Opacity Vs Water Vapor

[techv]

We are installing a Liquid Waste Incinerator and is in the stage of Bids evaluation. Environmental regulations stipulate limit on 'Visual Emissions' as "10% Opacity" for Flue Gas. In order to meet this, one leading Supplier used cooling of scrubber water for bringing down the water vapor content of flue gas, consuming huge CW. But we are very short of CW supply. The Supplier assumed Water Vapor for opacity limit saying it contributes to opacity. Opacity definition (elsewhere) refers to only air contaminants i.e. SO2, NOx, PM etc. and not Water Vapor. The supplier suggested to get official clarification/waiver from Regulatory body if Opacity should exclude water vapor, in which case CW load can be brought down significantly.

Forum folks are requested to through some light and offer advice.

Regards

 

[ash9144]

I don't know if it is state dependent or not, but in TX water vapor is not included as opacity. Water vapor in a gas stream off of a stack will quickly dissipate while particulates and pollutants will tail off a stack and this is what you should base your measurement off of. But to repeat don't know if state dependent.

 

[SylvestreW]

Like previous poster, don't know the location but in Ontario (Canada) water vapour is specifically excluded from opacity calcs.
If not, cooling towers would be failing everywhere.

 

[orenda1168]

The opacity measurement should be prior to the flue gas exiting the stack, and therefore not be influenced by water vapor as that will still be in a gaseous state.

Orenda

 

[ChemE123]

EPA Method 9 for visual opacity observation specifically excludes water vapor from the opacity measurement. The point for opacity determination is at the first point beyond condensed water vapor plume, or about 6 inches above stack exit if no water vapor is present. Opacity measurement before stack release is unacceptable as it may not catch condensable fraction of particulate matter, thus giving "false" low reading. Method 9 also has strict requirements on sun position relative to observer. Method 9 cannot be conducted at night and must be done with the sun at observers back. The angle of view through the plume is another critical factor. A search on EPA Method 9 in Google or any other search engine should provide more information on specifics for making an accurate opacity determination.

Good luck.

 

[Dionigi]

How do you separate vapor contibution from pollutants contribution to opacity? Out of a wet scrubber you got water-saturated gases sometimes at 70-80°C and the vapor will condensate immediately out of the stack.