14.03.2003 - Sodium carbonate or soda ash is mainly required for the production of glass, detergents and paper. As an alternative to the procedure of refining trona ore into soda ash, Ernest Solvay developed about 140 years ago a process for the industrial production of soda ash using common salt, ammonia, carbon dioxide and lime.

Within this process, 3 compressors are normally required to compress a mixture of CO2 and inert gas coming out of the lime kiln and the calcination plants. The CO2 content of these gases vary between 35% and 80%. Due to the washer and cooler installed in front of the compressors, there is always a slight vacuum on the suction side. The required discharge pressure varies between 2.8 and 4.5 bar abs. To adapt the compressor performance to the process requirements a large turndown in compressor flow is mandatory.

New plants nearly exclusively use screw compressors for this application. Compared to the former used reciprocating type, screw compressors offer a much higher reliability. With the injection of large amounts of water screw compressors can handle a dust content up to 300 mg/m³ without problems. Centrifugal compressors have also been used for this service, however, the sensitivity to dust and liquid droplets means a much higher degree of preconditioning of the gas is required. The variation from 35% to 100% gas flow is accompanied by a similar variation in compressor speed and power demand.
Identical screw compressor sizes can be used for all three duties. Mostly back pressure steam turbines drivers are used, although high speed electric motors have also been used in the past.

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