Torrefaction Process Research Articles

Torrefaction of spruce, beech, and oak pellets in order to improve calorific value

Native spruce, beech, and oak pellets were treated by torrefaction. The torrefaction was performed without oxygen, in an electric oven, at temperatures of 170 °C, 190 °C, and 210 °C and treatment periods of 1, 2, and 3 h. The results showed an increase in the calorific value of the pellets by raising the parameters of the treatment regime (temperature and duration), achieving maximum values of 18.93 MJ/kg in the case of beech pellets for 3 h and 190 °C, 18.97 MJ/kg for the roughest regime with 3 h and 210 °C in the case of spruce pellets, and 18.84 MJ/kg in the case of oak pellets with 3 h and 190 °C. The torrefaction process for beech and oak must be stopped at 190 °C and 3 hours, becoming ineffective after these values of the treatment regime. The shear strength of the pellets were decreased slightly (10 to 15%) by the torrefaction treatment, but ash content slightly increased from 17.7% for spruce pellets to 29.1% for beech pellets. The results suggest that direct torrefaction of native pellets is possible without the use of nitrogen, i.e., by turning off the oxygen intake in the torrefaction oven, with good results for increasing the calorific value with 8.7% for beech pellets, 7.5% for spruce pellets, and 7.9% for oak pellets.

Impact of Biochar Addition in Microwave Torrefaction of Camelina Straw and Switchgrass for Biofuel Production

The possibility of applying biochar in mild torrefaction treatment to improve the thermochemical characteristics of ground biomass was the focus of the study. Camelina straw and switchgrass were torrefied in a reactor using microwave irradiation at torrefaction temperatures of 250 °C and 300 °C with residence times 10, 15 and 20 min, under nitrogen-activated inert conditions. Both biochar addition of more than 10% and residence time significantly affected the product yields, as MW torrefaction temperatures shifted from 250 °C to 300 °C. Overall, the results indicated a slight increase in ash content, mass loss percentage intensification, heating values, and fixed carbon, while moisture content and volatile matter decreased in camelina straw and switchgrass, with or without biochar. Biochar addition with a long residence time (20 min) at 250 °C reduced energy requirement during the microwave torrefaction process. The combustion index values showed that torrefied camelina straw or switchgrass with biochar addition suits co-combustion with coal in a coal-fired plant and is a potential biomaterial for biofuel pellets.

Assessments and analysis of lumped and detailed pyrolysis kinetics for biomass torrefaction with particle-scale modeling

A one-dimensional model with consideration of internal and external heat transfer, particle shrinkage, moisture evaporation, and pyrolysis kinetics is developed to predict biomass torrefaction behaviors. Three different kinetic schemes (i.e. a lump kinetic scheme and two detailed kinetic schemes (Andrés Anca-Couce and IngwaldObernberger, 2016, and Debiagi et al., 2018) are evaluated to find the suitable pyrolysis kinetics for biomass torrefaction process. The modeling results are compared with single beechwood particle torrefaction experiments. The results show that the detailed kinetic scheme proposed by Debiagi et al. shows the best performance among the three kinetic schemes, and it can correctly predict particle shrinkage, particle conversion, mass loss history, and biochar C/H/O compositions, while the lump kinetic scheme underestimates torrefaction rates and particle shrinkage degree at low temperature conditions (280–370 °C), and the kinetic scheme proposed by Andrés and Ingwald underestimates carbon concentration and overestimates the oxygen concentration of torrefied wood at high temperature conditions (370, 400, and 430 °C). Therefore, the kinetic scheme of Debiagi et al. is considered to be the most promising kinetics in particle-scale modeling of the torrefaction process. A sensitivity analysis is also performed to evaluate the effects of modeling parameters on modeling results as well as study the control mechanism of torrefaction process. The results show that modeling results are significantly influenced by parameters involved with external and external heat transfer related, boundary conditions, and reaction rate, indicating torrefaction process of large particles is controlled by both internal and external heat transfer, and kinetics.

초본계 바이오매스 발전사업 타당성 분석 연구

The purpose of this study was to analyze the economic feasibility of a project assuming 9.9 MW Kenaf biomass power generation by producing Kenaf on approximately 1,100 ha on Saemangeum reclaimed land, manufacturing high-quality Kenaf power generation fuel through ash reduction and torrefaction processes. The Profit Index (PI) method was applied for the economic analysis. Results confirmed that the profitability index (PI) of the business was 0.55, which did not secure economic feasibility. Sensitivity was analyzed using the power plant use rate, facility investment cost, fuel manufacturing cost, as well as REC weight as major variables. As a result, even if the power plant use rate is reflected as 100%, the profitability index is 0.86, which does not secure economic feasibility. If the facility investment cost is lowered from 39.24 million USD to 0.49 million USD, economic feasibility is secured, However, the possibility of realization is significantly low. If the fuel manufacturing cost is reduced from 241.13 thousand won/ton to 40.50 thousand won/ton, economic feasibility is secured. However, it is difficult to realize because it requires high technology development cost and time. Regarding the REC weight, economic feasibility can be secured at 1.96, similar to the REC weight “2” currently given to the power generation of unused forest biomass. As a result of analyzing the complex sensitivity using the power plant use rate as well as REC weight as the main variables, economic feasibility can be secured in the section wherein the REC weight is lower than “1” when the power plant use rate is 80% or more. REC weighting, continuous technology development, as well as policy support for Kenaf biomass power generation, expected to play a critical role as a greenhouse gas sink in the future, are highly needed.

Advancing biomass pyrolysis by torrefaction pretreatment: Linking the productions of bio-oil and oxygenated chemicals to torrefaction severity

Torrefaction is an efficient pretreatment method to improve the quality of biomass feedstock and resulting bio-oil. Herein, the relationships of torrefaction severity of sweet sorghum bagasse (SSB) with its physicochemical properties and resulting pyrolytic product distributions were systemically investigated. The SSB was first pretreated by torrefaction at different temperatures (230, 260, and 290 °C) with a constant residence time of 30 min, and the resulting torrefied SSB was subsequently pyrolyzed at 500 °C for the production of bio-oil. The carbon enrichment index (CEI) is used as an indicator to quantitatively reflect the torrefaction severity of SSB. The results show that the extents of decarbonization, dehydrogenation, and deoxygenation reactions of SSB increase linearly with the increase of CEI, and the extent of deoxygenation reaction is the most severe among them. Torrefaction can effectively regulate the pyrolytic production distributions of SSB, and severe torrefaction favors the formation of biochar. The productions of bio-oil and major oxygenated chemicals (e.g., ketones, carboxylic acids, and phenols) in bio-oil as the functions of CEI could be fitted well by quadratic polynomial functions. The findings can guide the rational design and optimization of the torrefaction process for improved biomass pyrolysis.

Three-stage pretreatment of food waste to improve fuel characteristics and incineration performance with recovery of process by-products

As of 2020, the annual generation of municipal solid waste (MSW) in China has surged to 235.12 Mt, and food waste (FW) accounts for more than 60 %. The most common treatment method is incineration, which accounts for 62.13 %. This research proposes a three-stage pretreatment method for FW that is suitable for incineration while recovering by-products and energy from the pretreatment process. The first stage is dehydration; as compared to hot air drying (HAD) processes, freeze drying (FD) exhibits a higher dehydration and oil preservation rate, allowing for the preservation of organic matter content and the recovery of freshwater resources from FW. The second stage is oil recovery; the FW extracted oil (FWEO) can be used to produce biodiesel, and this stage also helps to improve the effectiveness of the subsequent torrefaction process. The third stage improves the energy and fuel characteristics of the organic residue of FW and enhances the combustion performance by optimizing the torrefaction temperature. The solid fuel obtained at a torrefaction temperature of 350 °C shows the best combustion performance, with a solid yield of 35.76 %, a torrefaction temperature of 300 °C might be chosen to further improve the solid yield.

Torrefaction Upgrading of Heterogenous Wastes Containing Cork and Chlorinated Polymers

Torrefaction of two mixed wastes composed of cork and chlorinated polymers was studied at temperatures from 200 to 350 °C, for residence times of 30 and 60 min. These wastes were recovered from sandwich panels with cork core, have different contents of cork biomass and chlorinated polymers and present poor fuel properties for energy recovery applications. The raw wastes and the produced biochars were characterized for proximate and ultimate analysis, chlorine content, mineral composition, calorific value, mass yield, energy density, particle size distribution, and adsorption capacity towards cationic and anionic dyes. Torrefaction enabled the production of biochars with mass yields from 97.2 to 54.5%, with an increase in 12.1 to 37.9% in apparent density relative to the raw wastes, and HHV from 18.2 to 20.7 MJ/kg. Nevertheless, the chlorine content of the biochars was increased to values higher than 5%, inadequate for solid fuels. Dechlorination of the biochars by washing with hot water enabled 84 to 91% removal of the chlorine species achieving final concentrations lower than 1%, without significant reduction in the biochars calorific values. For the waste with higher polymer and ash content, the torrefaction process reduced the heating value; therefore, energy valorization was not adequate. Both the raw wastes and the biochars were tested as adsorbents for cationic and anionic dyes. After activation with KOH, both the raw materials and the biochars had removal efficiencies higher than 90% for methylene blue, a cationic dye often found in industrial effluents. The results showed that torrefaction combined with hot water washing converted these wastes to biochars with the potential for energy or material valorization contributing to a circular economy in the cork industrial sector.

Aktivitas Antibakteri Hand Sanitizer Berbahan Dasar Asap Cair Hasil Torefaksi Cangkang Kelapa Sawit Terhadap Bakteri Escherichia coli

Antibacterial activity of hand sanitizer based on liquid smoke from torrefaction of palm oil against Escherichia coli has been done. The liquid smoke produced from the oil palm shell torrefaction process has the potential to be used as an antiseptic base for hand sanitizer products. This is due to its high phenol and acetic acid content. Many other compounds must be separated from liquid smoke, one of the processes that can be separated with distillation. Compounds of liquid smoke from distillation are phenol, propanoic acid, 2-propanone, and acetic acid. This research was conducted by varying the concentration of liquid smoke in a hand sanitizer by 15%, 25%, and 35%. The results showed that the number of bacterial colonies at a concentration of 15% was 910,000 CFU/ml, 25% was 1,130,000 CFU/ml, and 35% was 1,140,000 CFU/ml. The effective concentration to kill bacteria is in hand sanitizer based on liquid smoke with a concentration of 15% was 57,59%.
 Keywords: palm kernel shells, liquid smoke, Escherichia coli

A comparison of conventional and oxidative torrefaction of microalga Nannochloropsis Oceanica through energy efficiency analysis and life cycle assessment

Torrefaction is a promising method for producing microalgal solid biofuel. This study compared conventional torrefaction and oxidative torrefaction for microalgal solid biofuel production. Particular attention was paid to evaluating energy efficiency analysis and life cycle assessment, and several parameters and indexes were adopted and calculated. The results showed that mild oxidative torrefaction was the most energy-efficient operation, with the maximum value of relative upgrading energy index and relative energy return on investment. The life cycle assessment indicates that oxidative torrefaction had a lower environmental impact than conventional torrefaction, mainly due to its lower carrier gas consumption and electricity input. The environmental impact positively correlated with the torrefaction severity. The obtained results in this study can provide new insights on improving the cognition of energy efficiency evaluation and environmental impact assessment of the torrefaction process, which helps select optimal torrefaction conditions.

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.

Effects of oxygen deficient and flue gas torrefaction on the surface property and structural feature of typical agriculture waste: Rice husk

Effects of torrefaction condition on fuel qualities and combustion characteristics of rice husk were studied. The distribution of typical elements and components exhibited that rising torrefaction severity initially decreased and subsequently increased the values of H/C and O/C. The effects of torrefaction condition on lignin content and heating value for torrefied samples expressed identical law. Increasing torrefaction severity decreased the solid yield monotonically, while the corresponding energy yield expressed first upward and then downward trend. The participation of H2O in the torrefaction process was beneficial to the generation of edge nitrogen and the enrichment of reactive functionalities at the expense of hydrophilic groups. The addition of multiple oxidants was conducive to enlarging specific surface area and optimizing fuel combustion behavior at mild temperatures. According to the results obtained from this research, the upgraded sample derived from torrefaction occurred in wet flue gas at 543 K expressed the best fuel quality.

Impact of torrefaction on thermal behavior of wheat straw and groundnut stalk biomass: Kinetic and thermodynamic study

This study investigates the physicochemical behavior of Wheat Straw and Groundnut Stalk biomass and its impact on the thermal behavior during torrefaction process. The torrefaction was experimentally investigated by thermogravimetric analysis (TGA) at five isothermal heating rates of 20, 30, 40 and 50 °C/min. Results revealed that during the torrefaction process, significant fraction of hemicellulose and volatile content reduces that improves the high heating value. The results indicated that torrefaction treatment improved the fuel properties with elevated torrefaction temperature, including the lower volatile content, higher carbon content, and higher heating value. Kinetic parameter analysis indicated that the Ozawa–Flynn–Wall and Starink model were significant in calculating the activation energy, and the average activation energy was 240 kJ/mol and 238 kJ/mol (Wheat Stalk and torrified wheat Stalk) 127 kJ/mol and 129 kJ/mol (Groundnut Stalk and torrified Groundnut Stalk). An excellent linear relationship between lnA and Eα was observed, indicating that the compensation effect existed between the Eα and lnA during torrification. These results provide important basic data support for the thermochemical conversion of cornstalk to energy and chemicals.

Methods for Treatment of Animal and Plant-Based Biomass Waste

Abstract In the work presented, effective methods of biomass processing for its reuse in the framework of the circular economy were determined. Based on various sources, a definition of biomass was obtained. The review covers preliminary operations, i.e., screening and grinding, as well as the methods of pressure and non-pressure agglomeration of plant and animal biomass, as well as the process of torrefaction of plant biomass. The analysis of the literature indicates various process and technological solutions for biomass processing, as well as provides numerous examples of the use of biomass in combination with other types of industrial waste and mineral additives. The activities undertaken as part of the work are consistent with the assumptions of the European Green Deal and are carried out in order to improve the management of waste streams (green productivity) and to increase the amount of recovered energy produced.

Development and application of a detailed kinetic model to evaluate the torrefaction process of rice-based biomass

Development and application of a detailed kinetic model to evaluate the torrefaction process of rice-based biomass

Kinetics mechanism of inert and oxidative torrefaction of biomass

Torrefaction of biomass is a promising pre-treatment process capable of substantially improving the properties of raw biomass for its use as a solid biofuel, among many other potential applications. Oxygen-lean torrefaction can effectively reduce the cost and complexity of inert torrefaction. In this work, torrefaction tests of crushed olive stones were conducted in a thermogravimetric analyzer in various oxygen concentrations, under both non-isothermal and isothermal conditions. Non-isothermal torrefaction measurements were used to gain fundamental knowledge on the inert and oxidative torrefaction processes by applying a model-fitting kinetics method. Analysis of these measurements showed that an accurate description of inert torrefaction based on a two-step reaction mechanism is possible, whereas a three-step reaction mechanism is necessary for oxidative torrefaction. The new three-step mechanism was found to be accurate for describing the global mass loss during isothermal torrefaction, obtaining average root mean squared errors between the model predictions and the TGA measurements below 2.0 % for inert and oxidative torrefaction of olive stones. Furthermore, predictions using the extended mechanism were in good agreement with the more fundamental torrefaction reactions derived from the kinetics analysis of the non-isothermal torrefaction measurements.

Valorization of corncob through torrefaction process

Corncobs is a waste of post-harvest corn processing that has great potential to be used as a source of renewable solid fuel. Its high moisture and volatile solids content produces a lot of smoke when corncob is burned, so it is rarely used as fuel. This study aims to improve the quality of corncob fuel through the torrefaction process. The corncob was naturally dried using sunrays for two days and cut into pieces of 1-3 cm in size. The torrefaction process was carried out using a cylindrical rotary reactor which operated at a speed of 30 RPM and was heated using an external heat source. The variations of torrefaction time were 30, 40, and 60 minutes. The parameters to be observed included moisture content, ash content, volatile content, calorific value, and hydrophobicity of materials. The results showed that the torrefaction process improved the quality of corncobs as seen from an increase in calorific value, an increase in hydrophobicity. In this study, the calorific value of the torrefied corncobs was 18.89 MJ/kg to 21.61 MJ/kg, which was higher than the caloric value of the non-torrefied corncobs of 17.66 MJ/kg. The torrefied corncobs are also more hydrophobic and absorb less water than the non-torrefied corncobs.

Biomass torrefaction: An overview of process and technology assessment based on global readiness level

Biomass is a potential renewable energy source as it is abundantly available and does not cost much. However, some property characteristics, such as high moisture content, low energy yield, and inefficient storage and handling operations, make raw biomass less feasible for utilization. To curtail this limitation, it needs to be pretreated before being converted into an energy-efficient fuel. Torrefaction proves to be one such method of conversion wherein the raw biomass is subjected to a temperature range of 200–300 °C with the medium being limited oxygen or inert such as nitrogen and results in solid biofuels with upgraded physicochemical properties such as higher energy density, lower moisture, higher calorific value, hydrophobic nature, and better grindability. Torrefied biomass may be utilized as an alternative to conventional fuel for different industries (e.g., power, steel, sugar, etc.) and plays a significant role in reducing environmental pollution and dependency on fossil fuels. A lot of research is ongoing on torrefaction to compile this technology globally. Hence, this review paper presents an overview of recent advances in torrefaction technology. In addition, factors governing the torrefaction reaction mechanism and various reactors utilized for torrefaction are discussed in detail, along with environmental and economic aspects of the torrefaction process. Moreover, a technology readiness level (TRL) approach has also been discussed, highlighting the possible scenarios based on the existing setups. Lastly, the potential applications are discussed, thereby concluding this work.

Modeling of Volatile Composition during Heating and Isothermal Stages of the Torrefaction Process

AbstractThe two‐step mechanism reaction model is widely used to represent solid degradation during the torrefaction process at fixed temperature. However, solid degradation during the heating period was neglected and the lack of the model for predicting volatile composition. Thus, the original model was extended to cover heating and isothermal stages during the torrefaction process based on thermogravimetric analysis using empty fruit bunch as case study. Torrefaction experiments were conducted at different temperature ranges for various heating rates. Based on the results, a good agreement between experimental and extended model was obtained with an absolute error of < 1 % indicating the high reliability of model prediction in estimating volatile composition.

Thermogravimetric analysis of the torrefied Austrian pine

ABSTRACT This work investigated the impact of thermal pre-treatment on the thermal kinetics of pinecones. An improvised muffle furnace was used for the torrefaction process. The kinetic parameters for thermal decomposition of torrefied pinecones and the raw pinecones were determined from the isoconversional methods (Friedman, Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS)). The reaction mechanism (RM) of the raw and thermally processed pinecones was obtained by the Criado master plots. Thermogravimetric analyses of both the raw and thermally pre-treated pinecones were performed at a heating rate of 5°C·min−1, 10°C·min−1 and 15°C·min−1. Nitrogen gas was used as an inert medium for both thermal pre-treatment and pyrolysis of raw pinecones. The activation energies estimated from OFW and KAS, and Friedman for torrefied pinecones are 165.87 kJ·mol−1, 169.66 kJ·mol−1 and 130.68 kJ·mol−1,respectively. The calculated value of activation energy from OFW and KAS for the torrefied pinecones was estimated to be 8.66–8.93% higher than that of raw pinecones; however, in the case of the differential method, it decreased by a margin of 10%. The reduced reaction rate of the torrefied pinecones was slightly higher than that of the raw pinecones. However, no change in the characteristics of the reduced reaction rate of torrefied pinecones was noticed with respect to its raw form, in relation to thermal conversion. The clean gas generation after processing the raw pinecones was noticed to be 27.54% higher than its raw form. The weight percentages of alkali elements were increased by 24% after the torrefaction process.

Torrefaction of Napier Grass and Oil Palm Petiole Waste Using Drop-Type Fixed-Bed Pyrolysis Reactor.

The torrefaction process in the preparation of energy materials has garnered a lot of attention and has been investigated as a means of improving biomass solid fuels. The aim of this study is to study the effect of the temperature and holding time of two biomass samples: wild Napier grass and oil palm petiole. The torrefied samples are operated in a pyrolysis reactor to replicate the torrefaction procedure. The temperature parameter ranges between 220 and 300 °C while the holding time of the reaction parameter ranges from 10 to 50 min. It is found that with increasing temperature and time, the moisture content and number of O and H atoms decrease and also cause both mass and energy yield to decrease. It is found that the calorific value and the energy density increase with both parameters, which shows that optimization is needed for better solid fuel production. Between the two parameters, temperature changes have more significant effects on the torrefied samples. The optimized temperature and time are found to be 260 °C and 30 min, respectively. The usage of the pyrolysis reactor for the torrefaction reaction has been proven to serve as a good option due to similar product characteristics and equivalent results.