Airflow versus pressure drop for a mixture of bulk wood chips and bark at different moisture contents

Abstract

Moist irregular wood chips or wood bark are used in packed beds for reducing odour and other gaseous emissions from waste gases. Moisture control of packing materials is essential for effective waste gas treatment. Therefore, simple experiments have been carried out to determine the influence of moisture content in a biofiltration bed made up of a mixture of irregular wood chips and wood bark in proportion 50:50 by mass on the pressure drop of air flowing through that bed. Nine moisture content levels varying from 8.1% to 64.5% (w.b.) were tested. The limiting empty bed residence time (EBRT) has been determined for each level. The influence of moisture content on true density, porosity and specific surface of the bed was determined. Above the moisture content of 28.3% (w.b.) there was a drastic change in the physical parameters of the biofilter packing. For moisture contents ≤28.3% (w.b.) the pressure drop increased slightly, while at values greater than 28.3% (w.b.) the opposite trend was observed. The Ergun equation was used to describe the relationship between the pressure drop through the bed and the superficial air velocity. For moisture contents ≤28.3% (w.b.) an approximate Ergun-type equation was proposed to describe pressure drop through the bed and the superficial air velocity.