April 2021

22 | Plant & Works Engineering www.pwemag.co.uk April 2021 Process, Controls & Plant Focus on: Compressed Air Approximately 70% of energy is recoverable from oil-injected screw compressors, and up to 94% from oil-free water-cooled screw compressors. 5: Ensure the correct size of compressor is installed Choosing the wrong size air compressor for a facility can lead to problems with production and or increased costs due to wasted energy. When selecting a compressor, manufacturers should ask themselves these questions: What is the application? How much air flow does their facility/workshop use? What is the minimum pressure needed within the facility? Do they need clean/dry air (use of dryer and filters)? How many hours per year does their compressor operate? How many shifts do they run per day? Is there fluctuation in flow demand between shifts (if so, a VSD compressor could be a good option and offer significant savings)? Are there any plans for future expansion? Once they have answered those questions, they should select the compressor not based solely on the initial purchase price but based on the one with the lowest total lifecycle costs. Since 70% of the total LCC of a compressor is spent on energy, the right choice will add up to a significantly reduced bottom line for the factory. 6: Ensure the correct type of compressor technology is installed Many applications in the food and beverage, electronics, automotive, textile and pharmaceutical industries will require oil-free air to guarantee product integrity and quality (often specified as Class 0). Oil-free compressed air technology will help to avoid expensive filter replacements, cut the cost of oil condensate treatment and reduce energy loss from pressure drop in filters and, in food & beverage applications, the use of expensive food-grade lubricants. There are some extremely energy-efficient oil-free compressors on the market. For example, a ZR 90-160 VSD+ oil-free rotary screw air compressors offer up to 10% more output and 15% lower energy consumption compared to previous models. They even have the optional benefit of having an integrated, guaranteed -40ºC pressure dew-point dryer that offers almost zero energy consumption. If the application is very large-scale, a centrifugal compressor should be considered, since these offer unbeatable energy efficiency in process air or bulk air applications presenting a flat load, or when providing a baseline flow in mixed installations with VSD screw compressors. 7: Consider a Variable Speed Drive (VSD) compressor Most production processes require different levels of demand in different periods, which may mean that the compressor is running off-load or idle (not producing any compressed air) for long periods of time. Considerable savings can be made if a variable speed drive unit can replace a fixed speed compressor, as it only produces compressed air as and when required. This also minimises off-load running of the compressor, which is known to waste energy. A VSD compressor saves an average 35% energy and a VSD+ unit can save as much as 50% compared to a fixed speed unit, even at full load. As a fixed speed compressor has a fixed amount of motor starts an hour, the compressor runs off-load for a set time which limits the number of motor starts to ensure overheating of the motor does not occur. As a VSD unit ramps up and down in a controlled fashion, the maximum number of starts and stops per hour may be increased, and it also avoids peaks in current when starting. 8: Get an air audit Compressed air consumption should never rely on guess work. To find out how to increase efficiency, the system needs an assessment or an audit. Cost is usually the most significant difference between the two, as a simple compressed air assessment can be a complementary walk-the-line visual inspection. In contrast, an in-depth audit based on data logging can cost £1000s and take weeks or months to complete, depending on the size of the facility and the desired outcome. Companies may be reluctant to perform a full air audit due to costs associated with such services, but the outcomes can far outweigh the initial investment. It is essential to understand that the benefits from assessments and audits do not end only with lowering energy costs, but also improving the overall efficiency of the production, therefore positively affecting the bottom line. Not every facility needs to do a full compressed air audit or air scan, as sometimes a simple walk-the- line assessment can satisfy the needs and result in substantial energy savings. Switching or updating a compressed air installation to the latest technology can reduce energy consumption by up to a quarter. If there is an old or inefficient compressor, the cost to replace it with a new compressor is often less than the current running costs. A modern air compressor with the latest controllers and energy-efficient motors will contribute to the bottom line from day one, meaning a short payback time. A complete compressor replacement is not the only route, however. Exchange programmes offer the possibility of replacing major components of a compressor with new, more efficient parts. For example, upgrading a compressor with the latest type of electronic controller will allow manufacturers to take advantage of the most advanced compressor control management, reduced unloaded running and higher efficiency. And if an old, lower efficiency motor is replaced with a new, high- efficiency one, energy savings are guaranteed. 9: Reap the benefits of modern compressed air equipment Air compressors are long term investments that will play a significant part in a business for years to come. The average factory changes air compressors every 7-10 years, meaning that the initial capital expenditure is only a fraction of how much a compressor will cost in total. 70% or more of an air compressor’s lifecycle cost will come down to its energy usage. 10: Don’t forget the impact of regular maintenance The best way to ensure compressed air availability is by investing in regular preventative maintenance, which will sustain the efficiency that is gained by purchasing a new compressor or improve the performance of an older unit. If manufacturers prefer to purchase spare parts only and perform maintenance in-house, they can sign up to a planned maintenance programme at pre-determined intervals from the manufacturer or approved distributor or choose a total responsibility package that covers breakdowns and leaves no room for surprises, the main thing to remember is that reduced compressor performance is not inevitable as the machine gets older. Regular servicing, using OEM genuine parts, will improve equipment uptime and energy efficiency: the opposite could lead to more downtime, increased energy consumption and potentially a costly breakdown. Lastly, gather some data. For example, most Atlas Copco compressors come fitted with a Smartlink data box which can provide live information on the compressor status, and can also map the compressor’s operating hours, with off-load / on-load hours and, of course, warning information.