8 replies to this topic

[smadhami]

Dear All,

I am currently working on scheme for removal of chlorine from sulfuric acid via air stripping. My system load is very low as I have used 40 m3/hr of sulfuric acid having 700 ppm of chlorine and want to stripped it less than 25 ppm chlorine .

Kindly refer me a suitable book for guidance or any spread sheet

Regards
Adhami

[breizh]

smadhami,

Thanks to let us know the cause of the contamination ! It might help us to support your query .

 

Breizh

[smadhami]

Dear Breizh,

 

Basically this system is used for the removal of chlorine form sulfuric acid . sulfuric acid is used in chlor alkali industry to remove moisture from chlorine since sulfuric acid is very good dehydrating agent. Our system is based upon three effect counter current contact between chlorine and sulfuric acid. Sulfuric acid is charged as 98 % concentration which after passing three stages reduces to 80 % .  Then 80% sulfuric acid is  been used as a sale able product.

 

Currently we installed packed tower which utilizes air as stripping medium to strip adsorbed chlorine in sulfuric acid. As of now what we are experiencing is outlet concentration of 200 ppm of chlorine  in sulfuric acid which is needs to be reduce to 25 ppm ( customer demand )

 

I am looking for  guidance on above query. A good literature or spread sheet or software will be very helpful. 

 

Regards

smadhami

[PingPong]

Currently we installed packed tower which utilizes air as stripping medium to strip adsorbed chlorine in sulfuric acid.

Who designed that packed tower? And what is his excuse that it does not work properly?

 

This is a very specific problem that can only be solved if one has data concerning equilibrium between chlorine in air and chlorine dissolved in 80 % sulfuric acid. I don't think any of us has such data.

 

Maybe a process simulator like Aspen Plus may give reasonable results, but without literature data to verify that result one is still not sure.

 

In general:

When stripping component i from a liquid using some (inert) gas, a certain number of theoretical stages n is required, as well as a sufficiently high Vapor/Liquid molar ratio. What matters is the Stripping Factor S_i = K_i*V/L in which K_i is the equilibrium constant for chlorine between air and 80% sulfuric acid at the temperature and pressure that your column operates. The combination of Si and n and a graph called the Kremser Plot gives you a quick idea what percentage of i will be stripped.

 

Problem is: we don't know what the value of K_i is.

Number of theoritical stages n depends on packing type and packing height, as well as properties of the vapor and liquid passing through it. What the HETP in this case is? I don't think anybody here knows.

 

So there you have it: K_i is unknown, so S_i can not be determined, and also n is unknown.

All we know is that chlorine stripping is insufficient.

You need to strip 97 % of the chlorine but the column only strips 71 %, that is a big difference.

 

 

Now there are four possiblilties:

1) the column does not have enough theoretical stages (but amount of stripping air is high enough),

2) the amount of stripping air is too low (but number of theoretical stages is sufficient),

3) both the number of stages and amount of stripping air is too low.

4) the sulfuric acid temperature is too low, resulting in low K_i and high HETP (due to higher viscosity)

Edited by PingPong, 04 August 2014 - 08:25 AM.

[breizh]

smadhami ,

 

Consider this paper !

 

Hope this can help you .

 

Breizh

 

smadhami ,

 

Consider these  documents !

 

Hope this can help you .

 

Breizh

Edited by breizh, 04 August 2014 - 11:26 PM.

[S.R.Shah]

Hi Smadhami

Please try to add preheater for 80% Sulfuric acid feed.

You can take trial in laboratory with heating sulfuric acid and checking final analysis

[S.R.Shah]

Hi Smadhami

Please try to add preheater for 80% Sulfuric acid feed.

You can take trial in laboratory with heating sulfuric acid and checking final analysis

[P.K.Rao]

I will add a little more. Pass nitrogen while heating to about 100 deg C. Exit  nitrogen should be freed from chlorine by absorbing in lime to prevent atmospheric pollution .

[S.R.Shah]

Nitrogen purging during lab heating shall imitate real scrubber and give more reliable results