CFB Performance ROZELLE DOE 2006

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CFB Performance ROZELLE DOE 2006 Powered By Docstoc
					Models for Predicting Bed-Related
 CFB Performance Parameters


                          Pete Rozelle
             U.S. Department of Energy
                 ARIPPA, May 23, 2006
             Some CFB Plant Issues
               Related to Solids
              Characteristics and
                    Flows




Undersized
Bottom Ash
Equipment
             Some CFB Plant Issues
               Related to Solids
              Characteristics and
                    Flows




                       Excessive Upper
                       Combustor
Undersized
                       Temperature
Bottom Ash
                       (Delta P Too Low)
Equipment
                 Some CFB Plant Issues
                   Related to Solids
                  Characteristics and
                        Flows




Excessive
Limestone
Consumption
                           Excessive Upper
                           Combustor
    Undersized
                           Temperature
    Bottom Ash
                           (Delta P Too Low)
    Equipment
  Two Items to be Covered Today
• Bottom Ash Flow Rate
  – Based on Readily Measured Fuel Properties
• Limestone Consumption
  – Based on Ash and Limestone properties
• Both of the Above
  – Based on Boiler Operating Parameters (DCS
    Data)
  – Boiler Solids Partition Function
Solids Flows in Mineral Processing
 Physical Separation Equipment

                         Product
                         Stream

                   Separation
 Feed
                    Stimulus
Stream


                         Tailings
                         Stream
  Quantifying the Separation by a Coal
   Preparation Circuit: the Partition
                Function
                                                                 Coal



                                                     Partition
    Raw Coal                                         Function
                                                     k(y)




                                                                 Refuse


k(y) is the mass fraction of particles of specific gravity y that reports to the coal
stream The sum of each gravity interval times k(y) is the clean coal yield.
Applying the Partition Function to a
            CFB Boiler
                                                                Flyash Flow
                                                                Ffa


                                                    Partition
    Composite Ash                                   Function
    (Reconstituted Feed)
    Flow                                            kd(x)



                                                                Bottom Ash Flow
                                                                Fba


kd(x) is the mass fraction of particles of ash size interval x that reports to bottom
ash stream The sum of each size interval times kd(x) is the bottom ash flow rate.
Example of a Generic Partition
          Function



   kd(x)




           Decreasing Particle Size
          What is Needed to Develop a
         Partition Function for a Boiler
•    Flyash and Bottom Ash Size Analyses
•    Flyash and Bottom Ash Flow Rates
    1.    Major and Minor Oxide Analyses for Flyash, Bottom Ash,
          Limestone, and Fuel Ash
    2.    Flyash and Bottom Ash Flow Rates can be Calculated from a
          System of Simultaneous Material Balances (see Next Slide)
•    Composite Ash Flow (by Particle Size) Calculated from
     Flyash and Bottom Ash Flow Rates and Size Analyses
•    Partition Function Calculated from Composite Ash Flow
     (by Size) and Bottom Ash Flow (by Size)
  Calculating Ash Flow Rates from
  Simultaneous Material Balances
CaO and SiO2 Material Balances:
     F f  CaO f  Fs  CaOs  Fba  CaOba  F fa  CaOba
      Ff  SiO2 f  Fs  SiO2 s  Fba  SiO2ba  Ffa  SiO2ba
Lab Analyses:
CaOf: Fuel CaO Content
CaOs: Limestone CaO Content
                                     DCS Quantities:
CaOba: Bottom Ash CaO Content
                                     Ff: Fuel Feed Rate
CaOfa: Flyash CaO Content            Fs: Limestone Feed Rate
SiO2f: Fuel SiO2 Content
SiO2s: Limestone SiO2 Content       Unknowns
SiO2ba: Bottom Ash SiO2 Content     Fba: Bottom Ash Flow Rate
                                    Ffa: Flyash Flow Rate
SiO2fa: Flyash SiO2 Content
  Calculating Ash Flow Rates from
  Simultaneous Material Balances
CaO and SiO2 Material Balances:
     F f  CaO f  Fs  CaOs  Fba  CaOba  F fa  CaOba
      Ff  SiO2 f  Fs  SiO2 s  Fba  SiO2ba  Ffa  SiO2ba
Lab Analyses:
CaOf: Fuel CaO Content            2 Equations and 2 Unknowns
CaOs: Limestone CaO Content
                                      DCS Quantities:
CaOba: Bottom Ash CaO Content
                                      Ff: Fuel Feed Rate
CaOfa: Flyash CaO Content             Fs: Limestone Feed Rate
SiO2f: Fuel SiO2 Content
SiO2s: Limestone SiO2 Content         Unknowns
SiO2ba: Bottom Ash SiO2 Content       Fba: Bottom Ash Flow Rate
                                      Ffa: Flyash Flow Rate
SiO2fa: Flyash SiO2 Content
Calculating the Composite Ash Flow
          Rate by Size- 1
Calculate the Flow Rate of Each Size with
Each Ash Stream- Example:
Bottom Ash Flow Rate = 35,000 pph,
12% of Bottom Ash is 80 Mesh by 100 Mesh,

Flow Rate of 80 by 100 Mesh Size with
Bottom Ash=
       0.12 X 35,000 pph = 4,200 pph
Calculating the Composite Ash Flow
          Rate by Size- 2

Flyash Ash Flow Rate = 45,000 pph,
7% of Flyash Ash is 80 Mesh by 100 Mesh,

Flow Rate of 80 by 100 Mesh Size with Flyash
Ash=
       0.07 X 45,000 pph = 3,150 pph
Calculating the Composite Ash Flow
          Rate by Size- 3
Flow Rate of 80 by 100 Mesh Size with
Bottom Ash = 4,200 pph
Flow rate of 80 by 100 Mesh Size with Flyash
= 3,150 pph

Flow Rate of 80 by 100 Mesh Size with
Composite Ash =
     4,200 pph + 3,150 pph = 7,350 pph
Calculating the Partition Function
              Values

                    f ba  x 
          kd x  
                    f ca  x 

  fba(x) is the flow rate of size interval x with the bottom ash
  (calculated)
  fca(x) is the flow rate of size interval x with the composite ash
  (calculated)
Calculating the Partition Function
              Values

From our Example:


kd(x) for x = 80 by 100 mesh is:


       (4,200 pph)/(7,350 pph) = 0.57
Example of a Partition Function for
          a CFB Boiler
                                        100%
Wt% of Particles to Bottom Ash Stream




                                        90%
                                        80%
                                        70%
                                        60%
                                        50%
                                        40%
                                        30%
                                        20%
                                        10%
                                         0%
                                               3500   530   252       120        72    46   19
                                                            Particle Siz e , Microns
Calculating Ash Flow Rates and the
        Partition Function

• Using Simultaneous Material Balances can reduce
  Effort Required for Measuring the Ash Split
• The Partition Function can be a Useful
  Determinant of Cyclone Performance.
Prediction of Bottom Ash Flow Rate
What is Needed:
• Partition Function
• DCS Data:
  – Solids, Air, and Main Steam Flow Rates
• Solids Analyses
  – Short Prox for Fuel
  – Major and Minor Oxides for Fuel and
    Limestone
  – Float Sinks for Fuel
       The Significance of Float Sink
                 Analyses
They Split the Fuel up by Specific Gravity and Ash
  Content.
Sink      Float     Direct          Direct          Cumulative Cumulative
                    Wt%             Ash%            Wt%        Ash%
             1.50             5.0             5.0          5.0        5.0
   1.50      1.60            10.0             9.0         15.0       7.67
   1.60      1.70            20.0            14.0         35.0      11.28
   1.70      1.80            12.0            19.0         47.0      13.36
   1.80      1.90             8.0            28.0         55.0      15.40
   1.90                      45.0            76.0        100.0     42.67
        The Significance of Float Sink
                  Analyses
                         Combustion Behavior
Low Ash Fuel Particle




High Ash Fuel Particle
                 The Attrition Index
   The Fraction of a Particle Originally Large enough
    to make Bottom Ash that Reports to the Flyash
                        Stream
Low Ash Fuel Particle= 1




High Ash Fuel Particle=0
    And Now Some Model Results:
Quantifying Bottom Ash Flow in Terms of
    Fuel and Limestone Properties
Laboratory Combustor Partition Curve
     The Bottom Ash Model: The Fuel
              Contribution

                                               
                 nx   
Fba , f  F f  k d  x  1  K f ,a  y  M f  x, y A x, y 
                x 1 y 1



From DCS:                            kd(x): The partition function
                                     calculated from boiler data
Ff: The Fuel Feed Rate               Kf(y) the fuel attrition index based
From Float Sink Table:               on particle specific gravity (i.e.
Mf(x,y): The Mass Fraction of        ash content)
Fuel with in Size and Specific       The Result:
Gravity Increment x,y                Fba,f: The flow rate of bottom ash
A(x,y): The Ash Content of the       derived from the fuel
Above Fuel Increment
             Float Sink Analyses

              Mf(x,y)              A(x,y)


Sink      Float         Direct          Direct          Cumulative Cumulative
                        Wt%             Ash%            Wt%        Ash%
             1.50                 5.0             5.0          5.0        5.0
   1.50      1.60                10.0             9.0         15.0       7.67
   1.60      1.70                20.0            14.0         35.0      11.28
   1.70      1.80                12.0            19.0         47.0      13.36
   1.80      1.90                 8.0            28.0         55.0      15.40
   1.90                          45.0            76.0        100.0     42.67
          The Bottom Ash Model: The
            Limestone Contribution

  Fba ,s  Fs 1  Ls 1  S  k d x M s x 1  K s ,a 
                                nx


                                x 1


From DCS:                            kd(x): The partition function
                                     calculated from boiler data
Fs: The Limestone Feed Rate          Ks,a the limestone attrition index
From a Lab Analysis:                 The Result:
Ms(x): The Mass Fraction of          Fba,s: The flow rate of bottom ash
Limestone in Size Increment x        derived from the Limestone
Ls: The Limestone LOI
S: fractional SO3 Content of
Limestone in Bottom Ash
The Bottom Ash Model: The Result




    F'ba  Fba ,s  Fba ,f
  The Bottom Ash Model: some Test
              Results
                     Analyses of Fuels Tested



Fuel                    I          II          III     IV      V       VI

Wt% Ash*                30.2        50.2        35.8    50.2    28.4    40.8

Wt% S*                       2.2         5.5     3.4     5.5     2.6     3.9

HHV, MJ/kg**            22.0        15.0        19.7    15.0    23.2    17.8

Preparation Method     (1)         (1)         (1)     (2)     (3)     (3)

Parent Fuel             I          II          III     II      III     II
The Bottom Ash Model: some Test
            Results
   Preparation Method                  Preparation Method 3
    1 and 2



                        Double Roll
                        Crusher

                                                   -6.25 mm
                                                                  6.25 mm x 1 mm


                                      1 mm Deck
                                                                    Concentrating
                                                                    Table
                                                  -1mm
             Topsize:

             Preparation Method 1:
             6.25 mm

             Preparation Method 2:
             4.00 mm                                                           Refuse
                                                  Prepared Fuel
The Bottom Ash Model: some Test
            Results
   Conditions Used for Combustion Tests


    Firing Rate, MJ/hr                     253

    Superficial Gas Velocity, m/s           3.1

    Sorbent Feed Rate, Molar Ca:S           2.2

    Bed Pressure Drop, Pa                 2,250

    Bed Temperature, K                    1,230
The Bottom Ash Model: some Test
            Results
                                           6
 Measured Bottom Ash Removal Rate, kg/hr




                                           5


                                           4


                                           3


                                           2
                                                                              Predicted Rate = Measured Rate

                                           1


                                           0
                                               0          1            2          3           4           5        6
                                                               Predicted Bottom Ash Removal Rate, kg/hr

                                                   Comparison of Predicted and Measured Bottom Ash Removal Rates
         The Bottom Ash Model

• Reducing the Presence of Coarse, High Ash Content Fuel
  Particles in the Feed can Bias the Ash Split Toward
  Flyash
• Identifying the Species that Create Bottom Ash can
  Narrow the Search for Fuel Constituents that can Cause
  Ash Cooler Problems
• Updated Version is Being Developed
         Prediction of Limestone
              Consumption
What is Needed:
• Partition Function
• DCS Data:
  – Solids, Air, and Main Steam Flow Rates
• Solids Analyses
  – Short Prox for Fuel
  – Major and Minor Oxides for Fuel and Limestone
  – Float Sinks for Fuel
• Limestone Attrition Index
• Limestone Sulfation Levels in Ash Streams
                  The Limestone Model

        ba  1  I s ,a  k d x M s x 
                                          nx


                                          x 1


Ms(x) is the mass fraction of limestone          The Result:
of size x                                        ba: The Fraction of Limestone
Is,a is a CaO Attrition Index                    CaO that will report to the
                                                 Bottom Ash Stream


A word on Limestone and Attrition: Sparry Stones Attrit a Lot more than Micritic
Stones
Limestone Attrition Products




 Micritic Stone     Sparry Stone
The Limestone Model

  fa  1  ba

 fa: The Fraction of
 Limestone CaO that will
 report to the Flyash
 Stream
                The Limestone Model

                               Ff Sf       MWCaO 1
          Fs' 
                       ba         fa  MWs Ca s
                     
                      R                
                       ba          R fa 
                                         

Ff: Fuel Feed rate
                                       MWCaO: The Molecular Weight of CaO
Sf: Sulfur Content of Fuel
                                       MWS: The Molecular Weight of Sulfur
: Fractional Sulfur Capture
                                       Cas: CaO Content of Limestone
Rba: Sulfation Level Characteristic
                                       The Result:
of Bottom Ash
                                       F’s: The Predicted Limestone Consumption
Rfa: Sulfation Level Characteristic
                                       by the Boiler
of Flyash
 The Limestone Model: Comparison
      with Boiler Test Results
             Chemical Analyses of Sorbents Examined

Sorbent                1           2            3            4           11
Wt% CaO                    55.7        55.2         51.9         49.5         42.8
Wt% MgO                    0.41        0.54         0.46         2.86         6.45
Wt% Fe2O3                  0.07        0.05         1.41         0.30         0.61
Wt% SiO2                   0.69        0.74         3.18         3.57         6.65
Wt% Al2O3                  0.31        0.35         0.25         0.45         1.47
Wt% LOI*                   43.4        43.2         42.0         42.1         40.4
Grain Size        Micrite         Spar        Micrite      Micrite      Spar
 The Limestone Model: Comparison
      with Boiler Test Results
                Particle Size Distributions of Sorbents Tested in the Boiler

Particle Size, mm                                    Sorbent (wt% direct)
Passing         Retained       Mean         1         2          3         4        11
      4000            2360        3180           3         3          5         4        3
      2360            1000        1680          16        14         18        14    18
      1000             707            853       15         8         16        17    12
          707          180            443       14         3         13        14        9
          180          149            164        7         3          7         8        6
          149           75            112       10         7          9         9    10
           75              0           38       35        62         32        34    42
The Limestone Model: Comparison
     with Boiler Test Results

                                    7
  Measured Boiler Sorbent Demand,




                                    6
                                    5
                                    4
               Ca:S




                                    3
                                    2
                                    1                   Measured Value=Predicted Value

                                    0
                                        0          2          4            6              8
                                                Predicted Sorbent Demand, Ca:S


    Sorbent 1                               Sorbent 2    Sorbent 3      Sorbent 4        Sorbent 11
    Uses for the Limestone Model
• Predicting Limestone Consumption Based
  on Boiler Parameters and Limestone Lab
  Analyses
• Helping to Select the Lowest Cost Stone
• Whether Changes to a Grinding Circuit can
  Lower Costs
What is required to use these Models

• Lab Analyses of Solids
• DCS Data
• Inexpensive Software
  – MathCad
  – Excel
A Word on Limestone
       A Word on Limestone

• Limestones under Boiler Conditions have
  been shown to still Absorb SO2 1-2 hours
  after introduction to the System.
• The Mean Bed Residence Time in a Rock
  Burner is Determined by Fuel Ash and
  Sulfur Content and Delta P. It may be less
  than an Hour.
• Reducing Ash and Sulfur Content can
  Increase Mean Bed Residence Time

				
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posted:8/5/2012
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