Chemistry: physical processes – Physical processes – Agglomerating
Patent
1997-09-26
2000-12-12
Straub, Gary P.
Chemistry: physical processes
Physical processes
Agglomerating
23293R, 34369, 71 6404, 422142, 4234152, 425222, C01B 1510
Patent
active
061592528
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
This invention relates to a process for the production of granulates by fluidised bed spray granulation and to a device which is particularly suitable for the performance of the process.
Originally liquid products, in particular suspensions and solutions, but also melts, may be converted by fluidised bed spray granulation into free-flowing, low dust, granular solids, hereinafter termed granulates. In fluidised bed spray granulation, solid particles, which are substantially smaller than the particles to be produced are sprayed with a liquid starting material and simultaneously dried until the particles have achieved the desired grain size. The term "substantially" should be taken to mean that particles of the desired grain size may also be present in addition to the above-stated smaller particles, which also includes the nuclei. In order to guarantee a continuous process, it must be ensured that the nuclei are constantly introduced into the fluidised bed or these nuclei are directly formed in the fluidised bed and granulate is drawn off from the fluidised bed. In order to obtain a granulate with a narrow grain size range, the material is discharged from the fluidised bed with classification or is classified using conventional external pneumatic classifiers; the fine particles obtained during classification, which are not of the desired grain size, are reintroduced into the fluidised bed as nuclei. In the event of discharge with classification and recirculation of undersized particles, the fluidised bed contains all grain size fractions from the nucleus up to the granulate of the desired grain size. A review of continuous fluidised bed spray granulation is provided by H. Uhlemann in Chem.-Ing.-Tech. 62 (1990), no. 10, pages 822-834; this document, which is included in the disclosure of the present application, describes the principles of fluidised bed spray granulation, features of grain growth and fluidisation, various process variants and components of fluidised bed spray granulators.
Depending upon the design of the fluidised bed spray granulator, the liquid starting material containing the dissolved and/or suspended solids or a melt is sprayed into the bed from above, from the side or from below. In order to ensure a sufficient material throughput, the spray nozzles arranged in the device must cover the entire fluidised bed. Uniform surface loading must be achieved. Numerous nozzles must be installed to this end, so entailing considerable capital costs due to the pipework and the necessary measurement and control instrumentation. Moreover, so many nozzles are also susceptible to plugging and encrustation such that shutdowns are frequently necessary for cleaning purposes.
The object of the present invention is to provide an improved process for fluidised bed spray granulation, which avoids the above-stated disadvantages; an elevated fluid throughput should thus be achieved using few nozzles. Due to the superproportional increase in the momentum of the spray at a constant output droplet diameter and the greater spread of the jet as nozzle size increases, a way had to be found to prevent the spray jet from striking through onto the bottom in the case of spraying from the top downwards, onto the walls of the granulation device when spraying from the side or into the gas space above the actual fluidised bed when spraying upwards from below, as such strike-throughs generally bring about a rapid collapse of the process.
This object is achieved by a process for the production of granulates by fluidised bed spray granulation, comprising spraying one or more liquid starting materials by means of spray nozzles into a fluidised bed containing solid particles which are substantially smaller than the granulates to be produced, vaporising volatile constituents of the sprayed starting material(s), introducing nuclei into the fluidised bed or/and forming nuclei therein and discharging granulates from the fluidised bed, which process is characterised in that in each case at least two spray nozzles at least
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Alt Hans-Christian
Bewersdorf Martin
Klasen Claas-Jurgen
Schutte Rudiger
Degussa-Hus Aktiengesellschaft
Straub Gary P.
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