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| Van Air Systems |
2950 Mechanic Street
Lake City, PA 16423 USA |
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Phone: 800-840-9906
Corporate Fax: 814-774-0778
Order Entry Fax: 814-774-3482 |
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Case Study - Single Tower Freedom Dryer for Mobile Blasting
At the Chesapeake Bay Bridge and Tunnel, under strict environmental regulations, Van Air air-cooled after-coolers, single tower deliquescent Freedom Dryers, and particulate and coalescing filters played a major role in the efficient operation of steel grit blasting equipment, cost-effective recycling of steel grit, and successful separation of lead-based hazardous waste contained within the blast medium after cleaning.
The Hartman Walsh Corporation of St. Louis, Missouri was the contractor chosen to meet the mighty challenge of cleaning and painting the Bay Bridge. The lead-based paint to be removed is classified as a hazardous waste. As such, proper disposal of the paint, rust and scale removed from the bridge is environmentally mandated. Furthermore, no residue from the blast cleaning process was permitted to escape into the atmosphere or fall into the water below. This required a containment structure for the blast media.
Additionally, the combination bridge and tunnel structure passes through the heart of the Chesapeake National Game Preserve, making environmentally sound practices of even greater importance. "These factors were foremost in our thinking as we planned this project," said a Hartman Walsh spokesman.
To remove and recover hazardous lead waste, a Van Air portable air drying system consisting of an air-cooled after-cooler, a Freedom Dryer model D48, and particulate and coalescing filters was designed. Also included in each equipment package were dust collectors and four-steel grit blasting machines with storage and transfer capability for grit recovery, separation of waste and recycling of the grit.
All of the equipment was air operated. The only other electrical source was the 12 volt DC from the batteries on a 1300 scfm compressor used to supply the compressed air.
Steel grit was the preferred blast medium, since this abrasive can be separated and recycled. According to the abrasive manufacturer, steel abrasives can be recycled hundreds of times. If an abrasive, such as sand or slag, which is not economically recycled, were used, many tons of abrasive would be classified as hazardous waste due to lead paint contamination. Recycling steel grit substantially reduced project costs for abrasive and disposal.
After design, three systems were built for Hartman Walsh to use on the 1-mile-long steel bridge section of the project. The components of each system were skid-mounted for portability. Lifting eyes and fork lift pockets allowed loading of equipment onto barges for the Bay Bridge project. The configuration of the equipment permits loading onto standard over-the-road trailers for legal size and weight hauling to the next job site. Equipment can be operating directly from the trailers.
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| Problem |
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One major consideration when blasting and using steel grit is moisture in the compressed air. Moisture can cause rapid oxidation in a freshly blasted surface. Moreover, when steel abrasive gets wet (or even damp) it begins to rust. The abrasive then clings together in large masses, rendering it, as well as the blast machinery, useless. Inadequate drying is the most frequently encountered problem when using steel grit. |
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| Solution |
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Each blasting system was designed to include Van Air drying and filtering products. Each system included a Van Air air-cooled after-cooler, a Freedom Dryer model D48, a F101 series particulate filter, and a F101 series coalescing filter. The Freedom Dryer was chosen to meet the requirements for reliably dry air, portability, and energy-free operation. In their final form, the components were skid-mounted to include wet air inlet and dry air outlet manifolds and all interconnecting valves and piping. The skid included a steel frame to protect the components from damage during shipment and operation.
Each system works like this: Air exits the compressor at 150°F at 150 PSIG and enters the Van Air air-cooled after-cooler. Design specifications called for after-cooler discharge with a 5°F approach temperature, which is to be cooled to within 5°F of the ambient air temperature. Actual on-site performance exceeds these standards. The water condensed by this superior level of after-cooler processing is collected and discharged.
Air then flows to the D48 Freedom Dryer, where the pressure dew point is lowered by 20°F. Thus, no moisture can condense since the dew point temperature of the compressed air is always lower than that of the ambient air. Dryer operation automatically compensates for variable operating temperatures, flow rates and pressures.
Freedom dryers operate energy free and have no potentially troublesome moving parts. Moisture is absorbed by Dry-O-Lite, a special drying agent known as a deliquescent desiccant. Dry-O-Lite tablets slowly dissolve. The condensate drops into a claim area for draining. This condensation is environmentally safe. In over five months of operation, the D48 only consumed one-half of its charge of Dry-O-Lite.
F101 particulate pre-filters and coalescing after-filters remove harmful contaminants for a clean, trouble-free supply of compressed air.
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| Results |
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With clean and dry process air, the steel grit blasting machines operated reliably 12 hours a day, six days a week, for more than five months. No moisture-related problems, such as grit oxidation or surface rusting, were reported. Hartman Walsh officials reported complete satisfaction with their Van Air compressed air treatment equipment, and for subsequent jobs, Van Air compressed air dryers, coolers, and filters were specified.
Van Air officials also report the successful use of its Freedom Dryers and Blast Paks in numerous mobile abrasive blasting projects across the United States, Canada, and Australia. Reduced downtime, increased productivity, improved tool performance and longer service life are cited as key benefits.
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| Have a question? Call toll free or contact us: 1-800-840-9906| Email Us |
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