US2414580A

US2414580A - Heated endless conveyer structure for dehydrating foods

Info

Publication number: US2414580A
Application number: US477437A
Authority: US
Inventors: Birdseye Clarence
Original assignee: Dehydration Inc
Current assignee: Dehydration Inc
Priority date: 1943-02-27
Filing date: 1943-02-27
Publication date: 1947-01-21
Anticipated expiration: 1964-01-21

Description

c. BIRDSEYE 2,414,580 HEATED ENDLESS 'CONVEYER STRUCTURE FOR DEHYDRATING FOODS Jan. 21, 1947;

Filed Feb. 27, 1943 PROOUC T "V quality by removing moisture a manac MATEID ENDLESS CYQNVEYEQ STRUG'IIURE FER DEHYDRA'ZKNG FCINDES Clarence Birdseye, Gloucester, l lllasa, assignor to Dehydration,

line Gloucester,

tion oi Massachusetts Application February 27,, rate, serial No. eraser i Claims.

vide a more rapid and less expensive process and apparatus than have been heretofore available for producing dehydrated food products of high from a product while spread on heat-conductive surfaces in layers of greater thicknessthan can be satisfactorily employed in present types of drum driers.

Drum drying, as heretofore carried out, has

presented two serious disadvantages, ,The first of these drawbacks, has been the necessity for employing only large, smoothly-surfaced, very expensive drum of corrosion-resistant metal; and the second, the need for spreading the prodnot in a very thin-layer upon the drum. This second characteristic requirement of present drum drying is brought about by the fact that if a thicker layer of product is applied to the drum surface, that portion 01' the layer near to the drum becomes scorched before the moisture has been removed from the center and outer portions of the layer. Or, if the temperature of the drum is kept relatively low in order to prevent such'sco'rching and to dry the layer more uniformly throughout its thickness, the drying time is thereby so greatly extended that the cost of the operation becomes excessive. If, on the other hand, an effort is made to decrease the required drying time for a relatively thick layer of product by passing over the outer surface of the product a, hot, arid dehydrating gas, failure results because a case-hardened film or skin is formed on said outer surface and escape of moisture from the center of the layer to the'gas is thereby greatly retarded.

f ion. se se) Mesa, a corpora= 2 If a relatively thick, adhered layer of comesti= ble is heated simultaneously from both surfaces as described above, moisture is driven to its outer surface so rapidly that a dehydrating gas having a relatively high temperature, for example 325 F. may be employed, without danger of scorching the product, because evaporation from the prod= not is sufliciently rapid to prevent such scorching-or'overheating. Moreover, while by present methods of drum drying the thickness of the product layer applied to the drum must usually be less than 1 it is entirely practical by my methods and apparatus. to apply a, product layer as thick as 1%" without either scorching the product or unduly prolonging the drying time.

The process of my invention is characterized by employing a thin and relatively inexpensive band or ribbon of stainless steel or other noncorrosive material aSa. conveyer or carrier for the product layer. In carrying out such process the product comes into contact only with the band or ribbon and there is no necessity for carefully machining the drum or making it of stain- The process of my invention is based largely upon the discovery that if a relatively thick layer of food product adhering to aheated, moving,

heat-conductive surface is subjected to radiant energy applied to the outer surface of the layer, the layer becomes evenly heated throughout its thickness and then may be subjected on its outer surface to a current of very hot, arid dehydrating gas without the formation of a case-hardened skin on the said outer surface. Although I have found that radiant energy, particularly in the form of infra-red radiation, constitutes an adless steel. All that is required is a drum which may be heated and which will properly guide the band in the required path. Another advantage of my process and apparatus is that since heat can be applied to the product by both conduction through the metal band and radiation direct to the product over practically its entire distance of travel from the food hopper to the productremoving knife, the capacity of the apparatus canbe made almost unlimited with relatively low initial cost.

An important field of use for my invention is in dehydrating more or lessviscous masses of food product which may be spread in a thin layer upon a conveyer and caused to adhere thereto by a preliminary drying step. Meat or fish ground and reduced to a paste is ,an example of such products. It is convenient to spread a thin layer of the product upon a substantially horizontal reach of an endless co'nveyer belt where it may be caused to adhere to the belt by heating and then'carried by the belt through an endless path in which it may ascend or descend while being subjected to radiant energy and a current of hot arid gas. Thus is secured a. ver favorable distribution for conthe heat required in the process I am enabled to employ a minimum volume of gas and so efaerated 3 feet considerable saving over processes hereto fore employed. The relatively small volum or dehydrating gas.required in carrying out the process of my invention makes it possible to reduce the size of the apparatus and still operate with high capacity.

Another important advantage of my process is that, while I may use arid gas hotter than the product during theearly stages of dehydration, while substantially all the product surface is still wet and consequently being cooled by rapid evaporation, in the later stages of the process the arid gas may be cooler than the product to which heat is constantly furnished by radiant energy, and by employing this procedure overheating and damage is avoided to those portions of the product which have become so dry that it no longer has the protection of a. substantial amount of surface moisture.

These and other features and characteristics of my invention will be best understood and appreciated from thefollowing description of a preferred form of apparatus'by which it may be put into practice, selected for purposes of illustration and shown in the accompanying drawing in which. Y

Fig. 1 is a view in end elevation, partly in section, of combined drum and belt apparatus,

1 Fig. 2 is a corresponding view in front elevaarranged to rotate about a horizontal axis and an endless conveyer belt IZI which runs on the drum and'over an idler roll I22 mounted at one side thereof and in such position that the upper reach of the belt is guided in a substantially horizontal path. The means for mounting, rotating and heating the drum are omitted from the showing of Figs. 1 and 2 which are more or less diagrammatic in their disclosure of the apparatus. The-drum I28 may be heated by steam connections, not shown, or by any other convenient heating means. The conveyer belt IZI may be of thin flexible sheet metal or of wire mesh or of a moisture absorbing fabric, depending on the product it is desired to dehydrate.

The product to be dried may be supplied to the belt from a hopper I23 located above the horizontal reach of the belt adjacent to the idler roll I22 and serving to spread the product evenly upon the moving surface of the belt. The fiat portion of the conveyer belt between the hopper and the drum I20 passes between spaced electric heating plates IZ I and I25, the latter of which heats both the belt and the product thereon by conduction, and causes the product to adhere to the surfaceof the belt. The heating element IZt is.not in contact with the product on the belt IZI, but radiant energy from said element reaches and heats the product, which at this point is thus heated on both sides and by both conduction and radiation. Another electric heating plate I26 is located adjacent to the conveyer belt where it passes upwardly and forwardly to the idler roll I22 thus serving to heat the belt as it approaches its product receiving station.

- a tion, or otherwise mounted in the apparatus, is a segment-shaped heater I32 of the radiant energy type and this is arranged so as to direct radiant energy upon the product as it is carried on the belt I'2I about the circumference of the drum I220. .The inner chamber within the partition I3I is connected at its upper end through an inlet duct I33 to a fan casing I34 in which is provided heating means so that air or gas may be delivered to the inlet H3 in a hot arid condition and caused to flow through the inner segmental chamber and to sweep in concurrent flow over the product which is be-.

ing carried therethrough upon the belt I20. The partition I3! terminates short of the end of the casing I30 so that the dehydrating gas current, now somewhat cooled by its passage over the product, is directed in a return direction through the outer chamber ofthe casing I30 to an outlet duct I35through which it may be in part recirculated to the fan I34. A duct I36 leads into the outer chamber of the casing I30 below the outlet duct I35 and this serves as a means for removing the spent or partially saturated dehydrating gas for dehydration treatment and heating and also as a means for supplying make-up gas when necessary to the system. A valve or damper I29 located opposite the end of the duct I36 may be manipulated to control the character of the dehydrating gas. An air inlet I28 is provided between the hopper I23 and the end of the heating element I24 and an outlet duct I21 equipped with an exhaustfan' is provided adjacent to the inner end of this heater. A path is thus provided for air to pass in concurrent flow over the product moving toward the drum and for discharging air together with whatever vapor or steam may be driven from the heated product.

A blade I31 is located adjacent to the idler roll I22, in contact with the flexed area of the conveyer belt and is effective to scrape the now relatively dry product from the belt permitting it to fall into the receptacle I38.

The drum I20 may be of any convenient length or diameter commensurate with the capacity desired in the particular apparatus. As herein shown in Fig. 2 the drum and its associated casing I30 are of a width to require two recirculating blowers I36 in order to supply and distribute the requisite volume of hot arid gas. The

hopper I23 15 correspondinglyelongated and a receptacle or receiving hopper I38 is provided in The drum I20 is enclosed throughout part of gitudinally intov two curved chambers by an intermediate partition I3I. Secured to' this partifrom the belt I2I at the edge of the blade I31. The capacity of the apparatus may be increased by moving the idler roll I22 further from the drum IZd thus increasing the total drying area of the belt IZI. T

In carrying out the process of my invention with the assistance of the'illustrated apparatus it will be seen that'the product is delivered to the heated conveyor belt I2I and spread in a thin" layer thereon as it passes from the hopper 23 to the belt in the flat horizontal portion of its travel where there is no tendency to displacement. Throughout the horizontalportion of the path the product layer is preliminarily heated and dried by heat from the hot belt and the heaters I26 and I 25. These heaters and the travel of the belt are so adjusted that the product layer becomes adhered to the belt. Consequently, after the belt passes its point of tangency with respect to the drum I20 and begins to travel downhill in-a circular curved path about the drum, the product is held in position by its adherence to the belt. The thin layer of food product travels with the belt in this adherent condition downwardly about the circumference of the drum and where the belt is deflected in a curved path the product layer is convexly flexed so'that it is elongated and made thinner as compared to its condition upon the horizontal portion of the belt. a The product layer is, of course, outwardly directed While moving in the curved portion of its path. It passes on the drum into the casing I30 where it is subjected to the hot arid gas current and simultaneously to radiant energy supplied by the segmentalheater I32.

In its progress about the circumference of the drum, the product is internally heated by the radiant energy thus supplied, although its maximum temperature is restricted by constant surface evaporation of moisture forced outwardly by the application of radiant energy and conducted heat from the belt. The current of hot arid gas meanwhile becomes somewhat reduced in temperature as the product becomes drier and drier inits progress through the casing I30. Upon leaving the casing the adherent and now dehydrated layer of food product is carried by the conveyer belt upwardly to the edge of the scrap-.. ing blade I31 by which it is removed from the belt and may be discharged from the apparatus.

The present application .is a continuation in part of my copending application, Ser. No. 440,- 967, filed April 29, 1942.

The apparatus shown and described has been selected to illustrate my invention and may be modified in many details of construction within the scope thereof. For example, it has already been suggested that by increasing the distance between the drum I28 and the idler roll I22 a greater length of belt and of drying surface may be made available than can be utilized in apparatus of the proportions illustrated in Fig. 1.

Alternatively the elements of the apparatus may be rearranged as suggested diagrammatically in Fig. 3, that is to say, the drum may be reduced to a pulley and the product dried in the horizontal portion of the belt travel. As shown in Fig. 3 small drums or pulleys I40 and MI may be mounted on substantially the same level and arranged to drive a conveyer belt I42. A heating unit 543 extends between the pillleys in position to support and heat the upper reach of the conveyer belt. A casing I44 encloses the upper reach of the belt between the pulleys and in this is provided a means for supplying radiant heat to the product distributed upon the belt. This means is herein represented as a multiplicity of electric lamps or units I45 and these may be individually or collectively provided with reflecting means for concentrating their radiant energy upon the product being treated. At the inlet end of the apparatus is provided a'hopper I 46 through which the product is delivered and spread in a continuous layer upon the belt I42. An inlet duct I41 for hot dehydrating gas or air enters the casing I44 adjacent to the pulley I40. A corresponding outlet duct I48 is arranged adjacent to the pulley I. A scraping blade I49 is arranged to bear upon the belt as it passes downwardly about the outer side of the pulley I4I to scrape the dehydrated product from the belt I42.

The apparatus of Fig. 3 may require more linear floor space than that of Figs. 1 and 2, but possesses many of the advantages already discussed. The effective area of the'belt I42 may be many times that of a single drum of the type heretofore used in drum drying apparatus. The product is spread upon the belt while the belt is maintained fiat and in horizontal position most favorable for the spreading operation. The product is immediately heated by conduction through the belt from the heater I43 and by radiant energy from the units I45. A continuous current of dehydrating gas sweeps over the product evaporating moisture from its surface, thus holding the temperature to which it may be heated to safe limits and greatly expediting the drying process.

Having thus disclosed my invention and described various details of apparatus for illustrative purposes I claim as new and desire to secure by Letters Patent:

1. Apparatus for dehydrating food products, comprising a heated drum, 'a roll spaced therefrom and disposed at substantially the same level as the top of the drum, an endless conveyer operating in a horizontal path between the drum and roll and following the circumference of the drum thereafter, means for delivering a product to the conveyer in its horizontal path and in an area adjacent tothe said roll, means for heating the conveyer on its way to the drum to cause the product to adhere thereto, a radiant heater disposed concentrically with respect to the drum and arranged to heat the product as it is thinned out upon the conveyer curved upon the drum, and means for directing a current of dehydrating gas to the product and over it in its directionof movement while moving with the conveyer about the path and in an area adjacent to the said roll,

means for heating the conveyer in its horizontal paths to cause the product to adhere thereto and subsequently to be thinned in passing on the conveyer about the circumference of the drum, a casing arranged concentrically about part of the drum, a source of radiant energy in said casing, and means for circulating a current of arid gas through the casing. a

- 3. Apparatus for dehydrating food products, comprising a heated drum, a metallic conveyer movable in an endless path including'a portion of the circumference of the drum, contiguous segmental ducts having a common partition and beingcons'tructed and arranged to embrace a portion of the conveyer upon the drum, and means for directing dehydrating gas in one direction of flow through the inner of said ducts and in the opposite direction through the outer of said ducts.

4. Apparatus for dehydrating food products, comprising a heated drum, a metallic conveyer movable in an endless path including a portion of the circumference of the drum and a. horizontal fiat portion, a contiguous segmental radiant heater forming in part a duct disposed concentricallywith respect to the drum, means for delivering moist food product in a layer upon a flat area of the conveyer whereby the layer may be thinned in passing about the circumference of the drum, and means for directing dehydrating gas to fiow in the duct thus provided.

CLARENCE BIRDSEYE.