A kinetic-empirical model for particle size distribution evolution during pulverised fuel combustion

Particle size is an essential parameter in pulverised fuel (PF) combustion as many of the problems or further areas of development in these systems are strongly influenced by the fuel and ash size distribution. This is particularly true for dynamic processes like pollutant formation, corrosion, erosion, slagging and fouling and the related decrease of the combustion and boiler efficiency. The evolution of particle size distribution (PSD) is a complex interaction of various competing chemical and physical transformations. Char oxidation, devolatilization and fragmentation, etc. represent first line physical and chemical transformations which can amend the particle size in the radiation zone. The evolution of the PSD represents the convolution of all of these physical and chemical transformations, operating over the entire size distribution. As a consequence, it is difficult to extract the relative importance of all competing size altering processes from the experiments. Various models such as break-up, thermal stress, shrinking core, percolation and particle-population model have been developed by incorporating numerous ash transformation mechanisms to predict the particle size evolution during the pulverised fuel combustion. The present work describes an adaptation of the numerical kinetic-based particle-population balance for predicting particle size evolution during PF combustion developed by Dunn-Rankin and Mitchell. The model is further simplified analytically and validated against experimental results. Several empirical parameters derived from the experiments are incorporated into the model. The resulting simplified PSD evolution model shows good agreement with literature and experimental results, with maximum 10% absolute standard deviation.     

The influence of oxygen ambient annealing conditions on the quality of Al/SiO2/n-type 4H-SiC MOS structure

The effect of reoxidation process in O₂ on the electrical properties of metal-oxide-semiconductor (MOS) capacitors fabricated on n-type 4H-SiC (0 0 0 1) is investigated. All samples were oxidized in wet oxygen at temperature of 1175 °C. Reoxidation process was carried out on four of the five samples. Samples were annealed at temperature of 700 °C and 800 °C for different process times. The reoxidation process in oxygen improves the quality of the dielectric layer and the interface of Al/SiO₂/n-type 4H-SiC MOS structure. The best quality of the SiO₂/SiC interface can be achieved for the MOS structure annealed in O₂ at higher temperature (800 °C) for longer time. However, higher and more uniformly distributed values of breakdown voltage were obtained for MOS structures reoxidized at temperature of 700 °C.     

Antioxidants in thermally treated buckwheat groats

The seeds of buckwheat (Fagopyrum esculentum Moench L.) were dehulled and then, following milling, extruded on a counter rotating, twin-screw extruder with the different barrel temperature profiles: 120, 160, and 200 degrees C. After extrusion cooking process, the following compounds were analyzed: free and conjugated phenolic acids, total polyphenols (TPC), tocopherols (T) and tocotrienols (T3), inositol phosphates (IP), reduced glutathione (GSH), and melatonin (MLT). The antioxidant capacity and superoxide dismutase-like activity (SOD-like activity) were determined in the groats and extrudates. Extrusion caused a significant decrease in all the compounds tested, except for phenolic acids. The content of IP decreased by 13%, that of GSH by 42%, and that of T + T3 by 62%. A three-fold lower level of MLT and TPC was noted whereas the SOD-like activity disappeared when compared to the nonextruded material. A two-fold higher content of phenolic acids (free and released from ester bonds) was observed. In spite of the clear decrease in the investigated antioxidants, the extruded dehulled buckwheat seeds contained still significant content of bioactive compounds, which resulted in as little as an average 10% decrease of the antioxidant capacity.     

Iatrogenic or congenital arteriovenous fistula of left upper arm used for hemodialysis after venous superficialization

The authors report a case of iatrogenic brachial arteriovenous fistula (AVF) on the left arm in a 20‐year‐old man with a history of autosomal dominant polycystic kidney and failing kidney transplant. An attempt to create vascular access for hemodialysis by utilization of an existing iatrogenic brachial AVF was undertaken. The patient underwent surgical superficialization of a concomitant enlarged and deeply located vein. Four weeks after the procedure, the AVF was successfully cannulated for hemodialysis. In this case, iatrogenic/congenital AVF was successfully converted to vascular access for hemodialysis.     

Fast-curing polyurethane adhesives derived from environmentally friendly hyperbranched polyglycerols - The effect of macromonomer structure

Transformation of glycerol to hyperbranched polyglycerols (HBPGs) and their further application as macromonomers for fast-curing polyurethane adhesives were described. An approach allowing for using of hyperbranched polyglycerols derived from renewable glycerol in adhesive technology was investigated. Four hyperbranched polyglycerols of different structures and functionalities were synthesized and crosslinked with polymeric methylenediphenyldiisocyanate (pMDI) and hexamethylenediisocyanate (HDI). Macromolecule functionality and functional group distribution were shown to be a critical factor in terms of the adhesive performance. The studied approach allowed to conclude that environmentally friendly polyglycerols - derived from renewable glycerol - when properly designed could successfully replace petroleum-based ones.     

Hydrogen production by direct injection of ethanol microdroplets into nitrogen microwave plasma flame

Liquid ethanol introduced as microdroplets into the tip of microwave nitrogen plasma, operating at 2.45 GHz under atmospheric pressure, has been investigated. Injection of ethanol outside the region of plasma generation eliminated a problem of soot formation at that region, which was responsible for short reactor lifetime. Using liquid ethanol allows to save energy needed for vaporization. Hydrogen, carbon monoxide and solid carbon were the main outlet products. Other products detected with gas chromatography were CH₄, C₂H₄ and C₂H₂. The best results concerning hydrogen production were as follows: concentration in the outlet gas up to 28%, production rate up to 1043 L/h, energy yield up to 209 L per kWh of microwave power, and were obtained for liquid C₂H₅OH flow rate of 3.7 L/h. A numerical 0D model was used to determine contributions of chemical reactions in formation of measured gaseous products. Simplified model involving only radical reactions without any ions and electrons predicts final concentrations of main compounds quite well for microwave power up to 4 kW.     

MIP model for efficient dimensioning of real-world FTTH trees

We propose a mixed-integer programming (MIP) formulation for a problem of optimal dimensioning of equipment of the fiber-to-the-home optical access network (FTTH-OAN). The optimization aims at minimizing capital expenditures (CAPEX) related to deployment of the FTTH-OAN, i.e., the cost of active equipment (OLTs and OLT cards), cost of passive equipment (optical splitters, cables, fibers, fibers terminations, splices, closures), cost of site preparations (building, cabinets), and cost of necessary labor (duct preparation and rollout of cables). The formulation has been implemented and validated. General results based on selected real-world scale numerical experiments are presented.     

Experimental determination of intrinsic permeability of limestone and concrete: Comparison between in situ and laboratory results

The study is concerned with development of the method of in situ measurement of air permeability of porous media. The method applied consists of creating a vacuum in a drilled hole and then studying the increase in pressure over time. The dimensions of the hole are small enough to consider the test as being nondestructive. The paper is composed of three parts. The first one develops the theoretical background used for interpretation of experimental results. The second part describes experimental procedure and device for in situ measurements. The parametric studies of principal factors which may influence the measurements such as the sampling frequency, the observation time and the boundary conditions were performed. The last part includes a discussion of results of the measurements of air permeability performed on large blocks of limestone and concrete. These blocks simulate in situ conditions. On the other hand, from these blocks, cylindrical samples were cored and standard gas and liquid laboratory tests were carried out. The results obtained show good agreement between intrinsic permeability obtained with the in situ device and laboratory tests, confirming the usefulness of the proposed tool.