7 replies to this topic

[CMangesh]

Dear all,

We are facing high dew point issue in instrument air.

Due to high dew point we changed desiccant which was four years old. Desiccant is air regenerated type 4mm size. following items are checked to find out root cause.

1) prefilter of desiccant

2) compressor side filters & moisture traps.

3) Regeneration cycle of 4 minutes.

 

Still with new desiccant we are facing high dew point issue. After replacing of desiccant only one day dew point was -35 deg. C. after that it drops to -5 deg. C.

 

If anyone  have more information or anything to be check please share.

Thanks & Regards,

[manojkaila]

Dear,

 

1 Check your air consumption. If air consumption increase suddenly this may be also problem.

2 Atmosphere air quality.

3 Regeneration quality. ( Regeneration air flow, timer condition, water trap)

4 Cooling water flow ( If you have any inter cooler). 

5 Any leakage in inter cooler.

6 Reliability of analyzer. Cross check with other instrument.

 

I hope this will help.

 

Good Luck

[Art Montemayor]

CMangesh:

 

You give our members very little information and basic data.  You say:

• You experienced a high dew point air product using 4-year old adsorbent;
• You are using an adsorbent that is 4 mm in size and is "air generated";
• You are pre-filtering the adsorbent;
• You are using compressor "side filters" and moisture traps;
• Your adsorbent regeneration cycle lasts 4 minutes;
• You replaced your adsorbent with fresh material and saw an exit dew point of -35 ^oC increase to -5 ^oC after only one day of usage.

A lot of more data and information is needed before addressing your query in a logical, rational engineering manner:

• Furnish a detailed sketch of your air drying adsorbent unit.  I assume that you are using an adsorbent (not a "dessicant") such as silica gel, activated alumina, or molecular sieve;
• Include the air compressor in your sketch with all its inter and aftercoolers, including moisture traps and other liquid water removal devices you are using;
• Give a detailed description of your drying and regeneration cycles: what is the conditions of the air entering the dryer - pressure, temperature, water saturation.  How, specifically are you regenerating the spent bed?  (I assume you have two beds - one adsorbing and the other regenerating).  What is the temperature and pressure of the regeneration gas used?  What is the time length of the drying cycle?  What is the heating and cooling time length of the regeneration cycle?
• What type of dew point measuring device are you using?
• Who designed and built your drying unit?  What are the original capacity and drying specifications for the unit?  Are these still the same as originally employed?  Has your compressed air input capacity and quality changed?
• What is the physical size of each of the adsorption vessels and how much adsorbent does each hold?
• What is the desired dew point (at atmospheric pressure) that you require for your produced compressed air?

Without specific data and information like the above, our members are only guessing and nothing of real value can be contributed to your query.  Refer to the attached Excel workbook for an example of what a typical adsorption unit sketch should look like.

 

 Adsorption Gas Dehydration.xlsx   159.42KB   67 downloads

 

[benabed]

CMangesh,

 

I think it's a valves issue. Check  the vessels isolation valves may be they are passing.

The air desiccant which is generally activated alumina can last more than 05 years without any problem.

Personally i have experienced the same problem in the past.

 

Regards,

 

[Ganesh Buddha]

when you have correct dew point in the first cycle and then it defaults, the reasons can be as follows:

 

* regeneration is not proper. it can be the flow rate during regeneration, or if it is heated regeneration it can be due to less regeneration temperature.

* or the flowrate during adsorption is more...

[Shankar12]

May be regeneration is not complete. So check your regeneration temperature and pressure while regeneration. Because regeneration at high air pressure do not  result in complete regeneration

[CMangesh]

Thanks all of you. Some of the comments will really add value in our troubleshooting.

[Ahmed12536]

Is this Problem solved? We do face the same issue here as well..
 
One of the Instrument air driers  is giving dew point of -50°C at start but in 12 -20 hours it goes above -40°C. All possible checks like regen sequence, passing of XVs, defective 4 way valves have been done .Finally the alumina desiccant also was replaced. Still the same behavior. The other driers in the other areas is perfect and they have the common Prefilter and after filter.

A few days ago, with drier in isolated condition (inlet air open, outlet closed) wetness was seen on the tower (incidentally, high humidity in ambient air) and in the outlet manifold chilling was noticed with water dripping from some valve joints! This is seen for the first time.

Please find the attached Sheets as well a.) Drawing b.) A filled Sheet (questionnaire) from Supplier but could not help much

Attached Files

•  Drawing.pdf   171.56KB   24 downloads
•  Questionnaire.pdf   130.46KB   19 downloads