Mine Asset Management Assignment

DEPARTMENT OF MINING ENGINEERING

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Milthon

Texto escrito a máquina

311548

Milthon


MINE ASSET MANAGEMENT AND SERVICES

Milthon


Milthon


Dr. MAHINDA KURUPPU

Milthon


MINING SERVICES

Milthon


Milthon Chambi (ID: 15321327)

Milthon


30/05/2013

Milthon


Milthon Chambi

Mine Asset Management Assignment 3

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Table of Contents

1. INTRODUCTION................................................................................................................... 2

2. DEWATERING AND OTHER SERVICES ........................................................................ 3

2.1. Pump selection. ........................................................................................................... 3

2.2. Total mine power requirement. ................................................................................ 8

3. WINDERS .............................................................................................................................. 8

3.1. Mechanism of single winder. ................................................................................... 8

3.2. Mechanism of double winder. ................................................................................ 10

3.3. Mechanism Koepe. .................................................................................................... 11

4. SPEED VARIATION AND TYPICAL HOIST CYCLE. ................................................. 12

5. TENSION HOISTS CALCULATION ............................................................................... 14

6. HOISTING’S PARTS DESCRIPTION ............................................................................. 15

6.1. Head rope .................................................................................................................... 15

6.2. Tail rope ....................................................................................................................... 15

6.3. Angle of wrap of rope drums system (Koepe winder) and variations. ....... 16

6.4. Rope fleet angle. ........................................................................................................ 16

6.5. Main features of a typical rope construction. .................................................... 17


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1. INTRODUCTION The following report is related to important issues, equipment and parts associated

to underground mining. The first part of the report shows how to deal with a problem

related to mine dewatering. Operation point, pumps selection according to the

power consumption and size (B:3 and B:4 pumps) are presented in this part.

Furthermore, a short calculation of the total cost related to power consumption per

shift ($404.6 per shift) for pumps, mine ventilation and a jumbo drill is shown in this

part.

The second part of the report is related to hoisting systems. Types of hoisting

systems, rope characteristics, tensions calculation are shown in this part.


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2. DEWATERING AND OTHER SERVICES

2.1. Pump selection. An underground hard rock mine having two shallow levels in its development

phase is confronted with finding a suitable solution for dewatering. The depths

and the average estimated flow rates are given below:

Level 1 – 75 m below surface, Q= 10l/s; Level 2 – 150m below surface, Q=15 l/s

The mine personnel are considering 2 options:

a. Option 1: Pump directly from each level to the surface discharge point. A

pump should be located at each level. Pipe diameters are 70 mm (level 1)

and 80 mm (level 2) respectively.

Operation point of the pump.- The operation point equation of the pump is

derived from the Bernoulli equation and depends on the difference between

discharge and suction levels as well as losses in the system. The following

equation represents the head of the pump.

Hpump = (Z2 – Z1) + Hlosses

Hlosses = Losses in pipes + Losses in accessories

Losses in pipes = 90/1000 = 0.09 metres/metre

Level 1 to ground surface Hpump = 75 + 0.09 x (75+50)

Hpump = 86.25 metres

Power requirement (Pumping water from level 1 to ground surface):

9800 86.25 0.010.8

10.6


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Hpump = 168 metres


9800 168 0.015

0.830.9

b. Option 2: Pump to the upper level (or surface from level 1). Pipe diameters

are 100 mm (surface to level 1) and 80 mm (level 1 to level 2).




9800 86.25 0.0250.8 26.4

Level 2 to ground surface Hpump = 75 + 0.09 x 75


Power requirement (Pumping water from level 2 to level 1):

9800 81.75 0.0150.8 15

Determine the power requirements assuming that all pumps work at 80%

efficiency. Also select suitable pumps using the pump performance curves

attached.


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Table 1. Summary of power requirement (kw) and pump size for different options.

Option Pump service QuantityHead pump

Power (Kw) Pump

selected (l/s) (m) (Kw)

1 From level 1 to ground surface 10 86.25 10.57 B:3From level 2 to ground surface 15 168.00 30.87 B:5

2 From level 1 to ground surface 25 86.25 26.41 B:4From level 2 to level 1 15 81.75 15.00 B:3

Figure 1. Pumping system configuration for option 1.


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Figure 2. Pumping system configuration for option 2.

c. Pump selection.- The following considerations have been taken into account to choose the best

option:

Power consumption for option.

Size of the pump (Cost increases as size increase)

Regarding power consumption (see table 1), there is no significant difference

between option 2 (41.41 kw) and option 1 (41.44 kw).

Regarding size of the pump (see table 1), option 2 is the most effective option

because the pumping system involves smaller sizes (B4 and B3) compared to

option 1 (B3 and B5); smaller sizes involve less capital costs.

Answer: Therefore, option 2 is the best choice.


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Graph 1: Pump selection option 1

Graph 2: Pump selection option 2


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2.2. Total mine power requirement. Determine the total mine power requirement considering other electrical

equipment that includes jumbo drills (200 kW total and 40% utilisation);

ventilation fan, compressor and general power (300 kW total). What would be

the cost of electrical power per 8-hr shift @$0.12/Kwh?

Solution: In order to calculate the energy cost, it has been considered that fans and

pumps are working 8 hours per shift.

Utilized hours for Jumbo drill = Available hours x Utilization = 8 x 0.4 = 3.2

hours.

Energy cost (kw – h) for the jumbo drills, ventilation and pumps is as follow:

- Energy cost for jumbo drills = 200 x 3.2 x 0.12 = $76.8/shift

- Energy cost for ventilation = 300 x 8 x 0.12 = $288/shift

- Energy cost for pumps = (26.42 + 15) x 8 x 0.12 = $39.8/shift

Then,

Total power consumption per shift = 76.8 + 288 + 39.8 = $404.6/shift

3. WINDERS Winders can be classified into single, double, Koepe and Blair multi rope. The

following lines will describe only the three first winders.

3.1. Mechanism of single winder. In a single winder mechanism the rope is storaged in only one winder (drum).

According to the winder configuration single winder hoists can be single drum or

divided single drum (see figure 3). In addition, single winder hoists can be

balanced (divided single drum) and unbalanced (single drum). In balanced

hoists due to the payload and weight of the rope, the maximum unbalanced load

occurs when the loaded conveyance is at the bottom of the shaft.


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Single drum - unbalanced hoist has one rope and one conveyance. These hoists

are used generally for shaft sinking and auxiliary hoists. The common

application is for escape, low service applications and shallow services.

Single drum – counterweighted hoist has two ropes and the winding occur in

opposite direction; in this way one conveyance descends while the other one

ascends.

Favourable features:

• Single winder hoist are suitable for shallow shafts with one layer of rope.

• Divided single drums are suitable for deeper shafts.

• Regarding balanced divided single drum, this can efficiently serve more

than one level since the counterweight location is not important.

• Single winder hoists are applied commonly to vertical shafts up to

approximately 460 metres depth. Shafts with slopes between 150 – 300

are up to approximately 1100 metres.

• Simple electrical control.

• Simple design of the winders foundation compared to double and friction

winders.

Drawbacks:

• Unbalanced systems hoists have high operating costs and this rises with

long hoist distances and higher tonnages. In other words, unbalanced

hoists require high torque and therefore high power consumption.

• Efficiency reduces when these hoists are used in multilevel production

because of the skip spotting in different levels.


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Figure 3. Schematic of hoist classification.

Source: Handbook of mining Engineering 2nd Edition.

3.2. Mechanism of double winder. These hoisting mechanisms are more complex compared to single drum

winders. Double drum winders are equipped with clutch mechanisms. In a

double drum winder the ropes are rolled in different drums (see figure 3)


• High efficiency to serve different levels.

• Double drum winders can be regulated to operate in multiple levels.

• Less energy consumption due to the balancing of the loads; however a

high torque is required to begin the cycle.

• The ropes can be adjusted to serve different levels because the presence

of skip and counterweight.

• Quick rope adjustments when enlargement of the rope occur.

• The life expectancy for these ropes is between 100 000 and 150 000

cycles.

• Easy procedures to change ropes compared to Koepe winders.

• Complex electrical control compared to single winders.


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Drawbacks:

• Higher acquisition cost compared to single drum winder. Big drum sizes

involve more weight, complex fabrication costs (bigger machines).

• Complex installation procedures compared to single winder hoists. In

addition high skill workers are required to align the drums.

• Requires complex design of foundation compared to single winders.

3.3. Mechanism Koepe. The winder Koepe is constituted by a wheel with a groove lined with friction

material to avoid slippage. Compared to other hoisting systems, in this case the

hoist rope is not stored on the wheel. Köepe winders are usually applied for

operating two positions (loading and dumping) at the same time.


• Lower power and torque required. Smaller ropes sizes are used in Koepe

winder. This involves smaller drum sizes; as a result these winders have

lower torque, lower power and lower manufacturing costs. For instance,

the cost in Koepe winders is 60% of the cost of a drum hoist with the

same capacity.

• Koepe Winders work efficiently with high payloads and relatively shorter

hoisting distances compared to drum winder.

• Smaller motors are used because of the load balance (loading – dumping

cycle).

• Single conveyance configuration has the same flexibility at single drum

winders.

• Lighter construction because no multilayers ropes are used compared to

drum winders.

• Higher rope’s life (200 000 to 350 000 cycles) compared to winder drums

(100 000 to 150 000 cycles).


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Drawbacks:

• Köepe or friction winders are less flexible to hoist from multiple

elevations. This is because the conveyances have a fixed position

between them (loading and dumping conveyances).

• Limited payload range capacity (no more than 0.5 times the weight).

• There is not flexibility to manage different load ranges consecutively. The

tension in the ropes needs to be kept similar to avoid excessive wear.

• High capital cost when changes of ropes are required.

• There is risk when head ropes are wet because large breaking and

acceleration forces are produced. This occurs because the friction

coefficient changes with wet conditions.

4. SPEED VARIATION AND TYPICAL HOIST CYCLE. In order to convey loads from a lower level to an upper level changes on speed and

times are presented. The variation of speed versus time is named as cycle time. The

cycle time for a hoisting system usually starts with loading (ore material) and finishes

with dumping. Figure 4 shows a cycle time for a mine hoisting system and the

description of it is shown below.

Acceleration time of the creep (tac).- This acceleration occur at constant acceleration

rate with skip loaded (short time) from a point in an upper level to the loading point in

a lower level).

Time of the creep speed out (tco).- This time depends on the guides system and

tipically this speed is ±0.5 m/s in the head frame for hoist drums and friction hoists.

Acceleration time (ta).- It is the time that takes to reach a speed of constant velocity

at a constant rate of acceleration. Depending of the application the acceleration rate

can vary. The rates of the acceleration for drum hoisting systems are between 0.6

m/s2 and 1 m/s2 and between 0.5 m/s2 and 0.8 m/s2 for man and material hoist,

while for friction hoist systems are limited to 1.5 m/s2.


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Full speed time (tfs).- It is the time at constant speed with skip loaded after. Generally

it is the largest conveyance distance. Conveyance speed are less than 18 m/s for

double drums hoisting, 10 m/s for single drum and 18 m/s for friction hoisting.

Retardation time (td).- It is the time required to reduce the speed at a constant

acceleration rate to allow stop the hoist for dumping purposes. During this stage the

energy is dissipated as friction through the brake systems. For drum winders the

retardation is usually between 0.5 m/s2 and 0.9 m/s2. For Koepe hoist the retardation

rate is limited to 1.52 m/s2.

Creep speed in (tci).- The distance depends on the type of mechanism and it is

between 5m to 7m.

Loading and dumping time.- This depends on the load (tonnage) , rates and ways of

loading and dumping and type of skip.

Figure 4. Schematic of hoist classification.

Source: Handbook of mining Engineering 2nd Edition.


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The formulas to calculate the cycle time are:

5. TENSION HOISTS CALCULATION The high tension of a friction winder rope in one side of the driving drum is 20 kN.

Find the low tension. The angle of wrap is 180˚. Assume that the coefficient of

friction is 0.23

Solution: Tension values in a hoist drum can be calculated by the following equation:


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Where:

T1 : Tension of the rope (high tension) = 20KN

T2 : Tension of the rope (low tension)

µ: Friction coefficient between sheave and rope =0.23

θ: Contact angle between sheave and rope = 1800 = π radians.

20 .

9.7

6. HOISTING’S PARTS DESCRIPTION 6.1. Head rope

Head ropes are used in Koepe winders hoisting systems to pull the conveyance

device toward the dumping point. These ropes work in direct contact with the

winder drum friction (see figure 5). The two extremes of the rope are connected

to the conveyance (one end rope connected to a different conveyance).

Regarding design and operation considerations, the following parameters should

be taken into account:

• The tension on the rope shouldn’t differ significantly to avoid wearing.

• The load (payload) cannot exceed 11.5% of the breaking force for static

conditions and 15% for dynamic conditions.

The main functions of a head rope are:

- Pull the conveyance (skip) from the loading point to the dumping point. Head

ropes are perhaps some of the most important parts in a hosting system. These

are subject to excessive wear and fatigue loads.

6.2. Tail rope Tail ropes are placed in the inferior part of the friction system with opposite

direction to the head rope. In friction hoisting systems, using tail ropes make


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possible to balance the head rope weight. As a result, lower peak horsepower

can be achieved compared to drum hoisting systems. Most of the problems with

the use of tail ropes are related to the balance of the hoisting system. Therefore

ratio tail/head rope is very important to reduce the parameters listed below:

• The maximum and RMS torque of the puller motor/shaft.

• The maximum motor power.

• The required braking torque.

6.3. Angle of wrap of rope drums system (Koepe winder) and variations.

The angle of wrap is the contact angle formed between the sheave and rope. In

most of the cases the wrap angle is 1800. For purposes of tension calculation of

the ropes, θ is expressed in radians. Adjacent sheaves in the systems can

cause a reduction of the wrap angle. In addition, low wrap angles may produce

slippage of the rope around the drum, diminishing the life of the rope when

fluctuation of loads occurs suddenly.

Figure 4.Wrap angle “θ” between sheave and rope.

6.4. Rope fleet angle. The fleeting angle is the angle made by the head rope between the drum and

the sheave (see figure 5). In order to avoid excessive wear of the rope, large

fleet angles should be avoided. In addition, large fleet angles may cause the


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rope either piles up at the drum or disorder by jumping pitches across the drum

when the rope return to the drum. It is recommended that the fleet angle should

not exceed 1.5° for triangular strand and 2° for grooved drums in parallel, being

0.25° the minimum fleet angle for multi-layer coiling. Angles off this range can

cause coiling of the rope itself; as a result damage to the drum and rope can be

caused.

Figure 5. Fleet angle in a hoisting system.

6.5. Main features of a typical rope construction. In the construction of most wire ropes, a number of individual wires are wound

around a core to form a strand. Since ropes applications demand high

resistance for extremely fluctuant loads their construction structure is quite

complex (see figure 6 and figure 7). Depending on the direction of the wound,

ropes can be regular and lang lay wounded (see figure 8). Figure 7 shows how

the strands are rolled around a core to form the rope.


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Figure 6. Constitution of a rope.

Source: Mining Engineering Handbook 3rd Edition.

Figure 7.1. Rope types (A) regular and (B) Lang lay, Figure 7.2. Cross section of

a rope. Source: Mining Engineering Handbook 3rd Edition.

The main features to be considered in rope construction are the wire, strands,

cores, and lay. Varying these factors, ropes with different characteristics can be

constructed. The shape of the wire, strand, strand configuration arrangement

and wounded direction will determine the two main characteristics for rope which

are: breaking strength and weight per unit length. Furthermore, there are three

main type of ropes used in mining hoisting and these depends on the way and

direction of how each individual wire and strand are wounded. These are round-


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strand, flattened –strand and locked-coil (see figure 8). Additional ropes

characteristics for rope selection are shown below:

• Resistance to fatigue loads.

• Resistance to abrasion.

• Resistance to crushing and distortion.

Rope selection also involve diameter of the drum or sheaves, fleet angles and

factor of safety (FOS). For hoisting applications, FOS is the critical parameter

that should be consider. This depends on the hoisting application and the load to

be conveyed (personnel or material). FOS specification can vary depend on the

country and mining regulations. In the case of WA, the mining regulations for

ropes are specified in the Part 11 of “Mine Safety and Inspection Regulations

1995”. “AS3569 – 2010” gives guidelines for minimum requirements for rope

selection (Based on 2408: 2004 and ISO 17893: 2004).

Table 2: Rope applications and main features (strengths and weight per length). Source: Handbook of mining Engineering 2nd Edition.


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Figure 8.1. Rope types according to cross section

Source: Introductory to mining engineering.

Mine Asset Management & Services

MINE SERVICES - INDIVIDUAL ASSIGNMENT 3 (20%)

Attach this to your submission.

1. Dewatering and other services (12 marks)

An underground hard rock mine having two shallow levels in its development phase is confronted with finding a suitable solution for dewatering. The depths and the average estimated flow rates are given below:

Level 1 – 75 m below surface, Q= 10 l/s; Level 2 – 150 m below surface, Q= 15l/s

The mine personnel are considering 2 options:

Option 1: Pump directly from each level to the surface discharge point.A pump should be located at each level. Pipe diameters are70 mm (level 1) and 80 mm (level 2) respectively.

Option 2: Pump to the upper level (or surface from level 1).Pipe diameters are 100 mm (surface to level 1) and 80 mm (level 1 to level 2).

Pipe head losses are 90 m per 1000 m length. Pipes are laid vertically via a service shaft and discharged at a point 50 m from the shaft entry (this section laid horizontally). Consider pipe friction and ignore other pipe losses. Determine the power requirements assuming that all pumps work at 80% efficiency. Also select suitable pumps using the pump performance curves attached. Considering both the likely capital costs and the running costs which option is better? Give reasons while stating any assumptions that you make. Note that the capital cost increases with pump size and capacity.

Other: determine the total mine power requirement considering other electrical equipment that includes jumbo drills (200 kW total and 40% utilisation);ventilation fan, compressor and general power (300 kW total). What would be the cost of electrical power per 8-hr shift @$0.12/Kwh?

2. Winders (8 marks)

2a. Describe the mechanisms of single, double and Koepe winders and list their favourable features and drawbacks.

2b. What are the phases of speed variation associated with a typical hoist cycle? Give the reasons for such variation.

2c. The high tension of a friction winder rope in one side of the driving drum is 20 kN. Find the low tension. The angle of wrap is 180˚.Assume that the coefficient of friction is 0.23.

2d. Briefly describe the following:

• Head rope and its function • Tail rope and its function • Angle of wrap of rope-drum system (Koepe winder), and how can it be varied • Rope fleet angle • Main features of a typical rope construction

Assessment criteria:

Answer is numerically correct, with all workings clearly laid out

Full marks

A small error exists in assumptions or background calculations. All workings are clearly laid out

Reduced marks

A small error exists in assumptions or background calculations. Answer is NOT clearly laid out.

No marks

Major errors exist in assumptions or background calculations. Answer is clearly laid out.

No marks

Major errors exist in assumptions or background calculations. Answer is NOT clearly laid out.

No marks

Question is only partially attempted or not attempted at all.

No marks

• This assignment is to be solved individually. Submit a full report. • Attach a copy of your working calculations • Submit by 12 noon on Friday 31 May. • Late penalty – zero marks.

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Mine Asset Management Assignment