NOVELTY - The closed-loop process comprises: introducing trichlorosilane and hydrogen to a first fluidized bed reactor to produce polycrystalline silicon and a first effluent gas comprising silicon tetrachloride, hydrogen and unreacted trichlorosilane; introducing silicon and an amount of silicon tetrachloride and hydrogen from the effluent gas into a hydrogenation reactor/second fluidized bed reactor to produce a second effluent gas comprising trichlorosilane, unreacted hydrogen, hydrogen chloride (6) and unreacted silicon tetrachloride; and contacting hydrogen chloride and silicon.    USE - The closed-loop process is useful for producing polycrystalline silicon for producing integrated circuits and photovoltaic cells such as solar cells.    ADVANTAGE - The closed-loop process is capable of economically producing the polycrystalline silicon with high corrosion resistance and without dust.    DETAILED DESCRIPTION - The closed-loop process comprises: introducing trichlorosilane and hydrogen to a first fluidized bed reactor to produce polycrystalline silicon and a first effluent gas comprising silicon tetrachloride, hydrogen and unreacted trichlorosilane; introducing silicon and an amount of silicon tetrachloride and hydrogen from the effluent gas into a hydrogenation reactor/second fluidized bed reactor to produce a second effluent gas comprising trichlorosilane, unreacted hydrogen, hydrogen chloride (6) and unreacted silicon tetrachloride; contacting hydrogen chloride and silicon to produce trichlorosilane and silicon tetrachloride; introducing the trichlorosilane produced by contacting hydrogen chloride and silicon into the first fluidized bed reactor to produce polycrystalline silicon; and introducing a chlorinated product gas (10) into a purification system (4) to produce a purified trichlorosilane stream and a purified silicon tetrachloride stream. The hydrogen chloride and silicon are introduced into a chlorination reactor (7) to produce the chlorinated product gas comprising trichlorosilane and silicon tetrachloride. The purified trichlorosilane stream is introduced into the first fluidized bed reactor. The first effluent gas is introduced into a first effluent gas separator such as a vapor-liquid separator to separate hydrogen from trichlorosilane and silicon tetrachloride. The trichlorosilane and silicon tetrachloride are introduced into a chlorinated product gas purification system. The purified silicon tetrachloride stream is introduced into the second fluidized bed reactor/hydrogenation reactor and the second fluidized bed reactor. The second effluent gas is introduced into a second effluent gas separator system such as a vapor-liquid separator to separate trichlorosilane and unreacted silicon tetrachloride from hydrogen, and comprises hydrogen and hydrogen chloride. The trichlorosilane and unreacted silicon tetrachloride are introduced into the chlorinated gas purification system. The silicon tetrachloride and hydrogen are introduced into the hydrogenation reactor to produce a hydrogenated gas comprising trichlorosilane, hydrogen chloride, unreacted hydrogen and unreacted silicon tetrachloride. The hydrogenated gas is introduced into a hydrogenated gas separator such as a vapor-liquid separator to separate trichlorosilane and unreacted silicon tetrachloride from hydrogen and unreacted hydrogen chloride. The trichlorosilane and unreacted silicon tetrachloride are introduced into the chlorinated gas purification system. The hydrogen and hydrogen chloride gas are introduced into a separation system to separate hydrogen and hydrogen chloride. The separated hydrogen chloride is introduced into the chlorination reactor. The separated hydrogen is introduced into the fluidized bed reactor and/or hydrogenation reactor. The chlorinated product gas comprises trichlorosilane, silicon tetrachloride, hydrogen and unreacted hydrogen chloride, and is introduced into a chlorinated gas separator such as a vapor-liquid separator of the purification system to separate trichlorosilane and silicon tetrachloride from hydrogen and unreacted hydrogen chloride. The purification system comprises a silicon tetrachloride separator such as a distillation column and a trichlorosilane purifier such as a distillation column. The separated trichlorosilane and silicon tetrachloride are introduced into the silicon tetrachloride separator to separate silicon tetrachloride from trichlorosilane and produce trichlorosilane feed gas. The trichlorosilane feed gas is introduced into the trichlorosilane purifier to remove impurities from the feed gas. The purified trichlorosilane feed gas is introduced into the first fluidized bed reactor to produce the polycrystalline silicon. The separated hydrogen and unreacted hydrogen chloride are introduced into a separation system to separate hydrogen and hydrogen chloride. The separated hydrogen chloride is introduced into the chlorination reactor. The separated hydrogen is introduced into the first fluidized bed reactor and/or second fluidized bed reactor/ hydrogenation reactor. The separation system comprises a hydrogen separator such as bubbler, a hydrogen purifier such as an adsorber, and a hydrogen chloride purifier such as a distillation column. The hydrogen and hydrogen chloride are introduced into the hydrogen separator to produce a hydrogen recycle gas and a hydrogen chloride recycle gas. The hydrogen recycle gas is introduced into the hydrogen purifier to remove impurities from the hydrogen recycle gas. The hydrogen chloride recycle gas is introduced into the hydrogen chloride purifier to remove impurities from the hydrogen chloride gas. The purified hydrogen recycle gas is introduced into the first fluidized bed reactor and/or second fluidized bed reactor/hydrogenation reactor. The purified hydrogen chloride recycle gas is introduced into the chlorination reactor. A molar ratio of chlorine added as a make-up to polycrystalline silicon product that is produced is less than 2:1, less than 1:1, less than 1:1.2, less than 1:1.5, less than 1:2, less than 1:2.5 and 2:1-1:5 or 1:1-1:5. A molar ratio of hydrogen added as a make-up to polycrystalline silicon product that is produced is less than 1:1, less than 1:2, less than 1:3, less than 1:5, less than 1:10 and 1:1-1:20 or 1:2-1:10. An INDEPENDENT CLAIM is included for a system for producing polycrystalline silicon.    DESCRIPTION OF DRAWING(S) - The diagram shows a flow chart a system for producing polycrystalline silicon.    Source of silicon (3)    Purification system (4)    Hydrogen chloride (6)    Chlorination reactor (7)    Chlorinated product gas. (10)