Design of control configuration for highly heat-integrated HDA process

Abstract

The design plantwide control structures for a highly heat integrated plant is quite difficult task since the highly heat integrated plant has a few utility unit (i.e. heater and cooler) to absorb thermal disturbance load. This problem can be solved by adding auxiliary utility unit. However, more auxiliary utility unit will be increase capital operating and maintenance costs. In this research, we propose the strategy to design the workable highly heat integrated plant like alternatives 5 and 6 of hydrodealkylation of toluene (HDA) process with minimum auxiliary utility unit. It starts with specifying the disturbances and their magnitudes, next designing the worst case condition, and then designing the heat pathway. Finally, the minimum auxiliary utility units are evaluated. We can solve the control difficulties associated with alternatives 5 and 6 by adding an auxiliary utility unit to the process instead of three and four as suggested by Luyben (1999), respectively. The three new control structures are proposed and their performances are evaluated. As shown in dynamic simulation study, the control performance for the highly heat integrated plant with minimum auxiliary utility unit is same with the highly heat integrated plant with full auxiliary utility units. CS1 is the best control structure for handle disturbances due to it gives better control performances. In this control structure, the selective controller with low selector switch (LSS) is employed to achieve dynamic maximum energy recovery that can save energy about 0.45 % for change in the heat load disturbance of cold stream. Besides, the inlet hot temperature at entrance of reboiler is maintained to prevent the propagation of thermal disturbance to separation section.