NOVELTY - Producing polycrystalline silicon in closed-loop process involves introducing trichlorosilane into disproportionation system to form silicon tetrachloride and one of silane and dichlorosilane; introducing silane/dichlorosilane into fluidized bed reactor to form polycrystalline silicon and effluent gas comprising hydrogen and unreacted silane/dichlorosilane; introducing an amount of silicon tetrachloride and effluent gas hydrogen into a hydrogenation reactor; and introducing hydrogen chloride and silicon into chlorination reactor, followed by introducing to disproportionation system.    USE - For producing polycrystalline silicon (claimed) which is used as raw material to produce many commercial products including e.g. integrated circuits and photovoltaic (i.e. solar) cells.    ADVANTAGE - The method produces polycrystalline silicon by reducing the amount of hydrogen and chlorine used relative to conventional methods; and is closed-loop process.    DETAILED DESCRIPTION - Producing polycrystalline silicon in closed-loop process involves introducing trichlorosilane into a disproportionation system to produce silicon tetrachloride and at least one of silane and dichlorosilane; introducing silane or dichlorosilane produced from the disproportionation system into a fluidized bed reactor to produce polycrystalline silicon and an effluent gas comprising hydrogen and unreacted silane or dichlorosilane; introducing an amount of silicon tetrachloride produced from the disproportionation system and an amount of hydrogen from the effluent gas into a hydrogenation reactor to produce trichlorosilane and hydrogen chloride; introducing an amount of hydrogen chloride produced from the hydrogenation reactor and silicon into a chlorination reactor to produce a chlorinated gas comprising trichlorosilane and silicon tetrachloride; and introducing trichlorosilane produced from the chlorination reactor to the disproportionation system to produce silicon tetrachloride and at least one of silane and dichlorosilane. An INDEPENDENT CLAIM is included for a system (s1) for producing polycrystalline silicon, and is closed-loop with respect to hydrogen and chlorine-containing compounds, comprising: a chlorination reactor in which hydrogen chloride is contacted with silicon to produce trichlorosilane and silicon tetrachloride; a disproportionation system in which trichlorosilane is converted to silane or dichlorosilane; a fluidized bed reactor in which silane or dichlorosilane is decomposed to produce polycrystalline silicon; and a hydrogenation reactor in which silicon tetrachloride and hydrogen are introduced to produce trichlorosilane.