When compressed air is used in the production of pharmaceuticals, food, beverages, medical devices, and other products, there seems to be confusion on what testing needs to be performed. By defining compressed air contaminants, reviewing ISO , and discussing how to designate a quality class per ISO , this article will help clear up some of that confusion. It will also provide best practices for setting up a compressed air monitoring program. What are the Contaminants in Compressed Air? It does not include classes for gases or microorganisms. Jar washers using contaminated compressed air may adulterate the final product.
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Compressed Air Contamination Contaminants originate from three general sources. Contaminants in the surrounding ambient are drawn into the air system through the intake of the air compressor. Ingested contaminants appear in the form of water vapor, hydrocarbon vapors, natural particles and airborne particulates.
As result of the mechanical compression process, additional impurities may be introduced into the air system. Generated contaminants include compressor lubricant, wear particles and vaporized lubricant. A compressed air system will contain in-built contamination. Piping distribution and air storage tanks, more prevalent in older systems, will have contaminant in the form of rust, pipe scale, mineral deposits and bacteria.
Water Water vapor enters the system through the intake of the air compressor. In total volume, condensed water vapor represents the majority of liquid contamination in a compressed air system. This moisture will spoil food products, cause pneumatic machinery failure and promote bacterial growth in the compressed air piping. Compressed air systems serving the food processing industry must maintain dry, moisture free conditions mitigating the risk of micro-organism growth.
Since compressed air used in food processing operations may come in direct contact with the food, a compressed air dryer producing a sub-zero pressure dew point is required. Desiccant dryers- using activated alumina- will adsorb water vapor from the air most effectively, delivering ISO At this level of dryness, bacteria will cease to grow. End users are given the choice of selecting from several air compressor technologies, some of which require lubrication in the compression chamber for cooling and sealing purposes, and others that operate less lubricant in the compression chamber.
The end user determines which compressor design best meets the desired requirements. The purpose of this discussion is not to tip the scale toward either technology, but to address air treatment requirements in food processing applications. Lubricated compressors are typically less expensive to purchase and have a lower cost of ownership. A well maintained scfm lubricated air compressor, with a conservative 4 parts per million carry-over, will add up to 4.
Lubricant free compressors generally have a higher initial cost and greater maintenance costs over the life cycle of the equipment. Lubricant is only required for the bearings and timing gears, which is segregated from the compression chamber. This compressor technology presents no risk of lubricant migrating into the process air. Both air compressor technologies are subject to the inherent challenges presented by quality of the intake air.
Ingested contamination in the form of water vapor, solid particulate and hydrocarbon vapor must be addressed regardless if the compressor is lubricated or free from lubricant. Depending on the location of the compressor intake, oil vapor levels in industrial areas may contain ppm of airborne hydrocarbon aerosols. Hydrocarbon vapors, the primary component of fossil fuel combustion, will condense in a piping system when cooled forming a liquid contaminant.
Because compressed air may come in direct and indirect contact with food processing, an elevated level of filtration is required. A high efficiency coalescing filter capable of removing solids and liquids is recommended. It should be capable of removing solid and liquid aerosols 0. The remaining oil content should be 0. An activated carbon filter, installed in series, is also recommended downstream of the coalescing filter.
The adsorption filter will remove trace odors and oil vapor to 0. This filter combination will ensure specified filtration levels achieve ISO When this ambient air is compressed to psig, the concentration of solid contamination will reach significant proportions. Spores, pollen and bacteria are less than 2 micron in size.
This may seem like a lot of particulate matter, but keep in mind, a solid particle 40 um in size is barely visible to the naked eye. Even a well maintained and routinely changed intake filter will allow solid particles to enter the air system.
Solid particulate must be removed from process air serving the food industry. In pneumatic control circuits, solids particles plug control valve orifices, affect accuracy of gauging and score air cylinders walls, causing leaks.
Particles may restrict flow through air jet nozzles used to clean food preparation surfaces or adversely affect the consistency of spray coatings applied on food products. To achieve the recommended ISO The particulate filter will also enhance the service life of high performance coalescing filters by minimizing solid loading.
Using this, the end-user can make educated decisions as to the filtration performance required to generate a certain quality level. However, this standard does not address how manufacturers are to test and rate the filters.
The playing field is not level and consumers become confused. The ISO filter standard addresses this issue and establishes how manufacturers test and rate compressed air filters. The standard defines critical performance parameters namely, inlet oil challenge, inlet compressed air temperature and pressure measurement techniques that will deliver certifiable filter performance information suitable for comparative purposes.
ISO is a multi-part standard, with ISO encompassing the testing of coalescing filters for oil aerosol removal performance, ISO quantifies vapor removal capacity of adsorption filters, and; ISO outlines requirements to test particulate filters for solid contaminant removal. Three separate test laboratories were constructed, each equipped with stainless steel piping, state of the art instrumentation and contaminant measurement equipment.
How to ensure system reliability, while reducing pressure drop and demand, is explored through System Assessment case studies. ISO — Filters for Compressed Air — Part 1: Oil Aerosols ISO has identified two opposing inlet oil aerosols concentrations to determine the performance and pressure drop characteristics of coalescing filters. Filter manufacturer may elect to publish performance date at either of the two inlet concentrations.
The challenge concentration selected shall appear in published technical data. Testing conditions shall be controlled: inlet air pressure- An initial dry pressure drop measurement is taken. Initial pressure drop ratings are relevant to quantify cost of operation in that condition. A Laskin nozzle generator develops a supply of aerosol s with a peak distribution profile 0. Aerosols in this range are the most difficult to remove. These oil aerosols are injected into the clean compressed air stream.
Air then enters the coalescing type filter. A white light scattering photometer is used to measure of penetration of the oil aerosols through the coalescing element. The pressure drop across the filter housing is also measured and recorded. Three sets readings are taken. The manufacturer publishes the average performance value derived from the three tests.
Adsorption filters, utilizing an activated carbon medium, possess the polarity to attract hydrocarbon vapors from an air stream onto a porous surface. The adsorption process will continue until the activated carbon media is fully consumed. The ISO adsorption filter test begins with a clean, reliable source of compressed air. A precision rotameter measures the concentration of n-hexane liquid.
N-hexane is widely used in laboratory testing for hydrocarbon measurement and possesses the properties required to conduct adsorption filter testing, i. A heater vaporizes the n-hexane liquid at When heated, n-hexane changes phase and turns into a vapor.
The vapor enriched air is injected and mixed with the clean air source. The mixture of air and n-hexane vapor enters the adsorption filter.
Note: Adsorption filters are designed to remove vapor and not liquid contaminants. Establishing a dry pressure drop is useful to determine cost of operation. An infrared spectrometer is used to detect the presence of n-hexane vapor at the filter outlet. The filter is continually monitored until vapor penetrates through the adsorptive filter element.
Breakthrough indicates the filter is fully consumed and is incapable of adsorbing additional vapor. An adsorptive capacity value total amount adsorbed is established in milligrams.
Three filters of the same size shall be tested under identical conditions. The manufacturer is publishes the average performance value derived from the three tests. ISO provides guidance for the testing and methods for determining particulate filter removal efficiency, by particle size. Filters shall be challenged by solid particulate in the range 0. The ISO particulate filter test begins with a clean, reliable source of compressed air. Initial pressure drop measurements across the filter housing are taken and recorded.
To generate solid particles for the test, a salt solution is atomized and then dried, forming salt particles ranging from 0. These particles are then injected into the clean air stream. The manufacturer publishes the average performance values derived from the three tests.
Environmental chamber to test Compressed Air Dryers to standard and non-standard conditions Complementing Each Other The ISO standard will continue to benefit end-users by defining air quality levels and methods to determine contaminants present in their air system. The ISO test standards will benefit air treatment manufacturers by providing the means to commercially separate filter products through certifiable performance.
We all benefit, appreciating that ISO, a global international standards organization, continues to refine its standards for the betterment of the compressed air industry and private sector.
Using ISO 8573-1 to Test Compressed Air: Clearing the Confusion
IS/ISO 8573-1: Compressed air, Part 1: Contaminants and purity classes