A significant portion of the energy we use today still comes from fossil fuels and as a result, CO2 and other greenhouse gas levels are rising. Industry needs not only to reduce reliance on carbon-based sources, but also reduce energy demands and make more efficient use of energy that is used. Solely focusing on the production of sustainable energy will not answer future needs because energy reduction is the only way to a carbon-neutral economy – and it can start in the compressor room.
Compressed air production comes at a cost, with effects on a company’s bottom line as well as the environment. Energy costs make up around 75% of a compressor’s total cost of ownership. So, the wise course of action for responsible compressor owners and users is to take immediate and sustainable steps to help lower their energy consumption, reduce their carbon footprint, and make direct savings that will cost little to implement.
This 10-step guide demonstrates the fact that many of these steps can be taken right away and require hardly any financial commitment. While others may involve infrastructure investments, they will see a significant return in the short term.
The guide should not be seen just as a one-off exercise − it should be a continuous process to help maintain peak production efficiency.
Step 1: Application & Installation - the benefits of matching equipment to applications
Understanding the compressed air application
Companies waste up to 50% of the power needed to generate compressed air through inappropriate use or inefficient systems design. That is why in taking the appropriate 10 steps the compressor user’s journey should start with a greater understanding of the application needs and the essential factors that have to be considered.
Before expanding, replacing, or improving an existing compressed air system, compressor users should first look to eliminate wastage in their current installation.
A common mistake is to base the selection of new equipment on the size of the existing hardware and then simply scale it up to take into account anticipated growth.
It might be surprising to learn that in many cases, they may actually be able to invest in smaller equipment – and therefore save a great deal of money – as long as they have eliminated any existing inefficiencies.
What can be done to make a compressed air system much more efficient?
1) Isolate equipment when it is not in use. Using a simple manual isolation valve or an electronic valve, isolate any production equipment that is not in use to reduce the potential for equipment leakage.
2) Keep cool. The location of compressors impacts their efficiency. Compressed air equipment should be installed in the coolest location in the facility having made sure that any heat generated is properly removed from the compressor room. Every 5°C rise in air temperature results in a 2% loss in efficiency, so compressors should be kept cool.
3) Keep clean. Excessive dust in the air will result in blocked filters. Every 3 millibar pressure drop in the intake filter increases power consumption by approx. 1%, so a dirty and dusty compressor room can quickly add to electric bills.
4) Keep working pressure as low as possible. The working pressure of a system directly affects the power required to supply the compressed air. A higher working pressure means a higher power requirement and, as a result, higher energy costs and a larger carbon footprint.
Step 2: Storage and Distribution - the importance of air storage, pipework design, and air treatment
The size of an air receiver and the connected pipework can directly impact energy consumption. Air receivers reduce the cycling time of air compressors, which increases their reliability and longevity. A larger air receiver – or stored volume in the pipework – can reduce the operating pressure differential of compressors and therefore the power consumption and carbon footprint.
Consider separate compressed air systems if the majority of the production requires a lower pressure than the highest pressure requirement.
Review the design of compressed air pipework
As their operations grow, companies often simply extend their pipework to meet the needs of new equipment. Such changes in the pipework causes pressure drops in the system. Too often, that pressure drop is compensated by increasing the operating pressure of the existing air compressors or purchasing new ones. But there are three much simpler (and less expensive) ways to address these pressure drops and keep the carbon footprint small:
- Increase the size of the main distribution pipework diameter. This will enlarge the stored volume and also reduce air velocity to reduce pressure drop.
- Convert a dead-end or single pipework system into a ring main pipework system. This increases the overall volume and helps smooth out the pressure loss from sudden air demand surges. In addition, it allows the air to flow from multiple directions, which lowers the internal velocity and therefore also the pressure drop.
Lowering pressure differential by 0.5 bar can reduce the energy consumption of a compressor by up to 4%.
- Plug the leaks. It is estimated that the average production facility loses up to 20% of the compressed air it generates to leaks. That means the compressed air system is very likely leaking money. In fact, some companies are running compressors that only make up for the end loss to leaks. That is another reason why simply turning up the pressure is a bad idea.
It may be possible to find large leaks by simply walking through the facility and listening for hissing sounds. Otherwise, carry out a leak detection survey on the pipework distribution system to eliminate leakage in pipe joints. Then, after this has been done, it will be the right time to perform a flow demand survey. This will avoid recording a false impression of a plant’s air consumption.
Step 3: Air Quality - compressor users need to know their air purity requirement
Treating compressed air has its cost – both in terms of energy and money. That is why operators should always know which level of air purity their applications require. Cleaning up the air too much wastes energy and puts unnecessary strain on the environment. Cleaning up too little can jeopardize production quality and reliability.
The ISO 8573.1: 2001 table defines the various air quality classes.
The importance of air treatment
Proper air treatment is important and will not only increase the quality of compressed air but also the service life of production equipment.
Atmospheric air contains water vapour and dust. When that air is compressed, the concentration of these contaminants also increases, and they have to be filtered out to protect downstream equipment and to maintain the required level of air purity.
Compressed air dryers play a major role in the production of high-quality air. However, some types of dryers can also greatly contribute to the energy consumption of such a system. So it pays to check the compressed air requirements of individual production equipment to check whether it would be better to use a central drying system or point-of-use dryers. Selecting the correctly sized air treatment products can minimise the pressure drop, which in turn will reduce the compressor’s power consumption.
The type of dryer needed depends mainly on the dew point or allowable moisture content in the process or the equipment which is using the compressed air. If it is very low, it will likely require a desiccant dryer. However, they are not the best choice for applications with an average dew point. That need is best served by a refrigerant dryer.
Once the type of dryer has been identified, there are many ways to find energy savings. For example, refrigerant dryers are also available with the highly efficient variable speed drive technology, while a desiccant dryer, with the option of dew point dependent switching, can also offer substantial reductions of energy demand.
Step 4: Volume & Flow Pattern - understanding the air demand is the key to greener production
It is important to be aware of the flow pattern of all air users and to take into account shift operations - peak production periods on weekdays but much lower air demand on nights and weekends, for example.
With a better understanding of air demand, it may be possible to save a substantial amount of money when investing in a new compressor. By eliminating the inefficiencies of a compressed air network and benefitting from the increased performance gained from the latest technologies, the next compressor may be much smaller than the existing unit. It is even possible that a new one may not be needed.
Step 5: Core Technology - different compressor types and their benefits
There are many different types of air compressor, and each has specific advantages usually based on the operating pressure and volume flow rate requirement. Even the most efficient compressor may not prove to be the most profitable solution in all cases.
For example, while variable speed drive compressors are nearly always the best solution for operations with varying air demand, a less expensive, fixed-speed compressor may be the perfect choice for production environments with a stable air requirement. There may also be situations in which a mix of compressors provides the most energy-efficient solution.
Here is an outline of the main technologies as a starting point in determining which machine is right for a specific application:
Piston compressor: Highly efficient on-load and off-load but may not be suitable for all duty cycles. Attention must be paid to the specific requirements of installation and lifecycle costs when running a piston compressor.
Scroll compressor: Mainly used in applications requiring small and clean oil-free airflows. Best used in intermittent air demand applications. Simple and easy to maintain.
Tooth compressor: Oil-free, rotary tooth compressors are suitable for small to medium-sized applications. Good for both intermittent and continuous duty applications.
Rotary screw compressor: The most common type of industrial compressor, used in a broad range of applications from small workshop operations with intermittent demand to large industrial production processes with continuous demand for 24 hours per day. Screw compressors are available with both oil-lubricated and oil-free technologies and can maintain peak efficiency over a wide variety of flows.
Centrifugal compressor: Centrifugal compressors are most efficient when continuously running and are generally the most efficient technology for large volumes of compressed air.
Step 6: Equipment Control - all control systems are related to pressure
It pays to watch system pressure closely. There is a simple rule when it comes to compressed air: more pressure means more energy consumption, which means a larger electric bill and an increased carbon footprint. Unlike the initial equipment investment, these costs associated with energy will keep on adding up. That is why it pays to be mindful of the generated pressure.
Control methods differ, so it depends on the flow pattern to determine which one is best for a given installation. Generally, compressors are set to run within a pressure band, and the wider the pressure band the more potential there is to consume energy. There are various ways to narrow a pressure band and to make production greener and more energy efficient. One method is to use variable speed drive technology that can quickly react to changes in compressed air demand, only delivering compressed air that is needed.
Some compressors are controlled simply by turning them on and off. Others rely on load/unload control technology. For operations with fixed-speed compressors and constant air demand, the modulation method of controlling the inlet valve and regulating the output of the compressor is efficient.
But when that demand varies, compressors equipped with a variable speed drive (VSD), which controls the speed of the motor, are the best solution and offers potential for the largest savings.
Step 7: System Control - optimising compressor control
In a compressed air system with multiple compressors, even the most efficient machines cannot reach their potential without the proper controller. A central controller can be set to prevent unequal wear of compressors, equalising the running hours on multiple machines for more efficient service scheduling.
In a system that relies on basic start sequence control, the load/unload pressure of each compressor can be set to react to changes in air demand and, if the system pressure drops, an additional compressor will switch to loaded running. However, the sequence will always be the same, and any economic advantages offered by VSD-powered compressors in the installation will not be fully utilised.
Central controllers are the backbone of an optimised compressor installation, managing the whole compressor room, matching the air supply to demand while offering pressure stability, and contributing significantly to energy efficiency, and reduction of carbon footprint. It is a general rule of thumb that 1bar pressure reduction can achieve as much as 7% in direct energy cost savings.
Stable pressure also contributes to better production reliability. A smart, central controller that accommodates different compressor technologies and control types links all compressors and dryers and will select the best machine combination. It will lower the overall pressure bands to deliver the required air output in the most efficient way.
Step 8: Energy Recovery - saving energy by using waste heat
A compressor installation that consumes 500 kW for 8,000 operating hours per year represents a yearly energy consumption of 4 million kWh or 2828 Metric tons of CO2. Fortunately, the possibilities for recovering substantial amounts of waste heat from the compression process via hot air or hot water are very real.
Compressing air generates a lot of heat. In fact, up to 90% of the electrical energy a compressor uses is converted into heat. Unless that heat is captured and reused that is allowing money to vanish into thin air. That is why energy recovery is the single best option to help reduce overall energy consumption.
Effective compressor heat recovery does not need to be a sophisticated system, e.g., heat in the form of hot air can simply be captured and routed through to a place where it is useful via simple ductwork installation, for example, to warm a factory during the winter, otherwise the heat can be removed from the cooling system via plate heat exchangers to heat water for boilers or showers.
Step 9: System Maintenance - the role of system maintenance in efficient production
It is very important for companies to view maintenance as an essential component of an energy optimisation system and not as a burdensome chore that sometimes shuts down production. In the end, a well-maintained compressed-air system will more than pay for its maintenance costs through energy savings.
Maintenance is even more crucial for compressors. In most industrial applications, compressors are required to run every day and sometimes continuously without stop. There is nothing to be gained by delaying scheduled maintenance. An untimely breakdown will cause a production shutdown and any unchecked problems could be contributing to increased energy consumption.
Having a service level that meets your needs will keep production running efficiently and ensure operational costs are under control. It will pay to call in the suppliers’ well-trained and experienced service experts. They are best placed to be able to perform services more quickly, optimise equipment, spot and fix potential problems early, and prevent efficiency loss and breakdowns.
Step 10: Remote monitoring - keeping an eye on compressor performance
Remote monitoring makes it possible to stay informed, optimise equipment performance from any location and receive messages that highlight potential issues. In addition, remote monitoring prompts rapid reaction when energy consumption increases but not compressor output. It will show the need to investigate where a system is experiencing performance inefficiencies.
Smart remote monitoring technologies make it possible to connect industrial equipment over a secure network to mobile devices, tablets, and smartphones. By facilitating remote monitoring, operators can keep track of key compressor performance parameters, including pressure, flow, motor and dryer speeds, and make adjustments when necessary, via a compressor’s manual interface.
Knowing the status of compressed air equipment at all times acts as the best way to spot any developing problems, reveal potential energy savings, and deliver maximum uptime for compressors and production lines.
In practice, a sensor fitted to legacy equipment or integrated into new compressors gathers a broad range of data that also includes run hours, temperature, and oil levels. On new, leading brand compressors the smart sensor comes as standard but for retrofit applications, where the sensor is not built-in, installation can be completed within a couple of hours. The data is transmitted wirelessly, or via ethernet, to a central server where it is analysed and presented via a simple customer dashboard, highlighting information on events, such as potential failure/pressure drops/required maintenance.
This capability provides plant managers with far more flexible and meaningful insight into their day-to-day operations and compressed air production– improving efficiency and saving energy.
10 steps in the right direction
Through adopting the 10 Steps strategy not only do compressor owners derive the environmental, financial and productivity benefits that result, they are able also to make progress towards achieving ISO50001 standard certification. The objective of the ISO50001 standard is to provide a framework whereby a company can continually improve energy performance and efficiency. Certification demonstrates an organisation’s commitment to its energy management system and processes that reduce energy use, energy costs, and its greenhouse gas emissions
Over 70% of companies are continuing to prioritise sustainability and environmental management issues*. Many of this number will include production companies with compressor systems that have taken all the right steps and benefitted from the adoption of green technology. Adopting good practice and adapting or replacing their compressed air system with energy efficient solutions is their guarantee of a reliable and sustainable air supply to aid productivity, minimise costs, and promote a greener, cleaner environment.
References
*https://www.carbontrust.com/resources/corporate-attitudes-towards-sustainability-2020
Link for publication: https://www.atlascopco.com/en-uk/compressors/greenproduction
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