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GENERAL DESIGN ENERGY PRINCIPLES FOR BULK CONVEYING OF PARTICULATE SOLIDS John Dartnall, 200 ! INTRODUCTION These notes relate to belt conveyors, screw conveyors, bucket elevators and other derivatives of these devices that continuously carry or slide particulate dry or partially wet (not where the fluid is used as a carrier) solid materials. The notes do not apply directly to pneumatic and hydraulic conveyors in which the solids are “swept” along by a carrier fluid such as air or water. The no
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  GENERAL DESIGN ENERGY PRINCIPLES FOR BULK CONVEYING OF PARTICULATE SOLIDSJohn Dartnall,200 !INTRODUCTION These notes relate to belt conveyors, screw conveyors, bucket elevators and other derivativesof these devices that continuously carry or slide particulate dry or partially wet (not where thefluid is used as a carrier) solid materials. The notes do not apply directly to pneumatic andhydraulic conveyors in which the solids are “swept” along by a carrier fluid such as air or water.The notes treat the systems in a general way and their purpose is to give an understanding of the underlying general principles. They are not intended to be used for detailed design or selection of equipment. There are design manuals, tables, charts and software programs for this purpose. 2GENERAL LAYOUT OF E UIP#ENT  igure ! shows a general arrangement of typical elements of a system. The diagram shows theconveyors as being hori ontal and the elevators as being vertical. This is not always thesituation. #ften the hori ontal and$or the vertical materials handlers may be inclined. %variable often present is the inclination angle of the conveyors or elevators.&ach of the materials handling units is an independent machine that has its own merits. 'ucketelevators are usually employed for lifting materials vertically, whilst screw conveyors, whichare used to both move and lift material, are often mildly inclined. 'elt conveyors are used predominantly to move bulk solids long distances often involving some undulation.igure  illustrate some machines in a more realistic way than igure !.!   Horozontal conveyor:Chute, Belt conveyor, screw conveyor, air slide, pneumatic conveyor, drag conveyor, other.Friction losses:Machine losses per unit lengthMaterial friction losses per unit lengthEntry lossEit loss Motor and ransmission:Motor losses!ransmission ertical conveyor #elevator$:Buc%et elevator, screw conveyor, pneumatic conveyor. drag conveyor, other.Friction losses:Machine losses per unit lengthMaterial friction losses per unit lengthEntry lossEit loss Motor and ransmission:Motor losses!ransmission losses Feeder:&ower consumed. Hopper:&ower consumed'mass flowm(mass flowm( H) Figure 1: Possible general arrangement of conveyor and/or elevator  or a designer, these systems, whose purpose is to cause flow of the particulate solids, are basically systems of individual machines involving motors, transmissions, friction, corrosion,wear, environmental, structural strength, control, maintenance considerations, etc. Thematerial flow could be called “interruptedcontinuous”. This is because it often ceases whenemerging from one materials handling machine into the feeding hopper of another. %t this point the kinetic energy (and some potential energy) in the material is lost and further energyis often required to feed the ne*t machine.The material does not necessarily flow in the easier way that many liquids do. There is alwaysfriction in the machine elements and this is present even when the machine is not loaded withany material. %dditionally the bulk solid will e*hibit friction both internally as it movesagainst itself and e*ternally as it slides against machine members. +hen a machine isoperating  hours per day for the whole year e*cept for downtime the friction energy canamount to a considerable cost.The machine designer$specifier needs to understand where energy is lost and how to ma*imisethe efficiency of these machines.% simplified -.&..%. formula for power to drive a conveyor belt is/0ower (k+) 1 !2223!.4   $  5 $ 6 ((k7 8 k9 (+m 8 +b) 8 2.2!:+b) 8 (; $ +m))  +here/ ã 5 1;ori ontal distance between pulley centres (m ) ã ; 16ertical distance between pulley centres (m) ã 6 1'elt velocity (m$s) ã +m 1ass of material per metre run (kg) ã +b 1 ass of belt per metre run (kg) ã 2.2!: 1 actor accounting for friction in return belt run ã k7 1factor from belt slip and idler rotational resistance ã <k7 12.222=3(+m 8 +b) 8 2.2 (rotating mass of idlers per metre) (kg$m)> ã k9 1resistance of belt to fle*ure as it moves over the idlers Length   Lift   kY   kY   kY   kY   m   m   500t/hr.   1000t/hr.   2000t/hr.   3000t/hr.   100   20   0,035   0,030   0,026   0,022   200   20   0,032   0,026   0,022   0,020   200   40   0,030   0,022   0,020   0,020   400   20   0,030   0,022   0,020   0,020   400   40   0,026   0,020   0,020   0,020   800   40   0,022   0,020   0,020   0,020   1000   40   0,020   0,020   0,020   0,020   Table 1: Selection of the kY factor based on belt length, lift and capacity % number of other formulae have been used over the years and these are constantly beingrefined (?taples, !44!@ Aordell, !443@ Aordell, !444). ?oftware has been developed thatassists with design optimi ations, taking costs into account, %shford (!443).or each of these bulk materials handling machines there are various approaches available for energy analysis. Bt is worth pointing out that the energy analysis is serve a double purpose. BtC  enables us to look at the running cost of the machines and it also (iteratively during design)enables us to design the machine and its elements for strength to accommodate safety andreliability. FUNDA#ENTALS OF ENERGY ANALYSIS FOR T%ESE#ATERIAL %ANDLING DEVICES +e may view the various empirical power equations as being built up from some basicelements. These equations are intended to assist understanding and not intended for direct use/ 1Po!er to lift the material  rom an ideal point of view, none of these machines needs any power unless it lifts thematerial, in which case the power consumed will be/  gH m P  elevating   ′= Po!er to accelerate the material  #ften the machines are required to dig or accelerate a “static” input (feed). Bn this case thiscomponent of power consumed will be/  ! V m P  accel   ′= #Po!er to overcome machine friction $other than prime mover and transmissionlosses% achines are often tested under standard conditions with no material present such as the beltconveyor operating hori ontally. % similar standard testis done with screw conveyors, of standard pitch and mounted hori ontally (Damage, !442) ),E,,( !  parametersm A L  f   P    frictionmac  = − The parameters are like the k7 and k9 above and are available from all sorts of tables..  Po!er to overcome both internal and machine/material interface friction due to thematerial flo!ing ),E,,(   parametersm A L  f   P    friction  flow  = − 

Economics

Jul 23, 2017
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