Torrefaction Conditions Research Articles

Chemical profiling of Jatropha tissues under different torrefaction conditions: application to biomass waste recovery.

Gradual depletion of the world petroleum reserves and the impact of environmental pollution highlight the importance of developing alternative energy resources such as plant biomass. To address these issues, intensive research has focused on the plant Jatropha curcas, which serves as a rich source of biodiesel because of its high seed oil content. However, producing biodiesel from Jatropha generates large amounts of biomass waste that are difficult to use. Therefore, the objective of our research was to analyze the effects of different conditions of torrefaction on Jatropha biomass. Six different types of Jatropha tissues (seed coat, kernel, stem, xylem, bark, and leaf) were torrefied at four different temperature conditions (200°C, 250°C, 300°C, and 350°C), and changes in the metabolite composition of the torrefied products were determined by Fourier transform-infrared spectroscopy and nuclear magnetic resonance analyses. Cellulose was gradually converted to oligosaccharides in the temperature range of 200°C–300°C and completely degraded at 350°C. Hemicellulose residues showed different degradation patterns depending on the tissue, whereas glucuronoxylan efficiently decomposed between 300°C and 350°C. Heat-induced depolymerization of starch to maltodextrin started between 200°C and 250°C, and oligomer sugar structure degradation occurred at higher temperatures. Lignin degraded at each temperature, e.g., syringyl (S) degraded at lower temperatures than guaiacyl (G). Finally, the toxic compound phorbol ester degraded gradually starting at 235°C and efficiently just below 300°C. These results suggest that torrefaction is a feasible treatment for further processing of residual biomass to biorefinery stock or fertilizer.

Effects of the Torrefaction Conditions on the Fixed-Bed Pyrolysis of Norway Spruce

Fixed-bed pyrolysis of Norway spruce wood previously subjected to torrefaction at temperatures between 533 and 583 K and retention times between 8 and 25 min was studied. Although the thermal pretreatment always results in an increased production of char at the expense of volatile products, appropriate torrefaction conditions give rise to maximum percentages of anhydrosugars, guaiacols possessing a carbonyl group, and phenols in the liquid fraction. Other carbohydrates (e.g., acetic acid, formic acid, hydroxyacetaldehyde, hydroxypropanone, furfural, and furfuryl alcohol) and the large majority of guaiacols show continuously decreasing values. The percentages of carbon monoxide and carbon dioxide in the gas product remain approximately the same, but that of methane slightly increases. The pyrolysis temperatures of torrefied wood are lower than those of the raw material, mainly because of the partial or complete absence of the exothermic contribution associated with extractives and hemicellulose degradation.

Catalytic Fast Pyrolysis of Biomass Pretreated by Torrefaction with Varying Severity

Pretreatment of corncobs using torrefaction was performed in a tubular reactor with varying reaction temperature (210, 240, 270, or 300 °C) and residence time (20, 40, or 60 min). The torrefied corncobs were subsequently catalytically fast pyrolyzed over nanosized HZSM-5 in a semibatch pyroprobe reactor. The torrefied corncobs were characterized by elemental analysis, thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (FTIR), and FTIR. The aromatic production was online analyzed by gas chromatography mass spectroscopy. The effect of torrefaction severity on product distribution and aromatic selectivity from catalytic fast pyrolysis of torrefied corncobs was investigated. The experimental results show that torrefaction can serve as an effective thermal pretreatment for improving the selectivity of BTX (benzene, toluene, and xylenes). Light and mild torrefaction (torrefaction at 210 and 240 °C) has little impact on the aromatic yield. However, severe torrefaction (torrefaction at 270 or 300 °C) can lead to the sharp increase of coke yield and reduction of aromatic yield. The results could be explained by the serious cross-linking and charring of corncob under severe torrefaction conditions. The optimal torrefaction condition is 210–240 °C with residence time of 40 min.

Torrefaction of Conservation Reserve Program biomass: A techno-economic evaluation

The Conservation Reserve Program (CRP), which was initiated to prevent soil erosion, provides a large amount of cellulosic biomass that is potentially useful for bioenergy production. We investigated the effects of torrefaction conditions on the physicochemical properties of CRP biomass using an elemental analyzer, a thermogravimetric analyzer, and a calorimeter. Results suggest that the upgraded biomass is a hydrophobic, high-energy density, and low-moisture-content material. The study on biomass polymer composition showed how polymer components changed with processing conditions. The polysaccharides in biomass were degraded significantly at 300°C, suggesting that processing conditions should be managed properly for sugar or energy recovery. Our economic analysis suggested that the processing cost for a torrefaction plant with an annual capacity of 100,000tons of CRP biomass is $16.3 per ton of feedstock. Further analysis of the effects of torrefaction on the biomass supply chain suggested that processing could save pelletization and transportation costs.

Effect of temperature during wood torrefaction on the formation of lignin liquid intermediates

Torrefaction enhances physical properties of lignocellulosic biomass and improves its grindability. Energy densification, via fuel pellets production, is one of the most promising uses of torrefaction. Lignin contributes to self-bonding of wood particles during pelletization. In biomass thermal pretreatment, part of lignin (in the form of lignin liquid intermediates – LLI) migrates from the cell wall and middle lamella and deposits on the fibers’ surfaces and/or inner surface of the secondary cell wall. This material can play an important role on bonding particles during wood pelletization as well as production of wood composites. The objective of this paper was to investigate the influence of torrefaction conditions on amount, composition, molecular weight, and pattern of deposition of LLI on wood cells. Torrefaction of extracted ponderosa pine in the range of temperatures 225–350°C was conducted in a tube furnace reactor and the torrefied wood was extracted with dichloromethane (DCM) to isolate the lignin-rich soluble material. A maximum yield of DCM-soluble material was observed in wood torrefied at approximately 300°C for 30min. ESI/MS revealed that the molecular weight of the removed material is less than 1200gmol−1 and decreases as torrefaction temperature augments. Semiquantitative Py-GC/MS of the DCM-soluble material suggests that this lignin-rich material migrates and deposits on cells’ surfaces in amounts that depend on the torrefaction conditions. Py-GC/MS of the solid fraction after the DCM process showed a progressive reduction of products of the pyrolysis of lignin and levoglucosan as torrefaction temperature increased, revealing that lignin content in the solid decreased due in part to migration. SEM of torrefied particles helped to show the apparent formation of LLI during torrefaction. Results suggest that it is possible to control the thermal pretreatment conditions to increase or reduce the amount of lignin-rich material on fiber surfaces as required for downstream processes (e.g., fuel pellets or wood composites manufacture).

The integrated process of microwave torrefaction and pyrolysis of corn stover for biofuel production

The integrated process of torrefaction and pyrolysis of corn stover were investigated in this study. The effects of torrefaction conditions on both torrefaction and pyrolysis products were determined. The heating values of torrefied biomass were similar to those of coals and increased comparing to raw biomass. The torrefaction oils contained high value chemicals such as furans and phenolics. The torrefaction process caused a decrease in the pyrolytic oil yields but the total bio-oil yield from torrefaction and pyrolysis were similar to those from raw biomass pyrolysis. The pyrolytic oil from torrefied biomass contained more hydrocarbons and phenols and less organic acids than raw biomass pyrolysis, which indicates that the quality of pyrolytic oil was improved with torrefaction as a thermal pretreatment. The optimum torrefaction condition for both high yield and quality of pyrolytic oil was determined at the reaction temperature around 275°C and torrefaction time of 30min. This study implied that torrefaction as a pretreatment can be combined with the pyrolysis for high quality biofuel production.

Torrefaction of wheat and barley straw after microwave heating

Microwave irradiation was used in this study for the torrefaction of wheat and barley straw. The torrefaction effect was studied by varying the microwave power level (200–300W), reaction time (10–20min) and moisture content of biomass (5–15%). Mass yield and energy yield of the torrefied biomass was determined. Fuel properties like H/C and O/C ratio were assessed from elemental composition. Grinding characteristics and hydrophobicity of the torrefied sample were studied and compared with the raw biomass. Barley straw tended to carbonize more under microwave irradiation with 29.1% increase in the C content against 16.2% in the case of wheat straw when torrefied at 300W for 20min. Both H/C and O/C ratio decreased with increase in power and reaction time. The energy density increased by 14–15% in wheat straw and 21–23% in barley straw under suitable reaction condition. Mass and energy yields were 64.0–97.8% and 73.8–98.4%, respectively for wheat straw. In barley straw, mass and energy yields were 42.7–97.4% and 52.5–97.3%, respectively. Moisture content of the biomass did not affect the reaction as much as other parameters and the mass yields were comparable between different moisture contents. Grindability of the biomass improved significantly after torrefaction. The particle size ratio between torrefied and untreated straw after grinding was 0.66 and 0.61 for wheat and barley, respectively. The torrefied biomass was more hydrophobic and the moisture uptake was reduced by 61–68% under suitable torrefaction condition. Microwave irradiation can be used effectively for torrefaction of the two biomass investigated at moderate power and short process time.

Carbon Dioxide Torrefaction of Woody Biomass

The major drawback of biomass for direct combustion applications is its lower heating values and poor grindability when compared to conventional fossil fuels. Torrefaction is one of the thermochemical pretreatment techniques used to improve the properties of biomass. An inert environment is maintained to prevent oxidation of biomass during torrefaction. A novel method for utilization of carbon dioxide as the pretreatment medium for woody biomass has been investigated in the current study. Previous studies on smaller samples using thermogravimetric analysis (TGA) showed an increased mass loss in the CO2 environment, which was attributed to possible structural changes in the biomass and potential effect of ash constituents in the biomass. However, those claims were not validated. The current study on bigger batches of samples also resulted in increased mass loss when using CO2 compared to using N2 as the torrefaction medium. Scanning electron microscopy (SEM) studies and Brunauer–Emmett–Teller (BET) surface area investigation on the torrefied samples from different environments showed increased internal surface area indicating a mild effect of the CO2 reacting with the samples at temperatures normally employed for torrefaction conditions (200–300 °C). Further, grindability studies were performed on the samples pretreated in CO2 and torrefied in N2. The results on grindability showed improved grindability on using CO2 as the pretreatment medium. Proximate and heating value analysis on the pretreated samples showed an increasing trend in the heating value of the samples with increased temperature. Comparable mass loss at lower temparatures improved grindability and improved fuel properties, makes utilization of carbon dioxide as a torrefaction medium for pretreating biomass for combustion applications an attractive technology.

Thermal with Mass Spectroscopic Analysis of Wood and Cereal Biomass Torrefaction

Torrefaction is a mild form of pyrolysis that, when applied to biomass, has the effect of improving the energy density of biomass-derived solid fuels. In this study, thermogravimetric analysis (coupled with mass spectrometry) was applied to two biomass fuels (pine wood and white maize ear) to investigate a potential representative torrefaction thermal treatment process. The mass loss from the torrefaction process was indicative of emission of aliphatic hydrocarbons, evidenced by mass spectroscopic data and it is evident that optimal torrefaction conditions are determined by the type of biomass to which torrefaction processing is applied.

낙엽송(Larix kaempferi) 고밀도 에너지화를 위한 반탄화 최적조건 탐색

In this study, torrefaction was performed to improve fuel properties of Larch. The optimal condition for torrefaction was investigated by response surface methodology. The torrefaction temperature and time ranged and 20~80 min, respectively. As the torrefaction temperature and time increased, the carbon content of torrefied biomass increased from 49.36 to 56.65%, while its hydrogen and oxygen contents decreased from 5.56 to 5.48% and from 37.62 to 31.67%, respectively. The weight loss and calorific value increased with SF, while energy yield decreased. At the severe torrefaction condition (SF 7), the weight loss and calorific value were 26.58% and 22.30 MJ/kg, respectively. The energy contained in torrefied biomass increased to 20.41%, when compared with the untreated biomass. As the torrefaction severity increased, the energy yield decreased due to the relatively high weight loss of biomass. Therefore, the highest energy yield was obtained at high calorific value and low weight loss of biomass (SF 5.72).

반응표면분석법을 이용한 유칼립투스의 반탄화 최적조건 탐색

유칼립투스(Eucalyptus globulus)의 반탄화 최적조건을 탐색하기 위하여 반응표면분석법을 이용하였다. 반탄화 바이오매스의 탄소함량은 반탄화 정도를 나타내는 severity factor (SF)에 따라 증가하였으며 바이오매스에 포함된 수소와 산소의 함량은 감소하였다. 반탄화 바이오매스의 발열량은 조건에 따라 20.23~21.29 MJ/kg을 나타냈으며 처리 전 바이오매스와 비교하여 1.6~6.9% 에너지함량이 증가한 것으로 나타났다. 바이오매스의 중량감소율은 SF 증가에 따라 증가하였다. 에너지수율에서 반탄화 온도는 중요한 인자로 작용하였으며 상대적으로 반응시간에 대한 영향은 낮았다. 최대 에너지수율은 낮은 SF에서 반탄화를 수행하였을 때 얻을 수 있었다. The optimal condition for the torrefaction of eucalyptus (Eucalyptus globulus) was investigated by response surface methodology. The carbon content in the torrefied biomass increased with the severity factor (SF), while hydrogen and oxygen contents decreased. The calorific value of torrefied biomass ranged from 20.23 to 21.29 MJ/kg, depending on the torrefaction conditions. This implied that the energy contained in the torrefied biomass increased by 1.6 to 6.9%, when compared with that of the untreated biomass. The weight loss of biomass increased as the SF increased. The Code level of reaction temperature had the highest impact on the energy yield of torrefied biomass, while the effect of Code level of reaction time was considerably low. The highest energy yield was obtained at low SF.

Comparative Assessment of Wet Torrefaction

Wet torrefaction of typical Norwegian biomass fuels was studied within the temperature window of 175–225 °C, using a benchtop autoclave reactor of 250 mL in volume from Parr Instrument. Two types of local biomass fuels were employed as feedstock, Norway spruce (softwood) and birch (hardwood). Effects of process parameters including pressure, reaction temperature, holding time, and feedstock particle size on the yield and properties of the solid products were investigated. It appears that birch wood is more reactive and produces less solid products than spruce wood in the same wet torrefaction conditions. Increasing pressure above the saturated vapor pressure of water enhances the torrefaction rate. Both reaction temperature and holding time have significant effects on solid product yield and fuel properties of wet torrefied biomass. The yield of solid products is slightly reduced with decreasing feedstock particle size. The ash content of biomass fuel is significantly reduced by wet torrefaction. In addit...

Inverse analysis of wood pyrolysis with long residence times in the temperature range 210–290 °C: Selection of multi-step kinetic models based on mass loss residues

The aim of this paper is to evaluate different types of kinetic models and to propose a set of kinetic parameters for simulating the heat treatment of woody biomass under temperatures representative of torrefaction conditions. The mass loss of three wood types, locust, spruce and eucalyptus, as well as their main components, cellulose, xylan, glucomannan and lignin, has been determined in a TGA at different isothermal temperatures between 210 and 290°C for residence times of up to ten hours. These data were used to evaluate the kinetic parameters corresponding to various multi-step series reaction mechanisms proposed in the literature. A computational solution of the multi-step formulation was derived, which allows the exact conditions undergone by the sample to be used as input parameters. The inverse procedure takes into account simultaneously the different temperature levels for each species. A comprehensive table summarizes all results, among which the dimensionless residues, proposed as a guideline to choose the relevant mechanism complexity. Overall we find that 2-step series reaction models provide acceptable accuracy for reproducing the mass loss from lignocellulosic biomass and their constituents under torrefaction conditions.

Optimization of torrefaction conditions for high energy density solid biofuel from oil palm biomass and fast growing species available in Malaysia

Without appropriate treatment, lignocellulosic biomass is not suitable to be fed into existing combustion systems because of its high moisture content, low bulk energy density and difficulties in transport, handling and storage. The aim of this study was to investigate the effects of torrefaction treatment on the weight loss and energy properties of fast growing species in Malaysia (Acacia spp., and Macaranga spp.) as well as oil palm biomass (oil palm trunk and empty fruit bunch). The lignocellulosic biomass was torrefied at three different temperatures 200, 250 and 300°C for 15, 30 and 45min. Response surface methodology was used for optimization of torrefaction conditions, so that biofuel of high energy density, maximized energy properties and minimum weight loss could be manufactured. The analyses showed that increase in heating values was affected by treatment severity (cumulated effect of temperature and time). Our results clearly demonstrated an increased degradation of the material due to the combined effects of temperature and treatment time. While the reaction time had less impact on the energy density of torrefied biomass, the effect of reaction temperature was considerably stronger under the torrefaction conditions used in this study. It was demonstrated that each biomass type had its own unique set of operating conditions to achieve the same product quality. The optimized torrefaction conditions were verified empirically and applicability of the model was confirmed. The torrefied biomass occurred more suitable than raw biomass in terms of calorific value, physical and chemical properties. The results of this study could be used as a guide for the production of high energy density solid biofuel from lignocellulosic biomass available in Malaysia.

Effects of torrefaction on the physiochemical properties of oil palm empty fruit bunches, mesocarp fiber and kernel shell

In this work, the effects of torrefaction on the physiochemical properties of empty fruit bunches (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) are investigated. The change of properties of these biomass residues such as CHNS mass fraction, gross calorific value (GCV), mass and energy yields and surface structure when subjected to torrefaction process are studied. In this work, these materials with particle size in the range of 355–500 μm are torrefied under light torrefaction conditions (200, 220 and 240 °C) and severe torrefaction conditions (260, 280 and 300 °C). TGA is used to monitor the mass loss during torrefaction while tube furnace is used to produce significant amount of products for chemical analyses. In general, the study reveals torrefaction process of palm oil biomass can be divided into two main stages through the observation on the mass loss distribution. The first stage is the dehydration process at the temperature below than 105 °C where the mass loss is in the range of 3–5%. In the second stage, the decomposition reaction takes place at temperature of 200–300 °C. Furthermore, the study reveals that carbon mass fraction and gross calorific value (GCV) increase with the increase of torrefaction temperature but the O/C ratio, hydrogen and oxygen mass fractions decrease for all biomass. Among the biomass, torrefied PKS has the highest carbon mass fraction of 55.6% when torrefied at 300 °C while PMF has the highest GCV of 23.73 MJ kg−1 when torrefied at the same temperature. Both EFB and PMF produce lower mass fraction than PKS when subjected to same torrefaction temperature. In terms of energy yield, PKS produces 86–92% yield when torrefied at light to severe torrefaction conditions, until 280 °C. However, both EFB and PMF only produce 70–78% yield at light torrefaction conditions, until 240 °C. Overall, the mass loss of 45–55% of these biomasses is observed when subjected to torrefaction process. Moreover, SEM images reveal that torrefaction has more severe impact on surface structure of EFB and PMF than that of PKS especially under severe torrefaction conditions. The study concludes that the torrefaction process of these biomass has to be optimized based on the type of the biomass in order to offset the mass loss of these materials through the process and increase the energy value of the solid product.

Devolatilization studies of oil palm biomass for torrefaction process optimization

Torrefaction of palm biomass, namely Empty Fruit Bunch (EFB) and Palm Kernel Shell (PKS), was conducted using thermogravimetric analyser (TGA). The experiment was conducted in variation of temperatures of 200 °C, 260 °C and 300 °C at a constant residence time of 30 minutes. During the torrefaction process, the sample went through identifiable drying and devolatilization stages from the TGA mass loss. The percentage of volatile gases released was then derived for each condition referring to proximate analysis results for both biomass. It was observed an average of 96.64% and 87.53 % of the total moisture is released for EFB and PKS respectively. In all cases the volatiles released was observed to increase as the torrefaction temperature was increased with significant variation between EFB and PKS. At 300°C EFB lost almost half of its volatiles matter while PKS lost slightly over one third. Results obtained can be used to optimise condition of torrefaction according to different types of oil palm biomass.

Chemical and cellulose crystallite changes in Pinus radiata during torrefaction

The impact on the chemical composition and changes to the cellulose crystallites in Pinus radiata wood chips under light (ca. 230 °C), mild (ca. 260 °C), and severe (290+ °C) torrefaction temperatures at a range of times was examined by solid state 13C CP-MAS and Dipolar Dephased NMR spectroscopy, TGA, and synchrotron based X-ray diffraction. Results indicated the decomposition of hemicelluloses into furfurals at the lowest temperature with little modification to the lignin or cellulose. De-polymerisation of lignin and cellulose was observed as torrefaction severity increased. The increased hydrophobicity under light and mild torrefaction severity was attributed to a combination of thermo-chemical modifications to hemicelluloses and lignin, along with cellulose crystal lattice changes. The observed decrease in hydrophobicity under severe torrefaction conditions was attributed to the degradation of cellulose crystallites.

Torrefaction and densification of different species of softwood residues

Torrefaction and densification of British Columbia (BC) softwoods, including pine, fir, spruce, SPF (a mixture of spruce, pine and fir) and pine bark, have been conducted for the production of high quality torrefied wood pellets. A bench-scale fixed bed tubular reactor was used for the torrefaction test at temperatures of 240–340°C. Densification was conducted in a press machine in order to identify the suitable conditions for making strong torrefied pellets. Results showed that the mass loss of BC softwood mainly depended on the torrefaction temperature and time. The heating value of torrefied sawdust particles had a close relationship with the mass loss, increasing with increasing the severity of torrefaction. It was more difficult to compress torrefied samples into strong pellets than the raw material under the same conditions as used for making the control (regular and non-torrefied) pellets, and either a higher die temperature or adding moisture into torrefied particles could improve the compression process. The moisture content of torrefied pellets prepared in this study was lower than control pellets, and the density of torrefied pellets was slightly lower than control pellets. At the same time, more energy was consumed for compacting torrefied softwood particles into pellets. Increasing torrefaction severity increased the heating value and decreased the moisture uptake of torrefied pellets, but decreased the energy yield and the hardness of torrefied pellets. Considering the quality of torrefied pellets, the optimal torrefaction condition appeared to be around 30% mass loss, which gave a 20% increase in pellet higher heating value and a reasonable low water update rate. The suitable densification conditions for torrefied softwoods corresponded to a die temperature of 170–230°C for unconditioned samples, or about 110°C for samples preconditioned to ∼10% moisture content.

Torrefaction of oil palm mesocarp fiber and their effect on pelletizing

The optimal condition for the torrefaction of oil palm mesocarp fiber was investigated by response surface methodology. Pelletizing properties of torrefied biomass were analyzed depending on torrefaction conditions. The elemental composition of torrefied biomass was influenced by the Severity Factor (SF) of torrefaction. The carbon content in the torrefied biomass increased from 48.02 to 54.83%, while the hydrogen and oxygen contents decreased with the SF. The calorific value of torrefied biomass ranged from 19.15 to 22.82 MJ kg−1. This implied that the energy contained in the torrefied biomass increased by 5–19%, when compared with untreated biomass. The calorific value and weight loss in the biomass increased as the SF increased. The energy yield was high at a low SF, allowing for weight loss and calorific value. At a high SF, no pellets were made by torrefied biomass, or many defects were shown in the torrefied pellet, while the pellets were produced with good formation at a low SF.

Sewage sludge torrefaction in a fluidized bed reactor

Torrefaction of sewage sludge in a lab-scale fluidized bed reactor was studied in order to know if this pre-treatment could enhance the properties of this waste in subsequent thermochemical processing, such as pyrolysis. The influence was studied of two important torrefaction operational parameters, temperature (220–320°C) and solid residence time (3.6–10.2min), on the product distribution and properties. Taking into account the operation conditions evaluated in this work, torrefaction temperature affects solid product properties at long solid residence times (longer than 6.1min) and that the effect of solid residence time is only significant at the highest temperature (320°C). Severe torrefaction conditions result in the release of bonded water which could enhance some properties of the liquid obtained in the ensuing pyrolysis process. However, the torrefaction pre-treatment also implies that part of the extractives is lost from the raw material. Compared to dry raw sewage sludge, the energy density of sewage sludge after torrefaction increases under certain conditions. The removal of H2O and CO2 during the torrefaction step reduces the O/C ratio in the torrefied solid up to 0.12 (66.70% reduction compared to 0.37 in raw sewage sludge) which could be a benefit for subsequent thermochemical treatments. For example, one of the main drawbacks of pyrolysis liquids is their high oxygen content.