IE84315B1 - A process for producing purified tallow - Google Patents

Abstract

ABSTRACT A process for producing purified tallow compri ses the steps of adjusting the temperature of rough tallow to a temperature of (750) to (80°C), delivering the temperature adjusted tallow into a tallow bath, and rotating a filtration drum through the tallow in the bath, the drum having a filtration media on the outer surface thereof and having an interior for receiving filtered tallow. The tallow is drawn through the filtration media by applying a vacuum to the drum interior. The filtered tallow received in the drum interior is separated form entrained air. The process involves heating the filtered tallow to a temperature of approximately (137°C) and applying a pressure of about (3) bar abs to the heated tallow for a period of about (20) minutes to produce sterilised purified tallow.

Description

“A process for producing purified tallow” Introduction The invention relates to a process for producing purified tallow.

Rendering processes are used to treat waste by—products from meat slaughterhouses and cutting plants. The materials which are rendered include non-saleable tissues such as internal organs; hooves; feet and jaws; blood; intestines and stomachs: skeletal bones; and extraneous materials.

Such materials tend to have a high level of bacterial contamination due to their origin and non—refrigerated means of storage and distribution in air. The latter also contributes to deterioration in tissue quality due to an increase in their fat content of free fatty acids and oxidative rancidity. This means that rendering plant tallow is of lower grade than other fats.

There is therefore a need for a process for producing purified tallow which will not only reduce waste disposal but also provide a product which is fit for re-use in other products such as animal feed.

Statements of Invention According to the invention there is provided a process for producing purified tallow comprising the steps of: adjusting the temperature of rough tallow to a temperature of from 75° to °C; delivering the temperature adjusted tallow into a tallow bath; rotating a filtration drum through the tallow in the bath, the drum having a filtration media on the outer surface thereof and having an interior for receiving filtered tallow; drawing the tallow through the filtration media by applying a vacuum to the drum interior; separating the filtered tallow received in the drum interior for entrained air; heating the filtered tallow to a temperature of approximately 137°C; applying a pressure of about 3 bar abs to the heated tallow for a period of about 20 minutes; and delivering the sterilised purified tallow to a storage tank. ln one embodiment the process comprises the steps of:- delivering rough tallow at a temperature of about 110°C from a rendering process into a reception tank; adjusting the temperature of the tallow in the reception tank to a temperature of from 75°C to 80°C ln another embodiment the process comprises the steps of:- delivering the temperature adjusted tallow into a buffer tank; and circulating tallow from the buffer tank to the tallow bath to maintain a substantially consistent level of tallow in the bath.

Preferably the filtration drum is rotated through the tallow bath at a speed of from 2 to 3 revolutions per minute.

The vacuum maintained in the interior of the filtration drum is approximately 300mbar.

In one embodiment the step of removing deposits from the filtration medium as the drum is rotated. The deposits may be removed periodically. Alternatively, the deposits may be removed continuously as the drum is rotated.

In one embodiment the filtered tallow is separated by leading the filtered tallow and entrained air through a cyclone separator under a vacuum.

In a preferred embodiment the separated tallow is delivered into a pre-sterilisation storage tank and the separated tallow is pre-heated in the pre-sterilisation storage tank to a temperature of from 70°C to 120°C prior to delivery into a sterilisation vessel.

Brief Description of the Drawings The invention will be more clearly understood from the following description given by way ofexample only, in which:- Fig. 1 is a schematic diagram illustrating the process of the invention; and Fig. 2 is a cross sectional view of a portion of a filtration drum used in the process of the invention.

Detailed Description The rendering process involves mixing and feeding raw materials through a metal detector and bone crusher. The materials are transported to the main render cooker which comprises a horizontal steam jacketed vessel with a large steam heated screw type central impeller which imports heat to the mixture. Cooking involves heating the tissue so as to boil off most ofthe water content at lO0°C to l l0°C under slightly less than atmospheric pressures. The cooking also melts the fat tissue and converts it to beeftallow which is pure lipids.

Cooked product (solids and fat) continuously leaves the cooker and passes through a perforated conveyor. Fat goes one way, solids (called meat and bone meal) go the other. The meat and bone meal pass through presses to squeeze out more fat. All fat then passes through a centrifuge to remove solid protein particles. The fat still contains suspended levels of impurities. ln general, the process of the invention involves initially cooling rough tallow as represented by block 1, filtration of the rough tallow as represented by block 2 and. sterilisation of filtered tallow as represented by block 3.

Two tallow cooling tanks 5, 6 receive hot tallow 7 at about ll0° from a rendering process. These tanks 5, 6 are used to cool the product to 75°C to 80°C using ambient cooling over a 24 hour cycle. The tanks 5, 6 are kept under a negative pressure to ensure odour containment which is sent to an on-site bio-filter. A steam coil 8, 9 is present in the tanks to re-heat the product should overcooling occur. An auger type pump 10 fitted with steam injectors (to clear lines after each pump) and trace heated insulated pip-work feeds product from the cooling tanks 5, 6 to a filtration buffer tank l2.

Tallow at 75°C to 80°C is filtered using a rotary vacuum drum filtration system. The system consists ofa slowly rotating variable speed drum 20 which dips into a bath 25 of infeed tallow which is under constant circulation to/from the buffer tank I2 via an auger pump 26 thus keeping a constant level in the bath 25 and preventing sedimentation of impurities in the bath 25. The inner shell 28 of the drum 20 is maintained at a vacuum of 300 mbar using a 1,400 m3/hr centrifugal pump 27.

Referring in particular to Fig. 2, at start up. a nylon fabric mesh 30 (300 micron dia pores) is applied to the drum 20 while under vacuum. On top ofthis a 90mm layer of filtration media 31 (Filtron 120) is applied. This media 31 consists ofan organic, cellulose based, free—flowing wood fibre powder with particle size 100 to 120 microns. A layer of rough tallow 35 prior to filtration is shown schematically on the outside ofthe filtration media 31 in Fig. 2.

In use, the drum 20 is slowly rotated at a speed of typically 2 to 3 revolutions per minute through the bath 25 of rough tallow. The rotation of the drum 20 clips the media 31 and mesh 30 into the bath 25 of tallow. The vacuum applied inside the drum causes the tallow to be strained through the media 31 and mesh 30 into the inner drum shell and thus, filters the fat. Impurities build up on the outside layer of the media 32. This contaminated layer is scraped offthe drums 20 as it rotates out of the bath 25 and towards a scraper station 36 which consists of an adjustable knife.

The contaminated layer removed per revolution is normally in the range of l20 to 250 microns. The machine operator controls the degree of filtration by observing the build up of contamination present on the filter medium after the scraper 36 and, if required, adjusts the scraper depth and drum rotation to ensure that build up is minimised. Normally, a 90mm layer of media lasts approximately 24 hours of production.

Purified tallow and entrained air is transported along a line 40 via the vacuum pump 27 to a separator cyclone 41 which separates the tallow from the air and protects the vacuum pump 27 from tallow carryover. The slightly contaminated air rejoins a main air supply which is periodically circulated to an on-site bio-filter for cleaning.

The purified tallow is delivered by a pump 46 to two 35 tonne pre-sterilisation storage tanks 48. These tanks 48 are used to store and pre—heat the fat from 70°C to °C using steam coils 50 prior to sterilisation.

The system can process up to 3.5 tonnes/hr of tallow and reduces insoluble impurities from 0.2 — 0.4% to 0.01 — 0.01%. it reduces polythene content from ppm to 30ppm.

A pump 51 is used to deliver the filtered tallow from which air has been separated into a pressure vessel. The tallow is introduced into a 14 tonne pressure vessel and subjected to the following sequence. The steriliser top vent 54 is opened and tallow is pumped into the vessel. As tallow is being introduced, a steam coil is activated to commence heating to 137°C. When the tallow has reached a high set point. pumping is stopped. When a tal low temperature of 137°C is reached, the top vent 54 is closed and dry compressed air is introduced through an inlet 59 into the top of the vessel headspace to pressurise the tallow to 3.1 bar abs (2.1 barg). When the headspace pressure reaches 3.1 bar abs, a timer is activated and these pressure-temperature conditions are maintained for 21 minutes. After 21 minutes, steam heating supply to the coil is shut off and the vessel is de-pressurised by releasing the tallow from a base outlet of the tank at a defined rate which is actuated by a stepper motor and valve 62. Full de-pressurisation can take less than 2 minutes with this method without causing fat foaming. When headspace pressure reaches 0.5 barg, the out- feed pump 65 is activated to remove the fat from the steriliser to a pre-set low level and send it to 35 tonne final storage tanks 66.

The operation of the entire steriliser sequence is controlled by dedicated PLC 70 which feeds relevant process parameters to an on-site SCADA based monitoring and control system 71 .

The system typically processes 13 tonnes per batch and a typical cycle time is 40 minutes.

The system enables render animal fat to be filtered and sterilised so that the fat contains less than 0.15% insoluble impurities by weight. The tallow produced by the process of the invention can be sold as animal feed which represents a considerable economic premium over other market outlets such as oleo-chemical or fuel applications. The process also removes a large proportion of polythene based impurities which is of particular importance to downstream oleo-chemical and fuel markets. The process is robust, efficient and relatively simple to operate and maintain.

The invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims (9)

1. A process for producing purified tallow comprising the steps of: adjusting the temperature of rough tallow to a temperature of from 75° to 80°C; delivering the temperature adjusted tallow into a tallow bath; rotating a filtration drum through the tallow in the bath, the drum having a filtration media on the outer surface thereof and having an interior for receiving filtered tallow; drawing the tallow through the filtration media by applying a vacuum to the drum interior; separating the filtered tallow received in the drum interior from entrained air; heating the filtered tallow to a temperature of approximately 137°C; applying a pressure of about 3 bar abs to the heated tallow for a period of about 20 minutes; and delivering the sterilised purified tallow to a storage tank.
2. A process as claimed in claim 1 comprising the steps of:- delivering rough tallow at a temperature of about ll0°C from a rendering process into a reception tank; adjusting the temperature of the tallow in the reception tank to a temperature of from 75°C to 80°C
3. 3. A process as claimed in claim 1 or 2 comprising the steps of‘:- delivering the temperature adjusted tallow into a buffer tank; and circulating tallow from the buffer tank to the tallow bath to maintain a substantially consistent level oftallow in the bath.
4. 4. A process as claimed in any preceding claim wherein the filtration drum is rotated through the tallow bath at a speed of from 2 to 3 revolutions per minute.
5. 5. A process as claimed in any preceding claim wherein the vacuum maintained in the interior of the filtration drum is approximately 300mbar.
6. 6. A process as claimed in any preceding claim comprising the step of removing deposits from the filtration medium as the drum is rotated.
7. 7. A process as claimed in claim 6 wherein the deposits are removed periodically.
8. 8. A process as claimed in claim 6 wherein the deposits are removed continuously as the drum is rotated.
9. 9. A process as claimed in any preceding claim wherein the filtered tallow is separated by leading the filtered tallow and entrained air through a cyclone separator under a vacuum. A process as claimed in any preceding claim wherein the separated tallow is delivered into a pre-sterilisation storage tank and the separated tallow is pre- heated in the pre-sterilisation storage tank to a temperature of from 70°C to 120°C prior to delivery into a sterilisation vessel. A process for producing purified tallow substantially as hereinbefore described with reference to the accompanying drawings. Purified tallow when produced by a process as claimed in any preceding claim.