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Vertical raw mill pradeep kumar

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Vertical raw mill pradeep kumar

  1. 1. Vertical raw millK.P.PRADEEP KUMARSr G M OperationKarikkali WorksChettinad Cements Ltd
  2. 2. The principle of vertical millresembles like ammi kallu, attaankallu,Or ennai chekku vandi
  3. 3. History of grinding technology
  4. 4. •Grinding•Separation•Drying•ConveyingFour functions in one machine makesVRM a compact grinding systemFunctions of Roller Mill
  5. 5. Vertical mill
  6. 6. General Design
  7. 7. material to air ratio,0.5 – 0.6 kgs/m3
  8. 8. Vertical mills of various suppliersLoeschemillRaymond milFLS Atox millGebr Pfeiffer , MPSKrupp PolysiusWilliams millCP Mill (claudius Peters)Babcock E ring mill
  9. 9. Raw mills of different designers
  10. 10. Investigation of the feed materialDifferent materials are characterized byhigh resistance to grindingsevere abrasivenessin homogeneous grindability , moisture content and grain sizestendency not to form a stable bed , so that the material leavesthe grinding bowl prematurely
  11. 11. High resistant to grinding - coal below 45 hard groove or petcoke- lime stone above 9 kwh/t at 12% on 90microns- clinkerFlowabity - poor drawing in behavior- poor bed formation properties- tendency for quartz accumulation ongrinding bowlCombination of different - low and high grindabilityproperties - moist and dry- coarse and fine fractionsAbrasiveness - high quartz content,particularly above 90microns particles- pyrites- felspars- shelly lime stoneInvestigation of the feed material
  12. 12. 3.2 How does a vertical mil work?The raw materials are fed directly to the centre of the grinding plate,which, thanks tocentrifugal forces and the pushing effect of the incoming materials themselves (both freshand separator coarse material), are distributed evenly under the grinding rollers. The turningspeed of the grinding plate, together with the pressure of the grinding rollers, create thenecessary friction for grinding the materials. After being ground, the material is transported tothe dynamic separator by the (more or less hot) gas flow, where the selection of the materialtakes place.The gas flow, besides transporting the material, performs other important tasks:• First material selection; the coarse particles tend to fall back on thegrinding plate.• Thermal exchange; more efficient compared to tubular ball mills,thanks to the complete mix of gases and materials.The coarse material coming from the separator is directed back to thecentre of the grinding plate in order to be ground again.The grinding process starts with the preparation of the so-called grindingbed, where the coarse material is crushed. Then the material in compressedand ground by the grinding rollers. For a stable grinding procedure thefollowing parameters are important:• The vibrations of the grinding plate.• The ∆P of the grinding system.• The height of the grinding bed(formed by a small border on the grinding plate).• The pressure of the grinding rollers.•The speed of the grinding plate.
  13. 13. P.GUNASEKARANMECHANICAL FOREMAN.
  14. 14. Common aspects of operation with regard to the grinding processand generally exhibits the following characteristics.Compression is the main mechanism of size reduction , although someelements of attrition , shear and impact will be presentGrinding takes place selectively, with most of the initial grinding action appliedto the larger particles at the start of the process .Then progressively with thetime the mill starts to ac on the mass of smaller particles resulting from thereduction of the larger , more friable onesThe resistance of the rollers to motion through the product decreases as thematerial bed becomes shallower .Consequently , the power absorbed by thegrinder decreases with the decrease of the crushed flow and vice versa.The effective grinding in the mill depends on many parameters . Importantamong them are area , gripping angle, nip angle, maximum grinding pressure ,grinding bed thickness between grinding surfaces , rolling friction factor - µ
  15. 15. Grinding theory of vertical roller millGrinding in roller mill is effected by shear and compaction.The effective grinding In the mill depends on many parameters .Important among them area : the gripping angle , nip angle,maximum grinding pressure , grinding bed thickness between theGrinding surfaces , rolling friction factor- µGripping angle(ligament angle)It is the angle between the surface of roller and table. Thematerial throughput Between the grinding surfaces is determinedby the maximum angle. From the diagram it Is understood thatthe increase in the gripping angle will result in a Thicker bed .But the maximum gripping angle is limited by the internal frictionand the Stability of the material.
  16. 16. Comminution Process in Roller Mills
  17. 17. Material Track
  18. 18. Grinding Action in Roller Mill
  19. 19. Multiple point contacts by particles on a particle: inter particlecomminution
  20. 20. Comminution Process in Roller Mills
  21. 21. 3.2 How does a vertical mil work?The raw materials are fed directly to the centre of the grinding plate,which,thanks to centrifugal forces and the pushing effect of the incoming materialsthemselves (both fresh and separator coarse material), are distributed evenlyunder the grinding rollers. The turning speed of thegrinding plate, together with the pressure of the grinding rollers, create thenecessary friction for grinding the materials. After being ground, the material istransported to the dynamic separator by the (more or less hot) gas flow, wherethe selection of the material takes place.The gas flow, besides transporting the material, performs other importanttasks:• First material selection; the coarse particles tend to fall back on the grinding plate• Thermal exchange; more efficient compared to tubular ball mills,thanks to the complete mix of gases and materials. The coarse material comingfrom the separator is directed back to the centre of the grinding plate in order to beground again. The grinding process starts with the preparation of the so- calledgrinding bed, where the coarse material is crushed. Then the material incompressed and ground by the grinding rollers. For a stable grinding procedure thefollowing parameters are important:
  22. 22. The material , which flows over the damn ring is caught by thevertical gas flow from the nozzle ring and lifeted up. Coarseparticles fall back to the grinding table and Finer ones are sweptup to the separator for being classified. The internal circulationRate depends mainly on the grindability of the ground materialand can amount up to 15 to 25 cycles.Reducing the gas speed in the nozzle ring adjustment of the open Arealeads ti falling through of larger particles. The fall through material has to beExtracted with scrapers and mechanically recirculated to the mill feed.SeparationThe use of modern separators in roller mils is state of the art.A sharp separation Improves the rawmeal quality and avoidsOver grinding ( saving of energy). Coarse Tailings , fed through thetailings cone to the center of the grinding table, helps theFormation of a more stable grinding bed. The raw meal finenessis easily controlled By the adjustment of the cage rotor speed.
  23. 23. Friction factor µ : Ιt affects the material movement on the table.Material with low Friction factor tends to have high radialvelocity in relation with the table speed and has The backwardsliding tendency. So certain amount of material falling on thetable flows To the table edge without passing under the roller.The µ increases with increasing pressure;However thecapacity of the mill does not grow in proportional to thepressure. So it is economical if we design a slightly larger millwith lower Specific pressure that allows a less strained designand an longer life Of the machinery instead of sizing a mill withhigh grinding pressure.The amount of material passing between the grinding surfacesis The product of grinding bed thickness , roller width , rollerdiameter And the density of the pressed material. For a certainroller speed and material and material , the capacity of theroller mill is directly Proportional to the grinding thickness.
  24. 24. Power taken by the millThe power taken up by the vertical roller mill is givenby the following expressionN =( I. µ .KT .DR .W.Dm. π.n ) / 60 K WWhere ,I = no.of rollersµ = friction factor (0.07-0.14 for raw materials , 0.09-0.1 for coal)ΚT = specific roller pressure , kN/m2(400 – 800 for raw and coal)DR = roller diameter , mW = roller width , mDm = mean diameter of the track , mN = table speed , rpmFor a given mill design, the expression reduces toN = (constant) .m .KT.Do 2.5
  25. 25. Roller Specificforce curve
  26. 26. • 2.1 vertical roller mill vibration is too large:(1) Feed uneven, when the mixture into the vertical roller millover the powder, the vertical roller mills loading rate, leading tothe vertical roller mill on the thin material, and even disc directcontact with the roller,resulting in mechanical milling; when intothe vertical roller mill multimaterial mixture materials for theblock, the resulting pressure grinding roll instability, resulting inmechanical milling. The solution is to stabilizethe particle size of materials into the vertical roller mill, theappropriate adjustment of feed rate or reduce the grindingpressure, the assurance required under the premise of thefineness of materials, appropriate to reduce the classifier speed.(2) Metal piece into the vertical roller mill, check the metaldetectors
  27. 27. Controlling Vibrations•Know the vibration limit and optimum grinding bed thickness for yourmill•Have reliable, calibrated bed depth monitors•Adjust the mill dam ring height to compensate for table wear•Match grinding pressure to mill throughput – establish relationshipbetween feedrate and hydraulic pressure. Consider control loop beddepth vs hydraulic pressure•Maintain an even bed, avoid big stones in mill, avoid excessive finesin mill feed, avoid uncontrolled feed variations, even distribution ofmaterial to each of the rollers, feed to the centre of the table,adjustment of feed chute and or use of guide vanes (ploughs)•Apply stable water spray to the control bed, normally fed to the feedside of each roller, check flow consistency on each spray•Know the critical level of gasflow and pressure drop for your mill•Maintain stable mill gasflow to keep internal circulation consistent –apply automatic control loop•Avoid magnetic and non-magnetic objects entering mill
  28. 28. 1.Operation points• 1.1 Stable Beds: to maintain stability and bed material, which isgrinding roller grinding bed basis, the normal operation of thekey. Material thickness can be adjusted to adjust the height ofretaining ring material, a suitable thickness and theirrelationship with the correspondence between the verticalroller mill output should be in the debugging stage of the firstto find out. Lower fuel layer thick grinding efficiency, materiallayer is too thin will cause vibration. Such as roll up,then finepowder generated much thinner material layer; roll reduction,disc material thicker, more appropriate to return the materials,material layer thickening. vertical roller mill speed increase,increase in internal circulation, material layer thickness,reducing the wind speed, reducing the inner loop, materiallayer thinning. Under normal operation by the vertical rollermill feed roller bed thickness after compaction should not beless than 40 ~ 50ram.
  29. 29. 1.2 Control of grinding pressure:The pressure is affecting the grinding mill output,power mill grinding efficiency and the main factor. vertical rollermill is to impose by means of the material bed crushing pressureand the pressure to increase production increased, but reacheda certain critical value does not change, the pressure increasefollowed by a increase in power, resulting in unit powerconsumption increase, so the appropriate roll to production andenergy consumption both. This value depends on materialproperties, particle size and volume of feed. In the testproduction grinding to find the right pressure and wind pressurecan form a reasonable good internal circulation, so that thematerial layer disc proper, stable, high grinding efficiency. In theproduction process, when the wind area of a certain ring, thewind speed from the wind decide. Production capacity with thecorrespondence between, to ensure the grinding effect.
  30. 30. 1.2 Control of grinding pressure: the pressure is affecting thegrinding mill out put,power mill grinding efficiency and themain factor. vertical roller mill is to impose by means of thematerial bed crushing pressure and the pressure toincrease production increased, but reached a certain criticalvalue does not change, the pressure increase followed by aincrease in power, resulting in unit power consumptionincrease, so the appropriate roll to production and energyconsumption both. This value depends on material properties,particle size and volume of feed. In the test productiongrinding to find the right pressure and wind pressure canform a reasonable good internal circulation, so that thematerial layer disc proper, stable, high grinding efficiency. Inthe production process, when the wind area of a certain ring,the wind speed from the wind decide. Production capacitywith the correspondence between, to ensure the grindingeffect.
  31. 31. 1.3 The guarantee of the grinding temperature: vertical rollermill is drying and grinding system, the ground temperature is ameasure of whether the normal drying operation comprehensiveindex. In order to ensure good drying of raw materials, thegrinding of materials is less than 0.5% moisture, the generalcontrol of mill outlet temperature at 90 ~ C or so. If thetemperature is too low then finished water, causing the efficiencyof grinding efficiency and reduce the separator, dust collectionsystem may cause condensation; If too high, humidity isnot enough that gas cooling, dust collection will also affect theresults.
  32. 32. 2. Exception handling• 2.1 vertical roller mill vibration is too large:(1) Feed uneven, when the mixture into the vertical roller millover the powder, the vertical roller mills loading rate, leadingto the vertical roller mill on the thin material, and even discdirect contact with the roller, resulting in mechanical milling;when into the vertical roller mill multimaterial mixture materialsfor the block, the resulting pressure grinding roll instability,resulting in mechanical milling. The solution is to stabilizethe particle size of materials into the vertical roller mill, theappropriate adjustment of feed rate or reduce the grindingpressure, the assurance required under the premise of thefineness of materials, appropriate to reduce the classifierspeed.(2) Metal piece into the vertical roller mill, check the metaldetectors
  33. 33. Static separators: Produce wide psd, fineness adjustment byvanes cause high ∆P and poor efficiencyConventional rotor type: Fineness adjustment by rotor speed,wide psd, low ∆P, tailings fall spread over grinding tableCage rotor with guide vanes: Operate with high air speed (4.5-6m/s), produce narrow psd steep slope R200/R90 = 0.02-0.05
  34. 34. Air dragCentrifugal forceGenerated by rotor cageGravitational force
  35. 35. Air dragGravitational forceCentrifugal forceStationary vanesRotary cageFunction of classifier15 – 18 m/s5 m/s
  36. 36. Classifier
  37. 37. Separator or Classifier
  38. 38. Loeshe mill separator inlet stationary vanes
  39. 39. If product has more coarse then classifier seal needs inspectionand rectification. Production drops drastically.Classifier rotor seal
  40. 40. 1000 500 400 100 90 80 70 60 50 40 30 20 micrejects100%80603010100%806030101000 500 400 100 90 80 70 60 50 40 30 20mic1000 500 400 100 90 80 70 60 50 40 30 20micIdeal separatorGround material to separatorSharpness η = d75 / d 25Value =0.8 – 0.85 is a veryEfficient classifierSize fractionBy pass fraction
  41. 41. Nozzle ring velocity45 – 60 m/svelocity above rollerV = 1.5 Do to 2.5 DoVelocity through rotorvanes = 5.0 m/sGrinding bed thickness = 1 - 2 % of DoFor cement grinding = 0.2 % of DoMill Dp = 350 Do mMill exit velocity = 10 m/sCage rotor with guide vanes:Operate with high air speed (4.5-6 m/s),produce narrow psdsteep slope R200/R90 = 0.02-0.05operating rpm , N = 56 / Do5 – 6 m/s
  42. 42. Counter measures in wear parts
  43. 43. Atox mill dimensions and characteristics
  44. 44. Atox mill dimensions and characteristics
  45. 45. Foster wheeler energy company
  46. 46. Innovation and patented
  47. 47. Thank you for your kind attentionK.P.Pradeep KumarSr G.M.OperationKarikkali worksChettinad cements Ltd

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