Spotlight Feature Articles ME Elecmetal Comminution Mar17 | Page 2

COMMINUTION AND CRUSHING thyssenkrupp POLYCOM units are designed for throughput rates in excess of 5,000 t / h . The mill feed material can be dry or moist and with particle sizes ranging from below 1 mm to more than 75 mm

The pinch point

Paul Moore looks at some advances being made by the key players to increase throughput and reduce energy consumption

Comminution alone has been estimated to represent 2 to 3 % of the world ' s electricity consumption so anything that can make it more efficient and consume less energy is of paramount importance to the industry and its technology providers .

Throughout its history , Metso says it has built its leadership on improving the comminution process “ by developing and offering ever more energy-efficient technology , and this has become an essential driver of our innovation .” It cites the Vertimill™ as a good example of a product that contributes significantly to the sustainability equation by using 25-30 % less energy than existing fine grinding technology . Metso has also developed and introduced its high-pressure grinding roll technology , Metso ’ s HRC™ , which it states is 10 % more energy efficient than its peers , and also increases circuit capacity .
However , the company also points out that there are also non-grinding technologies that can reduce the energy spent in comminution . Metso is launching two new fine wet classification devices . Both units , when inserted in a closed-circuit comminution flowsheet , provide a sharper particle classification , allowing right-sized product to bypass the grinding mill , thus saving a significant amount of energy . Many of the remaining advances in reducing comminution energy consumption will be made in these types of technology areas rather than the crushing and grinding itself .
Tower mills and vertical mills
In 2014 , Miaogou Iron Mine in China launched a
technological transformation project , which included replacing the original tertiary ball mills with Metso ’ s Vertimill VTM1500 vertical grinding mill . The result was a decrease in both power and grinding media consumption .
The Miaogou Iron Mine , part of the Hebei Iron and Steel Group , is located in China ’ s Qinglong County , some 300 km east of Beijing . Its annual iron concentrate production is 800,000 t . Due to the recent downturn in the iron and steel industry , Miaogou ’ s concentration costs were exceeding the price of iron concentrate . This put significant pressure on the company ’ s operations .
The mine ’ s original grinding circuit consisted of ball mills exclusively . The primary stage comprised five ball mills , the secondary stage three ball mills , and the final , tertiary stage two ball mills . The original tertiary grinding fineness was - 325 mesh with 71-73 % passing . Iron concentrate grade was 65 % and the average recovery rate 87 %.
In 2014 , Miaogou Iron Mine in China launched a technological transformation project , which included replacing the original tertiary ball mills with Metso ’ s Vertimill VTM1500 vertical grinding mill
“ Since the technological transformation , the concentration costs have basically paralleled the current price of iron concentrate . Under the current market situation , the normal production of the mine can still be guaranteed . Through the introduction of Metso ’ s Vertimill ® VTM1500 vertical grinding mill , Miaogou Iron Mine has not only successfully achieved the goal of the technological transformation , it has also laid the foundation for smoothly riding out the current market ’ s difficulties .”
“ After replacing the original tertiary ball mills with a Vertimill VTM1500 , the grinding fineness was increased from 71-73 % to 88-90 % passing - 325 mesh , the iron concentrate grade from 65 % to 66 %, and the average recovery from 87 % to 89 %. At the same time , the silica content was decreased by 1 %,” says Zhang Runshen , General Chief of Miaogou Iron Mine Project and Chief of the Concentration Plant .
In addition to having helped improve the recovery rate , the Vertimill has a lower energy and grinding media consumption rate than the ball mill . It also takes up much less space .
“ We would have needed a larger ball mill to achieve the current grinding fineness . However , the original plant space was limited . Thanks to its compact dimensions and the ease of installation , it only took us two weeks to complete the equipment installation . At present , the VTM1500 runs at an 85 % load to achieve a
International Mining | MARCH 2017