Hello there

We have a GE frame 6B gas turbine installed at our plant. just wondering if someone can help to know the maximum temperature/pressure of the following:

Atomizing air into compressor (accessory driven)?
Atomizing air outlet compressor (accessory driven)?
Atomizing air output pressure (after AA compressor)?
Maximum air temp into pre-cooler/heat exchanger?
Maximum air temp outlet pre-cooler/heat exchanger?

Hope to hear from you

Thanks

 

hassanj,

The answer given presumes a typical GE-design Frame 6B heavy duty gas turbine with a centrifugal Accessory Gear-driven Main Atomizing Air Compressor (the most commonly used compressor was manufactured by Atlas-Copco), and a water-cooled Atomizing Air Precooler with a Robertshaw (or similar) temperature regulating valve, similar to what has been the standard for nearly thirty years.

> Atomizing air into compressor (accessory driven)?

Should be 225 deg F, under normal running conditions (approximately 20-30 minutes after reaching FSNL. This temperature value is chosen to prevent moisture condensation in the cooler, which if carried over to the Main AA Compressor can cause severe damage. The temperature should not be above 275 deg F for any appreciable length of time when the unit is at rated speed as excessive inlet temperature will also cause severe damage to the compressor. The temperature is to be set/adjusted using the AA Precooler temperature regulating valve (I believe its designation is VTR2-1, but I may also be wrong--I don't have any P&IDs to verify that with at this writing) when the unit has reached rated speed. The Robertshaw temperature-regulating valves are very slow to respond and can take as much as one to two hours to adjust properly (AFTER ready the manufacturer's instructions as the adjustment is NOT intuitive.) High AA Compressor Inlet Temperature alarms during starting and acceleration <b>ARE NORMAL</b> and to be expec even when the temperature-regulating valve is adjusted properly! It's a characteristic of the valve (it's trying to get the cooler outlet temp to 225 deg F when then unit is not running (prior to a START) so it has shut off the flow of cooling water to the cooler. When the unit is being started it can take 30-45 minutes for the temperature-regulating valve to start controlling the air temperature properly when properly adjusted. TOO many people crank down on the valve's manual operator trying to prevent the alarms on start-up--resulting in air that's too cold when running and moisture condensation and eventual Main AA Compressor damage.)

> Atomizing air outlet compressor (accessory driven)?

Not controlled nor normally measured. Some machines do have a thermowell on the outlet of the main AA Compressor where a temperature gauge or temperature transmitter or T/C could be installed. But it was not deemed a critical value for decades.

> Atomizing air output pressure (after AA compressor)?

Usually on the order of 1.2 times CPD (absolute) when running on liquid fuel; about 1.1 times CPD (absolute) when running on gas fuel for gas-distillate machines. The pressure varies with CPD (regardless of fuel).

> Maximum air temp into pre-cooler/heat exchanger?

That would be stamped on the nameplate of the cooler shell, and should not be higher than Axial Compressor Discharge Temperature (CTDA). And if I recall correct CTDA is about 700 deg F or thereabouts when the IGVs are fully open and then unit is at Base Load.

> Maximum air temp outlet pre-cooler/heat exchanger?

Again, this should be about 225 deg F, maximum, above the saturation temperature to prevent condensation of moisture in the cooler which can carry over to the Main AA Compressor and cause severe damage to the compressor.

You should refer to the P&IDs for your unit, as well as the Device Summary, and the System Descriptions in the Instruction Manuals provided with the unit for information like this for your particular machine.

By the way, except on newer machine with newer AA Temperature-regulating valves, none of the parameters are controlled by the Speedtronic. In fact, on many machines most of the parameters are not even monitored by the Speedtronic; a human operator has to visually look at gauges and adjust the temperature regulating valve to achieve these conditions. Newer machines have transmitters to monitor some parameters, and a pneumatically-operated temperature regulating valve which is positioned by the Speedtronic. The AA Compressor discharge pressure is a function of CPD and orifice sizes, including the fuel nozzle AA orifice size; so it's not adjustable or controlled by the Speedtronic or any other throttling/adjusting device.

Hope this helps!

 

Thanks CSA, much appreciated.

Hassan