Compressed air
Compressed air , also known colloquially as compressed air , refers to compressed air . It serves several purposes
- as an energy source , for example to operate compressed air brakes in rail vehicles or to drive machines underground in mining
- as a control medium (in the compressed air brake system)
- as a filler, spring and damping element in compressed air suspension , expansion vessel , hydraulic accumulator and jumping mat
- Hupfburg and other inflatables were typically operated (filled and kept filled) with a fan, i.e. compressed air at low pressure and high volume throughput
- Skydancers are also recoil driven at the outlet openings
- Hupfburg and other inflatables were typically operated (filled and kept filled) with a fan, i.e. compressed air at low pressure and high volume throughput
- as a conveyor drive for granular substances or liquids in pipes
- as a means of conveying drinks from barrels with
- as a recoil medium in flight attempts
- for cleaning
- as breathing gas
- for cooling
- for nitrogen generation
- as a noise reduction technology for bubble curtains
- to operate a horn
If other gases or mixtures are used instead of air, one speaks of compressed gas .
generation
Historically, compressed air at low pressure through bellows , for example, for a forge eat or generates a church organ. Compressed air for filling inflatable boats is still generated today by large-volume hand pumps or foot-operated bellows.
Depending on the intended use, air is brought to a higher pressure with compressors and treated differently depending on the application. The energy expenditure when compressing is considerable, since a lot of thermal energy is generated, which usually remains unused. Compressed air is therefore an expensive energy source . With rising energy prices and in combination with heat recovery and regular leak repair, the costs can be reduced significantly.
Two different systems are mainly used to generate compressed air: reciprocating compressors (mostly 2-stage) or screw compressors . 3-stage piston compressors ensure compression pressures of up to 3000 bar . In addition to these types, rotary compressors and, occasionally, diaphragm compressors are also in use. The performance of a compressor is given in l / min or m³ / h. It shows the delivery performance of a compressor.
In addition to the use of so-called load / no-load compressors, which have their best energy yield with continuous operation, there have also been models with frequency control for some years . The advantage of this technology is that the motor power and the required amount of compressed air are always controlled by a control system, which then increases or decreases the speed of the compressor element. According to various manufacturers, savings of 50% and more should be possible here.
Oil-free compressed air
Compressed air from all types of oil-lubricated compressors (including oil-free compressors) contains oil, and is therefore not suitable for high-purity applications without treatment / filtration . Compressed air from oil-free compressors is not completely oil-free, since the compressed air after compression can contain the oil components contained in the intake air and other hydrocarbons from the environment. For example, in the food industry , medical applications, as breathing gas for diving or in paint shops, only oil-free compressed air can be used. The compressed air quality is classified according to the ISO 8573-1 standard. The definition of oil already includes hydrocarbons (C5 +) and is basically to be determined in the overall context of steam, aerosols and droplets. It is not important whether the compression is oil- or water-lubricated or oil-free. Only the purity of the compressed air is important and it should be possible to maintain it under all operating conditions. Breathing air is generated with suitable compressors. Filters in conjunction with oil vapor adsorbers or catalytic converters are used to clean the compressed air; it is monitored for the absence of oil with suitable measuring devices. The quality requirement "oil-free compressed air" is thus achieved and permanently ensured.
Dehumidification
If atmospheric air is compressed, the dew point temperature increases with the partial pressure of the humidity contained as vapor . Because of the simultaneous increase in temperature, the relative humidity drops. If the compressed air cools below its new pressure dew point , the moisture can condense. This is why compressed air is often dehumidified with refrigeration dryers immediately after compression . The pressure dew point is set so that it is below the storage and transport temperature. Depending on the size and type of the system, hygroscopic materials are also used for drying.
In order to linguistically differentiate the (pressure) dew point of compressed air from the dew point of uncompressed air, the latter is also called the atmospheric dew point . This means that the compressed air can also be used at lower ambient temperatures without water condensing in the pressure lines or transport containers.
Compressed air distribution
In addition to compressed air generation, compressed air storage, compressed air preparation and the use of compressed air, compressed air distribution is also a very important part of a compressed air system. Technically less demanding and often neglected in many installations, improper planning and execution of the compressed air distribution can cause enormous operating costs.
Direct losses can be all leaks in which compressed air escapes unused on the way from generation to use from the compressed air pipeline or the installed systems and devices. Even today, depending on the design, around 10% losses are factored in when calculating the compressed air requirement. However, if the leaks are eliminated, the running time of the compressors can be reduced and an already installed auxiliary compressor can only be used rarely or not at all.
Indirect losses result from incorrectly planned and dimensioned compressed air piping. Long stub lines are installed, although a ring line would be better. Smaller diameters are selected, although the higher investment for a larger diameter pays for itself very quickly in operation. The indirect losses are the pressure losses caused by the flowing compressed air in the pipeline. Whenever there is insufficient pressure at the point of demand, an insufficiently large compressor is often thought of. Often, however, an optimization of the compressed air pipeline can solve the problem and, in the best case, the pressure on the compressor can also be reduced.
Safety accessories
Sudden relaxation when disconnecting the compressed air connection can cause the so-called whiplash effect. In order to avoid this, the employers' liability insurance association requires the use of safety quick-release couplings in accordance with ISO standard 4414 and safety standard EN 983 "... quick-release couplings must be selected so that when they are coupled or uncoupled, the pressure does not throw the coupling part dangerously away ...".
- Mains-side compressed air safety quick coupling for small and medium-sized consumers, DN 7 to 11, Q up to approx. 80 l / s
- Network-side compressed air safety quick coupling for large consumers, DN 12 to 38, Q up to approx. 2 100 l / s
application
Energy source
Compressed air is used to drive of cylinders , turbines or even pneumatic tube used with the air while relaxing the energy in linear motion is converted or rotational movement. The compressed air can be mixed with oil here . The oil acts as a lubricant .
In general, this application is also known as pneumatic known: compressed air can be used as an energy medium Examples include airpod , compressed air engine , compressed air energy storage , compressed air weapon , used in the paint or in construction work, examples include pneumatic hammers , pneumatic chisel.
In rail operations, compressed air is used to control rail vehicles and as an energy source for the compressed air brake . Air brakes are also used in road traffic, especially in trucks .
At the end of the 19th century, compressed air networks for energy distribution were created, as electrical energy transmission with alternating current was still in its infancy at that time . From 1888 a larger compressed air network was built in Paris to drive elevators , sewage pumps , direct current generators and other machines. The pipes were laid in the sewers , where, unlike electrical cables, they were not affected by moisture. The network reached a length of 900 km in the 1960s. The 400 million cubic meters of air used annually were generated by three compressor systems. The network was only stopped in 1994.
control
For a long time, compressed air was the first choice for signaling (standard signal 0.2–1 bar) and for operating control elements (approx. 6 bar) in potentially explosive areas. Today the electronic solutions are cheaper and more flexible (intrinsically safe circuits).
Compressed air was used in the first vehicles of the Train du Mont-Blanc from 1901 to control multiple units . The vehicles were connected by two air lines running through the entire train - one for forward travel, the other for reverse. The five speed levels of the railcars were indicated by different pressures in the lines.
In Paris, in addition to the compressed air network for energy transmission, there was also a system for operating a clock system , whereby the slave clocks were synchronized with the master clock via compressed air pulses of 0.75 bar emitted every minute. The network, the lines of which were laid in the sewer system, began operating on December 31, 1880. In 1887 the largest expansion was achieved with 7050 watches for 3185 subscribers. In 1927 the company was closed.
Breathing gas
Air is either distributed as purified and processed breathing gas in a stationary compressed air network, for example in a hospital , or stored in compressed air cylinders by means of respiratory protection compressors to reduce space and, if necessary, used via regulators for breathing with breathing apparatus and for scuba diving . Relaxed compressed air contains a very low relative humidity due to the dehumidification , so for long-term use on (intubated) patients it has to be supplied with artificial humidity to prevent the lungs from drying out.
When using special breathing gases, for example when diving with nitrox , only oil-free compressed air may be added.
cleaning
Relaxing the air in a nozzle creates a rapid flow of air that can be used to blow away particles and liquids .
In connection with abrasive particles, which are accelerated by compressed air, an intensive surface cleaning can be achieved with sand , ball or dry ice blasting .
cooling
Compressed air is used for cooling in many technical processes . This makes use of the fact that compressed air cools down during expansion due to the Joule-Thomson effect .
Nitrogen generation
More and more users are using nitrogen generators to meet a company's nitrogen requirement (e.g. in the food industry). With the help of these generators, nitrogen is separated from the rest of the air in a special absorption process. The nitrogen obtained has a purity level of up to 99.999% (5.0).
Other uses
Compressed air from compressed air cylinders is also used for certain other activities, such as filling lifting bags .
There were conducted flight tests in the USA in the 1950s, which were based on the vertically directed recoil of nozzles with compressed air from a high-pressure cylinder package.
Usage pressure
As an energy source or for cleaning, compressed air usually has a pressure of 6 to 8 bar . In individual cases up to 16 bar are required. For starting large engines e.g. B. in ships, compressed air with 20 to 30 bar is used to either operate a compressed air starter, or to direct the compressed air directly into one or more combustion chambers and thus set the engine in motion. As breathing air for scuba diving, in breathing apparatus, the compressed air in the bottles or cartridges is below 200 to 300 bar. Special bottles (made of CFRP, for example ) are also filled, which are used at pressures of up to 300 bar in portable compressed air tools ( pneumatic nailers ) or compressed air guns . When conveying bulk materials pneumatically, pressures below 4.5 bar are generally required.
Use as a warehouse
In air bearings , moving parts can be stored almost without friction.
The air cushion table is a level application .
literature
- Erwin Ruppelt (Hrsg.): Compressed air manual. Vulkan-Verlag, Essen, 4th edition 2002, ISBN 978-3-8027-2548-7
Web links
Individual evidence
- ^ Alfred Böge (Ed.): Manual of mechanical engineering . Basics and applications of mechanical engineering. 20th edition. Springer, 2011 ( limited preview in Google Book Search).
- ↑ a b Tristan de la Broise, Florence Meffre: Histoire de la SUDAC (1877-1996). (PDF; 980 kB) November 7, 1996, accessed October 27, 2013 (French).
- ↑ Christophe Jacquet: Les Z 200. In: Train du Mont Blanc. October 8, 2012, accessed October 27, 2013 (French).
- ↑ Curious & deadly: Weapons of a different kind - Flying soldiers spiegel.de, August 21, 2012, accessed July 14, 2019. - Video about 47 min, 32:49 before the end.