Abstract: A corrosive liquid such as sulphuric acid is concentrated using two spaced concentric tubes. A film of the acid flows down the inside of the inner tube and hot flue gases contact the outside of the outer tube. Advantageously, the inner tube transmits radiant energy, e.g. is made of quartz, so the outer tube heats the inner tube by radiation. This absence of mechanical stress on the inner tube increases its life. The water vapor is taken off at the top of the inner tube and concentrated solution at the bottom. If desired, the tubes could be reversed with the flue gases going through the inner tube and the outer tube being of quartz with the liquid flowing on its outside.

Abstract: A multi-stage apparatus suited for concentrating sulphuric acid comprising at least one high temperature stage and one low temperature stage, the high temperature stage including a surrounding wall defining a flue gas channel, means for delivering hot flue gas to said channel, and means for withdrawing from said channel cooled flue gas, the flue gas heating said surrounding wall which in turn imparts heat to material to be heated thereby, the low temperature stage including a heat exchanger with a first flow path for a heating agent and a second flow path for a material to be heated thereby, means for supplying the said second flow path material to be heated, means for withdrawing from said second flow path material after having been heated therein, and means for withdrawing from said first flow path spent heating agent, the means for withdrawing cooled flue gas from said flue channel of said high temperature stage forwarding heat from said cooled flue gas to said first flow path of said low temperature stage

Abstract: To increase the degree of separation of liquid droplets from a stream of gas by means of a separator consisting of a packet of wire gauze arranged in a pipe, the packet is subdivided along its height by discharge channels arranged transverse to the direction of flow.