Recovery Boiler Research Needs An Industry Perspective

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Recovery Boiler Research Needs An Industry
Perspective

• Andrew Jones
• International Paper
• St. Petersburg Recovery Cycle Seminar

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International Paper

• We have sales of about 25B/yr
• We employ 83,000 people
• We operate 19 pulp and paper mills around the
  world including the USA, Russia, Poland, France,
  Brazil. With many more smaller facilities (paper
  mills, converting plants) in over 120 countries
• We currently operate 42 recovery boilers
• The largest is 7.4MM lbs DS/day (3350 Metric
  tons/day)
• The smallest is 0.8MMlbs DS/day (363 Metric
  tons/day)
• We have many older boilers currently 36 of our
  boilers are more than 20 years old

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About me

• Ive worked for International Paper for 9 years
  and Im responsible for making sure our recovery
  boilers operate with the highest energy
  efficiency, with minimum downtime due to fouling
  and that improvements are made to our recovery
  boilers when justified
• Prior to my current job I worked for
  ABB-Combustion Engineering on recovery boiler
  operations/design and RD
• I received my PhD from the Institute of Paper
  Chemistry in 1989 topic was CFD modeling of a
  Kraft recovery boiler
• Past Conference and Program Chair of the
  International Chemical Recovery Conference
• Adjunct Professor at the University of Toronto

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International Paper Recovery Operation Goals

• Key Concerns of International Paper regarding
  recovery boiler operations
• Minimize downtime on recovery boiler, with the
  goal of eliminating water washes and dry cleaning
  between annual outages
• Operating strategies that generate the most net
  energy from black liquor
• Positive impact of the recovery boiler on
  recovery cycle energy efficiency
• Minimize penalty of operating older technology
  versus new boiler performance
• In some cases maximizing recovery boiler
  throughput is very important

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Minimizing Downtime

• Recovery Boiler downtime costs from 100,000 to
  300,000 per day at our facilities
• Water washes if a boiler is severely fouled take
  from 24-40 hours
• We also have to do frequent dry cleanings on our
  boilers where we stop liquor firing and operate
  sootblowers continuously in the superheater and
  generating bank areas of the boilers this can
  damage the recovery boiler due to cyclic fatigue
• Our goal is to eliminate both of these causes of
  downtime on our recovery boilers

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Minimizing Downtime

• What we require are
• Recovery boiler operating strategies that
  minimize fouling
• Tools for assessing the impact of changes in
  chemistry on boiler fouling in order to make wise
  choices on how to reduce levels of chloride and
  potassium (the most important elements affecting
  fouling)
• Guidelines on how to most effectively use
  sootblowers or other cleaning methods to minimize
  boiler fouling
• Identification of upgrades to boiler operating
  equipment that are most effective in reducing
  fouling

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Strategies to increase recovery boiler net
thermal efficiency

• Maximize percent solids
• Maximize steam temperature
• Maximize steam flow
• Minimize excess air at stack
• Minimize fouling
• Minimize sootblowing
• Minimize auxiliary power use

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Maximize Percent Solids

• Stabilize at as a high a percent solids as
  possible from concentrator
• Controls and better understanding of fouling
  process
• Minimize the use of direct heating with steam
• Higher percent solids in liquor
• With direct contact evaporators minimize the use
  of dilution water
• Control solids at evaporator outlet to normally
  not require dilution in cascade or cyclone

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Maximize Steam Temperature

• Steam temperature can be reduced if Chloride
  levels in black liquor are high
• Can be a significant justification for cost of
  chloride control
• Corrosion may require more attemporation in order
  to limit exit steam temperature
• Higher steam temperatures results in additional
  power generation
• This can be of considerable value

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Maximize Steam Flow

• This goal applies on steam limited recovery
  boilers
• Apply controls so that the boiler operates as
  close as possible to the steam limit (Consumed
  air controls)
• Allows you to generate as much low cost steam as
  possible
• Also helps production!

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Minimize Excess Air At Stack

• Excess air can be coming in through fans or as
  leakage (tramp) air in the areas of the boiler
  with high draft
• From an efficiency standpoint the goal is to
  minimize excess air at the stack
• Combustion air can be minimized by good air
  system operation and control
• Leakage air minimization requires good
  maintenance practices

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Minimize Fouling

• This is beneficial for a number of reasons
• Increases the thermal efficiency of the boiler
• Reduces sootblowing steam usage
• Reduces ID fan horsepower as these are typically
  variable speed drives
• Knowing all about how we can do this from an
  operational, chemistry and cleaning strategy is
  vital

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Minimize Sootblowing

• The steam used for sootblowing can often be very
  expensive
• In the USA it can be as much as 10/1000 lbs
  (4.5/Metric Ton)
• In 2005 International Paper spent about 35
  million on soot blowing steam company-wide
• Many methods exist for reducing consumption of
  sootblowing steam while not negatively impacting
  recovery boiler fouling
• What are the most effective methods and where
  should they be applied?

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Minimize Auxiliary Power/Steam Use

• Fans consume a lot of power
• Examine if they are oversized, if so they can be
  replaced
• Excessive air temperature may be consuming high
  cost steam
• It generates steam on the recovery boiler but
  there is some efficiency loss
• Condensate systems on steam coil air heaters can
  be inefficient

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Impact of the Recovery Boiler on Cycle Efficiency

• High dregs
• Low reduction
• Variable baume from dissolving tank

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High Dregs

• The main negative impact of high recovery boiler
  dregs is on the mud solids on the lime kiln
• Mud solids decrease
• Increases fuel usage on the kiln
• High recovery boiler dregs can be due to poor
  operation and control of the recovery boiler

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Low Reduction Efficiency

• The main negative impact of low reduction
  efficiency is increased evaporation of the water
  associated with the sodium sulfate
• Cost of low reduction efficiency is not fully
  understood

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Poor Control of Green Liquor Strength

• High variability in green liquor strength (baume)
  will result in variability in the causticizing
  efficiency
• This increases the evaporative load due to the
  water associated with the sodium carbonate

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Minimize the Penalty of Operating Older
Technology

• We will continue to operate direct contact
  boilers for many years
• These boilers have lower thermal efficiency as
  they use direct heating of liquor with flue has
  as a means to evaporate water
• Typically 20 less steam generation for same
  amount of black liquor burned
• How to minimize the negative impact of these
  boilers
• Avoid over-oxidizing the liquor
• Maximize percent solids
• Minimize downtime due to more complex operating
  systems
• Upgrade air systems to reduce excess air used

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Maximizing Recovery Boiler Throughput

• Minimizing downtime is important as stated
  earlier, but maximizing throughput also requires
  operating the boiler at as high a load as
  possible
• Means of doing this
• Upgrade to components of the boiler
• Air system generally most important
• Better controls that allow operation closer to
  maximum level
• Reducing the rate of boiler fouling
• Reduced levels of Chloride in black liquor most
  important
• The challenge is to determine which steps are
  most critical for a certain boiler and to make
  the correct improvements

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Critical Research Needs

• Research need 1 Maximizing and stabilizing
  concentrator product solids at maximum levels,
  how to this and what is the energy impact
• Research need 2 Maximum exit steam temperatures
  as a function of materials and deposit properties
  and the energy, how to do this and what is the
  energy impact

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Research Needs

• Research need 3 Minimizing fouling and the
  impact on boiler efficiency
• Research need 4 Methods for reducing
  sootblowing steam consumption and the energy
  impact
• Research need 5 Minimizing recovery boiler
  dregs formation
• Research need 6 Energy impact of low reduction
  and causticizing efficiency

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Definitions of Terms

• Dry Cleaning a way of cleaning a recovery
  boiler where the burning of liquor is stopped
  (and sometimes of all other fuels as well) and
  the sootblowers are operated in just the
  superheater area (sometimes in the generating
  bank as well)
• Sootblowers A rotating lance that is inserted
  into the boiler with two nozzles at the end of
  the lance that direct superheated steam at the
  deposits in a recovery boiler in order to remove
  them
• Dilution Water water added in a cascade
  evaporator or a cyclone evaporator in order to
  reduce the percent solids of the black liquor
  produced by this equipment, done in order to
  prevent the formation of high viscosity black
  liquor

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Definition of Terms

• Leakage air air that enters a boiler other than
  through the air openings. For example the liquor
  gun openings, the smelt spouts and any openings
  in the boiler other than the air openings
• Dregs undissolved material (organic and
  inorganic) that is suspended in the green liquor
  formed from a recovery boiler
• Baume A measure of the specific gravity
  (density versus the density of water) for a
  liquid stream containing dissolved solids
• Causticizing the process of converting sodium
  carbonate to sodium sulfide by the use of slacked
  lime (calcium hydroxide)
• Percent reduction (or chemical reduction)
  sodium sulfide (mole fraction) divided by sodium
  sulfide sodium sulfate (mole fractions) times
  100, typically has a value of about 90-95 in
  green liquor