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# Steam turbine combined cycle flow rate

## Steam turbine combined cycle flow rate

(OP)
Hey all , I review a start up curve for a real steam turbine and it gives pressure vs load , what I understand is at a certain load , there must be a certain pressure at the inlet of the turbine , but what about the flow rate is there must be a certain flow rate at each load ?

### RE: Steam turbine combined cycle flow rate

For a steam turbine in a combined cycle application, the pressure at the turbine inlet is a function of the steam flow into the turbine. After start-up and initial loading of the steam turbine, the governing valves will be wide open and the power output from the turbine will be determined by the steam flow produced by the HRSG(s). Load on the gas turbine(s) will determine the amount of steam produced by the HRSG(s). In other words, the steam turbine load will "follow" the load on the gas turbine(s) and the pressure at the steam turbine inlet will be a function of the steam flow produced in the HRSG(s).

Best of luck!

P.S. Please note that the inlet pressure vs. steam flow curve is "theoretical", based on ideal (design) conditions. The "actual" curve is the result of tolerances in the manufacture of components and their assembly. Typically, the pressure shown on an inlet pressure vs. steam flow curve can vary by plus/minus five percent (5%). An ASME type performance test would be necessary to determine the "actual" inlet pressure vs. steam flow curve.

### RE: Steam turbine combined cycle flow rate

(OP)
Thank you , There are 3 hrsgs from 4 working each produce 100 MW , the load on the steam turbine is 98 MW and the inlet pressure is 70 bar , the bypass is open in this case and we are on " position control mode " , but on the start up curve , the steam turbine's load of 98 mw requires a pressure of 55 bar so why the pressure is 70 bar and don't follow the curve ?

### RE: Steam turbine combined cycle flow rate

What is the flow through the bypass - if indeed it is open?

### RE: Steam turbine combined cycle flow rate

With 3 of 4 HRSGs operating, an inlet pressure of 70 bar and the bypass open, it appears that the plant is still in a "start-up" mode rather than in the "normal operating" mode. The inlet pressure of 70 bar may be a minimum operating pressure for the HRSGs. In addition, this pressure may be required to allow the fourth HRSG to be brought into service. I suggest that you review the start-up procedures for the plant.

Best of luck!

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