Improved purity of product: This device helps remove undesirable constituents from the product—especially impurities that are mechanically carried-over, entrapped, or non-selectively-attached to the froth bubbles. In testing, the products that had been processed using the University's device had 60% less ash content and 33% less sulfur content than AFRA standards predicted.


Increased throughput: Throughput of a froth flotation device is increased by enhancing the probability of removing contaminants from the froth (i.e., reducing mechanical carryover of impurities and minimizing impurities that are trapped in the froth). Tests with this device demonstrated combustible recoveries of 80% to 95%.


Greatly decreased number of repeat runs: In a single processing run, attached to a subaeration cell with a normal throughput rate, this device has produced a finished product (from coal refuse) that was significantly cleaner than that produced by a standard flotation column. Tests with this device demonstrated combustible recoveries that were twice as high as levels predicted by AFRA standards.


Greatly reduced operating costs: Since the number of times an output stream must be processed and the time required to process a given tonnage are dramatically reduced, so are the equipment required and resulting costs.


Ease of implementation: The device can be used as a simple and inexpensive add-on to an existing flotation device; it can also be easily integrated in the design of new flotation devices. Its use does not require modifying any plant processes.

Separating one type of coarse or fine particles from another type is a necessary step in processing many kinds of minerals. Most fine mineral particles are hydrophobic or hydrophilic to some extent (or those properties can be induced), and froth flotation techniques are used to separate hydrophobic particles from hydrophilic particles in various applications, including coal processing.

Existing methods of froth flotation use subaeration cells and/or froth flotation columns. Subaeration cells employ an impeller to introduce air bubbles to form a froth and to create turbulence for the purpose of inducing collisions between particles and air bubbles. This turbulent system has the ability to process large quantities of material. However, it does not provide effective cleaning of the product because the turbulence allows undesirable particles to become trapped in the froth and carried out of the cell with the product stream.

Froth flotation columns, which create fine bubbles without heavy agitation of the feed slurry, can produce a very clean product but work more slowly and lack the capacity of subaeration cells. To achieve sufficient cleaning with subaeration cells, gangs of cells must be employed to clean the product in successive steps; to achieve sufficient capacity with flotation columns, extra columns must be employed in the plant.

The level of cleaning by subaeration cells and froth flotation columns, both, can be improved somewhat by increasing the height (i.e., thickness) of the froth column, but excessive thickness compacts and destroys the bubbles at the bottom of the column. The level of cleaning by either system can also be (and has been) improved by rinsing the froth at the top of the cell or column to wash out the impurities before the froth leaves the flotation device. However, because the rinsing takes place inside the flotation device, the impurities washed out of the upper levels of the froth migrate downward and become concentrated in the lower levels. The end result is a reduced effectiveness of the froth washing.

With the University’s froth washer attachment installed on a subaeration cell or flotation column, the froth is separated from the turbulence of the flotation device while it is being washed. The effective height of the froth column is increased without excessively compacting the bubbles at the bottom of the froth. By restricting the thickness of the froth column that is washed and separating the return flow of impurities washed out of the froth from the product-bearing froth, recontamination of the froth is nearly eliminated. Using this device, a subaeration cell provides cleaning properties equivalent to those of a flotation column without impairing the subaeration cell’s inherently greater throughput.

This new froth washer attachment can be applied to new or existing froth flotation devices. A mineral processing facility employing benches of subaeration cells to repeatedly process the product stream will be able to provide the same level of cleaning and capacity with many fewer cells. Similarly, it will be possible to drastically increase the capacity of the cleaning plant at relatively minor initial cost by installing the device on its existing cells.

Testing

Testing has shown that under optimum conditions, a flotation device equipped with this attachment surpassed the best performance of any flotation device, as predicted by the advanced flotation release analysis (AFRA) standards (see Figures 1 and 2). Test results demonstrated significant improvements in combustible recovery as well as in sulfur and ash rejection.

Similar levels of ash and sulfur rejection were demonstrated while processing a sample of coal cleaning plant refuse (see Figures 3, and 4). In these tests, a product containing as little as 3.7% ash was generated from a refuse sample containing 29.8% ash at combustible recoveries ranging from 82% to 94%. The AFRA-predicted combustible recoveries for the same ash content of the product were about half of the recovery achieved with the froth washer attachment. The sulfur rejection in these tests was also greater than that predicted by the AFRA (Figs. 3 and 4). The pyritic sulfur content of the product was significantly less than that predicted by the AFRA for comparable combustible recoveries for the material (Fig. 4).

Figure 1: Comparison of combustible recovery versus ash content in the cleaned products produced from a slurry (5% solids) of coal refuse and fine coal mixture (24% ash) with the 1.3 ft 3 subaeration cell equipped with a froth washer attachment in the laboratory and in a plant on coal refuse (3% solids with 26% feed ash). The AFRA for the slurry is shown as a standard.

At a 90% recovery rate of combustibles, the AFRA curve predicted that the product would have an ash content of about 11.5%. The ash content of the products produced using the froth washer attachment in the plant tests was about 4.5% (under optimum conditions). For the same ash content, the recovery of combustible material predicted by the AFRA curve was about 42%, while the system with the froth washer attachment produced about 90% recovery. So, compared to the AFRA standard, the University’s device offers improved combustible recovery at a given ash content and significantly reduced ash content at a given level of combustible recovery.

Figure 2: Comparison of combustible recovery vs. total sulfur in the cleaned products produced from a slurry (5% solids) of coal refuse and fine coal (3.44% sulfur) with the 1.3 ft 3subaeration cell equipped with the froth washer attachment in the laboratory and in a plant on coal refuse (3% solids and 2.15 % sulfur). The AFRA for the slurry is shown for comparison.

The froth washer attachment was highly effective in removing sulfur from fine coal slurry. Tests showed the sulfur content of the recovered combustible material to be consistently almost 1/3 less than that predicted by the AFRA, independent of the level of combustible recovery.

Figure 3: Comparison between combustible recovery versus the total sulfur content of the products produced from a refuse containing 1.36% sulfur (solids feeding rate 82 lbs/hr to 200 lbs/hr) with a laboratory size subaeration cell equipped with the froth washer attachment, and those predicted by AFRA curve.

The froth washer attachment achieved significantly higher sulfur rejection than that predicted by AFRA for high combustible recovery levels (i.e., between 80 and 100 percent).

Figure 4: Comparison between combustible recovery versus the pyritic sulfur content of the products produced from a refuse containing 1.36% sulfur (solids feeding rate 82 lb/hr to 200lb/hr) with subaeration cell equipped with the froth washer attachment (triangles), and those predicted by the AFRA (solid line).

The pyritic sulfur content of the cleaned fine coal was significantly less than that predicted by the AFRA for comparable combustible recoveries for the material. So, the froth washer attachment achieved significantly higher sulfur rejection than that predicted by AFRA for high combustible recovery levels (i.e., between 80 and 100 percent).

The technology is currently undergoing near full-scale testing at a coal cleaning plant in Illinois.

Patent Application

This technology has U.S. and international patents pending.

Technical Papers

• " The Significance of Illinois Coal and the Illinois State Geological Survey (ISGS) Washer," by Latif A. Khan, William R. Roy, and Ken K. Ho. To be published as ISGS publication after the patent application has been filed.
  
  
• "Testing of the ISGS Washer on a 100-Cubic Foot Subaeration Cell to Recover Fine Coal," Final Technical Report by Latif A. Khan, William R. Roy, and Ken K. Ho, March 1, 2001 through July 31, 2002.
  
  
• "Testing of the ISGS Washer on a 100-Cubic Foot Subaeration Cell to Recover Fine Coal," Interim Final Technical Report by Latif A. Khan, William R. Roy, and Ken K. Ho, March 1, 2001 through October 31, 2001.
  
  
• "Use of Subaeration Cell and ISGS Washer to Process 100 lb. of Tailings/hour in a Commercial Plant," Interim Final Technical Report by Latif A. Khan, William R. Roy, and Ken K. Ho., November 1, 1999 through October 31, 2000.
  
  
• "Scale Up of the ISGS Froth Washer for Testing in a Commercial Plant," Final Technical Report by Latif A. Khan, John M.. Lytle, William R. Roy, Ken K. Ho, Y. Simpson, H. Massood and D. Patil, November 1, 1998-January 1, 2000.
  
  
• "Testing the ISGS Froth Washer on a Stream of Coal Prep Plant Fines," Final Technical Report by Latif A. Khan, John M. Lytle, and Ken K. Ho, September 1, 1997 through September 30, 1998.
  
  
• "Testing of Improved Froth Washing & Drainage Device for Flotation Machines," Final Technical Report by Latif A. Khan, John M. Lytle, and Ken K. Ho, September 1, 1996 through August 31, 1997.

Press Coverage

• The News Gazette: "Researchers Focus on Coal" (July 29, 2001)
  
  
• The News Gazette: "System converts dirty coal waste" (November 20, 2001)
  

Presentations

• "Impact of ISGS Washer on Performance of Flotation Devices" 26th Technical Conference on Coal Utilization and Fuel Systems, Clearwater, Florida, 2001
  
  
• "The significance of Illinois Coal and the Illinois State Geological Survey (ISGS) Washer," Proceedings, 27th Technical Conference on Coal Utilization and Fuel Systems, Clearwater, Florida, 2002
  

The University of Illinois at Urbana–Champaign is offering its froth washer attachment for license or joint development by qualified companies.

For more information about this licensing opportunity, please contact:

, (919) 303-5874