TURBINE INLET PRESSURE ISSUES

[granttown]

90 MW GEC Alsthrom turbine with inlet pressure issues. It seems every time the unit is cycled up and down the inlet pressure gets worse, design of the unit is 1350 but in years past we have always maintained 1280 to 1290 throttle prssure. As it stands at this point to run 80 net with a back pressure of 2.15 our throttle pressure is running 1375 to 1385 which gives us a sh 3 outlet pressure on the boilers just shortly under the safety lifting pressure 0f 1460. Our gland steam system has been overloaded for some time now, but since the last unit start the throttle pressure has come up another 10 to 15 pounds and the gland steam dump percentage has backed off as if the steam is not getting to the chest and to the bleads on the govenor valves. Large amount of vibration and high pitched noise at the left turbine stop valve.

 

[byrdj]

I'm confussed, I guess by the differance in terminology.

I think you are saying the boiler pressure had to be increased to obtain less MWs.

are you positive the control (governor) valves are going full open.
for the units I've seen, the stop valves are sized so that 100% can be passed with one closed, however real world is the flow would be reduced slightly

 

[JJPellin]

I am also confused. This manufacturer and model are unknown to me. I am not sure what pressures you are referring to. I don't know what units you are using on the pressures you provide (all in psi?). A better description will yield better responses.

Johnny Pellin

 

[granttown]

Im not saying the boiler pressure has to be increased, it is increasing as the throttle and first stage pressures of the unit increase. I mispoke or mistyped when I stated that the design throttle pressure was 1350 PSIG, its actually 1315 by design. In years past we have ran 1285 to 1290 on the throttle pressure with one out of the 4 governor valves (being D) actually throttled. Our first stage pressure would run in the area of 965 to 970 PSIG now its running 1020 to 1030.

 

[byrdj]

if first (or any stage) pressure increases with loss of MWs, there is a restriction down stream (deposits or damage)
there should also be a reduction in feedwater flow
or
the increase in stage pressure indicates an increase in mass flow. if the mass flow goes through the turbine, there would be an increase in MWs. if the increase in flow is due to erision and opening of the steam path, the heat rate will suffer.
if there is a loss of MWs with the increase flow, then there would be a loss of mass from the steam path, possibly into feedwater heating

 

[dougarthur42]

Maybe you should check you actual inlet valve position. We also run an ahlstrom unit configured much the same. We have had at time the cams on the inlet valve slip so the inlet shows 85 to 90 % open. but they are actually only about 70% opened. Our design inlet pressure is 1340 psi and we run around 1250 psi right now but we control to this pressure with any where from 70 to 80 % inlet position. we are not inlet valve limited we can keep our pressure whereever we want.If your D valve works like our than it may be throttled. Our D valve opens when our inlet valves reach 91-92 % open then D opens to by pass steam around the inlet steam chest to a secondary chamber. this allows our inlet to control well. I have more info if needed