concentrations and flowrates are known, the separators (the second layer of the onion) can be designed. The basic process heat and material balance is now in place, and the heat exchanger network (the third layer) can be designed. The remaining heating and cooling duties are handled by the utility system (the fourth layer). The process utility system may be a part of a centralised site-wide utility system.

A Pinch Analysis starts with the heat and material balance for the process. Using Pinch Technology, it is possible to identify appropriate changes in the core process conditions that can have an impact on energy savings (onion layers one and two). After the heat and material balance is established, targets for energy saving can be set prior to the design of the heat exchanger network. The Pinch Design Method ensures that these targets are achieved during the network design. Targets can also be set for the utility loads at various levels (e.g. steam and refrigeration levels). The utility levels supplied to the process may be a part of a centralised site-wide utility system (e.g. site steam system). Pinch Technology extends to the site level, wherein appropriate loads on the various steam mains can be identified in order to minimise the site wide energy consumption. Pinch Technology therefore provides a consistent methodology for energy saving, from the basic heat and material balance to the total site utility system.

1.3 From Flowsheet to Pinch Data

PinchExpress and SuperTarget PROCESS can carry out automatic data extraction from a converged simulation. What follows here is a brief overview of how flowsheet data are used in pinch analysis. Data extraction is covered in more depth in "Data Extraction Principles".

1.3.1 Data Extraction Flowsheet

Data extraction relates to the extraction of information required for Pinch Analysis from a given process heat and material balance. Figure (a) shows an example process flow-sheet involving a two stage reactor and a distillation column. The process already has heat recovery, represented by the two process to process heat exchangers. The hot utility demand

Pinch Technology Introduction

of the process is 1200 units (shown by H) and the cold utility demand is 360 units (shown by C). Pinch Analysis principles will be applied to identify the energy saving potential (or target) for the process and subsequently to aid the design of the heat exchanger network to achieve that targeted saving.

Data Extraction for Pinch Analysis

In order to start the Pinch Analysis the necessary thermal data must be extracted from the process. This involves the identification of process heating and cooling duties. Figure(b) shows the flow-sheet representation of the example process which highlights the heating and cooling demands of the streams without any reference to the existing exchangers. This is called the data extraction flow-sheet representation. The reboiler and condenser duties have been excluded from the analysis for simplicity. In an actual study however, these duties should be included. The assumption in the data extraction flow-sheet is that any process cooling duty is available to match against any heating duty in the process. No existing heat exchanger is assumed unless it is excluded from Pinch Analysis for specific reasons.

1.3.3 Thermal Data

Tmin = 10°C

Utilities: Steam at 200°C. CW at 25°C → 30°C

Thermal Data required for Pinch Analysis

The above table shows the thermal data for Pinch Analysis. "Hot steams" are the streams that need cooling (i.e. heat sources) while "cold streams" are the streams that need heating (i.e. heat sinks). The supply temperature of the stream is denoted as Ts and target temperature as Tt. The heat capacity flow rate (CP) is the mass flowrate times the specific heat capacity i.e.