Developing Optimization Criteria for Processes of Separating Low-Boiling Gases

Abstract Optimization criteria are proposed for processes of separating ethylene and propylene from a mixture of low-boiling gases. These criteria are based on the physicochemical properties of substances and take into account special techniques used for separating such mixtures. Unlike the existing criteria based on considering the heat input to the reboiler and the heat output from the condenser of a distillation column, these optimality criteria more accurately evaluate the economic performance of the process, because they include the refrigerant preparation cost, which plays a decisive role in separating low-boiling gases. Four known methods of separating mixtures of low-boiling gases are considered: (A) separation in a column with steam as the heat-transfer medium in the column reboiler and with a refrigerant in the condenser, (B) separation in a column with the condensation of the vapor of a refrigerant in the column reboiler and with the same refrigerant in the condenser, (C) separation in a column with the condensation of the vapor of the ith refrigerant in the column reboiler and with the jth refrigerant in the condenser, and (D) separation in a column with steam as a heat-transfer medium in the column reboiler and with recirculating water in the condenser. Parameters that are expediently used as optimality criteria are identified. New approaches to creating the optimal processes of separating low-boiling gases are developed and theoretically justified for further implementation.