Abstract: One or more quartz tubes (1) are utilized in apparatus for the concentration of an acid. Each quartz tube is heated from the outside, and the acid is fed in at the upper part of each tube. Concentrated acid is drained off from the lower part of each tube into a vessel (3) and the vapors driven off from the acid during the concentrating rise inside each tube, and are led off from the upper part thereof. Inside each tube, the acid first passes through a rectification zone (A) in the upper part of the tube, and then passes through a liquid film zone and a reservoir zone.

Abstract: For concentration and possible purification of mineral acids, particularly sulphuric acid, a furnace which can be heated is utilized, in which one or several long quartz tubes are placed. The quartz tubes are sealed at the upper and lower parts of the furnace and inside the furnace the quartz tube is heated from the outside with the utilized means. The acid which is to be treated is fed to the respective quartz tube via the upper parts of this, and the purified acid is collected in a vessel located at the lower parts of the quartz tube. Packings of small and/or medium dimensions are arranged in the quartz tubes.

Abstract: The present invention provides a unique structure for concentrating mineral acids, and particularly sulphuric acid wherein a plurality of long quartz tubes extend vertically through a furnace and have vertically lower ends in communication with a receiving vessel. The quartz tubes are surrounded by tube units and flow passageways are created on either side of the tube units for directing hot combustion gases along the quartz tubes, providing convective and radiative heat transfer to the tubes as required to heat the acid flowing therethrough. An assembly is positioned for generating turbulance within the gas flow passageway to achieve a vigorous turbulance of the hot combustion gases.

Abstract: The evaporating tubes of an acid concentrating system are positioned within a double-walled tube unit which directs heating gases over the tube and are supported at their lower ends on a spherical bearing surface which permits relative movement of the components without inducing unacceptable stress levels.