Capital cost targets for mass exchange networks A special case: Water minimisation

• Published in: Chemical engineering science 1998, Vol.53 (2), p.293-313
• Main Authors: Hallale, N., Fraser, D.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Capital cost targets; Chemical engineering; Exact sciences and technology; Heat and mass transfer. Packings, plates; mass exchange networks; pinch analysis; water minimisation
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/S0009-2509(97)00191-7

Pinch analysis has been applied to mass exchange network synthesis. Until now, minimum utility targets have existed, but not capital cost targets. Previous work minimised the number of units in a network, but this paper shows that this does not necessarily minimise the capital cost. This paper focuses on the special case of water minimisation. It considers a simple example involving a network of absorption columns which use water to remove sulphur dioxide from a set of gas streams. The paper describes the first known method for targeting the minimum number of trays in the network, based on a specified ‘minimum composition difference’. This is then translated into a capital cost target. An interactive design method is presented which allows the targets to be approached to within 5%. The example is then extended to demonstrate how the targets can be used to trade off capital and operating costs in order to optimise the network before design. A further extension deals with multiple water sources. This work may be extended to other absorbents and generalised to other mass exchange networks.