Chemical scrubbers are a highly appreciated odor control technology. The scrubber works on the basic principle of providing a contact between chemicals, water and odorous air, to oxidize or entrain the odor creating entities. The scrubber liquid absorbs the odorous compounds. The entities are oxidized in this liquid and eliminated from the scrubber in the form of blow down stream or overflow. This article discusses the mechanism of chemical scrubbers, along with the design considerations.
Mechanism:
The major components of a chemical scrubber are- mist eliminator, sump, recirculation pump, system for liquid recirculation having spray nozzles and packing material. The odorous air is pushed into the scrubber with the help of a fan. The odorous air is passed through the packing bed. The nozzles spray the liquid solution over the packing bed. The odorous air comes in contact with this solution and is absorbed into it. After passing the packing bed, the liquid solution falls inside the sump, and here it is discarded or re-circulated. Through the mist eliminator, the air exits from the packing bed.
Design considerations:
The following factors need to be considered while designing the chemical scrubber.
The type of odorous compounds:
The selection of the chemical treatment depends upon the contaminants to be eliminated. Contaminants like hydrogen sulphide can be treated by using the solution of sodium hydroxide and sodium hypochlorite. To treat ammonia, you can use a sulfuric acid solution. Wet chemical systems are not effective to treat VOCs.
Number of stages needed:
If you need to remove multiple contaminants like ammonia and hydrogen sulfide, you need to use a scrubber system with multiple stages. They should also be used for the elimination of very high concentrations of contaminants. In this range, two and three systems are commonly used.
Control of liquid solutions:
It is important to properly monitor and control the liquid solution, to ensure proper levels of ORP and pH, in the solution of the scrubber. This is important for efficient operation. It is also vital to monitor and control the liquid levels.
Packing material:
The ratio of surface area to volume in the packing material should be very high, to offer adequate time for detention. The sizes and shapes of the packing material should also be proper to minimize the pressure drop. There is a variation in the materials, based upon the contaminants being treated and the air's temperature.
The Odor Control Systems of chemical scrubbers are proven to remove about 99.5% of ammonia and hydrogen sulfide, even when the concentrations are very high. These systems require small footprint relatively, but need significant maintenance and operational attention. They also need proper storage and chemical handling, and need proper disposal of the wastewater resulting from scrubber effluent. As these systems require special handling of the chemicals, the operators are provided with extensive training for handling these systems. These systems are not suitable for the treatment of volatile organic compounds.
Conclusion:
Chemical scrubbers are ideal for odor control problems occurring in industries and wastewater treatment plants. There are various companies that manufacture high quality chemical scrubbers, efficient enough to eliminate all odorous components.
