WO2016042289A1

WO2016042289A1 - Toroidal bed reactor

Info

Publication number: WO2016042289A1
Application number: PCT/GB2015/052499
Authority: WO
Inventors: Chris DODSON
Original assignee: Mortimer Technology Holdings Ltd
Priority date: 2014-09-19
Filing date: 2015-08-28
Publication date: 2016-03-24
Also published as: GB2558162A; GB2558162A8; GB201416584D0

Abstract

The present invention relates to an apparatus for processing a particulate material, the apparatus comprising: a chamber; means for introducing particulate material into the chamber; and a plurality of fluid inlets for introducing a flow of fluid into the chamber, wherein the plurality of inlets are arranged such that fluid can be introduced at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

Description

TOROIDAL BED REACTOR

The present application relates to a method of processing a particulate material. The present application also relates to apparatus for processing a particulate material.

Treatment of particulate material commonly uses a fluid stream and more particularly a gaseous stream. The particulate material may function as a catalyst, absorption medium or as a source of reactants which react with or are treated by the fluid stream. It has been thought for some time that the best mode for treating beds of particulate material is to fluidise the bed with a gaseous stream.

A method and apparatus for processing matter is known from

WO2006/032919. This application discloses a processing chamber into which a hot gas is introduced to provide a helical flow. A particulate material is supplied into the chamber and under the influence of the hot gas is circulated within the chamber.

The inventors of the invention have developed similar apparatus to enhance the processing capabilities of such apparatus.

According to a first aspect of the invention, there is provided apparatus for processing a particulate material, the apparatus comprising: a chamber; means for introducing particulate material into the chamber; at least one fluid inlet for introducing a flow of fluid into the chamber; and separation means within the chamber, wherein the separation means is arranged to separate the particulate material from the fluid flow, and defines a processing zone having a substantially circular cross-section.

Preferably, the separation means has a plurality of apertures through which the particulate material can pass.

Preferably, the separation means comprises a sleeve having at least one aperture formed therein.

Preferably, the apertures extend in parallel with the longitudinal axis of the sleeve.

According to a second aspect of the invention, there is provided apparatus for processing a particulate material, the apparatus comprising: a chamber; means for introducing particulate material into the chamber; and a plurality of fluid inlets for introducing a flow of fluid into the chamber, wherein the plurality of inlets are arranged such that fluid can be introduced at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

Preferably, a density of the plurality of fluid inlets is greater at the first radial distance than at the second radial distance.

Preferably, a plurality of the fluid inlets at the second radial distance each have an opening area that is smaller than the opening area of each of a plurality of the fluid inlets at the first radial distance.

According to a third aspect of the invention, there is provided apparatus for processing a particulate material, the apparatus comprising: a chamber having a tapered lower section; means for introducing particulate material into the chamber; and a plurality of fluid inlets for introducing a flow of fluid into the chamber, the fluid inlets provided in the tapered section.

Preferably, the plurality of inlets are arranged such that fluid can be introduced at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

According to a fourth aspect of the invention there is provided apparatus for processing a particulate material, the apparatus comprising: a chamber; means for introducing particulate material into the chamber; at least one fluid inlet for introducing a flow of fluid into the chamber; means for monitoring the mass or density of processed particulate material; and controllable means for removing an amount of processed particulate material from the chamber based on the monitored mass or density.

Preferably, the means for monitoring density comprises an electromagnetic radiation sensor.

Preferably, the means for monitoring density comprises means for radiating electromagnetic radiation within the chamber.

Preferably, the sensor is arranged to sense microwaves.

Preferably, the controllable means is an outlet for particulate material. Preferably, the outlet is located at the radially outermost extent of the chamber.

According to a fifth aspect of the invention, there is provided a method of processing a particulate material, the method comprising the steps of: (a) introducing the particulate material into a chamber; (b) introducing a flow of fluid into the chamber to establish a fluid flow following a substantially helical path thereby entraining the particulate material; (c) restricting the flow of fluid with separation means arranged to separate the particulate material from the fluid flow, the separation means defining a processing zone within the chamber and having a substantially circular cross-section; and (d) removing processed particulate material from the chamber.

According to a sixth aspect of the invention, there is provided a method of processing a particulate material, the method comprising the steps of: (a) introducing the particulate material into a chamber provided with a plurality of fluid inlets; (b) introducing a flow of fluid through each inlet to establish a fluid flow following a substantially helical path thereby entraining the particulate material; and (c) removing processed particulate material from the chamber, wherein step (b) comprises introducing fluid at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

According to a seventh aspect of the invention, there is provided a method of processing a particulate material, the method comprising the steps of: (a) introducing the particulate material into a chamber having tapered lower section provided with a plurality of fluid inlets; (b) introducing a flow of fluid through each inlet to establish a fluid flow following a substantially helical path thereby entraining the particulate material; and (c) removing processed particulate material from the chamber.

Preferably, step (b) comprises introducing fluid at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance. According to an eighth aspect of the invention, there is provided method of processing a particulate material, the method comprising the steps of: (a) introducing the particulate material into a chamber; (b) introducing a flow of fluid into the chamber to establish a fluid flow following a substantially helical path thereby entraining the particulate material; (c) monitoring the mass or density of processed particulate material; and (d) removing an amount of processed particulate material from the chamber based on the monitored mass or density.

Preferably, step (c) comprises measuring electromagnetic radiation within the chamber.

Preferably, step (c) comprises emitting electromagnetic radiation within the chamber.

Preferably, the electromagnetic radiation is microwave radiation.

Preferably, step (d) comprises opening an outlet for particulate material.

The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. For a better understanding of the invention, and to show how the same may be put into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

Figure 1 shows a horizontal cross-sectional view of a prior art reactor, schematically representing a flow of fluid;

Figure 2 shows a vertical cross-sectional view of the reactor of Figure 1 ;

Figure 3 shows a vertical cross-sectional view of a reactor of a first embodiment of the invention;

Figure 4 shows a vertical cross-sectional view of a reactor of a second embodiment of the invention;

Figure 5 shows a vertical cross-sectional view of a reactor of a third embodiment of the invention; and

Figure 6 shows a plan view of the base of the reactor of Figure 5.

A toroidal bed reactor 1 known in the prior art is shown in Figures 1 and 2. The reactor 1 comprises a cylindrical housing 3 inside of which a processing zone 5 is formed. The processing zone 5 is annular in shape and extends co-axially with th housing 3. The upper end of the housing 3 may be completely open or may have an end closure with an opening (not shown) formed therein for egress of processing fluid. The opening can also be used to provide more particulate material.

A cross-sectional view of the lower portion of the reactor 1 is shown in Figure 1. A tapered section 7 is preferably provided at the base of the housing 3 (although the tapered section 7 is shown in all of the accompanying drawings, it is not essential and a housing 3 of constant width would be possible). The tapered section 7 is inclined downwardly towards the centre of the reactor 1. Gas is introduced into the reactor 1 through a series of inlets 9 provided at the base below the tapered section 7. The inlets 9 establish a desired fluid flow path A within the housing 3.

The inlets 9 direct the gas flow so that it enters the processing zone 5 at an angle a with respect to a tangent B of the substantially circular transverse cross- section of the processing zone, as shown in Figure 1 . The angle a is approximately 30° in this example.

In contrast, when the gas is introduced into the reactor 1 in accordance with the present invention (e.g. a is 30° and β is 15°), it follows a helical flow path (E), as shown in Figure 2. The processing zone 5 is defined by the helical flow of the gas in the housing 3. The particulate material is entrained in the vortex formed by the gas in the processing zone 5 and is transported vertically before being progressively separated from the fluid stream due to centrifugal force. By this means, the processing zone 5 utilising the present invention contains a rapidly and uniformly circulating mass of particulate material evenly distributed in the processing zone 5. A path F followed by the particulate material 1 1 introduced into the reactor 1 is shown in Figure 2.

As shown in Figure 2, the particulate material 1 1 is displaced upwardly by the fluid flow in the processing zone 5 and then expelled radially outwardly. The particulate material 1 1 then falls to the base of the housing 3 and a moving bed of particulate material is formed by the tapered portion 7 of the reactor 1 . The moving bed returns the particulate material to the processing zone 5 under the action of gravity. The cycle is thereby repeated. This cyclical motion of the particulate material allows the reaction in the reactor 1 to be carefully controlled.

The velocity of the gas entering into the processing zone 5 is advantageously controlled to ensure that it is greater than the terminal velocity of the particulate material. This control of the fluid flow helps to reduce or prevent the collection of particulate material at the base of the reactor 1 . The processing zone 5 is generally annular in shape because of the helical fluid flow inside the housing 3.

The circulating particles are accelerated by the gas flow in the processing zone 5 in both horizontal and vertical directions to travel tangentially of said circumferential flow until such accelerated particles lose their energy and settle into the flowing bed arranged circumferentially of the processing zone 5. By

displacement in the flowing bed, the circulating particles are returned to the base of the processing zone 5 thereby ensuring that all of the particles in the bed are exposed to the processing gases to provide for uniform and rapid processing of said particles.

The method of the present invention involves the circulation of a flow of fluid which entrains a particulate material to be processed.

The fluid and the material in the processing chamber can be heated by at least partial combustion of the material or the fluid. The extent of this combustion can be used to determine the temperature within the processing chamber. This can be controlled by carefully managing the level of oxygen in the fluid admitted into the chamber. This can be easily controlled by using two or more distinct or premixed fluids. It is preferred that one of the fluids is air or a substantially pure oxygen feed. It is preferred that one of the fluids is recycled gas taken from the gaseous exhaust of the chamber. The fluid can be a combustible gas, such as natural gas.

It is especially preferred that recycled gas taken from the chamber is used to dilute added oxygen or air. The exhaust gases can be passed through a heat exchanger to recover thermal energy and/or warm newly added gas streams. The use of a heat exchanger also serves to drop the temperature of the gases before further combustion to ensure that the temperature can be kept stable. Dropping the temperature also facilitates the use of a fan to accelerate the recycled gases back into the processing chamber.

Preferably the fluid used in the method is a blend of recycled gas and air or a substantially oxygen gas (preferably 95vol% oxygen or more). The blend is preferably controlled such that the level of oxygen in the fluid is from 1 to 10vol%, more preferably from 2 to 5vol%. The use of a substantially oxygen gas is preferred because it avoids dilution with nitrogen.

The inventors have developed three improvements to the reactor of Figures 1 and 2. Any of these three improvements can be individually applied, or can advantageously be combined in a single reactor. Furthermore, embodiments having these improvements may have any of the features described above with respect to the prior art reactor.

Figure 3 shows a first embodiment of the invention. The reactor comprises a generally cylindrical chamber 3. A tapered section 7 may be provided at the base of the chamber 3.

The inventors have discovered that the helical flow can be improved by restriction thereof over a vertical distance L. However, such a restriction should not prevent the entrained particulate material from leaving the helical flow. Accordingly, the provision of some form of separation means arranged to separate the particulate material from the fluid flow can aid the circulation of particulate material within the chamber 3.

The provision of the separation means defines the processing zone 5.

Preferably, the separation means is arranged so that the processing zone 5 is annular in shape and extends co-axially with the chamber 3. The separation means may comprise a simple sleeve 10 having slots 15 formed therein through which particulate material may leave the processing zone 5.

Since the slots 15 allow egress of particulate material from the separation means, the upper end of the flow control means may extend away from the base of the chamber 3 by a distance greater than the maximum height reached by the particulate material within the chamber.

The separation means may be located within the chamber 3 at a height above the base that provides a gap for the descending particulate material to re-enter the gas flow in the processing zone 5. In preferred embodiments, the separation means is positioned such that at least one fluid inlet 9 (and preferably all fluid inlets 9) directs the processing fluid into the separation means. In other words, it is preferable that the lower end of the separation means is in line with or extends past a line extending in the direction of at least one of the inlets 9.

In preferred embodiments, the separation means extends upwardly to the uppermost extent of the chamber 3. In some embodiments, the upper end of the chamber 3 will have an opening for egress of processing fluid. The separation means may extend to meet the end of the chamber 3 and surround the opening.

The slots 15 may extend upwardly from the base of the chamber. The users' requirements for the particular process that the toroidal bed reactor 1 will carry out will dictate the arrangement of the slots - the vertical extent of the slots can be chosen in dependence upon the required particle size of the processed particulate material.

The width of the separation means may depend upon the particular use of the toroidal bed reactor. In embodiments in which a tapered section 7 is provided, it may be preferable that the width of the separation means corresponds with or is substantially the same as the width of the lowermost tapered part of the chamber 3.

In the embodiment of Figure 3, the slots are orientated in parallel with the rotational axis of the flow control means. However, this is not essential, and helically extending slots may be appropriate in some applications. Slots that are tapered in the vertical direction are also considered.

Whilst a sleeve having a plurality of slots is a preferable form of separation means, it is not essential, and alternative separation means could be provided.

For example, instead of slots the separation means may have a plurality of holes distributed across its surface. Indeed, the separation means may be embodied with a plurality of apertures of any form.

Alternative separation means to the aperture sleeve may include a plurality of vertically extending baffles or vanes spaced in a circular arrangement. Figure 4 shows a second embodiment of the invention. The reactor comprises a generally cylindrical chamber 3. A tapered section 7 may be provided at the base of the chamber 3.

In this embodiment, there is further provided controllable means for removing particulate material from the chamber 3. Preferably, the controllable means for removing particulate material is in the form of one or more outlets 22.

Preferably, the controllable means for removing particulate material may be located at or near the outermost edge of the base of the chamber 3. If a tapered section 7 is provided, then the controllable means for removing particulate material may be located at or near the uppermost extent of the tapered section 7.

The one or more outlets 22 may be in any controllable form. For example actuatable doors, belt or screw conveyors,

Preferably, the one or more outlets 22 are located at the radially outermost extent of the base of the chamber 3, or at the radially outermost extent of the tapered portion 7, if provided.

It is envisaged that the controllable means for removing particulate material may comprise one or more further outlets at different heights within the chamber. Advantageously, by providing outlets at a variety of heights, particulate material of varying densities can be separately collected.

The reactor may comprise a sensor 20 that provides a control signal for determining when the one or more outlets 22 should be opened to allow particulate material to leave the chamber 3. A controller 26 may be provided to receive a signal from the sensor 20, and use this to instruct the one or more outlets 22 to open.

The controller 26 may process the signal from the sensor 20 to establish when the mass or density of the processed material exceeds a threshold. For example, the signal from the sensor 20 can be simply compared with a threshold.

The sensor 20 may be a passive sensor, such as an infrared camera, which passively senses electromagnetic radiation. For example, this can sense infrared radiation generated by the heat from the processing fluid. Alternatively, the sensor 20 is arranged to sense different forms of electromagnetic waves, such as microwaves. In which case, the reactor may include an emitter 25 to provide a source of electromagnetic radiation. In which case, the sensor 20 may simply measure the attenuation of the transmitted electromagnetic radiation (either as it passes through the mass of particulate material or as it reflects from the mass of particulate material).

The sensor 20 is configured to output a signal indicative of the mass or density of the particulate material in the chamber 3.

The arrangement of the vanes 109 at the base of the reactor 1 will now be described in greater detail. A single vane 109 is shown in Figure 7A, 7B and 7C. The vanes 109 each have a leading edge 1 13, a trailing edge 1 14 and three slots 1 15 formed in the surface thereof. As shown in Figure 7B, the vanes 109 are tapered towards the leading edge 1 13 to form a tapered region 1 17 which serves to align the vanes 109 relative to each other. The slots 1 15 each extend from the leading edge 1 13 in a transverse direction across the tapered region 1 17. A chamfered region 1 19 is provided at the trailing edge of each vane 109, diametrically opposed from the tapered region 1 17. A front view of a vane 109 is shown in Figure 7C.

The slots 1 15 extend at an angle β relative to a reference axis perpendicular to the leading edge 1 13 of the vane 109, as shown in Figures 7A and 7C. The angular offset of the slots 1 15 causes the gas to be introduced into the reactor 1 upwardly, at said angle β, relative to a horizontal plane, as described above.

A top view of the vanes 109 arranged in an assembly 121 ready for use is shown in Figure 8A. A side view of the assembly 121 is shown in Figure 8B. The tapered region 1 17 of each of the vanes 109 determines the angular orientation of the vanes relative to each other and, thereby, the angular orientation of the slots 1 15. Thus, the taper angle of the tapered region 1 17 defines the angle a at which the gas is introduced into the processing zone 5.

The processing zone 5 is generally annular in shape because of the helical fluid flow inside the housing 3.

By controlling the angle of entry of the fluid into the processing zone to maintain it larger than 10° but less than 75° relative to the tangent to the radial line at the point of entry and to be greater than 5° but less than 45° relative to said horizontal plane, as shown in Figures 1 and 2 respectively, the fluid and particulate flows can be made to circulate along a helical path.

Figures 5 and 6 show a third embodiment of the invention. The reactor comprises a generally cylindrical chamber 3 having a tapered section 30 at the base thereof. As with all of the embodiments disclosed herein, whilst a tapered section 7, 30 is preferable, it is not essential. In the third embodiment, the plurality of inlets may be provided in a wall of a chamber 3 having a constant width.

In WO 2006/032919, processing fluid is introduced from a cylindrical wall that extends between the base and the end of a tapered section.

In the third embodiment, processing fluid is introduced into the reactor through a plurality of inlets 9 provided in the tapered section 30 of the chamber. This has found to more effectively entrain the circulating particulate material as is descend across the tapered section.

The inventors have further discovered that the entrainment can be improved by providing a greater flow of fluid in a central region of the base of the chamber 3 and a lesser flow of fluid spaced radially out from the centre of the chamber 3.

One way of achieving this advantageous flow is shown in Figures 5A and 6A.

As can be seen in Figures 5A and 6A, the density of fluid inlets 32 (i.e., the number of fluid inlets 32 per unit area of the tapered section 30) is greater at small radial distances from the centre of the chamber 3 than at large radial distances. Preferably, the plurality of inlets 32 are provided on the tapered section 30.

Such an embodiment would include a first plurality of fluid inlets 32 at a first radial distance from the centre of the chamber 3 and a second plurality of fluid inlets 32 at a second radial distance from the centre of the chamber 3. The first radial distance is less than the second radial distance, and the first plurality of inlets 32 are spaced apart by shorter distances than the second plurality of inlets 32.

An alternative way of achieving the advantageous flow is shown in Figures 5B and 6B. As can be seen in these figures, the opening area of fluid inlets 37 is greater at small radial distances from the centre of the chamber 3 than at large radial distances.

Such an embodiment would include a first plurality of fluid inlets 37 at a first radial distance from the centre of the chamber 3 and a second plurality of fluid inlets 37 at a second radial distance from the centre of the chamber 3. The first radial distance is less than the second radial distance, and the first plurality of inlets 37 have larger opening areas than the second plurality of inlets 37.

Of course, the approaches of Figures 5A and 6A and Figures 5B and 6B could be combined such that the density of fluid inlets 32 is greater and the opening area of fluid inlets 37 is greater at small radial distances from the centre of the chamber 3 than at large radial distances.

The fluid inlets 32, 37 may be provided on the tapered section 30 by forming the tapered section from a plurality of vanes 109 described above with reference to Figures 7 and 8. In contrast with Figures 7 and 8, which are depicted in a cylindrical arrangement, the tapered section 30 may be formed by orienting the vanes such that there upper ends are further from the center of the chamber than their lower ends.

The opening area of fluid inlets 37 formed with vanes 109 can be varied by varying the cross-sectional area of the slots 1 15.

The density of fluid inlets 32 formed with vanes 109 can be varied by varying the spacing between the slots 1 15.

Furthermore, the density of fluid inlets may be varied by forming the tapered section 30 from a plurality of vanes 109 such that each of the plurality of vanes 109 has a fluid inlet 32 at a first radial distance, but a smaller number of vanes 109 has a further fluid inlet 32 at a second, larger radial distance.

Although Figures 6A and 6B show fluid inlets 32, 37 of different size or radial distances in communication with a common fluid supply, the inventors have envisaged embodiments in which different processing fluids may be introduced through different inlets 32, 37.

In which case, a first set of fluid inlets 32, 37 may be in communication with a first supply of a first processing fluid, while a second set of fluid inlets 32, 37 may be in communication with a second supply of a second processing fluid.

As discussed above, a first processing fluid may be air or an oxygen gas. A second processing fluid may be recycled gas taken from the gaseous exhaust of the chamber. The second fluid may contain a combustible gas, such as natural gas.

Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or of the appended claims.

Claims

Claims:

1. Apparatus for processing a particulate material, the apparatus comprising: a chamber;

means for introducing particulate material into the chamber; and

a plurality of fluid inlets for introducing a flow of fluid into the chamber, wherein the plurality of inlets are arranged such that fluid can be introduced at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

2. The apparatus of claim 1 , wherein a density of the plurality of fluid inlets is greater at the first radial distance than at the second radial distance.

3. The apparatus of claim 1 or claim 2, wherein a plurality of the fluid inlets at the second radial distance each have an opening area that is smaller than the opening area of each of a plurality of the fluid inlets at the first radial distance.

4. The apparatus of any preceding claim, further comprising separation means within the chamber, wherein the separation means is arranged to separate the particulate material from the fluid flow, and defines a processing zone having a substantially circular cross-section.

5. The apparatus of claim 4, wherein the separation means has a plurality of apertures through which the particulate material can pass.

6. The apparatus of claim 4 or claim 5, wherein the separation means comprises a sleeve having at least one aperture formed therein.

7. The apparatus of claim 6, wherein the apertures extend in parallel with the longitudinal axis of the sleeve.

8. The apparatus of any preceding claim, further comprising:

means for monitoring the mass or density of processed particulate material; and controllable means for removing an amount of processed particulate material from the chamber based on the monitored mass or density.

9. The apparatus of claim 8, wherein the means for monitoring density comprises an electromagnetic radiation sensor.

10. The apparatus of claim 9, wherein the means for monitoring density comprises means for radiating electromagnetic radiation within the chamber.

1 1 . The apparatus of claim 9 or 10, wherein the sensor is arranged to sense microwaves.

12. The apparatus of any one of claims 8 to 1 1 , wherein the controllable means is an outlet for particulate material.

13. The apparatus of claim 12, wherein the outlet for particulate material is located at the radially outermost extent of the chamber.

14. A method of processing a particulate material, the method comprising the steps of:

(a) introducing the particulate material into a chamber provided with a plurality of fluid inlets;

(b) introducing a flow of fluid through each inlet to establish a fluid flow following a substantially helical path thereby entraining the particulate material; and (c) removing processed particulate material from the chamber,

wherein step (b) comprises introducing fluid at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

15. The apparatus of claim 14, wherein step (b) comprises introducing fluid at a greater rate at a first radial distance from the centre of the chamber than at a second radial distance from the centre of the chamber, the second radial distance being greater than the first radial distance.

16. The method of claim 14 or claim 15, the method further comprising the step of restricting the flow of fluid with separation means arranged to separate the particulate material from the fluid flow, the separation means defining a processing zone within the chamber and having a substantially circular cross-section.

17. The method of any one of claims 14 to 16, the method further comprising the step of monitoring the mass or density of processed particulate material,

wherein the step of removing processed particulate material from the chamber comprises removing an amount of processed particulate material from the chamber based on the monitored mass or density.

18. The method of claim 17, wherein step (c) comprises measuring

electromagnetic radiation within the chamber.

19. The method of claim 18, wherein step (c) comprises emitting electromagnetic radiation within the chamber.

20. The method of claim 17 or 18, wherein the electromagnetic radiation is microwave radiation.

21 . The method of any one of claims 17 to 20, wherein step (d) comprises opening an outlet for particulate material.