8 replies to this topic

[AndySiarto]

Dear all,
in the production of the nitric acid plant, the NOx emissions play a crucial role concerning the environmental impact.
NOx emissions reduction can be achieved basically by:
- catalytic reduction of NOx in the tail gas N2 and O2 using an end-of-pipe technology (DeNOx)
- improvement of the NOx absorption efficiency
Concerning the absorption efficiency, besides the obvious temperature and pressure effects, there seems to be another interesting approach to improve the NOx absorption efficiency - adding of hydrogen peroxide [1].

Questions:
- does anybody have any experiences with this approach? (what are the typical amounts of H2O2 you add and corresponding NOx ppm- reduction?, what are the challenges there - risk&safety...)
- would ozone (O3) addition cause a similar effect?
- any other ideas to reduce NOx emissions?

Regards,
Andy

[1] http://www.h2o2.com/...xides-Abatement

[Dazzler]

Hi Andy
The catalytic reduction method involves the use of a small injection of ammonia as this is needed for the reaction.
Dazzler

[breizh]

http://www.h2o2.com/...xides-Abatement

Consider this resource to support your query .
Safety study is a must regarding the use of these materials .
Hope this helps
Breizh

[Technical Bard]

I have seen an nitric acid plant where they added a peroxide wash column to convert NO to NO2. This reduced NOx emissions and increased HNO3 capacity. However, I do not have any information on the peroxide rate. I do recall the column was quite large however.

[johnrwalton]

Attached is a presentation on this technology made last year at the NAUG (Nitric Acid Users Group) conference. Please consider it as an introduction/overview only, and not as a prescription for its application. A process hazards review should be done before any field level tests. Kind regards, John

Attached Files

•  NAUG presentation H2O2 - HNO3 process overv.pdf   1.22MB   75 downloads

[AndySiarto]

Hi all, many thanks for valuable input!
@johnrwalton: do you have any information whether the presence of H2O2 has an influence on the N2O concentration in the flue gas?

Thanks and regards,
Andy

[siretb]

Hello Andy
I have considered the H2O2 process as well as others a few years ago. I speak of using H2O2 at T>800°K, not of using H2O2 directly in a scrubber.
The following is only my own opinion, and not more than that.

Several other oxidants will, if used at a high enough temperature convert NO to NO2/nitric.
Methanol
Ozone
(Phosphorus)

Both work and have been demonstarted.
H2O2 works, in my view, less well to accomplish the same task.
a combination of both reagents have been proposed

a key factor will be the residence time, at a sufficient temperature. The dat I have is confidential, so I cannot disclose time_temperature domain.
to my knowledge N2O is not a problem.

the absorption is carried in a wet scrubber, and also is problematic. One must maintain in the scrubber a Redoxpotential low enough, and it is not that easy, because, in presence of O2 NO2 will oxidize far more than one mole of sulfites per mole of NO2. Or go all the way in the other direction with very high redox to oxidize to nitric.
I would not trust the mere use of H2O2 in a scrubber to acheive more than 40% removal, chiefly because the NO to NO2 conversion must be done in the gas phase, not in the scrubbing liquid. On this ground ozone works best,

So, overall, my own position is the following:
This kind of process suffers many limitations, starting from the maximum NOx removal efficiency.
There is nothing better than a well designed SCR, possibly coupled with primary means to limit NOx formation.
The reagent ( ammonia is cheap), the process well undestood, and the only drawback is initial investment
For a nitric plant SCR would be my choice.
If (and only if) the NOx concentrations are very high, then a wet scrubbing process using dilute HNO3 can be used to trim the NOx.
I do not trust much NOx reduction just by H2O2 scrubbing, if one wants more than 40% reduction.

[AndySiarto]

Hi siretb,
thanks for your feedback.
I fully agree with your opinion that the main part of the NOx removal should be done in a WELL designed SCR (DeNOx). I am now mainly concerned with the NOx peaks which occur during summer, when the high temperature decreases the NOx absorption efficiency.
For this purpose, the use of an oxidant seems to me quite a plausible solution, since you can basically use your existing technology, i.e. no extra CAPEX needed.

Edited by AndySiarto, 19 June 2012 - 03:40 AM.

[siretb]

Chlorine dioxide (ClO2) or sodium chlorite (NaClO2) is also an option.
NaClO2 is expensive, but the process is well proven, safe and works. Some care is needed to avoid ClO2 leaks at stack.