Vertical Pressure Leaf Filtration
Vertical Pressure Leaf Filtration System
The vertical pressure leaf filter is a high-capacity, pressure-driven filtration system widely used in industries requiring excellent filtrate clarity and efficient handling of low-to-moderate solids slurries. Its vertically oriented leaves inside a cylindrical vessel provide a large filtration area in a compact footprint, making it ideal for batch or semi-continuous operations in edible oils, sugar refining, chemicals, pharmaceuticals, and catalyst recovery.
System Design & Components
The system consists of a vertical cylindrical pressure vessel containing multiple vertically suspended filter leaves. Each leaf is constructed around a rigid internal drainage structure (often stainless steel) covered with fine filter media — typically stainless steel wire mesh, woven cloth, or synthetic fabric. All leaves connect to a central manifold or header pipe that collects and removes the filtrate.
Filtration Cycle
The filtration process follows a clear sequence:
- Precoating — A slurry of filter aid (diatomaceous earth, perlite, or cellulose) is recirculated to deposit a thin, uniform porous layer (1.5–3 mm) on both sides of each leaf.
- Main Filtration — Feed slurry is pumped into the vessel under pressure; liquid passes through the precoat and leaf media while solids build a growing filter cake.
- Cake Build-up — Filtration continues until differential pressure reaches the preset limit (indicating cake thickness has restricted flow) or cycle time is complete.
- Optional Washing / Drying — Cake may be washed with clean liquid to remove solubles or dried with compressed air / inert gas to reduce moisture.
- Cake Discharge — Cake is removed either dry (via vibration) or wet (via sluicing), then the cycle restarts with new precoating.
Cake Discharge Methods
| Method | Description | Typical Moisture Content | Best Suited For |
|---|---|---|---|
| Dry Discharge (Vibration) | Cake is dried in place, then the entire leaf bundle is vibrated pneumatically to fracture and drop the cake to the vessel bottom for removal through a large valve. | 20–35% | Valuable dry solids (catalysts, carbon, pigments), minimal product retention |
| Wet Discharge (Sluicing) | High-pressure oscillating jets or rotating spray headers wash the cake off the leaves, reslurrying it for pumping out through the bottom discharge port. | 60–80% (as slurry) | Thin/sticky cakes, fast turnaround, disposable solids |
| Hybrid / Partial Dry | Combination: partial drying followed by vibration or sluicing depending on cake properties. | 30–60% | Applications needing flexibility in cake handling |
Typical Operating Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Operating Pressure | 2–7 bar (30–100 psi) | Higher for viscous liquids or finer filtration |
| Filtration Area per Vessel | 10–300 m² (100–3200 ft²) | Scalable by vessel diameter and number of leaves |
| Precoat Dosage | 500–1200 g/m² (10–25 lb/100 ft²) | Depends on required clarity and particle size |
| Cycle Time | 4–24 hours | Longer with low solids, shorter with high solids |
Common Applications & Advantages
| Industry / Application | Typical Product Filtered | Primary Goal |
|---|---|---|
| Edible Oils | Crude / bleached / winterized oils | Remove bleaching earth, nickel catalyst, waxes |
| Sugar Industry | Raw / refined syrup, liquor | Color removal, polishing, carbon / resin fines |
| Chemicals & Catalysts | Slurries with precious catalysts, activated carbon | Solids recovery, high-clarity filtrate |
| Pharmaceuticals | API intermediates, fermentation broths | Fine clarification, sterile-grade filtration |
| Molten Sulphur | Liquid sulphur | Remove ash and particulates |
Key Advantages of Vertical Pressure Leaf Filters
- Very high filtration area in a small footprint
- Excellent filtrate clarity (often sparkling clear)
- Uniform cake formation on both sides of leaves
- Enclosed, pressure operation — safe for hazardous materials
- Efficient dry or wet cake discharge options
- Robust, low-maintenance design with long media life