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TechnicalBulletin

Modern Gas Cleaning TechniquesFor TRS and SO

2

Control in thePulp and Paper Industry

No.2

The control of SO
2 and total reducedsulfur (TRS) emissions in the pulp and paper industry can be effectively achieved using the RotaBed TRS emissions.These designs operate by increasing the absorption of contaminant gases by extending the scrubbing liquid surface.
™ Fluidized Bed Scrubber*.As the US pulp and paper industry develops and implements strategies to meet the Cluster Rule require- ments, particular attention will be paid to the control of both sulfur dioxide (SO

Comparison ScrubberTypes for Absorption

Common absorbers are usually oneof the following type:
2 ) and total reducedsulfur compounds (TRS). 1. Spray Tower 2. Tray Tower

Sources of SO

2 3. Packed Tower

emissions may be:

4. Venturi Scrubber Power Boilers 5. Fluidized Bed Scrubber (Swirling or Ebullient) Waste Sludge Boilers (Incinerators) Table 1 provides a comparison ofthese various scrubber types.The common purpose of all of these absorbers is to place a large surface area of scrubbing liquid into direct contact with the flue gas.The gas diffuses to the liquid surface, penetrates into and through the liquid film, and is absorbed.Once the gas is absorbed into the liquid, the chemicals in the liquid react with the absorbed gas usually forming a low vapor pressure salt.These devices all accomplish the same desired result using vastly different techniques. Noncondensible Gas (NCG) Thermal Oxidizers Lime Sludge Kilns burning NCGs Recovery Boilers

Sources requiring TRScontrol may include:

Low Concentration High Volume NCG Sources High Concentration Low Volume NCG Sources Dissolving Tank Vents Miscellaneous Mill Odorous SourcesTo meet the Cluster Rules’MACT Iand MACT II guidelines, odorous mercaptan and hydrogen sulfide sources are collected and scrubbed or are thermally oxidized either in stand-alone oxidizers or are injected into the combustion zone of a lime- kiln or boiler.In some cases, a wet scrubber using a chemical oxidant (such as sodium hypochlorite or chlorine dioxide) is used to oxidize water-soluble TRS compounds. Emissions from thermal oxidation type devices are typically controlled using a wet scrubber with traditional alkaline chemistry to scrub out the SO

Traditional ScrubberTechnology

Spray Tower

The spray tower may be a hydrauli-cally atomized unit or may use steam or air atomized spray.The atomized droplets create the liquid surface area.This technology requires that the scrubbing liquid be elevated in pressure, passed through a small orifice spray nozzle, and then flashed back down to atmospheric pressure in the scrubber vessel.The energy imparted into the liquid is primarily used to create the liquid droplets. The gas pressure drop, in contrast, is low.Spray towers have been used for decades on utility power boiler flue gas desulfurization (FGD) systems usually by administering a spray of lime or limestone.
2 .Many paper mills are alreadytreating their odorous emissions sources using these techniques.Until recently, packed towers, traytowers, and spray towers were commonly used to control SO
2 and
RotaBed ™ and ScrubPac ™ are trademarks of Bionomic Industries,Inc.Patent Pending.