Fluidized bed heating process and apparatus

Claim 2

An improved process for the heating of particles suspended in a surrounding gas flow in a fluidized bed reaction zone comprising applying an A.C. voltage potential between spaced-apart electrodes positioned in contact with said fluidized bed, at least one of said electrodes having a dielectric coating thereon, said voltage potential and the electrical frequency being sufficient to create electrical currents through the individual solid particles such that heat is dissipated predominantly within the individual particles, whereby the resulting heat flow passes from the individual particles to the surrounding gas within the fluidized bed and then exits through the walls of the reaction zone or with the gas flow from said zone, the individual particles thus constituting the hottest portion of said fluidized bed reaction zone.

Claim 3

The process of claim 1 in which said voltage potential is applied between one said electrode positioned in the interior of the fluidized bed and the wall of the reaction zone, said wall serving as a separate said electrode.

Claim 4

The process of claim 1 in which both of said electrodes comprise dielectric coated electrodes.

Claim 5

The process of claim 1 in which said voltage potential is applied across two electrodes both of which are positioned within said fluidized bed.

Claim 6

The process of claim 1 in which said voltage is applied across a grid of said electrodes.

Claim 7

The process of claim 1 in which said particles are suspended at slightly above minimum fluidization conditions.

Claim 8

The process of claim 1 in which said voltage potential is applied between the walls of a dielectric coated cylindrical reaction zone comprising one electrode and an internal, centrally located electrode.

Claim 9

The process of claim 7 in which said internal electrode comprises a dielectric coated electrode.

Claim 10

The process of claim 3 in which said coating comprises high purity quartz.

Claim 11

An improved process for the production of high purity, polycrystalline silicon in a fluidized bed reaction zone comprising: (a) introducing a silicon-containing gas capable of gas phase decomposition into a fluidized bed of silicon seed particles in a reaction zone maintained within the decomposition temperature range of said gas and below the melting point temperature of silicon, said decomposition temperature being maintained by applying an A.C. voltage potental between spaced-apart electrodes positioned in contact with said fluidized bed, at least one of said electrodes having a dielectric coating thereon, said voltage potential and the electrical frequency being sufficient to create electrical currents through the individual solid particles in said fluidized bed, with the heat dissipated within said individual particles being the predominant heat dissipated in said fluidized bed; (b) removing unreacted fluidizing vapor and reaction by-product gases from said fluidized bed reaction zone; and (c) withdrawing said particles having silicon product deposited thereon from said reaction zone, whereby silicon is recoverable as low-cost, high purity polycrystalline product capable of being produced at relatively high production rates on a semicontinuous or continuous basis, the heat flow within said reaction zone passing from the individual particles to the surrounding gas within the fluidized bed and then exiting through the wall of the reaction zone or with said fluidizing vapor and by-product gases, the individual silicon particles thus being the hottest portion of the reaction zone, thereby enhancing the heterogeneous depositing of silicon on the seed particles and minimizing undesired coating of silicon on the wall of the reaction zone and the homogeneous formation of fine silicon powder within said reaction zone.

Claim 12

An improved process for the production of high purity, polycrystalline silicon in a fluidized bed reaction zone comprising: (a) introducing a silicon-containing gas capable of gas phase decomposition into a fluidized bed of silicon seed particles in a reaction zone maintained within the decomposition temperature range of said gas and below the melting point temperature of silicon, said decomposition temperature being maintained by applying an A.C. voltage potental between spaced-apart electrodes positioned in contact with said fluidized bed, at least one of said electrodes having a dielectric coating thereon, said voltage potential and the electrical frequency being sufficient to create electrical currents through the individual solid particles in said fluidized bed, with the heat dissipated within said individual particles being the predominant heat dissipated in said fluidized bed; (b) removing unreacted fluidizing vapor and reaction by-product gases from said fluidized bed reaction zone; and (c) withdrawing said particles having silicon product deposited thereon from said reaction zone, whereby silicon is recoverable as low-cost, high purity polycrystalline product capable of being produced at relatively high production rates on a semicontinuous or continuous basis, the heat flow within said reaction zone passing from the individual particles to the surrounding gas within the fluidized bed and then exiting through the wall of the reaction zone or with said fluidizing vapor and by-product gases, the individual silicon particles thus being the hottest portion of the reaction zone, thereby enhancing the heterogeneous depositing of silicon on the seed particles and minimizing undesired coating of silicon on the wall of the reaction zone and the homogeneous formation of fine silicon powder within said reaction zone.

Claim 13

The process of claim 10 in which said decomposition temperature is from about 390° C. to about 1400° C.

Claim 14

The process of claim 11 in which said decomposition temperature is from about 550° C. to about 1000° C.

Claim 15

The process of claim 10 in which said silicon-containing gas is taken from the group consisting of silane and halo-silanes.

Claim 16

The process of claim 13 in which said gas comprises silane, said by-product gas being hydrogen.

Claim 17

The process of claim 13 in which said gas comprises trichlorosilane.

Claim 18

The process of claim 13 in which said gas comprises dichlorosilane.

Claim 19

The process of claim 13 in which said gas comprises tetrachlorosilane.

Claim 20

The process of claim 14 in which said silane is diluted with hydrogen or an inert carrier gas prior to being introduced to said reaction zone.

Claim 21

The process of claim 18 in which said carrier gas comprises hydrogen.

Claim 22

The process of claim 19 and including recycling by-product hydrogen as said carrier gas.

Claim 23

The process of claim 10 in which said voltage potential is applied between one said electrode positioned in the interior of the fluidized bed and the wall of the reaction zone, the interior side of said wall being coated with a dielectric coating, said dielectric coated wall serving as one said electrode.

Claim 24

The process of claim 21 in which said dielectric coating comprises high purity quartz, said quartz minimizing environmental contamination of the silicon product.

Claim 25

The process of claim 21 in which said gas comprises silane, said by-product gas being hydrogen.

Claim 26

The process of claim 10 in which said voltage potential is applied across two electrodes both of which are positioned within said fluidized bed.

Claim 27

The process of claim 10 in which said voltage is applied across a grid of said electrodes.

Claim 28

The process of claim 21 in which said electrode positioned in the interior of the fluidized bed comprises a dielectric coated electrode.

Claim 29

The process of claim 10 in which said particles are suspended at slightly above minimum fluidization conditions, the resulting relatively high particle density in the fluidized bed enhancing the capacitive electrical heating of the fluidized bed.

Claim 30

The process of claim 26 in which said dielectric coating comprises high purity quartz.

Claim 31

The process of claim 28 in which said coating has a thickness of from about 0.05 to about 10 mils.

Claim 32

The process of claim 29 in which said coating thickness is from about 0.1 to about 1.0 mils.

Claim 33

The process of claim 28 in which said A.C. current has a frequency of from about 1 kilo Hz to about 5 mega Hz.

Claim 34

The process of claim 31 in which said frequency is from about 10 to about 500 kilo Hz.

Claim 35

In a fluidized bed reaction chamber for the heating of particles suspended in a surrounding gas flow, an improved apparatus for supplying heat to said chamber comprising: (a) an A.C. power supply for supplying electrical power to said chamber; (b) spaced-apart electrodes positioned so as to contact said fluidized bed zone within the reaction chamber, at least one of said electrodes having a dielectric coating thereon; and (c) electrical connection leads connecting said A.C. power supply to said electrodes, whereby the activation of the power supply applies an alternating voltage potential between the spaced-apart electrodes positioned within the fluidized bed, causing the fluidized particles in the bed to be heated, the resulting heat passing from the individual particles to the surrounding gas and through the walls of the reaction zone or with the gas flow from said zone, the individual particles thus constituting the hottest portion of the heated fluidized bed reaction chamber.

Claim 36

In a fluidized bed reaction chamber for the heating of particles suspended in a surrounding gas flow, an improved apparatus for supplying heat to said chamber comprising: (a) an A.C. power supply for supplying electrical power to said chamber; (b) spaced-apart electrodes positioned so as to contact said fluidized bed zone within the reaction chamber, at least one of said electrodes having a dielectric coating thereon; and (c) electrical connection leads connecting said A.C. power supply to said electrodes, whereby the activation of the power supply applies an alternating voltage potential between the spaced-apart electrodes positioned within the fluidized bed, causing the fluidized particles in the bed to be heated, the resulting heat passing from the individual particles to the surrounding gas and through the walls of the reaction zone or with the gas flow from said zone, the individual particles thus constituting the hottest portion of the heated fluidized bed reaction chamber.

Claim 37

The apparatus of claim 33 in which one said electrode is positioned in the interior of the fluidized bed and including a dielectric coating on the inside portion of the wall of the reaction chamber, said dielectric coated wall serving as a separate electrode, one of said connection leads thus being connected to said dielectric coated reaction chamber wall.

Claim 38

The apparatus of claim 34 in which said dielectric coating comprises high purity quartz.

Claim 39

The apparatus of claim 33 in which two electrodes are positioned within said fluidized bed zone of the reaction chamber.

Claim 40

The apparatus of claim 33 in which said electrodes comprise a grid of individual electrodes positioned within said reaction zone.

Claim 41

The apparatus of claim 34 in which said electrode positioned in the interior of said fluidized bed comprises a dielectric coated electrode.

Claim 42

The apparatus of claim 34 in which said reaction chamber coprises a cylindrical reaction chamber and said electrode positioned in the interior of the fluidized bed is centrally located within the reaction chamber.

Claim 43

The apparatus of claim 38 in which said dielectric coating comprises high purity quartz.

Claim 44

The apparatus of claim 38 in which said dielectric coating has a thickness of from about 0.05 to about 10 mils.

Claim 45

The apparatus of claim 41 in which said dielectric coating thickness is from about 0.1 to about 1.0 mils.

Claim 46

The apparatus of claim 41 in whcih said dielectric coating comprises high purity quartz.

Claim 47

The apparatus of claim 41 in which said dielectric coating comprises aluminum oxide.