CBK Liquid Ring Compressor for High Discharge Pressure Gas Service

A liquid ring compressor is usually chosen when the process gas is wet, corrosive, toxic, or flammable, and a dry machine would struggle. Buyers sometimes shorten the name to “liquid compressor”, although it is the gas, not the liquid, that gets compressed. Within this family, duties split clearly by pressure and by flow. Some services need to move a large volume with a modest pressure rise. Others need to push a smaller volume to a much higher discharge pressure.

Kenflo's CBK liquid ring vacuum compressor is built for the second case. It delivers a discharge pressure of 0 to 0.7 MPa(G), about 7 bar(g) or 100 psig, across a capacity range of 1 to 150 m³/min. Kenflo describes it as its latest energy-saving vacuum compressor, designed to be safe, reliable, and easy to maintain.

This article explains the high discharge pressure demands of a liquid ring machine, how the CBK design meets each demand, and where the compressor is typically installed in refinery and chemical plants.

Where CBK Fits in a Liquid Ring Compressor Range

Kenflo offers two liquid ring compressor models that cover opposite corners of the pressure-flow map. The figures below come from the official product pages.

CBK reaches almost three times the discharge pressure of CBA2, while CBA2 moves close to ten times the volume. For a gas that must be lifted to several bar before recovery, storage, or a downstream unit, CBK is the starting point. For higher pressures still, Kenflo also offers a tandem unit, covered later in this article.

What High Discharge Pressure Demands from the Design

In any liquid ring compressor, an impeller turns inside the casing and throws the service liquid outward into a rotating ring. The cells between the vanes and the ring shrink as they approach the discharge port, compressing the gas trapped in them. Because the gas is in direct contact with the liquid, much of the heat of compression passes into the liquid. The process therefore runs nearly isothermally, and the discharge temperature stays far below what adiabatic compression would produce.

Raising the discharge pressure changes the mechanical picture. The larger pressure difference loads the impeller and shaft. The casing joints must hold a higher internal pressure. The shaft seal must contain a gas that is often toxic or flammable. The CBK design responds to each of these points.

Balanced axial thrust

The CBK uses a symmetrical impeller with double suction and double discharge. Gas enters and leaves on both sides in the same way, so the pressure forces on the two halves cancel and the theoretical axial force is zero. The bearings then only need to locate the rotor, rather than carry a large thrust load that grows with discharge pressure.

Bearings at both shaft ends

The shaft is supported at both ends. Two cylindrical roller bearings, mounted symmetrically, carry the radial load, and a pair of angular contact ball bearings fixes the rotor’s axial position. All bearings are SKF. Supporting the rotor on both sides of the impeller keeps shaft deflection low under load, which protects clearances and the shaft seal.

Shaft and impeller

The impellers are dynamically balanced, which limits vibration at operating speed. The shaft is made of duplex stainless steel 1.4462, a high-strength grade that also brings good corrosion resistance to the wetted end.

Casing and shaft sealing

Rubber O-rings seal the casing joints and are rated to withstand high pressure. At the shaft, the CBK can be fitted with a single mechanical seal, a double mechanical seal, or a dry gas seal. The choice usually follows the gas hazard and the site's leakage limits.

Maintenance access

The rigid casing gives a strong structure, and the overall design is simple. Open-type end shields and an open-type impeller make the compressor straightforward to assemble, dismantle, and inspect.

Seal Liquid, Separator and Wetted-Part Materials

A liquid ring compressor never runs alone. Some seal liquid leaves with the gas, so a downstream separator splits the two streams. The recovered liquid is cooled and returned to the compressor, and a make-up supply keeps the ring at the right volume. Kenflo supplies complete compression packages that include this auxiliary equipment, along with process-matched instrumentation and controls.

The seal liquid also affects system performance. Vapours in the inlet gas that condense at the seal liquid temperature reduce the volume the compressor must handle. The condensate then leaves with the discharged liquid and is drawn off at the separator.

Water is the most common seal liquid, but almost any process-compatible liquid can be used. A well-known industrial example is dry chlorine compression, where concentrated sulfuric acid is widely used as the seal liquid. Water-sealed stainless steel compressors are a common choice for gases such as carbon dioxide, sulfur dioxide, and hydrogen sulfide. When a non-flammable liquid such as water forms the ring, published tests show that a liquid ring compressor can act as a flame arrester. This is one reason the technology is trusted with flammable or toxic gases. For explosive atmospheres, Kenflo offers CE- and ATEX-certified options.

On the CBK, wetted-end parts are available in SS304, SS304L, SS316L, and duplex stainless steel. Choose the right grade based on the gas, the seal liquid, and any condensate, since all three contact the same surfaces.

Typical CBK Duties

The CBK is listed for six process duties. Each one involves a gas that is hard on conventional compressors and must be raised to a useful pressure.

• Refinery tower gas recovery. In atmospheric and vacuum distillation, the CBK recovers gas from the atmospheric tower and the primary tower overhead so it can be sent on for further use.
• Adipic acid production. The CBK compresses nitrous acid gas in the hexanedioic acid industry (NOx-bearing off-gas from adipic acid production). In the nitric acid oxidation step, this off-gas contains nitrogen oxides and carbon dioxide, which requires corrosion-resistant wetted parts.
• Chlor-alkali plants. The CBK compresses dry chlorine gas and dry hydrogen gas, two of the main products of brine electrolysis.
• Chemical plant flare systems. The CBK recovers exhaust gas from flare apparatus. Liquid ring compressors are often preferred here because they tolerate liquids and vapours carried in with the gas.
• Salt mines. The CBK recovers flue exhaust gas at salt mine operations.
• Offshore oil platforms. The CBK compresses oil gas on the platform, where reliability and a compact package matter.

When CBK Is Not the Right Choice

The CBK covers a defined part of the pressure-flow map. Outside it, another arrangement serves the duty better.

• Discharge pressure above 0.7 MPa(G). A single CBK reaches its limit here. Kenflo’s tandem liquid ring compressor package, the 2BWX, connects compressors in series and reaches an ultimate discharge pressure of 1.3 MPa(G).
• Large flow at low pressure. When the gas volume is high and the pressure rise is modest, the CBA2 is the better fit. It handles up to 1,400 m³/min at discharge pressures up to 0.25 MPa(G), with material options that extend to titanium alloy and Hastelloy.
• Clean, dry, and non-hazardous gas. Liquid ring machines trade some efficiency for their tolerance of difficult gases. Published studies put their efficiency at around 35–40%, lower than many other compressor types. Where the gas poses none of the problems above, a different technology may cost less to run.

Conclusion

The CBK is a high-pressure liquid ring compressor for process gas that is corrosive, toxic, flammable, or vapour-laden. Its balanced impeller, two-end bearing support and choice of shaft seals suit it to discharge pressures up to 0.7 MPa(G), across 1 to 150 m³/min.

Guangdong Kenflo Pump Co., Ltd. was founded in 1954 and has grown into a liquid ring compressor manufacturer with 7 manufacturing bases and more than 1,300 employees. Its systems are certified to ISO 9001, ISO 14001, and ISO 45001, and to CE. To confirm whether the CBK fits your gas and pressure conditions, contact the Kenflo engineering team.