CA1175040A - Mixer system with container attached baffles - Google Patents

Abstract

ROGERS, BERESKIN & PARR C A N A D A

Title: MIXER SYSTEM WITH CONTAINER
ATTACHED BAFFLES

ABSTRACT OF THE DISCLOSURE

The invention relates to a mixer system for improving the quality of mixing of liquid especially viscous media in stirred tank reactors, wherein a change in direction of the medium set in motion is brought about at one point or at several points of the inner wall of the reactor at different levels, in a direction vertical to the angle of approaching flow (attack). The system is especially suitable for fermentation reactions.

Description

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To perform reactions in the liquid phase, it is necessary to convey ~he 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 zones of highly varying temperature (so-called temperature nests), since the heat generated by the reaction is not dissipa-ted, 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 unfavorably, 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 volum~ 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 agqlomer-ates beyond a certain size due to shearing forces acting on the reaction system. Especially when used in fermentation reactors, ' ~7~

these agitator means have been optimi7ed mainly with a view to the quality of the mass transfer ~rom 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 o~ 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 for the purpose of mixing them are in most cases of a multi-level type (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, reactors 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 turbulence 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-descri~ed 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 therefor relates to a process ~or 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 o~ 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 (de~lectors), 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 periphery of the reactor at different levels, which elements cause a change in direction ofthe flow lS in a direction vertical to the angle of approaching flow.
All liquid systems such as gassed suspensions, emulsions and/or dispersions can be used in the process of the invention.
The process according to the present invention is particularly suitable for gassed fermentation broths.
The advantages of the process of the invention are particu-larly evident in the case of viscous, especially non-Newtonian intrinsically viscous liquid systems wherein the viscosity is above 400 cP, particularly of from 1,000 to 5,000 cP.
Examples of suitable liquid systems which can be used in the present invention include Tylose ~ solutions,`starch solutions, polymerization mixtures, fermentation broths for preparing antibiotics such as penicillin, tetracycline, cephalo-sporin, streptomycin, xanthan fermentations and so on.

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The flow of liquid caused to move by the stirring means radially a~d tangentially with respect to the reactor wall are deflected according to the invention in a vertical direction with regard to the angle of approaching flow, that is in the direction of the longitudinal axis of the reactor or the axis of the stirring means. Deflection in most cases takes place in one direction only, namely upward or downward. Under certain circumstances it may ~e advantageous to deflect alternately downward and upward. The de1ection force depends on the angle of in,clination of the individual baffle elements of the deflectorr on the viscosity of the liquid medium and on the stirring energy. In accordance with the present invention, as a result of the change in direction of the flowing medium the motion of the mixture is increased in a defined preferential direction in the zones close to the reactor wall, while the speed of the flowing medium is increased.
The stirred tank reactor according to the invention may theoretically have any shape. Generally, however, a vertical cylinder is used.
The deflector (elements) arranged in the reactor according to the present invention consist of a number of thin flat elements, preferably plates, which are mounted in the direction of the longitudinal axis of the reactor. Preferably they are arranged in a vertical direction with one above the other and inclined towards the angle of approaching 10w, i.e. to a level vertical to the longitudinal axis of the reactor or of the stirrer.
This inclination angle decreases as the viscosity of the medium decreases and the speed of the approaching flow increases.

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- Sa -This angle is suitably from - 20 to - 85, preferably from - 30 to - 60. Generally this angle is identical for all elements of one deflection unit. If there are several deflection units in the reactor, they may have different angles of approaching S flow, especially alternating angles of approaching flow~ In the latter case the flow is deflected alternately in one direc-tion (upward) and then in the opposite direction opposed (down-ward).
The plate-shaped baffle elements of the deflector according to the invention are in most cases of rectangular or quadrangular structure. They may be of flat or curved construction. In special cases these plate-shaped elements may consist of close-meshed nets, provided that they withstand the pressure of the approaching flow. The dimension of the baffle elements is in most cases such that the distance to the wall of the reactor is of from 0.01 to 0.1 D (D = diameter of the reactor), preferably O.Ol to 0.05 D. Furthermore they extend in a radial direction and preferably over 8 to 20 % of the diametex of the reactor.
Generally the baffle elements are arranged one above the other in the deflection unit and may be fixed directly to the inner wall of the vessel. Preferably, however, they are mounted on adequate holding means consisting for example of one or two rods which extend in the longitudinal direction of the reactor, in a manner such that the angle 'L~

-of approaching flow may be adjusted in variab~e manner. The distance of the individual baffle elements ~rom one another is preferably f.rom 3 to 30, preferably 10 to 15, % of the diameter of the reactor. The number of the indivldual elements 4~ one deflector unit depends on the height of the vessel.
Genexally from 2 to 20 individual elements per meter of reactor height will be sufficient.
The number of the deflection units according to the invention is preferably from 1 to 8, preferably 4.
In a further embodiment of the invention the deflec-tion unsits, that is the holding means and the individual baf1e elements, may be hollow to permit the~introduction of a cool.ing or heati.n~3 medium.
As s~tirring means according to the present invention there ma~v be used generally all means known for this purpose which ensure adequate flow characteristics and a satisfactory stirrer efficlency, for example impeller mixers, turbine mixes, pitched flat blade impellers, flat blade mixers,int~r-multiblade countercurrent impeller, multiblade countercurrent impeller~ self aspiring stirrer and so on.
Stirring mec~ns of the above type which are ~ ~ for the purpose of the present invention are described, for example, in-the article o~
Kiplce titled "Ruhren von dunnflussigen ulld mittelviskosen Medien", CIT 51 (1979), pages 430-436 or irl t~1e arti.cle of Sittiny and Heine titled "Erfahrungen mit yroBtechnischen eingesetzten Bioreaktorenl', CIT 49 (1977), Nr. 8, pages 5q5-605. Preferably ther~ are used in accordance with the present invention multi-level blade stirrers or multi-level disk stirrers, wi-th a distance between the individual levels of from 1 to 3 times the stirrer diame.ter. The number of the bla~es per propeller is generally from 3 to 6 and the ratio of diamet~r of stirrer to diameter of reactor is in most cases from 0.35 to 0.65.
The stirLed tank reactor according to the present inventi.on ~oreover contains the usual i.nserts, for example funnel tubes, valves, pumps, tubes, control and measurin~
instruments and optionally ~geY~ag means such as reflux condensers.
W~.en the stirred tank ractor ~K~d1~gL~ ';h~
is usea for fermentalion purposes, it is pro-vided with the usual m~ans for gas~ing the reaction medium., i.e. corresponding inlets and outle-ts and a tubuIar nozzle ~enerally connected with the inlet; alternatively single nozzles or an air jet belt may be used. In the case of highly endothermic or exothermic reactions the reactor is moreover provided with a double jacket ensurlng an 10 adequate jacket cooling.
The process and the device according to the present invention will be illustrated, by way of example, in the accompanying drawings wherein Figure 1 repres~nts a lateral sectional view of the reactor along lime I-I of Fig~lre 2, 15 and Figure 2 represents a cross-sectional top view alona line II-II of Figure 1, and in the description referring to the drawings.
In Fi.gure 1 ~umeral (1) represents the reactor shaped as~vertical cylinder, ~2) represents the multi-level blade 20 stirrer provided with blades (3). The reaction gas is injected into the reactor via inlet ~4) throu~h jet belt (5), aspirated by the stirrer together with the fluid reac-tion suspension and moved radi.ally and tangentially in the direction of the ractor wall, where the flow is deflected 25 downward along the flow lines (8) by the deElection uni-ts according to the inven-tion, which consist of indivi.dual elements (6) and holding means (7) consistiny of two rods.
This brings about a defined preferential direction of the movement of the mixture and simultaneously a higher speed 30 of the nixture in the zones close to the wall~ as a result o which the heat transfer to cooling jacket (9) is also improved .
Exampl~ 1 ,~,~,/o~
A 1.3 % ~ soluti.on was mixed in a 130 liter 35 stirred tank equipped with four deflection uni.ts accor-ding to the invention eacll of which consisting of S rectan-gular baffle plates of 0.0032 m2 surface area each and with one two-leve.l blad~ s~irrer tnumber of blades: 6). The ; mixin~ time was deterrnined by measuremenls of the color ~ 8 change. I~he angle of approaciling flow of the baffle ele-ments of the deflection units according to the invention was 45. The baffle plates were ~ounted on two rods fixed to the bottom and to the top of the reaator and extended in radial direction over 10 % of the diameter of the reactor at a distance to the reactor wall of about 0.01 D.
With a mechanical power input (stirrer energy) of 5 kW/m3 the mixing time was 12 seconds.
Comparative Example When using four conventional de1ector units of 45 mm width that are arranged vertically with regard to the angle of approaching flow the mixing time was found to be 20 seconds.
Example 2 Example 1 was xepeated using, however, a flat blade stirrer instead of a two-level disk stirrer. With a power input (stirring energy) of about 1 kW/m3 the mixing time was found to be 18 seconds.
Comparative.Exam _ .
When using conventional deflectors under the condi-tions of Rxample 2 the mixing time was 50 seconds.
Example 3 Penicillin was prepared in a fermentation vessel of 25 40 m3 vo]ume equipped with four deflection units accord.incJ
to the invention each consisting of 18 rectangular haffle plates of 0.075 m2 surface area each. The baffle plates extended in radial dlrection over 9 % of the diameter of , ;
. ~ the vessel~ at a di.stance of the wall of about 0.15 D.
30 The angle of approaching flow was ahout 40. Three turbine impellers were used Eor stirring and gassing was effected by a device as shown in Figure 1.
26 m3 of drinking water were placed in the fermenta-tion vessel and the following raw materials were added 35 thereto:
1 J 320 kg o.. soybean flour, 250 kg of sodium t:hiosul.fate, 230 kg OL calcium carbona-t.e, 165 kg of soybean oil, h7~
g : ~
3,300 kg of lactose and 150 kg o~ ph~no~yacetic acid.
The pH of the resulting suspension was adjusted to 6.0 with~sodium hydroxide solution and sterilization was brought about by steaming at 120C for ~0 minutes. Af-ter cooling of the nutrient solution to 25C, the fermentation vessel was inoculated with 3000 liters of a well washed inoculum of penicillin. The contents of the vessel were subjected to fermentation at 25C while aerating with 10 0.5 liter of air per liter of liquid ~olu~e~and minute with a stirring energy of from 2.5 to 3 kW/m . Soybean oil was added during the fermentation process in several portions of about 5 liters in a total ~uantity of from 5 to 1,000 lite~s to defoam the fermentation mixture. The 15 fermentation time was 150 hours and the yield was 14,950 U/ml.
Comparative Exampl_ Example 3 was repeated using, however, a Eermentation vessel equipped with conventional deflection units o-E 0.1 D
width each instead of the four deflection units according 20 to the invention.
The yield was found to be about 13 ! 500 U/ml.
Example 4 Into the fermentation vessel according to Example 3 there were introduced 22 m3 of drinking water, whereto the 25 following raw materials were added:
1,100 kg of peanut flour, 1,250 ky of crystal sugar, 143 kg of amrnonium sulfa-te, 310 kg of calcium carbonate, 25 kg of citric acid, 65 kg of lard, 20 kg of Na2HP04 12 H20, 19 kg of MgS04 7H20,

2.5 kg of MnS04 1 H20i 5.0 kg of ZnS04 7 H20, 0.310 kc of FeS04 7 H20 and 0.310 kg of Al2(S04)3 18 H20-The nutrient solu-tion was steri1ize~ with dixect steam ~ 10 -at 120C for 30 minute~, cooled to a temperature of 28C
and inoculated with 1,500 liters of well wash~d tetracyc-line inoculum. Fermentation was carried ou~ at 28C up to the twelEth hour and was carried to completion at 25C. Aeration was effected with 0.5 liter of air per liter of liquid volume and minute. The stirring energy was 2 kW/m3. After about 48 hours there was added a solu tion of 750 kg of sugar and 180 kg of ammonium suIfate in 2,000 litersof drinking water which had been sterilized at 120C for 30 minutes. A second portion consisting of 750 kg of suga~ in 2,000 litersof ~rinking water that had been stcrrili~ as specified above was added after about 72 hours.
To defoam the fermentation mixture there was added during the fermentation lard oil and soybean oil, depending on the foaming behavior. The final volume was found to be about 32 m2. Fermentation was complete after 160 hours.
l'he yield was about 9,359 U/ml.
Comparative Example Example 4 was repeated using, however, a fermentation vessel equipped with 4 conventional deflection units each having 0.1 D width. The yield was about 8,300 u/ml.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A reaction vessel for intimate and homogeneous mixing of liquid viscous media which comprises, in combination, a mixing vessel having a mixing chamber, inlet and outlet means for charging gas and liquid viscous media to said vessel, mixing means for effecting liquid media flow, aeration means, cooling means comprising a cooling jacket cooperating with the exterior wall of said mixing vessel and flow deflector means comprising holding means for positioning one or more deflector units each unit having a plurality of baffle elements located at one or more points along the periphery of the vessel at a distance from the vessel wall equal to 1% to 10% of the vessel diameter and located at a plurality of points along the longitudinal axis of the vessel and separated from each other along said longitudinal axis at a distance equal to 3% to 20% of the vessel diameter, said baffle elements being positioned towards the direction of approaching liquid media flow such that said direction of flow is varied along a defined path which is vertical to said direction of approaching flow.

2. The reaction vessel of claim 1 containing from 1 to 8 deflector units.

3. The reaction vessel of claim 1 wherein said baffle element is positioned to form an angle between -20° to -85° with respect to the direction of approaching liquid media flow whereby said angle decreases with decreasing viscosity of the liquid viscous media.

4. The reaction vessel of claim 1 wherein said baffle elements have a quadrangular or rectangular plate shape.

5. The reaction vessel of claim 1 wherein the baffle elements of at least one deflector unit are affixed to the vessel wall.

6. The reaction vessel of claim 1 wherein said holding means consists of one or more rods extending along the longitudinal axis of said vessel and positioned to controllably vary the direction of approaching liquid media flow.

7. The reaction vessel of claim 6 wherein said rods and deflec-tor units are hollow and adapted to receive heating or cooling medium.

8. The reaction vessel of claim 1 having 2 to 20 baffle elements per meter of vessel height.

9. The reaction vessel of claim 1 further containing inserts such as flow and temperature measuring devices, valves and tubes.