Torrefaction Process Research Articles

Rice Straw Biomass to High Energy Yield Biocoal by Torrefaction:Indian Perspective

India is an agriculture based country and generates more than 600 million tonnes of biomass waste from different crops and produces 140 million tonnes of rice straw alone annually. To dispose the rice straw for making field ready for next crop, farmers are burning it in the fields. Burning of rice straw in agriculture fields poses lot of environmental, health and economic issues in various parts of the country. On one hand, rice straw is a good source of renewable energy but on the other hand it has some inherent problems. Therefore, to mitigate problems due to the burning of rice straw, in this study, an effort is made to convert rice straw into an useful product by torrefaction process, i.e. biocoal. The biocoal which has the calorific value equivalent to that of bituminous coal is used in thermal power plants. By optimizing the processing parameters of torrefaction process, desired calorific value of torrefied product has been archived. The 10% use of torrefied product with coal can consume 140 million tonnes of rice straw and as a consequence, it reduces the consumption of fossil fuels. This can greatly solve problems arising due to burning of rice straw and reduce greenhouse gas emission significantly.

Development and validation of mass reduction model to optimize torrefaction for agricultural byproduct biomass

Global warming and environmental pollution are accelerating due to the continued use of fossil fuels. To address these problems, biomass is being considered as an alternative and renewable energy source. In this study, the use of agricultural byproducts as a new bioenergy resource was investigated considering their conversion into a fuel via the torrefaction process. In particular, pepper stems (Capsicum annuum) were selected as a renewable agricultural byproduct for this energy conversion process. The longer residence time and the higher temperature, The larger amount of mass reduction and the higher heating value by torrefaction, which showed that there was a correlation between the heating value and mass reduction (R2 = 0.9621). The reaction rate constants for the mass reduction model were then derived from the empirical Arrhenius equation.Thermogravimetric analysis was conducted to obtain frequency factors and activation energies of the biomass at different heating rates. The experimental results were in good agreement with simulated results (r2 = 0.9639; root mean square error = 0.0363) when a heating rate of 7.5 °C/min was used, which also corresponded well with the rate of temperature increase inside the biomass.

Simplified model of torrefaction-grinding process integrated with a power plant

A simple method is presented to formulate the total energy consumption of a biomass torrefaction process operating as a standalone unit or integrated with a downstream power plant. New expressions are derived to estimate the volatiles heating value, mass yield at autothermal operation, and mass yield at minimum energy consumption. Experimental data reported in the literature for grinding torrefied beech in a knife-mill are correlated to estimate the specific grinding energy. The presented model accurately predicts the critical moisture content and the auxiliary heat input of a 150 MWth torrefaction plant producing torrefied woodcutting. Illustrative numerical results are presented for an integrated application using willow and beech as two woody feedstocks. The autothermal solid yield is found to be higher than that at optimum energy consumption. The autothermal solid yield declines with moisture content and it is approximately the same for both feedstocks. For every percentage point increase in the power plant efficiency, the optimum solid yield increases 0.67% and 0.15% for willow and beech, respectively, whereas the energy consumption decreases by 7.1 kJ/kg (willow) and 5.75 kJ/kg (beech). The results suggest that the design of torrefaction plants is highly feedstock-dependent. The method presented can be applied to any type of feedstock and both upstream and downstream applications. It is a simple and effective tool that can be used to have a quick estimate of optimum operating point and energy consumption at early design stages.

A novel on-site wheat straw pretreatment method: Enclosed torrefaction

In this study, a novel on-site torrefaction method was proposed for the pretreatment of wheat straw, in which the wheat straw was placed in an enclosed environment for torrefaction. The effects of different torrefaction conditions on the properties of both solid and gaseous products were investigated. When the temperature of enclosed torrefaction increased from 200 °C to 250 °C, the higher heating value, fixed carbon and C content of wheat straw increased by 12.7%, 80.3% and 18.1%, respectively, and the moisture decreased by 25.0%. Enclosed torrefaction causes more mass loss due to the smoldering of wheat straw, and a strong decomposition of the hemicellulose of wheat straw during the torrefaction process. The gaseous products obtained by enclosed torrefaction have fewer acids and more esters than conventional torrefaction. Compared with conventional torrefaction, enclosed torrefaction performs similarly, or even better, in improving the properties of wheat straw.

Preparation and Characterization of the Glycerol-Embedded Hybrid Coal

The molasses embedded hybrid coal (Hybrid Coal by Korea Institute of Energy Research; HCK) was previously proposed as an attractive alternative to low-rank coals that tend to show low calorific values and high CO2 emissions. HCK was synthesized by mixing molasses with a low-rank coal to enhance its heating value. Nevertheless, food ethics regarding molasses additives still have impeded its commercial acceptance. In this study, we propose a glycerol (nonfood)-based coal upgrading process to improve the combustion kinetics and heating value of hybrid coal in comparison to the previous HCK. The process involves drying at 105 °C followed by torrefaction process at 250 °C. During torrefaction, the glycerol additive starts to evaporate at about 180 °C and then is almost vaporized out to the coal surface. To avoid glycerol loss, we employ sulfuric acid as a torrefaction catalyst to suppress glycerol evaporation. In comparison to the molasses yield of 65% after torrefaction in the previous HCK synthesis process, ...

Resistance of in natura and torrefied eucalyptus wood to Cryptotermes brevis (Isoptera)

The shorter natural durability and low energy density of eucalyptus wood hampers its use in generating energy. Torrefaction or pre-carbonization, which is treatment in low oxygen with temperatures between 200 °C and 300 °C, accumulates carbon and lignin, decreases the hygroscopicity, increases the energy efficiency, and reduces the attractiveness of wood to xylophagous organisms, such as termites. The objective of this study was to evaluate the resistance of fresh and torrefied Eucalyptus urophylla (20 min at temperatures of 180 °C, 220 °C, and 260 °C) to dry wood termites (Cryptotermes brevis), following IPT standards. The torrefaction process increased the resistance to dry wood termite attack after 45 d of exposure, with mass losses five times greater in the in natura wood compared with the wood torrefied at 260 °C. The larger visual damage to the in natura chips confirmed its lower resistance to dry wood termites. Torrefaction at 260 °C increased the resistance to dry wood termites and was more efficient with a lower mass loss and wear, and caused a greater mortality of dry wood termites.

Assessment of energy potential of wood industry wastes through thermochemical conversions

Three kinds of waste resulting from woods from the Colombian industry were selected (PinusPátula, Tectona Grandis and Acacia Mangium) in order to assess their energy potential. Several techniques of physicochemical characterization were used to predict the most appropriate energy exploitation process in each case; which was validated at laboratory scale by carrying out the torrefaction, gasification and combustion process. Results allowed us to the identification of the high energy potential of such wood waste as well as their feasibility to generate torrefied products and synthesis gas as products with greater added values. As a special case, the species Tectona Grandis displayed the greatest conversion and synthesis gas quality on the basis of the gasification process, due to its physicochemical characteristics. These samples can be torrefacted in order to get a new product with higher energy potential than the original sample. Experimental study carried out, allowed us to demonstrate that there is a relationship between biomass chemical composition, yield, and process products. In addition, applying an additivity law of individual effects of the component, it is not possible to predict the process performances.

Properties Prediction of Torrefied Municipal Solid Waste using Linear Correlation Model

Abstract In Malaysia, municipal solid waste (MSW) management has been one of the main issues that closely related to the environmental pollutions and human health risks. One of the promising method to utilize MSW as a fuel is gasification. However, MSW possess some drawbacks in terms of its properties such as high moisture content and low high heating value (HHV) which lead to the reduction of gasifier efficiencies and the quality of product gas produced. In order to overcome the problem, torrefaction process can be employed for upgrading the properties of MSW. Although torrefaction process has been widely implemented but correlation analysis of the quality of torrefied product is rather limited. This correlation analysis is indeed important as a tool to assess the suitability of biomass in torrefaction process. This is due to the fact that although the torrefaction process is able to increase some of the properties, the increment for certain biomass is deemed low and insignificant. Therefore, there is a need for a simple correlation analysis to help in the biomass selection for torrefaction purposes. In this work linear correlation models for MSW involving food waste and wood waste have been developed as a function of mass loss in order to predict the ultimate analysis of C, H, and O elements, proximate analysis of ash content, volatile matter (VM) and fixed carbon (FC) as well as high heating value (HHV) and energy yield (EY). In this study high coefficient determination was achieved using the developed linear correlation models (R2 > 0.87) for predicting H element, O element, VM, FC, HHV and EY. This suggests that the linear correlation models can be used to predict of the MSW characteristics after torrefaction process.

High quality product gas from biomass steam gasification combined with torrefaction and carbon dioxide capture processes

Gasification is currently recognized as a mature technology to convert biomass into useful and versatile product gas for further energy and fuel applications. However, there are some remaining problems relating to the process operation and process efficiency due to inherent properties of biomass feedstock such as high moisture content, low energy density and high oxygen content. Strategies to improve the efficiency of biomass gasification as well as the quality of product gas are thus required. For this purpose, a combined process of torrefaction, gasification, and carbon dioxide capture is developed and simulated in a commercial simulator to investigate the performance of a biomass gasification coupled with a pre-treatment and a post-treatment processes. The results show that the quality of product gas is enhanced when combining gasification with a torrefaction and a CO2 capture processes. The heating value of the product gas and the cold gas efficiency are both increased with additional torrefaction. The CO2 capture process using monoethanolamine offers a CO2 removal efficiency of about 83% and consequently increase the product gas heating value up to 27%.

Oxygen influence on the process of low-temperature pyrolysis of biomass

The installation for studying the processes of low-temperature pyrolysis of biomass was created in JIHT RAS. A feature of the installation is heated biomass through the exhaust gas of the internal combustion engine (mini-power stations) through the solid granules, the dried biomass (pellets). A series of experiments was conducted to study the effect of oxygen on the process of torrefaction on the installation. The oxygen content in the combustion products varied from 0.8 to 2% in the course of the experiments. Studies have shown that a slight increase in oxygen content increases the rate of heating of the processed raw materials.

Upgrading Physicochemical Properties using Torrefaction Process and Anhydrous Weight Loss Modelling for Palm Mesocarp Fiber

Abstract Torrefaction is a thermal process for upgrading biomass properties in order to promote biomass utilization for sustainable energy production. It is performed under inert condition at temperature range 200 - 300°C with residence times between 15 – 60 minutes. Torrefied product usually have high energy content, low moisture content and hygroscopic nature which overcome the limitation of raw biomass as biofuel. Therefore, the objective of this study is to investigate the characteristics of torrefied palm mesocarp fiber (PMF) and evolution of volatiles components during torrefaction at 240°C, 270°C, and 300°C in an inert condition. The condensable and non-condensable gases were analyzed using high performance liquid chromatography (HPLC) and gas chromatography mass spectrometry (GC-MS) respectively. Concurrently, a kinetic model using two reactions in series namely Di Blasi and Lanzetta model is developed to predict the evolution of solid and volatile products during torrefaction process for PMF samples. Based on torrefaction experiments, the mass and energy yields are decreased due to the severe decomposition of biomass at higher temperature but the higher heating value of biomass is increased by 27%. Meanwhile the proximate analysis shows that fixed carbon and ash content are increased by 45% and 25% respectively but volatile matter is decreased by 20%. In addition, the ultimate analysis shows that the elemental ratios of hydrogen to carbon (H/C) and oxygen to carbon (O/C) are decreased by 88% and 20% respectively. For the volatile analysis, 70 – 80% of the total volatile yield is made up from non-condensable gases with high percentage of carbon monoxide (CO) and methane (CH4), while the condensable gases formed was 20-30%. Finally, the anhydrous weight loss model is successfully developed for representing the decomposition of PMF where the kinetic parameters estimated from the model give a good agreement with the residual mass obtained from thermogravimetric analysis.

Possibility of the use of exothermic-reactions heat from thermal destruction of biomass to increase the energy efficiency of the torrefaction process

New results of investigation of exothermic effects accompanying the process of plant biomass torrefaction are presented in this paper, which is a continuation of experimental research carried out on the model lab-scale test-bench and devoted to the study of the exothermic effect. A distinctive feature of this work is using of a large-scale pilot torrefaction unit as a test item. This unit operation as close as possible simulates the processes taking place during industrial torrefaction. At this work stage a truncated version of the torrefaction unit was used (the upper hopper was demounted). Experimental data obtained on a pilot torrefaction unit confirm the possibility of exothermic reactions heat usage for process intensifying. It is shown that such operation mode provides increased unit productivity on conditions that gas piston engine is operating at a constant power mode. The characteristics of the fuel obtained in the proposed process organization, as well as the fuel obtained as a result of torrefaction process excluding the influence of exothermic effect heat, are compared. As the main directions of further research, the problem of low-temperature pyrolysis volatile products utilization and the development of operating parameters at a full-scale torrefaction unit have been chosen.

Utilization of waste forest biomass: pelletization studies of torrefied sawmill wood chips

The paper presents the effects pelletization process of torrefied waste forest biomass – sawmill wastes. The sawmill waste are generated in significant quantities and has significant energy potential. The use of torrefaction and pelletization process enables to produce mechanically durable fuel pellets. Aim of the studies was to evaluate the effect of different kind of additives (binders) to torrefied waste forest biomass on pelletization process characteristic (production capacity, energy consumption) and properties of produced pellets (i.e. density, mechanical durability). The most effective binder among the tested was modified wheat starch. Pellets made with this addition were characterized by the highest mechanical strength.

Virginia Mallow as an energy crop - current status and energy perspectives

Currently, the energy crops are designed as promising renewable energy source. The most popular are Miscanthus Giganteus, willow and Virginia mallow. They are well known as plans, but use as a fuel in energy production still needs more investigations. It results from some disadvantages such as biological degradation, low bulk density and low energy density of Virginia mallow. That is why, pre-treatment processes are required to enhance combustible properties. Thus, this paper demonstrates the current state and energy perspectives of Virginia mallow which can be one of the most promising energy crops in Poland. The study of Virginia mallow focuses on combustion characteristics of torrefied biomass using both experiments and modelling. This energy crop was torrefied using TGA apparatus. The studied biomass was characterized in terms of its ultimate and proximate analysis. After the torrefaction process of Virginia mallow, improvements in energy properties were observed. The impact of torrefaction was confirmed by enhancing fuels properties (higher carbon content, and HHV, lower moisture content, lower ratio O/C). The Chemkin calculations showed changes in composition of the main evolved gaseous products.

Influence of different temperature regimes at torrefaction of chicken litter on yield and properties of products

The purpose of the research is study the influence of the torrefaction process on the fuel properties of the chicken litter. Experimental studies on lab-scale system at five temperature regimes of torrefaction (220, 240, 260, 280, and 300 °C) with a holding time determined using thermogravimetric analysis were conducted. The products of the torrefaction are solid residue, non-condensable gases, and tar. For the feedstock and torrefied material the elemental composition, the lower calorific value, hygroscopicity limit and bulk density are determined. For liquid fraction the analysis of the chemical composition is carried out. The properties of non-condensable gases as chemical composition and calorific value - are investigated. Mass yields of the solid residue and tar, and specific volume yield of the non-condensable gases are presented. The conclusion about the optimum temperature regime for torrefaction of chicken litter based on the results of experimental studies is made.

Surface characterization of Miscanthus × giganteus and Willow subjected to torrefaction

The main goal of this work was to determine the differences in the composition of the surface and bulk of lignocellulosic feedstock subjected to torrefaction. Miscanthus × giganteus and Willow were used as widely available types of second generation of biomass. The surface of the samples was primarily characterized by time-of-flight secondary ion mass spectrometry. The bulk of the investigated biomass was analyzed by Fourier transform infrared spectroscopy, thermogravimetry and classical chemical methods. The results obtained show that the destruction of the surface of both Miscanthus × giganteus and Willow begin at lower temperature than that observed for the bulk. Moreover, in the case of Miscanthus × giganteus the possibility of the partial surface decomposition of not only the hemicellulose and cellulose but also lignin structure is pointed out. The observed differences between the behavior of the uppermost and deeper layers of the studied biomass samples indicate that the efficiency of their thermal degradation is different and should be taken into account when discussing the torrefaction process.

Furfural production from microwave catalytic torrefaction of Douglas fir sawdust

The torrefaction bio-oil is composed of a number of chemical compounds with low concentrations, which results in a low efficiency of its application. To improve the concentrations of high-value chemicals such as furfural in the torrefaction bio-oil, four metal chlorides and hydrochloric acid were investigated as catalysts in the torrefaction of Douglas fir by microwave heating. The number of chemical compounds in the attained bio-oil was significantly reduced with introducing MgCl2, FeCl3, and AlCl3 being into the process of torrefaction. The bio-oil obtained with these three catalysts were dominated by furfural with the concentration over 20 mg/g with the torrefaction temperature, time, and catalyst/reactant ratio of 250 °C, 10 min, and 8 wt.%, respectively. The effects of torrefaction conditions on product yield were investigated by selecting MgCl2 as the catalyst, and the results indicated that the yield of torrefied biomass decreased significantly with the increase of reaction temperature, time, and catalyst loading while the yield of bio-oil collected simultaneously was increased. Further analysis for the bio-oil suggested that low temperature, long reaction time, and high catalyst loading favored furfural production. The analysis for non-condensable gas suggested that high reaction temperature and catalyst loading promoted the methane and carbon monoxide production during torrefaction. According to bio-oil and non-condensable gas analysis, a reaction pathway was proposed to explain biomass catalytic torrefaction using MgCl2.

Experimental Study on Utilization of Indonesian Non-Recycled Organic Waste as Renewable Solid Fuel Using Wet Torrefaction Process

Municipal solid waste (MSW) is a complex problem in major cities in Indonesia that has not been resolved. MSW is currently only collected and disposed to final landfill. On the other hand, national energy security is also an issue to be solved. Utilization of MSW, which is dominated by organic waste, as solid fuel can be a solution for both problems. This paper discusses an experimental study on utilization of organic waste as renewable solid fuel using a wet torrefaction process. Four types of samples were chosen to represent the four types of organic waste in MSW with the highest mass fraction found in a field survey: leaf litter, food waste, vegetable waste and fruit waste. Each sample was treated with wet torrefaction under four conditions: 150, 175, 200 and 225 oC with holding time 30 minutes. The experimental results showed that the optimum wet torrefaction temperature for mixed organic waste is between 200 and 225 °C, which is predicted to produce a solid product with a heating value (db) of 23.22-24.44 MJ/kg, volatile matter content of 61.18-66.00%, fixed carbon content of 26.04-31.35%, ash content of 7.47-7.96%, and energy yield equal to 58%. A higher operating temperature will increase the calorific value, followed by a decrease in mass yield as a consequence of the process severity degree. However, food waste torrefaction showed different characterisics: the increase in calorific value was followed by an increase in mass yield. This is unique and different from the results of wet torrefaction on other organic wastes. Keywords: Indonesian organic MSW, national energy security, wet torrefaction, renewable solid fuel.

Predictive modelling of the higher heating value in biomass torrefaction for the energy treatment process using machine-learning techniques

Torrefaction of biomass can be described as a mild form of pyrolysis at temperatures typically ranging between 200 and 300 °C in the absence of oxygen. Common biomass reactions during torrefaction include devolatilization, depolymerization, and carbonization of hemicellulose, lignin, and cellulose. Torrefaction of biomass improves properties like moisture content as well as calorific value. The aim of this study was to obtain a predictive model able to perform an early detection of the higher heating value (HHV) in a biomass torrefaction process. This study presents a novel hybrid algorithm, based on support vector machines (SVMs) in combination with the particle swarm optimization (PSO) technique, for predicting the HHV of biomass from operation input parameters determined experimentally during the torrefaction process. Additionally, a multilayer perceptron network (MLP) and random forest (RF) were fitted to the experimental data for comparison purposes. To this end, the most important physical–chemical parameters of this industrial process are monitored and analysed. The results of the present study are two-fold. In the first place, the significance of each physical–chemical variables on the HHV is presented through the model. Secondly, several models for forecasting the calorific value of torrefied biomass are obtained. Indeed, when this hybrid PSO–SVM-based model with cubic kernel function was applied to the experimental dataset and regression with optimal hyperparameters was carried out, a coefficient of determination equal to 0.94 was obtained for the higher heating value estimation of torrefied biomass. Furthermore, the results obtained with the MLP approach and RF-based model are worse than the best obtained with the PSO–SVM-based model. The agreement between experimental data and the model confirmed the good performance of the latter. Finally, we expose the conclusions of this study.

Torrefaction of eucalyptus-tree residues: A new method for energy and mass balances of the process with the best torrefaction conditions

Torrefaction of eucalyptus-tree residues was performed in a lab-scale batch reactor, to evaluate the influence of temperature and time on the process. A new response variable, called Energy Gain (EG), was proposed and it was demonstrated that it is better than the response variable Energy Yield (EY) that has been traditionally used to measure the torrefaction efficiency, because it makes a compromise between high HHV and low mass loss. The experiment with the best Energy Gain was subjected to a further analysis and its solid and gaseous effluents were characterized. Differential Scanning Calorimetry (DSC) was used as a new method to estimate the heat involved in the torrefaction process, in a more accurate fashion than other reported estimation methods. The process led to a solid fuel with an energy densification of 29% compared to the raw biomass, and with characteristics close to lignite coal. An integrated process, where the combustion of exhaust gases from the torrefaction is used to generate the necessary heat for drying and torrefaction, allowed providing 72% of the energy needs.