Patent ID: 8722141

Claim:
A process for the production of high-purity polysilicon granules comprising depositing a reaction gas on silicon granules in a fluidized bed reactor, the process comprising: providing a reactor having a reactor wall defining the extent of the fluidized bed, the reactor having a reactor space comprising at least two zones lying one above the other, wherein a first, lower zone is weakly fluidized by the introduction of a silicon-free gas into silicon granules contained in the lower zone, wherein the height of the lower zone is within the range of 50 to 300 mm, by means of a plurality of individual dilution gas nozzles, wherein the maximum exit velocity of the dilution gas from the nozzles is within the range of 20 to 200 m/s and wherein the dilution gas is fed in an amount such that the gas velocity in the lower zone is 1.2 to 2.3 times the minimum fluidization velocity, and a second, reaction zone directly abutting the first, lower zone, the reaction zone heated via its outwardly bounding reactor wall, introducing a silicon-containing reaction gas as a vertically directed gas jet into the reaction zone by one or a plurality of reaction gas nozzles, wherein the local gas velocities of the gases or of the gas mixtures at the exit of the nozzle systems are within the range of 1 to 140 m/s, wherein above the reaction gas nozzles local reaction gas jets surrounded by bubble-forming fluidized bed form, within which the silicon-containing gas decomposes at silicon particle surfaces and leads to silicon particle growth, introducing the reaction gas such that it has fully reacted or reacted to at least 85% chemical equilibrium conversion before it reaches either the reactor wall or the fluidized bed upper surface; and wherein in combination with the detection of the amounts of reaction and dilution gas fed and a computational model for the particle population, the addition of seed particles and the product take-off are controlled such that the desired grain size distribution in the reactor and the amount of granules in the fluidized bed is kept stable at a steady state over a production campaign.