A process for preparing polycrystalline silicon in a fluidized bed reactor, comprising: a. feeding gases comprising hydrogen and a silicon bearing source gas comprising a silicon monomer into a bubbling fluidized bed containing silicon particles, wherein at least a portion of the bubbling fluidized bed resides in a tapered section of the fluidized bed reactor, wherein the tapered section expands upward and outward at a cone angle from vertical and wherein the fluidized bed reactor further comprises a gas distributor located beneath the tapered section wherein i. a product withdrawal tube is mounted to the gas distributor wherein all, or a portion, of the hydrogen is fed into the fluidized bed reactor through the product withdrawal tube, ii. the gas distributor defines a plurality of feed inlets and the silicon bearing source gas is fed into the fluidized bed reactor through the feed inlets, and iii. the feed inlets are located between the product withdrawal tube and an outer edge of the gas distributor, and b. feeding silicon particles into the fluidized bed reactor above the tapered section; c. heating the fluidized bed reactor, thereby causing thermal decomposition of the silicon monomer to produce polycrystalline silicon on surfaces of the silicon particles, thereby producing larger diameter particles; and d. removing the larger diameter particles from the fluidized bed reactor through the product withdrawal tube. a. feeding gases comprising hydrogen and a silicon bearing source gas comprising a silicon monomer into a bubbling fluidized bed containing silicon particles, wherein at least a portion of the bubbling fluidized bed resides in a tapered section of the fluidized bed reactor, wherein the tapered section expands upward and outward at a cone angle from vertical and wherein the fluidized bed reactor further comprises a gas distributor located beneath the tapered section wherein i. a product withdrawal tube is mounted to the gas distributor wherein all, or a portion, of the hydrogen is fed into the fluidized bed reactor through the product withdrawal tube, ii. the gas distributor defines a plurality of feed inlets and the silicon bearing source gas is fed into the fluidized bed reactor through the feed inlets, and iii. the feed inlets are located between the product withdrawal tube and an outer edge of the gas distributor, and i. a product withdrawal tube is mounted to the gas distributor wherein all, or a portion, of the hydrogen is fed into the fluidized bed reactor through the product withdrawal tube, ii. the gas distributor defines a plurality of feed inlets and the silicon bearing source gas is fed into the fluidized bed reactor through the feed inlets, and iii. the feed inlets are located between the product withdrawal tube and an outer edge of the gas distributor, and b. feeding silicon particles into the fluidized bed reactor above the tapered section; c. heating the fluidized bed reactor, thereby causing thermal decomposition of the silicon monomer to produce polycrystalline silicon on surfaces of the silicon particles, thereby producing larger diameter particles; and d. removing the larger diameter particles from the fluidized bed reactor through the product withdrawal tube.