what is the purpose of 96GN-1/2/3 transmitters in GE 9FA DLN2+ machine?

 

I was hoping someone else would respond to this one.

Are you having some problems with these transmitters?

Are you having some trouble understanding what these transmitters do in the sequencing?

Because you should be able to see how these transmitters are connected on the Fuel Gas Piping Schematic drawing (P&ID).

They are "described" in the Device Summary drawing.

So, what is it specifically that is causing you to have doubts?

 

in device summary, it is mentioned as "gas fuel nozzle pressure transmitter".

as per PID, tappings are taken from CPD transmitter line and gas manifold header pressure.

gn-1 - differential pressure of diffusion manifold and cpd
like wise gn-2 for cpd and pm1 & gn-3 for cpd and pm4.

last month only our unit commissioned and i want to know what it is doing in the operation sequence?

 

These are actually differential pressure transmitters, and one of the functions they normally provide is to ensure that there is a proper pressure differential on the gas manifolds during operation. Depending on the configuration of the turbine (single fuel, dual fuel, etc.) there can be reverse flows of hot combustion gases through gas manifolds during various combustion modes. These transmitters are usually monitoring the differential pressures to ensure this isn't happening, that any purge system is working properly.

You would need to look in the application code of the Speedtronic panel to see exactly what kinds of protection these transmitters provide, whether they just enunciate an alarm on low differential pressure, or initiate a shutdown on low differential pressure, or a trip on low differential pressure.

These transmitters were also used many years ago to monitor/calculate fuel flow-rates and fuel flow-rate differentials. It was a very complicated scheme, and I believe it has since been abandoned in new unit configurations, but there may still be some units out there with the systems and sequencing.

But, to be sure how any I/O is used in the operation, protection and/or monitoring of the unit at your site, you need to look at the application code running in the Speedtronic turbine control panel. (I'm presuming the Speedtronic is either a Mark VI or a Mark VIe, since you say it was just commissioned. If it it's a Mark V, it would be the sequencing (Control Sequence Program, or CSP) which is running in the Mark V.)

 

These transmitters are used by the DLN tuning specialist as a tool to determine the fuel flow proportion out of the PM2 and PM3 fuel nozzles.

They won't trip, shutdown or even runback a unit.

 

thanks for your reply....

ours is a mark vie control system. i checked only the alarm list, but in that nothing is there. but during base load (premix operation- only PM1 and PM4 gas nozzles will be in service and D5 line will be purged with air), CPD is maintaining at 14.9kg/cm2 and gn-01 = -1.6kg/cm2 (negative value), gn-02 = 1.5kg/cm2 and finally gn-03 = 3.5kg/cm2 showing. whether gn-01 value is right or not?

 

I had the DLN 2.6 system in mind when I responded. Sorry it was late as you can see from the time stamp of my original reply. I don't know what those pressure readings should be but if you look at your device summary in the O&M manual it will tell you what it is comparing. For example, 96GN-2 in the DLN 2.6 system would compare CPD to PM2 manifold pressure. You should be able to find manifold pressure reading (maybe labeled as pressure at the outlet of a gas control valve) on a gauge panel in the gas valve compartment or somewhere near it.

 

>the purpose of these three 96gn-1, 2, 3 transmitters is to maintain a positive differential pressure between the gas and air inside the combustion chamber. normally gas pressure should be more than the air pressure which is inside the combustion chamber. otherwise there is a problem of back flow

 

Surya,

How do these transmitters maintain a positive differential on the manifold vs. combustor liner pressure?

Some combustion modes do not have gas flowing through the manifold(s).

Does a low dp activate purging somehow?

Are these transmitters now part of this "compressorless purge" sequencing that's being used recently?

It's possible they could be used in a control scheme to maintain a positive dp to prevent backflow, but it's not clear how the transmitters themselves would do that. Monitoring the dp, yes. Measuring the dp, yes. But controlling the dp, that's kind of a stretch.

Can you provide some more information, please?

Thanks!