Analysis on Technical Parameters of Glass Fiber Coalescing Separator Filter for Water Removal Efficiency

Analysis on Technical Parameters of Glass Fiber Coalescing Separator Filter

for Water Removal Efficiency

1. Introduction

Glass fiber composite coalescing separation filter elements are the core consumables of liquid-liquid separation systems, widely applied in turbine oil purification of thermal power and nuclear power plants, aviation fuel dehydration, hydraulic lubricating oil regeneration, petrochemical organic liquid separation and other industrial scenarios. Different from single-layer filter media only intercepting solid particles, multi-gradient borosilicate glass fiber composite materials rely on the unique hydrophilic and oleophilic wettability of micro-fibers to realize the integrated function of solid impurity interception and emulsified micro-water coalescence separation. Water removal efficiency is the most core performance index to judge the grade of coalescing filter elements, which directly determines whether the outlet fluid water content meets the industrial standard, the service life of downstream precision equipment such as bearings and servo valves, and the replacement cycle of filter elements judged by differential pressure (0.15 MPa standard for power plant turbine oil filters).

At present, many industrial users only pay attention to nominal filtration precision and ignore the systematic connotation of water removal efficiency parameters, resulting in mismatched filter elements, rapid attenuation of dehydration capacity after short-term operation, frequent differential pressure alarm and other on-site problems. This paper systematically sorts out the definition, classification, test standard system, media structural characteristic parameters, operating boundary parameters and interference correction parameters of water removal efficiency of glass fiber composite coalescing filter elements, analyzes the internal coupling relationship between each parameter and dehydration performance, and summarizes the parameter discrimination method for on-site engineering selection and quality acceptance, providing standardized technical reference for fluid purification design, equipment maintenance and spare parts procurement.

2. Definition, Classification and Unified Test Standards of Coalescing Water Removal Efficiency

2.1 Core Definition of Water Removal Efficiency

Water removal efficiency (ηw) refers to the percentage of removed dispersed water and emulsified water after the polluted fluid containing known water content passes through the glass fiber composite coalescing filter element under rated test conditions, and the calculation formula is standardized as follows:

ηw = [(Cin – Cout) / Cin] × 100%

Where:

Cin = Inlet total water content of fluid (unit: ppm, mg/L);

Cout = Outlet residual free water + emulsified water content after separation (unit: ppm, mg/L).

It is necessary to distinguish three forms of water in hydrocarbon oil: dissolved water, free water and emulsified micro-water. The glass fiber composite coalescing medium can only remove free water and emulsified droplets with particle size ≥0.1 μm, while dissolved water mixed with oil molecules cannot be separated by physical coalescence and needs vacuum dehydration auxiliary treatment. Therefore, the industrial water removal efficiency index only counts separable dispersed water, excluding dissolved water, which is a key premise to avoid parameter misjudgment.

2.2 Three Classification Grades of Industrial Water Removal Efficiency

Combined with API aviation fuel standards, power plant turbine oil maintenance specifications and national filtration industry standards, the water removal efficiency of glass fiber coalescing elements is divided into three fixed grades, with clear applicable scenarios and residual water control indicators:

Standard industrial grade: ηw ≥ 98.5%, outlet residual free water ≤ 50 ppm, suitable for general base-load thermal power turbine oil, ordinary hydraulic oil offline purification;

High-efficiency precision grade: ηw ≥ 99.5%, outlet residual free water ≤ 15 ppm, mainstream matching for peak-shaving units, coastal high-humidity power plants, diesel fuel dehydration;

Ultra-high efficiency coalescence grade: ηw ≥ 99.97%, outlet residual free water ≤ 5 ppm, exclusive for nuclear power turbine oil, aviation kerosene, high-purity chemical solvent separation, requiring strict fluid cleanliness NAS 5 grade control.

2.3 Unified International & Domestic Test Standard System

The authenticity and comparability of water removal efficiency parameters depend on standardized test conditions. All qualified glass fiber composite coalescing filter elements must complete water separation performance test under the following unified specifications:

ASTM D726: Standard test method for liquid coalescing separation efficiency of fiber media, the global authoritative standard for glass fiber coalescing material performance testing;

ISO 16889: Multi-pass test for solid particle filtration efficiency, matched to test solid pollutant load interference on water removal efficiency;

GB/T 39208: Domestic standard for coalescing separation filter elements for industrial lubricating oil, specifying test oil temperature, rated flow, inlet water content and droplet particle size distribution;

API RP 1581: Aviation fuel filter separation performance specification, widely referenced for high-efficiency coalescing element acceptance of power station turbine oil purification equipment.

Standard fixed test working conditions (baseline for all efficiency parameter marking):

Test medium: ISO VG46 turbine oil / No.3 aviation kerosene;

Rated operating temperature: 50℃ (viscosity baseline of conventional industrial oil);

Inlet standardized water content: 1000 ppm emulsified water, droplet median diameter D50=3 μm;

Test flow: Filter element rated design flow, surface flow velocity of filter media controlled at 0.5–1.0 cm/s;

Solid pollutant matching: ISO A3 medium dust 200 mg/L, simulating mixed pollution of particles and water on site.

Any efficiency data tested under non-standard temperature, flow or inlet water content cannot be used as the basis for engineering selection, which is the primary rule to identify false labeling of filter element parameters.

3. Glass Fiber Composite Media Structural Characteristic Parameters Determining Intrinsic Water Removal Efficiency

The multi-layer gradient composite structure of borosilicate glass fiber is the fundamental carrier to realize coalescence and separation, and a series of media physical parameters directly restrict the upper limit of water removal efficiency. This chapter analyzes the coupling influence of each core structural parameter on dehydration performance one by one.

3.1 Glass Fiber Diameter Gradient Matching Parameter

The composite coalescing layer adopts multi-layer fiber gradient layout, and the fiber diameter of each layer forms a decreasing sequence from outside to inside: outer pre-filter layer 3–5 μm fiber, middle coalescence transition layer 1–3 μm fiber, inner ultra-fine hydrophilic coalescence layer 0.5–1 μm fiber.

Outer coarse fiber layer parameter function: Intercept large solid wear particles above 10 μm, avoid large impurities embedding into the fine fiber layer to block the water coalescence channel; if the outer fiber diameter is too small, the filter element will be quickly blocked by solid pollutants, resulting in the rapid decline of water removal efficiency within 1–3 months of operation;

Inner ultra-fine fiber core parameter function: Form dense three-dimensional hydrophilic network structure, capture submicron emulsified water droplets of 0.1–3 μm, complete droplet collision, adsorption and coalescence growth; the industry optimal matching parameter is inner layer fiber diameter 0.7–1.2 μm, with water removal efficiency up to 99.9% under standard test conditions.

If the single-layer equal-diameter glass fiber is used without gradient composite, the capture rate of emulsified droplets below 3 μm drops by more than 40%, and the water removal efficiency can only reach below 95%, which belongs to low-cost simplified media configuration.

3.2 Media Pore Size Distribution & Bubble Point Parameter

Maximum pore size and average pore size are key parameters affecting droplet penetration, tested by ASTM F316 bubble point method:

Average pore size of coalescing composite media: Standard grade 3–5 μm, high-efficiency grade 1.5–3 μm, ultra-high efficiency grade 0.8–1.5 μm. Too large average pore size leads to incomplete capture of micro-droplets, too small pore size increases initial differential pressure and accelerates blockage;

Bubble point pressure index: Reflect the maximum through-pore size of the media. For power plant turbine oil coalescing elements, the qualified bubble point pressure ≥ 0.5 MPa; if the bubble point is lower than 0.3 MPa, a large number of uncoalesced micro-water droplets directly penetrate the filter media, and the actual water removal efficiency is far lower than the nominal marking value.

Uniform pore size distribution is more important than single pore size index. High-quality composite glass fiber media has pore size dispersion coefficient ≤ 0.3, avoiding local large leakage pores causing separation failure.

3.3 Media Thickness Multi-Layer Composite Parameter

The total thickness of glass fiber composite coalescing layer is controlled at 0.4–0.7 mm, divided into 3–5 independent thin fiber layers with different wettability, instead of single thick fiber felt:

Single-layer media thickness >0.8 mm: Excessive flow resistance, initial differential pressure exceeds 0.05 MPa, easy to reach 0.15 MPa replacement threshold in advance;

Composite multi-layer thickness 0.5 mm (optimal configuration): The fluid retention time in the fiber network reaches the standard 0.12–0.18 s, which is enough for micro-droplets to complete collision coalescence; the residence time less than 0.1 s will lead to insufficient droplet growth and reduced separation efficiency.

4. Conclusion

The water removal efficiency of glass fiber composite coalescing separation filter elements is not an isolated single index, but a comprehensive performance result jointly determined by media gradient fiber diameter, pore size distribution, thickness, surface hydrophilic contact angle and dirt holding capacity structural parameters, and constrained by operating temperature, flow velocity, inlet water content and differential pressure boundary parameters. Nominal laboratory efficiency data can only be used as a reference; the actual long-term dehydration capacity on site must be judged by combining the full set of supporting technical parameters under standardized test conditions.

For power plant turbine oil purification, taking 0.15 MPa differential pressure replacement threshold as the safety limit, users need to match the corresponding grade of water removal efficiency parameters according to unit operation mode and environmental humidity, and verify the media composite structure and auxiliary anti-interference parameters during incoming acceptance to avoid selecting simplified low-performance filter elements with false efficiency marking. Scientific matching of full-set water removal related technical parameters can maintain the long-term stability of oil fluid low water content, reduce the corrosion and wear risk of turbine bearings and servo control valves, extend the service cycle of turbine oil, and reduce the comprehensive operation and maintenance cost of fluid purification systems.