Bag filter
Bag Filter
The design features of the horizontally or vertically installed flat-bag filter elements especially in combination with the different -off line- cleaning systems included in the range of products allow
- the reliable observance of requested residual particle contents in the clean gas
- long filter fabric service lives
at low space requirement and low maintenance.
Flat-bag filters are used
for gas volumes of 1,000 m³/h
up to more than 1,000,000 m³/h.
General design
The filter housing is divided into crude gas and clean gas chamber by means of perforated plates. The flat-bag filter elements, each consisting of flat-bag and support cage, are mounted form the clean gas side. The flat-bag filter elements are precisely fitted in the housing. They are fixed in the holes of the perforated plate, secured without the use of screws and provide a perfect seal against dust leaks. The gas flow through the textile filter fabric is from outside to inside and the particles are retained on the outside.
The filter housing is divided into crude gas and clean gas chamber by means of perforated plates. The flat-bag filter elements, each consisting of flat-bag and support cage, are mounted form the clean gas side. The flat-bag filter elements are precisely fitted in the housing. They are fixed in the holes of the perforated plate, secured without the use of screws and provide a perfect seal against dust leaks. The gas flow through the textile filter fabric is from outside to inside and the particles are retained on the outside.
The advantages of a flat-bag filter with horizontally installed filter elements can only partially be used in case of vertical installation of filter elements.
Cleaning systems
The clean gas chamber is provided with vertically installed, easy to remove compressed air injectors, arranged in front of each bag row. Compressed air and clean gas as secondary gas are injected sequentially into two adjacent bag rows by means of injectors, designed in accordance with aerodynamic principles. The bag rows are cleaned in pairs by a brief pulse of jet air, injected into the bags contrary to the filtration flow, thus removing the particle cake from the fabric filter.
The clean gas chamber is divided into several chambers. Each chamber is connected with the clean gas collective channel and can be isolated. At the beginning of the cleaning process in one chamber the corresponding isolation damper on the clean gas side will be closed. The flat-bags are cleaned during interrupted filtration process by means of compressed air.
On request, the complete crude gas area of the filter housing can also be divided into chambers, thus offering the possibility to isolate separate chambers for inspection and/or repair whilst the other chambers are still available for the filtration process. In principle this will also be possible in case of a compressed air -on line- cleaning system.
The cleaning of the flat-bag rows takes place sequentially in steps by means of a cleaning device, travelling within the clean gas chamber and provided with compressed air feeding and injector tubes. The cleaning device covers three vertical filter bag rows, the middle of them being cleaned with a brief, about 0.5 sec., pulse of compressed air and clean gas as secondary gas. A lip seal along the carriage travel serves as reliable sealing, proved in continuous operation.
The cleaning of the flat-bag rows takes place sequentially in steps by means of a cleaning device, travelling within the clean gas chamber. The cleaning air is injected into one flat-bag row by means of a medium pressure fan, whilst the two adjacent flat-bag rows to the row being cleaned are not charged by the crude gas during the cleaning process. A lip seal along the carriage travel serves as reliable sealing, proved in continuous operation. This cleaning system does not require compressed air.
ADVANTAGEOUS SPECIAL FEATURES OF THE FLAT TUBE FILTERS
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.
LUEHR FILTER
IN BRIEF
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