Effects of low temperature steam to a Turbine Generator 2

[crawfishdaddi]

Due to increased production rates at our cogen plant, we have been sending alot of low superheated steam to one of our turbine generators. The design parameters for the inlet steam to this GE turbine are 540 PSIG at 750F. We have been sending steam as low as 680F recently and I wanted to know the possible effects this could have internally on the turbine (i.e. blade corrosion or possible failure).

Thanks,
C.F.D.

 

[marada93]

I'd say minimal or no adverse effects. Going from 750 to 680 F on inlet steam temperature drops superheat at the throttle from approx 270 to around 200 F. (provided the pressure remained at 540 psig)

Most turbine manufacturers bottom line is a minimum of 100 F superheat before admitting steam to the turbine. This to guarantee superheat throughout the turbine blade path and exhausting the turbine with a minimum left.

As long as the turbine temperature change is happening very rapidly (say over 10 F / min) you'll probably be fine.

 

[marada93]

Correction to my last post...

The last sentence shoud say- "As long as the turbine steam temperature ISN'T changing to rapidly, etc.

 

[ilan7]

crawfishdaddi - That's New Orleans isn't 't???
To the turbine. I assume the pressure is also dropped, in order to stay at the same degree of supperheating. Check the emount of water drainind from the stages drainage. If it is the same or less then it was with the higher temp. means you'r OK.

 

[Trublu97]

If the turbine is exhausting extraction steam (back pressure turbine) then the impact will be zero (as far as the turbine is concerned )as long as the extraction steam temp/pressure meets the system's requirements. In my experience (paper mill, steel mill, food) the steam extracted has always been superheated but I refrain from saying there are no applications where saturated steam is extracted because I don't know for sure.

If you continue to lower the stm inlet temp at some point you will not meet the operation's minimum steam press/temp requirements. Check the exhaust stm temp to see if it has lowered.

If your turbine exhausts to a condenser then you will have wet steam at the L-0, L-1 blades. Typically, you will have condensate erosion on these blades and will have wet steam even under normal conditions. Lowering the inlet temp will make this normal expected condition worse, but not to a point that would accelerate the wear of the last stage blades or cause a forced outage (IMO). These blades are designed to operate with wet steam and will have stellite inlays in the front edge to reduce erosion.

During shutdowns I inspect the L-0 blades for wear to estimate turbine repair scopes and have data points for blade wear. You should be able to access the exhaust hood though a man hole cover (assuming the turbine is not really small) and you can see the full blade profile of the last stage.