GB742891A - Process and apparatus for crystallizing from solution - Google Patents

Abstract

<PICT:0742891/III/1> In crystallizers with internal cooling systems, the cooling system is resiliently mounted and subjected to periodic impulses to detach from the cooling surface crystals forming in the periods between the impulses. In the apparatus of Fig. 1 a vertical cylinder 2, insulated on the inside with vulcanite and provided with a water jacket 1a to prevent crystal growth on the walls, houses a double pipe coil cooling system 13, 14 supported by brackets 15 from a central tube 16, the whole being supported by a ball race 20 on a rubber mounting 19. Cooling liquid enters at 17 passes down the tube 16, up the coils 13, 14 and out at 18. The cooling system may be rotated by the motor 21, resulting centrifugal force clearing crystals and any slime from the cooling system. The upper end of tube 16 carries an anvil 24 which is periodically struck by a hammer 23 which imparts periodic shocks to the cooling system and also sets up a free longitudinal vibration therein. The cylinder 2 is supplied with crystallizing solution tangentially at 6, a rotary motion being thereby imparted to the solution. Excess solution is fed in, the excess being taken off by overflow 9, a constant level being thus maintained. Crystals and mother liquor are continuously or intermittently removed through valve 5. The apparatus of Fig. 2 is similar to that of Fig. 1 but the cooling system does not rotate, is suspended by five springs and the cooling coils pass through and are rigidly secured to three radial plates which are rigid with the central tube and extend up to a top cap so that the impulses imparted by the hammer are directly transmitted to the cooling coils. By synchronizing the impulses with the natural period of vibration of the cooling system and springs a large amplitude low frequency oscillation may be maintained in the cooling system as a whole as well as higher frequency damped vibration in the cooling coils set up by each impulse from the hammer. A constant level of liquid is maintained by a float valve and crystals and mother liquor are continuously removed by a vane valve. The parts of the cooling system are preferably highly polished and may be chromium plated to assist detachment of crystals therefrom. The cooling pipes may be of circular or oval section with the major axis vertical.