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Table 5 Agglomeration and fouling indicators of the lime-treated wheat straw solid fraction (experimental and corrected for 85% calcium recycle) original wheat straw feedstock and untreated wood

From: Pilot-scale conversion of lime-treated wheat straw into bioethanol: quality assessment of bioethanol and valorization of side streams by anaerobic digestion and combustion

Source composition Lime-treated wheat straw solid fraction (experimental) Lime-treated wheat straw solid fraction (corrected for 85% calcium recycle) Wheat straw original feedstock (harvest 2003) Wood (untreated, average)[28]
Fluidized bed combustion agglomeration indicators a
Sinter-induced b      
(1) Na + K/2S + Cl more than 1   0.1 0.4 2.7 1.4
(2) (Na + K + Si)/(Ca + P + Mg) more than 2   0.8 3 7.0 0.2
Smelt-induced c      
(3a) K + Na/Si more than 0.6   0.1 0.1 0.5 2.6
(3b) K + Na more than 1 g/kg   5 5 15 2.3
(3c) Si more than 1.5 g/kg   40 44 28 0.9
(3d) K2O + Na2O + SiO2 more than 50% ash   34 52 68 30
Fluidized bed combustion fouling indicators (at 50% moisture content) a
3 Cl +S more than 1% weightar   2.1 0.6 0.9 0.2
Na + K + Zn more than 1% weightar   0.2 0.3 0.4 0.2
Dust fraction of ash more than 30% Unknown Unknown   Unknown
Alkali/DOE indexd kg/GJ HHVe 0.3 --- 0.9 0.1
  1. aVisser and Laughlin [29].
  2. bThe second indicator is relevant if the first indicator is exceeded.
  3. cThe more the indicators exceed the limit value, the more likely it is that smelt bed agglomeration will occur.
  4. dMiles et al [30]: if the value of the index is higher than 0.17, probably fouling; if more than 0.34, certainly fouling.
  5. eHigher heating value.
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