Hello all:

I am trying to find physical location of the specific humidity sensor/transmitter for a G.E. 7FA gas turbine, I have been looking at the instruments diagrams but I have not found it yet.

The only piece of information I have found so far is in the TC2Krept file, which is:

GCP 5390 96RHTBB004 <R> TBQB 049 VDC4QH 96RH-1 CMHUM HUMID Specific humidity
GCP 5391 96RHTBB005 <R> TBQB 050 VDC4QL 96RH-1 CMHUM HUMID Specific humidity.

I would appreciate if someone can help me find this device.

Thank you.
Antonio.

 

It should be on the "back" of the vertical inlet duct, just above the Turbine Compartment roof.

Or, it could be on either side of the vertical inlet duct just above the slanted portion that narrows down to the bellmohuth (the axial compressor inlet).

Or it could be on the vertical inlet duct just above the Generstor Coupling Compartment

Or, it could be on either side of the horizontal inlet duct just above the generator.

It's usually behind a small "cube"-like box which is bolted to the outside of the inlet duct, and there will be a piece of conduit running into the bottom of the cube.

Hope this helps. Please let us know where you found it!!!

 

Thanks a lot for the information, sensor is located above the gas turbine roof, @ left hand side if you are looking from the turbine to the generator. And indeed, it is hidden inside a metallic box with no tags/labels on it.

Just in case someone else needs to know, this sensor is connected to a dewmaster series DM200 analizer (protimeter brand) located on the right hand side of the Mark V panel in the PEECC module, which sends the humidity measurement to Mark's V, R core through TBQB's 49 and 50 pins.

Once again, thank you for your help.

Best Regards.
Antonio.

P.S. I think, as a suggestion, that it would be great if we could upload pics in the posts, it would make things clearer.

 

Thanks a lot for the information, sensor is located above the gas turbine roof, @ left hand side if you are looking from the turbine to the generator. And indeed, it is hidden inside a metallic box with no tags/labels on it.

Just in case someone else needs to know, this sensor is connected to a dewmaster series DM200 analizer (protimeter brand) located on the right hand side of the Mark V panel in the PEECC module, which sends the humidity measurement to Mark's V, R core through TBQB's 49 and 50 pins.

Once again, thank you for your help.

Best Regards.
Antonio.

P.S. I think, as a suggestion, that it would be great if we could upload pics in the posts, it would make things clearer.

Hello,
Thanks for your clarification. I am curious that why these RH sensors are relocated after Evap coolers. According to my observation the relative humidity of ambient air changes after passing through Evap coolers. Then the relative humidity read by sensor is not ambient air humity then what is the purpose of it.

 

The sensors are measuring the relative humidity of the air entering the axial compressor--not just the ambient humidity. If the evaporative coolers are increasing the humidity of the air entering the axial compressor, placing the relative humidity sensor in front of the evaporative coolers will not include that added moisture in the calculation.

 

The sensors are measuring the relative humidity of the air entering the axial compressor--not just the ambient humidity. If the evaporative coolers are increasing the humidity of the air entering the axial compressor, placing the relative humidity sensor in front of the evaporative coolers will not include that added moisture in the calculation.

Dear CSA,

I am still wondering what is the use of 96 RH.
I have read some where that it would help in calculating the injection ratio so what is the reason behind this . Or there are some other reasons also.

 

syed taha ahmed,

Primarily, humidity sensors are used on GE-design heavy duty gas turbines when water- or steam injection is used for NOx emissions reduction. Even some machines with DLN (Dry Low NOx) combustion systems that burn both gas fuel and liquid fuel may use water- or steam (usually water) injection for emissions reductions.

The amount of airborne moisture (humidity) will affect the amount of water or steam required to reduce NOx emissions. More humidity means less water is required, and less humidity means more water is required. This is important because the water used for water injection or to produce the steam for steam injection must be boiler-quality water--meaning it must be treated water (demineralized at a minimum). AND, when water or steam is injected into the gas turbine it leaves the gas turbine through the exhaust, into the atmosphere. Which means that water or steam is lost and gone forever, so it has to be continually sourced and treated, which in today's world can be very, very expensive. So, keeping the injection rate as low as possible while maintaining the proper NOx emissions is important to the profitability of the plant.

Humidity sensors are also used when inlet air heating is necessary for anti-icing to protect the axial compressor inlet during low ambient temperature situations where the inlet air has a high moisture content (humidity)--usually from an un-natural source of humidity such as an evaporative cooling tower plume which gets drawn into the turbine/compressor inlet, or a large settling pond or evaporation pond nearby.

Lastly, humidity sensors have even been used as part of the calculation of turbine firing temperature for emission combustion mode switching purposes. I don't think that's common any more, but it was used for a few years in the early days of DLN combustion systems and control schemes.

Hope this helps!