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Air Dryer Co2 Peak


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#1 Ranga v

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Posted 12 January 2019 - 09:44 PM

Air separation plant --CO2 starts to breakthrough  is observed from one of the air dryers during start up after 50% of the service cycle .Normal air flow is 13500Nmph.Suspected cause was moisture ingresss from wash tower into dryer .We have taken shutdown and done exceptional and extended regeneration of both the media two times . Observed normal heat peaks during the regeneration. Media has completed 8 yrs of life.

What else trouble shoot options or should we continue extended regeneration other than media replacement.



#2 Bodhisatya

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Posted 13 January 2019 - 09:32 AM

Air separation plant --CO2 starts to breakthrough  is observed from one of the air dryers during start up after 50% of the service cycle .Normal air flow is 13500Nmph.Suspected cause was moisture ingresss from wash tower into dryer .We have taken shutdown and done exceptional and extended regeneration of both the media two times . Observed normal heat peaks during the regeneration. Media has completed 8 yrs of life.

What else trouble shoot options or should we continue extended regeneration other than media replacement.

(a) Moisture Ingress, what's the basis of this? Has the performance of your pre-cooling section deteriorated from normal design practice? What was the design outlet temp as per design, and what is the one that you are maintaining?

(B) Do you have LPDs (Low Point Drains) at Mol Sieve inlet? Did you inspect them, for physical carryover of water form Direct Contact Air Cooler? What is the PDI across DCAC packing and demister dP, are they normal?

© Is the slippage at the start of the cycle or towards the fag end of the cycle?

(d) Check for the depressurization and pressurization rate, are they too fast? Can lead to possible attrition of the desiccants. Check for the physical level of adsorbents in the vessels, possibly top up would be required.

(e) What were the recorded Heating Dip and Cooling Peaks during Adsorbents baking (Exceptional Regeneration)?

 

Regards

Bodhisatya.



#3 Ranga v

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Posted 13 January 2019 - 10:40 AM

Basis for water ingress;  AWT CW level was running high against normal 50% as their was problem in CW outlet flow from the column, AWT outlet temp was high 24 deg C as cooling water flow was reduced to maintain level.After shutdown all deposits at the bottom was cleaned now the AWT is level is maintained

 

Yes some amount of moisture was observed from the LPD. Thier is no  means to check the DP across demister other than shut down, column DP is normal.

 

Dryer cyclic switch over are programmed . Attrition not suspected as dust could be observed during blowing

 

Exceptional peaks: 203 deg C and 15 eg C, Normal Reg :-10 deg C and 106 deg C.



#4 Ranga v

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Posted 13 January 2019 - 10:19 PM

In continuation we have MS 13 X 1/16" pellets but original was 13 X beads 1.5 mm...Than this be substituted.



#5 Bodhisatya

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Posted 13 January 2019 - 11:08 PM

Basis for water ingress;  AWT CW level was running high against normal 50% as their was problem in CW outlet flow from the column, AWT outlet temp was high 24 deg C as cooling water flow was reduced to maintain level.After shutdown all deposits at the bottom was cleaned now the AWT is level is maintained

 

Yes some amount of moisture was observed from the LPD. Thier is no  means to check the DP across demister other than shut down, column DP is normal.

 

Dryer cyclic switch over are programmed . Attrition not suspected as dust could be observed during blowing

 

Exceptional peaks: 203 deg C and 15 eg C, Normal Reg :-10 deg C and 106 deg C.

I am surprised to hear that dP across Demister is not in a provision for Direct Contact Air Coolers.It is a mandatory requirement and if you flip books of ASUs, phsycial carry over of Water to PPUs is the most common incident ,due to lack of proper instrumentation.Suggesting to raise an Engineering Management of Change and install PDTs across the DCAC ,with PDHH hardwired to Main Air Compressor Unload. What is the LAHH for DCAC?

 

Not satisfied with your High Level in DCAC as possible water ingress reason. Did you check the Vessel GA to find out what is the gap between Air inlet line and Level being maintained at 50 %? IF DCAC dP and demister dP are fine, physical carryover of water can be ruled out. What you see at LPD is normal as Air gets condensed, so slight water is normal.

 

Two questions to my post remains unanswered : (a) What was the design o/L temp  of air ex DCAC,you say it operated at 24 degC, which appears quite high, thus increasing Moisture Load, as Moisture has a stronger affinity towards Mol Sieve than Co2, can be a reason of possible breakthrough for Co2. (B) When does the breakthrough starts, start of the cycle or towards the end, Is it a 4-hour cycle bed or 8 hours cycle bed.

 

Regards

Bodhisatya.



#6 Bodhisatya

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Posted 13 January 2019 - 11:14 PM

In continuation we have MS 13 X 1/16" pellets but original was 13 X beads 1.5 mm...Than this be substituted.

 

Please check the dynamic adsorption capacity for both the variants and the crushing strength mentioned in the Datasheet provided by Vendor.

 

It's quite possible you need to vary the Cycle time and check to find the best match if the situation doesn't improve.

 

Also please mention the Heater o/l temp maintained during normal and exceptional Regn Case.

 

Regards

Bodhisatya.

 

Regards

Bodhisatya.



#7 Ranga v

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Posted 14 January 2019 - 01:19 AM

Sir DCAC has PDI for monitoring but their is no  interlock  .DCAC has a trip on level high (90% )  in this case level was at 75 % .Yes in our new ASU we have trip on DCAC PDHH. 

 

AWT design inlet and out let temp are 38 & 15.7 deg C . Dryer is a four hr cycle . Heater outlet temp were 280 deg C in exceptional and 150 deg C during normal regn. Cycle time can be altered if the at the end that is  15 minst before completion of service.

 

Presently after 25000NM3 air pass CO2 starts to rise against design 56000NM3.

 

MS 13 X pellets having similar properties wrt to beads will same quantity reqquired. Will their be any change in DP across dryer



#8 breizh

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Posted 14 January 2019 - 04:01 AM

Hi ,

You should consult the vendor about the difference between pellets ( cylinder like) and beads (sphere like). most probably the DP will be different …….consider Ergun equation to calculate the DP of the bed .

 

My view

Breizh



#9 Bodhisatya

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Posted 14 January 2019 - 09:56 AM

Sir DCAC has PDI for monitoring but their is no  interlock  .DCAC has a trip on level high (90% )  in this case level was at 75 % .Yes in our new ASU we have trip on DCAC PDHH. 

 

AWT design inlet and out let temp are 38 & 15.7 deg C . Dryer is a four hr cycle . Heater outlet temp were 280 deg C in exceptional and 150 deg C during normal regn. Cycle time can be altered if the at the end that is  15 minst before completion of service.

 

Presently after 25000NM3 air pass CO2 starts to rise against design 56000NM3.

 

MS 13 X pellets having similar properties wrt to beads will same quantity reqquired. Will their be any change in DP across dryer

 

Even after extended regeneration, if the situation doesn't improve, I fear you need to check the quality and quantity of adsorbents used. Check by vessel inspection, if there is any channelling of feed or not. Alternately reduce cycle time to say 3 hrs and see how long the new adsorbents can sustain.

 

dP across the bed can be easily checked as you have PTs at MAC discharge as well as Mol Sieve outlet.

 

Regards

Bodhisatya.






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