The batch processing of a suspension from storage tanks, in particular the processing of excess yeast in beer filtration, is already known. Beer and yeast concentrate are obtained as by-products in the processing of excess yeast.

In known processes for membrane filtration, a suspension from a tank is fed into a closed system where it is circulated around the circuit, a heat exchanger to cool the suspension and a membrane filter being positioned in the circuit. The suspension is circulated causing permeate to run off until a given concentration of the suspension is reached. The concentrated suspension remaining in the system, residual yeast in the case of beer filtration, is drained from the system which is subsequently cleaned. A separate container is provided for cleaning in which lye concentrate and acid concentrate is diluted with hot and/or cold water and fed into the circuit. Systems for carrying out the process are costly and therefore uneconomical for processing on a small or medium-sized scale.

The object of the invention is to create a process for membrane filtration of the generic type which can be carried out quickly and cost-effectively using a system of simple design. In addition, the object of the invention is to create a membrane filtration system of the generic type with which the process for membrane filtration can be carried out.

The object of creating such a process is achieved by means of a process with the features of claim 1. The object of creating such a system is achieved by means of a membrane filtration system with the features of claim 14.

The process as disclosed in the invention is particularly suitable for filtration using ceramic membranes. It can be carried out in a system comprising simply a container and a membrane filter positioned in a circuit with the container.

The membrane filtration system can be of favourable modular design, with the cleaning station being integrated in the module. A membrane filtration system designed to carry out the process can be standardised to a significant extent, thus reducing the investment costs of procurement.

In the process, the pressure in the container is generated by the application of carbon dioxide, the container pressure ranging from 2 to 3.5 bar.

The application of pressure primes the system, thereby eliminating the need to degasify the suspension, particularly the beer. The suspension is usefully cooled during filtration by means of a cooling system integrated in the container which is designed, particularly, as a cooling jacket. In this way the heat generated by the circulation of the suspension can be dissipated. The cooling jacket represents a simple and cost-effect method of cooling the entire system. By cooling the entire container it is possible to achieve short process times and guarantee an even temperature level in the membrane filters.

In at least one filtration phase, the volume flowing out as permeate is usefully replaced by a suspension flowing into the container, in particular the level in the container being measured and kept at a constant value by the supply of suspension. The supply of suspension to the container prevents the suspension in the container from becoming concentrated too quickly. The container volume is used optimally since the amount of suspension to be filtered is not limited by the filter volume, but can in fact be permitted to exceed it by the supply of suspension during filtration.

A second filtration phase begins as soon as the quotient of the flow on the permeate side and the pressure on the suspension side falls below a first predetermined limit value. In particular, during the second filtration stage the suspension contained in the circuit is concentrated until the quotient of the flow on the permeate side and the pressure on the suspension side reaches a second predetermined limit value. In particular, at the end of the second filtration phase the concentrated suspension is pasteurised or autolysed. To do this, however, a steam lance must be provided in the container. The pasteurised or autolysed suspension, in particular the yeast concentrate, can be fed from the system directly to other processes.

The second filtration phase is usefully followed by a cleaning phase. During the cleaning phase the membrane filter is usefully rinsed with water, in particular hot water, the water flowing from the permeate side to the suspension side of the membrane filter. This reverse rinsing is particularly advantageous in the case of ceramic membrane filters. During the cleaning phase, the system is cleaned with lye, the lye being produced over a predetermined period of time by circulating hot water contained in the container around a circuit comprising the container and adding lye concentrate. During the cleaning phase, in particular after the cleaning with lye, the system is usefully cleaned with acid, the acid being produced like the lye before it over a predetermined period of time by circulating hot water contained in the container around a circuit comprising the container and adding acid concentrate. In this manner, both lye and acid can be produced in the container in the relevant concentrations without the need for complex equipment. Both the lye and the acid are rinsed out with water prior to the subsequent cleaning stage. During the cleaning phase, acids and/or lyes are usefully circulated around a circuit through the container from the suspension side of the membrane filter to the permeate side. The process is designed to run at least partially and in particular fully automatically. The process is well suited to automation and can be rendered fully automatic with relative simplicity.

The membrane filtration system is designed such that the container has a cooling jacket. There is usefully a circuit running through the container into which a lye concentrate inlet and an acid concentrate inlet discharge. In this circuit, lye and acid to clean the system can be produced without the need for a further container. A supply line to feed suspension into the container is provided as part of the circuit, a pump being positioned in this part of the circuit. The pump thus serves both to supply suspension to the container and to circulate a fluid in the circuit through the container. A heat exchanger is advantageously positioned upstream of the acid concentrate inlet. The heat exchanger serves to heat the cleaning fluid to cleaning temperature. A line runs from the permeate side of the membrane filter into the container. Via this line, the membrane filter can be rinsed with cleaning fluid which runs in a circuit out of the container from the suspension side of the membrane filter to the permeate side and back into the container again.

An embodiment of the invention is explained below with reference to the single figure in the drawing which provides a schematic illustration of a membrane filtration system for carrying out the process for membrane filtration.

The membrane filtration system illustrated in the figure comprises two membrane filters (1) positioned one behind the other in the direction of flow. The membrane filters (1) are in particular designed as membrane modules, but other designs may also prove advantageous. The membrane filters (1) have in particular ceramic membranes. A suspension, in particular beer/yeast, can be fed through the membrane filters (1) from a container (2) through a line (31) in a closed circuit by means of a pump (6). The container (2) has a cooling jacket (3) through which the coolant, for example glycol, is able to flow from the coolant inlet (4) to the coolant outlet (5).

At the start of filtration, the membrane filtration system is cleaned and filled with water. Coolant flows through the cooling jacket (3) which cools the container (2). The water is forced out of the container (2) through a floor drain valve (35). The floor drain valve (35) is then closed and carbon dioxide is applied to the system until a pressure of approx. 1 to 2 bar is reached. Controlled by a valve (32), the carbon dioxide flows from the carbon dioxide inlet (16) through a line (42) into the container (2), into which it flows through a spray ball (34), for example. The container (2) is sealed so that it is gas tight. The pressure in the container (2) is measured by means of a pressure sensor (20). Having reached a pressure of 1 to 2 bar, the system is filled with suspension, in particular excess yeast, to the maximum level via the suspension inlet (7) and the supply line (43) by means of the pump (28). This causes the container pressure to increase and means that the maximum operating pressure, which may be 3.2 bar for example, can be exceeded. The container pressure can be adjusted manually via the pressure keeping valve (44). The circuit pump (6) is then connected and the permeate side filled until the system is filled as far as the full level sensor (24). A further full level sensor (23) is positioned in section (41) of the line.

While the system is being filled, a pressure of approx. 3 bar is maintained in the container by the application of carbon dioxide, during which time the container pressure is measured by the pressure sensor (20) and the amount of carbon dioxide flowing in is set to regulate the pressure by means of the valve (32).

In a first filtration phase which follows the filling process, the cooled suspension is pumped from the container (2) through the membrane filters (1) and the line (31) around the circuit by means of the pump (6). In order to avoid pressure impacts in the system, when the pump (6) is advantageously started gradually. The flow volume which drains away as permeate through the line (33) during filtration is measured by the full level sensor (19) in the container (2) and replaced by suspension which is fed into the container (2) through the suspension inlet (7) by means of a pump (28). In this manner, the volume in the circuit is maintained at a constant level. During filtration, a pressure sensor (27) measures the pressure of the suspension before it enters the filter. On the permeate side, a pressure sensor (26) measures the pressure in the line (33) and a flow sensor measures the volume flow. If the quotient of the flow on the permeate side measured by the flow sensor (25) and the pressure on the suspension side measured at the pressure sensor (27) falls below a first limit value, a second filtration phase begins.

In the second filtration phase, the flow of suspension through the suspension inlet (7) into the container (2) is stopped. In this phase, the suspension is circulated around the circuit, the volume decreasing and the suspension concentrating quickly as permeate continues to drain away.

If the quotient of permeate side flow and suspension side pressure falls below a second limit value, the second filtration phase comes to an end as the suspension is sufficiently concentrated.

The concentrated suspension which represents the residue can be pasteurised or autolysed in the container (2) at the end of the filtration phase. The residue is then removed from the container (2). However, the residue can also be removed without first undergoing a pasteurisation or autolysis process. To remove the residue, the valves (36) are opened and the valve (37) which is designed as a regulating valve is closed. The residue flows through the residue outlet (9) out of the system. Here the valve (32) which is designed as a regulating valve and restricts the flow of carbon dioxide to the container (2) can be open or closed. If the fill level sensor (19) indicates that the container (2) is empty, the permeate remaining in the system is forced out of the system via the permeate outlet (10), the system is depressurised and the cleaning process is started automatically.

At the start of the cleaning process the system is empty, cold and soiled by a residue of concentrated suspension, in particular yeast suspension. The system is twice filled to a level of approx. 20% from a cold water inlet (17), rinsed with the valve (37) in the open position supplied through the line (31) in the circuit and emptied via the floor drain valve (35). The system is then filled with cold water to a level of approx. 40% and the valve (37) is closed. The membrane filtration system comprises a further circuit through the container (1) into which an acid concentrate inlet (15) and a lye concentrate inlet (14) discharge. Part of the circuit is formed by the supply line (43) in which the pump (28) is positioned. The pump (28) therefore serves both to feed suspension into the container (2) during the filtration phase and also to circulate the fluid around the circuit during the cleaning phase. A heat exchanger (21) is positioned upstream of the acid concentrate inlet. The water in the container (2) is heated by the heat exchanger (21), being pumped through line (38) in the circuit. The heat exchanger (21) is designed as a condenser to which steam at a pressure of 6 bar is supplied via the steam inlet (12) and from which the condensate is discharged through the condensate outlet (13). The volume of steam flowing into the heat exchanger (21) is regulated by the pressure sensor (22). Once the cleaning temperature has been reached, the membrane filter (1) is rinsed from the permeate side to the suspension side. To achieve this, hot water flows from the hot water inlet (18) via a line (40) which connects the permeate side of the membrane filter (1) to the hot water inlet (18), the cold water inlet (17) and the container (2), through the membrane filter (1) and fills the container (2) via the line (31) until it is 100% full of hot water. The container (2) is then emptied via the flow drain valve (35).

In the next cleaning stage, the container (2) is filled with a minimal amount of hot water via the spray ball (34).

The hot water is circulated around the circuit through the line (38) by means of the pump (28). Lye concentrate is metered into the hot water from the lye concentrate inlet (14) by means of the pump (29), this process taking place over a specified period of time. At the end of the metering period, the lye is circulated around the circuit from the suspension side to the permeate side of the membrane filter (1) and along the line (40) into the container (2) with the valve (39) open and the system is then drained. In the next stage of the process, the system is filled to a level of approx. 20% with hot water, rinsed around the system through the line (40) and then emptied.

In a second cleaning stage, the system is treated with acid. The container (2) is filled with a minimal amount of hot water and the hot water is circulated around the system through the line (38), acid concentrate being metered into to the hot water from the acid concentrate inlet (15) by means of the pump (30) for a predetermined period. The acid is circulated around the circuit through the membrane filter (1) along the line (40), and the system then emptied. To rinse out the acid, the container (2) is filled to a level of approx. 20% with hot water, the water is rinsed around the circuit through the line (40) and the system is then emptied once again.

The cleaning phase is completed by rinsing the system with water and cooling the system. To achieve this the container (2) is filled with hot water from the hot water inlet (18) and the water is rinsed around the circuit along the line (40). The water is thus cooled by means of the cooling jacket (3). After cooling, the system is ready for the next filtration cycle. Cooling can start in the preceding stages of the process, in particular during the rinsing of the system with acid. In the stages of the process following the acid rinsing, cold water can be added to the hot water to accelerate cooling. The suspension does not have to be cooled in the container (2) by means of the cooling jacket (3). It can be advantageous to cool the suspension using a cooling jacket in an external heat exchanger instead.

The filtration and cleaning process can be fully automated.

In addition, various levels of automation of the process are possible.