Heat recovery steam modulating dampers


Thread Starter



When giving shutdown command to HRSG, the sequence is that bypass damper to open fully in 80 sec. then inlet damper to fully close in another 80 sec. In our case, if GTG load is high (i.e above 45 MW) the unit (GTG) trips on an external trip signal. GTG load should be reduced to safely shutdown the GTG.

I tried to link out the relation between power loads and modulating dampers but unfortunately failed.

Anybody has an idea in this regard.

yanbunet [at] gmail [dot] com
Damper closure time delay is 80 sec, hence if within 80 secs, diverter damper is not fully closed (L33BB1 not high), then an external trip signal is generated which will trip GT. Logic L86BMST will be activated (for Frame - VI machines)

There is no link between power loads and bypass damper modulation, but it sure is linked to an increase/decrease exhaust flow to HRSG for an increased/decreased HRSG steam production. You have not furnished full information about the problem like how the operation was when your unit was commissioned?

since how long have you experienced this problem?

have you followed the recommended O&M practices with regards to dampers preventive maintenance?

Does the damper operate smoothly without jerks etc?

I do not believe there is any logic in tripping the unit above 45 MW for shutting down the HRSG. Note if your dampers do not operate within the preset time, you will trip the unit regardless of higher or lower unit load.