Reducing compressed air costs and energy usage.
The most effective way to maximise potential energy saving and minimise maintenance and downtime in modern compressor plants is to run the compressed air reticulation system within the narrowest possible operating pressure band. To ensure maximum energy saving and operating efficiency the air reticulation pressure should not vary by more than 0,2 bar.
Innovative concept
The old school of thought suggested that longer unloading cycles meant energy saving, good performance and economic operation. With modern rotary compressors this statement no longer holds true because they have more sophisticated control. Most are controlled by on-board microprocessors managing operating modes far more accurately. This means that the modern compressors are capable of delivering closer to the actual plant demand than their predecessors.
Modern systems
Modern compressors can be controlled with much more flexibility, far more accurately and reliably than older equipment. This translates into cost savings, especially on energy - the biggest cost on air compressors - but also on maintenance and downtime. The best way to achieve this objective is to operate the air reticulation system as an installation of multiple air compressors, preferably of dissimilar size. There are a number of ways to achieve this objective. For instance the compressor plant may be purchased outright, be hired on contract or air may be purchased as a utility and paid for on a monthly basis.
Energy saving through dissimilar capacities
By running an installation of multiple compressors of unlike size together and controlling them with an industrial computer-based management system, the prescribed condition of a 0,2 bar pressure band can easily be obtained. With this type of arrangement, maximum energy saving, optimum wear and tear and reduced maintenance can be achieved even without the inclusion of a variable speed compressor.
Energy saving though variable speed
An installation incorporating a variable speed compressor will function as follows and can offer tangible energy savings in the same way as an installation incorporating fixed speed and modulating automatic start/stop compressors.
The variable speed compressor will start up using soft-start principles and will raise the system to the desired operating pressure. Once the variable speed drive reaches 90% of its speed band the inverter will automatically activate the start up of the nominated base-load compressor under soft-starting conditions as the air reticulation is already charged up to full pressure. The base-load compressor will then assume maximum load and the variable speed will reduce its running speed to the actual demand level, thereby ensuring maximum potential energy saving.
When the air demand changes and the variable speed unit runs down below 40% speed it will automatically de-activate the relevant base-load compressor rendering it to standby status and the smallest compressor in the system or the variable speed unit will re-assume the load required. Once again ensuring maximum energy saving potential by optimising running speed against the actual demand required.
This type of system can offer measurable energy savings of up to 35% and at the same time reduce maintenance costs associated with compressors that are constantly operating in on-load off-load cycles. This is an important consideration in view of long term energy and maintenance cost saving versus short term savings to meet a capital expenditure budget.
An air management system
Plant reliability, efficiency and expansion could also be bettered by having a multiple compressor installation sized in accordance with plant usage, which is normally determined by conducting an air survey.
This constitutes the installation of a compressor system incorporating units with different capacities connected into a common plant management system running on an industrial computer.
This type of system will run efficiently and create energy savings of up to 35% even when the demand drops below 40%. It has the ability to deliver a certain % above the base-load capacity normally required by the plant, depending on the actual units selected.
The system software balances loading and running hours on all units, thereby managing maintenance costs efficiently and effectively over the life cycle of the plant while assuring 100% standby ability and fully utilising all equipment at all times.
Air Bank Corporation offers free air surveys and specialises in the supply of technically analysed systems, air contracts and the supply of compressed air as a utility.
For more information contact Kevin Rushmer, Air Bank Corporation, +27 (0)11 908 4169, [email protected], www.airbankcorp.co.za
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