Severity Of Torrefaction Research Articles

Catalytic pyrolysis of torrefied biomass with molecular sieve catalysts to produce hydrocarbon rich biocrude

AbstractThe downstream processing of biocrudes obtained from direct biomass pyrolysis poses significant challenges due to stability issues, necessitating costly upgrading for further coprocessing with refinery feeds. This study examines the impact of torrefaction pretreatment on pyrolysis product distribution and biocrude composition using sawdust (SD) and groundnut shell (GS) feeds. Torrefaction was conducted at varying temperatures (200, 250 and 300°C) for 30 min under different reactor conditions. Increasing the severity of torrefaction resulted in decreased biocrude yields with reduced water content and gas formation, particularly evident with GS. A torrefaction temperature of 250°C and 30 min of pretreatment yielded higher phenolics and hydrocarbons. This increase in phenolics can be attributed to lignin enrichment during torrefaction, which, in the presence of a catalyst, undergoes deoxygenation leading to hydrocarbon formation. The influence of feed particle size, whether in powder or pellet form, on biocrude yield and composition was found to be minimal. Catalytic pyrolysis of SD using molecular sieve catalysts yielded the highest hydrocarbon (42%) and aromatic content (44%) at catalyst to biomass ratios of 1:1 and 2:3. The combination of torrefaction and pyrolysis was shown to enhance the quality of biocrude by increasing its hydrocarbon content, but at the expense of lower liquid yields. Experimental observations were supported by statistical analysis tools such as principal component analysis, which assessed pyrolysis product yields and composition.

Effect of oxidative torrefaction on the pyrolysis of Clitocybe maxima stipe: Pyrolysis behaviour, and products' properties

In this study, oxidative torrefaction (OT) was used as the pretreatment process for the pyrolysis of Clitocybe maxima stipe (CMS) which is one kind of typical mushroom wastes, in order to evaluate the influence of OT on pyrolysis behaviour of torrefied CMS and products’ properties. The experimental results demonstrated that OT enhanced the degree of aromatization, and improved the thermal stability of the torrefied CMS compared with inert torrefaction (IT). The biochar (T9-P700) obtained by OT (9% oxygen) coupled pyrolysis (700 °C) had the improved pore structure with the highest specific surface area of 661.61 m2/g, while the obtained liquid products were less acidic with an increased formation of N-containing compounds (up to 19.15%) and phenolic compounds (8.08%). Furthermore, T9-P700 had a higher adsorption efficiency and adsorption capacity (147.31 mg/g) for Pb(Ⅱ). C-O, CO, -COOH, and -OH on the obtained biochar participated in the adsorption process of Pb(Ⅱ), attributing to the adsorption mechanism interpreted as physical adsorption, precipitation, and functional group complexation. Higher oxygen concentrations increased the severity of torrefaction, which facilitated a better pore structure in the CMS biochar generated during the subsequent pyrolysis process and the generation of liquid products with better qualities. Therefore, OT coupled pyrolysis may be an effective way to improve the quality of pyrolysis products.

Torrefied herb residues in nitrogen, air and oxygen atmosphere: Thermal decomposition behavior and pyrolytic products characters

The thermal decomposition behavior and pyrolytic products characters of herb residue (HR) torrefied in N2, air and O2 were investigated in present work. The clear gradual regularity of samples in Van Krevelen diagram exhibited the severity and some similarities of torrefaction. The activation energy (E) calculated by distributed activation energy model (DAEM) found that the E values of torrefied samples was higher than raw HR if the conversion is below 0.8. Torrefaction treatment would beneficial to increase the yield of gas but inhibit the formation of oil, and the compounds of gas and bio-oil under different torrefaction conditions are also quite different. It should be noticed that the presence of oxygen in the torrefaction atmosphere would reduce the torrefaction temperature significantly, while maintaining the severity of torrefaction and pyrolytic products distribution.

Co-pyrolysis of different torrefied Chinese herb residues and low-density polyethylene: Kinetic and products distribution

In present work, the synergistic effects during co-pyrolysis of low-density polyethylene (LDPE) and torrefied Chinese herb residues (CHR) have been investigated by thermogravimetric analysis. The kinetic parameters of co-pyrolysis were calculated by Coats-Redfern method, and the difference values of experiment and theoretical were also investigated for gas and oil compounds. The results show that the extent of synergistic or inhibitory effects of co-pyrolysis was connection with the severity of CHR torrefaction, and the activation energy depend on the blend ratio of LDPE and CHRs. In addition, co-pyrolysis tends to generate more small molecule products and reduce oil yield, and increase the CO content but decreases CH4 in the gas product. The results also found that the liquid products have a significant interaction during the co-pyrolysis process, because the content of aliphatic hydrocarbons and alcohols in the blends pyrolysis oil has been greatly increased, and improving the quality of oil.

Combustion and Kinetics Parameters Investigation of Raw and Torrefied Cocoa Pod Shells by Thermogravimetric Analysis

Torrefaction is one of the techniques to produce solid fuel from cocoa pod shell (CPS). In this research, changing combustion characteristic and kinetics of CPS after torrefaction process was investigated using Coats – Redfern Method. Torrefied CPS processed at temperatures of 200, 250, and 300°C and holding times of 0, 30, 60, and 90 min were used in this investigation. The results proved that the ignition and burnout temperatures shifted to higher value, while the peak mass loss rate tend to lower value when the torrefaction temperature and the holding time increased. The period of volatile release during the combustion process was shorter along with longer holding time and higher temperature of torrefaction. The maximum mass loss rate of raw CPS was 0.12005 g/min, while torrefied CPS has range between 0.046 to 0.114 g/min. The maximum mass loss rates of all samples decrease with increasing fuel ratio (FR). The activation energy increases gradually with increasing severity of torrefaction. The value of activation energy in the devolatilization and volatile combustion stage is greater compared to that of the char combustion stage.

Carbon dioxide torrefaction of oil palm empty fruit bunches pellets: characterisation and optimisation by response surface methodology

The carbon dioxide (CO2) torrefaction of oil palm empty fruit bunch (OPEFB) pellets was investigated at various temperatures from 250 to 300 °C and residence times from 15 to 60 minutes. The objective was to investigate the effects of CO2 torrefaction on the yield and characteristics of the torrefied products. The optimal conditions for maximum mass yield (MY) of CO2 torrefaction were also examined by response surface methodology (RSM) using full factorial design. Results revealed that temperature and time significantly influenced the mass (MY), liquid (LY) and gas (GY) yields. The MY and energy yield (EY) decreased with increasing severity of torrefaction, whereas the LY, GY, energy density (DE) and higher heating value (HHV) increased during the process. Characterisation revealed substantial improvements in the microstructure, pH, hydrophobicity and grindability of the torrefied pellets compared with the raw pellets. The thermal ignition and degradation characteristics of the OPEFB pellets were also significantly transformed after torrefaction. The liquid torrefaction products contained an acidic, turbid and pungent mixture of water and organic compounds. RSM optimisation revealed the optimal conditions: temperature of 275 °C and residence time of 35 minutes with the predicted MY of 50.54%, mass loss of ML = 49.46% and HHV = 24.47 MJ/kg. The findings revealed that CO2 torrefaction is a practical approach to clean energy recovery.

Upgrading rice husk via oxidative torrefaction: Characterization of solid, liquid, gaseous products and a comparison with non-oxidative torrefaction

In this study, oxidative torrefaction and non-oxidative torrefaction of rice husks were performed under different severities, and the effects of temperature (220–300 °C) and O2 concentration (0–15 vol%) on the properties of the solid, liquid, and gas products were investigated. Oxidation of hydrocarbons play an important role in thermal degradation of samples, and higher O2 concentration promotes the severity of torrefaction. Oxygen content in rice husk decreased whether the torrefaction temperature increased or the O2 concentration increased. Consequently, the H/C and O/C ratios as well as the mass and energy yield of the sample remarkably decreased, even at small O2 concentrations of 2%.Gas yield in the oxidative torrefaction process was higher than that in non-oxidative torrefaction. CO2 was the dominant gas, and volume fraction of CO2 further increased during oxidative torrefaction. This may be contributed to enhanced thermal degradation of rice husk and to the combustion reaction between CO and O2, especially at a higher torrefaction temperature and with a higher concentration of O2. In the case of liquid products, acids and phenolswerethe dominant organic components. However, formation of water and acetic acid was promoted, whereas the presence of O2 inhibited generation of levoglucosan. On the basis of products distribution and the evaluation of O2 that participates in torrefaction, it was concluded that O2-containing atmosphere could be a potential agent to replace a pure N2 atmosphere, which may reduce operational costs and make biomass torrefaction more commercially feasible.

Optimizing the torrefaction of pigeon pea stalk (cajanus cajan) using response surface methodology (RSM) and characterization of solid, liquid and gaseous products

Response surface methodology was employed to determine the optimum condition for the torrefaction of pigeon pea stalk. Based on the statistical analysis, the effect of operating parameters on responses (HHV and energy yield) was temperature > residence time > heating rate. The optimum condition for maximum HHV and maximum energy yield was obtained at 248.20 °C, 60 min, and 16.03 °C/min, with desirability being 54.0%. The HHV and energy yield at optimum conditions were 21.15 MJ/kg and 78.80%, respectively. The HHV and fixed carbon increased by 25.07% and 185.86% respectively, whereas oxygen content decreased by 13.05%, at optimum condition. Scanning electron microscope and Fourier transform infrared spectroscopy analysis confirmed the effect of torrefaction on the physicochemical properties of biomass. X-ray diffraction pattern revealed a decrease in Crystallinity index value from 39.39% to 22.28% for torrefied biomass at optimum condition. Water content in the liquid products decreased with increasing severity of torrefaction. Gas chromatograph-mass spectrometry analysis confirmed the presence of phenol, furan, and ketones derivatives along with acetic acid in the liquid product obtained from torrefaction. Non-condensable gases mainly consisted of CO and CO2. At optimum condition, concentrations of H2, CO, and CO2 were 2.79, 29.78, and 67.43 vol %, respectively.

Functional mapping of torrefied product characteristics with index of torrefaction

Torrefaction converts raw biomass into a product with higher energy density, higher fixed carbon, better grindability, HHV and longer shelf life. The extent of improvement in these and other properties can be governed by appropriately regulating the reactor operating conditions for a specified biomass. The industrial applications ranging from biofuels to chemicals have different priorities for the specific characteristics of the torrefied biomass. Some of the earlier studies on torrefaction have quantified the overall process performance by defining a parameter or index for the degree or severity of torrefaction. However, very few attempts have been made to relate the torrefaction severity to the properties of the torrefied biomass. In this paper, we have simplified the reference condition for earlier proposed definition of index of torrefaction (Basu et al. [1]) and showed that there exists a quantifiable functional relationship between the defined index and the characteristics of the torrefied biomass. The mapping co-relations depend on the type of biomass feedstock, and the index informs the type of biomass appropriate for a specific application. While this paper focuses only on classical torrefaction characteristics such as energy density, proximate and elemental analyses, and batch and continuous grindability, this analysis can be generalized to quantify other non-classical characteristics such as densification, cooking fuel characteristics, and biochar-soil interactions.

Torrefaction of biomass macroalga Ulva intestinalis using TGA

The torrefaction of Malaysian marine biomass specie called Ulva intestinalis was studied using thermogravimetric analyser (TGA). The torrefaction temperature and residence time were varied in the range of 200 – 300 °C and 30 – 90 minutes, respectively. The chemical functional groups in the torrefied U. intestinalis were identified by Fourier transform infrared (FTIR). TGA results showed that the torrefaction temperature has a greater influence on the weight loss and changes in the U. intestinalis’s properties after the torrefaction as compared to the torrefaction time. The increased in fixed carbon (FC), and carbon (C) content and decreased in volatile matter (VM), moisture content (MC) and oxygen (O) with the severity of torrefaction reflects the improvement of calorific values for the torrefied U. intestinalis. Analysis of the FTIR showed that the torrefaction decreased the spectra intensity of the main functional groups (O-H, C=C, C-O and C-H) as a consequence of structural alteration within the biomass. The present findings may provide useful information for the development of industrial torrefaction processes to turn U. intestinalis into a carbon enrichment solid fuel.

Torrefaction and combustion behaviour of beech wood pellets

Use of renewable sources is still a crucial option for energy supply in view of environmental consequences of fossil fuel-dependent industry. Today, only 10% of world’s energy needs have been met by biomass sources. This is lower than expectations considering vast interest on biomass energy and necessitates more practical approaches to substitute fossil fuel usage. Torrefaction is a promising technique to obtain coal-like solids which can be incorporated into today’s power systems. In this study, torrefaction of beech wood sawdust pellets and their combustion behaviour were investigated using a vertical furnace with a wire mesh basket and necessary equipments. Torrefaction experiments were made as a poly-particles bed in the basket under nitrogen flow and at 493, 533 and 573 K temperatures corresponding to light, mild and severe conditions, respectively. Combustion experiments, however, were carried out by recording mass of single raw or torrefied burning pellet under natural convection airflow at 873, 973 and 1073 K temperatures. It was observed that mild torrefaction was appropriate to obtain a torrefied product retaining over 75% mass of raw pellets but having calorific values higher than most lignite. Volatiles ignition times of torrefied pellets were affected by their moisture contents. This effect lessened with increasing temperatures due to faster heating of pellets. Although torrefied pellets became more porous as severity of torrefaction increased, their carbon combustion rates were generally lower than those of raw pellets and decreased with combustion temperature as well as torrefaction severity.

Comparing severity of continuous torrefaction for five biomass with a wide range of bulk density and particle size

This study presents five continuous torrefaction experiments using five lignocellulosic biomass feedstocks: coppiced willow, wheat straw, cattail (typha), moringa leaf, and spruce pellets. Experiments were conducted in a horizontal moving bed pilot plant operating at 250 °C and 6.8–10 min residence time to evaluate the flexibility of this torrefaction reactor. Differences in particle mass, bulk density, and physical form were examined as to how they affect the severity of torrefaction.Torrefaction mass yield for these experiments ranged from 73.7 wt% (moringa) to 91.2 wt% (spruce pellets), increasing with particle mass and bulk density. Individual particle mass had the most direct linear correlation to mass yield, while the bulk density correlated indirectly to mass yield through mass feed rate for 4/5 biomass; Ym = 0.35Q+0.7 (R2 = 0.98).Wheat straw was the outlier in both correlations, having significantly higher mass yield than expected. The long, slender shape and resulting low sphericity are thought to limit heating and mass loss for this feedstock.These and other experiments along with the correlations presented illustrate the flexibility of the horizontal moving bed pilot plant; a wide range of biomass particle size, and form can be accommodated; however some shapes/forms of biomass may limit mass loss.

Effect of torrefaction on the physicochemical properties of pigeon pea stalk (Cajanus cajan) and estimation of kinetic parameters

Torrefaction of biomass is an important preprocessing step which increases energy density and higher heating value. Torrefaction of pigeon pea stalk has been carried out in a tubular quartz reactor at different temperatures under nitrogen atmosphere. DT-TGA data have been used to predict the pyrolysis behavior and in estimating kinetic parameters using Arrhenius method. The effect of temperature was more pronounced as compared to residence time on the yield of solid product during torrefaction. Both O/C ratio and H/C ratios have decreased with increase in temperature. There was 28.6% increase in HHV of torrefied biomass at 275 °C and 45 min residence time as compared to raw biomass. There has been increase in energy density for torrefied biomass as compared to raw biomass. Moisture reabsorption, loose and tapped bulk density decreased for torrefied biomass as compared to raw biomass. For pigeon pea stalk Carr Compressibility index has decreased and Hausner Ratio has increased, resulting in lesser compactability and improved flowability respectively for torrefied biomass. Torrefied pigeon pea stalk exhibited better combustible properties. The activation energies of hemicellulose and cellulose have been decreased by 32.5% and 28.2% due to severe torrefaction. The contribution factor for hemicellulose decreased with increasing severity of torrefaction.

Determining the Severity of Torrefaction for Multiple Biomass Types Using Carbon Content

This research concerns the investigation of an alternative measurement to directly indicate the severity of torrefaction. Composition and process data from both batch and continuous torrefaction experiments using willow, wheat straw, and cattail biomass were combined and analyzed. The mass yield, which is an indication of torrefaction severity was correlated to the net change in residual carbon concentration (ΔC), and second the total change in mass (ΔMt) was correlated to net change in mass of carbon per 100 g of feedstock (ΔMc). Analysis of the experimental data show a polynomial relationship between the dry mass yield (Ym) and the change residual carbon concentration (ΔC). This relationship is Ym = 5.05ΔC2 – 3.96ΔC + 0.98 (R2 = 0.89). The uncertainty in this correlation is ±7.3% (w/w). The relation between total change in mass (ΔMt) and change in carbon mass (ΔMc) meanwhile was found to fit a linear model by ΔMc = 0.36ΔMt + 1.04 with a coefficient of determination of 0.96. Each of these models was then...

Ultrasonic pelleting of torrefied lignocellulosic biomass for bioenergy production

Abstract Torrefaction has been explored to increase the heating value and hydrophobicity of biomass. Pellets made from torrefied biomass can be used as a high-quality feedstock in gasification and as a substitute for coal in power plants. One existing challenge is that pelleting torrefied biomass is more difficult under the same operating conditions as used for pelleting untreated biomass. To address this challenge, this study employed ultrasonic vibration as an assistance to densify torrefied wheat straw biomass into pellets. Biomass with different severities of torrefaction was produced. Pellet properties and pelleting energy consumption were investigated. It was found torrefied wheat straw biomass could be densified into pellets of good quality with the assistance of ultrasonic vibration; whereas, with the same pelleting pressure but without ultrasonic vibration, good pellets could barely be made. It was also observed that the densities of torrefied biomass pellets were lower than the untreated biomass pellets. However, pellets made from biomass torrefied at a higher temperature had a higher durability. It was also found the energy density and heating value were enhanced as the severity of torrefaction increased. In addition, the energy consumption for pelleting torrefied biomass was higher than untreated biomass under the same pelleting condition.

Uncovering Structure–Reactivity Relationships in Pyrolysis and Gasification of Biomass with Varying Severity of Torrefaction

The objective of this study is to establish the structure–reactivity relationships in pyrolysis and gasification of biomass with varying severity of torrefaction. Pine was torrefied in a bench scale tubular reactor with varying torrefaction temperature (220–300 °C). The structural alterations in torrefied pine and its derived biochar were characterized by solid-state nuclear magnetic resonance spectroscopy (NMR) and Raman spectroscopy, respectively. The effect of torrefaction severity, as well as the resulting structural changes in pine, upon subsequent pyrolysis and gasification reactivity were systematically studied. The experimental results showed that the pyrolysis reactivity of pine was promoted by torrefaction, whereas the gasification reactivity of biochar derived from pine was reduced by torrefaction. The results were mainly attributed to the severe degradation, polycondensation, and carbonization of hemicellulose and lignin fractions during torrefaction of pine. The pyrolysis and gasification rea...

Reactor scale study of self-heating and self-ignition of torrefied wood in contact with oxygen

This experimental work aims at investigating the potential development of self-heating when torrefied wood chips enter into contact with oxygen. Two kilograms of dried beech chips have been torrefied under nitrogen in a cylindrical reactor at 250 °C or 285 °C. The temperature was then leveled down between 100 °C and 160 °C and nitrogen flow was replaced by oxygen-containing flow. Influences of oxygen volumetric fraction and sweeping gas flow rate were investigated. Temperatures at different bed locations and gaseous product volumetric fractions at the bed output were monitored continuously. In some of the experiments a limited temperature rise was observed while in others a temperature runaway occurred. Thermal considerations indicate a clear enhancement of self-heating propensity with the severity of torrefaction. Gas phase analysis and molecule oxygen balance reveal an adsorption mechanism pathway and a higher rate of oxygen adsorption for the severely torrefied wood. Lowering the oxygen volumetric fraction or increasing the flow rate decrease self-heating behavior and was used to stop self-ignition of the bed.

Effect of torrefaction temperature on lignin macromolecule and product distribution from HZSM-5 catalytic pyrolysis

Torrefaction is a low-temperature process considered as an effective pretreatment technique to improve the grindability of biomass as well as enhance the production of aromatic hydrocarbons from Catalytic Fast Pyrolysis (CFP). This study was performed to understand the effect of torrefaction temperature on structural changes in the lignin macromolecule and its subsequent influence on in-situ CFP process. Lignin extracted from southern pine and switchgrass (via organosolv treatment) was torrefied at four different temperatures (150, 175, 200 and 225°C) in a tubular reactor. Between the two biomass types studied, lignin from pine appeared to have greater thermal stability during torrefaction when compared with switchgrass lignin. The structural changes in lignin as a result of torrefaction were followed by using FTIR spectroscopy, solid state CP/MAS 13C NMR, 31P NMR spectroscopy and it was found that higher torrefaction temperature (200 and 225°C) caused polycondensation and de-methoxylation of the aromatic units of lignin. Gel permeation chromatography analysis revealed that polycondensation during torrefaction resulted in an increase in the molecular weight and polydispersity of lignin. The torrefied lignin was subsequently used in CFP experiments using H+ZSM-5 catalyst in a micro-reactor (Py-GC/MS) to understand the effect of torrefaction on the product distribution from pyrolysis. It was observed that although the selectivity of benzene-toluene-xylene compounds from CFP of pine improved from 58.3% (torrefaction temp at 150°C) to 69.0% (torrefaction temp at 225°C), the severity of torrefaction resulted in a loss of overall aromatic hydrocarbon yield from 11.6% to 4.9% under same conditions. Torrefaction at higher temperatures also increased the yield of carbonaceous residues from 63.9% to 72.8%. Overall, torrefying lignin caused structural transformations in both type of lignins (switchgrass and pine), which is ultimately detrimental to achieving a higher aromatic hydrocarbon yield from CFP.

Torrefaction of bamboo under nitrogen atmosphere: Influence of temperature and time on the structure and properties of the solid product

Torrefaction of bamboo was performed in a horizontal tubular reactor under nitrogen atmosphere at 220, 240, 260, and 280°C for 10, 30, and 60min, respectively. It was found that with an increase of the severity of torrefaction, the mass yield and energy yield decreased while the high heating value increased. Due to the release of hydroxyl groups, the torrefied bamboo became more hydrophobic and the maximum content of absorbed moisture was reduced by 53.89%. The elemental components of torrefied bamboo tended to that of coal since carbon content was enriched with the increase of torrefaction severity. The removal of hemicelluloses and the enrichment of lignin produced samples with more uniform quality. This study suggested that torrefaction of bamboo under nitrogen produced a good feedstock for the application in burning.

Thermal behaviour and kinetic study for woody biomass torrefaction and torrefied biomass pyrolysis by TGA

The thermal decomposition behaviour and kinetics of Douglas fir sawdust torrefaction and torrefied sawdust pyrolysis were investigated using a thermogravimetric analyser (TGA). The mass loss of samples in torrefaction was highly related to the torrefaction temperature. The two-step reaction model fitted well for Douglas fir sawdust torrefaction. The activation energies of the first and second reaction stages were 112 kJ mol−1 and 150 kJ mol−1, respectively. Torrefied biomass exhibited different thermo decomposition behaviours compared to untreated biomass. The start point of torrefied biomass decomposition was shifted and the degree of shift increased with the severity of torrefaction. The final biochar yield of torrefied biomass was also increased with the increase of torrefaction temperature. Derivative thermogravimetric (DTG) curves showed that the shoulder of hemicelluloses decomposition in torrefied biomass pyrolysis was eliminated. The decomposition rate of torrefied biomass has a decreasing trend due to the mass depletion in torrefaction. A first-order one-step global model with the average activation energies in the range of 195–204 kJ mol−1 can describe the raw and torrefied biomass pyrolysis. The kinetic analysis also showed that the torrefied biomass pyrolysis from high torrefaction temperature might be multiple-step reactions.