PROCESS FOR PRODUCING POLYCRYSTALLINE SILICON GRANULATE

20230286809

18/016155

July 17, 2020

Silicon granulate is produced in a fluidized bed reactor having a fluidized bed region fluidized by a gas flow and heated by a heating apparatus. Seed particles and a feed gas including hydrogen and silane and/or halosilane is continuously supplied, and elemental silicon is deposited on the seed particles to form the silicon granulate, which is discharged as a continuous product stream from the reactor. The fluidized bed temperature affects the quality and formation of the product stream, which may be determined as the temperature of an offgas stream from the fluidized bend region. The temperature, as a responding variable may be determined and controlled by means of the mass and energy balance of a defined scheme.

WACKER CHEMIE AG (Munich, DE)

1.-14. (canceled)

15. A method of producing polycrystalline silicon granulate comprising: providing a reactor having reactor tube with a fluidized bed region therein, the fluidized bed region being fluidized by a gas flow of a gas and heated by a heating apparatus; continuously supplying seed particles and a feed gas to the fluidized bed region, the feed gas including hydrogen, and silane and/or halosilane; determining a fluidized bed temperature (TWS) based on an offgas stream temperature (Toffgas,WS) represented by formula (12): [mathematical expression included] wherein, {dot over (m)}22,offgas,WS is an offgas mass flow from the fluidized bed region and {dot over (H)}22 is an enthalpy of the offgas mass flow from the fluidized bed ({dot over (m)}22,offgas,WS), and the enthalpy ({dot over (H)}22) of the offgas mass flow from the fluidized bed is represented by formula (10): {dot over (H)}22={dot over (H)}16−{dot over (H)}18−Q24−ΔRH23+Q20+{dot over (H)}21  (10), wherein, {dot over (H)}16 is an enthalpy of a feed gas stream ({dot over (m)}16,feed gas), {dot over (H)}18 is an enthalpy of a product stream {dot over (m)}18,Product, Q24 is energy removal from the reactor in the fluidized bed region, ΔR{dot over (H)}23 is a reaction enthalpy, Q20 is a heating output of the heating apparatus, {dot over (H)}21 is an enthalpy of a seed particle stream into the fluidized bed region ({dot over (m)}21,KP,WS), and/or formula (11): {dot over (H)}22=−{dot over (H)}21+{dot over (H)}17−{dot over (H)}19−Q25  (11); wherein, {dot over (H)}17 is an enthalpy of the seed particle stream into the reactor ({dot over (m)}17,KP,Reactor), {dot over (H)}19 is an enthalpy of an offgas stream from the reactor ({dot over (m)}19,offgas,Reactor), and Q25 is energy removal from the reactor in a region above the fluidized bed; and controlling the heating output (Q20) of the heating apparatus such that the fluidized bed temperature (TWS) is 700° C. to 1200° C., the heating output (Q20) being 0.5 to 3 kW per kilogram of silicon in the reactor tube; wherein, elemental silicon is deposited on the seed particles to form a polycrystalline silicon granulate product that is discharged from the reactor as the product stream.

16. The method of claim 15, wherein the heating output (Q20) is 1 to 2 kW per kilogram of silicon in the reactor tube.

17. The method of claim 15, wherein the heating output (Q20) is 1.3 to 1.6 kW per kilogram of silicon in the reactor tube.

18. The method of claim 15, further comprising controlling fluidization in the fluidized bed region such that a ratio (u/umf) of a superficial gas velocity (u) to a minimum fluidization velocity (umf) is 1 to 6, the superficial gas velocity (u) represented by formula (14): [mathematical expression included] wherein, M is an average molar mass of the gas in the fluidized bed region, {dot over (N)} is an amount-of-substance flow of an offgas from the fluidized bed region, A is a cross-sectional area of the fluidized bed region, and ρGas is a density of the gas in the fluidized bed region, and umf is represented by formula (15): [mathematical expression included] wherein, ψ is a fixed bed porosity, ν is a viscosity of the gas in the fluidized bed region, dS is a Sauter diameter of the seed particles in the fluidized bed region, Ψmf is an incipient fluidization porosity, ρparticle is a density of the seed particles in the fluidized bed region, and g is 9.81 m/s2.

19. The method of claim 18, wherein the ratio (u/umf) is 2 to 5.

20. The method of claim 18, wherein the density of the seed particles in the fluidized bed region (ρparticle) is 2.250 to 2.330 g/cm3.

21. The method of claim 18, wherein the density of the seed particles in the fluidized bed region (ρparticle) is 2.280 to 2.330 g/cm3.

22. The method of claim 18, wherein the density of the gas in the fluidized bed region (ρgas) is 0.5 to 2 kg/m3.

23. The method of claim 18, wherein the density of the gas in the fluidized bed region (ρgas) is 0.7 to 1.2 kg/m3.

24. The method of claim 18, wherein the fixed bed porosity (ψ) is 0.3 to 0.36 kg/m3.

25. The method of claim 18, wherein the incipient fluidization porosity (Ψmf) is 0.33 to 0.4

26. The method of claim 18, wherein the Sauter diameter of the seed particles in the fluidized bed region (dS) is 150 to 10 000 μm.

27. The method of claim 18, wherein the Sauter diameter of the seed particles in the fluidized bed region (dS) is 500 to 5000 μm.

28. The method of claim 15, wherein the seed particles are supplied at a rate of 0.01 to 0.05 kilograms of seed particles per kilogram of silicon in the reactor tube.

29. The method of claim 15, wherein the seed particles are supplied at a rate of 0.02 to 0.03 kilograms of seed particles per kilogram of silicon in the reactor tube.

30. The method of claim 15, wherein the fluidized bed temperature (TWS) is 800° C. to 1150° C.

31. The method of claim 15, wherein the fluidized bed temperature (TWS) is 850° C. to 1100° C.

32. The method of claim 15, wherein the polycrystalline silicon granulate product has a chlorine content of 10 to 70 ppmw.

33. The method of claim 15, wherein the polycrystalline silicon granulate product has a chlorine content of 15 to 40 ppmw.

34. The method of claim 15, further comprising determining a composition of an offgas stream via a gas chromatograph.

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