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Hot Ash Treatment: Preliminary Experimental
Results and Thermodynamic Insights
Cyril Jose E. Bajamundi [Presentor], Kirsi Korpijärvi, Martti Aho
Pasi Vainikka, Jukka Konttinen
FINNISH-SWEDISH FLAME DAYS 2013
Jyväskylän Paviljonki, Jyväskylä Finland
17th-18th April, 2013
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cyril.bajamundi@vtt.fi
Background
Waste and biomass co-firing has been in constant development to meet energy
demand, independence and environmental requirements.
Biomass : carbon neutral energy source
Waste: alternative energy source/sanitary disposal
Several issues in co-firing are still being resolved, one of which is…
ASH DISPOSAL or UTILIZATION
Huge material resource
Country specific legislations
Uses: Earth construction applications, forest fertilizers
Challenges: Heavy metal content, variability in chemical and physical properties
A cleaner ash is desirable.
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About this study
Examine the concentration of seven elements (Zn, Cu, Ar, Ni, Pb, and Sb) as the
cyclone temperature in a BFB test reactor is varied.
Features of the reactor
20 kW BFB test reactor at VTT.
With electric heaters for
stabilization are in place.
Natural sand with dp = 0.1-0.6 as
bed material.
= 0.5 cm/s sufficient to
transport particles smaller than
100 m to the cylcone.
gas
Figure 1. Schematic diagram of the Bubbling Fluidized Bed setup at VTT and
the temperature during the experimental runs.
Temperature of the cyclone for different test runs.
Test Run
Cyclone
Temp., [oC]
1
2
3
4
5
512
622
724
827
937
4
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About this study
Fuel blend of RDF, bark, and chromated
copper arsenate impregnated wood
(CCA) at 28/70/2 mass portion was
burnt.
Mean fuel feeding rate was 51.6 g/min
and combustion air feeding rate 11.16
mol/min (+ 1.24 mol/min N2 via the fuel
feeding line) corresponding to an
air/fuel ratio of 1.33.
Ultimate analysis of the RDF-Bark-CCA wood mixture.
Compone nt
C
H
N
O[calc]
Si
Al
Fe
Ti
Ca
Mg
P
Na
K
S
Cl
Unit
m% d.s.
mg/kg d.s.
Conc.
52.5
6.2
0.4
37.9
5222
2512
633
503
12300
1023
450
560
2000
1400
2700
Compone nt
Unit
As
mg/kg d.s.
Cd
Co
Cr
Cu
Hg
Mn
Ni
Pb
Sb
Tl
V
Zn
H2O
m%a.r.
Calorific Value MJ/kg d.s.
Conc.
32
0.3
0.7
50
56
0.07
380
2.2
45
13
0.1
1.3
190
28.1
20.21
Elemental analysis of the ash follows the SFS/EN 13656 standard.
Thermodynamic modeling implemented in FactSage 6.3 at P= 1bar and with 319 ideal
gas species and 421 pure solid species. In addition salt (FTSalt) and oxide (FTOxide)
solid solution species were also included.
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Experimental Results
Elements can be classified into two categories based on their dependency with the
cyclone temperature.
Class I
(elements showing clear
dependency with Tcyclone)
1000
Cr
Cu
Zn
3000
2800
Concentration [mg/ kgdry solid]
Concentration [mg/ kgdry solid]
3200
2600
2400
2200
2000
1800
900
Ni
Sb
As
Pb
800
700
Chromium
Antimony
Lead
600
500
Class II
(elements without clear
dependency with Tcyclone)
400
300
1600
500
600
700
800
o
Temperature [ C]
900
1000
Copper
Zinc
200
500
600
700
800
900
o
Temperature [ C]
1000
Arsenic
Nickel
Trace element concentration profile for the cyclone fly ashes collected.
Class 1 , in general, exhibited increasing concentration with Tcyclone, with Pb showing
some special behavior.
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Thermodynamic Insights
Volatilization of elements according to thermodynamic equilibrium calculations.
1
Fraction in Gas [molGas/molIn]
1
Cr
Cu
Zn
Ni
Sb
As
Pb
0
0
500 600 700 800 900 1000 1100
Temperature [oC]
500 600 700 800 900 1000 1100
Temperature [oC]
Fraction of elements (thermodynamically) expected to be in the gas phase at different temperature settings.
Thermodynamic equilibrium expects Pb to be in the vapor phase at the studied
temperature range, however it was found in the cyclone fly ash.
• Limitation of thermodynamic model.
Results for Cu and Cr suggests decreasing concentration vs. temperature due to
volatilization.
• In contrast with the experimentally measured.
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Thermodynamic Insights
Key speciation of Class 1 vs Class 2 elements.
1E-3
0.0030
Pb(g)
PbO(g)
PbCl(g)
PbCl2(g)
0.0025
As Species [mol]
Arsenic
• Has remained solid within the
temperature range under
consideration.
• AlAsO4(s) and K3AsO4(s) were
formed.
0.0035
1E-4
Pb Species [mol]
Lead
• Shift from PbCl2 as the
dominant gas species to PbO as
the temperature increases.
0.01
1E-5
1E-6
1E-7
0.0020
AsCl3(g)
AlAsO4(s)
K3AsO4(s)
0.0015
0.0010
0.0005
1E-8
0.0000
1E-9
500
600
700
800
900 1000
Temperaure [oC]
500
600
700
800
Temperaure [oC]
Speciation of Pb (an element classified as C1)
and As (an element classified as C2).
900
1000
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Thermodynamic Insights
A look at the minor ash forming elements.
0.0044
2.0
O
1.0
Element
Al
Si
0.0042
K
Cl
0.5
P
S
Cl
K
0.0040
Cond
0.0
Ca
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Coeff. of Variation
K and Cl are elements having
the largest variation at the
temperature range under
consideration.
K
Cl
1.5
Concentration [wt% ]
Mg
Fraction Condensed
Fraction in Gas [molGas/molIn]
Na
1.0
0.5
0.0038
0.0
400
500
600
700
800
900 1000
Temperature [oC]
K and Cl volatilize and
significantly affect the amount
of condensed formed.
500
600
700
800
900 1000
Temperature [oC]
Volatilization of K and Cl is
supported by XRF
measurements of the ash
samples.
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In summary
Thermodynamic models suggest that the trend in the concentrations of elements
under class C1 can be explained by either or combination of the following reasons
Inability of the trace elements to vaporize.
kinetic and transport restriction
elements originally present as chlorides have probably lost Cl, which
strongly weakened their volatilization as function of temperature leading
to apparent increase in concentration
Loss of major ash forming elements due to volatilization.
Cl and K exists favorably in gaseous state as the temperature is increased.
As for the elements in class C2, they remain in the solid phase thus their
concentration did not vary significantly.
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Acknowledgements
We are thankful to VTT, and OSER project, Metso Power, Foster Wheeler, and the
European Regional Development Fund for the resources shared to this study.
Raili Taipale and Esa Kallio are acknowledged for providing key experimental data
and information on the test parameters.
Thank you.
I am now ready for your
questions.
Cyril Jose E. Bajamundi
Research Scientist
cyril.bajamundi@vtt.fi
+358 40 512 2673
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cyril.bajamundi@vtt.fi
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