Oxygen production with PSA plants in an African gold mine. (© HAUG Sauer Kompressoren AG)
In many gold mines in Africa, oxygen is essential for the extraction of the precious metal. The self-sufficient supply of the gas is achieved by using a process that generates oxygen from air by means of pressure swing adsorption. Sauer Compressors' oil-free compressors from the HAUG product line make an important contribution here. The sophisticated boosting of the generated oxygen is handled by the piston compressors of the HAUG.Sirius series, which are developed and manufactured by the long-established Swiss company HAUG Sauer Kompressoren AG.
Logistics and supply problems are widespread on the African continent. Lack of infrastructure as well as capacity and efficiency deficiencies can affect supply chains and make them more expensive. Gold mines, which are often located in secluded areas, therefore seek to provide their entire infrastructure themselves. Even the oxygen required for efficient gold extraction by cyanide leaching is therefore not delivered but generated on site.
Oxygen production with PSA plants in an African gold mine, on the left in the picture a HAUG.Sirius oxygen compressor. (© HAUG Sauer Kompressoren AG)
Oxygen as a Key Element
The extraction of gold from rock by using cyanide relies on oxygen as a key element. Its use provides several important benefits. For example, a higher dissolved oxygen content increases the gold extraction rate, and increased ore throughput shortens the leaching time by up to 50 percent. In addition, less cyanide is consumed, which lowers costs and reduces environmental risks.
The gold mines produce the oxygen with oxygen generators based on PSA technology (Pressure Swing Adsorption). They produce oxygen of up to 95 percent purity and an outlet pressure between 44 and 73 psig (3 to 5 bar(g)). Afterwards, the oxygen produced by the PSA plants must be boosted to a final pressure of 118 to 191 psig (8 to 13 bar(g)).
The hermetically gas-tight oxygen compressor HAUG.Sirius with water cooling can be operated reliably at high ambient temperatures. (© HAUG Sauer Compressors AG)
Risky Oxygen Compression
The compression of oxygen is technically demanding. Since the gas is a strong oxidant and highly reactive, the compressor must not allow high temperatures and friction. The same applies to contamination by foreign substances, oils and greases, which could ignite the oxygen and inevitably set the compressor on fire. There are very few compressors in the world that can cope with such high demands. HAUG compressors have been among the safest machines on the market for decades and are used in the PSA plants of the leading suppliers and by the gas suppliers of the gold mines. In African mines alone, more than 30 compressors of the HAUG.Sirius series are in service today.
The unit is a completely oil-free, dry-running piston compressor. Thanks to the magnetic coupling drive used, the machine is hermetically gas-tight during operation and standstill. This hermetically sealed and absolutely wear-free drive was first used in a HAUG piston compressor in 1989 and can be used for suction pressures up to 441 psig (30 bar(g)). From its construction, instrumentation, operation and maintenance, the compressor is designed to efficiently dissipate heat and minimize friction. Special oxygen-compatible materials of the components in contact with the medium ensure safe operation. The modular compressor concept allows individual adaptation of the configuration to the respective customer requirements. In addition, the robust compressor is designed for continuous operation.
The high ambient temperatures of up to 113°F (45 °C) typical in Africa are no problem. The HAUG.Sirius offers the option of water cooling including a water after-cooling system for autonomous operation. Cooling water temperature requirements are compressor inlet 5-25 °C (41-77 °F), and cooling water pressure 3-10 barg (43-145 psig). Temperature sensors on each cylinder ensure safety. A specially designed intake filter protects against contaminants from the PSA system.
Diagram of an oxygen generating system. It is important to note that HAUG is supplying only the booster for the pressure increase after the oxygen generating system. HAUG only provides the compressor not a full oxygen generating system. (© HAUG Sauer Kompressoren AG)
About HAUG Sauer Kompressoren
The development and manufacture of compressors in the HAUG product line are the core competences of the long-established Swiss company HAUG Sauer Kompressoren AG based in St. Gallen. Founded in 1896, the company has been part of the Sauer Compressors Group since 2016, where it forms the global centre for oil-free compression technologies. Sauer Compressors is a medium-sized German group of companies with 14 international subsidiaries. The company looks back on more than 135 years of history and over 85 years of experience in compressed air and gas technology. These days, the focus is on the development, manufacture and sale of oil-lubricated and oil-free medium- and high-pressure compressors for applications in commercial shipping, industry, petro industry and the defence sector. The four product lines SAUER, HAUG, GIRODIN and EK focus on specific fields of application. The SAUER line comprises oil-lubricated high-pressure compressors for a wide variety of applications, while HAUG stands for oil-free and hermetically gas-tight compressors. The GIRODIN and EK lines offer special compressors for the naval market. The modern reciprocating compressors for compressing air as well as a variety of gases reach pressures of 20 to 500 bar(g). In addition to standard products, customised solutions are offered for every type of application for individual customers, OEMs and globally active companies. With a worldwide network of representatives and partners, Sauer is always close to its customers. By supplementing the compressor range with high-quality accessories, engineering services, assembly and service concepts, Sauer provides complete system solutions right up to complete turnkey installations.
Paul Frank, Technical Proposal Manager, Sauer Compressors USA.
Further information at: www.sauercompressors.com and www.haug.ch.
To read similar Air Compressor Technology articles, visit www.airbestpractices.com/technology/air-compressors.
Visit our Webinar Archives to listen to expert presentations on Air Compressor Technology at www.airbestpractices.com/webinars.