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Case studies related_to_paper_machine_operation

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Several case studies related to paper machine operation are discussed. Specially useful for papermakers.

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Case studies related_to_paper_machine_operation

  1. 1. Case Studies Related toCase Studies Related to Paper Machine Operation By: D K Singhal
  2. 2. Problems We’ll Discuss Vacuum Pump Operational Efficiency Fan Pump Bearing Failure 2 Fan Pump Bearing Failure Basis Weight Variation VFD synchronization problem And many more…. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  3. 3. Mechanical, Electricals 3 You might find some cases more suitable for mechanical or electrical people.mechanical or electrical people. Anyway, you’d like these. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  4. 4. Vacuum Pump Operational Efficiency 4 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  5. 5. Why to Check 5 Is existing vacuum pump sufficient for our needs? Do we need to change the vacuum pump, orDo we need to change the vacuum pump, or relocation may be tried? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  6. 6. Existing Trends 6 No standard available information on efficiency determination on operationalefficiency determination on operational conditions. Standard methods use standard conditions, which generally are entirely different than the mill environment. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  7. 7. No Flow Vacuum 7 This is also called as “peak vacuum” of the pump.pump. Some mills check the level of vacuum developed with inlet valves closed. A drop in gauge vacuum over the documented value is considered a drop in vacuum pump efficiency. Yet, if you are operating the pump at low vacuum levels, the result obtained by this may be misleading. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  8. 8. Wet & Dry Operation 8 Routine tests account only for dry air. The air is sucked in the vacuum pump at 100% RHThe air is sucked in the vacuum pump at 100% RH with some entrained water. When the pressure of this increases in the vacuum pump, some of the water vapor (moisture) condenses. So, at exhaust side, you get slightly lesser airflow. Also at vacuum pump inlet, during normal operationAlso at vacuum pump inlet, during normal operation due to water evaporation, you get lower gauge reading. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  9. 9. Points to Remember 9 Exhaust airflow reduces with increase in vacuum.vacuum. An old vacuum may give (almost) same airflow as rated at low vacuum levels, but at high vacuum levels, capacity reduces rapidly. Seal water consumption may be high at suchSeal water consumption may be high at such conditions. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  10. 10. Typical Pump Data 10 Take a look at a typical data supplied by a manufacturer.manufacturer. mmHg Inlet Flow Capacity Loss 0 3000 0.0 50 2990 10.0 100 2970 30.0 200 2940 60.0 300 2900 100.0300 2900 100.0 400 2800 200.0 500 2700 300.0 600 2400 600.0 660 2040 960.0 Data Supplied Calculated Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  11. 11. De-rating at Increased Vacuum 11 For normal operating ranges between 200mmHG and 500mmHg, the capacity drop200mmHG and 500mmHg, the capacity drop can be linearly correlated with vacuum level. y = 0.82x - 122 R2 = 0.9689 200.0 250.0 300.0 350.0 CapacityDrop 0.0 50.0 100.0 150.0 0 100 200 300 400 500 600 CapacityDrop Vacuum Level, mmHG Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  12. 12. Why does the Vacuum Reduce? 12 The drop of capacity is mainly due to two reasons-reasons- At higher vacuum level, some exhaust air gets short circuited to inlet air, no matter how good is sealing. This process increases as the vacuum pump gets older due to wear and tear. At higher vacuum levels, there is a lot of moisture in process air to be handled. This moisture condenses in vacuum pump, andto be handled. This moisture condenses in vacuum pump, and exhaust volume is lower than expected. So, dry checking of vacuum pump is generally not satisfactory for many process applications. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  13. 13. What to Check? 13 Obtain existing performance data on vacuum y = 0.82x - 122 R2 = 0.9689 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 0 100 200 300 400 500 600 Vacuum Level, mmHG CapacityDrop Obtain existing performance data on vacuum pump. Preferably, it should be at exhaust side, and the inlet side may be calculated as under- Inlet flow = (760-mmHg)*Outlet Flow / 760Inlet flow = (760-mmHg)*Outlet Flow / 760 Vacuum levels can be changed by throttling the inlet valves, while the machine clothing is running in wet condition. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  14. 14. Instruments for Flow Measurement 14 As flow is to be checked at exhaust side, a conventionalexhaust side, a conventional vane flow anemometer can be used easily. A hot wire anemometer, if used, has to be calibrated properly at operating temperature and humidity conditions.humidity conditions. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  15. 15. Sample Calculations 15 In this typical case, volumetric efficiency is reducing more at higher vacuum levels.reducing more at higher vacuum levels. Vacuum Exh. Flow Inlet Flow Inlet Flow Volumetric mmHg (Measured) (Calculated) (Design) Efficiency 0 2950 2950 3000 98% 50 2700 2890 2990 97% 100 2370 2729 2970 92% 200 1900 2579 2940 88%200 1900 2579 2940 88% 300 1500 2478 2900 85% 400 1050 2217 2800 79% 500 650 1900 2700 70% 550 250 1188 2400 49% 600 - - - - Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  16. 16. Operational Efficiency 16 As we can see that the operational efficiency is reducing rapidly with increase in vacuum levels.reducing rapidly with increase in vacuum levels. For practical purposes, the efficiency at the operational levels can be considered. For example, if the pump has to be operated at 400mmHg vacuum, the efficiency would be 79%.79%. Or, we may consider that vacuum pump is giving 79% of the rated airflow. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  17. 17. Results 17 On the basis of this analysis, we may conclude something like this-something like this- “This vacuum can be used for low vacuum applications”. “On an 400mmHg operating vacuum, the pump has been de-rated by 21%. So, if it does not serve the process requirement, it should be replaced.”replaced.” “If it is serving the process right now, we may replace the same with a new pump of smaller capacity and save power (same 21%).” Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  18. 18. 18 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  19. 19. Fan Pump Bearing 19 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  20. 20. Fan Pump In paper mills, we use a pump called Fan Pump. It is named because the flow rate is much higher, 20 It is named because the flow rate is much higher, while the pressure required is relatively low. The present one is a real case which baffled the minds of the mill maintenance team. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  21. 21. The Fan Pump 21 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  22. 22. Pump Tripping 22 The plant was running for years, but once there was a problem of pump tripping.a problem of pump tripping. On checking, pump was jammed. Obviously, the pump was opened up. It was found that the bearings were broken.It was found that the bearings were broken. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  23. 23. Pump Checking Bearing problem! Replace the bearings. Yes. The mill did the same. But after a couple of 23 Yes. The mill did the same. But after a couple of days, these broke again. Maybe, there was some problem from bearing side. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  24. 24. Bearing Quality 24 The mill ordered bearings from other supplier. By the time new bearings were received, theBy the time new bearings were received, the running one bearing failed again. Anyway, new bearings reached in plant in time, and these were mounted. Everyone hoped that these bearings were of reputed make, so there should be no problem in future. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  25. 25. Better Bearings New bearings could run for 3-4 days. Should I say, 50-70% better life? 25 Should I say, 50-70% better life? Fed up with the problem, the mill decided to procure SKF bearings. As there was a risk of getting fake SKF bearings, the mill procured from two different vendors, hoping at least one supplier will give genuine ones. These failed again within 3-4 days. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  26. 26. Failure Review 26 Bearing: 6314 Operating Load: Less than normal.Operating Load: Less than normal. Pump Sound: OK Operating Vibrations: OK Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  27. 27. Bearing Failure 27 Actions Taken: Check mounting procedure.Check mounting procedure. Replace pump shaft. Replace supplier. Switch to original bearing. Nothing worked, so Replaced the pump with a new one.Replaced the pump with a new one. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  28. 28. Pump Plant parameters were normal. The new fan pump was running at same pressure 28 The new fan pump was running at same pressure and flow rate as earlier. The motor load was also normal. But bearings were failing so fast that the mill increased inventory level for that bearing from 2 earlier to 8. Still everybody was clueless. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  29. 29. Pump Breakdowns are not always bad. Some breakdowns also give clue about the problem. 29 also give clue about the problem. In a such particular failure, the mill observed small pieces of ceramic tiles in the pump volute. How could that come into system? Oh!. Ceramic tiled detached from the chest and entered into the pump along with pulp stock. No one could see these earlier. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  30. 30. Got Clue 30 After a couple of days while the pump was stopped for the same problem, some ceramic tiles piecesfor the same problem, some ceramic tiles pieces were observed in it. A ceramic tile piece can damage the pump easily. On inspection, the pieces of tiles were found separated from the floor and walls of the storage chest. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  31. 31. Back to Operation 31 The civil work was taken and the same pump operated for several years without any problem.operated for several years without any problem. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  32. 32. Pump There could be many reasons for bearing failure- Improper mounting 32 Improper mounting Inadequate lubrication Substandard bearing Bad or corrosive environment But, sometimes,But, sometimes, You need to find out like a detective! Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  33. 33. Lesson: 33 Don’t just stop relying on your equipment (bearing, in this case) after a couple of breakdowns!in this case) after a couple of breakdowns! If you don’t get a clue after a breakdown, never ignore the need to find a reason for it. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  34. 34. 34 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  35. 35. Basis Weight Variation 35 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  36. 36. Initial Variation 36 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  37. 37. Sourcing 37 Sudden variation of 0.6-1.2 gsm. The machine has no centricleaners.The machine has no centricleaners. Variation frequency is too low. Pressure screen reject to secondary screen. Secondary screen reject timer controlled. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  38. 38. Analysis 38 As the reject screen reject valve is timer operated, when the reject valve opened that resulted in somewhen the reject valve opened that resulted in some (minor) fiber loss. As a result, GSM decreases. The plot indicates clearly that the variations are cyclic in nature. Please see the zoomed MD profile on the next slide. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  39. 39. Variation Zoomed 39 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  40. 40. Action Taken- 40 Reduced the pressure of secondary screen. That resulted in reduced inlet flow rate to it.That resulted in reduced inlet flow rate to it. That resulted in reduced change in operating parameters. The variation reduced to half. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  41. 41. 41 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  42. 42. Head Box Level Control 42 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  43. 43. Generally Used Approaches 43 DCS SCADASCADA PLC PID Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  44. 44. Initial Work 44 Initially, a PID controller was mounted and used. The scheme was using a blower to supply air, andThe scheme was using a blower to supply air, and releasing air through a valve. PID output controlled the blower so that the level is maintained. Faced several problems in the scheme. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  45. 45. Problem 45 On investigation, it was observed that there was a filter (Strainer) mounted on the suction side offilter (Strainer) mounted on the suction side of blower. With time, slowly it got dirty, thus reducing the airflow. To compensate, the VFD increased blower RPM. When as a routine, the shift crew whipped the blower with an intention to clean the filter, the result was more airflow, and hence reduced level inwas more airflow, and hence reduced level in headbox, which took some time to restabilize; thus creating problems. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  46. 46. Back to Manual 46 So, it was decided to go back to manual system, which is shown on the next slide.which is shown on the next slide. The operator need to use clutch to increase or decrease the headbox level. If level is low, just vent some air, and if level is high, allow some compressed air to get into headbox. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  47. 47. Used Level Control System 47 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  48. 48. Performance 48 The system is working well for 2-3 years. There is normally no need for operator interferenceThere is normally no need for operator interference except once a day or only at machine startup. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  49. 49. 49 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  50. 50. Press Roll Run Out 50 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  51. 51. Press Section 51 In paper mills, wet web of paper is pressed between two rolls.between two rolls. These rolls are called “Press Rolls”. The objective of pressing is to squeeze out water from the wet web so that paper can be dried easily in the next section. (Image courtesy: Google) Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  52. 52. A Typical Press Section 52 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  53. 53. Roll Wobbles After Startup 53 After mounting the roll, it was observed that therewas observed that there was a severe run out in the roll surface. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  54. 54. Possible Reasons 54 Roll journal appeared shifted from its position. It looked as if the roll center and journal centers became different. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  55. 55. Press Roll Journal 55 A typical normal press roll Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  56. 56. Press Roll Journal Shifted 56 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  57. 57. Can a Roll Journal Shift? 57 A roll is made up of a shell, generally of MS, with hubs press fit on both ends.hubs press fit on both ends. In the hub, journals are press fitted. Thus, it seems impossible in the normal case that journal had shifted. Journal bending was also not appearing to be there in this case. What else could be the cause, then? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  58. 58. Improper Bearing Fitting 58 Could it be misalignment? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  59. 59. Investigation 59 For a roll to rotate perfectly, we need to review a simple rule-simple rule- Roll rotates around the bearing centerline, while to our eyes, roll surface must seem to rotate around roll centerline.around roll centerline. In case the bearing center is different from the roll center, problem will appear. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  60. 60. What Could be the Problem? 60 It may result a haste decision to replace a roll journal, resulting a significant amount of time,journal, resulting a significant amount of time, money and downtime. The roll had been taken out by then, but there was no sign of any shifting of journal. The journal as measured against roll surface, was found OK. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  61. 61. The Clue 61 After investigation, it was thought that possibly the sleeve was not properly fitted and the same wassleeve was not properly fitted and the same was tilted. This caused the bearing center moved away from the roll journal center and hence the problem started. To recheck, the same roll was mounted again, andTo recheck, the same roll was mounted again, and this time, this showed no problem at all. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  62. 62. Improper Bearing Fitting 62 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  63. 63. Lesson Learnt 63 Mounting bearings need special care, as a carelessness may result in severe losses also.carelessness may result in severe losses also. Had the mill not taken decision to evaluate the real cause of the problem, probably the roll was sent to the supplier for journal replacement. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  64. 64. 64 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  65. 65. MG Gearbox Failure 65 The MG paper machine was being driven by a line shaft.shaft. There were four sections- Wire Paper Press Part MG Pope Reel Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  66. 66. Paper Machine Overview 66 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  67. 67. The Paper Machine 67 Paper is formed from pulp in the wire part, by dewatering water through a wire mesh.dewatering water through a wire mesh. In the press part, paper web is squeezed further. On MG cylinder, paper is dried. Finally, it is rolled on a roll at the pope reel. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  68. 68. MG 68 MG stands for Mono Glaze. This is a large drying cylinder on which the paper isThis is a large drying cylinder on which the paper is dried. This is a large cylinder, so the rotational speed is low. For the same a gearbox followed with a gear pinion was installed. The gear box was a helical U:1200 model one. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  69. 69. Gearbox 69 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  70. 70. Gear Box- Joint Shaft 70 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  71. 71. Gear-Pinion 71 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  72. 72. Drive Arrangement 72 You may see the cone pulley at the left side of gear box in the next slide.box in the next slide. The flat belt drives this cone pulley, while the drive cone pulley is mounted on the line shaft (Shown in another slide). Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  73. 73. Driven Cone Pulley 73 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  74. 74. Line Shaft Cone Pulley 74 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  75. 75. Failure On a day, joint shaft broken. Immediately, a new shaft was arranged and 75 Immediately, a new shaft was arranged and mounted in its place. The machine was started, and production continued. After a couple of days, the shaft broke again. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  76. 76. Failure Continued 76 The reason for shaft breakage was considered the weakness of the shaft.weakness of the shaft. It was decided to increase the shaft diameter from 100mm to 150mm. To use same coupling and pinion, the shaft diameter was higher in the center (where breakages were occurring) and the same 100mm at both ends.occurring) and the same 100mm at both ends. Everyone was sure about the shaft now. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  77. 77. Failure Shifts 77 After a few days, the gearbox broken. Well, another one was arranged and mounted.Well, another one was arranged and mounted. A few days later, the shaft broke. This started becoming a routine. Shaft-shaft-gearbox-shaft-gearbox… Finally 4 shafts and 3 gearboxes failed, within aFinally 4 shafts and 3 gearboxes failed, within a couple of months. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  78. 78. Why? Why all this started? What could have been done? 78 What could have been done? Was it an operational problem? Was it a design problem? Were the gearbox or shaft undersized? Supplier said he used to give U-1000, but gave a bigger U1200 just as a factor of safety.bigger U1200 just as a factor of safety. The mill ordered a bigger gearbox. U-1600 against U-1200 running. Was this decision right? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  79. 79. Problem Identification Later, in a meeting the possibility of backlash appeared. 79 appeared. The question was- “How to check for it?” Another question was, “Why this problem started after nearly an year from startup?” Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  80. 80. Backlash The problem with the machine was that there are two coupled rolls running in the machine with the 80 two coupled rolls running in the machine with the same drive. Press roll was being driven by one cone pulley. MG was also been driven by one cone pulley. Both the press roll and MG were finally driving the MG felt. In such cases, any speed difference can create backlash. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  81. 81. Mechanical Connection 81 After the press section, the paper goes with the felt and passes through another nip to get wrapped onand passes through another nip to get wrapped on MG cylinder. You may notice the felt in the next slide, behind the yellow color railing. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  82. 82. The Paper Machine 82 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  83. 83. Backlash In such a case, the line shaft drives two different cone pulleys, to their matching cone pulleys, to the different 83 pulleys, to their matching cone pulleys, to the different gearboxes, to their joint shafts and finally to two different rolls. But, the rolls nips are connected mechanically through the felt. A speed difference WILL create backlash in any of the gearbox.gearbox. Most gearboxes are not designed to operate with backlash. How can one check backlash? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  84. 84. Problem Identification 84 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  85. 85. Checking Backlash 85 As shown in the figure in the previous slide, the coupling bolts were removed.coupling bolts were removed. A chalk mark was made on both sides of coupling (As shown in yellow line). Now, the both sections were started, the left part of coupling rotates at a speed proportional to MG drive.drive. The right part of coupling rotates at a speed proportional to press drive. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  86. 86. Checking Backlash 86 By this, it is possible to practically ‘see’ the backlash.backlash. In the above case, one side of coupling took 10 turns, while the other took 9 turns before the chalk marks coincided with each other again. Thus there was more than 10% speed difference. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  87. 87. Problem Solved After you know the problem, you can always take corrective actions. 87 corrective actions. There has been no such failure reported after the problem was solved in past more than 10 years. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  88. 88. Origin 88 After the problem was solved, the next food for thought was to identify the reason for the same.thought was to identify the reason for the same. After discussions with operators, it was found that the running flat belt broke one day, and the mill had no stock. As an alternate, conventional belt generally used for agricultural purpose was mounted, afterfor agricultural purpose was mounted, after improper jointing. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  89. 89. 89 This belt was loose, so it was slipping on the pulleys. The position of the belt was adjusted in order toThe position of the belt was adjusted in order to compensate for the slippage. After a few days, when the new belt arrived, it was mounted on the same position without checking the speed difference. A little negligence resulted in heavy loss to the mill. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  90. 90. Lesson: 90 Ensure proper mountings of all accessories. Try to evaluate the root cause of the problem ratherTry to evaluate the root cause of the problem rather than blindly changing equipment to higher size. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  91. 91. 91 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  92. 92. Startup Troubles 92 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  93. 93. Problem 93 The case is of a paper drying cylinder installed in a paper mill. The mill complained that after the startup from a shut of a few hours or more, the paper was not drying properly. The steam pressure in the cylinder (yankee cylinder) was normal. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  94. 94. The Process 94 Live steam enters the dryer through thermo- compressor and the condensate is sent to a pressurecompressor and the condensate is sent to a pressure vessel. The flash vapors generated from this pressure vessel are again taken by the same thermo-compressor. The condensate is sent to the condensate tank through a pump.through a pump. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  95. 95. The Process 95 Simultaneously, a part of live steam is used in hood’s live steam coils to heat up the air, which ishood’s live steam coils to heat up the air, which is impinged on to the surface of paper for faster drying & hence faster production rates. The condensate from these is also sent to the same condensate tank. From condensate tank, it goes to boiler feed waterFrom condensate tank, it goes to boiler feed water tank. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  96. 96. Problem 96 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  97. 97. Back to Problem 97 The production for some time remains low even at the operating steam pressure.the operating steam pressure. After say 10-20 hours, slowly and slowly it increases to normal. In case of frequent web breaks, the production rate comes to normal relatively faster. In case there is a web break, the operators need to vent out a part of steam from the drying cylinder. Are the above two points interconnected? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  98. 98. Operator Observation 98 Considering the experience, the operators started using the knowledge gained to vent out a part ofusing the knowledge gained to vent out a part of steam for some time in case the production rate is not normal. This practice resulted in maintaining the production rate. But, what was the cause of it? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  99. 99. Non Condensable 99 Presence of non condensable reduces the heat transfer from the steam side drastically.transfer from the steam side drastically. When the plant is shut for a long time, the steam inside the system condenses and thus a vacuum is created inside the yankee dryer. As a result air enters through gland packing etc. into the system.into the system. Cold gland packing allows steam to enter the system easily. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  100. 100. Steam Venting 100 While some steam is vented, non condensable gases also escape out from the system, resulting thealso escape out from the system, resulting the system to work normally. But excess venting also means steam wastage. As a solution, a part of the flash steam was used in direct heating applications. This way, the excess air got released soon, and the problem was solved.got released soon, and the problem was solved. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  101. 101. Steam Venting 101 In fact, the similar problem was also faced in a large paper machine, where the system andlarge paper machine, where the system and condensate system was being operated in cascading mode. It was noticed that by adopting the steam venting the production could be increased by more than 10%.10%. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  102. 102. 102 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  103. 103. About MG Cylinder 103 A large drying cylinder for a paper mill needs to be replaced. Its dimensions are-be replaced. Its dimensions are- Face: 3200mm Diameter: 4267mm Shell Thickness: 75mm Dish End Thickness: 65mm Tie Rods: 80mm∅ X 12 Nos.Tie Rods: 80mm∅ X 12 Nos. Ribs: 8 nos. each side X 42mm thick Journal Diameter: 320mm Weight: Approx. 42-45MT Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  104. 104. About MG 104 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  105. 105. MG 105 It is a carbon steel cylinder. As the diameter is large, the shell is fabricated byAs the diameter is large, the shell is fabricated by welding two steel plates together. The typical location of welding joints can be seen in the next sketch. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  106. 106. MG Welding Joints 106 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  107. 107. Joints on Surface 107 Welding on the surface results in uneven drying on paper due to operational deformation of shell nearpaper due to operational deformation of shell near welding joints. Hence, stress relieving is done to remove stresses developed during the plate welding process. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  108. 108. Stress Relieving 108 For stress relieving, the temperature of the whole cylinder needs to be increased gradually to 620⁰C,cylinder needs to be increased gradually to 620⁰C, and then reduced slowly. For this you need a big furnace in which such a huge equipment can be put. Let’s review it as a practical assignment problem for newcomers. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  109. 109. A Practical Case 109 Your mill has placed the order to the manufacturer in Ahmedabad, but, such huge furnace is available at Vadodara. Ahmedabad, but, such huge furnace is available at Vadodara. Ahmedabad & Vadodara are two cities around 350km apart. Fabricate Transport to Vadodara for SRTransport to Vadodara for SR Get SR Done Transport back to Ahmedabad Get it machined Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  110. 110. Costs Involved 110 This way, the additional costs involved include- Loading & Unloading at both places. Transportation to and from SR Charges Typically, these aggregate to nearly 10-15% of landed equipment cost. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  111. 111. A Cheaper Alternate 111 While you are busy with negotiating with transporters, the manufacturer comes up with a simple alternate-the manufacturer comes up with a simple alternate- The cylinder shall be covered with glass wool From the manhole, HSD and combustion air shall be injected and fired inside the cylinder. Exhaust gases will come out from the manhole and the journal steam entry opening. Cost for SR alone shall be nearly the half. However, in place of reaching a temperature of 620⁰C, it could be around 500⁰C or so. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  112. 112. Market Trends 112 As per the supplier, only a few mills opt for Vadodara option, as in paper mills, the cylinder has to operate atoption, as in paper mills, the cylinder has to operate at a maximum temperature of 170⁰C -180⁰C only. Most mills follow the same path and save money. A few mills in the past had decided not to get the SR done, and use the cylinder after fabrication and machining only. Their cylinders are also running well.machining only. Their cylinders are also running well. Now, you have to decide! Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  113. 113. Your Choices are- 113 Get SR done at Vadodara. 4.0-8.0 L4.0-8.0 L Get SR done at Ahmedabad only. 1.0-2.0 L Go ahead without SR. Free! Your answer? Why? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  114. 114. Clues 114 As you want to decide, you may ask the quantity of HSD expected to be consumed for SR in bothHSD expected to be consumed for SR in both process. An In-Situ process reportedly needs around 300- 400 lit., while in furnace, it may need around 1000- 1200 lit., as the furnace is really big enough. Does HSD consumption figure help you in deciding?Does HSD consumption figure help you in deciding? Vadodara? or Ahmedabad? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  115. 115. How to Check Temperature Achieved? 115 In both cases, the person doing SR will mount three sensors on the surface of cylinder, and the readingssensors on the surface of cylinder, and the readings shall be recorded on a plotter. He is ready to show you the calibration certificate also. Still, if he can manage to display higher readings on plotter, can you check it? How? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  116. 116. Temperature Cross Checks 116 Color of the job At temperatures above 400⁰C, the color of object canAt temperatures above 400⁰C, the color of object can be used to roughly estimate the temperature. Use of magnet Magnet loses magnetism at temperatures beyond 300⁰C. This property can be used to roughly cross check the rate of temperature increase.check the rate of temperature increase. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  117. 117. Temperature Cross Checks 117 TEMPINDIC Crayons Various temperature indicative crayons are available inVarious temperature indicative crayons are available in the market. Just mark something on the metal with a crayon of suitable range, and after cooling after SR, the smearing of mark will indicate if the desired temperature was reached or not. Fuel ConsumedFuel Consumed Combustion calculations may be used to evaluate the theoretical fuel consumption to achieve the specified temperature. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  118. 118. Combustion Calculations 118 The weight of the object is known. As the temperature of the object has to beAs the temperature of the object has to be increased rapidly and for practically smaller duration, the only a part of refractory will get heated. The same may be considered accordingly. Now, using mass multiplied by specific heat multiplied by temperature rise, one can calculatemultiplied by temperature rise, one can calculate total heat required. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  119. 119. Combustion Calculations 119 As the combustion gases exit the system at temperature higher than the object temperature, thetemperature higher than the object temperature, the overall heating efficiency needs to be taken into account. With these, one can find total heat input required. Using the calorific value of fuel used, one can calculate the theoretical quantity of fuel required.calculate the theoretical quantity of fuel required. In case the actual fuel consumption is much less, one may doubt about the temperature actually achieved. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  120. 120. Additional Points 120 In case of internal firing, you need to supply combustion air and fuel to inside of cylinder, whilecombustion air and fuel to inside of cylinder, while the combustion products must escape out the cylinder simultaneously. You need nearly three hours to increase temperature @100-150⁰C per hour. The cylinder has two openings, first the manhole,The cylinder has two openings, first the manhole, and second just the 125mm bore inside one of the journal (for steam entry). Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  121. 121. Internal Firing 121 Are these two openings sufficient enough to accommodate the air supply and exhaust gasesaccommodate the air supply and exhaust gases release from the cylinder? It is not important what the mill did. It is more important that you understand the process of making decisions.making decisions. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  122. 122. Lesson 122 Thorough evaluation helps making your decisions faster and firmly.faster and firmly. Making decisions based on proper calculations saves you from choosing a wrong alternate. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  123. 123. 123 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  124. 124. AC VFD Failure 124 An AC drive was being used in a paper mill for paper machine main motor. The motor rating waspaper machine main motor. The motor rating was 160kW, while the operating load remained below 100-105kW. One day, there was a voltage fluctuation, VFD tripped; and when restarted the drive, it did not start.start. The shift electrician tried cold start, but no use either. The drive was dead. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  125. 125. Repair Work 125 Obviously, the option left was just to call the supplier’s engineer, and get the drive repaired.supplier’s engineer, and get the drive repaired. The same was done. This took a couple of days & a lot of money, and the drive was running again. But again, here is the same question. “Why?” Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  126. 126. Failure Again 126 After 2-3 months, the problem repeated again. It was discussed with the supplier, suppliers of otherIt was discussed with the supplier, suppliers of other makes of drives, service engineers but, nothing could be found out. In fact, we had nothing to tell them, except saying, that the drive failed to run while started again after a voltage fluctuation. On checking one of theafter a voltage fluctuation. On checking one of the thyristors was found to be blown. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  127. 127. Source Appears 127 On a normal day, the machine was running smooth, and there was a voltage fluctuation. The driveand there was a voltage fluctuation. The drive tripped, and the papermaker rushed to restart it at the earliest. Within a couple of minutes, the paper was reeled. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  128. 128. Clue 128 But that gave a weak clue- Does restarting the drive too fast could be a source of this problem?problem? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  129. 129. Quick Restart 129 Often the production men are so much in a hurry to meet their production targets, sometimes, they domeet their production targets, sometimes, they do things much faster than our sophisticated machines. Every drive (VFD) supplier suggests to give a time of 1-2 minutes before restarting the drive. It is just so small thing that we often forget, and problem appears.appears. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  130. 130. Put a Speed Breaker 130 We informed all process people that if a drive trips for any reason or switched off (no cold Reset!), itfor any reason or switched off (no cold Reset!), it should NEVER be started within 1-2 minutes. After this such failures stopped fully. Similar problem was faced in some nearby mills also, and we informed them about our case, and now such problem is eliminated from there also.now such problem is eliminated from there also. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  131. 131. Lesson Learnt 131 Pay proper attention to minor things also. Never stop searching for the root cause of theNever stop searching for the root cause of the problem you faced earlier. The earlier you find the reason, the quicker it would be solved permanently. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  132. 132. 132 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  133. 133. Drive Synchronization 133 In a paper mill, three different sections of the machine (MG, Press and Pope Reel) were being runmachine (MG, Press and Pope Reel) were being run using a mechanical coupling (line shaft). The wire part was with another drive. It was decided to split out pope reel using different VFD, synchronized with the drive of line shaft. The paper machine was started and paper reeled.The paper machine was started and paper reeled. Initially, everything was perfect. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  134. 134. Drive Synchronization Failure 134 But suddenly after half an hour or so, severe speed difference appeared.difference appeared. As obvious, there was a paper break. Operators adjusted the speed by adjusting the speed difference between master and slave, and the paper was running again. The problem repeated after some time.The problem repeated after some time. This continued but we had no answer to “why”? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  135. 135. A Move Backwards 135 After a lot of trials, speed difference problem, we finally decided to come back to previous position.finally decided to come back to previous position. A shut was taken, and the necessary arrangements were made for the paper machine to bring it to original position. For a couple of days, the matter was discussed telephonically with several experts, but no one wastelephonically with several experts, but no one was able to suggest anything without actually seeing the problem. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  136. 136. It was a Failure 136 However, all experts confirmed that our line of action was correct, and we did everything thataction was correct, and we did everything that could have been done. Finally, we left behind the issue as a failure and within a year or so started forgetting the incident. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  137. 137. Two Drive Operation 137 Now the whole paper machine section was running with two drives.with two drives. Around after 8-10 months, one day, the similar problem started appearing with these two drives also. There was a severe speed fluctuation in paper machine speed, and we could notice that paper wasmachine speed, and we could notice that paper was getting thicker for a few seconds. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  138. 138. A Clue 138 The problem appeared again and again after every 1-1.5 hours. However, we noticed that even ifevery 1-1.5 hours. However, we noticed that even if we did nothing, we were able to pass the paper after a joint just within 2 minutes after every problem. So, this was just 2 minutes production loss after almost every hour. One smart operator observed that when ever another equipment (rewinder) was started, this problem appeared. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  139. 139. No Direct Link 139 There was no direct link- either mechanical or electrical- between rewinder and paper machine.electrical- between rewinder and paper machine. But, even between two independent motor- switchgears, there is some connection. What is that? Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  140. 140. Ground 140 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  141. 141. The Grounding Problem 141 A layout of the existing ground was prepared to discuss with experts.discuss with experts. By the time it completed, we were getting clues. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  142. 142. 142 Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  143. 143. Improper Grounding 143 The rewinder grounding to CGB was broken at one place.place. Furthermore, couch supply cable had a joint, and the shielding was not connected at joints. This cable’s armor was not grounded at any end. After all the rectification work was done, problem solved.solved. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  144. 144. Cause of the Problem 144 The issue was discussed with many electrical engineers, consultants and suppliers.engineers, consultants and suppliers. As the plant was running since long, no one could guess something might go wrong with earthing. After some mechanical work, the earthing strip had been left unattended. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  145. 145. Lesson Learnt 145 Never overlook tiny changes in plant, check thoroughly each and every thing that may bethoroughly each and every thing that may be connected with the problem. Take earthing/grounding seriously. With the increase in electronics and digital drives, poor earthing may result in problems. Electrical engineers love to keep a copy of wiringElectrical engineers love to keep a copy of wiring diagrams, ensure you also have a copy of earthing diagrams with you. Case Studies Related to Paper Machine Operation, D K Singhal, 2018
  146. 146. 146 Thank You. Case Studies Related to Paper Machine Operation, D K Singhal, 2018

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