Environmental Engineering Reference
In-Depth Information
Assuming t = 0, when hold is released (cutoff valve: OPEN), g (0) = hold value and
f (0) = lower limit.
g ( t ) = f ( t ) * k ( t ) + g (0) (1 - k ( t ))
When k (0) = 0 is established, the right side of the equation above is g (0). This
means that the hold value is the start level. Assuming the convergence time of step
response to be T , k ( T ) = 1 is established to result in g ( T ) = f ( T ). This indicates a
convergence to the measurement signal.
The middle section in Figure 5.53 shows the result of correction using the
monotonic increasing function ( y = Ax ). This appears quite practical, but the effect
of attenuation on the control performance must be tested. Simulations will have to
be conducted to verify the effect, and the optimum attenuation model will have to
be selected.
The in-furnace pressure is controlled by changing the aperture of the damper
and the rpm of the exhaust gas fan, as shown in Figure 5.54 . The characteristics
with respect to the degree of activation and the resultant furnace pressure can be
defined on the basis of the responses to stepwise variations to these devices. Further,
a change in the combustion amount changes the exhaust gas flow rate and in-furnace
temperature, thus influencing the in-furnace pressure. The characteristics of the effect
of disturbance on the control system involving the combustion amount and the in-
furnace pressure can be defined from the responses to the stepwise variations. A
simulation of a change in the furnace pressure in accordance with the changed
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FIGURE 5.53 Controlled COG flow rate.
Combustion
amount control
Furnace pressure
measurement
Furnace
pressure damper Exhaust gas fan rpm
STEP INPUT
PI
STEP INPUT
STEP INPUT
FIC
VVVF
I / P
I/ P
FIGURE 5.54 Schematic diagram for pressure measurement.
 
 
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