GT trip during Fuel Change Over


Thread Starter

s das


We are having 3 frame 5 gas Turbines each 20MW mark V control system. Recently one more new 20MW mark VI control Gas Turbine we added due to our refinery expansion. Both GTs are running on naphtha fuel & HSD is kept as standby fuel. HSD line is always in charged condition, where as naphtha we are taking from separate line. One three-way Valve is located at the junction of Both naphtha & HSD fuel line to supply fuel to the main fuel line to GTs.

Scheme is as below:

Individual Fuel line = 50m filter--naphtha pump--accumulator(50lt)--Control Valve--filter SKid--3WAY VALVE---THEN SHUT OFF VALVE to GTs

Whenever we are giving fuel change over command (naphtha to HSD or HSD to Naphtha), For fully C/O it's taking 13Sec to 15 Sec. In the mean time Fuel Pressure is getting reduced to < 1.5kG/cm2 & GTs are getting Tripped on low liquid fuel Pressure. We tuned our existing Naphtha & HSD Control Valves, also provided recirculation Line. BUT the above said problem still Persists, even in the newly commissioned Mark VI GT. So now we are afraid of Fuel change Over during Emergency condition also. From the date of commissioning till now > 20 times GTs has got tripped on Fuel change Over.

In order to avoid the problem sir,

Can we use an accumulator as a pressure compensator after the 3-Way transfer valve?

Shall we put one accumulator after the 3-WAY Valve & before the SHUTOFF VALVE? Normally for that 10 Sec Fuel requirement will be 25lt. Please note that already one accumulator(50 lit) is connected at the discharge end of fuel Pumps, which is needed only during Fuel Pump change Over.OR Can we put one accumulator of 25-35 lt capacity. Or can we shift that existing accumulator to this new place.

I m eagerly waiting for your reply

Thank You