Topic last reviewed: November 2022
Sectors: Downstream, Midstream, Upstream
Pinch analysis is a systematic technique for analysing heat flow through an industrial process and is based on fundamental thermodynamics [Reference 1]. The pinch method readily identifies opportunities that are very difficult to find without it, especially in complex heat exchanger networks and when there are significant heat duty requirements. Also, because pinch analysis generates targets for heat recovery, it provides a convenient way of quantifying how close any given design option is to the optimum. Specific pinch expertise is required to identify the optimum capital expenditure versus against the incremental savings breakeven point, taking into account potential physical constraints.
This technique has been widely applied in downstream sectors, particularly in refineries and petrochemical facilities, where there are complex networks of heat exchangers and available hot and cold streams. The main application is in the design of heat exchanger networks or preheat trains to reduce the external heat duty requirements and subsequently lower emissions. Application of pinch analysis in upstream operations has been more limited as upstream facilities have lower complexity processing units and varying production profiles over the lifetime of the facilities, introducing a different complexity for optimization of heating and cooling. For improved energy efficiency, detailed pinch analysis techniques can be considered but require appropriate expertise. The extent of the analysis should take into consideration the main energy drivers for a site (e.g., upstream facilities tend to need energy for driving equipment, downstream facilities tend to have high heat requirements).
Pinch analysis can be utilized both for new plant designs and retrofits [Reference 2] [Reference 3]. Pinch methods are also used for debottlenecking processes, to optimize the use of utilities (especially steam at various pressure levels), and in improving the energy efficiency of distillation systems [Reference 4]. Some of the more recent developments in pinch analysis focus on the management of material resources, such as water and wastewater [Reference 5] [Reference 6], hydrogen [Reference 7], and carbon pinch [Reference 13].
This topic will primarily focus on temperature pinch analysis, which aims to recover hot/cold duty and thus reduce net hot and cold utility demand.
The key concept underlying the pinch principle is that over the range energy (Qi ) required by the process, which includes both heating (Qh) and cooling (Qc), heat can be transferred from a higher temperature level to a lower temperature level by heat recovery in the process. By doing that in an optimum fashion, the net heat input (Qh) by burning fuel in fired heaters or steam boilers is minimized, and hence the associated cost and emissions are minimized. At the same time, the net waste heat discharged to cooling water or ambient air (Qc ) is minimized as well.
These concepts are illustrated in the hot and cold composite curves shown in Figure 1, which represent the overall heat release and heat demand of a process as a function of temperature. When these two curves are placed together on a single temperature–enthalpy plot (as in Figure 1) it is apparent that heat can be recovered within the process wherever there is a portion of the hot composite curve above a portion of the cold composite curve, i.e., heat can flow from a higher temperature part of the process to a lower temperature part. Qi is the maximum opportunity for process heat integration, i.e., the maximum opportunity for heat recovery from the hot stream to the cold stream. There has to be a minimum allowable temperature approach, ΔTmin, to ensure that equipment sizes are reasonable.
A ‘pinch’ occurs where the vertical distance between the hot and cold composite curves equals ΔTmin. The selection of the ΔTmin is based on the trade-off between the equipment and operating costs. In general, a larger ΔTmin will result in lower equipment cost and higher utility cost. Systematic techniques for establishing energy targets and designing heat exchanger networks and other pinch applications have been developed based on an understanding of the pinch and its relevance to energy usage. Detailed procedures for establishing energy targets and designing heat exchanger networks and utility system optimization are described in more detail in Reference 1, Reference 2, and Reference 3.
The pinch point divides the system into two thermodynamic regions: above pinch and below pinch. The above-pinch region requires external heat and the ‘belowpinch’ region requires external cooling. Cross-pinch heat transfer means heat is transferred from the above-pinch region to the below-pinch region for a given ΔTmin. This will result in additional external heating and cooling requirements over the thermodynamic minimum, resulting in an increase in fuel demand of fired heaters and steam reboilers (Qh) as well as the heat rejected in cooling water (Qc ).
These pinch techniques are currently built into software applications to allow for the curves and heat exchanger networks to be developed automatically. In some software applications, proposed heat exchanger pairings can automatically be determined. However, these should be used with caution as there could be some other key considerations, such as physical distance between the heat exchangers and changes to the process control requirements. For more details, refer to constraints discussed in the sections that follow.
|Offshore viability||Yes but opportunities are likely limited for upstream brownfield due to space and routing limitations|
|Years of experience in industry||30+|
|Years of experience in oil and gas industry||30+|
Project examples in the industry
Pinch techniques are most beneficial, recognizing the additional design and operational complexity of heat exchanger networks, where there are heat exchangers in series recovering heat right upstream of a fired heater, for example in downstream refining, especially in preheat trains of crude units (greater than 80% of the scope) and fluid catalytic cracking (FCC) units.
In simple upstream units, pinch principles can be applied to obtain an energyefficient design. With built-in software readily available and automatic data extraction, it could be beneficial to check whether the system has been fully optimized by checking the hot and cold composite curves and required hot and cold utilities across the various production profiles.
Examples of available hot streams and cold streams that could be included for upstream facilities for heat recovery and development of composite curves are given in Table 1.
Table 1: Hot and cold streams
|Hot streams (to be cooled down)||Cold streams (to be heated up)|
|Gas turbine exhausts||Feed into acid gas regenerator|
|Product rundowns to meet export or storage specifications, e.g., produced oil||Feed into distillation column (e.g., oil stabilization unit)|
|Stream exiting acid gas regenerator bottoms||Utility (such as boiler feedwater and thermal oil) to be preheated|
|Distillation condenser stream||Stream (cold gas and condensate) exiting dew point system|
|Produced water, which needs cooling if too high to meet disposal specifications|
|Gas sent to dew point systems|
|Gas entering the molecular sieve|
|Range of application||Process units with significant demand for purchased heating and/or cooling, especially if the process has a complex heat exchanger network|
|Energy key performance indicators||Actual reduction of hot utility (Qh) and/or cold utility (Qc ) compared with pinch target hot/cold utility|
|Guideline capital costs|
Methodology (i.e., cost to perform pinch analysis): costs for consulting services and software, which are comparatively inexpensive. Alternatively, depending on the size of the organization, in-house capability can be developed and utilized, and the cost is only the software cost.
Costs to implement the pinch analysis results: Capital expense for new heat exchanger (if required, as it could also be beneficial to change the order of the heat exchangers) and associated installation costs (e.g., piping for rerouting, civil, instrumentation).
In general, cost– benefit analysis between the capital expenditure cost for the new exchanger and associated installation and operating expenditure (OPEX) savings, i.e., the cost of the energy savings is to be calculated prior to any design changes.
|Guideline operational costs|
Operational costs refer to maintenance costs of new heat exchangers against savings of hot and/or cold utility.
|Greenhouse gas (GHG) reduction potential|
Up to 25% of total refinery GHG emissions [Reference 1, pp. 303–306] [Reference 8, pp. 88, 341]. The actual GHG reduction potential will depend on the starting point, i.e. quality of the heat integration during the design stage.
|Time to perform engineering and installation|
Methodology: 1–3 months (depending on the availability of plant simulation and compatibility with pinch software).
Implementation of pinch analysis results: 2–3 years depending on complexity of installation (refer to Heat Exchangers topic) and shutdown window (e.g. turnaround) available for implementation.
|Typical scope of work description|
Due to the availability of software, engineers in a wide range of organizations can carry out pinch analysis, at least at a basic level.
For most advanced pinch analysis, work is carried out by specialized consultants, often in small companies. Some of the larger engineering companies maintain a capability in the technology, and several academic institutions are engaged in both research and industrial applications. Whoever performs the pinch work itself, it is important that pinch activities should not be carried out in isolation. Rather, they should be integrated into a larger engineering organization to ensure the proper flow of information, evaluation of results, and eventual implementation of projects [Reference 9].
The scope of a typical pinch project [Reference 2] includes:
Pinch analysis is particularly valuable in large, complex industrial facilities, where systematic methods are needed to identify the best opportunities to improve energy efficiency [Reference 3, p. 6].
Efficient deployment of capital
Reduced associated taxation
No other techniques that are currently commercially available are as effective at optimizing heat recovery systems as pinch analysis. Alternative methods, such as deterministic-optimization-based methods and stochastic-optimizationbased methods, have been developed, although they are not available in commercial tools [Reference 11] [Reference 12].
Pinch analysis is best performed during the early project design phase as modifications to the heat exchanger network are most cost-effective then. Pinch analysis on an existing brownfield asset is nevertheless still possible, but implementation of identified opportunities may require more CAPEX compared to a greenfield design.
Good heat exchanger design practices should be observed while implementing the results of pinch analysis. An ideal pinch design should be modified to reflect the required operability, flexibility, and control requirements. The ‘ideal’ pinch design may include heat exchangers that are inherently hazardous because of risks associated with large pressure differences between streams or crosscontamination of products. The design temperature, design pressure, and associated safety facilities should be adequately modified to reflect such a match. Ideal pinch analysis may lead to a network design with multiple parallel heat exchangers. The number of parallel heat exchangers required can be reduced by paying a small penalty in energy or they should be adequately designed to avoid low velocities/shear stress. Low velocities/shear stress could lead to high fouling rates and consequently poor energy efficiency. Pinch designs should be modified as required to address control, operability, and flexibility issues. An experienced subject-matter expert should be consulted as necessary. Hazard analyses should always be carried out, and dynamic simulations can be conducted if needed to address operability concerns.
In particular, for brownfield application introduction of new exchangers as a result of pinch analysis should be reviewed for control, start-up, shutdown, and other operability cases. Before the design basis and constraints are set for the pinch study, all assumptions should be challenged to ensure a sustainable, energy-efficient design is developed. For the resulting design, adequate modifications should be made to ensure the final design is flexible, operable, and controllable. These are generally managed through a proper design review and change management work process.
Additionally, constructability, distance between streams, and space constraints are to be considered in a brownfield application. This can be mitigated by limiting the streams within the pinch scope based on distance between the streams.
- Energy savings of up to 25% depending on the starting point
- Reduction in the size and number of furnaces, boilers, and cooling towers in new designs; for example, the heat exchanger(s) can replace the entire, or part of the duty provided by a furnace
- Improve energy efficiencies and realize debottlenecking with retrofits
- Reduction in associated GHG emissions to provide heating or cooling duty required from utilities
Industry case studies
- Reference 1 (pp. 313–378) describes case studies from several industry sectors
- Reference 2 is a detailed case study of a recent crude unit retrofit pinch analysis
- Reference 8 (pp. 335–343) summarizes results from seven case studies in several industry sectors
- Reference 10 is a detailed case study of an FCC unit retrofit pinch analysis available online
- Reference 15 is a detailed case study conducted in 2021 in an oil refinery
- Reference 1 is a case study conducted for a stabilization unit in an upstream facility
Case study 1: Application of pinch technology in an oil refinery
Reference 15, published in 2021, investigated the opportunities for increased energy efficiency using pinch technology at the heat exchanger network for the crude preheat train of a crude distillation unit. The study involved the following key steps using simulation tools:
- Development of detailed process simulation
- Development of process data extraction and heat exchanger network grid representation
- Pinch analysis of the heat exchanger network and retrofit analysis
The key highlights from this study are:
- The energy targets are a function of the ΔTmin and the cost index is quite sensitive to this variation
- The heat exchanger rearrangement combined with economic analysis (acceptable payback versus energy cost savings) result in 8% total energy savings compared with the base case
For more details, refer to Reference 1.
Case study 2: Pinch technology application at upstream seperation and stabilization plant
Reference 16, published in May 2016, investigated the use of pinch analysis to identify the opportunities and effectiveness of heat integration. This method was conducted on a generic process flow schema of an upstream separation and stabilization plant in an upstream facility as shown in Figure 2.
The ΔTmin used was 10°C and based on the pinch analysis the study concluded that there would be no cold utility required. The conventional design includes a product (water-cooled) cooler to reduce the temperature to 40°C. Based on the pinch analysis, this indicated that the product cooler could be eliminated with savings of 345,300 MJ/hour of energy.
Although the study indicated that the cooler is not required based on pinch principles, this trim cooler may still be required to ensure that the final product specifications are met and that the process can be controlled. The new sizing of the cooler can then be reduced, which is a saving in terms of CAPEX.
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