Process and device for improving the quality of mixing of liquid

Details Process and device for improving the quality of mixing of liquid Process and device for improving the quality of mixing of liquid

1981-03-26

1983-03-29

Warden, Robert J.

Chemistry: molecular biology and microbiology

Micro-organism, per se ; compositions thereof; proces of...

261 93, 261123, 435313, 435314, 435315, 435316, C12N 100, C12M 104, C12M 106, C12M 108

Patent

active

043784364

DESCRIPTION:

BRIEF SUMMARY
To perform reactions in the liquid phase, it is necessary to convey the reactants required to the zone where the reaction takes place by mixing and/or stirring, followed by removal of the reaction products. The transport paths in the case of catalytic reactions are determined by the distribution of the catalytically active substances and in the case of fermentations by the distribution of the cells.
It is known to carry out reactions of the above type in stirred tanks. Particularly with highly viscous and non-Newtonian or intrinsically viscous reaction mixtures dead zones are formed in those areas which are only slightly stirred which due to disintegration phenomena, no longer participate in the supply and removal of matter. With chemical reactions this may lead to so-called temperature nests since the heat generated by the reaction is not dissipated, or to a breakdown of the reaction caused by self-locking as a result of over-concentrations. In the case of fermentation reactions, this formation of dead zones influences the desired metabolic reactions, which may even result in irreversible damage and destruction of the cells. In the case of batch fermentation of antibiotics of up to 300 hours, nearly all cells remain occasionally in such zones, even if the latter represent only 2 to 3% of the volume of the reactor.
The stirring means serves to mix the reaction system, to divide and disperse the injected gas, to dissipate the reaction heat via the reactor jacket and/or via cooling inserts and under certain circumstances to prevent the formation of agglomerates beyond a certain size due to shearing forces acting on the reaction system. Especially when used in fermentation reactors, these agitator means have been optimized mainly with a view to the quality of the mass transfer from the gas phase into the liquid phase attributable thereto and not so much with a view to the quality of their mixing effect. The agitator efficiency has been improved and the volumes of the reactor have been increased, while the efficiency of the biological cell cultures increased, and the reactors, the contents of which were considered as homogeneously mixed, have been divided into aeration, degassing and heat exchange zones.
The nutrient solutions in actual use exhibit a non-Newtonian intrinsically viscous behavior. The stirrers used have in most cases three to five levels and the ratio of diameter of the stirrer to diameter of the tank is from 0.35 to 0.65. To prevent rotation of the contents of the reactor at the same speed as the stirrer, are used wherein deflectors are mounted close to the wall wherein the width of the deflectors in vertical orientation to the angle of approaching flow is about 8 to 10% of the diameter of the vessel. Especially in the case of intrinsically viscous reaction mixtures stationary pockets of turbulences or even dead zones having the above-described disadvantages are formed behind these deflectors.
It is an objective of the present invention to overcome the disadvantages of the present state of the art and particularly to control the flow direction in such a way that the above-described dead zones do not occur, the mixing effect of the stirrer means and the heat transfer are improved and rotational movement of the reaction mixture in the reactor with little mixing effect is prevented.
The present invention therefore relates to a process for improving the quality of mixing of liquid, in particular viscous media in stirred tank reactors, which comprises changing the direction of the medium set in motion by stirring means, at one or several locations along the internal wall of the reactor and at different levels, in a direction vertical to the angle of approaching flow.
The present invention moreover relates to a stirred tank reactor provided with the usual stirrer means, with elements acting on the flow, i.e., deflectors, optionally with further inserts, with jacket cooling elements and with aerating means, wherein the deflectors are baffle elements that are arranged at one or several points along the

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