Linking pinch analysis and bridge analysis to save energy by heat-exchanger network retrofit

• Published in: Applied thermal engineering 2016-08, Vol.106, p.443-472
• Main Authors: Bonhivers, Jean-Christophe, Moussavi, Alireza, Alva-Argaez, Alberto, Stuart, Paul R.
• Format: Article
• Language: English
• Subjects: Energy efficiency; Heat-exchanger network; Process integration; Retrofit
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2016.05.174

[Display omitted] •The flow rate of cascaded heat in exchangers is presented between composite curves.•Reducing energy consumption implies decreasing the flow rate of cascaded heat.•Removing cross-pinch transfers is not necessary to reduce energy consumption.•Bridge modifications are necessary to reduce energy consumption.•Bridge modifications are evaluated on the Heat Exchanger Load Diagram. Reduction of energy requirements in the process industries results in increased profitability and better environmental performance. Methods for heat exchanger network (HEN) retrofit are based on thermodynamic analysis and insights, numerical optimization, or combined approaches. Numerical optimization-based methods are highly complex and may not guarantee identification of the global optimum. Pinch analysis, which is an approach based on thermodynamic analysis and composite curves, is the most widely used in the industry. Its simplicity, the use of graphical tools, and the possibility for the user to interact at each step of the design process help identify solutions with consideration of practical feasibility. In the last few years, bridge analysis has been developed for HEN retrofit. It includes the following tools: (a) the definition of the necessary conditions to reduce energy consumption which are expressed in the bridge formulation, (b) a method for enumerating the bridges, (c) the representation of the flow rate of cascaded heat through each existing exchanger on the energy transfer diagram (ETD), and (4) the use of the Heat Exchanger Load Diagram (HELD) to identify a suitable HEN configuration corresponding to modifications. It has been shown that reducing energy consumption implies decreasing the flow rate of cascaded heat through the existing exchangers across the entire temperature range between the hot and cold utilities. The ETD shows all possibilities to reduce the flow rate of cascaded heat through a HEN. The objective of this paper is to link these tools with the composite curves and concepts from pinch analysis into a consistent method for HEN retrofit. First, the relations between the composite curves, the ETD and the HELD are described, and a method for HEN retrofit which combines the insights from pinch analysis with the recently developed tools is proposed. Then the method is used to reduce energy consumption in three case studies. Comparison between results from pinch analysis and bridge analysis shows that the latter identifies supplementary sol