A novel reforming method for hydrogen production from biomass steam gasification

In this work, an experimental study of biomass gasification in different operation conditions has been carried out in an updraft gasifier combined with a porous ceramic reformer. The effects of gasifier temperature, steam to biomass ratio (S/B), and reforming temperature on the gas characteristic parameters were investigated with and without porous ceramic filled in reformer. The results indicated that considerable synergistics effects were observed as the porous ceramic was filled in reformer leading to an increase in the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, hydrogen yield increased from 49.97 to 79.91 g H₂/kg biomass. Steam/biomass ratio of 2.05 seemed to be optimal in all steam-gasification runs. The effect of reforming temperature for water-soluble tar produced in porous ceramic reforming was also investigated, and it was found that the conversion ratio of total organic carbon (TOC) contents is between 71.08% and 75.74%.     

Steam reforming of biodiesel by-product to make renewable hydrogen

The aim of this paper was to investigate the viability of steam reforming the combined glycerol and water by-product streams of a biodiesel plant. A platinum alumina catalyst was used to optimise the operating conditions for glycerol steam reforming and mass spectroscopy was chosen to measure reformer gas yield. The problem is that glycerol steam reforming is relatively untested even with pure glycerol and the by-product quality may be too poor. The strategy was therefore to optimise the process using pure glycerol and compare the performance with by-product glycerol. To test catalyst degradation caused by carbon deposition, a Solid Oxide fuel cell (SOFC) was used as a separate reformer and electrical performance was measured to indicate carbon deposition. This is the first time a SOFC has been run on glycerol. The results showed that thermodynamic theory can be used to predict reformer performance. At high temperatures high gas yield can be reached (almost 100%) and selectivities of 70% (dry basis) obtained. The optimum conditions for glycerol reforming were 860 °C temperature (maximum tested), 0.12 mols/min glycerol flow per kg of catalyst and 2.5 steam/carbon ratio. Reforming catalysts lasted for several days of continuous operation with minimal degradation, 0.4% of feed deposited. By-product glycerol performed slightly worse with a lower yield and more carbon deposition, 2% of feed. The results show that glycerol steam reforming is a viable alternative use for glycerol and potentially a better option than purification.     

Tar reduction in pyrolysis vapours from biomass over a hot char bed

The behaviour of pyrolysis vapours over char was investigated in order to maximise tar conversion for the development of a new fixed bed gasifier. Wood samples were decomposed at a typical pyrolysis temperature (500 °C) and the pyrolysis vapours were then passed directly through a tar cracking zone in a tubular reactor. The product yields and properties of the condensable phases and non-condensable gases were studied for different bed lengths of char (0–450 mm), temperatures (500–800 °C), particle sizes (10 and 15 mm) and nitrogen purge rates (1.84–14.70 mm/s). The carbon in the condensable phases showed about 66% reduction by a 300 mm long char section at 800 °C, compared to that for pyrolysis at 500 °C. The amount of heavy condensable phase decreased with increasing temperature from about 18.4 wt% of the biomass input at 500 °C to 8.0 wt% at 800 °C, forming CO, H₂ and other light molecules. The main mode of tar conversion was found to be in the vapour phase when compared to the results without the presence of char. The composition of the heavy condensable phase was simplified into much fewer secondary and tertiary tar components at 800 °C. Additional measures were required to maximise the heterogeneous effect of char for tar reduction.     

Steam reforming of bio-oil from rice husks fast pyrolysis for hydrogen production

Steam reforming of two kinds of bio-oil from rice husks fast pyrolysis was conducted for hydrogen production at three temperatures (650, 750 and 850 °C) with Ni-based catalyst in a fixed-bed reactor. The gas composition and organic compounds in liquid condensate were detected by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS), respectively. In addition, the carbon deposition was also investigated. The results showed that the mole fraction range of hydrogen was within 55.8-61.3% at all temperatures and more hydrogen was produced at the higher temperature. The highest H? efficiency of bio-oil steam reforming was 45.33% when extra water was added. The bio-oil with lower content of chemical compounds has a higher H? efficiency, but its hydrogen volume was less. Analysis of the liquid condensate showed that most of the organic compounds were circularity compounds. The carbon deposition can decrease the bio-oil conversion, and it was easier to form at the temperature of 750 °C.     

Hydrogen production by sorption-enhanced steam reforming of glycerol

Catalytic steam reforming of glycerol for H₂ production has been evaluated experimentally in a continuous flow fixed-bed reactor. The experiments were carried out under atmospheric pressure within a temperature range of 400–700 °C. A commercial Ni-based catalyst and a dolomite sorbent were used for the steam reforming reactions and in situ CO₂ removal. The product gases were measured by on-line gas analysers. The results show that H₂ productivity is greatly increased with increasing temperature and the formation of methane by-product becomes negligible above 500 °C. The results suggest an optimal temperature of ∼500 °C for the glycerol steam reforming with in situ CO₂ removal using calcined dolomite as the sorbent, at which the CO₂ breakthrough time is longest and the H₂ purity is highest. The shrinking core model and the 1D-diffusion model describe well the CO₂ removal under the conditions of this work.     

The mechanism for thermal decomposition of cellulose and its main products

Experiment is performed to investigate the mechanism of the cellulose pyrolysis and the formation of the main products. The evolution of the gaseous products is examined by the 3-D FTIR spectrogram at the heating rate of 5–60 K/min. A pyrolysis unit, composed of fluidized bed reactor, carbon filter, vapour condensing system and gas storage, is employed to investigate the products of the cellulose pyrolysis under different temperatures (430–730 °C) and residence time (0.44–1.32 s). The composition in the bio-oil is characterized by GC–MS while the gases sample is analyzed by GC. The effects of temperature and residence time on the main products in bio-oil (LG, 5-HMF, FF, HAA, HA and PA) are examined thoroughly. Furthermore the possible routes for the formation of the products are developed from the direct conversion of cellulose molecules and the secondary reactions of the fragments. It is found that the formation of CO is enhanced with elevated temperature and residence time, while slight change is observed for the yield of CO₂.     

Production of 2,3-butanediol by Klebsiella pneumoniae grown on acid hydrolyzed wood hemicellulose

Summary Previously steam explosion had been used to enhance the enzymatic hydrolysis of lignocellulosic substrates to glucose. The conditions for pretreating aspen wood chips were optimized so that highest amounts of undegraded hemicellulose could be obtained after washing the steam exploded chips. The hemicellulose rich water soluble fractions showing highest pentosan yields were then acid hydrolysed to their composite sugars. Approximately 65–75% of the total reducing sugars detected in the wood hydrolysates were in the form of monosaccharides with D-xylose being the major component. Klebsiella pneumoniae was grown in media containing these wood hydrolysates as the substrate and 2,3-butanediol yields of 0.4–0.5 g per g of monosaccharide utilised were obtained.     

Effects of gasifying conditions and bed materials on fluidized bed steam gasification of wood biomass

The effect of steam gasification conditions on products properties was investigated in a bubbling fluidized bed reactor, using larch wood as the starting material. For bed material effect, calcined limestone and calcined waste concrete gave high content of H(2) and CO(2), while silica sand provided the high content of CO. At 650 degrees C, calcined limestone proved to be most effective for tar adsorption and showed high ability to adsorb CO(2) in bed. At 750 degrees C it could not capture CO(2) but still gave the highest cold gas efficiency (% LHV) of 79.61%. Steam gasification gave higher amount of gas product and higher H(2)/CO ratio than those obtained with N(2) pyrolysis. The combined use of calcined limestone and calcined waste concrete with equal proportion contributed relatively the same gas composition, gas yield and cold gas efficiency as those of calcined limestone, but showed less attrition, sintering, and agglomeration propensities similar to the use of calcined waste concrete alone.     

Anaerobic fermentation of woody biomass treated by various methods

Anaerobic fermentation was attempted to produce methane from the wood chip (Eucalyptus globulus). By the pretreatment of the wood chip using hot water with high temperature, NaOH, and steam explosion, the production of methane gas was enhanced. The pretreatment using steam explosion resulted in more amount of methane gas produced than the treatment using either hot water or 1% (w/w) NaOH with high temperature, and the steam explosion at a steam pressure of 25 atm and a steaming time of 3 min was the most effective for the methane production. The amount of methane gas produced depended on the ratio of weight of Klason lignin, a high molecular weight lignin, in the treated wood chip.     

Pyrolysis of ramie residue: kinetic study and fuel gas produced in a cyclone furnace

The thermal decomposition behavior of ramie residue (RR) and the characteristics of fuel gas produced in a cyclone furnace were studied. The pyrolysis kinetics was investigated using thermogravimetric analysis (TGA) at heating rates of 5-20°C/min. The results showed that RR mainly decomposed between 250 and 390°C, and the apparent activation energy ranged from 200 to 258 kJ/mol. In the cyclone furnace, fast pyrolysis, partial combustion and gasification occurred almost simultaneously, and the thermal energy was supplied by partial combustion of RR powder at the hypo stoichiometric amount of air. Higher effect of equivalence ratio (ER) led to higher reaction temperature and fewer contents of tar and char, but too high ER lowered fuel gas content and degraded fuel gas quality. Over the ranges of the experimental conditions, the gas yield varied between 1.07 and 2.08 N m(3)/kg and the LHV was between 3350 and 4798 kJ/Nm(3).     

Biomass as an energy source: thermodynamic constraints on the performance of the conversion process

In the present work an equilibrium model (gas-solid), based on the minimization of the Gibbs energy, has been used in order to estimate the theoretical yield and the equilibrium composition of the reaction products (syngas and char) of biomass thermochemical conversion processes (pyrolysis and gasification). The data obtained from this model have also been used to calculate the heating value of the fuel gas, in order to evaluate the overall energy efficiency of the thermal conversion stage. The proposed model has been applied both to partial oxidation and steam gasification processes with varying air to biomass (ER) and steam to carbon (SC) ratio values and using different feedstocks; the obtained results have been compared with experimental data and with other model predictions obtaining a satisfactory agreement.     

Two-stage steam gasification of waste biomass in fluidized bed at low temperature: parametric investigations and performance optimization

Steam gasification of waste biomass has been studied in a two-stage fluidized bed reactor, which has the primary pyrolysis fluidized bed using silica sand as bed material and the secondary reforming fixed bed with catalyst. The main objectives are parametric investigation and performance improvement especially at low temperature of around 600 °C using the wood chip and the pig manure compost as feedstock. Main operating variables studied are pyrolysis temperature, catalytic temperature, steam/biomass-C ratio, space velocity and different catalyst. Reaction temperatures and steam/C ratio have important role on the gasification process. About 60 vol.% H2 (dry and N2 free) and about 2.0 Nm3/kg biomass (dry and ash free basis) can be obtained under good conditions. Compared to Ni/Al2O3, Ni/BCC (Ni-loaded brown coal char) has a better ability and a hopeful prospect for the stability with coking resistance.     

Efficient hydrogen production from ethanol and glycerol by vapour-phase reforming processes with new cobalt-based catalysts

The aim of this study was to investigate biohydrogen production from biofuel-reforming processes using new multi-component bulk-type cobalt-based catalysts. The addition of different components to improve the catalytic performance was studied. Monometallic cobalt catalyst and catalysts containing Ru (ca. 1%) and/or Na (ca. 0.5%) were characterized and tested in the 623-673 K temperature range in ethanol steam reforming (ESR) with a steam/carbon ratio (S/C) of 3. The catalysts showed a high performance for hydrogen production and, except for H(2) and CO(2), only small amounts of by-products were obtained, depending on the temperature and the catalyst used. The catalyst containing both Ru and Na (Co-Ru(Na)) showed the best catalytic behavior in ESR. It operated stably for at least 12 days under cycles of oxidative steam reforming of glycerol/ethanol mixtures (S/C=2) and activation under O(2).     

Conversion of Japanese red pine wood (Pinus densiflora) into valuable chemicals under subcritical water conditions

A comparative study on the decomposition of Japanese red pine wood under subcritical water conditions in the presence and absence of phosphate buffer was investigated in a batch-type reaction vessel. Since cellulose makes up more than 40-45% of the components found in most wood species, a series of experiments were also carried out using pure cellulose as a model for woody biomass. Several parameters such as temperature and residence time, as well as pH effects, were investigated in detail. The best temperature for decomposition and hydrolysis of pure cellulose was found around 270 °C. The effects of the initial pH of the solution which ranged from 1.5 to 6.5 were studied. It was found that the pH has a considerable effect on the hydrolysis and decomposition of the cellulose. Several products in the aqueous phase were identified and quantified. The conditions obtained from the subcritical water treatment of pure cellulose were applied for the Japanese red pine wood chips. As a result, even in the absence of acid catalyst, a large amount of wood sample was hydrolyzed in water; however, by using phosphate buffer at pH 2, there was an increase in the hydrolysis and dissolution of the wood chips. In addition to the water-soluble phase, acetone-soluble and water-acetone-insoluble phases were also isolated after subcritical water treatment (which can be attributed mainly to the degraded lignin, tar, and unreacted wood chips, respectively). The initial wood:acid ratio in the case of reactions catalyzed by phosphate buffer was also investigated. The results showed that this weight ratio can be as high as 3:1 without changing the catalytic activity. The size of the wood chips as one of the most important experimental parameters was also investigated.     

Biomass downdraft gasifier with internal cyclonic combustion chamber: design, construction, and experimental results

An exploratory downdraft gasifier design with unique biomass pyrolysis and tar cracking mechanism is evolved at Oklahoma State University. This design has an internal separate combustion section where turbulent, swirling high-temperature combustion flows are generated. A series of research trials were conducted using wood shavings as the gasifier feedstock. Maximum tar cracking temperatures were above 1100°C. Average volumetric concentration levels of major combustible components in the product gas were 22% CO and 11% H(2). Hot and cold gas efficiencies were 72% and 66%, respectively.     

SO2-catalysed prehydrolysis of coniferous wood for ethanol production

Summary This paper reports studies of large scale, 1500 kg/h, SO₂-catalysed prehydrolysis of coniferous wood chips, samples then being hydrolyzed by a wood-saccharifying enzyme system followed by fermentation to ethanol in the laboratory. Hemicellulose hydrolysis using SO₂ catalyst (prehydrolysis) was found to be more effective than steam alone (autohydrolysis). Prehydrolysis time was 2 min, with steam pressure at 1.2 to 1.7 MPa (175 to 250 psig), and SO₂ catalyst 2.0 to 2.6% on dry wood. The amount of sugars recovered upon enzyme saccharification of the prehydrolysed wood was about 70% of the weight of the wood. When these combined hemicellulose and cellulose sugars were fermented by a pentose-fermenting strain of yeast,Pichia stipitis R, 372 L ethanol/tonne of (dry) wood was obtained.     

Steam pretreatment of lignocellulosic material for enhanced enzymatic hydrolysis

Pretreatment methods were compared with steam explosion, and differing views on the relative importance of mechanical and chemical effects were outlined. Hydrolysis was desirable; pyrolysis was undesirable. The effects of initial moisture content on steam consumption, mechanism and rate of heat transfer, pentosan solubilization, and subsequent glucose yield were summarized. The insignificant effect, after treatment at 240 degrees C, of 90% pressure bleed-down before explosion on subsequent simultaneous saccharification and fermentation (SSF) yields was described. Treatment at 190 degrees C with complete bleed-down (no explosion), when compared with that at 240 degrees C with explosion from full pressure, showed at least as good solubilizatoin of pentosan, enzymatic hydrolysis, and SSF but showed greater pentosan destruction for the same degree of pentosan removal. Water washing of unexploded steamed aspenwood chips was at least as efficient as that of similarly treated but exploded chips. Scanning electron micrographs of unexploded chips showed extensive rupturing of vessel pit membranes and other morphological features associated with steam-exploded wood. Neither the explosion nor the high temperatures (above 190 degrees C) are necessary.     

Low temperature catalytic gasification of pig compost to produce H2 rich gas

The low temperature catalytic gasification of pig compost before and after acid washing was carried out to produce H2 rich gas using a two-stage fixed-bed reactor. Little effect of the minerals on the manure pyrolysis is determined. Under the presence of Ni/Al2O3 catalyst nearly all the tarry matters were cracked into H2, CO, CO2 and residual carbon. High H2 and CO yields were obtained by low temperature catalytic steam gasification. Acid washing results in the decrease in the content of the ease-hydrolyzed organic components, which volatilize at low temperature. The change in the gas yields from the manure during catalytic decomposition is in accordance with its pyrolysis behavior.     

Dead wood biomass and turnover time,measured by radiocarbon,along a subalpine elevation gradient

Dead wood biomass can be a substantial fraction of stored carbon in forest ecosystems, and coarse woody debris (CWD) decay rates may be sensitive to climate warming. We used an elevation gradient in Colorado Rocky Mountain subalpine forest to examine climate and species effects on dead wood biomass, and on CWD decay rate. Using a new radiocarbon approach, we determined that the turnover time of lodgepole pine CWD (340±130 years) was roughly half as long in a site with 2.5–3°C warmer air temperature, as that of pine (630±400 years) or Engelmann spruce CWD (800±960 and 650±410 years) in cooler sites. Across all sites and both species, CWD age ranged from 2 to 600 years, and turnover time was 580±180 years. Total standing and fallen dead wood biomass ranged from 4.7±0.2 to 54±1 Mg ha^–1, and from 2.8 to 60% of aboveground live tree biomass. Dead wood biomass increased 75 kg ha^–1 per meter gain in elevation and decreased 13 Mg ha^–1 for every degree C increase in mean air temperature. Differences in biomass and decay rates along the elevation gradient suggest that climate warming will lead to a loss of dead wood carbon from subalpine forest.Electronic Supplementary Material Supplementary material is available for this article at     

Particulate organic carbon and nitrogen in the Orinoco river (Venezuela)

Total suspended solids (TSS), particulate organic carbon (POC) and particulate nitrogen (PN) were measured over a two year period, 1983–1985, in the Orinoco River at Ciudad Bolívar, 450 km from its mouth. Additionally, samples of the main stem at other localities and main tributaries were included in the present study.The suspended sediment concentrations showed a peculiar pattern of temporal variations: two maxima (May–June and November) and two minima (March–April and August–September).The POC and PN concentrations fluctuated with the water discharge, and higher values were observed during the rising limb than during the falling limb of the hydrograph. As dry weight percent of solids, the values ranged between 0.84 and 9.06% for organic carbon and between 0.08 and 1.45% for total nitrogen. The carbon-nitrogen ratio in the sediment averaged 9.1. The major contribution of organic carbon and nitrogen in particulate form to the Orinoco main stem comes from the left margin tributaries, which have their headwater in the mountainous regions of the Andes.