EFFECT OF LOW MAIN STEAM TEMPERATURE
EFFECT OF LOW MAIN STEAM TEMPERATURE
(OP)
One of Our Steam Power Plant Unit was in trouble. Originally the main steam temperature was set 540 C and the main steam press was set 170 kg/cm2. But, there was a problem. We reduced the steam temp setting to 515 C. After we reduced the setting of main Steam Temp, the turbine bearing vibration increased. Our Queston are:
1. Was Our action correct?
2. Is there any correlation between the main steam temperature and bearing vibration?
1. Was Our action correct?
2. Is there any correlation between the main steam temperature and bearing vibration?





RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
What was the type of vibration before and after the incident?
Did you experience any pressure drop or flow in the main header?
When the boiler recovered did the vibration change?
Did you notice any other physical parameter changes?
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
Is it enough to cause a problem? It depends on the turbine curves.
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
All in all, I am with UncleSyd in that not much real information was presented that would have allowed for any real type of analysis.
What type of trouble was the unit in that caused the decision to be made to reduce the inlet temperature? Which bearing (or is it all) is vibrating?
rmw
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
Just making a hypothesis with the few information passed on to us.
Initially you were dealing with superheated steam at 170 kg/cm2 (gauge I presume) at temperature of 540 °C. With these conditions the density of steam is 50.38 kg/m3.
Reducing temperature at 515 °C, keeping pressure constant at 170 kg/cm2 (gauge) density becomes 53 kg/m3 (a 5% increase). If the mass flow rate is unchanged, the steam velocity will increase, and this possibly could lead to bothers.
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
lowering the temperature increases the likelihood of wet steam in the exit and thus high bearing vib., so lowering the SH is not a good idea.
need to engage the TG supplier on the issue in advance
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
To ione's point, if anything, the inefficiencies created by the lowering of the SH would shift the tail end of the expansion line to the right somewhat and that would result in less moisture, not more as the end point climbs up along the 2-3"hg line.
It does as ione has noted reduct the overall delta h of the expansion line, hence requiring more steam flow for the same amount of power output.
What it does do is change the volumetric flow rate through all stages, and it is possible that that could have caused some deleterious effects. But without knowing which bearing....... who knows.
rmw
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
Not according to the expansion line drawn on a Mollier diagram. The moisture lessens, not increases with the efficiency loss as the slope of the expansion line decreases.
Hacksaw, that would be something that would work with a BP turbine as long as the exhaust pressure was above the saturation line. But BP turbines are not very common in steam power plants.
rmw
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
I ran a high efficiency turbine with very low outlet pressure and I hit two phase. Until we get exact conditions of outlet and turbine eff, we don't know for sure.
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
RE: EFFECT OF LOW MAIN STEAM TEMPERATURE
rmw