Hydrogen-rich gas from catalytic steam gasification of biomass in a fixed bed reactor: Influence of particle size on gasification performance

The catalytic steam gasification of biomass was carried out in a lab-scale fixed bed reactor in order to evaluate the effects of particle size at different bed temperatures on the gasification performance. The bed temperature was varied from 600 to 900 °C and the biomass was separated into five different size fractions (below 0.075 mm, 0.075–0.15 mm, 0.15–0.3 mm, 0.3–0.6 mm and 0.6–1.2 mm). The results show that with decreasing particle size, the dry gas yield, carbon conversion efficiency and H₂ yield increased, and the content of char and tar decreased. And the differences due to particle sizes in gasification performance practically disappear as the higher temperature bound is approached. Hydrogen and carbon monoxide contents in the produced gas increase with decreasing particle size at 900 °C, reaching to 51.2% and 22.4%, respectively.     

Hydrogen production from supercritical water gasification of alkaline wheat straw pulping black liquor in continuous flow system

Supercritical water gasification of alkaline black liquor was investigated in a continuous flow system. The experiments were carried out at 400–600 °C, 25 MPa, with residence times ranging from 4.94 to 13.71 s. The results showed that the increase of temperature and residence time and the decrease of feeding concentration enhanced the gasification. The gaseous product contained high level of hydrogen (40.26–61.02%). Maximum COD removal efficiency (88.69%) was obtained at 600 °C. The alkalis in black liquor were found to be precipitated in the reactor during the gasification, which decreased the pH of the effluent to the neutral region (6.4–8.0). The precipitated alkalis were dissolved in the water when the fluid temperature in the reactor was cooled to about 360 °C which increased the pH of the effluent to 11.0. A simplified kinetic study for COD removal efficiency was done by the pseudo-first order reaction assumption. The apparent activated energy was 74.38 kJ/mol and the apparent pre-exponential factor was 10^4.05 s⁻¹.     

Hydrogen-rich gas production from biomass catalytic gasification using hot blast furnace slag as heat carrier and catalyst in moving-bed reactor

A new concept that a heat recovery system from blast furnace (BF) slag which would generate hydrogen-rich gas was proposed and a continuous moving-bed biomass gasification reactor was designed to evaluate the feasibility. The influences of temperature and particle size of BF slag on gasification product distribution and gas characterization were discussed. The results show that BF slag demonstrated better catalytic performance in improving tar cracking, enhancing char gasification and reforming of hydrocarbons; higher BF slag temperature and smaller particles size can produce more light gases, less char and condensate; as temperature of BF slag being 1200 °C and its size below 2 mm, gas yield and H₂ content achieved the maximum being 1.28 N m³/kg and 46.54%, respectively.     

Effect of calcium based catalyst on production of synthesis gas in gasification of waste bamboo chopsticks

This study investigated the effects of calcium based catalyst (calcium oxide) on variation of gas composition in catalytic gasification reaction stages by controlling the gasification temperature between 600 °C and 900 °C whilst varying a catalyst/biomass ratio from 0 to 0.2 w/w. The tested biomass generated from used bamboo chopsticks were used as the feedstock. To assess the gas composition variation, the ratio of H₂/CO, H₂/CO₂, CO/CO₂, and 3H₂/CH₄ are four important factors that affect the performance of catalytic gasification process. The maximum ratio of H₂/CO increased from 0.23 to 0.72 in the gasification temperature range between 600 °C and 900 °C and 0%–20% calcium based catalyst addition ratio. This is due to enhanced H₂ production as a result of the facilitated water–gas shift reaction. The ratios of CO/CO₂ and 3H₂/CH₄ increased significantly from 0.9 to 2.1 and from 2.6 to 4.1, respectively, when the gasification temperature increased from 600 °C to 900 °C and 20% catalyst addition ratio. Obviously, the high temperature and catalyst addition are favorable for production of CO and H₂ during gasification of tested biomass. In conclusion, the tested mineral calcium based catalyst (CaO) can help facilitating the reaction rate of partial oxidation and water–gas shift reaction, enhancing the quality of synthesis gas, and reduction of the gasification reaction time. This catalyst has potential application in gasification of waste bamboo chopsticks in the future.     

Low temperature steam gasification to produce hydrogen rich gas from kitchen food waste: Influence of steam flow rate and temperature

Large amount of food waste is generated from Indian kitchens and disposing off such a large amount possesses a great challenge in terms of environmental degradation and viable food waste processing technology. In this work, steam gasification was tested as an alternative viable technology to process the kitchen food waste. Preliminary study was carried out at low temperature on steam gasification in a fixed bed reactor to study the influence of steam flow rate (SFR) and temperature on the syngas yield, syngas composition, hydrogen yield. Performance parameters such as carbon conversion efficiency (CCE), and apparent thermal efficiency (ATE) are also calculated. Steam flow rates are varied from 0.125 mL/min to 0.75 mL/min and the temperatures are varied from 700 °C to 800 °C. The highest hydrogen yield is obtained at 0.5 mL/min SFR and 800 °C temperature and its highest value is 1.2 m³/kg. The highest value of performance parameters, CCE and ATE are found to be 63% and 1.8.     

Influence of catalyst and temperature on gasification performance of pig compost for hydrogen-rich gas production

The catalytic steam gasification of pig compost (PC) for hydrogen-rich gas production was conducted in a fixed-bed reactor. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 700–850 °C, for weight hourly space velocity (WHSV) in the range of 0.30–0.60 h⁻¹. The results indicate that the developed NiO on modified dolomite (NiO/MD) catalyst reveals better catalytic performance on the tar elimination and hydrogen yield than calcined MD or NiO/γ-Al₂O₃ catalyst. Meanwhile, the lower WHSV and higher reactor temperature can contribute to more hydrogen production and gas yield. Moreover, the char from catalytic steam gasification of PC has a highest ash content of 75.84% at 850 °C. In conclusion, pig compost is a potential candidate for hydrogen gas production through catalytic steam gasification technology.     

Noncatalytic gasification of isooctane in supercritical water: A Strategy for high-yield hydrogen production

Continuous supercritical water gasification of isooctane, a model gasoline compound, is investigated using an updraft gasification system. A new reactor material, Haynes^® 230^® alloy, is employed to run gasification reactions at high temperature and pressure (763 ± 2 °C; 25 MPa). A large-volume reactor is used (170 mL) to enable the gasification to be run at a long residence time, up to 120 s. Various gasification experiments are performed by changing the residence time (60-120 s), the isooctane concentration (6.3-14.7 wt%), and the oxidant concentration (equivalent oxidant ratio 0-0.3). The total gas yield and the hydrogen gas yield increase with increasing residence time. At 106 s and an isooctane concentration of 6.3 wt%, a very high hydrogen gas yield of 12.4 mol/mol isooctane, which is 50% of the theoretical maximum hydrogen gas yield and 92% of the equilibrium hydrogen gas yield under the given conditions, is achieved. Under these conditions, supercritical water partial oxidation does not increase the hydrogen gas yield significantly. The produced gases are hydrogen (68 mol%), carbon dioxide (20 mol%), methane (9.8 mol%), carbon monoxide (1.3 mol%), and ethane (0.9 mol%). The carbon gasification efficiency is in the range 75-91%, depending on the oxidant concentration. A comparison of supercritical water gasification with other conventional methods, including steam reforming, autothermal reforming, and partial oxidation, is also presented.     

Hydrothermal decomposition of xylan as a model substance for plant biomass waste – Hydrothermolysis in subcritical water

Beech wood xylan, as a model substance for hemicellulose contained in plant biomass waste, was subjected to thermohydrolysis in subcritical water. The composition of the product fractions obtained as a result of its hydrothermal decomposition was studied: the water fraction, the oil fraction and the solid fraction of charred post-reaction residue. An increase in temperature favors xylan thermohydrolysis, leading to the production of saccharides – the products of its hydrolytic depolymerization. The yield of the saccharides contained in the water-soluble product fraction reaches it maximum value at 220 °C and 235 °C, with the retention time of 0 min. Both extending reaction time up to 30 min and further increasing the temperature favor the occurring of secondary reactions – saccharide decomposition – leading to the production, among others, of carboxylic acids, furfurals and aldehydes, and their further carbonization and gasification.     

Copper oxide nanoparticle made by flame spray pyrolysis for photoelectrochemical water splitting – Part I. CuO nanoparticle preparation

Copper oxide (CuO) semiconductor nanoparticles are of interest because of their promising use for electronic and optoelectronic devices, and the size of the CuO particles for these applications is important. In this work, near spherical CuO nanoparticles with aspect ratio of 1.2–1.3 were made by a flame spray pyrolysis (FSP) method. In FPS, flame temperature, residence time, precursor concentration can be used to control particle size. As the precursor concentration increased from 0.5% to 35% w/w, primary particle diameter increased from 7 ± 2 to 20 ± 11 nm. Larger primary particle diameters were observed in the low gas flow system (set B) due to the long residence time in the high temperature zone. For the dependence of temperature on particle diameter, particles grew to similar diameter, i.e. ∼11 nm, in both flame conditions within the hot temperature zone (80% of melting point of CuO) but for particles having longer residence time, i.e. 550 ms in set B, the standard deviation of particle diameter is 45% larger than for particles with 66 ms as residence time in set A. Modeling gave a result for CuO final particle diameter, based on collision/sintering theory with sintering by solid state diffusion, of 6.7 and 9.0 nm for set A and set B, respectively, with surface tension assumed to be 0.5 J/m².Comparison with the experiment results, 11 ± 4 nm diameter for both flame conditions, indicates the simulations were reasonable.     

Hydrogen production by non-catalytic partial oxidation of coal in supercritical water: Explore the way to complete gasification of lignite and bituminous coal

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by non-catalytic partial oxidation of coal was systematically investigated in supercritical water (SCW) with quartz batch reactors for the first time. The influences of the main operating parameters including residence time, temperature, oxidant equivalent ratio (ER) and feed concentration on the gasification characteristics of coal were investigated. The experimental results showed that H₂ yield and carbon gasification efficiency (CE) increased with increasing temperature and decreasing feed concentration. CE increased with increasing ER, and H₂ yield peaked when ER equaled 0.1. CE increased quickly within 1 min and then tended to be stable between 2 and 3 min. In particular, complete gasification of lignite was obtained at 950 °C when ER equaled 0.1, as for bituminous coal, at a higher temperature of 980 °C when ER equaled 0.2.     

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 H₂ 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.     

Hydrogen-rich syngas production from municipal solid waste gasification through the application of central composite design: An optimization study

This study aims to investigate the influence and interaction of experimental parameters on the production of optimum H₂ and other gases (CO, CO₂, and CH₄) from gasification of municipal solid waste (MSW). Response surface method in assistance with the central composite design was employed to design the fifteen experiments to find the effect of three independent variables (i.e., temperature, equivalence ratio and residence time) on the yields of gases, char and tar. The optimum H₂ production of 41.36 mol % (15.963 mol kg-MSW⁻¹) was achieved at the conditions of 757.65 °C, 0.241, and 22.26 min for temperature, ER, and residence time respectively. In terms of syngas properties, the lower heating value and molar ratio (H₂/CO) ranged between 9.33 and 12.48 MJ/Nm³ and 0.45–0.93. The predicted model of statistical analysis indicated a good fit with experimental data. The gasification of MSW utilizing air as a gasifying agent was found to be an effective approach to recover the qualitative and quantitate products (H₂ and total gas yield) from the MSW.     

Production of hydrogen via an Iron/Iron oxide looping cycle: Thermodynamic modeling and experimental validation

An incremental thermodynamic equilibrium model has been developed for the chemical reactions driving a clean, hydrogen producing iron/iron oxide looping cycle. The model approximates a well-mixed reactor with continuous reactant gas flow through a stationary solid matrix, where the gas residence time is long compared to time constants associated with chemical kinetics and species transport. The model, which computes the theoretical limit for steam-to-hydrogen conversion, has been experimentally validated for the oxidation reaction using an externally heated, 21 mm inner diameter, tubular fluidized bed reactor. Experiments were carried out at 660 and 960 °C with steam flow rates ranging from 0.9 to 3.5 g/min. For small flow rates, i.e., for long residence times, the experimentally observed cumulative steam-to-hydrogen conversion approaches the theoretically predicted conversion. At a 960 °C operating temperature, the measured hydrogen yield approaches the theoretical limit (experimental yields are always within 50% of the theoretical limit), and the yield is insensitive to variations in the steam flow rate. In contrast, the measured hydrogen yield deviates significantly from the theoretical limit at a 660 °C operating temperature, and strong variations in hydrogen yield are observed with variations in steam flow rate. This observation suggests that the reaction kinetics are significantly slower at lower temperature, and the model assumption is not satisfied.     

Low temperature sugar cane bagasse pyrolysis for the production of high purity hydrogen through steam reforming and CO2 capture

Biomass pyrolysis offers a fast route to produce elevated yields towards highly valued liquid products. This research aims the determination of optimal experimental conditions for a slow and low temperature pyrolysis to produce the highest yield towards condensable (CVM) and non-condensable (NCVM) volatile matter from Mexican cane bagasse and to quantify and characterize the compounds that constitute CVM and NCVM obtained. Results indicate that yield towards volatiles is strongly dependent on temperature. The highest yield was achieved at temperatures greater than 500 °C at a heating rate of 10 °C/min, residence time of 60 min and a particle size between of 420 and 840 μm. Product quantification under isothermal conditions determined that at 550 °C the NCVM, CVM and solid residue was of 26, 57 and 16%, respectively. Preliminary thermodynamic analysis of steam reforming and CO₂ absorption reactions using one of the main CVM products resulted in a potential high hydrogen production yield.     

Hydrogen production from glycerol by supercritical water gasification in a continuous flow tubular reactor

In this work, glycerol was used for hydrogen production by supercritical water gasification. Experiments were conducted in a continuous flow tubular reactor at 445∼600 °C, 25 MPa, with a short residence time of 3.9∼9.0 s. The effects of reaction temperature, residence time, glycerol concentration and alkali catalysts on gasification were systematically studied. The results showed that the gasification efficiency increased sharply with increasing temperature above 487 °C. A short residence time of 7.0 s was enough for 10 wt% glycerol gasification at 567 °C. With the increase of glycerol concentration from 10 to 50 wt%, the gasification efficiency decreased from 88% to 71% at 567 °C. The alkali catalysts greatly enhanced water-gas shift reaction and the hydrogen yield in relation to catalysts was in the following order: NaOH > Na₂CO₃>KOH > K₂CO₃. The hydrogen yield of 4.93 mol/mol was achieved at 526 °C with 0.1 wt% NaOH. No char or tar was observed in all experiments. The apparent activation energy and apparent pre-exponential factor for glycerol carbon gasification were obtained by assuming pseudo first-order kinetics.     

A comparative study for synthesis methods of nano-structured (9Ni–2Mg–Y) alloy catalysts and effect of the produced alloy on hydrogen desorption properties of MgH2

9Ni–2Mg–Y alloy powders were prepared by arc melting, induction melting, mechanical alloying, solid state reaction and subsequent ball milling processes. The results showed that melting processes are not suitable for preparation of 9Ni–2Mg–Y alloy due to high losses of Mg and Y. Therefore, 9Ni–2Mg–Y alloy powder was prepared by three methods including: 1) mechanical alloying, 2) mechanical alloying + solid state reaction + ball milling, and 3) mixing + solid state reaction + ball milling. The prepared 9Ni–2Mg–Y alloy powders were compared for their catalytic effects on hydrogen desorption of MgH₂. It is found that 9Ni–2Mg–Y alloy powder prepared by mechanical alloying + solid state reaction + ball milling method has a smaller particle size (1–5 μm) and higher surface area (1.7 m² g⁻¹) than that of other methods. H₂ desorption tests revealed that addition of 9Ni–2Mg–Y alloy prepared by mechanical alloying + solid state reaction + ball milling to MgH₂ decreases the hydrogen desorption temperature of MgH₂ from 425 to 210 °C and improves the hydrogen desorption capacity from 0 to 3.5 wt.% at 350 °C during 8 min.     

Hydrogen production from lignite via supercritical water in flow-type reactor

A supercritical water reactor with throughput of 10  kg/h was set up, which was operated with continuous feeding of coal water slurry. The effects of reaction temperature (500–650 °C), pressure (20.0–30.0 MPa), Ca/C molar ratio (0–0.45) and O/C molar ratio (0–0.35) on the hydrogen generation characteristics were investigated. It is found that there is a notable increase in the hydrogen content and yield with the increase of reaction temperature. The hydrogen yield increases from 24.67 ml/g to 135.73 ml/g when the temperature increases from 500 °C to 650 °C. The contents of CO₂ in gas product decrease, while that of hydrogen increases with the increase of Ca/C molar ratio. At Ca/C molar ratio of 0.45, nearly all CO₂ is fixed. Correspondingly, the content of hydrogen in gas is 73.29%, and the yield of hydrogen is 348.30 ml/g compared to 135.42 ml/g in the absent of CaO. Moreover, both of CaO and KOH catalyze gasification and water-shift reaction. The formation of hydrogen and the carbon gasification efficiency are improved by the added H₂O₂ when O/C ratio is less than 0.3.     

Steam gasification of biochars derived from pruned apple branch with various pyrolysis temperatures

In this study, the gas production behavior from the steam gasification of the biochar derived from the pruned apple brunch was investigated using a fixed-bed reactor. The optimal biochar obtained at the pyrolysis temperature of 550 °C was gasified under different operating conditions for the hydrogen rich gas production. The experimental results indicated that high reaction temperature and high water flow rate were both beneficial to the hydrogen gas yield, but excess steam had a negative impact contrarily. Besides, the small size particles (0.5–1.0 mm) showed better performance in the hydrogen gas production at the low water flow rates (0.05–0.20 g/min); while the large size particles (1.0–2.8 mm) showed better performance at the high water flow rates (0.25–0.30 g/min). The suitable operating conditions for the gasification of the biochar were determined as the reaction temperature of 850 °C, water flow rate of 0.25 g/min, and particle size of 1.0–2.8 mm.     

Hydrogen-rich gas from catalytic steam gasification of eucalyptus using nickel-loaded Thai brown coal char catalyst

Hydrogen gas production from eucalyptus by catalytic steam gasification was carried out in an atmospheric pressure of two-stage fixed bed. The gasifier was operated with the temperature range of 500–650 °C and steam partial pressure of 16, 30 and 45 kPa; nickel-loaded Thai brown coal char was used as a catalyst. The yields and compositions of the gasification products depend on the operating conditions, especially, the reaction temperature and the steam. The yield of H₂ increased at elevated temperatures, from 26.94 to 46.68%, while that of CO dramatically decreased, from 70.21 to 37.71 mol%. The highest H₂ yield, 46.68%, was obtained at the final gasifying temperature of 650 °C. Eucalyptus catalytic steam gasification indicated that the maximum H₂/CO ratio reached 1.24 at the gasification temperature of 650 °C and the steam partial pressure of 30 kPa. It can be concluded that eucalyptus is appropriate for synthesis gas production from eucalyptus volatiles by catalytic steam gasification while using nickel-loaded brown coal char as a catalyst.     

Effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat

This paper reports the effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat. The unsteady model was set up, which has been applied to investigate the effects of particle sizes (1.77 mm–14.60 mm) on particle temperature, heat transfer quantity, overall coefficient of heat-transfer, etc. The heat transfer performance of waste heat recovery heat exchanger is improved when the particle size increases, which is conducive to increase hydrogen production. The particle temperature change rate, the specific enthalpy change rate, the moving velocity of the maximum heat release rate particle, the contribution rate of solid phases, the heat release rate and the overall coefficient of heat-transfer increase, but the effective time of heat transfer decreases. When the particle size increases from 1.77 mm to 14.60 mm, the solid phase average contribution rate increases from 89.43% to 94.03%, the overall coefficient of heat-transfer increases from 1.39 W m⁻² K⁻¹ to 13.41 W m⁻² K⁻¹, the heat release rate increases from 48.9% to 99.9% and the effective time of heat transfer reduces from 48 h to 6.7 h.