Release of Chlorine and Sulfur during Biomass Torrefaction and Pyrolysis

Abstract

The release of chlorine (Cl) and sulfur (S) during biomass torrefaction and pyrolysis has been investigated via experiments in two laboratory-scale reactors: a rotating reactor and a fixed bed reactor. Six biomasses with different chemical compositions covering a wide range of ash content and ash-forming elements were torrefied/pyrolyzed in the temperature range of 150−500 °C. The relative release of chlorine and sulfur was calculated based on mass balance and analysis of the biomass before and after torrefaction. In selected cases, measurement of methyl chloride (CH 3 Cl) in the gas from straw torrefaction has furthermore been conducted. The release of chlorine from straw was first observed at 250 °C and peaked with about 60−70% at 350 °C. Analysis of the released gas showed that most of the chlorine was released as methyl chloride. Increasing the straw content in the reactor resulted in a lower fractional release of Cl, probably due to more reactive sites in contact with gas phase Cl species leading to secondary binding of Cl to the solid product. Almost complete release of chlorine was observed for woody biomass at 350 °C. This result is in agreement with previous studies reporting that biomasses with a lower chlorine content release a higher fraction of chlorine during the pyrolysis process. A significant sulfur release (about 60%) was observed from the six biomasses investigated at 350 °C. The initial sulfur content in the biomass did not influence the fraction of sulfur release during torrefaction.

Effects of water washing and torrefaction pretreatments on rice husk pyrolysis by microwave heating

“…It is noteworthy that sulfur contents had a trend to decrease with torrefaction for both RH and W-RH. Similar results could be found in other researches (Chen et al, 2012a,b;Saleh et al, 2014).…”

Upgrading of Rice Husk by Torrefaction and its Influence on the Fuel Properties

“…Knudsen et al (2004) indicated that the release of sulfur begins with the cysteine and methionine units (two main S-containing precursors for plant protein) which start to decompose at 178 and 183 °C, respectively (Knudsen et al 2004). Similar results were found by Saleh et al (2014). In their study, the release of sulfur from straw and miscanthus was approximately 20% at 250 °C and then gradually increased to approximately 50% at 350 °C.…”

Properties of Torrefied U.S. Waste Blends

“…There was evidence that at the working temperatures of the torrefaction experiments (300 • C) in this study, chlorine from the plastic materials should have been released as HCl (Saleh et al, 2014). Further, Bar-Ziv and Saveliev (2013) measured HCl in the torrefaction gas stream that was equivalent to the chlorine reduction in the solid phase.…”