3 replies to this topic

[siraj paracha]

We have a steam driven turbine with steam inlet pressure of 39.6 kg/cm2 and exhaust pressure of 4.5 kg/cm2. It is coupled with a pump which is used to deliver steam condensate from common condenser at around 100 Tph. Pump is submersible type with suction pressure of -0.68 kg/cm2 and discharge pressure of 6.5 kg/cm2.

Level of condenser is controlled by level control valve located at d/s of pump. Normally it control the level at around 45 % valve opening.

Turbine rpm are normal running at around 2790.

 

From last few days we have been experiencing variation in turbine rpm of around 100 to 150 rpms, with the increase in speed of turbine; variation reduces but after some time it again appears and the problem persist. Also initially when the level control valve was put on manual mode from auto turbine variation stopped but as soon as it was put on auto, when ever opening of valve  increases above 55 % variation in turbine rpm again appears.

 

We have checked the TTV of the turbine, no abnormality observed. Preventively its oil was replaced. Also we have checked the turbine in decoupled condition and it shows no variation, but in coupled condition and with level control valve on auto with more than 55 % opening; turbine shows variation in rpm and slowly level increase in condenser starts which causes higher opening of level control valve and difficulty in level controlling.

 

Turbine remains smooth if the level control valve opening is around 45 % with valve on auto mode.

 

I need to ask that if some body can tell me that why turbine is showing variation in rpm if level control valve opening increases beyond 50 % where as around 45 % turbine remains smooth. what could be the possible problem.

[Bobby Strain]

It appears to me, given the operation you describe, that the turbine is not delivering enough power required for higher condensate flow. This could be caused by deposits on the turbine blades, or damage. You should be able to check efficiency by monitoring turbine inlet and discharge conditions. And observe the governor valve position. Otherwise it can be a pump problem, but this is less likely. I presume that the pumps have operated OK in the past. This is not a new installation is it?

 

Bobby

[siraj paracha]

Turbine inlet and discharge conditions are similar to that of before. No such change observed which we have analyzed. Turbine capacity valve was also opened further by 25 % but variation is as such. One more thing is that when condensate load increases this phenomena is more prominent like during nights or early morning when CW temperatures are low and condensate load is less, turbine variation is minimum but during day times this variation increases. 

 

I think pump has problem of losing flow at higher loads, what do you reckon.

Pump is submersible type, is there any possibility of internal bypassing or any seal leakage with in the pump?

 

Thanks

[siraj paracha]

No its not a new installation. We have been running with this pump since long. We have also increased its impeller size in past. But as recently we have carried annual turnaround of Plant and currently Plant is running at higher loads i.e. 120 % of its design.