Effect of torrefaction pretreatment on the pyrolysis of rubber wood sawdust analyzed by Py-GC/MS

The aim of this study was to investigate the effect of torrefaction on the pyrolysis of rubber wood sawdust (RWS) using pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). Three typical torrefaction temperatures (200, 250, and 300 °C) and pyrolysis temperatures (450, 500, and 550 °C) were considered. The results suggested that only diethyl phthalate, belonging to esters, was detected at the torrefaction temperatures of 200 and 250 °C, revealing hemicellulose degradation. With the torrefaction temperature of 300 °C, esters, aldehydes, and phenols were detected, suggesting the predominant decomposition of hemicellulose and lignin. The double-shot pyrolysis indicated that the contents of oxy-compounds such as acids and aldehydes in pyrolysis bio-oil decreased with rising torrefaction temperature, implying that increasing torrefaction severity abated oxygen content in the bio-oil. With the torrefaction temperature of 300 °C, relatively more cellulose was retained in the biomass because the carbohydrate content in the pyrolysis bio-oil increased significantly

Coupled effect of torrefaction and densification pre-treatment on biomass energetic and physical properties

Leucaena (Leucaena leucocepphala) and oil palm empty fruit bunch, EFB (Elaeis guineesis) were selected as a woody and non-woody biomass samples, respectively in order to produce torrefied biomass pellets. In this study, torrefaction was performed at 300°C, three minute-residence time before pelletization. Then, the pellets have been characterized energetically and physically including volumetric energy density, and hygroscopic behavior. The results showed the torrefaction insignificantly enhanced high heating value of Leucaena from 19.3 MJ/kg to 19.5 MJ/kg and 18.3 MJ/kg to 19.1 MJ/kg for EFB. Moreover, torrefaction also improved the water resistance ability. While, the densification enhanced bulk density of biomass from 500 kg/m3 to 527 kg/m3 and 553 kg/m3 to 574 kg/m3 for Leucaena and EFB, respectively. The volumetric energy density was logically increased for both Leucaena and EFB biomass

Coupled effect of torrefaction and blending on chemical and energy properties for combustion of major open burned agriculture residues in Thailand

Thailand is an agriculture-based country. It produces large amounts of open burned agricultural residues. A strategy to use them as biofuel all year round is to enhance their fuel properties by coupling blending and thermochemical pre-treatment. In this study, the pyrolytic behaviour of major residues (napier grass , rice straw, cassava stalks and corn cob) exposed to a high torrefaction temperature (300°C) was investigated for various blending ratios, i.e. 100:0, 50:50 and 70:30. The release of chlorine was quantified for each biomass blend, including, a new fouling risk index ratio. Also, the synergistic effects of both ignition and burnout temperatures were analysed. Rice starw and napier grass were found to be characterised by a high ash content and so large amounts of solid yield after torrefaction. Raw biomasses and untreated biomass blends were found to be less suitable as biofuel than torrefied biomasses. The ratio K2O:SiO2, indicator of fouling risk during combustion, was found to be low for all torrefied blends. The HHV:Cl ratio, indicator of combustion quality, indicated that NG mixed with RS (50:50 proportion) is the most promising blend. Significant synergetic effects were observed for biomasses mixed before torrefaction. The burnout temperatures for raw and torrefied biomasses were identified in the range 773-787 °C and 786-795 °C. (Résumé d'auteur

Effects of torrefaction on energy properties of Eucalyptus grandis wood

Torrefaction is a thermal treatment that promotes homogenization and improvement of energy properties of biomass. This study aims to evaluate the effects of torrefaction on the main energy properties of Eucalyptus grandis wood. Wood was torrefied at three distinct temperatures (220°C, 250°C and 280°C) and analyzed for gravimetric yield (ratio of dry wood mass to torrefied wood mass), bulk density (ratio of dry torrefied mass to dry torrefied volume), heating value (higher-HHV, lower - LI-IV and useful - UHV), energy density (ratio of heating value to bulk density) and energy yield (product of gravimetric yield and ratio of HHV of torrefied wood to HHV of feedstock). The obtained results revealed significant differences for all properties being analyzed except for bulk density, which showed no statistical difference between the control and the treatment at 220°C. Temperature 250°C generated the best energy density as a function of the increase in heating value and the slight decrease in bulk density. (Résumé d'auteur

Optimization of multiple hearth furnace for biomass torrefaction

Gasification in entrained flow reactor and co-combustion of biomass in coal power plant are promising technologies of thermo-chemical conversion to produce electricity, heat, fuels and chemicals. Prior to injection in those reactors, biomass must be dried and ground to fine particles, until several hundreds of micrometers. These preliminary steps, especially grinding, consume large amounts of energy and represent obstacles that need to be overcome in order to expand the use of biomass in thermo-chemical processes. Torrefaction is a mild pyrolysis process carried out at 200 - 300 °C under inert atmosphere. It is a technology which allows moisture and low weight organic volatile components of biomass to be removed, producing a hydrophobic solid residue with an increased energy density (on a mass basis) and greatly reduced grinding energy consumption compared to fresh biomass. Electricity requirements for size reduction of torrefied wood are 50 to 85 % smaller in comparison with fresh wood. Therefore torrefaction leads to a more suitable product for transportation, storage and feeding. Currently, main applications for torrefied products are gasification and co-firing in coal power plant. Products can be used as a fuel either in pellet or powder after grinding. A state of the art of the existing torrefaction technologies has been performed. On the outcome of this study it appears that CMI's torrefaction process is one of the most promising technologies. It's a multiple hearth furnace whom main advantages are to allow the biomass torrefaction over a large range of residence time, temperature and biomass feedstocks. Within the framework of collaboration between French research centres CEA and CIRAD and the Belgium company CMI, the multiple hearth furnace developed by CMI has been adapted and optimized to torrefaction purpose. The main objectives were to reduce the production costs while improving significantly biomass properties. To achieve the objectives, an extensive experimental program was conducted in the torrefaction pilot plant of CMI which has a 40 kg/h capacity. Sampling methods and instrumentations were developed to analyse solids and gas products. The optimized process has proved experimentally its capacity to obtain well-torrefied product and its flexibility towards operating conditions and feedstock, which can be either wood or agricultural resources. Besides experimental work, a model of the torrefaction plant was built with Fluent®, CFD simulation software. This model has a supporting role in the extrapolation to industrial scale of the technology CMI. Thanks to furnace technical improvements, residence time has been reduced and reactor capacity has been increased. According to previous works, the torrefied products were characterized by a higher carbon content and energy density. Products had also more homogeneous properties and were much more friable than raw material. These results valid the adaptation choices, and allow to be confident for the upscaling to an industrial plant. (Texte intégral

Torrefaction behaviour of various biomass types: kinetics of solid mass loss and release of volatiles

Feedstock variability is a crucial issue for industrialization of biomass conversion processes. Indeed, this variability may imply large differences of chemical reaction rates and products yields and therefore differences of reactors design. In this context, the present study, which is part of the French-Brazilian ANR-FINEP project AMAZON, aims at characterising the behaviours of various biomass types during torrefaction in terms of solid mass loss kinetics and volatiles release. This should enable (i) to draw conclusions regarding their use in a process and (ii) to develop predictive kinetic models valid for various biomass feedstocks. The experiments are performed on 17 biomass including different kinds of wood (French woods: beech, pine, eucalyptus, false acacia and poplar Short Rotation Coppice (SRC) and Short Rotation Forestry (SRF); Brazilian woods: angelim, faveira, maçaramduba) and agricultural biomass (wheat straw, immature annual crop: triticale, forage grass : tall fescue and perennial herbaceous crops harvested dry in late winter: :miscanthus, switchgrass;). For study of solid mass loss kinetics, TGA experiments are performed during several hours at three final temperatures (230; 250 ; 280°C). For study of volatiles release, experiments are carried out at 250°C in a lab-scale reactor in which it is possible to close the mass balance during torrefaction of several grams of biomass. Gaseous species are continuously quantified thanks to a ?GC, and condensable species contents are measured using a GC-MS analyser. Three different kinetic behaviours can be observed depending on the species and their chemical composition, notably their hemicelluloses / xylose content. Mass loss is relatively slow for mature woods during the first hour, but then keeps on being significant even for very long durations. Initial mass loss is very sharp for the straw, the annual crop and the forage grass but then attains a plateau. Perennials and SRF/SRC exhibit the same behaviour, with an intermediate mass loss between mature wood and the other group of agricultural biomasses during the first hour and then a significant mass loss for long duration. These behaviours can be successfully modelled with the Di Blasi-Lanzetta scheme 1, based on two successive steps constituted of two parallel reactions, and able to describe the influence of temperature on solid yield. In a process viewpoint, to keep a reasonable mass loss, these results imply that agricultural biomass must be torrefied under less severe conditions than wood. Regarding gas release, contents and distribution of water, condensable species and non condensable species depend on the type of biomass and their chemical composition. The same previous three main families can be observed. In particular, for condensable species, acid fraction is low for wood, more important for perennials, and is the major part for the straw, annual and forage crops family. Some products are typically found in significant amounts in one family (formaldehyde in wood; formic acid in perennials crops and glycoaldehydedimer in straw, annual and forage crops family). In a process viewpoint, this means that cleaning step and further products recovery may be different according to the biomass type. (Résumé d'auteur

Torrefaction of biomass: influence of operating conditions on products and grindability

Biomass is a renewable fuel, increasingly considered as an important resource for alternative fuels with significant environmental advantages. Thermo-chemical conversion of biomass is a mean to produce energy and to reduce greenhouse gases. Rapid gasification of biomass at high temperature is one of the most promising technologies for the syngas production and can be achieved in several seconds in an entrained flow reactor. At high temperature (1400°C), it is possible to obtain a syngas (CO, H2 and CO2) containing very small amounts of residual hydrocarbons and solid carbon (char). Heat and mass transfers are very effective in this kind of reactor, but the biomass must be dried and ground to particles measuring several hundreds of micrometers prior to injection. These preliminary steps, especially grinding, consume large amounts of energy and represent obstacles that need to be overcome in order to expand the use of biomass in thermo-chemical processes. Torrefaction is a technology which allows moisture and low weight organic volatile components of biomass to be removed, producing a hydrophobic solid residue with an increased energy density (on a mass basis) and greatly reduced grinding energy consumption compared to fresh biomass1. Electricity requirements for size reduction of torrefied wood are 50 to 85 % smaller in comparison with fresh wood2. In this work, a specially designed crossed fixed-bed reactor was used to characterise influence of operating conditions on torrefied biomass properties. Condensable species were recovered thank to a cooling device afterwards the crossed fixed bed; gaseous species were continuously quantified by a ?GC. Mass balance was evaluated by quantification of the biomass mass loss and species released. The nature of biomass (wood, straw) was considered. For each sample of torrefied biomass, mass loss, proximate analysis and lower heating value were quantified. The torrefied wood grindability was evaluated thank to the energy consumption of a specific grinder. (Texte intégral

A study of the importance of secondary reactions in char formation and pyrolysis : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process Engineering at Massey University, Manawatū, New Zealand

Anthropogenic climate change, caused primarily by excessive emissions of carbon dioxide, has led to a renewed interest in char, the solid product of pyrolysis. When applied to soil as biochar it can both sequester carbon and improve soil function. To make its manufacture environmentally friendly and economically viable it is important to maximise char yield, which can be done by promoting secondary reactions. This research shows that secondary reactions, which are enhanced by prolonged vapour-phase residence time and concentration, not only increase the char yield but are the source of the majority of the char formed. All four biomass constituents (extractives, cellulose, hemicellulose and lignin) undergo secondary reactions concurrent with primary reactions over the entire pyrolysis range ≈ 140 to 500 °C, which makes it practically impossible to separate them. Secondary char formation was confirmed to be exothermic which affects the overall heat of pyrolysis. Impregnating the feedstock with the elements K, Mg and P, which are plant macro-nutrients naturally present in biomass, resulted in the catalysis of secondary char formation. The results reveal that a first order reaction model does not describe pyrolysis accurately when char formation is enhanced by catalysis and secondary reactions. Secondary char can be enhanced by increasing the particle size but there is a limit due to increased cracking and fracturing of the pyrolysing solid. This limitation is overcome by pyrolysis in an enclosed vessel, termed autogenous pressure pyrolysis, which was discovered to cause significant changes in the volatile pyrolysis products; indicating the co-production of a high quality liquid. This process, however, negatively affects the char properties relevant for biochar like the surface area, similar to self-charring and co-carbonisation of condensed volatile pyrolysis products. To increase research capabilities a unique high temperature/ high pressure reactor (600 °C at 20 MPa) was designed to allow the detailed characterisation of all three pyrolysis product classes under extreme pyrolysis conditions. This was demonstrated to be invaluable for understanding the underlying pyrolysis mechanism and physical processes at play