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

• Main Author: ELSIDDIG, ABDELBAGI OSMAN
• Format: Thesis
• Language: English
• Published: 2011
• Online Access: http://utpedia.utp.edu.my/2767/1/A.Bagi._PhD_Thesis.pdf; http://utpedia.utp.edu.my/2767/

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 (HRAT) 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 vi using one of the retrofit options from 4.1% to 10.5% when applying the full range of the TF in HEN.