IES65612B2 - A blood meal production process - Google Patents

Abstract

Blood meal is produced in an entirely mechanical process in which there is pre-treatment by in-line milling of received blood by a hammermill followed by continuous agitation in supply tanks. An homogenous and consistent blood supply is therefore directed to a continuous part of the process in which the blood is pre-heated at 25 to a temperature of 50-70{C by direct injection of steam in which there is a good deal of agitation caused by injection of the steam from underneath. There is significantly more agitation of the blood in a coagulator 28 having a relatively small diameter for a relatively high speed for the given transfer rate. During passage through the coagulator (28), steam is injected through 2 mm apertures in a screen (29) which surrounds the full internal surface of the coagulator (28). Dewatering is carried out by centrifuging in a decanter (32) to provide a crac portion having a solids content of at least 55% by weight which delivered to a disc drier 35 which is particularly effective at drying the crac to the desired moisture content with relatively little adherence of the blood to the moving members. A cooling auger (39) has the effect of substantially cooling the meal and also of ensuring that it is of uniform particle size, before it is screened (40) to provide the desired output. Oversize particles of the screen (40) are milled in a hammermill (41) having a 3 mm screen size.

Description

A Blood Meal Production ProcessThe inventions relates to a process for the production of blood 'lineal. More particularly, the invention relates to a-process whereby the, blood meal is produced solely using mechanical: operat ions including heating, coagulating, ·* ·, t. dewatering-and drying the blood to form the blood meal.

Such a process is described in British Patent Specification No.GB 1,019,089 (Alfa-Laval) published in 1966. Since 1966, the technology of blood meal production has evolved in different ways. These directions are generally quite different. One direction has been to use chemical treatment in an attempt to improve efficiency. For example, in United States Patent Specification No. US 5,089,287, a method is described in which acid solution is added to maintain the pH at 2 and in which an acidified product is formed and is subsequently mixed with diatomaceous earth. In British Patent Specification No. GB 2,222,065, lactic acid is added before allowing a blood mixture to ferment. In Japanese Patent Specification No. JP 61202660, there is high speed mixing followed by addition of acetic acid and alcohol. In PCT Patent Specification No. WO 84/00098, a process is described in which the blood is salted with nitrite pickling salt and is treated with aroma substances. All of these processes are relatively complex.

Another general direction of the technology has been to keep to solely mechanical operations for blood meal production. For example, in Japanese Patent Specification No. JP 63167763, a dry blood component is treated with superheated steam and then immediately cooled to below 110°C. In Japanese Patent Specification No. JP 63157936, there is dehydration followed by breaking of clots and then contacting with hot air of less than 109°C, further moisture removal and addition of cooling hot air to - 2 dehumidify. In Soviet Union Patent Specification No. SU 1,292,704, a process is described in which there is simultaneous heating and mechanical action to break clots and an intermediate container is used as the temperature in the main container of the coagulator rises. In Japanese Patent Specification No. JP 57170149, received blood is left standing for sedimentation and algal mud is later added. In GB 2,002,218, the blood is treated to prevent natural coagulation by addition of a compound. In Soviet Union Patent Specification No. SU 961,638, the blood is initially sieved for removal of large particles and foreign matter. There is then simultaneous vibration, heating, and agitation with contra-rotating blades in a coagulator. This is followed by centrifuging and drying in a screw dryer. In this latter prior art document, it would appear that the simultaneous vibration, heating and agitation with contra-rotating blades would be a particularly complex operation in which expensive equipment would be required and whereby maintenance would be expensive and difficult. Further, it would appear that initially passing through a sieve would result in a high loss of the raw material. Further, the use of a screw dryer generally tends to cause adherence of the blood product to the screw and loss of efficiency and difficulty in maintenance. In general, the mechanically-based prior art processes are quite complex in which very close control is required and in which expensive equipment and comprehensive maintenance would often be required.

The invention is directed towards providing a blood meal production process which is simpler than has been the general trend in recent years. Another object is that the yield of the process be improved.

According to the invention, there is provided a blood meal production process comprising the steps of :3 pre-treating received blood before initiation of continuous blood meal production steps by carrying out in-line milling of blood as it is received and transferring the milled blood to process supply tanks in which there is continuous agitation; carrying out production operations on the blood as it is pumped in a continuous flow, these production operations comprising the steps of:pre-heating the blood to a temperature in the range of 50°C-70°C by direct injection of steam; coagulating the blood by passing it through a relatively narrow duct to provide a substantial speed increase for the transfer rate and in which there is direct steam injection through apertures in the screen which surrounds the blood within the duct; centrifuging the coagulated blood to remove serum and leaving a crac portion having a solids content in excess of 55% by weight; drying the crac portion in a disc drier in which the temperature is raised to a level in the range of 105°C to 130°C; cooling the dried blood in an auger; and screening the cooled blood to provide a fine particle blood meal.

In one embodiment, the blood transfer rate for the continuous flow part of the process is approximately 900 1100% that of steam which is injected at the pre-heating and coagulation operations.

Preferably, steam is injected at the coagulator at a pressure in the range of 2 to 3 bar through apertures having a diameter lower than 2.5 mm.

In another embodiment, the pre-treatment milling of the blood is carried out using a hammermill having a screen size of approximately 6 mm.

Preferably, the disc drier is fed with drying steam at a pressure of approximately 0.75 bar.

In one embodiment, the output of the cooling auger is screened to provide an output blood meal having a particle size of 1 mm or less, and in which oversize particles from the screen are milled in a hammermill having a screen size of approximately 3 mm.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which :Fig. 1 is a schematic representation of production plant for pre-treatment of blood before a continuous process is initiated; and Fig. 2 is a schematic representation of production plant for the continuous production of blood meal after pre-treatment with the plant illustrated in Fig. 1.

Referring to the drawings, and initially to Fig. 1, pretreatment of blood which is received is illustrated. The received blood may be from beef, pig or sheep slaughter houses and is transferred in vacuum tankers having a capacity of approximately 25,000 litres. The blood is received at an inlet 2 and is immediately milled by a hammermill 3 having a 6 mm screen. This milling operation is carried in-line as the blood is received and is extremely effective at breaking up any flesh, bone or congealed lumps in the received bloods. It has been found that a hammermill is particularly effective at milling the received blood to the desired consistency to ensure that there is little or no loss of the received raw material. The milled blood is fed by gravity to a transfer tank 5 having a relatively low capacity 7.8 m3. The transfer tank 5 is used for the purposes of allowing a pumping system 7 direct the blood to one of three relatively large supply tanks, each having a capacity of 145 m3. The supply tanks 8 have load cells for continuous monitoring of their inputs for control of the pump system 7. The pump system 7 uses 150 mm diameter stainless steel pipes and positive displacement pumps which are inverter controlled to provide accurate volume control. These pumps are marketed under the trade name MONO MERLIN”* and have been found to be particularly suitable for this application. Shut-off valves 9 are used for delivery of blood to the relevant tank 8.

Within each of the tanks 8, the blood is continuously agitated by an agitator 10 rotating about a horizontal axis. This continuous agitation is important as it helps to ensure that the consistency of the milled blood is maintained pending continuous blood meal production steps. Positive displacement output pumps 11 are mounted beneath the tanks 8 and direct the blood from a tank 8 selected on a first-in-first-out basis. The blood is fed through the continuous production plant illustrated in Fig. 2. By virtue of the pumping action of the positive displacement pumps, there is a certain degree of agitation of the blood before the continuous operations start, however, to ensure that the blood is comprehensively agitated before they start, it is pumped initially to a feed tank 21 between a relatively small capacity of 9.4 m3. This tank has an impeller 22 rotating about a horizontal axis for comprehensive agitation of the blood at this stage. There are two output lines of the tank 21, namely, an output line 23 for delivery of the blood to a second continuous process plant and an output line 26 for delivery to the first process plant, namely that which is illustrated. The above-described positive displacement pumps are used throughout the continuous production phase and they are controlled to provide a blood transfer rate of approximately 5,000 kg/hr, and more generally a rate in the range of 4,500 - 5,500 kg/hr. This feed rate is synchronised with a boiler steam transfer rate to two direct steam injection stations for a steam transfer rate of 500 kg/hr. The first of these stations is a preheating tank 25 having a capacity of 2 m3 and in which the transfer rate maintains a blood volume within the tank 25 of approximately 1 m3. Six ports 26 mounted in the lower side of the tank 25 are provided for injection of the steam at the rate of 500 kg/hr and a pressure of 2 bar. These relative flow rates have the dual effect of comprehensively agitating the blood and also of preheating the blood to a temperature which is generally in the range of 50°C to 70°C and in this embodiment is 60°C.

Following pre-heating, the blood is pumped to a coagulator 28. The coagulator 28 comprises a tube which is 75 mm in diameter and 700 mm long. The tube has a very small capacity by comparison, for example, with the pre-heating tank 25. A fine steam inlet screen 29 is mounted internally in the coagulator 28 and this has 2 mm diameter apertures. The screen 29 provides for comprehensive input of steam at hundreds of small apertures throughout the internal circumference of the coagulator 28 from a steam duct 30. The steam duct 30 transfers steam at the abovementioned transfer rate of 500 kg/hr and in this case a pressure of 2.5 bar, the latter being more generally in the range of 2 - 3 bar. It has been found that by pumping the blood through a relatively small tube or duct with comprehensive direct injection of steam through a large number of apertures, the blood is very quickly and comprehensively heated to a temperature in the range 80 to 100°C and in this embodiment, 100°C.

It has been found that the combination of the manner in which the blood is pre-treated which involves milling and continuous agitation, the pre-heating in the tank 25 with direct injection of steam, and the high-speed blood transfer in a relatively narrow coagulator with comprehensive injection of steam from all sides provides for comprehensive coagulation with minimal raw material loss, and for low-cost equipment and simple maintenance. For example, mechanical agitators are not required for either the pre-heating or the coagulation steps. Further, because of the high speed involved during coagulation, adherence of the coagulated blood to production plant surfaces is minimal. This latter feature is largely contributed also to the fact that there is such comprehensive direct injection of steam.

The coagulated blood is pumped to a decanter 32 for dewatering by centrifuging. Approximately 70% by weight of the received blood is separated out as serum which itself has a solids content of approximately 2%. Depending on the commercial circumstances, the serum may be evaporated, or may be simply disposed of by dispersal on land in a prescribed manner. The output of the decanter 32 is approximately 30% of the received weight and is referred to as crac which in this embodiment has a solid content of approximately 60%. This is pumped to a disc drier 35 which comprises a set of parallel blades 36 which are V-shaped in cross-section narrowing in thickness away from the rotational axis. Steam is inputted to the drier 35 at a temperature of 0.75 bar into both a steam jacket and within the shaft 37. It has been found that by using a disc drier, there is very little adherence of blood to the moving surfaces. This is achieved because the discs have the effect of directing the crac outwardly where it tends to move along towards the left as viewed in Fig. 2 under the action of the crac being pumped in from the right hand side. Steam which is generated in the crac during the drying process is outputted at an evaporation vent 38. The disc drier 35 has the effect of substantially reducing the liquid content from approximately 40% to a value in the range of 1 to 12%, depending on the speed with which the shaft is operated and the steam temperature and pressure. In the example illustrated, the steam temperature is 0.75 bar and is superheated to 200°C to provide an output dried crac having a temperature of approximately 130°C. This is transferred through a slowly-rotating auger 39 having a cooling jacket which has the effect of cooling the crac to approximately 30°C.

At this temperature, the crac is easily separated by a vibratory screen 40 having a 1 mm screen size to provide an output blood meal having particles which are smaller than 1 mm in size. Any oversize from the screen 40 is gravity fed to a hammermill 41 having a 3 mm screen. Such a hammermill is extremely effective at reducing the particle size to approximately 1 mm and there is no need to deliver the hammermill output onto the screen 40 and it is fed directly into the output bin 42.

It has been found that by operating a decanter 2 to dewater the blood to achieve a crac having moisture content of approximately 40%, the crac may be easily handled in a dryer where there is relatively little adherence of solids to the mechanical members. This is also contributed to by the fact that a disc dryer is used, the configuration of the discs helping to urge the crac outwardly into the conveying path. This is found to be particularly important as in practice the drying of blood tends to be a particularly difficult operation as over a period of time the blood blocks certain ducts and a major loss of efficiency results. In extreme cases, there can also be considerable downtime of equipment. It has also been found that a hammermill is particularly effective at milling any oversize particles to provide the output blood meal.

It will be appreciated that the invention provides a process which does not require the chemical treatment of the raw material at any stage. Further, the process is relatively simple to carry out and there is a high efficiency as practically none of the raw material is lost, other than the serum which is separated at the decanter 32. Further, even at the decanter 32 the efficiency of separation is extremely high because of the manner in which the blood is pre-treated by milling and agitation, by which it is pre-heated and then coagulated in the coagulator 28.

The Invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (5)

1. A blood meal production process comprising the steps of :pre-treating received blood before initiation of continuous blood meal production steps by carrying out in-line milling of blood as it is received and transferring the milled blood to process supply tanks in which there is continuous agitation; carrying out production operations on the blood as it is pumped in a continuous flow, these production operations comprising the steps of:pre-heating the blood to a temperature in the range of 50°C-70°C by direct injection of steam; coagulating the blood by passing it through a relatively narrow duct to provide a substantial speed increase for the transfer rate and in which there is direct steam injection through apertures in the screen which surrounds the blood within the duct; centrifuging the coagulated blood to remove serum and leaving a crac portion having a solids content in excess of 55% by weight; drying the crac portion in a disc drier in which the temperature is raised to a level in the range of 105°C to 130°C; cooling the dried blood in an auger; and screening the cooled blood to provide a fine particle blood meal.

2. A process as claimed in claim 1, wherein the blood transfer rate for the continuous flow part of the 5 process is approximately 900 - 1100% that of steam which is injected at the pre-heating and coagulation operations.

3. A process as claimed in claims 1 or 2 wherein steam is injected at the coagulator at a 10 pressure in the range of 2 to 3 bar through apertures having a diameter lower than 2.5 mm.

4. A production process substantially as hereinbefore described, with reference to and as illustrated 15 in the accompanying drawings.

5. Blood meal whenever produced by a process as claimed in any preceding claim.