Influence deNOx on wastewater treatment 1

[EMKWR]

Currently I am working on a project concerning the waste water treatment of a power plant. It has been installed to convert the waste water of the FGD (flue gas desulphurization). The power plant is going to install a deNOx which will result in the introduction of ammoniumsulfate and an increase of quicksilver in the water. The installation is of the flocculation/filtration type. Does it remove the ammoniumsulfate and quicksilver ? Will its performance be influenced negatively ? Any suggestions or additional information ?

Thanks in Advance

Edwin

 

[bimr]

I assume that you are talking about a coal-fired plant? The FGD blowdown stream is difficult to treat because of the significant concentrations of TDS, chlorides, etc. among the other pollutant parameters that are present. It is common for an evaporator to be used because it is the only feasible method to lower the TDS.

If you have a wastewater treatment process suitable for handling FGD blowdown, the additional wastewater loadings from a denox process should not be much of an issue.

To develop a more thorough response to your question, it will be necessary to have detailed information on your application. Wastewater questions should be posted in the wastewater forum.

 

[siretb]

Too much ammonium can interfere with waste water treatment.
Specially with metals like Cadmium and Zinc.
If the NOx removal system is of the SCR (catalytic), this should not be much of a concern, since the ammonia slip is usually kept to a minimum (say 5 mg/Nm3).
However, if NOx removal is of the SNCR (non catalytic, urea or NH3) the ammonia slip is much higher and NH4+ becomes a problem.
Floculation will not remove NH4+. A biological treatment will.

Why do you say that NOx removal will increase Hg? The waste water treament, should, anyway be able to handle the mercury.

 

[EMKWR]

Thanks for the info so far. The installation under study is a coal-fired power plant in which an SCR will be placed.

Practice has shown that a power plant fitted emits less Hg to the air (cause unknown by me). However, to keep the mass balance correct, our client assumes worst case that this might end up in the waste water.

 

[siretb]

THe reason why less Hg is emitted is that the SCR catalyst will convert some elemental mercury (oxidation state zero) to ionic mercury (oxidation state (+II); Hg(+II) is much more readily scrubbed.
So in terms of mass balance, certainly the mercury goes somewhere.
You should perform a mass balance, counting the kilograms of mercury, and compare to the bleed rate of the scrubbers, to see whether this will be significant.
As for the ammonium concentration, do the same with the ammonia slip from SCR reactor.
Hope this helps

 

[EMKWR]

I already suspected that this might be the reason for the change in Hg-emission. Thanks for the info.

 

[bimr]

Not really sure what you are trying to do with your treatment.

A flocculation/filtration process is not going to any significant effect if you are trying to treat FGD blowdown. If you intend to discharge the FGD blowdown offsite after treatment, it is likely that you are going to have to remove dissolved solids from the FGD blowdown stream (using an evaporator). Some of these FGD applications also have trace elements like boron that complicate things.

As far as the ammonium goes, the pH is probably elevated so that the ammonium will be converted into the ammonia form (NH3}. Like sireth says, flocculation/filtration will not have any effect on NH3. Biological treatment is probably not feasible because you are dealing with an inorganic wastewater stream with little organic material.

To remove the ammonia, you will have to use a physical chemical treatment process such as stripping or chlorine oxidization. The preferred alternative is to strip the ammonia out and recycle it to the generating unit. The ammonia will readily come out of solution.

Mercury will probably settle out of any treatment process along with the waste