Biomass torrefaction characteristics in inert and oxidative atmospheres at various superficial velocities

Low-temperature biochar production from torrefaction for wastewater treatment: A review

Biochar, a carbon-rich and por ous material derived from waste biomass resources, has demonstrated tremendous potential in wastewater treatment. Torrefaction technology offers a favorable low-temperature biochar production method, and torrefied biochar can be used not only as a solid biofuel but also as a pollutant adsorbent. This review compares torrefaction technology with other thermochemical processes and discusses recent advancements in torrefaction techniques. Additionally, the applications of torrefied biochar in wastewater treatment (dyes, oil spills, heavy metals, and emerging pollutants) are comprehensively explored. Many studies have shown that high productivity, high survival of oxygen-containing functional groups, low temperature, and low energy consumption of dried biochar production make it attractive as an adsorbent for wastewater treatment. Moreover, used biochar's treatment, reuse, and safe disposal are introduced, providing valuable insights and contributions to developing sustainable environmental remediation strategies by biochar.

Comparative advantages analysis of oxidative torrefaction for solid biofuel production and property upgrading

This study performs the comparative advantage analysis of oxidative torrefaction of corn stalks to investigate the advantages of oxidative torrefaction for biochar fuel property upgrading. The obtained results indicate that oxidative torrefaction is more efficient in realizing mass loss and energy density improvement, as well as elemental carbon accumulation and surface functional groups removal, and thus leads to a better fuel property. The maximum values of relative mass loss, higher heating value, enhancement factor, and energy yield are 3.00, 1.10, 1.03, and 0.87, respectively. The relative elemental carbon, hydrogen, and oxygen content ranges are 1.30-3.10, 1.50-3.30, and 2.00-6.80, respectively. In addition, an excellent linear distribution is obtained between the comprehensive pyrolysis index and torrefaction severity index, with elemental carbon and oxygen component variation stemming from pyrolysis performance correlating to the elemental component and valance.

Effects of Torrefaction Pretreatment on the Structural Features and Combustion Characteristics of Biomass-Based Fuel

Wheat straw, a typical agricultural solid waste, was employed to clarify the effects of torrefaction on the structural features and combustion reactivity of biomass. Two typical torrefaction temperatures (543 K and 573 K), four atmospheres (argon, 6 vol.% O₂, dry flue gas and raw flue gas) were selected. The elemental distribution, compositional variation, surface physicochemical structure and combustion reactivity of each sample were identified using elemental analysis, XPS, N₂ adsorption, TGA and FOW methods. Oxidative torrefaction tended to optimize the fuel quality of biomass effectively, and the enhancement of torrefaction severity improved the fuel quality of wheat straw. The O₂, CO₂ and H₂O in flue gas could synergistically enhance the desorption of hydrophilic structures during oxidative torrefaction process, especially at high temperatures. Meanwhile, the variations in microstructure of wheat straw promoted the conversion of N-A into edge nitrogen structures (N-5 and N-6), especially N-5, which is a precursor of HCN. Additionally, mild surface oxidation tended to promote the generation of some new oxygen-containing functionalities with high reactivity on the surface of wheat straw particles after undergoing oxidative torrefaction pretreatment. Due to the removal of hemicellulose and cellulose from wheat straw particles and the generation of new functional groups on the particle surfaces, the ignition temperature of each torrefied sample expressed an increasing tendency, while the Ea clearly decreased. According to the results obtained from this research, it could be concluded that torrefaction conducted in a raw flue gas atmosphere at 573 K would improve the fuel quality and reactivity of wheat straw most significantly.

Heat balance analysis for self-heating torrefaction of dairy manure using a mathematical model

A self-heating torrefaction system was developed to overcome the difficulties in converting high-moisture biomass to biochar. In self-heating torrefaction, the ventilation rate and ambient pressure must be set properly to initiate the process. However, the minimum temperature at which self-heating begins is unclear because the effects of these operating variables on the heat balance are not theoretically understood. The present report presents a mathematical model for the self-heating of dairy manure based on the heat balance equation. The first step was to estimate the heat source; experimental data showed that the activation energy for the chemical oxidation of dairy manure is 67.5 kJ/mol. Next, the heat balance of feedstock in the process was analyzed. Results revealed that the higher the ambient pressure and the lower the ventilation rate at any given pressure, the lower the temperature at which self-heating is induced. The lowest induction temperature was 71 °C at a ventilation rate of 0.05 L min^-1 kg-AFS^-1 (AFS: ash-free solid). The model also revealed that the ventilation rate significantly affects the heat balance of feedstock and drying rate, suggesting an optimal range for ventilation.

Thermochemical conversion of large-size woody biomass for carbon neutrality: Principles, applications, and issues

Large-size woody biomass is a valuable renewable resource to replace fossil fuels in biorefinery processes. The preprocessing of wood chips and briquettes is challenging to manage, especially in an industrial setting, as it generates a significant amount of dust and noise and occasionally causes unexpected accidents. As a result, a substantial amount of resources, energy, labor, and space are needed. The thermochemical conversion behavior of large-size woody biomass was studied to reduce energy consumption for chipping. Large-size wood was 1.5 m in length, 0.1 m in breadth, and stacked 90 cm in height. This strategy has many benefits, including increased effectiveness and reduced CO₂ emissions. The target of this paper presents the thermochemical process, and large-size wood was chosen because it provides high-quality product gas while reducing the preprocessing fuel cost. This review examines the benefits of thermochemical conversion technologies for assessing the likelihood of carbon neutrality.

Investigation of the Effects of Torrefaction Temperature and Residence Time on the Fuel Quality of Corncobs in a Fixed-Bed Reactor

Biomass from agriculture is a promising alternative fuel due to its carbon-neutral feature. However, raw biomass does not have properties required for its direct utilization for energy generation. Torrefaction is considered as a pretreatment method to improve the properties of biomass for energy applications. This study was aimed at investigating the effects of torrefaction temperature and residence time on some physical and chemical properties of torrefied corncobs. Therefore, a fixed-bed torrefaction reactor was developed and used in the torrefaction of corncobs. The torrefaction process parameters investigated were the torrefaction temperature (200, 240, and 280 °C) and the residence time (30, 60, and 90 min). The effects of these parameters on the mass loss, grindability, chemical composition, and calorific value of biomass were investigated. It was shown that the mass loss increased with increasing torrefaction temperature and residence time. The grinding throughput of the biomass was improved by increasing both the torrefaction temperature and the residence time. Torrefaction at higher temperatures and longer residence times had greater effects on the reduction in particle size of the milled corncobs. The calorific value was highest at a torrefaction temperature of 280 °C and a residence time of 90 min. The energy yield for all treatments ranged between 92.8 and 99.2%. The results obtained in this study could be useful in the operation and design of torrefaction reactors. They also provided insight into parameters to be investigated for optimization of the torrefaction reactor.

Flue gas torrefaction of municipal solid waste: Fuel properties, combustion characterizations, and nitrogen /sulfur emissions

Flue gas torrefaction (FGT) was proposed as the pretreatment of the municipal solid waste (MSW) combustion process to improve the fuel properties of MSW and achieve better combustion performance. The optimal FGT parameters were obtained at 300 ℃ and 30 min, with the energy-mass co-benefit index (EMCI) reaching the maximum of 23.38. FGT could significantly increase the heating value and energy density of MSW while reducing the H/C and O/C ratio. Then, the pyrolysis and combustion experiments were performed by tube furnace and TG-MS. The results proved the chemical compositions of MSW were altered, and the heat transfer was enhanced. With FGT, NO_x and SO₂ emissions could be reduced by 25.7 % and 52.4 %, respectively. This study provides an in-depth understanding of the mechanism of FGT and paves the way for the clean treatment and energy utilization of MSW.

Flue gas torrefaction of distilled spirit lees and the effects on the combustion and nitrogen oxide emission

Flue gas torrefaction (FGT) integrated with combustion was introduced for the clean treatment of distilled spirit lees (DSL). The effects of temperature, residence time, and volumetric flow rate of FGTs were investigated. The improvement in the physicochemical and combustion characteristics of the torrefied DSL and the reaction mechanisms were clarified by a tube furnace and the TG-MS device. The results showed that FGT could effectively improve the properties of DSL. With increasing temperature, residence time, and volumetric flow rate, the mass and energy yields decreased. FGT showed positive effects on the removal of free and bonding water, as well as the enrichment of lignin. FGT effectively inhibited the release of NO_x. The overall emission of NO_x was reduced by 57.3%. Additionally, the cost of DSL drying and denitrification could be greatly reduced by FGT. This study provided a practical treatment for DSL and new insight into FGT.

Torrefaction of Woody and Agricultural Biomass: Influence of the Presence of Water Vapor in the Gaseous Atmosphere

Biomass preheating in torrefaction at an industrial scale is possible through a direct contact with the hot gases released. However, their high water-content implies introducing moisture (around 20% v/v) in the torrefaction atmosphere, which may impact biomass thermochemical transformation. In this work, this situation was investigated for wheat straw, beech wood and pine forest residue in torrefaction in two complementary experimental devices. Firstly, experiments in chemical regime carried out in a thermogravimetric analyzer (TGA) showed that biomass degradation started from lower temperatures and was faster under a moist atmosphere (20% v/v water content) for all biomass samples. This suggests that moisture might promote biomass components’ degradation reactions from lower temperatures than those observed under a dry atmosphere. Furthermore, biomass inorganic composition might play a role in the extent of biomass degradation in torrefaction in the presence of moisture. Secondly, torrefaction experiments on a lab-scale device made possible to assess the influence of temperature and residence time under dry and 100% moist atmosphere. In this case, the difference in solid mass loss between dry and moist torrefaction was only significant for wheat straw. Globally, an effect of water vapor on biomass transformation through torrefaction was observed (maximum 10%db), which appeared to be dependent on the biomass type and composition.

Physico-chemical assessment of torrefied Eurasian pinecones

BACKGROUND

Biomass pre-treatment is gaining attention as a standalone process to improve the qualitative aspect of the lignocellulosic material. It has been gaining ground in the power station by replacing the coal with the pre-treated biomass. In this context, this paper enlightens the operating condition of carrying out the torrefaction so that the process can be made relatively more effective. The influence of physico-chemical characteristics on the heat of reaction of pyrolysis reactions, mass loss and temperature regimes are evaluated by thermogravimetry of the pre-treated samples of the pinecone; whereas, the structural transformation in the basic constituents is determined via knowing the fractional change in cellulose, hemicellulose and acid-insoluble lignin contents of the pine cone. The thermogravimetric (TGA) and differential thermal analysis (DTA) were performed to determine the physical as well as the thermal behaviour of the thermally processed biomass. The samples had undergone thermal decomposition at heating rates of 5 °C min^-1, 10 °C min^-1 and 15 °C min^-1. Nitrogen gas was used as a purge gas for the pyrolysis of the pre-treated samples. The volumetric rate of 200 ml min^-1 was pre-set for the thermal decomposition of the samples at 600 °C; whereas, the selected torrefaction temperature range varied from 210 to 250 °C.

RESULTS

The heat of reaction for the pre-treated samples was found to vary from 1.04 to 1.52 MJ kg^-1; whereas, it was 0.91-1.54 MJ kg^-1 for the raw samples. The total annual production cost of processing 3.6 Mg of fuel in a year at a pilot scale was $ 36.72; whereas, the fiscal burden per kilogram of fuel during thermal degradation of the processed fuel was reduced by 0.08-1.5ȼ. The entropy of the system decreased with an increasing ramp rate. The exergetic gain in the system increased by 1-2%. The loss of energy during the energy-intensive processing of the pre-treated fuel was relatively low at a heating rate of 5 °C min^-1.

CONCLUSION

By the physico-chemical assessment, it was determined that pinecones required the highest torrefaction temperature and time to provide the upgraded pinecones. It was concluded that the duration of the torrefaction should be at least 15 min for a temperature of 250 °C so that the chemical exergy of the system, energy yield and the energy density of the processed material are qualitatively improved. The volatile and ash contents were noticed to decrease during the torrefaction process. The least fractional change in the volatile content was estimated at 210 °C for a torrefaction time of 15 min; whereas, the ash content was minimum at 210 °C for a torrefaction time of 5 min.

Impacts of non-oxidative torrefaction conditions on the fuel properties of indigenous biomass (bagasse)

Biomass is considered as the largest renewable energy source in the world. However, some of its inherent properties such as hygroscopicity, lower energy content, low mass density and bio-degradation on storage hinder its extensive application in energy generation processes. Torrefaction, a thermochemical process carried out at 200-300°C in a non-oxidative environment, can address these inherent problems of the biomass. In this work, torrefaction of bagasse was performed in a bench-scale tubular reactor at 250°C and 275°C with residence times of 30, 60 and 90 mins. The effects of torrefaction conditions on the elemental composition, mass yield, energy yield, oxygen/carbon (O/C) and hydrogen/carbon (H/C) ratios, higher heating values and structural composition were investigated and compared with the commercially available 'Thar 6' and 'Tunnel C' coal. Based on the targeted mass and energy yields of 80% and 90% respectively, the optimal process conditions turned out to be 250°C and 30 mins. Torrefaction of the bagasse conducted at 275°C and 90 min raised the carbon content in bagasse to 58.14% and resulted in a high heating value of 23.84 MJ/kg. The structural and thermal analysis of the torrefied bagasse indicates that the moisture, non-structural carbohydrates and hemicellulose were reduced, which induced the hydrophobicity in the bagasse and enhanced its energy value. These findings showed that torrefaction can be a sustainable pre-treatment process to improve the fuel and structural properties of biomass as a feedstock for energy generation processes.

Thermo-Acoustic Catalytic Effect on Oxidizing Woody Torrefaction

The torrefaction (mild pyrolysis) process modifies biomass chemical and physical properties and is applied as a thermochemical route to upgrade solid fuel. In this work, the catalytic effect of thermo-acoustic on oxidizing woody torrefaction is assessed. The combined effect of two acoustic frequencies (1411, 2696 Hz) and three temperatures (230, 250, and 290 °C) was evaluated through weight loss and its deviation curves, calculated torrefaction severity index (TSI), as well as proximate, calorific, and compression strength analysis of Eucalyptus grandis. A new index to account for the catalytic effects on torrefaction (TCEI) was introduced, providing the quantitative analysis of acoustic frequencies influence. A two-step consecutive reaction numerical model allowed the thermo-acoustic experiment evaluation. For instance, the thermogravimetric profiles revealed that the acoustic field has a catalytic effect on wood torrefaction and enhances the biomass oxidation process for severe treatments. The kinetic simulation of the acoustic coupling resulted in faster conversion rates for the solid pseudo-components showing the boosting effect of acoustic frequencies in anticipating hemicellulose decomposition and enhancing second step oxidizing reaction.

Determination of the Optimal Operative Conditions for the Torrefaction of Olive Waste Biomass

The need for new energy sources and the problems associated with waste in the agroforestry industry are an opportunity for the recovery of this waste. For the use of this agricultural waste as energy, different pretreatments, such as torrefaction, can be carried out. Torrefaction is a thermochemical treatment involving energetic densification of biomass at temperatures ranging from 200 to 300 °C under an inert and anaerobic environment. This study developed a numerical model to evaluate the effect of temperature and residence time of torrefaction on biomass from olive tree waste to determine optimum operative conditions for the process. Four temperatures and four residence times, in the operation range of the process, were tested to determine the weight loss and the higher heating values (HHVs) of the torrefied sample. From these data, a numerical model was developed to infer the complete behavior of the process in the temperature range between 200 and 300 °C and in the residence time range of a few minutes to 2 h. The HHV of the torrefied sample increased at a temperature between 200 and 275 °C. However, from 275 to 300 °C, there was an HHV decrease. The effect of the residence time depended on the torrefaction temperature. At low temperatures, there were no statistically significant differences, although an increase of HHV was detected under 120 min. However, at 250 °C this effect was reversed, and statistically significant differences were not observed between 30 and 120 min. Overall, the increase of temperature in the torrefaction process reduces the residence time needed to achieve the maximum HHV. As a result, the optimum conditions of torrefaction for this biomass were, approximately, 275 °C and 30 min of residence time. This reaction yielded an optimum 5830 cal/g HHV.

Influence of Torrefaction and Pelletizing of Sawdust on the Design Parameters of a Fixed Bed Gasifier

Gasification of biomass in fixed bed gasifiers is a well-known technology, with its origins dating back to the beginning of 20th century. It is a technology with good prospects, in terms of small scale, decentralized power co-generation. However, the understanding of the process is still not fully developed. Therefore, assessment of the changes in the design of a gasifier is typically performed with extensive prototyping stage, thus introducing significant cost. This study presents experimental results of gasification of a single pellet and bed of particles of raw and torrefied wood. The procedure can be used for obtaining design parameters of a fixed bed gasifier. Results of two suits of experiments, namely pyrolysis and CO2 gasification are presented. Moreover, results of pyrolysis of pellets are compared against a numerical model, developed for thermally thick particles. Pyrolysis time, predicted by model, was in good agreement with experimental results, despite some differences in the time when half of the initial mass was converted. Conversion times for CO2 gasification were much longer, despite higher temperature of the process, indicating importance of the reduction reactions. Overall, the obtained results could be helpful in developing a complete model of gasification of thermally thick particles in a fixed bed.

Biomass torrefaction as an emerging technology to aid in energy production

Biomass torrefaction has gained widespread attention due to its benefits as a standalone process to improve biomass properties to be at par or similar to those for coal in electricity generation or as a pretreatment step before pyrolysis and gasification processes. It has also found application in other processes like steel production where it is aiming to replace coal or work alongside coal by co-firing the coal with biomass at certain proportions. There have been a lot of papers on biomass torrefaction review, but this paper tried to look at a different angle to show other aspects of torrefaction and how it links to other technologies as well as the chemistry behind it. Overall, the process has seen a big shift in the technology it utilizes, and the hope is that it will make the process more viable and applicable in future. The focus starts from the raw biomass, how it is analysed and the different analysis that are performed to determine relevant information about biomass properties. There are different reactors that are used but to date there is not a preferred one as they have their pros and cons. However, the focus mostly is the process not which reactor to use as they have all not shown any significant differences. The main product of the process, torrefied biomass determines the efficiency and how it can be applied to other technologies. To date, biomass torrefaction is for co-firing with coal for energy generation and as a pretreatment step for pyrolysis and gasification. Due to varying types of biomass in different countries, the technology has not yet reached its full potential, but the hope is it will with calls for use of renewable sources of energy. Other areas like modelling torrefaction of biomass have not been looked at in this review. However, the paper sets the foundations for such detailed reviews.

A new torrefaction system employing spontaneous self-heating of livestock manure under elevated pressure

This report describes a new oxidative torrefaction method employing spontaneous self-heating of feedstock as a means of overcoming practical difficulties in converting livestock manure to biochar. We examined the initiating temperature required to induce self-heating of wet dairy cattle manure under 1.0 MPa pressure and conducted elemental and calorific analyses of the solid products prepared at 200, 250, and 300 °C. Self-heating was initiated with oxidation below 100 °C, and the lower limit of the initiation temperature was between 85 and 90 °C. Comparing processes performed at 0.1 and 1.0 MPa, the higher pressure promoted self-heating by both preventing heat loss due to moisture evaporation occurring at approximately 100 °C and supplying oxygen to the high-moisture feedstock. In addition, as drying occurred at 160-170 °C during the process, the system did not require pre- or post-drying. Although the heating values of the solid products decreased due to high ash content, the elemental composition of the products was altered to that of peat-like (200 °C) and lignite-like (250 and 300 °C) materials. Cessation of self-heating of the manure is recommended at approximately 250 °C to avoid severe decomposition at higher temperatures. Overall, these results demonstrated the utility of the proposed method for converting wet manure into dried biochar through self-heating as well as potential applications in manure management systems.

Torrefaction as a Valorization Method Used Prior to the Gasification of Sewage Sludge

The gasification and torrefaction of sewage sludge have the potential to make the thermal utilization of sewage sludge fully sustainable, thus limiting the use of expensive fossil fuels in the process. This includes sustainability in terms of electricity consumption. Although a great deal of work has been performed so far regarding the gasification of sewage sludge and some investigations have been performed in the area of its torrefaction, there is still a gap in terms of the influence of the torrefaction of the sewage sludge on its subsequent gasification. This study presents the results from the torrefaction tests, performed on a pilot scale reactor, as well as two consecutive steam gasification tests, performed in an allothermal fixed bed gasifier, in order to determine if torrefaction can be deemed as a primary method of the reduction of tar content for the producer gas, from the aforementioned gasification process. A comparative analysis is performed based on the results obtained during both tests, with special emphasis on the concentrations of condensable compounds (tars). The obtained results show that the torrefaction of sewage sludge, performed prior to gasification, can indeed have a positive influence on the gas quality. This is beneficial especially in terms of the content of heavy tars with melting points above 40 °C.

Investigation of representative components of flue gas used as torrefaction pretreatment atmosphere and its effects on fast pyrolysis behaviors

In this study, three torrefaction atmosphere (N₂, CO₂ and 2 vol% O₂ with N₂ balance) were used to study effects of representative main components of flue gas during torrefaction and subsequent pyrolysis. Torrefaction pretreatment was carried out in a fixed-bed reactor at 230 °C and 250 °C, respectively. Results showed after torrefaction, torrefied samples from oxygenated atmosphere presented severer hemicellulose decomposition. And its effects on fast pyrolysis were investigated in thermogravimetry analysis and bench-scale fixed-bed reactor. It was found that oxygenated atmosphere preferred to give higher relative content of phenols at 230 °C and furans at 250 °C. For CO₂, higher relative content of ketones and lowest phenols were got. The result also indicated that it's the O₂ in flue gas which significantly improved the char yield. These results will be beneficial reference to predict and interpret alterations of pyrolysis behaviors when flue gas constitution changes in industrial application.

Torrefaction of landfill food waste for possible application in biomass co-firing

Greenhouse gas emissions and municipal solid waste management have presented challenges globally. This study aims to produce a high-quality biochar with properties close to bituminous coal from landfill food waste (FW). FW was analyzed by proximate and ultimate analyses to determine its fuel properties and elemental composition before torrefaction. Temperature was varied from 200 to 300 °C at a constant residence time of 40 min and 10 °C/min heating rate. Calorific value, mass yield, energy yield and energy density were computed and used to determine the quality of the resulting biochar. Quality of raw food waste was also determined by elemental analysis. Thermal evolution was then investigated using hyphenated Thermogravimetric Analysis (TGA) and Fourier Transform Infra-Red Spectrometry (FTIR). Torrefaction was done at 225 °C, 275 °C and 300 °C. The calorific value was upgraded from 19.76 MJ/kg for dried raw food waste to 26.15 MJ/kg for torrefied food waste at the appropriate conditions which were 275 °C, 40 min and 10 °C/min. The higher heating value was comparable to that of bituminous coal from Anglo Mafube in South Africa. Elemental analysis of biochar showed an increase in carbon content with temperature due to loss of oxygen containing volatiles. This agreed with TG curves and FTIR spectra which confirmed release of H₂O, CO and CO₂. This resulted in a more hydrophobic solid fuel with high energy density. Food waste can therefore be upgraded to a biochar with similar fuel properties as pulverized coal used in coal fired boilers.

Torrefaction of empty fruit bunches under biomass combustion gas atmosphere

Torrefaction of oil palm empty fruit bunches (EFB) under combustion gas atmosphere was conducted in a batch reactor at 473, 523 and 573K in order to investigate the effect of real combustion gas on torrefaction behavior. The solid mass yield of torrefaction in combustion gas was smaller than that of torrefaction in nitrogen. This may be attributed to the decomposition enhancement effect by oxygen and carbon dioxide in combustion gas. Under combustion gas atmosphere, the solid yield for torrefaction of EFB became smaller as the temperature increased. The representative products of combustion gas torrefaction were carbon dioxide and carbon monoxide (gas phase) and water, phenol and acetic acid (liquid phase). By comparing torrefaction in combustion gas with torrefaction in nitrogen gas, it was found that combustion gas can be utilized as torrefaction gas to save energy and inert gas.

Predictions of biochar yield and elemental composition during torrefaction of forest residues

In this work, a direct prediction method coupled with a consecutive reaction model is developed to estimate the biochar yield and elemental composition in a biomass torrefaction process. Norway forest residues were chosen as feedstock and torrefied at different temperatures under nitrogen atmosphere in a thermogravimetric analyzer. Obtained data were modeled to predict the mass loss during torrefaction. Distributions of initial, intermediate and final solid products as well as torrefaction kinetic parameters are reported. Thereafter, a direct method to predict the elemental composition of biochar is introduced. The results show that the decomposition of initial biomass to form an intermediate solid has higher conversion rate than the degradation of the intermediate. Moreover, the predictions reproduce well the experimental thermogravimetric curves and show composition trends similar to the literature data. This method is useful for the design and optimization of industrial torrefaction processes with predictable biochar yield and elemental composition.

Product characteristics from the torrefaction of oil palm fiber pellets in inert and oxidative atmospheres

The aim of this work was to study the characteristics of solid and liquid products from the torrefaction of oil palm fiber pellets (OPFP) in inert and oxidative environments. The torrefaction temperature and O2 concentration in the carrier gas were in the ranges of 275-350°C and 0-10 vol%, respectively, while the torrefaction duration was 30 min. The oxidative torrefaction of OPFP at 275°C drastically intensified the HHV of the biomass when compared to the non-oxidative torrefaction. OPFP torrefied at 300°C is recommended to upgrade the biomass, irrespective of the atmosphere. The HHV of condensed liquid was between 10.1 and 13.2 MJ kg(-)(1), and was promoted to 23.2-28.7 MJ kg(-)(1) following dewatering. This accounts for 92-139% improvement in the calorific value of the liquid. This reveals that the recovery of condensed liquid with dewatering is able to enhance the energy efficiency of a torrefaction system.

Development of a biomass torrefaction process integrated with oxy-fuel combustion

Torrefaction of forest residues was studied under conditions relevant to oxy-fuel combustion flue gases. The results showed that the torrefaction in CO2 had a lower solid mass yield (81.36%) than that (83.06%) in N2. Addition of steam into CO2 (CO2/H2O=1/0.7 mole/mole) resulted in a higher mass yield (83.30%) compared to 81.36% in CO2. The energy yield was consistently increased from 79.17% to 84.12% or 88.32% for the torrefaction in N2, CO2, or the CO2 and steam mixture, respectively. On the other hand, additions of O2 into the mixture of steam and CO2 led to reductions in both mass yield (from 83.30% to 82.57% or 76.44%) and energy yield (from 88.32% to 84.65% or 79.16%, for the torrefaction in steam and CO2 without O2, with 5% v/v, or 10% v/v of O2, respectively).

Torrefaction of cedarwood in a pilot scale rotary kiln and the influence of industrial flue gas

Torrefaction of cedarwood was performed in a pilot-scale rotary kiln at various temperatures (200, 230, 260 and 290°C). The torrefaction properties, the influence on the grindability and hydroscopicity of the torrefied biomass were investigated in detail as well as the combustion performance. It turned out that, compared with raw biomass, the grindability and the hydrophobicity of the torrefied biomass were significantly improved, and the increasing torrefaction temperature resulted in a decrease in grinding energy consumption and an increase in the proportion of smaller-sized particles. The use of industrial flue gas had a significant influence on the behavior of cedarwood during torrefaction and the properties of the resultant solid products. To optimize the energy density and energy yield, the temperature of torrefaction using flue gas should be controlled within 260°C. Additionally, the combustion of torrefied samples was mainly the combustion of chars, with similar combustion characteristics to lignite.

Pretreatment of biomass by torrefaction and carbonization for coal blend used in pulverized coal injection

To evaluate the utility potential of pretreated biomass in blast furnaces, the fuel properties, including fuel ratio, ignition temperature, and burnout, of bamboo, oil palm, rice husk, sugarcane bagasse, and Madagascar almond undergoing torrefaction and carbonization in a rotary furnace are analyzed and compared to those of a high-volatile coal and a low-volatile one used in pulverized coal injection (PCI). The energy densities of bamboo and Madagascar almond are improved drastically from carbonization, whereas the increase in the calorific value of rice husk from the pretreatment is not obvious. Intensifying pretreatment extent significantly increases the fuel ratio and ignition temperature of biomass, but decreases burnout. The fuel properties of pretreated biomass materials are superior to those of the low-volatile coal. For biomass torrefied at 300°C or carbonized at temperatures below 500°C, the pretreated biomass can be blended with coals for PCI.

An experimental and theoretical investigation on torrefaction of a large wet wood particle

A competitive kinetic scheme representing primary and secondary reactions is proposed for torrefaction of large wet wood particles. Drying and diffusive, convective and radiative mode of heat transfer is considered including particle shrinking during torrefaction. The model prediction compares well with the experimental results of both mass fraction residue and temperature profiles for biomass particles. The effect of temperature, residence time and particle size on torrefaction of cylindrical wood particles is investigated through model simulations. For large biomass particles heat transfer is identified as one of the controlling factor for torrefaction. The optimum torrefaction temperature, residence time and particle size are identified. The model may thus be integrated with CFD analysis to estimate the performance of an existing torrefier for a given feedstock. The performance analysis may also provide useful insight for design and development of an efficient torrefier.