Control of Odors From Fish Drying 1

[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?

 

[elguero]

Scrubbers may not be the right answer. I visited a sewage treatment plant about a year ago. There, the many odor producers were connected though ducts and a suction fan to what was called a "wood chip bed."

The ducts leading to the fan were about 24" diameter. The bed measured about 12 ft by 30 ft. The description of what was going on went like this: "New wood chips are introduced on an infrequent basis (2 times a year?). A recirculating stream of water soaks the chips constantly. Colonies of microbes grow in the water and on the chips. The microbes devour organic matter in the air stream."

The bed of chips appeared to be about 3 ft thick.

 

[waterexpert]

As well as wood chips, other media may be used for a bio-filter, including peat, heather, seashells,calcified seaweed. Sizing of dusct leading to the filte ris usually base don superficial velocity of no more than 15m/s or so. Bed depth is restricted by pressure drop. Bed plan area is designed to give sufficent treatment capacity.

As far as your scrubbers are concerned, I'd be tempted to do a plain water scrub or plain acid scrub up front to remove the readily water soluble components like ammonia and simple amines. There are catalysts such as zinc oxide which boost the power of oxidative scrubbers.

Seán

http://www.seanmoran.co.uk