26 May 2020
Standards for measuring compressed air quality
Estimated Reading Time: 5 minutes
Compressed air is used in a large number of manufacturing and trading companies. The air is generated from the ambient atmosphere around the compressor and typically contains contaminants in the form of dust and water, two naturally occurring contaminants, while a third contaminant, namely oil, is added to the compressed air by the compression process. While oil can be avoided/ eliminated by using 100% oil-free compressors, the other contaminantsnamely dust and water can, without proper treatment, reduce the efficiency of your compressed air system, increase your operating costs and endanger product quality. However, if the compressed air quality is improved by treatment.
Typical impurities in compressed air:
- Dust particles (from the ambient air and/or from the desiccant)
- Liquid water and water vapor
- Liquid oil and oil vapor (from oil-injected compressors)
- Hydrocarbon vapor
- Rust particles
- Pipe shed
- Acidic condensates
How do you define your air quality - ISO air quality standard (ISO 8573-1:2010)
The quality of the compressed air used in industrial processes is specified in the international standard ISO 8573-1. Untreated compressed air typically contains 3 types of contaminants: dirt, water and oil. The quality classes indicate the maximum permissable limit values.
Class 2: 4: 1 means, for example - dirt: max. 400,000 particles in the range from 0.1-0.5 µm, 6,000 particles from 0.5-1 µm and 100 from 1-5 µm - water: max. 3°C PDP oil: max. 0.01 mg/m³
A) Danger of dust
Since the compressed air is drawn from the atmosphere, dust particles with a size of 0.1 micron to 3 micron would get into the compressed air stream. This can be detrimental to the downstream devices and lead to product rejection/contamination and plant downtime due to malfunction of actuating valves and operating machines. In applications such as pharmaceuticals, food and beverage, manufacturing, several critical applications require sterile air to remove dust and bacteria. This can be achieved by adequate filtration.
B) Danger of moisture
The water concentration increases with the compression and with the subsequent cooling, liquid water is released in the downstream pipes if no treatment is used.
This creates a great risk of product contamination and damage to the downstream systems operated with compressed air. In addition, the humid air causes corrosion and failure of metal pipes and accessories. For example, a tiny hole of 3 mm can cause leaks of up to 27,156 kW/h, which corresponds to annual costs of CHF 10800 in terms of energy consumption.
C) Danger of oil
Oil is not a natural contaminant, but is added due to the type of compressor chosen. Compressors with oil injection in particular cause a problem of oil splillage that can be reduced by using coalescence filters. Howeer, the filtration efficiency is completely dependent on the temperature. Higher ambient temperatures lead to greater oil carryover from the compressor and have a cascade effect on the efficiency and service life of the filter. The attached diagram shows the filtration efficiency and the influence of the temperature.
Coalescence filters can help reduce oil spillage, but they cannot completely remove oil spills. In addition, filters must be routinely services for 4000 hours for general purpose and highly efficient filters, and 1oo0 hours for activated carbon filters.
