GB2118204A

GB2118204A - Energy efficient continuous rendering system

Info

Publication number: GB2118204A
Application number: GB08308199A
Authority: GB
Inventors: William F Schottelkotte
Original assignee: Dupps Co
Current assignee: Dupps Co
Priority date: 1982-04-09
Filing date: 1983-03-24
Publication date: 1983-10-26
Also published as: NL8301102A; SE8301340L; SE8301340D0; DE3310553C2; GB8308199D0; DK157283D0; DE3310553A1; FR2524900A1; AU1259783A; FR2524900B1; AU570199B2; NZ203543A; IT8367377A0; IT1158933B; BE896298A; JPS58187496A; CA1219878A; NO831229L; GB2118204B; SE458528B

Abstract

A rendering system wherein raw materials in the form of animal, poultry and fish by-products are hogged in hogger (5), heated to form a slurry in tank (6), pressed in screw press (9) to divide the slurry into two fractions, the first fraction comprising free-run fluids and soft moisture bearing material, and the second fraction comprising the oversize. The first fraction is fed to an evaporator (14) wherein it is partially dehydrated, the partially dehydrated first fraction and the second fraction from the press being fed via pipes (26, 11) into the inlet end of a cooker (12) wherein the materials are blended and cooked, the cooked material being removed from the outlet end of the cooker for separation of the cooked material into fat and tankage at screw conveyor (28). The moisture vapor from the cooker is collected in trap (15) and fed via conduit (16) to heat the evaporator. Residual solids are removed from fat by centrifuge (31) and fat may be recycled to heat slurry tank (6) via line 34 and/or discharged via line 35. <IMAGE>

Description

SPECIFICATION Energy efficient continuous rendering system This invention relates to the dry rendering of animal, fish and poultry by-products, and has to do more particularly with a continuous rendering system wherein the raw materials are continuously processed as opposed to being processed on a batch or step-by-step basis.

Background of the invention The present invention is based on the type of continuous rendering system taught in U.S.

Patents Nos. 3,506,407 and 3,673,227 which teach a simplified continuous rendering system wherein the raw materials, upon being initially hogged, are subjected to a single cooking and blending operation. While systems in accordance with the subject patents are in widespread use and have been highly successful, their overall efficiency has decreased due to the ever increasing cost of the energy required to operate them. Consequently, anything which can be done to decrease energy consumption will result in substantial savings in the operation of the system.

In addition to the use of cookers to release the fats from the materials being processed, various types of evaporators have been used for such purpose, either alone or in series, with the materials moving from one evaporator to another as the rendering operation proceeds. While evaporators are energy efficient, they nonetheless require much finer grinding of the raw materials than does a cooker, and consequently their overall energy efficiency is diminished, particularly where the nature of the raw materials is such that a substantial amount of energy must be expended to initially process the raw materials for introduction into the evaporators.

The present invention contemplates the utilization of both a cooker and an evaporator, together with an initial separation of the raw materials in a manner which requires substantialiy less energy than would be required utilizing either cookers or evaporators alone.

Summary of the invention In accordance with the invention, the initially hogged materials, in the form of chunks and pieces, are collected in a slurry tank or similar holding vessel and the raw materials heated to a temperature in the range of 1 30-2050F to form a slurry. The slurry so formed is then introduced into a screw press. The function of the press is twofold: first, to allow free-run fluids to drain out of the slurry through the press openings; and second, to separate soft moisture bearing materials from residual solids by means of a pressing action.Thus, immediately following initial hogging and heating, the slurry of raw materials is divided into two fractions, the first fraction comprising the free-run fluids and soft moisture bearing materials, and the second comprising the "oversize" or residual materials which do not pass through the openings in the press.

The first fraction, i.e., the free-run fluids and soft moisture bearing materials, are fed directly to an evaporator, such as a single effect evaporator, wherein the moisture content of the first fraction is reduced. The second fraction from the screw press, i.e., the "oversize", is conveyed directly to a cooker, preferably of the type disclosed in the aforementioned U.S. Patent Nos. 3,506,407 and 3,673,227. A significant feature of the invention resides on the fact that the first fraction, after being partially dehydrated in the evaporator, is also conveyed to the cooker wherein it is admixed and blended with the second fraction and the blended fractions maintained for a residual time sufficient to break down the protein cells and free the fats therefrom, which is accompanied by the release of moisture from the blended fractions.The released moisture is collected and introduced into the evaporator where it serves as the heat source to effect the initial dehydration of the first fraction. Thus a primary saving in energy is effected by utilizing the moisture generated during the cooking operation to operate the evaporator, the evaporator being operated under vacuum to thereby lower the boiling point of the moisture in the first fraction. Efficiencies are also realized in the operation of the cooker in that cooking time is a function of the amount of moisture which must be removed from the materials being cooked.

Since the materials introduced into the cooker will have a reduced moisture content due in part to the initial pressing of the slurry which removes some of the moisture from the second fraction and in part to the partial dehydration of the first fraction in the evaporator, the reduced moisture content of the materials being cooked will require less cooking time and hence less energy in the form of heat required to complete the cooking cycle.

A secondary, yet important, savings in energy results from the use of a screw press to effect separation of the raw materials, as opposed to the use of additional hoggers or other types of mills to reduce the materials to a condition in which they can be fed to the evaporator. For example, a press of a size suitable to form the required fractions at a throughput rate of about 24,000 pounds per hour requires a 50-75 horsepower motor, whereas comparable hoggers or mills require a 300-600 horsepower motor.

Upon the heating of the mixture in the cooker to the desired end point temperature, the mixture is discharged into a draining device where the free-run fat may be separated from the solids by means of gravity drainage. Since the drained fat will contain residual solids, a sediment tank is provided in which the heavier solids are removed, the partially clarified fat being pumped to a decanting type centrifuge where remaining residual solids are removed. The residual solids discharged from the draining device, together with the solids recovered from the sediment tank and from the centrifuge, are conveyed to a finishing press wherein the solids are compacted into a cake. Any residual fats recovered during the final pressing operation are returned to the sediment tank for further clarification.

Description of the drawing Figure 1 is a schematic view of a dry rendering system in accordance with the invention.

Figure 2 is a fragmentary schematic view of a portion of the system illustrating a modification in the manner in which the initially hogged material is heated to form a slurry.

Figure 3 is a fragmentary schematic view of another modification in the manner in which the initially hogged material is heated.

Description of the preferred embodiment An important feature of the present invention resides in the utilization of essentially conventional rendering equipment, and to this end the system of the present invention is particularly adapted for the retrofitting of existing systems utilizing continuous cookers and/or evaporators to achieve material savings in energy consumption, both steam and electrical. The principles of the invention also may be applied to systems utilizing batch cookers, an essential consideration being to effectively increase the throughput of the system per unit of time, thereby decreasing the amount of energy required to process a given volume of materials.

The raw materials to be processed are initially collected in a raw material bin 1 having screw conveyors 2 which convey the raw materials to an inclined screw conveyor 3 which delivers the raw materials to an electromagnet and chute assembly 4 for the separation of tramp metal, the raw materials falling directly from the chute assembly 4 into a hogger 5 which acts to reduce the raw materials to the desired mean particle size. Preferably, the hogger will reduce the material particle size to chunks and pieces approximating 1/2 to 3/4" cubes with no pieces larger than about a 3" cube.

In the embodiment illustrated in Figure 1, the sized raw materials from the hogger 5 are transported to a slurry tank 6 wherein a sufficient amount of hot recycled fat is admixed with the sized raw materials to provide a pumpable slurry.

In this connection, it will be understood that the addition of the hot fat, which is recycled from the fat recovered from the raw materials being processed, acts to initially heat the raw materials and in itself will effect the release of a portion of the fats contained in the raw materials.

Optionally, the hogged raw material may be heated by other means, such as by providing a steam jacket on the slurry tank 6 to which steam is supplied through a steam conduit 7, or by using separate raw material preheaters as will be discussed hereinafter. The essential consideration is the provision of a heated slurry which, in the embodiment of Figure 1, is pumped from the slurry tank 6 by feed pump 8 directly to the screw press 9 which is preferably of the flow through type having one or more screws of diminishing pitch and/or increasing root diameter of the screw shafts, the screw or screws being surrounded by perforated screen or barrel bars, the arrangement being such that as the raw materials are compacted by the screw or screws, the perforated screen or barrel bars will permit free-run fluids to drain from the press.As the raw materials are compacted, the press will separate soft moisture bearing materials from the residual solids. To this end, a retarding choke may be used at the discharge end of the press.

The utilization of a screw press at this stage is an important feature of the invention in that there is a considerable savings in electrical energy due to the fact that the screw press requires substantially less horsepower than other types of equipment, such as the mills heretofore utilized to hydraulically grind the raw materials in their own liquid, i.e., fat and moisture. Thus, instead of utilizing the power necessary to finely comminute the raw materials to the size necessary for passage through an evaporator, the screw press is utilized to obtain a first fraction composed of the free-run fluids and soft moisture bearing materials which can be discharged directly into an evaporator feed tank 10.The second fraction, or "oversize" from the screw press, is conveyed by screw conveyors 11 to the inlet end of the cooker 12, the function and operation of which will be discussed hereinafter.

The first fraction of raw material contained in evaporator feed tank 10 is pumped by evaporator feed pump 13 into the tube side of the evaporator 14, which is of conventional construction, wherein the first fraction of free-run fluids and soft materials is heated by means of atmospheric steam generated in the cooker 12 and conveyed to the shell side of the evaporator by means of an entrainment trap 1 5 and conduit 1 6. Preferably, the tube side of the evaporator will be operated under a 26" Hg. vacuum to lower the boiling point of the water contained in the first fraction; and in accordance with conventional practice, the heated fraction is circulated from the evaporator 1 4 to the separator 1 7 and back through the evaporator several times either by natural circulation or by forced circulation. The water vapor evaporated from the first fraction in the separator is discharged through conduit 1 8 to a condenser 19, the condensate being discharged through conduit 20 to a sewer. Non-condensibles from the shell of the evaporator 14 will be discharged through conduit 21 and combined with the non-consensibles from the condenser 1 9 for discharge through a conduit 22. The discharge conduit 22 may be connected to a scrubber (not shown) to remove obnoxious odors prior to release into the atmosphere. A vacuum pump 23 is used to draw a vacuum on the evaporator 14, separator 17, and condenser 1 9.

After circulation through the evaporator system several times the partially dehydrated first fraction is pumped from the separator 17 by discharge pump 24 and conduit 25, the partially dehydrated fraction being fed through conduit 26 to the entrance end of cooker 1 2 where it is introduced into the cooker along with the "oversize" fraction from screw press 9.

In the cooker 1 2 the "oversize" from the screw press 9 and the partially dehydrated fraction from the evaporator 14 are admixed and heated under essentially atmospheric pressure. Preferably, the cooker will comprise an elongated vessel surrounded by a steam jacket, the vessel having a steam shaft and steam tubes rotatably mounted within the vessel together with agitating means to thoroughly admix the blended fractions as they are heated in the cooker. Alternatively, disc type or batch type cookers may be used.When the mixture is heated to the desired end point temperature, which is preferably about 2750F, it is discharged from the cooker by a suitable discharge control device, such as a variable speed bucket elevator (not shown), onto a screw type conveyor 27 which delivers the mixture to a drainage type screw conveyor 28 wherein the free-run fat is separated from the residual solids by means of gravity drainage through a suitable screen. The drained fat, which contains some residual solids, falls into a sediment tank 29 provided with a screw conveyor 30 arranged to remove solids collected by gravity separation. The partially clarified fat in the sediment tank 29 is pumped to a decanter-type continuous centrifuge 31 which acts to remove residual solids from the fat, the fat being discharged through conduit 32 to fat surge tank 33.From this tank the fat may be either recycled to the slurry tank 6 through conduit 34 or discharged through conduit 35 to a fat storage tank (not shown), or portions of the fat may be simultaneously fed in both directions.

Residual solids from the centrifuge 31 are conveyed by a screw conveyor 36 to the outlet side of the drainage screw 28 where they are combined with the residual solids discharged from the drainage screw, the combined solids being conveyed by a screw conveyor 37 for final pressing in a finishing press of known construction (not shown) which may embody an hydraulic sleeve type choke having automatic compensating characteristics to accommodate variations in the composition of the residual material. Normally the final pressing operation will be conducted under high pressure to remove residual fat which is returned to the sediment tank 29. The solids from the final pressing operation are compacted into a cake and discharged from the system.

In an exemplary embodiment of the invention utilizing a continuous cooker having a heat transfer area of 900 square feet and operating at a steam pressure of 1 50 psi, with the heated raw materials fed to the press at a temperature of 1 650F, and using a vertical evaporator having one-hundred and fifty-three tubes each with a 1.78" inside diameter and a length of 20', the system is capable of a raw material throughput of approximately 24,360 pounds per hour utilizing raw material having a water content of approximately 60% and a fat content of approximately 21%. With the cooker operating at an endpoint temperature of about 2750F, approximately 6940 pounds of water will be evaporated per hour, the moisture vapor from the cooker being collected and utilized to heat the raw material introduced into the evaporator to a temperature of approximately 1 380F under a 26" Hg vacuum, the evaporator acting to evaporate approximately 7460 pounds of water per hour.

The system output is approximately 4580 pounds per hour of finished fat and 5380 pounds per hour of pressed cake or crax having a water content of approximately 4%. The thermal efficiency (pounds per steam per pound of water evaporated) of the system when so operated is .83.

A material savings in energy is achieved by utilizing a screw press to initially separate the free-run fluids and the soft moisture bearing material from the residual solids in that a screw press of a size sufficient to handle the throughput of the system may be operated utilizing a motor which requires only a fraction of the horsepower required to operate the equipment normally utilized to grind the raw material to a size suitable for dehydrating in an evaporator. An even greater savings in energy is realized in utilizing the moisture-vapor generated in the cooker to heat the evaporator. In this connection, at least 50% of the moisture in the raw materials should be sent to the evaporator for the system to operate at maximum efficiency and fully utilize all of the moisture-vapor from the cooker.It is only when exceedingly dry raw materials are encountered that the first fraction will contain less than 50% of the moisture in the raw materials. With the normal seiection and mix of raw materials, first fraction will contain 6080% of the moisture in the raw materials and optimum efficiency will be attained. When exceedingly dry raw materials are encountered, as noted above, the system will operate satisfactorily but optimum efficiency may not be attained.

Modifications may be made in the invention without departing from its spirit and purpose. One such modification is shown in Figure 2 wherein a surge bin 38 is interposed between the logger 5 and the slurry tank 6, the surge bin having a variable speed screw conveyor 39 for delivering the raw materials to the slurry tank, the surge bin being provided with load cells 40 to control the feeding speed of the conveyor 3 which delivers raw materials to the hogger. The provision of the surge bin facilitates the continuous operation of the system by controlling raw material input and ensuring the necessary residence time in the slurry tank to effect the desired heating of raw materials prior to their delivery to the press.

Figure 3 illustrates another embodiment of the invention wherein the raw materials from the hogger 5 are deposited on a screw conveyor 41 which conveys the raw materials through a preheater 42, which may be heated by steam from steam conduit 7a, the heated raw materials being fed from the preheater directly the press 9.

If desired, provision can be made to introduce recycled hot fat into the raw materials through conduit 34a in advance of passage of the raw materials through the preheater 42, the recycled fat serving to supplement the heating action of the preheated. It is also within the spirit of the invention to utilize a surge bin, as shown in Figure 2, with the preheater of Figure 3 to provide additional control over the operation of the system.

Claims

1. In combination in a system for the dry rendering of raw materials in the form of animal, poultry and fish by-products to produce fat and tankage: a. hogger means for initially reducing the raw materials to chunks and pieces, b. heating means for heating the chunks and pieces from the hogger to form a slurry, c. press means for dividing the heated slurry into two fractions, the first fraction comprising free-run fluids and soft moisture bearing material, and the second fraction comprising the oversize, d. evaporator means for receiving the first fraction from said press means and for partially dehydrating the first fraction, e. a cooking vessel having an inlet end and an outlet end, f. means for delivering both the partially dehydrated first fraction from said evaporator and the second fraction from the press means into the inlet end of said cooking vessel, and g. separating means for receiving cooked materials dischaged from the outlet end of said cooking vessel, said separating means acting to separate the fat from the cooked material.

2. The system claimed in nlaim 1 wherein the heating means comprises a slurry tank having means for introducing heated fat therein.

3. The system claimed in claim 1 wherein the heating means comprises a steam heated slurry tank.

4. The system claimed in claim 3 wherein said heating means includes means for introducing heated fat into said slurry tank.

5. The system claimed in claim 1 wherein said heating means comprises a preheater, and means for transporting the raw materials through said preheater.

6. The system claimed in claim 5 including means for introducing heated fat into the raw materials fed through the preheater.

7. The system claimed in claim 1 wherein said press means comprises a screw press.

8. The system claimed in claim 1 including means for collecting moisture vapor generated in said cooker and introducing the collected moisture vapor into said evaporator to serve as a heat source for said evaporator.

9. The system claimed in claim 1 including a surge tank for receiving the raw materials from said hopper, and conveyor means for delivering the raw materials from said surge tank to said heating means.

10. The system claimed in claim 1 including means for inducing a vacuum in the evaporator means.

11. A process for the dry rendering of raw materials in the form of animal, poultry and fish by-products to produce fat and tankage, comprising the steps of: a. initially reducing the raw materials to chunks and pieces, b. heating the chunks and pieces to form a heated slurry, c. pressing the heated slurry to separate it into a first fraction comprising free-run fluids and soft moisture bearing material, and a second fraction comprising the oversize, d. partially dehydrating the first fraction in an evaporator, e. introducing the partially dehydrated first fraction and the second fraction into a cooking vessel and admixing and cooking the fractions in the cooking vessel, and f. removing the cooked material from the cooking vessel and separating the fat from the cooked materials.

1 2. The process claimed in claim 11 including the step of operating the evaporator under vacuum.

1 3. The process claimed in claim 12 including the steps of collecting moisture vapor generated in the cooker and utilizing the collected moisture vapor as the heat source for the evaporator.

14. The process claimed in claim 13 including the step of retaining at least 50% of the moisture initially contained in the raw materials in the first fraction formed during the pressing operation.

1 5. The process claimed in claim 11 including the step of utilizing heated fat to heat the chunks and pieces of raw materials.

1 6. The process claimed in claim 1 5 wherein the heated fat is recycled from the fat separated from the cooked materials.

1 7. The process claimed in claim 11 including the step of utilizing steam to heat the chunks and pieces of raw materials.

18. The process claimed in any one of claims 1 5, 16 or 17 wherein the chunks and pieces are heated to a temperature of from 130 to 2050F.