A liquid is concentrated by evaporating water in an evaporator. The available measurements and control valves are shown in Fig. E. During normal operation, the concentration controller output Pac is less than or equal to 80%. Also, the product concentration is to be controlled by adjusting the steam control valve, while the feed flow rate is regulated via a flow controller. However, 11 the feed concentration is low for a sustained time period, the concentration controller tends to saturate, and consequently, the product concentration can be significantly below its set point. Both control valves are fail close, whereas each transmitter is direct acting. In order to cope with this undesirable situation, it is proposed to temporarily (and automatically) reduce the teed flow rate when the concentration controller output signal exceeds 80%. Propose a control strategy that will accomplish this goal and draw the corresponding schematic diagram. Justify your choice. (Note: The feed composition cannot be measured.)

Transcribed Image Text:

Steam FC Steam Feed Condensate AC AT Product