HL Series Walnut Shell Filter | Walnut Shell Media Filter

Working Principle During filtration, oily wastewater is pumped into the vessel and evenly distributed over the walnut shell media bed through an upper distribution header. The shell surface is oleophilic and hydrophobic, so oil droplets adhere to the media surface while suspended solids are mechanically trapped in the bed's pores. Clean water exits through the bottom collection assembly. What sets walnut shell media apart: it maintains flow capacity even after absorbing oil, unlike quartz sand, which tends to cake. When the media reaches oil saturation or differential pressure hits the set point, the unit switches to backwash. Walnut shells have a density close to water, so a relatively low backwash intensity is enough to fully fluidize and tumble the media, flushing oil and intercepted debris out with the backwash water. After backwash, the media resettles and stratifies, restoring filtration capacity. Walnut shell media can be regenerated repeatedly, with a typical lifespan of 1–2 years. Application Fields 1.Oilfield & Petroleum Production: Produced water deoiling, reinjection water treatment 2.Refining & Petrochemical: Refinery oily wastewater purification, petrochemical plant drainage treatment 3.Steel & Metallurgy: Rolling and continuous casting turbid circulating water deoiling, removing iron oxide scale and emulsified oil 4.Machining: Metalworking coolant wastewater and cold rolling emulsion wastewater deoiling FAQ Q1: What kind of oily wastewater can the HL Series Walnut Shell Filter handle? A: It targets wastewater containing emulsified and dispersed oil, with inlet oil content typically under 100 mg/L and outlet oil reducible to below 10 mg/L. It also captures suspended solids effectively. If inlet oil content is higher, a grease trap or swirl deoiler is recommended for pretreatment. Walnut shell media has limited effectiveness on free oil — that should be removed first with a skimming device. Q2: What's the difference between walnut shell media and quartz sand media? A: Walnut shells are oleophilic and hydrophobic — they're made to absorb oil. Quartz sand is hydrophilic and oleophobic — it's made to intercept suspended solids. When treating oily wastewater, quartz sand gets bound together by oil, and flow capacity drops fast. Walnut shells keep their porous structure after absorbing oil and resist caking. Also, walnut shells have a density close to water, so backwash requires lower intensity and less backwash water. The trade-off: walnut shells are softer than quartz sand, so service life is shorter — typically 1–2 years before topping up or replacement. Q3: What are the main components of the HL Series Walnut Shell Filter? A: The main body is a carbon steel anti-corrosion or stainless steel cylindrical vessel. Internals include: distribution header for even inlet flow; walnut shell media bed, typically 800–1200 mm deep; support layer of graded gravel to prevent media loss; collection assembly for water collection and backwash distribution. External connections include inlet, outlet, backwash water, and backwash air piping with valves. Manholes on the vessel allow for media loading and replacement. Control options are manual or fully automatic, triggered by differential pressure or time.