JPH0221938A - Circular heating fluidized bed reactor - Google Patents

Abstract

PURPOSE: To pyrolyze silane-contg. gas and to obtain high-purity polycrystalline silicon product particles by providing the peripheral heating zone enclosing an internal fluidized bed reaction zone with an upper inlet for introducing the particles from the fluidized bed and a lower outlet for introducing the heated particles to the internal reaction zone. CONSTITUTION: The silicon particles 16 pass the upper inlet 13 and enter the heating zone annulus 27 where the silicon particles begin to fluidize at the fluidizing gas velocity lower at which the particles pass the heating zone annulus 27 than the gas velocity in the internal fluidized bed reaction zone 25. The silicon particles 24 beginning to fluidize downwardly pass the peripheral heating zone annulus 27, where the particles receive heat from a heat source 14. The silicon particles 24 are then introduced from the lower inlet 17 of the peripheral heating zone annulus 27 into the fluidized bed reaction zone 23. On the other hand, the silane feed gas entering the fluidized bed reaction zone 23 via a perforated plate 2 is pyrolyzed to silicon, which is deposited on the silicon particles 16. The silicon particles 16 increase their sizes, thereby forming the silicon product parts 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved heated fluidized bed reactor and method of heating such a reactor. In a preferred embodiment, the present invention is directed to an improved heated fluidized bed reactor for use in the production of polycrystalline silicon by pyrolysis of silane-containing gases.

The present invention is directed to preferred embodiments of the pyrolysis of silane-containing gases to silicon. The invention is equally applicable to other types of fluidized bed operations requiring heat input. Examples of such operations include catalytic reactions, ion exchange reactions, separation operations, etc. where a fluidized bed of particles requires heat input.

As used herein, "heterogeneous decomposition" refers to the reduction of silane or silane to silicon that occurs in two or more phases, such as when decomposition occurs at the interface between a gas and a solid phase. This heterogeneous decomposition results in silicon being deposited on the silicon particles of the fluidized bed or on the internal surfaces of the fluidized bed reactor.

"Homogeneous decomposition" occurs in a single phase, such as a gaseous phase, and produces a high surface area silicon powder or dust in the micron or submicron size range.

Generally, at a given temperature, the decomposition of silanes and silanes is heterogeneous and/or uniform depending on the concentration of the silane and silane-containing gases.

Generally, low silane and/or non-rosilane feed concentrations are desirable to maintain the decomposition of the silane-containing gas and the non-rosilane-containing gas to silicon in a non-uniform manner. However, if the feed concentration of the silane-containing gas and/or the halosilane-containing gas is too low, a high production rate of silicon cannot be obtained.

The term "silicon seed particles" means fluidized bed particles ranging in size from about 50 microns to about 400 microns. Such particles grow and become thicker as silicon is deposited thereon, which is eventually collected as silicon product particles.

"Silicon product particles" are at least about 400 microns in size, preferably from about 400 microns to about 130 microns in size.
Silicon seed particles grown over a size range of 0 microns. Such silicon product particles can be separated in a collection zone near the bottom of the reaction zone and recovered by conventional means. The term "silicon particles" includes both fluidized bed silicon seed particles and silicon product particles.

The term "silicon powder" refers to powders of approximately 1 to 1 micron, which result from the homogeneous decomposition of silane and/or halosilane-containing gases.
Refers to silicon with a large surface area in the submicron range.

As used herein, the term "silane-containing gas" refers to a gas containing silane and/or halosilane, unless otherwise specified.

As used herein, the term "total fluidizing gas" refers to the silane-containing gas and any gas added to the fluidized bed reactor to aid in fluidizing the silicon particles and/or to control reaction rates or heat transfer. Refers to the combination with any other additional carrier gas.

Polycrystalline silicon is produced by introducing a stream of silane-containing gas into a heated fluidized bed of silicon particles suspended in a reaction zone. These silicon particles are suspended by the upward flow of silane-containing gas and carrier gas entering through the reaction zone. The total gas velocity through the reaction zone is maintained above the minimum fluidization velocity of the silicon particles. The temperature of the silicon particles in the reaction zone is maintained between the decomposition temperature of the silane-containing gas and the melting point temperature of silicon. The silane-containing gas is
It decomposes to form silicon, which is deposited on the surface of the silicon particles. As silicon is deposited onto silicon particles, such particles become larger and separate in a collection zone near the bottom of the fluidized bed. The trapped product particles are recovered from the collection zone by conventional means.

The silane-containing gas can be introduced into the fluidized bed reaction zone from its bottom according to conventional practices, such as a gas distributor.

The silane-containing gas may be introduced undiluted or it may be diluted with hydrogen or an inert carrier gas such as argon, helium, or the like.

In the gas distribution zone, the distributor surface is cooled by cooling water, nitrogen, or the like to a temperature ranging from about 200°C to about 400°C. The cooler temperature is maintained to prevent premature decomposition of the silane-containing gas.

As used herein, the term "average diameter" means the sum of the quotients of a given particle diameter and the respective weight fraction that a particle of a given diameter is assumed to have. do. Preferably, the fluidizing gas velocity is about 4 to 6 times the minimum fluidizing velocity for the seed particles of the fluidized bed. The minimum fluidization rate can be determined by conventional means known in the art, such as the following equation:

Here ■. = minimum surface gas velocity for fluidization (f t/s
) D = average diameter of the particles in the bed (,,) ρ = density of the fluidizing gas (g/y++3) ρ = density of the particles (13 in gz) φ8 = sphericity of the particles 6 = particles at minimum fluidization Porosity of the bed μ = Absolute viscosity of fluidizing gas (jb/fft-5) = Acceleration of gravity (ft/s) Minimum fluidization velocity depends on gas viscosity and gas density, as well as average particle diameter, particle shape and void Therefore, the minimum fluidization velocity covers a wide range with small changes in the above factors.

In FIG. 1, silicon particles 16 are fluidized in a reactor useful for producing high purity polycrystalline silicon product particles 19 by pyrolysis of silane-containing gases. The silane-containing gas in conduit 21 enters the bottom of fluidized bed reactor 12 below a portion 25 of the gas distribution plate located directly below fluidized bed reaction zone 23 .

Hydrogen gas in line 21 also enters the bottom of the fluidized bed reactor vessel 12 below the portion 26 of the gas distribution plate immediately below the peripheral heating zone ring 27. The hydrogen gas and silane-containing gas introduced into the bottom of the fluidized bed shakuhachi 12 are separated by the wall 3o so that they cannot come into contact with each other until after they have passed through the gas distribution plate. The mixing of hydrogen gas and silane-containing gas in the fluidized bed reactor 12 on the gas distributor is controlled by the internal reaction zone, taking into account the gap necessary to reintroduce the heated particles 24 into the fluidized bed reaction zone 23. It is preferably limited by locating the lower end of the wall 15 as close as possible to the distribution plate. Hydrogen gas passes upwardly through portion 26 of the gas distribution plate and flows through particles 24 in heating zone ring 27 without a substantial amount of silane-containing gas being mixed into the hydrogen gas. become The silane-containing gas is supplied to the fluidized bed reaction zone 23 directly below the bed of particles 160.
and preferably passes straight upwards to fluidize the bed 23 without contaminating the hydrogen.

Any mixing that may occur preferably occurs by mixing hydrogen gas into the silane-containing gas, as opposed to mixing the silane-containing gas into the hydrogen-containing gas. By isolating the external heating zone wall 10 (eg, a quartz liner) from the silane-containing gas, the amount of silicon deposited on the heat transfer surface of the external heating zone wall 10 is minimized.

Due to the silicon particles 16 passing through the peripheral heating zone ring 27,
The fluidized bed reaction zone 23 may also pass through the internal reaction zone wall 15.
heat is supplied to The peripheral heating zone ring 27 occupies the space between the internal reaction zone wall 15 of the fluidized bed reaction zone 23 and the external heating zone wall 10 of the reaction vessel 12.
7 contains laterally confined silicon particles 16. The silicon particles pass through the upper inlet 13 to the heating zone ring 27.
This is what was included in the . The silicon particles 16 are in a fluidized state due to the lower fluidizing gas velocity passing through the heating zone 27 compared to the gas velocity in the reaction zone 23. Heat is supplied from the heat source 14 through the external heating zone wall 10 to the fluidized silicon particles 24 by conductive heat transfer. The fluidized silicon particles 24 pass downwardly through a peripheral heating zone ring 27 where the particles 24 pick up heat from the heat source 14 . Near the bottom of peripheral heating zone ring 27 there is an outlet 17 for introducing silicon particles 24 from heating zone ring 27 into fluidized bed reaction zone 23 . The lower inlet 17 of the heating zone ring may use some type of driving force (such as a pulsed gas jet) to facilitate the introduction of silicon particles 24 into the fluidized bed reaction zone 23.

Silane feed gas entering fluidized bed reaction zone 23 via perforated plate 25 is pyrolyzed to silicon and precipitated on silicon particles 16 . The silicon particles 16 become thick and form silicon product particles 19 which separate in a collection zone near the bottom of the fluidized bed reaction zone 23 and are indicated by arrows (→) 22. The by-product hydrogen and other fluidizing gases entering the bottom of the bed leave the fluidized bed reactor 23 via the upper outlet 11 (.

The heating zone annulus 27 isolates the outer heating zone wall 10 from the silane-containing gas, thereby inhibiting silicon precipitation.
This is a condition that reduces the efficiency of heat transfer to the heating zone 27.

Although silicon will precipitate on the walls 15 of the internal reaction zone 23, resulting in a reduction in heat transfer efficiency through the walls 15, such a reduction may be due to the fact that the primary source of heat transfer to the reaction zone 23 is , the heat introduced by the heated silicon particles 24 re-entering the internal reaction zone 23 has minimal impact.

With respect to FIG. 2, the peripheral heating zone ring 27
is formed by concentrically arranged walls 15 and an outer heating zone wall 10. Heat is supplied to the heating zone annulus by a heating source 14 through the outer reaction zone wall 10. In the annular region between the reaction zone wall 15 and the outer heating zone wall 10, silicon particles in an initially fluidized state are supplied. There are 24. This silicon particle 2
4 consists of the silicon particles 16 of the reaction zone 23 which entered the heating zone annulus 27 via the upper inlet 13 and are finally reintroduced into the reaction zone 23.

Modifications and changes to the preferred embodiments of the invention described herein may be made without departing from the spirit and scope of the invention. The following examples are illustrative of the invention but are not intended to be limiting.

The following examples are carried out in a fluidized bed reactor similar to that illustrated in FIG. The fluidized bed reaction zone is bounded by a reaction zone quartz wall with a diameter of 30 cm. The fluidized bed reaction zone is encased in a stainless steel jacket having a diameter of 60 cm and surrounded by insulation 10CT11 thick.

1. A Kanthal heater operating at 200°C is attached to the inner wall of the stainless steel jacket. This heater has an internal diameter of approximately 50 cm. Between the reaction zone wall and the Kanthal heater, an internal diameter of 39.5 cm and a thickness of 0.5 cm
M's quartz liner. The quartz liner has a thickness of 4.75 cm between the reaction area inner wall and the quartz liner.
m annular heating area is isolated from the Kanthal heater. The fluidized bed reaction zone contains silicon particles ranging from 300 to 800 microns in diameter. The particles in the fluidized bed reaction zone are fluidized by a gaseous mixture of 20 volumes χ of silane and 80 volumes Nχ of hydrogen. The particles occupying the annular heating zone are fluidized by 100 volumes of hydrogen. Silane and hydrogen gas enter the fluidized bed reaction zone and annular heating zone through a conventional gas distributor located below the reaction zone and annular heating zone. The hydrogen gas and the silane-containing gas are introduced downstream from the gas distributor into a separate chamber in which the hydrogen gas and the silane-containing gas are not mixed. Hydrogen gas (773°
K) in a chamber below the location of the gas distributor below the annular heating zone. The silane-containing gas (300'K) is
into a chamber directly below the location of the gas distributor below the fluidized bed reaction zone. The apparent velocity of the silane-containing gas in the gas distributor for the fluidized bed reaction zone is about 70 cTIl/sec, corresponding to a minimum flow rate of 800 micron particles in the reaction zone.

The apparent velocity of hydrogen gas at the gas distributor is approximately 42 cm/7 seconds. The silane gas distributor has a diameter of about 5 cm at the small end with a diameter of about 30 cm at the large end and a height of about 5 cm. The stainless steel jacket section is held in place by three flanges with an outside diameter of 92 cm and a thickness of 9 cm. The reaction vessel has a height of 263.0 cm and 1
113. above the top of the fluidized bed with a height of 50.0 cm.
It is growing by 0cm.

The reactor pressure is maintained at approximately 2 atmospheres.

The temperature at the top of the fluidized bed is 923° and the temperature at the bottom of the fluidized bed is 823°. The temperature of the distributor cone through which the silane-containing gas passes is approximately 300° below the ambient temperature.
and maintained at 523°K. The temperature of the portion of the distributor used to introduce hydrogen gas into the annulus is approximately 773°
It is.

The temperature of the heating zone annulus is approximately 933°. The dense phase of the fluidized bed exhibits a porosity of about 0.46 and the annular heating zone exhibits a porosity of about 0.46. The heat transfer characteristics of the fluidized bed are summarized below. Thermal conductivity of Niliner: 0.0116 cal/cm2
・sec・'c Emissivity of liner: 0.60 Thermal conductivity of insulator; 3.45X10-5cal/C
m2-sec・'c Heat capacity of silicon; 0.168 c
The mass flow rate of particles through the al/g H'c heating zone annulus and into the fluidized bed reaction zone is 11 kg/sec.

The downward particle velocity through the annulus is 8.62 cm/sec. The total power input to the reactor from the Kanthal heater is 110 kilowatts with a canthal heater approximately 115.0 cm tall surrounding a quartz liner forming the outer heating zone wall.

Taking into account heat losses and inputs due to: (1
) silane distributor; (2) product and effluent streams; (3) flanges; (4) radiation from the top and bottom of the fluidized bed; (5)
insulation and (6) heat transfer from the Kanthal heater through the fluidized bed walls: and assuming that: (1) the temperature in the fluidized bed reaction zone is constant everywhere except for a small area at the bottom of the fluidized bed; (2) the temperature of the heating zone annulus is constant everywhere; (3) heat transfer through the quartz wall between the reaction zone and the heating zone is ignored; (4) the temperature of the quartz liner is uniform in the axial direction; (5) the silane distributor temperature is constant and the heat transfer between the fluidized bed and the silane distributor is determined by the temperature of the fluidized bed and the temperature of the distributor; (6) the hydrogen distribution temperature is the same as the hydrogen feed gas; (7) heat transfer between the heater and liner occurs solely by radiation; (8) the silane feed stream is at ambient temperature in the distributor (9) The circulating silicon particles enter the annular heating zone at the temperature of the fluidized bed and the product silicon and the effluent gas leave the reactor at the temperature of the fluidized bed; Separated at temperature: and 00) The fluidized bed and heater radiate as a black body; The temperature of the fluidized bed is determined to be 650° C., which is clearly suitable for economical decomposition of silane-containing gas to silicon.

The present invention provides a fluidized bed, such as a fluidized bed for decomposing silane to silicon, with high heat flux in the region close to the cooled distributor where there is a large amount of heat loss.

The present invention also provides an equally important advantage in silane pyrolysis reactors where silicon deposition on heated surfaces can be suppressed or avoided by directing the silane-containing feed gas away from the heated reactor walls. have. Furthermore, any reduction in heat transfer efficiency caused by silicon deposition on the internal reaction zone walls is minimal. This is because the primary source of heat transfer to the internal reaction zone is the introduction of the heated particles of the annular heating zone into the internal reaction zone.

The invention has been described in terms of various embodiments, including advantageous applications and parameters. Those skilled in the art after reading the above specification will be able to make various changes, equivalent substitutions, and other modifications without departing from the broad concepts described herein. Accordingly, the scope of the claims as claimed herein is to be limited only by the provisions contained in the appended claims and the scope of equivalents thereto.

[Brief explanation of the drawing]

FIG. 1 illustrates a cross section of a heated annular fluidized bed reactor according to a preferred embodiment of the invention. FIG. 2 is a top cross-sectional view of an annular fluidized bed reactor according to a preferred embodiment of the invention. 411 [Person Union, Carbide, Corporation Proceedings Practice 1 January 2

Claims (1)

Claims: 1. (a) a reaction vessel; (b) means located within the reaction vessel defining a peripheral heating zone ring surrounding an internal fluidized bed reaction zone, wherein the heating zone ring is The heating zone ring contains laterally confined particles from the fluidized bed in the fluidized starting state, the heating zone ring having an upper inlet for introducing the particles from the fluidized bed and introducing the heated particles into the inner reaction zone. (c) the heated particles of the heating zone ring entering the inner reaction zone through the lower outlet of the heating zone ring supplying heat to the inner reaction zone; An improved heated fluidized bed reactor comprising: means for defining an internal fluidized bed reaction zone; and (d) heating means for supplying heat to a heating zone ring. 2. The improved heated fluidized bed reactor of claim 1, wherein the means defining the peripheral heating zone ring includes an internal reaction zone wall and an external heating zone wall. 3. The improved heated fluidized bed reactor of claim 2, wherein the heating means supplies heat to an external heating zone wall that partially defines a peripheral heating zone ring. 4. The improved heated fluidized bed reactor of claim 2, wherein the external heating zone that partially defines the peripheral heating zone ring is a quartz liner. 5. The improved heated fluidized bed reactor of claim 2, wherein the means defining the internal fluidized bed reaction zone includes an internal reaction zone wall that partially defines the heating zone ring. 6. The improved heated fluidized bed reactor of claim 1, wherein the lower outlet of the peripheral heating zone ring includes means for introducing heated particles from the heating zone ring into the reaction zone. 7. The improved heated fluidized bed reactor of claim 6, wherein the means for introducing the heated particles into the reaction zone includes a pulsed gas jet directed into the reaction zone. 8. The reaction zone is characterized by a fluidized gas velocity ranging from about 2 times to 8 times the minimum fluidization velocity required for fluidized particles having an average diameter in the fluidized bed.
The improved heated fluidized bed reactor described. 9. (a) Lower inlet for silane-containing gas, lower outlet for removal of silicon product particles, and upper outlet for removal of unreacted silane-containing gas and gaseous by-products of the pyrolysis of the silane-containing gas. (b) means for defining a peripheral heating zone ring disposed within the reaction vessel, the peripheral heating zone ring containing laterally confined silicon particles in the fluidized starting state; the heating zone ring includes an upper inlet for the introduction of silicon particles from the fluidized bed and a lower outlet for introducing heated silicon particles into the internal reaction zone; (c) means defining an internal reaction zone surrounded by a peripheral heating zone ring; (d) heating means for supplying heat to a heating zone ring, wherein the temperature of the particles in the heating zone ring ranges between the pyrolysis temperature of the silane-containing gas and the melting point temperature of the silicon particles; An improved heated fluidized bed reactor for use in the production of polycrystalline silicon by pyrolysis of silane-containing gases, comprising certain of the aforementioned means. 10. The improved heated fluidized bed reactor of claim 9, wherein the means defining the peripheral heating zone ring includes an internal reaction zone wall and an external heating zone wall. 11. The improved heated fluidized bed reactor of claim 10, wherein the heating means supplies heat to an external heating zone wall that partially defines a peripheral heating zone ring. 12. The improved heated fluidized bed reactor of claim 10, wherein the external heating zone wall partially defining the peripheral heating zone ring includes a quartz liner. 13. The improved heated fluidized bed reactor of claim 10, wherein the internal reaction zone wall that partially defines the peripheral heating zone ring defines the internal reaction zone. 14. The improved heated fluidized bed reactor of claim 10, wherein the lower outlet of the peripheral heating zone ring includes means for introducing heated silicon particles into the internal reaction zone. 15. The improved heated fluidized bed reaction of claim 10, wherein the height of the peripheral heated zone ring ranges from approximately the height of one bed of silicon particles to the height of about 5 beds of silicon particles in the internal fluidized bed. vessel. 16. The improved heated fluidized bed reactor of claim 10, wherein the silane-containing gas is selected from the group consisting of silane, halosilane, hydrogen, and mixtures thereof. 17. The improved heated fluidized bed reactor of claim 14, wherein the means for introducing heated silicon particles into the internal reaction zone includes a pulsed gas jet directed into the internal reaction zone. 18. The inner reaction zone wall has a diameter of about 15 cm to about 12 cm.
18. The improved heated fluidized bed reactor of claim 17 over a range of 2 cm. 19. The improved heated fluidized bed reactor of claim 17, wherein the outer heating zone wall, which partially defines the peripheral heating zone ring, has a diameter ranging from about 18 cm to about 142 cm. 20, (a) a lower inlet for silane-containing gas, a lower outlet for removal of silicon product particles, and an upper outlet for removing unreacted silane-containing gas and gaseous by-products of the pyrolysis of the silane-containing gas; (b) an inner reaction zone wall having a diameter of about 30 cm and disposed concentrically within the cylindrical reaction vessel and surrounding the inner reaction zone; (c) having a diameter of about 41 cm. , an outer heating zone wall forming a peripheral heating zone ring between the inner reaction zone wall and the outer heating zone back, the heating zone ring containing laterally confined silicon particles in the fluidization starting state. Contains
The heating zone ring includes an upper inlet for the introduction of silicon particles and a lower outlet containing a pulsed gas jet for introducing the heated silicon particles into the internal reaction zone, the heating zone ring having a lower outlet. heated silicon particles introduced into the inner reaction zone from said outer heating zone wall supplying heat to the inner reaction zone; and (d) heating means for supplying heat to the heating zone ring through the outer heating zone. It's hot,
Here, the temperature of the particles in the heating zone ring is about 550°C to about 1
An improved heated fluidized bed reactor for the production of polycrystalline silicon by pyrolysis of a silane-containing gas, comprising: 21, (a) supplying heat to a peripheral heating zone ring surrounding the internal reaction zone in the reaction vessel, where the peripheral heating zone ring includes an upper inlet for introducing particles from the fluidized bed and a heating part for the internal reaction. The particles contained in the heating zone ring are in an initial fluidized state and are laterally confined by the inner reaction zone wall and the outer heating zone wall, and the external heating zone includes a lower outlet for introduction into the zone. heat is supplied to the particles of the peripheral heating zone ring through the external heating zone wall by heating means arranged externally to the zone wall; and (b) introducing the heated particles into the internal fluidized bed reaction zone. A method of heating a fluidized bed reaction zone comprising the steps of: 22. The method of claim 21, wherein the lower outlet of the peripheral heating zone ring includes a pulsed gas jet, the pulsed gas jet serving to facilitate introduction of the heated particles of the heating zone ring into the internal reaction zone. 23. The method of claim 21, wherein the internal reaction zone includes fluidized gas velocities ranging from about 2 to about 8 times the minimum fluidization velocity based on the average diameter particles in the fluidized bed. 24. The method of claim 21, wherein the particles of the fluidized bed are silicon particles useful for pyrolyzing silane-containing gases to silicon. 25. A method for producing high-purity crystalline silicon by pyrolyzing a silane-containing gas in a heated internal fluidized bed reaction zone contained in a reaction vessel, comprising: (a) heating silicon particles in a surrounding heating zone ring; supplying heat to the internal reaction zone by introducing heat into the internal reaction zone, wherein the heated silicon particles are heated in a peripheral heating zone ring, the peripheral heating zone ring defining the internal reaction zone. supplying heat to the silicon particles in the peripheral heating zone ring by means of a heating means arranged outside the external heating zone wall, comprising an annular space between the wall and the external heating zone wall. How to improve the method. 26. The peripheral heating zone ring further includes an upper inlet for the introduction of silicon particles and a lower outlet, the lower outlet containing a pulsed gas jet for introducing the heated silicon particles into the inner reaction zone. 26. The method according to claim 25.