Plant Services - August 2007 - (Page 50) 12 10 EFFICIENCY Compressors Gear milling Is your bottom-line getting held up by your compressed air system? ExperienceProvenResults.com In spite of effortsDrilling to protect the en8 vironment, the composition of the intake air remains the biggest prob6 lem in guaranteeing high air quality. Turning The compressor sucks in, and concen4 trates, the contaminants in the ambient air. Fortunately, the cooling fluid/ 2 oil has a cleaning side-effect. The adOther manufacturing ditives in the oil neutralize sulfur di0 oxide and the oil traps solid particles. TimeCooling and energy efficiency This results in longer filter service Airend discharge temperature has intervals compared to oil-free sysan effect on energy efficiency. The tems. Synthetic cooling fluids, such warmer the air during compression, as polyalphaolefin, that have a greater the greater the energy requirement. contamination extraction capacity This, combined with reliability, favors compared to mineral oils, have since multistage oil-free compressors over come into widespread use power requirementsingle-stage units. enabling Theoretical specific N = 1, for compression from 1 bar 4=k extended fluid change intervals. (a) For compression ratios greater than (for air) Isentropic 4:1 (Figure 2), using intercooling to n = 1, 3 keep the discharge temperature below Condensate must be treated n 1, 1 392°F for each=stage provides energyAs condensate in an oil-free compresand mechanical-controllability. While sor collects in the aftercooler, the SO2 n = 1, 0 oil-free compressors can be cooled only in the air reacts with the moisture Isothermic indirectly via jacket-cooler, intercoolto form sulfurous acid. The resulting er or aftercooler, screw compressors condensate has a pH value below 6. with oil or fluid injection are directly The combination of low pH and the cooled. This is highly efficient as the levels of heavy metals mean that the oil/fluid injected into the compression condensate can’t simply be discharged Pressure chamber acts as a cooling medium. into the wastewater system. Addition- ratio About 80% of the heat of compresally, sulfurous acid requires stainless Positive cleaning effect mg/m3 steel heat exchangers and piping to eliminate leaks and repairs corrosion would cause. The assertion that “the condensate is always oil-free and can be directly drained away without treatment”[3] can only be interpreted as an instruction to break the law. Compressed air condensate must be treated before disposal. Going downhill in real time Filter element pressure differential with time ∆ρ (bar) 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 0,05% 90% Time Figure 3. The pressure differential starts to increase significantly only when the filter is near the end of its service life. Energy losses can be avoided by changing the filter elements 90% of the way through their recommended service life. 50 www.PLANTSERVICES.com Headline Pspec (kWm3/min) August 2007 http://ExperienceProvenResults.com http://ExperienceProvenResults.com http://www.PLANTSERVICES.com
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