Process integration

Process integration is a term in chemical engineering which has two possible meanings.

1. A holistic approach to process design which emphasizes the unity of the process and considers the interactions between different unit operations from the outset, rather than optimising them separately. This can also be called integrated process design or process synthesis. El-Halwagi (1997 and 2006) and Smith (2005) describes the approach well. An important first step is often product design (Cussler and Moggridge 2003) which develops the specification for the product to fulfil its required purpose.

2. Pinch analysis, a technique for designing a process to minimise energy consumption and maximise heat recovery, also known as heat integration, energy integration or pinch technology. The technique calculates thermodynamically attainable energy targets for a given process and identifies how to achieve them. A key insight is the pinch temperature, which is the most constrained point in the process. The most detailed explanation of the techniques is by Linnhoff et al. (1982), Shenoy (1995) and Kemp (2006). This definition reflects the fact that the first major success for process integration was the thermal pinch analysis addressing energy problems and pioneered by Linnhoff and co-workers. Later, other pinch analyses were developed for several applications such as mass-exchange networks (El-Halwagi and Manousiouthakis, 1989), water minimization (Wang and Smith, 1994), and material recycle (El-Halwagi et al., 2003).

In the context of chemical engineering, Process Integration can be defined as a holistic approach to process design and optimization, which exploits the interactions between different units in order to employ resources effectively and minimize costs.

Note that Process Integration is not limited to the design of new plants, but it also covers retrofit design (e.g. new units to be installed in an old plant) and the operation of existing systems.

The main advantage of process integration is to (this is wrong) consider a system as a whole (i.e. integrated or holistic approach) in order to improve their design and/or operation. In contrast, an analytical approach would attempt to improve or optimize process units separately without necessarily taking advantage of potential interactions among them.

For instance, by using process integration techniques it might be possible to identify that a process can use the heat rejected by another unit and reduce the overall energy consumption, even if the units are not running at optimum conditions on their own. Such an opportunity would be missed with an analytical approach, as it would seek to optimize each unit, and thereafter it wouldn’t be possible to re-use the heat internally.

Typically, process integration techniques are employed at the beginning of a project (e.g. a new plant or the improvement of an existing one) to screen out promising options to optimize the design and/or operation of a process plant.

Also it is often employed, in conjunction with simulation and mathematical optimization tools to identify opportunities in order to better integrate a system (new or existing) and reduce capital and/or operating costs.

Most process integration techniques employ Pinch Analysis or Pinch Tools to evaluate several processes as a whole system. Therefore, strictly speaking, both concepts are not the same, even if in certain contexts they are used interchangeably.

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References

Cussler, E.L. and Moggridge, G.D. (2001). Chemical Product Design. Cambridge University Press (Cambridge Series in Chemical Engineering). ISBN 0521791839

El-Halwagi, M. M., (2006) "Process Integration", Elsevier

El-Halwagi, M. M., (1997) "Pollution Prevention through Process Integration", Academic Press

El-Halwagi, M. M., F. Gabriel, and D. Harell, (2003) “Rigorous Graphical Targeting for Resource Conservation via Material Recycle/Reuse Networks”, Ind. Eng. Chem. Res., 42, 4319-4328

El-Halwagi, M. M., and Manousiouthakis, V. (1989). Synthesis of mass exchange networks. AIChE J. 35(8), 1233-1244.

Kemp, I.C. (2006). Pinch Analysis and Process Integration: A User Guide on Process Integration for the Efficient Use of Energy, 2nd edition. Butterworth-Heinemann. ISBN 0750682604. Includes downloadable spreadsheet software.

Linnhoff, B., D.W. Townsend, D. Boland, G.F. Hewitt, B.E.A. Thomas, A.R. Guy and R.H. Marsland, (1982) “A User Guide on Process Integration for the Efficient Use of Efficient Use of Energy," IChemE UK

Shenoy, U.V. (1995). "Heat Exchanger Network Synthesis: Process Optimization by Energy and Resource Analysis". Includes two computer disks. Gulf Publishing Company, Houston, TX, USA. ISBN 0884153916.

Smith, R. (2005). Chemical Process Design and Integration. John Wiley and Sons. ISBN 0471486809

Wang, Y. P. and R. Smith (1994). Wastewater Minimisation. Chem. Eng. Sci., 49, 981-1006