Having a clear idea of all the Compressed Air Systems Costs when installing or updating a compressed air system will minimise the likelihood of financial surprises, says Mark Whitmore, General Manager at BOGE.
Compressed air – similarly to tap water – has traditionally been regarded as a ‘free’ resource within the factory. However, compressed air is effectively another utility and just as gas, electricity and water prices have risen, so the cost of compressed air has increased.
There is a growing awareness that compressed air is a precious utility. In order to best manage the cost of compressed air, it is first important to understand where these costs come from.
Subscribe to PII and receive:
Our long-established bi-monthly digital magazine *Process Industry Informer*, featuring exclusive articles, news and updates across the Process Industries, plus commentary from our three industry experts:
Sean Moran
Gavin Smith
Dave Green
PLUS:
- Process Industry Update — our weekly e-newsletter
- PII Podcast
- Special messages from our advertising partners
The largest single one-off cost will be the upfront investment of installing the system and its associated pipework. There will, however, be significant costs to keep the system running – particularly energy bills – meaning that energy efficiency will be a critical factor in cost control.
The cost of maintenance may also be substantial, but when done properly will help to reduce more expensive problems like breakdowns and downtime. Add to this expenses such as oil disposal, and it becomes obvious that cost control is critical.
This all adds up to a total cost of ownership (TCO) – and the aim is to keep this as low as possible. Understanding TCO is critical in ensuring that that there are few unexpected financial surprises throughout the system’s lifespan.
Energy efficiency
The main expense throughout a compressed air system’s lifespan is the associated energy costs and output. Typically, this accounts for approximately 75% of total costs across the life cycle, usually being five times more than the original purchase price of the system.
But energy is not always used efficiently and this is certainly the case for compressors: it’s estimated that more than half the energy used to power compressors is wasted. Because of typical system inefficiencies – such as leaks or supercharging – only about 45% of the input energy is used to compress the air. The other 55% is typically wasted.
However, easy alterations can be made to help cut the energy needs of compressors by up to 50%. This is just as well, considering that compressed air typically accounts for nearly one-third of a site’s total electricity usage.
In total, it takes the output of one and a half power stations – around 10TWh of energy – to run all the UK’s compressed air applications every year. Energy efficiency measures could begin to start reducing that enormous demand, whilst also cutting utility bills.
One approach is to use an intelligent energy management system, which can makes savings of 30-50%. This provides a transparent and current picture of how efficiently the compressor is performing, helping to control
Compressed Air Systems Costs
At the same time, a high proportion of the energy used for air compression is converted into heat – up to 94% of which can be recovered and used elsewhere in the plant, such as for heating water. A heat recovery system such as the BOGE Duotherm can recover up to 75% of the electrical power, thus reducing utility bills as well as environmental impact.
An energy audit can identify whether a compressed air line is running at excessive pressure. Lowering system pressure can mean that fewer compressors are needed – with consequent reductions in energy and service costs. Maintenance is cheaper with fewer compressors – and is a key part of the strategy.
A new standard called ISO 11011 has been introduced to control the use of compressed air, in an attempt to lessen its huge demand on energy resources. Its guidelines include the need for energy audits, to establish the amount of compressed air that a company uses – and how much it costs to generate.
Compressed Air System Maintenance and aftercare
Maintenance and aftercare will cut the likelihood of more expensive problems down the line – which are caused by malfunctions such as oil or air leaks. Regular maintenance makes a system as cost and energy efficient as possible, and there is more than one option when selecting a maintenance schedule.
A fixed maintenance is pre-set, meaning many components are repaired, serviced or replaced after a certain amount of time, whether or not it is needed. The main disadvantage is the replacement of parts that are still in good working order, or parts that are problem-free at the time of fixed maintenance – but fail before the next check.
Status-based maintenance, however, uses diagnostic tools to carry out continuous monitoring. This will pick up on a variety of potentially damaging processes, such as high temperatures and vibration. It goes hand in hand with a robust aftercare programme. While this has proven to be more cost-effective and reliable across the lifespan of a compressed air system, these tools must be used properly, and data gathered must be correctly analysed.
Compressed Air Leak Detection
One of the biggest fault areas is air leakage. The Carbon Trust estimates that a 3mm hole in a compressed air line could cost a business as much as £700 per year in wasted energy. But this cost could easily be avoided by conducting regular leak detection surveys as part of a maintenance programme.
As air escapes through a leak hole it creates a tiny sound that is inaudible to the human ear but easily detectable by specialist ultrasound detection equipment – which transforms it into an audible sound and indicates it optically.
Leaks can be detected from a long distance – up to 15m – which is useful in places that are not easily accessible or visible.
An energy audit can help to identify leaks. Some newer compressor models feature an in-build leakage monitor that calculates wasted energy consumed during no production periods.
However leaks are identified, a maintenance schedule must then be put in place to plug them – otherwise the benefits of detection will be short-lived.
Oil leakage is another challenge, and can be highly damaging to the performance of a compressed air system when undetected. As well as compromising efficiency it can – in the case of food production – have potentially serious consequences, if oil traces come into contact with the product or even the packaging. Fixing an oil leak can be expensive; fixing the consequences of it contaminating food is potentially catastrophic.
Pure performance
Many unwanted substances can easily be drawn into compressed air systems. These contaminants include dust, pollen, micro-organisms, moisture and compressor oil, which can all have an adverse effect on air quality and the operation of valves, cylinders and ancillary devices.
The biggest threat is from airborne particles of dust, grit and pollen. In a factory, where product and manufacturing by-products and dust are generally denser, each cubic metre of untreated ambient air can contain up to 180 million particles of dirt as well as 50-80% suspension of water vapour and oil. During compression, the concentration of these particles increases: at a pressure of 10 bar, for example, the effective density of contaminants will increase to around two billion particles per cubic metre.
Particles can combine with moisture, compressor oil or other lubricants to form an abrasive or corrosive solution. This can accumulate and stick to stationary and moving surfaces inside pneumatic devices, causing valves to stick and seals and moving parts to wear, leading to machine failure and downtime.
Water vapour can condense when the warm air emitted from a compressor comes into contact with the cooler surfaces of downstream equipment. Drains can remove condensate, but will not effectively eliminate vaporised droplets of moisture suspended in the air flow. Problems can occur as moisture eventually breaks down lubricating oils, leading to corrosion on exposed metal surfaces, and increased friction and wear between moving parts.
Compressor oil, emitted as an oil vapour, can condense as a film within valves and cylinders, acting as a trap for particles of dust and other contaminants. The heat of the compression process can oxidise the oil, making it acidic. If transmitted downstream, this can affect other lubricants and the integrity of rubber seals and gaskets.
There are various solutions to these problems. One is to attach a filter to the compressor intake, which will normally remove larger airborne particles. However, there are limitations on the size of filter, as it must not impede air flow to the compressor. As a result, downstream air preparation devices will also be required to remove smaller particles, together with oil and moisture.
Many filtration devices use a mechanical coalescing system that removes aerosols of water and oil, as well as solid particulates. Ideally, these should be installed in pairs and in series: the first unit acts as a general-purpose filter, to protect the second high-efficiency filter from bulk contamination.
While most air compressors include an after-cooler, which removes the condensation caused by compression, an extra dryer is often needed to eliminate downstream water vapour.
It should be recognised that different applications require different levels of compressed air treatment. The ideal compressed air for use in the textile industry, for example, may be totally unsuitable for the food or surface-coating sectors. So it is important to match the air treatment system to the specific needs of the application, including factors such as volume air flow and air quality.
Compressed air is a critical resource in a factory, and there is no doubt that it requires major investment. By looking carefully at upfront Compressed Air Systems Costs – and running costs such as energy and maintenance – manufacturers can ensure that they run their system as cost effectively as possible.
Compressed Air System Costs
Capital outlay: initial consultation and design, pre-purchasing, pipeline, purchase and installation, repayment or rental cost.
Energy: electricity and fuel costs needed to run and heat or cool the compressor mean that efficiency is critical.
Maintenance: servicing and aftercare, parts, labour costs (such as fitter’s and operator’s wages) and lubrication.
Oil: disposal and storage costs (Note: not relevant if using an oil-free compressor)
Downtime: fixed maintenance breaks, unexpected failure or leaks that interrupt production – leaving employees with little to do. On a smaller scale, breakdowns eat into time and add cost.
System renewal and replacement: even a properly maintained system will not last indefinitely, so the cost of an entirely new one must be considered at some point.
Boosting energy efficiency
1. Demand analysis/leakage measurement
Considering the energy demands of compressors is not enough. Leaks have a huge effect on energy consumption – and reducing them offers massive saving potential. To do this, the optimal running of the compressors must be determined, based on demand analysis and regular leak measurements.
2. System design
Efficient operation of individual components is only the first step towards energy savings. Optimal interaction of these components – and aligning the entire system to specific needs – has a positive effect. Intelligent design of the process chain helps optimise both energy and resources.
3. System Renewal
For older compressed air systems, a complete overhaul can be useful – depending on the technical state of the system and its energy efficiency. Modern compressors have high-efficiency motors and airends, with modern fans and heat recovery. Investing in new plant – often supported by government – can quickly pay for itself.
4. Intelligent control
An optimal ratio for load and idle times can be achieved through intelligent control systems, which select the most efficient air compressor combination according to demand. This keeps idle time and pressure at an optimum level. In addition, the parameters of your system become more apparent.
5. Heat Recovery
During air compression, much of the energy is converted into heat. Modern, efficient systems ensure that this energy is not wasted. Up to 94% of the heat generated in a compressor can be recovered – then routed to where it is needed, or used in the form of hot water.
