Wood Char Research Articles

Kinetic modelling of steam gasification of various woody biomass chars: Influence of inorganic elements

A study was performed on the influence of wood variability on char steam gasification kinetics. Isothermal experiments were carried out in a thermobalance in chemical regime on various wood chars produced under the same conditions. The samples exhibited large differences of average reaction rate. These differences were linked neither with the biomass species nor age and may be related to the biomass inorganic elements. A modelling approach was developed to give a quantitative insight to these observations. The grain model was used on one biomass of reference for temperatures between 750 and 900°C and steam partial pressures between 0 and 0.27bar. The model was applied to the other samples through the addition of an integral parameter specific to each sample. A satisfactory correlation was found between this parameter and the ratio potassium/silicium. This result highlighted the catalytic effect of potassium and inhibitor effect of silicium on the reaction.

Effects of wood char and activated carbon on the hydrolysis of cellobiose by β-glucosidase from Aspergillus niger

Biochar amendments to soils have been suggested as a strategy to sequester carbon and therefore mitigate global climate change. The enrichment of soils with charred materials also increases their fertility. This fertilising effect of biochar may be caused by various mechanisms; an acceleration of nutrient cycling has been suggested as one such mechanism. The rate-limiting step in nutrient cycling is thought to be the extracellular enzymatic attack on biological macromolecules. In this study, therefore, the effects of chestnut wood char (specific surface area 2.0 m 2 g −1) and of activated carbon (specific surface area approximately 900 m 2 g −1) on an extracellular enzymatic reaction involved in the degradation of cellulose (i.e., hydrolysis of cellobiose by β-glucosidase from Aspergillus niger) were investigated. Cellobiose was not adsorbed by chestnut wood char, whereas activated carbon absorbed more than 97% of it. Both charred materials adsorbed more than 99% of β-glucosidase. For chestnut wood char, adsorption of the enzyme caused a decrease of approximately 30% in the reaction rate, whereas for activated carbon, the nearly complete absorption of both substrate and enzyme entirely inhibited the reaction. These results show that β-glucosidase from A. niger retains most of its activity when adsorbed to chestnut wood char and that the reaction it catalyses in nature is only slightly affected by this charred material. On the other hand, a material characterised by a high specific surface area and high porosity, such as activated carbon, can make even a highly soluble substrate unavailable for soil enzymes and therefore completely inhibit the reaction. Thus, charred materials may affect nutrient cycling mainly by regulating the availability of substrates: the degradation of highly soluble substrates may be accelerated by materials with low specific surface area, which maintain an active and protected enzyme pool, whereas materials with high specific surface and high porosity may slow down the degradation by making substrates unavailable.

Application of Response Surface Methodology for the Removal of Methylene Blue by Acacia Auriculiformis Scrap Wood Char

Application of Response Surface Methodology for the Removal of Methylene Blue by Acacia Auriculiformis Scrap Wood Char

Influence of Pyrolysis Temperature on Biochar Property and Function as a Heavy Metal Sorbent in Soil

While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood≪cottonseed hull≈grass≈pine needle≪broiler litter. To examine how biochar properties translate into its function as a heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to the surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.

Decomposition and gasification of pyrolysis volatiles from pine wood through a bed of hot char

Pine wood was pyrolyzed in a fixed bed reactor at a heating rate of 10°C and a final temperature of 700°C, and the resultant volatiles were allowed to be secondarily cracked through a tubular reactor in a temperature range of 500–700°C with and without packing a bed of char. The thermal effect and the catalytic effect of char on the cracking of tar were investigated. An attempt was made to deconvolute the intermingled contributions of the char-catalyzed tar cracking and the char gasification to the yields of gaseous and liquid products. It was found that the wood char (charcoal) was catalytically active for the tar cracking at 500–600°C, while at 650–700°C, the thermal effect became a dominant mode of the tar cracking. Above 600°C, the autogenerated steam gasified the charcoal, resulting in a marked increase in the yield of gaseous product and a significant change in the gas composition. An anthracite char (A-char), a bituminous coal char (B-char), a lignite char (L-char) and graphite also behaved with catalytic activities towards the tar cracking at lower temperature, but only L-char showed reactivity for gasification at higher temperature.

Sulfuric Acid Intercalation and Exfoliation of Nano Shell Carbon from Ni-catalyzed Wood Char

Sulfuric Acid Intercalation and Exfoliation of Nano Shell Carbon from Ni-catalyzed Wood Char

Char and char-supported nickel catalysts for secondary syngas cleanup and conditioning

Tars in biomass gasification systems need to be removed to avoid damaging and clogging downstream pipes or equipment. In this study, Ni-based catalysts were made by mechanically mixing NiO and char particles at various ratios. Catalytic performance of the Ni/char catalysts was studied and compared with performance of wood char and coal char without Ni for syngas cleanup in a laboratory-scale updraft biomass gasifier. Reforming parameters investigated were reaction temperature (650–850 °C), NiO loading (5–20% of the weight of char support), and gas residence time (0.1–1.2 s). The Ni/coalchar and Ni/woodchar catalysts removed more than 97% of tars in syngas at 800 °C reforming temperature, 15% NiO loading, and 0.3 s gas residence time. Analysis of syngas composition indicated that concentrations of H 2 and CO in syngas significantly. Furthermore, performance of the Ni/coalchar catalyst was continuously tested for 8 h. There was slight deactivation of the catalyst in the early stage of tar/syngas reforming; however, the catalyst was able to stabilize soon after. It was concluded that chars especially coal char can be an effective and inexpensive support of NiO for biomass gasification tar removal and syngas conditioning.

Material properties and external factors influencing the charring rate of solid wood and glue‐laminated timber

AbstractIn fire design of timber structures the charring rate of the material is a very important property, but the charring rate varies with the conditions in the fire compartment and the characteristics of the wood. Many experiments have been carried out through the years, trying to determine the effect of various properties on the charring rate of wood. This paper gives a summary of the material properties and external factors found in the literature to have the largest influence on the charring rate of exposed wood, i.e. the density, moisture content, chemical composition, grain orientation, permeability, scale effect, thermal exposure, char contraction, char oxidation, oxygen concentration and opening factor, resulting from experiments found in the literature. It has not been possible to determine which properties or factors have the most significant influence on the charring rate of wood, due to large differences between the test conditions and methods, wood species and measurement methods. There is a great need for further testing to determine the relative effect of these properties and factors, and international test methods need to be developed to enable comparison of results from research all over the world. More information about the most important properties and factors can help standardise the calculation of charring of wood, and improve the input to computer models for fire safety design. This will result in more economic fire design of wooden structures, as the calculated residual cross sections will be closer to reality. Copyright © 2010 John Wiley & Sons, Ltd.

Synthesis of Carbon-Encapsulated Metal Nanoparticles from Wood Char

Carbon-encapsulated metal nanoparticles were synthesized by thermal treatment of wood char, with or without transition metal ions pre-impregnated, at 900°C to 1,100°C. Nanoparticles with concentric multilayer shells were observed. The nanoparticles were analyzed by scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX) spectroscopy. The EDX spectrum showed that carbon was the dominant element in the shells. TEM and XRD analysis indicated that the generated carbon shells had structures similar to that of graphite with an average interplanar distance of 0.34 nm. The effects of temperature and pre-impregnation of metal ions on the yield of carbon-encapsulated metal nanoparticles were studied.

Woods Charred at Low Temperatures and Their Modification for the Adsorption of Cr(VI) Ions from Aqueous Solution

Despite being prepared at higher temperatures and involving greater energy consumption, activated carbons always show a smaller capacity and affinity towards the adsorption of Cr(VI) ions. After a brief review regarding Cr(VI) ion contamination and treatment, the preparation of a novel biosorbent from pyrolyzed wood char for Cr(VI) ion adsorption is described. Pyrolysis was conducted at temperatures within the range 200-350 °C, thereby helping to protect beneficial functional groups, saving energy and hence reducing costs. The influence of pH, concentration, adsorbent dosage, ionic strength and equilibration time on Cr(VI) ion adsorption by this biosorbent was investigated. It was shown that the char obtained at 200 °C possessed the highest Cr(VI) ion retention capacity (31.96 mg/g) but required the longest equilibration time (> 47 d). Coating the char with nano-scale iron oxide greatly improved its adsorption affinity towards Cr(VI) ions, with a higher adsorption affinity (Henry's law Kd = 2.988 l/mg) an...

Steam gasification reactivity of char from rapid pyrolysis of bio-oil/char slurry

A slurry of bio-oil and char originating from wood pyrolysis is a promising gasifier feed-stock because of its high energy density. When such a slurry is injected into a high temperature gasifier it undergoes a rapid pyrolysis yielding a char which then reacts with steam. The char produced by pyrolysis of an 80 wt% bio-oil/20 wt% char mixture at heating rates of 100–10,000 °C/s was subjected to steam gasification in a thermogravimetric analyzer. The original wood char from the bio-oil production was also tested. Gasification was conducted with 10–50 mol% steam at temperatures from 800 to 1200 °C. Reactivity of the slurry chars increased with pyrolysis heating rate, but was lower than that of the original chars. Kinetic parameters were established for a power-law rate model of the steam-char reaction, and compared to values from the literature. At temperatures over 1000 °C, the gasification rates appeared to be affected by diffusional resistance.

Can Chlorofluorocarbon Sorption to Black Carbon (Char) Affect Groundwater Age Determinations?

Although adsorption is not generally considered important in low f(oc) (fraction organic carbon) aquifers, we show that chlorofluorocarbon (CFC) adsorption to black carbon (BC) is sufficiently large to retard transport and affect groundwater ages obtained with CFCs. Sorption isotherms of CFC-11, -12, and -113 to synthetic wood char were nonlinear (Freundlich n = 0.71-0.94) while humic acid isotherms were linear. Moreover, sorption to char was 10-1000 times greater than to humic acid for all three CFCs at the lowest observed concentrations, C(w)/S approximately 10(-8)-10(-7). We used the observed isotherms for char and humic acid to represent sorption to BC and amorphous organic matter, respectively, in a dual mode model to estimate retardation factors for a low f(oc) aquifer (= 0.06% gC g(-1)). The estimated retardation factors for the char-containing aquifer (presumed BC fraction = 9% of f(oc)) were approximately 6.8-10.6 at C(w)/S = 10(-8) and >5 times those estimated assuming amorphous organic matter partitioning only. The results indicate that unless CFC adsorption to BC is evaluated in transport, the groundwater age determined may be biased toward older than true ages. The CFC data archived in BC-containing aquifers may contain information about its adsorbent properties that could be useful to predict retardation of other chlorinated organic contaminants.

A new experimental Continuous Fixed Bed Reactor to characterise wood char gasification

Two-stage fixed bed gasification is one of the most promising technologies for low and medium energy production from biomass. In industrial processes, control and optimisation is often based on constructor know-how rather than on an understanding of the mechanisms involved. We present a new original tool, the Continuous Fixed Bed Reactor (CFiBR), which was specifically designed and built to enable a fine understanding of the limiting stage of a gasifier: the char bed gasification zone. The reactor, the instrumentation, the operating procedure and set-up tests are described in detail. The potential of the reactor is demonstrated through the characterisation of the gasification of a continuous wood char bed. Temperature profiles and gas concentrations along the 65 cm bed were established and showed that the most reactive zone was the first 10 cm of the char bed. Accurate energy and mass balances provided relevant information regarding the contributions of the main reactions involved in the fixed char bed gasification process.

A simple expression for the apparent reaction rate of large wood char gasification with steam

A simple expression for the apparent reaction rate of large wood char gasification with steam is proposed. Large char samples were gasified under steam atmosphere using a thermo-balance reactor. The apparent reaction rate was expressed as the product of the intrinsic rate and the effective factor. The effective factor was modified to include the effect of change in char diameter and intrinsic reaction rate during the reaction. Assuming uniform conversion ratio throughout a particle, the simplified reaction scheme was divided into three stages. In the initial stage, the local conversion ratio increases without particle shrinkage. In the middle stage, the particle shrinks following the shrinking core model without change in the local conversion ratio. In the final stage, the local conversion ratio increases without particle shrinkage. The validity of the modified effective value was confirmed by comparison with experimental results.

Bioavailability of adsorbed phenanthrene by black carbon and multi-walled carbon nanotubes to Agrobacterium

Carbonaceous sorbents including black carbon (BC) and carbon nanotubes have attracted research attention around the world because of their effects on bioavailability of hydrophobic organic compounds (HOCs) in sediments and soils. In this research, 14C-labeled and unlabeled phenanthrene were spiked into three artificial sediments: (i) a sediment sample without amorphous organic carbon (OC) and with BC collected from the Yangtze River (BC-YR), (ii) a sediment without OC and with multi-walled carbon nanotubes (MWCNTs), and (iii) a sediment without OC and with fresh wood char. Biodegradation and mineralization of adsorbed phenanthrene by Agrobacterium and XAD-2 assisted abiotic desorption of adsorbed phenanthrene were studied. The results showed that microbes could utilize a fraction of adsorbed phenanthrene by BC and MWCNTs after aging for 21–40 d. With aging for 28 d, the biodegradation efficiencies of phenanthrene after incubation for 21 d were 83.8%, 73.5% and 54.2% for BC-YR, char and MWCNTs, respectively; with aging for 40 d, the mineralization rates of 14C-labeled phenanthrene after incubation for 25 d were 38.3%, 25.1% and 24.6%, respectively. The desorption and biodegradation processes showed similar residual concentration of phenanthrene. However, the biodegradation rates were higher than the desorption rates during the fast biodegradation stage, suggesting that bacteria could promote desorption or access and utilize the sorbed phenanthrene. The biodegradation and mineralization efficiencies of phenanthrene associated with MWCNTs were significantly lower than with BC ( p < 0.01), implying adsorption by MWCNTs may lead to a greater decrease of HOCs bioavailability in the environment.

Fragmentation Effect on Batches of Pine Wood Char Burning in a Fluidized Bed

Batches of Pinus pinea char particles with average diameters of 2.2, 2.8, and 3.6 mm were burned in a bubbling fluidized bed at temperatures of 600, 700, and 750 °C, with a velocities ratio U/Umf = 9. The results show that only primary fragmentation occurs with an average fragmentation ratio of 1.5. No effect of the secondary fragmentation phenomena is observed. The increase in the number of particles in the bed because of fragmentation is accounted over the burning time, and its effect is evaluated on the determination of the global combustion resistance.

Experimental analysis of cross-laminated timber panels in fire

Design models of timber structures in fire usually take into account the loss in cross-section due to charring of wood. For cross-laminated timber panels in fire only little information on charring is available. The paper describes and discusses the results of an extensive testing programme on the fire behaviour of cross-laminated timber panels under ISO-fire exposure. The fire tests were performed on the small horizontal furnace (1.0×0.8 m) at the Empa in Duebendorf. Particular attention is given to the comparison of the fire behaviour of cross-laminated timber panels with homogeneous timber panels. The results of the fire tests showed that the fire behaviour of cross-laminated timber panels is strongly influenced by the behaviour of the adhesive used for bonding the cross-laminated timber panels. Depending on the properties of the adhesives at elevated temperatures falling off of the charred layers was clearly observed during the fire tests, leading to increased charring rates in comparison to homogeneous timber panels. This is the same effect as observed for initially protected timber members after the fire protection has fallen off. For the specimens where no falling off of the charred layers was observed the fire behaviour was similar to that of homogeneous timber panels.

Effect of micropores diffusion on kinetics of CH 4 decomposition over a wood-derived carbon catalyst

In order to optimise hydrogen production from biomass gasification, catalytic conversion of methane contained in a surrogate biomass syngas (CH 4 14%; CO 19%; CO 2 14%; H 2 16%; H 2O 30%; N 2 7%) is investigated over a fixed bed of porous wood char as a function of temperature (800–1000 °C) and space time (1.6–6.2 min g L −1). Determination of Thiele modulus evidences a change of kinetic regime from chemically- to diffusion-controlled when the temperature increases; this finding is particularly relevant when porous chars having an average pore width of 1 nm are used as catalysts. Mass diffusion transfers are accounted for by a model introducing an internal effectiveness factor. Knudsen diffusion in micropores is shown to limit the conversion rate of methane per unit mass of catalyst, and explains why such a rate is not proportional to the BET surface area, especially when the latter is higher than typically 300 m 2/g. It is concluded that diffusion limitations in micropores should be taken into account, otherwise underestimated activation energy and intrinsic kinetic constant are obtained in some experimental conditions.

Wood/plastic copyrolysis in an auger reactor: Chemical and physical analysis of the products

Previous studies observed that slow copyrolysis of wood and plastic in enclosed autoclaves produced an upgraded raw bio-oil with increased hydrogen content. We now demonstrate that fast simultaneous pyrolyses of 50:50, w/w, pine wood/waste plastics in a 2 kg/h lab scale auger-fed reactor at 1 atm, with a short vapor residence time, generates higher heating value upgraded bio-oils. Three plastics: polystyrene (PS), high density polyethylene (HDPE) and polypropylene (PP) were individually copyrolyzed with southern yellow pine wood at 525, 450 and 450 °C, respectively, to generate modified bio-oils upon condensation. These liquids exhibited higher carbon and hydrogen contents, significantly lower oxygen contents, higher heats of combustion and lower water contents, acid values and viscosities than pine bio-oil. The formation of cross-over wood/plastic reaction products was negligible in the oils. Simultaneous pyrolysis process design requires using a temperature at which the plastic’s thermal decomposition kinetics produce vapors rapidly enough to prevent vaporized plastic from condensing on wood chars and exiting the reactor.

P209 木材のニッケル及び鉄触媒による二次炭化処理の効果(ポスター発表)

P209 木材のニッケル及び鉄触媒による二次炭化処理の効果(ポスター発表)