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Tsa Natural Gas Dehydration Unit – Regeneration Gas Loop Design

tsa natural gas dehydration

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#1 svetor

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Posted 28 May 2020 - 07:33 AM

Dear Gents,

I’m a chemical engineer, trying to understand the potential effect of changing regeneration gas loop design configuration on overall TSA mole sieve unit energy efficiency for sweet natural gas dehydration service (DHU).

 

In a typical two-tower TSA DHU, one has two basic options for organizing his regeneration loop (using the same gas):

  • Regeneration gas is a slip stream (typically 10-15%) of dry treated gas driven by means of regeneration compressor, and sent back to the feed (open loop type 1) – used to obtain very low dew points of NG;
  • Regeneration gas is a slip stream (typically 10-15%) of wet DHU feed gas driven by means of regeneration compressor, and sent back to the feed (open loop type 2) – used to obtain low & moderate dew points of NG.

Both types of heating & cooling cycles are extensively discussed in literature, but there is a third type, of which little practical studies can be found:

  • Regeneration heating & cooling cycles are performed by recirculating (by means of regeneration compressor) the same portion of spent regeneration gas to the inlet of the adsorbent bed that is being regenerated (closed-loop).

Little attention has been paid to this specific case of regeneration loop design on this forum, except for one useful thread which proposed such regeneration loop design for selective adsorption of CO2 in the supercritical state:

https://www.cheresou...ut-an-air-flow/

Since this closed loop is commonly used in air drying applications I would like to understand if using such regeneration loop design can be beneficial for a two-tower NG TSA DHU? Can a closed loop help to reduce regeneration heater/cooler rating requirements and increase overall energy efficiency of the dehydration unit and how can I calculate it (assuming that I know how to calculate open-loop)? What effect closed loop has on regeneration gas flow rate? What practical dew points can be achieved?

 

Thank you for any help. All suggestions very much appreciated!

 

Best regards,

Svetor

 



#2 Bobby Strain

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Posted 28 May 2020 - 09:32 AM

You don't see much about it because it is a foolish idea.

 

Bobby



#3 svetor

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Posted 28 May 2020 - 11:34 AM

Dear Bobby,

Why is that? Could you provide more details? I'm pretty sure that such designs exist. 



#4 Bobby Strain

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Posted 28 May 2020 - 02:40 PM

If you regenerate with wet gas the beds will contain more sieves. If you regenerate with dry gas the beds will contain more sieves. So, there is no incentive to use a wet gas regen method. Dry regen gas will produce a much lower dewpoint product and thus eliminate many potential problems. Natural gas processing plants often use dry residue gas for regeneration and send the regen effluent to the residue gas header.

 

Years ago some designers thought they could reduce the cost of dehydrators by using internal insulation. Problems soon developed with poor insulation that allowed wet gas bypass. These design were  quickly abandoned.

 

The lesson? Don't be penny-wise and pound foolish. And be careful of "design by group consensus."

 

Bobby






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