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Choose the Correct Air Compressor

Nov. 9, 2022
When selecting an air compressor, focusing on the energy bill for the current unit and potential savings can lead to a suboptimum choice. Instead, users should keep five key points in mind during the selection process.

Chemical makers demand the highest quality possible when it comes to compressed air. Efficiency also is very important to the competitiveness of chemical processors. A recent study by Atlas Copco pointed to the potential of saving 13 billion kWh in the United States through efficiency improvements.

“If it’s not broken, then don’t fix it” is a foolish strategy for compressed air. On the contrary, waiting for the compressor to schedule its own replacement time could cause you to suffer lost production and force you to make quick decisions, both of which can cost a lot of money. The challenge of trying to be efficient with compressed air is that you most likely will just baseline and benchmark using your energy bill. However, what if the energy bill always has inefficiency built into it? A 10% saving might look like a great job — but what’s the real potential? Understanding that requires considering five factors when selecting a compressor.

1. WHAT DOES AN AUDIT REVEAL?

Never replace like for like — focus on an audit first. One of the key things an audit examines is inappropriate uses of compressed air and artificial demand, both of which could have boosted your compressed air usage and energy bill for many years.
Audits come in two primary types (as well as many sub-types) but the two basic elements to audit are system efficiency and quality, and air quality. Detailed supply- and demand-side audits always must be conducted on-site.
The term audit also often is used for more-straightforward studies that involve data-logging machines and monitoring performance over a defined period; we refer to these as surveys rather than audits. Its simple installation means the equipment necessary for a survey can be sent to the customer without the need for somebody to go on-site to set it up. Then, the hardware is returned, and the data are put into a modeling system to produce graphs that show where savings can be made. This all can be done remotely if the customer desires.
Air quality testing is something that quite understandably continues to gain significance; it even is mandated inside critical industries like food and beverage. This always involves gathering an air sample on-site while making sure not to contaminate the sample before it is sent away for testing.
The two most-common examples of artificial demand are leaks and air consumers left on when not required. Leaks can cause problems within your system that result in more energy consumption and costly resources needed to combat the issue. It’s important to identify and repair all leaks, starting with the leak that consumes the most compressed air. After fixes are made, you should implement a continuous leak detection and elimination program to prevent future leaks.
It’s also important to stop the supply of compressed air to applications that are not in operation. This can be accomplished by various methods, from manually closing a discharge valve to adding a solenoid valve and a control system in the air supply to each application. Closing the valve at night or on the weekend and preventing the compressor from turning on to fill leaks when production is not running can provide a huge source of energy savings.

2. MULTIPLE MACHINES CAN SAVE YOU MONEY

Compressor (or blower) applications fall into three general categories:
  • low-pressure air — output pressure of 150 psi (10 bar);
  • medium-pressure air — output pressure between 150 and 1,000 psi (10.4 to 68.9 bar); and
  • high-pressure air — outlet pressure above 1,000 psi (69 bar).
Determining what equipment works best for you can depend on the applications you are running.
Using higher-than-needed pressures and extended cycle times will result in excessive air usage. Open-blowing applications also waste compressed air that easily can add unnecessary costs to your energy bill.
Typical applications for medium-pressure air within chemical processing include pneumatic controls and valves, general plant air for rotating equipment and tooling and even for product drying. Using high-quality low-pressure air really can offer a large cost-saving opportunity in the following applications:
Refining. This includes petroleum refining and the variety of processes employed in converting crude oil into useful products, including gasoline, kerosene, jet fuel and diesel oil.
Pneumatic Conveying. Chemical processors use pneumatic conveyancing to transport dry bulk materials, including powders and granular forms as well as chips and pellets. Because manufacturing plants that use pneumatic conveying have employees working nearby, worker safety requires using blowers with low-noise and low-vibration technologies.
Wastewater Treatment. Plants treat wastewater using aerobic biological processes to digest waste byproducts. The millions of bacteria feeding on organic waste to break it into carbon dioxide, nitrogen gas and water need oxygen; so, large amounts of air are blown into aeration tanks.
Processors often rely on high-pressure air (or other high-pressure gases) if they are making their own packaging or perhaps even running their own fleets on renewable natural gas.
Every plant manager knows the cost of downtime. Fortunately, it’s possible to build a system that can eliminate or reduce downtime. One way is by adding a second compressor or running two smaller ones instead of one large one; doing this has never been easier. Another option involves treating compressed air, which often is called the “fourth utility” inside a plant, like the other utilities — gas, electricity and water — in essence, buying air and not the actual compressors. For the right customer, this has several advantages, including avoiding a significant capital expenditure at the start of the project as well as maintenance responsibility for the equipment — which the manufacturer instead handles.

3. FOCUS ON QUALITY

This relates to both clean and dry air. First, when it comes to clean air, the highest quality of compressed air is essential; it must be guaranteed ISO 8573-1 oil-free — also known as Class Zero. Contamination by even the smallest quantities of oil can result in costly production downtime and product spoilage.
Removing moisture for corrosion protection also is important for the equipment using the air and the air system itself. Particulate created from rust and scale can foul lines and damage components of the air system. In the worst case, corrosion could lead to failure in the pipe work, creating leaks and preventing air from reaching the process where it is needed.
Most manufacturers use compressed air dryers as one of the methods for removing moisture. Air exiting a compressor is heated and 100% saturated with water. As the air cools, water begins to condense. Because the air typically gets cooler the further it gets into the system (air systems also often pass through cold areas like the outdoors before reaching the process), it is much more effective to dry the air prior to distributing it.
Filters and separators can remove liquid moisture droplets from a system. However, they can’t remove water vapor — that requires a dryer.

4. CAN YOU ADD ON-SITE NITROGEN INTO THE MIX?

Taking control of your industrial gas supply is a growing trend across multiple industries. Did you know that running a compressed air system means you are already 50% of the way toward making your own nitrogen?
Chemical blanketing, also called tank padding or inerting, is a very simple process of applying nitrogen to the empty vapor space inside a container or vessel to control the composition of a specific chemical. The gas is used during production, storage, transportation and final packaging, and can be employed in a variety of container sizes, ranging from a small bottle to a million-gallon tank. But why use nitrogen specifically? Simple: it’s an inert gas, meaning it’s non-combustible and will help prevent fires and explosions. Additionally, nitrogen helps to displace oxygen, thus preserving the integrity of products that otherwise would degrade in oxygen’s presence and preventing unwanted chemical reactions. For these reasons, it is considered as the security blanket of the chemical industry!
So, when sizing a compressor, it’s sensible to consider whether you would also like to include the capacity for current or future on-site nitrogen production.

5. WHAT TO LOOK FOR IN A SUPPLIER

We at Atlas Copco aren’t fans of the term “total-solutions provider” when it comes to our business. However, we can provide most of what is needed in your compressor room — compressors, blowers, vacuum pumps, dryers, chillers, and nitrogen and oxygen generators. All these pieces of equipment have the same controllers and are specifically designed to work together. This offers enormous benefits when it comes to central connectivity, remote monitoring, service contacts, and operator use.
The old way to deal with a service issue was to call the manufacturer. Its service representative would ask, “What message do you see on the controller?” You would answer. Then, the person would ask you to do something — but, if you didn’t happen to be next to your compressor, you might have to call back. If you were lucky, you’d reconnect with the same service representative so you didn’t have to explain everything over again. Today, compressor users and the manufacturer can access system data at the same time in real time. Everyone can see the system’s history and the sequence of events that might have led to the issue. Technicians can connect into the compressor ahead of time, shortlist what they believe to be the issue, and be more proactive. Their visits can be shorter, reducing any downtime (Figure 1).
In terms of service operations, leading manufacturers use systems to optimize their fleet of technicians on the road. Global positioning system (GPS) technology keeps office specialists in constant contact with field-based teams and pinpoints their whereabouts. Direct relaying of address details for the next job to the service vehicle’s GPS system ensures accurate communication. All of this makes scheduling more efficient and allows the company to respond in line with the urgent needs of the current day.
The last and perhaps most important element, relates to that time-tested maxim: an ounce of prevention is worth a pound of cure. The latest monitoring equipment for compressors can detect heat changes, altered vibration and other issues, enabling taking corrective action, such as shutting down a compressor to forestall overheating, before a problem becomes more serious. Remote 24/7 monitoring now is widely available for compressed air systems. This development has spurred manufacturers to set up remote monitoring centers. A simple analogy here is this: we entrust alarm companies to monitor our homes in exchange for peace of mind — why not have the same peace of mind for your compressor? We can assure you that your plant cannot operate without compressed air!
About the Author

Paul Humphreys

Paul Humphreys is vice president, communications and branding, for Atlas Copco Compressors US, Rock Hill, S.C. Email him at [email protected].

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