Non-uniform filtration velocity of process gas passing through a long bag filter

•Filtration velocity of a long bag filter is numerically investigated.•Filtration velocity becomes more non-uniform as the length of the filter increases.•Maximum filtration velocity linearly increases with the filter length. Filtration velocity is one of the dominant parameters that determine the pressure drop through a bag filter. Experimental investigation of the air flow pattern around a bag filter inside a bag house is very difficult because of the complexity of the 3-D air flow. For this reason, we numerically investigated flow characteristics along a bag filter in detail. We newly found that the filtration velocity is non-uniform along the axial direction of a long bag filter when the height of the filter is greater than 10 m. The filtration velocity is very small at the bottom of the bag filter but very large at the top. For bag filter lengths of over 10 m, 70% of total inlet flow is filtered in just the top 30% of the long bag filter. This indicates that the top section of the long bag filter could deteriorate faster than the bottom section, making it necessary to develop a new method to avoid the problem. We developed an equation that can help predict the initial pressure drop across long bag filters with different heights, but identical filtration characteristics.