Transportation of coal
Transportation of coal
Submitted to:Mam Sumaira kanwalSubmitted by Navira YounasRoll no# 2225/June/2015
INTRODUCTION Coal: Coal is heterogeneous, sedimentary organic rock. It originates from plant material, under elevated pressure and temperature for a long period of time.
Methods of extracting coal:
Generally Coal is extracted by two mining methods:Surface miningUnderground miningSurface mining: If coal seam is near to the surface, then it can extracted by surface mining methods. Underground mining: While if coal seam is under considerable depth, then it is extracted by underground mining methods.
After excavation of coal, transportation of coal from mine to plant is necessary for usage of coal.
The factors that influence the design of transport system of any mine are:
Seam heightReserve tonnageDesired daily productionNumber of shifts worked per dayGeneral shape of propertySeam contoursCharacter of roof and floorAverage seam rejectsDaily tonnage of mine rock handledType of mining equipmentMining plan and general projectionsMaximum length of main haulage
The environmental impacts of coal transportation include:
Air pollutionWater pollutionSolid wastesNoise levelSafety hazardTraffic hazards Direct environmental impacts: Direct environmental impacts can occur at the mine, where the coal transferred, transported or loaded.Indirect environmental impacts: Indirect environmental impacts from coal transportation largely results from the combustion of fuel for the transportation itself.
Following equipments are used for transportation of coal:
Railroad trainsCoal slurry pipelinesBarge transportHighway trucksConveyers belt
Railroad trains: The two types of train configuration used for transportation of coalGeneral freight trainDesignated unit train coalGeneral freight train: A general freight train carries numerous types of cars, some of which can be coal carrying hopper cars. General freight trains typically handle from 1500 to 6000 net tons. Typical haul distance for coal being moved by general train is 100 to 500 miles. Designated unit train: The specifically designated unit coal only handles coal from a single origin to a single destination so that it much faster and cheaper than the general trains for coal movement. Unit trains generally have one way haul distances of 250 to 2000 miles and carry from 2500 to 12500 net tons per trip.
Coal slurry pipelines:In a coal slurry pipeline, the coal must first be ground to a uniform size of 100%-14 mesh with not more than 20%-325 mesh by successive crushing and pulverization. The coal is then distributed in the liquid phase by agitation and mixing and passed through the pipeline to the end use point. Coal slurry pipeline can make use of water, methanol, crude oil, or other liquid transport medium. The coal is separated from liquid phase at the destination for subsequent use in combustion. The liquid may then disposed of by reuse or as fuel, discharge to receiving waters or returned to the point where the coal is added the pipeline. The major variables affecting slurry pipelinesPipe diameterPipeline lengthSlurry velocitySolids concentration. Slurry pipelines can ranges up to 48 inches in diameter and can have length ranging from 100 to 1200 miles. Solids flow velocity is about five feet per second.
Slurry pipelines have following advantages:
It can be able to move large amounts of coal over long distances.Efficient cost with minimum potential for en-route environmental disruption.Operating costs for labor is low.
Disadvantages: Two major disadvantages of slurry pipelines are:Water requirements. Low degree of operational flexibility. A source of water is required in the amount of 220 to 270 gallons per ton of coal moved for a one-way, once through slurry pipeline. Water consumption can be reduced to between 50 to 75 gallons per ton of coal if a two-way recirculating slurry pipeline is employed. It can also be reduced by using methanol and crude oil as a transport medium. The major operational problem is operational flexibility because of the critical transport velocity.
Barge transport:Coal is normally moved in open hopper barges which range in capacity from 1,000 to 3,000 net tons, with average of 1,500 net tons. Ten to s barges are normally located in series. A typical shipment will contain up to 30,000 net tons of coal moving in 10 barges at an average speed of 6 miles per hour. Fuel requirements for barge movement: Fuel requirements for barge movement of coal can be low as 300 to 500 Btu per net ton-mile for downstream movement of large barges, or as high as 800 to 1100 Btu per net ton-mile for upstream movement or coastal movement in small barges. The potentially significant environmental impacts of waterways movement of coal are dust loses during loading, unloading or transport, oil losses from fuel systems of barges, and the emissions from towboat fuel combustion.
Highway truck:There are two type of trucks used in surface mining:Off high wayRegularOff high way: Off high way trucks are used for haulage because of their inbuilt ability for continuous uninterrupted operation.They are of two types:The bottom dumpThe rear dump trucksThe bottom dump trucks will handle aggregate and unconsolidated materials and dump while in motion. The gradient for their efficient operation is 4%. They are primarily used for coal haulage.The rear dump trucks are of three types:Small to medium two axel trucks: good for small pits.Large two axle trucks: can handle large loads and negotiate steep gradients.Large size three axle trucks.
Trucks do suffer from several disadvantages relative to other transportation methods:
Highest unit energy consumption requirements.Highest net operating cost.Greater external damage to highway.
Belt conveyers: Conveyors enable continuous transport of overburden or coal. They are the coal economic means of transport in coal seams with more than 10-12 inclination for working in deep pits 250 m or more where truck transport will become uneconomic. The belt conveyors can be worked up to a gradient of 1 in 3 and thus lead distance is shortened. Besides, belt conveyor are not affected by rain whereas haul roads are deteriorated in rains. Advantages :Conveyor haulage is less sensitive to inflanationary pressures and to fuel shortage.Conveyor haulage is much less labor intensive.Conveyor haulage is environmentally preferable, because it is much quieter and has fewer particulate emissions.Lower unit cost may extend the economic pit life.Operation is less sensitive to inclement weather.Conveyor is more reliable. They can achieve an availability of 90-95%.Disadvantages:The initial cost of conveyor is high.It is location inflexible, which making a truck haul still necessary.Coal dust losses during loading, unloading and transport have adverse environment impact.
Types of belt conveyors
There are many types of belt conveyors used:
Cross pit conveyorHigh angle conveyorShift able spoils conveyor Cross pit conveyor: It can result in lower capital and transportation costs. Loading of cross pit conveyor can be done by dragline, face shovel, bucket wheel. High angle conveyors: High angle conveyors can build with belt widths of up to 3m to carry up to 9000 t of material/hour, provide a lift of over 300 m with steel cord belt and angle of slopes of up to 60. The major advantages of high angle conveyors are:More efficient use of energy. More efficient for elevating material to great heights.Less labor intensives.Shift able spoils conveyors: It conveys the overburden material from the collecting conveyors to the mobile tripper car and is located on the edge of the backed filled benches. The shift able conveyors are stationary.
Long distance electrical transmission: As an alternative solid fuel movement, energy in coal can be sent indirectly to the point of end use via electrical transmission. Transmission of electricity can occur as either alternating or direct current, but in US it is transmitted by high voltage alternating current. Electricity is normally transmitted at 138,000 volts near load centers, but is usually transmitted at either 345 kV or 765 kV over extended distances.
The greatest single environmental problem from coal transportation is coal dust entertainment. Adding water to coal can significantly reduce dust entertainment; the critical dusting moisture content varies with the type of coal. The use of covered hopper cars is not practical for coal transport because of loading difficulties. Chemical additives as well as crude oil or kerosene can also be added to coal, but may also undesirable pollutants.