Grinding & Classification Circuits

Grinding & Classification Circuits 2017-03-23T09:46:37+00:00
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Performance Improvement at SAG Mill through Lining Redesign (11 replies)

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

A lining redesign (shell lifters, grate plates and pulp lifters) done at the Cortez Gold Mines (Crescent Valley, Nevada) SAG mill has produced a very definite reduction in power draft; it is estimated that the power decreases in the 230-370 kW range. Hence, energy consumption per ton of ore milled decreases by 0.3-1.3 kWh/t, in the 10% range.

Furthermore, a 1%-10% reduction in recirculation was noticed due to the efficient impact breakage of critical size material. All of these results amount to a significant reduction in operating costs.

Have anyone any case to share about the impact of lining redesign to improve the SAG mill performance? 

Obersturmbann
1 year ago
Obersturmbann 1 year ago

I have authored and co-authored 5 papers on liner redesign based on our modifications to the 40 ft Cadia SAG Mill. These papers were published in SAG 2001 and 2006.

The modifications increased throughput by up to 6 %, reduced liner replacement by 47%, when you index total tons ground, and reduced liner change-out time by reducing the number of bolted connections.

I then showed further improvements were possible to obtain much greater gains in kW-hrs/ton, liner life and change-out time. The later required an increase in the liner handler mass lift rating. Cadia did increase the changer from 3.5 tons to 6 tons, but where not interested in further liner design changes.

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

To enrich the discussion, I think that a redesign project of mill liners must be conducted with a view toward increasing total mill performance through energy and cost efficiency, having in mind that the total mill performance is a function of all factors around the mill (ore, grinding media, operation and lining design).

Obersturmbann
1 year ago
Obersturmbann 1 year ago

We further offer to show via our DEM simulation the benefits at no cost until proven with a new lifter design. We would also encourage you to modify the mill ends. I have not doubts that we can make a major improvement. You must take the first step and ask how, how long, and how much.

If less than 2% kW-hrs/ton and increased life improvement, then you pay nothing. We must show both analytically and with field throughput and life benefits to collect our reward. We would need to work with a reputable liner supplier that we both accept.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

Was this redesign related to the implementation of Outotec Turbo Pulp Lifter?

It’s great to care about efficiency increasing in grinding mills continuously. We’ve changed shell liner design in GEG Iron Ore Company, Iran (32 foot dry SAG) and it resulted in 30 % capacity increase without scarifying discharge size distribution. Also we are working on changing liner design in Sarcheshmeh Copper Complex (32 foots wet SAG). GMT (Grinding Media Trajectory Software) with a scaled down Laboratory mill help us to simulate the charge behaviour. 

Rahil Khan
1 year ago
Rahil Khan 1 year ago

My question is and not comment why the SAG mill chute chock every time? It’s the size of rock crush or the feed end position?

Alan Carter
1 year ago
Alan Carter 1 year ago

Whether the design of this design has been tested on seed producing companies mine the other?

Raje Singh
1 year ago
Raje Singh 1 year ago

The Face angle was 7 degree. Size of Feed is always a reason for chocking the SAG feed chute like at the end of gyratory crusher chamber liners life that are worn. Also sometimes something is wrong with water addition system in SAG mills. For example feed-forward control loop of SAG solid percentage (Dead time of reaction of control valve causes lots of problems). The arrangement of water addition pipes is also important for preventing of SAG feed chute chocking.

Rahil Khan
1 year ago
Rahil Khan 1 year ago

Exactly the crusher liners cause this problem, what I needed if you can send me brochure for sag mill production or all parameters to have a good results.

Carl Jenkins
1 year ago
Carl Jenkins 1 year ago

I have worked with a liner manufacturer and yes, 10% was achievable in some place. When we design a mill, we do not take into account that parameter yet! It is still neglected. I do believe in an optimum design but it might end as a case-to-case basis as the ore hardness and grain size varies from one ore body to another. I would like to have your paper if you don't mind. Are you looking to present that paper somewhere?

Maya Rothman
1 year ago
Maya Rothman 1 year ago

If the applied energy fell between 230 and 370 kW, is a sign that you gave less power to the balls. If the grinding maintaining with the same quality (for example, the same rate and even P80) means that the new profile used is actually more efficient.

Mill with a high height of the lifters, creates a low amount of large impacts. A coating too low (in relation to the ball) and not slide up the ball enough, indicates power failure signal applied and the coating must be replaced (or invert the mill rotation, if possible). The ideal is a wave height compatible with the size of your spare ball, enough to lift and manages a number of smaller and more efficient impacts to the ore.

In times of stability of feed rate and% solids, note if the power of the mill is very oscillating. If this happen, is a sign of wrong coating design, which raises the balls erratically (can also apply your ear).

Obersturmbann
1 year ago
Obersturmbann 1 year ago

We have evaluated more than 50 AG/SAG mills from different plants around the world, and their PI or equivalent databases. We simulated the operating parameters and were able to match the same power, size reduction, wear rate, kW-hrs/ton, and throughput, regardless of ore: ball ratio. In most cases the ball content was lower than optimal. In all cases the mill lifter/liner geometries could significantly improve by increasing the lifter height and reducing the lifter number.

In 1995, our DEM investigation demonstrated there is an optimal lifter geometry and number that is independent of mill size, if you want to maximize the comminution rate. Separately, the ball content must be correlated to the ore strength, grate size, and re-circulating rate. The comminution target should be to maximize the ore surface area increase for the given power draw, while also maximizing liner life between changes.

Today, the same DEM analysis is made much easier with new comminution breakage protocols and new computer hardware. What took 1 month in 2000 now takes about 3 days. The total time to optimize a mill use to take about 3 months, now can take 2 weeks. The greatest amount of time is used to wear the mill down while mapping all the performance factors. The larger lifter configuration takes longer to wear.

The release angle is only one parameter in the lifter design. Our release angle on the Cadia 40 ft mill was about 35-37 degrees. But, that sole number is not important without knowing the lifter height (570 mm), lifter toe or root radius, lifter tip radius, and lifter number to start.

The note above on the higher lifter height reducing the impact value is not relevant, if you believe the large amount of literature on this subject. The main goal of a good mill design, for the set mill dimensions, is to maximize the ore circulation rate through the charge toe, while maximizing the shoulder height (hydrostatic load on toe).

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