Recommendations for a Kalman filter to estimate and control freeze and sublime rates of gaseous diffusion plant freezer/sublimer systems.

摘要

A signal is required to control the flow of UF(sub 6) in gaseous diffusion plant freezer/sublimer systems. The original strategy envisioned for deriving a flow signal was to take the derivative of the freezer/sublimer weigh cell signal. However, the derivative of the digitized weight signal is noisy, preventing good control. In addition, a disturbance is introduced into the weight derivative signal because a refrigerant is circulated through a shell-and-tube heat exchanger inside the freezer/sublimer. The weight of the refrigerant is included in the weight measured by the weigh cell. If the circulation rate of the refrigerant is not steady state, a disturbance exists. Measurements of upstream pressure, vessel pressure, and output to the system control valve are available to the control system. Thus, if the flow through the control valve is characterized properly by these measurements, a Kalman filter can be used in conjunction with these auxiliary inputs and the weigh cell input to overcome the noise and disturbance problem and provide an improved estimate of flow rate. A discussion of the development of a Kalman filter that could be used for this application is given, and recommendations are given for its implementation.