Tripping of Gas Turbine Generator (GTG) on Failure of Extraction Fan

[norzul]

Hi,

We had discussion this morning on GTG protection. Is it common to trip a gas turbine due to failure of extraction fans?

Fyi, the GTG is located inside an ecoustic enclosure. There are 2 X 100% extraction fan (1 ruuning + 1 standby). I was told that if both the extraction fans are not working, this will triger the trip funtion of the GTG.

Just wonder, the sophisticated & very expensive GTG is dependent on these 2 small extraction fans? Makes sense?

Any experiences to share?

Thanks

norzul

 

[CESSNA1]

NORZUL:

What do the extraction fans do? Assuming they ventilate the enclosure of the GTG; if they fail then the temperature in the enclosure would rise rapidly. Dpeending on what else is in the enclosure (equipment, people, etc) this could be significant.

I suggest that you confirm that this is the case and try to find the logic behind it

Regards
Dave

 

[TPL]

The purpose of the fans is mostly safety related, hence the trip function.

By ensuring a continuous change of air in side the enclosure, small gas leaks do not become large pockets of potential explosion – larger gas leaks get picked up by gas detectors.

The continuous air flow helps to keep the enclosure temperature down. This will help ancillary pieces of equipment to survive longer (e.g. flame detectors, dampers)

You should have enclosure temperature detectors fitted to your installation. By lowering the enclosure temperature, the temperature sensors can pick up a significant change in enclosure temperature (possible leaks from cooling air supplied to PT or exhaust gas) at an earlier stage.

 

[norzul]

I do understand the purpose of extraction fan is mostly due to safety related but why do we need to trip the GT. Is it not adequate if just giving an alarm? and also rely on gas detector?

I guess in order for the explosion to happen, we need to have more than triple jeorpardy cases:
1) 1 normal running extraction fan fails
2) 1 standby extration fan also fails
3) The natural gas leaks
4) Temperature above auto ignition or there's ignition source
5) Alarm doesn't trigger

I don't know how fast the temp rise if both the extraction fails. In our case, the GTG is designed to be unmanned i.e. not normal for the people to be inside the enclosure.

Anyway based on your experience, is this kind of arrangement normal?

 

[rmw]

In addition to the safety issue due to fuel build up, there may be elecrical or electronic components that would be adversely affected by higher temperatures in the enclosure if the ventilation fans failed.

rmw

 

[yates]

For starters, it seems odd that the GT trips if both fans are not working.(Or do you not rather mean if neither fan is working ?) A standby fan will substitute for breakdown of the main fan, and even then why go through all the worries of wear and tear on the turbine for unnecessary trip. I assume the GT is unmanned so temperature rise in case of fan breakdown does not probably warrant turbine trip, but normal shutdown. Trips are to be avoided at all costs, as each trip is equivalent in hot gas path part wear to many hours normal operation.

 

[jsummerfield]

Have the GE, Solar or the appropriate manufacturer explain their package interlocks. HVAC issues could even pertain to the inability of someone to open the door due to pressure imbalance. Heat and explosive gas mixtures or other toxic issues could apply. The turbine interlocks are usually established by the manufacturer.

John

 

[briand2]

Assuming the fans are there at least in part to ensure dilution of any gas leaks, then your "triple jeapordy" is really just the "fire triangle" - if you have fuel, oxygen and a source of ignition then you will get a fire.

A lot of people believe that as long as you exclude any one of these three (e.g. the source of ignition) then safety is assured. However, in the UK, it is generally accepted that if you have present both fuel AND oxygen, then God will provide a source of ignition!

Brian

 

[abeltio]

norzul,
the trip function associated with the fans depends on what are you protecting.

some compartments are pressurized above ambient pressure, some are maintained below ambient pressure... what kind of fuel are you using?

if the fuel is toxic (like syn gas) then surely the oem added a trip in case the ventilation system fails.

if the concern is temperature rise, then the failure of the 2nd fan should alert the operator and a normal shutdown initiated when the compartment temperature reaches the alarm level.

if the concern is the presence of hazardous gases then the haz gas detectors should detect the condition and initiate the appropriate protection actions, e.g. a trip.

HTH





saludos.
a.