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Lecture 4 MINE LOADING AND TRANSPORTATION Introduction  Once the rock has been fragmented it needs to be moved to its final destination which could be a waste rock muck pile or ore’s stock pile to feed the processing plant.  From the working face materials are loaded with the use of any of the muc...

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Lecture 4 MINE LOADING AND TRANSPORTATION

Introduction  Once the rock has been fragmented it needs to be moved to

its final destination which could be a waste rock muck pile or ore’s stock pile to feed the processing plant.  From the working face materials are loaded with the use of any of the mucking units into a conveyance which carries it through horizontal, inclined, vertical or combination of both horizontal and vertical routes to the discharge point  Movement of the muck through a horizontal or slightly inclined path is known as haulage and through the steeply inclined to vertical path (up or down) as hoisting

Haulage system

 This can be described under two headings – track and

trackless.  Track haulage includes rope and locomotive haulage, which runs on rail or track.  Trackless systems includes automobile (e.g. trucks), conveyors and transportation through pipes.

Load and haul • In mining, load and haul is necessary for movement of ore and waste from the face to stockpiles or processing plant • There are differences in methods applied depending on the mining method, topography, flexibility and distance from the face to material destination.

Selection of load and haul equipment Loading equipment • Material characteristics of the mine • Capacity • Equipment operating time/life of equipment • Cost Haulage equipment • Haul route requirements • Maneuvering space • Dumping conditions • Engine power and altitude limitations • Axle configuration • Mechanical or electrical drive system

Load and haul terminologies • Capacity -refers to the volume of material that a loading or haulage unit can hold at any point in time e.g. volume of loading machine bucket or truck tray. • Struck Capacity; Volume of material that a loading or haulage is filled to the top with no additional material above the sides or carried on any external attachments such as bucket teeth. • Heaped Capacity; Maximum volume of material that a loading or haulage unit can handle without spillage based on material angle of repose.

• Bank cubic meters (BCM) – is the volume of the insitu/unbroken rock. • Loose cubic meters (LCM) is the rated capacity of bucket carrying loose/fragmented material • Swell factor – is the factor by which fragmented material swell/expand from its insitu condition. LCM Swell factor  BCM • Bucket fill factor - percent of available volume in bucket that is actually filled with material

Surface load and haul There are common systems used in modern mining operations to extract, load and haul waste and ore. They include; • Dragline systems • Loader and hauler systems • Bucket-wheel excavator systems • In-pit crushing and conveying system

Draglines • Draglines are used most frequently in waste stripping to cast material directly because they have higher bucket capacities and greater reach abilities than other excavation equipment • The largest dragline can have up to 170m3 bucket, 122m boom length and weigh 12,700t. Buckets are capable of moving 30– 35 million BCM per year.

Dragline selection The parameters used in the analysis are • ß = High wall slope with the horizontal in degrees • = Spoil pile slope with the horizontal in degrees • D = Overburden depth, • OR = Dragline operating radius • P = Dragline positioning, • RF = Dragline reach factor • S = Spoil pile swell factor, expressed as a decimal • W = Pit width • h = Height of the spoil pile peak above the top surface of the coal • T = Coal thickness

The two major parameters used to select a dragline are dump/operating radius and allowable load Reach factor

RF 

OR  P  RF

Operating radius Height of spoil

Stacking height

D(1  S ) W D   tan  4 tan 

h

RF  D cot  T cot 

Hs  h  D

Example Given the coal mine has a high-wall angle of 71.5 degrees, spoil pile angle of 38.7 degrees and overburden height of 27m. If the material swell factor is 25%, pit width is 37m and coal thickness 2m; calculate dragline reach factor and height of the spoil D(1  S ) W D   tan  4 tan  27(1  0.25) 37 27    60.3m RF  tan 38.7 4 tan 71.6

RF 

RF  D cot   T  h cot 

60.3  27

1 2 tan 71.6  39.5m 1 tan 38.7

Loader and hauler system More material is moved by loaders and truck haulers than by all other excavation systems combined. They are mostly preferred due to their flexibility. There are three different types of loaders used in mining industry; • Wheel loader: 27–45 t • Hydraulic shovel: 27–81 t • Mining shovel: 54–110 t

Wheel loader

Hydraulic shovel

Mining shovel

Bucket size selection • The amount of material in the bucket depends on size and shape of the bucket, digging force and rock characteristics. • Size of the bucket can be calculated when production per hour is known as follows; P T Q 3600  BF  U  A

• Where Q is the bucket capacity, P is the required production (LCM per hour), T is cycle time, BF is the bucket fill factor, U is utilization, and A is the mechanical availability expected over the period of operation.

Sample calculation Given that the annual production of coal required in one mine is 40 million BCM. The mine is planning to operate two shovels of the same size to attain

the required production. Select the bucket size for each shovel given the following information.

•

Estimated Work Cycle = 52 seconds

•

Operating days a year = 350

•

Operating time/day =20hrs

•

Swell factor = 1.2

•

Dipper/bucket Fill Factor = 0.8

• Availability and utilization = 0.9 Note: Average Bucket Payload = Heaped Bucket Capacity x Bucket Fill Factor

40000000 1.2 production / hr   6857m3 350  20 P T 6857  52 Q  3600  BF  U  A 3600  0.8  0.9  0.9 Q  152m

3

Bucket wheel excavators (BWE). • This is one of the continuous operating excavator, others are chain bucket excavators etc. • The BWE digs with a series of evenly spaced buckets attached to the circular wheel at one end of the unit. • The excavated material is fed via a transfer point in the wheel to the belt conveyor system of the excavator for discharge.

BWE production calculations Q

60  F  s Swell factor

where • Q is the theoretical output in bank cubic meters per hour, • F is the capacity of each individual bucket, • s is the number of buckets discharged per minute, and • swell factor is that of the material being excavated

60  V  n D • Where V is the speed of rotation in m/s, n is number of buckets in a wheel and D wheel diameter. s

Sample calculations BWE has buckets with capacity of 2m3/bucket. The wheel has a diameter of 20m with 16 buckets attached to it. If it rotates at a velocity is 0.5m/s and material swell factor is 1.2, find the production per hour if the speed does not change.

60  V  n 60  0.5  16 s   7.64 buckets / min D   20 60  F  s 60  2  7.64 Q   763m3 / hr Swell factor 1.2

In pit crushing and conveying system • Crushing is done in-pit mainly to allow transport of the material out of the pit by a conveyor system. It is used to eliminated a problem of high-cost road construction and maintenance in wet soft ground. • In pit crushing system ranges from completely mobile to fixed systems.

Discrete units haulers • Productivity of mobile equipments like trucks depends on the its carrying capacity and trips per hour which is a function of distance travelled, truck power and road conditions. • Rigid dump trucks are the backbone of haulage equipment for the worldwide mining industry. They are available primarily from five global OEMs Caterpillar, Komatsu, Bucyrus, Liebherr and Hitachi, and with capacities ranging from 36 to 360 t.

Cycle time • Cycle time of haulage trucks include spotting time at the loader, loading, hauling, spotting at the dump, dumping and returning time • Load time; depends on the cycle time of the loader and number of passes required to fill the truck • Haul time; depend on the weight carried, road conditions, travel distance, total rolling resistance • Dumping time; maneuvering and dumping, depending on truck and dumping area conditions; normally 0.6min • Return time; less than haul time since the equipment is empty, and opposite of the grade.

Cycle time

Fleet size estimation • Size of the truck depends on required production and should be matched to size of loader. Rule of thumb suggests 3 to 5 passes loading • Number of trucks is dependent on loading time and production requirements. • Fleet size is the number of trucks required to attain production taking into considerations trucks availability Loading time 

Capacity of haul unit  Cycle time of loader Bucket capacity of loader

Number of required trucks  Fleet size 

Total haulage cycle Spotting time at the loader  Loading time

Number of trucks required in production Availabili ty of a truck

Sample calculation • Given that cycle time of a loader is 30seconds for a loader with bucket capacity of 30t. The loader has to fill a truck of 160t capacity. The distance between the face to dumping location is 3.5 km and the truck travels at the speed of 25 km/h when loaded and 40km/hr when empty. If dumping time is 1.0 minute and trucks have availability of 90%, i. Calculate the fleet size required to match loader’s production. ii. Calculate the production per hour.

160  30 Loading time   2.67min 30  60 3.5  60 travel loaded   8.4min 25 3.5  60 Travel empty   5.25min 40 cycle time  2.67  8.4  1  5.25  17.32 17.32 number trucks   6.5  7 2.67 7 Fleet size   8 trucks 0.9 Production  8  160  1280 t/hr

Underground transportation load and haul • One of the common transportation method in underground is by using loaders and trucks • Size and capacity of machines depends on the required production, energy requirements, headings size, production requirement and working conditions • They are generally smaller as compared to surface equipment.

Load Haul and Dump units(LHD) They are mainly used for underground loading, hauling and dumping in few (10s) metres to low-profile dumper, rail or ore-pass

Underground haulers • There are two kinds of discrete units; those that follow a predetermined path and those that are free to move in any direction • Non-fixed path include the dump trucks while those with fixed path include rail haulage

Theoretical truck productivity • Theoretical productivity is the tones or cubic meters per hour produced by an operating unit if no delays were encountered. This indicates 100% potential, which is rarely achieved. 60  truck rating tonnes / hr  cycle time (min)

Locomotive haulage • Rail transport can be used as gathering and main haulage in the underground mines and tunnels. • The locomotive haulage system works on track and is mainly used as a long distance haulage with gradient ranging from 0.5% to less than 3% • Good roads, efficient maintenance, large output and adequate ventilation are the basic requirements for the success of this system • The weight of rails varies depending upon the weight of locomotive and the number of wheels it has (which could be either four or six). The range is 15–50 kg/m for locomotive weight that varies from 5 to 100 tons.

• Locomotives can either be electric which uses direct current , battery which uses storage batteries, combination of electric and battery, compressed air and diesel operated locomotives • The total force delivered by the motive power of locomotive to make it move/roll, through the gearing, at wheel treads is called Tractive effort. This force is the product of locomotive weight and the coefficient of adhesion between the wheels and rails

Locomotive calculations

TE  RO (WL  WT )

RO    1000 sin   P

TE  V



a g

Where; TE - Total tractive effort in kg RO= running resistance in kg/t WL = Weight of locomotive in tons μ- Frictional resistance in kg/tonne – haul grade angle + for up and – for down a – acceleration of train in m/sec2 + for acc. and – for retardation g – acceleration due to gravity, 9.81m/sec2 P= locomotive power , W V = train velocity in m/s = efficiency of the system

Conveyor system • Belt conveyors have their applications both for surface as well as underground mines. A belt conveyor is basically a continuous strap stretched between two drums • Conveyors can be used when the production is as high as 8,000,000tonnes per year, vertical height of up to 1,200m and gradient of 11%. Conveyors have efficiency of up to 85%

Conveyor capacity Hourly production , T  abV  3600 Where T - is hourly production in tons. a – average cross-section of material loaded on conveyor, and it is given by W2/10 to W2/12 depending on type of material W– is the width of belt in m b – bulk density of material loaded in t/m3. V – belt conveyor speed in m/s.

Shaft hoisting system A shaft hoisting system consists of six major sections, • A loading station for ore or a service station for workers and material • Shaft conveyances called skips for ore transport and cages for transporting workers and material • Ropes that suspend the conveyances • A shaft that connects the underground to the surface and that is equipped with a system to guide the conveyances as they move in the shaft • A head-frame, located on the surface, that supports either the hoist itself and provides the tipping arrangements for the rock • A hoist and hoist room

Hoisting components

Two basic types of hoists are commonly used today: • Drum hoists, in which the hoist rope is stored on a drum. Drum hoists are usually located some distance from the shaft and require a headframe and sheaves to center the hoisting ropes in the shaft compartment and maintain a rope fleeting angle of less than 2° as shown in Figure below. Drum hoist consist of • • • • • •

Single drum hoist Divided single drum hoist Differential Diameter Drum Double-Drum Hoist Multiple rope hoist Bicylindrical Conical Drum Hoists

Drum hoists

Frictional hoists

• Friction hoists in which the rope passes over the wheel during the hoisting cycle. • It consists of a wheel with grooved liner or liners made from a friction material to resist slippage. The hoist rope is not attached or stored on the wheel. • In early installations, the hoist was mounted on the ground, and a single rope was wound around the drum and over the head sheaves to the two conveyances in a balanced arrangement. In addition, a tail rope of the same weight per unit length as the headrope was suspended in the shaft below each conveyance. Thus the only out-of-balance load was simply the payload. Friction hoists can either be a tower mounted or ground mounted.

Hoist production Tonnage of ore that can be handled with each skip can be calculated from SL 

( D / V )  0.4V  12 3600 / TPH

Where • SL- tonnage to be handled by each skip • D- depth in ft • V- velocity in ft/s • And TPH is capacity in tons per hour

The equation is based on the assumption that delay is 12 seconds and acceleration/deceleration rates 2.5ft/s2 (0.3m/s2)

Cycle time of the hoisting system consists of acceleration time ta, constant speed time tv, retardation time tr and load or dump time td. Thus cycle time t in seconds can be numerically expressed as:

Cycle time :t t  2(t a  tc  t r  t d ) Accelerati on time : t a  V / a

Re tardation time : t r  V / r

Accelerati on dis tan ce : ha  0.5at a

Re tardation dis tan ce : hr  0.5rtr

2

2

Where: V – is hoisting speed; a and r – are the acceleration and retardation rates; ha– acceleration distance; hr– retardation distance; hv– constant velocity distance; ht– total hoisting distance from loading pocket to head frame bin.

From the cycle time, skip production per hour can be calculated from 3600  Sc P Tt

Where • P= skip production per hour • Sc = skip capacity • And Tt = skip cycle time

Ore passes • Ore-passes provide a low-cost method to move ore and waste downward between operational horizons in a mine • Flow of material in the ore-pass is mostly by gravity. Material movement is critical to success of ore-passes • Orepass inclination angles are greater than 60° and should have a small amount of inclination from vertical to allow the dumped material’s energy to be dissipated on the orepass footwall and therefore prevent free fall of the material to the orepass bottom. • Orepass fingers that connect to chutes can be as low as 50° in order to reduce the amount of energy transfer from the ore in the orepass onto the chute...