Large-Scale Oil Terminal Solutions
The vapour leaving a terminal does not wait for the loading bay. It leaves all night, through the tank breathers, at a rate nobody watches until the fence-line monitor starts recording.
Wohong builds skid-mounted vapour recovery units for tank farms and loading terminals, 100 to 1,000 m³/h in a single skid. The 500–1,000 m³/h models sit inside one explosion-proof type certificate, and 400 and 800 m³/h units are already in service at terminals in China.
A terminal is not a bigger petrol station
Four things separate a terminal job from a retail one. Get any of them wrong and the unit either sits idle or runs itself to death.
Flow arrives in batches, not in a line
A bay that is quiet at ten can pull 800 m³/h at two and nothing by four. The unit is sized on the peak and has to stay stable at a tenth of it. Variable-frequency drive, plus a cold store that holds its temperature between batches, is how one skid covers both ends.
The tank cannot be pushed
A storage tank has a narrow band of pressure it is allowed to live in. Pull too hard and you lift the roof seal or draw air in through the breather; leave it alone and the breather does the emitting for you. Set-points on tank pressure, not suction on the compressor, should decide when the unit runs.
Oxygen is the hard stop
Air drawn into a vapour header puts the whole recovery train inside the flammable envelope. A terminal unit has to measure oxygen on the inlet and stop on it — not raise an alarm and hope somebody looks at the screen. On a header fed by several tanks, that measurement belongs upstream of every branch, or the trip is a guess.
The fence line is close
Terminals sit next to ports, roads and, increasingly, housing. The number that matters to the permit is not the recovery percentage — it is what the stack reads during the worst hour of the year, when the wind is wrong and a batch has just landed. Round-the-clock efficiency means nothing if that hour fails.
Three sources, one header
Most terminals only instrument the third one. The first two run every day of the year without anyone counting them — and they are usually the reason a site fails its first stack test.
| Source | What drives it | How it is captured |
|---|---|---|
| Tank breathingsmall breathing | Day-to-night temperature swing and barometric change. Continuous, low concentration, easy to ignore — and the largest annual mass on many sites. | Each tank's pressure/vacuum valve feeds a vapour header into a common manifold tied to the unit inlet. |
| Bulk transferlarge breathing | Receipt of a road tanker, a rail car or a pipeline batch. Displaced vapour volume equals liquid volume, so the unit sees the transfer curve, not an average. | Header tied to the tank being filled; the unit ramps with the transfer instead of cycling on its own set-point. |
| Loading rackif present on site | Every loaded compartment displaces its own volume. Highest instantaneous rate on the site, shortest duration. | Rack vapour line into the same header. An existing rack can normally be tied in without changing the loading arms. |
Two routes, chosen by the number in your permit
Compression and condensation are in both. What changes is the last stage — and that stage is decided by the stack limit, not by preference.
Compression + condensation + membrane
Oil is compressed to just below its dew point, condensed against air, and the remaining hydrocarbon is pulled through a selective membrane and returned to the tank as liquid. Nothing is consumed and nothing has to be replaced on a schedule.
- Outletaround 10 g/m³ NMHC
- Consumablenone
- Cold sideabove 0 °C, no defrost cycle Best whenlimit is in the g/m³ range
- Membrane life2-year warranty, 8–10 year design
Compression + condensation + carbon
Two carbon vessels in alternating duty, regenerated in place under vacuum so the carbon is not carted away and replaced. This is the route used where the stack has to read in the tens of mg/m³, which is where most terminal permits now sit.
- Outlet≤120 mg/m³ NMHC, measured
- Consumablecarbon, vacuum-regenerated in place
- Extra dutyvacuum pump, 40 m³/h class
- Best whenlimit is in the tens of mg/m³
- Safetyflame arrestor on each vessel inlet ul>
Six sizes, one frame family
All six are built on the same skid logic: same control philosophy, same compressor type, same membrane construction. What changes is duty and module count — which is why a 400 m³/h reference site tells a buyer something real about the 1,000 m³/h unit.
| Model | Vapour duty | Execution | Status |
|---|---|---|---|
| WHSH-100 | 100 m³/h | Single skid | standard |
| WHSH-400 | 400 m³/h | Single skid | in service |
| WHSH-500 | 500 m³/h | Single skid | in certificate |
| WHSH-600 | 600 m³/h | Single skid | in certificate |
| WHSH-800 | 800 m³/h | Single skid | in service |
| WHSH-1000 | 1,000 m³/h | Single skid | in certificate |
Above 1,000 m³/h the unit is assembled from parallel skids sharing one control system and one stack, not from a larger single frame. A 5,000 m³/h condensation–membrane unit has been built on exactly that logic for gas processing — same modules, four trains.
The tank sets the schedule, the unit follows
On a terminal, the recovery unit is a slave to the tank pressure. Everything below is standard on our skids — not an option list.
Start and ramp
Header pressure crosses the upper set-point: the unit starts and the compressor runs up to duty under PID control of inlet pressure.
Modulate
The drive trims back. Flow follows the batch instead of cycling the motor on and off, which is what kills compressors on transfer duty.
Stop, hold, wait
The unit stops and stays sealed. Tank pressure recovers on its own; the next batch restarts the same sequence with no operator action.
Liquid handling
Separator level opens the return pump and its valve at 500 mm and closes them at 200 mm. Recovered product goes back to the tank, not to a drum.
Automatic trips
- 5%Inlet oxygen above limit — stop, no restart until purged
- PHeader over-pressure — relieve and trip
- TDischarge over-temperature
- LSeparator level high-high
- WCooling or instrument air loss
- EPower failure — valves fail to the safe position
Trips are hard-wired as well as programmed. The PLC is Siemens S7-1200 with a touch panel, Ethernet TCP/IP to the terminal DCS.
Built for the zone it stands in
A terminal recovery unit is installed inside the hazardous area, not beside it. The electrical documentation has to satisfy an inspector who has never seen the plant before.
| Item | Execution | Why it matters on site |
|---|---|---|
| Whole unit | Ex d ib mb IIB T4 Gb, type certificate covering the 500 / 600 / 800 / 1,000 m³/h models | The frame is assessed as one assembly, not as a collection of certified parts. |
| Field instruments | Ex d IIB T4, IP55; transmitters with local display | A technician can read pressure and temperature at the skid without opening a panel. |
| Installation, maintenance, repair | Company holds hazardous-area installation, maintenance and repair accreditation under the IECEx scheme | Your local contractor can be supervised by people whose scope covers the work, not just the sale. |
| Flame arresters | DN150 detonation-arresting type on each tank branch | Stops a header event from propagating back into a tank. |
| Earthing | Common grid for working, protective, lightning and static earthing, below 4 Ω | Static is the ignition source nobody plans for. |
| Pressure vessels | Design to 0.8 MPa(G), SS304 wetted parts | Condensers and separators see the full compressor discharge. |
| Seismic | Designed for intensity 8 | Coastal and delta terminals are not all in low-seismic zones. |
What has actually been built
Design basis on one side, measured result on the other. The terminals behind these lines stay confidential — the numbers do not.
| Application | Duty | Process | Result |
|---|---|---|---|
| Product terminaltank farm | 400 m³/h | Compression + condensation + membrane | ≥95% recovery |
| Product terminaltank farm | 800 m³/h | Compression + condensation + membrane | ≥95% recovery |
| Depot tank farmlow-concentration vapour | 50 m³/h | Compression + condensation + carbon | ≥95%, NMHC ≤120 mg/m³ |
| Gas processingreference for scale, not a terminal | 5,000 m³/h | Condensation + membrane, four parallel trains | ≥95% separation |
Several 400 m³/h units are in service on the same skid design. The working envelope the 1,000 m³/h model covers is the one those units have already been running inside.
From signature to a running unit
Layout and P&ID
General arrangement, P&ID and foundation drawing released within one week of contract.
Formal drawing set
Issued-for-construction set, three hard copies, plus the electrical and utility schedules.
Manufacture
50 days for a compact frame, 90 days for the large single-skid models, ex-works.
Installation and commissioning
Our engineers attend the first unit on site: setting, wiring checks, loop test, start-up, handover.
Response and attendance
Twelve hours to a technical answer, forty-eight hours to a person on site.
Design life and spares
Main equipment specified for ten years or more; spare parts supplied for the life of the unit.
Four numbers and we can size the skid
We do not quote from a table. Send these four and what comes back is a dimensioned proposal — skid layout, utility list, utility consumption and a stack figure we will put in writing.
Peak and average vapour flow, in m³/h — not the tank volume, the vapour rate the header actually sees.
Product and vapour composition — gasoline, diesel, crude, ethanol blend; the hydrocarbon mix sets the condenser duty.
The pressure band your tanks allow, in Pa, from the tank design — this sets the start and stop points.
The stack limit you must meet, in mg/m³ NMHC, and the method and averaging period used to measure it.
If the fourth number is still open, say so. The choice between membrane and carbon is usually decided by that number alone, and it is better to settle it before the skid is drawn than after.
Before the first meeting
The terminal is already built. Can a unit be added later?
Usually yes, and it is the normal case. The unit arrives as a skid: you provide a hardstanding, a vapour header from the tanks, a liquid return line and a power feed. The work inside the bund is limited to the header connection and the return point.
What has to be checked first is the tank pressure band and the existing P/V valve setting — a recovery unit changes the duty those valves see.
Is 1,000 m³/h a single skid, or several in parallel?
A single skid, and it is one of the models inside the unit type certificate. Above that, units are assembled from parallel skids sharing one control system and one stack — the 5,000 m³/h gas processing unit was built that way, in four trains.
Where does the recovered liquid actually go?
Back into the tank it came from, through a magnetically coupled return pump sized for the skid. Nothing is drummed, and there is no wastewater stream: the condenser is air-cooled, so the unit needs no process water at all.
What happens on a power failure or an over-pressure?
The unit trips and the valves go to their fail-safe position; the tank keeps its own mechanical P/V protection, which is independent of our control system. Trips are hard-wired as well as programmed, so a PLC fault does not leave a compressor running against a closed header.
Send us the four numbers.
A terminal assessment starts with the vapour rate, the product, the tank pressure band and the stack limit. With those we will tell you which model fits, and whether membrane or carbon is the honest answer for your permit.
- Company
- Luoyang Wohong Petrochemical Equipment Co., Ltd.
- Address
- W2-1, Dongda Science & Technology Park, Luoxin Industrial Cluster, Xin'an County, Luoyang, China
- lixiang@vohon.cn
- Phone / WeChat
- +86 135 2699 0215
- +86 185 3794 6079
Tell us the site location if you can. Terminal permits are local documents, and the stack figure we commit to depends on how your authority measures it.
