DYNAMICS AND CONTROL OF A PACKED DISTILLATION COLUMN FOR THE ISOTOPIC ENRICHMENT OF PLASMA EXHAUSTS FROM CONTROLLED THERMONUCLEAR REACTORS

A control scheme is proposed based on analysis of the disturbances expected during normal operation of the lead column in the fuel enrichment distillation cascade for a near-term tokamak fusion reactor fuel cycle. The primary objective of this control scheme is to minimize both the time and the amount that the atom percent protium in the bottoms product is above a setpoint level. As a secondary objective, distillate stream flow and composition fluctuations should be minimized to avoid downstream operational and control problems without requiring intermediate storage. A fixed material balance control scheme was found to be satisfactory for meeting the control requirements of this system. Because the concentration of protium in the bottoms product (the controlled variable) was relatively small, the distillate stream composition and the tritium/deuterium ratio in the bottoms stream proved to be essentially independent of the choice of controller parameters. This insensitivity permitted the controller parameters to be chosen solely on the basis of the primary objective and led to a high gain setting and low reset value for the controller. With the provision of a bottoms storage to dampen out the effect of oscillatory response, these controller settings minimized the overshoot and produced an averaged protium concentration in the bottoms very close to the setpoint level.