Heavy Metals could dictate Limestone Grinding Decisions - Hot Topic Hour September 10
It was a surprise to participants and speakers that a Hot Topic debate on Dry vs. Wet Grinding of Limestone introduced an important new factor. This factor is the grinding contribution to heavy metal discharges in the wastewater.
The two speakers were Scott Eck, Senior Sales Engineer at FLSmidth Air Tech, Inc., and Guillermo Benjumea, Senior Engineer Sales & Marketing at Loesche. At the end of Scott’s presentation on ball mills for wet grinding Bob McIlvaine posed the heavy metal question. In the previous week’s webinar Tom Higgins of CH2M Hill startled the audience by observing that the attrition of the iron balls in the ball mill was a contributor to the toxic metal discharge in the FGD wastewater. He also pointed out the difficulty and expense of reducing these parts per trillion amounts.
Scott answered the first half of the question as to why the balls contribute substantially to the contamination. He explained that the balls contain significant amounts of chromium, nickel and other alloys to reduce ball wear. As to how to reduce this contribution, Scott says that ceramic balls can be used instead of iron. The only problem is that you need bigger ball mills. One solution would be to operate both the primary and standby ball mills in parallel. But this would result in a lack of redundancy. Any other solution would be capital intensive.
Guillermo discussed the regional dry grinding and observed that the contamination from loss of metal on the rollers would be lower than from the balls. So this could be an argument for regional dry grinding vs. local wet grinding. He also pointed out the lower energy cost with dry grinding and the resultant impact on CO2 emissions.
Scott quoted the adage that you should grind wet or grind dry but not in between. With dry grinding you have to contend with six percent or greater moisture in the stone. Guillermo countered with the claim that the Loesche mills both dry the material and grind it.
The bio and abstract can be viewed as follows: september_10_bios_abstracts_photos.htm
The individual slides are in the FGD Decision Tree and can be viewed as follows:
Scott Eck - FLSmidth
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FGD Continuing Decision Process For: Products
FGD Ball Mill Grinding Systems, presented by Scott Eck, FLSmidth. Hot Topic Hour September 10, 2009.