method and control system for a plant of crystallization by evaporation is continuous for the crystallization of the sugar or similar products

摘要

1316706 Crystallization of solid from solution by evaporation of solvent FIVES LILLECAIL 19 April 1971 [19 March 1970] 24433/71 Heading B1B [Also in Division C6] Crystals are produced from sugar juice (or other solution) by a continuous evaporation process carried out in steam-heated vessel 14 which is divided by partitions 18 into cells 1 to 7 through which the boiling solution flows in series; sub-saturated feed solution is supplied to the last cell 7 at a rate which is automatically controlled by valve 54 and regulator 56 so as to keep constant the sugar content of the mixture of crystals and solution withdrawn from the last cell by pump 78; and subsaturated feed solution is supplied to cells 3, 4, 5, 6 at a total rate controlled by valve 60 to maintain a control value calculated by computer 63 from a given mathematical formula involving the rate of flow of steam-condensate measured by flow meter 64 and the concentration of the feed solution measured by densimeter 66, so as to obtain a constant percentage of sugar in the mixture of crystals and saturated solution supplied to the last cell 7. In the apparatus shown, some of the feed solution undergoes preliminary concentration in concentrator 12 before it enters cell 1; this proportion of the solution being part of the total flow controlled by the computer. As it flows from the concentrator to the first cell, the solution receives crystal-nuclii at A. Subsaturated solution is supplied to cells 1 and 2 at rates controlled by regulators 40 and 42, respectively. The pressure in the system is controlled by a valve 30 in the vapour outlet conduit. A modified apparatus is described wherein the concentration of the feed solution introduced into cells 3 to 6 is maintained constant by controlled addition to the feed solution of a proportion of the solution withdrawn from the concentrator.