What Is a Boil Off Compressor? Meet AZS – A Reliable Boil Off Compressor Manufacturer in China
If you work with LNG (liquefied natural gas) or cryogenic liquids, you’ve seen a problem: the liquid constantly evaporates, even in well‑insulated tanks. That vapor is called “boil off gas.” You need a boil off compressor to collect that gas and either re‑liquefy it or send it to a pipeline.
I’ll explain how a boil off gas compressor works, introduce AZS – a Chinese manufacturer that builds them, and break down the price. No complex engineering – just clear, useful info.
Boil Off Gas Compressor – Simple Working Principle
A boil off gas compressor (also called BOG compressor) does the same job as a normal compressor: suck in gas, squeeze it, push it out. But the conditions are extreme. Here’s the step‑by‑step:
Step 1 – Cold gas enters
Boil off gas is very cold – sometimes as low as -160°C. Special cold‑resistant valves and seals allow the gas to flow into the cylinder without freezing or cracking.
Step 2 – Compression
The piston moves forward. The gas temperature rises (by physics law), but it stays below flammable limits. The cylinder walls are made of stainless steel or bronze to handle thermal shock.
Step 3 – Cooling & discharge
After compression, the hot gas goes through a heat exchanger (or is sent directly to a re‑liquefaction unit). Then it’s discharged into a pipeline or back to the tank’s vapor space.
Why AZS’s BOG Compressor Is Different
Most standard compressors would fail in 10 minutes at -160°C. AZS uses PTFE piston rings that stay flexible in extreme cold, double dry‑gas seals with nitrogen purge, and a special crankcase heater to prevent oil thickening. That’s engineering that lasts.
AZS – A Trusted Boil Off Compressor Manufacturer in China
AZS has been making gas compressors for over 15 years. Their boil off compressor models are used in small LNG satellite stations and large import terminals across Asia and the Middle East.
Key Features of AZS Boil Off Compressors
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Material: Stainless steel 316L or Ductile iron for low‑temp service.
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Seal type: Magnetic coupling or double mechanical seals with leak detection.
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Safety: ATEX‑certified motors and explosion‑proof electrical boxes.
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Capacity: From 50 m³/h up to 3,000 m³/h, with discharge pressure up to 25 bar.
Quality Testing
Every boil off gas compressor is helium leak‑tested and cold‑cycled in AZS’s factory. You get a test report showing performance at -160°C. No shortcuts.
Boil Off Compressor Price – What You Actually Pay For
Prices vary widely. A small, single‑stage BOG compressor (100 m³/h) starts around $18,000. A large two‑stage unit (1,500 m³/h) can cost $120,000 or more. Here’s what drives the cost:
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Inlet temperature range – Colder gas needs more expensive alloys and thicker insulation. Adding -196°C capability adds 30% to price.
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Compressor type – Reciprocating (piston) is cheaper upfront. Screw type is more efficient for continuous duty but costs 40‑60% more. AZS mainly builds reciprocating BOG compressors.
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Sealing system – Magnetic drive (sealless) costs more but guarantees zero leakage. Mechanical seals are cheaper but require regular nitrogen purge.
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Capacity and stages – Higher flow needs bigger cylinders. Higher pressure (above 15 bar) requires two stages with an intercooler – that adds $15,000‑25,000.
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Custom accessories – Remote monitoring, vibration sensors, or explosion‑proof enclosures add 10‑20%.
AZS tip: Always ask for a price breakdown by material, seal type, and instrumentation. Avoid quotes that don’t specify cold‑service materials – they may send you a standard air compressor that will crack.
FAQ
1. Can I use a boil off compressor for other gases like nitrogen?
Yes – but you must change the piston rings and valve materials. AZS can adapt a BOG compressor for nitrogen, methane, or ethylene. Tell them your gas composition and inlet temperature.
**2. How often should I service a boil off gas compressor?
Every 2,000 running hours or annually. Key tasks: check piston rings, replace valve plates, test seals for leaks, change crankcase oil (special low‑temp oil). AZS provides service kits with step‑by‑step instructions.
3. What happens if a BOG compressor fails?
Tank pressure rises. Relief valves will vent gas to a flare or atmosphere – that’s lost product and an environmental concern. That’s why AZS recommends a backup boil off compressor for critical LNG plants. A spare unit is not a luxury; it’s insurance.
4. Does AZS offer explosion‑proof BOG compressors?
Yes. All AZS boil off compressors for LNG service come with explosion‑proof motors (Ex d IIB T4) and ATEX‑certified sensors. Tell them your zone classification (e.g., Zone 1 or Zone 2).
5. What’s delivery time from AZS China?
Standard models (300 m³/h, stainless steel, mechanical seals) take 45‑60 days. Custom low‑temp magnetic drive units take 90‑120 days. Spare parts ship within 7 days.
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