【DO oxygen-rich technical description】
Micro-giant BioEngineering 2009.06.19
In the process of microbial culture, if it is aerobic bacteria (some facultative bacteria, depending on the metabolic status), there is often an urgent need for a large amount of oxygen in a certain culture stage, so the high dissolved oxygen (DO CASCADE) control strategy is explained as follows: (Note that high dissolved oxygen is often accompanied by a large amount of foaming in high-density fermentation)
1. Agitation speed:
In the process of liquid fermentation, the mass and energy can be transferred quickly through effective agitation, and it also includes the improvement of the degree of oxygen in the air dissolved in the fermentation liquid. However, excessive agitation speed will cause a sharp increase in shear force, so each time the computer increases or decreases the speed setting value, it needs to wait for a while, observe the change of the DO value, and then automatically correct it. And it must be accompanied by the upper and lower limit settings of the speed to limit the variation factor to be adjusted within a certain range, not to increase or decrease the speed without limit to achieve the DO setting value. However, if the upper limit is reached and the dissolved oxygen cannot be increased to the expected value, the program can automatically transfer to the next control strategy by setting. This automatic transfer control strategy, the object is not a direct object and has the control of "transfer" and "indirect" The method is called CASCADE.
2. Ventilation:
Increasing ventilation is often a more direct and effective way. However, when it increases to a certain level, it shows a significant slowdown, and the DO value does not increase. Therefore, the maximum ventilation vvm at the beginning of the hardware design is a certain value. Considering factors such as dispersion capacity, bubble retention time, pathway, and body surface area, just increasing the ventilation volume will limit the value, and it will easily promote the formation of foam, which becomes another Major troubled project. Therefore, by setting the upper and lower limits to find the appropriate ventilation volume. If the DO target value is not reached, it can be controlled by the next control factor through the "CASCADE" control to make it suitable in time.
3. The vessel pressure:
Increase the vessel pressure to increase the bubble residence time. However, the changeable range of the vessel pressure is usually not large (0.1~0.5kg/cm2), because overpressure is not conducive to the growth of most microorganisms, and only the vessel pressure above 0.5kg/cm2 can significantly increase DO, so this strategy is not used now.
4. Oxygen:
Use the "CASCADE" mode with O2 setting to control the appropriate ventilation volume, so that it can be activated to add O2 when other control factors reach the upper limit, to achieve the concept of effective and energy saving. When adding O2, pay attention to the source pressure setting. Generally, the O2 line must be > Air line 0.2kg/cm2 or more and a non-return valve must be installed. Pure oxygen cannot be directly injected into the fermentation vessels, and a gas mixer must be added to mix with air in a certain proportion before entering the tank. The above slender vessel design is combined with the aeration ring and dispersion type blade (appropriate diameter and number of segments) to achieve uniform dissolved oxygen distribution.
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