The utilization of biomass sources can reduce greenhouse gas emission. Presently, biomass is being considered as a potential energy resource to substitute fossil fuel for large-scale power generation through combustion as well as a chemical feedstock. Gasification can turn biomass into convenient product gas that could be used for both energy conversion and chemical production. Biomass gasification is being recognized as an alternative to combustion for the production of clean energy and provision of syn gas for production of chemicals. However, major limitation of the biomass gasification is the tar produced during the process and the high-energy cost associated with its removal from the product gas. Torrefaction is a new pretreatment method for biomass that has positive features such as reduced the storage, transportation cost, increased energy density, easier grinding. The torrefaction process partially removes the low quality volatiles matter thereby making the gas cleaning simpler and increasing energy density of the biomass. Furthermore, it lowers the O/C ratio of biomass fuel making it more favorable for gasification. To examine the above potential steam-gasification of raw biomass char and torrefied biomass char was investigated and studied their product gas composition and its other attributes. In this study, poplar wood was torrefied at 250oC and 275oC for 1 hour and gasified at different gasification temperatures (700-950oC). Measured and analyzed syngas gas yield, syngas composition and heating value. The kinetics of the process was also studied and it showed that torrefied (250oC with 1 hour residence time) biomass char had activation energy of 92.30 kJ/mol. Furthermore, SEM analysis of the char produced from the torrefied biomass and raw biomass was conducted to observe any difference in the microstructure their structure. The gasification experiments indicated that torrefied biomass produces slightly higher concentration of hydrogen and lower concentration of carbon dioxide than untreated biomass. Furthermore, this study showed that torrefaction has minor reduction in syngas yield, but major reduction in tar production. Overall combination of torrefaction and gasification of biomass is a promising technology for the future energy generation.

The research presented focuses on the use of Carbon-dioxide (CO₂), Nitrogen (N₂) and Argon (Ar) as purge gases for torrefaction. Torrefaction using CO₂ as a purge gas may further improve the fuel characteristics of the torrefied fuel when compared to N₂ and Ar (which are entirely inert), making it better suited for use as a fuel for co-firing with coal or gasification. Three different biomasses were investigated: Juniper wood chips, Mesquite wood chips, and forage Sorghum. Experiments were conducted using a thermo-gravimetric analyzer (TGA, TA Instruments Model Q-600) to determine the effect of the purge gas over a wide range of torrefaction temperatures (200-300°C). TGA weight traces (thermograms) showed an increased mass loss when using CO2 as a purge gas when compared to N₂. The increased mass loss when CO₂ was used is attributed to a hypothesized reaction between the CO₂ and fixed Carbon contained within the biomass. Torrefaction of biomass, using Ar as the purge gas, produced results similar to torrefaction using N₂. Derivative Thermo-Gravimetric analysis (DTG) was done to determine the temperature ranges over which the three main components of biomass (hemicellulose, cellulose, and lignin) decomposed. The DTG results are in agreement with previously published research. From TGA thermograms and DTG analysis it was determined that torrefaction at higher temperatures (>260°C) likely result in the breakdown of cellulose during torrefaction, an undesired outcome. Proximate, ultimate, and heat value analysis was done on all three biomasses. All three contain a relatively high Oxygen content, which serves to decrease the higher heating value (HHV) of the biomass. The HHV of Juniper, Mesquite, and Sorghum on a dry ash-free (DAF) basis were 20,584 kJ/kg, 20,128 kJ/kg, and 19,389 kJ/kg respectively. The HHV of the three biomasses were relatively constant as expected for agricultural biomass. From TGA analysis (thermograms and DTG), an optimal torrefaction temperature was determined (240°C) based upon the amount of mass lost during torrefaction and estimates of energy retained. Batch torrefaction of all three biomasses at the optimal torrefaction temperature was completed using a laboratory oven. All three biomasses were torrefied using CO₂, N₂, and Ar as a purge gas. Proximate, ultimate, and heat value analysis was done for each of the torrefied fuels and compared. Results of the fuel property analysis showed torrefaction reduced the moisture content and oxygen percentage of the fuel resulting in the torrefied biomass having a larger HHV when compared to raw biomass. Due to inherent mass lost during torrefaction, the amount of energy retained in the torrefied biomass was calculated to determine the percentage of the virgin biomass energy content that remained. Torrefaction using CO2 resulted in the lowest amount of energy retention of all three purge gases tested (78.86% for Juniper); conversely, Nitrogen resulted in the highest amount of energy retention (91.81% for Sorghum.) Torrefaction of the biomass also increased the fixed carbon (FC) content of the fuel. The grindability of the torrefied biomass was investigated via size distribution analysis of the raw and ground biomass. Initial size distribution analysis showed that torrefaction of Mesquite and Juniper resulted in smaller particle sizes; with a greater fraction of the torrefied biomass passing through smaller meshes. Analysis of the ground biomass samples showed that torrefaction improved the grindability of the fuel. The percent of torrefied biomass that passed through an 840 micrometer mesh increased by over 20% for both Mesquite and Juniper when ground. Sorghum exhibited similar increases; however, the amount of increase is less apparent due to the smaller particle size distribution of the raw Sorghum.

Mozambique has vast forestry resources and also considerable biomass waste material such as bagasse, rice husks, sawdust, coconut husks and shells, cashew nut shell and lump charcoal waste. The potential of the total residues from the agricultural sector and the forest industry is estimated to be approximately 13 PJ. This amount of energy covers totally the production of charcoal which amounted to approximately 12.7 PJ in 2006. Although biomass is an attractive renewable source of energy, it is generally difficult to handle, transport, storage and use due to its lower homogeneity, its lower energy density and the presence of non-combustible inorganic constituents, which leads to different problems in energy conversion units such as deposition, sintering, agglomeration, fouling and corrosion. Therefore, a pretreatment of the biomass to solve these problems could lead to a change of current biomass utilization situation. The aim of this study is to convert Mozambican woody biomass residue into a solid biochar that resembles low-grade coal. In this work the current energy situation in Mozambique has been reviewed, and the available and potential renewable sources including residues from agricultural crops and forest industry as energy have been assessed. It was found that the country is endowed with great potential for biofuel, solar, hydro and wind energy production. However, the production today is still far from fulfilling the energy needs of the country, and the majority of people are still not benefiting from these resources. Charcoal and firewood are still the main sources of energy and will continue to play a very important role in the near future. Additionally, enormous amounts of energy resources are wasted, especially in the agricultural sector. These residues are not visible on national energy statistics. The chemical composition and the fuelwood value index (FVI) showed that by failing to efficiently utilise residues from Afzelia quanzensis, Millettia stuhlmannii and Pterocarpus angolensis, an opportunity to reduce some of the energy related problems is missed. An evaluation of effect of a mild wet torrefaction pretreatment showed that the chemical composition of the biochar is substantially different than the feedstock. The use of diluted acid as catalysts improves the biochar quality, namely in terms of the energy density and ash characteristics; however, the increment of the S content in the final product should be considered for market acceptance (because the fuels have a maximum allowance for S concentration). The thermal behaviour of the untreated and treated biomass was also investigated. The pyrolytic products of umbila and spruce were affected by the treatment and catalyst in terms of yield and composition of the vapours. / <p>QC 20150202</p>

Torrefaction is a thermo-chemical pre-treatment of biomass within a narrow temperature range from 200°C to 300°C, where mostly the hemicellulose components of a biomass depolymerise. This treatment is carried out under atmospheric conditions in a non-oxidizing environment at low heating rates (< 50°C/min) and for a relatively long reactor residence time. Torrefaction increases the energy density of a biomass and reduces its O/C and H/C ratio, so its properties approach to that of coal. Biomass is usually referred to as lignocellulose, as its major mass constituents are cellulose, hemicelluloses and lignin. Research on torrefaction carried out to date deals solely with lignocellulose biomasses, and their degradation mechanism is explained primarily in terms of hemicellulose. However, there are biomasses which are non-lignocellulosic, have a small fraction of fibres in them or could possibly benefit from torrefaction. These include municipal solid waste, sewage sludge, animal waste, etc. Experiments were conducted on three non-cellulose biomasses (poultry waste, digested sludge, and undigested sludge) along with three typical lignocellulose biomasses (wood pellet and switchgrass and an agricultural waste – coffee bean husks). Results showed that non-lignocellulose biomasses torrefy similarly to their lignocellulose counterparts. Due to the immense potential of the torrefaction process, numerous manufacturers have developed their own patented technology for torrefying. Nevertheless, choosing the right torrefaction technology has become exceptionally difficult because of a near absence of a comparative assessment of different types of reactors. An experimental work was conducted to review the major generic types of reactors such as rotating drum, convective bed, fluidized bed and microwave, delineating the essential features of generic types of reactors. According to the results of this study, biomass torrefaction in a rotating drum gave the highest energy dense product, followed by fluidized bed and convective bed; the microwave reactor showed over-torrefaction at the core, while leaving the exterior green. To help effective design of a torrefier, several systematic experiments were conducted to investigate the effects of some of the more important operating parameters, such as torrefaction temperature, residence time and biomass particles size on the torrefaction yield. Although the mass yield decreased with the torrefaction temperature, energy density increased with it. Moreover, torrefaction yield varied for different biomass particle sizes depending on the type of reactor used, but the particle size did not have any clear effect on the energy density of the torrefied product.

Torrefaction has become a topic of interest in recent times not only because farmers could increase their income due to more farming activities for biomass feedstock demands but also it promotes opportunities for green job creation, provides alternative fuel source for coal fired plants, and contributes to greenhouse gas emission mitigation. Hence, this thesis explored the torrefaction behaviour of both herbaceous (switchgrass, miscanthus, wheat straw) and short rotation (willow) agricultural energy crops in terms of hydrophobicity, grindability and energy density. The lignocellulosic compositions of raw and treated switchgrass and bulk density of raw and treated miscanthus were also determined. Hence, the outcomes of these experimental investigations facilitated the development of a torrefaction definition. The research also studied the heat transfer mechanisms of torrefaction and developed mathematical models to simulate the heat generation profile due to the internal and spontaneous combustion of a cylindrically-shaped poplar wood. COMSOL modeling software was used to analyze and simulate the heat generation profiles that were closely similar to those from the experiments; hence led to a development of a correction factor to scale treatment inputs. / Thesis / OMAFRA HQP

The purpose of this study is to investigate the torrefaction and pelletization behavior, hydrophobicity, storage behavior, ash analysis on three different biomasses: one (willow pellets) from wood products, one (oat pellets) from agricultural products and one (poultry litter) from the non-lignocellulosic biomass products during the processes. Four different torrefaction temperatures from 200°C-300°C, at 10-60 minute residence times, 0%-2.4% oxygen concentration, were considered. Of these, 285°C for willow pellets, 270°C for oat pellets and 275°C for poultry litter were found to be optimum for hydrophobicity. Studies of XRD and SEM of biomass ash at 800°C, 900°C and 1000°C were also carried out. The aforementioned results indicate that torrefaction is a feasible alternative to improve energy properties of ordinary biomass and prevent moisture re-absorption during storage.

A novel compacted, torrefied, spherical biomass pellet, known as the "Q'Pellet", is aimed at overcoming the challenges of modern biomass pellets by building on the bene fits of torrefaction and utilizing the durability of a sphere. Pellets were made from both untreated hybrid poplar sawdust and material that had been partially torrefied at 250 C, allowing the torrefaction and pelletizing stages to be decoupled. A pelletizing die pre-heated to 280 C was successfully used to heat and torrefy room temperature raw and pre-torrefi ed material, greatly reducing the time required to produce each pellet. All Q'Pellets demonstrated 100% mechanical durability, and did not abrade during a tumbling can test or fracture during an impact resistance (drop) test. The gross calori fic value (GCV), ash and nitrogen content of pellets produced from raw hybrid poplar were 21.29+/-0.08 MJ/kg, 2.42+/-0.23 wt%, and <0.01 wt%, respectively. The GCV, ash and nitrogen content of pellets produced from pre-torre ed material were 21.25+/-0.34 MJ/kg, 3.58+/-1.11 wt%, and 0.42+/-0.03 wt%, respectively. The Q'Pellet was compared to biomass fuel speci fications in Europe and North America. The experiments performed herein provided an understanding of the material and process properties and limitations. Design speci fications for the development of a continuous pelletizing process were outlined. BGM Metalworks Inc has been hired by Queen's University to assist in the design and to fabricate the continuous pelletizing apparatus. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2014-05-06 14:04:54.059

L'ochratoxine A (OTA) est un métabolite secondaire produit par des espèces appartenant aux genres Aspergillus et Penicillium qui a été liée à certaines conditions avec des effets néphrotoxiques, immunotoxiques, tératogènes et cancérogènes. La présence d'OTA dans le café vert a été détectée depuis 1974 et sa transmission à la boisson a été mise en évidence en 1989. La torréfaction du café est un procédé thermique qui peut avoir un effet sur la teneur en OTA, avant 1988, on pensait que l'OTA était détruite pendant la torréfaction, mais après plusieurs chercher sont des résultats contradictoires publiés dans % de réduction (de 0 à 100%). Plusieurs auteurs émis les hypothèses suivantes pour expliquer cette réduction : Isomérisation de la toxine dans la position C3 formant un diastéréoisomère moins toxique (Studer-Rohr et al, 1995 et Bruinink et al, 1997), protection de la dégradation d’OTA par l'humidité du grain (Boudra et al 1995; Blanc et al, 1998 et Stegen et al, 2001.), existence de réactions avec le café toxine parent ou réarrangements de la molécule OTA à températures de torréfaction (Suarez-Quiroz et al, 2005). Une autre étude sur la dégradation thermique de OTA pure a montré la formation de deux composés moins toxiques, 14-(R)-ochratoxine A et de la 14-descarboxi-ochratoxine A (Cramer et al, 2008). Parce qu'il n'y a pas de données concluantes sur l'effet de la torréfaction sur l'OTA dans le grain et le besoin de bases scientifiques pour établir des règles pour l'exportation de café vert, l'objectif de ce travail était d'étudier l'impact des différents types de torréfaction sur la stabilité thermique de l'OTA dans le café et l'élucidation chimique des produits de transformation. Deux niveaux de contamination ont été obtenus à partir de café contaminés artificiellement par Aspergillus westerdijkiae (5,3 et 57,2 ppb d'OTA). Ces lots sont grillés à 230° en utilisant deux méthodes : La torréfaction à tambour (TR) et à lit fluidisé (LF). Les échantillons ont été prélevés toutes les 3 min pour TR et chaque min 0,9 pour LF pour quantifier la valeur résiduelle d¡¯OTA. Les résultats ont montré que le procédé de torréfaction par TR (plus lent) était plus efficace que la FL dans l'élimination de l'OTA (67% et 36%, respectivement, pour une torréfaction moyenne). Nous avons déterminé le taux de dégradation thermique de OTA pure et de l'OTA mélangée avec les composants du café (5 sucres, 3 acides aminés, la caféine et les acides chlorogéniques), montrant que les interactions se déroulent en fonction des conditions de pH et de pKa des composants testés, dans ce cas, en influant sur la réactivité et la vitesse de dégradation de l'OTA. Un produit de transformation (PT) a été observé sur les chromatogrammes obtenus à partir de l'interaction de l'OTA avec les composants du café. Des tests d'alcalinisation et de chauffage de OTA pure ont confirmé que le PT provient de la modification structurale de la molécule d'OTA et n’est pas un produit de l'interaction avec les composants naturels du café. L'effet du pH et de la température sur l'extraction de l'OTA dans le café contaminé a été testé dans ce travail, les résultats ont montré une plus grande extraction de la toxine à un pH de 8,5 et 6°. Au même pH à 20° il y avait une plus importante formation d'un produit de transformation. Le PT a été purifié pour mener à bien sa caractérisation chimique. La nature chimique du produit de transformation, les données spectroscopiques telles que celles obtenus sous UV-Vis (max: 237nm), l'affinité avec la phase mobile de l'OTA, l'analyse de l'alcalinisation (phénomène de régénération de l'OTA et PT), l'analyse d’isotopes stables (SIDA’s) et le spectre de masse (ion moléculaire M+1: 420 m/z), suggèrent que la structure de le PT d'OTA durant le processus de torréfaction correspond à un analogue de l'OTA qui conserve son groupe carboxyle acide et conformément à la fragmentation correspond à la Hydroxy-ochratoxine A (OH-OTA), avec des quantités mineures d’ OTA et de ses isomères. / Ochratoxin A (OTA) is a secondary metabolite produced by species belonging to the genera Aspergillus and Penicillium and this toxin has been associated with certain illnesses within nephrotoxic effects, immunotoxic, teratogenic and carcinogenic. The presence of OTA in green coffee was detected in 1974 and its transmission into the beverage was made evident in 1989. Roasting coffee is a thermal process that have an effect on the OTA content. Before 1988 it was thought that the OTA was destroyed during roasting, but after several investigations, results published are contradictory results published in the % reduction (from 0 to 100%). Several authors have established hypothesis that try explain this reduction: Isomerization of the toxin in the C3 position forming a less toxic diastereomers (Studer-Rohr et al., 1995 and Bruinink et al., 1997), Protection of grain moisture degradation OTA (Boudra et al., 1995; Blanc et al., 1998 and Stegen et al., 2001), Existence of reactions with the parent toxin coffee or rearrangements of the OTA molecule roasting temperatures (200¡ã and 250¡ãC) (Su¨¢rez-Quiroz et al., 2005). Another study on thermal degradation of pure OTA showed the formation of two less toxic compounds 14 - (R)-ochratoxin A and the 14-descarboxi-Ochratoxin A (Cramer et al., 2008).Because there are no conclusive data regarding the effect of roasting on OTA in grain and the need for scientific bases for establishing regulations for export of green coffee, the objective of this work was to study the impact of different types of roasting on the thermal stability of OTA in coffee and chemical elucidation of the transformation products.Two levels of contamination were obtained by the contamination of coffee with a strain of A. westerdijkiae (5.3 and 57.2 ppb of OTA). These lots were roasted at 230 ¡ã C using two methods: Drum rotation (TR) and fluidized bed (LF). Samples were taken every 3 min from TR and every 0.9 min for LF to quantify the residual OTA. The results showed that in roasting process by TR (slower), it was more effective than with LF in the elimination of OTA (67% and 36%, respectively, for a medium roast). The thermal degradation rate of pure OTA and of OTA mixed with the components of coffee (5 sugars, 3 amino acids, caffeine and chlorogenic acids), were determined, showing that interactions took place dependent themselves on the conditions of pH and pKa values of the components tested, in this case by influencing by the reactivity and the rate of degradation of OTA. A transformation product (TP) was observed in the chromatograms obtained from the interaction of OTA with the components of coffee. A test of alkalinization and warming of pure OTA confirmed that the TP comes from the structural modification of the OTA molecule and is not a product of interaction with the natural components of coffee. The pH and temperature showed an effect in extraction of OTA in contaminated coffee, the results show better extraction of the toxin at pH 8.5 at 60 ¡ãC. At the same pH at 20 ¡ãC, it was shown a greater formation of the transformation product.The TP was purified to carry out its chemical characterization. The chemical nature of compound transformation and spectroscopic data such as UV-Vis (¦Ëmax: 237nm), the affinity with the mobile phase of the OTA, the analysis of alkalinization (OTA regeneration phenomenon and TP) analysis of stable isotopes (SIDA's) and the mass spectrum (molecular ion M +: 420 m / z), suggest that structurally the TP of OTA during the roasting process corresponds to an analogue of OTA which retains its acidic carboxyl group and in accordance to fragmentation corresponds to the Hydroxi- Ochratoxin A (OH-OTA), as well as minor amounts of OTA and its isomers.

Increasing the share of biomass, preferably by replacing fossil fuels, is one way to mitigate the present climate change. Fossil coal can be directly replaced by co-combustion of coal and biomass and fossil engine fuels (gasoline and diesel) could potentially partly be replaced by synthetic renewable fuels produced via entrained flow gasification of biomass. The use of biomass in these processes is so far limited, partly because of the fibrous and hygroscopic nature of biomass which leads to problem in storing, transportation, handling and feeding. This thesis demonstrates how the challenging characteristics of raw biomass are mitigated by the pretreatment method torrefaction. Torrefaction is a process where biomass is heated in an oxygen deficient atmosphere to typically between 240 and 350°C for a time period of 2 minutes to 1 hour. Most of the torrefaction R&amp;D in the literature have so far been performed with bench-scale batch reactors. For the purpose of carefully studying continuous torrefaction, a 20 kg/h torrefaction pilot plant was therefore designed, constructed and evaluated. The overall conclusion from this thesis is that the many benefits of torrefied biomass are valid also when produced with a continuous pilot plant and for typically Swedish forest biomasses. Some of the documented improved biomass properties are increased heating value, increased energy density, higher friability (lower milling energy) and less hydrophilic biomass (less moisture uptake). Most of the improvements can be attributed to the decomposition of hemicellulose and cellulose during torrefaction. The most common variables for describing the torrefaction degree are mass yield or anhydrous weight loss but both are challenging to determine for continuous processes. We therefore evaluated three different methods (one existing and two new suggestions) to determine degree of torrefaction that not require measurement of mass loss. The degree of torrefaction based on analyzed higher heating value of the raw and torrefied biomass (DTFHHV) predicted mass yield most accurate and had lowest combined uncertainty. Pelletizing biomass enhance transportation and handling but results from pelletization of torrefied biomass is still very limited in the literature and mainly reported from single pellet presses. A pelletization study of torrefied spruce with a ring die in pilot scale was therefore performed. The bulk energy density was found to be 14.6 GJ/m3 for pelletized torrefied spruce (mass yield 75%), a 40% increase compared to regular white pellets and therefore are torrefied pellets more favorable for long distance transports. More optimization of the torrefied biomass and the pelletization process is though needed for acquiring industrial quality pellets with lower amount of fines and higher pellet durability than attained in the present study. Powders from milled raw biomass are generally problematic for feeding and handling and torrefied biomass has been proposed to mitigate these issues. The influence of torrefaction and pelletization on powder and particle properties after milling was therefore studied. The results show that powder from torrefied biomass were enhanced with higher bulk densities, lower angle of repose as well as smaller less elongated particles with less surface roughness. Even higher powder qualities were achieved by pelletizing the torrefied biomass before milling, i.e. another reason for commercial torrefied biomass to be pelletized. Entrained flow gasification (EFG) is a promising option for conversion of biomass to other more convenient renewable energy carriers such as electricity, liquid biofuels and green petrochemicals. Also for EFGs are torrefied fuels very limited studied. Raw and torrefied logging residues were successfully gasified in a pilot scale pressurized entrained flow biomass gasifier at 2 bar(a) with a fuel feed corresponding to 270 kWth. Significantly lower methane content (50% decrease) in the syngas was also demonstrated for the torrefied fuel with mass yield 49%. The low milling energy consumption for the torrefied fuels compared to the raw fuel was beneficial for the gasification plant efficiency.

The co-firing of biomass and coal plays an important role in increasing the biomass power capacity and reducing greenhouse gas (GHG) emissions. The challenges of the large percentage biomass co-firing (over 20% on energy basis) in existing pulverized coal boilers are keeping the same steam parameters and having a high boiler efficiency and a stable operating. The primary goal of this thesis is to develop a combustion concept for coal-fired boilers to enablea large percentage of biomass co-firing with up to a 100% fuel switch; these changes should increase the combustion efficiency, reduce CO2  and NOx emissions, improve the process efficiency, while maintaining the same steam parameters after switching fuels. To achieve these goals,  a  typical  biomass  pretreatment technology  called  torrefaction  has  been  employed to upgrade  the  biofuel  quality  in  terms  of  both  energy  density  and  chemical  properties. Consequently, a torrefaction based co-firing system has been proposed. In addition, a novel biomass combustion method called volumetric combustion has been designed; this process involves intense mixing and flue gas internal recirculation inside the combustion chamber, increasing the residence time of the biomass particles and making the temperature and gas species more uniform. In this thesis, a series of studies based on experiments, CFD modelling, and process simulations have been performed. First, the raw material was palm kernel shells (PKS) that were torrefied over same residence time but at different temperatures in a laboratory-scale torrefaction reactor, producing three torrefied biomasses with different degrees of torrefaction. The devolatilization kinetics and char oxidation kinetics were determined based a series of high-temperature high-heating-rate tests in an isothermal plug flow reactor (IPFR), the obtained kinetic parameters were adopted for CFD modeling. Continually, the numerical investigations on the flame properties of the torrefied biomass and a 220 MWe coal-fired boiler performance were conducted, to understand the predicted results of the coal-fired boiler performance at varying biomass co-firing ratios. Afterward, analyses of the impacts of the degree of torrefaction and the biomass co-firing ratio on process operation, performance and electricity efficiency of a torrefaction based co-firing power plant were performed. Finally, the properties of the pollutants emitted from biomass volumetric combustions under various combustion modes and co-firing ratios were studied using Aspen Plus. According to the results, the following conclusions can be reached: 1) a high heating rate enhances the yields of the volatiles for biomass devolatilization processes with the same final temperature; 2) the enhanced drag force on the biomass particles causes a late release of volatile matter and delays the ignition of the fuel-air mixture. Furthermore, oxidizers with lower oxygen concentrations normally generate larger flame volumes, lower peak flame temperatures and lower NO emission; 3) the co-firing simulation reveals that a boiler load reduction of less than 10% is observed when firing 100% torrefied biomass; 4) deep torrefaction is not recommended because the energy saved during biomass grinding is lower than that consumed by the additional torrefaction process; the electrical efficiency of power plant is reduced when increasing either the degree of torrefaction or the biomass substitution ratio; 5) the amount of flue gas that needs to be recycled for NOx reduction decreased when the percentage of co-fired biomass increased. Overall, from the perspective of combustion, both the torrefaction process and volumetric combustion are promising steps toward realizing large percentage biomass co-firing in coal-fired boilers with high efficiency and reduced emissions. / <p>QC 20140130</p>