Abstract
The “bridge framework” is a systematic decision-making support tool for process integration retrofit of industrial plants, which proposes the use of “bridge analysis” in a structured fashion. Its potential of rigorously analysing industrial processes has been discussed, but no applications on actually operating plants considering process constraints have been presented to date.The paper demonstrates the capabilities of the bridge framework in analysing an actually operating milk powder production plant. Its step-by-step application is thoroughly described and discussed, highlighting inherent strengths and weaknesses of the method. Moreover, a clarification of the “energy transfer diagram” is proposed, distinguishing avoidable and unavoidable heat degradation in the heat exchanger network by introducing the concept of “limit heat transfer interface”.The results proved that the bridge framework is a rigorous tool, which provided valuable insight to the analyst aiding the open-ended decision-making activities related to the retrofit of both process operations and heat exchanger network. Seven design proposals were identified, out of which the best resulted in 54000 €/y of economic saving with an internal rate of return of 34% and a minimum risk level. The step-by-step application of the method demonstrated that good engineering judgement is critical for achieving beneficial solutions. Expertise on process operations as well as energy analytics is essential for completing the project. Finally, the concept of “limit heat transfer interface” allowed to completely link bridge analysis and pinch analysis and to clarify the meaning of the “grand composite curve”.
Highlights
Process Integration methods (Kemp, 2007) have proved to be highly effective tools for identifying opportunities for increasing energy efficiency of industrial processes
The case study was analysed by means of the bridge framework proposed by Moussavi and Stuart (2020)
A modified version of the grid diagram following the conventions of the energy transfer diagram and a novel method for calculating the energy-saving potential of bridge modifications were introduced
Summary
Process Integration methods (Kemp, 2007) have proved to be highly effective tools for identifying opportunities for increasing energy efficiency of industrial processes. Reported case studies have demonstrated that significant reduction in energy demand can be achieved in various industrial sectors, such as the petrochemical industry (detected savings ranged from 10 % Bakhtiari and Bedard, 2013 up to 33% Nordman and Berntsson, 2009), the chemical industry (53% Yong et al, 2014 and 75% Pouransari et al, 2014), food industry (24% Bergamini et al, 2016 and 25% Muster-Slawitsch et al, 2011), pulp and paper (66% Ruohonen and Ahtila, 2010), and textile industry (51 % Dalsgaard et al, 2002), to cite a few This often directly translates to emissions reduction, as these industrial processes are conventionally supplied by fossil fuel-driven utilities. The ‘‘bridge method’’ (Bonhivers et al, 2017) was proposed as an improvement of existing process integration methods with regards to problem (i) and (iii). The ETD (Bonhivers et al, 2014) is a map representing the flow rate
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