Energy Saving in Industrial Wood Drying Addressed by a Multiscale Computational Model: Board, Stack, and Kiln

This article proposes a multiscale computational model able to calculate energy consumption in a batch lumber kiln. A dual-scale computational model of wood drying deals with the boards/stack interaction and serves as a basis for the present work. A new module was added here that calculates heat losses through kiln walls (convection, condensation) and the energy used by each kiln component (fans, heating elements, humidifier, vacuum pump, etc.). The corresponding mathematical formulation is presented and then theoretical results are compared to those collected in an industrial vacuum kiln. As application example, the effect of air reversal, air velocity, and kiln insulation are exhibited, which depicts the great potential and prospects of this new tool for energy savings in relation to the product quality.     

High intakes of Cr, Ni, and Zn in clinker: Part II. Influence on the hydration properties

This work presents the results of the hydration of cements with high intakes of Cr, Ni, and Zn. The cements were produced from clinkers that were doped with 200 to 25,000 ppm of heavy metal. Investigations on the clinkers were presented in Part I. In this paper the rate of heat generation of the cements in the first 2 days was analysed by differential scanning calorimetry. The hydration products were investigated by scanning electron microscopy combined with energy-dispersive X-ray spectrometer and also by X-ray powder diffraction. The initial setting of some samples was tested, as well as the strength. The results show that heavy metals only have an influence on the hydration properties of the cements if the dosage is much higher than in ordinary Portland cement.     

Application of the reaction engineering approach (REA) for modeling intermittent drying under time-varying humidity and temperature

A ‘good’ drying model is important for the design of dryer, evaluation of dryer performance and prediction of product quality. Among the available models, the reaction engineering approach (REA) is a lumped model, proven to be simple, robust and accurate to model drying of several materials. In this paper, the REA is implemented to model intermittent drying, which is usually practiced for saving energy consumption and maintaining product quality during drying, under time-varying drying air temperature and humidity, which is a challenging drying case to model. For this purpose, the equilibrium activation energy (ΔE_v,b) is defined according to the drying settings in each time period and combined with the relative activation energy (ΔE_v/ΔE_v,b) generated from the convective drying experimental data obtained under constant drying conditions. The mass and heat balances also implement the corresponding drying settings in each time period during the intermittent drying. The results indicate that the REA can describe both the moisture content and temperature profiles of the intermittent drying under time-varying drying air temperature and humidity well. The accuracy, simplicity and robustness of the REA for the intermittent drying under time-varying drying air temperature and humidity are proven here. This has provided a major and significant extension of the REA on modeling challenging drying cases.     

Influence of chemical and physical characteristics of cement kiln dusts (CKDs) on their hydration behavior and potential suitability for soil stabilization

The interaction of CKDs with a given soil depends on the chemical and physical characteristics of the CKDs. Hence, the characterization of CKDs and their hydration products may lead to better understanding of their suitability as soil stabilizers. In the present article, four different CKD powders are characterized and their hydration products are evaluated. A detailed chemical (X-ray diffraction), thermogravimetric and morphological (scanning electron microscope) analyses of both the CKD powders and the hydrated CKD pastes are presented. In general, high free-lime content (~ 14–29%) CKDs, when reacted with water produced significant amounts of calcium hydroxide, ettringite and syngenite. These CKDs also developed higher unconfined compressive strength and higher temperature of hydration compared to CKDs with lower amounts of free-lime. An attempt was made to qualitatively correlate the performance of CKD pastes with the chemical and physical characteristics of the original CKD powders and to determine their potential suitability as soil stabilizers. To that effect a limited unconfined compressive strength testing of CKD-treated kaolinite clays was performed. The results of this study suggest that both the compressive strength and the temperature of hydration of the CKD paste can give early indications of the suitability of particular CKD for soil stabilization.     

Optimization of Kiln Drying for Softwood through Simulation of Wood Stack Drying, Energy Use, and Wood Color Change

An integrated modeling system was developed to simulate the drying processing, energy use, and wood color change in kiln drying of softwood timber. The model has been applied for a temperature range from 50 to 70°C and an airspeed from 3 to 9 m/s. The model is based on theoretical analysis and contains components such as kiln configuration and practical operations. From the model simulation, optimized drying schedules for minimizing color change and energy use are recommended with dry bulb temperature of 60 to 70°C and wet bulb depression of 15 to 20°C.     

Optimization of Kiln Drying for Softwood through Simulation of Wood Stack Drying,Energy Use,and Wood Color Change

An integrated modeling system was developed to simulate the drying processing, energy use, and wood color change in kiln drying of softwood timber. The model has been applied for a temperature range from 50 to 70°C and an airspeed from 3 to 9 m/s. The model is based on theoretical analysis and contains components such as kiln configuration and practical operations. From the model simulation, optimized drying schedules for minimizing color change and energy use are recommended with dry bulb temperature of 60 to 70°C and wet bulb depression of 15 to 20°C.     

A novel reverse flow reactor coupling endothermic and exothermic reactions. Part I: comparison of reactor configurations for irreversible endothermic reactions

A new reactor concept is studied for highly endothermic heterogeneously catalysed gas phase reactions at high temperatures with rapid but reversible catalyst deactivation. The reactor concept aims to achieve an indirect coupling of energy necessary for endothermic reactions and energy released by exothermic reactions, without mixing of the endothermic and exothermic reactants, in closed-loop reverse flow operation. Periodic gas flow reversal incorporates regenerative heat exchange inside the reactor. The reactor concept is studied for the coupling between the non-oxidative propane dehydrogenation and methane combustion over a monolithic catalyst.Two different reactor configurations are considered: the sequential reactor configuration, where the endothermic and exothermic reactants are fed sequentially to the same catalyst bed acting as an energy repository and the simultaneous reactor configuration, where the endothermic and exothermic reactants are fed continuously to two different compartments directly exchanging energy. The dynamic reactor behaviour is studied by detailed simulation for both reactor configurations. Energy constraints, relating the endothermic and exothermic operating conditions, to achieve a cyclic steady state are discussed. Furthermore, it is indicated how the operating conditions should be matched in order to control the maximum temperature. Also, it is shown that for a single first order exothermic reaction the maximum dimensionless temperature in reverse flow reactors depends on a single dimensionless number. Finally, both reactor configurations are compared based on their operating conditions. It is shown that only in the sequential reactor configuration the endothermic inlet concentration can be optimised independently of the gas velocities at high throughput and maximum reaction coupling energy efficiency, by the choice of a proper switching scheme with inherently zero differential creep velocity and using the ratio of the cycle times.In this first part, both the propane dehydrogenation and the methane combustion have been considered as first order irreversible reactions. However, the propane dehydrogenation is an equilibrium reaction and the low exit temperatures resulting from the reverse flow concept entail considerable propane conversion losses. How this ‘back-conversion’ can be counteracted is discussed in part II Chemical Engineering Science, 57, (2002), 855-872.     

Towards sustainable production and consumption: A novel DEcision-Support Framework IntegRating Economic,Environmental and Social Sustainability (DESIRES)

The idea of sustainable production and consumption is becoming a widely-accepted societal goal worldwide. However, its implementation is slow and the world continues to speed down an unsustainable path. One of the difficulties is the sheer complexity of production and consumption systems that would need to be re-engineered in a more sustainable way as well as the number of sustainability constraints that have to be considered and satisfied simultaneously. This paper argues that bringing about sustainable production and consumption requires a systems approach underpinned by life cycle thinking as well as an integration of economic, environmental and social aspects. In an attempt to aid this process, a novel decision-support framework DESIRES has been developed comprising a suite of tools, including scenario analysis, life cycle costing, life cycle assessment, social sustainability assessment, system optimisation and multi-attribute decision analysis. An application of the framework is illustrated by a case study related to energy.     

回转焙烧炉在催化裂化催化剂行业的应用及其结构优化

介绍了回转焙烧炉在催化裂化（FCC）催化剂行业的应用,根据实际应用情况进行了设备结构优化,实现节能降耗,提高产品收率。     

Combined Electrohydrodynamic (EHD) and Vacuum Freeze Drying of Sea Cucumber

A combination of electrohydrodynamic drying (EHD) and vacuum freeze drying (FD) is examined as an improved method for dehydrating sea cucumbers. The energy consumption, shrinkage and rehydration ratio, protein content, and sensory properties, such as the color and trimness, of the dried product in the EHD–FD method are measured. Compared with FD, the combined process consumes less drying time and has lower energy consumption than EHD drying alone. Also, the product processed by combined drying displays lower shrinkage, higher rehydration rate and higher protein content, along with better sensory qualities.     

Hydrogenated hydroxy-functionalized polyisoprene (H-HTPI) and isocyanurate of isophorone diisocyanates (I-IPDI): reaction kinetics study using FTIR spectroscopy

The reaction between a hydrogenated hydroxyl-functionalized polyisoprene (H-HTPI) and isophorone diisocyanate isocyanurate (I-IPDI) is followed by using direct FTIR spectroscopy. The reaction kinetics is studied using a simple model taking into consideration the I-IPDI structure. The rates of individual isocyanate groups are described by a second order equation. Influence of dibutyltin dilaurate (DBTL) concentration and temperature on selectivity, defined as the ratio between the rate constant of secondary isocyanate group and the rate constant of the primary isocyanate group, is investigated. It is observed that selectivity decreases when temperature or DBTL concentration increases. Eyring parameters are determined for the catalyzed [ΔH^*=77/35 (kJ mol⁻¹), ΔS^*=12/−100 (J mol⁻¹ K⁻¹)] and uncatalyzed reactions [ΔH^*=48/43 (kJ mol⁻¹), ΔS^*=−179/−167 (J mol⁻¹ K⁻¹)] primary and secondary isocyanate groups being differentiated.     

Remote actuation of hydrogel nanocomposites: Heating analysis,modeling, and simulations

Recently, there has been increasing interest in remote heating of polymer nanocomposites for applications such as actuators, microfluidic valves, drug delivery devices, and hyperthermia treatment of cancer. In this study, magnetic hydrogel nanocomposites of poly(ethylene glycol) (PEG) with varying amounts of iron oxide nanoparticle loadings were synthesized. The nanocomposites were remotely heated using an alternating magnetic field (AMF) at three different AMF amplitudes, and the resultant temperatures were recorded. The rate of the temperature rise and the steady state temperatures were analyzed with a heat transfer model, and a correlation of heat generation per unit mass with the nanoparticle loadings was established for different AMF amplitudes. The temperature rise data of a PEG system with different swelling properties were found to be accurately predicted by the model. Furthermore, the correlations were used to simulate the temperatures of the nanocomposite and the surrounding tissue for potential hyperthermia cancer treatment applications. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Kinetic studies of liquid phase ethyl tert-butyl ether (ETBE) synthesis using macroporous and gelular ion exchange resin catalysts

Ethyl tert-butyl ether (ETBE) synthesis from ethanol (EtOH) and tert-butyl alcohol (TBA) was studied with different macroporous and gelular ion exchange resin catalysts. Purolite^® (CT-124, CT-145H, CT-151, CT-175 and CT-275) and Amberlyst^® (15 and 35) ion exchange resins were used for the present work. Effect of various parameters such as catalyst type, temperature, reactants feed molar ratio and catalyst loading were studied for the optimisation of reaction condition. Among the catalysts studied, Purolite CT-124 gave the best results for TBA conversion and selectivity towards ETBE. Kinetic modelling was performed with this catalyst and activation energy and water inhibition coefficient were determined. Heterogeneous kinetic models [e.g., Eley-Rideal (ER), Langmuir-Hinshelwood-Hougen-Watson (LHHW)] were unable to predict the behaviour of this etherification reaction, whilst the quasi-homogeneous (QH) model represented the system very well over wide range of reaction conditions.     

Rational modeling of the CPO of methane over platinum gauze: Elementary gas-phase and surface mechanisms coupled with flow simulations

The high-temperature catalytic partial oxidation of methane (CPOM) over a platinum gauze reactor was modeled by integrating 3D numerical simulations of the flow field coupled with heat transport as well as detailed micro-kinetic models including gas-phase and surface reaction mechanisms. Model results describe well CPO experiments over Pt-gauzes in the literature. The conversions of CH₄ and O₂ increase with an increased contact time and were constant in the temperature range of 1000–1200 K. The selectivity to CO linearly increases with temperature. H₂ was only observed above 1200 K, below this temperature H₂O was the only hydrogen-containing product. The contribution of heterogeneous steps in the overall process is prominent, but in the later stages of the reactor, gas-phase reactions become important at certain conditions of temperature, pressure and residence time. Simulations predicted significant gas-phase production of ethane and ethylene via methane oxidative coupling upon increasing the total pressure and residence time. Consequently, homogeneous and heterogeneous processes should be simultaneously implemented in order to accomplish a solid reactor modeling.     

The magnesia-silica gel phase in slag cements: alkali (K, Cs) sorption potential of synthetic gels

Blends of Portland cement with blast furnace slag hydrate to yield two gel phases, one essentially a calcium silicate hydrate (C-S-H) composition, the other a magnesium silicate hydrate (M-S-H) composition: the two gel phases are essentially immiscible. Together, the gel phases comprise an important source of sorption potential for the alkalis present in ordinary cement and blending agents. M-S-H gels have been synthesised and their sorption potential measured for postassium (K) and cesium (Cs) at 25 °C by using fresh gels as well as gels previously aged at 85 °C for 6 months. The ability of slag-cement blends to lower pore fluid alkalinity generally, and in nuclear waste technology to incorporate Cs, is interpreted in terms of the sorption data.     

Kinetic modeling of tungsten silicide chemical vapor deposition from WF6 and Si2H6: Determination of the reaction scheme and the gas-phase reaction rates

Kinetic studies were carried out on tungsten silicide (WSi_x) chemical vapor deposition from WF₆/Si₂H₆ in a hot-wall type tubular reactor, focusing on the axial distributions of step coverage and composition ratio. The growth-rate profile within the tubular reactor showed exponential decay, which suggests first-order reaction kinetics. The silicon content of the film increased downstream in the reactor, but the step coverage quality was independent of axial position. The reactive sticking probabilities obtained from the step coverage profile were about 0.33. Two reaction models were investigated to explain these experimental results. The first model is a parallel deposition model, in which W-containing species and Si-containing species are depositing separately. The other model is a consecutive reaction model, in which W-species and Si-species react in the gas phase to form intermediate species containing W and Si. Considering these plausible kinetic mechanisms, consecutive reactions in the gas phase to form W and Si containing species were found to be the controlling factor in the WF₆/Si₂H₆ process. These gas-phase homogeneous reaction-rate constants of the WF₆/Si₂H₆ process were obtained from axial distribution of film composition ratio based on this kinetic model, and the activation energy is about 25 kJ/mol.     

Mathematical Modeling of Kiln Drying of Softwood Timber: Model Development, Validation, and Practical Application

Mathematical modeling of wood drying is a powerful tool to better understand and quantify the effects of wood properties as well as the effects of drying and post-drying treatment conditions on drying and thus the wood drying models can be used to improve drying quality. The models that have been developed can be divided into three categories: models for drying a single board, models for drying a kiln-wide stack, and models for drying stress and deformation. The single-board drying model employs comprehensive heat and moisture mass transfer equations and can be used to investigate the influence of wood variability. The kiln-wide drying model, which is based on the transfer processes between wood and the drying medium, is able to examine the influence of drying schedules and wood properties. The stress model can predict stress development in drying and stress relief in final steam conditioning and post-kiln treatment. An integrated model can be used to optimize drying schedules and develop strategies for high-quality dried timber.     

Synthesis, properties and biomedical applications of poly(glycerol sebacate) (PGS): A review

Poly(glycerol sebacate) (PGS) is a biodegradable polymer increasingly used in a variety of biomedical applications. This polyester is prepared by polycondensation of glycerol and sebacic acid. PGS exhibits biocompatibility and biodegradability, both highly relevant properties in biomedical applications. PGS also involves cost effective production with the possibility of up scaling to industrial production. In addition, the mechanical properties and degradation kinetics of PGS can be tailored to match the requirements of intended applications by controlling curing time, curing temperature, reactants concentration and the degree of acrylation in acrylated PGS. Because of the flexible and elastomeric nature of PGS, its biomedical applications have mainly targeted soft tissue replacement and the engineering of soft tissues, such as cardiac muscle, blood, nerve, cartilage and retina. However, applications of PGS are being expanded to include drug delivery, tissue adhesive and hard tissue (i.e., bone) regeneration. The design and fabrication of PGS based devices for applications that mimic native physiological conditions are also being pursued. Novel designs range from accordion-like honeycomb structures for cardiac patches, gecko-like surfaces for tissue adhesives to PGS (nano) fibers for extra cellular matrix (ECM) like constructs; new design avenues are being investigated to meet the ever growing demand for replacement tissues and organs. In less than a decade PGS has become a material of great scrutiny and interest by the biomedical research community. In this review we consolidate the valuable existing knowledge in the fields of synthesis, properties and biomedical applications of PGS and PGS-related biomaterials and devices.