"INTRODUCTION This Data Item introduces Process Integration@ the most significant tool for energy analysis that has appeared in recent years. Its key advantages are: (i) a definite target for the energy use of a process plant is found and (ii) it gives systematic design methods to achieve this target. The importance of this systematic approach@ in contrast to past methods of installing energy efficiency projects piecemeal@ is illustrated by Sketch 2.1. Over a period of many years@ the energy use of the chemical process shown was reduced in successive designs. The learning curve thus obtained is typical of process plant development. However@ if Process Integration techniques had been available initially@ the target could have been found and the ultimate design identified in one step. Process Integration@ when eventually applied@ still identified a practical and economic saving of 30%. Process Integration targets should be distinguished from good housekeeping targets set by management to try and reduce wastage. The latter targets are chosen by guesswork and experience and are ""making the best of what you've got"". Process Integration targets are rigorous and are based on a thermodynamic analysis of the process. They show ways of improving the flowsheet so that the plant inherently requires less energy to produce the same quantity and quality of product. Sketch 2.2@ using averages from a large number of case studies@ shows energy savings identified by Process Integration compared with those from good housekeeping and control measures. These savings were for heat recovery projects. On many plants combined heat and power (CHP) schemes@ which can also be identified by Process Integration techniques and are covered briefly in Section 10.4@ offer even greater reductions in energy costs. This Data Item introduces the concepts and applies them to heat recovery@ in particular to the design of heat exchanger networks and the associated site heating and cooling or utility systems. The emphasis is on the practical application of the techniques and is illustrated by a major case study which shows the methodology being applied to a real situation. This Data Item may be used to carry out simple studies or as a guideline when working with Process Integration consultants@ enabling their methods to be followed and their findings understood. Process Integration is a systematic method and the stages of any study can be clearly delineated. The stages@ discussed in Sections 5 to 8@ are: (i) collect process data@ (ii) form heat and mass balances@ (iii) extract the Process Integration stream data@ (iv) select the minimum temperature approach between hot and cold streams@ (v) calculate energy targets and the pinch point@ (vi) examine possibilities for process change and recalculate targets if necessary@ (vii) design an ideal heat exchanger network to achieve the targets@ (viii) relax this network to give a variety of practical energy-saving projects@ (ix) do an economic evaluation and select the best possibilities. The proposed projects are compared and evaluated by conventional detailed design methods. Process Integration provides an overall energy strategy and enables the most cost effective projects to be identified rapidly. Time spent in the analysis is more than recouped by not needing to evaluate large numbers of possible designs in order to choose between them whilst@ at the same time@ obtaining a deep understanding of the energy flows within a process and how they relate to one another."