Torrefaction of Pulp Industry Sludge to Enhance Its Fuel Characteristics

Tharaka Rama Krishna C. Doddapaneni (), Linnar Pärn and Timo Kikas
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Tharaka Rama Krishna C. Doddapaneni: Chair of Biosystems Engineering, Institute of Forestry and Engineering, Estonian University of Life Sciences, Kreutzwaldi 56, 51014 Tartu, Estonia
Linnar Pärn: Institute of Forestry and Engineering, Estonian University of Life Sciences, Kreutzwaldi 5, 51014 Tartu, Estonia
Timo Kikas: Chair of Biosystems Engineering, Institute of Forestry and Engineering, Estonian University of Life Sciences, Kreutzwaldi 56, 51014 Tartu, Estonia

Energies, 2022, vol. 15, issue 17, 1-15

Abstract: Recently, under COP26, several countries agreed to phase-out coal from their energy systems. The torrefaction industry can take advantage of this, as the fuel characteristics of torrefied biomasses are comparable to those of coal. However, in terms of economic feasibility, torrefied biomass pellets are not yet competitive with coal without subsidies because of the high price of woody biomass. Thus, there is a need to produce torrefied pellets from low-cost feedstock; pulp industry sludge is one such feedstock. In this context, this study was focused on the torrefaction of pulp industry sludge. Torrefaction experiments were carried out using a continuous reactor, at temperatures of 250, 275, and 300 °C. The heating value of the sludge increased from 19 to 22 MJ/kg after torrefaction at 300 °C. The fixed carbon content increased from 16 wt.% for dried pulp sludge to 30 wt.% for torrefied pulp sludge. The fuel ratio was in the range of 0.27 to 0.61. The ash content of the pulp sludge was comparable to that of agricultural waste, i.e., around 12 wt.% (dry basis). The cellulose content in the sludge was reduced from 35 to 12 wt.% at 300 °C. Ash related issues such as slagging, fouling, and bed agglomeration tendency of the sludge were moderate. This study shows that torrefaction treatment can improve the fuel properties of pulp industry sludge to a level comparable to that of low-rank coal.

Keywords: continuous torrefaction; pulp industry sludge; ash melting behavior; fuel ratio; resource recovery; torrefaction; thermochemical conversion; biochar; pellets (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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