A Discussion on Yankee Safety Issues

1
A Discussion on Yankee Safety Issues
By D K Singhal
2
Disclaimer

• This presentation is supplied as a self learning
  presentation, and is subjected to the condition
  that the author accepts no liability from the use
  of the same or from the techniques or information
  provided within the same.
• The information provided herewith is supplied
  exclusively for mild steel fabricated yankee
  cylinders, and expected to be beneficial to the
  users, however in case of any problem, may it be
  operational, mechanical, breakdown or any other
  type, the author cannot be held responsible for
  the same. Users are welcome to consult the author
  in case any problem is observed.
• It is strongly recommended to consult your
  machinery supplier, yankee supplier, mechanical
  engineer, and process engineer etc., before
  making any changes to the existing system.

3
Issues

• To protect yankee from unwanted maintenance, e.g.
  grinding etc.
• To ensure proper safety of two Ms Man and
  Machine.

4
Common Reasons for failure

• Increased steam pressure inside yankee.
• Increased condensate level inside yankee.
• Increased touch roll loading.
• Increased moisture with incoming paper web.

5
Pressure inside yankee

• Pressure is normally controlled using a manual
  globe valve or alternatively with a pneumatically
  controlled valve set at desired setpoint.
• Manual control has its own limitations, while
  pneumatic control may allow more steam to enter
  yankee cylinder in case of a malfunction.

6
Increased Condensate Level

• Increased condensate level can be due to
  following reasons-
• 1. Siphon pipes leakage or broken.
• 2. Steam trap failure, strainer chocking etc.
• 3. Rotary joint sealing or guide rings broken.

7
Increased Condensate Level

• In most of the cases, an increase in condensate
  level remains unnoticed. This results undesirable
  load due to both increased weight of yankee as
  well as increased pressure inside yankee to
  compensate for reduced heat transfer area due to
  condensate.

8
Increased Touch Roll Loading

• Sometimes, in case of pneumatic or hydraulic
  system failure (as the case may be), the load on
  touch roll may increase beyond permissible limits.

9
Increased Moisture

• This is also possible that due to sudden change
  in vacuum, or some other process variables, the
  paper web moisture content increases suddenly
  resulting in undesirable stress on yankee.

10
STEAM PRESSURE CONTROL
11
Steam Pressure Control

• It is strongly recommended to check all upstream
  side valves, pressure gauges etc. periodically to
  minimize the probability of failure of the same.
  Pressure gauges must be calibrated at regular
  intervals.
• One mill reportedly uses two pressure gauges, one
  for normal use and another (normally valve shut
  off) for cross checking in case the reading of
  the first is doubtful.

12
Steam Pressure Control

• In addition, a pressure switch should be
  installed at steam inlet line after final control
  valve, but before rotary joint.
• This switch should be connected to an alarm to
  activate if the pressure increases beyond limit.
  Any increase in steam pressure to MG will
  therefore help the operators to do corrective
  action.

13
Steam Pressure Control

• A safety valve should also be installed at the
  same line as above, set to bleed off some amount
  of steam from yankee in case steam pressure
  increases. Since, this is very rarely to operate,
  periodic checking and calibration of the same
  MUST be done.

14
INCREASED CONDENSATE LEVELS
15
Increased Condensate Level

• In case siphon pipe or trey is broken or cracked,
  it becomes impossible for the condensate to reach
  to rotary joint. As a result, condensate level
  increases.
• These should be checked periodically, at least
  once a year to ensure these are properly
  welded/bolted.

16
Increased Condensate Level

• In case of plugged strainers, or malfunctioning
  of steam traps, condensate cannot be removed from
  yankee, and hence water level increases. Such
  situation occurs in case of air locking, steam
  locking, mechanical failure of trap or scaling
  deposition in steam trap and strainers.

17
Increased Condensate Level

• Rotary joint carbon rings (seal rings and guide
  rings) if broken, may allow a part of steam from
  inlet side to escape from the condensate side
  without entering yankee at all.
• Such a situation will result in increased
  pressure at condensate line, and hence condensate
  will not be removed from yankee.

18
INCREASED TOUCH ROLL LOADING
19
Increased Touch Roll Loading

• Malfunctioning of pressure regulating valve in
  hydraulic or pneumatic system may result in
  sudden increase in touch roll loading.
• In one study, it has been observed that out of
  total forces acting on a yankee, the touch roll
  loading accounts for nearly 24 of load.

20
Increased Touch Roll Loading

• Carefully designed hydraulic or pneumatic systems
  with provision to control the pressure beyond a
  certain value are a must.
• It has been observed that presence of moisture in
  pneumatic system results in premature failure of
  regulators. Air should be free from moisture.
• In case of hydraulic system, periodical cleaning
  of oil filter should be done to avoid any oil
  contamination.

21
INCREASED MOISTURE IN THE WEB
22
Increased Moisture

• Sudden reduction in touch roll load, vacuum or
  some other process variable may result in
  increased moisture in paper web. Due to increased
  moisture, when a hot yankee comes in contact with
  plenty of moisture, its surface temperature
  reduces significantly. This thermal shock can
  also affect yankee adversely.

23
Increased Moisture

• To avoid such situations, system must be audited
  for its safeguards against failures.
• In a typical case, it was noticed that the touch
  roll load reduced to such a low value that it
  lowered resulting in paper web break at yankee
  section, and chocked uhle boxes. Only a timely
  emergency stoppage could protect felts from
  permanent damage.

24
Increased Moisture

• For the case above, the mill installed a pressure
  switch in pneumatic pipeline to activate an alarm
  if the pneumatic pressure reduced below minimum
  desired pressure. Compressor failure, severe
  leakage in pneumatic piping etc. result in alarm
  so that the machine operator can take a
  corrective or preventive action as the case may
  be.

25
PROTECTION TECHNIQUES
26
Pressure Inside Yankee
27
PRESSURE INSIDE YANKEE

• An inlet pipeline is given on the following slide
  to illustrate how pressure measurement and
  control can be effectively done for a yankee.

28
Typical Yankee Inlet Piping Schematic
PI
PS
SV
To Yankee
From Steam Header
CV
CV
Hooter
PS Pressure Switch PI Pressure Gauge SV Safety
Valve CV Control Valve
29
Yankee Inlet Piping

• It is very important to understand that the
  pressure indicated by a pressure gauge -may it be
  a bourdon tube type, or a pressure transmitter
  with indicator or controller- is NOT the pressure
  inside yankee as it is considered. It IS the
  pressure at inlet of rotary joint, and the
  pressure inside yankee would be gauge pressure
  minus pressure drop across rotary joint.

30
Yankee Inlet Piping

• As the steam consumption, and hence steam flow
  rate increases through yankee, this pressure drop
  across rotary joint increases. That means, you
  actually provide much lower pressure inside
  yankee than the pressure gauge indicates.
• Though seem unbelievable, this pressure drop may
  be to the tune of half of the gauge reading in
  some of the cases, i.e., if the gauge indicates
  an inlet pressure of 3.2 Kg/cm2, fair chances are
  that the inlet pressure id 1.8-2.0 Kg/cm2 only.

31
Measuring Actual Yankee Inlet Pressure

• Well, it is not practically possible, and
  advisable too, to install a pressure gauge on
  rotating yankee. But the same can be done using a
  trick.
• Condensate is removed form a cylinder at a
  temperature corresponding to the saturation
  temperature of steam at that pressure.
• If a temperature gauge is installed just after
  rotary joint, we can find out the steam pressure
  inside yankee.

32
Measuring Actual Yankee Pressure

• The results obtained by this technique are often
  surprising. In some cases, it has been found that
  the hydraulic testing of yankee at the fabricator
  site had been done at a pressure 8 or 10 times
  more than that is required for papermaking.
• But, does that mean yankee is safe?

33
Yankee Pressure- Operational Vs. Intermittent

• In most of the cases, when the paper is not
  running on machine, heat losses through yankee
  shall are low, and hence steam flow rate. That is
  why, the pressure drop through rotary joint
  reduces and pressure inside yankee increase, even
  though the pressure gauge indicates a reduction
  in the same.

34
Yankee Pressure A Typical Case

• In a particular case, a fabricated yankee was
  analyzed as discussed above. The design and
  operating data are as under-
• Diameter 4.2M
• Shall Thickness 62mm
• Material A36 (ASTM)
• Pressure at Inlet Piping 3.3-3.7Kg/cm2

35
Yankee Pressure A Typical Case

• That mill earlier considered that the pressure
  inside yankee is to the tune of 3.3-3.7Kg/cm2.
  But, considering the above, temperature
  measurement of the condensate just after rotary
  joint was done, and found that the condensate
  temperature was to the tune of 127-128C. This
  corresponds to 2.0Kg/cm2.

36
Why to Install Safety Valve?

• In case of paper running over yankee, it extracts
  heat from yankee, as a result of which, pressure
  reduces. But when the paper is not there, e.g.,
  in case of a paper break, the pressure inside
  yankee may increase and affect the yankee
  adversely. To avoid the same, a safety valve or
  pressure switch connected to an alarm is
  recommended.

37
Non-Condensable Gases

• Non condensable gases are another major source of
  pressure increase in yankee.
• A minute quantity of non condensable gases can
  easily reduce down heat transfer rates
  significantly, due to which the operator is bound
  to increase steam pressure to maintain the
  desired production rates.

38
From Where Non-Condensable Gases Appear?

• In case where boiler feed water is hard, and
  boiler water is also highly contaminated, some
  de-scaling chemicals generate gases like CO2 etc.
• Also, if boiler feedwater temperature is very
  low, presence of dissolved oxygen and air in
  feedwater is released within boiler and these
  gases travel alongwith the steam to enter yankee.
  From the yankee, these cannot be easily removed
  as steam trap does not normally allow these gases
  to escape out.

39
Detection of Non-Condensable Gases in the System

• Often it is very difficult to detect presence of
  these gases within the system, particularly if
  there is a scope of increasing production rates.
• On machines where the production is limited by
  drying capacity, an increase in pressure could be
  an indication for the same.

40
Detection Techniques

• For every grade of paper, and for every speed and
  basis weight, note down the normal operating
  pressure.
• In absence of any other system, any increase in
  pressure could be a possible indication of
  presence of non-condensable gases in the system.

41
Detection Techniques

• Here, the properties of steam can be used to
  detect the presence of non-condensable in steam.
• We know that Boiling point of water increases
  with increase in pressure.
• Hence, the temperature of condensate just after
  the rotary joint increases with increase in
  pressure inside yankee.
• Due to presence of non-condensable gases, heat
  transfer is reduces, which is compensated by
  increasing steam pressure inside yankee.

42
Using Condensate Temperature

• Thus, regular monitoring can reveal presence of
  non-condensable gases in yankee.
• For example, if normally the condensate
  temperature id to the tune of 125-127C, any
  increase beyond 5C can be considered possibly
  due to the same.

43
Minimizing Non-Condensable Gases

• The first step is to minimize the generation of
  these from the boiler itself.
• Desired number of blowdown, use of suitable
  descaling and scale preventing chemicals, timely
  descaling, maintaining appropriate feedwater
  temperature should be observed.

44
Minimizing Non-Condensable Gases

• In case non-condensable gases have entered the
  system, another simple technique is to let it
  blow away. This can be done by bypassing steam
  trap in the condensate line. Though this may lead
  to minor steam leakage, yet in many cases, the
  effect is noticeable, and condensate temperature
  decreases indicating clearly that the heat
  transfer has improved substantially.

45
INCREASED CONDENSATE LEVEL
46
Increased Condensate Level

• The problem with increased condensate level is
  that in most of the cases, it go unnoticed for a
  long time. It is quite possible that machine is
  running smooth without a break of paper for a
  long time, and sudden effect of condensate level
  increase is noticed.

47
Increased Condensate Level

• In a typical case, vibrations started to appear
  in yankee framings, and it was decided to shut
  the machine and check yankee internally. Boiler
  steam supply was discontinued, and it was decided
  to run the paper without steam as long as
  possible to get yankee cooled down early.

48
Increased Condensate Level

• Under that situation, machine could be run for
  nearly 30-40 minutes without steam.
• On checking, it was found that the yankee was ¾
  full (height wise).
• One can understand how dangerous it can be to
  operate a yankee under such circumstances, but
  without knowing the condensate level in yankee
  what can be done?

49
Condensate Removal per Rotation of Yankee

• It is easy to estimate condensate removed from
  yankee per revolution. Divide machine speed with
  yankee circumference to achieve yankee RPM. Now
  divide condensate removal (or steam consumption)
  per hour and divide the same with 60 (to convert
  hours to minutes) and then with yankee RPM.

50
Condensate Removal per Rotation of Yankee

• For a typical case, steam consumption was 3000
  kg/Hr. Machine speed was 210mpm and yankee
  circumference was 13.3M.
• So the condensate removal per yankee rotation
  would be calculated as-
• Yankee RPM 210/13.3 15.79 rpm
• Condensate 3000/(6015.79) 3.16 kg per
  revolution.

51
Condensate Removal per Rotation of Yankee

• As one can see that this is a very small
  quantity. Also, considering two treys in a
  yankee, the water to be lifted per trey operation
  is less than two liters.

52
Effect of Condensate Level Increase

• While condensate level is increased, the trey do
  lift condensate to transfer the same to siphon
  pipe, from where it cannot move forward, and
  fells back into yankee. But due to the size of
  treys, these bear a resistance to move, which can
  be observed by fluctuating drive load. The more
  is the trey size, the more would be load
  fluctuation.

53
Effect of Condensate Level Increase

• With increase in condensate level, some
  vibrations do start in the yankee framings. In
  case the mill has installed vibration analyzers,
  any increase in condensate level can be easily
  noticed. For the mills which do not have
  installed vibration analyzers in yankee framings,
  or do not intend to do so due to high cost, here
  is a simple solution.

54
Indicating Vibrations in Yankee Framings

• If any member such as angle or channel is mounted
  with yankee framings in such a way that it is
  supported at one end, and the other end is free,
  it will oscillate due to vibrations. A regular
  observation to its other end if vibrating
  severely will indicate the possibility of some
  problem such as condensate filling inside yankee.

55
Indicating Vibrations in Yankee Framings
Vibrating Member
Yankee Frame
Yankee Frame
56
Using Ampere Meters.

• In some cases, the yankee framings may be so
  rigid that there are no significant vibrations
  observed in case condensate gets filled up in
  yankee. An alternate to the technique shown above
  is to put an analogue ampere meter for yankee
  drive load. A fluctuation in load, particularly
  twice in every rotation of yankee (For two treys)
  is a clear indication for the same.

57
Using Ampere Meters.

• In case the dimension of treys is relatively
  small, these will not create any resistance to
  condensate and hence amperage fluctuation as
  indicated above would be very small. As the trey
  has to handle only a very small amount of
  condensate every time, there is no need to
  increase trey size. So another technique is
  proposed here to get informed in case of
  condensate level increase.

58
A Design Modification

• The treys are normally designed in such a way
  that the condensate collected by these is
  immediately transferred to siphon pipes, from
  where it can be removed through rotary joint. In
  case some of the condensate does not move to
  siphon pipe, it falls back inside yankee shall,
  but it does apply some extra load on drive
  system.A similar design with increased area will
  create more resistance to drive.

59
Normal Trey System
Yankee
Trey
60
Proposed Baffles
Proposed Baffle
61
Proposed Baffles

• As indicated in the drawing in the previous
  slide, the dimensions of the same are designed
  considering the steam consumption, yankee
  dimensions, trey dimensions, drive system
  (whether sectional or line shaft) etc. This
  baffles are not welded to shall hence one can be
  assured that there would be no surface
  deformation. Yet, as a matter of precaution,
  baffles must be welded before yankee grinding.

62
Before Installation

• Before installation of baffle, one must ensure
  that the yankee is balanced.For the same, all
  other driven elements, e.g. wire part, press
  part, pope reel etc. are stopped in case of a
  line shaft drive. Yankee is rotated at very slow
  speed with all doctor blades unloaded, and touch
  roll lowered.
• Any unbalance will result in fluctuation of load
  (amperage) once for every revolution of yankee
  multiplied by number of baffles.
• Baffle should be installed only after balancing.

63
Baffle Commissioning

• After installation of baffle, first of all,
  balancing of yankee has to be checked. Having
  done that, the baffles should be checked for
  suitability. For the same, water is filled inside
  yankee, and condensate line is flanged dummy.
  This way, no condensate (water) can be removed
  from yankee. Now yankee is rotated at different
  speeds, and fluctuation in load (difference
  between maximum and minimum amperes) is
  noted.This load fluctuation will be more at
  higher speeds than that at lower speeds.

64
Baffle Commissioning

• From the noted amperage fluctuation values, it
  must be ensured that the drive should not trip at
  maximum load condition.
• Also, baffles should be mechanically strong
  enough to withstand shock load that may arise
  during operation in case of flooding yankee.
• It should also be checked that the baffles do not
  obstruct condensate flow in case of normal
  operation of yankee.

65
Conclusion

• The basic approach to be followed is to detect,
  measure and correct for any action that has to be
  done for the safety of any equipment.
• Above all, a team work and association of every
  individual towards the goal of COMPLETE SAFETY is
  a must.

66
A Final Word.

• Let us-
• HOPE FOR THE BEST
• PREPARE FOR THE WORST.

67
Feedback

• Please send your feedback to
• D K Singhal
• Deveshksinghal_at_rediffmail.com
• Deveshksinghal_at_gmail.com

68
D K Singhal

• Basically an M.E. (Pulp Paper) from Institute
  of Paper Technology, (University of Roorkee, now
  IIT, Roorkee), Saharanpur, 1993. Did B.E. (Pulp
  Paper) from the same institute in 1990. Certified
  Energy Auditor from Bureau of Energy Efficiency
  (BEE), India.
• Having about 15 years of experience and author
  of more than three dozen technical research
  papers covering a vide range of topics including
  waste paper sorting, pulping, waste paper
  recycling, energy conservation, optimization,
  chemical recovery, paper mill electricals, power
  generation, rewinder optimization for trim loss
  minimization, paper making, process
  instrumentation automation, computer
  simulation, quality monitoring etc.
• Contact
• D K Singhal, Sargam Theatre,
• Chandpur 247 625, Dist. Bijnor
• Phone [phone],222330 (O)
• Fax [phone] Mobile [phone]
• E-mail deveshksinghal_at_rediffmail.com
  chandpurpapers_at_yahoo.com