Control constant-volume-feed system

Figure 2. Constant-volume-feed system control...

The continuously operated stirred tank reactor is fed with reactants at the same time as the products are removed by an overflow or a level control system (Figure 8.1). This ensures a constant volume and, consequently with a constant volume flow rate of the feed, a constant space hme. We further assume the reactor contents... 

The final pH adjustment (Figure 6B) takes place in the feed system to the extraction (WE-1) column. Preneutralized solution in Tank WM-1 is recirculated to provide mixing. Part of the recirculated solution is diverted to the WM-2 static mixer tank where it is mixed with NaOH the volume of NaOH added is controlled by the pH of the WM-2 tank outlet stream. Most of the solution leaving the WM-2 tank is returned to the WM-1 tank the remaining portion feeds the WE-1 Column. The flowrate of this latter stream is adjusted to maintain the liquid level in the WM-1 tank approximately constant. When functioning satisfactorily, the two-stage acid adjustment procedure provides an aqueous E1F stream at pH 0.75 flowing at a constant rate to the extraction column. 

There are two different ways of operating a continuous stirred-tank fermentor, namely chemostat and turbidostat. In the chemostat, the flow rate of the feed medium and the liquid volume in the fermentor are kept constant. The rate of cell growth will then adjusts itself to the substrate concentration, which depends on the feed rate and substrate consumption by the growing cells. In the turbidostat the liquid volume in the fermentor and the liquid turbidity, which varies with the cell concentration, are kept constant by adjusting the liquid flow rate. Whereas, turbidostat operation requires a device to monitor the cell concentration (e.g., an optical sensor) and a control system for the flow rate, chemostat is much simpler to operate and hence is far more commonly used for continuous fermentation. The characteristics of the continuous stirred-tank fermentor (CSTF), when operated as a chemostat, is discussed in Chapter 12. 

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