GB1303425A - - Google Patents

Abstract

1303425 Gas heater LAPORTE INDUSTRIES Ltd 27 Jan 1970 [28 Jan 1969] 4665/69 Heading H5H [Also in Division C1] A gas heater comprises an assembly 1 of graphite heating elements 2 which have been roughened by heating to at least 1000‹ C. in air and means for maintaining the elements in contact, the shape of the elements and configuration of the assembly being such that the " nominal contact " area between adjacent elements 2, i.e. the area of overlap, and the relative positions of the elements 2 remain unchanged in use. As shown the gas heater comprises a plurality of heating columns 1 formed by square section graphite rods 2. Each column has seven pairs of rods 2 stacked on top of one another, the elements of each pair being spaced apart for gas flow and having their axes parallel and perpendicular the axis of the column. Alternate pairs have their axes at right angles. Graphite pressure plates 6 at the top and bottom of each column keep the heating elements 2 in contact and graphite connector plates join the heat columns 1 in series between electrodes 8. Graphite baffles 9 prevent vertical temperature gradients in gas flowing through brick chamber 3 from inlet 4 to outlet 5. The heating elements 2 may be of inverted channel shape with one end of the base removed if desired. In the latter case, the elements are stacked on top of one another in a housing with the removed portions of the bases of adjacent channel elements at opposite ends so that a zig-zag gas passage is formed through the assembly. A heating column assembly with a zig-zag gas passage may be formed using rectangular plate heating element located in a casing by two columns of L-shaped heating elements, the rows of L-shaped elements being arranged along a pair of opposite sides of the column. The heating column assemblies 1 may be formed of stacked rods of, e.g. rectangular section, with the axes of the heating rods perpendicular to the column axis, and the axes of adjacent rods perpendicular. Where the heating assemblies comprise vertical stacks of heating elements contact pressure may be ensured by weights on top of the assemblies. If the columns are horizontal and the elements rest on a horizontal surface, contact pressure is applied by weighted levers. The surface on which the elements rest may be inclined so that frictional forces on the elements causing differential contact pressures on expansion or contraction may be counteracted by gravity. Alternatively, the heating elements may rest on rollers or rails. The heating columns 1 may be fed from a three-phase supply. The columns are arranged in three groups, each of which occupies a different length of casing 3 and is connected to one phase. The apparatus may be used for preheating a mixture of titanium tetrachloride and aluminium chloride vapour to 1000‹ C. prior to its vapour-phase oxidation in the manufacture of titanium dioxide incorporating alumina. Halides of silicon, zirconium and iron may also be heated in the apparatus.