The use of compressed or blown air in factories, process plants and a whole host of other industrial facilities dates back decades. Deciding which is best for the application has long-sent the finest engineering minds into a quandary. However, it can be determined that selection in most instances tends to hinge on key factors that include operating pressure, energy efficiency, price, footprint and noise levels.
In terms of design, a compressor uses a compression chamber to reduce atmospheric air volume and in turn, increase pressure. A compressed air system, be it reciprocating, rotary screw or centrifugal, will typically come complete with dryer and filtration packages. In contrast, an air blower is a stand-alone system where air is simply moved from one point to another, often exiting via a gun. Taking the example of a rotary lobe air blower, the principle of positive displacement is facilitated by two parallel rotors mounted in a housing that rotate in opposite directions. Timed rotation of the rotors against the wall of the chamber creates air flow direction. Screw-type and centrifugal-type air blowers are also available.
The main difference between choosing an air blower and a compressor is operating pressure, according to Roy Brooks, technical development officer at the British Compressed Air Society (BCAS) and Russell Frost, chair of the BCAS low-pressure and vacuum committee. They explain: “A typical blower, depending on design, will be classed as ‘low pressure’, and can operate up to or around 2-2.5 barG. Anything above this pressure would normally be classed as an air compressor, with higher pressure achieved through single or multi-stage design.”
So, why typically would an air compressor be specified over an air blower, and vice versa, and what type of company prefers which? “The key difference between a compressor and air blower is the pressure of the air that needs to be generated,” says Saverio Mattucci, product manager at Gardner Denver. “Therefore, the reason for specifying a compressor over an air blower, and vice versa, will depend on the application and its air demands.”
He adds: “Typical preferred applications for air blowers might include wastewater treatment; pneumatic conveying and molecular evaporation in the chemical and pharmaceutical sector; and bed combustion fluidisation and flue gas desulphurisation in the power generation industry. In contrast, compressed air systems are found commonly in product handling and fluid pumps in the food and beverage sector, through plasma cutting, welding and air-operated tools in the automotive arena, to PCB cleaning and pick-and-place machines in the electronics industry.”
So what of noise and noise attenuation limits? These factors are now a major requirement of most designs and specifications and are covered by various standards, including ISO 2151 ‘Acoustics – noise test code for compressors and vacuum pumps’. However, both systems are typically available with silenced or super-silenced acoustic canopies.
Of course, a major issue in the environmental age is energy efficiency. In the past, fingers have been wagged at compressors and air blowers in this regard. It’s probably why compressed air is often referred to as the ‘fourth utility’, with 10% of all electricity in industry used to drive compressors.
“Air blowers and compressors both require considerable amounts of energy to operate, and this can be up to 70% of whole life cycle costs,” agree Brooks and Frost. “There are many different designs available that can reduce energy consumption, such as rotary screw and high-speed turbo or centrifugal compressors. However, this can be limited to the application and local site conditions. The life cycle costs of air blowers and air compressors differ immensely due to the many different designs and applications, but the breakdown in costs is very similar in both designs, with up to 70% comprised of operating costs, and the remaining 30% split between the actual purchase cost and maintenance/servicing.”
Mattucci is also keen to express his views on energy efficiency. Compressors and air blower systems face many of the same challenges and opportunities around energy consumption, and the environmental impact they pose. For instance, the energy consumed is driven by many factors, but among the most important is operating pressure. Ways that pressure drops can be avoided include shortening pipe distances and ensuring smooth bends. “Air leaks can also influence pressure drop,” states Mattucci. “In fact, air leaks are a leading cause of energy loss in industrial air systems, wasting 20-30% of output. Investing in energy audits and effective maintenance strategies can help to overcome this issue.”
One opportunity to consider is a system installed with Industry 4.0 capability. Data analytics provides a valuable means of understanding where energy-efficiency improvements can be made, helping users to optimise processes. Predictive maintenance models can be established to reduce energy consumption, improve process efficiencies and minimise risk.
Mattucci also picks up on the noise issue: “A noise output higher than 85 dB(A) can be considered harmful with prolonged exposure. Fortunately, most modern systems are quieter than this, and today it’s common practice that equipment will feature integrated sound-reduction devices to help reduce noise levels. The latest technology is also making great strides to reduce noise output as much as possible. For example, the Ultima compressor has a noise level of only 69 dB(A), while Robox rotary lobe blowers offer noise levels lower than 80 dB(A).”
At Atlas Copco Compressors, which also supplies both compressed air and air blower solutions, the noise issue continues to resonate. “All machines generate sound and vibration, including air blowers and compressors,” says Andy Pulley, team leader and product specialist. “The average noise level for an air compressor is 85 dB(A), which is higher than a phone’s ringtone [70 dB(A)], but lower than most headphones, which can go up to 110 dB(A). Due to their structure, piston compressors are the least quiet. In contrast, rotary screw compressors are considerably quieter as the air element helical screws do not touch one another. This is the reason that Atlas Copco’s VSD+ compressors can run as low as 62 dB(A).”
For smaller businesses, such as automotive workshops, Atlas Copco’s G/GX range, which is based on rotary screw technology, is said to emit up to 13% less noise compared with other variants. Further up the scale, the principal innovation of the mid-range GA VSD+ compressor is the absence of couplings or gears between the motor and screw element, which makes it both quiet and energy-efficient.
In terms of air blowers from Atlas Copco, Rob Boughton, the company’s low-pressure sales manager, says that “it’s possible to enjoy quieter operation and reduce installation costs by choosing a blower with intelligent internal baffle design and canopy configuration. Sound levels can be down to 72 dB(A), so there is no need to provide noise-insulated rooms and doors.”
At Nex Flow Air Products, a whitepaper was produced to draw comparisons between blower and compressed air operated accessories (www.is.gd/rofuhu). One of the key differences is cited as size. Blower operated air guns are typically large, heavy and harder to handle. In contrast, compressed air-operated accessories are smaller and easier to work with because they are simply connected to the compressed air supply. Ultimately, ease-of-use translates to higher productivity. Having said that, if space is available and the cost consideration favours a blower-operated system, this might be the option to pick, reports Nex Flow.
The company concludes its report by stating that the best choice should always be the system which costs the least overall, takes up the least time in company resources, and maximises production output.