PROCESS AND DEVICE FOR THE PRODUCTION OF MILK WITH A PREDETERMINED FAT CONTENT

Abstract: Described is a process for the production of milk and cream with a predetermined fat content, in which raw milk is separated by a centrifuge into a high-fat fraction (cream) and a low-fat fraction (skimmed milk), in which the fat content in the hight-fat fraction is determined and the fat content in the low-fat fraction is kept at a negligibly low level, the volume flow of the low-fat fraction is determined, and a specific part of the high-fat fraction is then added to the low-fat fraction for obtaining milk of the desired fat content (standardized milk), and the remaining part of the high-fat fraction (cream) is drained off through a control valve (8), which is characterized in that the part of the high-fat fraction added to the low-fat fraction is regulated by means of a control valve (12) which in conjunction with the control valve (8) for discharge of the remaining part of the high-fat fraction is controlled on the basis of the volume flow (10) of the low-fat fraction, on the basis of the volume flow (11) of the part of the high-fat fraction added to the low-fat fraction, and on the basis of the density measurement (7) of the high-fat fraction, in such a way that the density of the high-fat fraction - and thus the fat content - is maintained at a set volume. Also is described a device for carrying out the process according to the invention.

Description: Short title: Process and device for the production of milk with a predetermined fat content. The present invention relates to a process for the production of milk and cream with a predetermined fat content, in which raw milk is separated by a centrifuge into a high-fat fraction (cream) and a low-fat fraction (skimmed milk), in which the fat content in the high-fat fraction is determined and the fat content in the low- fat fraction is kept at a negligibly low level, the volume flow of the low-fat fraction is determined, and a specific part of the high-fat fraction is then added to the low-fat fraction for obtaining milk of the desired fat content (standardized milk), and the remaining part of the high-fat fraction (cream) is discharged through a control valve. Such a process is known from Dutch Patent 180715. In this known process the fat content of both the high- fat fraction and the low-fat fraction is maintained at a desired value by means of separate control circuits having valves controlled by the density or by the pressure, and the part of the high-fat fraction added to the- low-fat fraction is regulated by means of the control valve for discharge of the remaining part of the high-fat fraction, said control valve being controlled on the basis of values of the volume flow of the low-fat fraction and of the volume flow of the part of the high- fat fraction added to the low-fat fraction. This known process has the disadvantage that the adjustment of the control valve produces pressure variations in the pipe sections of the high-fat fraction. These pressure variations can affect the working range and the setting of the centrifuge. When there is a change in pressure the centrifuge therefore has to find a new working point, which takes some time, so that the control process is consequently slow. In addition, the control range is limited because, in order to be able to add a part of the high-fat fraction to the low-fat fraction, a certain pressure difference has to be present between the high-fat fraction and the low-fat fraction. In the known process this pressure difference depends partly on the position of the control valve, and there is a risk that the pressure in the high-fat fraction will become too low for it to be possible to add an adequate quantity of the high-fat fraction to the low-fat fraction. The object of the present invention is to produce a process for the production of milk and cream with a predetermined fat content, in which a quicker control than in the known process is possible. This object is achieved according to the invention in that the part of the high-fat fraction added to the low-fat fraction is regulated by means of a control valve which in conjunction with the control valve for discharge of the remaining part of the high-fat fraction is controlled on the basis of the volume flow of the low-fat fraction, on the basis of the volume flow of the part of the high-fat fraction added to the low-fat fraction, and on the basis of the density measurement of the high-fat fraction, in such a way that the density of the high-fat fraction - and thus the fat content - is maintained at a set value. By means of these two control valves the ratio between the quantity of cream to be added to the low-fat fraction and the quantity of cream to be discharged can be set without the pressure in the high-fat fraction thereby being affected. The pressure in the high-fat fraction is controlled by the two valves on the basis of the density measurement, which again indicates a measure of the fat content. Since the pressure in the high-fat fraction is thus held constant, the centrifuge remains in the same working point. In an advantageous embodiment of the process according to the invention the volume flow of the high- fat fraction is measured and the control valves are controlled partly on the basis of this measured value. A change in the volume flow of the high-fat fraction is in fact accompanied by a change in the fat content of that fraction. Since the densimeter reacts with some time lag to a change in the fat content, this change is already anticipated by the change detected in the volume flow. This means that the position of the control valves can be adjusted more rapidly to the changing situation. If the standardized milk is conveyed to a homogenizer, it is advantageous according to the invention for the raw milk to be conveyed to the centrifuge via a control valve which is controlled in such a way that the pressure in the low-fat fraction remains constant. With the use of a homogenizer it is a requirement that the volume flow to the homogenizer should be constant. The pressure in the low-fat fraction is thus stabilized using this regulable valve. The invention is also embodied in a device for the application of the process, comprising a centrifuge with a supply pipe for the raw milk and a discharge pipe for the high-fat fraction and a discharge pipe for the low- fat fraction, a connecting pipe which connects the discharge pipe for the high-fat fraction to the discharge pipe for the low-fat fraction, a densimeter in the pipe for the high-fat fraction in the region between the centrifuge and the connecting pipe, and a control valve in the discharge pipe for the high-fat fraction, disposed downstream of the connection of the connecting pipe, viewed in the direction of flow, a volume flow meter in the connecting pipe, and a volume flow meter in the discharge pipe for the low-fat fraction in the region between the centrifuge and the connection of the connecting pipe, said device being characterized in that the connecting pipe is provided with a control valve which together with the control valve in the discharge pipe of the high-fat fraction is connected to a control element which controls the two control valves on the basis of the measured value of the two volume flow meters and of the densimeter in the pipe for the high- fat fraction, in such a way that the density, and thus the fat content, in the high-fat fraction remains constant. In a preferred embodiment of the invention a volume flow meter which emits a signal to the control element is provided in the discharge pipe for the high-fat fraction. The invention is explained in greater detail with reference to the drawing, which shows an example of an embodiment of the device according to the invention in a single figure. In the figure reference number 1 indicates a centrifuge, to which a supply pipe 2 for raw milk and a discharge pipe 3 for the high-fat fraction (cream) and a discharge pipe 4 for the low-fat fraction are connected. The discharge pipes 3 and 4 are connected to each other by means of a connecting pipe 5, which divides each of the discharge pipes 3 and 4 into two sections 3, 3' and 4, 4'. A volume flow meter 6 and a densimeter 7 are incorporated in the discharge pipe 3 between the centrifuge 1 and the connection of the connecting pipe 5, while a control valve 8 is disposed downstream of the connecting pipe 5. A pressure-controlled valve 9 for setting the working point of the centrifuge and a volume flow meter 10 are disposed in the discharge pipe 4 for the low-fat fraction between the centrifuge and the connection of the connecting pipe. Finally, a volume flow meter 11 and a control valve 12 are provided in the connecting pipe 5. The device is provided with a control element 13 which controls the two control valves 8 and 12 on the basis of measured values coming from the volume flow meters 10 and 11 and from the densimeter 7. The two control valves thus have a dual purpose. On the one hand, they regulate the amount of cream conveyed through the connecting pipe 5 to the low-fat fraction and, on the other, these two control valves keep the fat content in the cream constant by means of the densimeter 7. A change in the fat content in the high-fat fraction will generally be reflected in a change in the volume flow of the high-fat fraction. Such a change will be detected by the densimeter 7 with some time lag. In order to be able to make the control element 13 react more quickly to such a change, provision is made for the volume flow meter 6, which emits a signal to the control element, so that when the fat content is changed the control element can react more quickly to it. It will be clear that the volume flow meters 6 and 10 and 11 can also be provided in a different way in the pipes, in such a way that the volume flow can be derived or calculated in each of the pipes or pipe sections. If the standardized milk is fed to a homogenizer 14 disposed in the pipe section 4 1 before being discharged, it is necessary to keep the volume flow in the pipe section 4' constant. For this purpose, provision is made in the raw milk supply pipe connected to the centrifuge for a control valve 15 which is controlled by means of a pressure recorder 16 disposed in the pipe 4, in order to keep the.pressure in this pipe at a constant value. By means of the device described above it is thus possible to produce both cream and standardized milk with predetermined fat percentages. Since the control is designed in such a way that the action of the centrifuge is not thereby affected, a very rapid control is possible, with a sufficiently high pressure difference between the high-fat fraction and the low-fat fraction being maintained for it to be possible always to add an adequate required quantity of cream via the pipe 5 to the low-fat fraction so that the device has a wide control range.

Claims: CLAIMS 1. Process for the production of milk and cream with predetermined fat content, in which raw milk is separated by centrifuge into a high-fat fraction (cream) and a low-fat fraction (skimmed milk), in which the fat content in the high-fat fraction is determined and the fat content in the low-fat fraction is kept at a negligibly low level, the volum flow of the low-fat fraction is determined, and a specific pa of the high-fat fraction is then added to the low-fat fractio for obtaining milk of the desired fat content (standardized milk), and the remaining part of the high-fat fraction (cream) is drained off through a control valve (8), characterized in that the part of the high-fat fraction added to the low-fat fraction is regulated by means of a control valve (12) which in conjunction with the control valve (8) fo discharge of the remaining part of the high-fat fraction is controlled on the basis of the volume flow (10) of the low-fa fraction, on the basis of the volume flow (11) of the part of the high-fat fraction added to the low-fat fraction, and on t basis of the density measurement (7) of the high-fat fraction, in such a way that the density of the high-fat fraction - and thus the fat content - is maintained at a set value. 2. Process according to Claim 1, characterized in tha the volume flow (6) of the high-fat fraction is measured and the control valves (8,12) are partly controlled on the basis this measured value. 3. Process according to Claim 1 or 2, in which the standardized milk is conveyed to a homogenizer (14), characterized in that the raw milk is fed to the centrifuge (1 via a control valve (15) which is controlled in such a way th the pressure in the low-fat fraction remains constant. 4. Device for the application of the process accordin to one of the preceding claims, comprising a centrifuge (1) wi a supply pipe (2) for the raw milk and a discharge pipe (3) f the high-fat fraction and a discharge pipe (4) for the low-fa fraction, a connecting pipe (5) which connects the discharge pipe (3) for the high-fat fraction to the discharge pipe (4) for the low-fat fraction, a densimeter (7) in the pipe (3) fo the high-fat fraction in the region between the centrifuge (1 and the connecting pipe (5) and a control valve (8) in the discharge pipe (3 ) for the high-fat fraction, disposed downstream of the connection of the connecting pipe (5) , view in the direction of flow, a volume flow meter (11) in the connecting pipe (5), and a volume flow meter (10) in the discharge pipe (4) for the low-fat fraction in the region between the centrifuge (1) and the connection of the connecti pipe (5) , characterized in that the connecting pipe (5) is provided with a control valve (12) which together with the control valve (8) in the discharge pipe (3 ) of the high-fat fraction is connected to a control element (13) which control the two control valves (8,12) on the basis of the measured value of the two volume flow meters (6,10) and of the densimeter (7) in the pipe (3) for the high-fat fraction, in such a way that the density and thus the fat content in the high-fat fraction remains constant. 5. Device according to Claim 4, characterized in tha a volume flow meter (6) which emits a signal to the control element (13) is provided in the discharge pipe (3) for the high-fat fraction. 6. Device according to Claim 4 or 5, in which the standardized milk is conveyed to a homogenizer (14), characterized in that a control valve (15) is accommodated i the supply pipe (2) for ra milk to the centrifuge (1) , said control valve (15) being controlled by means of the pressure the discharge pipe (4) for the low-fat fraction in order to keep this pressure constant.

Inventors: VAN HOEK JOHANNES WILHELMUS, VAN SCHAGEN HANS WALTER, VAN HOEK, JOHANNES, WILHELMUS, VAN SCHAGEN, HANS, WALTER
Applicants: STORK AMSTERDAM, STORK AMSTERDAM B.V.
Application year: 1989
Main classification: A23C9
IPC codes: A01J11, A23C9