Feed manipulation

REACTOR TEMPERATURE CONTROL USING FEED MANIPULATION... 

Figure 3.49 Relay-feedback test with feed manipulation TR — F0.

However there are occasions where use of the scheme proves necessary. For example, if the bottoms flow represents only a small part of the feed, manipulating it over its fiiU range may not be sufficient to control column level. The remaining MVs, that will be used for composition control are bottoms flow, which determines cut, and reflux flow, which determines separation. 

Feed Manipulation Can involve selection of optimal biological conditions (sludge retention time, etc.), additives (polymers, adsorbents), and so forth. 

Stea.dy-Sta.teFeedforwa.rd, The simplest form of feedforward (FF) control utilizes a steady-state energy or mass balance to determine the appropriate manipulated variable adjustment. This form of feedforward control does not account for the process dynamics of the disturbance or manipulated variables on the controlled variable. Consider the steam heater shown ia Figure 15. If a steady-state feedforward control is designed to compensate for feed rate disturbances, then a steady-state energy balance around the heater yields ... 

In this chapter, by using the examples of -lactams we have briefly examined how microbial cultures may be used to produce sufficient antibiotics to meet market demands. We have also explained how enzymes (or cells) may be used to biotransform, and thereby diversify, antibiotics. By outlining the history of penicillin production, we explained how analysis and manipulation of culture regimes may be used to enhance the yields of antibiotics (and other secondary products). These studies led to die concept of directed biosynthesis by precursor feeding. 

As stated in the previous section, the major reactant feed was chosen as the manipulated variable. In the trial this feed was subjected to a pseudo-random binary sequence (PRBS) signal in an open loop operation of the process. The results of the trial, plotted in Fig. 2, show a strong -- but delayed -- cross-correlation between the manipulated feed rate and the reactor temperature. Using techniques described by Box and Jenkins (2), a transfer function relating the manipulated variable to the control variable of interest can be developed. The general form of this transfer function is... 

Transgenic E. coli accumulate comparatively low levels of carotenoids " compared to microbial algae, yeasts, and bacteria. Many efforts ° have focused on increasing accumulation by manipulation of factors affecting metabolic flux and metabolite accnmnlation (listed and discnssed in Sections 5.3.1.1 and 5.3.1.3 A) and have been reviewed." - " In bacterial systems, approaches to control can be categorized as either infrastructural (plasmids, enzymes, strains) or ultrastructural (media and feeding, enviromnent, precursor pools, substrate flux). 

An example of cascade control could be based on the simulation example DEACT and this is shown in Fig. 2.35. The problem involves a loop reactor with a deactivating catalyst, and a control strategy is needed to keep the product concentration Cp constant. This could be done by manipulating the feed rate into the system to control the product concentration at a desired level, Cjet- In this cascade control, the first controller establishes the setpoint for flow rate. The second controller uses a measurement of flow rate to establish the valve position. This control procedure would then counteract the influence of decreasing catalyst activity. 

Feedback control can never be perfect as it only reacts to the disturbances which are already measured in the system output. The feed-forward method tries to eliminate this drawback by an alternative approach. Instead of using the process output, the measured variable is taken as the measured inlet disturbances and its effect on the process is anticipated via the use of a model. The action is taken on the manipulated variable using the model to relate the measured variable at the inlet, the manipulated variable and the process output. The success of this control strategy depends largely on the accuracy of the model prediction, which is often imperfect as models can rarely predict the... 

Figure 2.35. Cascade control to maintain product concentration by manipulating the reactant concentration in the feed.

The reactor temperature is controlled by manipulating the feed rate according to... 

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