I am actually looking foe GE made gas turbine of 9E series. If I use 2 similar gas turbine of 125MW range of that series and 1 steam turbine cycle, what will be the possible problems in that kind of installation? What will be the maximum rating of steam turbine I can use for such a plant? Is Supplementary fired Heat Recovery Steam Generator is economical here?

 

Suman,

The only question we can possibly answer based on the information provided is the one about how much electricity can be generated from a steam turbine in combined cycle operation.

The generally accepted guideline is that a steam turbine can be used to generate approximately 0.5 MW for every 1.0 MW of gas turbine generation. So, roughly half of the total gas turbine generation.

Some boilers are more efficient than others, but not significantly more than this without auxiliary firing.

And, in my experience, auxiliary firing does NOT usually produce sufficient steam generation to pay for the cost of the fuel to produce the additional steam. Now, that's only my experience; perhaps otised, another respected contributor to control.com, can add more additional information about when it would be beneficial, but in my experience once plants calculate the cost of the additional generation they usually don't continuously use auxiliary firing. They only use it when it's economically advantageous, say during high demand (peak) periods.