Design of plantwide control structure of HDA process with energy integration schemes

Although several general designs of plantwide control have been developed, none of them has reported the energy management for energy-integrated plants, particularly in manipulating heat pathways in order to achieve dynamic maximum energy recovery (DMER). In this dissertation, the new heuristic of selection and manipulation of heat pathways for plantwide process control has been developed. The proposed heat pathway heuristics (HPH) is used in conjunction with Luybens plantwide control procedure to model heat pathway management systems and the control configurations of the hydrodealkylation of toluene (HDA) process with different energy integration schemes (i.e. alternatives 1, 4 and 6). Various heat pathways throughout the network are systematically investigated for the purpose of plantwide energy management. An appropriate heat pathway is selected by means of a selective controller with low selector switch (LSS) to direct the disturbance load to a heating or cooling utility unit in order to achieve DMER. Such control system is rigorously examined in HYSYS dynamic simulation environment. This study reveals that the LSS plays a significant role in selecting proper heat pathway through a complex energy-integrated plant in order to direct and manage the disturbance load in such a way that DMER can be achieved. The new designed plantwide control structure is compared with the earlier work given by Luyben et al. (1999). Better responses of the furnace and cooler utility consumptions are achieved here compared to the Luybens control structure, since the duties for both furnace and cooler utilities could be reduced according to the input heat load disturbance. As shown in dynamic simulation study, the HPH is therefore considered useful to achieve the highest possible DMER. This study also confirms that the complex energy integration deteriorates the dynamic performances of the process.