Odor Control For Fish Drying

[orcaanman]

Need some advice regarding operation of two-stage packed tower scrubber systems used to control odorous emissions from a fish-waste drying facility. The facility dries fish using rotary dryers into a fish-protein powder.

Emissions from the rotary fish dryers include ammonia, hydrogen sulfide, various amines and mercaptans. Exhaust from each dryer first passes through a cyclone and then through a heat exchanger where the temperature of the exhaust is dropped to less than 100 F. The exhaust is then routed through a two-stage packed tower scrubber system. In the first stage, a sulfuric acid solution is used and the pH is maintained at about 2.5. Oxidation-reduction potential (ORP) is maintained at 600-mv using chlorine dioxide as an oxidant. In the second stage, sodium hydroxide is used to maintain the pH at 10.5, and ORP is maintained at 650 mv, again using chlorine dioxide.

Testing of the scrubber systems showed that they are achieving 98% control of trimethyl amine and hydrogen sulfide. However, there are still emissions that are causing odor complaints. Odors are described as “fishy” and sometimes “chlorine + fishy.”

Does anyone have any suggestions regarding improving operation of our scrubbers? Has anyone else had better luck with different scrubber chemistry? Is there any drawback to using an oxidant in the first stage scrubber?


Thanks

ORCAA Man

 

[PB500]

Orcaa Man this is absolutely not a suggestion on a different chemicals mixing at upstream configuration, but an end-of-pipe suggestion: is it feasible, in the current plant setting, to install a vent network and a thermal oxidation section? Thermal oxidation is maybe the definitive solution to malodorous compounds in waste gases and it is widespread among food manufacturers for this specific purpose.

 

[jppmj]

Orcaa Man, I am not sure that using an oxidant like chlorine dioxide in the first stage is necessary because you can get chloramines which are very odorous and toxic.

The second stage is good.

What are flowrate and concentration at the outlet of your second stage.
May be it is possible to install a biofilter.
JPPMJ

 

[elguero]

I visited a sewage treatment plant last year. They covered all their digesters with covers connected through ducts to a fan. The fan discharged under a bed of earth and sod that were supported by a bed of gravel. Air and gases from the digesters was introduced in a plenum under the gravel. The area serving a 36" duct measured about 20 feet square and was kept moist by water sprays in the gravel. Microbes fed on the nutrients carried by the gas. Standing 10 feet away, I couldn't smell anything.

You could build a trial unit for little money. Almost any sturdy grass could be used as the plant material.

 

[waterexpert]

Biofilters similar to that described by the last poster can also be constructed from chopped peat and heather, calcified seaweed, mussel shells, or other media, with a much lower air headloss. They take up quite a bit of space though.

Seán

http://www.expertise-limited.co.uk