Compressed-air systems

The cost of the filter station includes not only the installed cost of the filter itself but also that of all the accessories dedicated to the filtration operation. Examples are feed pumps and storage facihties, precoat tanks, vacuum systems (often a major cost factor for a vacuum filter station), and compressed-air systems. The dehvered cost of the accessories plus the cost of installation of filter and accessories generally is of the same order of magnitude as the dehvered filter cost and commonly is several times as large. Installation costs, of course, must be estimated with reference to local labor costs and site-specific considerations. 

Humidified Compressed Air Injeetion System are about the same. This is due to the faet that though the initial eost to install the Compressed Air System, for a turbine of about 100 MW, is about 3.7 million as compared to about 1.7 million for a steam injection system, the power generated by the Heated and Humidified Compressed Air Injection System is much higher. 

Compressed air system explosions in engines, pipelines, separators, etc., are characteristic of this same type of mist explosion. 

This contrasts with the engine cycles studied for these, net area measured shaft work output, but for compressed-air systems, net area measures work lost. Remember, completely available energy, shaft work, runs compressed-air systems higher-temperature heat runs engine cycles. 

Adiabatic expansion of the air in the engine causes a maximum temperature drop of the exhaust. Adiabatic compression causes a maximum temperature rise of the compressed air. These effects combine to cause the greatest work loss of any compressed-air system, when pressurized air must be cooled back to atmospheric temperature. The energy analysis parallels the one just made for the polytropic system. This shows that net areas on both PV and TS graphs measure the work lost. 

Compressed air systems should be checked frequently for air leakage, as the loss of air is frequently unnoticed due to the noise of escaping air being masked by other production noises. Modem air compressor systems composed of multi-compressors produce much heat, and it is now possible to recover this for space heating purposes. 

The main consideration in the selection of a compressor plant is the production of an adequate supply of compressed air at the lowest cost consistent with reliable service. The installation of a compressed air system, as with all forms of power transmission, calls for capital investment with consequent operating and maintenance costs. The information on which the selection of plant is based should be as accurate as possible. Important factors to be considered are the following. 

In certain plants, especially in the chemical industry or in the neighborhood of such plants, the air is often polluted with acidic and corrosive gases that can cause corrosion in the compressor and the compressed air system. Special filtration methods and/or materials may have to be used and the supplier should be consulted. 

The physical laws of thermodynamics, which define their efficiency and system dynamics, govern compressed-air systems and compressors. This section discusses both the first and second laws of thermodynamics, which apply to all compressors and compressed-air systems. Also applying to these systems are the ideal gas law and the concepts of pressure and compression. 

Small leaks or breaks in the compressed air system can cause minute particles to be blown at surprisingly high speeds. Always wear safety glasses when working in the vicinity of any compressed air system. Goggles in place of glasses are recommended if contact lenses are worn. 

Pressurized air can do the same type of damage as pressurized water. Treat all operations on compressed air systems with the same care taken on liquid systems. Closed valves should be slowly cracked open and both sides allowed to equalize prior to opening the valve further. 

Three properties of gases must be well understood in order to gain an understanding of pneumatic power systems. These are its temperature, pressure, and volume. Physical laws that define their efficiency and system dynamics govern compressed air systems and compressors. These laws include ... 

Both the first and second laws of thermodynamics apply to all compressors and compressed air systems. These laws state ... 

In conventional compressed air systems, vapor and liquid removal is limited. Most two-stage compressors will include an intercooler between stages. On air-cooled units for 100 to 200psig service, the air between stages is not cooled sufficiently to cause substantial liquid drop out and provision is not usually made for its removal. Water-cooled intercoolers used on larger compressors will usually cool sufficiently to condense considerable moisture at cooler pressure. Drainage facilities must always... 

All compressed air systems should always include a water-cooled aftercooler between the compressor and receiver tank. Properly designed and maintained aftercoolers, in normal summer conditions, condense at lOOpsig, up to 70 per cent of the vapor entering the system. Most of this condensation will collect in the aftercooler or the receiver tank. Therefore, both must be constantly drained. 

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. 

All compressed air systems that use a positive displacement compressor must be fitted with a pressure relief or safety valve that will limit the discharge or inter-stage pressures to a safe maximum limit. Most dynamic compressors must have similar protection due to restrictions placed on casing pressure, power input and/or keeping out of surge range. 

Most state laws and safe practice require a safety relief valve ahead of the first stop valve in every positive displacement compressed air system. It is set to release at 1.25 times the normal discharge pressure of the compressor or at the maximum working pressure of the system, whichever is lower. The relief valve piping system sometimes includes a manual vent valve and/or a bypass valve to the suction to facilitate startup and shutdown operations. Quick line sizing equations are (1) line connection, (i/1.75 (2) bypass, ii/4.5 (3) vent, dl63 and (4) relief valve port, cU9. 

The amount of moisture that air can hold is inversely proportional to the pressure of the air. As the pressure of the air increases, the amount of moisture that air can hold decreases. The amount of moisture air can hold is also proportional to the temperature of the air. As the temperature of the air decreases, the amount of moisture it can hold decreases. The pressure change of compressed air is larger than the temperature change of the compressed air. This causes the moisture in the air to condense out of the compressed air. The moisture in compressed air systems can cause corrosion, water hammers, and freeze damage. Therefore, it is important to avoid moisture in compressed air systems. Coolers are used to address the problems by moisture in compressed air systems. 

Unit driers for small compressed air systems need to have capacity control, so as to maintain a steady working dewpoint when there is a variation in air demand. 

There have been fires and explosions in compressed air systems. The fuel is a combustible lubricant that has entered the air system from the compressor. Al th 0 ugh m ai nte n an ce of th e ch eck val ves wi 11 m i n i m ize th e h aza rd, th e val ves can stick open from scale or other causes that can affect even recently serviced valves. The explosion potential can be minimized by replacing the combustible lubricants with noncombustible lubricants. 

To describe guideline for the validation of the oil-free compressed air system... 

Two types of compressed air systems are found in an aseptic manufacturing facility ... 

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