Torrefaction Process Research Articles

Effect of Heating Temperature and Residence Time on Morphology and Bonding Behavior of Torrefied Biochar from Oil Palm Empty Fruit Bunch

This study was conducted to identify the potential of torrefied oil palm empty fruit bunch (OPEFB) biochar as a renewable energy sources by underwent torrefaction process based on holding temperature and residence time. The process has been carried out within holding temperature varied from 200 to 300°C in the absence of oxygen under low heating rate by using furnace in 30 to 90 minutes of their residence time, respectively. In brief, this study focused on the morphology as well as the bonding behavior of the torrefied OPEFB biochar due to its properties and functional groups in order to enhance the potential of the OPEFB as renewable energy sources by the aids of Scanning Electron Microscope (SEM) and Fourier Transformation Infrared Spectroscopy (FTIR). SEM images showed the surface morphology of OPEFB after undergo torrefaction by which it was completely decomposed by initiating pores while the structure become flattened with almost left sharp edge compared to the raw OPEFB. The changes of presence functional groups before and after the torrefaction process were observed under certain wavelength which were C=O (1750- 1680cm-1 ), N-H (3500-3100cm-1 ) and C-N (1350-1000cm-1 ). These functional groups determined the changes of functional groups as well as the wavelength whereby the degradation of hemicellulose, cellulose and lignin take place.

Optimization and Characterization on Elemental and Crystallinity Index of Torrefied Biochar from Oil Palm Empty Fruit Bunch

This research was conducted to optimize the torrefied oil palm empty fruit bunch (OPEFB) biochar yield from torrefaction process as an alternative renewable energy sources. The influence of three major torrefaction parameters namely particle size, holding temperature and residence time on calorific values was investigated. By using the response surface method (RSM), Box-Benhken model had been applied for generating shortest experiment run, and analysis of variance (ANOVA) had been utilized for optimization analysis. From ANOVA, the suggested parameters were the torrefaction at 300°C of holding temperature and 90 minutes of residence time in case to obtain the highest calorific value. Characterization of torrefied OPEFB biochar by elemental analyser and X-ray diffraction (XRD) were conducted to support the data. The carbon element in the torrefied OPEFB biochar was increased when the holding temperature and residence time increased while oxygen element amount is decreasing. This is due to decomposition of hemicellulose occurred in this region. For crystallinity index (CrI) by XRD, there was decreasing pattern occurred as the holding temperature and residence time increased from 200 – 300°C and 30 – 90 minutes respectively. This showes that the torrefied OPEFB biochar’s cellulose crystallinity is reduced as the cellulose become completely amorphous.

The Influence of Torrefaction Temperature on Hydrophobic Properties of Waste Biomass from Food Processing

The annual potential of waste biomass production from food processing in Europe is 16.9 million tonnes. Unfortunately, most of these organic wastes are utilized without the energy gain, mainly due to the high moisture content and the ability to the fast rotting and decomposition. One of the options to increase its value in terms of energy applications is to valorize its properties. Torrefaction process is one of the pre-treatment technology of raw biomass that increases the quality of the fuel, especially in the context of resistance to moisture absorption. However, little is known about the influence of torrefaction temperature on the degree of valorization of some specific waste biomass. The aim of this paper was to analyze the influence of the temperature of the torrefaction on the hydrophobic properties of waste biomass, such as black currant pomace, apple pomace, orange peels, walnut shells, and pumpkin seeds. The torrefaction process was carried out at temperatures of 200 °C, 220 °C, 240 °C, 260 °C, 280 °C, and 300 °C. The hydrophobic properties were analyzed using the water drop penetration time (WDPT) test. The torrefied waste biomass was compared with the raw material dried at 105 °C. The obtained results revealed that subjecting the biomass to the torrefaction process improved its hydrophobic properties. Biomass samples changed their hydrophobic properties from hydrophilic to extremely hydrophobic depending on the temperature of the process. Apple pomace was the most hydrophilic sample; its water drop penetration was under 60 s. Black currant and apple pomaces reached extremely hydrophobic properties at a temperature of 300 °C, only. In the case of orange peels, walnut shells, and pumpkin seeds, already at the temperature of 220 °C, the samples were characterized by severely hydrophobic properties with a penetration time over 1000 s. At the temperature of 260 °C, orange peels, walnut shells, and pumpkin seeds reached extremely hydrophobic properties. Furthermore, in most cases, the increase of torrefaction temperature improved the resistance to moisture absorption, which is probably related to the removal of hydroxyl groups and structural changes occurring during this thermal process.

Catalytic torrefaction of pelletized agro-residues with Cu/Al2O3 catalysts

The effect of the addition of a Cu/Al2O3 catalyst on the product distribution of gas-phase products during torrefaction of pelletized corn residues was investigated at temperatures between 220 and 300 °C. Pelletized corn residues were mechanically mixed with Cu/Al2O3 catalyst pellets. The mixture was then thermally treated in a fixed bed reactor for 40 min of residence time at low temperatures of wet flue gas simulated by O2 (4% v/v), CO2 (12% v/v), and steam (14% v/v), balanced with N2. The higher heating value (HHV) of torrefied pellets was also examined within the operating conditions. It was found that torrefaction temperature affected the product distribution, yields, and HHV significantly, while the presence of Cu/Al2O3 catalyst pellets promoted the conversion of CO to CO2 and the production of H2 from raw biomass pellets via CO oxidation and water-gas shift reactions. This finding provides a favorable outlook for the energy utilization of pelletized agro-residues via torrefaction with wet flue gas as a pretreatment method, in which inexpensive catalysts could be applied to eliminate toxic gases and/or generate valuable hydrogen during the torrefaction process.

Vitrification of environmentally harmful by-products from biomass torrefaction process

The paper evaluates the possibility of efficiently processing waste generated in the process of biomass torrefaction into a non-toxic material, suitable for practical reuse. The water was evaporated from the liquid fraction resulting from the torrefaction of Virginia mallow, after which the resulting sludge was subjected to vitrification. The vitrification process was carried out at 1450 °C using tempered glass cullet, which constituted 85% by weight of the total processed material. The obtained product was subjected to the following analyses: microstructural characterization, X-ray diffraction, energy dispersive spectroscopy, spectroscopic tests, as well as measurements of hardness and ion leachability in an aqueous medium. It was found that vitrification of the sludge obtained from the waste liquid fraction leads to incorporation of the inorganic components of the waste into the glass structure, and in the case of organic components, causes their thermal decomposition. As a result of vitrification, a product was obtained that has no toxic properties and is characterized by favorable utility properties, i.e. low ion leachability and high hardness, higher than the hardness of the glass used in the vitrification process. The conducted research showed that vitrification is an effective method to recycle waste generated in the production process of treated biomass, and the product of the vitrification process can be used, for example, in the production of glassy building materials.

Physicochemical structure and reactivity of char from torrefied rice husk: Effects of inorganic species and torrefaction temperature

This study aims to evaluate the effects of inorganic species (K) and torrefaction temperature on the physicochemical structure and reactivity of char from pyrolysis of torrefied rice husk in a laboratory-scale fluidized-bed apparatus. Washed rice husk (WRH) and washed rice husk with impregnating of potassium (0.1K-WRH) were torrefied at the different temperatures of 230–270 °C. The physicochemical structure of char samples were determined by elemental composition, pore structure (N2 adsorption-desorption) and carbon microstructure (Raman spectroscopy). Furthermore, the char reactivity in air was analyzed using thermogravimetric analyzer (TGA). The results indicated that the changes in elemental composition, pore structure and carbon microstructure of char samples caused by the combined effects of torrefaction process and the presence of K have the important role on the char reactivity. The dimensionless index (DI) accounted for the physicochemical structure was defined, which exhibited a strongly linear relationship between the oxidation activity index (S) of char samples. In general, both of the torrefaction temperature and the inorganic species (K) contained in rice husk samples have the important effects on the physicochemical structure and reactivity of char samples.

Waste to Carbon: Biocoal from Elephant Dung as New Cooking Fuel

The paper presents, for the first time, the results of fuel characteristics of biochars from torrefaction (a.k.a., roasting or low-temperature pyrolysis) of elephant dung (manure). Elephant dung could be processed and valorized by torrefaction to produce fuel with improved qualities for cooking. The work aimed to examine the possibility of using torrefaction to (1) valorize elephant waste and to (2) determine the impact of technological parameters (temperature and duration of the torrefaction process) on the waste conversion rate and fuel properties of resulting biochar (biocoal). In addition, the influence of temperature on the kinetics of the torrefaction and its energy consumption was examined. The lab-scale experiment was based on the production of biocoals at six temperatures (200–300 °C; 20 °C interval) and three process durations of the torrefaction (20, 40, 60 min). The generated biocoals were characterized in terms of moisture content, organic matter, ash, and higher heating values. In addition, thermogravimetric and differential scanning calorimetry analyses were also used for process kinetics assessment. The results show that torrefaction is a feasible method for elephant dung valorization and it could be used as fuel. The process temperature ranging from 200 to 260 °C did not affect the key fuel properties (high heating value, HHV, HHVdaf, regardless of the process duration), i.e., important practical information for proposed low-tech applications. However, the higher heating values of the biocoal decreased above 260 °C. Further research is needed regarding the torrefaction of elephant dung focused on scaling up, techno-economic analyses, and the possibility of improving access to reliable energy sources in rural areas.

Effect of the temperature on the spent coffee grounds torrefaction process in a continuous pilot-scale reactor

Several studies in Literature have analyzed the torrefaction treatment process of biomass in batch reactors. Nevertheless, in order to check the industrial applicability of a process, it is more interesting to carry out torrefaction tests in continuous pilot plant reactors. Thus, the present study reports the results of continuous semi-industrial scale (500 kg/h) torrefaction experiments employing spent coffee grounds (SCG) as a feedstock in a horizontal rotary reactor. Torrefaction tests were carried out at three different temperatures (210 °C, 235 °C, and 260 °C) for 90 min, in order to evaluate the yields of solid, liquid (water and tar) and gaseous products and their composition. In particular, the effectiveness of the decarbonization and deoxygenation processes was investigated, analyzing the carbon and oxygen distribution. Within the temperature range, torrefaction yielded solid of 55.2–85.8 wt% with an increase of the higher heating value (HHV) of 5.1–15.4% compared to the raw material. Liquid fraction yield was in the range of 11.3–34.3 wt%, with a moisture content of 73.7–91.9% and HHV between 18.8 and 23.4 MJ/kg on dry basis. Gas fraction represented 2.9–10.5 wt% of the raw biomass withHHVbetween 1.95 and 3.55 MJ/Nm3. Acids (mainly acetic acid) were the major compounds in the tar fraction, accounted up to 68 wt%, while CO2 was the main product of the deoxygenation reactions in the gaseous fraction (76.6–86.9 vol%). From the perspective of mass yield and energy density enhancement, 260 °C was considered to be the optimal temperature for torrefaction of SCG.

Effect of temperature and residence time on the characteristics of torrefied food

Malaysia generated food waste (FW) is approximately 15 000 tons every day and expected to increase every year. Currently, Malaysia is applying the landfilling method to dispose all of the MSW which cause potential threat towards the environment and society. FW may be converted into more valuable products through reutilizing as a renewable energy source through torrefaction. The objective of this study is to investigate the effect of torrefaction temperature and residence time towards the characteristics of torrefied FW. The torrefaction process was carried out in a fixed bed reactor with continuous flow of nitrogen, at various torrefaction temperature (260 to 320 °C) and residence time (15 to 60 minutes). The torrefied FW was evaluated in terms of its mass yield, thermal behaviour and the produced functional groups through the Fourier transform infrared spectroscopy (FTIR). It can be observed that the higher the torrefaction temperature and residence time reduces the mass yield. Meanwhile, the FTIR spectra for raw and torrefied FW at different residence time was executed the functional group of C=C, C=O, C-O and C-H were present in sample. From this study, it is established that there were significant effects of both parameters towards the characteristic of FW.

Thermal Degradation and Kinetic Study of Cassava Rhizome for Torrefaction Application

Thermal decomposition kinetics of cassava rhizome (CR) is an important key in the torrefaction process. Kinetic analysis of the cassava rhizome torrefaction was investigated using a thermogravimetric analyser in which CR weight loss is measured under nitrogen atmosphere from ambient temperature to 973K at 5, 10, 20, and 30 K·min−1. Two model-free iso-conversional methods, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) have been used to determine activation energies as a function of the extent of degradation. In this work, the CR particles were separated into 3 study groups, 0.125-0.425 mm, 0.425-0.850, and 0.850-2 mm. The average activation energies calculated by using the methods are relatively similar for all three-particle size samples. The average activation energy values calculated by FWO method were 170.509, 172.593, and 130.149 kJ·mol−1, respectively. These data were comparable to KAS method in which the average activation energy numbers were 170.647, 177.276, and 128.620 kJ·mol−1. Both methods indicated that the activation energy was relatively constant until the conversion of 0.5. The pre-exponential factor values from FWO and KAS ranged 4.87E+17 s−1 and 7.28E+14 s−1, respectively. The experimental results show that kinetic parameters from both methods are suitable and effective to help describe the thermal degradation of the cassava rhizome.

Product Characteristics of Torrefied Wood Sawdust in Normal and Vacuum Environments

To investigate the efficacy of torrefaction in a vacuum environment, wood sawdust was torrefied at various temperatures (200–300 °C) in different atmospheres (nitrogen and vacuum) with different residence times (30 and 60 min). It was found that the amount of biochar reduced at the same rate—regardless of atmosphere type—throughout the torrefaction process. In terms of energy density, the vacuum system produced biochar with better higher heating value (HHV, MJ/kg) than the nitrogen system below 250 °C. This was the case because the moisture and the high volatility compounds such as aldehydes diffused more easily in a vacuum. Over 250 °C, however, a greater amount of low volatility compounds evaded from the vacuum system, resulting in lower higher heating value in the biochar. Despite the mixed results with the solid products, the vacuum system increased the higher heating value of its liquid products more significantly than did the nitrogen system regardless of torrefaction temperature. It was found that 23% of the total energy output came from the liquid products in the vacuum system; the corresponding ratio was 19% in the nitrogen system. With liquid products contributing to a larger share of the total energy output, the vacuum system outperformed the nitrogen system in terms of energy density.

EVALUATING INTEGRATION OF BIOMASS GASIFICATION PROCESS WITH SOLID OXIDE FUEL CELL AND TORREFACTION PROCESS

In the present study, the integration of a solid oxide fuel cell with the biomass gasification process in which the torrefied biomass produced in a torrefaction process is used as the feedstock has been investigated. This novel design gives the power generation system the advantage of eliminating the filtration of the fuel cell inlet gas. This is because of the absence of sulfur and its derivatives in the synthesized gas owing to the terrified biomass, as the feedstock of the gasification process. Moreover, the integration of the processes makes it possible to employ the heat recovery methods. Therefore, by using the high-grade thermal energies for preheating process flows, the presented design considers the maximum available heat recovery and minimum heat and mass losses. The optimum design is determined by the sensitivity analysis and then simulated using the ASPEN PLUS software and its performance has been studied. It was specified that in the optimum operation state, the gasifier outlet temperature and pressure are 950 °C and 5 bar, respectively. Also, the oxygen flow rate in the anode of SOFC and the combustion chamber are 3.03 and 0.81 kmol/h, respectively. Moreover, the results showed that the presented design causes an improvement in the performance of the fuel cell. The electrical efficiency and the overall efficiency of the system are determined to be in the range of 63-69% and 80-85%, respectively. Also, it was revealed that the presented design has the power generation capacity of 100 to 997 kW.

Analysis through thermogravimetric analyses of the impact of torrefaction processes performed under a non-oxidative atmosphere on hydrolysis lignin samples

Hydrolysis lignin samples were torrefied in a fixed bed reactor under a nitrogen flow, under four different isothermal temperatures (225, 250, 275 or 300 °C) and during 30 or 60 min. The impact of such torrefaction conditions on the hydrolysis lignin samples was analyzed through thermogravimetric analyses performed under non-oxidative or oxidative atmospheres and under a heating rate of 5 °C/min. The thermogravimetric profile and the reactivity of the raw and torrefied samples were compared. The optimal values of the kinetic parameters were determined using the EIPR model, first determining the number of constituents to be considered, then their proportions applying Van Soest’s protocol to the raw material and adjusting them for the torrefied samples. These values of the kinetic parameters were validated through observations of the experimental and simulated mass and mass rate curves and computations of the maximal difference between these curves. The values of the kinetic parameters did not significantly vary with the isothermal temperature or with the torrefaction residence time.

The effect of an inhibitor on the torrefaction of pellets inside a quiescent layer of bentonite clay

Biomass fuel pellets are an important product for the energy sector. The disadvantages of biomass as a sustainable alternative fuel when compared with coal and other fossil fuels are mainly attributed to its low energy density. To improve the biomass properties the torrefaction process can be used. This study aims at investigating the new technique of pellets torrefaction inside a quiescent layer of bentonite under the atmospheric conditions. This process of torrefaction is carried out without the use of inert gas that makes it attractive from the economic and ecological points of view. The main purpose of bentonite in this technique is to limit oxygen access to the biomass from the environment since oxygen excess leads to the decrease in the energy yield. It is also proposed to use the salts of alkali metals as an inhibitor of the oxidation reactions. In this work, the effect of sodium hydrocarbonate addition on the mass and energy yields of biomass is analyzed at varying torrefaction temperature, duration and height of the mineral layer. Pyrolytic behavior of torrefied biomass is analyzed with the use of thermogravimetry and differential scanning calorimetry measurements. It is established that the mass and energy yields occur to be higher in case of torrefaction in the bentonite-soda blend than in case of torrefaction in pure bentonit. Furthermore, the use of bentonite-soda blend favors the decrease in enhancement factor of HHV. It is shown that energyyield≈1.15⋅massyield.

An "In-Situ Binding" Approach to Produce Torrefied Biomass Briquettes.

Biomass-derived coal or “biocoal” produced using a torrefaction process presents a carbon-neutral option of coal for power generation. While torrefaction delivers a carbon content and hydrophobicity comparable to coal, it lowers its density and creates material handling, storage, and transportation challenges. Densification into briquettes would help mitigate these challenges. However, the torrefied biomass is difficult to densify and may require the use of binders, which are expensive and can be incompatible with respect to material and emissions. A cost-effective approach to utilize lignin in-situ of the biomass to promote binding during densification was demonstrated using a pilot-scale briquetter unit during this study. Lignin, a cross-linked polymer, tends to break down and lose its binding ability under high-temperature conditions of torrefaction. In this paper, we investigated the use of a lightly torrefied material as a binder―LTM (biomass torrefied in the transition region of non-reactive and reactive temperature ranges of torrefaction). When mixed with torrefied biomass and densified together under suitable moisture and temperature conditions, the lignin is shown to mobilize and provide binding to the briquettes. The results showed that briquettes produced using LTM as binder and 10% to 11% moisture provided in-situ binding, improved density and durability, and produced hydrophobic briquettes.

An Oxyfuel Combustion-Based Torrefaction Process: Technoeconomic Analysis

Abstract A torrefaction process operating on oxyfuel combustion concept is introduced. The working fluid employed in the process is carbon dioxide captured from the combustion products. The thermodynamic modeling of the process is carried out to determine the energy requirement, recycled CO2 flow rate, energy yield, and CO2 production rate at various torrefaction conditions. The total capital investment and production costs of the new system are also estimated. By increasing the torrefaction severity, the CO2 production rate, recycled gas mass, and the process thermal energy requirement increase, whereas the grinding energy and the energy yield decrease. A comparison made between the performance and economic parameters of the new and a conventional torrefaction processes shows that the proposed process is expected to produce torrefied wood pellet of compatible fuel quality and overall efficiency while eliminating CO2 and NOx emissions at the expense of 11.5% and 9% increase in the capital and production costs, respectively. The proposed torrefaction process requires 91.8 M$ capital investment and 113.2 $ to produce 1 ton of torrefied wood pellets with 91% energy yield and 88% overall plant efficiency. Sensitivity analysis shows that the reactor type and raw biomass costs have significant impact on cost structures.

The Selected Results of the Experimental Research of Solid Fuel Pneumatic Transportation to Ship’s Boiler

AbstractThe article presents the problems related to the application of alternative fuel like solid biomass in the shipbuilding. The decreasing resources of the crude oil, the requirements regarding environmental protection as well as the increase of the liquid fuel prices were the reason for the study. The solid biomass comparing to the liquid or gaseous forms has relatively low calorific value. In order to increase this value the solid biomass is subject to the densification or torrefaction process and most often occurs in the shape of pellets. In this form it could be useful on ships. A test stand has been characterised where it can be experimentally verified whether ship’s rolling does affect the changes in flow resistance values during the pneumatic transportation of solid fuel from the storage facility to the boiler. On the basis of the measurements the hydraulic characteristics have been provided for the piping located on the movable platform with and without granular material. The changes in the platform oscillation period have influence on the change in the pressure inside transport piping for each investigated material. The results also show that the platform constantly inclinations do exert an influence on the pressure drop in the transport pipeline during transporting the granular material. It is smaller when the position is inclined. Comparing the results obtained for the different transported materials of a similar nature of the pressure fluctuations could be observed.

Torrefaction of wheat-barley straw: Composition and toxicity of torrefaction condensates

Until now, few studies on the valorisation of torrefaction condensable volatiles (condensates) have been performed. The composition and toxicity of torrefaction condensable volatiles determine their possible applications. Therefore, a study on the composition of wheat-barley straw torrefaction condensates, combined with toxicity tests, was performed. This analysis was mainly aimed at the utilisation of these condensates as an anaerobic digestion substrate. The torrefaction process was performed in a batch-scale reactor at temperatures from 240 °C to 320 °C. The condensates were analysed using GC/MS, and quantitative analysis was based on the calibration curves (external standard method). Toxicity tests were performed for vascular plants (Lemna sp. Growth Inhibition Test), saltwater bacteria (Microtox® bioassay) and freshwater crustaceans (Daphtoxkit F magna® survival bioassay). The condensates were classified as highly toxic for the tested organisms. Compounds that are inhibitory and/or toxic to anaerobic bacteria were detected in the samples, e.g. furfural, guaiacol, palmitic acid and oleic acid. Taking into account the condensates’ high toxicity for the tested organisms and the presence of anaerobic digestion process inhibitors, there is a significant likelihood that prior detoxification of the condensates is necessary before they can be utilised as anaerobic digestion substrates.

Impacts and release characteristics of K and Mg contained in rice husk during torrefaction process

This work evaluated the catalytic effect and release characteristics of potassium (K) and magnesium (Mg) contained in rice husk during the torrefaction process. Torrefaction of rice husk samples with and without impregnating K and Mg at different torrefaction temperatures (210–270 °C) was carried out in thermogravimetric analyzer (TGA) and laboratory-scale fixed-bed apparatus. TGA studies indicated that K increased the weight loss more rapidly, while the weight losses were slightly decreased with the presence of Mg. Laboratory-scale studies also found that the solid yields of WRH, 0.1 K-WRH and 0.1 Mg-WRH were 90.2%–74.0%, 86.6%–71.8% and 90.0%–74.1% as the torrefaction temperature increased from 230 to 270 °C. K showed an obvious increase of the carbon content of solid product because of its significant catalytic deoxygenation effect. In addition, K and Mg both had the promoting effect on the formation of small molecule gas products from the catalytic conversion of the macromolecular liquid products, and K had stronger catalytic action than Mg. Besides, most K and Mg, 94.6–98.5% for K and 97.9–99.5% for Mg, were remained in the solid product while only a small amount of K and Mg were released to the volatiles during torrefaction process.

Upgrading almond-tree pruning as a biofuel via wet torrefaction

Two series of six wet torrefaction tests were performed using a pressurized batch reactor in order to upgrade almond-tree pruning (a largely available agricultural waste in Mediterranean areas) as a fuel. The assayed maximum temperatures were in the range of 175–300 °C, held for either 10 or 60 min. Raw almond-tree pruning and wet-torrefied solid products were systematically characterized through a wide range of analytical procedures, such as bulk density, particle size, structural and elemental composition, ash content, heating values, moisture uptake, FTIR spectra and SEM micrographs. The effects of temperature and time on the wet torrefaction process of almond-tree pruning were simultaneously evaluated through the severity factor. Higher temperatures and longer holding times brought the fuel properties of wet-torrefied solid products closer to those of sub-bituminous coal. The most severe operating conditions (i.e., 300 °C held for 60 min, or a severity factor equal to 7.68) allowed achieving an energy densification ratio of 1.67. However, the optimal processing conditions in terms of energy yield, which were found at a severity factor of 5.78, led to 57.1 wt% solid yields, with a higher heating value of 24.0 MJ/kg and an energy densification ratio of 1.36.