The influence of different chemical compositions in biomass on gasification tar formation

To elucidate the relationship between biomass composition and tar formation, forest residue sawdust, rich in lignin, and agriculture waste cornstalks, rich in cellulose, were gasified in a spout-fluidized bed reactor from 700 °C to 900 °C. Gel permeation chromatography (GPC) coupled with a photodiode array detector (PDA) and gas chromatography – mass spectrometry (GC–MS) were used to analyze the tar character. The GPC results showed that the molecular mass distribution of the gasified tars were unchanged, only the amount of each component changed when the temperature increased during gasification. The amount of heaviest molecular mass components decreased, while the lighter components increased with temperature. Sawdust tar and cornstalks tar both showed aromatic character, while cornstalks tar contained more aliphatic compounds than sawdust tar. The tar formation mechanism has been proposed from the experimental data analysis.     

Effects of step-deposition on structures and properties of transparent conducting aluminum-doped zinc oxide films prepared by DC magnetron sputtering

The 2 wt% aluminum-doped zinc oxide films (AZO) was sputtered on corning glass plate at temperatures of 30–200 °C by DC magnetron sputtering using ceramic target. The microstructures and electrical resistivity of thin films were investigated by scanning electron microscope (SEM) and the van der Pauw method. The optical transmittances of films were measured by UV visible spectrophotometer in the wavelength of 300–900 nm. It was found that the average optical transmittances of specimens were 88%. Highly oriented AZO films in the (0 0 2) direction was observed in specimens as increasing of the substrate temperature. The dense film increased as the temperature increases. In addition, craters of greater depth with more compactness were obtained by step-deposition. The lowest resistivity of 9×10⁻⁴ Ω cm with film thickness of 700 nm was found in specimen grown by step-deposition at 200 °C.     

Solid-phase crystallization of amorphous silicon on ZnO:Al for thin-film solar cells

The suitability of ZnO:Al thin films for polycrystalline silicon (poly-Si) thin-film solar cell fabrication was investigated. The electrical and optical properties of 700 -nm-thick ZnO:Al films on glass were analyzed after typical annealing steps occurring during poly-Si film preparation. If the ZnO:Al layer is covered by a 30 nm thin silicon film, the initial sheet resistance of ZnO:Al drops from 4.2 to 2.2 Ω after 22 h annealing at 600 °C and only slightly increases for a 200 s heat treatment at 900 °C. A thin-film solar cell concept consisting of poly-Si films on ZnO:Al coated glass is introduced. First solar cell results will be presented using absorber layers either prepared by solid-phase crystallization (SPC) or by direct deposition at 600 °C.     

Hydropyrolysis of a Turkish lignite (Tunçbilek) and effect of temperature and pressure on product distribution

The hydropyrolysis of a Turkish lignite (Tunçbilek) in a swept fixed bed reactor connected with a thermo-balance was performed at a heating rate of 3 °C/min up to 950 °C under 0.5 MPa, 1 MPa and 10 MPa hydrogen pressures. The formation rates of gaseous hydrocarbons, carbon oxides, water and tar were determined. The difference between the weight loss due to tar formation of the non-condensable total and the weight loss of the sample recorded continuously with the thermo-balance showed the corresponding curve of tar formation rate as a function of temperature. It was shown that the total conversion and the formation rate of the products during hydropyrolysis could be influenced by varying the pressure. On the other hand, the volatile matter evolved during pyrolysis was substantially increased in the presence of hydrogen and especially when elevated hydrogen pressure was used.     

Thermo-economic analysis for the optimal conceptual design of biomass gasification energy conversion systems

This study addresses the thermo-economic assessment of a mid-scale (20 MW_th,wood) wood gasification, gas cleaning and energy conversion process, with particular attention given to electricity generation costs and tar control. Product distributions were estimated with a parametric stoichiometric equilibrium model calibrated using atmospheric air gasification data. A multi-objective optimisation problem was defined for a superstructure of alternative energy flow diagrams for each processing step. The trade-off between total investment costs and the exergy efficiency of electricity production was obtained, and analysed to identify operating conditions that minimise tar formation to prevent equipment fouling. The use of air, oxygen or steam fluidised bed gasifiers, closed coupled to an internal combustion engine combined cycle (ICE-CC) requiring cold gas cleaning, or gas turbine combined cycle (GT-CC) requiring hot gas cleaning have been considered. The operating conditions that maximise ICE-CC efficiency with cold gas cleaning (low pressure and high temperatures) also favour minimal tar formation. For GT-CC tar concentrations are higher, but this should not be of concern provided that hot gas cleaning can effectively prevent tar condensation. The trade-off appears to be optimal for steam gasification, with minimal specific costs of 2.1 €/W_e for GT-CC, and 2.7 €/W_e for ICE-CC. However, further calibration of the reaction model is still needed to properly assess product formation for other oxidants than air, and to properly take account of the impact of pressure on product distributions. For air gasification, the minimal specific cost of GT-CC is 2.5 €/W_e, and that of ICE-CC 3.1 €/W_e.     

Electrochemical characteristics of needle coke refined by molten caustic leaching as an anode material for a lithium-ion battery

Needle coke, the remaining material after refining petroleum, is used as an anode of a lithium-ion secondary battery. Sulfur is separated from the needle coke to below 0.1 wt.% using the molten caustic leaching (MCL) method developed at the Korea Institute of Energy Research. The needle coke with high-purity is carbonized at various temperatures, namely 0, 500, 700 and 900 °C. The coke treated at 700 °C gives a first and second discharge capacity of more than 560 and 460 mAh g⁻¹, respectively, between 0 and 2.0 V. By contrast, the first and second discharge capacity of untreated coke is over 420 and 340 mAh g⁻¹, respectively, between 0.05 and 2.0 V.The first discharge capacity of 560 mAh g⁻¹ is beyond the theoretical maximum capacity of 372 mAh g⁻¹ for LiC₆. Though the cycle efficiency is not consistent, the needle coke heat-treated at 700 °C persistently maintains an efficiency of over 90% until the 50th cycle, except on the first cycle. This study demonstrates that the needle coke with high-purity could be a good candidate for an anode material in fabricating high-capacity lithium-ion secondary batteries.     

Low temperature performance of nanophase Li4Ti5O12

The low temperature electrochemical performances of 700 and 350 nm Li₄Ti₅O₁₂ were compared. At high rate, room temperature and at low rate and low temperature (0, −10, −20 and −30 °C), the 350 nm Li₄Ti₅O₁₂ showed higher capacity than the 700 nm Li₄Ti₅O₁₂. This difference is proposed to result from the shorter diffusion lengths and higher number of lithium insertion sites in the 350 nm Li₄Ti₅O₁₂ compared to the 700 nm Li₄Ti₅O₁₂. However, at high rate and low temperature, a transition in performance was observed, that is, the 700 nm material had higher capacity. At high rate and low temperature, it is proposed that interparticle contact resistance becomes rate limiting owing to the temperature dependence of this property and this accounts for the different behavior at low temperature and high rate.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Structural evolution of Eucalyptus tar pitch-based carbons during carbonization

Wood tar pitches are generated as by-products by the charcoal manufacturing industry. They have a macromolecular structure constituted mainly by phenolic, guaiacylic, and siringylic units common to lignin. Due to their characteristics, biopitches are been investigated as precursors of carbon materials such as carbon fibers, bioelectrodes and activated carbons. In the present work the structural evolution of Eucalyptus tar pitches under carbonization is investigated, which is important for the improvement of planning and control of pitch processing and end-product properties during carbon material production. The studies involve X-ray diffraction and infrared analyses, besides helium density, BET surface area and BJH pore volume measurements. The results showed that the conversion of pitch into carbon basically involves three steps: (1) Up to around 600 °C the material has an highly disordered structure, being the release of aliphatic side chains and volatiles the main events taking place. (2) Between 600 °C and 800 °C, condensation of aromatic rings occurs to form bi-dimensional hexagonal networks so that micro- and mesoporosity are developed. The 800 °C-coke is constituted by two phases: one highly disordered and another more crystalline. (3) Over 800 °C, both phases are gradually ordered. As defects are gradually removed, surface area and porosity decrease, approaching zero for the 2100 °C-coke.     

Upgrading of syngas derived from biomass gasification: A thermodynamic analysis

Hydrogen yields in the syngas produced from non-catalytic biomass gasification are generally low. The hydrogen fraction, however, can be increased by converting CO, CH₄, higher hydrocarbons, and tar in a secondary reactor downstream. This paper discusses thermodynamic limits of the synthesis gas upgrading process. The method used in this process is minimization of Gibbs free energy function. The analysis is performed for temperature ranges from 400 to 1300 K, pressure of 1–10 atm (0.1–1 MPa), and different carbon to steam ratios. The study concludes that to get optimum H₂ yields, with negligible CH₄ and coke formation, upgrading syngas is best practiced at a temperature range of 900–1100 K. At these temperatures, H₂ could be possibly increased by 43–124% of its generally observed values at the gasifier exit. The analysis revealed that increasing steam resulted in a positive effect. The study also concluded that increasing pressure from 1 to 3 atm can be applied at a temperature >1000 K to further increase H₂ yields.     

The steam reforming of naphthalene over a nickel–dolomite cracking catalyst

With naphthalene as a model compound, catalytic cracking experiments on biomass tar were made on Ni–dolomite catalysts. The performance of catalyst preparation, activity, coke formation and regeneration were analysed. The results showed that the ratio of the one-step conversion of naphthalene was 95% at space velocity 0.81 h⁻¹ and 700 °C; with saturated wet air as regeneration gas, the regeneration time was within 0.5 h; compared with thermal cracking at the same reaction temperature, the catalytic cracking was propitious to deep cracking of naphthalene.     

Activation of raw pitch coke with alkali hydroxide to prepare high performance carbon for electric double layer capacitor

Powder of raw pitch coke was activated with alkali hydroxides at 500–900 °C to prepare carbon electrode of high capacitance for electric double layer capacitor (EDLC). KOH provided very high surface area of 2320 m²/g at 800 °C, while NaOH did moderate surface area of 1000 m²/g at 650–750 °C. High surface area provided by KOH led to a high capacitance per weight of 39 F/g. However, its capacitance per volume was as low as 16 F/ml. Although the coke of moderate surface area activated with NaOH showed a similar capacitance per weight, its capacity per volume was as high as 28 F/ml because of its high density. Adequate porosity must be selectively introduced by NaOH activation to the coke to obtain moderate surface area. Much smaller expansion of layers in the present needle type coke activated by NaOH than that by KOH is indicative for the higher density of the former activated coke.     

Effect of pyrolysis temperature on the composition of the oils obtained from sewage sludge

Sewage sludge was pyrolysed in a quartz reactor at 350, 450, 550 and 950 °C. The pyrolysis oils from the sewage sludge were characterized in detail by means of gas chromatography–mass spectrometry (GC–MS). Changes in the composition of the oils related to the process conditions were assessed by normalizing the areas of the peaks. It was demonstrated that, as the temperature of pyrolysis increased from 350 to 950 °C, the concentration of mono-aromatic hydrocarbons in the oils also increased. Conversely, phenol and its alkyl derivatives showed a strong decrease in their concentration as temperature rose. Polycyclic aromatic hydrocarbons (PAHs) with two to three rings passed through a maximum at a pyrolysis temperature of 450 °C. PAHs with 4–5 rings also presented a major increase as temperature increased up to 450 °C, the concentration at 950 °C being slightly higher than that at 450 °C. Quantification of the main compounds showed that sewage sludge pyrolysis oils contain significant quantities of potentially high-value hydrocarbons such as mono-aromatic hydrocarbons and phenolic compounds. The oils also contain substantial concentrations of PAHs, even at the lowest temperature of 350 °C. The pathway to PAH formation is believed to be via the Diels–Alder reaction and also via secondary reactions of oxygenated compounds such as phenols.     

Synthesis and electrochemical properties of Mo-doped Li[Ni1/3Mn1/3Co1/3]O2 cathode materials for Li-ion battery

The layered Li[Ni_(1−x)/3Mn_(1−x)/3Co_(1−x)/3Mo_x]O₂ cathode materials (x = 0, 0.005, 0.01, and 0.02) were prepared by a solid-state pyrolysis method (700, 800, 850, and 900 °C). Its structure and electrochemical properties were characterized by XRD, SEM, XPS, cyclic voltammetry, and charge/discharge tests. It can be learned that the doped sample of x = 0.01 calcined at 800 °C shows the highest first discharge capacity of 221.6 mAh g⁻¹ at a current density of 20 mA g⁻¹ in the voltage range of 2.3–4.6 V, and the Mo-doped samples exhibit higher discharge capacity and better cycle-ability than the undoped one at room temperature.     

Effect of annealing temperature on electrochemical performance of thin-film LiMn2O4 cathode

Spinel LiMn₂O₄ thin-film cathodes were obtained by spin-coating the chitosan-containing precursor solution on a Pt-coated silicon substrate followed by a two-stage heat-treatment procedure. The LiMn₂O₄ film calcined at 700 °C for 1 h showed the highest Li-ion diffusion coefficient, 1.55 × 10⁻¹² cm² s⁻¹ (PSCA measurement) among all calcined films. It is attributed to the larger interstitial space and better crystal perfection of LiMn₂O₄ film calcined at 700 °C for 1 h. Consequently, the 700 °C-calcined LiMn₂O₄ film exhibited the best rate performance in comparison with the ones calcined at other temperatures.     

100 t/a-Scale demonstration of direct dimethyl ether synthesis from corncob-derived syngas

Direct conversion of biomass-derived syngas (bio-syngas) to dimethyl ether (DME) at pilot-scale (100 t/a) was carried out via pyrolysis/gasification of corncob. The yield rate of raw bio-syngas was 40–45 Nm³/h with less than 20 mg/Nm³ of tar content when the feedrate of dried corncob was 45–50 kg/h. After absorption of O₂, S, Cl by a series of absorbers and partial removal of CO₂ by the pressure-swing adsorption (PSA) unit sequentially, the obtained bio-syngas (H₂/CO≈1) was directly synthesized to DME over Cu/Zn/Al/HZSM-5 catalyst in the fixed-bed tubular reactor. CO conversion and DME space-time yield (STY) were 67.7% and 281.2 kg/m_cat³/h respectively at 260 °C, 4.3 MPa and 3000 h^?1(GHSV, syngas hourly space velocity). Synthesis performance would be increased if the tail gas (H₂/CO > 2) was recycled to the reactor when GHSV was 650–3000 h^?1.     

Part I: Experimental studies on a pulverised fuel stove

This paper is concerned with development of a pulverised fuel stove with improved conversion efficiency and minimal emissions at near constant power level without the use of external power. The design originates from a cylindrical sawdust stove with a central porthole being lit from the bottom. Such a stove will have a flame in port with enhanced sooting tendency. For similar configuration, stable premixed combustion behaviour of the combustible gases from the port of the fuel block (known as the gasification mode) has been achieved by use of air supply through a thin slot at the bottom, for at least 30 min of stove operation. In order to ensure stable combustion of the gases at exit, a metal device is used. In an attempt to extend gasification duration, studies are conducted in single port configuration having air entry from the bottom with a horizontal baffle to control the flow rate. This configuration worked in gasification mode for about 20 min but there have been problems of flame extinction. To overcome these drawbacks multi-port design with vertical air entry is employed with success.The stove has exhibited conversion efficiency in excess of 37% due to well focused nature of flame at exit. CO emission factors are about 12 g (kg fuel)⁻¹, a performance superior to conventional biomass stoves (∼45 g kg⁻¹). NO_x emission factors are about 1 g kg⁻¹ fuel which falls in the range of reported data for NO_x. Studies with different pulverised leafy fuels have indicated these fuels have lower volatile release rates and therefore exhibit lower power level operation for a given port configuration compared to sawdust fuel.     

Evaporation characteristics of kerosene droplets with dilute concentrations of ligand-protected aluminum nanoparticles at elevated temperatures

The evaporation characteristics of kerosene droplets containing dilute concentrations (0.1%, 0.5%, and 1.0% by weight) of ligand-protected aluminum (Al) nanoparticles (NPs) suspended on silicon carbide fiber were studied experimentally at different ambient temperatures (400–800 °C) under normal gravity. The evaporation behavior of pure and stabilized kerosene droplets was also examined for comparison. The results show that at relatively low temperatures (400–600 °C), the evaporation behavior of suspended kerosene droplets containing dilute concentrations of Al NPs was similar to that of pure kerosene droplets and exhibited two-stage evaporation following the classical d²-law. However, at relatively high temperatures (700–800 °C), bubble formation and micro-explosions were observed, which were not detected in pure or stabilized kerosene droplets. For all Al NP suspensions, regardless of the concentration, the evaporation rate remained higher than that of pure and stabilized kerosene droplets in the range 400–800 °C. At relatively low temperatures, the evaporation rate increased slightly. However, at relatively high temperatures (700–800 °C), the melting of Al NPs led to substantial enhancement of evaporation. The maximum increase in the evaporation rate (56.7%) was observed for the 0.5% Al NP suspension at 800 °C.     

Devolatilization of wood particles in a hot fluidized bed: Product yields and conversion rates

Spherical wood particles of various well-defined diameters were fed into a bed of fluidized olivine maintained at temperatures in the range of 700–900 °C. The fluidizing gas was either nitrogen or a steam–nitrogen mixture, and the wooden spheres were introduced in two different ways: on to the bed surface and deep into the bed itself. The resulting gas, tar and char yields were found to be influenced by the method of feed introduction as well as by the bed temperature, fluidizing gas composition and wood particle diameter. The total devolatilization time was correlated by means of a power law expression similar to that used for coal devolatilization and having the advantage of being able to fit well the experimental data over the full temperature range in both nitrogen and steam–nitrogen atmospheres.     

Cresol–formaldehyde based carbon aerogel as electrode material for electrochemical capacitor

Carbon aerogels have been prepared through a polycondensation of cresol (Cm) with formaldehyde (F) and an ambient pressure drying followed by carbonization at 900 °C. Modification of the porous structures of the carbon aerogel can be achieved by CO₂ activation at various temperatures (800, 850, 900 °C) for 1–3 h. This process could be considered as an alternative economic route to the classic RF gels synthesis. The obtained carbon aerogels have been attempted as electrode materials in electric double-layer capacitors. The relevant electrochemical behaviors were characterized by constant current charge–discharge experiments, cyclic voltammetry and electrochemical impedance spectroscopy in an electrolyte of 30% KOH aqueous solution. The results indicate that a mass specific capacitance of up to 78 F g⁻¹ for the non-activated aerogel can be obtained at current density 1 mA cm⁻². CO₂ activation can effectively improve the specific capacitance of the carbon aerogel. After CO₂ activation performed at 900 °C for 2 h, the specific capacitance increases to 146 F g⁻¹ at the same current. Only a slight decrease in capacitance, from 146 to 131 F g⁻¹, was observed when the current density increases from 1 to 20 mA cm⁻², indicating a stable electrochemical property of carbon aerogel electrodes in 30% KOH aqueous electrolyte with various currents.