Surface texture of a grey-white needle-punched felt filter medium
Dust filter bags run steadily under ambient conditions, but once the flue gas turns hot and humid the medium takes up moisture and cakes, the cleaning cycle shortens, operating resistance rises, and the filter bags have to be replaced more often with it.
Chemi Tech supplies water repellents for the water-repellent finishing of filter bags and industrial textiles, drawn from the water repellent KMF-801 series; the finishing liquor ratio is set by the medium weight, the fibre type and the finishing process. KMF-801 is designed for continuous water repellency with the hand feel kept in view: the film on the fibre surface is continuous and does not readily fail after washing; it is compatible in the same bath with common binders and softeners, and it contains no perfluorinated compounds. Chemi Tech verifies water repellency and compatibility against the medium weight and the finishing process, and supplies the water repellent that fits.
Advantages of Chemi Tech Water Repellents
Chemi Tech water repellent KMF-801 series is designed around continuous water repellency, with the film on the fibre surface continuous, so the medium does not readily cake after taking up moisture; in addition, it withstands washing, the water repellency decays slowly after washing, and the replacement cycle of the filter bags is extended with it; and it is compatible in the same bath with common binders and softeners, so the finishing process needs no splitting; it contains no perfluorinated compounds, so the concern over perfluorinated indices in export orders is reduced accordingly.
Industry Pain Points and Solutions
The difficulty in water repellency for filter bags is that water does not spread along the surface of the medium but penetrates inward along the channels between fibres; even when the initial splash rating is up to standard, a discontinuous film still lets the filter bag take up moisture in hot, humid flue gas.
A mismatch between medium weight and wet pickup is a common oversight. Thin media have a larger specific surface, the finishing liquor taken up is insufficient, the film is intermittent, and they fail first after a period of running. Chemi Tech assesses weight and wet pickup together, and calibrates the finishing liquor concentration and the curing conditions as one.
The core difficulty lies in the continuity of the film. Filter bags take repeated pulse-jet impacts during cleaning, the film breaks first where it is discontinuous, and moisture penetrates inward through the breach. Chemi Tech considers finishing liquor concentration and curing temperature together, so that the film stays intact under the repeated impacts of pulse-jet cleaning.
The last item is the balance between water repellency and operating resistance. Too high a loading of the finishing agent closes the gaps between fibres and operating resistance rises; too low a loading leaves the water repellency short. Chemi Tech KMF-801 gives the addition level in bands by medium weight, so that water repellency and operating resistance fall in the same range.
Typical Conditions and Verification
Customer: an environmental filter media producer in Jiangsu, for the water-repellent finishing line of polyester needle-punched felt.
The filter bags this plant made began caking after a period of running in hot, humid flue gas and were hard to clean; the customer reported that operating resistance was on the high side, and the finishing agent used before was inconsistent in wash resistance. The solution Chemi Tech water repellent gave for this was: against the medium weight and the fibre type, KMF-801 was selected, the finishing liquor concentration and the curing conditions were re-calibrated, and the softener used in the same bath was checked for compatibility at the same time. After the finishing line was adjusted, caking of the medium was noticeably reduced, the cleaning cycle returned to the design range, and operating resistance came down with it.
Frequently Asked Questions
After water-repellent finishing, will the pulse impacts during cleaning make the water-repellent layer fail?
It is indeed possible, since some finishing agents form a brittle film and their water repellency decays after only a few pulse-cleaning cycles. Chemi Tech has verified the water repellency of KMF-801 against cleaning and washing conditions, and only recommends it for the line once the film-continuity data is stable. The finishing liquor concentration depends on the medium weight and the wet pickup, and Chemi Tech gives its recommendation after comparison of cleaning and washing.