Factors to Consider when Choosing Compressed Air Systems

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Choosing compressors

Rotary screw compressor is the most popular design for pharmaceutical manufacturing applications. Two types of compressors exist: two-stage oil-free and oil-injected. Oil-injected compressors flood the compression chamber with synthetic oil to aid in removing the heat produced by compression, as well as sealing and lubrication. The oil-free rotary compressor separates the lubrication system and the compression of the air, so that no oil comes in contact with the air.

Some manufacturers have validated this attribute of their oil-free rotary compressors using ISO 8573.1 class 0 for oil content, which means that the oil content measured was negligible or less than 0.01 mg/m3. This marketing effort helps promote the lower risk with oil-free compressors over oil-injected compressors. Majority of pharmaceutical manufacturing companies prefer to use oilfree compressors.

Can oil-injected compressors be used with filtration and achieve ISO 8573 part 1 class 0 air? It is not very likely; however, class 0 is typically not a user requirement. Therefore, oil-injected compressors can be used in sterile applications, but there are several things to be considered.

Firstly, injecting oil into the air and then separating it can be expensive. Through the life of the oil-injected compressor, multiple changes of oil separators and oil, as well as make up oil, are required, which add to the operating cost per year. Power cost also increases because of the pressure drop caused by the additional filtration. Disposal costs and sustainability goals are also major considerations with oil-injected compressors.

Of course, the risk of sending more oil downstream than allowed in the URS is reduced with oil-free compressors. Oil-free rotary compressors are at a significant premium over oil-injected compressors; therefore, the first cost must be weighed against operating costs.

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