Abstract: A fluidized bed reactor containing a heat exchange apparatus for conveying a heat transfer medium comprising at least one pipe which extends in a vertical direction from the top of the reaction chamber into the fluidized bed with one end of the vertical pipe which points in the direction of the gas flow having a conical tapered end and/or a jacket on the outside of the reactor wall in the form of a serpentine conduit having a rectangular cross section and a domed cover.

Abstract: A process of melting down and purifying silicon, which comprises melting silicon in at least half of the amount up to double of the amount of a silicate melt heated by resistance heating up to a temperature of at least 1,420.degree. C., said melt consisting of 2-30% by weight of calcium oxide, 5-35% by weight of magnesium oxide, wherein the sum of calcium oxide and magnesium oxide will be 15-38% by weight, 0.5-28% by weight of aluminum oxide and 45-70% by weight of silicon dioxide, and wherein, to the melt are added at least 0.29% by weight of elementary and/or chemically bound copper, preferably 0.50-3% by weight, calculated on the silicon amount.