Air separation control technology
Section snippets
Process characteristics
There are two primary methods of separating air into its two main components. If a lower volume, gaseous oxygen or nitrogen product is required, then an adsorption process driven by the pressure difference between the adsorption step and the desorption/reactivation steps may be used. On the other hand, for liquid products, larger volume gaseous products, high purity products, or the recovery of argon, cryogenic processes will be used. Fig. 1 (Air Products, 1997) indicates the ranges of capacity
Operability index
The benefits and challenges of evaluating the impact of design complexity on the operability of a facility were the subject of work by the author (Vinson, 1997, Vinson, 2000). One of the results of that work was the definition of a measure called the operability index (OI). In order to calculate the OI, a number of operating spaces were defined, some of those spaces are identified here:
- (1)
Available input space (AIS)—represents the range over which the inputs of the process are able to change.
- (2)
Proposed directions for future research
Air separation is often viewed as a mature technology, yet significant advances continue to be made in the design efficiency and operating optimization of these processes. The recent rise in energy prices will drive further improvements in the industry which may catalyze additional research aimed at further improvements in control and operability of air separation processes. Suggested directions for future research in HPPC are described below.
The air separation industry is characterized by the
Summary and conclusion
The air separation industry has demonstrated continued improvement in process efficiency and operating cost. A large contributor to the improvements has been the utilization of advanced control techniques. Recent increases in the cost of energy will continue to fuel the drive for optimized design and operation. The ability to achieve maximum improvements is dependent upon continued progress in the research of advanced process control techniques.
Acknowledgements
I would like to thank to my colleagues at Air Products and Chemicals Inc. for joining me in the continuing battle to achieve HPPC in our operating plants, especially those that have served with me over the years in Advanced Control.
References (42)
- et al.
Compartmental modeling of high purity air separation columns
Computers and Chemical Engineering
(2005) - et al.
On the operability of continuous processes
Control Engineering Practice
(2003) - et al.
A model predictive control strategy for supply chain optimization
Computers and Chemical Engineering
(2003) - et al.
First principles dynamic modeling and multivariable control of a cryogenic distillation process
Computers and Chemical Engineering
(2000) - et al.
Design of robust model-based controllers via parametric programming
Automatica
(2004) - et al.
A case study for control structure selection: air separation plant
Journal of Process Control
(2000) - et al.
RPN tuning strategy for model predictive control
Journal of Process Control
(2003) - et al.
A new measure of process output controllability
Journal of Process Control
(2000) - et al.
An efficient off-line formulation of robust model predictive control using linear matrix inequalities
Automatica
(2003) - et al.
Perturbation techniques for accelerated convergence of cyclic steady state (CSS) in oxygen VSA simulations
Chemical Engineering Science
(2002)