3684
A New Model to Predict the Power Draw in Tumbling Mills
Roddy Valle Peche
FLSmidth, Peru
ABSTRACT: or sizing tumbling mills, the first step is to determine the specific energy according to ore breakage
properties and reduction work from a known feed size to a desired product size. For this first step, specific energy
models are used, then the required power draw is determined by multiplying the specific energy by the desired
throughput. If the first step is miscalculated, the consequence will be a failure to reach the desired throughput
and/or product size, resulting in detrimental economic results for the stakeholders. However, if the first step is
well calculated, the second step is to determine the right mill dimensions and operating conditions, such as ball
load, total load, and speed that will draw the required power.
The specific energy determination was discussed by the author (R. Valle – IMPC 2020 &Procemin 2020)
presenting a new model of variable exponent in function of feed size. This paper deals with determining the
required power draw from mill dimensions and operating variables for AG, SAG and Ball Mills, to have an
accurate sizing of wet tumbling mills, ensuring the objective throughput and product size of mining projects.
The enhanced model to predict the power draw has been proven with 191 industrial data sets in a wide range
of gross power draw, from 6 to 22,800 kW. The relative errors of predicted vs actual gross power draw have a
normal distribution with a standard deviation of 4.7% for all mills AG, SAG and Ball Mills, giving a precision
of +/-9.2% with 95% confidence level. The mathematical model has the same form, regardless of mill type the
only difference between grate and overflow discharge mills is the coefficient of the model.
INTRODUCTION
Comminution is strongly related to an amount of energy
per ore tonne referred as specific energy (kWh/t) for an
expected duty. After calculating specific energy, it is easy
to determine what is the required power, accomplished by
multiplying the specific energy by the desired throughput
however, the required power is a function of the mill type,
mill dimensions, aspect ratio and operating conditions:
such as ball load, total load, speed, %solids, etc.
For sizing tumbling mills to meet with the desired
throughput and product size there are two steps. First,
the calculation of the specific energy, which is outside the
scope of this paper. The second step is to calculate the mill
dimensions and operating conditions to reach the required
power. This paper is focused on determining the power
draw for wet tumbling mills.
In the mineral processing field, wet tumbling mills
are typically categorized as grate and overflow discharge.
In most cases the grate type corresponds to AG and SAG
mills, and the overflow type corresponds to ball mills. The
data sets for this paper deal with this type of mills.
In this paper the range of industrial data sets under
analysis are shown in the Table 1.
The 191 data sets have been compiled from techni-
cal papers and comprehensive surveys including tumbling
mills around the world.
A New Model to Predict the Power Draw in Tumbling Mills
Roddy Valle Peche
FLSmidth, Peru
ABSTRACT: or sizing tumbling mills, the first step is to determine the specific energy according to ore breakage
properties and reduction work from a known feed size to a desired product size. For this first step, specific energy
models are used, then the required power draw is determined by multiplying the specific energy by the desired
throughput. If the first step is miscalculated, the consequence will be a failure to reach the desired throughput
and/or product size, resulting in detrimental economic results for the stakeholders. However, if the first step is
well calculated, the second step is to determine the right mill dimensions and operating conditions, such as ball
load, total load, and speed that will draw the required power.
The specific energy determination was discussed by the author (R. Valle – IMPC 2020 &Procemin 2020)
presenting a new model of variable exponent in function of feed size. This paper deals with determining the
required power draw from mill dimensions and operating variables for AG, SAG and Ball Mills, to have an
accurate sizing of wet tumbling mills, ensuring the objective throughput and product size of mining projects.
The enhanced model to predict the power draw has been proven with 191 industrial data sets in a wide range
of gross power draw, from 6 to 22,800 kW. The relative errors of predicted vs actual gross power draw have a
normal distribution with a standard deviation of 4.7% for all mills AG, SAG and Ball Mills, giving a precision
of +/-9.2% with 95% confidence level. The mathematical model has the same form, regardless of mill type the
only difference between grate and overflow discharge mills is the coefficient of the model.
INTRODUCTION
Comminution is strongly related to an amount of energy
per ore tonne referred as specific energy (kWh/t) for an
expected duty. After calculating specific energy, it is easy
to determine what is the required power, accomplished by
multiplying the specific energy by the desired throughput
however, the required power is a function of the mill type,
mill dimensions, aspect ratio and operating conditions:
such as ball load, total load, speed, %solids, etc.
For sizing tumbling mills to meet with the desired
throughput and product size there are two steps. First,
the calculation of the specific energy, which is outside the
scope of this paper. The second step is to calculate the mill
dimensions and operating conditions to reach the required
power. This paper is focused on determining the power
draw for wet tumbling mills.
In the mineral processing field, wet tumbling mills
are typically categorized as grate and overflow discharge.
In most cases the grate type corresponds to AG and SAG
mills, and the overflow type corresponds to ball mills. The
data sets for this paper deal with this type of mills.
In this paper the range of industrial data sets under
analysis are shown in the Table 1.
The 191 data sets have been compiled from techni-
cal papers and comprehensive surveys including tumbling
mills around the world.