Air inlet DP high

Good day!!

If air inlet greater than the alarm limit (180 mmH2O), what precaution should be taken?

Will it advisable to force the automatic shutdown logic L63TFH to zero?

There is no difference in CPD.

Take care
G.Rajesh
 
G.Rajesh.

There should be an alarm switch and at least one shutdown switch (which are set slightly higher than the alarm). If the dp is allowed to continue to climb then the Speedtronic should initiate a shutdown (some actually trip the turbine; most just a shutdown).

The risks involved with running with inlet filters with a high dp are that one or more inlet filter elements can rupture and then all of the dirt and debris trapped in the filter (including the filter backing and material) can be sucked into the turbine inlet. Some large portions might be cause by the trash screen but some would not; that's a pretty coarse screen.

And when you get foreign objects trying to pass through the axial compressor, bad things can and usually do happen.

Some inlet filter houses have what are known as implosion doors. If the inlet filter dp gets too high the vacuum in the inlet will open the door--which lets completely unfiltered air and debris into the axial compressor inlet. This is to prevent collapsing the inlet filters or, worse, collapsing the inlet ductwork.

You need to look at the filters at your site to determine what the contamination is and what it might be caused by. High humidity in combination with dust and dirt can combine to increase filter dp sooner than would otherwise be expected--but it is still a high dp, which represents all the problems noted above.

It's a site call. Some sites actually try (and do) change filter elements on the fly (with the unit running). There's some risk associated with that (open area while filter is being replaced) as well as dirt and debris dislodging from the old filter being removed and being drawn in through the opening.

It's not a good think to "choke" a heavy duty gas turbine. The compressor might even go into a stall depending on conditions, and that cold cause a really nasty chain of events to occur resulting in a lot of damage to the inlet duct work, combustion liners, compressor blades (stationary and rotating), etc.

Again, it's a site call. If the high dp is unexpected or has just occurred quickly then there's a chance something has changed in the ambient that is affecting the condition of the filters (high humidity; construction in the are causing increased dust; etc.). So, you have to ask the best first question: "When did this problem start" and then analyze the situation and take appropriate action for your site conditions and management disposition. Making sure everyone understands the consequences of any action--as well as an inaction.

Please write back to let us know how you fare.
 
Thank you CSA as usual valuable feedback!!

Well, the DP is fluctuating from 110 to 230 mmH2O. During rain and early morning it was at high side and during day time it is in normal state.

CPD is maintaining same at both sides.

So except than replacing the filters, can do anything to improve performance?

Thank you & take care
G.Rajesh
 
Dear G. Rajesh

Usually Rain louvers are installed at filters house of gas turbine, which do collect rain and drain out, So what is arrangement at your site and earlier in the morning what is the behaviour of frequency at your end? What is site location is at sea side?

In winter air travels from land to sea side and in Summer air travels from sea to land, therefore frequency of chokage of filters is much more in winter as compared with summer.

CSA has well explained about drawbacks of running GT at high filter DP.

One thing I want to add regarding filters DP high, if you keep to run machine at high DP then there are chances of icing due to higher velocities of air molecules in the winter season even ambient temp is not zer or in minus value.

If you want to run the machine then reduce the machine load at specific timing you suffer the problem, also compare filter DP reading from local PDI's

Hope this will be a little bit helpful to you, as I am newer on this wonderful site
 
Rain louvers are certainly an option, but one has to ask: How long has the site been having this problem of fluctuating inlet filter dp?

Since initial commissioning?

Has the weather pattern changed in the last couple of years?

Has a different filter supplier been used for this set of inlet air filters than in previous years? Or was a different filter composition used the last time the filter elements were replaced?

One would think that if rain hoods were necessary they would have been installed at the time of original installation. That's not always the case, but if the packager of the turbine thinks the prevailing winds would blow rain into the inlet air path/filter elements then they would certainly have recommended rain louver/hoods at the time.

Some filter houses, though, don't have the capability to install rain louvers/hoods.

Whenever an issue like this arises--especially on units which have been running without similar problems in the past, one has to stop and think about all the things that might have changed to contribute to the problem. I've been to sites that started complaining about increased filter fouling only to find a road was being constructed directly upwind of the turbine inlet air filter house and dust and debris was being sucked into the filters. And, this was allegedly a Speedtronic problem! Yes; a Speedtronic turbine control system problem, because high filter dp's were causing shutdowns.

And, the unit has been running fine for more than two years before the new road was begun. And, then the Speedtronic caused nuisance, unplanned shutdowns. And that particular Customer REFUSED to believe the high filter dp's were caused by dust and dirt from the road construction, even though it was clear that the prevailing winds were blowing the contaminants directly into the air inlet filter house. They insisted, and are probably still insisting to this day, the problem was caused by the Speedtronic--because everyone knows it controls the filter dp. (And that unit did not self-cleaning inlet filters, either.) I spent eight-and-a-half days at that site because the Customer refused to let me leave until the Speedtronic was "fixed."

Sometimes, on older sites, it takes a little more detective work to learn how many different types of filters have been used over the years, and what the issues were with each one that caused a constant change of supplier/type each time filters were replaced.

Some would call this "root cause analysis": searching for the root cause of "excessive" filter dp and/or replacement. Call it whatever one likes--it's still just part and parcel of analyzing the situation which has developed to determine what has changed and why it might be impacting the turbine in the way that it is.

Best of luck!
 
The Filter Dp is generally being measured using Impulse tubes. LP tapping on Cleanside of the Filters, while the HP side is left open to atmosphere. This behaviour could be because of

1)some dirt/condensation in the LP tapping, which can be blown off during the GT Shutdown

2)HP Tapping is having some dirt & blocking the atmospheric pressure change reaching to the transmitter.

Generally HP Tapping is common for all transmitters & if all measurements are facing issues, it is most likely cause.

Regards,
 
You didn't mention what type of air filtration system you are using. Self cleaning (Pulse jet) type filters can start to get very high pressure drops in high humidity or rain when the filter is beginning to get contaminated. You mentioned high diff. in the morning and getting better in the afternoon. this is a very big sign of initial dust clogging the filter as it gets wet then drying out as the day gets warmer and drier. even traditional media filters will do the same. If you have pulse jet filters, don't try to pulse them when they are wet. it will make them even worse. The latest systems have Humidity meters and shut down the filter pulsing above an RH value.
 
Thank you ALL for your valuable feedback.

Since we have 3 days holiday I couldn't reply.

SB
Usually Rain louvers are installed at filters house of gas turbine, which do collect rain and drain out, So what is arrangement at your site and earlier in the morning what is the behaviour of frequency at your end? What is site location is at sea side?

We don't have rain louvers but we have dust louver motors. Site is not near sea, we experienced rain in the past week.

If you want to run the machine then reduce the machine load at specific timing you suffer the problem, also compare filter DP reading from local PDI's.

We verified both PDI's and transmitter are reading same. Moreover pressure switch also issuing shutdown command when DP is very high. So it is not because of faulty instruments.

CSA
How long has the site been having this problem of fluctuating inlet filter dp?
From past one month

Since initial commissioning?
No

Has the weather pattern changed in the last couple of years?
There was rain in the past week.

Has a different filter supplier been used for this set of inlet air filters than in previous years? Or was a different filter composition used the last time the filter elements were replaced?

Same supplier only used (Donaldson).

Niraj,
The Filter DP is generally being measured using Impulse tubes.
We have inspected and all three were found normal.

Bob Johnston,
You didn't mention what type of air filtration system you are using.
We have pulse cleaning system.

The latest systems have Humidity meters and shut down the filter pulsing above an RH value.
yes it has RH meter.

Thank you once again

Take care
G.Rajesh
 
Now summer has started and DP is not going more than 95 mmH2O.

We are practicing to stop the pulse cleaning during raining season.

Thank you again for all your feedback's.

Take care
G.Rajesh
 
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