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Analysis and optimization of exergy losses in a heavy water distillation column

Rupsha Bhattacharyya

Abstract


Heavy water (D2O) of isotopic purity 99.9% and more is used as the moderator and the coolant in pressurized heavy water nuclear reactors (PHWRs). This purity is maintained by vacuum distillation. In the column there are various sources of irreversibility and thermodynamic inefficiency. This work presents an analysis of these losses in a typical heavy water distillation column and their dependence on various design and operating parameters of the column. Optimal selection of independent operating parameters has been carried out by the method of parametric sensitivity analysis using a steady state simplified calculation model and a systematic search through the decision variable space. The decision variable search space is identified on the basis of practical considerations and common heuristics. The objective is to find out the values of the decision variables at the design stage itself to achieve the lowest possible exergy destruction and thus the highest thermodynamic efficiency in the water distillation process. Exergy losses range between 10 to 45 kW for a feed isotopic purity between 98 and 90% at a feed flow rate of 40 LPH in the column. These losses are found to be most sensitive to the utility stream temperatures and the reflux ratio.

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DOI: https://doi.org/10.37628/jcep.v4i2.611

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