EP3405674B1

EP3405674B1 - Membrane pump with leakage detection

Info

Publication number: EP3405674B1
Application number: EP17700440.5A
Authority: EP
Inventors: Per-Anders HALLIN; Nils Wendestam; Isac SALMAN; Johan STENBECK
Original assignee: Tetra Laval Holdings and Finance SA
Current assignee: Tetra Laval Holdings and Finance SA
Priority date: 2016-01-21
Filing date: 2017-01-16
Publication date: 2021-07-28
Anticipated expiration: 2037-01-16
Also published as: WO2017125349A1; EP3405674A1

Description

Technical field

The invention relates to a membrane pump with leakage detection.

Background art

Today it is well known to use homogenizers within the food processing industry. For instance, within the dairy industry homogenizers are used for dividing fat globules into minor parts in order to obtain a stable fat emulsion against gravity separation. In other words, by homogenizing milk one can avoid that a cream layer is formed on top of the milk product. Other reasons for homogenizing food products are to achieve a more appetizing colour, reduced sensitivity of fat oxidation, more full bodied flavor, improved mouthfeel and better stability of cultured milk products.
Generally a homogenizer can be divided in two main parts, a high pressure pump forming a high pressure and a homogenizing device providing a gap through which the product is forced. Today, most often the high pressure pump is a piston pump with three to five pistons. In order to make sure that unwanted microorganisms are not spread to the product when the pistons are moving back and forth piston seals are used. A common approach is to have at least two piston seals placed apart from each other such that a barrier can be formed between the product, placed on a so-called hygienic side, and non-hygienic parts of the homogenizer, such as crankcase and crankshaft using hydraulic oil, placed on a so-called non-hygienic side.
For example, in non-aseptic homogenizers, i.e. homogenizers placed upstream a heat treatment station, a common approach is to have double piston seals with water provided between the seals to lubricate the pistons. In aseptic homogenizers, i.e. homogenizers placed downstream a heat treatment station, a mixture of hot condensate and steam may be supplied between the seals in order to prevent re-infection.
The homogenizer and the homogenizing process are further described in "Dairy Processing Handbook" published by Tetra Pak.
Since it is difficult to keep the hygienic side and the non-hygienic side apart when the pistons are moving back and forth some food producers have decided to use only food graded oils as a precautionary measure. By doing so they reduce the risk of causing health issues, but if the oil finds its way to the product the product properties are nevertheless negatively affected.
For the above mentioned reasons, it is today requested from food producers to make sure that the oil does not end up with the product in order to avoid health issues and product losses.
Further, apart from reducing the risk that oil does not end up with the product it is important that the technical solution is cost efficient both from capital expenditure perspective and operational performance expenditure. In other words, the technical solution should require a reasonable investment cost for the food producer and when running the technical solution the need for utilities should be kept at a low level, and providing service should be possible without increasing operational costs significantly.
Some relevant prior art is described in patent documents WO2014095898A1 , EP1479910A2 , DE19829084A1 and US5244360 .

Summary of the invention

It is an object of the present invention to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solve at least the above mentioned problem.
According to the invention, these and other objects are achieved in full, or at least in part, by a membrane pump comprising a first membrane, and a second membrane. A membrane interior space with vacuum is formed between the first membrane and the second membrane. The membrane interior space comprises a first element and a second element, wherein the first element and the second element are separated and electrically insulated by the vacuum in the interior space. The membrane pump further comprises a resistance meter which is configured to detect a resistance between the first element and the second element arising from a fluid leakage into the membrane interior space due to rupture of the first membrane and/or the second membrane. Basically, if there is a fluid leakage from one of the membranes, the fluid will put the first element and the second element in communication with each other and a resistance will arise. The resistance will be detected by the resistance meter and thus indicate that there is a leakage from one or both of the membranes in the pump. The inventive membrane pump will therefore provide a more immediate and robust indication of any membrane rupture than any conventional membrane pump.
In a preferred embodiment, the first element and the second element, respectively, comprises an annular element with protruding lips. The first element and the second element may be attached to each other with some sort of separator between them so that they will be in no contact between them unless there is a rupture of one or both of the membranes and they are put in contact by means of a fluid entering into the interior space. That is, the first element and the second element may be integrally formed with a separator between them.
The membrane pump may further comprise a control unit which is connected to the resistance meter and adapted to monitor the resistance between the first element and the second element. The control unit may further be adapted to trigger an alarm when a resistance between the first element and the second element arises due to rupture of the first membrane and/or the second membrane.
The fluid entering into the interior space and breaking the vacuum may be a liquid from a component in the filling machine but could also just be plain air from the ambient.
According to a second aspect another membrane pump is described, comprising a first membrane having a net of metal threads, and a second membrane having net of metal threads. A membrane interior space is formed between the first membrane and the second membrane. The membrane pump further comprises a detection device which is configured to detect a change of an electrical property arising due to a rupture of at least one of the metal threads. The same advantages as presented above also apply for the membrane pump according to the second aspect. It should be further noted that this is a simple yet very effective embodiment of the membrane pump.
The electrical property measured by means of the detection meter may be resistance in which case a conventional resistance meter may be used as the detection device. Another possibility is to energize the metal threads and instead measure voltage by means of a voltage meter.
In one preferred embodiment of the second aspect, the net the first membrane may comprise a first layer of metal threads and a second layer of metal threads, and net of the second membrane may comprise a first layer of metal threads and a second layer of metal threads. Here, the detection device is configured to detect a short circuit between the first layer of metal threads and a second layer of metal threads in the first membrane and/or in the second membrane.
The membrane pump may further comprise a control unit which is connected to the detection device and adapted to monitor the information received from the same in order to detect any potential change of the electrical property. The control unit may further be adapted to trigger an alarm if a change of the electrical property is determined.
The membrane pump may further comprise a membrane ring connecting the first membrane and the second membrane to each other in order to form the membrane interior space.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise.

Brief description of the drawings

The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

Fig. 1 schematically illustrates a homogenizer.
Fig. 2 schematically illustrates a so-called wet end of the homogenizer of Fig. 1.
Fig. 3 schematically illustrates a wet end in a membrane equipped homogenizer.
Fig. 4 illustrates a number of different perspective views on a membrane.
Fig. 5a and 5b illustrate a membrane in a first mode and a second mode.
Fig. 6a, 6b and 6c illustrate the main components of a membrane pump.
Fig. 7 illustrates one exemplary embodiment of the membrane pump according to the invention.
Fig. 8a and 8b illustrate further exemplary embodiments of the membrane pump according to a second aspect.

Detailed description of preferred embodiments of the invention

Fig 1 generally illustrates a homogenizer 100, more particularly a homogenizer sold under the name Tetra Alex™ by Tetra Pak. Generally, the homogenizer 100 comprises two main parts, a high pressure pump and a homgenising device. The high pressure pump forms a high pressure and the homogenising device provides one or several gaps through which the product is forced with the effect that smaller fat globules are formed. Further effects of homogenization is more appetizing colour, reduced sensitivity to fat oxidation, more full-bodied flavour and better stability of cultured milk products.
In this example, the high pressure pump is a piston pump driven by a main drive motor 101 connected via a belt transmission 102 and a gearbox 103 to a crankshaft placed in a crankcase 104. By using the crankshaft the rotary motion is converted to a reciprocating motion driving pump pistons 105 back and forth. Today, it is common to have three to five pump pistons.
The pump pistons 105 run in cavities formed in a pump block 106 made to withstand the high pressure created by the pump pistons. Today it is common to increase the pressure from 300 kPa (3 bar) to about 10 - 25 MPa (100 - 250 bar), but higher pressures can be used as well.
Through cavities in the pump block 106 the product enters a first homogenizing device 107 and thereafter, in many cases, a second homogenizing device 108. As described above, by forcing the product through one or several gaps the properties of the product can be changed.
The reciprocating motion of the pump pistons 105 creates pulsations. To reduce the pulsations it is common practice today to place an inlet damper 109 on an inlet of the homogenizer. Further, in order to reduce vibrations and noise it is common practice to place an outlet damper 110 on an outlet.
Fig 2 illustrates a so-called wet end of the homogenizer in greater detail. As can be seen in this cross sectional view, the piston 105 is moving back and forth such that a high pressure is formed in a product chamber 200 in the pump block 106. One or several seals 202 are used for keeping a tight fitting between the piston 105 and a piston receiving element 204. The one or several seals 202 also keep the product in the product chamber 200 apart from the crankcase and other non-hygienic parts of the homogenizer. In order to further make sure that unwanted microorganisms do not end up in the product it is a common approach today to use steam barriers or the like in combination with the piston seals 202.
In fig 3 a wet end 300 of a membrane equipped homogenizer is illustrated. As the homogenizer illustrated in fig 1 and 2, the homogenizer is provided with a piston 302, or more correctly a number of pistons, although only one of them is illustrated in this cross sectional view. Further, the piston 302 is forming a high pressure in a pump block 304.
Unlike the homogenizer illustrated in fig 1 and 2, the wet end 300 is provided with a first membrane 306 and a second membrane 308. The first membrane 306 can be arranged such that a hydraulic oil chamber 310 and a membrane interior space 312, that is, a space formed between the first membrane 306 and the second membrane 308, is kept apart. The second membrane 308 can be arranged such that the membrane interior space 312 and a product chamber 314 are kept apart.
Further, a high pressure relief valve 316 can be connected to the hydraulic oil chamber 310 such that a pressure in the hydraulic oil chamber can be lowered by opening this valve. Although not illustrated, when opening the high pressure relief valve 316 hydraulic oil may be fed into a tank. This tank may also be connected to an inlet in the hydraulic oil chamber via an inlet valve such that hydraulic oil can be fed into the hydraulic oil chamber at a later stage. A positive effect of this set up is that the hydraulic oil released via the high pressure relief valve 316 can be re-used. An example set up is illustrated in fig 11.
The reason for having hydraulic oil is that this is used for forwarding the pressure formed by the piston 302 via the first membrane 306 and the second membrane 308 to the product chamber 314, but also for lubricating the seals and in that way extend the life time of the seals. Hence, unlike the wet end illustrated in fig 2, the piston is indirectly forming a pressure in the product chamber 314.
An advantage of having membranes separating the product chamber 314 from the piston 302, crankshaft, crankcase and other parts placed on the non-hygienic side is that a well defined border is formed. An effect of this is that the risk that unwanted microorganisms pass the membranes into the product chamber 314 is significantly lowered. Even if the same degree of food safety may be achieved using for instance steam barriers, the membranes solution has the benefit that no steam barriers are needed. The effect of this in turn is that the operational costs for running the homogenizer can be significantly reduced. Also from an environmental perspective, using less steam is of significant value.
A risk with membrane equipped homogenizers is that the membranes break and that hydraulic oil enters the product chamber. This may be a food safety hazard depending on the hydraulic oil being used, but it will with a high likelihood result in product losses. In order to overcome this risk, in the membrane interior space 312, that is, the space formed between the first membrane 306 and the second membrane 308, a fluid may be present. The aim of the fluid is to make it possible to detect a membrane rupture in a reliable, fast and cost efficient way.
Fig 4 illustrates a number of different perspective views of a membrane 400 that can be used as the first membrane 306 or the second membrane 308 in the wet end illustrated in fig 3.
In order to receive the force created by the piston in a way such that the membrane 400 is not worn out only after a short period of time, the membrane 400 may be provided with a raised section 402 placed between a periphery 404 of the membrane and a mid section 406 making sure that the membrane can flex between a first mode, illustrated in fig 5a, and a second mode, illustrated in fig 5b, without wearing out the material of the membrane. Further, an advantage of having the raised section may also be greater volume difference between the first mode and the second mode.
The mid section 406 may be strengthened by a strengthening portion 408, e.g. a metal portion incorporated in the membrane, in order to avoid so-called "coining", i.e. the membrane breaks such that a small portion of the mid section in the shape of a coin is torn from the membrane.
In fig 5a the membrane is in the first mode in which no force is exerted on the membrane, neither on a product chamber side (left side in fig 5a and 5b), nor on a hydraulic oil chamber side (right side in fig 5a and 5b).
In fig 5b the membrane is in the second mode in which a force is exerted on the hydraulic oil chamber side such that the mid section of the membrane is pushed towards the product chamber side.
In order to make sure that the membrane can be cleaned properly and efficiently the product chamber side of the membrane is preferably provided with properties such that food residues can be easily removed. Further, the product chamber side should also be able to withstand chemicals used when cleaning, e.g. lye and acid. The hydraulic oil chamber side should on the other hand preferably have properties suited to work well with the hydraulic oil. The membrane as a whole should be elastic such that the pressure formed by the piston can be forwarded to the product chamber without wearing out the membrane. Further, the membrane should also be elastic such that the membrane can be small, e.g. a diameter of 10-30 cm. A small membrane namely has the effect that the pump block can be made small, in turn implying that less material, e.g. stainless steel, is needed, which directly affect the investment cost for the food producer.
Returning to fig 5a and 5b, it is illustrated a membrane 500 comprising a main body 502 made of a rubber material, such as an elastomer. In one particular example the elastomer ethylenepropylenedienemonomer (EPDM) has been chosen, but since the choice of material depends on the hydraulic oil used other material can be chosen as well. Using a rubber material, such as an elastomer, for the main body, makes it possible to reduce the size of the membrane to about 10-30 cm or lower while still being able to forward the pressure from the piston satisfactorily.
In order to provide for that the product chamber side can be cleaned properly a coating 504 may be provided on this side. The coating 504 may be made of polytetrafluoroethylene (PTFE), but other plastic material suitable for food processing and possible to be coated can be used as well. Further, the coating can also protect the elastic material against the cleaning agents used during cleaning and also against abrasive products.
In order to provide for that the elastic properties of the main body 502 is not lost the coating 504 is preferably made thin, e.g. 0,5 mm. However, since different material has different properties the thickness of the coating may differ for different material.
It should be noted that fig 5a and 5b are mainly for illustrative purposes. In real applications, a difference between the first mode and the second mode may be less significant.
Fig 6a, 6b illustrate the main components of a membrane pump 600 comprising a first membrane 602, a second membrane 604, a membrane ring 606 and a sensor 608 in an exploded view from two different perspectives. In Fig 6c, the first and second membranes are attached to the membrane ring 606. As illustrated, both membranes may be of the kind illustrated in fig 4, 5a and 5b. By connecting the first membrane 602 and the second membrane 604 to each other in this way a closed space is formed, herein referred to as the membrane interior space. In this closed space the fluid can be held, thereby making it possible to easily replace one membrane module by another.
Fig. 7 illustrates one exemplary embodiment of the membrane pump 700 according to the invention. The membrane pump 700 comprises a first membrane 701, and a second membrane 702. A membrane interior space 704 with vacuum is formed between the first membrane 701 and the second membrane 702. The membrane interior space 704 comprises a first annular element 705 having lips 706 around its outer periphery, and a second annular element 707 having lips 708 around its outer periphery. The lips 706 of the first annular element 705 and the lips 708 of the second annular element 707 are separated from each other and electrically insulated by the vacuum in the membrane interior space 704. The membrane pump 700 further comprises a resistance meter 709 which is configured to detect the resistance between the first annular 705 element and the second annular element 707 that arises from a fluid leakage into the membrane interior space 704 due to rupture of the first membrane 701 and/or the second membrane 702. That is, when one or both of the first membrane 701 and the second membrane 702 is ruptured, fluid will leak into the membrane interior space 704 and put the lips 706 of the first annular element 705 and the lips 708 of the second annular element 707 in communication with each other. Thus, a resistance can be detected by means of the resistance meter 709.
In order to make the process completely automated, the membrane pump may further comprise a control unit (not shown). The control unit is connected to the resistance meter 709 and adapted to monitor the resistance detected by the same. When a resistance between the first element 705 and the second element 707 arises due to rupture of the first membrane 701 and/or the second membrane 702, the control unit will trigger an alarm so that any appropriate action can be initiated.
In Fig. 8a and 8b, another embodiment of the membrane pump 800 is illustrated. The membrane pump 800 comprises a first membrane 801 having a net of metal threads, and a second membrane 802 having net of metal threads. A membrane interior space 803 is formed between the first membrane 801 and the second membrane 802. The membrane pump 801 further comprises a detection device 804 configured to detect a change of an electrical property that arises due to a rupture of at least one of the metal threads. The electrical property measured by means of the detection device 804 may be resistance in which case a conventional resistance meter may be used as the detection device 804. Another possibility is to energize the metal threads and instead measure voltage by means of a voltage meter.
In order to make the process completely automated, the membrane pump 800 may further comprise a control unit (not shown). The control unit is connected to the detection device 804 and adapted to monitor the information received from the same in order to detect any potential change of the electrical property. When a change of the electrical property is determined the control unit will trigger an alarm so that any appropriate action can be initiated.
In one embodiment, the net of the first membrane 801 comprises a first layer of metal threads and a second layer of metal threads, and the net of the second membrane 802 comprises a first layer of metal threads and a second layer of metal threads. Here, the detection device 804 is configured to detect a short circuit between the first layer of metal threads and the second layer of metal threads in the first membrane 801 and/or in the second membrane 802.
It is understood that other variations in the present invention are contemplated and in some instances, some features of the invention can be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the scope of the invention.

Claims

A membrane pump (700), comprising
a first membrane (701),
a second membrane (702),
a membrane interior space (704) is formed between said first membrane (701) and said second membrane (702), said membrane interior space (704) comprising a first element (705) and a second element (707), and
a resistance meter (709) configured to detect a resistance between said first element (705) and said second element (707) arising from a fluid leakage into said membrane interior space (704) due to rupture of said first membrane (701) and/or said second membrane (702), characterized in that
the membrane interior space (704) is formed with vacuum between the first membrane (701) and the second membrane (702), and
the first element (705) and the second element (707) are separated and electrically insulated by said vacuum.
The membrane pump (700) according to claim 1, wherein said first element (705) and said second element (707), respectively, comprises an annular element with protruding lips (706, 708).
The membrane pump (700) according to claim 1 or 2, further comprising a control unit connected to the resistance meter (709) and adapted to monitor the resistance between the first element (705)and the second element (707).
The membrane pump (700) according to claim 3, wherein said control unit is adapted to trigger an alarm when a resistance between the first element (705) and the second element (707) arises due to rupture of the first membrane (701) and/or the second membrane (702).
The membrane pump (800) according to any one of the preceding claims, further comprising a membrane ring connecting said first membrane (701; 801) and said second membrane (702; 802) to each other such that said membrane interior space is formed (704; 803).