9 replies to this topic

[Reza.R]

Dear friends

 

I intend to evaluate manufacturing a wet scrubber for a power plant which use natural gas as its fuel and caused severe environmental problems.

 

First of all, we need to know what is the best solution for this problem? some people and company I met claimed that wet caustic scrubbers are the best one, actually a aqueous mixture of NaOH+NaHCO₃ (5%-5% in water).

 

The latest analyse from the flue gas of the stack revealed existence of some polluting gases like especially SO₂, NO  and CO₂ , NO₂ , H₂S.

 

The questions are:

 

1. Can NaOH and NaHCO₃ be a proper selection for this scrubber? SO₂ can be captured in alkali solutions like caustic, but what about NO ?? I had been studying several papers and find out solubility of NO is not as much as NO₂ & SO₂ in NaOH ! so is their claim true !?
2. In order to see a typical example about sizes of column, packing and operating parameters like temperature, absorber pressure, flowrate and composition of absorbing liquid of an existing caustic scrubber, what paper or resources do you recommend?  I search and see the following example but I need another one contains more details and guidelines about liquid type and its composition, L/G ratio, sizing of such a scrubber, ...
3. A basic question: Can wet scrubbers be able to remove contaminants such as NOx and SOx simultaneously in one vessel?

 

All the best 

Attached Files

•  SO2DesignExample.pdf   149.29KB   92 downloads

Edited by Reza.R, 29 March 2013 - 11:27 PM.

[Bobby Strain]

If the fuel is indeed natural gas, then you should treat the natural gas.

 

Bobby

[gegio1960]

Reza,

the treatment you've to apply depends by the "specifications" you've to meet (ie max allowed concentrations of NOX, SOx, dust, etc) and the type of fuel used.

You can choose between pre- and post-treatment.

Generally speaking:

- the best way to reduce NOX is thru the adoption of (very) low NOX burners (pre)

- if you have to further reduce NOX you should apply a DeNOX system (catalytic, post)

- SOX can be conveniently reduced by pretreatment of NG with amine washing

- DeSOX, wet (like yours) or dry (catalytic) can be applied downstream

- also SNOX systems (catalytic, post) are available to reduce both NOX and SOX

Hope this help.

[Reza.R]

Thanks for your replies

 

First of all I want to say the purpose is to install an effective treatment system with the lowest possible budget. Any altering in burner needs fundamental changes in power plant burners and I think this proposal would be rejected.

 

Regarding pre-treatment of natural gas, I think it is a interesting idea but this power plant uses heavier fuels as well especially in winters. So I think it would be better to use a scrubber before stack. 

 

Catalytic reactors for treatment of flue gas is also another interesting solution but unfortunately they insist on using the caustic scrubber !

 

A company I visit last week claimed that by using the mixture of aqueous NaOH+NaHCO3 mixture (5wt%-5wt%) they succeeded to lower NOx and SOx compositions simultaneously in one scrubber column much lower than allowed and maximum values. 

 

So our only option is using a caustic scrubber.

[wangyang]

Due to the limited experience on this area, I could only give you some rugh idea for this topic:

(1) Basically, that the low soubility of NO, It is almost impossible that remove SO2 and NOx, especially for NO, in one caustic scrubber;

(2) The main role using NaHCO3 and NaOH is to remove CO2, instead of NOx and SO2;

(3) To check the real treatment efficiency, the best way is to measure the target pollutants at both inlet and outlet at the same time;

 Just for your reference.

[Reza.R]

Thanks dear wangyang,

 

I think solubility of CO₂ in basic solutions can be reduced via adjusting PH of the liquid before entering from the top of the scrubber and optimize them for SOX absorption. Moreover, it seems that NO2 solubility in caustic solution is higher that No but unfortunately most of NOx constitute of NO instead of NO_2.

 

Actually this 5% wt concentration maybe is the reason for holding PH at the disired value;

[wangyang]

Thanks Reza for your comments. If most part of NOx were composed with NO instead of NO2, I thought that it almost impossible to remove NO by caustic scrubberr. Some other solution should be considered, such as SCR, SNCR.

[Reza.R]

Thanks dear for your comments;

 

SNCR is a proven substitute for NO removal and we must consider this as our final choice if others fail.

 

 

I wanna check the company's claim about NO removal by caustic scrubber and review again experimental data about NO solubility in NaOH and NaHCO3 and even water ! in various PH values.

[wangyang]

Hi Reza:

  You oculd find some data in the following article. I wish this documentation could give you some idea for this topic.

http://www.ncbi.nlm....pubmed/15771275

Good luck

Edited by wangyang, 02 April 2013 - 03:29 AM.

[Reza.R]

great 

 

thanks