Detailed Introduction on Oil-water Separation Performance of Aviation Kerosene Storage Coalescing Filter Cartridges

Detailed Introduction on Oil-water Separation Performance of Aviation Kerosene Storage Coalescing Filter Cartridges

1.Working Condition Characteristics of Airport Jet Fuel Storage & Transportation and Performance Boundary Requirements

1.1 Medium Pollution Characteristics of Jet A-1 Storage and Delivery System

This specification covers full links of airport fuel depots, tank farm storage, pipeline transmission, hydrant refueling pipeline and refueling vehicle terminal. High-performanceCoalescer & Separator Cartridge serves as the core purification component to guarantee aviation fuel quality, as Jet A-1 medium contains three types of pollutants that threaten flight safety: Solid particulate pollutants: Pipeline rust, storage tank scaling, catalyst fine powder, sand from tank truck transportation, wear debris of valves and pumps; Liquid water pollutants: Free settled water at the bottom of storage tanks, micro-emulsified water formed by oil-water stirring during tank switching and pumping, water mist generated by temperature fluctuation condensation; Trace interfering components: Anti-icing additive, anti-static agent, trace sulfide and aromatic hydrocarbons in jet fuel, which easily change the hydrophilic-lipophilic balance of ordinary filter media and weaken coalescing capacity. Long-term existence of excess water in jet fuel will trigger three major hidden dangers: microbial reproduction in storage tanks, ice crystal blockage of engine fuel nozzles at high altitude, corrosion of aircraft fuel system precision valves. Therefore, the qualified Coalescer & Separator Cartridge must simultaneously complete solid particle interception and micro-emulsified water coalescing separation, and meet the unified access index of aviation fuel terminals.

1.2 Mandatory Standard Limits for Oil-Water Separation Performance

All performance calibration of standard Coalescer & Separator Cartridge is based on EI 1581 7th edition classification (Category A/B/C corresponding to high/medium/low pollution sections) and domestic military standard GJB 610:

Outlet free water index: Category C terminal refueling ≤10 ppm; Category B tank farm outbound ≤12 ppm; Category A tank truck loading/unloading ≤15 ppm;

Overall water removal efficiency: For incoming fuel with water content up to 2000 ppm, coalescing separation efficiency ≥99.5%;

Solid particle cleanliness: Interception efficiency β₀.₅≥1000, outlet fuel reaches NAS 1638 Class 6 cleanliness standard;

Anti-re-entrainment limit: Under rated design flux, coalesced large water droplets will not be broken into secondary micro-emulsions by fluid shear force;

Long-term stability: After 1000h continuous operation with additive-containing jet fuel, separation efficiency attenuation ≤2%.

1.3 Failure Risks Caused by Insufficient Separation Performance

Emulsified water penetrates downstream, outlet water content exceeds standard, triggering airport fuel rejection and delayed refueling;

Fine water droplets pass through filter media to form water mist, leading to differential pressure abnormal fluctuation and shortened service cycle of cartridges;

Additives corrode ordinary single-layer filter media, surface coalescing functional coating falls off, and separation capacity drops sharply within 1–2 weeks, requiring immediate replacement of qualified Coalescer & Separator Cartridge;

High shear flow at peak flow breaks coalesced water droplets, forming cyclic emulsification pollution of storage tanks.

2. Multi-Layer Gradient Structure of Airport-Specific Coalescing Cartridges and Oil-Water Separation Mechanism

Airport jet fuel coalescing cartridges adopt four-layer gradient modified borosilicate glass fiber composite structure, with independent pre-filter layer, buffer coalescing layer, deep agglomeration layer and protective diversion layer, completing solid interception and micro-water coalescing in one cartridge, matching the low-shear flow demand of large-flow fuel delivery pipelines.

2.1 Structural Layer Function and Separation Logic

Outer pre-filter buffer layer (loose large-pore fiber)

Function: Uniform incoming jet fuel flow, intercept rust and scaling particles above 20μm, avoid coarse impurities scratching the inner fine coalescing layer; realize preliminary collision capture of large water droplets to reduce the load of deep coalescing layer.

Separation contribution: Remove 60% of free large water droplets and coarse solid pollutants at the inlet.

Middle core hydrophilic coalescing layer (ultra-fine modified glass fiber, core separation functional layer)

Surface treatment: Aviation-specific fluorinated hydrophilic-lipophilic balance impregnation, stable adsorption of 0.1–5μm micro-emulsified water droplets, unaffected by anti-static and anti-icing additives in jet fuel.

Separation mechanism: Micro-droplets are captured by fiber surface, continuously collide and merge along the fiber network, grow into large water droplets above 200μm through Brownian motion and inertial collision; gravity overcomes fluid traction to separate from oil phase and settle to the bottom water collection bin.

Inner dense support agglomeration layer (medium-density fiber matrix)

Function: Extend medium residence time to ensure incomplete coalesced tiny droplets complete secondary agglomeration; reduce oil flow velocity to weaken shear force and prevent large water droplets from being torn again.

Core parameter control: Minimum medium residence time ≥0.8s; Category C terminal high-precision cartridges require residence time ≥1.0s.

Innermost diversion protective layer (smooth low-resistance fiber mesh)

Function: Guide clean jet fuel to flow out evenly, eliminate local high-speed flow dead zones, reduce overall differential pressure loss of the cartridge.

2.2 Two-Stage Collaborative Separation System Matching

Complete airport fuel purification consists of coalescing cartridge + hydrophobic separation cartridge combination:

Primary coalescing cartridge: Complete most solid interception and micro-water agglomeration;

Secondary separation cartridge (pure PTFE hydrophobic screen): Repel residual tiny water droplets that fail to settle, block water droplets from entering downstream pipelines, and realize final deep dehydration to meet terminal fuel access standards.

3. Graded Oil-Water Separation Performance Index Matching for Different Airport Sections

Classified by EI 1581 Category A/B/C according to pollution load of storage and transportation links, with unified separation performance limit parameters under standard calibration conditions (jet fuel viscosity 1.3–1.6 mm²/s, medium temperature 10–40℃):

3.1 Category A: High Pollution Working Condition (Tank Truck Loading/Unloading, Tank Farm Inlet)

Medium inlet limit: Free water ≤2000 ppm, solid pollution NAS 8–10, mixed with a large amount of tank scaling and sand;

Cartridge matching grade: Standard thickened coalescing media;

Core separation indicators:

Water removal efficiency ≥99.5%, outlet free water ≤15 ppm;

Allowable unit area flux ≤60 L/(min·㎡);

Single cartridge dirt holding capacity ≥1300 g/㎡;

Adaptation feature: High dirt holding performance, tolerant of instantaneous high ash and high water impact during tank truck unloading.

3.2 Category B: Medium Pollution Working Condition (Tank Farm Outlet, Intermediate Transfer Pipeline Station)

Medium inlet limit: Free water ≤1000 ppm, solid pollution NAS 7–8, stable jet fuel with normal additive content;

Cartridge matching grade: Reinforced fluorinated modified coalescing media (mainstream for airport oil depots);

Core separation indicators:

Water removal efficiency ≥99.7%, outlet free water ≤12 ppm;

Allowable unit area flux ≤45 L/(min·㎡);

Single cartridge dirt holding capacity ≥1600 g/㎡;

Adaptation feature: Balanced dirt holding and coalescing stability, suitable for long-term continuous medium-flow pipeline operation.

4. Key Factors Affecting Long-Term Stability of Oil-Water Separation Performance

4.1 System Flux and Flow Shear Restriction

Fluid shear force is the primary factor destroying coalesced water droplets, so the maximum operating flow of the separator must be controlled according to cartridge grade flux limit:

When instantaneous pipeline peak flow exceeds the design value by more than 15%, open bypass flow dividing valve to reduce single-tank treatment load;

In summer high-temperature environment, jet fuel viscosity decreases and shear force increases, the allowable flux of all grades of cartridges shall be reduced by 10% to avoid water droplet re-entrainment.

4.2 Medium Temperature and Dew Point Control

When the medium temperature is lower than the fuel dew point, water mist condenses on the inner wall of the separator tank, forming secondary emulsified water to increase cartridge separation load; the tank body shall be equipped with thermal insulation and electric tracing to keep internal temperature ≥ dew point +8℃;

Long-term operation above 60℃ will accelerate the aging of the media hydrophilic coating, separation efficiency attenuates exponentially with temperature rise, so the continuous working temperature of the cartridge shall not exceed 55℃.

5. Judgment Standards for Separation Performance Attenuation of Coalescing Cartridges

Batch replacement of cartridges is required when any of the following measurable indicators reaches the limit value:

Two consecutive shift outlet fuel sampling tests show free water content exceeding the standard corresponding to the section grade;

Under rated design flow, water removal efficiency drops by more than 25% compared with new cartridges;

The daily differential pressure growth rate exceeds 0.008 MPa, and a large amount of oil sludge and solid impurities adhere to the media surface after disassembly inspection;

After disassembly observation, the surface hydrophilic coating peels off locally, fiber layer delamination occurs, and the agglomeration channel is blocked;

The cumulative continuous operation time reaches the design cycle upper limit: Category A 6 months, Category B 9 months, Category C 12 months.

6. Standard Operation and Maintenance Measures to Maintain Stable Separation Performance

Shift regular drainage: Operate the automatic drain valve of the separator water bin every 8 hours, record drainage volume to avoid re-entrainment of separated water;

Weekly pre-filter maintenance: Disassemble and clean the inlet metal mesh pre-filter, replace damaged mesh to reduce solid pollution load on coalescing cartridges;

Real-time flow monitoring: Limit the pipeline instantaneous flow within the rated matching flux range, open bypass for flow division when peak flow exceeds the standard;

Seasonal temperature adjustment: Reduce system operating flow by 10–20% in summer high temperature and winter low temperature to weaken fluid shear force and condensation water generation;

Periodic sampling inspection: Take outlet fuel samples every week to test free water content, track the change curve of separation efficiency in real time, and arrange cartridge replacement in advance when attenuation occurs;

Prohibited cleaning operation: Blocked coalescing cartridges shall not be washed with water, solvent or high-pressure air gun; cleaning will damage the surface hydrophilic functional coating and permanently lose oil-water separation capacity, only low-pressure internal back-blowing is allowed for early warning mild blockage (maximum 2 times in the whole service cycle).