Compressed-Air Supply System

Figure 41.1 shows a typical compressed air supply system. The following describes the functions of the system components ... 

Industrial clean compressed air supply systems normally operate at about 550 kPa to 710 kPa (80 psi to 100 psi) and this pressure may be sufficient for many forming applications. Certain pressure forming equipment operate at pressures up to about 2500 kPa (360 psi), with some processes operating up to at least 4 MPa (580 psi). These pressures are very low when compared to those commonly used for injection molding or extrusion (Chapters 4 and 5). 

Compressed air supply system Rotary screw air compressors supply air at 9 bar g for air-assisted liquid backwash to remove particulates from the membrane surface. It also supplies air for the Membrane Integrity Test as well as various plant instruments and controls. 

Exhaust air control systems 1 and 2 Liquid waste disposal systems 1, 2, 3 and 4 Drain pump system of vessels 21 and 22 Compressed air supply system... 

Of course, it is alternatively possible to adopt a decentralized compressed air supply system by installing compressors at various strategic points in the cement works, but it is a more expensive alternative in terms of capital cost. 

Most plants are highly dependent upon their compressed air supply and it should be assured that the air is in at least reasonable condition at all times, even if the drying system is out of use for maintenance or repair. It is possible that the line condensation would be so bad that some air applications would be handicapped or even shut down if there were no protection. A vital part of the entire endeavor to separate water in the conventional compressed air system is also the trapping of dirt, pipe scale and other contaminates. This is still necessary with a dried air system. As a minimum, all branch lines should be taken off the top of the main and all feeder lines off the top of branch lines. 

Here is another case history of a compressed air system that was modified to near disaster. Details of this incident are unavailable, but some years ago a chemical plant or refinery with multiple reciprocating air compressors and pneumatic instruments systems decided to modernize. The modernization project replaced the air supply system. Economics favored one large centrifugal air compressor, and no backup air supply was installed. 

A process vessel has a fluctuating pressure. The range of the fluctuations is from 15 to 35 psia. The pressure never exceeds 35 psia. A system is to be designed to admit air into jthis vessel at a steady rate of 1 Ibm/h. The compressed-air supply main is at 100 psia and 70"F. This temperature and this pressure do not fluctuate. 

Control systems that use an auxiliary source of power, in addition to the power provided through the primary element, are termed relay-operated controllers (Fig. 9-206 and c). This auxiliary power may be introduced into the measuring system, the error detector, or one or more amplifying relays. In the typical controller of Fig. 9-18, the measuring means is self-operated. The auxiliary power is provided by compressed air supplied at the bafile-and-jet error detector and at pilot-valve power amplifier. 

To move heavy columns electrically operated Master Mover can be used. Important is to check in advance the appropriate combination of the wheels (diameter and width) with the floor resistance (maximal peak pressure on floor). For fragile floors transport systems with an air cushion (hoover system for example from DELU-GmbFI/Germany) can be used, but such systems require smooth floors without any cracks or gaps and a compressed air supply on the transport way. 

As described abeady in Chap. 6, instrument air and compressed air for operating purposes are normally supplied by the ah compressor in the air separation unit A receiver in the instrument air system ensures a continuous supply during malfunctions for a period of 30 minutes. A diesel-powered auxiliary compressor is usually installed to start up the plant and ensure compressed air supply during downtimes. 

Description— These devices provide air to the wearer through a small-diameter, high-pressure hose line from a source of uncontaminated air. The source is usually derived from a compressed airline with a valve in the hose to reduce the pressure. A filter must be included in the hose line (between the compressed airline and the respirator) to remove oil and water mists, oil vapors, and any particulate matter that may be present in the compressed air. Internally lubricated compressors require that precautions be taken against overheating, as the heated oil will break down and form carbon monoxide. Where the air supply for airline respirators is taken from the compressed airline, a carbon monoxide alarm must be installed in the air supply system. Completion of a prior-to-operation preventive maintenance check on the carbon monoxide alarm system is critical. 

A third solution for the compressed air supply consists in providing a central installation, as described above, but connected toa radiating system of pipes to the individual consumer sections of the works. 

Filters — The use of an air purifying filter, is recommended for man cooling systems. It will serve two men in full suit systems (total flow of 50 scftn). The filter contains several filter materials, including activated charcoal, and will remove mists (including oil mist), water vapor and particles (down to 0.5 n in size) from the compressed air supply. Most important, it cleanses the air of any objectionable odor. The compressed air system should be tested for CO content. 

The fiill-face respirator has many attachments that can be incorporated to make it more versatile. As a filter respirator, it can be equipped with filters, chemical cartridges, canisters, and powered air-purifier systems. As an air-supplied respirator, it can be equipped with an air line arrangement or a tank-supplied compressed air/oxygen system, either for closed or open operation. 

Dust accumulated on the outside of the bags, when blown off the bag surface, falls into the hopper at the base of the baghouse. A large proportion of baghouse systems use a pulse jet blow-back (Figure 3.44), in which each bag has a separate valve from a compressed air supply above it, so that any bag can be blown free of... 

The so-called hyperbar vacuum filtration is a combination of vacuum and pressure filtration in a pull—push arrangement, whereby a vacuum pump of a fan generates vacuum downstream of the filter medium, while a compressor maintains higher-than-atmospheric pressure upstream. If, for example, the vacuum produced is 80 kPa, ie, absolute pressure of 20 kPa, and the absolute pressure before the filter is 150 kPa, the total pressure drop of 130 kPa is created across the filter medium. This is a new idea in principle but in practice requires three primary movers a Hquid pump to pump in the suspension, a vacuum pump to produce the vacuum, and a compressor to supply the compressed air. The cost of having to provide, install, and maintain one additional primary mover has deterred the development of hyperbar vacuum filtration only Andrit2 in Austria offers a system commercially. 

The isolation of certain mechanical equipment, e.g. conveyors, work on lifts, excavations, entry and positioning of cranes, isolation of various safety services , e.g. water or inert gas, stand-by power generation, water supply to sprinkler systems, compressed air for breathing apparatus. 

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