| 摘要 |
A process for producing powders or concentrates from solutions or suspensions comprises spraying the solution or suspension downwardly in a tower in the form of a rain of particles of diameter 5-2000 microns and providing an upwardly flowing stream of air or other gas introduced at a temperature of 0 DEG -60 DEG C., the conditions being adjusted so that the time during which the particles fall in contact with the air or other gas is not less than five seconds and the humidity of the gas passing out of contact with the particles is not less than 65%. The stream of gas is preferably pre-dried, e.g. by freezing or passing over a dehydrating agent. The gas may be air, when the materials being dried are insensitive to oxygen, or an inert gas, such as carbon dioxide or nitrogen, if they are sensitive to oxygen. The gas is preferably filtered to free it from dust particles. When the treated material is subject to enzymatic or fermentative reactions, the gas may also be sterilised. Suitable gas velocities are 0,01-3 meters/second. A suitable tower for the production of powders has a height of about 50 meters and a diameter of 5-80 meters. Auxiliary towers operating as preliminary concentration towers or wash towers may also be provided. The towers may be provided with a packing, e.g. Raschig rings or spiral bodies, or bubble caps and screen bottoms. Auxiliary devices such as heat exchangers and heat equalisers may be provided for purposes of economy. An annular free space may be provided along the walls of the tower, in which space no droplets fall but only gas rises to prevent particles settling on the walls. The spraying device may be mounted at a distance of 2-10 meters from the top of the tower. The gas stream may be introduced at the lower end of the tower, tangentially or horizontally or so that it rises straight up without spiral motion. The tower may have an intermediate, air-permeable, flat bottom at 0,5-0,6 meters above the actual bottom to retain the dehydrated product. Application of the process. The process is particularly applicable to dehydrating highly heat-sensitive and delicate chemical, pharmaceutical and food products. Extensive lists of materials which may be treated are given, representative materials being:-fruit and vegetable juices; milk products; eggs; coffee and tea extracts; vitamins and hormones; natural and synthetic jellies; blood and plasma; heat-sensitive dyes; hygroscopic sugar products such as honey; malt preparations; soaps and detergents; and pasty starch slurries. Particular reference is made to the use of the process to obtain anhydrous lactic acid (see Group IV(b) ). ALSO: Lactic acid is obtained from a solution thereof and in particular anhydrous iron-free lactic acid is obtained from calcium lactate solutions decomposed with sulphuric acid by spraying the solution or suspension downwardly in a tower in the form of a rain of particles of diameter 5-2,000 microns and providing an upwardly flowing stream of air or other gas introduced at a temperature of 0 DEG C.-60 DEG C., the conditions being adjusted so that the time during which the particles fall in contact with the air or other gas is not less than 5 seconds and the humidity of the gas passing out of contact with the particles is not less than 65%. The stream of gas is preferably pre-dried, e.g. by freezing or passing over a dehydrating agent. The gas may be air or an inert gas, such as carbon dioxide or nitrogen. The gas is preferably filtered to free it from dust particles. The gas may also be sterilised. Suitable gas velocities are 0.01-3 meters/second. A suitable tower for the production of powders has a height of about 50 meters and a diameter of 5-80 meters. Auxiliary towers operating as preliminary concentrating towers or wash towers may also be provided. The towers may be provided with a packing, e.g. Raschig rings or spiral bodies, bubble caps and screen bottoms. Auxiliary devices such as heat exchangers and heat equalisers may be provided for purposes of economy. An annular free space may be provided along the walls of the tower in which no droplets fall but only gas rises to prevent particles settling on the walls. The spraying device may be mounted at a distance of 2-10 meters from the top of the tower. The gas stream may be introduced at the lower end of the tower either tangentially or horizontally or so that it rises straight up without spiral motion. The tower may have an intermediate, air-permeable, flat bottom at 0.5-0.6 meters above the actual bottom to retain the dehydrated product. ALSO: A process for producing powders or concentrates from solutions or suspensions comprises spraying the solution or suspension downwardly in a tower in the form of a rain of particles of diameter 5-2000 microns and providing an upwardly flowing stream of air or other gas introduced at a temperature of 0-60 DEG C., the conditions being adjusted so that the time during which the particles fall in contact with the air or other gas is not less than 5 seconds and the humidity of the gas passing out of contact with the particles is not less than 65%. The stream of gas is preferably pre-dried, e.g. by freezing or passing over a dehydrating agent. The gas may be air when the materials being dried are insensitive to oxygen or an inert gas, such as carbon dioxide or nitrogen, if they are sensitive to oxygen. The gas is preferably filtered to free it from dust particles. When the treated material is subject to enzymatic or fermentative reactions the gas may also be sterilized. Suitable gas velocities are 0.01-3 meters/second. A suitable tower for the production of powders has a height of about 50 meters and a diameter of 5-80 meters. Auxiliary towers operating as preliminary concentrating towers or was towers may also be provided. The towers may be provided with a packing, e.g. Raschig rings or spiral bodies, bubble caps and screen bottoms. Auxiliary devices such as heat exchangers and heat equalizers may be provided for purposes of economy. An annular free space may be provided along the walls of the tower in which no droplets fall, but only gas rises to prevent particles settling on the walls. The spraying device may be mounted at a distance of 2-10 meters from the top of the tower. The gas stream may be introduced at the lower end of the tower either tangentially or horizontally or so that it rises straight up without spiral motion. The tower may have an intermediate, airpermeable, flat bottom at 0.5-0.6 meters above the actual bottom to retain the dehydrated product. Applications of the process.-The process is particularly applicable to dehydrating highly heat-sensitive and delicate chemical, pharmaceutical and food products. Extensive lists of materials which may be treated are given representative materials being: fruit and vegetable juices and pastes; milk products, including milk, butter and cheese; eggs; yeast; coffee and tea extracts; vitamins and hormones; natural and synthetic jellies; blood, blood plasma and liver extracts; heat-sensitive dyes; hygroscopic sugar products such as honey; malt preparations; puddings, cream sauce mixes and pasty starch slurries. Particular reference is made to the use of the process to obtain anhydrous lactic acid (see Group IV (b)). |
