11 replies to this topic

[chemag2012]

I am operating a solvent tank. It receives nitrogen gas mixed with organic solvent from another process. There is no treatment at the vent of the tank. Vent nozzle was designed long enough but much solvent is still vented with nitrogen.

 

Could you suggest me the most economical way to recover solvent from the nitrogen gas? is Installing condenser better? Please suggest me.

 

Thank you.

[gegio1960]

you're too much generic to obtain good answers

? solvent

? storage capacity

? conditions

? environment

[chemag2012]

A general answer is OK for me. I mean what is the best technology for this?

[thorium90]

If the solvent is expensive or environmentally hazardous, it is worth recovering. If it can condense, then you can use a condenser. If it is in a different phase, perhaps a KO pot might work. If it can be absorbed somehow, then use an absorber. Frankly, without much info, literally almost process that can separate stuff is possible... ie: your general answer is: anything will work.

I'm sorry, but you gotta be more specific to get any useful answers.

Edited by thorium90, 08 February 2013 - 04:43 AM.

[kkala]

Activated carbon "filters" could be an effective alternative, shown in a local demonstration (2001) by a US company. Arrangement could be simpler than the presented on last page of <http://www.symexamer...ion Package.pdf>. But it does not seem to be the most economical way out. I think extent of recovery has to be specified before trying to compare cost levels, differing from case to case.

Note: Venting solvent vapors to atmosphere is an environmental risk that may be locally prohibited in the future, <http://www.hydrocarb...he-outcome.html>. I have the impression that recovery / treatment aims at non rejection to atmosphere, value of recovered product itself would not justify the investment. However this can be assessed, based on specific data for the case.

Edited by kkala, 08 February 2013 - 05:09 PM.

[ankur2061]

I am operating a solvent tank. It receives nitrogen gas mixed with organic solvent from another process. There is no treatment at the vent of the tank. Vent nozzle was designed long enough but much solvent is still vented with nitrogen.

 

Could you suggest me the most economical way to recover solvent from the nitrogen gas? is Installing condenser better? Please suggest me.

 

Thank you.

 

chemag2012,

 

You don't need an ultra-sophisticated solvent recovery systems such as Activated carbon adsorption systems to arrest solvent loss from the tank vent.

 

Just install a vent condenser in the vent line of the solvent tank with chilled water (6-8°C) supply and return and your solvent losses should come down drastically. Obviously the vent system will have to be re-designed for accomodating a vent condenser but this can be designed with very little capital investment and in less time compared to something like an adsorption system which would certainly require much higher investment and a long lead time to acquire.

 

Also don't forget that any adsorption bed needs to be regenerated once it gets saturated which means additional CAPEX and OPEX for standby and regeneration system.

 

I have installed and run a vent condenser on a Methanol tank using chilled water and it worked fine. Methanol has a very low flash point (11°C) and thus the vent condenser required chilled water to prevent methanol loss. For 6 years till I worked in that company we never had a problem with the system and it was doing a fair job in arresting methanol losses form the tank.

 

Hope this helps.

 

Regards,

Ankur.

[gegio1960]

Ankur,

you're right if chilled water is available at the site.

Not so obvious!

regards

[breizh]

No indication about the product , the quantity to recover , just guess !

 

Breizh

[chemag2012]

Thanks Mr. Ankur. I get the idea from your explanation. There is a chilled water facility in here. I would study about the recovery system. Once again thank you.

[Steve Hall]

There's a problem with a vent condenser in this case because of the nitrogen. Vent condensers work best when there are no non-condensibles. But if the solvents are being swept out of the tank with a nitrogen stream, recovery efficiency is determined by the concentration of the solvents in the stream, their vapor pressure, and the temperature of the coolant in the condenser. Calculate the dewpoint composition at the condensing temperature for a rough estimate of what will pass through the condenser, then subtract from the concentration entering the condenser to estimate how much solvent can condense there. Another thing to consider are the duration and frequency of the venting event. Is this a continuous or intermittent vent? For intermittent vents, "finger" type vent condensers can be effective. They use ultra-low temperature coolant and basically freeze the solvent inside the condenser.

[gregga]

I concur with Mr. Ankur and others...there are many variables involved including the driving force for doing anything at all (environmental, governmental, solvent value).  You need to start with the material balance with a flash calculation to determine the amount of solvent you can squeeze out of a partial condenser.  With only nitrogen, remember that the mole fraction of solvent in the vapor will be approximately the vapor pressure of the solvent divided by the total pressure (1 atmos if venting to the air).  Since you have chilled water available, that would be the first and most probably economical step.  If you are rich in nitrogen, you probably won't get much solvent out (this will become evident in the flash calculation).  Again, depending on the driving force for doing anything, you could follow the vent condenser with additional technology: 1) vent scrubber (probably venturi type) 2) adsorption (carbon/sieve) 3) vapor recompression.  4) flare (if available on site)     Options 2 and 3 can get very expensive. 

[mann]

One better way to avoid solvent losses from storage tank, is to store solvent below its flashpoint. Solvent can be stored below its flash point temprature by providing solvent re-circulation through heat exhcanger with CHW utility.