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Novel distillation arrangements for NGL fractionation

Chida, Aamer (2015). Novel distillation arrangements for NGL fractionation. Master of Engineering Thesis, Charles Darwin University.

Document type: Thesis
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Author Chida, Aamer
Title Novel distillation arrangements for NGL fractionation
Institution Charles Darwin University
Publication Date 2015-10
Thesis Type Master of Engineering
Supervisor Koblov, Alexander
Diaz, Luis Herrera
0904 - Chemical Engineering
Abstract Distillation is one of the most widely used thermal separation methods in industry. Any improvement which gains industry acceptance can result in substantial benefits. This thesis considered modifications to the conventional Natural Gas Liquid (NGL) fractionation arrangement to offer energetic savings. Energy savings were demonstrated for a pre-flash (PF) modification, a deethaniser with side rectifier (DC2wSR) modification and a modified indirect arrangement with a side stripper on the initial column

Distillation arrangements were proposed that incorporated the DC2wSR and PF modifications. A detailed comparison was made of conventional NGL fractionation and the alternative arrangements in terms of viability, operability and capital and utility costs. The effect of capacity in terms of feed and utilities generation was considered using steam and a heat transfer fluid (HTF) as the heating medium to run the reboilers.

The PF arrangement provided a payback period between 2.2 and 4 years across all settings and heat transfer mediums. The arrangement lends itself to brownfield improvements as all modifications can occur without having to alter the distillation columns.

The payback for the DC2wSR arrangement using HTF was between 1.6 and 3.9 years making the arrangement the preferred option for greenfield or revamp settings. The arrangement is particularly suited for an offshore setting as it minimises unit operations and plot area requirements compared with the PF case.

The payback period for the DC2wSR arrangement using steam as the heating media was estimated to be between 9.5 to 16.5 years. This payback is still justifiable for offshore plants with a 20-30 year lifetime where plot area is critical.

It was proposed the fraction of butanes (C4s) and natural gasoline (C5+) components in a given feed would give some indication to the potential for energy recovery using the PF arrangement. Correlations were found between the fraction of C5+ components in a feed and (a) the energy recovery in the BS reboiler (b) the absolute utility savings compared with the Base Case and (c) the total annualised cost (TAC) deviation with the Base Case

The results confirm a link between the content of C5+ components and energy and utilities savings using the PF arrangement. It may be possible to derive an empirical correlation that relates feed composition to the effectiveness of the PF arrangement. The derivation of such a correlation is the subject of further work, and will be submitted in an article in the near future.
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Created: Wed, 02 Mar 2016, 13:46:56 CST by Jessie Ng