Training Manual on Energy Efficiency - APO Asian Productivity ...

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<strong>Training</strong> <strong>Manual</strong> on Energy Efficiency for Small and Medium Enterprises 9.5.4 Importance of maintenance for power consumption Table 9-2 Maintenance factors affecting power consumption S. No. Maintenance Factor - 94 - Excess Power Consumption (%) 1 Worn-out pistons and gland packing 3–5% 2 Worn-out valves 5–6% 3 Misaligned bearings 1–3% 4 Wrong grade oil 1% 5 Choked filter 3-5% 6 High cooling water temperature 1% 7 Loose Belts 4-6% 9.6 ENERGY EFFICIENCY OPPORTUNITIES IN COMPRESSED AIR SYSTEMS • Ensure that air intake to compressor is not warm and humid by locating compressors in a well-ventilated area or by drawing cold air from outside. Every 4 º C rise in air inlet temperature will increase power consumption by 1%. • Clean air-inlet filters regularly. Compressor efficiency will be reduced by 2% for every 250mm WC pressure drop increase across the filter. (A compressor is a breathing machine.) • Keep compressor valves in good condition by removing and inspecting them once every six months. Worn-out valves can reduce compressor efficiency by as much as 50%. • Install manometers across the filter and monitor the pressure drop as a guide to scheduled maintenance and replacement of elements. • Minimize low-load compressor operation; if air demand is less than 50% of compressor capacity, consider changing to a smaller compressor or reducing compressor speed appropriately (by reducing motor pulley size), in case of belt-driven compressors. • Consider the use of regenerative air dryers, which use the heat of compressed air to remove moisture. • Fouled inter-coolers reduce compressor efficiency and cause more water condensation in air receivers and distribution lines, resulting in increased corrosion. Periodic cleaning of inter-coolers must be ensured.
Energy Efficiency in Compressed Air Systems • Compressor free air delivery test (FAD) must be done periodically to check the present operating capacity against its design capacity, and corrective steps must be taken if required. • If more than one compressor is feeding to a common header, compressors must be operated in such a way that only one small compressor handles the load variations, while other compressors operate at full load. • The possibility of heat recovery from hot compressed air to generate hot air or water for process application must be economically analyzed, in cases of large compressors. • Consideration should be given to buying a two-stage or multi-stage compressor as it consumes less power for the same air output than a single-stage compressor. • If pressure requirements for processes are widely different (e.g. 3 bar to 7 bar), it is advisable to have two separate compressed air systems. • Reduce compressor delivery pressure, wherever possible, to save energy. • Provide extra air receivers at points of high cyclic-air demand, which permits operation without extra compressor capacity. • Retrofit with variable speed drives in big compressors (say over 100 kW) to eliminate the ‘unloaded’ running condition altogether. • Maintain the minimum possible range between load and unload pressure settings. • Automatic timer-controlled drain traps waste compressed air every time the valve opens. So frequency of drainage should be optimized. • Trans-vector nozzles are to be used for low and intermediate pressure air requirements at user points. These nozzles draw a small quantity of motive air at higher pressure and mix it with ambient air, to produce compressed air at intermediate pressure, in an efficient manner, as against routine valve control method. • Check air compressor logs regularly for abnormal readings, especially motor current cooling water flow and temperature, inter-stage and discharge pressures, and temperatures and compressor load-cycles. • Compressed air leakage of 40%–50% is not uncommon. Carry out periodic leak tests to estimate the quantity of leakage. • Install equipment interlocked solenoid cut-off valves in the air system so that air supply to a machine can be switched off when it is not in use. • Present energy prices justify liberal designs of pipeline sizes to reduce pressure drops. • Compressed air piping layout should be made preferably as a ring main to provide desired pressures for all users. • A smaller dedicated compressor can be installed at load point, located far away from the central compressor house, instead of supplying air through lengthy pipelines. - 95 -
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7. ENERGY EFFICIENCY IN PUMPS 64 7.
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LIST OF TABLES 1-1 Gross calorific
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