Does the "humming" or slight vibrations in the can annular combustor baskets effect the flame profile of gas turbines? And can the disturbances in flame profiles lead to abnormal behavior of gas turbine at specific speeds that they trip the turbine on spread?

 

Napster225,

Yes.

You mentioned tripping on high spreads at specific speeds (interpreted to mean speeds less than rated speed); the combustion monitor (which trips the turbine on high spreads) is not usually enabled until the turbine reaches 95% or 100% of rated speed. This is true of most GE-design heavy duty gas turbines driving generators which should operate at a relatively constant speed when synchronized to a grid with other generators. Two-shaft machines, which usually operate at varying speeds, have a slightly different control configuration for enabling the combustion monitor (usually based on LP speed).

If the fuel/air flows to the individual combustors are not similar, or there is some problem with the atomization of fuel (liquid, or gas!) in particular combustor or combustors then that can cause dynamic pressure pulsations which can sound like "humming" and lead to spread problems. Also, if water or steam is being injected into the combustors for NOx emissions reduction and the flows into the individual combustors are not virtually identical this can also cause dynamic pressure pulsations and flame instability.

So, it's likely the "humming" sounds you hear are the result of flame instability which would also manifest itself as spreads in the exhaust temperature readings.

If you could describe the turbine, turbine control system, and the problem(s) you are experiencing (speed/speed range; Process- and Diagnostic Alarms before, during, and after the "humming"/spread event; fuel being burned; type of combustors (conventional diffusion flame or version of DLN system)) we could probably help. If the turbine is dual fuel (natural gas/distillate), also please tell us that. If this problem just started, please tell us if it started after a maintenance outage, or after a trip from load, etc.