5 replies to this topic

[Afshin445]

Dear Experts,

 

Currently I am working in project which is about mixing of different gas with different composition.

 

The objective of project is to review whole system and see any mixing drum or inline mixing is necessary for gas mixing.

 

I know gas mixing is mass transfer issue and we need to find minimum length(time) which two gas with different composition need to mix together and reach to final composition but I don't know how. I also didn't find any reference in this topic.

 

I am wondering if anybody have same experince or have any reference in this topic and want to share it with me.

 

Regards

Afshin

[siretb]

Whether inline static mixers are necessary or not depends a lot on the Length/diameter available downstream the mixing point. And of the relative density of the different gaz.

Static mixers are cheap and do not cost much pressure drop, and we use them almost always (NH3/air)

[Afshin445]

Siretb,

 

First of all thank you for your reply.But could you advise me how I can calculate minimum required length in downstream of mixing point  (Assume there is no inline mixer) based on downstream pipe L/D ratio and density of mixing gases?

 

Afshin

[siretb]

Well, I think you should do a CFD study using Fluent of something like that.  You will see the distribution of all the gases  when distance from injection point varies.  If it is not critical, then a rule of thumb (like use 10-15 D) can be applied, but I do not think this is what you want.

 

Some data (not exactly what you want, but still relevant) are found in :

 

Perspctives on  B&W ammonia injection and gaseous static mixing in SCR retrofit applications    K.J. Rogers   M.G. Milobowski   presented at the 1999 MEGA Symposium, in Atlanta (aug 16-20, 1999) 

 

Some authors have studied the dispersion of very fine Activated carbon powders in ducts. Very fine powder will behave much like a gas.  Search the internet

 

Again, I would pay a CFD run. You have to be careful, the initial conditions (how the diffrent gases are introduced) will be important

[Afshin445]

Siteb,

 

Thank you for your answer.It was really useful.

 

Afshin

[Mabhiza]

Hi Afshin,

 

Why are you mixing those two gases? This is a kind of question you must have on your mind when considering the right equipment.

 

Firstly a thermo compressor might be a good option. Simply because you have one gas at high pressure than the other one passing through a nozzle and creates suction pressure in the suction chamber and hence drawing another gas. But please give more details on this one, we've just commissioned a gas mixing station in my company.

 

Rgds

 

Mabhiza