4 replies to this topic

[gimenobaires]

I am new member here. I am looking for information related to calculate quantity of reactants, in packed bed scrubber to treat a mix gas combustion , which come from combustion of diesel liquid in generator. I consider NOx, SO2, PM,CO2, hydrocarbon non combusted. Also the react time in the bed to complete the caption of contaminants. Many thanks in advance

[siretb]

Dear Gimenez

It's pretty straightforward
In a scrubber, using caustic soda, SO2 will react on a basis of 2 moles NaOH per mole of SO2 captured. Will be slightly under 2, in fact.
Usually, you do not want to get the CO2 in a scrubber (scaling problems, ...) so run at a pH under 7.5. No CO2 will captured
PM are not captured well enough in a plain scrubber (you need venturis, ....) . Anyway no reagent is used.
for Hydrocarbons, no reagent is used. Efficiency is limited (depends which hydrocarbon)
NOx is not scrubbed efficiently, unless reagents like sodium chlorite are used, and in your case iit should not be economical. SCR is the preferred choice. Then NH3 is used about on a mole/mole basis (one mole NH3 per mole NO)

Now the scrubber will be designed dependind on the removal efficiency required. This gives you a number of transfer units, in first approximation , if SO2 is the governing pollutant, NUT=Ln(SO2inlet/SO2outlet). The heigth of packing will be approximately NUT/2 meters, if you select a good packing. This is approx only, you need detailed design.

[gimenobaires]

Many Thanks Siretb
It is apreciated so much your help
I think that the SCR has an Expensive Equipment to install. I am considering to use sodium chlorite (ClO2Na) solution to remove NOx. What do you think about it?
Please, one more question:If I mix solution of sodium chlorite with caustic soda solution as a scrubbing liquid in the Scrubber ( Bed packed), Is it will work with a minimum of 70 % removal efficiency of NOx and SO2 ?.The exhaustion gases come from of thermal unit (electric generator), Gases flow 2550 m3/h; Temperature °C 480; liquid flow ,1703 lit/

One more time, thanks
gimenobaires

Dear Gimenez

It's pretty straightforward
In a scrubber, using caustic soda, SO2 will react on a basis of 2 moles NaOH per mole of SO2 captured. Will be slightly under 2, in fact.
Usually, you do not want to get the CO2 in a scrubber (scaling problems, ...) so run at a pH under 7.5. No CO2 will captured
PM are not captured well enough in a plain scrubber (you need venturis, ....) . Anyway no reagent is used.
for Hydrocarbons, no reagent is used. Efficiency is limited (depends which hydrocarbon)
NOx is not scrubbed efficiently, unless reagents like sodium chlorite are used, and in your case iit should not be economical. SCR is the preferred choice. Then NH3 is used about on a mole/mole basis (one mole NH3 per mole NO)

Now the scrubber will be designed dependind on the removal efficiency required. This gives you a number of transfer units, in first approximation , if SO2 is the governing pollutant, NUT=Ln(SO2inlet/SO2outlet). The heigth of packing will be approximately NUT/2 meters, if you select a good packing. This is approx only, you need detailed design.

[siretb]

The sodium chlorite is an expensive reagent. It works, and works all the better that you use it at a low pH. We have used it, with pH less than 3, meaning that the removal efficiency for SO2 is low (second srubber for SO2 was used) . If you increase the pH, you will manage to remove both SO2 and NOx, but you are wasting some chlorite for the SO2, that is, otherwise, easy to scrub.
I usually do not recommend the use of chlorite, except for trimming a small peak of NOx. I know that some people will disagree. On the other hand, your gas flowrate is so small that you could consider ir, a SCr for such a small stream would be expensive investment
If I were you I would setup a small lab experiment, using an impinger and checking the removal efficiency for both SO2 and NOx, varying the pH
Check the following paper HSIN CHU , TSUNG WEN CHIEN , BOUR WEI TWU Simultaneous absorption of SO2 and NO in a stirred tank reactor with NaClO2, Water, air and Soil pollution , pages 337-350 2003 Taiwan

For such small streams ozone might be an option, too

Hope this helps

[gimenobaires]

Better late than never...Many Thanks Siretb!

The sodium chlorite is an expensive reagent. It works, and works all the better that you use it at a low pH. We have used it, with pH less than 3, meaning that the removal efficiency for SO2 is low (second srubber for SO2 was used) . If you increase the pH, you will manage to remove both SO2 and NOx, but you are wasting some chlorite for the SO2, that is, otherwise, easy to scrub.
I usually do not recommend the use of chlorite, except for trimming a small peak of NOx. I know that some people will disagree. On the other hand, your gas flowrate is so small that you could consider ir, a SCr for such a small stream would be expensive investment
If I were you I would setup a small lab experiment, using an impinger and checking the removal efficiency for both SO2 and NOx, varying the pH
Check the following paper HSIN CHU , TSUNG WEN CHIEN , BOUR WEI TWU Simultaneous absorption of SO2 and NO in a stirred tank reactor with NaClO2, Water, air and Soil pollution , pages 337-350 2003 Taiwan

For such small streams ozone might be an option, too

Hope this helps