Despite their fundamental differences, compressed air and vacuum technology do have some things in common: expensive technology is required in order to generate high or low pressures. Variable-speed drives are the technology of choice for compressors and vacuum pumps alike in order to keep operating costs in check. The demand for contracting quotations is also increasing.
In industry, compressed air is taken from a socket outlet like electricity — and is therefore a much valued source of energy in many production processes. For example, about 62,000 compressed air systems are installed in Germany alone. And precisely because compressed air is so safe and easy to use, many operators do not keep a very watchful eye on the costs incurred by its use. A great deal of money literally vanishes into thin air through leakage, with loss rates tending towards 15 percent as a general rule — although the figure can be as high as 70 percent.
All the big names in the industry are now offering compressed air audits. The aims of such audits are to detect leaks, diagnose incorrectly dimensioned lines, and to identify instances where the generation of compressed air is not tailored to the specific application. The first step on the way to energy efficiency in the generation and distribution of compressed air is to analyze the present situation and identify the actual requirements. Once all the data are available, it is possible to work out what level of investment is needed. A study commissioned by the European Union showed potential energy savings of between five and 50 percent with compressed air systems. Moreover, most of the measures aimed at improving efficiency had payback periods of less than two years and would therefore be a very attractive economic prospect for the companies in question.
Optimized Compressed Air Management
The maximum possible energy efficiency of each individual component in the compressed air system may be a necessary precondition to optimizing the system as a whole, but is still a totally inadequate way of achieving this end.
With the exception of continual process engineering sequences, the profile of requirements obtained by analysis usually shows variations. It can then make sense to work with regulated-speed compressors. It is also advisable to use a primary control with larger systems. The advantage of this is that several compressors can be synchronized and operated at one station. The performance under load can then be made more efficient, e.g. by distributing (splitting) the load across several compressors of different sizes.
The Delcos XL developed by CompAir is an integrated touch screen controller which has been custom-designed for the L 30 - L 132 range of fixed-speed and regulated-speed compressors. It displays detailed statistics, including network pressure and average weekly flow rate, in the form of on-screen trend diagrams and graphs. By analyzing these trends it is possible to set precise parameters for the compressor.
A central compressed air station can be advantageous for the operator unless extremely long lines argue in favor of a decentralized supply system. If compressors can be combined there are more benefits to be reaped than just simplifying service and maintenance. The primary by-product of the compression process is heat, therefore a waste heat recovery system can reduce energy costs further. According to Kaeser, up to 96 percent of the energy supplied to the compressor can be recovered as waste heat and used for a second time (e.g. for heating purposes).
Boge demonstrates how efficient a system of this type can be: three compressors with a rated output of 632 kW are installed at a catalyst manufacturer. The thermal output which can be recovered and fed into the heating system is 757 kW. Is this the perpetual motion machine at long last? Not quite! The fact that more thermal output is recovered than is supplied in electricity is due to the intelligent use of the heat generated by the condensation of the air humidity intake in the compressed air after-cooler. This heat is available free of charge, as it were, in addition to the heat of compression.
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