Powder dispersion apparatus

Abstract

The present application concerns a powder dispersion apparatus for providing a mixture of a powder and a carrier gas to a target system such as a burner. The powder dispersion apparatus comprises a mixing unit, a separation unit and a gas extraction unit. The mixing unit is configured to provide a stream comprising powder and carrier gas. The separation unit is arranged downstream of the mixing unit and configured to separate the stream into a first stream portion comprising the mixture of powder and carrier gas and a second stream portion substantially comprising carrier gas. The separation unit comprising a first outlet arranged to discharge the first stream portion towards the target system and a second outlet arranged to discharge the second stream portion. The gas extraction unit is arranged downstream of the second outlet of the separation unit, and configured to control a flow rate of the second stream portion.

Description

[0001] POWDER DISPERSION APPARATUS

[0002] The present application concerns a powder dispersion apparatus for providing a mixture of a powder and a carrier gas to a target system such as a burner, a mixer, or a chemical reactor.

[0003] There are established markets for powder dispersion apparatuses like coating, pharmacological, or medical industries. An upcoming market is that of energy systems in which metal powders are used as energy carrier. Such systems are sometimes referred to as MEC. This might be one of the key solutions for the large-scale and long-term storage and import of sustainable energy for industry and society in the near future which can prevent or reduce the presence of CO2and NOx emissions. MEC technology relies on powder dispersion apparatuses to provide metal powder to metal firing burners.

[0004] It is an object of the application to provide a powder dispersion apparatus that can disperse powders in a range of powder dispersion rates and / or a range of carrier gas-to-powder ratios, as these parameters positively impact the performance of target systems such as combustion and reduction reactors involved in the MEC concept.

[0005] Currently available powder dispersion apparatuses rely on auger screw or rotating disk to provide powder. Such powder dispersion apparatuses are generally not ideal as they were often originally designed for dispersing other materials such as biomasses or coal. Using auger screws - or any such mechanical means or moving parts, for that matter - risks destroying the particles’ morphology and may agglomerate them, while these are parameters influencing the quality of the combustion of the metal powders. In addition, long-duration dispersing such metallic powders using rotating disk configuration dispersion systems may result in very fast erosion of their internal parts and need maintenance and change of some internal parts much sooner. All these disadvantages may lead to less favourability of using current dispersion systems for MEC applications.

[0006] It is a further object of the application to provide a powder dispersion apparatus in which these disadvantages are resolved or at least less prevalent.

[0007] These objects are at least partially achieved in a powder dispersion apparatus for providing a mixture of a power and a carrier gas to a target system such as a burner according to exemplary embodiments of the present disclosure. This powder dispersion apparatus comprises a mixing unit, a separation unit and a gas extraction unit. The mixing unit is configured to provide a stream comprising powder and carrier gas. The separation unit is arranged downstream of the mixing unit and configured to separate the stream into a first stream portion comprising the mixture of powder and carrier gas and a second stream portion substantially comprising carrier gas. The separation unit comprising a first outlet arranged to discharge the first stream portion towards the target system and a second outlet arranged to discharge the second stream portion. The gas extraction unit is arranged downstream of the second outlet of the separation unit, and configured to control a flow rate of the second stream portion.

[0008] By controlling the flow rate of the second stream portion substantially comprising carrier gas, the powder dispersion apparatus according to the invention can extract excess carrier gas from the stream provided by the mixing unit. This decouples the powder-dispersion rate and the carrier gas flow rate and therefore the powder dispersion apparatus can control the powder dispersion rate and / or carrier gas-to-powder ratio in a wider range than existing powder dispersion apparatuses.

[0009] Additionally, by controlling the flow rate of the second stream portion and discharging the powder with the first stream portion, the powder dispersion apparatus controls the powder dispersion rate and / or carrier gas-to-powder ratio with components not arranged in the stream or stream portions containing the powder (no moving parts). There is therefore less risk of changing particle morphology or causing agglomeration. The particles are dispersed with more favourable properties and the exact implementation of the gas extraction unit can be chosen more freely.

[0010] The gas extraction unit may be implemented with either active elements or passive elements.

[0011] In some embodiments the gas extraction unit comprises a pump, such as a vacuum pump. Such a pump may be configured to provide a low-pressure condition downstream of the second outlet gas extraction unit. These low-pressure conditions assist in drawing the excess carrier gas in the form of the second stream portion from the separation unit.

[0012] In other embodiments, the gas extraction unit comprises a valve configured to control a flowresistance that the second stream portion experiences when discharged through the second outlet. The first stream portion will also experience a particular flow resistance when discharged through the first outlet. The ratio between these flow resistances influences the ratio carrier gas in the first stream portion to carrier gas in the second stream portion, allowing for control of the powderdispersion rate and / or the range of carrier gas-to-powder ratio in the first stream portion.

[0013] It may be desired to monitor the amount of carrier gas extracted from the stream provided by the mixing unit, so in some embodiments, the gas extraction unit comprises a flow meter configured to measure the flow rate of the second stream portion. It may also be desired to adjust the amount of carrier gas extracted from the stream provided by the mixing unit, so preferably, the gas dispersion apparatus or, more specifically, the gas extraction unit, comprising a controller connected to the flow meter and configured to control the flow rate of the second flow portion based on the measured flow rate of the second stream portion.

[0014] Control using the aforementioned pump, may be achieved in embodiments where the controller is configured to increase the flow rate of the second stream portion by decreasing the pressure downstream of the second outlet and / or to decrease the flow rate of the second stream portion by increasing the pressure downstream of the second outlet. Control using the aforementioned valve, may be achieved in embodiments where the controller is configured to increase the flow rate of the second stream portion by widening the valve and decreasing the flow resistance and / or to decrease the flow rate of the second stream portion by narrowing the valve and increasing the flow resistance.

[0015] In a preferred embodiment, the powder in the stream comprises particles having a first characteristic and particles having a second characteristic, wherein the powder in the mixture in the first stream portion comprises particles having the first characteristic, wherein the second stream portion comprises powder particles having the second characteristic. In this embodiment, particles with undesirable characteristics may be removed from the stream and the powder dispersion apparatus may disperse a mixture of higher quality.

[0016] In a preferred embodiment, the gas extraction unit further comprising a filter, for instance a HEP A filter, configured to reduce the quantity of powder particles in the second stream portion. Performance and longevity of the filter may be improved in an embodiment where the second stream portion passes through the filter in a first direction, and wherein the gas extraction unit further comprises a gas flush unit configured to prove a further stream of gas through the filter in a second direction, opposite the first direction.

[0017] To provide the individual parts of the stream, the mixing unit may comprise a powder source, configured to contain powder and a first carrier gas source, configured to contain carrier gas. In a preferred embodiment, the mixing unit further comprises an ejector arranged downstream of the first carrier gas source and configured to draw in powder from the powder source. The ejector allows for drawing powder from the powder source without mechanical means or moving parts, further decreasing the risk of changing particle morphology or causing agglomeration.

[0018] The amount of carrier gas provided by the first gas source and the type of ejector, may influence and / or determine the powder-dispersion rate. In a preferred embodiment the mixing unit further comprises a second carrier gas source, configured to add carrier gas to the stream, downstream of the powder source. This also allows for providing enough carrier-gas flow rate throughout the powder dispersion apparatus to ensure the dispersed powder travels at or above terminal velocity, preventing sedimentation of the powder inside the powder dispersion apparatus.

[0019] In an exemplary embodiment comprising both the second carrier gas source and the ejector, the second carrier gas source may be configured to add carrier gas to the downstream of the ejector. The use of the second carrier gas source allows for changing the carrier gas-to-powder ratio of the stream at a point downstream of the ejector, allowing for control of these parameters in an even wider range.

[0020] In some embodiments, the separation unit comprises at least one a cyclone separator. Such a separator does not comprise mechanical means or moving parts, further decreasing the risk of changing particle morphology or causing agglomeration. Embodiments are also conceivable in which the separation unit comprises a cascade of cyclone separators including two or more cyclone separators disposed downstream of one another, allowing for control of these parameters in an even wider range. Such a cyclone separator may comprise an inlet downstream of the mixing unit configured to receive the stream of powder and carrier gas.

[0021] The powder dispersion apparatus according to the application can be configured for various types of powders. In some embodiments, the powder dispersion apparatus is configured for providing a mixture of carrier gas and an inorganic powder, preferably a metal powder such as iron powder, and / or a powder of which the particles have a Sauter diameter of at least 10 μm, at least 15 μm or at least 50 μm. In an embodiment that may be preferred in the field of MEC, the powder dispersion apparatus is configured to provide a powder dispersion rate between 50 milligrams per second and 5 grams per second, preferably between 100 milligrams per second and 1 gram per second, more preferably about 500 milligrams per second.

[0022] The abovementioned objects are also at least partially achieved in a combustor comprising a powder dispersion apparatus according to any of the abovementioned embodiments and a burner, arranged downstream of the first outlet and configured for the mixture to burn therein.

[0023] The abovementioned objects are also at least partially achieved in a method for dispersing a powder by providing a mixture of a powder and a carrier gas. The method comprises providing, using a mixing unit, a stream of powder and carrier gas, separating, using a separating unit comprising a first outlet and a second outlet, the stream into a first stream portion comprising the mixture and a second stream portion substantially comprising carrier gas, and discharging the first stream portion through the first outlet and the second stream portion through the second outlet, controlling, using a gas extraction unit arranged downstream of the second outlet, a flow rate of the second stream portion, and discharging the first stream portion to a target system, such as a burner.

[0024] Next, exemplifying embodiments will be described with reference to the appended drawings, wherein: figure 1 shows an embodiment of a powder dispersion apparatus and a burner, figures 2A and 2B show exemplary cyclonic separators, figure 2C schematically shows a cascade of cyclonic separators, figure 3 shows a method for dispersing a powder.

[0025] Powder dispersion apparatuses according to the invention can be configured in various ways. For example, types of powders for which the apparatus may be configured are organic powders, inorganic powders, mineral, metals, metalloids, plastics, ceramics, and ceramic-metal-composites. For example, particles sizes for which the dispersion apparatuses may be configured are Sauter diameters of at least 10 μm, at least 15 μm or at least 50 μm. For example, powder dispersion rates for which the apparatus may be configured are between 50 milligrams per second and 5 grams per second, preferably between 100 milligrams per second and 1 gram per second, more preferably about 500 milligrams per second.

[0026] Referring to figure 1, a powder dispersion apparatus 1 according to an embodiment of the invention and a burner 100 are shown. Apparatus 1 comprises a mixing unit 2, separation unit 3, and a gas extraction unit 4. In the embodiment shown, the powder dispersion apparatus 1 is configured for dispersing metal powders.

[0027] In the embodiment shown, mixing unit 2 is implemented by two carrier gas sources 20, 23, a powder source 21, an ejector 22 such as a vacuum ejector, a scale 24 and two valves V1, V2. Mixing unit 2 provides a stream P1 comprising powder and carrier gas. Scale 24 may be a load cell.

[0028] One gas source 20 provides a stream of carrier gas, controlled by valve V1, to ejector 22. Powder source 21 is also connected to ejector 22, and the stream of carrier gas passing through ejector 22 draws powder from the powder source. Ejector 22 outputs a stream P4 of powder and carrier gas. The skilled person will appreciate that carrier gas is a general and functional name. Any gas that can carry or assist in carrying the powder can be used. In some embodiments, the carrier gas is air. In some embodiments, it is a nitrogen mixture, or it can be or include other gases. Embodiments are conceivable in which gas source 20 also provides carrier gas, but of a type than gas source 23.

[0029] In some embodiments, powder source 21 is arranged on scale 24. This allows for monitoring the weight of powder source 21 and changes therein may be used to determine an amount of powder drawn from powder source 21.

[0030] In some embodiments, stream P4 and P1 are the same. In other exemplary embodiments, a second gas source 23 may provide an additional stream P5 of carrier gas, controlled by valve V2, that combines with the stream P4 downstream of ejector 22. The combination is provided by mixing unit 2 as stream P1. This additional stream P5 may increase the carrier gas flow rate in stream P1. An increased carrier gas flow rate helps prevent the dispersed powder settling down between mixing unit 2 before reaching the target system.

[0031] The streams P1-P5 throughout the powder dispersion apparatus and specifically the mixture that the powder dispersion apparatus provides to the target system may each be described by various properties such as the powder dispersion rate, the carrier gas flow rate and the carrier gas-to-powder ratio. In the embodiment shown in figure 1, the carrier gas flow rate of stream P4 determines the powder dispersion rate. Similarly, it may be said that the powder dispersion rate is controlled by valve V1, arranged between gas source 20 and ejector 22. The powder dispersion rate in stream P4, stream P1, and in the mixture are preferably the same. The carrier gas flow in streams P4 and P5 determine the carrier gas flow rate of stream P1. Similarly, it may be said that the powder dispersion rate is controlled by valve V2. The carrier gas-to-powder ratio in stream P2 and the mixture are at least in part determined by the carrier gas flow rate of stream P3. Similarly, it maybe said that the carrier gas-to-powder ratio in the mixture is controlled by valve V3 and / or pump 40.

[0032] In the embodiment show, separation unit 3 comprises an inlet 30 that receives stream P1 from mixing unit 2, and outlets 31 and 32 that output stream portions P2 and P3 respectively.

[0033] Separation unit 3 may be implemented by a cyclonic separator, examples of which are shown in figures 2A and 2B. In both of these figures, the exemplary cyclonic separators comprise inlets 30, and outlets 31 and 32. Figure 2B specifically shows a cross-section of a cyclonic separator having a substantially conic inner wall 33. Inlet 30 extends up to the wider end of conic inner wall 33. Outlet 31 extends away from the narrower end of the conic inner wall 33. At the wider end of conic inner wall 33, a duct 34 is provided that extends into the space defined by the inner wall 33, preferably parallel to the axis of the conic inner wall. Outlet 32 is connected to said duct 34. The stilled person will appreciate that the inner wall may also have other shapes. Other separators that can separate an incoming stream into a portion comprising a mixture of powder and carrier gas, and another portion of substantially carrier gas, may also be used.

[0034] A cyclonic separator works based on a difference in centrifugal forces that affect the particles of the powder and the carrier gas, due to the cyclonic pattern imposed on the stream. The centrifugal force affecting the heavier particles pushes them outward, towards the cyclonic separator’s inner wall 33. The flow of the carrier gas is concentrated at the central part of the cyclonic pattern. In this way, it is possible to separate particles from the carrier gas and vice-versa.

[0035] The cyclonic separator in particular is advantageous because it does not include mechanical means or moving parts. Therefore the powder that passes through does not have to interact with such mechanical means or moving parts. There is therefore less risk of damaging the particles, or otherwise changing the particles morphology. The particles are also less likely to agglomerate.

[0036] Cyclonic separators may be characterized by a minimum inlet velocity, preferably at least 10 m / s. In general, the minimum inlet velocity will depend on the type and / or mass of the powder particles. Based on the geometry and the inlet velocity of stream P1, the centrifugal force created within the cyclonic separator can also be used to separate particles with different characteristics from each other.

[0037] For some applications, all powder, or at least as much of it as possible, should be dispersed. In embodiments for these applications, there should be as few particles in the second stream portion as possible. For other applications, only part of the powder should be dispersed. In embodiments for these applications, it may also be useful to have the gas extraction unit extract particles of the powder from stream P1 with undesirable characteristics. In some embodiments, the separator unit may include a plurality of sub-separators. Separation of particles may, for example, be done by size and / or weight. In some embodiments, this plurality of sub-separators may be implemented by a cascade of cyclone separators. These may be configured to separate out particles of different shapes, sizes, or materials in stages.

[0038] Figure 2C shows an embodiment of the separating unit 3 that includes a cascade of eight cyclonic separators. Embodiments are also conceivable in which the cascade includes any other plurality of cyclonic separators, such as two. Similar to the embodiment shown in figures 2A and 2B, this embodiment receives a stream P1 and discharges a stream P2.

[0039] In the embodiment of figure 2C specifically, cyclonic separator 3 A receives stream P1 and extracts therefrom stream portion P3A. The rest of the carrier gas and powder flow passes through the cyclone to the next cyclonic separator. This process is repeated for cyclonic separators 3B, 3C, 3D, 3E, 3F, 3G, 3H. Depending on the requirements, different particles may be extracted by different cyclonic separators and thus there may be a difference in the contents of, e.g. the stream portions P3A and P3H. For example, the particles of the powder in extracted portion P3A may be smaller than the particles of the powder in extracted portion P3H thanks to higher laden particle flow velocity in the cyclonic separator 3A compared to cyclonic separator 3H.

[0040] In the embodiment shown, gas extraction unit 4 is implemented by a vacuum pump 40, a dump tank 41, flow meter 42, HEP A filter 43, flush unit 44, and two valves V3 and V4.

[0041] Vacuum pump 40 pumps carrier gas away from separation unit 3 and creates a low-pressure condition at its outlet 32. Other types of pumps may be used as well. This draws in carrier gas from separation unit 3 and removes excess carrier gas from stream P5. This removed excess carrier gas forms a stream P3 from separation unit 3 to gas extraction unit 4. How much of the carrier gas is extracted, depends on and / or is controlled by pump 40 and / or by the degree to which valve V3 and flow meter 42 are opened. In this embodiment in particular, pump 40 outputs this gas to an outside outlet or vent 12 of powder dispersion apparatus 1. In this embodiment specifically, how much carrier gas is extracted can be monitored by flow meter 42 arranged upstream of pump 40. The flow meter may also be arranged in other positions in gas extraction unit 4,

[0042] Preferably, stream P3 is first passed through HEPA filter 43. Other filters might be used alternatively or additionally. The term “filter,” as used in the present application, should be interpreted to cover any structure that can be used for blocking and / or allowing a selected substance or substances from / through the structure. This, because the second stream portion may be still contaminated by dispersed submicron or nano-size particles. The filter protects the pump from these contaminations. When using a filter, including the flush unit 44 is preferred. Unit 44 provides a stream of gas such as carrier gas or air, controlled by valve V4, through the filter in a direction opposite to stream P3, to remove, from the filter, particles of the powder

[0043] In some embodiments a tank 41 is arranged on the low-pressure side of pump 40. Such a tank may help prevent flow instabilities in the gas extraction unit, as the tank damps possible but unwanted oscillations and / or fluctuations in the pressure and / or flow imposed by pump 40. An example of a suitable tank may be an empty volume of about 20 litre, however the volume may also be higher or lower.

[0044] Figure 3 shows a flowchart reflecting a method for dispersing a powder according to an embodiment of the invention.

[0045] In step SI, a stream of powder and carrier gas is provided. Specifically, the stream may be provided by mixing unit 2 as described in relation to figure 1.

[0046] In step S2, this stream is separated into a first stream comprising the mixture and a second stream portion substantially comprising carrier gas. Specifically, the stream may be separated by separating unit 3 as described in relation to figure 1 or one or more cyclonic separators as shown in figures 2A-2C.

[0047] In step S3, the flow rate of the second stream portion is controlled. Specifically, the flow rate may be controlled by gas extraction unit 4 as described in relation to figure 1.

[0048] In step S4, the first stream portion may be discharged to a target system, such as a burner.

[0049] In the above, the present disclosure has been explained using detailed embodiments thereof. However, it should be appreciated that the disclosure is not limited to these embodiments and that various modifications are possible without deviating from the scope of the present disclosure as defined by the appended claims.

Claims

CLAIMS1. Powder dispersion apparatus for providing a mixture of a powder and a carrier gas to a target system, the powder dispersion apparatus comprising: a mixing unit, configured to provide a stream comprising powder and carrier gas; a separation unit, arranged downstream of the mixing unit and configured to separate the stream into a first stream portion comprising the mixture of powder and carrier gas and a second stream portion substantially comprising carrier gas, the separation unit comprising a first outlet arranged to discharge the first stream portion towards the target system and a second outlet arranged to discharge the second stream portion; a gas extraction unit, arranged downstream of the second outlet of the separation unit, and configured to control a flow rate of the second stream portion.

2. Powder dispersion apparatus as claimed in claim 1, wherein the gas extraction unit comprises a pump, such as a vacuum pump, configured to provide a low-pressure condition downstream of the second outlet gas extraction unit.

3. Powder dispersion apparatus as claimed in claim 1 or 2, wherein the gas extraction unit comprises a valve configured to control a flow resistance that the second stream portion experiences when discharged through the second outlet.

4. Powder dispersion apparatus as claimed in any of the preceding claims, wherein the gas extraction unit comprises a flow meter configured to measure the flow rate of the second stream portion.

5. Powder dispersion apparatus as claimed in claim 4, comprising a controller connected to the flow meter and configured to control the flow rate of the second flow portion based on the measured flow rate of the second stream portion.

6. Power dispersion apparatus as claimed in claims 2 and 5, wherein the controller is configured to increase the flow rate of the second stream portion by decreasing the pressure downstream of the second outlet and / or to decrease the flow rate of the second stream portion by increasing the pressure downstream of the second outlet.

7. Power dispersion apparatus as claimed in claims 3 and 5, wherein the controller is configured to increase the flow rate of the second stream portion by widening the valve anddecreasing the flow resistance and / or to decrease the flow rate of the second stream portion by narrowing the valve and increasing the flow resistance.

8. Powder dispersion apparatus as claimed in any of the preceding claims, wherein the powder in the stream comprises particles having a first characteristic and particles having a second characteristic, wherein the powder in the mixture in the first stream portion comprises particles having the first characteristic; wherein the second stream portion comprises powder particles having the second characteristic.

9. Powder dispersion apparatus as claimed in any of the preceding claims, the gas extraction unit further comprising a filter, for instance a HEP A filter, configured to reduce the quantity of powder particles in the second stream portion.

10. Powder dispersion apparatus as claimed in claim 9, wherein the second stream portion passes through the filter in a first direction; wherein the gas extraction unit further comprises a gas flush unit configured to provide a further stream of gas through the filter in a second direction, opposite the first direction.

11. Powder dispersion apparatus as claimed in any of the preceding claims, wherein the mixing unit comprises: a powder source, configured to contain powder; a first carrier gas source, configured to contain carrier gas.

12. Powder dispersion apparatus as claimed in claim 11, the mixing unit further comprising an ejector arranged downstream of the first carrier gas source and configured to draw in powder from the powder source.

13. Powder dispersion apparatus as claimed in claim 11, wherein the mixing unit further comprises a second carrier gas source, configured to add carrier gas to the stream, downstream of the powder source.

14. Powder dispersion apparatus as claimed in claims 12 and 13, wherein the second carrier gas source is further configured to add carrier gas to the stream downstream of the ejector.

15. Powder dispersion apparatus as claimed in any of the preceding claims, wherein the separation unit comprises at least one cyclone separator, preferably a cascade of cyclone separators including two or more cyclone separators, disposed downstream of one another.

16. Powder dispersion apparatus 15, wherein the cyclone separator comprises an inlet downstream of the mixing unit configured to receive the stream of powder and carrier gas.

17. Powder dispersion apparatus of any of the preceding claims, configured for providing a mixture of carrier gas and an inorganic powder, preferably a metal powder such as iron powder, and / or a powder of which the particles have a Sauter diameter of at least 10 μm, at least 15 μm or at least 50 μm.

18. Powder dispersion apparatus of any of the preceding claims, configured to provide a dispersion rate between 50 milligrams per second and 5 grams per second, preferably between 100 milligrams per second and 1 gram per second, more preferably about 500 milligrams per second.

19. Combustor, comprising a powder dispersion apparatus according to any of the preceding claims; a burner, arranged downstream of the first outlet and configured for the mixture to burn therein.

20. Method for dispersing a powder by providing a mixture of a powder and a carrier gas, comprising: providing, using a mixing unit, a stream of powder and carrier gas; separating, using a separating unit comprising a first outlet and a second outlet, the stream into a first stream portion comprising the mixture and a second stream portion substantially comprising carrier gas, and discharging the first stream portion through the first outlet and the second stream portion through the second outlet; controlling, using a gas extraction unit arranged downstream of the second outlet, a flow rate of the second stream portion; discharging the first stream portion to a target system.

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