WO2001039604A1

WO2001039604A1 - A process and device for sterilization and homogenization of liquid products

Info

Publication number: WO2001039604A1
Application number: PCT/IT2000/000439
Authority: WO
Inventors: Roberto Catelli; Alessio Lazzari; Luca Belletti
Original assignee: Rossi & Catelli S.P.A.
Priority date: 1999-11-30
Filing date: 2000-11-02
Publication date: 2001-06-07
Also published as: ITMO990265A1; AU1883301A; IT1311158B1; ITMO990265A0

Abstract

In the process and device of the invention, a liquid product (G) and steam (F) are introduced into a mixing chamber (4) of an injector,in which mixing chamber a two-stage steam-liquid mixture is created by aspiration of the liquid product, which exits from a liquid product outlet nozzle, by the steam, which exits from a steam outlet nozzle (2) at a sonic or supersonic velocity. An inlet speed of the liquid product (G) into the mixing chamber is kept at a maximum level at which the liquid can be kept in a liquid state. The two-stage steam-liquid mixture is compressed during a flow thereof internally of the injector, up until a single-stage liquid mixture is obtained. The invention enables a treatment of liquid products to be made, especially food products such as milk, cream and the like, as well as pharmaceutical products; the treatment is characterized by a high degree of stability and operative repeatability, as well as by high nutritional and aesthetic characteristics of the products obtained by the process.

Description

Description A Process and Device for Sterilization and Homogenization of Liquid Products.

Technical Field

The invention relates to a process and device for sterilization and homogenization of liquid products. In particular, though not exclusively, the invention relates to the sterilization and homogenization of food products such as milk, cream and the like, as well as pharmaceutical products. The invention is also applicable to the field of processes and relative devices for heating (for sterilization and/or pasteurization purposes) and homogenization of fluid products by high-speed direct steam-injection. During the course of the description reference will frequently be made, for the sake of simplicity, to the treatment of food products, even if this should not be seen as a limitation of the use of the invention. Background Art

Infusion processes for the treatment of food products have existed for some time; these processes provide high-quality products but are very expensive. Steam-injection processes have also been in existence for a considerable time, especially low-speed processes such as, for example, the one described in US patent 4, 160,002. These processes, which are lower-cost than the previously-cited ones, have the main drawback that during treatment in the injector the product temperature is not uniform, so that a part of the product passes a certain period of time at a temperature which is above the nominal sterilization temperature. This leads to loss of nutritional value as well as a reduced attractiveness in terms of appearance, taste and smell. Processes have been developed to combat this defect, using high-speed steam injection.

For example, in US patent 5,544,961, a device is described for actuating a process which, briefly, by injecting steam at supersonic speed enables a liquid to be compressed. The patent in question describes a pump constituted by a passive injector (i.e. an injector using only steam-flow energy). The patent in question suggests, in general terms, the possibility of using the device and the described process for sterilizing and homogenizing food products. The patent, as indeed the known theories for treating food products by means of injection systems, bases its operational mode mainly on the parameter represented by the regulation of the speed and the flow characteristics of the steam.

In practice, the application of these processes and relative devices to food products has not given satisfactory results due to the unstable, irregular and unpredictable functioning of the devices actuating the processes themselves. These factors together mean that the necessity' of having food products with very precise and well-defined chemical-physical characteristics cannot be attained. One of the drawbacks involved is concerned with the poor flexibility' of the treated-product quantity regulation. A further drawback is the rapid formation of encrustations of food, necessitating frequent production shutdowns while the injector is cleaned and sterilized. The above limitations and drawbacks become even more evident when the heat treatment temperature is higher, and become serious indeed when milk and its derivatives are undergoing UHT treatment. The fact is that though the theoretical chance of good results is real enough, industry has not applied this theory to the processes on offer. The aim of the present invention is to eliminate the above-mentioned drawbacks by providing a process and a device for actuating the process, whose operational parameters enable treatment of liquid products and which is characterised by a high degree of stability and operative repeatability.

An advantage of the invention is that it enables liquid food products to be treated at lower temperatures and in shorter times than any known process, thus obtaining an improvement in the final quality of the treated product. A further advantage is the long operational times obtainable, with no need for interruptions for washing and sterilizing operations.

A still further advantage is that a good level of homogenization is obtained in the treated product.

These aims and advantages and more besides are all attained by the present invention, as it is characterised in the appended claims.

Disclosure of Invention

Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of the various stages of the process of the invention, as well as the description of a possible device for actuating the process, illustrated herein purely by way of a non-limiting example in the accompanying figures of the drawings, in which: figure 1 is a schematic longitudinal section in vertical elevation of an injection device of the invention; figure 2 is a rough diagram indicating the speed of the liquid product, the steam and the two-stage product-steam mix during its movement through the injector; figure 3 is a diagram relating to the liquid product temperature/time, in three different cases: in the case described herein, in the case of an infusion process and, finally, what is obtained using injection processes at present adopted in industrial processes. With reference to figure 1, 1 denotes in its entirety a device for sterilizing and homogenizing liquid products, comprising a steam-liquid injector provided with a steam-outlet nozzle 2, a liquid-outlet nozzle 3 and a steam-liquid mixing chamber 4.

The steam outlet nozzle 2 comprises a first conduit 20 having an axis x-x and also having an inlet 21 and an outlet 22 for the steam. The first conduit 20 is arranged internally of a hollow body 5 and can slide along the axis x-x. The sliding of the first conduit 20 is regulated continuously by a setting device 6 which enables controlled forward and backward displacements to be made for positioning the first conduit 20.

The setting device 6 comprises a regulating ring nut with a micrometer screw and a lock nut. The device 6 enables the geometry of the product nozzle 3 to be very finely set and adjusted during injector operation, without any need for dismantling the injector itself. The movement of the setting device, especially the micrometer screw, can be motorized.

The steam nozzle 2 can also comprise, as in the illustrated case, a core 23 arranged inside the first conduit 21 which can form an annular passage for the steam inlet. This annular passage is preferable but not indispensable. The liquid product nozzle 3 is provided with a second conduit 30 having an inlet 31 for the liquid product and an axis which is perpendicular to the axis x-x, as well as an outlet 32 which is located in proximity of the steam outlet 22. The liquid nozzle 3 comprises an annular terminal outlet part which is coaxial and external to the steam outlet 22. The hollow body 5 internally exhibits a third conduit 40, 41, 42,

43, for the steam-liquid mix which extends, with a longitudinal axis x-x, starting from the steam and product outlet 22 and 32 zones and going right up to an outlet

44. The third conduit internally comprises the mixing chamber 4 and is formed by a converging first tract 40, a second converging tract 41 with a slight smaller angle of convergence to the first tract 40, a third tract 42 having a constant section and a fourth tract 43 which diverges. The third conduit is formed by a tubular insert 45 made of a non-stick material (preferably plastic, for example teflon, or non-stick ceramic). It has been noted that the use of these materials for the mixing chamber 4 considerably reduces fouling of the injector and the formation of encrustations. Thanks to the absence of encrustations, the shape of the mixing chamber 4 crossed by the two-stage mix is not modified even after a long operating period.

The tubular insert 45 can be substituted by another so that different flow-rates of the fluid can be treated with the same injector structure. Downstream of the outlet 44 of the mixing chamber there are located means of known type and not illustrated for generating within the chamber 4 an adjustable counterpressure which gives rise to a shock wave, which can be regulated in terms of intensity and position. These means can comprise, for example, an adjustable intercept valve or other device for fluids.

The annular outlet 32 for the liquid product is internally delimited by the outlet end of the first conduit 20 and externally delimited by a converging wall of the insert 45. The outlet 32 passage hole for the liquid product is continuously adjustable by controlled displacements along the axis x-x of the first conduit 20 by adjusting the setting device 6 by means of the micrometer screw. The diagram of figure 2 describes the velocity curves V of the liquid product alone (curve L), of the two-stage product-steam mix (curve LV), and of the steam alone (curve V) according to the position X along the longitudinal axis x-x of the device. I, II, III, IV and V indicate some characteristic sections along axis x-x indicated in figure 1 which are, in order: the annular passage of the liquid product alone and the annular passage of the steam alone (section I); steam outlet 22 surrounded by liquid product outlet 3, which enters into the steam flow at a high speed (section II of the start of a pre-mixing chamber defined by tract 40 of the conduit having a converging section with a relatively large angle of convergence); start of converging tract 41 of the mixing chamber with a relatively small angle of convergence (section III); start of tract 42, constant-section, of the mixing chamber (section IV); start of tract 43, with a diverging section, of the third conduit (section V).

During operation, the flow of steam enters the device 1 in the direction indicated by arrow F, through the inlet 21 of the first conduit, and flows down the annular passage with the converging section. The steam inlet speed is such that, in proximity of section II of the annular conduit outlet, the speed of the steam flow is sonic or supersonic and reaches, for example, around 200-300 metres per second. The liquid product to be sterilized enters the device in the direction indicated by arrow G, through the inlet 31, and is entrained towards the steam- mixing zone at a speed which increases progressively by virtue of the decreasing section of the passage conduit. The speed of the product in section II depends not only on the inlet characteristics (flow rate, temperature, viscosity etc.) But also on the desired predetermined values fixed for the treated product (homogeneity, sterility, speed of dispersion, etc.). The speed of introduction of the liquid product is about 20-30 metres per second and is controlled such that the product inlet speed into the mixing chamber 4 is kept to the maximum level allowed while the product is in liquid form. The product is introduced into the mixing chamber in the form of a slim annular crown with a breadth comprised between 0.15 and 2.5 mm. It has been seen that with a crown film breadth of less than 0.15 mm. undesirable and uncontrollable bubble cavitation phenomena occur in the product, upstream of the product outlet 32. The above-mentioned conditions (keeping the product in a liquid form and breadth of the liquid film (crown) comprised between 0.15 and 2.5 mm.) are achieved by regulation of the various parameters, among which, apart from the liquid and steam inlet speed, there is also the size of the passage hole through which the product enters the pre-mixing chamber (section II); this is regulated, as mentioned, by means of the setting device 6 with the micrometer screw being adjusted in order continuously to position the first conduit 20 along the axis x-x, until the limit position is reached, at which the product speed is the maximum possible, beyond which the product begins to vaporize upstream of the product outlet 32. The characteristic parameters of the product flow internally of the injector, especially its velocity and the slim conformation, determine high turbulence and excellent interchange between the product and the steam. Downstream of section II, where the product enters into contact with the steam flow, thanks to the geometrical shape of the conduit, a product aspiration zone is generated, which enables the product to flow into the steam current. The steam entrains the product, creating a two-stage mixture which crosses the converging section. In the pre-mixing chamber, defined by the tract 40, where steam condensation begins, the speed of the product-steam mixture is supersonic. Then the two-stage mixture enters the mixing chamber (defined by tracts 41, 42 and 43) at supersonic speed and undergoes progressive condensation of the steam into the liquid, so that the specific volume diminishes. Consequently the speed of sound of the mixture increases and the mixture passes from a supersonic speed to a subsonic speed. When the mixture flow crosses tract 42 it meets a shock wave by effect of which there is a rapid condensation of any gas remaining. The two-stage mixture is in effect compressed during its flow internally of the injector, up until a single-stage liquid mixture is obtained, which exits from the injector in direction H. Figure 3 describes the progress of the temperature of the liquid product over time during treatment in the injector. Figure 3 compares three progressions of the process in object (curves Ai, A2 and A3) to an infusion process (curves Bi, B2 and B3) and to a traditional injection process (Ci, C2 and C3). The curves Ci, C2 and Cs describe, respectively, the progress of the minimum, mean and maximum temperatures. Ts denotes the nominal sterilization temperature. As can be ob served, the flow of product under treatment exhibits considerable lack of temperature uniformity'. Curve C3 exceeds Ts, by a relatively large amount and stays above Ts for a considerable time, which means that a part of product remains at a decidedly higher temperature than Ts and for a relatively lone time tc, with a consequent degradation in the aesthetic and nutritional qualities of a part of the product. The corresponding curves Bi, B2 and B3 relating to the infusion processes, denote an improvement with respect to the previous processes described by Ci, C2 and C3, both because the maximum temperature reached by the product is lower, and because the time tb a part of the product remains at a temperature above Ts is lower than tc. The process of the invention (curves Ai, A2 and A3) provides a further improvement, especially in relation to the fact that the uniformity of the temperature in the whole product is reached in a very short time, so that the time ta a part of the product remains at a temperature above Ts is extremely short (round about a few hundredths of a second) and in any case lower than tb; thus the quality of the treated product is guaranteed. Basically, with the process and device of the invention, the steam transfers the condensation energy to the liquid in a very short tract of the injector, and for a very short time indeed. It has been observed that the present invention enables an excellent sterilization of the product at a relatively low temperature Ts. It is believed that this is due to a mechanical stress action on the microbe species in the product due to the considerable turbulence, especially in the zone where the steam and the product meet. Experiments have demonstrated that the product close to this zone is of a turbulence in the region of a Reynolds number of 5 to 7 million. The fact of introducing the steam in the injector at sonic or supersonic speed leads to a formation in the injector of a particularly homogeneous two-stage steam-liquid mixture with a very fine dispersion of the two stages. The injector has also been seen to function very stably, especially when compared to the prior- art injectors.

In another embodiment, not illustrated, the steam can enter the mixing chamber not only through a first inlet internally of the product inlet (as in figure 1) but also through a second annular inlet which surrounds the periphery of the product inlet. This solution is especially advantageous for very viscous liquid products as well as for relatively large quantities of product.

Claims

Qaims.

1). A process and device for sterilization and homogenization of liquid products, of a type which is actuated by means of a steam-liquid injector provided with a steam outlet nozzle, a liquid product outlet nozzle and a steam-liquid mixing chamber, which process comprises an introduction stage of the steam and the liquid into the mixing chamber by aspiration of the liquid by the steam which exits from the steam outlet nozzle, so as to create a two-stage steam-liquid mixture in the mixing chamber, wherein: an inlet speed of the product into the mixing chamber is kept up to a maximum possible while keeping the product in liquid form upstream of an outlet of the liquid product outlet nozzle; the two- stage steam-liquid mixture being compressed, during a flow thereof internally of the injector, up until a single-stage liquid mixture is obtained.

2). The process of claim 1, wherein a velocity of the steam at an outlet of the nozzle is sonic or supersonic.

3). The process of claim 1, wherein a velocity of the two-stage mixture is supersonic at least in a first zone of the mixing chamber.

4). The process of any one of the preceding claims, wherein there is a stage in which an adjustable counterpressure is created at an outlet of the injector.

5). The process of any one of the preceding claims, wherein the liquid product is introduced into the mixing chamber in an annular crown-shape having a width of between 0.15 and 2.5 mm. 6) The process of any one of the preceding claims, wherein, while the liquid product is being introduced into the mixing chamber, an outlet section of the liquid product nozzle is continuously regulated in order to vary the inlet speed of the product, and contemporaneously a check is made to make sure a limit speed is reached at which the product inlet speed is at a maximum which allows the liquid product to remain in a liquid state.

7). A device for sterilization and homogenization of liquid products, as in the process described in claim 1, of a type which comprises a steam-liquid injector provided with a steam outlet nozzle, a liquid product outlet nozzle and a steam- liquid mixing chamber connected to the steam and liquid product outlet nozzles, in which mixing chamber a two-stage steam-liquid mixture is created by aspiration of the liquid product by the steam exiting from the steam outlet nozzle, wherein the device comprises means for continuously regulating a geometry of the liquid product outlet nozzle.

8). The device of claim 7, wherein the means for continuously regulating continuously adjust a passage hole of the liquid product outlet.

9). The device of claim 7 or 8, wherein the means for continuously regulating comprise a setting device provided with a micrometer screw for regulating a position of the steam nozzle with respect to a longitudinal axis (x-x) of the mixing chamber.

10). The device of claim 9, wherein a movement of the setting device provided with a micrometer screw is motorized. 11). The device of any of the preceding claims from 7 to 10, wherein the mixing chamber is at least partially delimited by walls having non-stick properties.

12). The device of claim 11, wherein the material having non-stick properties is a non-stick plastic material.

13). The device of claim 11, wherein the material having non-stick properties is a non-stick ceramic material.