Propane moisture analyzer issues

[Jack2010]

Hello to all,

I am having some issues troubleshooting a propane drying system. Normal operations through calcium chloride yields -60 deg F dew point propane. It seems that after experiencing a slug of moisture or some other contaminant, our on-line moisture analyzers are not reading correctly. The dew point has jumped from -60 deg F to +30 deg F according to the analyzers. All other lab tests shows the moistures to be around the -60 deg F mark. All analyzers have been re-calibrated and purged since the event and still continue to read high. As another check we ran the rough field check freeze bomb test and the propane flowed for over 3 minutes and showed no signs of freezing up. As a check I ran the inlet propane and the bomb froze up after 1 minute and 30 seconds which told me that the system is drying. But why are my on-line analyzers still reading high if the lab and freeze tests are showing good? Any help or ideas are greatly appreciated.

 

[ash9144]

Make sure the inlet filters have been changed out not just purged. Also check for low points that could be holding water.

 

[Jack2010]

The inlet filters have been removed and manually cleaned. All piping to the analyzers have been purged and drained of any liquids in the system.

Is it possible for any interference of some other compound giving false moisture readings? The anlayzers are panametric style with the calibrated crystal probes. All of the probes have been changed as well.

 

[ash9144]

Do they read zero on cal gas? Were these analyzers reading correctly before your water slug?

I'd still say to replace the filters. I've never known of analyzer filters to be successfully cleaned when measuring low concentrations like you are trying.

 

[JLSeagull]

You could have installation issues. Search the web for "moisture traps" along with online moisture analysis.

 

[Jack2010]

I am in the process of running cal gas. The analyzers were reading correctly before and showed a significant step change after the slug.

My main concern was, is it possible for some known upstream chemical addition or process change that others may have experienced before interfere with the moisture analyzer? Due to the nature of the step change in analyzer moisture readings and how multiple cross checks on moisture have shown very low moisture levels, I tend to think that the analyzer could be in bad order.

 

[ash9144]

Seems unlikely that there would be a contaminant introduced at the same time you had a slug of water. Also seems unlikely there would be contaminants in a propane stream which would show up as water. I don't recall what the panametrics actually measure but you can find out and determine what compounds may interfere with it.

I still say change out filters. I've seen similar issues before.

 

[JLSeagull]

The moisture sensor uses aluminum oxide. An optional thermistor can measure temperature; an optional strain-gage can measure pressure.

 

[dcasto]

the probes do have a life that can be shortened by direct contact with water or methanol.