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

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

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% weight_ar		2.1	0.6	0.9	0.2
Na + K + Zn more than 1% weight_ar		0.2	0.3	0.4	0.2
Dust fraction of ash more than 30%		Unknown	Unknown		Unknown
Alkali/DOE index^d	kg/GJ HHV^e	0.3	---	0.9	0.1

^aVisser and Laughlin [29].
^bThe second indicator is relevant if the first indicator is exceeded.
^cThe more the indicators exceed the limit value, the more likely it is that smelt bed agglomeration will occur.
^dMiles et al [30]: if the value of the index is higher than 0.17, probably fouling; if more than 0.34, certainly fouling.
^eHigher heating value.

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