Compressed Air Best Practices - September 2008 - (Page 20) | 09/08 Focus Industry FOOD PACKAGING & PROCESSING | FOOD-GRADE COMPRESSED AIR SPECIFICATIONS In each category, the recommendations center on the recommended air quality levels relating to the removal of three contaminants: 1. 2. 3. Solid particulates including bacteria Humidity (water vapor) in terms of pressure dew point Total permissible oil (aerosols and vapor) covering the potential ingestion of hydrocarbons or other ambient gases by the compressor intake The food industry also has applications where there should not be compressed air contact with food — but there is a high risk that it will occur. For this reason, the U.K. Code created a category called “Non-Contact High Risk.” This category calls for the same air purity levels as the “Contact” category. Referencing the above table, the Code recommends for both categories: 1. Solid particulate filtration to 1 micron: This includes bacterial filtration if the presence of bacteria is established. Mr. Bordiak said, “the presence of bacteria is established by the use of ISO 8573-7.” 2. Pressure dew point of -40 °F (-40 °C): meaning the use of desiccant or membrane dryers. Mr. Bordiak commented, “the humidity class chosen needed to be below that at which bacteria are likely to be propagated, namely below a -18 °F (-28 °C) pressure dew point.” 3. Total Oil Removal to 0.008 ppm (0.01 mg/m3): “Total Oil Removal” signals the required use of both oil-coalescing filters and oil vapor (particularly hydrocarbon) removal filters. BCAS & BRC FOOD GRADE PURITY RECOMMENDATIONS: DIRT (SOLID PARTICULATE) MAX NUMBER OF PARTICLES PER M3 0.1–0.5 MICRON 0.5–1 MICRON 1–5 MICRON CONTACT RECOMMENDATION HUMIDITY (WATER VAPOUR) TOTAL OIL (AEROSOL + VAPOUR) ISO8573.1 EQUIVALENT Contact Non-Contact — Low Risk Non-Contact — High Risk 100,000 100,000 100,000 1,000 1,000 1,000 10 10 10 -40 ˚C PDP +3 ˚C PDP -40 ˚C PDP 0.01 mg/m3 0.01 mg/m 3 Class 2.2.1 Class 2.4.1 Class 2.2.1 0.01 mg/m3 Reference Conditions from ISO8573.1: Absolute atmospheric pressure 1 bar, Temperature = 20 ˚C. Humidity is measured at air line pressure. Chart provided courtesy of Parker domnick Hunter. The Contact and Non-Contact — High-Risk Categories Contact is defined in the Code as “the process where compressed air is used as a part of the production and processing including packaging and transportation of safe food production.” Compressed air can be in direct contact with food or mixed with it. In packaging machines, compressed air can come into contact with the packaging material, which in turn is directly in contact with the food product. The Non-Contact Low-Risk Category This category specifies the same levels of filtration as the Contact and High-Risk categories. The difference lies with the pressure dew point specification. This category allows for a +38 °F (+3 °C) pressure dew point. This means that a refrigerated air dryer is permissible for this category. Observation on Air Dryers A desiccant or membrane dryer will, as a general rule, consume more energy than a refrigerated air dryer. This is due to the energy required to regenerate the desiccant beds of the dryer. Many installations use desiccant dryers for 100% of their compressed air system due to 30% of the system coming into “contact” with the food process. If it is possible to isolate the compressed air supply to these areas, the use of a refrigerated dryer for the rest of the plant can reduce energy costs. Compressed air can come into direct and indirect contact with food products. 20 www.airbestpractices.com http://www.airbestpractices.com
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