we have steam Turbine with alternator of following Spec. 2 MW, 9000/1500rpm, inlet Pressure 38 Barg, back pressure 1.5 barg.

we need to operate this turbine on 0.1 Bar back pressure, are this safe and what are the disadvantageous to reduced Exhaust pressure as low 0.1 Barg?

 

Definitely the OEM of the steam turbine should confirm whether this is possible or not, but as a starter here are some points:

1. Reducing the pressure after the steam turbine and not chaging anything else (eg steam flow inlet to turbine) will result in more shaft power output. Is the turbine/gearbox/alternator assembly designed for this additional power?

2. Reducing back pressure will result in a change of axial forces from original design. Is the steam turbine's axial thrust control mechanism capable of taking up the additional forces induced in it?

3. You have not stated whether you have steam extractions from the turbine. If yes, these will also be affected, with the possibility that if these are uncontrolled extractions, the new pressure will be lower than original design.

4. Lowering the back pressure will result in lower steam temperatures at the last stages of the turbine. Are you sure that the new dryness fraction of the steam in these stages is still within the allowable limits. If not you are increasing the risk of erosion from possible water droplets that may form on the steam turbine blades due to the lower temperatures.

Are you trying to convert the steam turbine from a back pressure one to a fully condensing unit? If yes then as I said earlier, the OEM should be consulted.

 

answer of your point are as,

1. turbine operated independently, no chance of increase in load,

2. please clear us how we can calculate axial load, and confirm it is in safe range.

3. there is only back pressure turbine, (no extraction)

4.the sufficient deg. of super heat available in exhaust steam.