Search

• Rh-containing catalysts were prepared by sorption-hydrolytic deposition. • 1–2-nm metal particles homogeneously spread over supports. • Composite Rh/Zr 0.25 Ce 0.75 O 2-δ /FeCrAl wire mesh module show high activity. • Stable operation in n-hexadecane ATR for at least 75 h on stream. • Complete conversion of diesel with high aromatics content in autothermal reforming. Catalytic autothermal reforming is considered as one of the most effective methods for production of hydrogen from heavy hydrocarbon fuels for solid oxide fuel cells (SOFC). Diesel is an attractive fuel because of its high energy density, widespread use and well – developed infrastructure. Catalysts supported on structured carriers (e.g. FeCrAl modules) provide controlled reaction conditions throughout the reactor volume that favorably compete, for example, with fixed bed reactors. The use of structured catalysts provides efficient heat and mass transfer, low gas dynamic resistance, and high catalyst performance that facilitates the reduction of catalyst quantity per unit volume of the reactor. The ability to perform the process under controlled optimum conditions leads to increased selectivity and minimizes undesirable side reactions, such as coke formation. In the present work, the active component Rh/Ce 0.75 Zr 0.25 O 2-δ was supported on FeCrAl metal meshes using Al 2 O 3 as a binding structural component. The obtained catalysts Rh/Ce 0.75 Zr 0.25 O 2-δ -ƞ-Al 2 O 3 /FeCrAl were tested in laboratory and pilot scale reactors in n-hexadecane and diesel autothermal reaction conditions. Winter grade diesel used in the experiments contained up to 31% of aromatics. Operating conditions were found to provide a 100% conversion of n-hexadecane and diesel and stable catalyst activity for a long time-on-stream exposure. The catalysts provided equilibrium product distribution and a maximum syngas (CO + H 2) productivity of 3 m3L cat −1h−1 (STP) at the studied experimental conditions. The produced syngas can be supplied as a fuel for power generation units based on high-temperature solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Highlights • A mesh-pin rotor was designed with the purpose of anti-blockage in RPB reactor. • Mass transfer model of RPB reactor with this rotor was established and validated. • The liquid holdup correlations of different zones in RPB reactor were proposed. • The RPB reactor with this novel rotor displays potential application prospects. Abstract A rotating packed bed (RPB) reactor with full stainless steel wire mesh packing loaded in the rotor has excellent mass transfer performance. However, it has the blockage problem when applied to the reactions with solid generated on the surface of the packing. In this work, a mesh-pin rotor (MPR), combining an inner wire mesh packing zone (IMZ) and an outer resin pin zone (OPZ), was designed with the purpose of anti-blockage for the first time, expecting to possess the high mass transfer performance of wire mesh packing and self-cleaning performance of cylindrical pins. With the assistance of liquid holdup measurement by X-Ray CT scan technology, a mass transfer model was proposed for the RPB reactor with MPR and the liquid-side volumetric mass transfer coefficient (k L a e) was measured by using an oxygen-water desorption system. The predicted results by the model showed good agreement with the experimental results within a deviation of ±20%, displaying potential application prospects. [ABSTRACT FROM AUTHOR]

• The flow and breakage processes of two liquid jets impacting on SSM were studied. • Compared with 2 θ = 30°, the values of d avg at 2 θ = 90° decreased by 32%. • The breakage mode at mesoscale is result of surface tension and inertia force. • Deviation of L s / D 0 between calculated and experimental values was within ± 15%. The flow and breakage behaviors of two liquid jets is of great importance for liquid–liquid mixing and reaction applications. However, the flow behaviors and breakage processes of two liquid jets impacting on the stainless steel wire mesh (SSM) is not clear. In this work, the high-speed photograph method was employed to study the behaviors of two liquid jets impacting on SSM. Effects of impinging angle (2 θ), liquid initial velocity (u 0), mesh number (M), and liquid jet diameter (D 0) on liquid flow and breakage behaviors were investigated. Experimental results showed that the jets of water-water impacting on the SSM were broken into liquid jets and further broken into daughter droplets. The cone angle of dispersion increased with the increase of 2 θ , u 0 , M , and D 0 , and reached the maximum value of 180°. The average diameter of daughter droplets at 2 θ = 90° decreased maximally by 32%, compared with the condition of 2 θ = 30°. For two liquid jets of water- n -hexane impacting on the SSM, a liquid sheet was formed. Under different operating conditions, the breakage mode of liquid sheet could be divided into marginal breakup and internal breakup. The breakage model at mesoscale is the result of surface tension and inertia force, both of which are relevant to the complex impact and flow behaviors. The liquid sheet length (L s) decreased with the increase of u 0 and M. A correlation to calculate L s / D 0 was proposed and the calculated results lied within ± 15% of the experimental values. This study provided a theoretical basis for the guidance of mass transfer enhancement and the reactor design with liquid–liquid system. [ABSTRACT FROM AUTHOR]

Global (level swell) and local (WMS – Wire Mesh Sensor) measurements were made on waters of different purities and air, in a cylindrical laboratory bubble column (2 m tall, 0.127 m dia) using two different gas distributors: a perforated plate (to produce homogeneous flow) and a spider sparger (to produce heterogeneous flow). The level swell method provided the steady space-averaged gas holdup/gas flow rate data. The WMS method provided the actual gas holdups and bubble sizes resolved in time and space at one cross-sectional horizontal plane (1 m above distributor), whose integration yields the time-averaged data. The following results were obtained: The global and local data agree relatively well; there are distinct differences between the radial profiles and bubble size distributions between the two main flow regimes; the local information identifies why the predictions of published models, which account for the smaller and larger bubbles in the flow, may not perform well; the modelling approaches based on the hindrance and enhancement concepts prove to be suitable for the flow regime identification and description, including the transition range between the homogeneous and heterogeneous flows; based on the hydrodynamics, the specific interfacial area is obtained, together with the mass transfer coefficient. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cross-flow rotating packed bed for NO x oxidation and removal was developed. • Oxidation degree was increased by 1.7 times after internal optimization. • Cross-flow rotating packed bed intensified mass transfer between NO x and Na 2 SO 3. • Oxidation degree and removal efficiency can reach up to 92% and 84% respectively. Stricter emission standards of NO x from marine exhaust call for efficient NO x removal method. In this work, a wet denitration intensification method conducted in novel Cross-flow rotating packed bed (CFRPB) reactor was proposed to meet the confined space requirement. In the CFRPB, the enhancement of oxidation and absorption were simultaneously achieved during NO x removal process. The NaClO 2 and Na 2 SO 3 solution were employed as liquid oxidant and absorbent, respectively. NO x oxidation was intensified by Gas-phase disturbance internal (GPDI) and multilayer wire mesh internals. The oxidation degree (α) was increased by 1.7 times after internal optimization. NO x absorption process was intensified via the high-gravity environment created by rotating packing. Effects of various operation parameters on NO x oxidation and absorption were also investigated. α and NO x removal efficiency (η) can reach up to 92% and 84%, respectively. Compared with traditional scrubbers, CFRPB has higher value of volumetric mass-transfer coefficient, which displays great potential for NO x removal from marine exhaust. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D multiphase CFD model of an RPB with wire mesh packing is developed. • Macroscopic and microscopic characteristics of the liquid flow are analysed. • Dynamic evolution processes of liquid droplet in the packing region are analysed. • The interfacial areas between different phases in the RPB are analysed. An in-depth understanding of the liquid flow characteristics in rotating packed beds (RPBs) is very important for the optimization and modelling of RPB reactors. However, the complex and dense packing makes it very difficult to accurately obtain the dynamic and detailed characteristics of liquid flow in RPBs through experimental methods. Therefore, this paper carried out a 3D gas–liquid flow CFD simulation of an RPB with structured wire mesh packing to obtain detailed liquid flow information. Detailed macro and micro characteristics of the liquid flow in the packing region of the RPB are obtained. The dynamic evolution processes of droplets are observed and analysed. A new flow pattern of "branch flow" is observed in the packing region. In addition, two typical liquid disintegration modes of liquid ligament-droplet disintegration and liquid bridge-droplet disintegration are observed, and the disintegration mechanisms are analysed. Finally, the effects of contact angle and rotational speed on the characteristic parameters are investigated, and the interfacial areas between different phases in the RPB are analysed. In both hydrophilic and hydrophobic packings, the wetted packing surface area is always less than the gas–liquid interfacial area, and their ratio decreases with the increases of contact angle and/or rotational speed, but increases with the increase of the liquid viscosity. [ABSTRACT FROM AUTHOR]

Abstract: Pyrolysis is known to occur by decomposition processes followed by vapour phase reactions. The goal of this research is to develop a novel device to study the initial decomposition processes. For this, a novel wire-mesh reactor was constructed. A small sample (<0.1g) was clamped between two meshes that were heated fast (up to 10000°C/s, ΔT mesh ±35°C) by an electrical current. The mesh/feedstock was placed inside a vacumized (P <0.3mbar), liquid nitrogen cooled vessel (T wall <−80°C). These two last features were proven to result in a low vapour life time (<15–25ms versus ∼2s in typical pyrolysis). The vapour residence time and temperature could be increased by increasing the pressure inside the reactor and by removing of the liquid nitrogen cooling. Reproducible results concerning yields (mass balance closures 90–110wt%) and analysis were obtained (oil by SEC and NMR, gas by GC, char by FTIR). The yields and oil composition were changing with loading from 0.05g to 0.1g, despite the small sample amounts. Compared to more “conventional” pyrolysis processes, high oil yields (84wt%), very low char yields (5wt%) and low gas yields (8wt%) were obtained. Using a high speed camera, movies were made and together with accompanying pressure profiles, it was possible to estimate the conversion rate. At 500°C the conversion process was finished within 0.8s which is faster than previously reported in the literature. Especially an increase in gas yield (+14wt%, mainly CO) was observed in absence of cooling (P vac/No Cooling), while both the gas (+4wt%) and char yield (+3wt%) increased under atmospheric pressure (P atm/Cooling), all at the expense of oil yield. Compared to more “conventional” pyrolysis oil, the oil did contain: (i) heavier molecules and (ii) a sugar fraction. [Copyright &y& Elsevier]

Abstract: In fast pyrolysis, biomass decomposition processes are followed by vapor phase reactions. Experimental results were obtained in a unique wire-mesh reactor using pine wood, KCl impregnated pine wood and several model compounds (cellulose, xylan, lignin, levoglucosan, glucose). The wire-mesh reactor was typically operated at a set temperature of 500°C, high heating rates (up to 7000°C/s) under vacuum and with liquid nitrogen cooling to ensure a short vapor residence time (<15–25ms) and a low vapor phase temperature. In this way good suppression of vapor phase reactions and reactions inside the decomposing particle were achieved as shown by the (almost) complete recovery of glucose and levoglucosan after pyrolysis. The influence of temperature (250–700°C) and heating rate (50–7000°C/s) was studied on product yields and compositions (GC, SEC, NMR, FTIR, HPLC). A high oil yield of 84wt% and a low char yield of 5wt% was observed for pine wood around 500°C. Above this temperature a slight drop in oil yield was observed, but the oil yield was still 60wt% at 700°C. Also high oil yields and low char were obtained during the pyrolysis of cellulose (oil/char: 95/0wt%) and lignin (oil/char: 78/12wt%). Our data were interpreted with a physical–chemical mechanism. The basic idea behind this mechanism is that the amount and composition of the “decomposing biomass”, which can be in the solid or liquid state under the pyrolysis conditions, is changing in time due to competition between (cross)-linking reactions, scission reactions and mass transfer of decay fragments out of the decomposing particle. Observations such as the twice as large char yield for K-impregnated pine wood (10wt%) compared to untreated pine wood (5wt%) and the 20wt% increase in char yield from lignin when decreasing the heating rate from 6000 to 60°C/s could be explained by this mechanism. [Copyright &y& Elsevier]

Abstract: The objective of this work is to investigate characteristics of counter-current bubbly flow in a circular pipe with an inner diameter of 50mm by using wire mesh tomography (WMT). The accuracy of WMT on void fraction measurement is also clarified by comparing the result with a non-intrusive optical method. The accuracy is within ±10%. Local void fractions of many flow conditions are reported. Local void fraction profile affected by superficial liquid velocity and bubble size is shown and discussed. Furthermore, intrusive effects, including bubble break-up and bubble deceleration, are also investigated. Bubbles passing a transparent wire mesh sensor (WMS) are investigated by the optical method. It is shown that bubbles are broken and decelerated by wires of the sensor. It can be concluded that the bubble break-up rate increase with increasing of bubble velocity. However, the bubble deceleration is not depending on the bubble velocity. [Copyright &y& Elsevier]