To reduce emissions in the process industry, much emphasis has been put on making step changes in emission reduction, by developing new process technology and making renewable energy more affordable. However, the energy saving potential of existing systems cannot be simply ignored. In recent years, there have been significant advances in process integration technology with better modelling techniques and more advanced solution methods. These methods have been applied to the new design and retrofit studies in the process industry. Here attempts are made to apply these technologies to improve the environmental performance of existing facilities with operational changes. An industrial project was carried out to demonstrate the importance and effectiveness of exploiting the operational flexibility for energy conservation. By applying advanced optimisation technique to integrate the operation of distillation and heat recovery in a crude oil distillation unit, the energy consumption was reduced by 8% without capital expenditure. It shows that with correctly identified technology and the proper execution procedure, significant energy savings and emission reduction can be achieved very quickly without major capital expenditure. This allows the industry to improve its economic and environment performance at the same time. © 2012 Elsevier Ltd.