US2310650A

US2310650A - Drying apparatus and method

Info

Publication number: US2310650A
Application number: US349420A
Authority: US
Inventors: David D Peebles
Original assignee: Golden State Co Ltd
Current assignee: Golden State Co Ltd
Priority date: 1940-08-02
Filing date: 1940-08-02
Publication date: 1943-02-09
Anticipated expiration: 1960-02-09

Description

1943. D. D. PEEBLES 2,310,650

' DRYING APPARATUS AND METHOD Filed Aug. 2, 1940 INVENTOR fla /a eeb/es Wham ATTORNEY Patented Feb. 9, 1943 DRYING APPARATUS AND METHOD David D. Peebles, Berkeley, Oalifl, assignor to Golden State Company, Ltd., San Francisco, Calif a corporation of Delaware Application August 2, 1940, Serial No. 349,420

6 Claims. (01. 159-17) This invention relates generally to apparatus and processes for the manufacture of various powdered products from liquid materials. The invention is particularly applicable to the manufacture of various powdered milk products from lacteal materials such as skim milk.

It is an object of the invention to provide an apparatus and process of the above character which will be capable of relatively high operating economy.

A further object of the invention is to generally improve upon apparatus and processes such 4 as make use of a spray drier in conjunction with a gas washer. The present invention is characterized by the use of a heat exchanger in the liquid circulating path of the washer, and this exchanger also serves as a condenser for evaporating apparatus which rare-concentrates the liquid material being treated.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawing.

The apparatus illustrated diagrammatically in the attached drawing consists of a suitable spray drier III by means of which liquid material canbe converted to powder, As representative of suitable spray drying equipment, I have shown apparatus such as disclosed in my co-pending application Serial No. 349,419, filed Aug. 2, 1940;

Briefly, the spray drier consists of a desiccating chamber l I, into which hot drying gas is continuously introduced by conduit I2 and heater l3. Conduit l2 connects with an annular conduit l4 surrounding the upper portion of the desiccating chamber. Circumferentially spaced louvers l6 communicate between annular conduit l4 and the upper portion of the desiccating chamber, whereby the inflowing gas is directed in a tangential direction to cause a cyclonic movement of gas in the desiccating zone. A cluster of nozzles l1 serves to introduce the liquid material in finely atomized form into the deslccating chamber. Since the individual nozzles are spaced vertically and circumferentially, and are faced at angles of about 45 with respect to radii from the central axis 01 the chamber in the direction of swirling gas currents, the material is in effect atomized into a substantially cylindrically shaped primary drying zone. The majority of the dry powdered material is removed from the lower end of chamber it, together with some gas from within the chamber. e

To effect a final drying the material passes through a secondary chamber l8 which connects with the discharge conduit l9. Conduit l9 discharges into separator 20, the exhaust from which is returned to secondary chamber I 8 by conduit 2|. Another conduit 22 connects with chamber l8 for introducing additional drying gas. Conduits 2| and 22 connect tangentially to cause cyclonic movement in chamber it in the same direction as in chamber it.

The desiccating chamber is also provided with an exhaust conduit 23 which connects axially of the chamber through the top wall, and through which a large proportion of the gas is withdrawn together with some entrained powdered material. A baiiie 23a is interposed between the inlet end of conduit 23 and the nozzles l1. Conduit 23 is shown connected to a washer 24, whereby the exhaust gases are scrubbed with liquid for the removal of entrained powder. This washer can consist of a chamber 25 having a gas exhaust conduit 26, and having its interior equipped with spray head 21.

one or more liquid spray heads 21. The lower end of chamber 25 connects with a liquid drain pipe The liquid supplied to the washer 24 is liquid material being supplied to the, process. Tank 29 is shown for storage of this material, and pump 30 serves to deliver the liquid material through pipes 3i and 28 to a heat exchangeunit 33. Line 34 represents a part of the liquid discharging from heat exchanger 33 being supplied to the In order to maintain a constant level of liquid in the lower part of the washer, pipe 3| is shown provided with a valve 38, controlled by the inner float 31. Pipe 3| thus discharges into the washer chamber 25 at a rate suflicient to-maintain the level of liquid within the chamber substantially constant. Pump 38 in pipe line 28 delivers this liquid under a proper pressure head to the heat exchanger 33 and to the spray head 21.

Pipe 40 connects the discharge side of heat eitchanger 33 with the liquid inlet of the evaporat oi the type disclosed and claimed in Peebies and Manning Patent 2,090,984, which utilizes relativeiy high flow velocities through evaporating tubes. Pump 42 serves to introduce liquid from pipe 40 into the first efiect A. and liquid together with evolvedv vapor from this eifect passes through the separating trap 43. Separated liqtrap (I. is removed by way 01' line 44 for introduction into the second effect B. Line 46 represents introduction of steam into the jacket of the first effect A, while the jacket of the second effect is connected by conduit '41 with the trap 43. Lines 48 and 49 represent removal of condensate and non-condensables from the lower portions of both heating jackets.

Liquid withdrawn from the first effect through line 44 is delivered to the second unit B for further concentration. Vapor removed from the separator 52 of Unit B is delivered by line 53 to the heat exchange unit 33. Concentrate from separator 52 is removed by pump 55 and delivered by line 54 to the storage tank 56. From tank 56 the material is supplied to the nozzles of the spray drier by pump 51 and line 58. s

The heat exchanger 33 can be of the closed tube type in which the tubes through which the liquid circulates are heated by being contacted with vapor received through conduit 53. Pipe 59, communicating with the lower part of the heating jacket, connects with suitable means for removal of condensate and non-condensables.

Operation of the apparatus described above, and the carrying out of the present process, can be outlined as follows: It will be presumed that a lacteal material such as raw skim milk is being treated for the purpose of producing a dry powdered product. This liquid material is delivered from tank 29 through pipes 3i and 28 to theheat exchanger 33. As the skim milk leaves the heat exchanger 33, it is at an elevated temperature, and this temperature is delivered in part to the spray head 21 of the washer 24. Within this washer the liquid is intermingled with gas being received from the spray drier l0, and thus solid particles are taken up by the liquid from the gas, while the washed gas discharges through the conduit 26. The liquid collecting in the lower part of the washer is re-circulated through the heater 33. This collected liquid is at a substantially lower temperature than the temperature' of liquid supplied to pipe 34 and spray head 21, due toevaporation of moisture within chamber 25, while the liquid material is in contact with gas from the spray drier. Evolved vapor is absorbed by the gas from conduit 23 and passesout through conduit 26.

That part of the liquid material which is diverted from the heat exchanger 33 by way of line 40 enters the first efiect A of the evaporating apparatus. Concentrated liquid material being withdrawn by pump 55 from the second effect B is delivered by pipe 54, tank 56, pump 51 and line 58 to the atomizing nozzles of the spray drier I0. Where higher concentrations are required than are possible with a single pass through the two efiects of the evaporating apparatus, a certain amount of the concentrate delivered by pump 55 can be returned to the first stage by way of line 6|.

A partial vacuum is maintained upon the evaporating apparatus by virtue of the fact that the heat exchange unit 33 serves as a condenser for vapor supplied through conduit 53'. Thus, the heat exchanger 33 serves two important functions, namely it serves to preheat liquid being circulated through the washer 24, and it also serves as a condenser to maintain a partial vacuum upon the evaporating apparatus.

In one instance in which th invention was used for the purpose of producing dry skim milk powder, the raw skim milk was delivered by pump 38 at a temperature of 130 F., and was discharged from heat exchanger 33 at a temperature of 157 F.

With respect to operation of the washer 24, spraying the liquid material within this washer not only serves to remove and recover powder entrained with gas exhausting from the spray drier, but in addition a substantial amount of vapor is evolved from the hot liquid, which vapor is exhausted through conduit 26. Thus, liquid material being circulated through the washer is subjected to concentration by.evaporation, in addition to subsequent concentration in the evaporating apparatus 4 I.

Because of the particular way in which the heat exchanger 33 is incorporated in the apparatus and process, the invention affords utmost operating economy. Also, the apparatus is capable of high capacity for a given size of spray drier employed.

I claim:

1. In processes for treatment of liquid materials to produce powdered products, whereinthe raw liquid material is first circulated successively through preheating and washing operations and is then concentrated in an evaporating operation, after which it is subjected to spray drying, the spray drying operation being characterized by exhaust of gas from a desiccating zone together with some powdered material, the exhaust gases being supplied to the washing operation, the improvement comprising utilizing vapor evolved in the evaporating operation for supplying heat to the preheating operation, whereby conditions of partial vacuum are maintained for the material being evaporated and whereby heated vapor evolved in the evaporating operation is utilized to heat liquid material being circulated through the washing operation and being supplied to the evaporating operation.

2. In processes for treatment of liquid materials to produce powdered products, wherein the liquid material is successively preheated, concentrated by evaporation and then subjected to a. spray drying operation, the spray drying operation being characterized by continuous removal of drying gas from the desiccating zone together with some entrained powder, the improvement comprising the steps of continuously re-circulating liquid material into contact with said gas to remove entrained powder from the gas, preheating the liquid material being so re-circulated by transferring heat to the same from vapor evolved from the evaporating operation, and continuously diverting a part of the liquid material being recirculated for-supplying the same to the evaporating operation.

3. In processes for treatment of liquid materials to produce powdered products, characterized by use of spray drying apparatus, a washer receiving gas exhausted from said spray drying apparatus, a vacuum evaporator, and a heat transfer unit for preheating raw material being supplied to the process, the steps of continuously circulating the raw liquid material through said heat transfer unit and through the washer, diverting a part of the liquid material being so circulated and introducing the same into the vacuum evaporator to effect concentration of the same, supplying the concentrate to the spray drier, and conveying the vapor evolved from the vacuum evaporator to the heat transfer unit, whereby the heat transfer unit serves to condense such vapor.

4. In apparatus for the treatment of liquid materials to produce powdered products, spray drying apparatus adapted to convert liquid material into powder, said apparatus having an exhaust conduit for removing gas together with some entrained powdered material, a washer connected to said conduit, a heat, exchange unit, means for circulating liquid material through said heat exchange unit and through said washer, vacuum evaporating apparatus, a connection serving to divert part of the liquid material circulating through the heat exchange unit to the evaporating apparatus, a connection serving to supply concentrate from the evaporating apparatus to the spray drier, and means for forming a vapor connection from the evaporating apparatus.

to said heat transfer unit, whereby the heat transfer unit serves as a condenser for the evaporating apparatus.

5. In processes for treatment of liquid materials to produce powdered products, wherein the liquid material is first concentrated by evaporation and then subjected to a sp y drying peration, the spray drying operation being characterized by continuous removal of drying gas from the desiccating zone together with some entrained powder, the improvement comprising the step of condensing vapor evolved from the liquid material in the evaporating operation by transfering heat from such vapor to liquid material being supplied to the process, and washing gases withdrawn from said desiccation zone by contact with liquid material passed through said last named step, whereby said liquid material is cooled, and reusing said liquid material after such cooling for condensing vapor evolved from the liquid material in the evaporating operation.

6. In processes for treatment of liquid materials to produce powdered products, wherein the liquid material is first concentrated by evaporation and then subjected to aspray drying operation, the spray drying operation being characterized by continuous removal of drying gas from the desiccating zone together with some entrained powder, the improvement comprising the step of condensing vapor evolved from the liquid material in the evaporating operation, utilizing for the condensing operation a heat exchange operation in which heat absorbed from the vapor is transferred to liquid material being supplied to the process, washing gases withdrawn from said desiccating zone by contact with liquid material immediately after it has passed through said last DAVID D. PEEBLES.