Control characteristics of a cascade composed of cryogenic distillation columns with feedback streams

摘要

A control method was proposed for a two-column cascade composed of cryogenic distillation columns with feedback streams. The lead column process the exhaust gas from a plasma, and produces high purity tritium. The second column process the top stream from the lead column and hydrogen gases containing tritium from water detritiation and blanket systems. The top and bottom flow rates of the columns are adjusted against variations of feed compositions to control product purity. The method of parameter setting for the proportional-integral (PI) controller was proposed for step changes of the feed compositions. For the lead column, either the mole fraction of DT at top or the atom fraction of T at bottom can be chosen as the controlled variable. The mole fraction of DT is more favorable as the controlled variable than the atom fraction of T from the viewpoint of promptness of the control. However, only a short time lag in the measurement of the controlled variable is permissible. It is required to decrease the value for the proportional sensitivity to relax this restrict. The successful control is obtained for the second column to choose the mole fraction of HT at top. A considerably long time lag is permitted for the second column in contrast to the lead column. (author). (ERA citation 20:011858)