US20140252024A1

US20140252024A1 - High Vessel Outlet

Info

Publication number: US20140252024A1
Application number: US13/786,261
Authority: US
Inventors: E. Wayne Osborne; Matthew J. Miller; Michael V. Spangler
Original assignee: Rec Silicon Inc
Current assignee: Rec Silicon Inc
Priority date: 2013-03-05
Filing date: 2013-03-05
Publication date: 2014-09-11

Abstract

Embodiments of an outlet tube assembly for use with a dispensing vessel are disclosed. The dispensing vessel has a side wall defining a chamber; the side wall has an upper portion and has a lower portion that tapers downwardly to an outlet. The outlet tube assembly facilitates accurate measurement of a particulate material level within the dispensing vessel and/or reduces contamination of the particulate material.

Description

FIELD

The present disclosure relates to an outlet tube assembly for use with a dispensing vessel.

BACKGROUND

A dispensing vessel, such as a hopper, may have a lower portion (e.g., a frustoconical portion) tapering to an outlet for dispensing material, such as particulate material. This arrangement often produces a funnel-type flow pattern, making it difficult to accurately determine the level of a particulate solid (e.g., a powder or granules) within the dispensing vessel.
An inner metal surface of the dispensing vessel may be a contamination source. Metal transfer may occur as particulate material rolls down the inner walls of the dispensing vessel, resulting in particulate contamination. In certain industries, such contamination may be unacceptable. For example, the silicon purity demanded by industry for applications in the electronic and photovoltaic industries is extremely high and frequently only materials with trace amounts of contamination measured at the part per thousand level (electronic grade) or part per billion level (photovoltaic grade) are deemed acceptable. Extreme care must be taken in any handling, packaging or transportation operations to avoid contamination. At any time the polycrystalline silicon is in contact with a surface, there is a risk of contamination of the polycrystalline silicon with that surface material. If the extent of contamination exceeds certain industrial stipulations, then the ability to sell the material into these end applications may be restricted or even denied. In this respect minimizing contact metal contamination is a primary concern if silicon performance criteria in the semiconductor industries are to be attained. Thus, it is desirable to minimize contact of the dispensed particulate material with the dispensing vessel walls.

SUMMARY

A dispensing assembly includes a dispensing vessel and an outlet tube assembly connected to the dispensing vessel. The dispensing vessel has a side wall that defines a chamber suitable to contain particulate material, wherein the side wall has an upper portion and has a lower portion that tapers downwardly to an outlet. In some embodiments, the upper portion of the side wall is substantially vertical. The outlet tube assembly includes a tube having an inlet and an outlet in fluid communication with the inlet, wherein the tube extends upwardly through the outlet of the dispensing vessel, and wherein the tube has a sufficient length that the tube inlet is positioned to receive particulate material at or above the top of the lower portion of the side wall.
The dispensing assembly may further include a level sensor located in the chamber. In certain embodiments, the level sensor has a lower end positioned at a height below the tube inlet. The dispensing assembly may have a dispensing vessel inlet, optionally coupled to a particulate material source such that particulate material can be transferred into the chamber via the dispensing vessel inlet. When particulate material is transferred into the chamber, a stagnant bed of particulate material is formed.
The outlet tube assembly may include a base having an aperture therethrough that is dimensioned to receive the tube, wherein the aperture is in fluid communication with the outlet of the tube and the tube outlet is located within the aperture. In some examples, the base has an outer horizontal dimension greater than or equal to an inner horizontal dimension of the outlet of the dispensing vessel. In one arrangement, the tube is removably coupled to the base. In other arrangements, the outlet tube assembly has a unitary construction. In some embodiments, the base is attached to the dispensing vessel outlet. Optionally, the base is removably attached to the dispensing vessel outlet.
In some embodiments, at least a portion of an inner surface of the tube comprises a ceramic, graphite, glass, a martensitic stainless steel alloy, or a microcellular elastomeric polyurethane. In certain embodiments, the tube includes an upper tube portion coupled to a lower tube portion. The upper and lower tube portions may be constructed of different materials. In some arrangements, the upper tube portion comprises a ceramic, graphite, glass, or a martensitic steel alloy. At least a portion of an inner surface of the upper tube portion and/or an inner surface of the lower tube portion is coated with a microcellular elastomeric polyurethane.
A dispensing assembly for dispensing particulate polysilicon with mitigation of polysilicon contamination includes a dispensing vessel comprising a side wall that defines a chamber suitable to contain particulate polysilicon, wherein the side wall has an upper portion and has a lower portion that tapers downwardly to an outlet, and an outlet tube assembly comprising a tube having an inlet and an outlet in fluid communication with the inlet, wherein the tube extends upwardly through the outlet of the dispensing vessel, wherein the tube has a sufficient length that the tube inlet is positioned to receive particulate material at or above the top of the lower portion of the wall, and wherein at least a portion of an inner surface of the tube comprises a ceramic, graphite, glass, a martensitic steel alloy, or a microcellular elastomeric polyurethane coating. In some embodiments, the outlet tube assembly further comprises a base having an aperture therethrough that is dimensioned to receive the tube, wherein the aperture is in fluid communication with the outlet of the tube and the tube outlet is located within the aperture. At least a portion of the inner surface of the tube may comprise silicon carbide, silicon nitride, graphite, quartz, a martensitic stainless steel alloy, or a microcellular elastomeric polyurethane. In some arrangements, the dispensing assembly includes a level sensor located in the chamber, wherein the level sensor has a lower end positioned at a height below the tube inlet.
The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a dispensing vessel.

FIG. 2A is a perspective view of an outlet tube assembly for retrofitting a dispensing vessel.

FIG. 2B is a perspective view of an outlet tube.

FIG. 3 is a cross-sectional view of a dispensing vessel retrofitted with an outlet tube assembly.

DETAILED DESCRIPTION

Dispensing vessels may be used to dispense particulate material through an outlet in a lower wall, or portion, of the dispensing vessel. In some applications, it is useful to determine a volume of particulate material remaining in the dispensing vessel. Many level sensors are commercially available for use to measure a level of particulate material in dispensing vessels. Some sensors detect only whether an upper boundary of the particulate material is above or below the sensor, which may be attached to a wall of the vessel. Other sensors can measure the level of the particulate material by suitable means, for example, RF (radiofrequency) capacitance, RF admittance, conductivity, pressure, magnetic field interactions (magnetostrictive sensor), tuning/vibrating fork, ultrasound, or guided wave radar.
FIG. 1 illustrates one embodiment of a dispensing vessel 100 having a side wall 102 that has a substantially vertical upper portion 104 and a lower portion 106 that tapers downwardly to an outlet 108. As a particulate material 110 flows through outlet 108, a funnel flow pattern is established wherein an upper boundary 112 of the particular material is not substantially horizontal. As shown, the funnel flow pattern creates an upper particulate boundary 112 that is lower above outlet 108 than near side wall 102. The funnel flow pattern and ensuing variable upper boundary creates inaccurate readings from level sensor 114. The inaccuracy is magnified when level sensor 114 is positioned proximate side wall 102 and any portion of upper boundary 112 drops below upper portion 104 of side wall 102. Additionally, as upper boundary 112 drops below upper portion 104, particulate material 110 rolls down lower portion 106 of side wall 102 as it flows toward outlet 108, enabling increased contamination of particulate material 110 from contact with side wall 102.
Disclosed herein are embodiments of an outlet tube for retrofitting a dispensing vessel to enable an accurate level determination of particulate matter within the vessel. The disclosed outlet tube is particularly useful for a dispensing vessel having a lower portion tapering to an outlet, such as the vessel shown in FIG. 1. In some arrangements, the lower portion has a frustoconical shape.
FIG. 2A illustrates one embodiment of an outlet tube assembly 200. Outlet tube assembly 200 comprises a tube 201 having an inner surface 201 a, and an inlet 204 in fluid communication with an outlet 206 (not shown). In some embodiments, outlet tube assembly 200 further comprises a base 208 including an aperture 210 (not shown) therethrough. Aperture 210 is in fluid communication with outlet 206. Base 208 has an outer diameter greater than an outer diameter of tube 202. In some embodiments, aperture 210 is dimensioned to receive tube 201 so that tube 201 extends partially or entirely through base 208. In an exemplary arrangement, inlet 204, outlet 206, and aperture 210 have a similar diameter. In the embodiment of FIG. 2A, tube 201 is a vertical tube, or pipe, with a circular horizontal cross-section, and base 208 has a circular, horizontal cross-section with a planar, circular, horizontal upper surface 212 and a planar, circular, horizontal lower surface 214. Aperture 210 extends vertically through the base 208. A person of ordinary skill in the art will understand that tube 201 and base 208 may have a cross-sectional shape other than circular, e.g., square, hexagonal, octagonal, etc.
Outlet tube assembly 200 may be constructed of any material, or combination of materials, that (1) is compatible (e.g., non-reactive) with the particulate material and portions of the dispensing vessel that are in contact with the outlet tube assembly, and (2) has sufficient mechanical strength to maintain its structural integrity during use. Outlet tube 201 and base 208 may be constructed of the same or different materials.
In one embodiment, outlet tube assembly 200 has a unitary construction. In another embodiment, tube 201 is inserted into an aperture 210 through base 208 and secured therein by any suitable means. For example, tube 201 may include a plurality of threads (not shown) on a lower portion of its outer surface cooperatively dimensioned to engage with a plurality of threads (not shown) on an inner surface of the base aperture 210. A threaded arrangement allows tube 201 to be removed and/or replaced as desired. Tube 201 may be replaced, for example, if it becomes damaged or clogged during use. Tube 201 also may be replaced with another tube having a different length if desired. Alternatively, tube 201 may be secured within aperture 210 by welding, riveting, or using an adhesive. In yet another embodiment, tube 201 may include a flange (not shown) at its lower end, and the flange may be used to secure tube 201 to base 208, e.g., by welding, riveting, or inserting screws through the flange into the lower portion, etc.
For some particulate materials, an outlet tube may be a source of particulate contamination. As particulate material contacts an outlet tube, material contamination transfer (e.g., by galling, erosion, diffusion) can occur. Thus, tube 201 may be constructed of a material that is resistant to wear and material transfer when contacted by particulates, e.g., polysilicon granules. In some embodiments, such as when the particulate material comprises polysilicon, tube 201 is ceramic, graphite, glass, or a martensitic stainless steel alloy. Exemplary materials for tube 201 include silicon carbide, silicon nitride, graphite, and quartz. Particulate contamination from an outlet tube primarily occurs when granules contact an upper portion of the tube, e.g., proximate the tube inlet, as they enter into the tube. Thus, in some embodiments, at least an upper portion of an outer surface and/or inner surface of tube 201 comprises a material suitable for mitigating contamination, e.g., a ceramic, graphite, glass, or a martensitic stainless steel alloy (i.e., a steel alloy having a body-centered tetragonal crystal structure, and comprising less than 20% (w/w) chromium and less than 6% (w/w) nickel). The upper portion may be, for example, coated with a silicon carbide, silicon nitride, graphite, or quartz.
In some embodiments, tube 201 comprises a lower tube portion 202 and an upper tube portion 203 (FIG. 2B). Upper tube portion 203 is coupled to lower tube portion 202. Lower tube portion 202 and upper tube portion 203 have a substantially similar horizontal cross-section. Upper tube portion 203 is constructed of a material that is resistant to wear and material transfer when contacted by particulate material. In some embodiments, when the particulate material comprises polysilicon granules, upper portion 203 is ceramic, graphite, glass, or a martensitic stainless steel alloy. In certain examples, upper portion 203 comprises silicon carbide, silicon nitride, graphite, quartz, or a martensitic stainless steel alloy.
Upper tube portion 203 may be secured to lower tube portion 202 by any suitable means, including welding, adhesion, or interengaging threaded surfaces. For example, lower tube portion 202 may include a plurality of threads (not shown) on an upper portion of its outer surface cooperatively dimensioned to engage with a plurality of threads (not shown) on an inner surface of upper tube portion 203. Alternatively, lower tube portion 202 may include a plurality of threads (not shown) on an upper portion of its inner surface cooperatively dimensioned to engage with a plurality of threads (not shown) on an outer surface of upper tube portion 203. A threaded arrangement facilitates removal and/or replacement of upper tube portion 203. Upper tube portion 203 may be replaced, for example, with an upper tube portion constructed of a different material and/or having a different length.
Particulate contamination also can be reduced or eliminated by coating an inner surface 201 a of tube 201 with a suitable material. In some embodiments, inner surface 201 a comprises a ceramic, graphite, or glass. When tube 201 comprises lower and upper tube portions 202, 203, an inner surface of one or both portions may be coated.
In certain embodiments, at least a portion (e.g., at least 50% or at least 75%) of inner surface 201 a is coated with a protective liner comprising a polymer material, particularly a microcellular elastomeric polyurethane. When the particulate material is polysilicon, suitable microcellular elastomeric polyurethane may have a bulk density of 1150 kg/m³or less, and a Shore Hardness of at least 65 A. In one embodiment the elastomeric polyurethane has a Shore Hardness of up to 90 A, such as up to 85 A; and from at least 70 A. Thus, the Shore Hardness may range from 65 A to 90 A, such as 70 A to 85 A. Additionally, the suitable elastomeric polyurethane will have a bulk density of from at least 600 kg/m³, such as from at least 700 kg/m³and more preferably from at least 800 kg/m³; and up to 1100 kg/m³, such as up to 1050 kg/m³. Hence, the bulk density may range from 600-1100 kg/m³, such as 600-1050 kg/m³, 700-1100 kg/m³or 800-1100 kg/m³. In one embodiment, the elastomeric polyurethane has a Shore Hardness of from 65 A to 90 A and a bulk density of from 800 to 1100 kg/m³. The polyurethane liner typically will be present in an overall thickness of from at least 0.1 mm, such as from at least 0.5 mm, from at least 1.0 mm, or from at least 3.0 mm; and up to a thickness of about 10 mm, such as up to about 7 mm, or up to about 6 mm. Thus, embodiments of the polyurethane liner may have a thickness from 0.1-10 mm, such as 0.5-7 mm or 3-6 mm.
An exemplary retrofitted dispensing vessel 300 is shown in FIG. 3. The dispensing vessel 300 has a side wall 302 defining a chamber 303. Side wall 302 has a substantially vertical upper portion 304 and a lower portion 306 that tapers downwardly to an outlet 308. Particulate matter 310 within dispensing vessel 300 has an upper boundary 312. A level sensor 314 is positioned within chamber 303. Dispensing vessel 300 may further include an inlet 316 through which particulate material 310 can be added to chamber 303. Advantageously, inlet 316 is not positioned adjacent to level sensor 314. Dispensing vessel 300 optionally includes a service port 318 in lower portion 306 of side wall 302. Service port 318 may be used to remove particulate material 310 from the lower portion of chamber 303.
An exemplary outlet tube assembly 200 is positioned within outlet 308. Outlet tube assembly 200 includes a tube 201 having an inlet 204 in fluid communication with an outlet 206, and a base 208 having an aperture 210 therethrough. Aperture 210 is in fluid communication with outlet 206. Base 208 has an outer horizontal dimension D greater than or equal to an inner horizontal dimension of a lower end 309 of side wall 302. Outlet tube assembly 200 is positioned such that tube 201 extends vertically through outlet 308. Tube 202 has a length L sufficient to extend into dispensing vessel 300 so that inlet 204 is at a height at or above the top of lower portion 306 of side wall 302.
Advantageously, inlet 204 is positioned at a height at or just slightly above the intersection of portions 304 and 306 of side wall 302. This arrangement maximizes the usable volume of dispensing vessel 300 while minimizing or eliminating contamination produced by granules rolling down lower portion 306 of wall 302.
Outlet tube assembly 200 is secured to dispensing vessel 300 by any suitable means including, but not limited to, welding, riveting, adhesion, or engagement of threaded surfaces. For example, the base 208 of the outlet tube assembly 200 may be welded to lower end 309 of side wall 302. In one arrangement, one or more fasteners may be used, wherein one end of a fastener is attached (e.g., by welding or riveting) to base 208 and the other end of the fastener is attached to an outer surface of side wall 302. Alternatively, if the outer horizontal dimension of base 208 is substantially equal to an inner horizontal dimension of outlet 308, and a downward pressure of particulate material 310 on outlet tube assembly 200 is sufficiently small, the outlet tube assembly 200 may be inserted into outlet 308 and held in place by frictional forces between base 208 and an inner surface of outlet 308. In yet another example, an internally threaded collar (not shown) may be secured to wall 302 at the level of outlet 308. The collar may include a plurality of threads on a lower portion of its inner surface that are dimensioned to engage cooperatively with a plurality of threads (not shown) on an outer surface of an externally threaded base 208 or an externally threaded tube 201. A collared arrangement facilitates removal and/or replacement of tube assembly 200 as desired.
With reference to FIG. 3, outlet tube assembly 200 reduces or eliminates the funnel flow pattern found in a non-retrofitted dispensing vessel that has an inwardly sloping lower wall tapering to an outlet, thereby providing a more uniform upper boundary 312 across a width of chamber 303 defined by upper portion 304 of side wall 302. Outlet tube assembly 200 also creates a “dead zone” or stagnant region of no particulate flow in a lower portion of chamber 303, thereby producing a stagnant particulate bed 313 in the portion of chamber 303 defined by lower portion 306 of side wall 302. The dead zone magnitude can be minimized by adjusting the length L of tube 201 such that inlet 204 is at or just above the intersection of lower portion 306 and upper portion 304. The combination of a more uniform upper boundary 312 and a stagnant particulate bed 313 facilitates more accurate level readings from level sensor 314, in chamber 303.
The stagnant particulate bed 313 also minimizes particulate contamination from wall 302 of dispensing vessel 300. As particulate material fills chamber 303, stagnant particulate bed 313 forms in the portion defined by lower portion 306 of side wall 302. As additional particulate material fills chamber 303, granules flow across the stagnant particulate bed 313 as they flow toward inlet 204, thereby having little or no contact with wall 302.
Embodiments of the disclosed outlet tube assembly provide a low-cost means for retrofitting dispensing vessels so that (1) more accurate readings of a particulate matter level within the dispensing vessel can be obtained, and (2) particulate contamination from contact with the dispensing vessel is reduced or eliminated. The disclosed outlet assembly has utility in many applications where it is desirable to accurately measure a particulate material level in a dispensing vessel, such as when the dispensing vessel that has a lower portion in which the side wall tapers downwardly to an outlet. In one example, a dispensing vessel having a tapered lower portion may be retrofitted with an embodiment of the disclosed outlet tube assembly when a user desires to maintain a constant flow of particulate material from the dispensing vessel. The retrofitted dispensing vessel facilitates accurate material level determination by the level sensor and allows the user to adjust the inflow of the particulate material (constant or batchwise inflow) to maintain a constant, or substantially constant, rate of outflow from the dispensing vessel. Embodiments of the disclosed outlet assembly also have utility in applications where it is desirable to minimize product contamination. Suitable applications include, but are not limited to, any process wherein a particulate material is transferred from a dispensing vessel to another apparatus. Exemplary dispensing vessels include a feed hopper for charging a fluid bed reactor (e.g., a polysilicon fluid bed reactor), a feed hopper for charging a melting furnace, and a product storage and transfer vessel.
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.

Claims

We claim:

1. A dispensing assembly, comprising:

a dispensing vessel comprising a side wall that defines a chamber suitable to contain particulate material, wherein the side wall has an upper portion and has a lower portion that tapers downwardly to an outlet; and

an outlet tube assembly connected to the dispensing vessel, the outlet tube assembly comprising a tube having an inlet and an outlet in fluid communication with the inlet, wherein the tube extends upwardly through the outlet of the dispensing vessel, and wherein the tube has a sufficient length that the tube inlet is positioned to receive particulate material at or above the top of the lower portion of the side wall.

2. The dispensing assembly of claim 1, wherein the upper portion of the side wall is substantially vertical.

3. The dispensing assembly of claim 1, further comprising a level sensor located in the chamber.

4. The dispensing assembly of claim 3, wherein the level sensor has a lower end positioned at a height below the tube inlet.

5. The dispensing assembly of claim 1, wherein the outlet tube assembly further comprises a base having an aperture therethrough that is dimensioned to receive the tube, wherein the aperture is in fluid communication with the outlet of the tube and the tube outlet is located within the aperture.

6. The dispensing assembly of claim 5, wherein the base has an outer horizontal dimension greater than or equal to an inner horizontal dimension of the outlet of the dispensing vessel.

7. The dispensing assembly of claim 5, wherein the tube is removably coupled to the base.

8. The dispensing assembly of claim 5, wherein the outlet tube assembly has a unitary construction.

9. The dispensing assembly of claim 5, wherein the base is attached to the dispensing vessel outlet.

10. The dispensing assembly of claim 9, wherein the base is removably attached to the dispensing vessel outlet.

11. The dispensing assembly of claim 1, wherein the dispensing vessel has a dispensing vessel inlet.

12. The dispensing assembly of claim 11, wherein the dispensing vessel inlet is coupled to a particulate material source such that particulate material can be transferred into the chamber via the dispensing vessel inlet.

13. The dispensing assembly of claim 12, further comprising a stagnant bed of the particulate material in the chamber.

14. The dispensing assembly of claim 1, wherein at least a portion of an inner surface of the tube comprises a ceramic, graphite, glass, a martensitic stainless steel alloy, or a microcellular elastomeric polyurethane.

15. The dispensing assembly of claim 1, wherein the tube comprises an upper tube portion coupled to a lower tube portion.

16. The dispensing assembly of claim 15, wherein the upper tube portion and the lower tube portion are constructed of different materials.

17. The dispensing assembly of claim 15, wherein the upper tube portion comprises a ceramic, graphite, glass, or a martensitic steel alloy.

18. The dispensing assembly of claim 15, wherein at least a portion of an inner surface of the upper tube portion, an inner surface of the lower tube portion, or an inner surface of the upper tube portion and an inner surface of the lower tube portion is coated with a microcellular elastomeric polyurethane.

19. A dispensing assembly for dispensing particulate polysilicon with mitigation of polysilicon contamination, comprising:

a dispensing vessel comprising a side wall that defines a chamber suitable to contain particulate polysilicon, wherein the side wall has an upper portion and has a lower portion that tapers downwardly to an outlet; and

an outlet tube assembly comprising a tube having an inlet and an outlet in fluid communication with the inlet, wherein the tube extends upwardly through the outlet of the dispensing vessel, wherein the tube has a sufficient length that the tube inlet is positioned to receive particulate material at or above the top of the lower portion of the wall, and wherein at least a portion of an inner surface of the tube comprises a ceramic, graphite, glass, a martensitic steel alloy, or a microcellular elastomeric polyurethane coating.

20. The dispensing assembly of claim 19, wherein the outlet tube assembly further comprises a base having an aperture therethrough that is dimensioned to receive the tube, wherein the aperture is in fluid communication with the outlet of the tube and the tube outlet is located within the aperture.

21. The dispensing assembly of claim 20, wherein at least a portion of the inner surface of the tube comprises silicon carbide, silicon nitride, graphite, quartz, a martensitic stainless steel alloy, or a microcellular elastomeric polyurethane.

22. The dispensing assembly of claim 19, further comprising a level sensor located in the chamber, wherein the level sensor has a lower end positioned at a height below the tube inlet.