6 replies to this topic

[mgamil24]

I have to do inspection for the regenration gas heater in two towers silica gel dehydration unit. The job duration is 11 days. There is a restriction to have shutdwon for this long period; it was decided to study the effect of stopping the regeneration during the inspection work. I want to know if this will casue a sever damage to the silica gel or not ? and how will be this effect? and can i overcome?

The inlet for the dehydration water dew point is around +18 C.

The silicagel type is H& WS

This gas will comnigled later with a treated gas from another field so the water dew point for the comingle will be acceptable for the metering station. (calculated by ASPEN HYSYS).

 

Thanks

Mohamed

+201060008814

mgamil3 (skype)

[Art Montemayor]

Mohamed:

 

You don’t tell us, so I assume you are drying natural gas with a silica gel adsorption unit and you want to inspect the regeneration heater.  Why this simple job of blocking off and opening the heater (I also assume you have a direct fired heater; is that correct?) takes 11 days is something I don’t understand.  But if that is what you want to take to inspect a heater, then that is your decision.  You don’t tell us very much information and you fail to state what size of heater you have, the gas rates, the amount of silica gel in each bed, who designed it, etc., and what other regeneration options you have.  You could possibly use an independent heater (either direct fired or electric to regenerate your spent adsorption bed.

 

Stopping the regeneration of the silica gel is something that you should consult with your manufacturer of the adsorbent – not the sales person or the distributor.  The manufacturer is the one that can tell you whether the gel will be damaged by excessive water.  We don’t know what type “H& WS” is nor who manufactures it.

[mgamil24]

Dear Art,
sorry for the delay in answering. It is not a normal inspection job, it is a repair one as well. My big concern is if i stopped regenration and continue introducing gas to the silicgel, what will be the effect. I will take all necessary precautions to avoid free liquids entrance.
The manufacture is O-BASF. My mangment team refused to use a rental heater as it will be not well controlled.

Thanks
Mohamed

[ColinR33]

As Art mentioned, you should really contact BASF to see if they have any issues with this approach.  Right off the top of my head I can see a couple of problems,  the first being that your gas will go off spec on water dewpoint soon after you exceed your adsorption cycle time as the bed will become saturated with water and will not adsorb any more, and the gas will stay off spec until the bed is regenerated, so really not much point in continuing to flow through the beds.  Another issue is the possibility of damage/destruction of the gel during your first regeneration, if  there is enough water adsorbed onto the gel there is the possibility of flash vaporization that can pulverize the gel, I have seen the result of this in a similar situation, a good portion of the gel is reduced to dust and the entire bed must be changed.  Really, you should just shut down and bypass the system while you do your heater inspection/repair, either way your gas will be off spec and by bypassing the unit you eliminate the risk of destroying your gel bed - unless you have no way to bypass the system...

[mgamil24]

Colin,
we have no choice, we cant stop as we have high demand. As you mentioned i will get offspec gas during that period, but our gas is comingled with other plant before directing to the consumers - i did a HYSYS exercise - found the mixture specs OK.
ok, i will email OBASF to check. Moreover thanks for let me think about the first regeneration after long time of none .

Mohamed

[Art Montemayor]

Mohamed:

 

ColinR33 is giving some correct and experienced advice.  I have undergone and experienced the pulverization of silica gel when submitted to rapid and very hot regeneration gas.  By this time I would hope that the whole world knows of the propensity for silica gel to "dust" - revert to dust when subjected to attrition and bed movement.  This is one of the trade offs when using silica gel.  And that is mainly why I stopped using it when I obtained equal or better results from activated alumina.  Silica gel was developed for purposes other than drying gases and industry has put a lot of applications on it in the last 100 years.  Some of these applications go beyond its capabilities, in my opinion.  Please read the attached workbook that I compiled of one of my favorite adsorption articles.  I took the time and effort to make this workbook because I couldn't allow for the historical facts and data to be lost and not shared with other engineers.  The pioneering application at Carthage, Texas was done  60 years ago and the results all show us that silica gel hasn't changed at all in its performance data.  Note that the initial startup of the beds was done with a special "conditioning" procedure.  Even at that time, it was suspected that silica gel has limitations in how hot it can be regenerated.

 

Like ColinR33, I also advise you to be careful in how you regenerate a fully, 100% saturated silica gel bed.  If you can, it would be wise to obtain recommendations from BASF before applying heat to such a spent bed.  I also believe that your plant management is making a foolish and inexperienced decision in not applying a rental heater while inspecting the existing one.  Nevertheless, it is their call and they will learn from it - hopefully not too expensively.

 

 Natural Gas Dehydration With Silica Gel 1955.xlsx   567.84KB   45 downloads

[mgamil24]

Dear Art and colin
I really appreciate your valubale technicl advise. I stated clearly in the last meeting that we have use a rental heater but they refused again.
anyway i will do the conditioning operation for the tower when restart the regeneration to avoid silica gel damage.
Do we have anyother precautions should i peer in mind while first regeneration?
thanks alot
Mohamed