Info: What is a pinch analysis?

The industrial sector accounts for over a quarter of Germany's final energy consumption, of which around two thirds is accounted for by the provision of process heat and cooling [1].  Thus, this sector is responsible for a large part of the energy costs and emissions of companies. Similarly, there is considerable potential for increasing efficiency in this area, but this potential is often not quantified or exploited due to the large number of confusing energy flows.

In comparison to classical efficiency measures, which are mainly aimed at improving the efficiency of individual apparatuses, experience shows that there is a significantly greater savings potential when thermal energy flows are optimally linked in an overall system. This is the approach taken by a pinch analysis. In existing plants a savings potentials of thermal energy supply of approximately 10 to 30 % is likely to be realized [2].

Objective and application of pinch analysis

The focus of the pinch analysis is always on a holistic optimization of the thermal energy supply on process and plant level. Pinch analysis is a systematic procedure with the aim of determining the theoretically minimum possible energy requirement for the cold and heat supply of processes. This is primarily achieved by ideally interconnecting existing energy flows using heat exchangers for internal heat recovery. From this, direct measures for practical implementation can then be derived.

The basic prerequisite for the application of pinch analysis is the simultaneous presence of cooling and heating requirements that require one or more process steps. The areas of application range from individual production steps, to a sub-area of production (e.g. a production line), to a holistic view of one or more production plants with a local context.

Already in the planning of new plants it makes sense to use pinch analysis to avoid planning errors and to make the future process as efficient as possible and to integrate them optimally into the entire plant. Under the following conditions the application of a pinch analysis is particularly promising for existing plants:

  • Simultaneous presence of heating and cooling demand at different temperature levels.
  • The main thermal energy demand lies in the production processes (not in the building envelope).
  • Assumption of exhausted or unknown heat recovery possibilities


Process and procedure of a pinch analysis in practice



Abbildung 1:
Proceedings for a pinch analysis as a funtion of the time required (own presentation based on [2])

Figure 1 shows the three common steps for applying a pinch analysis. The first step already accounts for approx. 60 to 70 % of the total effort and includes mainly the acquisition, review and preparation of existing data and other relevant documents (e.g. hydraulic diagrams, process flow diagrams, parameters from process control systems etc.). It is crucial to gain an understanding of the process, not to structure the analysis too small and to evaluate the consumption of individual process steps in relation to the total energy consumption.

In a second step, the previously determined process conditions must be objectively questioned. This can already lead to the raising of energy saving potentials or help to define process requirements. These then serve as a starting point for the actual plant and process optimization in the context of the pinch analysis.

Abbildung 2: Schematic presentation for determining the pinch point using the composite curves

The pinch analysis procedure is shown schematically in Figure 2. An energy flow with a cooling requirement is called a "warm flow" because it is originally warm and must be cooled down. Similarly, currents with a heat requirement are called "cold current". The individual warm and cold flows of a process step describe its necessary heating or cooling requirement and are defined for any media, such as water, air, beer, chocolate, etc. The addition of the energy quantities of the hot and cold flows of the same temperature interval results in a composite curve (see Figure 2).

The point of contact of both composite curves is called the "pinch" where the "pinch-point temperature" is present and characterizes the system as follows:

  • All energy flows above the pinch point show a total heat deficit - an external heat supply for processes with heating requirements at a high temperature level may therefore only take place in this area.
  • All energy flows below the pinch point have a surplus of heat on the balance sheet - an external heat removal for processes with cooling demand at a low temperature level may therefore only take place in this area.
  • Hot streams above the pinch point may not be used for heating purposes below the pinch point.
  • The maximum possible (internal) heat recovery is shown directly in the diagram (see Figure 2).

This overall view of the thermal energy requirement then makes it possible to identify suitable heat flow pairs for internal heat recovery and to set up a heat exchanger network. For this purpose, more profound analysis methods are considered within the scope of the pinch analysis.

In a final step to the pinch analysis procedure, the results for internal heat recovery are checked with regard to their technical and economic feasibility and a prioritized list of measures is drawn up taking into account the cost-benefit ratio.


Literature

[1]

Energieeffizienz in Zahlen - Entwicklungen und Trends in Deutschland 2018. Berlin: Bundesministerium für Wirtschaft und Energie (BMWi), 2019.

[2]

Brunner, Florian; Krummenacher, Pierre: Einführung in die Prozessintegration mit der Pinch-Methode. Bern: Bundesamt für Energie, 2015.

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