Information about heat integration
Heat integration, as defined by the IEA since 1993, is the Systematic and General Methods for Designing Integrated Production Systems ranging from Individual Processes to Total Sites, with special emphasis on the Efficient Use of Energy and reducing Environmental Effects”. It joins basically all the technologies that can help minimize energy consumption of an industry, without changing the processes themselves. Heat integration considers industries as a whole, and intends to re-use all heat outputs of certain processes, if they can be usable in the moment or later.
Besides HI, Water (Mass) Integration was also developed for reducing waste water effluents based on PA that can also lead to reduced fresh water intake.
Description of technology, techniques and methods
As a general concept, heat integration was defined firstly in the 70s by Linhoff, developing HEN and pinch theories. As an example of the most used tool of heat integration analysis, in this case, the heating and cooling demand and the necessary temperatures of all the industrial processes is shown in a diagram. Out of this diagram, and developed Physical Analysis methods, some answers could be obtained:
Figure 1: Example of pinch integration 
- How much energy can be recovered from residual heat?
- How much external heat demand does the process have? At which temperature levels is it necessary?
- How much external cooling demand does the process have? At which temperature levels is it necessary?
Nevertheless, though pinch, for its simplicity in use and adaptability has been widely used, a different technique (based on Linear Programming) was developed by Papoulias and Grossman in the early 80s. It is much more complicated, but allows Multi-objective Optimisation problems, which makes it attractive for certain cases.
Heat integration was, in the beginning, developed for continuous processes, with a focus on conventional fuels and heating and cooling demands. The necessary holistic analysis including batch processes, stochastic energy sources (R.E.), and variable conventional energy costs pushed the development of other methods in the Heat Integration field, involving time (like Time Average Models, Time Slice Models, Cascade Analysis, Batch Utility Curves and Time Pinch Analysis) and the overall energy system, from its origin (Total Site Heat Integration).
Figure 2: Local Integrated Energy Systems (an integration of TSHI) 
The advantage of Heat Integration techniques is that there are extremely little changes in processes, and energy savings can be significant (though variable depending on the process).
The only required changes are the implementation of heat exchanger network, with pumps, pipes and heat exchangers, which will become the energy supply of the different processes. Problems can arise with machines that incorporate heating systems, pre-designed for steam or high temperature heat supply (or very low temperature supply).
 Gundersen T: A process integration primer — implementing agreement on process integration. Trondheim, Norway: International Energy Agency, SINTEF Energy Research; 2000
 Klemes. J., Kravanja, Z. Forty years of Heat Integration: Pinch Analysis (PA) and Mathematical Programming (MP) Current opinion on Chemical Engineering, 2014.