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Retrospective and predictive optimal scheduling of nitrogen liquefier units and the effect of renewable generation

Lookup NU author(s): Richard Adamson, Dr Mark Willis



This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).


The construction and application of a multiple nitrogen liquefier unit (NLU) optimal scheduling tool is discussed. Constrained by customer demands and subject to electricity spot market prices over a week-ahead horizon, a retrospective optimiser (RO) determines the minimum scheduling costs. Plant start-up penalties and inter-site optimisation capabilities are incorporated into the optimisation model to emulate realistic operational flexibilities and costs. Using operational data, actual process schedules are compared to the RO results leading to improved process scheduling insights; such as increasing afternoon NLU operation during the spring to utilise lower power pricing caused by high solar generation. The RO is used to output a trackable load management key performance indicator to quantify potential and achieved scheduling improvements. Subsequently, correlations between renewable energy generation and spot market power prices are developed. Forecast pricing is used within a predictive optimiser (PO) to automatically generate an optimal schedule for the week ahead to meet projected customer demands. The RO provides potential hindsight savings of around 11%, and the PO up to 8% (representing significant cost savings for such energy intensive processes).

Publication metadata

Author(s): Cummings T, Adamson R, Sugden A, Willis MJ

Publication type: Article

Publication status: Published

Journal: Applied Energy

Year: 2017

Volume: 208

Pages: 158-170

Print publication date: 15/12/2017

Online publication date: 18/10/2017

Acceptance date: 11/10/2017

Date deposited: 24/10/2017

ISSN (print): 0306-2619

ISSN (electronic): 1872-9118

Publisher: Pergamon Press


DOI: 10.1016/j.apenergy.2017.10.055


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