Air-Cooled + Membrane vs. Membrane-Only: Choosing the Right WHSH-M Model
The WHSH-M stage-3 vapor recovery unit is available in two configurations. Both use the same membrane separation technology and the same footprint, but they differ in process architecture, power draw and noise. This article explains the difference so a station can choose the right model.
The two models at a glance
| Item | Air-Cooled + Membrane | Membrane-Only (Combined-Pump) |
|——|———————-|——————————-|
| Process | Compression, air-cooled condensation, then membrane | Membrane separation directly, vacuum pump return |
| Power | 2.7 kW | 1.3 kW |
| Noise | ≤75 dB(A) | ≤63 dB(A) |
| Weight | 410 kg | 390 kg |
| Capacity | 4–20 m³/h | 4–20 m³/h |
| Dimensions | 1300×900×1160 mm | 1300×900×1160 mm |
| Installation | 1 day | 1 day |
How the air-cooled + membrane model works
In this configuration, the vapor first goes through a compressor, which raises the pressure and the dew point of the hydrocarbons. An air-cooled heat exchanger cools the compressed vapor, and a gas-liquid separator collects the condensed liquid, which returns to the tank by gravity. The remaining uncondensed vapor then passes through the membrane module for final separation. This arrangement handles higher vapor concentrations and heavier vapor loads, because a large part of the hydrocarbon is recovered by condensation before the membrane sees it.
How the membrane-only (combined-pump) model works
In this configuration, there is no compressor and no condensation step. Vapor from the tank goes directly to the membrane module. Hydrocarbons permeate the membrane preferentially, and a vacuum pump returns the concentrated stream to the tank, where it re-condenses naturally at tank saturation conditions. Clean air is discharged. With fewer major components, this model is lighter, quieter and uses about half the power.
Which model fits which station
There is no universal “best” — the choice depends on the conditions:
– Choose the air-cooled + membrane model when: vapor concentration is high, recovery volume is a priority, or the tank farm has a heavier vapor load (larger tanks, high throughput, warm climate). The condensation stage recovers liquid directly and reduces the load on the membrane.
– Choose the membrane-only model when: energy consumption and noise matter most — for example stations close to residential areas, stations with limited electrical supply, or operators who want the lowest operating cost. The 1.3 kW draw and 63 dB(A) noise level are both substantially lower.
Both models provide:
– NMHC treatment efficiency above 99% under normal operation
– Discharge concentration far below the national emission limit
– Automatic start/stop on tank pressure, unattended operation
– Membrane design life of 10+ years, no consumables
For stations in doubt, the practical approach is to provide basic information (tank capacity, throughput, ambient temperature range, power availability) and let the supplier recommend a configuration based on actual conditions.
For more information: +86 135 2699 0215 / lixiang@vohonoilpipe.com
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