Frame 6B GE Gas Turbine Power Load Hunting During Fuel Changeover

It could be a number of things from the fuel management system, bad/miscalibrated sensors, poor/off-spec fuel, dirty fuel system, clogged/sticking control valves, poor maintenance practices, etc., etc.

To learn how to solve all those problems engage the services of a factory trained service engineer and look over his shoulder.

The thing I notice is that you do not state what the liquid fuel is. All liquid fuels do not have the same BTU content. You must use the liquid fuel that the turbine is designed for and the BTU content, viscosity, etc are critical. If you go to a different fuel or use a lower or higher grade of the same fuel, the settings will need to change. I have seen customers get into trouble by using a tank that has gotten old or has absorbed moisture. The first thing to due is test you liquid fuel to be sure it the the same that the software is anticipating and that it has not degraded. Call GE field service. They can help. They may seem expensive but they are worth it. You are wasting money trying to solve it on your own.

I see two basic problems:

1. Tripping on High temperature.

2. Hunting when changing over one fuel to another.

Problem 1 can be one or more of followings:

1.1 Temperature of inlet air more than designed. If this is the case, then Scrubbing inlet air through evaporator cooler and bringing temperature of inlet air to less than designed can solve this. (every 1 deg rise in combustion air is approx. 2.7 Deg in exhaust).

1.2 Rich air to fuel mixture - carry out analysis of exhaust for excess O2, and adjust air fuel ratio in the governor.

1.3 Poor combustion or atomisation of fuel - check your pumps and nozzles. Maintain if necessary.

1.5 High back pressure to exhaust. Make a simple water manometer and check pressure drop between outlet of flue gases from turbine to that at outlet of chimney and if more than specified - carry out correction.

Regarding Hunting:

2.1 Could be that there is sudden or too fast change and sudden change in LHV of two fuels is resulting in this. If the control is via PLC - then make proper program - supervising df/dt in the PLC and permitting rate of transfer - keeping Delta F and df/dt within limits.

2.2 Or if Grid Power is available - hunting in frequency may not be felt if turbine is running parallel with Grid of sufficient capacity during changeover of one fuel to other.

To tell you, I have not come across any Gas Turbine Generator set (only seen photographs in Diesel and Turbine Worldwide Manual or from a distance of 100 meters while driving my car in Delhi and passing by side of Power Plants in Inderprasth area). I found the problems interesting, ponder over these and got some reasons in mind - from my long experience in Thermal and Diesel Power Generation and put the view above, thinking these might be of some help to you.

Regards,

Ramesh