WET FILM (PACKED TOWER) SCRUBBERS November 25th, 2015 WET FILM (PACKED TOWER) SCRUBBERS Application in the chemical synthesis of chlorine dioxide Alvaro M. Gonzalez Vogel Puu 0.4400 Environmental Engineering 1

INTRODUCTION Liquid phase scrubber + packing material. Both phases provide energy for the gas-liquid contact. The packing material to provide a large contact area between the phases, turbulent mixing, and sufficient residence time for the gas to contact the liquid. Particles may accumulate, plugging the void spaces in the packed beds. Wet-film scrubbers are not used when particle removal is the only concern. Variables affect absorption efficiency: Gas velocity, Liquid injection rate, Packing size, Packing height.

TOWER DESIGN Countercurrent flow Cocurrent flow Crosscurrent arrangement

PACKING MATERIAL Packing material provides a large surface for contact of the gas and liquid phase. The size, quantity, shape, and material would depend on the following characteristic: Cost, low pressure drop, corrosion resistance, Large specific area, Mechanical strength, Weight, Arrangement. Trademark packing material

EXHAUST GAS AND LIQUID DISTRIBUTION Exhaust Gas Distribution: Addition of support trays (plates or grids) for the packing material  Distribution baffle. Liquid Distribution: Even distribution of liquid phase to avoid flooding Three types: Perforated tube, weir distributor, and spray nozzles. Perforated tube distributor Trough and weir distributor

PULP BLEACHING Chlorine dioxide

ClO2 SYNTHESIS Chemical Process

ClO2 SYNTHESIS Chemical Process

ClO2 SYNTHESIS Chlorine dioxide Absorber: Bulk absorption of ClO2 Chlorine dioxide Absorber: Super Intalox ®, Ceramic Saddles Bottom section: 2 inches diameter. Top section: 1 inch diameter  Higher surface area. Fresh water from the middle, diluate ClO2 (2 g/l) from the top of the absorber. Final ClO2 concentration: 8 g/l. Exhaust gas is send to a vacuum ejector and then to the scrubber for full recovery of ClO2.

Absorption of residual ClO2 ClO2 SYNTHESIS Absorption of residual ClO2 Chlorine dioxide Scrubber: Super Intalox ®, Plastic Saddles Bottom section: 2 inches diameter. Top section: 1 inch diameter  Higher surface area. Intermediate gap for homogenization of gas and reduction of clogging. Final ClO2 concentration: 2 g/l. Exhaust gas is send to the atmosphere.

ClO2 SYNTHESIS Chlorine dioxide Recovery: Conclusions Chlorine dioxide Recovery: High removal efficiency is required (expensive chemical) No particles in the exhaust gas Good solubility of chlorine dioxide gas in water Oxidant and acidic compound Removal efficiency impact on a pulping mill economy 2 Stage scrubber system seems to be a good design for full recovery of ClO2 Chlorine dioxide 2.5 US$/kg Consumption 15 kg/BDt Daily prodction 3,000 BDt/d Annual production 1,065,000 BDt/y 39,937,500 MUS$/y -5% recovery 1,996,875