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## SAG Mill Power Model (11 replies and 5 comments)

Power model of SAG mill depend from follow parameters:

- Mill dimension
- Material of mill
- Speed rotation
- Ball size
- Coarse rock size (critical size).

I am more concerned about the cases where the center of mass of mill shifts to a new position, thus causing extra torque and more power consumption. Generally, it happens when you have coarse and/or hard ore going to the SAG mill, its center of mass shifts to a new position and mill drive consume more power because of the extra torque generated. It can also result in to the overloading of SAG mill (also depends on other process variables). I am facing an issue in predicting correct power consumption when ore hardness and size is changing, keeping other physical parameter constants.

My main objective is to predict the correct power consumption of SAG mill in a dynamic simulation where process variables and ore conditions are continuously changing with time.

What do you plan to do with your "correct power consumption" number? Is this the power draw at optimum loading, to be cascaded to a feed rate or mill speed controller? How will ore hardness be measured?

Those model calculate from three powers: empty mill, ball charge, rocks charge. Then this powers is summarized. What does you model calculate?

You may be running into a new area as most of the methods currently available are not designed for dynamic modelling but rather looking at discrete problems. Most (including the work by Hardinge and Bond) were geared to not under sizing mills.

Millsoft (Prof Raj Rajamani out of Utah and O2mtech) is used for these kinds of calculations (DEM based tool).

I was involved in developing a hybrid DEM/CFD model for mill simulation. It wasn't pretty.

Can we get some case studies and compare the power estimated from models and actual power being consumed in the practice. This kind of information would be of great value in cost estimates etc.

As you point very well, power will change with charge characteristics (holdup, PSD, density, etc.) and these characteristics are driven by operating conditions, especially feed material properties. If you want these "input disturbances" to reflect onto your simulated power, the only way is to actually calculate your charge characteristics dynamically, i.e. implement actual comminution and discharge models on top of your power model and perform a dynamic population balance. There are a number of books out there that will help you do that. My two favorites are from King and the JKMRC.

What is the effect of top size over F80 in SAG mill feed? Typically I have a topsize of 300 mm as top size and 180 mm is the gape set of Jaw crusher whose product is to be fed to SAG mill . Is reduction further in Jaw crushing stage desirable? My run of mine ore feeding Jaw crusher discharges 1200 mm boulders.

Crusher is METSO C-200 product size 300 mm , closed side setting 200 mm and power 400 KWH. SAG mill size is 28 ft dia x 16 ft lenth. ore density 3.4 WI 13.0

Hi, even if your C200 is capable of crushing those 1.2m rock boulders, it would be in the whole operation's interest to send the crusher and finer/small feed. You can drill tighter and blast harder + the smaller you can make the crusher discharge be, the better you SAG tonnage will be.

Look at the graph below https://www.911metallurgist.com/blog/choke-feeding-a-jaw-crusher it is the result of finers blasting and better/finer jaw crushing.

Do you have a grizzly ahead of you jaw crusher? What openning? Are you able to post a few photos of your working crusher? Ore pocket? Working crusher cavity?

What about your coarse ore stockpile; does it run full? How many feeders do you have VS how many are you using to the SAG mill?

Which power model is the most efficient to predict the correct power consumption in sag mill with change in process variables?

I have developed a few dynamic simulators for different mineral/metal processing plants. Prediction of correct sag mill power consumption with a change in ore hardness, solid percent (density) to the sag feed, rpm of sag and PSD has always been very tricky. So far, I have used Austin-Morrell model and Hogg- Fuerstenau power model, but these models seem to work well only under certain boundary conditions.

What are the other power models/strategies have been used to simulate the real sag power behavior?