BAG FILTER

Flat-bag filters are designed to achieve low residual concentrations of particulate in the clean gas and to maintain long filter fabric service lives. This is among others achieved by the low mechanical stress of filter fabric compared to other filter designs. Some corresponding aspects are mentioned below.

Support cage design

Support cages with a small wire mesh (approx. 25 x 25 mm) are used. This allows an even distribution of the differential pressure forces acting on the filter bags across the entire fabric surface. The smaller the mesh, the lower the load on the textile filter fabric near the wires.

Length of flat-bag filter elements

For the flat-bag filter construction, the length of filter elements is limited to 2.5 m for horizontal installation and to 3.0 m for the vertical installation. In comparison to other types of construction, this length limitation requires the installation of proportionally more filter elements for a filter surface of the same size; However, it offers considerable advantages:

Better distribution of the cleaning energy on the complete filter surface. The filter housings can be transported to construction site with already installed filter elements. The individual filter elements are easy to handle. No divided support cages are used.

Cleaning systems

Offline cleaning processes offer advantages over online processes:

• Lower mechanical stress of filter fabric
• Lower residual particle content in the clean gas by avoiding the “carpet beating” effect
• Higher cleaning efficiency
• Longer cleaning cycle

The medium pressure and compressed air – off line – cleaning systems with a travelling cleaning device in the clean gas chamber, are favourably priced flat-bag filter types. They benefit from the advantages of the – off line – cleaning systems, without having to accept the less favourable complex construction of the compartmentalised – off line – cleaning system.

Filter inlet to the filter elements

The preferably unhindered falling down of separated particles in the filter housing is important for the realisation of long cleaning cycles and by this low stress of filter fabric. When using one compartment filters, a crude gas inlet from above has therefore to be preferred. In case of an inlet from below or diagonally from below, as applied for single-compartment filters, a particle agglomerate removed from the filter fabric during cleaning can only fall down if its descent velocity is higher than the gas inlet in counter flow. Due to the fact that the descent velocity of particle agglomerates with about 200 µm only totals to approx. 1 m/sec., it is evident that in case of single-compartment filters exclusively a crude gas flow from above will be able to minimise undesired and uncontrolled particle redeposits, particularly of finest particles. This advantage holds true only in flat-bag filters with horizontally installed filter elements.