Opportunities to Improve Energy Efficiency on paper machine Dr. Vivek Kumar Department of Paper Tech

1
Opportunities to Improve Energy Efficiency
on paper machineDr. Vivek KumarDepartment of
Paper TechnologyIIT Roorkee, Saharanpur Campus
2
Introduction

• The paper mill area is a major energy consumer in
  most integrated pulp and paper mills.
• Energy consumption and cost per ton vary widely
  on paper machines.
• Mills have different energy costs based on mill
  configuration, vintage of papermaking equipment,
  geographic location, and other parameters.
• Each mill needs to develop an understanding of
  energy cost factors before preparing an effective
  energy reduction program.

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• Techniques for improving energy efficiency on
  paper machine i.e., Forming Section, Pressing
  section, Drying section.
• Optimize performance of equipment.
• Use steam, water, air, and vacuum pressures
  appropriate to processes.
• Minimize energy losses.
• Minimize water evaporated in the dryers.
• Heat Recovery.

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Forming section
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Vacuum system

• The vacuum system is among largest process in the
  paper mill with respect to space requirements,
  piping, and energy usage. Vacuum systems can have
  installed and required energy of 500 to 8,000 hp.
• Several steps are required to guarantee the
  vacuum system is operating as efficiently as
  possible.
• Vacuum system audits or surveys.
• Routine maintenance of vacuum pumps and auxiliary
  equipment, including belt and gear drives and
  motors
• Replacement and calibration of gauges and process
  instrumentation

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How do we control or minimize wasted energy?

• Vacuum system audits
• Once identified, some vacuum system problems
  may cause higher energy usage, costs, and
  inefficiencies for the entire system.
• Hot seal water.
• High seal water flow due to unregulated or high
  seal water pressure.
• Back pressure on the vacuum pumps due to system
  design or operational problems.
• Synchronous vs. induction motors, which may
  affect the power factor.

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Vacuum system........

• Elevated seal water will reduce vacuum pump
  efficiency and will lower vacuum system capacity.
• However, there are methods to reduce seal water
  consumption without sacrificing vacuum pump
  performance. This can involve a water recovery
  plan and/or cooling the water with a cooling
  tower. It is important to note that special,
  dirty-water cooling towers have been successful
  in this application.

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Vacuum system........

• We must have to maintain a vacuum system in such
  a way that it should not have more than 1 psig of
  back pressure measured at the pump discharge.
• Also we have to maintain the system clean and the
  scale build up as minimum as possible.
• In systems where a discharge sump is used, high
  water levels within the sump can cause back
  pressure as well as contribute to poor air/water
  separation within the sump.

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Vacuum system........

• MOTOR SIZE/VACUUM PUMP HORSEPOWER
• Another issue involving motors is the selection
  of the motor size with respect to the vacuum pump
  horsepower. Many mills elect to install oversized
  motors on equipment to reduce spare parts and
  storeroom inventory. Many vacuum pumps are
  installed and driven with a motor from an old
  refiner that may have 50 more horsepower than
  the vacuum pump requires.
• A frequent practice is to replace a correctly
  sized drive motor with a larger size to eliminate
  overloading and trip-out problems. This is an
  example of correcting the symptom rather than
  solving the problem.

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Vacuum system........

• MOTOR SIZE/VACUUM PUMP HORSEPOWER
• Older, inefficient vacuum pumps versus new,
  modern designs
• Scale build-up
• Process carryover and high seal water flows
• Piping losses or poor system design.

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Vacuum system........

• Newer larger pumps can reduce the quantity of
  pumps on a paper machine by one half.
• Scale, or calcium carbonate buildup, will
  increase vacuum pump horsepower requirements by
  as much as 20 to 30 and often locks up the
  rotor within the vacuum pump.
• Water treatment and descaling programs are useful
  in the prevention of scaling. Recirculated seal
  water systems with cooling towers, have
  experienced better control of the water quality
  for the vacuum pumps.

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• Case Study

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Vacuum system........

• In one audit it is mentioned as, the total vacuum
  system power consumption was 3,040 hp. Allowing
  for performance tolerances and drive losses, the
  system should require only 2,775 hp. This
  excessive power consumption of 265 hp was due to
  several factors affecting. The problems included
  overloading due to high seal water flows and
  internal scaling.
• Vacuum pump operated at 11.3 in. Hg,
• Highest vacuum level of the was 7.0 Hg. The
  extra horsepower to operate the vacuum pump at
  11.3 in. Hg required an additional 34 hp

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• Another vacuum pump was requiring 36 hp more than
  necessary due to the incorrect model being
  installed. This was a high vacuum model, designed
  for more efficient operation at above 15 in. Hg.
  However, the pump was on the low vacuum press
  zone and operated at only 7 in. Hg. A low vacuum
  model needed to be installed to reduce
  horsepower.
• By making some changes in felt conditioning,
  there was an opportunity to save an additional
  108 hp.

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Replacement of Existing Vacuum Pumps

• Current Situation
• In Paper machine No. 1 two vacuum pumps
  (capacity 1800 m3/hr rated vacuum 400 mm Hg
  each) are provided and having common header (i.e.
  for Flat Boxes uhle Boxes) and consuming 107
  kWh
• Suggestion Benefits
• As the suction vacuum requirement is only 200
  mm Hg. It is recommended to install a new vacuum
  pump of higher capacity (rated suction vacuum 300
  mmHg, capacity 3500 m3/hr) in place of existing 2
  vacuum pumps, which will consume about 65 kWh.
  Saving potential is 107 65 42 kWh or Rs. 8.05
  lacs/annum against investment of Rs. 3.00 lacs.

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• Situation Current
• In Paper machine No. 2 two vacuum pumps
  (capacity 1800 m3/hr rated vacuum 400 mmHg
  each) are provided and having common header (i.e.
  for Flat Boxes uhle Boxes) and consuming 77
  kWh.
• Suggestion Benefits
• As the vacuum requirement is only 200 mmHg.
  It is recommended to install a new vacuum pump of
  higher capacity (rated vacuum 300 mmHg, rated
  capacity 3200 m3/hr) in place of existing 2
  vacuum pumps, which will consume about 56 kWh.
  Saving potential is 77 56 21 kWh or Rs. 4.02
  lacs/annum against investment of Rs. 3.00 lacs.

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• Current Situation
• In paper machine No.4 one vacuum pump (KVM
  900 capacity 3600 m3/hr, Rated vacuum 500 mmHg)
  has been installed for uhle Box, which is
  consuming 104 kWh.
• Suggestion Benefits
• As the requirement of suction vacuum in
  uhle Box is around 200 mmHg. It is suggested to
  convent it as per the specification i.e. Capacity
  4125 m3/hr, Rated vacuum 300 mmHg. At these
  specification the power consumption will be about
  70 kWh. Therefore saving potential is 104 70
  34 kWh resulting in saving of Rs. 6.5 lacs/annum
  against investment of Rs. 5.00 lacs.

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• Current Situation
• In paper machine No.5 one vacuum pump (7LV
  Capacity 1410 m3/hr, Rated vacuum 660) has been
  installed for flat boxes, which is consuming 48.7
  kWh power.
• Suggestion Benefits
• As the requirement of suction vacuum is only
  200 mmHg in flat boxes, it is suggested to
  replace existing vacuum pump with KVM 300
  (Capacity 1500 m3/hr, Rated vacuum 300 mmHg),
  which will consume only 24.5 kWh power. Therefore
  saving potential is about 48.7-24.5 24 kWh
  resulting in saving of Rs. 4.6 lacs/annum against
  investment of Rs. 2.00 lacs.

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• Current Situation
• In the paper machine No.7 four vacuum pumps
  (all KVM 600) are running continuously and
  having common header for Couch, suction press,
  flat boxes uhle box. Requirement of suction
  vacuum in Couch and suction press is high i.e.
  upto 400 mmHg and in Flat Box and uhle Box, it is
  less i.e. 200 mmHg. All the four pumps are
  consuming about 273 kWh power.
• Suggestion Potential
• As the requirement of suction vacuum is
  less in case of Flat Boxes and uhle box it is
  recommended to fabricate separate lines for two
  vacuum pumps and reduce the rpm 500 from present
  550 rpm. A saving potential of 14 kWh is
  estimated against reduction of rpm resulting in
  saving of Rs. 2.7 lacs with an investment of Rs.
  50,000.

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• Improvement Effect(A) Rs. 32.96 lacs/annum
• Investment (B) Rs. 13.50 lacs
• Simple Pay Back (B/A) 5 months

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Energy Efficient Formers

• Twin wire forming is new principle had the
  advantages of avoiding the free surface between
  mix and air, of increasing the dewatering
  capacity by allowing dewatering capacity through
  two wires.
• The forming sections is very short and the
  formation takes place in a fraction of the time
  it takes for a Fourdrinier machine.

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• Produces a paper of equal and uniform quality at
  a higher rate of speed. Coupling the former with
  a press section rebuild or an improvement in the
  drying capacity increases production capacity by
  as much as 30.
• Energy savings come from reduced electricity
  consumption . The technology also may improve
  quality and electricity savings of 41 kWh/t of
  paper.

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High consistancy forming

• In high consistency forming, the furnish (process
  pulp) which enters at the forming stage has more
  than double the consistency (3) than normal
  furnish. This measure increases forming speed,
  and reduces dewatering and vacuum power
  requirements.
• Electricity savings are estimated at 8 that is
  about 41 kWh/t of paper.

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Pressing section
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PRESSING ARRANGEMENTS

• Drying the sheet of paper using steam heated
  dryers is a lot more expensive than using
  efficient presses. The primary function of the
  press section therefore is to remove as much
  water from the sheet as possible, consolidate the
  sheet and improve the surface smoothness.

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Extended nip press (Shoe press)

• The additional pressing area allows for greater
  water extraction, (about 5-7 more water removal)
  to a level of 35-50 dryness.
• This technology reduces the load on the dryer, it
  allows plants to increase capacity up to 25 in
  cases where the plant was dryer limited.
• Extended nip pressing also increases wet tensile
  strength.

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Hot pressing

• Pre-heating the water in the paper sheet before
  pressing can reduce the evaporation load.
• Use of steam showers has been estimated to reduce
  the steam requirement by 1 kg of steam per kg
  paper. We estimate steam energy savings of 0.61
  GJ/t paper through hot pressing.

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• Case Studies

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• Installation of Steam Boxes in the Press Sections
• Current Situation
• There are no steam boxes installed in the
  press section
• Suggestion
• With the Installation of steam boxes the
  following optimizations are possible
• Increase of production capacity or reduction of
  steam consumption in the dryer section
• Improve moisture profile

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• In general the design data of steam boxes are
• Steam consumption approx. 80 - 120 kg steam /
  tonne paper (the value depends on the dryness
  of the paper)
• Potential of warming up the paper web from 10 to
  15 K
• 10 K increase of paper web temperature
  corresponds with an increase of dryness after the
  press section of about 1
• 1 increase of dryness after press section leads
  to 5 higher production or 5 less steam demand
  in the drying section
• With the installation of steam boxes in the press
  sections of PM 4 and PM 5 the following steam
  reduction is possible-

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• PM 4 (3.26 t paper / hour)
•       Steam consumption 3.4 t/t 11 t/h
•       Steam saving in drying section 6 0.66
  t/h
•       Steam demand steam box 0.3 t/h.
• PM 5 (2,6 t paper / hour)
•       Steam consumption 3.9 t/t 10 t/h
•       Steam saving in drying section 6 0.6
  t/h
•       Steam demand steam box 0.23 t/h.
• Furthermore after installation of a steam box
  less evaporation (0.1 to 0.2 m³/h) occurs in the
  drying section which can reduce condensation in
  the pre-drier section of PM 5.

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potential

• Improvement Effect (A) Rs. 21.0 lacs/annum
  in PM 4
• (Steam reduction 2880 t/a)
• Rs.
  21.6 lacs/annum in PM 5
• 
  (Steam reduction 2960 t/a)
• Investment (B) 100.00 lacs / steam
  Box
• Simple Pay Back (B/A) 5 years

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• Drying Section

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DRYING ARRANGEMENTS

• To optimize energy use in the drying process, it
  is essential to clearly identify the areas and
  actions that offer measurable opportunities for
  improvement. Reducing the evaporation load to the
  dryer section is a smart starting point. Pressing
  improvements are the best way to reduce dryer
  section steam use.

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• Improving machine efficiency is another obvious
  path.
• Identifying losses from the dryer drainage system
  is essential.
• The cost of high-pressure steam should be
  factored into dryer energy cost.
• Minimizing the dryer air heating requirement.

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Improper siphon size

• Replacing rotary siphons with stationary siphons
  in dryers that discharge directly to the
  condenser offers potential for improvement.
  Stationary siphons are designed for a blowthrough
  steam flow of 10 versus 20 to 25 often
  required with rotary siphons.
• Proper siphon design is a key to keeping the
  system "tight".

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Maximize the Use of Low-Pressure Steam

• This allows the most electricity to be generated
  at the boiler house, using the high-pressure
  steam to power an electricity-generating turbine.
  
• Using dry low pressure steam is advantageous when
  considering energy efficiency due to high
  condensing heat rate.

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Minimize Dryer Air Heating Requirement

• Adjust the pocket ventilation air temperatures to
  match the drying requirements and hood design.
• The hood must be well sealed and have good
  insulation properties to operate with low pocket
  ventilation air temperatures.
• Air to air heat recovery systems on existing
  machines recover only about 15 of the energy
  contained in the hood exhaust air. This
  percentage could be increased to 60-70.

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• Paper machines with enclosed hoods require about
  one-half the amount of air per machine reduces
  thermal energy demands since a smaller volume of
  air is heated. Electricity requirements in the
  exhaust fan are also reduced. Steam savings of
  0.76 GJ/t paper and electricity savings of 6.3
  kWh/t paper by installing a closed hood and an
  optimized ventilation system is estimated.

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• Case Studies

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• Stopping of steam condensate leakages from the
  pocket ventilation system
• The Pocket ventilation system for dryer group
  (II) (III) consists of steam heaters for heating
  the inlet air. There are two rows of steam
  battery which operates on the steam pressure of
  3.5 Kg/ cm2 .

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• The condensate of steam is collected through
  bottom line in separate tank. It was found, that
  there was lot of steam and condensate leakages
  and all area below Pocket ventilation system
  nearby is flooded with condensate.
• RECOMMENDATION
• It is recommended that steam condensate
  leakages should be stopped immediately.

ECONOMICS Cost of 1 m3 condensate Rs. 60
(including heat value) Improvement Effect
Saving by stopping condensate
draining (5m3 daily) Approx 60 5 Rs.
300 wastage Annual Saving 300330 Rs.
99,000/- Investment Negligible Pay
back Immediate
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Closing of side panels doors of dryer hoods of
both machines

• Background
• It was observed that the lifting doors of both
  machines are always partially lifted and all
  basement area is open.
• The closed hood is therefore working as semi
  closed hood and lot of air infiltration is takes
  place from machine house.
• This reduces the drying efficiency of dryers and
  hence more steam is consumed for drying the same
  quantity of paper. It also reduces the
  efficiency of pocket ventilation system and also
  increases steam consumption in PV system.

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• Beside this the condition of side panels of hood
  was not proper resulting in heavy Infiltrations
  from sides .
• The insulation of side panels were also in bad
  shape. All these reduce the efficiency of hood,
  resulting in more power consumption at exhaust
  fans.
• Recommendation
• It is recommended that machine should run with
  lifting door in down position.
• The doors should be lifted only at the time of
  paper break and should be brought down after
  rethreading of paper.
• Also all infiltration should be stopped and
  insulation of side panels and roof should be
  repaired / replaced.

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• BENEFITS
• By proper insulation, repairing and stopping
  infiltration of air in hood efficiency in drying
  will be improved.
• By assuming 1 improvement in hood efficiency,
  mill can save 0.24 t/hr steam resulting in saving
  of Rs. 15.20 lacs/annum as shown below.
•   1 improvement in drying 0.24 t/hr after
  reducing in steam consumption.
• 
  0.24t/hr
• 
  5.76T/day or 1900 T/annum
• 
  1900 400
• ECONOMICS
•   Savings Rs. 15,20,320/-
• Investment Rs. 5,00,000
• Pay back 3 months

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Insulation of Hot Surfaces in Paper Machine

• BACKGROUND
• During the audit at mill, it was observed
• that various pipelines and Paper machine
• dryers having higher temperature are not
• insulated resulting in high heat losses
• through these uninsulated insulated
• surfaces in the form of radiations.

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• It is suggested to put proper insulation on all
  bare surfaces to reduce the heat loss through
  radiation and save the energy wastage.
• Detail of Uninsulated lines

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• Benefits
• By putting the insulation on the uninsulated
  surfaces enormous calories of heat energy can be
  saved, which is equivalent to a saving of 2127
  ton of steam per annum resulting in saving of
  Rs.8.51 lacs per annum with a payback period of
  2-8 months for putting the insulation.
•  Economics
• Improvement effect (B) Rs.
  8.51Lacs/annum
• Investment Amount (A) Rs. 4.28 Lacs
• Simple pay Back (B/A) 2-8 months

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Replacing of the missing air filter panels and
cleaning of air filters .

• RECOMMENDED
• It is recommended that air filter panel of PV
  system should be repaired and maintained in
  proper condition regularly. All missing filter
  panels should be placed in position and should
  be cleaned from dust.

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• BENEFITS
• By adopting this proposal, clean air will be
  purged in pocket ducts of dryer, reducing chance
  of dirty air to bleached paper.
• This would improve the paper surface quality.
  Also the energy consumed by PV fan would reduces
  marginally.

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Use of flash steam of main condensate tank in
pocket ventilation system

• The condensate of last group dryers are
  collected in the main condensate tank from where
  it is pumped to boiler house.
• It was observed that the flash steam from main
  condensate tank is vented to atmosphere.
• Without recovering its heat value. About 80 kg/hr
  flash steam is vented.

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• RECOMMENDATION
• It is recommended that this flash steam should be
  used in the steam battery of PV system. Since the
  flash steam is not sufficient for PV system, the
  live steam will also be used but the use of flash
  steam would reduce the use of live steam in PV
  system.
• BENEFITS
• Assuming 2 tonne flash steam per day utilized in
  the PV system, mill can save Rs. 3.96 lacs/annum
  by using it in PV system.

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• Installation of Heat Recovery System in Paper
  Machine 5
• Current Situation
• The pre-dryer section of PM 5 is equipped with a
  closed hood
• The current situation is as follows
•    Daily production of PM 4 60 t/d
•    Evaporation rate 4 m³/h (pre-drier
  section)
•    Exhaust pre-dryer section 1 17530 kg/h
  68.3C / 51.2
•    Exhaust pre-dryer section 2 14250 kg/h
  71.4C / 43.5
•    Exhaust air mass flow 31780
  kg/h
•    Supply air mass flow 21000
  kg/h(66 )
•    Leak air mass flow
  10780 kg/h

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Current Situation
17.530 kg/h 68,3C/51,2
14.250 kg/h 71,4C/43,5
29C / 33,3
Supply air for the hood coming from the hall
18.200 kg/h
Filter by-passed
Leak air from the hall into the hood
external air polluted
Exhaust air from the hood in the hall
Exhaust air from the vacuum system into the hall
50C/ 99/ 85,3 g/kg
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• There is no heat recovery system installed in the
  exhaust air system. The supply air (120C) is
  heated by live steam.
• The supply / exhaust air proportion (66 ) is
  within the range of recommended values.
• The filter in the external supply air system is
  by-passed.
• Furthermore wet exhaust air from the vacuum
  system is led into the basement. There is
  condensation in the hood when the hood is closed.

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Suggestion
25C /49
70C 32,000 kg/h
54C
44C 21,000 kg/h
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Suggestion

• To make hood closing possible and thus increasing
  the quality of paper it is suggested to increase
  the supply and exhaust air mass flows step by
  step (target values supply air mass flow 28,000
  kg/h / exhaust air mass flow 42,000 kg/h the
  target values might not be reached because of
  design of the existing air system).
• This leads to an increase of electricity
  consumption but also to a reduction of steam
  consumption. It is estimated that these changes
  in energy consumption are not affecting the
  operational costs.
• Furthermore it is recommended to lead the exhaust
  air from the vacuum system out of the hall and to
  lead the external supply air through the filters.
  

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• advances in drying

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Impulse Drying

• Impulse drying works by lowering the moisture
  content of the paper web entering the drying
  section by up to 38 percent. In a conventional
  papermaking operation, the web has a moisture
  content of 50 to 60 percent as it enters the
  drying phase.
• It is estimated that the operation of 65 impulse
  drying units in the year 2020 could save 13
  trillion Btus of energy annually for the
  industry.

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Infrared drying

• Along with improved energy efficiency, it
  increases the drying power output. Infrared
  dryers are powered by electricity, and require
  about 4.08 GJ of electricity/t paper versus 8.16
  GJ of steam/t paper for conventional steam dryers
  (Jaccard, Willis.). We therefore estimate primary
  energy savings of 3.3 GJ/t paper.
• Investment costs for infrared dryer installation
  are Rs.5203/t paper including OM costs
  requirements.

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Condebelt drying

• This drying technique has the potential to
  completely replace the drying section of a
  conventional paper machine, with a drying rate
  5-15 times higher than conventional steam drying.
• For large machines savings of 10-20 steam are
  possible (1.6 GJ/t of paper) and a slight
  reduction in electricity consumption (20 kWh/t of
  paper). Capital costs are considered to be high,
  although the size of the drying area can be
  reduced.
• This provides opportunities to enhance energy
  economy. Energy for the Condebelt has three
  components primary steam used per kg of
  evaporated water, recovery of the latent heat
  from the steam evaporated from the web, and
  electrical energy.

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• Typical steam consumption is about1.31.5 kg per
  kg of evaporated water.
• In the Condebelt process, about 85 of the heat
  can be recovered. Thus the temperature of the
  pulp entering the headbox can be increased by
  10C using the excess heat from the Condebelt.
• The total electrical energy consumption in a
  Condebelt dryer is comparable to that found in
  conventional cylinder drying.

63
Air impingement drying

• This technology can be combined with existing
  technologies. Heat input requirements have been
  modelled at 3 MJ/kg evaporated water, or a 10-40
  savings in steam requirements. Electricity
  requirements are expected to increase by 0-5.
• This involves optimization of the geometry of the
  nozzle pattern, nozzle type ,nozzle
  velocitydiameter, nozzle to sheer distance.

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Steam impingement drying

• Steam requirements are estimated at 4.5 GJ/t
  paper with additional savings available if the
  latent heat from the purge steam is captured. De
  Beer, estimates a savings of 10-15, with a
  slightly lower reduction in electricity
  requirements (5-10).

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• Thank you

66
Avoid Idle running of motor of hood blower in
paper machine

• Background
• During the visit it was observed that motor of
  hood blower of paper machine was running idle
  without fan.
• The shaft or connection between motor fan has
  been broken and motor runs continuously without
  fan for 24 hours.

67

• RECOMMENDATION
• It is recommended that proper maintenance
  should be taken care and all such system should
  be checked at least once a shift.
• BENEFITS
• Assuming the motor running goes unnoticed for
  a day, Loss in electrical energy 30kW X24
  720kWh.
• Assuming 30 load 216 kWh/ day
• Annual saving 216 1.61 330
• 1.14
  Lacs/annum

68

• ECONOMICS
• Investment Negligible
• Savings Rs. 1.14 Lacs/annum
• Pay back period with in one month

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Motor considerations

• Vacuum pumps are driven by induction and
  synchronous motors using v-belt drives and gear
  reducers, as required.
• The use of synchronous motors is based on
  reliability, space considerations, and
  elimination of the need for power transmission
  equipment (v-belt drives and gear reducers).
• Also it is observed that some mills elect to use
  higher speed synchronous motors (1,200 or 1,800
  rpm) and gear reducers that may offer cost
  savings over the larger, slow speed synchronous
  motors.

70

• Current Situation
• In Paper Machine No.3 one vacuum pump
  (KVM-600) has been installed for S. Couch and
  drawing 90 kWh.
• Suggestion Benefits
• As per the manufacturer performance table,
  motor should draw only 53 kWh against present 90
  kWh. Therefore it is suggested to contact the
  supplier for the root cause analysis of higher
  Energy Consumption. Saving potential is 90 69
  37 kWh resulting in saving of Rs.7.10 lacs /annum
  by maintenance of existing pump.

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