Numerical investigation of the oxy-fuel combustion in large scale boilers adopting the ECO-Scrub technology

The present paper presents a three-dimensional numerical investigation of a pulverized-fuel, tangentially-fired utility boiler located at Florina/Greece under air, partial and full oxy-fuel conditions. Heat and mass transfer and major species concentration, such as CO₂, CO and O₂ are calculated; whilst the results for the reference air case scenario studied are in good agreement with the corresponding operational data measured in the plant, both for combustion calculations and NO_x emissions. Results for the partial and full oxy-fuel operation scenarios are in line with similar experimental and numerical investigations found in the recent literature. This numerical investigation of oxy-fuel conditions scenarios prior to their implementation under real scale conditions demonstrates the utmost of its importance, since significant results regarding the operation of a boiler in terms of lignite particle trajectories and burning rates are attained. Furthermore, NO_x calculations have been performed for all the examined case studies.     

Modeling and Control of a Titania Aerosol Reactor

We focus on modeling and control of an aerosol flow reactor used to produce titania powder. We initially present a detailed population balance model for the process which accounts for simultaneous nucleation, Brownian and shearinduced coagulation, and convective transport and describe the spatio-temporal evolution of the aerosol volume distribution. Then, under the assumption of lognormal aerosol volume distribution, the method of moments is employed for the derivation of a model that describes the evolution of the three leading moments of the volume distribution. The moment model, together with the fundamental model that describes the temperature in the reactor and concentrations of the gas-phase species, are subsequently used to synthesize a nonlinear output feedback controller which manipulates the temperature of the reactor wall to achieve an aerosol size distribution in the outlet of the reactor with desired geometric average particle diameter. The nonlinear controller is successfully implemented on the process model and is shown to deal effectively with external disturbances.     

Single-step synthesis of N-doped TiO2 by flame aerosol method and the effect of synthesis parameters

We have established a novel route for the synthesis of N-doped TiO₂ by adopting flame aerosol (FSP) technique and investigated the effect of water content on the physico-chemical properties of the as-synthesized nanoparticles. The key characteristics of the developed method are to modify the precursor solution in order to incorporate nitrogen atoms into the TiO₂ lattice without altering the FSP set-up. The reduction of the flame enthalpy resulting in N-incorporation into the TiO₂ and the N-doping can be greatly enhanced further by the addition of secondary N-source (urea). Our XRD results reveal a shift of the (101) plane anatase diffraction peak to lower angles in our N-doped TiO₂ compared to undoped TiO_2, which suggest the distortion and strain in the crystal lattice prompted by the incorporation of the nitrogen atoms. The growth or expansion of crystal lattice can be attributed to the larger atomic radius of respective nitrogen atoms (r?=?1.7 Å) compared to oxygen (r?=?1.40 Å). Our XPS and EDX spectroscopy results elucidate that the nitrogen was effectively doped into the crystal lattice of TiO₂ in our as-synthesized N-TiO₂ catalysts predominantly in the form of interstitial nitrogen (Ti?O?N). The nitrogen atoms incorporation into the crystal lattice of titania modifies the electronic band structure of TiO₂, resulting in a new mid-gap energy state N 2p band formed above O 2p valence band. This occurrence narrows the band gap of TiO₂ (from 3.12 to ～2.51?eV) in our N-doped TiO₂ and shifts the optical absorption to the visible region.

Copyright © 2018 American Association for Aerosol Research     

Anthocyanin profiles of major red grape (Vitis vinifera L.) varieties cultivated in Greece and their relationship with in vitro antioxidant characteristics

A range of fourty‐six red grape (Vitis vinifera spp.) samples, originating from six widely cultivated varieties and covering major parts of the Hellenic vineyard, were assayed for their content in six principal anthocyanin pigments. Representative in vitro antioxidant parameters were also determined, including antiradical activity (A_AR), reducing power (P_R) and hydroxyl free radical scavenging activity (SA_HFR). Quantitative determination using high performance liquid chromatography showed that the prevalent pigment was malvidin 3‐O‐glucoside (average content 82.53 mg per 100 g fresh berry weight), followed by its coumarate derivative (29.26 mg per 100 g), paeonidin 3‐O‐glucoside (10.84 mg per 100 g), petunidin 3‐O‐glucoside (7.80 mg per 100 g) cyanidin 3‐O‐glucoside (5.67 mg per 100 g) and delphinidin 3‐O‐glucoside (1.28 mg per 100 g). The richest variety was Syrah, with total average anthocyanin content of 186.02 mg per 100 g, whereas the Hellenic native variety Xinomavro had the lowest average anthocyanin level (38.70 mg per 100 g). The establishment of correlations of individual and total anthocyanin contents with the values from the antioxidant test was accomplished with linear regression. The links of total anthocyanins were significant with all antioxidant parameters (P < 0.001), but more importantly with SA_HFR (R² = 0.740). Malvidin 3‐O‐glucoside content had the higher correlation with SA_HFR compared with all other anthocyanins (R² = 0.698, P < 0.001).     

The influence of alteration on the engineering properties of dolerites: The examples from the Pindos and Vourinos ophiolites (northern Greece)

The influence of alteration on the physico-mechanical properties of dolerites from the Pindos and Vourinos ophiolites, northern Greece, is investigated. Quantitative petrographic analysis shows that the samples display various percentages of secondary minerals. Two new micropetrographic indices are calculated from the results of petrographic modal analysis for the engineering assessment of dolerites: the micropetrographic strength index I_ps and the replacement index I_rep. The samples are also tested to determine water absorption, apparent density, total porosity, sand equivalent, uniaxial compressive strength, Los Angeles abrasion value, aggregate impact value, aggregate abrasion value and polished stone value. The influence of alteration on the rock quality and especially the relationships between the proposed micropetrographic indices and the engineering parameters are determined using regression analysis and the derived equations were verified by the t-test and the F-test. The relationships between the I_ps and I_rep indices and the engineering properties show that alteration products generally result in mechanically weaker rocks. However, the results of the physico-mechanical tests indicate that dolerites retain their strength and durability due to the low proportions of soft minerals and microcracks, along with the preservation of their igneous textures. The polishing resistance is the only engineering parameter that is positively affected by alteration processes, as expressed by the I_ps index. Particularly, the replacement of the primary mafic minerals by secondary minerals, expressed by the I_rep index, can enhance the polishing resistance of dolerites when used in the wearing surface of a road. The results also indicate strong positive correlations between the chlorite content and the water absorption and total porosity values.     

Implementation of response surface methodology to optimise extraction of onion (Allium cepa) solid waste phenolics

An experimental setup based on a 2³-full factorial, central composite design was implemented with the aim to optimising recovery of polyphenols from onion solid wastes (OSW). In order to allow for the establishment of a sustainable process, reusable and non-toxic solutions composed of water/ethanol/citric acid were employed as extracting media. The factors considered were (i) the pH of the medium, (ii) the extraction time and (iii) the ethanol concentration. The model obtained produced a satisfactory fitting of the experimental data with regard to total polyphenol extraction (R² = 0.97, p = 0.0025) and the reducing power of the extracts (R² = 0.97, p = 0.0033), but not with the antiradical activity (R² = 0.89, p = 0.0592). The 2nd order polynomial equations obtained after elaboration of the experimental data indicated that all parameters considered were significant in respect with the efficiency of total polyphenol recovery. The highest total polyphenol yield was theoretically predicted to be 9342 ± 1435 mg gallic acid equivalents per 100 g dry weight, under optimal conditions (60% EtOH, pH 2 and 4.2 h). Liquid chromatography-electrospray ionisation mass spectrometry of the optimally obtained extract revealed that the principal phytochemicals recovered were quercetin 3,4′-diglucoside, quercetin 4′-glucoside and quercetin. Simple linear regression analysis between the total polyphenol and the antiradical activity of the OSW extracts showed that there was no correlation in a statistically significant manner, as opposed to reducing power.Industrial relevanceThe recovery of value-added substances from agri-food industrial wastes is an issue with importance pertaining to both the reduction of the waste load released to the environment, and the development of novel, natural food additives with functional properties. Up to date, the examinations pertaining to the clarification of factors that can affect extractability were based on rather unilateral assessment, while it is generally accepted that the retrieval depends on several parameters, which render the phenomenon a particular complexity. In this view, the implementation of factorial design with respect to investigating in parallel several factors pertaining to efficient polyphenol recovery becomes imminent. Thus the establishment of models on such a sound experimental basis is expected to provide a reliable background for more costand resource-effective processes, with a potential direct industrial applicability.     

Model for Understanding, Preventing, and Resolving Project Disputes

Based on the comparative analysis of 24 construction disputes, this paper presents a process model that explains the development of disputes. The model examines the combined effect of project uncertainty, contract, working relations, and problem solving effectiveness on the development of disputes. The model develops a classification of problem situations, and identifies the problem-solving requirements and the potential for dispute in each situation. The model indicates that the prevention of complex, high cost disputes depends more on the planning and problem solving ability of the project organization, and less on the contractual terms. The paper identifies the following actions that can reduce the number and severity of claims: reduction of project uncertainty, reduction of contractual problems, reduction of opportunistic behavior, increased the project organization's problem-solving ability, and use of alternative dispute resolution methods to reduce resolution costs.     

Characterization of flicker noise in GaAs MESFET's for oscillatorapplications

GaAs MESFET oscillators commonly exhibit increased close-to-carrier noise, which is often attributed to upconversion of flicker noise from the MESFET. To establish and quantify this effect, this paper presents an experimental system that allows the simultaneous measurement of the flicker noise on the gate and drain terminals of a GaAs-MESFET, and of the noise imposed on an RF carrier when amplified by the MESFET. The cross correlations between these parameters can thus be determined; an analytical method is shown for extracting the levels of the effective sources of flicker noise from the results, and the manner in which these affect the RF carrier. In the tests performed, it was often found that the close-to-carrier noise was related directly to the low-frequency flicker noise