Study on the slurrying and rheological properties of coal–oilfield wastewater–slurry

In this study, oilfield wastewater (OWW) was used to prepare coal–oilfield wastewater–slurry (COWS), and the apparent viscosity, solid concentration, and rheological curve were studied. Compared with original coal–water–slurry (CWS), the maximum solid concentration of COWS increased, and the viscosity decreased; therefore, the slurrying ability of the coal slurry was improved with the use of OWW. However, although the oil in OWW promoted the slurrying ability of the coal slurry, its effectiveness was insufficient, and a chemical additive was still needed to obtain a coal slurry with enhanced slurrying ability. Both COWS and CWS exhibited shear-thinning behavior, and the rheological index value of COWS was lower, which indicated that pseudoplasticity of COWS was more obvious, and OWW improved the rheological properties of coal slurry.     

Enhancing the production of hydrogen via water–gas shift reaction using Pd-based membrane reactors

In this work, it is described an experimental study regarding the performance of a Pd–Ag membrane reactor recently proposed and suitable for the production of ultra-pure hydrogen. A dense metallic permeator tube was assembled by an innovative annealing and diffusion welding technique from a commercial flat sheet membrane of Pd–Ag. A “finger-like” configuration of the self-supported membrane has been designed and used as a packed-bed membrane reactor (MR) for producing ultra-pure hydrogen via water–gas shift reaction (WGS).     

Study of hydrogen production and storage based on aluminum–water reaction

The rate and yield of hydrogen production from the reaction between activated aluminum and water has been investigated. The effect of different parameters such as water–aluminum ratio, water temperature and aluminum particle size and shape was studied experimentally. The aluminum activation method developed in-house involves 1%–2.5% of lithium-based activator which is diffused into the aluminum particles, enabling sustained reaction with tap water or sea water at room temperature. Hydrogen production rates in the range of 200–600 ml/min/g Al, at a yield of about 90%, depending on operating parameters, were demonstrated. The work further studied the application in proton exchange membrane (PEM) fuel cells in order to generate green electric energy, demonstrating theoretical specific electric energy storage that can exceed batteries by 10–20 folds.     

β-Cyclodextrin grafted on alkali lignin as a dispersant for coal water slurry

A modified alkali lignin (AL) was synthesized by introducing β-cyclodextrin (β-CD) into AL with epichlorohydrin (EPI) copolymerization, which resulted in incorporating β-CD with AL by ether linkage. As a dispersant, β-CD copolymerized AL (β-CD-AL) was added into coal water slurry and its efficiency was evaluated. The effects of β-CD content on the performance of β-CD-AL were investigated via analyzing dispersity, zeta potential, and adsorption capacity. The results illustrated that β-CD-AL behaved better dispersion owing to the high slurry concentration at fixed apparent viscosity, which was mainly attributed to the synergistic effects of electrostatic repulsive force and steric hindrance. Steric hindrance originated from the side chain of β-CD gives better stability and less adsorption amount.     

A new hydrogenation-coupling approach for supra-equilibrium conversion in a water–gas shift reaction: Simultaneous hydrogen generation and chemical storage

This work reports a practical system of hydrogenation-coupled water–gas shift reaction (HC-WGSR) for simultaneous hydrogen production and storage. The performance of the HC-WGSR system was predicted through thermodynamic simulation. The proof-of-concept tandem water–gas shift and propene hydrogenation strategy was successfully demonstrated using a bifunctional catalyst. The hydrogen produced from the WGSR was successfully stored in propane simultaneously, and the overall CO conversion of nearly 100% overcame the equilibrium limitation of the WGSR over a wide range of space velocities (3000 - 6000 h⁻¹) at 200 ^°C and 1 bar. This study demonstrated that the in situ removal/storage of H₂ using the hydrogenation-coupling approach is promising even in a CO₂-rich environment (20% CO₂). The new approach shall see a great opportunity in using organic hydrogen carriers, e.g., benzene, toluene, N-ethylcarbazole, to expand the industrial applications, underpinning the global supply chain for hydrogen energy.     

Numerical investigations of catalyst–liquid slurry flow in the photocatalytic reactor for hydrogen production based on algebraic slip model

A new device of photocatalytic reactor with solar concentrator for hydrogen production was introduced in this paper. In order to investigate the effects of the slurry flow and catalyst distributions in the reactor on photocatalysis for hydrogen production, an algebraic slip mixture model (ASM) was used to simulate the dynamics of the catalyst–water slurry flow. A block-structured non-uniform grid was applied to discretize the entire domain and an algebraic multi-grid (AMG) method was used to solve the pressure field. The mean slurry pressure gradients obtained by the model were in agreement with the experimental data in former literature. Based on this verification, catalyst particle distributions, slurry velocity distributions and inter-phase slip velocity distributions in photocatalytic reactor pipe were investigated. The results show that the catalyst tends to distribute near the bottom of the pipe in the reactor, leading to a concentration gradient along the vertical direction of cross section. But due to the effects of turbulence force against the gravity, a heterogeneous suspending state will be achieved in a fully developed flow.     

Movable injection point–based syngas production in the context of underground coal gasification

Underground coal gasification (UCG) has been proven as a viable technology for the generation of high calorific value syngas using deep mine coal seams. The use of multiple injection points/movable injection point method could be an alternate technique for efficient gasification of high ash Indian coals. In this context, the present study is focused on evaluating the heating value of syngas using a variety of gasifying agents such as pure O₂, air, humidified O₂, and CO₂-O₂ dual-stage gasification under movable injection method for high ash coals. It is found that the use of movable injection point method had significantly increased the heating value of the product gas, compared with the fixed point injection method. For high and low ash coal under pure O₂ gasification, the calorific value of syngas obtained using movable injection point is 123.2 and 153.9 kJ/mol, which are 33.5% and 24.3% higher than the syngas calorific value obtained using fixed injection point, respectively. Further, the air as a gasification agent for high ash coals had increased the gross calorific value of the syngas by 24%, using this technology. The results of high ash coal gasification using humidified oxygen at optimum conditions (0.027-kg moisture/kg dry O₂) and CO₂-O₂ gas had enhanced the syngas calorific value by 12.6% and 5%, respectively. Humidified O₂ and CO₂-O₂ gasifying agents produced a high-quality syngas with the calorific value of 190 kJ/mol, among the gasifying agents used. The experimental results had shown that the movable injection point method is found to be a better alternative for the generation of calorific value-enriched syngas using high ash-based Indian coals.     

High-purity hydrogen gas from the reaction between BOF steel slag and water in the 473–673 K range

A novel method for producing hydrogen with water and BOF steel slag was developed. The steel slag was reacted with water during 2–57 days at 50 MPa for temperatures ranging from 473 to 673 K. The quantitative evolution of the slag and gas compositions indicated that the main H₂ producing reaction is:     

Co-precipitated Ni–Mg–Al catalysts for hydrogen production by supercritical water gasification of glucose

Supercritical water gasification (SCWG) is a promising process for hydrogen production from biomass. In this study, a series of Ni–Mg–Al catalysts with different Mg/Al molar ratios has been synthesized by a co-precipitation method for hydrogen production by SCWG of glucose. Effects of Mg addition on the catalytic activity, hydrothermal stability and anti-carbon performance of alumina supported nickel catalyst were investigated. The highly dispersed nickel catalysts prepared by co-precipitation could greatly enhance the gasification efficiency of glucose in supercritical water. Among the tested Ni–Mg–Al catalysts, NiMg_0.6Al_1.9 showed the highest catalytic activity with the hydrogen yield of 11.77 mmol/g (912% as that of non-catalytic test). NiMg_0.6Al_1.9 also showed the best hydrothermal stability probably due to the formation of MgAl₂O₄. Mg could efficiently improve the anti-carbon ability of Ni–Al catalyst by inhibiting the formation of graphite carbon. It is also confirmed that MgO supported nickel catalyst is not suitable for SCWG process owing to the difficulty on nickel oxides reduction in the precursors and the phase change of MgO to Mg(OH)₂ under the hydrothermal condition.     

The optimization of Nb loading amount over Cu–Nb–CeO2 catalysts for hydrogen production via the low-temperature water gas shift reaction

The effect of Nb promotion over a Cu–CeO₂ catalyst was investigated in the low-temperature water gas shift reaction. The Nb loading amount was systematically varied from 0 to 5 wt% for the Cu–Nb–CeO₂ catalyst, and the 1 wt% Nb promoted Cu–Nb–CeO₂ catalyst exhibited the highest catalytic performance even at extremely high GHSV of 72,152 h⁻¹. The catalysts were characterized through various techniques such as Brunauer-Emmet-Teller measurements, X-ray diffraction, N₂O-chemisorption, H₂-temperature programmed reduction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was found that the superior performance of the 1 wt% Nb promoted Cu–Nb–CeO₂ catalyst was due to its enhanced reducibility, high BET surface area, small metallic Cu crystallite size, and high number of oxygen vacancies.     

Comparison of co–gasification efficiencies of coal,lignocellulosic biomass and biomass hydrolysate for high yield hydrogen production

The diversity in the chemical composition of lignocellulosic feedstocks can affect the conversion technologies employed for hydrogen production. Gasification and co–gasification activities of lignocellulosic biomass, biomass hydrolysate, and coal were evaluated for hydrogen rich gas production. The hydrolysates of biomass materials showed the best performance for gasification. The results indicated that biomass hydrolysates obtained from lignocellulosic biomass were more sensitive to degradation and therefore, produced more hydrogen and gaseous products than that of lignocellulosic biomass. The effects of feed (kenaf and sorghum hydrolysate), flow rate (0.3–2.0 mL/min) and temperature (700–900 °C) on hydrogen production and gasification yields were investigated. It was observed that 0.5 mL/min the optimum feed flow rate for the maximum total gas and hydrogen production. Synergism effects were observed for co–gasification of coal/biomass and coal/biomass hydrolysate. In all co–gasification processes, the main component of the gas mixture was hydrogen (≥70%).     

Detailed analysis of the operational characteristics of the steam reformer and water–gas shift reactors for 5 kW HT-PEMFCs

The reactors designed for 5-kW high-temperature polymer electrolyte fuel cells are able to evaluate the performance of the steam reformer and each water–gas shift reactor independently. The goal of the experiments is to obtain the best overall performance for steam reforming while minimizing the CO concentration and maximizing the hydrogen yield. For this purpose, the performance of the steam reforming reactor unit with two types of flow paths was evaluated while evaluating the performance of various series of component combinations of the high-, middle-, and low-temperature shifts. Via experiment, thermal control followed by the appropriate heating and cooling mechanism is key to successful reaction performance. In addition to an individual unit-based experiment, numerical analyses were executed to understand the local chemical performance inside a reactor unit. These numerical analyses show good agreement with the experimental data measured at the outlet and provide a comprehensive detailed internal reaction mechanism such as the thermal conditions and CO concentration effect. Both experiments and numerical analyses can fundamentally improve the reaction performance by finding the optimal values of many control parameters.     

Production of ultrapure hydrogen in a Pd–Ag membrane reactor using noble metals supported on La–Si oxides. Heterogeneous modeling for the water gas shift reaction

Two different catalysts, Rh(0.6% wt/wt)/La₂O₃(27% wt/wt)·SiO₂ and Pt(0.6% wt/wt)/La₂O₃(27%)·SiO₂, were tested in the WGS reaction. Their performances were first studied in a conventional fixed-bed reactor. Their activities were similar and they were both very stable. However, as Pt(0.6)/La₂O₃(27)·SiO₂ showed a much higher selectivity to the desired reaction, the performance of a membrane reactor employing this catalyst was studied. The effects of the H₂O/CO ratio, space velocity, sweep gas flow rate and size of the catalyst particle on CO conversion and H₂ recovery were studied at laboratory scale under isothermal conditions. A 1-D heterogeneous model was developed in order to properly reproduce the experimental results obtaining good agreement between the simulation results and laboratory data. The experimental and theoretical results confirm the existence of significant external mass-transfer limitations in the fluid-particle interface for these very active formulations.     

Combustion of hydrogen–oxygen microfoam on the water base

On the basis of experimental study the paper analyzes the process of combustion wave propagation in the hydrogen–oxygen microfoam on the water base. Combustible microfoam consists of gaseous bubbles dispersed in the water solution of surfactant. Bubbles contain hydrogen and oxygen and their diameters are in the range from 60 to 230 μm. Expansion ratio of the combustible foam is in the range from 8 to 22. The paper establishes the influence of surfactant concentration, glycerol concentration, tube diameter and Shchelkin's spiral on the speed of flame propagation in the foam. It is shown that for considered range of regime parameters the characteristic mode of flame propagation in the semi-opened tube is the accelerated mode. The increase in glycerol content leads to the increase in flame speed. However after certain critical concentration of glycerol the foam loses the ability to burn. Total burning rate depends on surfactant concentration non-monotonically with characteristic maximum. Shchelkin's spiral installed at inner surface of the tube as well as the decrease in tube diameter favor flame deceleration.     

A kinetic study on the structural and functional roles of lanthana in iron-based high temperature water–gas shift catalysts

The structural and functional roles of varying amounts of lanthana in co-precipitated high temperature Fe₂O₃/Cr₂O₃/CuO water–gas shift catalysts were studied at 1 atm and 350–425 °C temperature range.     

Performance prediction and evaluation of the scroll-type hydrogen pump for FCVs based on CFD–Taguchi method

To improve hydrogen utilisation and provide superior water management, the recirculation hydrogen pump is one of the key components in a fuel-cell vehicle (FCV). This work focused on the performance estimation of a scroll-type hydrogen pump for FCVs. A series of CFD simulation cases were designed using the Taguchi method and were carried out to determine the optimum conditions for volumetric efficiency, and the effects of four factors, including pressure ratio, rotating speed, axial clearance, and radial clearance. The contributions of these factors on volumetric efficiency and shaft power were quantified by the analysis of variance (ANOVA) method. The results show that axial clearance and rotating speed are the main influencing factors on volumetric efficiency, and their contribution ratios are 45.3% and 39.6%, respectively, in the operational range of the hydrogen pump for FCVs. Pressure ratio and rotating speed should be considered first to reduce shaft power, and their contribution ratios are 40.9% and 55.4%, respectively. At last, the performance maps of the scroll-type hydrogen pump were obtained to reveal the dynamic changes at various working conditions. It is found that volumetric efficiency and shaft power are more sensitive to the change in rotating speed when the pressure ratio deviates from the designed value. The results can be used as guidelines for component matching in the design and operation of PEM fuel cell systems.     

Study on water–gas shift reaction performance using Pt-based catalysts at high temperatures

The water–gas shift reaction (WGSR) performance was experimentally studied using Pt-based catalysts for temperature, time factor and steam to carbon (S/C) molar ratio at ranges of 750–850 °C, 10–20 g_cat h/mol_CO, and 1–5, respectively. Al₂O₃ spheres were used as the catalyst support. For the high S/C cases, it was found that CO conversion can be enhanced when Pt/CeO₂/Al₂O₃ catalyst was used as compared with Pt/Al₂O₃. For the low S/C ratio cases, CO conversion enhancement was not significant with the addition of CeO₂. It was also found that CO conversion was not influenced by the CeO₂ amount to a large extent. Using bimetallic Pt–Ni/CeO₂/Al₂O₃ catalyst, it was found that higher CO conversion can be obtained as compared with CO conversions obtained from monometallic catalysts (Pt/Al₂O₃ or Pt/CeO₂/Al₂O₃). The experimental data also indicated that good thermal stability can be obtained for the Pt-based catalysts studied.     

Effect of Cu loading on Cu/ZnO water–gas shift catalysts for shut-down/start-up operation

Cu/ZnO catalysts with Cu loadings of 44–5 wt% were prepared by coprecipitation and evaluated in temperature-dependant and shut-down/start-up water–gas shift (WGS) reactions using realistic reformate. These catalysts had similar Cu crystallite sizes, and the metallic Cu surface area and surface Cu content increased with the Cu loading. In temperature-dependent reactions, the CO conversion on the 25wt%Cu/ZnO catalyst slightly exceeded that on 44wt%Cu/ZnO. In shut-down/start-up operation, which is imperative for mobile and residential fuel cell applications, the catalysts with Cu loadings higher than 5 wt% suffered slight activity loss. Among them, the 15wt%Cu/ZnO catalyst deactivated the most reluctantly. As a result, after three shut-down/start-up cycles the CO conversion on 15wt%Cu/ZnO, 25wt%Cu/ZnO, and 44wt%Cu/ZnO became comparable. These results demonstrate the feasibility to lower the Cu loading without degrading the WGS performance of the Cu/ZnO catalyst in shut-down/start-up operation, which will guarantee the operation safety when the catalyst will be operated unattended for domestic small-scale fuel cell applications. Unexpectedly, the CO conversion was doubled on 5wt%Cu/ZnO after one shut-down/start-up cycle, which is interpreted as the redispersion of Cu nanoparticles based on transmission electron microscopy (TEM) and temperature-programmed reduction (TPR).     

A study on the Fe–Cl thermochemical water splitting cycle for hydrogen production

Thermochemical water splitting cycles are recognized as one of the promising pathways for sustainable hydrogen production. In the present study, Iron-chlorine (Fe–Cl) cycle as one of the chlorine family thermochemical cycles where iron chloride is consumed for hydrogen production from water, is considered for a study. This four-step cycle is modelled by Aspen Plus software package and analyzed for performance investigation of each reaction step and system's components. The parametric studies are also performed to assess the effect of operation conditions such as temperature, pressure and steam to feed ratio on the reaction products and conversion rates. Results indicated that although the effect of pressure is not significant on reaction's production rates, an increase in temperature favors oxygen production in reverse deacon reaction and magnetite production in hydrolysis and lowers hydrogen production in the hydrolysis step. On the other hand, steam to chlorine (Cl₂) ratio is directly correlated with hydrochloric acid (HCl) and oxygen production in reverse deacon reaction and hydrogen production in hydrolysis.     

Reactivity tests of the water–gas shift reaction on fresh and used fluidized bed materials from industrial DFB biomass gasifiers

The dual fluidized bed gasification process, offers various advantages for biomass gasification as well as the utilization of other solid feedstocks. In order to improve the knowledge of the reactions in fluidized bed gasifier, different types of bed material used in the gasifier were tested in a micro-reactivity test rig. It has been previously observed that during long-term operation, the surface of the bed material used (calcined olivine) undergoes a modification that improves catalytic activity. The main reaction of interest is the water–gas shift reaction. Olivine taken from long-term operation at the 8 MW biomass gasifier at Güssing (Austria), fresh olivine as a reference, and calcite, which is commonly used for enhancing in-bed catalytic tar reduction, were tested using the micro-reactivity test rig. Tests were carried out at temperatures of 800, 850, and 900 °C and space velocities of 40,000 to 50,000 h⁻¹ were applied. CO conversions of up to 61.5% were achieved for calcite. Used olivine showed a similar behavior, representing a large improvement compared to fresh olivine, which had CO conversion rates of less than 20%.