Computational fluid dynamics‐based design of finned steam cracking reactors

The use of one‐dimensional reactor models to simulate industrial steam cracking reactors has been one of the main limiting factors for the development of new reactor designs and the evaluation of existing three‐dimensional (3‐D) reactor configurations. Therefore, a 3‐D computational fluid dynamics approach is proposed in which the detailed free‐radical chemistry is for the first time accounted for. As a demonstration case, the application of longitudinally and helicoidally finned tubes as steam cracking reactors was investigated under industrially relevant conditions. After experimental validation of the modeling approach, a comprehensive parametric study allowed to identify optimal values of the fin parameters, that is, fin height, number of fins, and helix angle to maximize heat transfer. Reactive simulations of an industrial Millisecond propane cracker were performed for four distinct finned reactors using a reaction network of 26 species and 203 elementary reactions. The start‐of‐run tube metal skin temperatures could be reduced by up to 50 K compared to conventionally applied tubular reactors when applying optimal fin parameters. Implementation of a validated coking model for light feedstocks shows that coking rates are reduced up to 50%. However, the increased friction and inner surface area lead to pressure drops higher by a factor from 1.22 to 1.66 causing minor but significant shifts in light olefin selectivity. For the optimized helicoidally finned reactor the ethene selectivity dropped, whereas propene and 1,3‐butadiene selectivity increased with a similar amount. The presented methodology can be applied in a straightforward way to other 3‐D reactor designs and can be extended to more complex feedstocks such as naphtha. © 2013 American Institute of Chemical Engineers AIChE J 60: 794–808, 2014     

Preparation of Fine, Spherical Yttria-Stabilized Zirconia by the Spray-Pyrolysis Method

Fine yttria-stabilized zirconia powders were prepared by the spray pyrolysis of aqueous solutions of ZrOCl₂·8H₂O and Y(NO₃)₃·5H₂O (3 mol%). An appropriate thermal treatment resulted in slightly porous spherical particles with a narrow size distribution. The sintering ability of these powders was evaluated.     

Tetralin hydrogenation catalyzed by Mo2C/Al2O3 and WC/Al2O3 in the presence of H2S

Supported molybdenum and tungsten carbides were synthesized by temperature-programmed reactions. These materials were characterized by XRD, EDS analysis, HRTEM and CO chemisorption. Hydrogenation of tetralin was carried out at a total pressure of 4 MPa (3.06 MPa of H₂), at 573 K, without or with sulfur (200 ppm of sulfur as DMDS). The resulting activities were compared with those of MoS₂/Al₂O₃ and Pt (1% (w/w) metal loading) supported on Al₂O₃ or SiO₂. In the absence of sulfur, WC/Al₂O₃ showed an initial activity similar to that of Pt/SiO₂, higher than that of MoS₂/Al₂O₃ but lower than that of Pt/Al₂O₃. In the presence of H₂S, WC/Al₂O₃ showed a steady-state activity similar to that of Pt/Al₂O₃ (which suffered a marked deactivation). Post-reaction characterization did not show any sulfur poisoning of the supported carbides. Therefore the supported carbides are sulfur-tolerant and promising catalysts for the hydrogenation of aromatics in diesel fuels in the presence of small amounts of S-containing compounds.     

Factors affecting the concentration of acrylamide during deep‐fat frying of potatoes

The paper describes the effect of different factors influencing the concentration of acrylamide in deep‐fat fried potato products. In French fries the amount of acrylamide increased with the temperature as well as the frying time, especially at temperatures higher than 175 °C. The increase of acrylamide with the time followed a linear function, whereas a non‐linear relationship was given with the temperature of frying. As a result, a reduction of the processing temperature led to lower concentrations of acrylamide in the product. Both, oil type and silicon oil as antifoaming agents had no significant influence upon the acrylamide concentration in the food. The variety of potatoes had a strong effect on the acrylamide concentration in potato crisps and French fries. The investigation showed a significant correlation (r = 0.73) between the concentration of acrylamide and reducing sugars in raw potatoes, and no significant correlation with the asparagine concentration. The storage temperature of the raw material had an effect on the acrylamide concentration in the product. Lowering of the storage temperature from 8 to 4 °C resulted in an increase of the concentration of reducing sugars in the raw material, which led to a higher potential of acrylamide formation in the products. The experiments showed that the acrylamide concentration of French fries depended on the surface‐to‐volume ratio (SVR).     

Impact of flue gas radiative properties and burner geometry in furnace simulations

Three fully coupled Computational Fluid Dynamics (CFD) simulations of a complete industrial steam cracking furnace equipped with floor burners are performed. The influence of the flue gas radiative properties and burner geometry on the flame front in the firebox, the heat transfer to the coils and the product selectivities has been investigated. A nine‐band model developed from the Exponential Wide Band Model (EWBM) is used as nongray gas radiation model to compare with the gray gas implementation of Weighted Sum of Gray Gas Model for the evaluation of the flue gas radiative properties. The gray gas radiation model predicts a flue gas outlet temperature that is 70 K lower than the temperature obtained with the nongray gas radiation model, resulting in a 3.6% higher thermal efficiency and 44 K higher average Coil Outlet Temperature (COT). Important differences between the 22 reactors in the furnace are seen because of shadow effects with and without accounting for the detailed burner geometry. The maximum difference between the COT of different reactors in the furnace caused by shadow effects is about 29 K which corresponds to a propene‐over‐ethene difference of 0.1. Full furnace CFD simulations prove thus to be essential in design and during debottlenecking, when aiming for a more uniform COT distribution to the reactors by feed or fuel distribution. © 2015 American Institute of Chemical Engineers AIChE J, 2015 2014 American Institute of Chemical Engineers AIChE J, 61: 936–954, 2015     

Effect of dehulling on the composition of antinutritive compounds in various cultivars of rapeseed

Eight different rapeseed cultivars (Brassica napus L.) have been dehulled by hand. The contents of glucosinolates, sinapine, condensed tannins and inositol phosphates have been investigated in the resulting fractions of dehulled seeds and hulls as well as in the whole seeds by HPLC methods and a spectroscopical method for condensed tannins. After dehulling the content of glucosinolates as well as the content of sinapine and inositol phosphates increased significantly (P = 0.01) in the seeds of the different cultivars by 2.0 to 35.0%, 14.1 to 57.1% and 11.9 to 38.2%, respectively. The content of condensed tannins decreased by 26.0 to 81.2% after the dehulling process. In most of the cultivars the enrichment of antinutritive compounds corresponded to the share of hulls separated from the seeds. Only in the case of condensed tannins unproportional losses in the dehulled seeds were observed.     

Full-wave electromagnetic modelling of fabrics and composites

In this paper different types of fabrics and composites with conducting yarns are considered. The topology of the fabrics or composites is described using the type of format used in software tools originally developed to model their mechanical properties. The topology is simplified using a special conversion technique in order to allow fast electromagnetic analysis. Different possible approximations of conducting yarns used in the electromagnetic analysis are discussed. The analysis itself consists of the solution of the integral equations for the electric currents flowing on the conducting yarns, using the method of moments (MoM). For plane wave excitation the shielding effectiveness is calculated. The agreement between theory and experiments confirms the validity of the approach.     

Using wireless technology to develop a virtual reality command and control centre

This paper investigates the applicability of wireless communication systems for use in command and control environments. Human positional data is transmitted over a wireless network. This data is then used to update a highly accurately modelled real-time 3D environment of the surroundings, with avatars positioned at the transmitted points. The data is displayed on a stereoscopic 3D screen enabling novel automatic tracking of human movement and allowing for more rapid and informed tactical decision making. The system has applicability in a variety of C4I environments, including the military and emergency services.     

Direct model optimisation for data inversion. Application to ultrasonic characterisation of heterogeneous welds

Numerous multipass welds in austenitic stainless steel are made on the primary circuits of nuclear power stations. The heterogeneous anisotropic nature of these welds causes disturbance to ultrasonic propagation. Simulation is a useful tool when attempting to understand physical phenomena. With this objective, a finite element code called ATHENA was developed. Sufficiently realistic modelling of the material is proposed by the Modelling anIsotropy from Notebook of Arc welding (MINA) model, which determines the orientation of the weld grains. Optimisation by inversion of the MINA model is proposed in this study. The results validate the strategy and open perspectives regarding use on real data.