Industrial Utility Efficiency    

6 Steps Metal Fabricators Take to Reduce Compressed Air Demand

Compressed air use in the metal fabrication industry is widespread. It is used to cool, clean, convey and coat a multitude of products and improve processes across the world. In fact, it is difficult to name processes in metal fabrication where compressed air cannot be found. A few processes where compressed air is used include: annealing and pickling, slitting, rolling, welding, stamping, punching, tube making, painting, finishing, turning, drilling, milling and sawing. Many of these processes and applications continue to use inefficient devices to deliver the compressed air, and — worse yet — many companies fail to recognize the simple implementation and significant payoff of improving compressed air efficiency.

Improving compressed air efficiency, or saving more of your compressed air capacity by minimizing compressed air demand, can be realized by following some simple procedures. Though there are many actions that can be taken to further improve compressed air efficiency, some simple and effective steps can be put to action quickly. While all of these suggestions are relevant to anyone with a compressed air system, steps three and four provide examples specific to metal fabrication. Here are six steps to reducing demand in your compressed air system.

 

Step 1: Measure the air consumption to identify sources that waste compressed air.

The first step is to have an appropriate flow meter, which can give an indication of how much air volume is being used. Flow meters can be installed on the main supply line of your system, and they will provide a good indication of overall use trends, while also being able to identify how much air is lost to leaks when the system is not being used for production. They can be installed on a smaller leg of the system that feeds a particular process or set of machines to indicate the demand from that section. Flow meters can also be installed at the machine level to track changes in flow due to maintenance, downtime or machine problems.

Another preferred feature of many flow meters is the ability to log the data. If calibrated correctly, data-logging flow meters can record data at many different intervals in order to provide a bigger picture of compressed air demand profiles. With the aid of a data-logging flow meter, any user can establish a baseline of air demand. Having this original compressed air demand baseline will be necessary in order to quantify and document any improvements in compressed air consumption and operating costs.

 

Step 2: Find and fix the leaks in your compressed air system.

Plants that are not maintained can waste up to 30 percent of the compressor output through leaks that go undetected. Compressing air is an expensive operation. Saving the compressed air wasted due to leaks reduces the overall operating costs and increases the effective capacity of your stored air. In large plants, the cost of a small air leak may be insignificant, but many small leaks — when located and repaired — can amount to huge energy savings. Reducing air lost to leaks can cause a rise in available pressure, which can provide additional energy to the point of use. With leaks fixed, the compressor will not have to operate as often to keep up with demand. Fixing leaks can minimize the required maintenance on the compressor as well.

 

Ultrasonic leak detector graph

Ultrasonic leak detectors (ULD) are a good choice for identifying leaks, because they are able to turn an inaudible ultrasonic sound signal into an audible tone that allows the operator to discover a leak.  

 

Step 3: Upgrade your blow off, cooling and drying operations using engineered compressed air products.

Engineered compressed air products are made to replace ordinary nozzles, homemade devices and open line blow offs. An ordinary nozzle with a thru hole and a cross-drilled hole can be an easy choice based upon price, but if you do not consider the operating cost, you do not really know how much it is costing you. An engineered compressed air product will pay for itself and lower operating costs — many times, within weeks. Engineered nozzles provide a range of efficiency and safety benefits; most notably a reduction in compressed air use, meeting the OSHA standard for dead-end pressure, and reducing noise exposure for personnel. They can also qualify for an energy savings rebate from a local utility. 

 

sak-sal-sancollage1

Engineered compressed air products like these help save compressed air and money while improving safety.

 

One common example is to use copper tube as a “nozzle” for blow-off applications. Found throughout metal fabrication facilities to eject parts, clean parts and cool parts, these nozzles should be primary targets for compressed air savings. A typical 1/4-inch OD copper tube will use as much as 33 scfm at 80 psig. The simplicity of installing a compression fitting on one end of the copper tube in order to accept an engineered nozzle makes this savings opportunity one of the simplest and fastest ways to begin reducing your compressed air demand.

Let’s take a closer look at the savings you can achieve for a very typical scenario in the metal fabrication industry. Recently, a customer sent in their copper tubes for a test to compare with some engineered air nozzles. The pressure at the customer site was 80 psig inlet pressure for twenty 1/4-inch open copper tubes (22 scfm each), during an operation running 8 hours a day and 250 days per year. Depending on where you are located in the United States, your electrical costs will vary: The following example uses an estimate of $0.25/1000 cubic feet of compressed air.

 

pipeVSnozzlewithVS

Engineered air nozzles are more efficient than open blow offs.

 

Open Copper Tube Cost of Operation:

20 pieces x 22 scfm = 440 scfm

440 scfm x 480 minutes per day = 211,200 cubic feet of compressed air required per day

211,200 x 250 days = 52,800,000 cubic feet required annually

52,800,000 / 1000 = 52,800 cubic feet

52,800 x $0.25 = $13,200.00 annual cost to operate twenty 1/4-inch open copper tubes

 

Engineered Air Nozzle Cost of Operation:

20 pieces x 10 scfm = 200 scfm

200 scfm x 480 minutes per day = 96,000 cubic feet per day (220,800 cubic feet saved per day)

96,000 x 250 days = 24,000,000 cubic feet annually (55,200,000 cubic feet saved annually)

24,000,000 / 1000 = 24,000 cubic feet

24,000 x $0.25 = $6,000.00 annual cost to operate twenty engineered air nozzles

$13,200.00 - $6,000.00 = $7,200.00 simple ROI in the first year, and payback time of 21 days!

 

Another repeat offender and candidate for an engineered upgrade in the metal fabrication industry is a standard section of pipe with holes drilled along its length. This is commonly done when needing to cover a wider area than an open tube or nozzle. We see this kind of solution when fabricators need to help separate metal sheets, blow liquid from parts coming out of a wash cycle, or remove machining chips as the part exits from a machining center. This next example is for two drilled pipes running at 60 psig inlet pressure, each with (25) 1/16-inch diameter holes on 1/2-inch centers, operating 8 hours per day and 250 days per year. We will again use the $0.25/1000 cubic feet of compressed air value for our calculations.

 

Drilled Pipe Cost of Operation:

2 pipes x 174 scfm = 348 scfm

348 scfm x 480 minutes per day = 167,040 cubic feet of compressed air required per day

167,040 x 250 days = 41,760,000 cubic feet required annually

41,760,000 / 1000 = 41,760

41,760 x $0.25 = $10,440.00 annual cost to operate two drilled pipes

 

Engineered Air Knife Cost of Operation:

Two 12-inch engineered air knives x 27.6 scfm = 55 scfm

55 scfm x 480 minutes per day = 26,400 cubic feet per day (140,640 cubic feet saved per day)

26,400 x 250 days = 6,600,000 cubic feet annually (35,160,000 cubic feet saved annually)

6,600,000 / 1000 = 6600

6600 x $0.25 = $1,650 annual cost to operate two 12” engineered air knives

$10,440.00 - $1,650.00 = $8,790.00 simple ROI in the first year and payback of 17 days!

Generally speaking, if it is a homemade solution being used, there is an opportunity for significant air savings.

 

Step 4: Turn off the compressed air when it is not in use.

A simple, manual ball valve and a responsible operator can provide air savings at every opportunity to close the valve and shut down the compressed air flow when it is not needed to a process or operation. But an automated solution is better for precise control, consistency and accuracy, which result in more compressed being air conserved. Automated solutions add solenoid valves that run independently with a sensor control, or can be run through machine controls. If the machine is off — or the process has stopped — close the solenoid valve and save your compressed air. Blow-off applications with space between parts can benefit by turning off the air during the part gaps.

Within the metal fabrication industry, we help customers who constantly blow air to remove stamped plugs when they could be letting more slugs build up before turning the air on. There are blow-off applications that are turned on with a machine or process but could be further optimized to eliminate blow off prior to a part reaching it. Also common are setups where air continues to blow during lunch or break time. For example, if a company kept its blow-off application running during its two daily 15-minute breaks and a 30-minute lunch, the company could save 15,000 minutes (250 hours) of blow-off cost every year! What’s the lesson? Turn off your air when not needed.

Here is an example of a company who eliminated 5 minutes of blow off from its process using an automated solution consisting of a sensor, solenoid and timer to control the air:

$3,393 Annual Air Savings on a Tank Blow-Off Operation

A company that refurbishes large tanks runs the tanks through an oven on a conveyor line to burn off old paint. Only one tank at a time can be processed, and each takes 6 minutes to complete the journey. Four 30-inch air knives are used for blow off at the exit of the oven. These knives were using compressed air every time the oven was turned on.

However, the tank travels through the oven for 5 minutes before it reaches the knives for a 1-minute blow-off cycle. The opportunity for savings was to turn the air on only when the tank reached the air knives for a one-minute blow off. At 80 psig, the four knives consume 348 scfm.  

The timer was set to “on/off delay.” The sensor was mounted at the oven exit and opened a solenoid valve to provide 1 minute of blow off instead of blowing all 6 minutes of the cycle. This application ran 30 tanks per day on average.

 

Old Method

Four 30-inch air knives at 87 scfm each = 348 scfm

348 scfm x 6 minutes = 2088 scfm per tank

2088 x 30 tanks per day = 62,640 cubic feet per day

62,640 x 250 days = 15,660,000 cubic feet annually

15,600,000 / 1000 = 15,660

15,600 x $0.25 = $3,915 annual compressed air cost

 

New Method: Sensor/Solenoid/Timer Solution
The sensor and solenoid control was installed to shut off the compressed air for the 5 minutes where no tank was present (one minute of air on).

Four 30” air knives at 87 scfm each = 348 scfm

348 scfm x 1 minute = 348 scfm per tank (1740 scfm saved per tank)

348 x 30 tanks per day = 10,440 cubic feet per day (52,200 cubic feet saved per day)

10,440 x 250 days = 2,610,000 cubic feet annually (13,050,000 cubic feet saved annually)

2,610,000 / 1000 = 2610

2610 x $0.25 = $652.50 annual cost with optimized setup ($3,262.50 annual savings)

$3,915 - $652.50 = $3,262.50 simple ROI in the first year and payback of 146 days!

 

Step 5: Use intermediate storage of compressed air near the point of use.

Also known as secondary receivers, intermediate air storage is especially effective when a system has shifting demands or large volume use in a specific area, generally in short bursts. The buffer created by intermediate storage (secondary receiver) prevents pressure fluctuations, which may impact other end-use operations and affect system reliability and product quality.

An application that is a good fit for a secondary receiver tank is one with a high intermittent demand of compressed air, short duration of this demand, and enough time in between demand events to replenish the receiver pressure without needing additional capacity from the compressor.

A properly outfitted intermediate storage tank includes a pressure relief valve to keep pressure to a value that does not exceed the tank limitation. A drain valve, typically mounted on the bottom of the receiver tank, releases condensate. A pressure gauge will allow you to view the tank pressure and ensure it is holding pressure. Pressure regulators will provide the proper pressure out of the tank and into the application.

Properly sized and located intermediate storage strategies can greatly improve compressed air system efficiencies by absorbing spikes from large compressed air events, allowing for slow and steady production of compressed air. Receiver tanks are easy to use and install, and require little maintenance.

Step 6: Control the operating air pressure at the point of use to minimize air consumption.

This is a very simple and easy process. All it requires is a pressure regulator. Installing a pressure regulator at all of your point-of-use applications will allow you to lower the pressure of these applications to the lowest pressure possible for success. Lowering the operating pressure of the application also lowers the air consumption. And it naturally follows that lower air consumption equals energy savings.

There are a wide variety of opportunities to reduce compressed air demand in the metal fabrication industry. All of the steps you can take, as described above, can be easily accomplished. Thousands of dollars can be saved by choosing to make a small investment in engineered products, which results in a return on investment of days or weeks. Additional benefits include meeting OSHA safety standards for dead-end pressure and noise exposure, which homemade and many commercial solutions do not meet. Finding the right vendor, with skilled expertise and a large selection of product to fit your needs, will help you to determine the best way to reduce your compressed air demand.

 

For more information, contact an Application Engineer at Techelp@exair.com, or visit www.exair.com

To read more about the Metal Industry, please visit www.airbestpractices.com/industries/metals.