Condensing steam turbines- how to calculate its outlet conditions

[vinho]

Is there anyone who may explain how is handled the outlet pressure control at a condensing steam turbine under slidding pressure operation and mass flow rate. Which is the best model to describe this off design condition?

 

[rmw]

If your turbine is condensing, the outlet pressure is related to the approach temperature to the cooling water outlet temperature (and to some extent the condenser arrangement). The cooling water temperature determines the saturation temperature of the exhaust vapor and your condenser performance determines how close the vapor can approach the saturation temperature/pressure at the CW outlet of the condenser tube bundle.

rmw

 

[stgrme]

Turbine performance and condenser performance are interactive.

If the condenser already exists, you can use the performance curves for the condenser (generally, a family of curves for condenser pressure versus heat load with varying cooling water inlet temperature). If you don't have condenser performnce curves, you can calculate performance using formulae and data in HEI (Heat Exchange Institute) Standards for Steam Surface Condensers.

Turbine exhaust conditions are more difficult to calculate. If the turbine already exists, if it is a non-reheat type, designed for constant inlet pressure, and if you have a heat balance at full load, you can calculate the isentropic efficiency of the turbine. For sliding pressure operation, assuming no throttling of the inlet valves, you can apply the same isentropic efficiency to estimate the exhaust conditions. The expansion lines on an H-S diagram (Mollier diagram) will be parallel for sliding pressure opertaion.

Since the turbine performance and condenser performance are interactive, you will have to iterate between the turbine and condenser performance to reach a solution.

Best of luck!

 

[vinho]

Thanks guys. It was a very helpful and usuful reply. rmw, it was good shot and you confirmed what I tough earlier.

best regards