REACTOR SYSTEMS HAVING EXTERNAL PRESSURE BALANCER

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62/266,377, filed December 11, 2015, which is incorporated herein by

reference in its entirety.

FIELD OF THE DISCLOSURE

[0002] The field of the disclosure relates to reactor systems having an external pressure balancer to counter-balance the hydrostatic end force of one or more system chambers .

BACKGROUND

[0003] Polycrystalline silicon may be produced economically and at relatively large scale by pyrolysis of thermally decomposable silicon-containing compounds (e.g., silane, trichlorosilane , dichlorosilane or

monochlorosilane) in a fluidized bed reactor. Such polycrystalline silicon may be used for production of solar cells or may be further processed according to the so- called Czochralski method to produce electronic grade single crystal silicon.

[0004] Recent advances in production of polycrystalline silicon involve use of relatively high reactor pressures (e.g., 3 bar or more) . Such pressures create a large hydrostatic force within the reactor and increase the closing force required to seal the reactor. The closing force reacts out the hydraulic end force and should provide adequate clamping force for the reactor internals. Due to the large hydrostatic end force of high pressure reactors, accurate control of the clamping force on internal components is difficult.

[0005] A continuing need exists for reactor systems that react out the hydrostatic end force of the reactor without changes to the force applied to internal components of the reactor. A need also exists for reactor systems that include an annular chamber external to the reaction chamber in which variation in the core to annulus pressure does not require adjustment of the clamping force on the internal components of the reactor.

[0006] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

SUMMARY

[0007] One aspect of the present disclosure is directed to a reactor system for producing a reaction product. The reactor system includes a reactor liner defining a reaction chamber therein for receiving reaction components. An outer shell is around the reactor liner. An annular chamber is formed between the reactor liner and the outer shell. The system includes a seal plate for sealing the annular chamber and the reaction chamber. The system includes a clamping assembly for securing the seal plate so that the components in the reaction chamber are separate from the annular chamber. A pressure balancer is in fluid communication with at least one of the annular chamber and the reaction chamber.

[0008] Another aspect is directed to a pressure balancer for counter-balancing the hydrostatic end force of one or more vessels . The pressure balancer includes an inner expansion joint defining an inner chamber therein and an outer expansion joint around the inner expansion joint. The inner expansion joint and outer expansion joint define an annular chamber between the inner expansion joint and the outer expansion joint.

[0009] Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present

disclosure may be incorporated into any of the above- described aspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a perspective view of a reactor system having a pressure balancer;

[0011] Figure 2 is a perspective cross-section view of the reactor system; [0012] Figure 3 is a perspective cross-section view of another embodiment of the reactor system having two pressure balancer expansion joints; and

[0013] Figure 4 is a perspective cross-section view of another embodiment of the reactor system having three pressure balancer expansion joints.

[0014] Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION

[0015] An embodiment of a reactor system for producing a reaction product is generally referred to as "5" in Figure 1. The reactor system 5 includes a reactor liner 17 (Fig. 2) that defines a reaction chamber 15 therein for receiving reaction components. The liner 17 may include a number of separate sections joined by gaskets to seal the various sections. An outer shell 20 surrounds the reaction liner 17 and an annular chamber 12 is formed between the reaction liner 17 and the outer shell 20. A seal plate 11 or reactor "head" seals the reaction chamber 15 and the annular chamber 12 to separate the fluids in each chamber.

[0016] A clamping assembly 29 (Fig. 1) secures the seal plate 11 by applying a clamping force between the seal plate 11 and the liner 17 and outer shell 20. The clamping assembly 29 generally resists the hydraulic end force from the reaction chamber 15 or annular chamber 12. The clamping assembly 29 adds additional force to the liner 17 to create a seal between the seal plate 11 and the liner 17. The hydraulic end force is balanced by one or more expansion joints discussed below. In the illustrated embodiment, the clamping assembly 29 is a number of powered cylinders (e.g., hydraulic or pneumatic cylinders) . The cylinders 29 are attached to the seal plate 11 and a clamping ring 31 that extends from the outer shell 20. In other embodiments, the clamping assembly 29 includes a number of springs, weights, screw jacks or counterbalances to seal the annular chamber and the reaction chamber.

[0017] The reactor system 5 includes a pressure balancer 10 to counteract changes in the reaction chamber 15 pressure and/or annular chamber 12 pressure. Generally the balancer 10 is external to the reactor components (e.g., external to the reaction chamber and/or the shell) . The pressure balancer 10 includes a balancer top head 8 and a bottom head 18.

[0018] An expansion joint 48 (Fig. 2) extends between the top head 8 and the bottom head 18. The expansion joint 48 has a flexible construction to allow for its expansion and contraction. As shown, expansion joint 48 (and additional expansion joints of other embodiments described below) is a bellows. Suitable bellows include formed bellows and edge welded bellows. The expansion joints may alternatively be composed of a material that stretches such as rubber.

[0019] The expansion joint 48 defines an inner chamber 52 within the expansion joint 48. The inner chamber 52 is in fluid communication with the reaction chamber 15 through piping conduit 57 that extends through an inner chamber outlet formed in the bottom head 18.

[0020] The pressure balancer 10 is rigidly attached to the seal plate 11 by supports 72. In other embodiments, the supports 72 are eliminated and the pressure balancer 10 is attached directly to the seal plate 11. In such embodiments, the bottom head 18 of the pressure balancer 10 may also be eliminated and the expansion joint 48 may be attached directly to the seal plate 11. The seal plate 11 may include additional openings (not shown) and/or fittings for removing or adding the process gases in the reaction chamber 15 and/or annular chamber 12.

[0021] The pressure balancer head 8 is also fixed with respect to the outer shell 20 by rigidly attaching the head 8 to the clamping ring 31 by tie-rods 76. As an alternative to tie-rods, the balancer head 8 may be fixed relative to the shell 20 by fixing both the shell 20 and the head 8 to external structures such as the building structure in which the reactor is located. The reactor system 5 includes an outer shell expansion joint 81 to allow for differential expansion of at least one of the reaction liner 17 and the outer shell 20.

[0022] The expansion joint 48 may be sized to provide equal effective areas pushing up and down on the seal plate 11 for the reaction chamber 15. The differential between the pressure of the reaction chamber 15 and the pressure of the annular chamber annular chamber 12 helps provide the clamping force between the seal plate 11 and the liner 17 and outer shell 20.

[0023] Another embodiment of the pressure balancer 10 is shown in Figure 3. The expansion joint 48 of the balancer 10 is an "outer" expansion joint and the balancer 10 also includes an inner expansion joint 40 that extends between the top head 8 and the bottom head 18. The inner expansion joint 40 defines an inner chamber 52 within the expansion joint 40. The inner chamber 52 is in fluid communication with the reaction chamber 15 through piping conduit 57 that extends through an inner chamber outlet formed in the bottom head 18.

[0024] The inner expansion joint 40 and outer expansion joint 48 form an annular chamber 54 (Fig. 3) . The annular chamber 54 is in fluid communication with the annular chamber 12 formed between the reaction liner 17 and the outer shell 20 by piping conduit 59 that extends through an inner chamber outlet formed in the bottom head 18. The chambers 52, 54 may be fluidly connected by use of additional conduits (not shown) . In other embodiments, the pressure balancer 10 is attached directly to the seal plate 11 and supports 72 are eliminated. In such embodiments, the bottom head 18 of the pressure balancer 10 may also be eliminated and the expansion joints 40, 48 may be attached directly to the seal plate 11. The seal plate 11 of the balancer 10 of Figure 3 may include additional openings and fittings (not shown) .

[0025] The inner expansion joint 40 acts as the division between the reaction chamber 15 and the annular chamber 12 and should be designed for both internal and external pressure. The inner expansion joint 40 may be sized to provide an equal effective areas pushing up and down on the seal plate 11 for the reaction chamber 15. The outer expansion 48 acts as the outer boundary to the annular chamber 12 and should be designed for internal pressure (or external pressure as in vacuum applications) The outer expansion joint 48 may be sized to provide equal effective areas pushing up and down on the seal plate 11 for the annular chamber 12. While the reactor system 5 may be generally described herein with reference to positive reaction chamber and/or annular chamber pressures, the reactor system 5 may also be used in vacuum pressure applications .

[0026] Another embodiment of the reactor system 5 is shown in Figure 4. The pressure balancer 10 includes a core expansion joint 84 defining a core chamber 88. A piping conduit 57 extends through the core chamber 88 and through the seal plate 11. The piping conduit 57 is in fluid communication with the reaction chamber 15 or, as in other embodiments, the annular chamber 12. The inner expansion joint 40 and core expansion joint 84 define the inner chamber 52. The core expansion joint 84 should be designed for external pressure (or internal pressure as in vacuum applications). In other embodiments, the pressure balancer 10 is attached directly to the seal plate 11 and supports 72 are eliminated. The seal plate 11 of the balancer of Figure 4 may include additional openings (not shown) and/or fittings for removing or adding the process gases in the reaction chamber 15 and/or annular chamber 12.

[0027] The reactor system 5 may be operated by reacting reactor fluids in the reaction chamber 15. A second fluid may be present in the annular chamber 12 to prevent the reaction chamber from being contaminated. The reaction fluid in the annular chamber 12 is generally inert to the reaction components within the reaction chamber 15. In some embodiments, the fluids in the reaction chamber 15 and annular chamber 12 are both gases . The annular chamber 12 may be operated at a pressure greater than the reaction chamber 15 such as at least about 0.01 bar greater or at least about 0.05 bar, at least about 0.1 bar, at least about 0.5 bar, at least about 1 bar or at least about 2 bar greater (e.g., from about 0.1 bar to about 5 bar, from about 0.1 bar to about 2 bar or from about 0.1 bar to about 0.9 bar greater) . In other embodiments, the pressure in the annular chamber 12 is less than the pressure in the reaction chamber 15 such as at least about 0.01 bar less or at least about 0.05 bar, at least about 0.1 bar, at least about 0.5 bar, at least about 1 bar or at least about 2 bar less (e.g., from about 0.1 bar to about 5 bar, from about 0.1 bar to about 2 bar or from about 0.1 bar to about 0.9 bar less) . The annular chamber 12 may include a heater (not shown) therein to heat the reactor components in the reaction chamber 15.

[0028] In some embodiments, the reactor system 5 is used to produce polycrystalline silicon. A silicon feed gas comprising a silicon-containing compound is introduced into the reaction chamber 15. The silicon feed gas may be introduced with a carrier gas such as hydrogen, argon, helium, silicon tetrachloride or combinations thereof. Silicon particles (e.g., seed particles) are fluidized in the reaction chamber 15 by the incoming gases. Silicon deposits on the particles by the thermal

decomposition of the silicon-containing compound. When the particulate has grown to sufficient size, particulate is withdrawn from the reaction chamber 15 through a product withdrawal tube (not shown) . Exhaust gases are withdrawn from gas withdrawal tube 57. The reaction chamber 15 may be maintained at a pressure of at least about -0.5 barg, at least about 0 barg, at least about 0.5 barg, at least about 1 barg, at least about 3 barg, at least about 5 barg or at least about 10 barg (e.g., from about -0.5 barg to about 25 barg, from about 3 barg to about 25 barg or from about 3 barg to about 10 barg) .

[0029] Incoming gases (silicon feed gas and carrier gases) may be pre-heated to a temperature of at least about 200°C (e.g., from about 200°C to about 500°C of from about 200 °C to about 350 °C) . The reactor chamber 15 may be maintained at a temperature of at least about 600°C (e.g., 600°C to about 900°C or from about 600°C to about 750 °C) by use of external heating means such as induction heating or use of resistive heating elements positioned in the annular chamber 12. The gas velocity through the fluidized bed reactor 30 may be generally maintained at a velocity of from about 1 to about 8 times the minimum fluidization velocity necessary to fluidize the particles within the fluidized bed. The mean diameter of the particulate polycrystalline silicon that is withdrawn from the reactor 30 may be at least about 600 μπι (e.g., from about 600 μπι to about 1500 μπι or from about 800 μπι to about 1200 μπι) . The mean diameter of the silicon seed particles introduced into the reactor may be less than about 600 μπι (e.g., from about 100 μπι to about 600 μπι) . Quench gases may be introduced into the reactor 30 (e.g., at a freeboard region of the reactor) to reduce the temperature of the effluent gas 39 before being discharged from the reactor to suppress formation of silicon dust.

[0030] Inert gas may be introduced into the annular chamber 15 and maintained at a pressure below or above the pressure of the process gases of the reaction chamber 15 as noted above to chemically isolate the reaction chamber. The thermally decomposable gases may be directed to the core region of the reactor and carrier gas (e.g., hydrogen) may be directed to the peripheral portion of the reactor near the reactor walls to reduce the deposition of silicon on the walls of the reactor as disclosed in U.S. Pat. No. 8,906,313 and U.S. Pat. Pub. No. 2011/0158888, both of which are incorporated herein by reference for all relevant and consistent purposes.

[0031] In embodiments in which silane is used as the thermally decomposable compound, the reactor may be operated in accordance with the reaction conditions disclosed in U.S. Patent Publication No. 2013/0084233, which is incorporated herein by reference for all relevant and consistent purposes. In embodiments in which

dichlorosilane is used as the thermally decomposable compound, the reactor may be operated in accordance with the reaction conditions disclosed in U.S. Patent

Publication No. 2012/0164323, which is incorporated herein by reference for all relevant and consistent purposes. In embodiments in which trichlorosilane is used as the thermally decomposable compound, the reactor may be operated in accordance with the reaction conditions disclosed in U.S. Patent Publication No. 2012/0100059, which is incorporated herein by reference for all relevant and consistent purposes.

[0032] During operation of the reactor system 5, the pressure balancer 10 responds to changes in the pressure of the reaction chamber 15. As the pressure increases, the pressure in the inner chamber 52 (Fig. 2) within the expansion joint 48 increases causing the expansion joint to exert a higher pressure and increase the clamping force applied to the seal plate 11 and the liner 17. In embodiments in which the pressure balance 10 includes a two or more pressure balancers (Figs. 3 and 4) the pressure balancer 10 can respond to a change in pressure in the annular chamber 12 to exert a force on the shell 20.

[0033] Compared to conventional reactor systems, embodiments of the reactor system 5 described above have several advantages. The pressure balancer 10 may vary the clamping force of the seal plate 11 based on changes in the pressure in the reaction chamber 15 and/or annular chamber 12. This allows the clamping assembly 29 to be simplified (e.g., a passive system may be used) as the clamping force of the apparatus is a function of gasket pressure and expansion joint 81 expansion/contraction.

Further, the pressure balancer 10 of Figures 3 and 4 operates in the event the reactor rupture disk (not shown) ruptures allowing the system to remain pressure balanced (i.e., a sudden decrease in reaction chamber 15 and/or annular chamber 12 pressure is counteracted by a sudden decrease in force applied by balancer 10) .

[0034] As used herein, the terms "about," "substantially, " "essentially" and "approximately" when used in conjunction with ranges of dimensions,

concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and/or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation. [0035] When introducing elements of the present disclosure or the embodiment (s) thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," "containing" and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., "top", "bottom", "side", etc.) is for convenience of description and does not require any particular orientation of the item described .

[0036] As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawing [s] shall be interpreted as

illustrative and not in a limiting sense.