Heat recovery in compressor systems
Compressor energy counts a large amount on your electricity bill
Compressed air is one of the most important utilities for the industry. It is also one of the largest consumers of energy. Therefore, compressor energy savings have a significant impact on costs and on the environment.
When looking at the typical carbon footprint of an air compressor - from the design phase right through to the equipment’s recycling - the energy consumed in its use accounts for 99% of CO2 emissions. As energy consumption also typically represents over 80% of a compressor’s lifecycle cost, energy savings in compressed air systems will have a significant impact towards preserving not only the environment but also your bottom line. While compressed air systems in general account for about 10% of total industrial electricity consumption, this can amount to as much as 40% of the electricity bill for certain plants.
Save energy with compressor heat recovery
Up to 94% of the input electrical energy is converted into compression heat. Without energy recovery, this heat is lost into the atmosphere via the cooling system and radiation.
As shown in the above graphic, electrical energy is not the only source of energy entering the compressor. Another important energy source is humidity that contains a lot of heat. Heat that is released to the system through condensation in inter and aftercooler. The changing from vapour to liquid state.
In the air flow inside the compressor, there are several instances where heat is generated and transferred. Every time this happens, the cooling water system takes up the heat in a very efficient manner.
Both in the low-pressure and high-pressure stages of an oil free compressor, part of the heat of compression is transferred to the cooling water running through the cooling jackets of the element housing.
In the intercooler and aftercooler, the hot air is cooled by transferring the heat to the cooling water.
The heat removed from the hot oil in the oil cooler, is also taken up by the cooling water system.
Some energy is lost through motor inefficiencies… through radiation in components like the element or the coolers… in residual heat in the outlet air… and in residual condensation heat, also in the outlet air.
If we combine all these factors in an overall view, we see that, despite some losses, the net result is an energy output as hot water that is typically 90-95% of the electrical input energy and under specific conditions can be up to 100%.
In other words, the energy that goes into the compressor is made available by the energy recovery system in the form of hot water.
The cooling water circuit and coolers are modified for compressors with an energy recovery option to guarantee recovery of the highest possible amount of energy at the highest possible temperature.
How does heat recovery work for oil-free compressors?
In order to harness the potential heat energy available in the cooling water, you need an energy recovery control unit to transfer the energy recovered from the compressors with optimal protection to the installation of users.
In an Atlas Copco oil-free air compressor, the control unit is installed between the compressor and the cooling water circuit of the customer. In this way the closed energy recovery circuit is completely separated from the cooling water circuit.
The control unit is able to cater the energy and water flow of multiple compressors, maximum total of 4 compressors can be connected to 1 control unit.
The total supplied energy is limited to the maximum capacity of the control unit.
The energy recovery control unit comes with several safety features, a de-aeration system, a pressure relieve valve and the expansion valve that controls the pressure in the water system.
The control unit can also be ordered with a several number of optional equipment:
- A stainless steel heat exchanger for the customers’ process water, a back-up heat exchanger to assure that the cooling water temperature delivered to the compressor is lower than 40 °C.
- It’s an intelligent and safe system that maintains the correct water temperature at all times, ensures proper cooling of the compressor and regulates the water pressure.
- The Elektronikon MKV is controlling all this and displays the temperatures, water pressure, recovered energy during operation, running hours etc.
Please contact an Atlas Copco consultant to harness your waste heat energy from your compressors and either modify an existing system or seek a new system that can pay itself off within a couple of years.
Energy efficiency at Atlas Copco
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