AIR LIFTING MECHANISMS FOR OXIDATION IN UNDERGROUND MINES
- Slides: 30
AIR LIFTING MECHANISMS FOR OXIDATION IN UNDERGROUND MINES Bruce Leavitt PE PG, Consulting Hydrogeologist Washington, Pennsylvania Prepared in conjunction with West Virginia University under a grant from the Office of Surface Mining Applied Science Research Program
In Situ Aeration l. Net alkaline mine drainage. l. Oxidize ferrous iron in mine drainage. l. Fe 2+ + 2. 5 H 2 O + 0. 25 O 2 = Fe(OH)3 + 2 H+ l. Reaction rate proportional to p. H. l. Lower reagent cost than hydrogen peroxide. l. Design parameters unknown. l. Potential for carbon dioxide removal.
Air Lift Operation
Air Lift Test Design l Flow Testing l 4 pipe diameters (12”, 10”, 8”, and 6”) l 2 diffusers l Multiple air flow rates l Oxygen Transfer Testing l High volume low DO source l Same pipe diameters and diffusers
Equipment Configuration
Diffusers Sintered glass diffuser medium bubble 2 inch dia. #10 well screen large bubble
Test Pipe with Auto Burper 6 inch 12 inch
Anemometer and Magnehelic
1. 5 hp Regenerative Blower
300 gallon bucket
Test Procedure l l l l Adjust dock height to less than ¼ inch from overflow Measure depth to diffuser. Warm up blower. Measure and adjust air flow. (before and after test) Read Magnehelic. Open 4 inch ball valve in dam. Close bypass valve & time tank filling. Pump produced water back into lake.
Water Production Drain Closed Drain Open
Water Production 8 inch pipe
Sulfur Run Borehole Closing the Ball Valve Date p. H DO ORP 9 -30 -2009 3. 35 0. 05 322 10 -3 -2009 3. 40 0. 09 313 10 -5 -2009 3. 41 0. 07 NA
Air Lift with Sampling Pipe
Oxygen Concentration Squares are set about 4 feet Diamonds are set about 3 feet
Oxygen Mass Transfer 12 inch
Oxygen Mass Transfer 10 inch
Oxygen Mass Transfer 8 inch
Oxygen Mass Transfer 6 inch
Oxygen Mass Transfer Comparison at 14 cfm Pipe Diameter Aeration stone Well Screen Improvement inch grams / minute percent 12 4. 14 3. 55 16. 6 10 5. 03 3. 38 48. 8 8 4. 87 3. 05 59. 6 6 3. 41 2. 01 69. 6
Air Lift Operation All air flows used in this testing can be achieved with a ¾ hp high-pressure regenerative blower. (smaller units are possible) l At $0. 10 / k. W hr the daily cost of operation would be $1. 34 or $490. 00 per year. l A ¾ hp high-pressure regenerative blower can be purchased for $700. 00 l
Conclusions The use of low pressure air to create flow in a zero static head setting has been demonstrated. l The volume of water moved with such a small volume of air surpassed expectations. l Five cubic feet of air per minute is able to generate 200 gallons per minute of water flow. l Oxygen transfer to the produced water only achieved 25 percent to 30 percent saturation under the best conditions. l
Conclusions continued In most tests, there is not a significant difference between the DO produced by the well screen and the stone diffuser at the same depth. l There is a tendency for the shallower depth setting to produce a higher DO than the deeper setting. l Based on the calculated oxygen delivery to the mine, between 23. 8 and 35. 1 grams of iron per minute can be oxidized. This rate of iron oxidation is equal to 75. 6 to 111. 4 pounds iron per day. l
Conclusions continued Based on these tests the 8 inch riser with stone diffusers is the most economical configuration. l Construction of a large diameter borehole may be expensive, but the cost of equipment and it’s operation is low. l Borehole maintenance will be required. l
Questions?
Task Force Reception 5: 30
Task Force Reception 5: 30
Task Force Reception 5: 30
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