1 ***Please save your paper as the surname of the first listed author and your reference number, eg Smith_076” XXV International Mineral Processing Congress (IMPC 2010) Comparing energy efficiency of multi-pass high pressure grinding roll (HPGR) circuits M Hilden and S P Suthers Reference Number: 342 Contact Author: Marko Hilden Senior Research Fellow University of Queensland JKMRC, Isles Rd, Indooroopilly, QLD 4068, Australia Phone: (07) 3346-5907 Fax: (07) 3365 5999 Mobile: Email: [email protected]
Transcript
1
***Please save your paper as the surname of the first listed author and your reference number, eg Smith_076”
XXV International Mineral Processing Congress (IMPC 2010)
Comparing energy efficiency of multi-pass high pressure grinding roll (HPGR) circuits
M Hilden and S P Suthers
Reference Number: 342 Contact Author: Marko Hilden Senior Research Fellow University of Queensland JKMRC, Isles Rd, Indooroopilly, QLD 4068, Australia Phone: (07) 3346-5907 Fax: (07) 3365 5999 Mobile: Email: [email protected]
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Comparing energy efficiency of multi-pass high pressure grinding roll (HPGR) circuits
M Hilden1 and S P Suthers2
1. Senior Research Fellow, University of Queensland, JKMRC, Isles Rd, Indooroopilly, QLD 4068, Australia. Email: [email protected] 2. MAusIMM, Research Project Leader, CSIRO Process Science and Engineering, PO Box 883, Kenmore, QLD 4069, Australia. Email: [email protected]
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ABSTRACT
With increased emphasis on reducing costs and carbon emissions in mineral processing, it is becoming
essential to employ the most efficient comminution devices and to use them to maximum effect. High
pressure grinding rolls (HPGR) are considered highly efficient compared with other devices, however their
relative efficiency in multi-HPGR circuits is less well understood.
A series of comminution tests was carried out to evaluate three multi-pass HPGR circuits and a jaw crusher-
ball mill circuit. Combinations of HPGR units (1.0 m and 0.25 m diameter), jaw crushers and Bond ball mills
were used to grind a 32 mm top size porphyry copper feed (BBWI = 12.1) to a product P80 size of about 150
µm. Up to three passes of HPGR were used in each circuit, with energy measurement and size analysis at
each point in the comminution process.
The energy efficiencies of individual comminution stages and of the overall circuits were quantified and
evaluated using three different approaches. The operating work index method for comparing comminution
energy efficiency underestimated HPGR performance due to the large amount of fines generated. The -75
µm efficiency factor and F50/P50 reduction ratio interpolation methods both give results that were more
credible because they better took into account the amount of fines generated by HPGR.
The results show that the relative comminution efficiencies of the three multi-pass HPGR circuits tested differ
by as much as 22%, providing insights as how to best employ HPGR in a comminution circuit. The most
energy efficient of the circuits tested was a three-pass HPGR circuit with a 1.0 m diameter roll on the first
pass in closed circuit with an 8 mm screen followed by a second and third pass in a 0.25 m roll.
Keywords: HPGR, high pressure grinding, comminution, energy efficiency, multi-pass
INTRODUCTION
High pressure grinding roll (HPGR) technology was introduced in 1985 to crush and grind relatively none-
abrasive materials in the cement industry. Now in the 21st century, HPGR technology is gaining acceptance
within the global mineral processing industry. HPGR units have been, or are being, installed in a wide range
of minerals processing projects, such as iron ore pellet feed preparation, and preparation of gold, copper,
PGM and molybdenite ores. As of 2009 there are a number of operating hard rock HPGR installations, such
as: Cerro Verde (McMoRan) in Peru (copper-molybdenum); Mogalakwena (Anglo American) in South Africa
(platinum); Boddington (Newmont) in Australia (copper-gold); and Grasberg (Freeport-McMoRan) in
Indonesia (copper-gold).
Ntsele and Sauermann (2007), Neumann (2006) and Morley (2006) described the principles of HPGR
operation in detail. The HPGR machine has two motor driven counter-rotating rolls, one of which is fixed,
while the other acts against hydraulic cylinders connected to pressurised nitrogen accumulators
(hydropneumatic springs). Rock is choke fed to the gap between the rolls via a small hopper located directly
above the rolls. The rolls nip and pre-break particles larger than the working gap by the mechanism of single-
particle comminution. As the feed passes between the pressurised rolls, a compressed bed forms in which
particles are crushed autogenously, predominantly by the mechanism of interparticle breakage. The transfer
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of energy directly from the HPGR rolls to the feed is thought to be more efficient when compared to tumbling
mills that break particles in a relatively random “hit or miss” manner (Fuerstenau and Abouzeid, 2007).
Benefits of using high pressure grinding rolls
Energy efficiency is the main benefit of HPGR. Large energy savings of around 20-50% relative to dry
grinding ball mills have been achieved in the cement industry (Otte, 1988; Patzelt, 1992); however, such
savings have not been reproduced in the minerals industry when comparing HPGR with wet grinding ball
mills. Direct energy savings of around 10-20% are estimated in most HPGR studies (Rosario and Hall, 2008;
Daniel 2007). Moreover, the cumulative energy savings are less when power used by additional equipment
such as crushers, conveyors, screens and dust extractors is considered (Rosario and Hall, 2008), but details
of realised energy savings for industrial installations are yet to be published. However, reduced grinding
media consumption for HPGR options over conventional mills can lead to significant additional savings in
cost and embodied energy. In some applications, such as replacing a SAG milling circuit, operating cost
reductions of the same order of magnitude as energy savings can be achieved (Morley 2006; Rule, Minnaar
and Sauermann, 2009).
Multiple high pressure grinding rolls flowsheets
HPGR devices are usually installed as single units within a closed circuit configuration. Using multiple HPGR
units in series would reduce the proportion of grinding done in ball mills.
Norgate and Weller (1994) reported that for the same specific energy consumption, greater size reduction
can be achieved by operating a number of HPGR units in series at a low specific grinding force than can be
achieved by operating a single HPGR at a higher specific grinding force. That is, a multi-pass HPGR
configuration can be more power efficient than a single-pass configuration. Moreover, doing a greater
proportion of the size reduction duty in crushing and HPGR relative to tumbling mills could increase the
overall energy efficiency (Morrell, 2008).
Daniel (2007) tested multiple pass HPGR circuits at a lab scale using 300 mm rolls and found that a three-
pass HPGR circuit used less energy overall compared with dry ball milling only. The present study aims to
repeat the experiments at a larger scale and to develop methodologies for estimating the energy efficiency of
HPGR circuits including open and closed circuit HPGR configurations.
EXPERIMENTAL
A sample of porphyry copper ore with a Bond Ball Work Index of 12.1 kWh/t was used for this testwork. The
ore was crushed to 32 mm top size, blended and split into representative portions of around 210 kg each.
Two HPGR units were used for this test work, namely, a 1.0 m (d) x 0.25 m (w) pilot scale Köppern unit at
AMMTEC laboratories in Perth, and a smaller laboratory scale 0.25 m (d) x 0.1 m (w) Polysius unit at CSIRO
in Brisbane. Six pressure response tests were carried out on the copper ore with the 1.0 m HPGR to
determine the optimum pressing force range. Following this, three multi-pass HPGR circuits (Flowsheets A-
C) and a jaw crusher-ball mill circuit (Flowsheet D) were trialled by batch testing (Figure 1). Energy
measurements and particle size distributions were obtained at each point in the circuit flowsheets.
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Flowsheet A is an open circuit triple-pass flowsheet using the large HPGR units only. The feed was pressed
in the 1.0 m HPGR and the product was pressed consecutively a further two times in the same unit to
simulate a three-pass circuit. No deagglomeration was done between passes other than that caused by
materials handling. Two tests were carried out using low (3 N/mm2) and moderate (4.5 N/mm2) pressing
forces.
Flowsheet B investigates an open circuit triple-pass flowsheet comprising a jaw crusher followed by two
smaller HPGR units. The feed was crushed in a single pass of a laboratory jaw crusher with a closed side
setting of 7 mm, followed by two consecutive passes in the 0.25 m HPGR. The jaw crushing step is
necessary because the maximum feed top size for the 0.25 m HPGR is about 10 mm.
Flowsheet C is a three-pass circuit with one large and two small HPGR units. The 1.0 m HPGR operates in
closed circuit with an 8 mm screen to provide a suitably sized feed to the smaller HPGR units. The locked
cycle tests (22% recycle load) were simulated by batch grinding and dry screening and the products were
then pressed two more times consecutively in the 0.25 m HPGR.
As well as the multi-HPGR flowsheets, a further flowsheet was tested (Flowsheet D) which comprised two
jaw crushers in series with closed side settings of 7 mm and 2.3 mm respectively.
Each flowsheet was followed by a Bond ball-milling step. If necessary, an additional 3.35 mm screening and
crushing step was applied to each of the products from the above-mentioned flowsheets to produce suitable
Bond test feed of 3.35 mm top size. Finally, grinding was carried out on each product using a standard Bond
ball mill work index (BBWI) test procedure, with a closing screen size of 212 µm to ensure that each circuit
terminated at approximately the same final grind size (see Figure 1). The energy of the final grind is
calculated from the Bond grindability (g/rev) converted to energy by assuming 60 J/rev, after Bond (1961).
The Bond mill itself uses around 90-93 J/rev as measured by Daniel (2007), however Bond’s 60 J estimate
incorporates an empirical scaling factor to relate dry lab-scale data with 2.4 m diameter wet grinding mills.
RESULTS AND DISCUSSION
Pressure response tests
The pressure response test examines the energy consumption and resulting size reduction for a range of
pressures applied to the HPGR rolls for a given ore. Six pressure response tests were carried out on the
copper ore with the 1.0 m HPGR.
The specific pressing force (Fsp) is the applied grinding force divided by the length and width of the rolls
(N/mm2); and the specific energy consumption (Ecs) is the net power input divided by the ore throughput rate
(kWh/t). The typical operating range of specific pressing forces for HPGR is 1-10 N/mm2. Figure 2 shows that
there is a linear relationship between the specific pressing force and specific energy consumption for the six
tests at pressing forces between 2 and 6 N/mm2.
The rate of fines generation by HPGR increases at a diminishing rate with increasing energy input (Bearman,
2006; Norgate and Weller, 1994). The feed and product size distributions for each pressure response test
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are shown in Figure 3 and it is clear that there is a large size reduction resulting from a pressing force of 2
N/mm2 but the size reductions at higher forces (e.g. 4 N/mm2) are not as correspondingly large.
The reduction ratio (Fx/Px) is the feed X% passing size divided by the product X% passing size. Reduction
ratios for 80%, 50% and 20% passing sizes from the pressure response tests are compared against specific
energy consumption in Figure 4, which shows that the reduction ratios increase at a decreasing rate with
increasing energy input. Furthermore, the reduction ratio is much greater for finer particles (F20/P20) relative
to the coarse particles (F80/P80), that is, the HPGR generates a large proportion of fines during comminution.
For an energy input of 3 kWh/t, the rate of increase in fines content in the HPGR product is still strong but
there is a disproportionately smaller rate of reduction for the coarser particles. Further increasing the
pressing force would eventually lead to saturation pressure where little overall size reduction would occur
despite a linear increase in energy input. It can be seen in Figure 4 that the reduction ratio at the F80/P80 size
appears to plateau at around 2.5 kWh/t (corresponding to a specific pressing force of about 4.5 N/mm2). For
this reason, the pressing force should be optimised to compromise between the reduction ratio, energy
efficiency and extent of micro-cracking imparted on the material (Norgate and Weller, 1994). Based on these
pressure test results, pressing forces of 3 N/mm2 and 4.5 N/mm2 were chosen for subsequent tests.
Flowsheet test results
Two sets of tests were carried out for Flowsheet A using a specific pressing force of either 4.5 N/mm2 or 3.0
N/mm2 for each of the three passes through the 1.0 m HPGR. The results for the 4.5 N/mm2 test are given in
Table 1. The final ball mill product size for this test is a P80 of 131 µm and the cumulative specific energy
consumption is 11.53 kWh/t.
The results for the Flowsheet A tests using a specific pressing force of 3.0 N/mm2 are given in Table 2. The
final ball mill product size for this test is a P80 of 138 µm and the cumulative specific energy consumption is
10.60 kWh/t.
The results for the Flowsheet B test (jaw crushing followed by two passes through the 0.25 m HPGR) are
given in Table 3. The final ball mill product size for this test is a P80 of 145 µm and the cumulative specific
energy consumption is 9.82 kWh/t.
Table 4 gives the results for the final HPGR circuit option, Flowsheet C, which is the 1.0 m HPGR in closed
circuit with an 8 mm screen followed by two passes through the 0.25 m HPGR. The final ball mill product size
for this test is a P80 of 136 µm and the cumulative specific energy consumption is 9.74 kWh/t.
Lastly, Flowsheet D, consisting only of jaw crushers in series followed by a ball mill was tested for
comparison with the above HPGR flowsheets. The results are given in Table 5, and show that the final ball
mill product size for this test is a P80 of 156 µm and the cumulative specific energy consumption is 9.00
kWh/t.
From the results in Table 1 to Table 5, it can be seen that:
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Flowsheet D has the lowest specific energy consumption (9.00 kWh/t), but the reduction ratio is the
lowest of all the tests (F50/P50 = 238) and the least amount of new -75 µm fines is generated (not
shown);
The Flowsheet A (4.5 N/mm2) configuration has the highest specific energy consumption (11.53
kWh/t), but it has the greatest reduction ratio (F50/P50 = 357) and the greatest amount of new -75 µm
fines is generated (not shown); and,
The difference in P80 between the coarsest and finest Bond mill product is only 25 µm, however, this
equates to a relative difference of 19.1%; similarly, the corresponding difference in specific energy is
2.53 kWh/t, which equates to a relative difference of 28.1%.
The measured specific energy consumption for each point in each of the circuits is plotted cumulatively
against the reduction ratio (F50/P50) in Figure 5. The data show that:
Flowsheet A with a pressing force configuration of 4.5 N/mm2 is clearly the least efficient circuit
overall;
The first two jaw crushing stages of Flowsheet D are the most efficient for coarse comminution for
reduction ratios of up to about 10;
For intermediate reduction ratios of around 100, the combination of the first three stages of
Flowsheet B (jaw crusher and 2 small HPGR units) is relatively efficient compared to the other
flowsheets. The combination of the first three stages of Flowsheet C (one large and 2 small HPGR
units) is similarly efficient;
Flowsheet C, overall, is more efficient than Flowsheet B and significantly more efficient than either of
the two Flowsheet A configurations; and
Flowsheet D uses the least energy overall, but it is difficult to compare its efficiency with Flowsheets
C and B because of the differences in reduction ratios.
In Figure 6, the first two stages of Flowsheet C are compared with the first three stages of Flowsheet A (3.0
N/mm2). It is clear from the graph that the performance of the 1.0 m HPGR in closed circuit is close to that of
two sequential passes through a 1.0 m HPGR (circled in Figure 6). However, note that the 0.25 m HPGR
outperformed the 1.0 m HPGR in the subsequent grinding step, which suggests that the smaller sized HPGR
is more efficient than the larger one.
The difference in P80 between the coarsest and finest final products from all the tests is only 20 µm. This may
seem trivial at first glance, but in terms of overall reduction ratio (F50/P50), this represents a factor of 119. It is
therefore important to consider methods for comparing comminution energy efficiency on a fair basis.
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Performance benchmarking
The specific energy used by each circuit is calculated by totalling the specific energy of each comminution
step including the calculated grind energy from the Bond ball mill test. Three methods are used to compare
the energy efficiency of each circuit. Each is discussed below.
Operating work index efficiency
The operating work index method (Bond, 1961) is a widely used measure of comminution efficiency that
compares the measured energy with the energy estimated from the Bond equation (Equation 1).
E = W i x (10/√P80 – 10/√F80) (1)
where
Wi = Bond Work Index (kWh/t)
E = Bond predicted specific energy (kWh/t)
P80 = 80% passing size of the product (µm)
F80 = 80% passing size of the circuit feed (µm)
However, Musa and Morrison (2008) observed that the work index method usually gives unrealistic efficiency
values when used for mills other than rod and ball mills, such as the AG/SAG mill, Vertimill and IsaMill. They
attributed this to differences in the correlation between P80 and -75 µm materials in the feed and product.
The predicted specific energy and operating work index efficiency have been calculated for each
comminution step in the flowsheet as well as the complete circuit (see the “Bond E predicted” and “Bond
efficiency” values in Tables 1 to 5).
Minus 75 µm efficiency factor
Musa and Morrison (2008) found a good correlation between measured energy consumption and the amount
of new -75 µm fines generated across a wide range of comminution equipment. The quantity of -75 µm fines
generated in the Bond test can be used to estimate the amount of -75 µm material produced per unit of
energy. For the material used in this study, the Bond test data suggests that approximately 0.173 kWh is
required for each one percent of -75 µm generated. This value is then used to predict the cumulative energy
input from the measured amount of -75 µm fines generated at each comminution step in any of the
flowsheets. The -75 µm efficiency factor (see Tables 1 to 5) is then calculated as the predicted energy input
divided by the measured energy consumption. Figure 7 shows that for the tested copper ore there is a good
linear relationship between the measured cumulative specific energy and total fraction of new -75 µm fines
generated at each point of the tested flowsheets.
Reduction ratio interpolation
A third comparison technique is to interpolate linearly between the ball milling stage and the preceding
comminution stage of each HPGR flowsheet to predict the specific energy required to achieve a particular
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reduction ratio (F50/P50). The smallest overall reduction ratio obtained from the tested flowsheets is used as
the reference point. Thus, the overall energy consumption for each circuit is normalised for small absolute
differences between the sizes of the final ball mill products. The cumulative specific energies of each HPGR
flowsheet were interpolated to the same reduction ratio as Flowsheet D (F50/P50 = 238) and are given in
Table 6 under the column titled “Ecs (interpolated)”. Note that the D50 achieved after ball milling in the latter
flowsheet is 70 µm (Table 5), which is close to the size used as reference for the -75 µm method.
Comparison of flowsheet efficiency
For ease of comparison, the efficiency factors obtained from the above three methods are converted to
relative efficiencies with respect to Flowsheet D. These relative efficiencies are compared in Table 6.
According to the work index efficiency results, the most efficient flowsheet is the jaw crusher-ball mill option
(Flowsheet D), which is 14% more efficient than Flowsheet A (4.5 N/mm2). With this method, Flowsheet C
appears to be 0.5% less efficient than Flowsheet D. However, the work index calculation is based on F80 and
P80 sizes. Note that in Tables 1-5 the work index efficiencies of the HPGR stages are consistently very low
relative to the jaw crushers and ball mills. Given the fact that HPGR generates a large amount of fines, it
would seem to be more realistic to compare results using alternative size parameters such as the fraction of -
75 µm fines generated or the F50/P50. In contrast to the relative work index efficiencies, the -75 µm efficiency
results indicate that Flowsheet C is 9.5% more efficient than Flowsheet D and 14% more efficient than
Flowsheet A (4.5 N/mm2). The F50/P50 method (interpolation) gives comparable results to the -75 µm method
and rates Flowsheet C as 13.4% more efficient than Flowsheet D and 21.5% more efficient than Flowsheet A
(4.5 N/mm2). From the results in Table 6, it is concluded that for the porphyry copper ore tested:
The three-pass flowsheet using large (1.0 m) HPGR units (Flowsheet A) is the least efficient
configuration of those tested; using a pressing force of 3.0 N/mm2 is up to 5% more efficient than
using 4.5 N/mm2 in such a configuration;
The two-pass flowsheet using small (0.25 m) HPGR units preceded by jaw crushing (Flowsheet B) is
up to 5% more efficient than the 3.0 N/mm2 three-pass HPGR flowsheet. However, the efficiency is
similar to that of the sequential jaw crusher configuration (Flowsheet D);
The three-pass flowsheet using a large (1.0 m) HPGR in closed circuit followed by two small (0.25
m) HPGR units (Flowsheet C) is the most energy efficient of the HPGR configurations tested; it is
about 4-12% more efficient than Flowsheet B and about 9-22% more efficient than Flowsheet A.
CONCLUSIONS
Three multi-pass HPGR circuits and a jaw crusher-ball mill circuit were trialled by batch testing. The energy
efficiency of each flowsheet was evaluated using efficiency factors derived from three different approaches.
It has been shown that the work index method is not ideally suited for comparing HPGR performance against
conventional crushers due to the large amount of fines generated by the HPGR. The -75 µm efficiency factor
and the F50/P50 reduction ratio interpolation method both give results that are more appropriate for HPGR
circuits because they better take into account the amount of fines generated by HPGR. The apparent
efficiency, in terms of reduction ratio versus specific energy, is sensitive to the reduction size chosen (see
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Figure 4). It is likely that the percent passing value chosen for the reduction ratio (Fx/Px) interpolation should
be such that it corresponds to a product Px size of approximately 75 µm, to be consistent with the -75 µm
method, but this needs to be verified with further data analysis.
Flowsheet C (1.0 m HPGR in closed circuit followed by two 0.25 m HPGR units) is overall the most energy
efficient circuit configuration of those tested, and the efficiency analysis indicates that this circuit is up to
13.4% more efficient than Flowsheet D (the jaw crusher-ball milling configuration). This result indicates that
HPGR units in series with decreasing roll diameter will perform better than a circuit with the same sized rolls.
The capital cost of circuits also needs to be considered when comparing process options, and in this case,
the large size reduction after two passes and the relatively small size reduction achieved by the third HPGR
in Flowsheet C suggest that it might be more cost effective to eliminate that third unit completely from the
flowsheet.
Flowsheet A (three sequential passes in a 1.0 m HPGR with a pressing force of 4.5 N/mm2) is the least
efficient of the circuit configurations tested and it is estimated to be up to 22% less efficient than Flowsheet C
is. The results suggest that this is not only due to the higher specific pressing forces used, but also because
the larger 1.0 m HPGR is less efficient than the smaller 0.25 m HPGR when the feed contains a large
proportion of fines.
Given that the HPGR generates large amounts of fines compared to conventional crushers, locating a
classifier ahead of the ball mill, rather than after it (as was done in the Bond ball mill tests in this work), may
be a further option to improve energy efficiency by reducing overgrinding in the ball mill.
ACKNOWLEDGEMENTS
This project is carried out under the auspice and with the financial support of the Centre for Sustainable
Resource Processing, which is established and supported under the Australian Government’s Cooperative
Research Centres Program. The authors would like to thank A Gardula, S Nadolski and C Wärnelöv of
Köppern Machinery Australia; R Vasquez, P Nielsen, J Douglas, B Karadkal, W Bruckard, S Jahanshahi and
R Holmes of CSIRO Process Science and Engineering; M Daniel of CMD Consulting; and M Powell and T
Napier-Munn of the JKMRC, for their input to the study.
REFERENCES
Bearman, R, 2006. High pressure grinding rolls – characterizing and defining process performance for
engineers, in Advances in Comminution (ed: S K Kawatra), pp 3-14 (The Society for Mining,
Metallurgy and Exploration: Littleton).
Bond, F C, 1961. Crushing & grinding calculations part I, British Chemical Engineering, 6(6):378-385.
Daniel, M, 2007. Energy efficient mineral liberation using HPGR technology, PhD thesis, University of
Queensland, Brisbane.
Fuerstenau, D W and Abouzeid, A –Z M, 2007. Role of feed moisture in high-pressure roll mill comminution,
International Journal of Mineral Processing, 82(4):203-210.
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Morley, C, 2006. High pressure grinding rolls – a technology review, in Advances in Comminution (ed: S K
Kawatra), pp 15-39 (The Society for Mining, Metallurgy and Exploration: Littleton).
Morrell, S, 2008. A method for predicting the specific energy requirement of comminution circuits and
assessing their energy utilization efficiency, Minerals Engineering, 21:224-233.
Musa, F and Morrison, R, 2008. A more sustainable approach to assessing comminution efficiency, in
Comminution 2008 [CDROM], (MEI: Falmouth).
Neumann, E W, 2006. Some basics on high pressure grinding rolls, in Advances in Comminution (ed: S K
Kawatra), pp 41-49 (The Society for Mining, Metallurgy and Exploration: Littleton).
Norgate, T N and Weller, K R, 1994. Selection and operation of high pressure rolls circuits for minimum
energy consumption, Minerals Engineering, 7(10):1253-1276.
Ntsele, C and Sauermann, G, 2007. The HPGR technology – the heart and future of the diamond liberation
process, in Diamonds – Source to Use 2007, 21 p (The Southern African Institute of Mining and
Metallurgy: Randburg).
Otte, O, 1988. Polycom high pressure grinding principles and industrial application, in Proceedings of the
Third Mill Operators’ Conference, pp131-136 (The Australasian Institute of Mining and Metallurgy:
Cobar)
Patzelt, N, 1992. High pressure grinding rolls, a survey of experience, in IEEE Cement Industry Technical
Conference, 10(14):149-181 (Institute of Electrical and Electronics Engineers: Dallas).
Rosario, P and Hall, R, 2008. Analyses of the total required energy for comminution of hard ores in SAG mill
and HPGR circuits, in Procemin 2008 V International Mineral Processing Seminar, pp 129-138
(University of Chile: Santiago).
Rule, C M, Minnaar, D M and Sauermann, G M, 2009. HPGR - revolution in platinum?, Journal of the
Southern African Institute of Mining and Metallurgy, 108:23-30.
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FIGURE CAPTIONS
Fig 1 – Flowsheets of the four circuit configurations tested and the Bond ball mill work index (BBWI) test.
Fig 2 – Relationship between specific pressing force and specific energy consumption, for 1.0 m high
pressure grinding rolls using porphyry copper ore.
Fig 3 – Effect of specific pressing force on product size distribution, for 1.0 m high pressure grinding rolls
using porphyry copper ore.
Fig 4 – Relationship between reduction ratio and specific energy consumption, for 1.0 m high pressure
grinding rolls using porphyry copper ore.
Fig 5 – Comparison of cumulative specific energy consumptions versus cumulative reduction ratios for the
flowsheet options tested.
Fig 6 – Comparison of the performance of Flowsheet A (3.0 N/mm2) against the first two stages of Flowsheet
C. Note that the 0.25 m high pressure grinding rolls (HPGR) outperforms the 1.0 m HPGR in the subsequent
grinding stage.
Fig 7 – Relationship between measured cumulative specific energy and the amount of new fines passing 75
µm generated.
TABLE CAPTIONS
Table 1
Test results for Flowsheet A using a specific pressing force of 4.5 N/mm2.
Table 2
Test results for Flowsheet A using a high pressure grinding roll (HPGR) specific pressing force of 3.0 N/mm2.
Table 3
Test results for Flowsheet B.
Table 4
Test results for Flowsheet C.
Table 5
Test results for Flowsheet D.
Table 6
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Specific energies of each flowsheet tested and the corresponding energy efficiencies relative to flowsheet D.
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FIGURES
Flowsheet A Flowsheet B
1.0 m HPGR
1.0 m HPGR
1.0 m HPGR
BBWI Test
0.25 m HPGR
0.25 m HPGR
7 mm CSS
BBWI Test
Flowsheet C Flowsheet D
1.0 m HPGR
0.25 m HPGR
0.25 m HPGR
8.0 mm Screen
BBWI Test
7 mm CSS
2.3 mm CSS
BBWI Test
BBWI Test
-0.212 mm
-3.35 mm
Bond Mill
Fig 1 – Flowsheets of the four circuit configurations tested and the Bond ball mill work index (BBWI) test.
15
y = 0.5306xR² = 0.9484
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Sp
ecific
ene
rgy c
on
su
mp
tion
(kW
h/t)
Specific pressing force (N/mm2)
Fig 2 – Relationship between specific pressing force and specific energy consumption, for 1.0 m high
pressure grinding rolls using porphyry copper ore.
