controlling process of egb damper

1. 11040505 LT
11040506 HT 20-Aug-20
Problem description:
Regarding EGB-1, when engines goes to load higher 12000KW. Its damper opens and start to
produce steam. But when steam pressure is higher setpoint (7 bar), the damper does not close.
damper control system:
Applying method of Elimination:
PID controller set point: same PID set point controller is used for another damper. As all
performing well, so PID controller set point is good. So we eliminate it. (PID set point
controller )
Damper controller card: Once it was changed with no. #5. But same result. (Damper
controller card )
Analog inductive position sensor of damper: This is the remaining one and problem is here.
In the following I am presenting the proof against analog inductive sensor.
Discussion: In electrical, it is called thermal run way or temperature co-efficient or temperature drift
problem. Which means that how much a device response (output parameter) changes with the change
PID
controller
SET point
Damper
controller
card
Damper
Analog inductive
position sensor of
damper

2. of surroundings temperature of the device changes. The lower change in output parameter with the
change of temperature,the better the device is. But in case of our analog inductive position sensor, its
temperature co-efficient is very high and which is negative temperature co-efficient.
( It is a inductive sensor but along with some semiconductor device which works as current source
and semiconductor device has thermal drift property).
Proof(one): we ran the engine #1 on 26 July and put the damper position at about 80%(manually). And
when plant goes shutdown, we kept the damper at same position at about (80%). But after some hours
we get the following damper position data.
But if we add the temperature curve with it we get the following curve

3. From the above curve we see that when temperature up the output response decrease and when
temperature goes down the output response goes up. This should not be happened. The temperature
varies 2 degree the response varies 10%.
Proof 2:
Now what is actually happens in EGB-1 when running it in auto mode?
Please pay a close attention in the following,

4. At point A the load is around 12000 KW damper opens 100%. But at point B the temperature around
the boiler is higher than normal because exhaust is passing through the boiler and now the sensor starts
to show its negative temperature co-efficient, which sending the lower position value (but physically it
is 100%) to controller which indicates the point C or next. when steam pressure higher than 7 bar,
damper controller is looking that damper is closed (0% from position sensor but physically 100%) so
no need to send close signal from controller. Thus, steam pressure increases to higher value.
Noted that: when Wartsila people came from Finland, they changed the controller but not the sensor
and calibrated it in no running condition, so I think they didn’t catch up the main problembecause
problemwas with the sensor(temperature drift) not with controller.
1st
solution attempt: changing the sensor with other one and take a look (easy solution)
2nd
solution attempt:put4-20ma currentsignal at running condition, and take a look on damper position
is changing or not with steam pressure (not easy solution)