Abstract
In this work, three decentralized control configuration designs—independent, sequential and simultaneous designs—were used in multivariable feedback configurations for PI control of the riser and regenerator temperatures of FCCU in order to compare their performances. Control design was formulated as optimization problem to minimize infinity norm of weighted sensitivity functions subject to μ-interaction measure bound on diagonal complementary functions of the closed loop system. The optimization problem was solved using augmented Lagrangian genetic algorithm. Simulation results show that simultaneous and independent designs give good response with less overshoot and with no oscillation. Bound on μ-interaction measure is satisfied for both designs meaning that their nominal stabilities are guaranteed; however, it is marginal for simultaneous design. Simultaneous design outperforms independent design in term of robust performance while independent design gives the best performance in terms of robust stability. Sequential design gives the worst performance out of the three designs.
Highlights
Fluid catalytic cracking (FCC) process is an added valued process that converts low-value crude heavy oil fractions into high-value light oil fractions of high quality fuels such as high-octane gasoline and olefins with the aid of a zeolite catalyst
Fluid catalytic cracking unit (FCCU) is an integration of strongly coupled complex non linear processes such as riser reactor, regenerator and fractionators which are characterized with the complex chemical reactions mechanism, complex hydrodynamics and many operating constraints [3]-[5]
Similar result was obtained for disk margin analysis, independent design gave largest variation as it indicates the closed-loop system will remain stable for simultaneous gain variations of [0.11 9.39] and phase margin variations of ±77.84 deg in the first input channel
Summary
Fluid catalytic cracking (FCC) process is an added valued process that converts low-value crude heavy oil fractions into high-value light oil fractions of high quality fuels such as high-octane gasoline and olefins with the aid of a zeolite catalyst. FCCU is an integration of strongly coupled complex non linear processes such as riser reactor, regenerator and fractionators which are characterized with the complex chemical reactions mechanism, complex hydrodynamics and many operating constraints [3]-[5] Great research efforts both from academic and industrial circles have been directed to development of FCCU focusing on improvement on catalysis of cracking process; modeling of complex dynamic behaviors of the unit with emphasis on bifurcation, steady state multiplicities and chaotic trend; both steady and dynamic optimization and advanced control. The three designs were applied to the control of riser-regenerator sub process of FCCU by formulating the weighted sensitivity function as optimization problem with some bounds as constraints so as to minimize its infinity norm in order to guarantee robustness in term of performance and stability of the closed loop system. The control designs rely on a simple dynamical model of the FCC unit
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