Studies on the Dynamic Behaviour and Hydraulic Characteristics of a Water Distillation Column

Author(s): Rupsha Bhattacharyya and Kalyan Bhanja

Heavy water (D2O) is used as the moderator as well as the coolant in pressurized heavy water nuclear reactors (PHWRs). To ensure neutron economy and best moderator performance, the isotopic purity of heavy water has to be ensured at about 99.95 % and above at all times during reactor operation. Vacuum distillation is the most widely practiced method for heavy water enrichment to nuclear reactor grade from pre concentrated (15% or more D2O in H2O) feed. A simple, versatile mathematical model for simulating the dynamic behaviour of such a column is presented in this work. Liquid hold up, pressure drop and flooding point calculations have been performed for the tower using known packing characteristics and fluid properties. To simulate the column performance, it has been modeled as an equivalent tray tower using a known value of the height equivalent to theoretical plate (HETP) and its dynamic behaviour under total reflux operation as well as its separation performance under continuous feeding with product withdrawal is predicted. The effect of parameters like temperature, reflux ratio, feed point location and feed composition on the final isotopic purity of top and bottom products at steady state has also been studied.

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