Filtration Technology in Industry

At IFAT trade show, BHS-Sonthofen was exhibiting candle filters from the further developed CF series for cleaning industrial waste water. They are particularly suitable for purification of industrial waste water with low solids content and reduce disposal costs to a fraction.

The BHS candle filters of the CF series have been specially developed for filtration of liquids with solid concentration of less than one per cent, i.e. an area of limited cake building capabilities in which other filters fail. Even in the case of very fine particles with low solids content, they produce a clear filtrate. With filter areas ranging from one to 150 squaremeter, they are designed for hourly throughput rates of up to several hundred cubicmeter.

One special feature of the candle filter is filtered solids do not form a sludge, but a pre-dried, semi-solid filter cake with a solids content of between 50 and 80 per cent. BHS thus significantly reduces the disposal volume compared with filter types with solids contents of 10 to 20 per cent. There is no need for further treatment of the filter cake, which can be disposed directly. The filters work automatically – no additional effort for exchanging and disposing of cartridges, or filter materials for deep bed filters is necessary. The manufacturer offers a broad range of process solutions based on candle filters for solid-liquid separation. Upstream and downstream process steps include pre-thickening, precoating and deep bed filtration or polishing-filtration. The result is always a clear filtrate.

Typical applications

  • Regeneration of industrial waste water in the chemical and pharmaceutical sectors
  • Regeneration of gray water in coal-to-gas plants
  • Recovery of abraded catalyst particles
  • Cleaning of amine solution from gas scrubbers
  • Desulfurizing of natural gas in the “amine sweetening process”
  • Treatment of the amine solution in the removal of sulfur dioxide from power station flue gases
  • Cleaning of electrolytes in galvanizing plants in the steel industry
A complete candle filter plant of type CF 24-113 for amine solution with a filter area of 76 m² prior to shipment

A complete candle filter plant of type CF 24-113 for amine solution with a filter area of 76 m² prior to shipment


The candle filter is an automatic, batch-operated filter bed with vertically arranged filter elements. The suspension is fed into the pressure vessel and continuously pumped. The filter cake is formed on the outside of each filter candle. The filtrate is discharged from the inside of the candles through immersion pipes. After filtration, the filter cake can be washed, reslurried or dried. Finally, the cake is lifted by a blast of compressed air and discharged. The candle filter is a compact unit with standardized modules that can be combined flexibly according to the specific requirements of the process. On request, BHS provides complete installations including fittings, instrumentation, piping, pumps, tanks, steel construction and control systems.

The plants consist of modules designed for easy transport and assembly. That reduces the customer’s planning effort and allows preassembly at the factory as well as comprehensive testing prior to shipment (FAT). On-site installation time is thus reduced and short overall delivery periods are possible.

This candle filter plant is used for cleaning the electrolyte of a coating plant in a German cold rolling mill. It comprises three type CF 21-049 candle filters, each with a filter area of 29.4 m²  – Photos: BHS Sonthofen GmbH