Heating, mixing and hydrating apparatus and process

Abstract

The invention relates to apparatus and a process for mixing a gas/vapour with a process liquid comprising a material and a carrier liquid. The apparatus comprises a passage (10) of polygonal cross section having an inlet (14), an outlet (16) for a process liquid comprising the material, and a nozzle (24) for introducing supersonic gas/vapour at a mixing zone (42) in a single plane.

Claims

1. Apparatus for mixing a material with a gas/vapour, the apparatus comprising: a passage defined by a wall and having an inlet and an outlet, wherein a process liquid comprising a material and a carrier liquid flows from said inlet to said outlet; and a nozzle for introducing a gas/vapour into said passage at a mixing zone, wherein the cross sectional profile of the passage at the mixing zone is polygonal and said nozzle is configured as a slit, wherein said slit runs in a direction substantially perpendicular to the direction of flow of said process liquid at said inlet such that said gas/vapour enters said passage in a single plane and wherein the cross sectional area of said passage at said mixing zone is smaller than the cross sectional area of said passage at said inlet and wherein said nozzle is positioned in said wall of said passage above said process liquid such that said gas/vapour flows downwards towards said process liquid; wherein said process liquid comprises a suspension of a solid in a liquid, a colloidal solution or suspension, or an emulsion; characterised in that: said nozzle is provided in a rotatable member, wherein said rotatable member is rotatable through an arc of at least 10 such that the angle between said direction of flow of said gas/vapour and said direction of flow of said process liquid can be varied; and said nozzle has a nozzle profile comprising a de Laval convergent-divergent section extending along the slit for introducing said gas/vapour at supersonic velocity into said passage at said mixing zone.

2. Apparatus as claimed in claim 1, wherein said material is selected from the group consisting of: (i) a polysaccharide selected from starch; (ii) natural gums such as agar, alginic acid, sodium alginate, carrageenan, gum Arabic, gum tragacanth, guar gum, locust bean gum, beta-glucan and xanthan gum; (iii) cellulose and carboxymethylcellulose; and (iv) a protein or a fat.

3. Apparatus as claimed in claim 1, wherein said material comprises a foodstuff.

4. Apparatus as claimed in claim 1, wherein said gas/vapour comprises steam.

5. Apparatus as claimed in claim 1, wherein said passage at said mixing zone is rectangular in cross section.

6. Apparatus as claimed in claim 1, wherein the angle between the direction of flow of said gas/vapour and said direction of flow of said process liquid is at least 10.

7. Apparatus as claimed in claim 1, wherein said rotatable member rotates through at least 20.

8. Apparatus as claimed in claim 1, wherein said wall of said passage forms a housing for said rotatable member.

9. Apparatus as claimed in claim 8, wherein the rotatable member can be rotated into a position in which the nozzle abuts the wall of the passage such that the outlet of the nozzle is closed off from the passage, preventing or substantially limiting the flow of gas/vapour.

10. Apparatus according to claim 1, further comprising one or more movable flaps mounted on said wall of the passage at said mixing zone.

11. Apparatus as claimed in claim 10, wherein said one or more movable flaps comprise a flap which is hinged at its upstream end and is rotatable through an arc of up to 60 between a first position and a second position in which it forms a lesser angle with the wall of the passage.

12. Apparatus as claimed in claim 1, wherein said carrier liquid comprises water or an aqueous solution containing one or more solutes.

13. A system for mixing a material with a gas/vapour, the system comprising: a reservoir for a process liquid comprising a material and a carrier liquid; apparatus according to claim 1, wherein said apparatus is in fluid connection with said reservoir; a collection vessel for mixed and/or hydrated material in fluid connection with said apparatus; a pump for pumping said process liquid from said reservoir through said apparatus and into said collection vessel; a source of gas/vapour in fluid connection with said nozzle; and a control system for controlling the pressure and/or temperature of said gas/vapour.

14. A system as claimed in claim 13, wherein said control system is further arranged and adapted to control one or more of: (i) a heating element for raising the temperature of said process liquid upstream of said mixing zone; (ii) a pump for pumping said process liquid through said apparatus; (iii) said rotatable member in order to vary the angle between said direction of flow of said gas/vapour and said direction of flow of said process liquid; and (iv) the positions of one or more movable flaps.

15. A process for mixing a material with a gas/vapour, the process comprising: providing a passage defined by a wall and having an inlet and an outlet and causing a process liquid comprising a material and a carrier liquid to flow from said inlet to said outlet; and introducing a gas/vapour into said passage at a mixing zone via a nozzle, wherein the cross sectional profile of the passage at the mixing zone is polygonal and wherein said nozzle is configured as a slit, wherein said slit runs in a direction substantially perpendicular to the direction of flow of said process liquid at said inlet such that said gas/vapour enters said passage in a single plane and wherein the cross sectional area of said passage at said mixing zone is smaller than the cross sectional area of said passage at said inlet and wherein said nozzle is positioned in said wall of said passage above said process liquid such that said gas/vapour flows downwards towards said process liquid; wherein said process liquid comprises a suspension of a solid in a liquid, a colloidal solution or suspension, or an emulsion; characterised in that: said nozzle is provided in a rotatable member wherein said rotatable member is rotatable through an arc of at least 10 such that the angle between the direction of said flow of said gas/vapour and said direction of flow of said process liquid can be varied; and said process further comprises introducing said gas/vapour at supersonic velocity into said passage at said mixing zone via said nozzle having a nozzle profile comprising a de Laval convergent-divergent section that extends along the slit.

16. A process as claimed in claim 15, wherein said material is selected from the group consisting of: (i) a polysaccharide selected from starch; (ii) natural gums such as agar, alginic acid, sodium alginate, carrageenan, gum Arabic, gum tragacanth, guar gum, locust bean gum, beta-glucan and xanthan gum; (iii) cellulose and carboxymethylcellulose; and (iv) a protein or a fat.

17. Apparatus for mixing a material with a gas/vapour, the apparatus comprising: a passage defined by a wall and having an inlet and an outlet, wherein a process liquid comprising a material and a carrier liquid flows from said inlet to said outlet; and a nozzle for introducing a gas/vapour into said passage at a mixing zone, wherein the cross sectional profile of the passage at the mixing zone is polygonal and said nozzle is configured as a slit, wherein said slit runs in a direction substantially perpendicular to the direction of flow of said process liquid at said inlet such that said gas/vapour enters said passage in a single plane and wherein the cross sectional area of said passage at said mixing zone is smaller than the cross sectional area of said passage at said inlet and wherein said nozzle is positioned in said wall of said passage above said process liquid such that said gas/vapour flows downwards towards said process liquid; wherein said process liquid comprises a suspension of a solid in a liquid, a colloidal solution or suspension, or an emulsion; characterised in that: said nozzle is provided in a rotatable member, wherein said rotatable member is rotatable through an arc of at least 10 such that the angle between said direction of flow of said gas/vapour and said direction of flow of said process liquid can be varied; and said nozzle has a nozzle profile comprising a de Laval convergent-divergent section for introducing said gas/vapour at supersonic velocity into said passage at said mixing zone and further comprising a flap positioned fully downstream of the nozzle.

Description

(1) The invention will now be described in greater detail with reference to the accompanying drawings in which:

(2) FIG. 1 is a cross sectional view of apparatus according to the invention.

(3) FIG. 2 is a similar view to FIG. 1 which shows apparatus with additional ports for the introduction of additional agents to the mixing zone and which shows the various regions of the passage where mixing takes place.

(4) FIG. 3A shows a further device similar to that of FIG. 1.

(5) FIG. 3B is a cross section through line C-C of FIG. 4A.

(6) FIG. 4 shows the device of FIG. 4 in which the movable flap has been rotated through an angle of 12 in order to reduce the cross sectional area of the mixing zone.

(7) FIG. 5 is a cross section of a detail of the mixing zone of an alternative embodiment in which an additional liquid is introduced via an ultrasonic droplet generating injection device.

(8) FIG. 6 is a schematic diagram of an example control system for a system comprising apparatus of the invention, in which US indicates upstream; DS indicates downstream; MZ indicates mixing zone; and SP indicates set point for a given variable (allowing for some deadband); and where the control loops may have proportional and/or integral and/or derivative function applied.

(9) FIG. 1 illustrates apparatus which comprises a passage (10) having substantially rectangular cross section and which is defined by a wall (12) formed from a metallic material such as stainless steel. The passage has an inlet (14) for a process liquid comprising a material to be mixed and hydrated and an outlet (16) for mixed hydrated material. The invention further comprises a cylinder (18) which is formed from a similar material to the wall (12) and which is housed in a housing (20) which forms a part of the wall (12) of the passage (10).

(10) The cylinder (18) has defined therein a passage (22) to allow steam to flow from an steam inlet (not shown) to a steam nozzle (24) which opens from the lower part (26) of the cylinder into the passage (10). The steam nozzle (24) is in the form of a slit which runs parallel to the longitudinal axis of the cylinder (18).

(11) The cylinder (18) is rotatable about its longitudinal axis so that the angle of the steam nozzle can vary with respect to the axis of the passage. At one extremity of the rotation, the nozzle (24) lies within the downstream end (26) of the housing (20) such that the nozzle is closed. At the other extremity of rotation, the nozzle (24) opens into the passage at a location adjacent the upstream end (28) of the housing (20).

(12) Opposite and just downstream of the cylinder (18) the wall (12) of the passage (10) forms a housing (30) for a moveable flap (32). The flap (32) is in the form of a segment of a cylinder and is hinged at its edge (34) and has a face (36) which is rotatably in contact with a wall (38) of the housing. The flap can therefore rotate through an arc defined by its face (36) and by the wall (38) of the housing (30).

(13) At one extremity of the rotation, the flap lies substantially within the housing (30) such that the greater part of the face (36) of the flap is in contact with the wall (38) of the housing and the flap (32) forms a large angle with the wall (12) of the passage. In this configuration the cross section of the passage (10) is slightly reduced in a region (42) which lies adjacent and immediately downstream of the cylinder (18), compared with the cross section of the passage upstream. This is the mixing zone where mixing of the process liquid with the steam and subsequent vaporisation of the process liquid takes place.

(14) At the other extremity, the flap is rotated so that it protrudes into the passage, such that a flat upper surface (40) of the flap forms a reduced angle (i.e. less than 180) with the wall (12), and such that the face (36) of the flap is only partially in contact with the wall (38) of the housing. In this configuration the cross section of the passage (10) is at the mixing zone (42) to a much greater extent than when the flap is at the other extremity of its movement.

(15) FIG. 2 shows a similar apparatus to FIG. 1 and illustrates how mixing takes place. FIG. 2 shows the pre-mixing zone (1) which is the region of the passage immediately upstream of the nozzle (24). In FIG. 2, zone (2) is the region inside the flow of steam issuing from nozzle (24) and zone (4) is the end point of the steam flow. Zone (3) is the low pressure side of the mixing zone and zone (5) is the re-condensation point, which effectively represents the end point of the mixing zone. In zone (6) there is a region of turbulence which assists with mixing.

(16) The device of FIG. 2 has further features which are not present in the device of FIG. 1. The device has a powder entrainment hopper (50) positioned downstream of the cylinder (18) so that powder (52) can be added to the mixing zone via port (54).

(17) In addition, the flap (32) is provided with an internal passage (56) such that a further agent, preferably a liquid can be added to the mixing zone via a port (58) which opens in the face (40) of the flap (32).

(18) In use, a process liquid containing a material to be hydrated is pumped into the passage (10) via the inlet (14). Steam is supplied to the passage (22) of the cylinder (18) at a temperature and pressure such that choked flow is achieved at the narrowest point of the steam nozzle (24) ensuring that steam enters the passage (10) from the nozzle (24) at supersonic speed.

(19) The steam from the nozzle (24) enters the passage (10) in the mixing zone (42) and strikes the process liquid causing heating and atomisation of the process liquid, which allows mixing with the steam and mixing/hydrating of the material.

(20) If the mixing and/or hydrating is not optimal, however, the flap (32) may be moved into and out of the housing (30) until the optimum configuration is determined for the mixing zone (42) of the passage.

(21) For further optimisation of the mixing and/or hydrating of the material, the cylinder (18) may be rotated such that the angle of impingement of the steam supplied from the steam nozzle (24) with the process liquid flowing from the inlet (14) is varied. The cylinder (18) may be rotated until the optimum angle of impingement of the steam on the process liquid has been determined.

(22) This optimum angle may vary depending upon the material, the process liquid and their respective proportions as well as other considerations such as the exact temperature of the process liquid when it enters at inlet (14). Indeed, the optimum angle may vary for different batches of the same material.

(23) Further ingredients may be added to the mixing zone via the hopper (50) and port (54) or via the passage (56) and port (58) formed in the flap.

(24) FIG. 3A shows a further device similar to that of FIG. 1 and FIG. 3B is a cross section through line C-C of FIG. 4A. From FIG. 4B it can be seen that the passage (10) has rectangular cross section and that the nozzle (24) is in the form of a slit running parallel to the axis of the cylinder (18). FIG. 4B also shows how the cross sectional area of the passage (10) is reduced at the mixing zone through movement of the flap (32) within the housing (36). In the device of FIG. 4, the flap (32) has a contoured face (41) and has a smaller range of rotation than in the device of FIG. 1. The movement of the flap is shown in FIG. 4, in which the flap (32) has been rotated through an angle of 12 so as to reduce the cross sectional area of the mixing zone with respect to the flap position of 0 shown in FIG. 4.

(25) FIG. 5 shows a detail of the mixing zone (42) of the passage (10) in an alternative embodiment which includes an ultrasonic droplet generating injection device (60). The ultrasonic injection device (60) is mounted in the wall of the passage (10) opposite the nozzle (24). The ultrasonic injection device (60) is mounted on seals (62), for example O-rings, which prevent the process liquid (68) from leaking from the passage (10) but which allow movement, especially vibration, of the ultrasonic injection device (60).

(26) A stream of liquid (66) enters the ultrasonic injection device and is split by ultrasonic resonance into droplets (76), such that the liquid (66) is pre-conditioned before it is contacted by the steam, which flows from the nozzle (24) as indicated by arrows (70).

(27) Contact of the droplets (76) with the steam produces atomised liquid (74). The process liquid (68) is also atomised by the steam and can therefore easily mix with the atomised liquid (74) to form a mixture.

(28) The liquid (66) may be an active agent which is designed to combine with the material in the process liquid (68). Alternatively, however, it may be a liquid, for example an oil, which is intended to form an emulsion, a double emulsion, a microemulsion or similar composition with the atomised process liquid.

(29) In an alternative embodiment, the ultrasonic injection device (60) may be mounted in a flap (32) of a device similar to that shown in FIG. 2.

(30) FIG. 6 shows an example of a control system for a system comprising apparatus of the present invention. The system comprises a reservoir for the process liquid which is in fluid connection with a device of FIG. 1, FIG. 2 or FIGS. 3 and 4. Downstream of the device is a collection vessel for mixed and hydrated process liquid.

(31) The process liquid is moved from the reservoir, through the device and into the collection vessel by a pump. The device is equipped with a number of sensors; including sensors for detecting the temperature of process liquid upstream and downstream of the mixing zone; a sensor for detecting the flow rate of the process liquid immediately downstream of the mixing zone; and shock sensors for detecting atomisation at the mixing zone and downstream of the mixing zone.

(32) The device also comprises an actuator for rotating the cylinder (18) such that the angle of impingement of the steam supplied from the steam nozzle (24) with the process liquid flowing from the inlet (14) is varied.

(33) The device further comprises an actuator for moving the flap (32) into and out of the housing (30).

(34) There are also means for adjusting the steam pressure and the speed of the pump.

(35) In use, the operator selects a suitable inlet temperature and an appropriate temperature difference across the device. The upstream temperature sensor detects the inlet temperature and downstream temperatures sensor detects the outlet temperature. As shown in FIG. 6, if the difference between the inlet and outlet temperatures falls below the selected appropriate temperature difference, the control system causes the actuator to rotate the cylinder (18) such that the angle between the flow of steam and the flow of process liquid is increased. On the other hand, if the temperature difference rises above the selected value or if the inlet temperature (US temperature) is approaching a selected maximum value, the control system causes the actuator to rotate the cylinder (18) such that the angle between the flow of steam and the flow of process liquid is decreased.

(36) The operator sets a required value for the flow rate through the apparatus. FIG. 6 shows that if the flow rate falls below the required value or if a stall in the flow is detected; or if the apparatus is stopped and is ready to start, the control system may: cause the actuator to rotate the cylinder (18) such that the angle between the flow of steam and the flow of process liquid is decreased; and/or decrease the angle of any flaps; and/or decrease the steam pressure; and/or increase the pump speed.

(37) It is important for efficient mixing that the process liquid is fully atomised in the mixing zone. Therefore, as shown in FIG. 6, if the shock sensor at the mixing zone (suitably a piezoelectric element) detects incomplete atomisation at the mixing zone, the control system causes the pressure of the steam supplied to the nozzle to be increased.

(38) On the other hand, it is not optimal for the process liquid to be atomised downstream of the mixing zone since this is a waste of energy. Therefore if the shock sensor downstream of the mixing zone detects atomisation, the control system causes the pressure of the steam supplied to the nozzle to be decreased.

(39) The present invention therefore provides apparatus which allows mixing and/or hydrating of a material mixed with a process liquid using steam. The apparatus comprises means for adjusting and optimising the configuration of the mixing zone where mixing and/or hydrating take place. In addition, the nozzle via which steam is introduced may be adjustable such that the angle of impingement of the steam on the process liquid can be varied in order to determine the optimum conditions.