Even after Stage I and Stage II vapor recovery retrofits, underground gasoline storage tanks still generate large volumes of volatile hydrocarbon vapors through tank‑breathing cycles during fuel unloading and temperature fluctuations. These accumulated vapors would otherwise vent directly to atmosphere, triggering VOC pollution, fuel loss, and non‑compliance with local emission codes. That is where a Stage III vapor recovery system with membrane technology comes in. The VOHON WHSH‑M unit uses proven membrane‑separation principle to treat tank vent vapors, and it must be deployed on gas stations already completed Stage 2 vapor recovery transformation.
At the heart of this system lies polymer membrane separation. Unlike activated‑carbon adsorption solutions that require frequent media replacement and produce solid waste, the membrane works on selective permeability: hydrocarbon vapor molecules pass through membrane fibres far faster than air molecules under pressure differential created by vacuum pump. The full workflow starts when tank pressure rises to the preset startup threshold (500 Pa). The booster pump draws tank vapors and applies pressurization. Vapor flows across the air‑cooled heat exchanger for cooling, then enters the gas‑liquid separation tank. A portion of gasoline condenses into liquid and flows back to underground storage. Remaining mixed gas feeds into the membrane module. Driven by vacuum pump negative pressure, hydrocarbon vapors penetrate the membrane and return to the tank for reuse. Clean air, which cannot pass the membrane barrier, is safely discharged to open air. Once tank pressure drops below stop‑pressure setpoint (50 Pa), the whole unit switches to standby mode and waits for next pressure rise深圳政府在….
VOHON’s membrane‑based Stage III system is built for hazardous gas‑station environments. It carries explosion‑proof rating Ex db eb ia mb IIB T4 Gb and IP55 enclosure protection for outdoor installation. The heavy‑duty cold‑rolled‑steel cabinet with electrostatic anti‑corrosion spray withstands ambient temperature ranging from ‑40 ℃ to 70 ℃ and relative humidity of 20‑90 %RH. Operating noise stays ≤75 dB, rated power sits 2.5‑3 kW, and processing capacity covers 4‑20 m³/h, matching small‑scale to large‑volume retail fuel sites. All explosion‑proof junction boxes require tight sealing; inspection or maintenance must be performed by certified technicians with combustible‑gas detector to confirm safe gas concentration before opening any explosion‑proof housing.
Intelligent PLC‑HMI control complements the membrane process. Operators view real‑time readings including inlet pressure, membrane‑module pressure, booster‑pump temperature and outlet emission concentration on the touch‑screen panel. System logs operational data every 30 seconds, stores historical curves, alarm events, and supports export of weekly, monthly and yearly reports. Reserved RS485 interface enables remote parameter adjustment, data download and equipment status monitoring. Built‑in fault self‑diagnosis alerts operators for phase‑sequence error, pump feedback loss or abnormal pressure, shortening troubleshooting cycles. The system runs unattended after commissioning, reducing routine labour cost for gas‑station operators.
Correct field installation guarantees stable membrane performance. Site teams need to prepare an elevated concrete foundation ≥200 mm above ground to avoid waterlogging. DN50 piping serves as vapor inlet and DN20 for liquid return. Flame arrestors and check valves must be fitted on corresponding pipelines, and full air‑tightness pressure test is mandatory before commissioning. Static‑grounding resistance shall be kept below 4 Ω following petrochemical standards.
Membrane‑driven Stage III vapor recovery offers gas‑station owners a low‑waste, automated path to meet tightening VOC emission rules, recover lost gasoline and maintain safe tank working pressure. For contractors and station operators seeking reliable outdoor vapor‑processing hardware, VOHON WHSH‑M delivers a complete membrane‑separation solution balancing safety, efficiency and easy maintainability.