Combined Tertiary Vapor Recovery Unit

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The combined tertiary Vapor recovery unit refers to an environmental protection device that scientifically integrates two or more Vapor recovery technologies (such as condensation, adsorption, and membrane separation) into a single system. It is specifically designed to treat the breathing loss of Vapor in gas station storage tanks caused by diurnal temperature variations and pressure changes, as well as residual Vapor collected and emitted when the gas-liquid ratio of the secondary Vapor recovery system is greater than 1.

With increasingly stringent environmental regulations, a single technology route can no longer achieve a balance between high recovery rate, low operating cost, and stable compliance. Combined processes have become the mainstream solution for tertiary Vapor recovery. The mainstream process adopts a condensation + adsorption combination technology, reducing the potential temperature risks of the adsorption bed through pre-cooling, achieving a non-methane total hydrocarbon concentration in the exhaust gas of 0.36-0.45 mg/m³. The product meets the requirements of the "Emission Standard of Air Pollutants for Gas Stations" (GB 20952-2020) and the "Technical Standard for Vapor Recovery and Treatment Facilities" (GB/T 50759-2022), with a treatment efficiency of ≥95% and an emission concentration of ≤25g/m³. It is a reliable choice for gas stations to achieve a win-win situation of environmental compliance and economic benefits.

2.1 Core Technology Concept
The core design concept of the combined process is "tiered treatment and complementary advantages": firstly, a primary technology (such as condensation) recovers most of the high-concentration Vapor ; then, a secondary technology (such as adsorption) deeply purifies the remaining low-concentration exhaust gas, ultimately achieving the dual goals of high recovery rate and ultra-low emissions. Each individual technology has its applicable scope and limitations; the combined process, through scientific matching, fully leverages the advantages of each technology and compensates for its shortcomings.

2.2 Core Process Technology Route
Currently, the main methods for treating tertiary Vapor recovery at gas stations both domestically and internationally include condensation, absorption, adsorption, and membrane separation, as well as their combined processes. The mainstream combined processes in the current market include the following solutions:

2.3 Condensation + Adsorption Combination – Detailed Process Flow Explanation

The condensation + adsorption combination is currently the most widely used and mature solution. Its process flow is as follows:

The adsorption method utilizes adsorbent materials such as activated carbon to adsorb organic matter in Vapor . After adsorption saturation, the Vapor are separated by vacuum desorption or steam desorption, and finally condensed into liquid oil. The condensation method uses low-temperature cooling to liquefy hydrocarbons in the Vapor , thereby achieving Vapor recovery. When the two methods are used in combination, the Vapor are first condensed to -75℃ (can be cooled in three stages). Alkanes with C3 or higher are basically condensed and recovered, with a recovery rate of 80%-90%. The remaining small amount of alkanes is sent to the adsorption system for adsorption and recovery treatment. Air that meets the standards after adsorption is discharged; a small amount of Vapor after desorption is returned to the system inlet for circulation. The recovery rate can reach over 97%. The refrigeration temperature setting is designed and formulated according to different operating conditions.

2.4 System Composition

The combined Vapor recovery unit mainly consists of the following core components:

In terms of control, PLC control and frequency conversion regulation technology are used to realize the automatic control of the entire process of Vapor collection, condensation and liquefaction, oil-water separation and condensate oil transportation into storage. The refrigeration unit can realize variable operating condition regulation and economical system operation.

3.1 Condensation + Adsorption Combination – Technical Parameters

3.2 Condensation + Membrane Separation Combination – Technical Parameters

5.1 Comparison of Mainstream Combination Schemes and Selection Recommendations

5.2 Key Selection Factors
Selection should not solely rely on the initial price; the following factors must be comprehensively evaluated:

• Vapor Concentration Fluctuation Range:Concentration is high during loading operations and low during daily respiration losses; the equipment must be adaptable to a wide range of operating conditions.
• Emission Limit Requirements: Some regions enforce stricter local standards; it is necessary to confirm whether the equipment's measured data consistently meets these standards.
• Average Daily Vapor Production:Determined by refueling volume, temperature difference, and storage tank volume, affecting the equipment's processing capacity.
• Site and Power Conditions: Skid-mounted equipment saves space, but the power load and explosion-proof rating must be assessed.
• Operation and Maintenance Capabilities: Adsorption equipment requires regular replacement of the packing material; condensation systems rely on professional refrigeration maintenance.
• Compliance Acceptance:The equipment must provide a third-party testing report and support online monitoring interfaces.

5.3 Selection Recommendations

For the vast majority of gas stations that need to meet national standards (annual sales exceeding 2000 tons), the condensation + adsorption combined process is currently the most comprehensive, widely used, and stable solution. The condensation + membrane separation solution has been successfully applied in some high-standard projects, and its advantages, such as low operating costs and no adsorbent replacement costs, are gaining wider recognition.

6.1 Multi-stage Cooling Upgrade

Four-stage condensation technology is available on the market, with condensation temperatures set from 3℃ to 40℃, 75℃, and 115℃. Adding a fourth stage of deep cooling down to -115℃ to the three-stage condensation system, employing two-stage cascade + self-cascade refrigeration technology (i.e., multi-stage coupled refrigeration), allows for flexible adjustment within the temperature range of -80℃ to -115℃, accommodating both extreme and moderate low-temperature operating modes to cope with varying Vapor compositions and large fluctuations in treatment concentrations, and adapting to increasingly stringent emission standards.

Some continuous production processes employ a dual-path switching process in the low-temperature section-if ice blockage occurs on one side, the system directly switches to the other path for heat exchange and condensation in the cold box, while defrosting is performed on the ice-blocked side to ensure continuous and stable recovery of overflowing gases.

6.2 Expanded Application Areas

Combined Vapor recovery devices have expanded from tertiary Vapor recovery at gas stations to a wider range of applications. They are suitable for Vapor recovery systems in refineries and oil depot tank trucks, associated gas recovery systems in oil fields, separation and recovery of chemical gases such as benzene, and the separation, concentration control, and recovery of mixed gases in chemical production processes. With increasingly stringent environmental standards, the application of combined processes in oil depots, docks, and chemical industrial parks is also continuously expanding.

7.1 Installation Conditions

Installation at gas stations that have completed secondary vapor recovery system upgrades.

Equipment foundations must be reserved. Installation must be in a well-ventilated, dedicated area away from heat sources.

A 380V 50Hz three-phase power supply is required; power output depends on the model.

Gas connection: DN40 or DN50 flange connection.

The exhaust pipe outlet should be at least 4 meters above ground level, away from areas with high foot traffic.

7.2 Selection Considerations

Establishment of the model requires an accurate assessment of the gas station's sales volume. An undersized model will result in insufficient recovery rates, while an oversized model will lead to wasted investment. Based on the policy requirement that gas stations with annual sales exceeding 2000 tons must install tertiary vapor recovery devices, a processing capacity of at least 8 m³/h is recommended, conforming to the framework agreement standards of large oil companies such as CNOOC. Local climate conditions should also be considered; in cold regions, anti-freezing measures (such as electric heat tracing, condenser unit anti-freezing protection, etc.) are necessary.

Specific pricing and delivery time are subject to actual inquiry.

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