There is much emphasis placed on compressed air systems because of their inherent inefficiency. There are many ideas and suggestions available that can be used to improve efficiencies, but usually only on a singular basis. But much can be done with the supply side of a compressed air system with the mindset of strategically moving forward with sustainable improvements.
When it comes to sustainability, we think nowadays of conservation, earth friendliness and being able to continuously use the resource in question without declining our existing fossil fuel reserves. Sustainability also means setting up a system and operating it consistently in the manner in which it was designed. Additionally, it means following through with planned and program-generated maintenance, as well as a routine set of maintenance tasks that will ensure maximum life of the air compressor with minimum unplanned downtime and maximum efficiency.
As a corporate engineer responsible for supporting operations, I write this article from the perspective of the plant/maintenance engineer who is responsible for the on-line operation of the compressed air system. This article can also help suppliers of compressed air systems gain some understanding of how their customers prioritize plant operations.
Compressed Air System Elements – Demand Side
A strategic approach to sustainable improvements starts by having a clear understanding of the overall compressed air system. Let’s split the system into three basic elements which will be the demand-side, distribution system and supply-side. Let’s first review the demand side.
The demand side of a compressed air system essentially describes how and where compressed air is consumed. Examples of devices using compressed air include air hoses, hand tools and pneumatic controls. Compressed air is also used to power cylinder and actuators that make any number of end-use machines work. The demand side of compressed air also factors in machine (pneumatic) controls, and air motors. Together, these machines typically determine the minimum air pressure needed throughout the plant. Changes to supply pressure can be complex and time consuming because they can affect production and/or quality performance of your plant.
Here are two primary issues you might encounter:
- Validation trials – These are controlled periods of time where pressure is reduced and operating parameters are monitored in earnest to help determine validity. These trials can take a long time to perform and need the buy-in of many parties. Your own plant operations staff may be reluctant to support these efforts because they would rather not expose themselves to any more chance of production interruptions (unless they can see a price tag associated with this insurance).
- OEM warranty and/or performance concerns, etc. – Changes in supply pressure can be complex. Equipment providers are often reluctant to guarantee their system will work at lower pressures. They have provided conservative estimates previously, which have accounted for resiliency to system losses that are beyond their control.
Compressed Air System Elements – Distribution System
Let’s look next at the compressed air distribution system. Its job is to transport the compressed air from its point of production (air compressors) to points of use. It consists primarily of the piping system, which encompasses headers, system piping and valves. Common issues include:
- Pipe sizing, spurs installed in the past, poor planning, etc. – The older your facility is, the more likely it is that equipment has been changed, added and/or deleted. Many times a compressed air supply was simply tapped to an existing pipe without looking upstream. The piping between the compressed air supply and your load might be a much longer (pipe) distance than thought because of how it was originally routed for past installations. There might already be significant load on that particular run in other areas.
- Air leaks – This is a constant issue in almost every plant. When making a survey and actually measuring flow, the leaks can be a significant part of that demand and can be an opportunity to reduce demand on the system and increase efficiency.
Compressed Air System Elements – Supply Side
The supply side of a compressed air system describes the components that generate, condition, store and centrally control the flow/pressure of compressed air. Typical components include:
- Air compressors
- Wet header
- Air dryers
- Filters and separators
- Dry headers
- Receiver tanks
- Central controls
The overall efficiency of the system often depends on the plant’s compressed air load and load variations, especially when multiple air compressors are involved. Your system most likely demands different amounts of air at different times of day. For example:
- A machine or process might have a surge of demand when starting up in order to fill cylinders, tanks, etc.
- There might be air hoses used at the end of a shift for cleaning the area (not the best practice but often a reality).
- Different processes might operate at different times of day, each with a different demand.
If you’re wondering why it’s important to have a thorough understanding of the complete compressed air system at your plant, consider the following:
- Compressed air as an energy source is less than 30% efficient when compared with the electricity used to drive the air compressor.
- Energy is typically the most expensive component in operating an air compressor throughout its useful life.
- While gaining traction, efficient operation of compressed air systems still represents an enormous opportunity for cost savings and reliability gains.
- New air compressor and control technologies present a host of opportunities to improve system performance and reliability.
Start With a Compressed Air Evaluation
As with many initiatives, the key question is where to begin. When deciding to make improvements in a compressed air system it’s often best to start with a system evaluation. Here are suggestions to implement a thorough and beneficial compressed air system evaluation.
As a first step, make an overview diagram of the compressed air system. This sketch might take days to create depending on the size and complexity of your system but it is important and it will be worth the effort once it’s finished (Compressed Air Best Practices® Magazine and Compressed Air Challenge offer helpful examples).
Shown is a typical compressed air system sketch, which has been mocked up based upon publicly available information. Click here to enlarge.
The diagram should include:
- A list all equipment, such as air compressors, dryers, headers and piping. List the sizes of the air compressors, as well as the size of piping. Include important data, such as the quantity of all equipment and the condition of the equipment.
- Document demand load points. Where does the air go and how much goes where? It is good to know what percentages of total plant air are going to which processes, or departments.
- Details about airflow, including:
- The total amount of air being produced for your plant.
- Where it goes, as mentioned above. Perhaps draw a map of how much air is used and how much is distributed to each department, or plant area.
- Airflow by time of day and/or day of the week.
- Load factor, including variation from minimum flow to maximum flow. Your plant demand varies by time of day. Perhaps a different data set is necessary for each shift or other particular times of day.
- Plant system pressure. What determines the system pressure setpoint? As described above, it is important to understand why system pressure is at the current level.
Create “Current-” and “Future-State” Diagrams
The next important step is to make a “current state” diagram simplified to just the air compressors, piping and demand areas of the plant. This way you can see where air comes from and where it goes. The diagram can be split into areas of the plant where flow can be measured and also designated points with specific demand for compressed air, or process areas.
It is also important to evaluate system performance. Doing so involves the use of an ammeter or a kilowatt meter to measure the power to the air compressor and comparing it with the actual airflow being delivered to the plant. Common ways to document performance are horsepower (HP) per cubic feet per minute (cfm) or cfm per kilowatt (kW), such as HP/100 cfm, or CFM/HP, or CFM/kW. It can also be documented by liters per minute per kW.
Depicted is a mockup of a current-state diagram based on publicly available information. Click here to enlarge.
It is also very important to calculate cost in order to justify changes you want to make. Operating cost, just in energy, can be calculated by multiplying hours per week times the kW demand, times electricity cost per kilowatt hour (kWh). If you have trouble with these numbers, a vendor can often help and they are normally quite straightforward with calculations and data provided.
The next step is to prepare a “future state” diagram that shows optimum equipment in place, including air compressors, dryers, filters, piping and end-use devices.
Depicted is a mockup of a future-state diagram based on publicly available information. Click here to enlarge.
This diagram can be designed with the help of a vendor, or service provider, or a consultant hired to conduct the compressed air audit. If you decide to hire a consultant to do the job, any work you do in advance will be valuable in giving him/her preliminary information gathered in the first part of an audit. If you want to justify the expense up front, be prepared to make the business case for the audit without concrete recommendations to improve the system. Also, be prepared to follow through on the easiest measures for costs savings to help pay for the audit. Chances are you will find ways to save that will pay much more than the cost of the audit.
Regardless of whether you hire a consultant, the future-state diagram, allows you to calculate the new operating cost in energy using the same formula described above with lower HP input values to deliver the same air. You might also have eliminated some air demand for which you can calculate an energy reduction savings.
You can also use the information in the diagram to reference monetary values when seeking capital funds. Again, the exact procedure of how this is done varies from company to company. You might have an informal process or one that is regimented and multi-faceted. Keep in mind this is a quick overview of what you can do and a rough guideline of how to do it.
Evaluate Distributors of Compressed Air Systems
Another important aspect of a reliable and efficient compressed air system has to do with the company selling and servicing the system. When evaluating companies, place more emphasis on the service department rather than the sales department. Ask yourself key questions as part of your approach, such as:
- Are your current air compressors being serviced reliably?
- Do you have many unplanned breakdowns?
- Do you already have a maintenance contract with a compressed air system firm?
- Are you confident in your supplier regarding reliability, timeliness and cost?
Get into a partnership with the company you have doing your service. If they do not perform, find another! Look at their reliability first, then examine parts availability, pricing, etc. Use the service reputation as the determining factor when purchasing, not price. You will spend many times the initial price on energy and maintenance during the life of your new air compressor.
As my grandfather used to say, “The sales department sells you your first car, the service department will sell you the rest!”
The Time to Start is Now
As a plant engineer or maintenance engineer, you are responsible for keeping compressed air in the lines for use in the plant. You are also probably responsible to some extent for the amount of energy used.
Addressing your compressed air system can be a good opportunity to reduce the electric bill at your facility, depending on the value of your system improvements. If you are successful in getting a project completed, look at your electric bills and communicate any measurable differences internally to enhance the success of your project and to increase the likelihood of similar investments in the future. Be prepared to communicate your findings clearly and to address common questions. For example, reductions resulting from the effort may erroneously be attributed to previous quality issues or disruptions. The time to get started is now.
About the Author
Kurt A. Kniss, P.E., C.E.M., was an Innovation Engineer with the Equipment and Process Innovation Group at Shaw Industries, Inc.
About Shaw Industries
Shaw Industries Group, Inc. is more than a flooring company – we are 22,000 people united in our vision of creating a better future for our customers, for our people, for our community and for our company. We provide carpet, resilient, hardwood, tile and stone, laminate, synthetic turf and other specialty items for residential and commercial markets worldwide. We meet diverse customer needs through an expansive portfolio of brands, including: Anderson Tuftex, Patcraft, Philadelphia Commercial, Shaw Contract, Shaw Floors, Shaw Hospitality, Shaw Sports Turf, Southwest Greens , USFloors/COREtec and more. Headquartered in Dalton, Georgia, Shaw is a wholly owned subsidiary of Berkshire Hathaway with more than \$6 billion in annual revenue and representation throughout the United States, as well as in Australia, Belgium, Brazil, Canada, Chile, China, France, India, Mexico, Singapore, United Arab Emirates, and the United Kingdom. For more information, visit www.shawinc.com.
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