A METHOD FOR INJECTING A PRODUCT INTO A FLUID, AND AN APPARATUS FOR CARRYING OUT THE METHOD

Abstract: In injection of steam, gas, liquid or a powdered or granulate product into a fluid in an injection apparatus having a substantially disc-shaped rotor (53), a product inlet (50) and a central product outlet (57), the injection is carried out in a limited intermediate zone above the disc-shaped rotor (53) at a distance from both the circumference and the center of the rotor (53). The fluid product which may be a liquid with considerable variation of dry solids content and viscosity is exposed to a radial displacement effect as well as a tangential dispersion effect.

Description: A method for injecting a product .into a fluid, and an apparatus for carrying out the method The invention relates to a method of injecting a product into a first fluid, whereby in an injection apparatus having a substantially disc-shaped rotor, a radial displacement effect is imparted to the first fluid, said product being injected into a limited intermediate zone above the disc-shaped rotor displaced from both the center and the circumference of the rotor, in which zone the first fluid is exposed to a tangential dispersion effect in addition to said displacement effect. Such an injection method is known from published international patent application WO 94/13395. Without in any manner being restricted thereto, the method according to the invention has substantial fields of application in, partly, heat treatment of liquids by injection of steam, for example bactericidal UHT treatment of milk products or pregelatinization of starch products, partly injection of gases, for example C0 2 or nitrogen into such liquids which are subsequently to be spray dried with the aim of reducing the density of a powder product obtained by the spray drying, partly injection of a liquid, for example water, into certain fatty or oily products with a view to reduction of the fat content and partly mixing of a solid product in powder or granulate form into a liquid. In connection with the spray drying of food products, for example milk products or fruit juice, it is known from US patents Nos. 3,185,580 and 3,222,193 to make an injection of a gas directly into an elongated mixing pipe through which the liquid starting material flows before supply to an atomizer in the spray drying apparatus. This type of gas injection is not suitable for heat treatment at higher temperatures, as it will inevitably lead to burning. Actually, the above patents also direct that a heat treatment of the product, for example for pasteurization purposes, be made in a conventional preheater. US patent No. 3,182,975 describes an apparatus for heat treatment of milk products at an increased tempera¬ ture after a prior preheating by injection of steam into a mixing chamber to which the product to be treated is supplied. Steam injection is carried out by means of a propeller-like rotor with perforated tubular blades where the steam extravasates on the back of the rotor blades seen in the direction of rotation at a relatively low pressure, whereby the pressure is increased through the mechanical influence from the rotation of the rotor. The intention is to obtain a rapid heating without burning. SU patent specification No. 578046 describes another method of heat treatment of milk products where the product is also supplied to a mixing chamber by a propeller-like rotor, but here the steam supply is made via a distributor system with annular distributing conduits arranged concentrically in relation to the rotor and controlled by means of a valve arrangement so that the steam in the central area of the chamber is supplied at a relatively low temperature and pressure, and in the peripheral area at a substantially increased temperature and pressure. The intention is to obtain a very rapid heating to sterilization level after a preheating in the central area. In this construction, however, the strong heat influence at the periphery involves a considerable risk of burning. It is known from US patent specification No. 4,479,908 to make an injection of gas into a fluid product of a higher density by a method in which a strong turbulence and high flow velocity are imparted to the fluid product by passing it through a conduit part with a curved wall in connection with a constricted flow section where the gas injection takes place through an adjustable nozzle. According to the patent, the method may also be used for heat treatment of milk products by injection of steam at a temperature of about 170°C. CH patent specification No. 531363 describes an apparatus for mixing a liquid raw material with a gas, for example with a view to foaming, whereby the mixing takes place in a mixing chamber by means of a rotor disc with projecting teeth moving between stationary teeth in a surrounding stator part, the rotor disc performing an eccentric circulatory movement about the axis of the stator frame. Similar embodiments of mixing heads with a rotor provided with teeth engaging with teeth in a stator system where the sets of teeth may be arranged in several steps mutually displaced in the radial and axial directions are known from DE patent No. 3127684, EP patent application No. 0253139 and published interna¬ tional patent application No. WO 91/07221. Whereas, in the two latter mixing methods the supply of the fluid product to be treated, and the injection of gas take place at the same place in the mixing chamber, preferably in its central part, the method disclosed in DE-C-3127684 provides for injection of the gas into a working space displaced from the inlet and outlet and delimited by projecting toothed rims from the rotor and stator, respectively. In all these prior art mixing methods as well as the injection method disclosed in WO 94/13395 the fluid product to be treated is caused to flow radially from center towards the circumference of the rotor. Whereas this does not play a significant role for pure mixing processes experiments have shown that in heat treatment processes the heated products may have a residence period in the rotor after the heat treatment of a duration entailing a risk of burning the product and formation of build-up deposits of burned material. The method of the invention is distinguished from this prior art in that said radial displacement is imparted with a direction from the circumference towards the center of the rotor. By injecting the product, which, as mentioned above, may be both steam or gas, a liquid, for example water, or a powdered or granulate product in a limited zone in the rotor casing, an exposing at the same time the first fluid to both a radial displacement effect directed from the circumference towards the center of the rotor and a tangential dispersion effect, it has proved possible not only to optimize the injection for a large number of different applications, but at the same time avoid deposits in heat treatment processes. In connection with heat treatment of foodstuffs and other products, for example the above UHT treatment of milk products, where heating to a temperature of about 120-150°C is required in order to obtain the desired bactericidal effect, the method according to the inven¬ tion thus, in comparison with prior art, causes an almost instantaneous heating as a result of the simulta¬ neous dispersion and displacement which causes an optimum distribution of the injected fluid. After the heat treatment the treated product is quickly discharged through the outlet which is provided in the central part of the apparatus. As a result of this, for example, UHT treatment of milk products may be carried out with a higher degree of retention of the original taste and nutritional qualities than possible so far, and without any form of burning. In a preferred embodiment of the method, said displacement and dispersion effects are caused by having the first fluid forced through slots in circumferential wall parts of the rotor and stationary wall parts of an oppositely positioned stator. The first fluid which is treated by means of the method according to the invention will preferably be a liquid, which may, however, exhibit considerable variation with regard to viscosity and dry solids content, ranging from a mobile liquid without any solids to a viscous paste-like consistency with a dry solids content of up to 90 per cent. The invention also relates to an apparatus for carrying out the method as defined in the foregoing, comprising a substantially disc-shaped rotor positioned parallel to and coaxial with a stator in a casing and having an inlet and an outlet for said first fluid arranged to define a mainly radial flow path for said first fluid, feed passages being formed in the stator for injection of said product into a limited interme¬ diate zone above the rotor displaced from both the center and the circumference of the rotor. The apparatus according to the invention is characterized in that said flow path extends from the circumference towards the center of the rotor. To obtain a good distribution of the second fluid during its introduction in the injection chamber is provided on the side facing the stator with at least one projecting cylindrical wall and the stator is provided on the side facing the rotor with at least two projec¬ ting coaxial cylindrical walls disposed on either side of the cylindrical wall on the rotor sharp-edged slots being formed to extend substantially parallel to the axis of the rotor in said coaxial"cylindrical walls on the rotor and the stator. The rotor may suitably have two projecting coaxial cylindrical walls projecting upwards, of which the radially innermost wall will be located radially inside the radially innermost wall of the stator. In a preferred embodiment of the apparatus the sharp-edged design of the slots in the cylindrical walls, which is important to an efficient dispersion effect, is obtained by the axis-parallel slots in the cylindrical walls being formed as axially directed bores from the free edges of these walls and having a diameter exceeding the wall thickness. As a substantial additional advantage it has proved possible to design the apparatus in an embodiment which is substantially more silent at steam injection into a liquid than the prior art apparatuses, in that the axis- parallel slots in the cylindrical walls are asymmetrically distributed in the circumferential direction. The invention will now be described in further detail below with reference to an embodiment shown in the drawing and by means of examples. In the drawing, Fig. 1 shows an axial cross-sectional view of a preferred embodiment of an apparatus according to the invention; Fig. 2 is a section along the line II-II in Fig. 1; Fig. 3 and 4 alternative designs of the stator part of the apparatus shown in figs. 1 and 2; and Fig. 5 a further alternative design of the appara¬ tus. In the embodiment shown in fig. 1 and 2, the apparatus according to the invention is of the same general structure as the apparatus disclosed in the above-mentioned international patent application WO 94/13395 comprises a relatively flat cylindrical casing having a bottom 1 and a side wall 2. A rotor disc 5 is fastened on a drive shaft 3 projecting through the bottom 1 and being connected with a driving engine 4 arranged below the casing, which rotor disc 5 has two concentric walls 7 and 8 arranged radially displaced from the hub bush 6 arranged on the drive shaft 3, whereas the rotor 5 is shown with a mainly flat base it can take any convenient form as suggested in the prior art e.g. as disclosed in the references mentioned herein before. An inlet pipe 11 for the fluid to be treated in the apparatus is connected-with the side wall 2 of the rotor casing, whereas the casing is closed upwards by a stator cover 9 in which a central outlet pipe 10 is provided for discharge of the product. Corresponding to the cylindrical walls 7 and 8 projecting upwards from the upper side of the rotor disc 5, the lower side of the stator cover 9 facing the rotor disc is formed with a tube 12 projecting downwards, at the lower end of which an annular " chamber 13 is formed between two coaxial cylinder walls 14 and 15. The tube structure 12 is arranged on the lower side of the stator cover 9 so that the walls 14 and 15 are positioned on either side of the radially outermost wall 8 projecting upwards on the rotor disc 5, when the stator cover 9 is arranged on the casing 1, 2. The coaxial cylinder walls 7, 8, and 14, 15 on the rotor disc 5 and the stator cover 9, respectively, are designed with such wall thicknesses and positions that they engage with each other with relatively little clearance. A number of tubular channels 16 are connected with an annular injection chamber 13 through bores 16' in the tube structure 12, and with an annular distributor pipe 17, to which a feed pipe 18 is connected for supply of the product to be injected into the fluid flowing through the apparatus from the peripheral inlet pipe 11 to the central outlet pipe 10. As best appears from Fig. 2, each of the cylindri¬ cal walls 7, 8 and 14, 15 on the rotor disc 5 and the stator cover 9, respectively, are divided into tooth¬ like wall segments 20 by a number of slots 19. In the embodiment shown, each of the walls thus has a total of sixteen such slots, but this number may be varied within wide limits. To obtain a very sharp-edged form of the individual slots 19 both at the inner side and the outer side of each of the cylindrical walls 7, 8 and 14, 15, which form is advantageous to the desired dispersion effect, the slots are preferably formed as axial bores in the walls from the free end edges thereof and have a diameter exceeding the wall thickness and a depth of bore which may, for example, be as shown by the dashed lines 21 and 22 in Fig. 1. As a result of the wall geometry, the radially outermost wall on the rotor disc 5 will rotate in the injection chamber 13 formed between the stator walls 14 and 15, while the radially innermost wall 7 on the rotor disc 5 rotates on the inside of the radially innermost stator wall 14 and together with it ensures good distribution of the product supplied through the feed pipe 18, before the product is passed into the chamber 13. The radially innermost rotor wall 7 is not, however, strictly necessary. The rotary velocity for the rotor disc 5 may vary from 100 to several 1000 rp depending on the current purpose of application. The fluid supplied through inlet pipe 11 is forced through the slots 19 in the rotor and stator walls 15, 8, 14 and 7 during the rotation and finishes by being passed out through the outlet 10. The product supplied through the feed pipe 18, the distributor pipe 17 and the channels 16 may be steam, gas or liquid or a powdered or granulate product and is injected into the second fluid in the injection chamber 13 between the stationary chamber walls 14 and 15, and owing to the radial displacement effect and the tangen¬ tial comminuting or dispersion effect deriving from the sharp-edged slots, an instantaneous entrainment of the injected product is obtained so that by heat treatment, for example, an almost instantaneous temperature increase is obtained without burning, which is due on one hand to the wall geometry with the little clearance between the walls 7, 8, 14 and 15 and the slots 19 therein, and, on the other hand, to the fact that after passage through the injection chamber 13 the treated fluid only remain in the rotor casing a very short time before being discharged through the central outlet pipe 10. In fig. 3 an alternative design of the stator cover is shown in which the product to be injected into the fluid, which may for instance be steam, which may be of any pressure suitable for the actual application, i.e both above and below atmospheric pressure, is supplied through a pipe section 22 to an annular feed chamber 23 communicating in a bottom region with a number of channels 24 leading to the annular clearance 25 between the cylindrical walls 14 and 15 in which the upwardly projecting cylindrical wall 8 on the rotor is received when the stator is connected with the rotor. As illustrated the alternative stator design in fig. 3 may be divided into several parts to facilitate its manufacture. A lower part 26 forms the stator cover to be connected with the rotor to close the rotor casing upwardly and is provided with a central outlet opening 27. The supply pipe section 22 for the product to be injected is connected with an opening in a funnel shaped intermediate wall 28, whereas the feed chamber 23 is inwardly limited by a separate funnel-shaped wall section 29 joining an upwardly projecting wall section 30 on the lower cover part 26. Similarly a separate outlet pipe 31 joins an upwardly projecting wall section 32 around the central outlet opening 27 in cover part 26. Upwardly an external collar 32 is arranged in extension of funnel-shaped wall 28 and a cylindrical wall section 33 in extension of funnel-shaped wall part 29, whereas the feed chamber 23 is closed upwardly by an annular disc-shaped cover 35 connected with the external collar 33 by a clamping member 36 and joining the external collar 33 as well as the cylindrical wall section 34 via sealing members 37 and 38, respectively. By this relatively simple design the complexity of the feed structure with numerous separate tubular channels in the embodiment of figures 1 and 2 is avoided. The intermediate funnel-shaped wall section serves to form an intermediate space 39 around the central outlet pipe 31 to avoid transfer of heat from the steam supplied through channel 22 to the product discharged through outlet tube 31. If desired the annular space 39 surrounding the outlet tube 31 may serve as a cooling channel or accommodate other cooling means. Fig. 4 shows another alternative design of the stator part of the apparatus intended in this case for supplying carbon dioxide as the product to be injected into the fluid treated in the apparatus. A carbon dioxide generator 40 is discharging carbon dioxide into a substantially linear pipe section 41 to which two branch channel 42 and 43 are connected said channels leading to diametrically opposed channels 44 and 45 in the lower cover part 46 serving to close the rotor casing and formed at its underside with projecting cylindrical walls 14'' and 15'' matching the configur¬ ation of upwardly projecting cylindrical walls 7 and 8 on the rotor. Also in this case a central outlet opening 47 is formed in the cover part 46 and connected with separate outlet pipe sections 48 and 49 in extension thereof. The branch channels 42 and 43 are shown partly in section. Fig. 5 illustrates schematically a modified design of the rotor casing where a fluid inlet pipe 50 is connected to a central pipe section 51 surrounding the shaft 52 of the rotating disc-shaped rotor 53. The central pipe section 51 is connected with the bottom of the rotor casing 54, which is closed upwardly by the stator cover 55 in which feed passages 56 for the product to be injected as well as a central outlet 57 are provided. As a further explanation of the invention, some non-restricting examples carried out in practice are given below. The following examples were carried out using the above embodiment of the apparatus according to the invention, in all cases with a rotary velocity of 2800 rpm. Example 1: A baby food product "Instant Formula" with a dry solids content of 42 per cent by weight and a viscosity of 52 cP was heat treated by injection of steam at a vapour pressure of 500 KPa and a temperature of 159°C from an initial temperature of 72°C to a sterilization temperature of 120°C. As a result of the heat treatment, the desired sterilization was obtained with a mortal effect on spore-forming bacteria and their spores. This result was obtained without any kind of burning, discoloration or other destruction of functional properties in the product. Example 2: A baby food product "Follow-Up Formula" with a dry solids content of 40.2 per cent by weight and a viscosi¬ ty of 48 cP was heated by steam injection at a vapour pressure of 500 KPa from an initial temperature of 67°C to a sterilization temperature of 120°C with the same good results as stated in Example 1. These examples illustrate only to a limited extent the application potential for the method and the appar- atus according to the invention, but confirm the good results obtained by steam injection. With regard to the application potential in general, the method and the apparatus according to the invention as mentioned above, are suitable for fluid products with a dry solids content ranging from 0 to 90 per cent by weight both in connection with steam injec¬ tion and by injection of a cold gas. The viscosity may also vary within a wide range from 0.1 to 100,000 cP. Also with regard to products, the method and the apparatus according to the invention have numerous capa¬ bilities within the treatment of food products, such as heat treatment, density-reducing gas injection, gelatinizing, and emulgation, and for technical prod¬ ucts, such as plastic materials to be foamed.

Claims: P A T E N T C L A I M S 1. A method of injecting a product into a first fluid, whereby in an injection apparatus having a substantially disc-shaped rotor (5) , a radial dis- placement effect is imparted to the first fluid, said product being injected into a limited intermediate zone on one side of disc-shaped rotor (5) displaced from both the center (10) and the circumference of the rotor, in which zone the first fluid is exposed to a tangential dispersion effect in addition to said displacement effect, characterized in that said radial displacement is imparted with a direction from the circumference towards the center of the rotor. 2. A method according to claim 1, characterized in that said displacement and dispersion effects are caused by forcing the first fluid through sharp-edged slots (19) extending substantially parallel to the rotor axis in opposed coaxial cylindrical wall parts (7, 14, 15) of the rotor (5) and a stator (9) positioned opposite the rotor. 3. A method according to claim 1 or 2, character¬ ized in that the first fluid is a liquid with a dry solids content ranging between 0 and 90 per cent. 4. A method according to claim 1, 2 or 3, charac- terized in that said product is a second fluid. 5. A method according to claim 1, characterized in that said product is steam injected at a temperature in the range of 60-200°C and a vapour pressure in the range of 0,25-12 bar for instantaneous heating of the first fluid. 6. A method according to claims 3, 4 or 5, charac¬ terized in that the first fluid is a concentrate dairy product. 7. A method according to claim 6, characterized in that said concentrated dairy product is a milk con¬ centrate 8. A method according to claim 5 and any of claims 6 or 7, characterized in that the steam is injected at a temperature in the range of 105-165°C and a vapour pressure in the range of 1,2-6 bar. 9. A method according to claims 2 or 3, character¬ ized in that the first fluid is a starch product intended for gelatinization. 10. A method according to claim 4, characterized in that the second fluid is a gas injected for reduction of the density of the first fluid or a product obtained by spray drying thereof. 11. A method according to claim 4, characterized in that the second fluid is a liquid injected for emulsification of or into the first fluid. 12. An apparatus for carrying out the method according to any of the preceding claims, comprising a substantially disc-shaped rotor (5) positioned parallel to and coaxial with a stator in a casing (1, 2) and having an inlet (11) and an outlet (10) for said fluid arranged to define a mainly radial flow path for said fluid, feed passages (16') being formed in the stator (9) for injection of said product into a limited intermediate zone (13) on one side of the rotor (5) dis¬ placed from both the center and the circumference of the rotor, characterized in that said flow path extends from the circumference towards the center of the rotor (5) . 13. An apparatus according to claim 12, charac¬ terized in that the rotor is provided on the side facing the stator (9) with at least one projecting cylindrical wall (7, 8) and the stator is provided on the side facing the rotor (5) with at least two projecting coaxial cylindrical walls (14, 15) disposed on either side of the cylindrical wall on the rotor (5) sharp- edged slots (19) being formed to extend substantially parallel to the axis of the rotor in said coaxial cylin¬ drical walls (7, 8, 14, 15) on the rotor (5) and the stator (9) . 14. An apparatus according to claim 13, character¬ ized in that the rotor (5) has two projecting coaxial cylindrical walls (7, 8), of which the radially inner¬ most wall (7) which is located radially inside the radially innermost wall (14) on the stator (9) . 15. An apparatus according to claim 13 or 14, char¬ acterized in that the projecting coaxial cylindrical walls (7, 8, 14, 15) on the rotor (5) and the stator (9) are positioned with a small clearance in the radial direction. 16. An apparatus according to any of claims 13 to 15, characterized in that the axis-parallel slots (19) in the cylindrical walls (7, 8, 14, 15) are formed as axially directed bores from the free edges of these walls and having a diameter exceeding the wall thick¬ ness. 17. An apparatus according to any of claims 13 to 16, characterized in that the slots (19) in the cylin¬ drical walls (7, 8, 14, 15) are distributed asymmetrically in the circumferential direction. 18. An apparatus according to any one of claims 12 to 17, characterized in that said feed passages compri¬ ses a number of tubular channels (16) , opening out into an injection chamber (13) defining said limited interme- diate zone. 19. An apparatus as claimed in any of claims 12 to 17, characterized in that said feed passages comprises an annular feed chamber (23) forming an integral part of the stator and being connected with said feed passages (24) . 20. An apparatus as claimed in any of claims 12 to 19, characterized in that said outlet (27, 31) is arranged in a central part of said stator. 21. An apparatus as claimed in claim 20, charac- terized in that said outlet (31) is surrounded by a cooling means. 22. An apparatus as claimed in claim 20 or 21, characterized in that said inlet (11) is arranged in a wall part (12) of the casing opposite the circumference of the rotor. 23. An apparatus as claimed in claim 20, charac¬ terized in that said inlet is arranged opposite a central part of the side of the rotor facing away from said limited zone.

Inventors: RASMUSSEN CARSTEN OLE, RASMUSSEN, CARSTEN, OLE
Applicants: NIRO HOLDING AS, RASMUSSEN CARSTEN OLE, NIRO HOLDING A/S, RASMUSSEN, CARSTEN, OLE
Application year: 1995
Main classification: B01F5
IPC codes: B01F5, B01F7