5 replies to this topic

[J_Leo]

Hello,

 

Can anyone give me some direction on the H2O content in the spent regen gas from molecular seive dryer? Is it based on saturation water content in the gas or some equilibrium with the molecular seive?

 

Thank you,

Leo

[ColinR33]

Are you referring to the regeneration gas coming off the tower during a regeneration gas cycle and flowing to the regeneration gas cooler?  Initially, there will be very little water content in the regen gas coming off the tower during the warm-up stage of the regeneration cycle.  During this stage the hot regen gas is simply heating up the vessel steel, the sieve and the water contained in the sieve, and very little water removal will occur.  Once the sieve has reached a certain temperature, the water will start to vaporize (desorb) from the sieve and the gas leaving the tower will be water staurated.  This is typically aound 130°C (266°F), but may vary a bit between sieve suppliers/types. As the regen front moves up the bed, the regen gas outlet temperature will remain essentially constant at this number, and once the bed is fully regenerated, the regen gas outlet temperature will spike up to with 30-50°F of the inlet temperature and water content will drop off.  This temperature spike is used to confirm that the bed is completely regenerated.  I have used these numbers successfully for the design of numerous mole sieve units over the years.

 

HTH

Cheers,

Colin

Edited by ColinR33, 20 February 2015 - 05:37 PM.

[J_Leo]

Hello Colin,

Thank you very much for the detailed explanation of the regeneration process. It is very helpful.

Is the regeneration temperature related to the regeneration pressure? You mention 266F when water is saturated. Maybe there is some relation among operating pressure, temperature, and regeneration pressure and temperature?

Thank you,
Leo

[gegio1960]

The regeneration temperature is generally defined by the kind of adsorbent.

[Art Montemayor]

J_Leo:

 

The amount of water content in regen gas used in an adsorption dryer depends on various process conditions.  You fail to state the specific conditions in your process and, consequently, it is next to impossible to reply to your query with specifics.  ColinR33 gives you information based on the specific process he refers to.  But we don’t know whether it applies to your process or not.

 

I’ve regenerated Molecular Sieve adsorbers under the following bed conditions:

• Under process pressure; in a co-current flow direction;
• Under atmospheric pressure; in a counter-current flow direction;
• Under process pressure; in a co-current flow direction; using saturated process feed gas;
• Under atmospheric pressure; in a counter-current flow direction; using dry product gas;
• Under atmospheric pressure; in a counter-current flow direction; using an inert gas;

There are other schemes available.  Which one is yours?

 

Depending on the Mol Sieve manufacturer, I would design my beds for attaining a bed temperature of no less than 500 ^oF.   Of course this depends on the feed gas composition, potential reactions, contaminants, and product gas purity requirements.   Of course, I can't be more specific since all I can base myself on is your two query sentences.

 

[J_Leo]

Hello Art,

 

Thank you very much for your info. The process I am talking about is for the natural gas treatment. The operating pressure is 1290 psig, and the regen pressure is around half of the normal operating pressure with a regen temperature at around 550°F.

 

It is in counter-current flow direction, using the residue gas from NGL. The NGL feed gas is the treated sweet gas after dehydration, mercury removal and amine treatment.

 

Thank you,

Leo