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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]

This paper presents a mathematical model to determine the minimum energy targets for a batch process with flexible schedule. Techniques developed for flexible-schedule batch processes typically result in nonlinear formulations. The proposed model was formulated as a mixed integer linear programming model (MILP). The model is developed based on the source-demand classification of process streams instead of the typical classification of hot and cold streams. In such classification, each stream is simultaneously treated as a source at its shifted supply temperature, and as a demand at its shifted target temperature. Such classification eliminates the model's non-linearity and reduces its complexity as well as the solution time. The mathematical model can be used to calculate the utility targets for a flexible-schedule batch process. Application of the proposed mathematical formulation demonstrates significant energy saving potential. The first illustrative example predicted a potential reduction of 11% cold utility and 14% hot utility. In the second illustrative example, up to 35% hot utility reduction and 62% cold utility reduction could be achieved. [ABSTRACT FROM AUTHOR]

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]

This paper proposed a novel methodology to retrofit Heat Exchanger Storage Networks (HESN) of batch processes using a modified graphical retrofit tool, namely batch Stream Temperature Enthalpy Plot (batch STEP). Unlike other graphical retrofit tools, batch STEP maintains individual characteristic of process streams as well as serves as the one-stop retrofit tool to retrofit direct and indirect HESN simultaneously. The conventional batch heat integration typically aimed to synthesise new Heat Recovery Loops (HRLs) for heat recovery enhancement without exploiting the benefits of reusing existing HRLs in saving the additional volume of heat storage units (HSUs) and space allocated for retrofit. Thus, this paper extends the STEP continuous retrofit methodology to batch processes by introducing a batch STEP diagram for identification of the potential process streams to be integrated into existing HRLs and potential modifications of existing HRLs operating temperature. The methodology also introduces HRL– problem table algorithm (HRL-PTA) and heuristics to target the maximum indirect heat recovery and integrate process streams into the existing HRLs systematically. The methodology proposed achieves plant savings of 23.9%–60.0% for hot utility, 25.9%–42.2% for cold utility and a reduction of 6.3%–8.1% for additional volume of HSUs required in two illustrative case studies. [Display omitted] • An extended STEP graphical tool for retrofitting HESN of batch processes. • Diagnosis of process streams to be integrated into existing heat recovery loops (HRLs). • Diagnosis of potential modification of existing HRLs operating temperature. • The maximum indirect heat recovery by existing HRLs is targeted. • Integration of heat supply and load into existing HRLs is guided. [ABSTRACT FROM AUTHOR]

Abstract: Supertargeting based on composite curves (CC) is widely used to determine the optimum approach temperature (ΔT min) that yields the minimum total cost for heat exchange networks (HEN). Supertargeting using CC has two key limitations. Firstly, the HEN area calculations are drastically simplified through the assumption that CC segments may be considered as pseudo-single hot and cold streams exchanging heat via only one exchanger that is governed by a single cost correlation. Secondly, the current Supertargeting approach of considering only one hot and one cold utility level may lead to a crude estimation of the total HEN cost and the optimum ΔT min. This work presents the stream temperature vs. enthalpy plot supertargeting (STEPS) method that overcomes these limitations. This paper proves that supertargeting based on CC can lead to up to 50% error in the total cost target and poor ΔT min estimations. [Copyright &y& Elsevier]

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]

This paper presents a systematic technique to select the optimal design target for the heat exchanger network ( HEN ) synthesis by using a new trade-off plot which considers aspects of design, controllability in terms of steady state flexibility and sensitivity analysis, and cost. By selecting the HEN design target according to this guideline, the designer is able to predict the design, operability, and controllability of the designed HEN at the beginning of the synthesis stage. In this study, the HEN design target that needs to be optimized is the value of the minimum temperature difference ( Δ T min ). In traditional HEN synthesis, designers only consider the trade-off between capital and operating costs in selecting the best Δ T min . As a result, the HEN design at the selected Δ T min may not be optimum in terms of steady state controllability. In addition to considering the capital and operating costs, the proposed new method provides additional design insights in terms of energy recovery, operability, controllability (steady state) through the flexibility and sensitivity. The proposed trade-off plot allows designers to choose the most suitable design target either for the purpose of improving a network’s energy recovery and/or controllability. A case study has been applied to test the capability of the new proposed trade-off plot. The results show that Δ T min = 40 °C is the optimal design target to synthesize flexible and operable HEN . [ABSTRACT FROM AUTHOR]

Pressure drop is an important consideration in Total Site Heat Integration (TSHI). This is due to the typically large distances between the different plants and the flow across plant elevations and equipment, including heat exchangers. Failure to consider pressure drop during utility targeting and heat exchanger network (HEN) synthesis may, at best, lead to optimistic energy targets, and at worst, an inoperable system if the pumps or compressors cannot overcome the actual pressure drop. Most studies have addressed the pressure drop factor in terms of pumping cost, forbidden matches or allowable pressure drop constraints in the optimisation of HEN. This study looks at the implication of pressure drop in the context of a Total Site. The graphical Pinch-based TSHI methodology is extended to consider the pressure drop factor during the minimum energy requirement (MER) targeting stage. The improved methodology provides a more realistic estimation of the MER targets and valuable insights for the implementation of the TSHI design. In the case study, when pressure drop in the steam distribution networks is considered, the heating and cooling duties increase by 14.5% and 4.5%. [ABSTRACT FROM AUTHOR]

Abstract: Total Site Heat Integration (TSHI) is a technique of exchanging heat among multiple processes via a centralised utility system. An analysis of the integrated multiple processes, also known as the Total Site (TS) system sensitivity, is needed to characterise the effects of a plant maintenance shutdown, to determine the operational changes needed for the utility production and to plan mitigation actions. This paper presents an improved Total Site Sensitivity Table (TSST) to be used as a systematic tool for this purpose. The TSST can be used to consider various ‘what if’ scenarios. This tool can be used to determine the optimum size of a utility generation system, to design the backup generators and piping needed in the system and to assess the external utilities that might need to be bought and stored. The methodology is demonstrated by using an Illustrated Case Study consisting of three processes. During the TS normal operation, the Total Site Problem Table Algorithm (TS-PTA) shows that the system requires 1065kW of High Pressure Steam and 645.5kW of Medium Pressure Steam as the heating utility, while for the cooling utility, 553.5kW of Low Pressure Steam and 3085kW of cooling water are required. The results of the modified TSST proposed that a boiler and a cooling tower with the system design requiring a maximum capacity of 2.172MW of steam and 4.1865MW of cooling water are needed to ensure an operational flexibility between the three integrated processes. [Copyright &y& Elsevier]