Investigation of thermal degradation of pine needles using multi-step reaction mechanisms

The objective of this study is to assess the relevance of several multi-step reaction mechanisms to describe the mass loss and the mass loss rate of pine needles in TGA at different heating rates in inert and oxidative atmospheres. The kinetic parameters of the different reactions were optimized using the Shuffled complex evolution (SCE) technique. Model results show that both mass loss and mass loss rate should be considered in order to evaluate properly the mechanism. The drying process is described accurately by a single reaction with a well-established set of kinetic parameters. The conversion of dry pine into char requires a five-step reaction mechanism that is combined of three reactions to describe the pyrolysis under inert atmosphere and another two reactions to describe the oxidative process. Less detailed mechanisms were found to be unable to reproduce the mass loss rate. In particular, the one-step reaction mechanism, widely used to model the pyrolysis process in wildland fire simulations, should be used with care. Finally, the char oxidation process can be described with a single step-reaction mechanism. The final complex mechanism is comprised of one reaction for drying, five reactions for the conversion of dry pine into char, and one reaction for the char oxidation, is promising. Further studies are required for its validation in large-scale experiments.     

Convection heat transfer in the cone calorimeter

Estimates of the convection heat transfer coefficient (HTC) in the cone calorimeter are obtained from a near-steady-state analysis of the temperature histories of horizontal coated steel plates. Corrections are applied to the derived HTC values to account for changes of the surface emissivity as a function of temperature. Furthermore, estimates are obtained of the additional heat losses through the sides of the sample holder and the insulation layer on which the test sample rests. The derived HTC values are analysed and correlations presented in the form of Nu=f(Ra) as well as h=f(T), where Nu is the plate Nusselt number, Ra is the plate Rayleigh number, h is the HTC and T is the plate temperature.     

Chemical characterization of pyrolysis liquids of wood-based composites and evaluation of their bio-efficiency

Pyrolysis of wood and wood-based wastes is considered to be one of the promising methods of supplying charcoal as solid material and liquids containing a number of valuable chemicals. In this study, we characterized the chemical components in the liquids from pyrolysis of solid wood and wood-based composites such as particleboard, plywood and medium density fiberboard (MDF) with phenol or urea-type adhesive. In addition, the effectiveness of the liquids to control fungal growth in vitro was examined with consideration of the bio-active components included in the liquids. Results showed that the chemical composition of the liquids obtained from solid wood were greatly different from those obtained from the composites. Fungicidal tests showed a significant difference in the effectiveness of controlling fungi between solid wood and the composites and the liquids from the composites revealed higher effectiveness against the fungi tested.     

A reappraisal of convection heat transfer in the cone calorimeter

The problem of estimating the convection heat transfer coefficient (CHTC) in the Cone Calorimeter (horizontal sample orientation) is revisited. In this contribution the CHTC is modelled by a Nusselt number correlation of the form Nu=CRaⁿ, where Ra is the Rayleigh number. The parameters C and n are estimated using optimisation techniques applied to two different heat transfer models—one that assumes the sample is perfectly insulated on its unexposed face and the other that includes heat transfer to the insulation layer beneath the test sample. The results suggest that the insulation layer influences the derived values of CHTC and this observation is explored.     

Flame size, heat release, and smoke points in materials flammability

The concept of using the flame size as a surrogate for heat release rate (HRR) has been explored. A technique for simultaneously obtaining the HRR, flame size (height and area), and the smoke point of the flame solely from visual images has been developed. The technique has been demonstrated on gaseous flames (methane, propane, ethylene, and propylene) and explored for five burning solid polymers. Estimations of the flame area from images of the stoichiometric contour based on the CH chemiluminescent region of the flames yielded a good linear correlation with measured HRR, valid for all of the gaseous and solid compounds tested, for burning rates above or below the smoke point. In contrast, flame heights and luminous images (i.e., from soot emission) were confounded by differing behavior above and below the smoke point.     

Model selection, identification and validation in anaerobic digestion: a review

Anaerobic digestion enables waste (water) treatment and energy production in the form of biogas. The successful implementation of this process has lead to an increasing interest worldwide. However, anaerobic digestion is a complex biological process, where hundreds of microbial populations are involved, and whose start-up and operation are delicate issues. In order to better understand the process dynamics and to optimize the operating conditions, the availability of dynamic models is of paramount importance. Such models have to be inferred from prior knowledge and experimental data collected from real plants. Modeling and parameter identification are vast subjects, offering a realm of approaches and methods, which can be difficult to fully understand by scientists and engineers dedicated to the plant operation and improvements. This review article discusses existing modeling frameworks and methodologies for parameter estimation and model validation in the field of anaerobic digestion processes. The point of view is pragmatic, intentionally focusing on simple but efficient methods.     

Effects of nanoclay and fire retardants on fire retardancy of a polymer blend of EVA and LDPE

The effects of nanoclay (organoclay) and fire retardants (aluminium tri-hydroxide and magnesium hydroxide) on the fire retardancy of a polymer blend of ethylene-vinyl acetate (EVA) and low-density polyethylene (LDPE) were assessed using thermogravimetric analysis (TGA) and the cone calorimeter. TGA measurements were conducted in nitrogen and air atmospheres at different heating rates (1–20 °C/min), whilst in the cone calorimeter square samples were tested under various external heat fluxes (15–60 kW/m²). The TGA results indicate that the nanoclay (NC) alone has little effect on the degradation of the polymer blend, whereas aluminium tri-hydroxide (ATH) and magnesium hydroxide (MH), used as fire retardants (FRs), generally decrease the onset degradation temperature and also reduce the peak mass loss rate. However, it was found in the cone calorimeter that, though having negligible effect on ignition, the nanoclay reduces the heat release rate (HRR), and increases smoke and CO yields. In comparison, FRs (ATH or MH) were found to delay ignition owing to loss of water at lower temperatures, reduce the HRR, and have similar smoke and CO yields compared to the polymer blend. The reduced HRRs for both the nanoclay and FRs can be attributed to the formation of a surface layer (a nano layer for nanoclay and a ceramic-like layer of Al₂O₃/MgO for FRs), which acts as mass and heat barriers to the unpyrolysed material underneath. The global effect of the surface layer for the polymer blend nanocomposite was examined using a previously developed numerical model, and a methodology for predicting the mass loss rate was subsequently developed and validated.     

掺P2O5水泥基材料水化动力学研究

基于水化动力学模型,采用SEM、XRD和C-80Ⅱ型导热式微量热仪研究了硅酸盐水泥和掺P2O5硅酸盐水泥胶凝体系的水化特性和水化动力学,分析了P2O5对硅酸盐水泥水化机制的影响规律。研究结果表明,掺入P2O5后硅酸盐水泥的水化产物数量和尺寸显著减小。P2O5掺量为3.5%时,硅酸盐水泥熟料水化热总量降低32.6%,硅酸盐水泥的初凝和终凝分别被延缓1.10 h和12.54 h。掺入P2O5复合体系的水化机制与硅酸盐水泥类似,加速期由自动催化反应控制,减速期由自动催化和扩散反应双重反应控制,稳定期扩散反应占据主导。P2O5会增加硅酸盐水泥在加速期和减速期的水化反应阻力,减小稳定期的水化反应阻力。掺入P2O5后,水泥在加速期和减速期的表观活化能增加,稳定期表观活化能略有降低。P2O5溶液环境有利于水泥熟料C3A的水化,延缓C3S和C2S的水化。     

Characterization of thermal properties and analysis of combustion behavior of PMMA in a cone calorimeter

This paper deals with the thermal degradation of a black poly(methyl)methacrylate (PMMA) in a cone calorimeter (CC) in air with a piloted ignition. The influence of several heat fluxes (11 kW m⁻² and 12 kW m⁻², and ten values from 15 to 60 kW m⁻² in steps of 5 kW m⁻²) on PMMA sample degradation and the decomposition chemistry has been studied. Thus, thermal properties have been deduced and calculated from ignition time and mass loss rate (MLR) curves. During our experiments, among compounds quantified simultaneously by a Fourier transformed infrared (FTIR) or gas analyzer, five main species (CO₂, CO, H₂O, NO and O₂) have been encountered, regardless of the external heat flux considered. The main product concentrations allow calculation of the corresponding emission yields. Thus, mass balances of C and H atoms contained in these exhaust gases were able to be compared with those included in the initial PMMA sample. Using the standard oxygen consumption method, heat release rate (HRR), total heat release (THR) and effective heat of combustion (EHC) have been calculated for each irradiance level. Therefore, these different results (thermal properties, emission yields, HRR, THR and EHC) are in quite good accordance (same order of magnitude) with those found in previous studies.     

Characterization of the degradation performance of the sulfamethazine antibiotic by photo-Fenton process

The present study provides results describing the degradation performance of the Sulfamethazine (SMT) antibiotic via photo-Fenton treatment. Experiments were carried out using 1 L solution samples of SMT (50 mg L⁻¹) under different conditions. HPLC results reveal that both Fenton and photo-Fenton reactions were able to completely remove SMT antibiotic from the studied samples in less than 2 min treatment. Half-life times and kinetic parameters (assuming a pseudo-first-order kinetics at reaction initial stage, far from the equilibrium) for SMT degradation were determined and discussed. Hence, appropriate Fenton reagent loads are given to attain different targets proposed. TOC and HPLC data also revealed the presence of reaction intermediates; thus toxicity assays were performed regarding bacterial growth rate. The toxicity of an SMT solution was shown to increase during its degradation by means of photo-Fenton reactions.     

Characterization of aerosols emissions from the combustion of dead shrub twigs and leaves using a cone calorimeter

This work is a contribution to the understanding of wildfire smoke emissions. It focuses on the characterization of aerosols emitted by the combustion of dead shrub leaves and twigs with different thickness (range of 0.75–20 mm). The experiments were carried out at bench scale with a cone calorimeter for the burning of Cistus monspeliensis leaves and twigs. Auto-ignition of the samples was obtained by heating their surface with a radiant heat flux of 50 kW/m². The smoke and aerosols emitted before ignition during pre-heating were analysed separately from the smoke and aerosols emitted during the flaming phase. Heat release rate (HRR) was also measured and we observed two different behaviours depending on the diameter of the twigs. Fuel samples with diameter smaller than 4 mm exhibit a single peak HRR whereas two peaks were observed for the twigs with larger diameters. The smoke production rate (SPR) was also measured and it showed that smoke was mainly emitted during the pre-heating phase. We also obtained a strong correlation between HRR and SPR during the flaming phase but no smoke was emitted during the glowing phase. Emission factors of aerosols were calculated depending on these combustion phases (pre-ignition and flaming) and for the range of thickness of the samples. The observations of the aerosols were performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical composition of organic carbon (OC) aerosols, emitted during the pre-ignition phase, were analysed using gas chromatography (GC) coupled with mass spectrometry (MS). Some carcinogenic compounds were identified. The sizes of OC and black carbon (BC) aerosols emitted were measured with an optical device. Most of the BC were PM_0.3, which corresponds to the alveolar fraction of particles.     

Phenol degradation in water through a heterogeneous photo-Fenton process catalyzed by Fe-treated laponite

New photo-Fenton catalysts have been prepared from synthetic layered clay laponite (laponite RD). Two series of Fe-laponite catalysts were synthesised, with or without thermal treatment of the mixture Fe polycations-laponite in the intercalation procedure. In each series, the intercalated solids underwent calcination at four temperatures, 250, 350, 450, and 550 °C. The catalysts were used for photo-assisted Fenton conversion of phenol, analyzing the influence of five operating factors: the wavelength of the light source (254 nm UV-C and 360 UV-A radiation), the amount of the catalyst (between 0 and 2 g/L), the initial phenol concentration (between 0.5 and 1.5 mmol/L), the initial concentration of hydrogen peroxide (between 20 and 100 mmol/L), and the initial pH of the solution (between 2.5 and 3.5). In all experiments, the temperature was kept constant at 30 °C. The results have shown that the almost complete conversion of phenol was possible, after only 5 min, under the following operating conditions: UV-C radiation; a pH of the aqueous solution of 3; a dose of 1 g_catalyst/L, and a hydrogen peroxide concentration of 50 mmol/L for a solution containing 1 mmol/L of phenol. The catalyst prepared under thermal treatment and calcined at 350 °C showed the best catalytic performance. A kinetic model was proposed for the process, testing its validity and estimating the rate constants.     

Char cracking of medium density fibreboard due to thermal shock effect induced pyrolysis shrinkage

Pyrolysis experiments were conducted on medium density fibreboard (MDF) in inert atmosphere and different ambient pressures, to investigate the char shrinkage and cracking. It is found that the char cracking under uniform heat flux is a typical thermal shock process induced by unbalance shrinkage along the sample thickness during pyrolysis. To predict the number of char fissures, the critical stress criterion and energy conservation theory are used to develop mathematical models under plane constitutive stress state, which reveal that under the same surface degradation the number of char fissures (blisters) strongly relates to the pyrolysis depth at cracking time. Increasing external heat flux decreases the pyrolysis depth and increases the number of char fissures. Both experiments and numerical modelling are used to validate the models. The experimental results show that the horizontal shrinkage is 11% of original length and the micro-structure of char fissures of MDF is less uniform compared to the one of natural wood with a cellular pattern. The surface stresses after cracking are found similarly close to the tensile strength under different heat fluxes, while the surface stresses are very different assuming no crack, which indicates the cracking process reduces the surface stress to lower than the tensile strength. The modelled cracking times are different from the observed cracking time as the fissures are hard to identify at its initial stage and only when they have expanded to certain size the fissures are visually observed. Using the modelled cracking time, the number of char blisters can be well correlated with the pyrolysis depth.     

Intumescent coating surface temperature measurement in a cone calorimeter using laser-induced phosphorescence

Intumescent coating acts as a thermal barrier for construction materials during fire hazards. The coating has the ability to expand by a factor of 40 or more during heat exposure. However, due to its fragile consistence, no physical or optical measurement technique has previously been able to measure the coating surface temperature during expansion. This is undesirable since without accurate information about the coating surface temperature, it will always be difficult to fully understand the heat transfer processes from the fire exposure to the coating and within the coating. Thermographic phosphor technique makes it possible to reliably measure intumescent coating surface thermometry. This paper presents the results of an experimental study using this technique. It compares experimental results with predictions of a calculation model for measurements made inside a cone calorimeter in well-controlled conditions.     

Improving environmental sustainability of concrete products: Investigation on MWC thermal and mechanical properties

This research focuses on the possibility of constituting a more sustainable lightweight concrete, Mineralized Wood Concrete (MWC), substituting natural aggregates with wastes from woodworking activities. Exploiting this type of aggregates, a triple purpose has been achieved: preservation of natural raw materials, reuse of wastes and energy saving. Furthermore, the use of wood aggregates is a way to try to develop a sustainable concrete characterized by high thermal inertia, high thermal resistance and low weight.In this paper, effects of the addition of wood aggregates on mechanical and thermal properties of concrete are studied. Mechanical performances have been investigated with compressive strength tests, while a one-dimensional heat flow model has been used to predict the thermal conductivity of MWC.The use of MWC can be associated with the idea of a different typology of relatively heavy building envelope: this union could competitively answer to the demand of well-insulated building envelope and concurrently characterized by high thermal mass. From this union, a series of other values can be derived: low weight, environmentally friendly, easily industrialized and easy on-site casting. Consequently, applications of wood concrete in building constructions may be an interesting solution in order to improve sustainability and building energy efficiency.     

Experimental characterization, modeling and simulation of a wood pellet micro-combined heat and power unit used as a heat source for a residential building

Cogeneration provides heat and power in a more efficient way than separate production. Micro-cogeneration (micro-CHP) is an emerging solution for the improvement of energy and environmental assessments of residential buildings. A wood pellet Stirling engine micro-CHP unit has been studied in order to characterize its annual performance when integrated to a building. First, through a test bench experiment, both transient and steady state behaviors of the micro-CHP unit have been characterized and modeled. Then a more complete model representing a hot water and heating system including the micro-CHP unit and a stratified storage tank has been carried out. This model has been coupled to a building model. A sensitivity analysis by simulation shows that the dimensioning of different elements of the system strongly influences its global energy performance.