Many instruments and controls operating in hazardous industrial environments require instrument grade compressed air to ensure effective operation. Without clean, dry air, quality control and process control systems may be subject to damage from water and contaminants resulting in costly downtime and maintenance.
Examples of hazardous environments include refineries, chemical processing plants, mines, grain mills and other facilities that may have high concentrations of flammable gases, vapors, combustible dusts, or ignitable fibers. Even a small spark can lead to a horrific explosion that can be dangerous to both workers and equipment in the area.
While industrial plants typically have centralized instrument-grade air lines, the air is often contaminated with water and can benefit from a point-of-use drying system that guarantees clean, dry air to a specific dew point. Traditional drying systems that use PSA (Pressure Swing Adsorption) or refrigerant drying technologies require expensive modifications to operate within hazardous areas. However, compressed air dryers that use membrane technology operate without electricity, therefore, no modifications are necessary for them to operate in hazardous areas.
Electrically operated equipment that is located in hazardous areas must be specifically designed to prevent ignition and explosion. Electrical enclosures found on the various types of traditional compressed air drying equipment (refrigerated dryers, chemical dryers and desiccant dryers) must be strong enough to contain an explosion within the cabinet. Therefore the walls of the enclosure must be very thick and heavy. The internals in the cabinet must operate at temperatures below the ignition temperature of the hazardous material. The cabinet must also be designed so that any ignition inside the cabinet would not immediately exit the cabinet; in other words, the ignited gases must be quenched so that the escaping gases don’t cause an explosion outside the cabinet. The added weight and heavy-duty designs of such equipment increase the cost and space requirements.
Membrane technology as an effective alternative
Membrane dryers are designed with no moving parts and require no electricity, making them inherently explosion proof. Membrane dryers use specially formulated membrane microtubes that are selectively permeable to water vapor. The microtubes provide an excellent medium for producing dry air from standard compressed air. As the compressed air travels along the length of the membrane, water vapor diffuses through the membrane, producing clean, dry compressed air at the outlet. A small fraction of the dry air is then directed along the outside surface of the membrane to sweep the moisture-laden air away from the membrane (Figure 1). These dryers can reduce the dew point of compressed air to as low as -40°F/°C. They operate with very little noise output - just a small amount of purge air is emitted through small exhaust ports. To free up floor space, membrane dryers can be wall-mounted. They contain no refrigerants or freons, making them environmentally safe. Membrane compressed air dryers are ideal for remote areas, Class I, II or III hazardous locations, sub-freezing environments, and applications requiring water vapor removal and a consistent dew point.
Figure 1: How membrane technology works
This post was contributed by David Connaughton, product manager, Parker Industrial Gas Filtration & Separation Division.