How to treat the volatile oil and gas during gasoline storage and transportation? The complete process of membrane separation, enrichment, and reflux
Release time: 2026-10-08
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In the storage and transportation chain of gasoline from refineries to terminals, evaporation losses occur continuously at various stages: refinery loading, oil depot receiving, dispatching, and storage, as well as gas station unloading and storage. Each stage involves the emission of oil vapor. These emissions pose both safety and environmental hazards and represent actual oil product losses. A common approach to addressing this issue is to install oil vapor recovery devices during the storage and transportation process. Membrane separation and enrichment for reflux is one of the widely adopted methods at present - enriching the oil vapor, liquefying it, and returning it to the tank for closed-loop circulation without external discharge. This article clarifies the loss stages, recovery processes, and key configuration points for each stage along the storage and transportation chain, providing a reference for site construction and renovation.
In which stages does evaporation loss occur
The evaporation loss in the storage and transportation chain is divided into three stages: the loading process between the refinery and the oil depot, where the concentration of oil vapor displaced from the loading arm is high and the instantaneous volume is large, accounting for the majority of the loss; the large and small breathing of oil storage tanks in the oil depot, which occurs continuously with oil receiving and dispatching operations and temperature differences between day and night, with small volumes but daily occurrence; and the loss during the unloading and storage process at gas stations, which are small-scale operations with numerous locations. The operating conditions for these three stages are different, and the configuration specifications of the recovery devices are also different - the loading process is configured according to peak gas volume, the tank breathing is configured according to continuous small flow, and gas stations mainly use small-scale skid-mounted devices for tertiary oil vapor recovery. Understanding the loss volume at each stage of one's own chain is the first step in configuring devices.
How to proceed with membrane separation enrichment reflux
The core of membrane separation and recovery lies in enrichment and reflux: the mixed gas of oil vapor and air enters the membrane unit after being collected and pressurized. The rubber-like separation layer has a high solubility for oil vapor and a permeation rate tens of times higher than that of air, allowing oil vapor to preferentially permeate through the membrane to form enriched gas. The enriched gas, with high concentration but small total volume, is sent back to the compressor inlet for another round of condensation and liquefaction, with the condensate flowing back to the storage tank. The retained air, with its hydrocarbon concentration significantly reduced, meets emission standards and is discharged. The entire process is a closed-loop cycle, with the enriched gas not being discharged externally, ensuring a high overall recovery rate. The membrane components are non-porous and dense structures, eliminating the risk of pore blockage, and there is no electrostatic accumulation during operation, making them well-suited for scenarios with strict explosion-proof requirements, such as gasoline storage and transportation.
How to configure each link
Configuration is determined by the process: the oil depot loading process is equipped with a combination of condensation and membrane, where condensation collects high-temperature and high-concentration parts, while the membrane controls the low-concentration segment, and the buffer tank reduces peak and fills valley; the gas volume in the tank breathing process is small, so a single-stage membrane unit plus a small condenser is sufficient, with light investment; the tertiary recovery at gas stations uses a skid-mounted device, where the underground tank breathing gas is enriched by the membrane and returned to the unloading circuit. The devices in each process can operate independently or be networked for centralized processing, determined by the layout and investment scope of the depot and station. The common principle is that there must be a filtration and dehumidification section before the membrane - liquid droplets and particulate matter reaching the membrane surface will halve its lifespan.
Configuration reference
| link | Operating condition characteristics | Configuration aperture |
|---|---|---|
| loading and shipping | High concentration and instantaneous large volume | Condensation and film-forming combination, buffering and peak shaving |
| Tank breathing | Continuous low flow | Single-stage membrane plus small condenser |
| Oil unloading and storage at gas stations | Numerous locations, small scale | Skid-mounted three-time recycling |
| Pre-treatment before membrane | Prevent liquid droplets and particles from entering the membrane | Filtration and dehumidification are commonly used |
| Where does the enriched gas go | High concentration and small total amount | Return to the compressor inlet for circulation |
| Emission side | The trapped air meets the standard | Submit inspection by batch and enter into the ledger |
Operation and reconciliation management
- Regular inspections of the leak tightness of collection pipelines in each link, and monthly inspections of breakaway couplings and valve groups;
- Record the membrane pressure difference and vacuum degree daily, and plot the trend on a weekly basis;
- The condensation temperature level is switched according to load levels, and electricity consumption is calculated on a monthly basis;
- The emission outlets are inspected in batches, and the data is archived along with the operation records;
- The recycling and turnover volumes are reconciled monthly, and any anomalies are first investigated at the collection end;
- The inspection of explosion-proof zones and electrostatic grounding has been included in the monthly checklist.
Frequently Asked Questions
What level can the recovery rate reach?
The overall recovery rate of the condensation and membrane combination can reach approximately 99%, with emission concentrations consistently below the limit; the specific level is related to concentration conditions and device load, and is subject to actual measured data from continuous operation.
Can old oil depots be renovated?
Okay. The existing condensation or absorption device can be retained after calculating the margin, and a membrane control section can be added later. The collection and buffering parts can be reused, resulting in a much lower investment for the renovation compared to a complete replacement, and the downtime for the business is also shorter.
How to evaluate an investment?
Estimate by segment: For the loading segment, estimate based on the peak gas volume at the crane position; for tank breathing, estimate based on tank capacity and turnover volume. First measure the concentration, then provide configuration and quotation. Consider the sensitivity range together to avoid estimation by guesswork.
This article is compiled by Luoyang Wohong Petrochemical Equipment Co., Ltd., which provides design, manufacturing, and operation and maintenance services for condensation recovery, membrane separation recovery, and complete solvent recovery equipment to chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please feel free to contact us for discussion.
