Author: Seán Fairest, country manager, Atlas Copco Compressors (Ireland)
Alongside water, electricity and gas, compressed air is such an important source of power for production that in many industries it is regarded as the fourth utility. We have all received enough bills to be acutely aware of the rising costs associated with the first three utilities. Coupled with environmental considerations, it is no surprise that energy efficiency has become such a priority. But compressed air, the fourth utility, should not be discounted from this drive for efficiency savings.
There are several ways in which compressed air can be managed and harnessed to deliver efficiency improvements. As Ireland emerges from recession into a period of improved growth, efficiency will be an important ally in terms of sustainable productivity.
The best starting point for any air compressor installation is to carry out an audit. This will give a highly accurate picture of how much compressed air is being used on site, as well as showing how much energy is being wasted in producing it. The survey will pinpoint any areas of energy drain so that appropriate action can be taken to achieve peak efficiency.
Additionally, analysis of usage patterns and a detailed report show precisely where the system could be improved for greater efficiency, flexibility and reduced costs.
One of the key ways of preventing energy wastage is to ensure that the practical demands of the compressed air application are met by the most appropriate compressed air system. This starts with compressor sizing. The nominal compressed air requirement of a system is determined by all of the consumers – tools, machines and processes. Therefore, the size of a compressor should be based not on the total air using equipment, but on the usage factor at any given time. The golden rule is to size the compressor to the largest air-using equipment only.
VARIABLE SPEED DRIVE
Variable speed-drive (VSD) technology has been used across numerous industries since the 1990s and has particularly benefited the compressed air sector, where the technology is especially suited to the unpredictable demands of modern manufacturing.
This year marks the twentieth anniversary of Atlas Copco introducing VSD technology into air compressors and, although huge progress has been made in implementing that technology, there is scope for wider use of VSD technology. Industries are losing out on energy savings worth hundreds of millions of euro, as well as a significant reduction in carbon emissions.
Variable speed drives are particularly suited to compressed air applications for their ability to boost compressor performance by matching air supply to air demand. In 80 per cent of all compressed air installations air demand shows fluctuations, which can prove costly if compressors are constantly operating at high capacity. The key feature of a VSD compressor is its inclusion of an integrated frequency converter that can cut the cost of compressed air energy by up to 35 per cent compared to conventional compressors.
In some cases, people are simply unaware that such energy savings can be made. The key is to understand usage levels to begin with. A detailed energy audit of a compressed air system, however, can identify potential savings. Energy-monitoring services are now being offered by many compressed air manufacturers and distributors.
One of the most innovative ways to derive maximum efficiency from compressors is through energy recovery, whereby excess heat from the compressor is recycled and redirected to heat air or water. This can often be used internally, either for process purposes or to provide heat within the building itself.
As much as 94 per cent of the electrical energy used by an industrial air compressor is converted into heat and lost through radiation in the compression process. A properly designed heat recovery unit can recover anywhere from 50 per cent to 94 per cent of this available thermal energy as low-grade heat, which can be used to raise air or water temperatures as high as 90°C.
An unusual example of energy recovery can be found at Greiner Packaging’s production plant in Northern Ireland, which is helping a neighbouring college cut its £40,000 annual heating bill by donating waste heat from its compressors and its process cooling installation. Dungannon Integrated College, a secondary school with 500 pupils, receives the heat into its central heating system via underground pipework, not only reducing costs but saving 200 metric tons of CO2.
Greiner Packaging, which is headquartered in Austria, specialises in the production of rigid packaging containers supplied to the food industry in the United Kingdom and Ireland. Compressed air is essential for all of the company’s production processes and is supplied by Atlas Copco oil-free, water-cooled Z-range compressors – with their outputs optimised by a central controller. It is the compressors’ water-cooling systems that provide a substantial addition to the waste heat supply to the nearby school.
This supply is combined with hot water derived from a large battery of cooling fans sited near the college, which assist the cooling cycle that is integral to the plastic forming processes undertaken at the plant.
GET THE BEST FROM BLOWERS
[caption id="attachment_14465" align="alignright" width="971"] Regular compressor maintenance keeps the production facility operating at maximum efficiency[/caption]
With investment in water treatment expected to increase in Ireland in coming years, the efficiency of blowers is another topic that deserves greater consideration.
A continuous and reliable supply of quality air is a critical requirement for the aeration diffuser systems within municipal and industrial wastewater treatment plants. Yet despite the vital role of that air supply, the majority of these plants rely on basic lobe blower technology that has seen little development since its introduction in the late 19th century.
Newer solutions incorporate screw technology to combine optimum performance with protection of the process, the environment and operational energy costs. The operating principles, proven components and feature benefits of these screw blowers were specifically developed to overcome the limitations of lobe type blowers.
However, the route to efficiency in blowers is clouded by inconsistencies in the way that the old and new technologies are compared. Lobe blower data is commonly offered by giving the air intake flow volume and the shaft power of the bare element whereas low-pressure screw compressors are quoted by listing the FAD (free air delivered) at the unit outlet and the power consumption at the terminals of the power supply, which is a more accurate measurement.
SERVICE AND MAINTENANCE
A fifth route to ensuring compressor efficiency is to have in place a regular servicing and maintenance plan. Regular compressor maintenance not only keeps the production facility operating at maximum efficiency, but it is also an opportunity to reduce running costs. Around 80 per cent of the lifecycle cost of a compressor is for electricity, whereas servicing is around 10 per cent.
Regular servicing will reduce the energy running costs of a compressor significantly, so the potential gains are enormous.
The regular replacement of ancillary parts, such as filters that can become clogged leading to pressure drops, will also reduce compressor installation running costs. A clogged filter or inefficient dryer will create a pressure drop and reduce energy efficiency. On average, for every one bar pressure drop incurred, an extra 7 per cent of electrical power will be required to meet production needs.
As with cars, some owners of compressors cut corners by using lower-cost replacement parts from third parties, rather than from the original manufacturer. While this short-term approach can produce early cost savings, there can be expensive consequences further down the line if the part is less durable than its official equivalent.
The supply of compressed air in any facility should be considered as a whole system, rather than a single unit. The method by which the compressed air is delivered to the end-user, for example, is hugely important.
Many industries are moving from galvanised steel piping, which is vulnerable to corrosion that can cause leaks and pressure drops. Instead, the more progressive businesses are using aluminium piping with aluminium and polymer fittings, which are resistant to rust and corrosion.