Dimensioning Compressor Installations
25 April, 2022
A number of decisions must be made when dimensioning compressed air installation for it to suit different needs, provide maximum operating economy and be prepared for future expansion. Learn more.
Cost Saving Opportunities for Compressors
In the world of compressors, there are often significant and unutilized energy-saving possibilities including energy recovery, pressure reduction, leakage reduction and optimization of operations through correct choice of a control and regulation system as well as the choice of compressor size.We are going to take a look at some of the opportunities for minimizing the compressor’s operating costs.
The power requirement concept
When making calculations, it is important to apply the overall power requirement concept. All energy consumers that belong to a compressor installation should be accounted for: for example, inlet filters, fans and pumps, dryers and separators. For comparisons between different investment alternatives, the use of comparable values is particularly important. Therefore, the values must be stated in accordance with internationally recognized standards and regulations, for example, as per ISO 1217 Ed.4 -2009.
The working pressure
The working pressure directly affects the power requirement. Higher pressure signifies higher energy consumption: on average 8% more power for 1 bar higher pressure. Increasing the working pressure to compensate for a pressure drop always results in impaired operating economy. Despite this adverse economic effect, increasing compressor pressure is a commonly-used method for overcoming pressure drops caused by an under dimensioned pipe system or clogged filters. In an installation fitted with several filters, especially if they have been operational for a long period of time without being replaced, the pressure drop can be significantly higher and therefore very costly if unattended for long periods of time. In many installations, it is not possible to implement large pressure reductions, but the use of modern regulation equipment allows the pressure to be realistically lowered by 0.5 bar. This represents a power savings of a few percent. This may seem to be insignificant, but considering that the total efficiency of the installation is increased by an equivalent degree, the value of this pressure reduction in terms of actual savings is more readily obvious.
Optimizing air consumption
By analyzing routines and the use of compressed air, solutions to provide a more balanced load on the compressed air system can be found. The need for increased air flow production can thereby be avoided to reduce operating costs.
Unprofitable consumption, which usually is a consequence of leakage, worn equipment, processes that have not been properly configured or the incorrect use of compressed air, is best rectified by increasing general awareness. Dividing the compressed air system into sections that can be separated using shut-off valves can serve to reduce consumption during the night and over weekends. In most installations, there is some degree of leakage, which represents a pure loss and must therefore be minimized. Frequently leakage can amount to 10-15% of the produced compressed air flow. Leakage is also proportional to the working pressure, which is why one method of reducing leakage is to repair leaking equipment, and thereby lowering the working pressure, for example, at night.
Lowering the pressure by only 0.3 bar reduces leakage by 4%. If the leakage in an installation of 100 m3/min is 12% and the pressure is reduced by 0.3 bar, this represents a saving of approx. 3 kW.
Regulation method
Using a modern master control system, the compressor central plant can be run optimally for different operating situations while enhancing safety and availability. Selecting the right regulation method encourages energy savings through lower system pressure and a better degree of utilization, which is optimized for each machine in the installation. At the same time availability increases, thereby reducing the risk of unplanned downtime. Also, central control allows programming for automatic pressure reduction in the entire system during operation at night and on weekends. As compressed air consumption is seldom constant, the compressor installation should have a flexible design, using a combination of compressors with different capacities and speed controlled motors. Compressors may run with speed control and screw compressors are particularly suited for this, as their flow rate and their power consumption are virtually proportional to their speed.
How does energy recovery work in compressors?
When using electricity, gas or oil for any form of heating within the production facilities or in the process, the possibility of fully or partly replacing this energy with recovered waste energy from the compressor installation should be investigated. The decisive factors are the energy cost in €/ kWh, the degree of utilization and the amount of additional investment necessary.
A well-planned investment in waste energy recovery often gives a payback time of only 1–3 years. Over 90% of the power supplied to the compressor can be recovered in the form of highly valuable heat. The temperature level of the recovered energy determines the possible application areas and, therefore, its value. The highest degree of efficiency is generally obtained from water-cooled installations, when the compressor installation's hot cooling water outlet can be connected directly to a continuous heating demand, for example the existing heating boiler's return circuit.
Recovered waste energy can then be effectively utilized year round. Different compressor designs give different prerequisites. In some situations requiring a large and peaking heat flow, long heat transport distances to the point of utilization, or a requirement that varies during the year, it may be interesting to look at the possibilities of selling the recovered energy in the form of heat or cooling or electricity, etc.
Learn more about energy recovery in compressor installations.
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