fuel flow in CT

R

Thread Starter

randy

Let us say we want x no of liter / min fuel flow for certain load conditions. Valve characteristic determines valve opening vs fuel flow. do we define characteristic of control valve in the control system to match what we have in the field, for fine adjustment? How do we measure CV and Importance of it? How fuel flow trimmer functions?
 
The concept of Cv has been covered many times before on control.com. I believe you can also find some information about Cv and how it's determined on other sites, such as www.wikipedia.org.

In my experience, the Cv of a valve is something that is designed and built into the valve and is specified by the manufacturer.

What kind of gas turbine and control system are you referring to?
 
any gas turbine, I want to know how fuel demand is matching with required fuel flow, can be oil or gas.
please help.
 
Most gas turbines use some kind of speed control, during start-up/acceleration or during loaded operation, so fuel is controlled in relation to the speed error either trying to minimize the error or in proportion to the error (depending on the type of speed control--which varies with manufacturer). Some gas turbines have an upper limit on speed control, called exhaust temperature control, or temperature control, and in that case fuel is controlled to make the exhaust temperature equal to the exhaust temperature reference.
 
randy,

This is something many people have a very difficult time understanding. They assume that the microprocessor-based gas turbine control system is calculating the amount of fuel required for the amount of air flowing through the machine to produce the desired power output.

But that just isn't so. I have never even seen a gas turbine (other than in a test condition) fitted with an oxygen sensor or accurate air flow measurement equipment. Even fuel flow measurement isn't very accurate; it's only as accurate as it needs to be for the purpose it's being used for--which is sometimes, just for monitoring and never for load control,

New machines are using something called MBC, Model-Based Control. This attempts to compare actual machine operating conditions (based on the instrumentation installed on the machine--which, again, don't usually include oxygen sensors, etc.) to an approximation ("model") of how an ideal turbine would operate under the current conditions and then make some minor adjustments and/or alarm the operator that something might be amiss. But, this is all based on calculations and simulations and still does not greatly affect how fuel flow to the turbine is being controlled.

Most digital, microprocessor-based turbine control systems were built to control fuel flow in the same way as older analog and even mechanical turbine control systems controlled fuel. And that never included accurate calculations of actual fuel and air flows versus power output.

Never.

Some turbine manufacturers have much more complicated control algorithms and schemes than others. But, in the end, Droop- and Isochronous Speed Control, and Acceleration Speed Control, are the real methods that control how much fuel is being admitted to the turbine.
 
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