Air, compressed

When small amounts of compressed air are required in a plant, it is supplied by pipe. An example is the air required for process control devices (rule of thumb 1 m of control air per hour per control device). 

Larger quantities are generated in the plant by air compressors, and hence the requirement can be expressed in terms of electrical energy [Coulson 1990]. The power Ntijeo required to compress a gas is obtained from Equation (2.4-27). 

Many operators find it hard to grasp the power of compressed air. Section 2.2 (a) describes how the end was blown off a pressure vessel, killing two men, because the vent was choked. Compressed air was being blown into the vessel, to prove that the inlet line was clear. It was estimated that the gauge pressure reached 20 psi (1.3 bar) when the burst occurred. The operators found it hard to believe that a pressure of only twenty pounds could do so much damage. Explosion experts had to be brought in to convince them that a chemical explosion had not occurred. 

Unfortunately, operators often confuse a force (such as 20 lbs) with a pressure (such as 20 psi) and forget to multiply the 20 lbs by the number of square inches in the end of the vessel. 

Section 13.5 describes a similar accident, while Section 5.2.2 describes other incidents in which equipment was damaged by compressed air. Because employees do not always appreciate the power of compressed air, it has sometimes been used to remove dust from workbenches or clothing. Consequently, dust and metal splinters have been blown into people s eyes or into cuts in the skin. Worse still, compressed air has been 

Fires have often occurred when air is compressed. Above 140°C, lubricating oil oxidizes and forms a carbonaceous deposit on the walls of air compressor delivery lines. If the deposit is thin, it is kept cool by conduction through the pipework. But when deposits get too thick, they can catch fire. Sometimes the delivery pipe has gotten so hot that it has burst or the aftercooler has been damaged. In one case the fire vaporized some of the water in the aftercooler and set up a shock wave, which caused serious damage to the cooling-water lines. 

Keep the delivery temperature below 140°C. It is easier to do this if the inlet filters are kept clean and the suction line is not throttled. On some rotary air compressors, a large oil surface is exposed to the air, deposits readily form and ignite, and the temperatures should be kept lower. 

The plant has two reciprocating oil-free compressors, with a total capacity of 20 m3/h. The oil-free Compressed Air is supplied to a stainless steel air receiver. The air then passes through the air filter along with the oil and water separator system and passes through the air dryer and is distributed through S.S. use points in the three buildings. Terminal sterile filtration (0.01 pm) is used at critical use points. 

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Utilities (fuel, steam, electricity, cooling water, process water, compressed air, inert gases, etc.)... 

Frasch process A process for obtaining sulphur by passing superheated water down a shaft to liquefy sulphur which is blown to the surface with compressed air. 

The tested blade is flowed through either with hot or cold compressed air with a duration of max. 5 seconds The maximum heat temperature can be adjusted at 250 °C. 

Let us consider one more physical phenomenon, which can influence upon PT sensitivity and efficiency. There is a process of liquid s penetration inside a capillary, physical nature of that is not obvious up to present time. Let us consider one-side-closed conical capillary immersed in a liquid. If a liquid wets capillary wall, it flows towards cannel s top due to capillary pressure pc. This process is very fast and capillary imbibition stage is going on until the liquid fills the channel up to the depth l , which corresponds the equality pcm = (Pc + Pa), where pa - atmospheric pressure and pcm - the pressure of compressed air blocked in the channel. 

When using a compressed air or diffused aeration system, the SORT has to be converted to a standard volume of air required per minute. This conversion can be accompHshed through the equation... 

The operating cycle is seldom less than two hours, and several sets of frames can be operated in rotation. The cake thickness should be more than 3 mm, 9 mm being a typical value. Sluicing of the cake with a jet of compressed air has been used to permit thinner cakes and shorter filtration times. The leaves are spaced sufficiendy far apart that there is always clearance between the finished cakes. 

A variation of the same principle is the DDS-vacuum pressure filter which has a number of small disks mounted on a shaft which rotates discontinuously. The cake is formed on both sides of the disks when they are at the bottom position, dipped into the slurry. When the disks come out of the slurry and reach the top position, hydrauhcaHy driven pistons squee2e the cake and the extra Hquid then drains from both sides of the cake. The cake is removed by blowback with compressed air. 

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. 

Fig. 14. The H.E. IS blow-and-blow machine (85). The gob is deUvered into a blank mold, setded with compressed air, and then preformed with a counter-blow. The parison or preform is then inverted and transferred into the blow mold where it is finished by blowing.

In the fumace/ketde batch process, a charge of drossed blast furnace buUion is treated in a reverberatory furnace or a kettie (see Fig. 12). Oxygen is supphed in the form of compressed air or as lead oxide blown into the bath through submerged pipes. The formation of lead oxide serves by mass action to assure the removal of the impurities to the desired low concentrations. The softening reactions are... 

The continuous softening process used by The Broken Hill Associated Smelters Pty., Ltd. is particularly suitable for lead buUion of fairly uniform impurity content. The copper-drossed blast furnace buUion continuously flows in the feed end of a reverberatory furnace at 420°C, and the softened lead leaves the opposite end at 750°C. Oxidation and agitation is provided by compressed air blown through pipes extending down through the arch of the furnace into the bath. 

A schematic flow diagram for the ALMA fluidized-bed process is shown in Figure 2 (121). Compressed air and butane are typically introduced... 

Industrial separations are conducted in gravity or bath separators for a coarse feed, and in centrifugal separators for a fine feed (2,6,10). In gravity-type separators the feed and medium are introduced to the surface of a large quiescent pool of the medium. The float material overflows or is scraped from the pool surface. The heavy particles sink to the bottom of the separator and are removed using a pump or compressed air. The dmm separator (Fig. 13), up to 4.6 m dia and 7 m long, processes approximately 800 t/h, and treats feed of size up to 30 cm dia, operates in the gravity or the... 

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphoms is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air suppHed by a forced or induced draft fan. Wetted-waU. plants use 25—50% excess combustion air to reduce the tail-gas volume, resulting in flame temperatures in excess of 2000°C. The combustion chamber maybe refractory lined or made of stainless steel. Acid sprays at the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphoms pentoxide. The sprays also cool the gas stream to below 100°C, thereby minimising corrosion to the mist-collecting equipment (typically type 316 stainless steel). 

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