Hi everyone,

GE 6FA - MARK V - DLN 2 - CC PLANT - NATURAL GAS FUEL.

I had read in some of the threads here regarding controlling exhaust temperature is achieved by Modulating IGV; means whenever the temperature reaches or goes beyond reference temperature, Speedtronic modulate IGV to achieve more air flow to cool the exhaust temperature (whether the turbine in speed droop or exhaust temperature control mode).

Now my query,

our GT 6fa Running in 91% of baseload with IGV Full open (86 DGA) In speed droop mode. Now if the exhaust temperature reaches turbine exhaust reference, then how it control the raising temperature with the IGV is in full open.

and if it Attains base load with temperature control mode, how it will be able to control the exhaust temperature. (IGV IS ALREADY IN full open position)...

and one more thing, If we start GT with IGV control mode ON( because of utilizing HRSG), up to which extent, the turbine with IGV temperature control (means when will IGV goes off automatically).

kindly do reply..thanks and regards,

 

I don't think you are quite understanding how Speedtronic works. FSR controls fuel and Exhaust Temperature Control controls FSR. Do you have a manual? I think you should read it.

 

jameelrahman,

DLN changes everything. When a GE-design heavy duty gas turbine has DLN combustors, IGVs are used to help control combustion reference temperature--and exhaust temperature control is secondary. In fact, IGV Temperature Control is always ON (it can't be disabled--not on any of the DLN combustor-equipped machines I've ever worked on anyway).

In DLN combustors, the fuel-air mixture is extremely lean--meaning there is almost too much air for the fuel. It is in fact, on the border of stable "combustion." GE doesn't like to say the fuel is burning--and, in fact it's not burning with a diffusion flame (the bright orange-yellow flame that emits UV like other stoichiometric combustion of fossil fuels emits). But, there is a temperature rise, and in my "book" that's combustion (burning).

When the unit is at or near Base Load and operating primarily in Premix combustion mode, again, the fuel-air mixture is very lean. And the definition of Base Load means the IGVs are at maximum operating angle and the actual exhaust temperature is equal to the CPR-biased exhaust temperature reference.

To unload the unit, the fuel has to be decreased--BUT, the fuel-air mixture is already very lean (and borderline unstable!). The ONLY way to reduce air flow to maintain the fuel-air mixture is to close the IGVs as fuel is reduced. That's the only "knob" to adjust air flow: controlling the IGV angle.

So, in order to prevent "overfiring" the machine, the unit operates continuously in IGV Temperature Control ON. I would venture to say that if your control system has a switch for IGV Temperature Control OFF, that, 1) it doesn't work, or, 2) there is some really special, unique sequencing in the Mark V for that turbine. Now the latter is possible--stranger things have happened, and will continue to happen. But, GE and the packagers of GE turbines tend to be pretty conservative when it comes to DLN and turbine operation and provide pretty standard sequencing. It is VERY common for HMI displays to have buttons on them that don't work, that shouldn't be there, and to even have buttons on them that weren't supplied by the packager. But, that's life with GE Mark V HMIs.

The IGVs are used to control exhaust temperature on units equipped with DLN combustors; they are used to control air flow. Fuel control is used primarily to control exhaust temperature when the IGVs are full open.

Hope this helps!

 

thanks CSA for your reply...

Could you please tell me what is the intention of Speed droop turbine control mode, means what it actually maintain during part load operation and what are the things, it has change.

 

jameelrahman,

The topic of Droop speed control has been covered SO MANY TIMES I have almost come to believe the site name should be droopspeedcontrol.com!

There is a 'Search' field cleverly hidden at the far right of the Menu bar of every webpage of the desktop version of control.com. The 'Search' function of mobile versions of control.com can be accessed under the 'Control.com' drop-down on the Menu bar. (It is recommended to use the Search 'Help' the first couple of times you use Search; the context is not like most search engines--but it is fast and powerful.)

Droop speed control is the primary fuel (or steam, for steam turbines; or water, for hydro turbines) control means for almost every type of prime mover governor for loads between zero- and Base Load for generator-sets synchronized to (paralleled with) other generator-sets on a grid. It is the way generator-sets provide power in a stable manner to grids with other generator-sets. It is one of two methods of controlling speed--and frequency--of generator-sets (the other being Isochronous speed control--which does not permit multiple generator-sets to be paralleled together stably).

AC (Alternating Current) power systems operate at a stable frequency (the better-run AC power systems, anyway), and frequency and speed are directly related. So, speed control is critical to generator-set operation. Droop speed control, again, allows multiple generator-sets to be synchronized together and all supply power in a stable manner.

If you want more information about Droop speed control, use the control.com 'Search' feature, and if you still have questions, we are here to help. We love to answer questions or provide clarification--but we don't like to respond to doubts. Doubt, by definition, implies distrust--and we are extremely trustworthy people here at control.com. (Take our word for it.)

Hope this helps!