GB479090A - Improvements in or relating to processes and apparatus for drying granular or powdered materials - Google Patents

Abstract

479,090. Drying grain. RILEY, G. W., and SCOTT & SON (LONDON), Ltd., G. July 30, 1936, No. 21137. [Class 58] [Also in Group XIII] A process of drying granular or powdered material, e.g. cereal grain, consists in continuously feeding the material at a controlled rate along'the interior of a heated first-stage vacuum-drier and into an unheated secondstage vacuum-drier normally communicating with the first-stage drier, the communication being periodically cut to allow the material in the second-stage drier to be completely dried while being subjected to a higher degree of vacuum, whereupon it is discharged and the operations are repeated so long as material is being fed to the first-stage drier. In the construction shown in Fig. 1, a first-stage vacuum-drier comprises a series of verticallydisposed tubes 2 around which steam is circulated. Each tube is fitted with a member 13 adapted to guide the grain that is uniformly heated. Above the tubes is a space 5 which receives the grain on entry past a feeding device comprising rubber rolls 14 arranged as described in Specification 377,502, [Group XIII]. The flow of material from the tubes 2 is controlled by an oscillating or revolving plate 12 within a space 6 in which the material is collected before delivery to the second-stage drier 9. The outlets from the spaces 6, 9 are controlled by hermetically-tight valves 8, 11. The space 5 is in communication with a condenser 25 and a wet vacuum-pump (not shown). The drier 9 is in communication with a condenser 28, the uncondensed vapour from which is passed into the condenser 25 by means of a steam jet pump 29. Valves 30, 31 are provided in association with the condensers. The valve 30 is closed and the valve 31 is opened while the valve 8 is open so that the wet vacuumpump builds up the required vacuum on the first-stage drier, after which the valve 8 is closed, the valve 31 is closed and the valve 30 is opened, enabling the steam jet to build up a higher vacuum in the drier 9. The valves controlling the supply and discharge of material may be controlled automatically by hydraulic means. The feeding means 14 may be replaced by a valve such as described in Specification 12316/00, [Class 32]. A further feeding means is shown in Fig. 2, in the form of a hopper 15 interposed between the space 5 and a primary supply hopper 16, the hopper 15 being cut off from the space 5 while being filled and being cut off from the hopper 16 while being emptied. In a further arrangement shown in Fig. 3, the material is conveyed to the vacuum system in a stream of water, being fed with water to a supply hopper 19, from which it is sucked by a pump 20 and delivered to a vacuum-chamber 21. Here the water is removed by means such as, for example, a centrifugal separator or a vibrating sieve. The material gravitates through a shoot 32 into the space 5 of the first-stage drier while the liquid flows down a pipe 23 to the hopper 19 to mix with a further supply of material. In a modification, a drier is employed in which steam circulates through a series of horizontallydisposed tubes spaced to provide serpentine passages between the tubes down which the material gravitates at a rate controlled by means of an oscillating or rotating plate.