PATH ANALYSIS FOR THE RETROFIT OF HEAT EXCHANGER NETWORKS AND THE UTILITY SYSTEM

This study introduced a new approach for HEN retrofit that featuring area addition to
the existing exchangers without massive topology changes in HEN. The approach has
developed based on a combinatorial method to combine the available utility paths in
HEN systematically to generate several alternatives for increasing the process-toprocess
heat recovery. To ensure feasible heat transfer between hot and cold streams,
the Heat Recovery Approach Temperature (HRA T) is maintained while increasing the
heat recovery. The available exchangers' pressure drop is considered in calculating
the film heat transfer coefficients. A demonstrative example showed several retrofit
options where the energy savings ranged from $150K/yr to $450K/yr with payback of
less than 2 years to refund the investment rose from the mandatory area addition. The
developed approach is termed as 'Paths Combination Approach for HEN Retrofit'.
Moreover, a concept of varying the process stream temperature has been established
to further increase the heat recovery and make the infeasible solutions more
competitive. This concept mainly depends on the process streams' flexibility to
changing the inlet and outlet temperature; and termed as the Temperature Flexibility
concept (TF concept). Implementation alternatives are generated and integrated into
the paths combination approach. Given that major changes in process conditions are
rarely desired, the temperature changes has been kept within a small magnitude
regardless of the usual process temperature oscillations. A user friendly computer
programme has been developed for performing the approach in view of the significant
number of iterations required. Most of the infeasible retrofit solutions have changed to
the feasible zone where higher savings are featured along the temperature flexibility
range. The energy savings derived from HEN retrofit have been further investigated
to study the impact on the utility system. Through a case study integrating HEN
retrofit and utility system, the most efficient way was found to redistribute the steam
surplus among the utility system devices while considering the turbines flow
constraints. Accordingly, the power production in the utility system has increased