Torrefied Pellets Research Articles

Effect of torrefaction on fuel properties of biopellets

The study aimed to determine the effects of torrefaction on the fuel properties of pellets. Therefore, firstly, torrefaction parameters of rose (Rosa Damascena Mill.) oil distillation solid waste and red pine sawdust were determined through the torrefaction optimization process in terms of temperature and holding time. Then, using the selected torrefaction parameters, 14 different raw and torrefied pellets containing RP, PS, and Turkish Elbistan Lignite were prepared in different weight ratios. Finally, the fuel properties of the prepared raw and torrefied pellets, namely dimensions, proximate analyses, higher heating values, tensile strength, durability, abrasive resistance, and water uptake resistances, were investigated. The findings demonstrated that the higher heating values and carbon content of raw biomass samples increased while their volatile matter content decreased. The use of lignite at high concentrations led to an increase in ash content and a decrease in the strength and durability of pellets, which should be emphasized. In addition, red pine sawdust was used in place of solid waste from rose oil distillation solid waste to produce pellets with greater strength. All pellet mixtures with torrefaction had higher heating values and energy densities despite the fact that their mass and energy efficiency had decreased. It was determined that torrefaction increased the pellets' resistance to absorbing water and gave them a more hydrophobic structure. Thus, it was determined that torrefaction could enhance the crucial fuel parameters of the biomass samples.

Potential exportation of wood pellets and torrefied biomass pellets logistics cost analysis: A comparative case study from Portugal

<abstract> <p>This study evaluates the logistics cost associated with transporting Wood Pellets (WP) and Torrefied Biomass Pellets (TBP) from Aveiro, Portugal's principal WP exporting port, to Northern European destinations. With increasing emphasis on sustainable energy, understanding the cost dynamics between WP and TBP becomes crucial for market competitiveness. Using data sourced from the Argus Biomass Markets report, we compared the energy in gigajoules per ton of both WP and TBP. Torrefaction results in pellets with superior energy and bulk densities, influencing their transportation logistics costs. The main metrics for comparison were cost per energy unit and the implications of energy and bulk densities on transport costs. Preliminary findings indicate that although torrefied pellets undergo more significant mass loss than energy loss, their enhanced energy and bulk densities present logistical advantages. These advantages manifest as more tons per volume unit and heightened energy per ton, which ultimately lead to reduced transportation cost per energy unit. The insights from this analysis provide valuable input for the biofuel sector. By understanding the cost benefits associated with TBP transportation in contrast to WP, stakeholders can make strategic decisions, bolstering the competitiveness of Portuguese biofuel products in the European domain.</p> </abstract>

Biomass pellets with organic binders - before and after torrefaction

Given the current energy situation in the world, torrefaction offers a promising technique to produce fuel that can be used as a substitute for coal in combustion. The pelletization process can be simplified by the addition of a binder. The aim of this study was to determine the influence of the binders on the mechanical and energetic properties of the pellets before and after torrefaction. The initial material was meadow hay. The hay was crushed and three binders (lignosulfonate, wheat flour, starch) were added – 2 and 15 wt% The basic powder characterisation (compressibility, internal friction, and angle of repose) were performed on all binders. Lignosulfonate had the best flowability and therefore appeared to be the most suitable from a process point of view. Testing were also carried out on non-torrefied and torrefied pellets. The mechanical-physical properties (hardness, mechanical resistance, wettability) were also determined. Hardness and mechanical resistance for non-torrefied pellets was increased by adding lignosulfonate (15 wt%) and flour (2 wt%). After torrefaction, hardness and pellet durability index of the pellets decreased significantly, but still the best pellets were those with lignosulfonate (15 wt%) and flour (2 wt%). Non-torrefied pellets do not have a good resistance to water absorption, but lignosulfonate in ratio of 15 wt% and as well as flour in ratio of 2 wt% have a positive effect on this feature. Moreover, torrefaction has a positive effect on the pellet's resistance to water absorption. The results were supported by FTIR analysis. Last but not least, a simple calculation of the consumption of pellets for heating and hot water heating for a family home is given.

Life cycle assessment of bioenergy production from wood sawdust

Bioenergy derived from wood waste plays a crucial role in mitigating climate change and contributing to the circular economy. This study performs a life cycle assessment of pellet production from wood sawdust and subsequent electricity generation through different pathways. Firstly, the environmental impact of producing pellets from untreated mixed sawdust, steam exploded (SE) shavings (at 180 °C for 9 min), and torrefied (TF) sawdust (at 230 °C for 45 min) was compared using the Functional unit (FU) of 1 Kg. Secondly, the environmental impact of generating 1 MJ electricity from untreated sawdust, SE pellets, and TF pellets was compared in terms of impact categories and damage assessment. The scope of the study was defined from the gate (received feedstock) to the gate (produced output ex-factory). The results revealed that TF pellets were more environmentally friendly relative to other forms except for two impact categories: ozone layer depletion and aquatic eutrophication. SE treatment was the most damaging alternative for producing pellets, especially with respect to global warming; it produced 0.56 kg CO2 equivalent (eq.) per FU around 4 times higher than untreated pellets (0.16 kg CO2 eq./FU). After environmental impact analysis, it was found that electricity generation from SE pellets caused more damage to the environment compared to the other feedstock paths for electricity production. Utilizing TF pellets for electricity generation is more beneficial in terms of ecosystem quality, climate change, and resource depletion.

Elemental composition of raw and torrefied pellets made from pine and pine-eucalyptus blends

Debarked Pinus radiata wood was blended with debarked Eucalyptus nitens wood in three different proportions: 100% pine (100P), 90% pine-10% eucalyptus (90P/10E) and 60% pine-40% eucalyptus (60P/40E). The pellets were torrefied in dry and non-oxidative conditions at different temperatures (210, 240, 270 and 300 °C) and residence times (40 and 60 min) to enhance the energy properties and determine the elemental composition (18 elements). For raw pellets, the concentrations of Na, K, Zn, B and Cl increased significantly with the proportion of eucalyptus wood, with Cl levels being 60% higher in the 60P/40E than in the 100P pellets. The concentrations of most elements (C, Mg, Al, P, Ca, Fe, Cu) tended to increase (+35% for C, +200–250% for the others) with torrefaction severity, independently of the mixture. Decreases in H and O concentrations were also independent of the mixture. Torrefaction decreased the Cl content by 63–77%, which compensated for the high levels in mixtures with eucalyptus. Increases in the high heating value (by as much as 37%) with torrefaction occurred in parallel with an increase in carbon content and a decrease in the atomic H:C and O:C ratios, particularly in the 260 to 300 °C transition. Torrefaction compensated for the negative effect of the inclusion of eucalyptus, with the alkali index remaining at a relatively safe maximum value of 0.10 kg GJ−1.

Quality Properties and Torrefaction Characteristics of Pellets: Rose Oil Distillation Solid Waste and Red Pine Sawdust

Two different biomass types, rose oil (Rosa damascena Mill.) distillation solid wastes (RDWs) and red pine sawdust (RPS), were pelletized in this study at different moisture and additives. The prepared pellets were also torrefied. This study revealed that the strength of the RPS and RDW pellets decreased as their moisture content increased in both their raw and torrefied forms. However, the tensile strength of the torrefied pellets increased with the increased binder ratio, which is similar to raw pellets. Compared to their raw form, the torrefied pellets generally had higher ash contents, fixed carbon contents, and higher heating values. As a result of torrefaction, the higher heating value of the RPS pellets increased from 17.51–18.80 MJ/kg to 20.20–21.73 MJ/kg, while the higher heating value of the RDW pellets increased from 17.42–18.54 MJ/kg to 19.13–20.92 MJ/kg. For the torrefied RPS and RDW pellets in this study, there was no statistically significant difference between initial moisture content and energy efficiency, energy density, or mass yield. On the other hand, energy density ratios in both the torrefied RPS and torrefied RDW pellets generally increased with increasing binder content. Furthermore, the torrefied pellets were found to be more stable in moisture absorption than the raw pellets.

Techno-economic analysis of torrefied fuel pellet production from agricultural residue via integrated torrefaction and pelletization process

Torrefied pellets have gained more commercial importance due to their excellent performance in combustion, co-firing and gasification. The present investigation provides a conceptual design for torrefied fuel pellets production via combined torrefaction and pelletization technologies with and without additives. The entire design contains torrefaction unit, grinding, preparation of pellet formulation, pelletizing, and finally cooling of pellets. Two scenarios, scenario 1 (pelletization of torrefied biomass with additives) and scenario 2 (pelletization of torrefied biomass without any external additives) were tested and compared. The economic analysis suggests that both scenarios are profitable. Both scenarios were simulated using Aspen plus™, and economic feasibility was estimated using a complete cash flow analysis for a base case plant with 40,080 tonne/y capacity. For both cases, a discounted cash flow is a useful tool for estimating the minimal selling price for torrefied pellets as well as the capital investment, production cost and operating costs. The cost of the reactor used for torrefaction was found to be the most important component of combined torrefaction and pelletization system. The lowest selling price of generated torrefied pellets was found to be $103.4 and $105.1 per tonne at the plant gate for scenarios 1 and 2, respectively. Sensitivity analysis shows that, among all variable costs, labor cost has the highest influence on both net present value (NPV) and minimum selling price (MSP) in making pellets for both the scenarios. Furthermore, the internal rate of return was found to be25% and 22% at 10% discounted cash flow rate for scenarios 1 and 2, respectively. The framework that was created was found to lessen over-dependence on wood or fossil fuels and facilitate the promotion of bioenergy in rural areas.

Hybrid sol-gel coatings for reducing wettability and storage degradation of biomass pellets

Long transport distances and extended storage of biomass pellets especially in humid environments provide a suitable setting for enhanced degradation in the form of moisture sorption, cracking and attrition. We developed an optically transparent, low-cost and environmentally friendly coating to reduce moisture sorption and storage degradation of pellets. The developed coating is a hybrid sol–gel, based on tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) precursors. We coated two types of untreated and one type of torrefied wood pellets and stored them in a climate chamber during 1 month simulating a ship's hold, at a constant condition of 40 °C and 85% relative humidity. After 1 month of storage, the mean water contact angle increased by a factor of two compared to the uncoated ones. The lower wettability of the sol-gel coated untreated pellets compared to the non-coated torrefied pellets might provide an alternative to torrefaction.

Identification of Optimal Binders for Torrefied Biomass Pellets

The pretreatment of biomass through torrefaction is an effective means of improving the fuel quality of woody biomass and its suitability for use in existing facilities burning thermal coal. Densification of torrefied biomass produces a fuel of similar energy density, moisture content, and fixed carbon content to low-grade coals. Additionally, if the torrefaction conditions are optimized, the produced torrefied pellet will be resistant to weathering and biological degradation, allowing for outdoor storage and transport in a manner similar to coal. In untreated biomass, lignin is the primary binding agent for biomass pellets and is activated by the heat and pressures of the pellet extrusion process. The thermal degradation of lignin during torrefaction reduces its binding ability, resulting in pellets of low durability not suitable for transportation. The use of a binding agent can increase the durability of torrefied pellets/briquettes through a number of different binding mechanisms depending on the binder used. This study gives a review of granular binding mechanisms, as they apply to torrefied biomass and assesses a variety of organic and inorganic binding agents, ranking them on their applicability to torrefied pellets based on a number of criteria, including durability, hydrophobicity, and cost. The best binders were found to be solid lignin by-product derived from pulp and paper processing, biomass tar derived from biomass pyrolysis, tall oil pitch, and lime.

Technoeconomic Feasibility of Bioenergy Production from Wood Sawdust

In this study, the technoeconomic feasibility of bioenergy production from sawdust under four different case scenarios is simulated and compared. These scenarios include: (1) heat and electricity generation from raw sawdust; (2) pellet production from sawdust; (3) and (4) integrated biorefinery approach for the simultaneous manufacturing of multiple products (steam-exploded and torrefied pellets) and co-products (furfural, hydroxy methyl furfural (HMF), acetic acid), along with heat and electricity generation. Economic assessments such as cost analysis, payback time (PBT), net present value (NPV) and internal rate of return (IRR) were determined for these scenarios. The results showed that the approach of producing torrefied pellets, furfural, and acetic acid, along with co-generated heat and electricity, in terms of multiproducts and profitability (NPV (at 7%): USD 38.29 M) was preferable over other alternatives. In terms of simplified technology and other economic indices (PBT: 2.49 year, IRR: 51.33%, and return on investment (ROI): 40.1%), the scenario for producing pellets from wood sawdust was more promising than others. If plant capacity was not a limiting factor, the optimal size for the combined heat and power (CHP) plant was between 250–300 kt for the main product. Additionally, untreated and treated pellet plants equipped with CHP had an optimal size of 150–200 kt of wood pellets per year.

Partially Oxidative Torrefaction of Woody Biomass Pellets: Burning Behaviour and Emission Analysis

Non-conventional torrefaction under partially oxidative conditions is an emerging cost-effective thermochemical pre-treatment method to improve the quality of biomass for energy applications. The literature lacks data on the combustion of biomass torrefied under oxygen-deficient atmosphere with actual reactor conditions (inevitable non-uniformities in the thermal environment). In this work, a dual mode fixed-bed biomass (torrefaction) reactor and combustor was operated on Australian biomass pellets, to torrefy the fuels at 275 °C for 30 min using partially oxidative atmosphere (O2: 5 vol%, balance N2) and then to combust them. Combustion behaviour with a particular focus on gaseous emissions of raw, blended (25% torrefied), and torrefied (100%) pellet fuels in a batch-type combustor was investigated. The decomposition behaviour was analysed in a thermogravimetric analyser to understand the impact of biomass constituents on the direct combustion of the tested samples. Results indicate that unlike the combustion of raw biomass, the fuels torrefied under partially oxidative conditions burned 45% faster, attained high packed-bed temperatures (1382 °C) and exhaust gas temperatures (657 °C) then latter (bed: 1128 °C, exhaust: 574 °C) at similar airflow. Additionally, 100% torrefied pellets emitted 38% less NOx compared to raw biomass pellets. However, low CO values for torrefied biomass were attained at higher primary airflows compared to raw. The combustion of 100% torrefied biomass in a fixed-bed was dominated by both flaming and smouldering phases with a modified combustion efficiency (MCE) value of 91%, whereas raw biomass combustion occurred in flaming phase with an MCE value of 98% at same airflow (0.35 kg·m−2·s−1). The outcomes of this work provide useful insights into the viability of using biomass fuels torrefied under partially oxidative conditions alongside other industrial processes generating (waste) heat and flue gases.

Swelling and softening behavior of iron ore-spent mushroom substrate composite pellets during carbothermal reduction

In the present day, we have reached close to an optimum condition of CO2 emission when using coal or coke for iron making process. Carbon neutrality is achieved during carbothermal reduction by employing biomass as a reducing agent in composite pellets. The swelling behavior of composite pellets during reduction has detrimental effects, and catastrophic swelling leads to subsequent disintegration of pellets, which causes low gas permeability through packed beds in the industry. In this study, we used coal, spent mushroom substrate, torrefied mushroom substrate (300 °C), and de-ashed torrefied mushroom substrate as reducing agents in our iron-ore composite pellets. Volume change of the composite was investigated with heating profile (15 °C/min until 1350 °C), reduction time is 70min, the maximum swelling observed in torrefied mushroom pellets is +158%, the pellets experienced swelling in between (700°C–1000 °C) and started to soften from 825 °C. However, no swelling is observed in the coal and de-ashed torrefied pellet. On the other hand, de-ashed torrefied pellets with the addition of alkali metal oxides and soda lime glass had significant swelling and decrease in softening temperature. With the presence of Na2O and K2O in pellets ash, during reduction in some localized areas, they form low melting slags like Soda-lime (∼1000 °C) and Potash-lime (∼1200 °C) compositions. These slags start to soften at a low temperature ∼700 °C for soda-lime composition. As the temperature increases, viscosity decreases, which causes pellets to soften more, and parallelly gas evolving from the pellet during reduction (mainly CO product of the Boudouard reaction) causes these slags to expand, like a glass blowing mechanism.

Enhancing the potential of sugarcane bagasse for the production of ENplus quality fuel pellets by torrefaction: an economic feasibility study

When fossil fuel substitution with biomass is viewed as a potential solution to global warming caused by greenhouse gas emissions, the demand for biomass fuel pellets has increased worldwide. Although agricultural waste is an attractive potential feedstock for fuel pellet production due to its relatively high calorific value and low cost, its excessive ash content is a major drawback. This research investigates the properties of sugarcane bagasse fuel pellets treated by dry and wet torrefaction and evaluates the economic value of selling the fuel pellets, which were priced based on their quality. It was found that the wet torrefaction could significantly reduce the ash content in the product (1% ash content at a torrefaction temperature of above 180°C), resulting in higher quality and more marketable fuel pellets. Consequently, the yield and the net present value of the production of wet torrefied fuel pellets were greater than those of dry torrefied pellets. Nevertheless, the production of fuel pellets from sugarcane bagasse treated by either process is shown to be economically viable.

Some properties of white and torrefied pellets obtained from oil palm trunk as raw material

Properties of unheated wood pellets were compared with those of torrefied wood pellets that had been heated to 270, 290, and 310 °C, with raw material taken from two different height levels of oil palm trunk (OPT). The gross calorific value, moisture content, ash content, volatile matter, fixed carbon, density, and weight loss were examined. Air drying or oven drying pretreatment was applied to the raw materials. The results showed that the heating values of samples increased when raw materials were torrefied, depending on the heat treatment temperature. The torrefied pellets were improved by as much as 66.4% in heating value compared with OPT pellet samples. The greatest improvement was found in torrefied pellet samples prepared at 310 °C, using air drying, and height levels of OPT between 0.3 to 1.5 m. The ash content of samples tended to increase when the torrefied temperature was increased, while the volatile matter value was reduced with high temperature. Based on the findings, OPT could be used as a raw material to produce value-added white and torrefied pellets as sustainable solid biofuel.

Study on the effects of storage conditions on pretreated and raw biomass

This study aims to investigate influential of the storage condition that affects biomass properties that are covering storages (covered and uncovered) of the torrefied and untorrefied pellets of wood and corncob pellets. And the properties of the pellet after storage for 6 months consist of higher heating value (HHV), moisture content, durability, and dry matter loss. The result shows that the torrefied (wood and corncob) pellets have higher HHV than untorrefied pellets around 15-30%. For the moisture content, the covered pellets have less moisture content than uncovered approximately 3% for both (wood and corncob pellets). Furthermore, the durability continuously decreases from start to 6 months until the durability of corncob black wood and corncob pellet decrease around 95.2% in the case uncovered while in the covered case of wood and corncob, the durability decline around 7.4% and 4.1% respectively. To sum up, the experiment demonstrates that piling a pellet under dry conditions (or covering the pellet to avoid moisture conditions) can upgrade the HHV and energy density of the pellet and the quality of torrefied pellet is greater than untorrefied pellet as well as the wood pellet quality is also better than corncob in term of a low increasing rate of moisture content and dry matter loss and higher of durability, HHV and energy density.

Complementary effects of torrefaction and pelletization for the production of fuel pellets from agricultural residues: A comparative study

Torrefaction is an effective technique to produce high quality coal-like material, which can be used as a substitute of coal in combustion or gasification processes. Combination of torrefaction and pelletization can be a promising technique for production of fuel pellet for long term storage and overseas transportation without deterioration of its quality. In the current study, two production pathways (I: co-pelletization of torrefied biomass, II: torrefaction of biomass pellet) have been compared in terms of fuel pellet quality (physical, mechanical, thermal, and hydrophobicity). Characteristics of pellets produced via co-densification of canola hull, oat hull with mustard meal were investigated. Although up to 75 wt% of oat hull/canola hull was successfully pelletized with mustard meal, 50:50 ratio of oat hull/ canola hull: mustard meal was optimum ratio based on pellet properties. Co-pelletization of torrefied biomass with raw biomass makes competitive quality pellet without use of external additives, high temperature and high pressure. Additionally, the higher heating value, energy density, hydrophobicity increased, and atomic ratios (H/C and O/C) decreased after torrefaction in both cases. Synchrotron-based computed tomography showed that porosity and diameter of cavity enlarged significantly for torrefied pellet than that for pellet produced from torrefied biomass. However, the moisture uptake rate for torrefied pellet is lower than that for torrefied biomass pellet. Higher heating values of pellet were more or less similar for pellets obtained from both pathways. In terms of energy consumption throughout the whole procedure, scheme II is slightly more intense as it requires more energy during grinding while scheme I requires more energy for pelleting. Therefore, co-pelletization of torrefied biomass was more effective considering overall energy consumption and fuel pellet product quality.

Calorific Characteristics of Larch (Larix decidua) and Oak (Quercus robur) Pellets Realized from Native and Torrefied Sawdust

This research aimed to evaluate the calorific characteristics of two biomasses from larch and oak sawdust in the form of native or torrefied pellets. Some calorific features of these two kinds of biomasses, such as ash content, higher and lower calorific values, calorific density and many others were highlighted, allowing for a comparison between oak and larch torrefied/not torrefied pellets. Installations and methods used for the process of torrefaction and for highlighting some of the calorific features were also evaluated. As a result of experiments, it was demonstrated that the larch and oak pellets were different in terms of density, but that after thermal treatment, the calorific values of both increased considerably. The investigations evidenced some increases in calorific value, up to 15.8%, for both the larch and oak sawdust/pellets. One of the main conclusions of this research was that, even though the role of biomass has diminished considerably in the last few decades, its role as a sustainable fuel remains relevant. Its use will become more widespread when the world’s population understands that fossil fuels are depletable and that they must be replaced by renewable fuels such as biomass.

Pelletization of torrefied canola residue: Effects of microwave power, residence time and bio-additives on fuel pellet quality

This study involves a sequential torrefaction and pelletization process to produce high-quality fuel pellets from canola residue. Firstly, canola residue was torrefied via microwave irradiation at 250–450 W for 10–20 min with 70–110 g feed load and further pelletized under 3500 N load for a relaxation time of 15 s. The Box-Behnken design was employed to understand the interactions between torrefaction operating conditions for optimal relaxed density, durability, and hardness of the pellets. The optimal torrefaction as determined at 250 W for 10 min with 90 g feed load having the highest relaxed density (1090 kg/m3), durability (83%) and mechanical strength (0.55 MPa) of fuel pellets. The results show that torrefaction significantly improved the energy content as well as hydrophobicity due to the degradation of the lignocellulosic structure. The goal of this study was to investigate the effects of bio-additives (i.e., lignin, sawdust, mustard meal and pyrolysis-derived bio-oil) to further improve the relaxed density, durability, tensile strength, energy density and hydrophobicity of fuel pellets. The combination of the mustard meal, lignin with bio-oil improved the density, durability, tensile strength by 21%, 20% and 123%, respectively. The energy densities of raw, torrefied pellets and torrefied pellets with additives were found to be 15.6, 19.4 and 21.2 GJ/m3, respectively.

Mechanical Durability and Grindability of Pellets after Torrefaction Process

Renewable energy sources and their part in the global energy mix are beneficial to energy diversification and environment protection. However, raw biomass is characterized by low heating value, hydrophilic properties, various mechanical durability, and the logistic challenges related to transportation and storage. One frequently used process of combined biomass valorization is torrefaction and pelletization, which increase the heating value, homogeneity, and hydrophobicity of the fuel. However, industrial clients need fuel characterized by favorable grindability, whereas, the individual clients (householders) need fuel with high mechanical durability. Due to the different expectations of final customers regarding biomass fuel properties, it is necessary to investigate the influence of the torrefaction on the mechanical durability of the pellets. In this paper, five various types of pellets and their torreficates (obtained at a temperature of 200 and 300 °C) were examined. Then the mechanical durability index DU and the grindability of the untreated and torrefied pellets were determined. The results indicated that the mechanical durability of untorrefied pellets is significantly greater than torrefied pellets. Interestingly, no significant differences in mechanical durability between torrefied pellets at 200 and 300 °C were observed, For sunflower husk pellets, the DU index amounted to 95.28 ± 0.72 (untorrefied), 47.22% ± 0.28% (torrefied at 200 °C), and 46.34% ± 0.72% (torrefied at 300 °C). Considering the grindability, as the treatment temperature increased the energy demand for grindability decreased. For example, the grindability of pine tree pellets was 15.96 ± 3.07 Wh·kg−1 (untreated), 1.86 ± 0.31 Wh·kg−1 (torrefied at 200 °C), and 0.99 ± 0.17 Wh·kg−1 (torrefied at 300 °C). The highest difference between raw and torrefied pellets was determined for beetroot pomace pellet: 36.31 ± 2.06 Wh·kg−1 (untreated), 3.85 ± 0.47 Wh·kg−1 (torrefied at 200 °C), and 1.03 ± 0.12 Wh·kg−1 (torrefied at 300 °C).

A comparative assessment of solid fuel pellets production from torrefied agro-residues and their blends

Energy densification of biomass is usually done by pelletizing the raw biomass and then its torrefaction to obtain clean fuel from renewable resources. The objective of this study is to compare the untorrefied and torrefied pellets of two agricultural biomass residues as cotton waste (CW) and wheat straws (WS) with the different mixing ratios i.e., 100:0, 75:25, 25:75, 50:50, 0:100, respectively. Torrefaction of the pure biomass and their blending pellets were performed at 300 °C in a tube furnace at a heating rate of 10 °C/min with a residence time of 30 min. Characterization of untorrefied pellets showed slightly increase in carbon contents and its energy contents enhancement due to densification of the biomass residue owing to pelletization. Furthermore, its blends showed higher carbon content with the addition of cotton waste. Moreover, mass and energy yield data and Van Krevelon plot showed that the torrefied pellets with high CW to WS ratio specified even more rise in carbon contents and energy value due to high rate of devolatilization of hemicelluloses in CW residue. Finally, torrefaction severity index revealed that CW dictates its high degree of degradation as compared to WS which is an indication of high rate of hydrogen and oxygen loss and resulting enhancement in carbon content.Experimental results showed increased values of carbon contents and energy contents, which shows significant synergistic effect of blending and torrefaction to produce carbon rich solid biofuel. As a result carbon contents and calorific value of blended 25% WS + 75%CW torrefied pellets increased from 41.5 % to 64.84 % and 18.322 MJ/Kg to 28.5 MJ/K g respectively, similarly energy yield and torrefaction index showed higher values of 91.67 % and 1.379 respectively compared to untorrefied pellets.