Increase Plant Efficiency and Reduce Energy Costs with a Pinch Analysis
19.04.2023 | Reading Time 5 min
Raphael Wittenburg
Pinch Analysis, a thermodynamic method to identify unused energy potentials in plants, derive appropriate measures for exploitation, and reduce operational costs.
Overview
What is a Pinch Analysis?
The Pinch Analysis is a method to examine the energy efficiency of a plant. It primarily serves to identify unused energy potentials in the form of waste heat and waste cold, and to derive measures for their exploitation. The goal of Pinch Analysis is to reduce the amount of energy supplied from external sources and thus sustainably lower the energy costs of an industrial plant.
Pinch Analysis is essentially based on the first and second laws of thermodynamics. By analyzing the mass and energy flows within the system, as well as the prevailing temperature levels, possibilities for internal use of waste heat and waste cold can be derived and appropriate utilization measures can be identified. These can include heat exchangers, energy storage systems, or large heat pumps.
Who is Pinch Analysis Interesting For?
Pinch Analysis is generally interesting for operators or owners of industrial plants with high energy demands. It is a relatively simple method to identify measures that sustainably reduce energy costs.
Especially companies where process heat or cooling constitutes a significant part of operational costs should consider conducting a Pinch Analysis to gain initial essential insights for process optimization.
Pinch Analysis Process
A Pinch Analysis is divided into the following central sub-processes:
- Analysis of the plant structure and the media flows within it.
- Creation of the “Composite Curves” including the identification of the “Pinch Point“.
- Identification of potential opportunities and definition of measures for technical exploitation, e.g., through heat exchangers, energy storage, or heat pumps.
- Evaluation of measures for technical and economic feasibility.
Energy Audit
The basis of a Pinch Analysis is an energy audit and a detailed examination of the plant structure and the media within it. Initially, it must be checked whether all necessary data are available, or if measurement systems need to be retrofitted to provide the required data on energy flows. Especially for complex plants, the energy audit is by far the most time-consuming sub-process of the Pinch Analysis.
Subsequently, the media streams to be heated and cooled are plotted in so-called composite curves. This is usually done in a Temperature-Enthalpy Flow Diagram.
Composite Curves
The composite curves are constructed by plotting media states, defined by the prevailing temperature and enthalpy flow. This approach follows the principle of superposition.
All required cooling or heating capacities in a certain temperature range are added together, so that the slope of the respective curve changes in this temperature interval. If there is a higher heat or cooling demand in a certain temperature range, the curve flattens out.
If a phase change dominates in a temperature range, it may occur that the composite curves run completely horizontally. This is based on the assumption that all energy supplied to the process or all energy removed is consumed for the phase change. The system remains isothermal.
Through this methodical approach, two so-called “Composite Curves” are obtained for the overall process – one for the total required heating capacity and another for the total necessary cooling capacity. These are illustrated in the following diagram.
Composite Curves of a Pinch Analysis in the Temperature-Enthalpy Flow Diagram
Subsequently, both composite curves are shifted along the abscissa against each other until an intersection point – the so-called “Pinch Point” – is established. This serves to define various regimes:
- On the left side of the pinch point, there is a heat surplus. This means there is more heat in the media to be cooled than is necessary for heating the cold streams. Additional cooling is required.
- On the right side of the pinch point, there is a lack of available heat. Therefore, more heat must be supplied than can be extracted from the warm stream. External heat input is needed.
The heat flow interval where both curves overlap is the area where heat recovery can be used to reduce external energy input. Here, the use of heat exchangers can be worthwhile to reduce energy costs.
Furthermore, it can be derived from the composite curves that external heat input is only sensible in the area above the pinch point. Additional cooling, on the other hand, should only be used in the area below the pinch point. If this is not observed, system efficiency deteriorates.
Identification of Potentials and Naming of Measures
Storage Integration to Cover Peak Load Demands
Examination of Technical and Economic Feasibility
All measures derived from the pinch analysis to increase efficiency must be examined for their feasibility. Various aspects are investigated here:
- Spatial feasibility (e.g., construction size of possible heat exchangers, distance of media routes, possibilities for infrastructural integration)
- Material compatibilities and tightness
- Risk analysis (failure probabilities, system complexity)
- Economic efficiency (reduction of operating costs through energy savings, investment costs, and maintenance costs)
Finally, proposals for energetic optimization of the plant are named and recommendations for action to plan the transformation are derived.
Why Theta Concepts is the Right Partner for Complex Pinch Analyses
Theta Concepts GmbH has experienced engineers in the fields of thermodynamics, process engineering, and automation. Our team has already supported numerous R projects with its expertise and is well-versed in thermodynamic analyses of various plants based on different methods – from pinch analyses to the development of a digital twin for dynamic analysis to high-resolution 3D CFD. Sound analyses for various requirements, all from a single source. Contact us!
