Working principle and application of coalescing separation filter element
1. Definition and function
The coalescing separation filter element is an effective filter element, which is mainly used to separate tiny droplets (such as oil, water) and particulate impurities from gas or liquid. Its core function is divided into two steps:
- Coalescing: merge micron-sized droplets into larger droplets.
- Separation: effectively separate large droplets from the medium by using density difference or structural design.
2. Working principle
- Coalescing process: When the fluid passes through multiple layers of fiber materials, tiny droplets adhere to the fiber surface due to inertial collision, interception and diffusion, and gradually coalesce into large droplets.
- Separation process: Large droplets detach from the fiber under the action of gravity or centrifugal force, settle into the collection tank (such as water in fuel) or are intercepted by a hydrophobic barrier (such as oil in compressed air).
3. Core structure
- Pre-filtration layer: intercept large particles and protect subsequent layers.
- Coalescing layer: high specific surface area fiber material (glass fiber, polypropylene) to promote droplet merging.
- Separation layer: hydrophobic/oleophilic material (such as PTFE membrane), preventing the separated liquid from entering the fluid again.
4. Key material properties
- Oleophilicity: used for oil agglomeration (such as fuel filter element).
- Hydrophilicity: suitable for water separation (such as compressed air drying).
- Chemical compatibility: need to withstand the corrosion of media (such as diesel, hydraulic oil).
5. Application areas
- Industrial compressed air: remove oil mist and condensed water, protect pneumatic equipment.
- Fuel purification: diesel generator sets, ship fuel systems, separate water and particles.
- Lubricating oil system: extend oil life and prevent emulsification.
- Aviation fuel: ensure the purity of jet fuel and avoid ice.
6. Selection and maintenance points
- Flow matching: too high flow rate will reduce the agglomeration efficiency (general design flow rate <1m/s).
- Pressure difference monitoring: the initial pressure difference is usually <0.2MPa, and the pressure difference needs to be replaced when it increases by 50%.
- Installation direction: strictly follow the arrow mark to prevent structural failure.
- Replacement cycle: according to the pollutant load (usually 6-12 months), it needs to be replaced in advance when demulsification fails.
7. Performance indicators
- Filtration accuracy: up to 0.1μm (coalescence layer).
- Separation efficiency: >99.9% (for droplets ≥0.3μm).
- Dust holding capacity: up to 500g/m² (multi-layer gradient structure).
8. Typical failure analysis
- Emulsion penetration: when the fluid contains surfactant, pre-emulsifier treatment is required.
- Secondary entrainment: Defects in the separation layer design cause droplets to be entrained by the airflow.
- Fiber migration: The structure is loose under high pulsation conditions, and the end cover seal needs to be strengthened.
9. Innovation trend
- Gradient pore size design: The outer layer with large pores intercepts particles, and the inner layer with small pores effectively coalesces.
- Nano coating technology: The contact angle of the super hydrophobic surface is >150°, which improves the separation efficiency.
- Intelligent monitoring: integrated differential pressure sensor for predictive maintenance.
Case application: In natural gas pipelines, coalescing filters can remove liquid hydrocarbons and solid impurities at the same time, ensuring stable calorific value and protecting downstream turbine machinery. Through the three-stage filter layer design, the liquid content of the outlet gas is less than 0.01ppm, far exceeding the ISO 8573-1 standard.
The coalescing separation filter element achieves the unity of microscopic droplet control and macroscopic separation performance through precise multi-scale structural design, and is one of the core components of modern industrial fluid processing.
