How Does a Vacuum Degasser Work? In‑Depth Look at Bubble Dynamics and Separation Efficiency

When drilling through a gas‑bearing formation, the returning drilling fluid often contains tiny bubbles that are not visible to the naked eye. These entrained gases are the silent enemy of mud density, pump performance, and rig safety. The machine that defeats them is the Vacuum Degasser. But how does it actually work at a mechanical and physical level? This standalone article explains the internal workings of a vacuum degasser, from bubble behavior under reduced pressure to the role of the vacuum pump, and why AIPU Solid Control Vacuum Degassers are trusted worldwide.

1. The Physics Behind the Process

A vacuum degasser works by exploiting two simple physical principles:

• Henry’s law: At lower pressure, less gas remains dissolved in a liquid.

• Bubble expansion: A gas bubble in a liquid grows larger when the surrounding pressure decreases.

When the degasser lowers the pressure above the mud, dissolved gas molecules come out of solution, and existing tiny bubbles swell. Larger bubbles have higher buoyancy and rise faster. The vacuum pump then removes them from the vessel.

No chemical additives are needed – only a controlled vacuum.

2. Main Components and Their Roles

To understand the working sequence, first know the key parts of a typical vertical vacuum degasser (like the AIPU APLCQ300):

3. Step‑by‑Step Working Cycle

Let us follow one liter of gas‑cut mud through an AIPU vacuum degasser.

Stage 1 – Entering the Vessel

Mud from the shale shaker compartment enters through a large‑diameter inlet (20″ on the AIPU APLCQ300). The large size minimizes pressure drop and prevents solids from jamming.

Stage 2 – Thin Film Generation

The mud strikes a high‑speed rotor (driven by a 22 kW motor in the APLCQ300). Centrifugal force flings the mud outward, creating a thin film only 1–3 mm thick on the vessel wall. This thin film exposes every gas bubble to the low‑pressure atmosphere. Without this step, bubbles deep inside the mud might not release.

Stage 3 – Vacuum Creation and Maintenance

A separate vacuum pump (1.1 kW in the APLCQ300) continuously evacuates the sealed vessel, maintaining a pressure of -0.02 to -0.04 MPa (gauge). At this pressure, the absolute pressure inside is only about 0.06–0.08 MPa – roughly half to two‑thirds of atmospheric pressure.

Stage 4 – Gas Expansion and Release

Under this reduced pressure, three things happen almost instantly:

• Dissolved gas (methane, H₂S, CO₂) comes out of solution – like opening a soda can.

• Entrained bubbles expand. A 0.5 mm bubble at atmospheric pressure grows to 2–3 mm.

• The expanded bubbles become highly buoyant and rise rapidly through the thin mud film to the top of the vessel.

Stage 5 – Gas Extraction

The vacuum pump draws the released gas out through a 1‑1/2″ vent line. If the gas is flammable or toxic (e.g., methane, H₂S), the vent line is connected to a flare ignitor or a scrubber. AIPU offers the APFI series electronic flare ignitors for safe combustion.

Stage 6 – Degassed Mud Discharge

Gas‑free mud falls to the bottom of the vessel and exits through a 6″ outlet. It flows back to the mud tank, usually into the degasser compartment, ready for further solids control (desander, desilter, centrifuge).

Stage 7 – Continuous Operation

The process repeats continuously. As long as mud flows in and the vacuum pump runs, gas is removed at ≥95% efficiency.

4. Why Vacuum Is More Effective Than Simple Gravity

An open tank or an atmospheric degasser allows some gas to escape naturally, but only from the surface. Bubbles deep in the mud remain trapped. By lowering the pressure throughout the whole vessel, a vacuum degasser makes bubbles expand everywhere, even those that would otherwise never reach the surface. That is why efficiency jumps from 70–85% (atmospheric) to 95% or more (vacuum).

5. Variations in Design – Different Ways to Create the Thin Film

While the vacuum principle is the same, different degasser designs spread mud differently.

5.1 Vertical Centrifugal Degasser (AIPU APLCQ300)

• Method: High‑speed rotor flings mud outward.

• Advantages: Compact, no clogging, easy to clean.

5.2 Tank‑Mounted Baffle Degasser (AIPU APZCQ series)

• Method: Mud flows by gravity over a series of baffles, creating multiple thin layers.

• Advantages: No external feed pump needed; very high capacity (240–360 m³/h).

5.3 Float‑Controlled Degasser (AIPU APVD series)

• Method: Internal float valve keeps a constant liquid level; mud slowly cascades.

• Advantages: Lowest power consumption, automatic operation.

All three types generate the same high‑efficiency gas removal, so your choice depends on rig space, flow rate, and power availability.

6. Technical Specifications – AIPU Vacuum Degassers

Here are the key numbers for AIPU vacuum degassers to help you understand performance capabilities.

AIPU APLCQ300 (Vertical)

AIPU APZCQ Series (Tank‑Mounted)

All AIPU degassers are built with:

• Three‑layer marine anti‑corrosion coating (sand‑blasted, epoxy primer, polyurethane topcoat)

• H₂S‑resistant steel option (316L or 2205 duplex) for sour gas fields

• ATEX / IECEX certification for hazardous areas

• Customizable electrical systems (380V/50Hz, 460V/60Hz, etc.)

7. How to Know If Your Degasser Is Working Properly

A well‑functioning vacuum degasser shows these signs:

• Stable vacuum between -0.02 and -0.04 MPa. Fluctuations indicate leaks or pump wear.

• Measurable density increase between inlet and outlet (0.03–0.10 SG, depending on gas content).

• Steady gas flow from the vent line (you can feel it with your hand near the outlet – but be cautious with toxic gas).

• No cavitation in downstream mud pumps.

If you see none of these, check for air leaks, worn vacuum pump, or a blocked vent line.

8. Common Operational Mistakes

• Running without the vacuum pump: The mud simply passes through but no gas removal occurs.

• Blocked vent line: Back pressure kills the vacuum; efficiency drops sharply.

• Feed rate too high: The degasser becomes flooded; mud does not form a thin film.

• Skipping maintenance: Worn seals or low vacuum pump oil destroy performance.

9. Why AIPU Vacuum Degassers Excel

AIPU Solid Control has been designing and manufacturing solids control equipment for over 20 years. Their vacuum degassers are used in more than 30 countries, with over 300 system‑equivalent units shipped. AIPU holds API, HSE, and multiple product certifications.

When you choose an AIPU vacuum degasser, you get:

• ≥95% gas removal efficiency – Restores mud density quickly.

• Rugged construction – Withstands the harshest drilling environments.

• Complete customization – H₂S‑resistant steel, ATEX/IECEX, any voltage/frequency.

• Global support – AIPU provides full documentation, installation guidance, and after‑sales service.

10. Conclusion

Now you know in detail how a vacuum degasser works: it creates a low‑pressure chamber that makes dissolved gas come out of solution and entrained bubbles expand. The expanded bubbles rise to the surface and are continuously sucked away by a vacuum pump. The result is clean, degassed mud that keeps your drilling operation safe and efficient.

Whether you need a compact vertical degasser (AIPU APLCQ300), a high‑capacity tank‑mounted unit (AIPU APZCQ series), or an energy‑saving float‑controlled model (AIPU APVD series), AIPU has the right solution for your rig.

Trust AIPU for reliable, high‑efficiency vacuum degassers – because gas belongs in the formation, not in your mud.