Condensation + Membrane Separation Three-Stage Vapor Recovery Unit

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The membrane separation-based tertiary Vapor recovery unit is a high-efficiency, eco-friendly system designed to address Vapor vapor emissions from gas station and oil depot storage tanks. Utilizing a combined process of membrane separation and condensation, the unit exploits the varying permeation rates of different gases through polymer separation membranes to achieve efficient separation of oil/gas vapors from air. The treated exhaust meets emission standards, and the recovered liquid fuel can be directly reused.

The product complies with the *Emission Standard of Air Pollutants for Gas Stations* (GB 20952-2020), featuring a treatment efficiency of ≥95% and an emission concentration of ≤25 g/m³. It represents an optimal choice for gas stations seeking to balance environmental compliance with economic benefits.

2.1 Core Technical Principle

Membrane separation technology is based on the solution-diffusion mechanism: when a gas mixture passes through a polymer membrane driven by a pressure differential, hydrocarbon VOC molecules (such as alkanes and aromatic hydrocarbons) and inert gas molecules (nitrogen and oxygen) exhibit significant differences in permeation rates, thereby enabling selective separation.

Two typical membrane separation mechanisms:

Glassy-state oil/gas-trapping membrane: At temperatures above the glass transition temperature (Tg), segmental motion occurs within the membrane and free volume increases, which helps enhance the membrane's selectivity for hydrocarbon VOC/air mixtures. Inert gas molecules first dissolve at the membrane surface, diffuse to the opposite side driven by a concentration gradient, and finally desorb.

2.3 Functions of Core Components

3.1 List of Standard Models

3.2 Detailed Technical Specifications

3.3 Explanation of Performance Indicators

Processing capacity unit: m³/h (standard cubic meters per hour); represents the volume of the oil-gas mixture the equipment can process per hour.

Start-up pressure: The pressure within the oil tank at which the equipment automatically starts.

Shut-down pressure: The pressure within the oil tank at which the equipment automatically stops.

Emission concentration: The content of non-methane total hydrocarbons in the treated exhaust gas; must comply with the national standard of ≤25 g/m³.

4.1 Advanced Membrane Separation Technology
High-quality imported separation membranes: Uses premium imported membranes that preferentially permeate air; prevents static electricity generation; ensures a safe and reliable treatment process.

High separation efficiency: Under experimental conditions with processing capacities ranging from 2.8 to 4.7 m³/h, the VOC concentration in the residual gas remains consistently below the 25 g/m³ emission limit.

Strong adaptability to pressure fluctuations: Membrane system separation performance is minimally affected by flow rate variations, ensuring compliance across a wide range of processing capacities.

4.2 Advantages of Combined Processes
Synergistic effect of membrane separation and condensation: The condensation process significantly extends the service life of membranes and adsorbents, thereby prolonging the overall lifespan of the unit.

Low-temperature, atmospheric-pressure operation: The entire treatment process operates at low temperatures and atmospheric pressure, ensuring safety and reliability.

Resource recovery: High-concentration Vapor return to the storage tank, where a portion naturally liquefies, generating direct economic benefits.

4.3 Intelligent Control System
Automatic start/stop: Real-time monitoring of tank pressure; automatic operation upon reaching the set value and automatic shutdown when dropping below the cutoff value.

Fully automatic PLC control: One-touch start/stop and round-the-clock automatic operation; no manual supervision required.

Dynamic pressure management: Automatically manages dynamic, minor fluctuations in tank pressure.

Online monitoring: Real-time monitoring of parameters such as inlet pressure, temperature, and flow rate; system operating status is clear at a glance.

4.4 Safe and Reliable Design
Explosion-proof rating: Ex d IIB T4 / Ex dib IIA T3; suitable for flammable and explosive environments.

Closed-loop circulation: Internal circulation design prevents Vapor leakage.

Intrinsically safe: The membrane separation process involves no phase changes or high temperatures, eliminating combustion and explosion risks.

4.5 Energy-saving and Environmental Benefits
Low operating costs: Compact footprint and low operating expenses.

Direct economic benefits: Recovered liquid oil returns to the storage tank, generating significant economic value.

Compliant emissions: Post-treatment tail gas concentration of non-methane total hydrocarbons is <25 mg/L (approx. 25 g/m³), far below national standards.

Carbon emission reduction: Significantly reduces VOC emissions, contributing to the achievement of "Dual Carbon" goals.
 

6.1 Selection Recommendations

6.2 Selection of Process Combinations

7.1 Installation Requirements
Install at gas stations that have completed the retrofit for Stage II vapor recovery systems.

Reserve a foundation for the equipment; install in a dedicated, well-ventilated area away from ignition sources.

Provide a 380V/50Hz power supply; power rating depends on the specific model.

Gas line connection: DN40 or DN50 flange connection.

7.2 Routine Maintenance
Maintenance Items Frequency Notes
Operating parameter check Daily Monitor pressure and temperature to ensure they are within normal ranges.
Membrane module performance check Every 3–6 months Check that emission concentrations meet standards.
Condenser cleaning Every 6 months Clean cooling fins for air-cooled models.
Membrane module replacement 3–5 years Assess based on any decline in separation efficiency.

7.3 Precautions
The inlet vapor stream must be free of solid particles and liquid oil droplets to prevent membrane fouling.

Prevent sulfur- and silicon-containing compounds from entering the membrane system to avoid membrane poisoning.

Regularly check the operating status of the vacuum pump to ensure the required pressure differential across the membrane.
 

This product complies with the following standards and policy requirements:

• "Emission Standard of Air Pollutants for Gas Stations" (GB 20952-2020): Treatment efficiency ≥95%; emission concentration ≤25 g/m³.
• Gas stations with an annual gasoline sales volume exceeding 2,000 tons are required to install Stage III vapor recovery systems.
• Some regions require an emission concentration of ≤10 g/m³ (higher-specification configurations are available).

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