Agitating – Having interrelated feed and discharge means – Recirculating from and to mixing chamber
Patent
1993-06-21
1994-09-20
Jenkins, Robert W.
Agitating
Having interrelated feed and discharge means
Recirculating from and to mixing chamber
366139, 366144, 366159, 366163, B01F 1502, B01F 1506, B01F 1306
Patent
active
053483901
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of mixing pulverous solids into a liquid phase and a corresponding apparatus.
Methods and apparatus of this kind are being used, for instance, in the production of magnetic tapes, printing inks, varnishes, and in the pharmaceutical industry. Often the liquid phase is a solvent.
An apparatus of the generic kind in question is known from EPA 0 291 209 with which pulverous solids are conveyed pneumatically with the aid of gas from a solids metering means into a mixing vessel. In this case the solids are added below the liquid level of the liquid phase contained in the mixing vessel (so-called below-level procedure) as this facilitates mixing with the liquid phase, especially if the particles are very small and light. The solids can be conveyed into the mixing vessel either under excess pressure, or they can be sucked into the mixing vessel by vacuum established inside the same. Whatever the case, a considerable amount of solvent escapes from the mixing vessel when the excess gas is sucked off or the vacuum created. This loss of solvent must be compensated because often the ratio between "solvent" and "solids" is strictly specified. Therefore, production costs are increased. Another problem results from the fact that such an apparatus no longer fulfills the conditions (e.g. TA-Luft--technical instruction concerning air) stipulated by public authorities during the past few years due to the increasing awareness of the environment.
A method of and an apparatus for scrubbing exhaust air which contains solvents are known from German patent 36 27 875. In that case the exhaust air first is pre-dehydrated in a cooler and then flows through an absorber in the form of a molecular screen. The absorber is regenerated by passing heated gas through the molecular screen. As an alternative, regeneration may be accomplished by low pressure. Although good purity of the exhaust air can be obtained in this manner, molecular screens are not suitable for scrubbing the kind of exhaust air produced with mixing apparatus of the generic kind in question. The possible contamination of the exhaust air with very fine pulverous material would cause clogging of the fine pores of a molecular screen within a short time, thus rendering it useless, even if a prefilter were provided.
GB 2 154 891A discloses the process principle of circulating a gas phase which is supplied to a mixer for mixing purposes and leaves the mixer after the mixing operation, then feeding it again to the mixer. Any components which are entrained by the gas phase as it leaves the mixer are filtered out by a separator before the scrubbed gas phase is returned to the mixer.
It is the object of the invention to devise a method and an apparatus for mixing pulverous solids into a liquid phase making it possible to fulfill stricter emission requirements and permitting better cost-efficient production while, at the same time, maintaining the advantages of the apparatus specified.
This object is met, in accordance with the invention, by a method and an apparatus.
The invention is based on the finding that the underlying problem can best be solved by means of a closed gas circuit. However, the gas serving merely as a means of conveyance cannot simply be returned through the solids metering means back into the mixing vessel because the circulating gas stream would become enriched up to the saturation limit with solvents and that would lead to an agglomeration of the solids being conveyed, thereby plugging up the solids metering means and any conduits down the line. In accordance with the invention, therefore, the liquid contained in the circulating gas flow is condensed off at least to such an extent as to avoid the risk of the material sticking together. The condensed liquid can be fed back at once into the mixing vessel.
An advantageous embodiment of the apparatus according to the invention comprises a condenser each upstream and downstream of the pumping means, with higher pressure prevailing in the condenser downstream of the pumping means tha
REFERENCES:
patent: 4518261 (1983-03-01), Sekimoto et al.
patent: 4863277 (1989-09-01), Neal
patent: 4955723 (1990-09-01), Schneider
patent: 5046856 (1991-09-01), McIntire
Erich Netzsch GmbH & Co. Holding KG
Jenkins Robert W.
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