washing of H2S by caustic soda

[jaloul]

hello
I have a project subtitled scrubbing from the fuser sulfur
if you have some documents about:
-how this dimension the gas scrubbing installation
_the different methods used for this subject
_information concerning the absorption of H2S by caustic soda
cordially

 

[bimr]

What is the source of the H2S and the concentration?

 

[jaloul]

The source of the H2S is the fusion of sulfur.
the concentration is 192 ppm.
if you have information concerning the absorption of H2S by caustic soda,please give me it.
Thank you

 

[PeterCasa]

This is a relatively common scrubbing technique with plenty of pre-designed scrubbers out there.

High-pH solution (using NaOH) will give you:

NaOH + H2S -> Na2S + 2 H2O

...you will also end up with Na2S03 and Na2SO4. Lots of books on this. Air Pollution Control Engineering by Wang & Pereira, for example.

Also a consultant or vendor could help you with conceptual design. Where are you located?

 

[bimr]

The Shell Claus off-gas treatment (SCOT) process and the Beavon process are similar, involving a hydrogenation step. In both processes the Claus tail gas reacts with a reducing gas to convert all sulfur species to H2S. the reaction step is followed by water quench in the SCOT and Beavon + MDEA processes. Absorption of the H2S into an amine, usually MDEA, solution follows. The H2S is recycled to the Claus plant. Hydrogenation-based processes typically boost the overall recovery of the Claus unit to greater than 99.8%.
One variation of the Beavon process replaces the MDEA absorber with a stretford unit.

http://sulfur.nigc.ir/sulfurproductionprocess-en.html

 

[jaloul]

Thank you very much PeterCasa
I am from Morocco. I'm making a final project study in a society that produces fertilizers. Then my manager suggested to me this subject (sizing of a gas washing installation (H2S)).

 

[jaloul]

Thank you very much bimr for your help.
I can not work with another solvent as a set of specifications requires me to use caustic soda to the wash.
if you have a document concerning the dimensioning of a scrubber pulvérisationgive me it.
cordially

 

[bimr]

Numerous other postings have addressed this issue. See thread127-121447 for example.

H2S absorption section
In the second stage H2S and other acid gases are absorbed. For example,

H2S+4NaClO -> Na2SO4 + 4NaCl-----(3)
H2S+2NaOH -> Na2S+2H2O-----------(4)

By using NaClO, acid odor gases can be efficiently absorbed. It is very important to control pH and ORP for the purpose of successful absorption. If not controlled, trouble such as sulfur particles and Cl2 gas will arise

The most common method of control of H2S gas is to pass the smelly gas through a vertical, packed bed wet scrubber. The air passes up the tower as the scrubbing liquid containing caustic (NaOH) and oxidizing agent (most often bleach or NaOCl, sodium hypochlorite) flows down the tower in counter-current fashion. The high pH provided by the caustic drives the mass transfer from gas to liquid phase by solubolizing H2S as HS- bisulfide and S-2 sulfide ions. Once in solution, the reaction between hydrogen sulfide and oxidizing agent is almost instantaneous (assuming sufficient oxidizing agent is present). This reaction converts the sulfide to sulfate (SO4-2) ion. The overall chemical reaction is described by the following equation:

H2S + 4NaOCl + 2NaOH -> Na2SO4 + 4NaCl + 2H2O

Therefore, theoretically, for each molecule of H2S destroyed, four molecules of bleach and two molecules of caustic are consumed. However, the chemistry is not quite so simple, as partial oxidation of H2S also takes place that forms elemental sulfur:

H2S + NaOCl -> NaCl + H2O + S

This reaction represents about 1% of the chemistry present in a wet scrubber. The presence of excess bleach helps to minimize the formation of elemental sulfur. But bleach is an expensive chemical. The use of two stage scrubbing is often employed both to minimize chemical consumption as well as to control sulfur deposits when scrubbing H2S. The first stage operates at~ 80% efficiency and uses a caustic only scrub at high pH (~ 12.5). The air then passes to the second stage, where the remaining H2S is scrubbed with caustic / bleach solution at pH ~9.5. The H2S present is destroyed at 99%+ efficiency. The blowdown from the 2nd stage, which will contain some amount of unused NaOCl, is sent to the sump of the 1st stage. In this way, additional H2S is destroyed and maximum consumption of expensive oxidizing agent is assured.

Never the less, there are losses of chemicals which cannot be prevented, which of course raise the cost of odor control scrubbing. These losses are due to the facts that bleach, NaOCl, slowly decomposes in storage as well as the fact that some amount of caustic is constantly lost to CO2 absorption in both scrubbing stages.

http://www.lantecp.com/technical/H2S_DesignExample.pdf

 

[jaloul]

thank you bimr for your help

as I told you my plan for the treatment of H2S by soda is a requirement, so I can not involve another solvent because we need as a product of NaSH.
if you have the necessary steps to design a spray column give me it
thank you for the link to download the book,but it's not free one.

cordialy

 

[TD2K]

"because we need as a product of NaSH"

It would be useful if you had provided this and any other requirement/constraint you have in your original request rather than revealing it later "oh, that won't work because of x, y or z".

If you want/need to design a scrubber column that your company is apparently willing to spend the money to build or you are working for a consulting company that has been asked to design it (why is another question since you apparently don't have the experience/knowledge but that's another question), surely they can afford you buy you the book or any other tools you need to do this. Otherwise, I suggest you hire a company to do your engineering for you, BIMR has given you a link where Lantecp can apparently do the engineering needed for this project.

 

[jaloul]

thank you TD2K for your reply

I want to inform you that I am not an employee in the company, I am a student who performed his internship in this entreprise.donc it is not easy to take money from it.
for the other point (It Would Be Useful if You Had Provided this and Any Other Requirement / constraint You have in your original request Rather Than Revealing it later "oh, that 'will not work Because Of x, y or z")
I'm sorry
cordially

 

[TD2K]

This might give you a starting point.

http://www.atmc.umassd.edu/media/um..._of_H2S_in_NaClO_Caustic_Aqueous_Solution.pdf

http://www.trimeric.com/HP0108-Mamrosh-to-print2.pdf

Unfortunately, I don't have the experience in this field to just give you a cookbook approach.

 

[jaloul]

TD2K thank you very much for your help

if you have any documents relating to the absorption with chemical reaction and the method for sizing a spray scrubber
thank you in advance

 

[biogataw]

Hello,
a easy way to reduce H2S is with the biotrickling technology.
H2S + ½ O2 -> S (solid) + H2O
S + 1,5 O2 + H2O -> H2SO4
total:
H2S + 2O2 -> H2SO4

BR biogataw