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The wide implementation of low-NOx combustion technologies in pulverized coal combustion can lead to higher levels of carbon in fly ash and increase the adsorptivity toward surfactants of the carbon. Consequently, the air entraining agent (AEA) requirements of the fly ash used for concrete production increases, which can complicate the stabilization of entrained air. In this study, a low-NOx tangential fired 875 MWth power plant burning bituminous coal have been operated under extreme conditions in order to test the impact of the operating conditions on fly ash adsorption behavior and NOx formation. It was found that the AEA adsorption of the fly ash was reduced up to five times compared to reference operation, when the plant was operated with minimum furnace air staging, three levels of burners instead of four and without recycled flue gas. The lower AEA requirements of the fly ash at these conditions were primarily caused by a reduction in total carbon content, while the AEA adsorptivity of the residual carbon was lowered to about 60% of reference value. The tested operation mode, however, increased the NOx level in the flue gas before the DeNOx plant by 60% compared to reference operation.

The cathodic delamination of a commercial magnesium silicate and titanium dioxide pigmented epoxy coating on abrasive cleaned cold rolled steel has been investigated. The rate of delamination was found to depend on interfacial transport from the artificial defect to the delamination front and thereby the substrate topography, whereas the coating thickness had little influence. The presence of a significant potential gradient between the anode and the cathode and the dependency of the delamination rate on the tortuosity of the steel surface suggests that cathodic delamination is controlled by migration of cations from the defect to the delamination front. This means that abrasive blasting, to some extent, can be applied to control and minimize the observed rate of cathodic delamination. The lifetime of the species causing disbondment suggested that sodium hydroxide or potassium hydroxide and not peroxide species or radicals are the causative agents at free corrosion potential (i.e. without impressed current).

The enzymatic hydrolysis of lignocellulosic biomass is known to be product-inhibited by glucose. In this study, the effects on cellulolytic glucose yields of glucose inhibition and in situ glucose removal were examined and modeled during extended treatment of heat-pretreated wheat straw with the cellulolytic enzyme system, Celluclast 1.5 L, from Trichoderma reesei, supplemented with a beta-glucosidase, Novozym 188, from Aspergillus niger. Addition of glucose (0-40 g/L) significantly decreased the enzyme-catalyzed glucose formation rates and final glucose yields, in a dose-dependent manner, during 96 h of reaction. When glucose was removed by dialysis during the enzymatic hydrolysis, the cellulose conversion rates and glucose yields increased. In fact, with dialytic in situ glucose removal, the rate of enzyme-catalyzed glucose release during 48-72 h of reaction recovered from 20-40% to become approximately 70% of the rate recorded during 6-24 h of reaction. Although Michaelis-Menten kinetics do not suffice to model the kinetics of the complex multi-enzymatic degradation of cellulose, the data for the glucose inhibition were surprisingly well described by simple Michaelis-Menten inhibition models without great significance of the inhibition mechanism. Moreover, the experimental in situ removal of glucose could be simulated by a Michaelis-Menten inhibition model. The data provide an important base for design of novel reactors and operating regimes which include continuous product removal during enzymatic hydrolysis of lignocellulose.

The main objective of this review is to describe some of the important topics related to the use of marine and protective coatings for anticorrosive purposes. In this context, “protective” refers to coatings for containers, offshore constructions, wind turbines, storage tanks, bridges, rail cars, and petrochemical plants while “marine” refers to coatings for ballast tanks, cargo holds and cargo tanks, decks, and engine rooms on ships. The review aims at providing a thorough picture of state-of-the-art in anticorrosive coatings systems. International and national legislation aiming at reducing the emission of volatile organic compounds (VOCs) have caused significant changes in the anticorrosive coating industry. The requirement for new VOC-compliant coating technologies means that coating manufacturers can no longer rely on the extensive track record of their time-served products to convince consumers of their suitability for use. An important aspect in the development of new VOC-compliant, high-performance anticorrosive coating systems is a thorough knowledge of the components in anticorrosive coatings, their interactions, their advantages and limitations, as well as a detailed knowledge on the failure modes of anticorrosive coatings. This review, which mainly deals with European experience and practice, includes a description of the different environments an anticorrosive coating system may encounter during service. In addition, examples of test methods and standards for determination of the performance and durability of anticorrosive coatings have been included. The different types of anticorrosive coatings are presented, and the most widely applied generic types of binders and pigments in anticorrosive coatings are listed and described. Furthermore, the protective mechanisms of barrier, sacrificial, and inhibitive coatings are outlined. In the past decades, several alternatives to organic solvent-borne coatings have reached the commercial market. This review also presents some of these technologies and discusses some of their advantages and limitations. Finally, some of the mechanisms leading to degradation and failure of organic coating systems are described, and the reported types of adhesion loss are discussed.

Modern antifouling coatings are generally based on cuprous oxide (Cu2O) and organic biocides as active ingredients. Cu2O is prone to bioaccumulation, and should therefore be replaced by more environmentally benign compounds when technically possible. However, cuprous oxide does not only provide antifouling properties, it is also a vital ingredient for the antifouling coating to obtain its polishing and leaching mechanism. In this paper, peroxides of strontium, calcium, magnesium, and zinc are tested as pigments in antifouling coatings. The peroxides react with seawater to create hydrogen peroxide and highly seawater-soluble ions of the metal. The goals have been to establish the antifouling potency of an antifouling coating that releases hydrogen peroxide as biocide, and to investigate the potential use of peroxides as water-soluble polishing and leaching pigments. The investigations have shown that it is possible to identify particulates that, when applied as pigments in antifouling coatings, will provide polishing and leaching rates comparable to those of Cu2O-based coatings. Furthermore, the combination of polishing and hydrogen peroxide leaching by a coating based on zinc peroxide in a suitable binder matrix provides antifouling properties exceeding those of a similar coating based entirely on zinc oxide.

The residual carbon in fly ash produced from pulverized coal combustion can adsorb the air-entraining admixtures (AEAs) added to enhance air entrainment in concrete. This behavior of the ash can be suppressed by exposing the fly ash to oxidizing species, which oxidizes the carbon surface and thus prevents the AEA to be adsorbed. In the present work, two fly ashes have been ozonated in a fixed bed reactor and the results showed that ozonation is a potential post-treatment method that can lower the AEA requirements of a fly ash up to 6 times. The kinetics of the carbon oxidation by ozone was found to be fast. A kinetic model has been formulated, describing the passivation of carbon, and it includes the stoichiometry of the ozone consumption (0.8 mol of O3/kg of C) and an ineffective ozone loss caused by catalytic decomposition. The simulated results correlated well with the experimental data.

The initial kinetics of direct sulfation of Faxe Bryozo, a porous bryozoan limestone was studied in the temperature interval from 873 to 973 K in a pilot entrained flow reactor with very short reaction times (between 0.1 and 0.6 s). The initial conversion rate of the limestone—for conversions less than 0.3%—was observed to be significantly promoted by higher SO2 concentrations and lower CO2 concentrations, whereas O2 showed negligible influence. A mathematical model for the sulfation of limestone involving chemical reaction at calcite grain surfaces and solid-state diffusion of carbonate ions in calcite grains is established. The validity of the model is limited to the initial sulfation period, in which nucleation of the solid product calcium sulphate is not started. This theoretical reaction-diffusion model gives a good simulation of the initial kinetics of the direct sulfation of Faxe Bryozo. The intrinsic rate of the direct sulfation of the limestone is estimated to have an activation energy of about 25 kJ/mol and reaction orders of about 0.9 and −0.75 for SO2 and CO2, respectively. The diffusivity of carbonate ions in the surface layer of the calcite grain is estimated to be about three orders of magnitude higher than the diffusivity of carbonate ions in the inner lattice of calcite grain and have an activation energy of about 202 kJ/mol. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Waste to energy (WtE) plants are utilised for the production of heat and electricity. However, due to corrosion at super heater surfaces a relatively low 25% of the waste lower heating value can with the present technology be converted to electricity. High contents of Cl, Na, K, Zn, Pb and S in waste cause relatively high super heater corrosion rates. The Cl-content in waste is one of the key-factors for volatilisation of alkali and heavy metals in WtE plants. Little is known about the release of Cl, Na, K, Zn, Pb, and S along grate of waste incineration plants. The 26 t h − 1 WtE plant Vestforbraending unit 5 in Denmark was used for measurements of temperature, gas-concentration (O 2 /CO/CO 2 ), and sampling of gas phase Cl, Na, K, Pb, Zn, and S. Unit 5 has 6 ports distributed along the 13 m long grate between 1.5–1.8 m above the grate. Five of these ports were used for measurements. Two aqueous absorption systems containing a solution of NH 3 or a solution of H 2 O 2 /HNO 3 were used to collect the gaseous samples. Tar was found to condense in the sampling system at the ports near the fuel inlet. The experiments showed the majority of Cl, Na, and K to be volatilised during the early stages of combustion. The maximum release of Cl, Na, and K was measured in port 2 as 177 ppm v , 71 ppm v , and 44 ppm v respectively. The maximum average gas temperature of 1140 was measured in port 3 compared to the temperatures at ports 2 and 4 of 816 and 551 respectively. It has been suggested to use flue gas from the area of the grate near port 3 with a high temperature, that contains relatively low amounts of corrosive elements, and lead to a separate high temperature super heater and thus increase the electrical efficiency.

Industrial utilization of fly ash from pulverized coal combustion plays an important role in environmentally clean and cost effective power generation. Today, the primary market for fly ash utilization is as pozzolanic additive in the production of concrete. However, the residual carbon in fly ash may interfere with air entraining admixtures (AEAs) added to enhance air entrainment in concrete in order to increase its workability and resistance toward freezing and thawing conditions. The problem has increased with implementation of low- NO x combustion technologies. This review presents the past work carried out to identify the mechanisms causing the interactions between AEAs and fly ash in concrete mixtures, emphasizing the residual carbon. It has been shown that not only the amount, but also the properties of carbon, such as particle size and surface chemistry, has an impact on the adsorption capacity of AEAs. The type of fuel used in the combustion process influences the amount and properties of the residual carbon. Fly ash derived from bituminous coal has generally higher carbon content compared with fly ash produced from subbituminous coal or lignite, but shows a lower AEA adsorption capacity per mass of carbon. Cases reporting increased residual carbon content due to low- NO x combustion are described, together with observations from a pilot scale experiment, where increased AEA adsorption capacity of carbon appeared to relate with firing at low- NO x conditions. Post-treatment methods applied to improve fly ash quality are described in the review. Ozonation, thermal treatment and physical cleaning of carbon have been found to improve the fly ash performance for concrete utilization. Ultimately, recommendations for further work are outlined in the discussion.

The direct sulfation of limestone (Iceland Spar) was studied at 973 K in a fixed-bed reactor. Scanning electron microscopy examinations of the sulfated limestone particles show that the sulfation process involves oriented nucleation and growth of the solid product, anhydrite. The reason for the occurrence of oriented nucleation and growth of the solid product is related to a close two-dimensional lattice match between the lattice plane {1,0,4} of calcite and the lattice plane {1,1,0} of anhydrite.

The oxidation of methanol in a flow reactor has been studied experimentally under diluted, fuel-lean conditions at 650–1350 K, over a wide range of O2 concentrations (1%–16%), and with and without the presence of nitric oxide. The reaction is initiated above 900 K, with the oxidation rate decreasing slightly with the increasing O2 concentration. Addition of NO results in a mutually promoted oxidation of CH3OH and NO in the 750–1100 K range. The experimental results are interpreted in terms of a revised chemical kinetic model. Owing to the high sensitivity of the mutual sensitization of CH3OH and NO oxidation to the partitioning of CH3O and CH2OH, the CH3OH + OH branching fraction could be estimated as α = 0.10 ± 0.05 at 990 K. Combined with low-temperature measurements, this value implies a branching fraction that is largely independent of temperature. It is in good agreement with recent theoretical estimates, but considerably lower than values employed in previous modeling studies. Modeling predictions with the present chemical kinetic model is in quantitative agreement with experimental results below 1100 K, but at higher temperatures and high O2 concentration the model underpredicts the oxidation rate. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 423–441, 2008

The applicability of four different heterogeneous palladium catalysts has been evaluated for the Buchwald–Hartwig amination reaction between p-bromotoluene and piperazine in the presence of the base NaO-t-Bu. The catalyst that provided the highest selectivity toward the desired amination reaction was found to be a polymer-supported palladium dichloride/triphenylphosphine catalyst. Experimental investigations of the catalyst in a reactor setup showed that the undesired reduction reaction of the aryl halide was dominant when the catalyst was reused and washed in solvent prior to reaction and when additional reactants were added to an already reacted reaction mixture. A significant washout of triphenylphosphine and palladium from the catalyst was also identified during the course of reaction and separation.

A systematic overview is presented of the literature that reports the antifouling (AF) protection of underwater structures via the action of enzymes. The overall aim of this review is to assess the state of the art of enzymatic AF technology, and to highlight the obstacles that have to be overcome for successful development of enzymatic AF coatings. The approaches described in the literature are divided into direct and indirect enzymatic AF, depending on the intended action of the enzymes. Direct antifouling is used when the enzymes themselves are active antifoulants. Indirect antifouling refers to the use of enzymes to release an active biocide with AF activity. For direct AF, several patents have been granted, and a commercial product has been launched. However, the achievement of an efficient broad-spectrum AF coating based on a single or a few enzymes has not yet been achieved. An indirect AF coating is not yet available commercially. The technology is mainly limited by the instability of substrate supply, whether the substrates are found in the surrounding seawater or in the coating itself. Legislative issues regarding which part(s) of an enzyme system should be regarded as biocidal for product registration purposes are also considered. The above question currently remains unanswered for technologies utilising indirect enzymatic AF.

In this work BET surface area measurements and mercury porosimetry are used to characterize leached layers formed when seawater-soluble pigments (Cu2O and ZnO) dissolve during accelerated leaching of simple antifouling coatings. Measurements on single-pigment coatings show that an increasing fraction of Cu2O or ZnO pigment particles becomes unavailable for dissolution when the concentration of the pigment decreases in the coating and the interparticle distance in the binder matrix becomes larger. Experimental data for a coating initially containing a mixture of Cu2O and TiO2 pigments suggest that a substantial fraction of the smaller and inert TiO2 particles may be lost from the coating upon dissolution of the larger Cu2O particles. This inert particle translocation effect is important to take into account when interpreting polishing and leaching data and when developing mathematical models of antifouling coating behaviour because the active binder surface area and porosity of the leached layer are substantially increased. A similar effect was not observed for a coating with a mixture of ZnO and TiO2 pigments. The two experimental methods are expected to be useful for practical analysis of leaching of seawater-soluble components from commercial antifouling coatings.

Combustion of tyre char particles with diameters between 102 and 212 μm was performed in an experimental laboratory reactor, at temperatures between 750 and 850 °C, in an oxidative atmosphere with up to 10 vol.% O 2 at 1 bar. The observed char combustion time varied from about 9 s at 750 °C to about 4 s at 850 °C. Under these conditions the experimental data indicated increasing mass transfer resistance with temperature. A diffusion reaction model was employed to study the effects of simultaneous mass transfer and kinetics in the experiments. An intrinsic reaction rate for tyre char combustion was estimated and comparison with literature data revealed good agreement.

The enhancement of the direct sulfation of limestone by various Li+-, Na+-, and K+-containing inorganic salts, calcium chloride, and hydrogen chloride has been studied in a bench-scale quartz react...

The foam index test is the method usually employed to determine the degree of fly ash interference with air entrainment agents in concrete. The test involves the use of commercial air-entraining agents (AEAs) and visual observation of foam stability. These facts reduce the reproducibility of the test, because commercially available AEAs vary in strength, and the criteria for foam stability are operator dependent. Therefore, it is of interest to develop a reproducible method, which is able to determine the fly ash quality with respect to air entrainment in concrete. This paper presents efforts toward the development of a new method based on dynamic surface tension measurements, using the bubble pressure method, on filtrate from a fly ash and cement suspension. A pure surfactant is added to the suspension as a substitute for a commercial AEA. The new method and the foam index test have been compared on fly ashes acquired from power plants in Denmark and the U.S. The results reveal a good relationship between the two methods, but the new method requires further work before a finished procedure is accomplished. Finally, it has been shown that changes in temperature affect both test methods.

The direct sulfation of limestone was studied in a laboratory fixed-bed reactor. It is found that the direct sulfation of limestone involves nucleation and crystal grain growth of the solid product (anhydrite). At 823 K and at low-conversions (less than about 0.5 %), the influences of SO2, O2 and CO2 on the direct sulfation of limestone corresponds to apparent reaction orders of about 0.2, 0.2 and −0.5, respectively. Water is observed to promote the sulfation reaction and increase the apparent reaction orders of SO2 and O2. The influence of O2 at high O2 concentrations (> about 15 %) becomes negligible. In the temperature interval from 723 K to 973 K, an apparent activation energy of about 104 kJ/mol is observed for the direct sulfation of limestone. At low temperatures and low conversions, the sulfation process is most likely under mixed control by chemical reaction and solid-state diffusion. The nucleation and crystal grain growth of the solid product, and this mixed control mechanism provide satisfactory explanations of the various phenomena related to the direct sulfation of limestone, such as porosity in the product layer, the variation of the apparent reaction orders of SO2, O2 and CO2 with reaction conditions and the influence of water. © 2007 American Institute of Chemical Engineers AIChE J, 53: 948–960, 2007

The combustion of alternative fuels in direct contact with the bed material of the rotary kiln may cause local reducing conditions and, subsequently, decomposition of sulfates from cement raw materials, increasing the SO2 concentration in the gas phase. The decomposition of sulfates increases the sulfur circulation and may be problematic because high sulfur circulation can cause sticky material buildup, affecting the process operation of the cement kiln system. The SO2 release from cement raw materials during combustion of pine wood and tire rubber has been studied experimentally in a high-temperature rotary drum, focusing on the influence of the fuel particle size and volatile content. The SO2 release increased with a decreasing fuel particle size and with an increasing fuel volatile content. Furthermore, CO, H2, and CH4, which are the main reducing gases released during fuel devolatilization, were introduced in different concentrations under the bed material. A threshold concentration for each reducing gas, below which no SO2 release occurs, was found. Introduction of the same molar amount of gas in different concentrations during different time periods showed that a higher reducing gas concentration during a short period (representing fuel devolatilization) released a higher total SO2 amount compared to a lower concentration during a long period (representing fuel char oxidation).

Et forskningsprojekt mellem HWAM A/S og DTU Kemiteknik har førttil udvikling af mere energieffektive og miljøvenlige brændeovne. Projektet – der er et EUDP-projekt – har bidraget til, at HWAM A/S har introduceret den første digitale styrede brændeovn på markedet.

The antifouling (AF) paint model of Kiil et al. [S. Kiil, C.E. Weinell, M.S. Pedersen, K. Dam-Johansen, Analysis of self-polishing antifouling paints using rotary experiments and mathematical modelling, Ind. Eng. Chem. Res. 40 (2001) 3906–3920] and the simplified biofilm growth model of Gujer and Wanner [W. Gujer, O. Wanner, Modeling mixed population biofilms, in: W.G. Characklis, K.C. Marshall (Eds.), Biofilms, Wiley–Interscience, New York, 1990] are used to provide a reaction engineering-based insight to the effects of marine microbial slimes on biocide leaching and, to a minor extent, polishing behaviour of AF paints. It is concluded that the perturbation of the local sea water conditions (e.g. pH), as a consequence of the metabolic activity of the biofilm should not affect the net biocide leaching and binder reaction rates significantly. This results from the thin and poorly active biofilms which presumably grow onto the highly effective modern AF paints. According to simulations, the experimental decrease in the biocide leaching rate caused by biofilm growth must be mainly attributed to adsorption of the biocide by the exopolymeric substances secreted by the microorganisms. The effects of biofilms on the leaching of any generic active compound (e.g. natural antifoulants) are discussed in relation to their potential release mechanisms. The largest influence of biofilms is predicted for those active compounds that are released by a diffusion-controlled mechanism (typically tin-free algaecides).

The dissolution of soluble pigments from both tin-based and tin-free chemically active antifouling (AF) paints is a key process influencing their polishing and biocide leaching rates. In this context, a low time- and resources-consuming method capable of screening the pigment behaviour in the search for the most promising materials or mixtures is of great interest. A preliminary attempt to develop such a method is presented in this paper based on the widely used ZnO pigments. While highly pure, nano-polished, monocrystalline ZnO substrates yielded very low dissolution rates in the order of 17.3 ± 3.7 μg Zn 2+ cm −2 day −1 , pellets prepared by compacting and sintering technical grade ZnO pigments dissolved about three times faster according to inductively-coupled plasma mass spectrometry (ICP-MS) measurements. The rougher and more porous surface exposed, together with the larger number of defects in the lattice structure, are hypothesised to be responsible for the faster sea water attack of the pellets compared to the ZnO crystals. In any case, the ZnO dissolution rates reported in this paper are markedly lower than those associated with the sea water dissolution of cuprous oxide (Cu 2 O) particles which are also used in AF paints. Experimental performance testing of model antifouling paints formulated with ZnO and/or Cu 2 O demonstrates that the binder/pigment interaction should not be disregarded if the leaching of sea water soluble pigments from paint systems is to be determined.

A systematic experimental study has been performed in order to investigate the effect of particle size and temperature on the devolatilization rate of large tyre rubber particles. Cylindrical tyre particles with diameters between 7.5 and 22 mm were devolatilised in a macro-TGA reactor, at temperatures between 490 and 840 °C in an inert atmosphere. The effect of particle size and surrounding temperature on the rate of devolatilization was observed to be significant, i.e. larger particle diameters and lower temperatures increased the devolatilization time. A detailed mathematical model for the devolatilization process including internal and external heat transfer, three parallel independent devolatilization reactions and reaction enthalpy effects has been developed and solved using an implicit finite difference method. Comparison of the model predictions with experimental data, reveals that the devolatilization process of large tyre rubber particles at temperatures above 490 °C can be considered to be controlled mainly by heat transfer and reaction kinetics. The model analysis further shows that exothermic devolatilization reaction enthalpy effects cannot be neglected in the prediction of the intra particle temperature rise. A sensitivity analysis of the model parameters, demonstrates that the specific heat capacity of the virgin fuel and the activation energies of the devolatilization reactions is the most important model parameters in the prediction of devolatilization times of large tyre rubber particles.

The Buchwald−Hartwig amination reaction between p-bromotoluene and piperazine in the presence of the homogeneous catalytic system Pd(dba)2/(±)-BINAP and the base NaO-t-Bu was investigated in two different classes of solvents: aprotic, nonpolar and aprotic, polar. The reaction was carried out using microwaves as the heating source, and it was found that the product distribution was strongly dependent on the class of the solvent. Based on the experimental results the selectivity towards the desired monosubstituted aryl piperazine was calculated, and it was found that the most appropriate solvent for the Buchwald−Hartwig amination reaction under the conditions applied was m-xylene.

Mathematical modeling has been used to characterize and validate the working mechanisms of tin-free, chemically-active antifouling (AF) paints. The model-based analysis of performance data from lab-scale rotary experiments has shown significant differences between antifouling technologies as regards the biocide leaching and the surface polishing processes. Hence, the modeling framework developed in this work is built so as to describe any generic, chemically-active AF paint through model parameters, the values of which can be obtained or adjusted from relatively fast measurements. The detailed quantitative information on reacting AF paint systems obtained can be used for accelerated product optimization purposes, thus facilitating the transition to cleaner antifouling technologies using, for example, fast-degrading natural or synthetic bioactive components. © 2006 American Institute of Chemical Engineers AIChE J, 2006

The use of biomass for power generation can result in significant economical and environmental benefits. The greenhouse emissions can be reduced as well as the cost of the produced electricity. However, ash-related problems, including slagging, agglomeration, and corrosion, can cause frequent unscheduled shutdowns, decreasing the availability and increasing the cost of the produced power. In addition, the fouling of the heat exchange surfaces reduces the system efficiency. In this work the melting and rheological properties of various biomass and biomass/coal ash samples were studied by using a high-temperature rotational viscometer and a hot stage XRD. The produced data were used to calculate the operating temperature of a pilot-scale entrained flow reactor during the cocombustion of biomass/coal samples in order to ensure the slag flow and to avoid corrosion of the walls due to liquid slag/metal interaction. Biomass ash proved to have significantly different melting behavior compared to that of the coal...

In the study by Liang et al. [2001. Analysis of constant rate period of spray drying of slurry. Chemical Engineering Science 56, 2205–2213] the Darcy flow of liquid through a pore system of primary particles to the surface of a slurry droplet was applied for the constant rate period. Steep primary particle concentration gradients inside ∼ 25 μ m droplets with a primary particle size of 0.2 μ m were observed. Unfortunately, the boundary condition at the droplet surface for the parabolic second-order PDE did not conserve the solid mass in the droplet, and the plots for the primary particle concentration profiles in the droplets were incorrect. In this letter we derive the correct boundary condition equation. Furthermore, we show that the primary particle concentration profiles inside the droplets are flat when the primary particles have a size of 0.2 μ m . We conclude that the model presented by Liang et al. is unable to predict the formation of hollow particles.

Marine microorganisms are capable of successfully colonizing toxic surfaces through the formation of biofilm structures. In this article, most of the literature reporting the presence of marine biofilms on chemically-active antifouling paints is briefly reviewed. Of special concern is the influence of the dense extracellular polymeric substances (EPS) matrix on the release rate of the compounds involved in antifouling paint performance (i.e. active compounds and controlled-release binder molecules). A deeper understanding of these phenomena is of interest for both environmental legislators and paint formulators.

Biofouling on ship hulls is prevented by the use of antifouling (A/F) paints. Typically, sea water soluble rosin or rosin-derivatives are used as the primary means of adjusting the polishing rate of the current chemically active self-polishing paint systems to a suitable value. Previous studies have shown that mathematical coating models based on a fundamental knowledge of the underlying mechanisms of A/F paints is a promising tool for accelerated product testing at different operational conditions of a sailing ship or a paint rotor. Such models can also be used for generation of ideas aiming at product optimisation and innovation (e.g. incorporation of natural active agents). This study seeks to attain scientifically founded knowledge of the reaction mechanisms and the rate of reaction with sea water of a Zn-carboxylate of a synthetic rosin compound. The kinetic expression attained can be used as input to mathematical models describing the behaviour of rosin-containing tin-free A/F paints. The experimental procedures developed can be easily implemented by marine paint companies for the screening of novel controlled-release binder materials for A/F paints. As a first step, it is demonstrated that the degradation of this Zn-containing rosin-derivative by sea water plays a key role in the polishing mechanism of paints formulated with such a resin. Then, the relevant literature available on the sea water behaviour of rosin and rosin-based binders is reviewed. Subsequently, two experimental procedures for the reaction rate estimation of the selected rosin-derived resin are presented; one is based on a gravimetric approach while the other uses flame atomic absorption spectroscopy (FAAS) to determine the total Zn 2+ released by the resin. Both methods yield well-defined reaction conditions and sufficiently high accuracies. The latter is important because very low steady state reaction rates (about 0.70 ± 0.26 μg Zn 2+ cm −2 day −1 at 25 °C and pH 8.2) are measured. Steady state reaction rates of Cu 2+ - and Mg 2+ -derivatives are also determined and discussed. The experimental procedures developed are used to investigate the influence of NaCl concentration (12–52 g/l), pH (7.8–8.5) and sea water temperature (10–35 °C) on the rate of reaction of the Zn-carboxylate. Within that range of sea water conditions, the following kinetic expression is found to describe the steady state Zn 2+ release rate resulting from the reaction of the Zn-carboxylate with sea water: ( − r ZnR ) = k 1 C O H − a − k − 1 C R − b C Z n 2 + c μ g Z n 2 + ( c m 2 film ) day k 1 = A e ( − E a / R T ) μ g Z n 2 + ( c m 2 film ) day 1 mol a k − 1 = k 1 C O H − a L ZnR 2 b − 2 ( C Z n 2 + ) eq b + c − 3 μ g Z n 2 + ( c m 2 film ) day 1 mol b + c where the natural logarithm of the pre-exponential factor, ln ( A ), is 18.0 ± 2.5 (the unit of A being the same as k 1 ), the activation energy, E a , is 18.5 ± 6.0 kJ/mol and the reaction order with respect to the hydroxide ion concentration, a , is 0.86 ± 0.42. L ZnR is the estimated solubility product of the ZnR resin which has a value of 3.1 × 10 −12 (mol/l) −3 (about 6 mg Zn 2+ /l in equilibrium). The low value of the activation energy is believed to result from the complex reaction mechanisms hypothesised rather than pointing at a certain diffusion control in the reaction rate experiments. The reverse reaction is found not to affect the hydrolysis rate within the pores of antifouling paints significantly. It is concluded, from the reaction mechanism proposed, that the observed partial exchange of Zn 2+ for Cu 2+ in the resin structure during paint dispersion and immersion results in a lower reaction rate compared to the pure ZnR. Cu-carboxylate has a reaction rate of about 5.8 ± 1.0 μg CuR cm −2 day −1 at 25 °C and pH 8.2. The presence of Mg and Na compounds (probably Mg- and Na-resinate) in the solid paint film has also been detected, and will influence the reaction rate by modifying the ZnR exposed surface area.

In larger combustion facilities, secondary reactions between char and chlorine and sulfur may be important. In this work, the interactions of chlorine and sulfur with biomass char during thermal conversion have been experimentally investigated. A laboratory-scale fixed-bed reactor was applied to study the capture of HCl and SO2 by biomass char in the temperature range of 400−950 °C. The observed reaction rate was sufficient for significant recapture of HCl and SO2 to occur under conditions typical for fixed-bed combustors. A maximum in the chlorine and sulfur retention existed at ∼600 °C. Relatively high amounts of chlorine and sulfur could be retained in the char samples over the entire temperature range, compared to the inherent chlorine and sulfur content in the biomass. Spectroscopic and chemical analyses revealed that HCl was mainly captured by the inherent metal species, whereas SO2 was mainly captured by the organic matrix. As a result, the maximum chlorine retention was dictated by the inherent me...

The transformation of inorganic constituents in annual biomass was experimentally investigated at grate-combustion conditions. A laboratory fixed-bed reactor was applied to obtain quantitative information of the release of Cl, K, and S to the gas phase from six distinctively different annual biomass fuels. Samples of 4.0 g of biomass were combusted at well-controlled conditions at temperatures from 500 to 1150 °C. The elemental release was quantified by analysis of the residual ash and a mass balance on the system. The experimental results revealed that potassium was released to the gas phase in significant amounts at combustion above 700 °C. The potassium release increased with the applied combustion temperature for all biomass fuels; however, the quantity released was largely determined by the ash composition. At 1150 °C, between 50 and 90% of the total potassium was released to the gas phase. The biomass fuels with an appreciable content of silicate showed the lower release of potassium. Between 25 and...

The imminent ban of environmentally harmful tributyltin (TBT)-based paint products has been the cause of a major change in the antifouling paint industry. In the past decade, several tin-free products have reached the commercial market, and claimed their effectiveness as regards the prevention of marine biofouling on ships in an environmentally friendly manner. The main objective of this review is to describe these products in as much detail as possible based on the knowledge available in the open literature. This knowledge has been supplemented by means of performance data provided, upon request, by some of the paint-producing companies. An exhaustive review of the historical development of antifouling systems and a detailed characterisation of sea water are also included. The need for studies on the behaviour of chemically active paints under different sea water conditions is emphasised. In addition, the most common booster biocides used to replace TBT-containing compounds are listed and described. It must be stressed that there is still a lack of knowledge of their potential environmental side effects. The current interest in providing innovative antifouling technologies based on an improved understanding of the biological principles of the biofouling process is also considered in this review. From the analysis of the factors affecting the biofouling process, the interference with the settlement and attachment mechanisms is the most promising environmentally benign option. This can be accomplished in two main ways: imitation of the natural antifouling processes and modification of the characteristics of the substrate. The former mostly focuses on the study of the large amount of secondary metabolites secreted by many different marine organisms to control the fouling on their surfaces. The many obstacles that need to be overcome for the success of this research are analysed. The potential development of broad-spectrum efficient coatings based on natural antifoulants is far from commercialisation. However, exploitation of a weakening of biofouling adhesion by means of the non-stick and fouling-release concepts is at a rather advanced stage of development. The main advantages and drawbacks of these systems are presented along with a brief introduction to their scientific basis. Finally, other alternatives, which may eventually give rise to an efficient and environmentally benign antifouling system, are outlined.

Straw is used as fuel in relatively small-scale combined heat and power producing (CHP) grate boilers in Denmark. The large content of potassium and chlorine in straw greatly increases the deposit ...

The oxidation of pyrite (FeS 2 ) has been investigated in a fixed-bed laboratory reactor to gain knowledge about the SO 2 formation mechanisms and kinetics at conditions relevant to the upper stages of a cyclone preheater tower in a modern dry kiln system for cement production. Experiments were carried out with a high sulfide containing shale (a mass-average diameter equal to 21 μm) and with pure FeS 2 particles (between 32 and 64 μm). Measurable SO 2 formation started at about 350°C for the shale and at 400°C for the FeS 2 particles and increased with temperature for both materials. Experiments showed that the conversion of pyritic sulfide to SO 2 was independent of the inlet SO 2 concentration up to at least 925 ppmv and that the conversion decreased as the O 2 concentration was increased from 5% to 20% (v/v). A shrinking-core reaction mechanism with FeS 2 as the core and with porous FeS as the intermediate product layer is proposed to account for the experimental observations. According to this mechanism, the oxidation of the FeS 2 core to FeS is relatively fast at moderate O 2 levels (e.g., 5%) because it is easy for O 2 and SO 2 to diffuse through the porous product layer of almost non-oxidized FeS. At increased O 2 levels (e.g., 20%), we believe that the FeS layer also starts to oxidize so its porous structure is disrupted whereby the resistance to diffusion through it increases and thus further oxidation of the FeS 2 core is inhibited, leading to lower overall conversions.

The influence of the air combustion mixing into the main flow, operating conditions and fuel type on the level of NO emission in the in-line low-NO x calciners was investigated. The analysis was carried out using a heterogeneous mathematical model based on non-isothermal diffusion-reaction models for char combustion and limestone calcination. The mixing in the oxidizing zone was modeled using a modified Zwietering approach, which supposes that only oxygen or both oxygen and nitrogen are gradually mixed into the sub-stoichiometric suspension leaving the reducing zone. The analysis shows that the difference in NO emission due to the mixing rate of the oxygen into the main flow is the consequence of the different local oxygen concentration in the oxidizing zone and different char-N oxidation rates. The change of limestone feed position in the oxidizing zone modifies greatly the temperature in the region up to the feed level and thereby the NO emission. In the case of bituminous coal, changing the limestone feed ratio in the reducing zone corresponds to an insignificant modification of the NO concentration. The increase of the air combustion temperature has a negative influence on NO emission.

An experimental study has been conducted to determine the ignition temperature of biomass at 21% O 2 , both under pulse ignition conditions and under thermogravimetric conditions. In the pulse ignition experiments, samples of about 2 g wheat straw were placed in an isothermal reactor. The ignition temperature was determined from the transient CO and CO 2 profiles to approximately 255 °C at a superficial gas velocity of 14 cm/s (STP). The ignition temperature increased for decreasing superficial gas velocity. Thermogravimetric experiments at 20% O 2 and heating rates of 5 °C/min with finely milled biomass indicated ignition temperatures of approximately 220 °C for wheat straw, 235 °C for poplar wood, and 285 °C for eucalyptus wood. These values are significantly lower than values obtained for coal under similar conditions and confirm the relationship between volatile matter content and ignition temperature previously reported for coal. A mechanistic model for ignition of biomass is proposed. We believe that the ignition process is initiated by oxidation reactions on the straw surface. These reactions raise the surface temperature above that of the surrounding gas and promote ignition of the volatiles. Once ignited, the volatiles may form a homogeneous diffusion flame away from the particle surface. The superficial gas velocity affects the particle heating rate as well as the transport of oxygen to the surface. For this reason the ignition process is not entirely controlled by kinetics at low temperatures.

The oxidation of formaldehyde in a flow reactor has been studied experimentally under diluted conditions at 800 to 1400 K and with the stoichiometry between fuel-rich and very lean. Of particular interest was the interaction of formaldehyde with nitrogen oxides. The results show that the oxidation of CH2O is initiated above 900 K, with the oxidation rate decreasing slightly with increasing [O2]. Addition of NO under fuel-rich conditions inhibits oxidation, while under lean conditions a mutually promoted oxidation of CH2O and NO is observed at 750–1100 K. Based partly on recent accurate measurements of key reactions of CH2O and HCO, a detailed reaction mechanism for the oxidation of formaldehyde under post-flame conditions is proposed. It provides a good description of the experimental measurements as well as data from the literature.

A bituminous coal was pyrolyzed in a nitrogen stream in an entrained flow reactor at various temperatures from 700 to 1475 degreesC. Char samples were collected at different positions along the reactor. Each collected sample was oxidized nonisothermally in a TGA for reactivity determination. The reactivity of the coal char was found to decrease rapidly with residence time until 0.5 s, after which it decreased only slightly. On the bases of the reactivity data at various temperatures, a new approach was utilized to obtaining the true activation energy distribution function for thermal annealing without the assumption of any distribution function form or a constant preexponential factor. It appears that the true activation energy distribution function consists of two separate parts corresponding to different temperature ranges, suggesting different mechanisms in different temperature ranges. Partially burnt coal chars were also collected along the reactor when the coal was oxidized in air at various temperatures from 700 to 1475 degreesC. The collected samples were analyzed for the residual carbon content and the specific reaction rate was estimated. The characteristic time of thermal deactivation was compared with that of oxidation under realistic conditions. The characteristic times were found to be close to each other, indicating the importance of thermal deactivation during combustion of the coal studied.

The development of chemically active antifouling paints has traditionally been based on an empirical approach. Optimisation and evaluation of novel and existing products are frequently conducted by means of, for example, systematic paint rotary tests in the laboratory or at sea sites. In this review, the usefulness of combining rotary experiments with the development of detailed mathematical models of paint behaviour will be discussed with reference to the relevant literature. Mathematical models can generally be used in the design of suitable release systems for various active components such as proteins or biocides, as well as for the estimation of release rates from different compositions of paints under various seawater conditions. Insoluble matrix, soluble matrix and self-polishing paints will be considered. Simulations from recent publications that show the effects of dynamic changes in seawater on paint behaviour will be presented. Examples of potential uses of paint models for accelerated polishing and leaching tests and screening of novel paint components will also be discussed. Directions of future modelling work are suggested.

The ash behaviour comprises one major obstacle towards the efficient utilization of municipal solid wastes, (MSW), in incineration plants. The presence of large amounts of inorganic constituents such as alkali and alkali earth metals, chlorine, sulfur and zinc increase significantly the ash reactivity and lead to severe ash-related problems such as fouling, slagging, corrosion and erosion during their thermal treatment. In this paper, the melting behaviour of various ash fractions originating from the incineration of MSW is studied using simultaneous, (DSC/TG), thermal analysis methods. The produced results provide the basis for improved modelling of the ash behaviour during the incineration of MSW.

This work concerns the on-going development of efficient and environmentally friendly antifouling paints for biofouling control on large ocean-going ships. It is illustrated how a detailed mathematical model for a self-polishing antifouling paint exposed to seawater can be used as a product engineering tool to obtain a quick estimate of the paint behaviour that a given seawater-soluble pigment will provide. In the present context, “pigment” refers to relevant particulate solids of organic-, inorganic-, or biological nature. Simulations performed at 15 and 30 °C suggest that pigment solubility and seawater diffusivity of dissolved pigment species have a significant influence on the polishing and leaching behaviour of a typical self-polishing paint system. The pigment size distribution, on the other hand, only has a minor influence on the paint–seawater interaction. Simulations also indicate that only compounds which are effective against biofouling at very low seawater concentrations are useful as active antifouling paint ingredients. The need for model verification and exploration of practical issues, subsequent a given pigment has been found of interest, is discussed. The model approach is of relevance in the search for novel antifouling paints and for the development of accelerated test methods.

We report on an extensive experimental study of char thermal deactivation based on reactivity experiments of different fuel chars collected from different reactors. The reactors include a Thermogravimetric Analyser (TGA), an entrained flow reactor and utility boilers. The results show that different fuels have different deactivation propensities. In the course of heat treatment in the TGA, some of the fuels present a gradual formation of two fractions of different reactivity. The mass-based reactivity of the least reactive phase approaches that of a commercial graphite at high heat treatment temperatures. Likely mechanisms responsible for the observed deactivation of the chars studied are discussed.

The reduction of the NOx content in in-line-calciner-type kiln systems can be made by optimization of the primary firing in the rotary kiln and of the secondary firing in the calciner. Because the optimization of calciner offers greater opportunities the mathematical modeling of this reactor is very important. A heterogeneous, dynamic mathematical model for an in-line low-NOx calciner based on non-isothermal diffusion–reaction models for char combustion and limestone calcination has been developed. The importance of the rate at which preheated combustion air was mixed into the main flow was particularly studied. The results of the simulations indicate that the external heat and mass transfer to the char particles is not limiting. Internal diffusion of O2, CO, NO and CO2 is important especially in the reducing zone and the first part of the oxidizing zone of the calciner and the internal heat transport limitation is significant for the endothermic limestone calcination. The rate at which preheated combustion air is mixed into the main flow directly influences the coal combustion rate, and thereby through the rate of heat release from combustion, it also influences the calcination rate and the temperature profile. The mixing rate has some influence on the CO concentration profile and an important influence on the overall degree of fuel-N to NO conversion.

Simulations with a heterogeneous model of an in-line low-NO x calciner, based on non-isothermal diffusion-reaction models for char combustion and limestone calcination combined with a kinetic model for NO formation and reduction, are reported. The analysis shows that the most important hydrodynamic parameter is the mixing rate of preheated combustion air into the sub-stoichiometric suspension leaving the reducing zone and the most important combustion parameter is the char reactivity. Also, the calcination rate modifies very much the temperature in the calciner, char and limestone conversion and NO emission. Carbon monoxide is a key component for the reduction of NO and reliable data for the kinetics of NO reduction by CO over CaO are very important for the prediction of the NO emission. The internal surface area of char and limestone particles influences the combustion and calcination rates and thereby the char and limestone conversion and the NO emission.

A fundamental mathematical model for a self-polishing antifouling paint was used to conduct a parameter study. The aims were to show how a mathematical model can reduce the amount of experimental work needed to estimate the behaviour of self-polishing antifouling paints at different conditions, and to suggest ways of controlling biocide release rates. A case study with an antifouling paint based on the well-known tributyltin self-polishing copolymer system showed that the rate of paint polishing was influenced, to various degrees, by the following parameters: seawater pH and concentration of NaCl, pigment particle size, pigment volume concentration of the paint, the rate of pigment dissolution, and the pore size distribution of the leached layer. The modelling approach can be applied to any type of self-polishing antifouling paint provided that kinetic, solubility and diffusivity data are available for the pertinent rate-influencing steps.

The kinetics of catalytic steam reforming of methane over an Ni-YSZ anode of a solid oxide fuel cell (SOFC) have been investigated with the cell placed in a stack configuration. In order to decrease the degree of conversion, a single cell stack with reduced area was used. Measurements were performed in the temperature range 600–800°C and the partial pressures of all reactants and products were varied. The obtained rates could be well fitted with a power law expression (r ∝PCH40.7). A simple model is presented which is capable of predicting the methane conversion in a stack configuration from intrinsic kinetics of the anode support material. The predictions are compared with the stack measurements presented here, and good agreement is observed.

The influence of inorganic material on the thermal deactivation of a biomass fuel and a coal was investigated. Reactivity experiments were performed for chars from wheat and leached wheat straw pyrolyzed at a wide range of heat treatment temperatures (HTT) in a thermogravimetric analyzer (TGA) and entrained flow reactor (EFR). The HTT were varied from 973 to 1673 K in the TGA, and 973 to 1613 K in the EFR. Reactivity experiments were also carried out for chars from the low rank coal, Dietz and demineralized Dietz, prepared in the TGA at the same conditions as the biomass chars. From the TGA data, the biomass chars show at any HTT a higher reactivity than the coal chars, but owing to thermal deactivation the reactivity of all fuel chars converge at the highest HTT. The influence of catalysts for char oxidation in both the biomass and the coal is significant up to HTT = 1273 K. Likely mechanisms for the loss of catalytic activity at high HTT in the TGA are discussed. The straw chars prepared in the EFR are ...

A detailed mathematical model for a self-polishing antifouling paint has been developed. The important rate-influencing steps, dissolution of pigment particles, hydrolysis and erosion of the active polymer binder, effective diffusion in the leached layer, and external mass transport of relevant species, were all included. The aims have been to produce a tool for estimating paint lifetimes at various seawater conditions and paint compositions, for possible product optimizations, and for supporting the development of novel and environmentally friendly antifouling paints. Experimental data for model verification, such as polishing rates and extent of pigment leaching, were obtained using a laboratory rotor. Simulations performed for different rotary speeds and temperatures matched experimental data for two of the three paints investigated. In the last case, the disagreement between model and experiment was explained by significant water swelling of the hydrolyzed polymer. The modeling tools developed are app...

Co-firing of straw and coal in existing pulverised coal-fired boilers is an option for biomass based power generation. However, the high chlorine and potassium content of straw may cause problems. Experiments with co-combustion of straw and coal in power plants have shown that when a moderate amount of straw is applied (up to 20% on a thermal basis), the most serious problems are deactivation of SCR catalysts applied for NO reduction and deterioration of the fly ash quality caused by potassium. To prevent these problems a pretreatment process is required in which the heating value of the straw is supplied to the boiler without introducing potassium into the furnace chamber. A pretreatment process based on pyrolysis and char wash was investigated. Straw is pyrolysed at moderate temperatures at which the potassium is retained in the char. Potassium and residual chlorine are then extracted from the char by water, and char and pyrolysis gases may be co-fired with coal. Fundamental laboratory studies and technical investigations were conducted to evaluate the pretreatment concept. The investigations indicate, that the low temperature pyrolysis of straw can be performed in a circulating fluid bed reactor applying only straw and straw char as bed material. With a bed temperature of approximately 550°C no significant amount of potassium is released to the gas phase. Applying a counter current moving bed to the char potassium extraction with water will probably be advantageous.

Thermal analysis is widely used in combustion research for both fundamental and practical investigations. Efficient combustion of solid fuels in power plants requires understanding of properties and behavior of fuel and ash under a wide range of conditions. At the Department of Chemical Engineering, Technical University of Denmark, thermogravimetric analysis and differential scanning calorimetry are applied in order to investigate various aspects of combustion and gasification processes: pyrolysis, char reactivity and ash melting behavior. This paper shows examples of the application of simultaneous thermal analysis in these three research areas, and it demonstrates the flexibility of this technique in combustion research.