A small number of compressed air systems in use today have an optimized cost structure. For those who don't have such, one is highly recommended. A key requirement for such system optimization is a detailed Compressed Air Demand Analysis (ADA) as already stated in this article HERE. Now, we will describe how the current state of an air system can be determined in practice.
A necessary condition for analysis and subsequent optimization is the presence of trust and cooperation between the user and the specialist in compressed air systems. This also includes prior provision of information by the user.
1. Operator information.
а) Layout plan
A layout plan of the production facility should be available for general orientation.
It should show the compressed air station’s compressed air main, connection lines and feeder line connections. Details of pipe diameters and materials, the main air take-off points and any take-off points for air at special pressures and qualities must also be shown.
b) Compressed air applications
As compressed air is a highly versatile medium, it is essential for the user to provide exact details regarding the specific air application: Given information should include, for example, whether the air is to be used as control air, for surface treatment, for rotating tools, for cleaning or as process air, etc.
c) Installed compressors
As well as model and type, the compressors’ technical data – such as working pressure, free air delivery, power consumption, type of cooling and use of heat recovery – should also be mentioned.
d) Compressed air treatment
As far as air treatment is concerned, it is important to know whether the air is treated centrally or locally and what classes of quality are required. Obviously, the technical specifications of the components should be listed and a flow diagram provides the necessary overview.
e) Compressor control and monitoring
As the efficiency of a compressed air system is significantly affected by the characteristics both of the individual compressors and the way they interact with one another, it is also important to include details regarding the control and monitoring systems that are used.
2. Discussions between the user and specialist.
Once the above information is made available, the compressed air specialist should be familiarised with the relevant documents and then a discussion should follow detailing any issues with the air supply. Such issues might include: low or fluctuating pressure, poor air quality, inadequate utilisation of compressors or problems with cooling.
The most revealing phase is an inspection of the compressed air system. This should always start in the most critical zone, i.e. where the greatest pressure drops or poor air quality are to be expected.
Experience shows that these are often the final compressed air take-off points.
a) Connection hoses, pressure regulators, water separators
The hose connections to the air consuming equipment are highly susceptible to leaks. These should be thoroughly checked. If pressure regulators are installed then their pressure settings (inlet and outlet pressure) should be checked under load.
Water separators installed upstream from pressure regulators should be checked for fl uid accumulation and contaminant build-up. The same applies to drainage pipes that lead straight down
b) Shut-off valves
Distribution lines and their fittings leading away from the main line significantly affect system efficiency. Shut-off valves and similar equipment also play an important role: they should be adequately sized, full-flow ball or butterfly types, not inefficient water taps or angle valves.
c) Main ring
The most important point is to detect causes of pressure drops such as narrowed sections.
d) Compressed air treatment system
The most important inspection criteria here are the pressure dew point achieved (degree of dryness) and the pressure drop across each component. Further quality checks may be required depending on the application.
e) Compressed air station
Of course the compressed air station itself may have its own shortcomings. In particular, the location of the compressors, ventilation, cooling and pipework should be checked. Furthermore, the cumulative pressure swing of the compressors, the size of the air receiver and the location of the pressure measurement points from which the compressors are controlled must be checked.
f) Determining ADA measurement points
When the inspection is completed, the specialist and the user decide on the points at which the measurements are to be taken. The minimum requirement is to measure points upstream and downstream of the air treatment system and at the outlet of the compressed air distribution network.
4. Measurement of pressure and air consumption (ADA)
During measurement of pressure and air consumption, the operation of the compressed air system is monitored over a period of at least 10 days with the help of advanced data logger technology. The data logger collects all relevant information and transfers it to a PC which uses this data to create an air demand profile. The graph shows pressure drops, fluctuations in pressure and consumption, off-load profiles, on-load and standstill periods of the compressors and the relationship of individual compressor performance to respective air consumption. In order to complete the picture, the leaks also have to be determined during this measurement process. This is carried out as described in the text for "Optimizing An Existing Air Distribution Network", and requires selective closure of defined sections of the air main over the course of a weekend.