1) Plantwide Inventory Control for Sustainable Process Operation
A robust plantwide regulatory control system is installed on continuous chemical processes to close all independent material and energy balances, driving the process operation toward a steady state. Economic and sustainability concerns are usually addressed by adjusting the regulatory setpoints to minimize the cost objective. At the optimum steady state, typically multiple constraints are active. Optimal process operation then boils down to designing the plant-wide control system such that the variability in the active constraint process variables (PVs) is minimized, driving the process operation as close as possible to the active constraint limits with just enough back-off to avoid constraint violation. Because material balance transients are usually a major source of variability in the constraint PVs, the design of the plant inventory control system that closes the individual unit operation, as well as the plantwide material balances, plays a key role in determining an operating plant's economic performance. This thesis comprehensively investigates the same.
There are two major decisions in the design of the plantwide inventory control system:
(i) The choice of the material flow stream rate that sets the process throughput, also referred to as the throughput manipulator (TPM)
(ii) The controller algorithm and tuning of each of the SISO inventory controllers.
The TPM choice (item (i) above) dictates an outwardly radiating material balance control structure that propagates flow transients away from the TPM. The severity of the flow transients thus typically increases as one moves further away from the TPM. The location of the TPM relative to the active constraint PVs then affects the variability in the active constraint PVs. The control algorithm and tuning of each of the SISO inventory controllers (item (ii) above) determine the severity of the propagated flow transients for a given flow disturbance. Typically, the loosest possible level control without violating the high/low level alarm limits is desired for all the surge inventories, such as the reflux drum or bottom sump level in a column. This maximizes flow filtering and is referred to as averaging level control (ALC).
2) Plantwide Process Synthesis, Design, and Control
Sustainability concerns—driven by increasingly stringent environmental discharge regulations, carbon taxation, and land-use constraints—have renewed focus on the “recovery, recycle, and reuse” paradigm that has underpinned chemical process design for over a century. Modern chemical processes are expected to achieve near-zero waste discharge, high energy efficiency, carbon neutrality, and minimal spatial footprint, objectives that are traditionally addressed through process integration involving the recovery and recycle of reactants and energy, as well as the synergistic exploitation of interactions among individual processing steps.
In addition to my doctoral thesis research, I actively pursue complementary work in this area by employing advanced process and heat integration tools—such as reactive distillation (RD), divided wall columns (DWC), reactive divided wall columns (RDWC), high- and low-pressure (HP–LP) heat recovery, and vapor recompression (VR)—to design and control flowsheets that are both economically efficient and operationally robust.