|ICESP X CONFERENCE PAPER ABSTRACTS 8C SERIES
Held in Cairns,
Conference on Electrostatic Precipitation (ICESP)
is the official conference of the International Society for Electrostatic
MANAGING BAG SHRINKAGE IN LOW TEMPERATURE FABRIC FILTER PLANTS
HENDRE D GROBBELAAR
Low temperature fabric filter plants normally utilize bags manufactured fromPolyacrylonitrile (PAN). Although these bags are cheaper than high temperature bags, manufactured from Polyphenylenesulphide (PPS), they are prone to shrinkage.
Shrinkage in a fabric filter plant is problematic in the sense that it not only affects the performance of the bags, but indeed, of the whole gas cleaning system. Some of the areas affected are permeability, cleanability and strength.
The shrinkage can be chemical of nature. This is related to the cyclisation of the PAN fibers due to heat or chemical attack. The shrinkage could also be physical of nature, which means the shrinkage is caused by the elastic memory of the fibers and stresses induced in the felt during manufacturing.
Heat setting of the fabric is very important and differences of parameters during the heat setting process are responsible for differences in the shrinkage behaviour of adjacent bags in the same bag house, constructed of the same fibre and in the same needling loom.
This paper deals with the reasons for bag shrinkage and how it could be managed.
M. JEDRUSIK, A. SWIERCZOK, J. PAJAK
The use of PPS in CFBs is not new, in fact the since the introduction of the original fibreRyton ® introduced by Phillips Co many thousands of filter bags have been installed and operated satisfactorily.
Today’s challenges are however substantially more demanding than they were 20 or even 10 years ago. Power Station Managers are not happy with bag lifetimes of two or three years as was the case on many of the earlier installations, the quest today is for lifetimes to meet with Power Station GO’s. This can mean bag lifetimes of > 48000hrs. This for a textile can be a huge demand, it is achievable but in turn Power Station Managers must also understand the factors which can affect the fabrics lifetime. These factors take three basic forms, chemical, thermal and physical.
The PPS fibre performance is the first issue and this is examined relative to the flue gas analysis and the operating temperatures inside the bag filter. Once established that the PPS fibre can withstand the chemical/thermal conditions then the construction of the needlefelt is taken into consideration. To achieve long lifetimes it is necessary to design a high efficiency needlefelt which would require less cleaning cycles than a normal PPS felt offers. These designs can take two basic forms. Firstly by applying a PTFE coating and secondly by blending PI fibres into the surface structure of the needlefelt.
Today we have the possibility to compare the standard PPS filter bag with the more sophisticated designs using a filter test rig according to VDI/DIN 3926. The rig allows us to compare the filtration performance of different fabrics under defined conditions.
The conclusion of the testing allows us to have more confidence in the selection of the correct filter media. We must however combine the gas data and the ash data to be able to make the correct selection.
Laboratory tests can of course only be used as indicators the experience gathered in from actual applications is and always will be the most effective criteria for fabric selection. Our experience in the field is extensive and from a wide reference list we highlight two interesting installations.
Gutsche introduced the first PTFE coated fabrics and the first blended fabrics in the mid 80s, the PTFE coated PPS has been successfully installed in many earlier stations such as Rooiwal and Kelvin Power Stations in South Africa, the first blends also being installed at Arnot Power Station in South Africa and Hohot Power Station in China.
Last updated: May 10, 2009.
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