Influence Of Torrefaction Research Articles

Effect of torrefaction on the properties of rice straw high temperature pyrolysis char: Pore structure, aromaticity and gasification activity

The influence of torrefaction on the physicochemical characteristics of char during raw and water washed rice straw pyrolysis at 800–1200°C is investigated. Pore structure, aromaticity and gasification activity of pyrolysis chars are compared between raw and torrefied samples. For raw straw, BET specific surface area decreases with the increased torrefaction temperature at the same pyrolysis temperature and it approximately increases linearly with weight loss during pyrolysis. The different pore structure evolutions relate to the different volatile matters and pore structures between raw and torrefied straw. Torrefaction at higher temperature would bring about a lower graphitization degree of char during pyrolysis of raw straw. Pore structure and carbon crystalline structure evolutions of raw and torrefied water washed straw are different from these of raw straw during pyrolysis. For both raw and water washed straw, CO2 gasification activities of pyrolysis chars are different between raw and torrefied samples.

Influence of torrefaction on the characteristics and pyrolysis behavior of cellulose

The influence of torrefaction on cellulose structural characteristics and the resulting pyrolysis behavior was investigated in this study. Torrefaction reduced O/C ratio in cellulose and increased its high heating value. The crystallinity of cellulose increased slightly first and then decreased sharply with the increase of torrefaction temperature, which could be ascribed to competitive degradation between crystalline region and amorphous region, as indicated by 13C CP/MAS NMR analysis. Besides, the cleavage of β-1,4-glycosidic bond and the dehydration of hydroxyl were the major reactions occurring in torrefaction. Avrami-Erofeev model was found to be the most suitable kinetic reaction model for explaining the thermogravimetric weight loss during the pyrolysis of the raw and torrefied cellulose. A distributed activation energy model based on Avrami-Erofeev model was subsequently used to reveal the pyrolytic kinetics. It was found that the changes in cellulose structure influenced the kinetic parameters greatly. Torrefaction also changed pyrolytic product distribution. The yields of furfural, alicyclic ketones and anhydrosugars increased while that of 5-hydroxymethyl-furfural decreased as torrefaction temperature increased.

Influence of Torrefaction on Single Particle Combustion of Wood

This study focuses on the influence of torrefaction on the char reactivity, char yield, and combustion time of 3–5 mm spherical wood particles in a single particle combustion reactor (SPC) operating at a nominal temperature of 1231 °C. The devolatilization times were reduced and the char burnout times were increased with increasing torrefaction degree. The devolatilization time depended linearly on the particle mass. The torrefaction pretreatment resulted in a marked increase in char yield and char particle density but no intrinsic reactivity change as determined by thermogravimetric analysis. The char yield and char particle density increased from 9 wt % and 123 kg/m3 for raw particles to 14 wt % and 259 kg/m3 for particles pretreated at 290 °C for 4 h. The results of this study demonstrate that the higher char yield and density are the main reasons for the longer combustion time of torrefied wood.

Furniture wood waste as a potential renewable energy source

In this study, the combustion behavior of raw waste wood from furniture and samples torrefied at temperatures of 473, 513, 553 and 593 K was investigated. TG-DTG analysis showed that the mass loss in the first stage of the process decreased with the temperature of torrefaction, whereas the temperature in the second stage increased. The influence of torrefaction and combustion parameters on greenhouse gas emissions were investigated by the FTIR technique. The characteristic combustion parameters were also determined. The ignition temperatures for the furniture wood waste and samples torrefied at 473, 513 and 553 K from 549 to 559 K, whereas that of the sample torrefied at 593 K was significantly higher (600 K). All samples were completely burnt at 813–843 K, after 29–35 min, depending on the torrefaction temperature. Kinetic parameters are determined using a two-step first-order reaction. The activation energy value for the first stage increased with the increasing temperature of torrefaction, from 68 to 125 kJ mol−1, whereas the temperature in the second stage decreased from 108 to 47 kJ mol−1. A similar correlation was observed for the pre-exponential value A. In the case of the torrefied furniture wood waste at 593 K, the combustion process runs as a single first-order reaction. The calculated data were fitted to the experimental data very accurately (R 2 > 0.9992 and standard deviation <6.7 %), and the kinetic model was correctly founded. The linear relationship between logA and E a provides a way to predict the kinetic parameters of the combustion process.

Influence of Torrefaction on Biomass Gasification Performance in a High-Temperature Entrained-Flow Reactor

In the present work, the gasification performances of two pairs of raw and torrefied biomasses, including raw forest residue and torrefied forest residue, and raw spruce and torrefied spruce in a high-temperature entrained-flow reactor, are numerically examined and compared to each other using a Eulerian–Lagrangian CFD model developed based on OpenFOAM. Moreover, the sensitivities of three important operating parameters (excess air ratio, steam/carbon molar ratio, and biomass particle diameter), which vary in the range of practical significance, are also tested. The calculated results are analyzed both qualitatively and quantitatively by five indicators: isothermal profiles, char consumption rate, gas compositions, species yield, and carbon conversion along the reactor length. The obtained results show that torrefied biomass can increase the maximum temperature in the reactor as compared to its raw parent fuel. During gasification, CO, H2, and CO2 are the major species in the product gas and CH4 accounts ...

CO2 gasification rates of char particles from torrefied pine shell, olive stones and straw

Single char particles with a diameter of 8 mm were produced in situ from pellets of raw and torrefied pine shell, olive stones and straw. The single char particles were then gasified at 800, 900 and 1000 °C in two or three CO2 concentrations at each temperature. In the experiments, CO concentrations were measured from the product gases. From the measured CO concentrations, the char conversions versus time were determined. The reactivity of the char from the torrefied olive stones was lower than the reactivity of the char from the raw olive stones, while the reactivity of the char from the torrefied straw was higher than the reactivity of the char from raw straw. For the raw and torrefied pine shell the char reactivities were similar. At 900 °C the influence of torrefaction on char gasification rates was minor, however, since the conversion occurred under Regime II conditions, i.e., the conversion rate is partly limited by mass transfer. A detailed single particle model, taking into consideration mass transfer effects, was used to extract kinetic parameters from the experimentally determined char conversions. For the six chars, activation energies of the adsorption step were in the range 175 and 285 kJ/mol, while activation energies of the desorption step were in the range 145 and 195 kJ/mol. In the study it was also tested whether the char conversion could be computed with unified activation energies for all the chars. The results show that by using unified activation energies – 240 kJ/mol for the adsorption step and 168 kJ/mol for the desorption step – the computed char conversions were in good agreement to the experimental char conversions.

Biomass gasification: Influence of torrefaction on syngas production and tar formation

The paper contains results of comparative gasification of standard wood biomass pellets, torrefied pellets and sawdust in a robust industrial fixed-bed gasifier. Parameters such as process stability, operating difficulties, gas parameters and tar content in syngas were analysed. The operating conditions were optimised to maximise production of liquid hydrocarbons, which can be both a problematic by-product and a valuable component. In order to collect the data concerning quantity and composition of the tars, the experimental set-up was equipped with a syngas cooler.The test runs conducted with sawdust and ordinary pellets did not cause any operational problems. The most complicated part of the experiment was maintaining process stability during gasification of torrefied pellets. The stabilisation effect of grinding of torrefied pellets and blending these pellets with wet sawdust were tested. It was concluded that effective and stable gasification of torrefied pellets in the tested type of fixed-bed gasifier is possible, but this type of fuel is much more suitable for co-gasification.The cleaned syngas from standard pellets had a relatively stable composition and calorific values in the range of 4.8–5.6MJ/Nm3. Cold gas efficiencies of the process were in the range of 0.72–0.77MJ/Nm3. Using torrefied pellets as a feedstock led to a higher calorific value of syngas, but the cold gas efficiency remained similar (0.75). For sawdust both the calorific value of syngas (LHV=3.0MJ/Nm3) and cold gas efficiency (0.57) were significantly lower than for pellets. The collected condensates contained a water fraction with dissolved organic compounds and thick viscous organic substances tar. It was observed that tar production from torrefied pellets is slower, characterised by lower yield, and technically more difficult in comparison to untreated biomass. The effectiveness of liquid hydrocarbon collection (tar to fuel ratio) varied between 0.0138 [kgtar/kgfuel] for torrefied pellets and 0.0213 [kg/kg] for sawdust. The main component of water fractions were organic acids. The content of organic acids in these fractions was as follows: 79.5% from South African pellets, 67% from Polish pellets, 64% from Polish sawdust and 59% from torrefied pellets respectively. The main organic species in tar from torrefied biomass remained acids, whereas in other cases tars were composed of alkylophenols, linear and cyclic aliphatic oxygenates and polyfunctional aromatic oxygenates.

Influence of torrefaction on the devolatilization and oxidation kinetics of wood

Devolatilization and oxidation kinetics of torrefied wood have been studied by evaluating thermogravimetric curves measured in nitrogen and air at various heating rates. Samples consist of Norway spruce wood chips torrefied at several process temperatures and residence times. Data about untreated wood have also been obtained for comparison. Measured curves are well predicted by means of a five-reaction mechanism, consisting of three devolatilization reactions for the pseudo-components hemicellulose, cellulose and lignin and, in air, of two additional reactions for char devolatilization and combustion. The torrefaction pre-treatment only requires model modifications in the amounts of volatiles generated from the decomposition of pseudo-components, indicating that only their relative percentages and not their reactivities are modified. On the other hand, a slightly different thermal stability is found for the char generated from torrefied wood, which results in higher activation energy and lower reaction order for the oxidation step. Hence torrefaction conditions can affect the subsequent conversion characteristics of the char product.

Influence of torrefaction on some chemical and energy properties of maritime pine and pedunculate oak

This study investigated the influence of heat treatment on the chemical composition and energy properties of maritime pine (Pinus pinaster) and pedunculate oak (Quercus robur). Samples were treated in a new experimental device at 220, 250, or 280 °C for 1 or 5 hours. Chemical and energy analyses were performed using standard methods. Our results clearly demonstrated an increased degradation of the material due to the combined effects of temperature and treatment duration. This mass loss was basically due to degradation of acid-soluble materials. The energy analysis showed that the fixed carbon content and higher heating value increased, for both species, whereas the volatile matter content decreased with increased extent of treatment (cumulated effects of temperature and time). In the range of temperature and duration studied here, the dimensionless energy properties for both species obeyed the same functions of overall mass loss. The relationships obtained allow quantification of the increase in wood energy concentration due to torrefaction. Mass loss is an excellent indicator of treatment extent. Analytical expressions allowing the prediction of energy and chemical properties as a function of overall mass loss, within the range of treatment extents studied here, are provided.

Influence of torrefaction on the grindability and reactivity of woody biomass

The use of biomass to produce energy is becoming more and more frequent as it helps to achieve a sustainable environmental scenario. However the exploitation of this fuel source does have drawbacks that need to be solved. In this work, the torrefaction of woody biomass (eucalyptus) was studied in order to improve its properties for pulverised systems. The process consisted in a heating treatment at moderate temperature (240, 260, 280 °C) under an inert atmosphere. The grindability of raw biomass and the treated samples was compared and an improvement in the grindability characteristics was observed after the torrefaction process. Thermogravimetric analysis of the samples was carried out in order to study their reactivity in air. The DTG curves of the torrefied biomass showed a double peak nature. The kinetic parameters were calculated for each reaction stage. The torrefaction process was found to influence the parameters of the first stage, whereas those corresponding to the second remained unaffected.