Alvaro M. Gonzalez Vogel

Puu 0.4400 Environmental Engineering 1

WET FILM (PACKED TOWER) SCRUBBERSApplication in the chemical synthesis of chlorine dioxide

November 25th, 2015

INTRODUCTION

Variables affect absorption efficiency: Gas velocity, Liquid injection rate, Packing size, Packing height.

• 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.

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

Perforated tube distributor

Trough and weir distributor

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.

PULP BLEACHING

Chlorine dioxide

ClO2 SYNTHESISChemical Process

ClO2 SYNTHESISChemical Process

ClO2 SYNTHESISBulk 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.

ClO2 SYNTHESISAbsorption 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 SYNTHESISConclusions

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

2 Stage scrubber system seems to be a good design for full recovery of ClO2

Removal efficiency impact on a pulping mill economy

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 MUS$/y