Tag: smelting

Aluminum Smelting: Cooling the Hot Spots!

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Aluminum smelting is an important process to change alumina ore into aluminum, a lightweight metal.  This process uses high heat for a period of time to separate the oxygen from the alumina.  The temperature can reach over 1000oF (538oC) to cause this separation.  As a reference, two pounds (0.9 Kg) of alumina ore is needed to make one pound (0.45 Kg) of aluminum.  Inside the ovens and exhaust ducts, they are lined with a cement brick to contain the heat and fumes.  Over time, the brick can get weak and have hot spots.  Once the brick is compromised, the system has to be shut down for days to replace the brick.  This is an expensive process and time-consuming.  To help reduce the hot spots and extend the life of the brick, the smelting company was using ¼” copper tubes to blow compressed air to reduce the heat.  This was costing the company a lot of money to operate; so, they contacted EXAIR for a better solution.     

They may be inefficient, but they sure are loud…

EXAIR has been manufacturing intelligent compressed air products since 1983.  And one thing that we know how to do is to save money on compressed air blow-off applications.  For this company above, they had 90 open pipes throughout their plant.  I was able to do a quick calculation for this customer to compare the copper tube to a Super Air Nozzle.  A ¼” copper tube will use roughly 33 SCFM (935 SLPM) of compressed air at 80 PSIG (5.5 bar).  As a replacement nozzle in a hot area, EXAIR recommended a model 1100SS Super Air Nozzle which will use 14 SCFM (396 SLPM) at 80 PSIG (5.5 bar).  With a simple connection, they could mount the ¼” NPT Super Air Nozzle at the end of each tube.  With the cost to make compressed air at $0.25/1,000 ft3, we can calculate the air savings.    

33 SCFM (copper tube) – 14 SCFM (Model 1100) = 19 SCFM savings

The operation for the smelting plant was 24 hours and 7 days a week.  The amount of savings is as follows:

19 ft3/min * 60 min/hr * 24 hr/day * 7 days/week * $0.25/1,000 ft3 = $47.88 savings per week per nozzle.

Since they have 90 nozzles, this would save them $4,309.20 each week! 

How can we do this?  With cooling capacities, it is dependent on the mass of air that can be moved.  With our Super Air Nozzles, we are near an amplification ratio of 25:1.  This means that for every one part of compressed air, we can entrain 25 parts of ambient air.  Also, with our Super Air Nozzles, we can generate a laminar air flow which has a velocity profile that has the air moving in the same direction.  An open pipe has turbulent flow, which means that the velocity is traveling in different directions and not working together.  And the amplification ratio is very low.  I did a demonstration to illustrate this effect here: Video Blog: Laminar and Turbulent Flows.  The large volume of air creates good cooling without using too much compressed air to reduce the hot spot temperatures.  In keeping the temperature under control, they could continue operations and lessen the concern for untimely shut-downs and costly maintenance.

By using air to cool, you can do it safely and efficiently.  As a benefit, the Super Air Nozzles reduced the noise level as well.  Saving a lot of money; having an effective way to reduce stress on the cement bricks; and reducing the noise nuisance were great replacements for this company.  If you would like to speak about cooling applications, you can contact an Application Engineer; even something as large as a smelting oven.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Vortex Tubes Cool a UV Scanner

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Copper smelting furnace

Safety is important when it comes to gas furnaces; and with large ovens, equipment is used to protect workers and equipment.  A copper company was using natural gas for smelting, and they had a UV scanner to monitor the flames.  If the burners go out, the scanner will turn off the gas valves to stop a potential explosion.   As with many instruments, it is important to keep the electronics cool for proper measurements.  In this case, they were having issues with accuracy from the high heat.  They contacted EXAIR for a solution. 

Air path flow for UV scanner

With their UV scanner, it was designed for a “cooling” device already.  This was basically compressed air that would blow around the instrument.  Because of the location, the compressed air was heating up to 125oF (52oC).  This heat would not cool the scanner properly, and it was causing unreliable readings and premature shutdowns.  They gave me the design specifications, and the scanner required 3.2 SCFM (90 SLPM) of air at atmospheric pressure with a maximum of 77oF (25oC).  I mentioned that we had the perfect solution to keep the UV scanner cool and operational; the EXAIR Vortex Tube.   This product can take elevated temperatures of compressed air and reduce it to lower temperatures.   It is a low cost, reliable, maintenance-free solution that uses compressed air to produce cold air as low as -50oF (-46oC).  With a range of cooling capacities from 135 BTU/hr to 10,200 BTU/hr, I was sure that we could meet the requirements for proper cooling. 

To determine the correct size, I had to look at the temperature drop and the flow requirement.  The temperature had to decrease from the 125oF (52oC) incoming compressed air to at least 77oF (25oC).  This would equate to a 48oF (27oC) temperature drop.  The other requirement was the amount of air flow, 3.2 SCFM (90 SLPM).  With the chart below, I see that we are able to get a 52oF (29oC) temperature drop at a 70% Cold Fraction and 40 PSIG (2.8 bar) inlet pressure.  EXAIR Vortex Tubes are very adjustable to get different outlet temperatures by changing the inlet pressure and the Cold Fraction.  The Cold Fraction (CF) is the amount of air that will be coming out the cold end.  With a 70% CF, that means that the adjusting screw on the hot end of the Vortex Tube is turned to allow 70% of the incoming compressed air to go out the cold end.  So, with that information, we can size to the correct model. 

In comparing the above information to the catalog data at 100 PSIG (6.9 bar), we have to consider the difference in absolute pressures.  With an atmospheric pressure of 14.5 PSIG (1 bar), the equation looks like this:

Qv = (Qc / CF) * (Pc + 14.5 PSIA) / (Ps + 14.5 PSIA)

Qv – Catalog Vortex Tube flow (SCFM)

Qc – Cold Air Flow (SCFM)

CF – Cold Fraction

Pc – Catalog Pressure – 100 PSIG

Ps – Supply Pressure – PSIG (Chart above)

From this equation, we can solve for the required Vortex Tube: 

                Qv = (3.2 SCFM / 0.7) * (100 + 14.5 PSIA) / (40 + 14.5 PSIA) = 9.6 SCFM. 

In looking at the catalog data, I recommended our model HT3210 Vortex Tube which uses 10 SCFM of compressed air at 100 PSIG.  The HT prefix is for our High Temperature models for use in temperatures in the range of 125oF to 200oF (52oC to 93oC).  So, after installing, the Vortex Tube was able to supply 73oF (23oC) air at a flow of 3.3 SCFM (94 SLPM); keeping the UV scanner reading correctly and accurately. 

Sometimes compressed air by itself is not enough to “cool” your instruments.  The EXAIR Vortex Tubes can reduce the temperature of your compressed air to very cold temperatures.  If you believe that your measuring equipment is being affected by elevated temperatures like the company above, you can contact an Application Engineer at EXAIR to find the correct solution for you. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Air Operated Conveyor helps Aluminum Smelting Process

Published on by John BallLeave a comment

An aluminum smelting plant had been using our model 150300 Heavy Duty Line Vac for over a year.  They wanted to share how extremely satisfied that they were with this product.  They were expanding their operations, and it was easy for them to contact EXAIR to buy two more units.  In this blog, I will share why they initially contacted EXAIR and why they continue to do so.

This company had a reactor that would melt 10 mm aluminum granules for die casting parts.   They had a portable hopper that was filled with aluminum pellets (reference photo above).  Before they started using the Heavy Duty Line Vac, the operators would have to use shovels to move the aluminum from the catch bin located below the hopper to the crucible inside the reactor.  This operation was tedious, back-breaking, and time-consuming.  After filling the crucible, they would have to do some housekeeping for the granules that fell during transport.  With safety concerns and slow operations, they needed a better way to move the aluminum granules to the reactor.  Hence, the reason for the first purchase of the model 150300 Heavy Duty Line Vac from EXAIR.

To expand a bit more on their operation, the hopper was placed roughly 10 feet (3 meters) away from the reactor, and the reactor used a hatch door that was 2 feet (0.6 meter) in diameter to expose the crucible.  Since the crucible was inside the reactor, they wanted to govern the velocity to feed the aluminum pellets at a controlled rate.  From flow and speed calculations, I found that the model 150300 would work the best for this particular application.  As an added feature to the EXAIR Air-Operated Conveyors, the Heavy Duty Line Vac is easy to control with a simple compressed air regulator to balance the speed and vacuum to move the material in a manageable way.  With the compact design, it worked well to attach a conveyance hose that would move the aluminum pellet directly through the hatch door and right into the crucible.  This was a benefit for quick filling without much manual labor or cleanup.

The reasons that EXAIR continues to grow as a business are the quality of our products, the enormous stock that we carry, and the exceptional customer service.  For these reasons, customers continue to return to EXAIR for solutions to pneumatic applications.  The quality of our products is second to none.  For the Heavy Duty Line Vacs, they are made from a hardened alloy material which makes them resistant to abrasion and wear.  They also do not have any moving parts or motors; so they are reliable and long-lasting.  The smelting company above have used the Heavy Duty Line Vac for over a year, and it is still working.  Can you imagine the number of shovel scoops that was eliminated with the purchase of this air-operated conveyor?  And, the work environment was safer ergonomically by removing the shovel loads and reducing cleanup.  As for customer service, EXAIR is staffed with Application Engineers that are Subject Matter Experts.  We can make recommendations to give you the best EXAIR product for your application.  With our technical support, fast deliveries, and problem-solving products; it was an easy decision for the above company to purchase two more model 150300 Heavy Duty Line Vacs.

If your company relies on moving product from point A to point B, EXAIR has a range of Air Operated Conveyors to do this type of operation for you.  From Threaded Line Vacs to Sanitary Flange Line Vacs to Heavy Duty Line Vacs, EXAIR stocks a variety of materials, types, and sizes to fit into your application.  An Application Engineer is sitting by to help improve your system as we did with the smelting company above.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb