WO2008046421A1

WO2008046421A1 - A trapping device for a particle separation arrangement, a process for separating particles, and use of the trapping device in a spray drying apparatus.

Info

Publication number: WO2008046421A1
Application number: PCT/DK2006/050063
Authority: WO
Inventors: Henrik Schwartzbach; Michelle Milling Madsen
Original assignee: Niro A/S
Priority date: 2006-10-18
Filing date: 2006-10-18
Publication date: 2008-04-24

Abstract

The trapping device (10) for a particle separator arrangement comprises a compartment (15) having a general longitudinal direction extending between an upper end (11) adapted to be connected to a powder source, for instance in the form of a cyclone (5), and a lower end (12) adapted to be connected to an ejector (20). The compartment (15) is provided with an inlet (13) adapted to receive a stream (50) of supply gas to supplement the amount of supply gas fed to the ejector in a separate, first stream (40) of supply gas.

Description

A trapping device for a particle separation arrangement, a process for separating particles, and use of the trapping device in a spray drying apparatus.

Field of the invention

The present invention relates to the general field of processing particulate material including spray drying technology applicable within a broad range of industries, e.g. the pharmaceutical, chemical and food industries. The term spray drying is here used in a broad sense as meaning not only processes for transforming a solid dissolved or suspended in a liquid into a particulate or powdery, possibly agglomerated material in a spray drying apparatus, but also processes in which an essential purpose is to agglomerate a particulate material by spraying and drying a liquid thereon.

Background of the invention

In a plant comprising i.a. spray drying and/or fluid bed processing of a particulate material, a number of processes are carried out. For instance, in a spray drying apparatus, the liquid feed is initially atomized and the flow of atomized material is subjected to drying gas in the drying chamber of the spray drying apparatus, following which the particulate material must be separated from the drying gas. A further example is separation of particulate material from a filter unit forming part of such a plant.

Within this field various well-recognized means for performing the separation process exist, which can be categorized as either external or internal separation means. Internal separation means are generally filters situated in the interior of the drying chamber and external separation means typically includes cyclones and/or filters, possibly followed by wet scrubbers, for final separation of particles entrapped in the spent drying gas. In the following, focus will be on particle separation arrangements comprising a powder source in the form of at least one cyclone. The theory underlying the function of such a cyclone is well known and is based on a vortex motion where the centrifugal force is acting on each particle and therefore causes the particle to move away from the cyclone axis towards the inner cyclone wall. However, the movement in the radial direction is the result of two opposing forces where the centrifugal force acts to move the particle to the wall, while the drag force of the gas acts to carry the particles into the axis. As the centrifugal force is predominant, a separation takes place. Particulate material and gas pass tangentially into the cyclone at equal velocities and swirl in a spiral form down to the base of the cyclone separating the particulate material out to the cyclone wall. Due to gravity, the particulate material moves downwards.

At the bottom of the cyclone there is an outlet through which the particulate material leaves the cyclone, either for collection into a collecting unit, or for further processing in the plant. A number of cyclones may also be connected to a common collecting unit. In one design, the outlet is provided with a locking device, which may be in form of a rotary valve, pneumatic valve or flap valve. This makes it possible to collect the particulate material which has moved downwards along the cyclone wall to the outlet. Although this design has proven to function well in many fields of application, it is not always advantageous due to a number of factors: First, there is a risk of clogging near or at the outlet. This problem is particularly pronounced in cyclones having a small diameter and if the particulate material is sticky. Furthermore, the particulate material entrained by the spent drying gas has a relatively high temperature (only slightly lower than the temperature of the drying gas) when it leaves the drying chamber, and is only cooled to a limited extent in the cyclone. Thus, the temperature at the outlet of the cyclone is relatively high as well, which increases the risk of deposits on the lower wall of the cyclone, which in turn increases the risk of clogging of the outlet. Second, there is a risk of drying gas escaping the locking device in an uncontrolled manner, particularly in arrangements, in which a number of cyclones are combined in a cyclone battery. This may lead to a pressure drop and, in turn, reduced efficiency of the cyclone. As an alternative, a trapping device may be positioned after the cyclone as a part of the particle separation arrangement such that the outlet of the cyclone is in connection with the inlet of the trapping device. In the cyclone, one portion of the spent drying gas spirals upwards along the centre axis of the cyclone and is extracted from the top of the cyclone, possibly for further transport to filter units. At the outlet of the trapping device, a portion of particulate material, is extracted by means of an ejector. This portion is pneumatically transported from the trapping device to further processing in the plant. However, although the ejector is supplied by gas in a separate stream of supply gas, it cannot be avoided that a quantity of drying gas is entrained when the particulate material is extracted from the trapping device. This, in turn, entails that spent drying gas from the powder source, i.e. in this case the cyclone, is sucked down into the trapping device when extracting the particulate material intended for further processing. In addition to disturbing the flow in the trapping device, this has a deteriorating effect on the cooling of the particulate material, as subjecting the particulate material to a quantity of drying gas having a relatively high temperature at this point slows the cooling process down.

Summary of the invention

With this background it is an object of the invention to provide a trapping device, in which the problem of clogging and reduced cooling of the particulate material is reduced. In one aspect of the invention, this and further objects are met by the provision of a trapping device for a particle separator arrangement, comprising a compartment having a general longitudinal direction extending between an upper end adapted to be connected to a powder source, and a lower end adapted to be connected to an ejector, characterized in that said compartment is provided with an inlet adapted to receive a stream of supply gas.

By providing the trapping device with an inlet adapted to receive a second stream of supply gas, a first stream of supply gas being supplied to the ejector, it has proven possible to outbalance the amount of gas extracted by the ejector, such that virtually no excessive drying gas is entrained from the powder source. The flow inside the compartment of the trapping device is not disturbed by flow of excessive drying gas. Furthermore, the inlet in the compartment makes it possible to introduce gas having a substantially lower temperature than the particulate material entrained in the drying gas, and hence, cooling may start at an earlier point. All in all, the reduced risk of clogging aimed at is achieved.

In an advantageous embodiment, said inlet is positioned in the upper half of said compartment. This position of the inlet provides a further possibility of initial cooling of the particulate material at a higher position in the trapping device. In this manner the effect of improved cooling and reduced risk of clogging aimed at are enhanced even further.

It is preferred that said inlet is a tangential inlet. This provides for an optimum flow path in the compartment of the trapping device

In order to provide a transition between the powder source and the trapping device, which makes it possible to separate the material from the drying gas, the cross-sectional dimensions of the compartment may in one embodiment increase steeply as measured along the longitudinal direction from the upper end in the direction toward the lower end. Preferably, the cross-sectional dimensions of the compartment increase to 2-10 times the dimensions at the upper end within the upper 25% of the longitudinal dimension of the compartment.

Alternatively, the cross-sectional dimensions of the compart- ment are substantially constant from the upper end to the lower end thus forming a substantially tubular compartment.

In a further embodiment, vortex affecting means are provided in said compartment. Advantageously, said vortex affecting means are substantially conical, the apex of the vortex affecting means being directed toward the upper end of the compartment. In a further development of this embodiment, the apex of the vortex affecting means is positioned closer to the upper end of the compartment than said inlet.

In another aspect of the invention a process for separating particles, comprising the steps of providing a stream of gas containing a particulate material constituting a powder source, guiding a stream of particulate material from the powder source to a trapping device including a compartment, extracting the particulate material from the trapping device by means of an ejector, supplying said ejector with a first stream of supply gas, and supplying a second stream of supply gas to an inlet in said compartment.

A further aspect provides for use of the trapping device in a particle separator arrangement connected to a powder source.

In principle, the trapping device may be utilized in any kind of plant, in which processing of a particulate material is carried out, examples being spray drying apparatus, fluid beds etc. The preferential fields of use include, but not exhaustively, a powder source in the form of a cyclone, a filter unit, or the drying chamber of a spray drying apparatus. Further details and advantages of the present invention will appear from the following description.

In the following the invention will be described in further detail by means of an embodiment thereof and the appended drawings.

Brief description of the drawings

Fig. 1 shows a schematic side view of a spray drying apparatus and separating means with an embodiment of a trapping device according to the invention;

Fig. 2 is a view, on a larger scale, of a detail of the spray drying apparatus separating means shown in Fig. 1;

Fig. 3 is a view corresponding to Fig. 2 of an alternative embodiment of the detail of the spray drying apparatus separating means; and

Figs 4 and 5 are views corresponding to Fig. 1, each represent- ing an alternative use of the trapping device according to the invention.

Detailed description of the invention and of preferred embodiments

Fig. 1 depicts a spray drying apparatus generally designated 1 in which a liquid feed to be atomized and dried is processed. In a manner known per se the spray drying apparatus 1 comprises a drying chamber 2 to which the liquid feed is supplied via a supply pipe (not shown). Drying gas is supplied to the drying chamber 2, likewise in a known but not shown manner. The drying gas may be air or any other gas suitable to the material to be dried. The liquid feed is fed to an atomizing device (not shown), which may be of any conventional design, e.g. a rotary atomizer wheel, a pressurized nozzle, a two-fluid nozzle or an ultrasonic nozzle. The form of the drying chamber is not critical to the present invention, and may as indicated comprise an upper part having an essentially cylindrical wall closed in the top with a wall forming a ceiling, and a lower part having a downward tapering frusto-conical wall. The downward tapering frusto-conical wall enters into an outlet 3 through which drying gas containing particulate material formed during the spray drying in the drying chamber 2 is taken out. The atomizing device may be mounted in the ceiling of the drying chamber 2 or, alternatively, or additionally, the spray drying apparatus may be provided with one or more nozzle arrangements in the walls of the upper and lower parts, respectively, of the drying chamber 2.

As mentioned in the above, the particulate material formed by the spray drying leaves the drying chamber 2 entrained in spent drying gas through the outlet 3 and further on through conduit 4, leading to a particle separation arrangement from which the particulate material is guided for further processing in the plant. As indicated in Fig. 1, the powder source in the particle separation arrangement shown consists of a primary cyclone 5, which is connected to a trapping device 10, which in turn is connected to an ejector 20 (also known as an eductor), from which the processed material is led to an end cyclone 30 via conduit 25. The resulting product in the form of particulate, or powdery, material is collected at an outlet 31 of the end cyclone 30. The function of in particular the trapping device 10 is to be described in further detail below.

The system containing the spray drying apparatus and its surrounding auxiliary equipment may be open or closed. In spray drying apparatus handling aqueous feed, an open cycle is normally utilized, whereas a closed cycle is utilized when spray drying feed containing organic solvents, when the product must not contact oxygen during drying, or when there is a risk of explosion of the recovered particulate material. In a closed cycle, spray drying is carried out in an inert gas atmosphere where e.g. nitrogen recycles within the dryer. Closed cycle systems are gas and powder tight, and are designed to the strictest safety standards, the inflammable solvent vapours being fully recovered in liquid form. However, the present invention is applicable both to open- and closed-cycle systems. Referring now in particular to Fig. 2, the structure and operation of the particle separation arrangement and in particular the trapping device 10 will be described in further detail.

Spent drying gas entraining particulate material is conducted to the primary cyclone 5 through conduit 4. In a manner known per se a vortex is generated, and particulate material and gas pass tangentially into the cyclone at equal velocities and swirl in a spiral form down to the base of the cyclone separating the particulate material out to the cyclone wall. Due to gravity, the particulate material moves downwards towards the outlet 9 of the primary cyclone 5. Some of the gas in the primary cyclone 5 spirals upwards along the centre axis of the cyclone and is taken out through the top 7 for transfer to the surroundings or further transport to a filter unit via conduit 8.

The trapping device 10 comprises a compartment 15 having a general longitudinal direction extending between an upper end 11 connected to the outlet 9 of the primary cyclone 5, and a lower end 12 connected to ejector 20. The compartment may have any suitable cross- section, e.g. cylindrical, square, rectangular, octagonal etc. With respect to the term "longitudinal direction" it is noted that this term applies to compartments having any possible relationship between its dimensions in the longitudinal direction and in directions transverse to the longitudinal direction. Hence, the longitudinal direction only indicates the general direction of transportation of the particulate material from the upper end to the lower end of the compartment due to gravity. For instance, the compartment may be as wide as it is tall. For reasons to be described in further detail below, the compartment 15 is provided with an inlet 13 adapted to receive a stream of supply gas. In the embodiment shown, the inlet 13 is positioned in the upper half of compartment 15. The inlet 13 may, in a manner known per se from arrangements including gas flow compartments, be a tangential inlet.

In the embodiment shown in Figs 1 and 2, the compartment has a shoulder section 15a followed, in the longitudinal direction, by a substantially cylindrical section 15b which in turn is followed by a conical section 15c. The cross-sectional dimensions of the compartment 15 increase steeply as measured along the longitudinal direction from the upper end 11 in the direction toward the lower end 12. The increase may be 2-10 times the dimensions at the upper end within the upper 25% of the longitudinal dimension of the compartment, i.e. within the shoulder section 15a. In the embodiment shown the ratio between the radius of the cylindrical section 15a and the radius at the upper end 11 is approximately 4. The function of the steep transition is to provide a velocity reduction of the drying gas entering from the primary cyclone 5.

Vortex affecting means 14 are provided in the compartment 15 in order to provide an obstacle to the drying gas vortex entering from the primary cyclone 5. Such vortex affecting means may in principle be formed in any suitable manner and may be positioned at any suitable place in the compartment. In the embodiment shown, the vortex affecting means 14 are designed as a substantially conical element, the apex of the vortex affecting means 14 being directed toward the upper end 11 of the compartment 15 and in such a position that the apex is positioned closer to the upper end 11 of the compartment 15 than said inlet 13. The vortex affecting means 14 may be mounted in the compartment 15 in any suitable manner, e.g. by fastening elements fastened to the shoulder portion 15a. The process for separating the particles thus comprise the steps of conducting a stream of gas containing a particulate material to a cyclone 5, guiding a stream of particulate material from the cyclone 5 to a trapping device 10 including a compartment 15, extracting the particulate material from the trapping device by means of an ejector, supplying said ejector with a first stream 40 of supply gas, and supplying a second stream 50 of supply gas to an inlet 13 in said compartment 15. The second stream 50 of supply gas is introduced through an inlet 13 in the upper portion of said compartment. The particulate material is extracted by said ejector 20 through a suction inlet (not shown) of the ejector connected to the lower end 12 of said compartment 15, and leaves the ejector through an outlet (not shown) of the ejector in an outlet stream of gas via conduit 25.

The flow rate of the gas containing particulate material may vary according to the overall size of the trapping device 10, the particulate material and the drying gas, but preferably, the flow rate lies in the interval 1 to 5 times the amount of material leaving the ejector as measured in kg/h. Examples of typical values (for small plants) are 10- 30 kg/h. The flow rate of the first stream of supply gas lies in the interval 1 to 10 times the amount of material leaving the ejector as measured in kg/h. Examples of typical values (for small plants) are 80- 120 kg/h. Eventually, the flow rate of the second stream of supply gas lies in the interval 1 to 10 times the amount of material leaving the ejector as measured in kg/h. Here, examples of typical values (for small plants) are 60-90 kg/h. In larger plants, the values may be considerably larger, e.g. up to 10 times larger than the values mentioned and in very small plants the values may be considerably smaller, e.g. down to 25% of the values mentioned. All in all, the respective amounts of gas, for instance in terms of flow rate measured in kg/h, should balance, such that the stream of gas containing particulate material entering the trapping device 10 plus the second stream 50 supplied to the inlet 13 plus the first stream 40 of gas supplied to the ejector substantially equals the stream coming out of the outlet of the ejector, i.e. via conduit 25. In this manner, no excess drying air is sucked from the cyclone 5. The temperature of the gas containing particulate material may lie in the interval 10⁰C to 200⁰C, but may vary according to the position of the particle separating arrangement within the plant. Preferably, the temperature of the first stream of supply gas lies in the interval -20⁰C to 50⁰C. The temperature of the second stream of supply gas may likewise lie in the interval -20 to 50⁰C. This provides for an effective cooling of the particulate material.

The supply gas of the first and second streams may be any suitable gas, for instance air or nitrogen. However, in the embodiment described the supply gas in both streams is air.

An alternative embodiment of the trapping device according to the invention is shown in Fig. 3. In this Figure, elements of the trapping device having the same or analogous function as in the embodiment described in the above carry the same reference numerals to which 100 has been added.

As in the above-mentioned embodiment, the upper end 111 of the compartment 115 of the trapping device 110 is connected to the outlet 9 of the primary cyclone 5. However, the cross-sectional dimensions of the compartment 115 are substantially constant from the upper end 111 to the lower end 112 thus forming a substantially tubular compartment. The term "tubular" should be interpreted as comprising any form of structure having a passageway therethrough, for instance a cylindrical body or a body having any cross-sectional shape, including square, rectangular, octagonal etc. In the above, the trapping device forms part of a particle separator arrangement connected to the drying chamber of a spray drying apparatus for the atomization of a liquid feed in a drying chamber by means of a drying gas. However, the trapping device may be utilized in any kind of particle separation arrangement forming part of a spray drying and/or fluid bed processing of particulate material. For instance, the powder source connected to the trapping device may be a filter unit, or the trapping device may be connected directly to the spray drying chamber, which in that case constitutes the powder source. Figs 4 and 5 show views corresponding to Fig. 1, each representing an alternative use of the trapping device according to the invention. The trapping device carries reference numeral 10 as in the embodiment of Figs 1 and 2. However, the trapping device may also be formed as in the alternative embodiment of Fig. 3, or of any other kind falling within the scope of the claims. In Fig. 4 the trapping device 10 is connected to the drying chamber 202 of a spray dryer 201, the powder source in this case thus being the drying chamber 202 itself.

In Fig. 5 the trapping device 10 is connected to a filter unit 301, filters being e.g. bag filters, metal filters or others.

Example

In a spray drying apparatus as indicated in the above description of Figs 1 and 2, a liquid feed was atomized and dried in the drying chamber with air as the drying gas at a flow rate of 1300 kg/h. The spray drying apparatus in question was a relatively small plant. Spent drying gas was conducted to the primary cyclone. In the trapping device the following data was gathered:

At the inlet, the drying gas entered the trapping device at a temperature of 90⁰C and a flow rate of 20 kg/h. Also the particulate material also entered the trapping device at a temperature of 90⁰C, but the flow rate of the particulate material only amounted to 5 kg/h. The second stream of supply gas introduced through the inlet in the compartment of the trapping device was air having a temperature of 20⁰C. This second stream of supply gas entered the compartment at a flow rate of 75 kg/h.

Air was also used as the supply gas of the first stream. This stream having a temperature of 20⁰C was supplied to the ejector at a flow rate of 100 kg/h. At the outlet of the ejector the gas (air) leaving the ejector at a flow rate of 195 kg/h had a temperature of 29°C. Furthermore, the particulate material was leaving the ejector at a flow rate of 5 kg/h and a temperature of 29°C.

Claims

C L A I M S

1. A trapping device for a particle separator arrangement, comprising a compartment having a general longitudinal direction extending between an upper end adapted to be connected to a powder source, and a lower end adapted to be connected to an ejector, c h a r a c t e r i z e d in that said compartment is provided with an inlet adapted to receive a stream of supply gas.

2. A trapping device according to claim 1, wherein said inlet is positioned in the upper half of said compartment.

3. A trapping device according to claim 2, wherein said inlet is a tangential inlet.

4. A trapping device according to any one of the preceding claims, wherein the cross-sectional dimensions of the compartment increase steeply as measured along the longitudinal direction from the upper end in the direction toward the lower end.

5. A trapping device according to claim 4, wherein the cross- sectional dimensions of the compartment increase to 2-10 times the dimensions at the upper end within the upper 25% of the longitudinal dimension of the compartment.

6. A trapping device according to any one of claims 1 to 3, wherein the cross-sectional dimensions of the compartment are substantially constant from the upper end to the lower end thus forming a substantially tubular compartment.

7. A trapping device according to any one of the preceding claims, wherein vortex affecting means are provided in said compartment.

8. A trapping device according to claim 7, wherein said vortex affecting means are substantially conical, the apex of the vortex affecting means being directed toward the upper end of the compartment.

9. A trapping device according to claim 8, wherein the apex of the vortex affecting means is positioned closer to the upper end of the compartment than said inlet.

10. A trapping device according to any one of the preceding claims, wherein the upper end of the compartment is adapted to be connected to a powder source in the form of a cyclone.

11. A trapping device according to any one of claims 1 to 9, wherein the upper end of the compartment is adapted to be connected to a powder source in the form of the drying chamber of a spray drying apparatus.

12. A trapping device according to any one of claims 1 to 9, wherein the upper end of the compartment is adapted to be connected to a powder source in the form of a filter unit.

13. A process for separating particles, comprising the steps of providing a stream of gas containing a particulate material constituting a powder source, guiding a stream of particulate material from the powder source to a trapping device including a compartment, extracting the particulate material from the trapping device by means of an ejector, supplying said ejector with a first stream of supply gas, and supplying a second stream of supply gas to an inlet in said compartment.

14. The process of claim 13, wherein said second stream of supply gas is introduced through an inlet in the upper portion of said compartment.

15. The process of claim 14, wherein said second stream of supply gas is introduced tangentially through said inlet.

16. The process of any one of claims 13 to 15, wherein the particulate material is extracted by said ejector through a suction inlet of the ejector connected to the lower end of said compartment, and is conducted through an outlet of the ejector in an outlet stream of gas.

17. The process of any one of claims 13 to 16, wherein the flow rate of the gas containing particulate material lies in the intervall to 5 times the amount of material leaving the ejector as measured in kg/h.

18. The process of any one of claims 13 to 17, wherein the flow rate of the first stream of supply gas lies in the intervall to 10 times the amount of material leaving the ejector as measured in kg/h.

19. The process of any one claims 13 to 18, wherein the flow rate of the second stream of supply gas lies in the intervall to 10 times the amount of material leaving the ejector as measured in kg/h.

20. The process of any one of claims 13 to 19, wherein the tem- perature of the gas containing particulate material lies in the interval

10⁰C to 200⁰C.

21. The process of any one of claims 13 to 20, wherein the temperature of the first stream of supply gas lies in the interval -20⁰C to 50°C.

22. The process of any one of claims 13 to 21, wherein the temperature of the second stream of supply gas lies in the interval -20 to 50⁰C.

23. The process of any one of claims 13 to 22, wherein the supply gas of the first and second streams is air or nitrogen.

24. Use of the trapping device according to any one of claims 1 to 12, wherein the powder source is a cyclone.

25. Use of the trapping device according to any one of claims 1 to 12, wherein the powder source is the drying chamber of a spray drying apparatus.

26. Use of the trapping device according to any one of claims 1 to 12, wherein the powder source is a filter unit.