VRU vapor recovery unit is the core processing equipment for stage‑Ⅲ hydrocarbon vapor treatment at gas stations. It collects gasoline‑rich vapor‑air mixture generated from underground storage tank breathing, tanker unloading and fuel dispensing operations. Vapor concentration fluctuates obviously under actual site conditions, surging during oil unloading and dropping in idle periods. The incoming gas stream may carry tiny oil mist, condensed liquid droplets and fine impurities, which may bring risks such as blockage or partial performance degradation to core processing components. The unit needs to handle intermittent variable‑load airflow continuously, satisfy emission compliance requirements, and realize liquid fuel recovery for economic benefits.
Traditional treatment modes have inherent shortcomings when coping with gas station vapor. Direct combustion can eliminate hydrocarbon pollutants completely, yet all recyclable fuel components are burned off, resulting in considerable resource loss. Combustion of hydrocarbon‑mixed gas may produce harmful by‑products, and supporting flue‑gas treatment increases overall investment and daily operating expenditure. Single activated‑carbon adsorption belongs to pollutant transfer technology rather than resource recycling solution. Under conditions of fluctuating vapor concentration and oil‑mist entrainment, adsorbent material is prone to early saturation and penetration. Frequent shutdown for media replacement generates large volumes of hazardous waste and raises long‑term operational costs. Simple low‑temperature condensation is subject to hydrocarbon partial‑pressure limitations. Satisfactory recovery performance can only be achieved under high‑concentration vapor input, while processing efficiency decreases sharply when vapor concentration declines, failing to deliver stable treatment effects under variable‑load working conditions.
Combined compression‑condensation‑membrane separation process adopts fully‑physical working principle without combustion or chemical reaction, well suited for gas‑station VRU application scenarios. Mixed vapor firstly flows into pre‑treatment modules, where multi‑stage filtration and demisting structures remove entrained oil mist, free liquid droplets and solid impurities, protecting downstream compressors, condensers and membrane elements from fouling and blockage. Purified vapor enters compression section to raise partial pressure of hydrocarbon molecules and create favorable conditions for liquefaction. Afterwards the gas flows into multi‑grade condensation modules, where most hydrocarbon components are liquefied and separated according to different boiling‑point ranges, accomplishing primary liquid‑fuel recovery.
Residual gas stream after condensation still contains certain hydrocarbon components and is delivered to high‑performance organic‑membrane separation assembly. Based on selective permeability differences between hydrocarbon molecules and air, membrane elements concentrate organic components. Purified air is discharged up to standard, and high‑concentration hydrocarbon‑enriched flow loops back to the front‑end of compressor for cyclic re‑processing inside the whole system. Closed‑loop cyclic operation maximizes vapor recovery potential. Recovered liquid gasoline passes through sedimentation and filtration procedures, and can be sent back to underground storage tanks after meeting quality requirements. Valuable fuel resources lost through volatilization are recycled, volatile organic compound emissions are cut down, and comprehensive costs including fuel consumption and waste disposal are reduced.
Design and configuration of VRU shall match real‑world operating conditions at gas stations. Media‑contact pipelines, valves and heat‑exchange assemblies adopt anti‑corrosion structural materials to resist erosion from oil‑borne impurities and condensed fractions. Complete over‑pressure, over‑temperature and leakage‑detection interlock mechanisms are configured to prevent safety risks brought by flammable hydrocarbon vapor. Automatic control system supports frequency‑conversion regulation, dynamically adjusting equipment running load following real‑time changes of vapor flow rate and concentration, adapting to intermittent vapor generation characteristics, avoiding overload operation or ineffective idling, and optimizing overall energy consumption. Hierarchical pre‑treatment intercepts oil mist and particulate contaminants effectively, extending service life of precision core components such as membrane elements and heat exchangers. Engineering design must take measured field data including vapor flow, component proportion, concentration range and impurity content into full account. Universal standardized models cannot be applied blindly. Proper skid layout, standardized installation procedure and periodic routine inspection guarantee long‑term stable operation of vapor‑processing system, fulfilling environmental compliance and resource‑recycling objectives for gas‑station storage and distribution facilities.