Inability control LP and HP steam on Back Pressure Turbine

[oresakri]

Hello,
It is observed that on a back pressure turbine we cannot control extraction and exhaust pressure. Particularly when extraction pressure is out of control exhaust pressure is stable. But when extraction pressure is in control ιt is observed oscillations on both pressures. Any ideas what would cause it? We use a digital turbine control system

 

[byrdj]

I don't really know stage pressure control schemes. However if you could provide a schematic showing valving, etc.

My number 1 guess when "control" oscilations occur is worn and sticky mechanical valve gear.

maybe the rule "One Valve can only control ONE variable" is trying to be broken

 

[ScottyUK]

Sounds like a poorly tuned loop or a rapidly varying extraction flow which exceeds the capability of the hardware to regulate it. Have you got any trends of flow and pressure data from the DEH system?

 

[stgrme]

In general for an automatic extraction, non-condensing (back pressure) turbine, the back pressure is controlled by a device downstream of the turbine exhaust rather than by the turbine.

Variations in the extraction pressure may occur if the extraction flow exceeds the capability at the operating throttle flow. Check the extraction performance map (or performance curves) for the turbine to determine the limits on extraction flow for various throttle flows.

Best of luck!

 

[waross]

A de-super heater may be used to supply steam in excess of the capability of the turbine.
A de-super heater will also supply low pressure steam when the turbine is out of service.

Bill
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