(735b) Simultaneous Design and Control of Pressure Swing Adsorption Processes

Simultaneous Design and Control of Pressure
Swing Adsorption Processes

In the last
few decades, pressure swing adsorption (PSA) has evidenced substantial growth
in terms of size, versatility and complexity. In addition to handling
multi-component separation and purification, it offers tremendous flexibility
at the design stage, requiring careful selection of key decision variables
including number of beds, time duration of process steps, bed length and
diameter. Further challenges are posed by the fact that the PSA operation is
periodic in nature and never attains a true steady state. Traditional approach
for the ?design? of such process systems usually employs a two step,
first-design-and-then-control, sequential treatment. In contrast, integrated
design and control (IDC) approach takes into account the fact that it is the design
of the system which determines its dynamic controllability. Its potential for
significant design improvements in terms of superior real time operability has
been realized from quite some time now. However, early contributions to this
field mostly performed analysis on the linear dynamic representation of the
original system. The application of IDC approach to inherently dynamic and
highly nonlinear system like PSA remains a challenging task and has never been
attempted before.

In this work,
a systematic and rigorous methodology for the simultaneous design and control
of PSA systems, incorporating a comprehensive treatment of its design and
operational constraints is presented. Towards this goal, a detailed first
principle based model is first developed for a double bed, 6 step PSA system
(Khajuria and Pistikopoulos, 2010). In the next step, the full scale integrated
design and control dynamic optimization problem is formulated and solved
incorporating all operational constraints (Bansal, et.al., 2000; Mohideen,
et.al., 1996; Sakizlis, et.al., 2004). The design objective for the PSA system
separating 70 % H₂ - 30 % CH₄ mixture into high purity
hydrogen, is to maximize the H₂ recovery, while the controller
objective is to minimize the integral square error (ISE) in purity from a set
point value of 99.99 %, for time varying disturbances in feed temperature and
feed rate. Furthermore, detailed studies are also conducted to compare the
optimal design obtained from integrated design and control case in terms of hydrogen
recovery and disturbance rejection, as compared to sequential design and
control case.

References:

Bansal,
V.; Perkins, J.; Pistikopoulos, E.; Ross, R. & van Schijndel, J. (2000),
'Simultaneous design and control optimisation under uncertainty', Computers
& Chemical Engineering 24(2-7), 261 - 266.

Khajuria,
H. & Pistikopoulos, E. N. (2011), 'Dynamic modeling and
explicit/multi-parametric MPC control of pressure swing adsorption systems', Journal
of Process Control 21(1), 151 - 163.

Mohideen,
M. J.; Perkins, J. D. & Pistikopoulos, E. N. (1996), 'Optimal Design of
Dynamic Systems under Uncertainty', AlChE Journal 42(8),
2251-2272.

Sakizlis,
V.; Perkins, J. D. & Pistikopoulos, E. N. (2004), 'Recent advances in
optimization-based simultaneous process and control design', Computers &
Chemical Engineering 28(10), 2069 - 2086.