CA1124059A - Drying process and apparatus for accomplishing the same - Google Patents

Abstract

UNITED STATES PATENT APPLICATION

Of: John M. Chambers For: DRYING PROCESS AND APPARATUS
FOR ACCOMPLISHING THE SAME

Abstract of the Disclosure There is provided a process and apparatus for drying wet solid material. The process comprises introducing wet solid material into a dryer bringing the material into contact with one side of a plurality of heated surfaces located in the dryer and vaporizing liquid contained in the wet solid material. The vaporized liquid is withdrawn from the dryer and compressed to a pressure greater than the pressure in the dryer and then returned to the other side of the plurality of heated surfaces where, upon condensation, the latent heat energy is released therefrom and is used to vaporize liquid contained in wet solid material on the opposite side of the heated surfaces and withdrawing the condensate from the heated surfaces and substantially dried solids from the dryer.
The drying apparatus provided comprises a housing having entrance and exit openings and means for delivering ma-terial to be dried into and dried material from the housing located in the opening and closing and isolating the interior of the dryer from the outside atmosphere. A plurality of hollow heat exchange means are disposed in the interior or the dryer housing and are connected to an external heat source and to the atmosphere, In addition, compressor means are connected to the housing in the vicinity of the entrance opening and to the hol-low heat exchange means, the compressor means operating at posi-tive pressure with respect to the pressure in the housing so that vaporized liquid is withdrawn from the housing or compressed and then led to the hollow heat exchange means where it is condensed, giving up its latent heat energy and thus vaporizing the liquid in wet solid material on the opposite surfaces of the hollow heat exchange means.

Description

CHAMBF -10 ll~
11 ,, ',1 t~
. il 1 , This inven~ion relates to a drying process and ap-

-2 ll paratus for accomplishing the same. More particularly, the in-vention relates to a vapor recompression drying process and 4 1 apparatus for carrying out such a process.
5 ¦ Background of the Invention 6 In a wide variety of industrial processes the primary :` 7 product or by-produc~ is at one tlme or another present as ` 8 ~ solid materia] wet with a liquid. This solid material must be 9 I produced as a "dried product". The drying operation is normally 10 ll carried out in a so-called dryer.
i 11 There are two primary types of dryers. In one primary ; 12 type, heat surfaces heated by steam under pressure are provided 13 1 and the wet solid material being dried does not come into 14 I direct contact with the steam. In the other primary type, hot I :
gasses are brought into direct contact with the wet solid mate-16 rial. In each case, the heat added must equal the sensible 17 heat of the mass plus the latent heat of vaporization of the 18 ~' liquid present in the wet soLid material. The liquid after 19 ' being vaporized is usually swept away with air or an inert 20 1 gas in dryers that utilize heated surfaces or by the hot gasses 21 1 themselves in dryers which function by direct contact drying.
22 ¦ While the primary types of dryers mentioned are satis-23 1 factory and have achieved wide commercial acceptance, they are 24 generally somewhat undesirable from the viewpoint of efficiency 1 with respect to heat utilization. For example, in known heated 26 1I surface evaporators and dryers employing direct contact with 27 1¦ hot gasses, the vaporized liquid from the wet solid material 28 1 is generally simply removed, collected and optionally condensed 29 ¦ without any utilization of the latent heat energy possessed ' thereby. Consequently, such known systems are disadvantageous , , .
;: :

C~AMB. i-10I

1 , in this respect, as well as requiring large amounts of heat 2 I energy to provide a substantially dry product, and there exists

3 ¦ a need for providing a drying process for a wet solid material

4 and an apparatus for achieving the same which do not exhibit the above mentioned short-comings. The present invention fulfill~
6 this need.
7 Brief Statement of the Invention 8 1 In accordance with this invention ~here is provided g 1, a process for drying wet solid material comprising introducing lO li the wet solid material into a dryer bringing ~he wet solid 11 material into contact with one side of a plurality of heated 12 l; surfaces located in the dryer andvapor~ing liquid conta~ed in ~ewet 3 1,l solid material, withdrawing the vaporized liquid from the dryer 4 1 and compressing the vaporized liquid to a pressure of at least from a~out 9 p.s.i.g. or more greater than the pressure in 16 the dryer and returning the compressed vapor to the other side 7 l of the plurality of heated surfaces in the dryer, condensing 18 the compressed vapor and vaporizing liquid contained in wet 19 solid material on the opposite side of the plurality of heated 20 1 surfaces with the latent heat of the condensate, and withdrawing 21 1 the condensate from the plurality of heated surfaces and sub-22 ¦ stantially dried solids from the dryer.
23 ¦ Further in accordance with this invention there is 24 provided drying apparatus for carrying out the drying process which comprises a~ housing, entrance and exit openings located 26 ¦ at opposite ends of the housing, means for delivering material 27 ¦ to be dried into and dried material from the housing disposed 28 ¦ in the respective openings and closing and isolating the interior 29 ~ o the housing substantially completely from the outside atmos-30 1 phere, a plurality of hollow heat exchange means located in the , 4 CHAMBEE~S- 10 ~ l i 1 i`, interior of the housing and connected to an external heat 2 l' source and to the atmosphere, and compressor means for with-3 drawing vaporous materials ~rom the housing and compressing the 4 vaporous materials connected to the housing in the vicinity of the entrance opening and to the plurality of hollow heat 6 exchange means.
7 The Drawings 1 8 ,l~ In order to illustrate the process and apparatus of 9 ll this invention more fully, attention is directed to the accompanyl , ing drawings which are to be taken in conjunction with the fol- !
11 lowing description and wherein:
12 . FIG. 1 is a view in elevation of a drying apparatus 13 " in accordance with the invention suitable for acomplishing the 14 , process and showing in detail the interior arrangement and dis-position of the hollow heat exchange means;
16 FIG,2 is a plan view in detail of a hollow heat ex- ¦
17 change means supported on the interior wall of the housing; and 18 FIG.3 is a plan view in detail showing a hollow heat 19 1' exchange means supported along the rod which lies along the central axis of the housing.

~3 i I

5~
CHAMB 1,-10, Description o~ the Pre~erred Embodiments It is to be understood that in its broad aspects the ; 2 11 present invention incorporates a compressor and a heated surface evaporator or dryer, the compressor taking the vaporized liquid 4 as it is driven from the wet solids material at the pressure in the dryer interior, which is generally substantially atmospheric ¦

6 pressure, and compressing it in a range of from about 9 to about

7 20 p.s.i.g. additional pressure. The higher pressure vapor is

8 ~ ~ then used at the heat source for the purpose o~ heating the g 1 heated surfaces and as it condenses, the latent heat energy 10 '~ therefrom heats the wet solid material adjacent the opposite 11 sides of the heated surfaces and vaporizes the liquid contained 12 Ij therein while a portion of the higher pressure vapor is passed 13 li directly into the housing of the dryer and through solid material 14 , therein to aerate the same and expedite flow through the dryer.
A primary factor to be considered in carrying out the 16 process of this in~ention with the apparatus thereof is vapor 17 ; loss. The dryer apparatus should be vapor tight so that vapor- , 18 ~ ous material is not lost if the dryer is operated above atmos-19 ~ pheric pressure or air is sucked in if it is operated below atmospheric pressure.
21 The Drying Apparatus 22 Turning more particularly to Fig. 1, the drying appara-¦
~ 23 tus comprises a generally circular housing 11 which may be made .1 24 1 of any suitable material such as stainless steel or the like, 25 ¦ The housing is provided with enkrance and exit openings 13 and 26 ¦ 15, respectively. Means for delivering material to ~e dried into¦
27 il and dried material from the housing such as screw conveyors 17 2~ 1 and 19, respectively, are disposed in the openings 13 and 15, 29 ~l closing and isolating the interior of housing substantially completely from the outside atmosphere. It is to be understood ':

CHAM:~r'n S -10 , f f l that the interior of the housing should be substantially vapor 2 " tight so that vapor in the housing is not lost if the pressure 3 l~ in the housing is above atmospheric or, if below atmospheric, 4 1 air will not be sucked into the housing. In this connection, 5 1I the means such as screw conveyros 17 and 19 are made to fit with 6 I close tolerances in the openings 13 and 15. The screw con~eyors I
7 ll are connected by a rod 21 passing through the central axis of the¦
8 housing and are driven by an external power source 23.
g A plurality of hollow heat exchange means, which are of metal construction and some of which are hollow donut-shaped 11 trays such as shown at 25 and some of which are hollow disk- I
12 shaped trays such as shown at 27 are dispoed along the interior f 13 of the housing.
14 ~ The hollow donut-shaped trays, such as shown at 25, 5 ` are circular and fixed to the interior wall of the housing in 16 any convenient manner, such as by supports (not shown).
17 The donut~shaped trays have a diameter substantially 18 equal to the internal diameter of the housing and are provided 19 , with two circumferential openings such as shown at 29 and 31 in 20 1I Fig. 2 which are substantially opposite each other and aligned 21 1, with openings such as shown at 33 and 35, respectively, in the 22 I housing 11. In addition, the central openings of the donut-23 !I shaped trays such as shown at 37 o Fig. 2 are relatively large, 24 ¦¦ the main body portion of the trays extending inwardly from the I circumferen~ial periphery towards the center axis of the housing 26 'f for a distance equal to about one-half to three-quarters of the 27 1I radius of the housing.
28 1l In contrast, the hollow disk-shaped trays which are 29 f likewise circular, have relatively small central openings such as shown at 39 in Fig. 3 with the main bodies of the disks ex-tending outwardly from the central axis of the housing for a distance equal to about one-quarter to one-half the radius of the housin~. The hollow disk-shaped trays are fixed to the interior wall of the housing in any convenient manner, such as by supports (not shown).
In addition, the hollow disk-shaped trays are pro-vided with openings 41 and 43, as shown in Fig. 3 which coope-rate with openings such as shown at 45 and 47 in the housing 11, being connected thereto through lines or conduits 49 and 51.
It is to be understood that seals, collars or other suitable joints or the like are employed to isolate the main body of the interior of the dryer housing at those locations where the openings in the trays and the housing and/or con-duits and the housing join each otherO
As can be seen from referring to Fig. 1 the interiors of the trays connect through openings in the housing such as shown at 35 and 47 to the outlet manifold 69 and liquid trap 71.
~n the other hand, the interiors of the trays are connected through openings in the housing such as shown at 33 and 45 through manifold means 53 to an external source of live high pressure stream 55 which in turn is connected in any convenient manner upstream therefrom to compressor means 57 which is con-nected to the interior of the housing 11 in the vicinity of the entrance opening 13 in any convenient manner.
It is to be understood that where the hollow heat ex-change means, such as the described trays are heated by an ex-ternal source of heat other than steam, such as, for example from an electrical source, the compressor may be directly con-nected to the interior of the trays through manifold means 53.
In a preferred form of apparatus, means such as con-duit or line 59 connects compressor means 57 directly to the ,46,~

- C~AMB~ 10 ; 1 , interior of the dryer from its downstream or compression side ~:: 2 ! so that a portion of compressed vaporous material removed from 3 ll the interior of the dryer can be returned directly into the 4 interior of the dryer and directly into contact with solid 5 material moving through the dryer to aerate the same and facili-` 6 1 tate the movement of the solid material through the drier.
7 1 In addition, conduit or line 61 provided with a suit-able pump 63 is provided at the exit end of the dryer to lead g 'i the dried material to collection or storage bin 65. Conduit or 10 ' line 61 is provided with a lead-in conduit 67 connected to a - 11 source of cold air (not shown) which serves to further cool the ~2 dried material and aid in moving it into bin 65.
13 The Process .
14 I While the drying process of this invention, as set .
forth broadly above, can be carried out under widely varying 16 temperatures and pressures, it is to be understood that the 17 ! temperature of the heated surfaces should be at least high enough 18 so that vaporization of liquid contained in the wet solid mater-19 , ial brought in~o contact with the heated surfaces will occur.
20 1 On the other hand, the temperature should not be so high that it 21 ,~ results in burning or decomposition of the solid material from 22 ¦¦ which the contained liquid is driven by vaporiza~ion. Moreover, 23 ¦¦ the particular temperature range suitable for drying a particu-24 ¦¦ lar wet solid material in accordance with the process of this 25 ¦ invention will be dependent upon the solid material per se and 26 ! the liquid contained therein and is readily determinable by 27 1 routine experimentation and calculation. In general,however, 28 1 temperatures in a range of from at least the temperature suf-29 1 ficient to cause vaporization of the liquid contained in the wet solid material being dried up to about 300F. or more are .
, 5~

generally employed in carrying out the process of this invention~
Furthermore, the heated surfaces located in the dryer can be brought to the desirable temperature from any convenient out-side source. For example, such heat may be, and is preferably, derived from an external source of live high pressure steam.
Like the temperature, the pressure employed in carry-ing out the drying process of this invention may vary widely.
The pressure within the dryer may be simply atmospheric pres-sure, or lesser or greater than atmospheric pressure. In general, however, the pressure employed within the dryer is ; generally at or near atmospheric pressure. On the other hand,the vaporized liquid is withdrawn from the dryer at a positive pressure at least sufficient to move the vaporized liquid from ;~ the dryer, after which it is compressed to an additional pres-sure of from at lecast about 9 p.s.i.g. or more greater than the pressure in t~e dryer and preferably to a pressure of at least about 20 p.s.i.g. or more greater than the pressure in the dryer. Compressior, results in increased heat energy. While the particviar amount of increased heat energy ~chieved wil~l depend upon the particular vaporized liquid being compressed as well as ihe par'cicular amount of pressure increase to which ; it is subjected by compression, the increased heat energy achievea and thus the increase in heat efficiency for any given -vaporized liquid is readily determinable by calculation~ For example, where the liquid is water, which has about 1000 BTU's per pound of latent heat, the energy required to compress vaporized steam through a 20 p.s.i.g. increase is about 100 BTU's per pound, thus giving the equivalen$ of about a ten-fold increase in heat efficiency.

,~ s .. ?
~ , , CHAMB~-S-10 .' I
l j As previously mentioned, the compressed vapor is the~
2 ~I returned to the other side of the plurality of heated surfaces 3 !l in the dryer where condensation thereof takes place and the 4 latent heat thereof is released and vaporizes liquid contained in wet solid material on the opposite side of the plurality of 6 ! heated surfaces, the condensate then beLng withdrawn from the 7 1! heated surfaces and discarded or recovered and used for other 8 ~~ purposes as desired. In this connection, it is to be understood ,

9 , that when carrying out the process of this invention where the ~ plurality of heated surfaces located in the dryer are heated 11 from an external source of heat other than steam, such as, for 12 example, an electrical source, the compressed vaporous liquid is ~` 13 led directly from the compressor to the plurality of heated 14 ' surfaces. On the other hand, where the external heat source is :,, 'I i live high pressure steam, compression takes place upstream 16 from the source of steam and the compressed vapor is led to the 17 plurality of heated surfaces with ingoing steam. In both cases, i, 18 however, the heat exchange means are brought to the desired 19 temperature by the steam or other external source of heat and 20 ~I by the latent heat of the compressed vaporized material, thus 21 I providing increased heat utilization or ef~iciency.
22 ~1 A wide variety of wet solid materials may be dried wit~
23 ,j the process and apparatus of this invention. ln general, any 24 i¦ wet solid material which contains vaporizable liquid can be 25 1I dried in the apparatus in accordance with the process. As 26 ~ exemplative, but not limitative, materials, there may be men- j 27 I tioned proteinaceous materials such as fish meal containing 28 essentially alcohol as the liquid, as well as other protein-29 aceous materials containing essentially alcohol and/or water as the liquid. Another exemplative solid material is stillage ' ' 5~1 CHAM~ S-lO;i ' I , il i . l I resulting from the fermentation of grains in the manufacture of 2 ' various products such as distilled spirits, beer and the like 3 ~ which generally contains essentially water as the liquid. Nu- ¦
4 1 merous other wet solid ma~erials which can be readily dried by 5 ~ the process of this invention utilizing the apparatus thereof 6 l~ will be readily apparent to those skilled in the art.
. 7 1l It is to be understood that this invention is not to 8 '~ be limited to the embodiments disclosed herein, there being many I g i variations thereof which can be made without departing from the .` `.
:. 10 ' spirit and scope of the inventive concept hereof as defined in 11 the appended claims , 29 , . .

Claims (19)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A process for drying wet solid material comprising introducing said wet solid material with the exclusion of air into a dryer at above atmospheric pressure, bringing said wet solid material into contact with the outside sur-faces of a plurality of hollow plates located in said dryer, heated within by condensing recirculated vapor and vaporizing liquid contained in said wet solid material, withdrawing the vaporized liquid from the solid inlet end of said dryer and compressing said vaporized liquid to a pressure of at least from about 9 p.s.i.g. or more greater than the pres-sure in said dryer and returning the compressed vapor to the inside cavity of the said plurality of hollow plates in said dryer, condensing said compressed vapor within the hollow plates and vaporizing liquid contained in wet solid mate-rial on the outside surfaces of said plurality of hollow plates with the latent heat of the condensing compressed vapors, and withdrawing the condensate from the inside of said plurality of hollow plates and substantially dried solids from said dryer.

2. A process according to claim 1, wherein about 15 percent or more of the compressed vapor with 40°F or more super heat is recirculated directly into the solid outlet end of the dryer and into direct contact with said mate-rial moving through said dryer.

3. A process according to claim 1, including using a source of steam connected to the plurality of heating ele-ments located in the dryer to start the drying cycle, then shutting off said steam as the compressor is turned on.

4. A process according to claim 1, including heating the plurality of heated surfaces located in the dryer with electric heaters to start the drying cycle, then turned off once the compressor is operating.

5. A process according to claim 1, wherein the vapor-ized liquid is compressed to a pressure of at least about 20 or more p.s.i.g. greater than the pressure in said dryer.

6. A process according to claim 1, wherein the solid material is fish meal and the liquid contained therein is essentially alcohol.

7. A process according to claim 1, wherein the solid material is protein and the liquid contained therein is essentially alcohol.

8. A process according to claim 1, wherein the solid material is protein and the liquid contained therein is essentially a mixture of alcohol and water.

9. A process according to claim 1, wherein the solid material is from stillage and the liquid contained therein is essentially a mixture of alcohol and water.

10. A process for drying wet solid material comprising introducing said wet solid material with the exclusion of air into a dryer at above atmospheric pressure, bringing said wet solid material into contact with the outside sur-faces of a plurality of heated hollow heat exchange means located in said dryer and heated within by condensing recirculated vapor, and vaporizing liquid contained in said wet solid material, withdrawing the vaporized liquid from the solid inlet end of said dryer and compressing said vaporized liquid to a pressure in a range of from at least about 9 to about 20 or more p.s.i.g. greater than the pressure in said dryer, returning the compressed vapor to said dryer to the inside cavity of the said plurality of said heated hollow heat exchange means, condensing said compressed vapor within said heated hollow heat exchange means and vaporizing liquid contained in wet solid material on the outside surfaces of said heated hollow heat exchange means with the latent heat of the condensing compressed vapors and withdrawing the condensed liquid from within said hollow heat exchange means and substantially dried solids from said dryer while recirculating a portion of said compressed and super-heated vapor directly through said dryer in direct contact with solid material moving through said dryer.

11. A process according to claim 10, wherein about 15 percent of the compressed vapor taken directly from the com-pressor discharge and highly superheated is recirculated directly into the solid discharge end of the dryer and into contact with solid material moving through said dryer.

12. Drying apparatus comprising a housing, entrance and exit openings located at opposite ends of said housing, means for delivering material to be dried into and dried material from said housing disposed in the respective open-ings and closing and isolating the interior of said housing substantially completely from the outside atmosphere for operation above atmospheric pressure, a plurality of hollow heat exchange means located in the interior of said housing and connected to an external inert source and to the atmosphere and compressor means for withdrawing vaporous materials from said housing and compressing said vaporous materials for delivery to or return of at least a portion thereof to said heat exchange means.

13. Drying apparatus according to claim 12, wherein said external heat source is a source of steam and said con-nection of the hollow heat exchange means to atmosphere is for discharge of condensate; and said compressor means is adapted to withdraw materials from said housing at the solid inlet end thereof.

14. Drying apparatus according to claim 12 or 13, where-in said compressing means is adapted to compress said vaporous materials for delivery to or return of at least a first portion thereof to said heat exchange means, and a second portion thereof to the interior of said dryer housing in the vicinity of said solid discharge opening.

15. Drying apparatus comprising a housing, entrance and exit openings located at opposite ends of said housing, means for delivering material to be dried into and dried material from said housing disposed in the respective openings and closing and isolating the interior of said housing substantially completely from the outside atmosphere for operation above atmospheric pressure, a plurality of hollow heat exchange trays located in the interior of said housing and connected to an external source of steam and to the atmosphere for discharge of condensate, compressor means for withdrawing vaporous materials from said housing at the solid inlet end thereof and compressing said vaporous materials, for delivery to an additional vessel in the vicinity of the solid discharge opening and provided with a superheated steam connection and means connecting the interior of said housing and said compressor means directly with each other for passing at least a portion of compressed vaporous material directly from said compressor means to the interior of said housing.

16. Drying apparatus according to claim 15, wherein said additional vessel is a distillation column.

17. Drying apparatus comprising a housing, entrance and exit openings located at opposite ends of said housing, means for delivering material to be dried into and dried material from said housing disposed in the respective openings and closing and isolating the interior of said housing substantially completely from the outside atmosphere, a plurality of hollow heat exchange trays located in the interior of said housing and connected to an external heat source and to the atmosphere, said hollow heat exchange trays being supported on the interior wall of said housing, at least some of said hollow heat exchange trays extending around the interior wall of said housing and inwardly towards the center thereof and having large central openings and the others of said hollow heat exchange trays having small central openings and extending outwardly partially toward the interior wall of said housing and being alternately disposed along the interior of said housing with respect to the trays having large central openings, compressor means for withdrawing vaporous mate-rials from said housing and compressing said vaporous mate-rials connected to said housing in the vicinity of the entrance opening and to said plurality of hollow heat exchange trays and means connecting the interior of said housing and said compressor means directly with each other for passing at least a portion of compressed vaporous mate-rials directly from said compressor means to the interior of said housing.

18. Drying apparatus according to claim 17, including a source of live high pressure steam located between the compressing means and the plurality of hollow heat exchange trays located in the interior of said housing.

19. Drying apparatus as defined in claim 17, wherein the means for delivering material to be dried into and dried material from the housing disposed in the respective entrance and exit openings are screw feeders.