Ratio control wild stream

As the name implies, ratio control involves keeping constant the ratio of two or more flow rates. The flow rate of the "wild or uncontrolled stream is measured and the flow rate of the manipulated stream is changed to keep the two streams at a constant ratio with each other. Common examples include (1) holding a constant reflux ratio on a distillation column, (2) keeping stoichiometric amounts... 

Ratio control is a special type of feedforward control where two disturbances (loads) are measured and held in a constant ratio to each other. It is mostly used to control the ratio of flow rates of two streams. Both flow rates are measured but only one can be controlled. The stream whose flow rate is not under control is usually referred to as wild stream. 

Figure 21.9a and b show two different ratio control configurations for two streams. Stream A is the wild stream. 

V.26 (a) Develop a ratio control system to regulate the temperature T of the resulting mixture of Figure PV.5. The following specifications are provided (1) Stream 1 is the wild stream. Its temperature remains constant but its flow rate changes in an unpredictable manner. (2) The temperature of stream 2 remains constant. 

Figure 9.41 shows the essentials of the process. Hydrogen and chlorine enter the burner separately. In most cases in the chlor-alkali industry, chlorine is the wild stream and the flow of hydrogen is controlled to give the desired ratio. The chlorine flow may be variable, as from the end of a process. When HCl production volume is large or... 

In the scheme shown in Figure 6.10, the flow of the wild stream y is measured and then multiplied by the desired ratio. The output from the multiplier is the set point for the controller, which compares it with the measured flow and adjusts the flow of y... 

Controlled stream is manipulated to maintain a constant ratio (R) of controlled flow (B) to wild flow (A). 

However, we ean describe the basie structure of several feedforward control systems. Figure 4.7 shows a blending system with one stream that acts as a disturbance both its flow rate and its composition can change. In Fig. 4.7a the conventional feedback controller senses the controlled composition of the total blended stream and changes the flow rate of a manipulated flow. In Fig. A.lb the manipulated Row is simply ratioed to the wild flow. This provides feedforward control for flow rate changes. Note that the disturbance must be measured to implement feedforward control. 

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