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Textile quality and the quality of Compressed Air.

Modern production systems and processes demand high quality compressed air, which is defined in the 6 classes outlined in international standard ISO 8573.1. These are only achievable with filtration, water separation and drying reveals Imtiaz Rastgar in this special report.

Compressed air is an important source of energy that is widely used throughout the textile value chain. Most textile industry processes have an essential requirement for clean, dry air to ensure their safe, efficient and profitable operation.

Water vapor and other contaminants that are not properly removed can lead to a decline in finished goods quality. Such textile related applications require the highest quality of clean, dry compressed air. System downtime due to sludge build up in downstream equipment is present in humid climates, where water vapors can easily enter a compressed air system. The textile related plants (ginning, spinning, weaving, knitting etc.,) located in such climates can experience quality and reliability issues, when water vapor is present in compressed air.

Types of contamination found in a compressed air system

Atmospheric Dirt

Atmospheric air in an industrial environment typically contains 183 million per yd3 (140 million per m3) of dirt particles. 80% of these particles are less than 2 microns in size and are too small to be captured by the compressor intake filter, therefore passing directly into the compressed air system.

Water Vapor, Condensed Water and Water Aerosols

Atmospheric air contains water vapor (water in a gaseous form). The ability of compressed air to hold water vapor is dependent upon it's temperature. The higher the temperature, the more water vapor that can be held by the air. During compression, the air temperature is increased significantly, which allows it to easily retain the incoming moisture. After the compression stage, air is normally cooled to a usable temperature. This reduces the airs ability to retain water vapor, resulting in a proportion of the water vapor being condensed into liquid water which is removed by a condensate drain tied to the compressor after-cooler. The air leaving the after-cooler is now 100% saturated with water vapor and any further cooling of the air will result in more water vapor condensing into liquid water. Condensation occurs at various stages throughout the system as the air is cooled further by the air receiver and piping and the expansion of valves, cylinders, tools and machinery.

The condensed water and water aerosols cause corrosion to the storage and distribution system, damage production equipment and the end product. It also reduces production efficiency and increases maintenance costs. Water in any form must be removed to enable efficient running of the system.

Micro-Organisms

Bacteria and viruses will also be drawn into the compressed air system through the compressor intake and warm, moist air provides an ideal environment for the growth of micro-organisms.

Liquid Oil and Oil Aerosols

Most air compressors use oil in the compression stage for sealing, lubrication and cooling. During operation, lubricating oil is carried over into the compressed air system as liquid oil and aerosols. This oil mixes with water vapor in the air and is often very acidic, causing damage to the compressed air storage and distribution system, production equipment and final product.

Oil Vapor

In addition to dirt and water vapor, atmospheric air also contains oil in the form of unburned hydrocarbons. The unburned hydrocarbons drawn into the compressor intake as well as vaporized oil from the compression stage of a lubricated compressor will carry over into a compressed air system, where it can cool and condense, causing the same contamination issues as liquid oil. Typical oil vapor concentrations vary between 0.05 and 0.5mg per cubic meter of air.

Rust and Pipe Scale

Rust and pipe scale can be found in air receivers and the piping of "wet systems" (systems without adequate purification equipment) or systems which were operated "wet" prior to purification being installed. Over time, this contamination breaks away to cause damage or blockage in production.

The impact of water vapor in compressed air systems can cause downstream equipment failure. In this context, the existing solutions in the market often require 3 to 4 individual water separators and coalescing filters working together to remove particulate and water. The problem with using water separators and coalescing filters is that water vapor can still move, downstream through the filters starting the growth of micro-organisms.

Compressed air dryers are being implemented into industrial automation processes to boost total system reliability. There are a few types of dryers in the market; the most commonly used is the adsorption type. Membrane dryers and refrigerant dryers are the next most commonly used dryers to treat and dry compressed air.

Selecting the proper dryer boils down to air quality. Pressure Dewpoint or PDP refers to the dewpoint of air above atmospheric pressure. A PDP of -40 F is recommended in most applications because a PDP better than -14F will not only stop corrosion, it will also inhibit the growth of microorganisms.

A strong connection needs to be drawn between quality of air and the quality of textile product it will produce. Shortcuts must be avoided when selecting compressed air elements like pipe, filters and filter elements.
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Publication:Pakistan Textile Journal
Geographic Code:9PAKI
Date:Jun 30, 2016
Words:932
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