3 replies to this topic

[ali]

Hello Dear friends,

I have got a problem with vacuum pressure transmitter. The pressure transmitter near the ejector of distillation tower is always fluctuating, while on the downstream of this PT there isn't any fluctuations. The pressure produced by afore-mentioned ejector is around 2 KPa. The pressure on top and bottom of the vacuum distillation tower is 8 and 14 KPa respectively.

[djack77494]

Ali,
Ypu must pay careful attention to the details of how the instrument is hooked up. When measuring such low pressures, any small interference will be significant relative to your measurement. What I would be most concerned with is moisture. If there are any spots in the impulse line (the tubing between your column's overhead line and your transmitter) where moisture can accumulate, a significant error can be generated. Even if the impulse line slopes continuously from the transmitter to your process, which it should do, if the diameter is too small then small slugs of water could accumulate and invalidate your readings. This would be due to the water's surface tension. I cannot comment on the short term fluctuations you are experiencing. If you think they may be real, contact the vendor of the ejectors to resolve.
Good luck,
Doug

[ali]

Ali,
Ypu must pay careful attention to the details of how the instrument is hooked up. When measuring such low pressures, any small interference will be significant relative to your measurement. What I would be most concerned with is moisture. If there are any spots in the impulse line (the tubing between your column's overhead line and your transmitter) where moisture can accumulate, a significant error can be generated. Even if the impulse line slopes continuously from the transmitter to your process, which it should do, if the diameter is too small then small slugs of water could accumulate and invalidate your readings. This would be due to the water's surface tension. I cannot comment on the short term fluctuations you are experiencing. If you think they may be real, contact the vendor of the ejectors to resolve.
Good luck,
Doug

Hi Dear Friend,

I appreciate your reply. I have to added that there is still another problem I have overlooked. The pressure observed adjacent to the ejector is usually more than the pressure away from ejector.
thanks

[paulo]

Dear Ali

Steam jet ejectors are static equipments.
If you disconnect the ejectors from the systems and test them, and even this way the suction pressure fluctuates, it may be a motive steam problem (motive steam pressure is going up and down) or a cooling water problem ( more or less water, affecting the condensation temperature and at the end the suction pressure).
Regarding the motive steam, you should also check if the orifice nozzle is not clogged.
Hope this helps.

Regards
Paulo