Model-Free Adaptive Control
of Fluidized-Bed Boilers
MFA tightly controls master steam
||• Pressure control is improved for a smoother
turbine generator operation.
MFA tightly controls steam temperature.
||• Temperature control is improved by at
least a 50% reduction in temperature variability
for higher combustion efficiency, reduced emission,
and lower fuel usage.
|• Feedback and Feedforward
MFA controls steam drum level under
large pressure load changes.
||• Boiler and steam system stability is improved
and meets flexible production needs for power and
The picture at left shows a fluidized bed steam generator
by Babcock Borsig Power. The middle and right
pictures show the difference in the steam temperature
and pressure under manual (L) and MFA control (R).
MFA at Jiang-Yuan Energy and Power Cogeneration Plant
Fluidized-bed boilers are becoming a strategic
operating unit in power and energy generation. The unique
design allows fuel such as coal powders to be fluidized
in the air so that they have better contact with the
surrounding air for better combustion. Fluidized-bed
boilers can burn low-grade fuel such as waste coal,
wood, and refuse derived fuel, etc. Most importantly,
less emissions such as COx and NOx are produced compared
to conventional boilers.
The Chinese government has issued a new regulation forcing
the shut down of all small power plants (200MW or less)
unless the boilers are changed to fluidizedbed boilers.
The purpose is to achieve economical benefits and reduce
air pollution at the same time.
A fluidized-bed boiler typically consists of several
key process variables: steam pressure, temperature,
coal feed rate, air supply, steam drum level, etc.
Control difficulties result from large time delays and
lags in the temperature loop, nonlinear nature of the
pressure loop, large load changes, and the shrink-andswell
problem in the steam drum level. Particularly, low-grade
fuel has an inconsistent Btu value causing good fuel-airratio
control to be very difficult.
According to Mr. Long-Bao Wu, chief engineer at Jiang-Yuan
Co-gen Plant, a CyboCon
CE control instrument and a CyboCon
software package have been installed
to control two 75 Ton/Hour fluidized-bed boilers. MFA
controllers are able to control steam temperature, steam
pressure, and steam drum level effectively. "These
loops are usually in manual control. We are very impressed
with the capability of MFA control and have certified
a document for the CyboSoft Shanghai company claiming
our successful installation." Mr. Wu commented.
Good control performance has been achieved with these
• Steam temperature variation +/-2 °C
• Steam pressure variation +/-0.1Mpa.