Machinery's Handbook, 31st Edition
2820 GAS CONDITIONING AND STABILIZATION Gas Conditioning and Stabilization.— In order to provide consistent, clean, dry gas sup ply; dryers, filters, oilers, receivers, silencers, and exhaust cleaners are used to condition and stabilize pressurized gas. Filters: Compressed gas used to perform work normally needs to be very clean to avoid fouling the devices in the system. Filters of various types are employed to clean com pressed air. Most manufacturers offer a range of high efficiency coalescing compressed air filters for the removal of water and oil aerosols, solid particulates and micro-organ - isms, and dust filters for the removal of dry particulate and micro-organisms from indus - trial compressed air systems. Filters are selected and sized based on what contaminant is to be removed, output cleanliness level, pressure capacity, flow capacity, pressure drop, and mounting method. Filters require regular preventative maintenance. Dryers: Compressed air supplies for pneumatic systems normally have moisture re- moved to prevent fouling and corrosion of the system components. For this purpose, com- pressed air dryers are employed. Dryer type and size is selected according to required air quality, pressure, dew point, and delivery volume. There are several types of commercial dryers available: refrigerated, desiccant, membrane, and deliquescent. A refrigerated dryer uses a compressor, heat exchanger, and refrigerant to pull liquid out of the gas. Normally a coalescing prefilter is installed immediately upstream of a refriger ated dryer to remove lubricating oil and other contaminants that have the potential to foul the dryer’s heat exchangers. A desiccant dryer passes compressed air through a pressure vessel filled with a media such as activated alumina, silica gel, molecular sieve or other desiccant material which pulls water out of the gas. Normally the desiccant can be regenerated. A membrane dryer requires no electricity to operate. Water vapor permeates a mem- brane of hollow fibers and is swept out with redirected dry air to exhaust, while the bulk of the dry air is passed back into the pressurized system. Normally a coalescing prefilter is installed immediately upstream of a membrane dryer to remove lubricating oil and other contaminants that have potential to foul the dryer’s membrane. A deliquescent dryer typically consists of a pressure vessel filled with a hygroscopic media that absorbs water vapor. The media gradually dissolves, or deliquesces. The vessel must be regularly drained and new media must be added. Lubricators: In some cases a small amount of oil or other lubricant is added to the com pressed air supply to lubricate components like actuators. Manufacturers will specify whether their components are “oil-free” or not. Lubricators are often combined with filters and regulators to form filter-regulator-lubri cator (FRL) units. Lubricators usually introduce a fine mist of lubricant into the air stream with particles in the micron range. Receivers: Most compressed gas systems have gas introduced in a pulsating supply. Receivers are essentially pressure vessels that act as reservoirs for the compressed gas. These reservoirs act to stabilize the system pressure by absorbing pressure pulsations. They also stabilize the system at times of fluctuating demand by supplying excess gas when demand peaks, and storing it when demand drops. Receivers are most effective when placed close to the pressure source in the system. A pressure regulator is placed after the receiver to provide constant pressure to the downstream components. Second- ary receivers are often placed near high demand to further stabilize the system pressure. Receivers may have valves at the bottom where collected condensate may be drained. Silencers and Exhaust Cleaners: When air is the gas employed, it is usually exhausted to atmosphere after it is used to perform work. When compressed air is released, sig- nificant noise can be produced. Silencers or mufflers are used to minimize this effect. The most common silencers are sintered metal, and they are very effective. Silencers are chosen based on port size, pressure, flow requirement, construction, material, and noise
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online