**6. Conclusions and recommendations**

To develop sustainable energy efficient facility design evolutionary-approach shall be adapted rather than the more time-consuming revolutionary-approach. The concept is to develop sustainable energy efficient process design of every individual process, which itself is challenging but might be realized. Subsequently, once all the processes are sustainable the facility is going to be sustainable in energy efficiency develop options for inter/intra/hybrid integration together with energy recovery technologies to form the facility "best in class" from energy perspective.

Definitely obtaining a sustainable energy efficient facility design is extremely challenging but the advantages from its enormous, even a design from only heat integration perspective are great. If a design, even at a process level from heat integration perspective is produced such it's fixed topology i.e. no new stream matches and energy efficiency improvements by area manipulation only will ends up in high energy as well as monetary savings. This is demonstrated through ADU-VDU sustainable design for a 400,000 BPD refinery, the advantages include energy savings of about \$100 million NPV (depending on energy vales) together with about 90 kilo tons of CO2 emissions reduction annually. The modification to boost energy efficiency does not require extended shut-down for energy projects but may well be drained normal shut-down window. Moreover, lesser capital expenditure is required for the design modifications as compared to retrofitting the conventional design case.

**Figure 10** summarizes the benefits of Sustainable Energy Efficient Design benefits, as the solutions are "off the shelves" design i.e. pre-engineered, it does not have shut-down, structural and/or plot plan limitations. Retrofits in normal design

#### **Figure 10.**

*Comparison between Normal versus sustainable energy efficient design.*

are generally limited initially by shut-down opportunities as initially energy savings projects are feasible but later obstructed by structural limitations which implies the topology can either restricted or resulted in retrofits with very high capital and ends up with the area constrains may leads to impracticable retrofits. The constrains of shut-down, structural and plot-plan limits the facility to be energy efficient solely up to a particular level which will not able to be energy efficient supporting the economic trade-off for its life-time. On the other hand, the capital needed to do the modifications is much less in sustainable design as the provision for the modifications were made during initial design. Consequently, the initial as well as final facility design are very close to be energy efficient based on the economic trade-off. Hence, it is highly recommended for all chemical engineering community to come together for developing methods, techniques and frame-work to achieve "Sustainable Energy Efficient Plant Design" and extend it to achieve the ultimate goal of "Sustainable Energy Efficient Facility Design".
