Rajiv Kalra

7/27/2019 Rajiv Kalra

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This paper Evaluates the merits of large geared mills versus gearless driven mills considering:

Currently available systems in terms of power and mill diameter

Drive type Present Max Power

Single motor geardrive

8000kW - 10000kW

Dual motor geardrive

16000kW20000kW

Gearless motordrive range

18000kW 35000kW

Gearless

Synchronous

Asynchronous

Overall efficiency of electrical power consumed vs mechanical output power

Capital cost Running costs Cooling: air vs water cooling Installation and delivery time


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REDUCED TORQUE PULSATIONS USING 24 PULSE SER DRIVES

USING PWM TECHNIQUES - SINUSOIDAL ROTOR CURRENTS

SMALL HARMONIC CONTENT - NO HARMONIC FILTERS REQUIRED

LOW TORQUE PULSATIONS - INCREASED GEAR LIFE

SER mature and ready for use 40 SER installations world wide

Speed variation required is in the range of +/- 15% of synchronous motor speeds. Successful operation of 2 x 6.5MW (Phu Kham, Laos) Three 2 x 7MW units under manufacture (Pascu Lama, South America) 2 X 10MW dual drive mills are achievable and quoted to various sites world wide Dual hydraulic inching drives provide safer and convenient operation with the added

advantage of locked charge detection.

Geared and Gearless SAG Mills must consider variable speed ability for process reasons

Issues regarding load sharing & torque pulsation Slip Energy Recovery (SER) and Variablefrequency drives have been resolved through technological advances

SLIP ENERGY RECOVERY DRIVE


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What type of drive system best suitsthe particular application??

Real data: efficiency, durability,

availability and value for money??

Lets clear up this confusion usingaccurate information obtained fromrecent projects.

CLIENT CONCERNS


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AGMA321.05 AGMA6004-F88 ANSI/AGMA6114-A06

1968 1988 2006

GEAR DESIGN

Mr Deneckis (FALK) paper presented at the 96 SAG conference, details the

then largest gear drive in operation on a SAG mill (34ft x 18ft) at Escondida13.4MW (18,000hp) - 1995

ISO 7

AGMA 10

HB300~350

Gear

ISO 5

AGMA 12Machineprecision

HRC57~61Tooth

Hardness

Pinion

Shop test runSINO Iron project

7.9m X 13.6m Ball MillTwin 7,800kW drives


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CITIC HIC 16m CNC gear hobber inproduction (Schiess Brighton)

HISTORY

Historically OEMs did not have access to

larger single piece special alloy castingsand larger gear cutters

To the benefit of consumers CITIC HIC hasnow overcome this limitation and mineoperators can now consider more costeffective large gear driven mills

Australia SINO

Iron Ball MillGear PourOD:11.7m Net

Wt:118tMolten steel

Wt:375t


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Inspection & testingInternational standardsCITIC HIC manufacturers over a hundred gear sets every yearAll activities are done in house from casting, forging, heat treatment, carburizing,machining, gear cutting, shop assembly and transport

Inspection and test plans follow international ASTM & ISO standards with a largeteam of NDT and inspection supervisors for all equipment

ManufactureTen gear cutters at a single works: 2 x 5m, 3 x 8m, 1 x 10m, 1 x 12m, 1 x13m and 2 x 16m (one in climate control).

MANUFACTURE

Gear CastingsMAGMA software utilizing full ring risers for solidification and cooling.Actual metal pour is approximately 2.5 times the net weight of the ring gear. (eg amolten pour of 375t result in a 118t gear)

The full ring gears at CITIC HIC are normally a single pour even though they may bein halves or quarters.Ensuring uniform chemical analysis and even hardness after heat treatmentPouring capacity is up to 600t and hence net gear weights of up to 250t.


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MECHANICAL INTERFACE

Total weight of the poles are approximately 20% heavier than the gear and need to beindividually installed after the rotating element is in place on the foundations


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MECHANICAL Motor Girth Gear Reducer Total Mechanical Efficiency

Gearless Drive 97% N/A N/A 97.0%

LS Synchronous 97% 99% N/A 96.0%

HS Asynchronous 96.5% 99% 98.5% 94.1%

ELECTRICAL Starter/VSD VSD TransformerHarmonic

FilterSupply

TransformerTotal Electrical Efficiency

Gearless Drive 99% 98.5% 99.5% N/A 97.0%

Fixed Speed Low SpeedSync (LCI)

99% 99% 99.5% N/A 97.5%

Variable Speed LowSpeed Sync (VSI)

98.5% 99% 99.5% N/A 97.0%

Fixed Speed High Speed

Asyn (LRS) 99.9% N/A N/A 99% 98.9%Variable Speed HighSpeed Asyn (SER)

99.7%99.8% (rotorcircuit only)

N/A 99% 98.5%

RESULTS

All the above figures are based on the averages of documented figures provided by vendors in datasheets or are derivedfrom published papers (referenced in this paper)

OVERALLMechanical Efficiency Electrical Efficiency Total Overall Efficiency

Gearless Drive 97% 97% 94.1%

Fixed Speed Low Speed Sync 96% 97.5% 93.6%

Variable Speed Low Speed Sync (VSI) 96% 97% 93.1%

Fixed Speed High Speed Asyn (LRS) 94.1% 98.9% 93.0%

Variable Speed High Speed Asyn (SER) 94.1% 98.5% 92.7%


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Approx. relative costGearless Drive Highest - 140%Fixed Speed Low Speed Sync 125%

Variable Speed Low Speed Sync 130%Fixed Speed High Speed Asyn (LRS) Lowest - 100%Variable Speed High Speed Asyn (SER) 110%Variable Speed High Speed Asyn (VSI) 115%

Capital cost comparison (excl Installation & Commissioning) 2x 10MW or 20 MW.

RESULTS

Running cost comparison.20 MW Fixed Speed Ball Mill

WRIM/LRS SYN/LCI GEARLESSSystem efficiency 93.0% 93.6% 94.1%

Power extra cost pa(due to inefficiencies) $963,802 $875,542 $802,851Gear Lubricant $130,000 $130,000 $0Lost interest due to extra capital cost 0 $368,000 $592,000Total pa $1,093,802 $1,373,542 $1,394,851

Total EXTRA pa over cheapest $0 $279,740 $301,049Over 20 years $0 $5,594,800 $6,020,980

20 MW Variable Speed SAG Mill

WRIM/SER SYN/VSI GEARLESS

System efficiency 92.7% 93.1% 94.1%Power extra cost pa(due to inefficiencies) $1,008,361 $949,013 $802,851

Gear Lubricant $130,000 $130,000 $0

Lost interest due to extra capital cost $0 $296,000 $440,000

Total pa $1,138,361 $1,375,013 $1,242,851

Total EXTRA pa over cheapest $0 $236,652 $104,490

Over 20 years $0 $4,733,040 $2,089,800


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Cooling requirements Air cooling is the most common form of cooling for motors and drives. Gearless motors and large cyclo convertors use water cooling

The heat dissipation represents the motor and drive losses (approx 4%) A 20MW drive requires approx 800 kW of heat dissipation In a GMD this equates to approx 2lpm for each kW representing approx 1600lpm of cooled

water Typically a cooling tower or chiller is required in a closed loop system due to the lack of fresh

water This adds approx $1million for 20MW and requires power to run, adding to running costs

(Approx 480kW for 20MW), or conservatively 1600lpm of water on a continuous basis.

Installation and delivery time for mills 15MW and above The girth gear is the longest lead time item on a geared mill at approximately 9 to 14

months On a gearless mill the Gearless drive is the longest lead time item at 12 to 18 months. The installation time for a geared drive is approx. 12 to 16 weeks (approx. 8000 man hrs) For a gearless drive it is approx. 10 to 12 weeks for the mill and 10 to 15 weeks for the

Gearless drive making a total of 18 to 24 weeks (minimum 20,000 man hours). This increases the capital cost of the installation by a minimum US$2 million and causes and

additional 2 to 3 months to the project schedule. The additional time and costs associated with commissioning of a gearless drive vs geared

drive has not even been considered

OTHER ISSUES


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CONCLUSIONS

For mills above 12.2m in diameter or over 20MW of power there is currently no viablealternative to a gearless drive.

For mills 12.2m or less in diameter and 20MW or under in power, gear driven systems offer amore viable alternative to gearless drives, delivering nearly equivalent efficiency, much lowercapital cost, easier installation, simpler cooling, shorter installation time and quicker (2-3 months)project overall startup schedule.

SAVINGS ON 20MW BALL MILL Capital cost approx. $8 million

Running cost approx. $6 million Cooling approx. $1 million Installation approx. $2 million Approx. saving over 20 years $17 million

SAVINGS ON 20MW SAG MILL

Capital cost approx. $6 million Running cost approx. $2 million Cooling approx. $1 million Installation approx. $2 million Approx. saving over 20 years $11 million

Rajiv Kalra

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