GB299838A - Improvements in drying methods and apparatus - Google Patents

Abstract

299,838. Olsson, J. G., and Stenfors, F. I. E. Nov. 3, 1927, [Convention date]. Air and gases, controlling temperature and humidity of; chambers, details of construction of;endless band conveyers; wheeled trucks, moving; rotary scraper apparatus.- Material is dried by a heated medium such as air, and the moisture so evaporated passes with the air through progressively colder parts of the apparatus to recover the heat, the air after further cooling and heating being recirculated. The material is moved on trucks 63 or an endless band 42 along a passage in which heating tubes 40 are disposed in a casing 44 so that air is circulated continuously by gravity or fans 69 in a plane at right angles to the length of the passage, past the tubes 40 and material in turn The tubes 40 carry air and steam from a chamber 39 heated externally by a supply pipe 43 containing steam or exhaust or flue gases. This heating chamber 39 may be placed centrally in the passage or at either end. Fans 69 at both sides circulate heated air down at each side in turn through slits 73 in the inner side walls 76 of the passage. The air and steam, after being drawn through the tubes 40 by a fan 52, reach an outlet 55 where the condensed water may be separated. The air is mixed or not with fresh air according to the position of the dampers 54, 57 and the degree of moisture in the apparatus or is otherwise cooled and returned by a pipe 89 to the heating chamber or outlet for the dried material. The tubes may extend to both ends of the passage or to one end only, and two heating chambers may be provided with tubes extending from both. Hot flue gases or steam may be added to the tubes 40 at desired points. The material passing out through a passage 59 may be cooled as it warms entering air. The separate heating chamber may be omitted, and the heating gas drawn directly through the tubes by a fan to a chimney with the saturated drying vapours (preferably partly formed by the heating gas) which have been circulated round the materials. Fresh air may be added, or gas from the chimney reused. In Fig. 11, granular material fed by a hopper 79 is moved by a conveyer worm 78 along a tube 76 to an outlet 80. The heating medium is supplied to a central casing 81 communicating by an opening 85 in a passage 84 with the tube 76 surrounded by another casing 83 at each side. Fresh air is supplied at 88 to the tube 76 and mixes with heating air at the opening 85, both being circulated in casings 83 and finally withdrawn by fans 87 in pipes 86 and re-used.