Liquid fuel for gas turbine

[MortenA]

How well does "dual fuel" gas turbines work? Could a gas turbine work with normal fuel: a NGL in liquid state and for startup: diesel _or_ fuel gas.

 

[TD2K]

The only experience I had were Allison FT-4 which were a dual fuel gas turbine and my knowledge is pretty limited.

They were started up on diesel and switched over to NGL vaporized through exhaust stack coils. Every so often, they switched back to diesel as the NGL had trace amounts of heavy hydrocarbons that would tend to foul the fuel nozzles and give them problems with temperature spread, switching back to diesel corrected the problem (those suckers used a lot of diesel, can't remember the actual numbers). They were also set up to burn crude as a backup but I was never able to find anyone who remembered them ever doing it, other than perhaps during initial commissioning and verification years and years ago.

Some other turbines (smaller ones for power generation) started up and fired directed on liquid NGL rather than vaporizing it before using it as fuel.

Sorry, I know this isn't much help.

 

[rrhoyt]

Most 'modern' gas turbines with dual fuel capability can be switched automatically between either supply. The system is usually setup to transfer on loss of the primary fuel (e.g. loss of pressure). Also, most have the option to operate at a percentage of each fuel.
As always, Check OEM spec for particular turbines.

 

[abeltio]

FOR INDUSTRIAL TYPE UNITS (NOT AIRCRAFT DERIVATIVES)
Dual fuel capability is extremely dependent on the model and size of the unit. If we understand dual fuel as a primary fuel (usually gas) and a secondary fuel (usually liquid) that kicks automatically upon loss of gas fuel supply pressure.
Another type of dual fuel unit is if you have a starting/stopping fuel and a "running fuel" for normal operation (e.g. diesel #2 for start/stop and bunker C or diesel #6 for running) - if you have a trip on heavy fuel you have like 20 min to re-start with #2 before everything is clogged up by the heavy fuel that is cooling down inside the passages.

Regarding the 1st option of dual fuel capability... the transfer from gas to liquid is automatic upon loss of gas fuel supply pressure, but going back to gas fuel requires a manual selection from the operator...
Why is it so dependent on size and model?
With the higher end, dry NOx control units to return back to gas fuel operation it is usually needed to unload the unit until the flame temperature allows the change.
Standard combustor, "old technology" units do not present this condition.
An important part of the tuning is to achieve fuel transfers without big changes in load (due to the different fuel quantity required if the LHV of the fuels is too different)
Summarizing, old suckers are more robust to withstand real dual fuel capability...

Another situation with liquid fuel is that it MUST be exercised regularly (sometimes even once per shift) to avoid coking inside the fuel passages (even though the passages are purged with air)and also maintain all the parts of the liquid fuel system lubricated and avoid deposits.

HTH
Saludos.
a.

 

[MortenA]

Thank you all for your informative responces

Best Regards

Morten