We are continuing our discussion on ozone for odor control applications. Last time we mentioned that ozone can be applied in the gas phase by mixing ozonated gas with contaminated air or that the ozone can be applied using a wet chemical scrubber with the ozone in the liquid phase.
The simplest arrangement is to work in the gas phase. This approach is only viable for low concentrations of odorants. For hydrogen sulfide, a common odor causing chemical, the concentration in the gas phase should be less than 5 ppm. At this level, ozone, normally made from an air fed ozone generator, can be mixed with the contaminated air and fed into a contactor. The contactor is a vessel that provides surface area and time for the ozone to react with the contaminant. The contactor should lower the gas velocity to less than 1 meter per second. In addition, the contactor should provide a high surface area for the reaction to take place. Plastic packing and aluminum screen are two choices for the materials to use to provide the necessary surface area.
When the concentration of contaminants is high, a wet chemical scrubber is a better way to introduce ozone.The picture above shows a schematic of a wet chemical scrubber used for ozone odor control.In the case of an acidic gas such as hydrogen sulfide, an alkaline scrubbing liquid such a dilute sodium hydroxide would be used.The scrubbing liquid would be mixed with ozone and then sprayed over a plastic packing.The design shown in the schematic, the contaminated air is blow across the scrubber in a perpendicular direction to the flow of the scrubbing liquid.
The scrubbing liquid captures the odorant in solution. The ozone then reacts with the odorant to neutralize the odor. The treated air passes through a demister to prevent the scrubbing liquid from leaving the scrubber. The bulk of the scrubbing liquid flows through the packing to the sump where it is circulated through the ozone mixing device and fed back to the scrubber. The concentration of the scrubbing liquid is adjusted as needed. A small portion of the scrubbing liquid is purged. In most cases the solution can be fed to the sewer without any environmental consequences.
There are numerous applications for ozone based odor control systems.These include municipal sewage plants, sewage collection systems including lift stations, rendering plants, exhaust from restaurant hoods, chemical plants, etc.Essentially any applications where the odor compounds can be oxidized.
Ozone based systems use less energy than thermal oxidation systems and don’t require the purchase or storage of chemical as with other chemical oxidants. Ozone is generated on site from air. So they only thing required is electricity.
Spartan Environmental Technologies supplies both types of ozone odor removal systems: gas phase and wet chemical scrubber. Contact us for further information.