, required with the usual cyclonic type separator and the like.

15 The present invention thus provides an im¬ proved rotary dryer apparatus for the efficient drying of material without scorching or excessive drying of the particles with a minimum space requirement.

Brief Description Of The Drawing Figures

20 The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description.

25 In the drawings:

Fig. 1 is a side elevation view of a rotary drying system constructed in accordance with the present invention;

Fig. 2 is a plan view of the system shown in

30 Fig. 1;

Fig. 3 is an enlarged fragmentary longitudinal section through the dryer illustrated in Fig. 1 and more fully and clearly illustrating the construction of a preferred embodiment of the present invention;

35. Fig. 4 is an end view with parts broken away

OMPI and sectioned from the hot air entrance end of the ro¬ tary dryer;

Fig. 5 is an end view with parts broken away and sections taken from the discharge end of the rotary dryer shown in Figs. 1 - 3.

Fig. 6 is an enlarged fragmentary view of a portion of Fig. 3 illustrating a sliding support for a drum cylinder; and

Fig. 7 is a sectional view taken on line 7-7 of Fig. 6.

Description Of The Illustrated Embodiment

Referring to the drawings and particularly to Fig. 1, a rotary dryer system is illustrated constructed in accordance with the teaching of the present inven- tion. Generally, the system includes a rotary dryer 1 ^'which is mounted for continuous rotation about a longi¬ tudinal horizontal axis. A furnace 2 is secured to the inlet end of the rotary dryer 1 in combination with a . particle material inlet section 3 for introducing of a moisture laden particles 4 or the like with hot drying gases 5 from the furnace into the .inlet end of the ro¬ tary dryer 1. The particle laden gases 5 pass through dryer 1 and are discharged from the opposite end with the particles 4 essentially dry. The dry particle laden air 5a is passed through drop-out box unit 6 where the heavier particles drop out of the air carrier onto a suitable receiver 6a such as a screw-type conveyor 6a. The fine particle laden air 5a continues into a particle separator 7 forming part of a closed loop system in ^{■ •} which the dried finer particles 4 are removed from the air 5a. As illustrated in Fig. 1, separator 7 is a cylindrical unit which is preferably mounted on a hori¬ zontal axis. The separator 7 may be a scroll-type cen¬ trifugal separator in which the particle laden air 5a moves axially through the unit 7 and then in a counter- flow direction adjacent to the outer surface of the inner passageway, with a skimming discharge unit 8 removing the peripheral air layer within which the particles 4 are concentrated as at 9 and the clean air 10 exiting from the central portion through a discharge unit 10a to a con¬ ventional stack.11. The dust laden air 6a from separator 7 is further processed in a small cyclone separator 12. The cyclone separator 12 as illustrated is of relatively small size compared to theusual cyclone separa- tor used as a primary particle separator in rotary dryer systems. If the air handling volume of one cyclone separator 12 is not adequate, a plurality of the small cyclone separators may be connected in parallel. The cyclone separators 12 is a well known device operating ^• on a centrifugal principle wherein the dust laden air 5b is introduced tangentially into theupper portion to establish a downward spiral flow toward and into a cone-shaped bottom portion which is open at the bottom. The particles 4 concentrate in the peripheral air layer and move downwardly throught the upper portion. The air carrier exhausts upwardly through a central outlet duct 13 while the heavier particles 4 drop under the force of gravity through the bottom cone portion of the separator and from the bottom opening onto a suitable receiver such as the screw-type 6a conveyor or the like located to receive the particles 4 from drop-out box. The exhaust air from thecyclone separator 12 is returned directly from the top of the separator to the dropout box 6 via a suitable duct 13a-'.and is recycled therefrom as a part of the carrier air into thescroll separator 7 to maintain the continuous and closed loop system. The recycled air is a small percentage of the total air through the separator 7 and adjustment of the cyclonic separator exhaust, such as usually provided, does not adversely effect the upstream press conditions such as may occur with theusual primary cyclonic separator systems. IN the illustrated embodiment of the inven tion, theonly exhaust air to atmosphere is theprimary air from the scroll separator 7 and/or the exhaust a vent and recycle stack of the furnace. Thus, the pri¬ mary exhaust air from the separator 7 is coupled to the ^" exhaust stack 11, and to furnace vent and recycle box 14 on the furnace 2. Thus the clean air may be wholly or in part recycled to the furnace.

The illustrated separator 12 is relatively small and clearly distinguished from the more conven¬ tional cyclone separator which has been and is widely employed as a primary particle separator in connection with the drying of grain and the like. Although such a prior art separator could be employed, effective pri¬ mary separation requires large cyclone chamber construc¬ tion and particularly a height substantially greater than the height of the rotary dryer 1 and associated equipment such as the furnace, the drop-out box, the

^'secondary cyclone separators and the like, and often the primary cyclone separator is twice the height of the dryer. The present minimal profile assembly has dis¬ tinctive advantages not only from original cost con- sideration construction but from the continuing mainte¬ nance and servicing considerations.

Thus, the present invention permits the con¬ struction of the total overall system as illustrated in Fig. 1 as an in-line system where the rotary dryer 1 essentially has the greatest vertical height and es¬ tablishes the maximum overall profile of the system, while establishing effective separation of particulate matter from the air carrier. The minimal vertical height may be of particular significance in application requiring enclosure of the drying system. Thus, with the illustrated embodiment, only roof openings required is that for the exhaust air and the like. In prior art systems, the building must be exceptionally high or sep¬ arate openings and/or construction provided to accomo- date the large primary cyclone type separator. The present invention is thus particularly di¬ rected to the rotary dryer 1 as well as the system which permits exiting through a simple vertical stack arrange¬ ment such that a minimized profile system can be pro- vided.

The several elements other than the rotary dryer 1 may therefore be of any suitable or desired con¬ struction. The scroll separator 7 as shown and as de¬ scribed hereinafter is preferably constructed in .accor- dance with the teaching of applicants' copending appli¬ cation entitled, "Fluid Borne Particulate Separator" and which was filed on even date with this application. The furnace may be of any well known construction but is preferably formed of a,modular type construction illus- trated to permit the convenience sizing of the furnace to installation. Thus, as previously noted for drying of alfalfa and the like an inlet temperature on the order of 2100 degrees Fahrenheit may be desired. For drying of bone meal and the like, the initial te per- ature may be as low as 700 or 800 degrees Fahrenheit. Similarly with wood grain products and the like, vari¬ ous other temperatures may be required. Such detail is readily understood by those skilled in the art and no further description thereof is given. More particularly, in the illustrated embodi¬ ment which is more clearly shown in Figs. 2-4, the ro¬ tary dryer apparatus 1 is a multiple cylinder unit con¬ sisting of an outer drum or cylinder 15, on interme¬ diate drum or cylinder 16 and a special inner drum or cylinder 17 which define a continuous flow path for the particle laden air 5. The inner cylinder .1-7 defines a central passageway 18 which extends from the furnace end of dryer 1 and which is joined to a intermediate return passageway 19 between cylinders 16 and 17. Passageway 19 is similarly joined to a final outer pass- agewau 20 between cylinders 15 and 16. Passageway 20 terminates in an axial discharge passageway 21 opposite the inlet end of the dryer 1.

The several cylinders 15 - 17 are connected to rotate as a unit on a pair of supports 22 and 23 for the outermost cylinder 15. The supports may be suit¬ able wheeled support of a suitable rotary pillow-type block.

As shown in Fig. _ 3, the outer cylinder 15 is provided with suitable end support rings 24 for vertical rotating support of the rotary drum. Suitable axial thrust rolls 25 are supported adjacent the inner faces of the one end ring 24. The rotary drum assembly is motor driven through a known chain and sprocket drive 26 secured to the discharge end of the rotary dryer 1, ^""and particularly to the outer cylinder 15.

More particularly, the outer cylinder 15 is formed with a suitable outer insulating shell 27 in combination with an outer physical cover 28 to enclose and protect the high temperature insulation. The in¬ sulation 27 is spaced inwardly from the outermost ends of the outer cylinder 15 to expose the bearing support area of cylinder 15 for the thrust rolls 25. The outer cylinder 15 is formed with integral partial end walls 29 and 30 which project radially inwardly from the end guide rings 24 essentially for the depth of the final discharge passageway 20 and define the opposite end walls thereof. As shown in Figs. 4-5, a plurality of circumferentially distributed and longitudinal flights 31 are secured to the interface of the outer cylinder 15 andproject radially inwardly to slightly less than one half the depth of the passageway 20. A single one of the flights 31 as well as all other flights hereinafter described, is shown in Fig. 2 for clarity of illustra- tion of the construction of the cylindrical wall and support means forming the several passageways. As shown inFig.3 flights 31 extend throughout the substantial central portion of the cylinder 15 and terminate at the opposite ends in spaced relation to the cylinder end walls 29 and 30. The inner wall of the outer passageway 20 is de¬ fined by the intermediate cylinder 16 which is concen¬ trically mounted on the common axis for all members 15 - 17 to define an annular passageway 20. A plurality of circumferentially distributed intermediate cylinder sup- port brackets 32 are secured within the opposite ends of the outer cylinder 15. The brackets 32 extend inwardly from the opposite ends of the end walls 29 and 30 be¬ neath the ends of cylinder 16. The brackets 32 adja¬ cent the inlet end 29 of the dryer 1 includes a flanged top wall to which a plurality of support plates 33 are secured. A suitable support ring 34 is secured to ends of cylinder 16, and the total assembly is bolted to¬ gether such that the end of cylinder 16 is firmly at¬ tached to the cylinder 15 at the transfer location at the end 29. Plates 33 may be a suitable relatively short plate welded or otherwise secured, one each to each of the brackets 32. The ring 34 may be a continu¬ ous ring secured to the outer face of cylinder 16. The cylinder 16 extends from the attachment means 33-34 with the opposite end overlying the brackets 32 adja¬ cent the discharge end of the dryer 1 and mounted with suitable replaceable sliding support means. The brac¬ kets 32 are top-flanged members with a replaceable wear plate means 35 bolted thereto and defining a slid- ing support. The intermediate cylinder 16 is affixed to the outer cylinder by a bolted interconnection imme¬ diately adjacent to the inlet end of the dryer, while the opposite ends of the cylinder 16 is allowed to move relative to the outer cylinder 15. As shown most clearly in Fig. 6, replaceable

-SURE Y

OMPI ^"

. A ™°^* wear means 35 includes a supporting segmented wear ring 36 which is releasably affixed to tops of the end of the circumferentially distributed end brackets 32. The wear ring 36 is formed of a plurality of similar segments to permit individual replacement of each segment. Each of the wear plate segments includes a circumferential mounting base 37 which is provided with bolt openings appropriately aligned with bolt openings in the tops of the several brackets 32 for bolting of the wear plate segments into position. A wear plate 38 is welded or otherwise secured to the mounting base 37. Each plate 38 extends circumferentially into abutting engagement with the adjacent plates 38. In the illustrated embodi¬ ment of the invention, the segments define a continuous wear surface, with each segment spanning 60 degrees and ^'six segments provided to define 360 degrees wear sur¬ f ce.

The adjacent portion of the intermediate cy¬ linder 16 is provided with an outer support ring 39. The ring 39 is a continuous ring member which is welded or otherwise firmly affixed to the outer periphery of the intermediate cylinder 16 in alignment with the wear- plate 38. The axial length of ring 39 is greater than that of the wear plate 38 and ring 39 is located to ex- tend beyond the opposite ends of wear plate 38 at least by the distance of relative movement during the normal operation of the rotary dryer 1. The wear ring 39 is also formed of a relatively hardened material, with the outer face finished to establish a smooth sliding sur- face to the shorter wear plate 38. During the relative movement between the intermediate cylinder 16 and its support bracket 32 wear created will be on the smaller length of the wear plate 38. As a result, a continuous and relatively smooth interface support engagement is maintained.

O If one or more of the wear plate 38 is exces¬ sively worn, that unit may be readily replaced by re¬ moval of a dryer end wall structure to permit access to the drum structure and particularly the cylinder sup- port structure 32. The worn wear plate unit 35 is readily replaced by unbolting and withdrawal of the worn section.

In the illustrated embodiment, intermediate cylinder 16 terminates generally in spaced relation to the end wa i 30 of the outer cylinder 15 to define an exit passageway 40 into the exhaust passageway unit 21 from the outermost dryer passageway 20. The end wall of the exit passageway 40 includes one or more remov¬ able end wall sections 41 which permit access to the ends of cylinder 16 and 17 to .permit-.-.-access to the re- ^•■•placeable wear means 35. A similar wear means 42 for cylinder 17 is subsequently described.

In the illustrated embodiment of the inven¬ tion, similar cone plates 43 are show in Fig. 3 secured in the corner of the entrance and exit ends of the outer cylinder 15 to assist the product flow into and from the passageway 20 and finally into discharge duct unit 21.

The opposite end of cylinder 16 is similarly spaced from end wall 29 to define a transfer passageway from passageway 19 to passageway 20 and supported on the brackets 32 adjacent wall 29. The securement is a fixed attachment with appropriate support rings 33 and 34 se¬ cured to the cylinder 16 and to brackets 32 with suit- able attachment bolts provided at each bracket.

The intermediate cylinder 16 is shown as a cylindrical member of constant diameter having flight 46 secured to its outer surface and extending essentially coextensive with the corresponding flights 31 of the outer cylinder 15. Flights 46 are offset by one half the distance between flights 31. .In addition, similar in¬ ner flights 47 are secured to the inner face of the intermediate cylinder 16 and extend from the transfer passageway portion with the opposite end spaced axially inwardly of the opposite end of cylinder It. The op¬ posite ends of intermediate passageway 19 are closed by suitable end walls 48 and 49 which with the inner cylinder 17 form passageway 19. End wall 48 is secured to wall 29 and extends radially inwardly and is welded or otherwise secured to the inner cylinder 17 and sup¬ ports the cylinder 17. End wall 49 is secured to the opposite end of cylinder 16. A plurality of support brackets 52 are secured to the end wall 49 and extend, inwardly beneath the inner cylinder 17, which is spaced from the end wall 49 to form and define a transfer pass- ^'ageway for the air and particles flowing from the cen¬ tral or inner passageway 18 to the intermediate pass¬ ageway 19. Suitable cone plates 52a at the transfer passage may again be provided for effective turning of the air from the inner passageway 18 into the interme¬ diate passageway 19. The sliding support and wear means 42 is secured to the brackets 52 and inner cylinder 17 to slidably support the cylinder 17. Thus, wear means 42 includes a segmented wear plate unit 53 secured to the outer face of cylinder 17 and a hardened wear ring 54, of greater axial length than the wear plate of unit 53, welded or otherwise secured to brackets 52. The wear means 42 is thus essentially the same as wear means 35 with the parts reversely mounted. The inner cylinder 17 is specially constructed as a generally continuously tapered member and prefer¬ ably as a conically shaped member having the inner end slidably supported on the end brackets 52 in spaced relation to the end wall 49 to define the transfer pass- ageway. The inner cylinder 17 extends axially and ra-

-,_ n

___ - ^~ dially from such large diameter inner end to a small dia¬ meter inlet end, with the outermost end fixedly support¬ ed by the end wall 48 upon the wall 29. Circumferen¬ tially distributed flights 57 are secured to the exter- ior face of the inner cylinder 17 and extend from the transfer passageway to the opposite end wall and thus through the intermediate passageway 19. Flights 57 are offset circumferentially to the center of the flights 47 on the interior of cylinder 16. Inner flights 58 are secured to the inner face of the conical inner cylinder 17. ' Flights 58 are shown as continuous with longitudinally spaced notches 59 along the length thereof to accommodate thermal expan¬ sion-. .^' Each flight may be formed of a series of short spaced flights with alternate rows overlapping.

The inlet end of the conical inner cylinder 17 is fixedly attached to an annular outer couplimg mem¬ ber 60 which projects outwardly into a tubular discharge member 61 of the adjacent heat source and particle mix- ing inlet section 5.

The discharge passageway unit 21 is formed to the opposite end of the inlet cylinder 17 and includes an end closure wall 62 with a generally cone-shaped cross-section for directing of the air from the central cylindrical passageway 18 into the transfer passages to passageway 19.

The discharge passageway 21 on the opposite side of wall 62 preferably includes an outer end wall 63 for directing of the dry particle laden air 59 out- wardly into the discharge duct work for the transfer to the drop-out box and.then centrifugal separator 7. The separator 7 as illustrated is a fan- driven unit having a fan wheel.unit 64 adapted to estab¬ lish a suction pressure through the upstream portion of the system and particularly at the furnace 2. Thus fan unit 64 constitutes the total air moving power source for the system for rapid movement of the particle borne air 5 from the furnace 2, through the rotary dryer 1 as well as the separator 7 and cyclone separator 12. Addi- 5 tional secondary fan systems may of course be supplied but are generally not required depending upon the parti¬ cular installation. The separator 7 may of course be of any suitable construction. A particularly advantageous construction is shown in the previously identified co-

10 pending application of the applicants. As more fully disclosed therein, a scroll type separator includes a central axially extended air duct 65 to the fan wheel assembly 64. The air flows thru and then reverses its direction into an outer passageway between the duct 65

15 and an outer cone-shaped duct 66. The fan unit 64 im- ^**parts a centrifugal motion to the particle laden air resulting in a spiral flow of the air back through the outer discharge passageway. The heavily particle laden air is concentrated in the outer layer and withdrawn

2.0 through the skimmer discharge unit 13 while the rela¬ tively clean air is discharged into an exhaust stack 11 for exhausting from the building or return for recycle. In operation the system operates basically in accordance with known functioning, wherein the furnace

25 2 provides appropriate heated air which is mixed with moist particulate matter and drawn inwardly into dryer 1 and particularly cylinder 17 to generate the air stream 6 for carrying of the particulate material in and through the multiple cylinders passageways 18-20. The 0 conically-shaped inner cylinder 17 results in an in¬ creased air velocity at the cylinder inlet and a re¬ duced air velocity at the end of the inner cylinder outlet. The cylinder 17 with the constant diameter cylinder 16 results in a similar passage 19, with vol- 5 u e throughout the length of the passageways increased.

__.

O -17-

This provides more effective resident time of the parti¬ culate matter 4 in the inner and intermediate passage¬ ways 18 and 19 where the hottest air exists. Conversely, with the illustrated arrangement and the outer passage- . way 20 may be reduced in volume proportionately to main¬ tain the desired product flow.

Conical inner cylinder 17 with the increased air velocity at the inlet end functions to increase the rate o separation of the smaller and/or dryer particles from the larger and/or more moist particles. Further, the arrangement tends to convey the dryer particles into the colder temperature region. The system thus parti¬ cularly increases the wet product resident time within the highest temperature region of passageways 18 and 19. The conical or progressively changing dia-

^'meter inner cylinder also establishes a higher gradient in the temperature versus length along the length of the inner cylinder. The taper from the inner end to the outlet also assists in the movement of the particles and this reduces the load of the hot fluid carrier.

Thus, movement of the particulate laden air through the system results in an optimum distribution of the particulate material in relationship to the tem¬ peratures. The relatively small inlet results in a relatively high inlet velocity which progressively de¬ creases as the particle laden air moves through the progressively enlarging inner cylinder to the discharge end, where it flows about the end of the cylinder and moves in a counterflow direction through the interme- diate passageway. This passageway again defines a progressively increasing volumetric chamber with a con¬ sequent similar flow characteristic and a corresponding maximum resident time of the particulate matter until the material reaches the discharge end of the interme- diate passageway 19 where the direction is again re-

versed for final passage through the outer passageway. In accordance with an optimum construction, the relative volumetric proportions are varied from that which is generally employed in the art. Generally, in accordance with the teachings of the inventors, the outermost pass¬ ageway 20 is of a reduced volume and cross-section while the intermediate passageway 19 is increased to optimize the resident time of the relatively moist particles in the highest temperature passageways while increasing the velocity and therefore decreasing the resident time in the relatively low temperature outer passageway 20. This not only provides for optimum time within the vari¬ ous passageways but results in an optimum support of the dryer particles in the final passageway 20- Thus, generally it is well known that a greatest proportion of the drying occurs within the innermost passageways and generally may be as high as 60 percent of the total drying affect. Once again the intermediate passageway may affect drying on the order of 25 percent while the final passageway affects a final drying of the last 15 percent level of the total drying affect. This has various distinct advantages where the system is proper¬ ly proportioned. For example, in a practical applica¬ tion for the drying of alfalfa, the inlet temperature may be and has been selected as 2100 degrees Fahrenheit. The expanding tapered cylinder 17 associated with the present invention results in more evaporative cooling of the particles and a decrease in the temperature to the order of 600 degrees Fahrenheit at the exit end of the inlet cylinder 17. Further cooling occurs in pass¬ ageways 18 and 20 with a discharge temperature substan¬ tially below 240 degrees Fahrenheit and in a practical application generally of the order of 250 degrees Fahrenheit. The temperature in the first cross over or transfer passageway from inner passageway 18 to inter-

_ O ^~ mediate passageway 19 is thus on the order of 600 de¬ grees Fahrenheit while the discharge temperature is approximately 230 degrees Fahrenheit. As a result, the temperature on the opposite sides of the intermediate cylinder 16 adjacent to the discharge passageway 21 will be at approximately the average of these two tempera¬ tures, namely.600 plus 230 divided by 2 or approximately 415 degrees Fahrenheit. This is significantly smaller than the average temperature in conventional triple pass dryers. The temperature of the intermediate wall 16 at the discharge or drum outlet is therefore corresponding¬ ly reduced in temperature. This is the location where the particles may come to rest on the exterior of cylin¬ der 16 before the particles exit the dryer. Thus, as the dried particles move through the final discharge ^"passageway, and in fact repeatedly come to rest on the exterior surface of the intermediate cylinder just prior to discharge. The particles at this point very closely approach the desired final moisture content and there- fore do not have any affective evaporative cooling. If the drum or cylinder temperature is above a certain level, discoloration of the particles, if not charring or other product degradation may result. For example, when drying of wood flakes or the like, significant dis- coloration of the dried product and a "blue haze" con¬ dition is often created in the usual triple pass dryer because of the temperature distribution. Similarly, in drying alfalfa, the dried product has lost much of its color during the drying process. This is true even though the starting temperature is often only 1600 de¬ grees. The reduction in temperature associated with the present invention essentially prevents such discolor¬ ation and/or -product quality degradation. For example, it has been found that in a practical implementation of the present invention, the dried product is visibly sig-

^' OMPI nificantly improved when compared to a conventional three-pass constant diameter dryer such as widely used in the prior art from the inception of the triple pass drum design. The high inlet temperature with the low outlet temperatures thus not only result in a superior quality product which is both readily analyzed from a technical standpoint but is also visibly apparent. The inlet/out¬ let temperature differential also indicates improved efficiency of operation with a maximum heat conversion in the drying process. Further, the total air volume supplied may be reduced because the product moves more readily thoirughout the system as the result of the ta¬ pered construction. This facilitates use of the single fan section or blower system of the scroll separator such as previously described.

Similarly, similar efficiencies and product quality improvements were noted when the unique dryer apparatus is applied to other materials. For example, in the application of the present invention to a blood meal dryer with an usual operating temperature of the order of 700 to 800 degrees Fahrenheit, a significant improvement in the quality was obtained. Thus the protein level of the blood mean resulting from the pro- cessing through the rotary dryer of this invention was generally on the 1-evel of 93 percent. This is in con¬ trast to a conventional constant diameter rotary dryer wherein the protein level of 85 percent is normally found as acceptable. The air velocity in the outer reduced volume passageway 20 results in a slightly increased flow rate. The particles are relatively fully dried during this final flow through passageway 20 and the increased velocity results in a somewhat improved entrainment of the particles in the air and particularly the small

OMPI dried particles. This holds the fine particles from the hottest temperature area and surfaces and minimized ex¬ cessive particle drying, and particularly protects such particles from dehydration and breaking of the particles into pollutants.

Various modifications to the described struc¬ tures may of course be provided. The intermediate drum may, for example, be tapered to further increase the cross-section, and provide an outer tapered passageway if the constant outer diameter cylinder is used. The surfaces adjacent the discharge area may also be pro¬ vided with insulation to further minimize internal hot spots. Although the present invention is particularly useful in the tirple pass rotary dryer, other rotary dryers with more or less passageways may be constructed "'using a tapered inner cylinder. ^• The reduced profile sys¬ tem could of course be constructed with a single pass rotary dryer. Further, although described as employing hot air as the carrier any other suitable fluid medium may of course be used. These and similar variations and modifications can be provided based on ordinary de¬ sign and no further description is therefore given herein.

The inventors have found that an inner coni- cally shaped cylinder be an essentially smoothe contin¬ uous surface to maintain the progressive change in the diameter of the wall to minimize particle entrainment and entrapment within the dryer.

Claims

-22-Various modes in carrying out theinvention are contemplated as being within the scope of the fol¬ lowing claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the inention.We claim:

1. A rotating dryer apparatus including a plurality of generally cylindrical members mounted on a common axis of rotation and defining a series of interconnected axial passageways including a central inlet passageway means, means for introducing a product laden fluid into one end of said central passageway means and establishing a fluid stream passing axially back and forth through said series of passageways means to an outermost passageway means, means for exiting said fluid from such outer passageway means, at least one of said members spaced radially inwardly of the outer member having a substantially tapered configuration having a relatively small inlet end and a relatively large discharge end and defining a progressively increasing cross-section passageways whereby said fluid enters the inlet end at a substantially higher velocity than the fluid exits from the opposite discharge end of the corresponding member and wherein product movement is facilated through said passageways.

2. The apparatus of claim 1 wherein a second of said members is of a constant diameter and is located adjacent said tapered member to define a progressively increasing flow passageway therebetween.

3. The apparatus of claim 1 wherein said tapered member is surrounded by an intermediate member of constant diameter.

4. A rotating dryer apparatus includinga plurality of at least three generally cylindrical members mounted on a common axis of rotation and defining a series of interconnected axial passageways including a central passageway means, means for intro¬ ducing a product laden fluid into one end of said central passageway means ;and establishing a fluid stream passing axially back and forth through said series of passageways to an outermost passageway means, means for exiting said fluid from such outer passageway means, at least one of said cylindrical members spaced . radially inwardly of said outercylindrical member having a substantially tapered configuration defining a relatively small diameter inlet end and a relatively large diameter discharge end whereby said fluid enters the inlet end at a substantially higher velocity than the fluid exits from the opposite discharge end of-^* the corresponding cylinder.

5. The apparatus of claim 4 wherein a second of said cylinder members is of a constant diameter and is located in adj cent said tapered cylinder to define a progressively increasing flow passageway therebetween.

6. The apparatus of claim 4 wherein said tapered cylinder member is surrounded by an intermediate round cylindrical member of constant diameter. ^•

7. The apparatus of claim 4 wherein said apparatus includes three cylindrical members defining three passageways and the central cylinder has said tapered construction.

8. The apparatus of claim 7 wherein said intermediate and outer passageways are proportioned substantially in>the ratio to the inner cylinder volume of one and one half and of two and one quarter.

9. The apparatus of claim 7 wherein the area of said intermediate and outerpassageways are in proportion and to the inner cylinder substantially in the ratio of one and one half and of two and one half.

10. The apparatus of claim 4 including only three of said cylindrical members and including an :■- :• innermost tapered cylinder, an intermediate constant diameter cylinder and an outer constant diameter cylinder, said cylinders being mounted on a common axis of rotation and offset to define coupling passageways between siad axial passageways.

11. A rotary dryer adapted to support a particle laden fluid stream for drying of the particles comprising an outer cylinder, an innermost tapered cylinder having a genreally conical taper from a small inlet end to a large discharge end and mounted coaxially of said outer cylinder, an intermediate cylinder located intermediate the outer cylinder and the inner cylinder and concentrically of said outer cylinder and defining an intermediate passageway and an outer passageway, said inner cylinder having said large discharge end interconnected to said intermediate passageway by a transfer passageway for transferring the fluid form the inlet passageway into the intermediate passageway, a transfer passageway between said intermediate passageway and said outer passageway adjacent the inlet end of the central cylinder, and a discharge passageway means -i secured to the outerpassageway adjacent to the transfer passageway between the innermost tapered cylinder and the intermediate cylinder at the discahrge end of the dryer.

OMPI

12 The rotary dryer of claim 11 wherein said intermediate cylinder has a constant diameter and said intermediate passageway means has an increasing cross-section from the inlet end of the discharge end.

13. The rotary dryer of claim 11 including means to establish an air temperature at the inlet end of the central cylinder of substantially 2100 degrees Fahrenheit, means for supplying product having 80 percent moisture content, said product being dischargedwith substantially 10 percent moisture content, and said air exiting at a temperature of less than 240 degrees Fahrenheit.

14. The rotary dryer of claim 11 wherein:, said temperature of said air is reduced to the order of 600 degree Fahrenheit at the transfer passageway between the inner passageway and the intermediate passageway.

15. The apparatus of claim 11 wherein the cross-sectional mean area of the inlet to said passageways are with respect to the inner cylinder inlet in the ratio of 1, of 1.5 and of 2.5 to 1.

16. The apparatus of claim 11 wherein the inner and intermediate passageway constitutes in excess of 50 percent of the total volume of the passageway and the volume of said intermediate passageway is significantly greater than said inlet passageway.

17. The apparatus of claimll wherein said inner passageway increases in cross-sectional area by a factor of substantially 1-1/2, said intermediate passageway increases by a factor of 1-1/2 and said outer discharge passage is constant substantially greater than the inlet opening by a factor of 2-1/2.

' L

:PT

18. In a particle drying system having a minimal profile, comprising a rotary dryer having an inlet end adjacent one end of the rotary dryer and a discharge end adjacent the opposite end of the rotary dryer, means for supporting of said rotary dryer for rotation on a horizontal axis, a heat source means mounted adjacent to the one end of the rotary dryer and coupled to supply hot fluid to the rotary dryer, a centrifugal scroll-type separator '> coupled to the discharge end of the rotary dryer and having a first means to discharge clean fluid and separate means to discharge particulate laden fluid, means mounting siad centrifugal separator with a horizontal axis generally in the plane of the horizontal axis of the rotary dryer, a vertical ^"" fluid discharge stack connected to said first means of said centrifugal separator and extending outwardly above the level of the centrifugal separator, said rotary dryer and said heat source means for discharge of the exhaust fluid.

19. The drying system of claim 18 including a cyclone separator connected to separate means of said scroll type separator, said cyclone separator being mounted with its top located generally in the horizontal plane of the rotary dryer.

20. The drying system of claim 18 including a drop-out box located between said separator and said dryer, a cyclone separator connected to said scroll separator and having an air exhaust coupled to said drop-out box to discharge the air from'the cyclone separator to the drop-out box to ^': form a closed air loop.

21. In the drying system of claim 20 wherein said centrifugal separator and said heat source have a substantially smaller dimension than said rotary dryer and are mounted substantially with a common horizontal plane, said dropout box and said cyclone separator being mounted with the upper ends in substantially the plane of the upper end of the rotary dryer.