Pressure Leaf Filtration
Pressure leaf filters generally consist of flat-screened elements or leaves that are installed either on a shaft or header and enclosed in a pressurized horizontal or vertical tank. Leaves are coated with a filter aid material to form a dynamic filtration membrane or cake.
This cake is a layer (about 3 mm thick) of fine material in the 8-30 micron range, capable of capturing particles as small as 0.5 micron.
Cleaning of the filter leaves is accomplished with either spray nozzles or, if air is used to dry the cake, a vibrating device to knock the cake off the screen. When there is a need for fine particle filtration in industrial process water, precoat filtration has been the technology of choice for over 60 years.
The removal of high concentrations of suspended solids is traditionally achieved with the addition of lime and ferric chloride in a continuous clarification process followed by a down flow sand filtration step. However, regulating lime feed and controlling the variability in the incoming raw water can be challenging in applications that are subject to upset conditions such as the clarification of river water seasonally influenced by heavy runoff.
To reduce the concentration of solids below 1 mg/l TSS and colloidal silica below 0.05 mg/l consistently and independently of influent quality even after heavy rains, upflow deep bed media filters such as L’eau Claire™ are cost-efficient alternatives to the conventional silica removal process by lime-fed clarification and down flow sand filtration which also take multiple times the footprint and substantially higher installation and operation costs.
Vertical filters such as Veolia’s High-Rate Downflow (HRD) are designed to stringent structural requirements to filter particles as small as 2 microns out of many challenging industrial wastewater effluents. The specific application determines the most suitable design flux range, media cleaning technique, materials of construction and internals design.
Oil and Gas Produced Water filtration for boiler feed commonly requires the installation of a multimedia filter after the lime softener. This filter usually operates at a low flux rate of 4-5 gpm/ft2 and does not incorporate air scouring capabilities. The filters operate at high temperatures up to 200°F and generally use 316 stainless steel or coated carbon steel coated internal parts. Filters are custom-designed to the specifications of customers that require strict compliance with oil field standards and sourcing of components of extremely high quality.
Wastewater effluents from the Hydrocarbon Processing and Chemical Processing industries are generally designed using flux rates that vary with the application, but are generally in the 8-10 gpm/ft2 range. They are also fabricated to conform to stringent specifications of the oil and gas industry.
The beneficiation of Copper and Nickel in the Mining Industry requires a coalescing media filter in the electrolyte circuit. HRD filters are designed to provide better quality electrolyte and cathode life by operating under flux rates in the 5 gpm/ft2 range.
Industrial boilers and Power plants require high purity feedwater to ensure the optimal operation of steam generation systems. When silica-rich solid content through the demineralizers is relatively high, the demineralizer resin life is shortened and the boilers have to be limited in pressure until adequately blown down to avoid potential turbine blade deposition. This solids carryover produces an accumulation of hardness deposits that results in inefficient operations, increased hardware maintenance and risk of potential equipment damage. HRD filters ensure reliable pretreatment of demineralizer and boiler feed water.