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Heat exchanger network (HEN) retrofit plays a major role in solving environmental issues and improving plants' performance. Development of HEN retrofit graphical tools has recently focused on detailed representation of existing HEN to facilitate retrofit problem-solving. This work presents a new customised approach for HEN retrofit that uses a combination of individual stream temperature versus enthalpy plot (STEP) to map hot and cold streams, a heat exchanger area versus enthalpy (A vs H) plot to minimise the required overall heat exchanger area and graphical cost screening tool and strategies to steer and customise a retrofit design toward a desired investment payback period. Application of the new retrofit methodology on a sunflower oil production plant shows comparable energy savings and 20% shorter payback period as compared other established retrofit methodologies. Image 1 • STEP and A vs H plot are employed to perform capital-energy trade-off for HEN retrofit. • STEP indicates the multiple utilities required. • A vs H plot visualises heat exchanger area and number of additional units. [ABSTRACT FROM AUTHOR]

Medium and large scale industries typically consume large amounts of energy, and are under pressure to increase energy efficiency and reduce energy wastages. Conventional insight-based heat exchanger network (HEN) retrofit methods typically combine graphical visualisation and algebraic tools to manage different retrofit stages. These stages often involve repetitive calculations of approach temperature, enthalpy balance and heat transfer area to assess the HEN feasibility and cost-effectiveness. This paper extends the individual stream temperature versus enthalpy plot (STEP) methodology that was introduced for HEN synthesis, to HEN retrofit. The STEP retrofit method proposed in this work enables users to simultaneously diagnose and retrofit existing HEN by using only the STEP diagram that maintains the characteristics of individual process streams. Users can graphically perform individual stream mapping without having to calculate stream enthalpies or to check for minimum temperature approach ( Δ T m i n ) violation during retrofit. Application of the new STEP retrofit method on an industrial case study demonstrates its advantages in terms of user interactiveness, simplicity of use, flexibility to customise the methodology to achieve retrofit goals of plant owners, and the least amount of efforts needed to achieve comparable results as those of established retrofit methods. [ABSTRACT FROM AUTHOR]

Recent developments of Pinch-based heat exchanger network (HEN) retrofit methodologies mainly focus on improvement of HENs, and much less on seeking opportunities to enhance energy efficiency of processes via process and utility changes. Conventionally, Pinch-based retrofit methodologies employ Composite Curves (CC) and Grand Composite Curve (GCC) to screen for process changes opportunities. However, CC and GCC cannot directly indicate the specific individual process and utility streams to undergo process changes as the streams are composited within the CC and GCC. This work extends the use of individual stream temperature versus enthalpy plot (STEP) to enable designers to scope, screen and selectively customise structural and parametric process and utility changes for existing HENs. STEP diagram can be used to graphically customise retrofit options involving beneficial process utility changes for an existing HEN, and improve overall process energy efficiency. Application of STEP diagram on an illustrative case study and an existing crude oil refinery plant show that STEP diagram enables a designer to graphically pinpoint the exact individual process streams to undergo process and utility changes based on the individual stream profile and to determine the optimal load and levels of multiple utilities required, as well as the limit of process changes that can be performed. Results of this work show that on top of performing HEN retrofit, customised process and utility changes can result in an additional 18.4% hot utility reduction. Image 1 • CC and GCC cannot identify specific individual process stream for process changes. • New methodology uses STEP for structural and parametric changes of existing HEN. • Proposed methodology is applied on an existing crude oil refinery plant. • Additional 18.4% Q H reduction is achieved by process change. • Large savings can be achieved by process change with little or no investment. [ABSTRACT FROM AUTHOR]