The reduction of compressed air system ( CAS) leaks has by far the highest potential gain on energy. Leakage is directly proportional to the system pressure (gauge). Leakages are present in every CAS and they are effective 24 hours a day, not only during production.
The percentage of compressor capacity lost to leakage should be less than 10 % in a well maintained large system. For small systems, leakage rates of less than 5 % are recommended. The amount of leakage in a poorly maintained 'historically grown' CAS can be up to 25 %.
Preventive maintenance programmes for compressed air systems should therefore include leak prevention measures and periodic leak tests. Once the leaks are found and repaired, the system should be re-evaluated. Tests should include the following:
●estimating the amount of leakage: all methods of estimating the amount of leakage in a CAS require no demands on the system, which means that all devices consuming air are turned off and therefore all air consumption is only due to leakage:，
●direct measurement is possible if a compressed air consumption measurement device is installed
●in a CAS with compressors that use start/stop controls, the estimation of the amount of leakage is possible by determination of the running time (on-load time) of the compressor in relation to the total time of the measurement. In order to get a representative value, the measurement time should include at least five starts of the compressor. Leakage expressed as a percentage of the compressor capacity is then calculated as follows:
Leakage (%) = 100 x running time/measurement time
in a CAS with other control strategies, leakage can be estimated if a valve is installed between the compressor and the system. An estimation of the total system volume downstream of that valve and a pressure gauge downstream of the valve are also required.
the system is then brought to operating pressure (P1), the compressor is switched off and the valve shut. The time (t) it takes for the system to drop from P1 to a lower pressure P2 is measured. P2 should be about 50 % of the operating pressure (P1). The leakage flow can then be calculated as follows:
●Leakage (m³/min) = system volume (m³) x (P1 (bar) − P2 ( bar)) x 1.25/t (min)
●The 1.25 multiplier is a correction for the reduced leakage with falling system pressure
●Leakage expressed as a percentage of the compressor capacity is then calculated as follows:
●Leakage (%) = 100 x leakage (m³/min)/compressor inlet volume flow (m³/min)
reducing the leakage: stopping leaks can be as simple a s tightening a connection or as complex as replacing faulty equipment such as couplings, fittings, pipe sections, hoses, joints, drains, and traps. In many cases, leaks are caused by badly or improperly applied thread sealant. Equipment or whole parts of the system no longer in use should be isolated from the active part of the CAS.
An additional way to reduce leakage is to lower the operating pressure of the system. With lower differential pressure across a leak, the leakage flowrate is reduced.
洩漏率%= 100 x 運轉時間 / 量測時間
●系統洩漏量=系統容積(m3) x P1壓力(大氣壓力) - P2(大氣壓力) x 1.25/公噸-分鐘
●洩漏率=100x 洩漏量(m3/分) / 壓縮機進氣空氣量 ((m3/分)
Generally applicable to all CASs (see Table 3.23).
The costs of leak detection and repair depend on the individual CAS and on the expertise of the maintenance crew of the plant. Typical savings in a medium size CAS of 50 kW are:
50 kW x 3000 h/yr x EUR 0.08/kWh x 20 % = EUR 2400/yr The typical costs for regular leakage detection and repair is EUR 1000/yr.
As leakage reduction is widely applicable (80 %) and gives the highest gains (20 %), it is the most important measure for reducing CAS energy consumption.
Energy Efficiency (2009) 3.7.6