Candle Filtration
Industrial Candle Filtration System
Industrial candle filters (also known as tubular pressure filters or cartridge filters) are precision filtration systems designed for fine particle removal, polishing, and clarification of liquids. They use an array of vertical or horizontal cylindrical filter elements (“candles”) inside a pressure vessel, making them ideal for applications requiring sub-micron retention, high filtrate clarity, and automated operation in industries such as pharmaceuticals, chemicals, polymers, food & beverage, and oil & gas processing.
System Design & Components
The candle filter consists of a pressure vessel (vertical or horizontal) containing multiple tubular filter elements mounted on tube sheets or headers. Each candle has a perforated core covered with filter media — sintered metal, woven wire mesh, pleated fabric, sintered powder, or depth media — allowing filtration from outside-to-inside (most common) or inside-to-outside.
Filtration Cycle
The typical operating sequence includes the following steps:
- Precoating (optional but common) — A dilute slurry of filter aid (DE, perlite, cellulose) is recirculated to form a thin, uniform precoat layer (0.5–3 mm) on the candle exterior for finer retention and media protection.
- Main Filtration — Feed slurry enters the vessel, surrounds the candles; liquid is forced through the media under pressure (2–10 bar typical), while solids deposit as a thin-to-moderate cake on the outside surface.
- Filtrate Collection — Clear filtrate flows through the candle core and exits via the header or manifold.
- Cycle Termination — Filtration stops when differential pressure reaches a set limit, cycle time expires, or filtrate turbidity increases.
- Cake Discharge — Cake is removed via back-pulsing, reverse flow, gas expansion, or mechanical aids — often without opening the vessel.
Cake Discharge Methods
| Method | Description | Cake Condition | Best Suited For |
|---|---|---|---|
| Back-Pulsing / Reverse Flow | Sharp gas (air/nitrogen) or liquid pulse from inside the candle expands media and dislodges cake. | Dry or reslurried | Automated, frequent cycles, fine/hazardous solids |
| Gas Blow-Down | Compressed gas blows through candles to dry and drop cake as dry solids to bottom. | Dry (20–40% moisture) | Valuable dry cake recovery (catalysts, APIs) |
| Reslurrying / Wet Discharge | Remaining liquid or added wash liquid reslurries cake for pumping out bottom valve. | Slurry (60–80% moisture) | Sticky/thin cakes, fast regeneration |
| Mechanical / Vibration | Mechanical rapping or vibration assists cake release (less common). | Dry or partial dry | Heavy or cohesive cakes |
Typical Operating Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Operating Pressure | 2–10 bar (30–150 psi) | Higher for viscous or fine filtration |
| Filtration Area per Vessel | 5–150 m² (50–1600 ft²) | Depends on number and length of candles |
| Precoat Dosage | 300–1000 g/m² (6–20 lb/100 ft²) | Lower than leaf filters due to thin-cake strategy |
| Cycle Time | 2–16 hours | Longer for low-solids polishing |
| Filtrate Flux Rate | 0.3–4 m³/m²·h | Higher with thin cake and good precoat |
| Retention Capability | 0.2–100 μm | Sub-micron possible with proper media/precoat |
Common Applications & Advantages
| Industry / Application | Typical Product Filtered | Primary Goal |
|---|---|---|
| Pharmaceuticals | API solutions, fermentation broths, intermediates | Sterile-grade clarification, fine particle removal |
| Chemicals & Polymers | Resins, solvents, polymer melts, catalysts | Polishing, catalyst recovery, high purity |
| Food & Beverage | Sugar syrup, edible oils, beverages, gelatin | Color/body removal, polishing |
| Oil & Gas | Amine/glycol solutions, produced water, fuel | Solids and contaminant removal |
| Wastewater / Utilities | Process water, rinse water | Fine filtration, reuse |
Key Advantages of Candle Filters
- Excellent sub-micron filtration capability
- Fully enclosed, safe for hazardous/toxic materials
- Automated backwash / cake discharge without opening vessel
- Thin-cake operation maintains high flux rates
- Low maintenance — replaceable or cleanable elements
- Compact design with high area in small volume
Also check out, “Vertical Pressure Leaf Filtration“