Energy costs account for the lion’s share of total compressed air supply costs. For an optimised compressed air supply produced by a new station with air-cooled compressors, the cost profile is divided as follows: commissioning and training of maintenance staff account for around just one percent of total costs; the same goes for condensate treatment. Installation expenses and the cost of controllers and process control systems come in at seven, and procurement of treatment equipment at five, with that of compressor equipment at around 13 percent. Maintenance of compressors accounts for three, whilst treatment system maintenance comes in at one percent. The largest cost block by a huge margin derives from energy expenses to supply compressors and treatment equipment, however, at 69 percent. This striking figure makes clear how energy performance is one of the most important indices for evaluating compressors. Years ago as part of its “Efficient Compressed Air” campaign (2000-2004) the Frauenhofer Institute established certain benchmarks that remain relevant today: for example, at a pressure of 6.5 bar (7.5 bar absolute), the specific power requirements should be between 5.5 and 7 kW m³/min. Energy consumption values above 7 kW m³/min are not cost effective, whilst those under 3.3 kW m³/min are technically impossible to achieve with current technology.
Energy efficiency considerations therefore play a central role in system planning, which always begins with a thorough analysis of the current air demand situation – for both new systems as well as renovations of existing ones. The audit can be carried out either by an external expert or the operator can take on the task internally. Leading providers in the compressed air sector additionally offer services in which an expert examines the system in detail using modern measurement and planning technology, then makes optimisation recommendations.
To facilitate the planning of new compressed air stations, the future operator is given a specialised planning questionnaire. This makes it possible to calculate the expected compressed air demand and the equipment necessary to achieve it – with the help of an experienced compressed air consultant. The questions cover all the key aspects to ensure a cost-effective and environmentally friendly compressed air supply.
In contrast to new projects, expansion proposals offer sufficient existing points of reference for determining a layout in accordance with demand. The expert shares measurement methods and tools with the user that make it possible to precisely determine the air demand in relevant parts of the company at various times. In this regard, it’s important to determine not just average values, but maximum and minimal values as well.
It’s also recommended with existing stations to occasionally determine – using computer-assisted analysis systems – whether the load on the compressors is (still) appropriate, whether the customer’s air demand has changed or whether the leakage rate remains within tolerances. Analysis programs should also be employed whenever old compressors are replaced with new ones. This offers the opportunity to replace potentially incorrect performance values with correct ones, improve compressor operating performance (especially in the partial-load range) and to plan for an optimised master controller. An expert should also be consulted whenever usage conditions change. After all, in many cases significant cost savings can be achieved simply by adapting the treatment equipment or pressures in the system.
To measure pressure and air consumption...
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