Synthesis of Heat Integrated Gas Separation Systems Incorporating Absorption

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Abstract

There is an economic incentive to substitute energy and capital-intensiveconventional gas separation schemes based on cryogenic distillation.Absorption has potential advantages over low-temperature schemes as itdoes not rely on high refrigeration requirements to perform theseparation.An optimisation-based synthesis framework has been developed thatintegrates distillation and absorption-desorption schemes. Thismethodology is able to quantitatively resolve the numerous tradeoffsbetween the various capital and operating factors and systematicallysuggest new design configurations.A multilevel modelling approach enables the accommodation ofabsorption-desorption separation options in the distillation orientatedframework supported by COLOM® (©Centre for Process Integration,University of Manchester). Improved shortcut models for reboiledabsorption and distillation columns have been proposed, which aresuitable for exploitation in the developed synthesis framework.A new methodology for heat integration is proposed that achieves efficientheat recovery and proposes a configuration of the heat exchanger network.This methodology works in harmony with the optimisation framework.Simultaneous optimisation of the separation system, the heat exchangernetwork and the refrigeration system offers the opportunity of achieving asuperior overall configuration.The structural and operating variables of the separation system areoptimised by Simulated Annealing. As a stochastic optimisation method,SA can deal with the large scale of the problem and its discontinuous andnon-linear nature imposed by the feasibility limits of the separations andthe model equations. The optimal separation configurations are selectedon the grounds of minimum capital and operating costs. An analysis ofcosting methods is provided which aims at rationalising the basis for costestimation.The application of the developed synthesis methodology is illustrated by anumber of examples of relevance to the natural gas processing andrefinery gas processing. Results will emphasise the functionality of themethodology as a tool for quantitative evaluation of preliminary designsand realisation of highly integrated and efficient process concepts.

Keyword(s)

Gas Separation absorption

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