Model-Free Adaptive Control
of Multi-Zone Temp Loops
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| • Multivariable
MFA handles interactions between
temperature zones. |
• Temperature control is improved by at
least a 50% reduction in temperature variability. |
| • Prevents product overheating. |
• Fuel consumption is sharply reduced. |
| • Reduces clogs in the vessel or pipes due
to improved temp consistency. |
• Less cleaning and maintenance are required.
Equipment life cycle is increased. |
| • Reduces variation in temperature and product
quality variable. |
• Product quality and production efficiency
is improved. |
| • Improves efficiency & productivity. |
• Full investment is returned in months
if not sooner. |
A 2-input-2-output MFA controller is able to handle
the interactions between the 2 combustion chambers in
this coking furnace so that tight temperature (green)
control is achieved for its +/-1 °C
specification.
Case History:
MFA at Guangzhou Petrochemical Complex reported
in Hydrocarbon Processing Magazine
Control of temperature loops in mult iple
zones can be problematic, especially when a narrow specification
is required. Successful installation of a Model-Free
Adaptive (MFA) Control system in the delayed coking
process at the Guang-Zhou Petrochemical Complex shows
how this problem can be resolved.
A coker consists of two coking furnaces, each with two
combustion chambers. High temperatures create carbon
that clogs pipes, and a b elow-spec temperature causes
an insufficient reaction so that the yield drops.
Control difficulties result from large time delays;
serious coupling between loops because the separation
wall between the two chambers is quite low; multiple
disturbances in gas pressure, oil flowrate, oil inflow
temperature and oil compos ition. The oil outlet temperature
is sensitive to gas flowrate change, and the temperature
specification is tight (+/-1 °C).
An MFA Control system running on a PC was networked
to the existing DCS. The original cascade control design
was simplified to eliminate disturbances and uncertainties.
The new system regulates fuel flow directly to control
the oil outlet temperature. A 2x2 Anti-delay
MFA controller on each furnace solved
large time delay and coupling problems. MFA controllers
compensated for dis turbances and uncertainties. Constraints
on controller outputs prevent temperatures running too
high or too low.
According to Mr. Delin Li, chief engineer at GPC, MFA
controllers started automatic control with no bumps
to the system. Commissioning took three days and resulted
in:
• Both furnaces being automatically controlled
under all conditions;
• Outlet oil temperature controlled to within
its +/-1 °C with energy savings and consistent product
quality;
• Operators have been relieved of tedious, ineffective
manual control responsibilities; and
• Higher efficiencies and yields have been achieved.
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