The objective of Task 15 of the IEA Photovoltaic Power Systems Programme is to create an enabling framework to accelerate the penetration of BIPV products in the global market of renewables, resulting in an equal playing field for BIPV products, BAPV products and regular building envelope components, respecting mandatory issues, aesthetic issues, reliability issues, and financial issues.

Subtask E of Task 15 is focused on pre-normative international research on BIPV characterisation methods and activity E.3 is dedicated to fire safety of BIPV modules and installations.

The number of tall buildings combining both a visible mass timber structure and large open floor plans is growing rapidly introducing new fire safety challenges. One risk is that of very rapid flame spread in the ceiling, originating from a severe but localized fire, resulting in fires where the majority of large compartments burn simultaneously. Such phenomena have been observed in both tests and accidents, but knowledge of effective mitigation without the use of sprinklers is scarce. In Europe, this problem is commonly addressed in construction by complying to prescriptive rules of reaction-to-fire classification of linings. The reaction-to-fire classification, primarily based on the single burning item (SBI) test of EN13832, characterizes the material’s contribution to a fire in the very initial phase of the fire. Treatments can be used to improve the reaction-to-fire class of mass timber, which will reduce the risk of substantial fire development. Fires can, however, develop and grow large even without the contribution of lining materials. For this reason, and in light of the recent findings of research of large open floor plan compartments, it is of interest to assess the effectiveness of treatments to reduce the risk of rapid flame spread. Therefore, eight tests in 18.0 × 2.3 × 2.2 m3 compartments were performed. Six had exposed timber surface with a clear coating or impregnation in the ceiling, complying with a reaction-to-fire class B and two served as untreated timber and non-combustible reference tests. The fire source, representing a fire in moveable fuel, was severe enough (3 - 3.7 MW) for flame impingement on the ceiling. The rate of at which wood ignited from the heat in the ceiling, the temperature development at different heights, as well as external flaming were assessed and were used as indicators of performance. Additional indicators were the estimated tenability and ceiling char depths throughout the compartment. The untreated timber and the non-combustible ceiling represented the two extremes for most indicators with the class-B treated timber surfaces falling in between. Close to the fire source, the test indicators for treated timber surfaces performed similar to those of the untreated timber surface while the non-combustible ceiling performed significantly better. With increasing distance from the fire source, indicators from treated timber tests more resembled the non-combustible ceiling. This behavior was noticed for all types of indicators. With increasing distance from the fire source, the fire exposure is naturally less severe and thus, more similar to the small burner exposure used in SBI-testing which the treatments were developed against. Both final charring depth and temperature developments for ignition and tenability were clearly improved by the treatment, but the SBI test results (FIGRA and THR600s) did not correlate well to the compartment test indicators (Figure 92 andFigure 93). Nevertheless, using treatments assessed by SBI is a common strategy to mitigate fire spread in newly constructed mass timber buildings and practitioners should be aware that while the treatments have significant effects on the flame spread they are not to be treated as incombustible. We propose that addressing the ceiling spread problem requires an additional indicative test with more severe exposure than the SBI test setup. The impregnated timber experienced loss of integrity due to substantial shrinkage of the timber during the severe exposure. Such phenomena were not captured in the SBI testing. Comparisons of performance of the impregnated specimens indicates that it can be beneficial for the performance to implement more impregnation than needed for reaction-to-fire class B. Whether this holds for all treatments cannot be concluded.

Biomass pyrolysis in the thermally thick regime is an important thermochemical phenomenon encountered in many different types of reactors. In this paper, a particle-resolved algorithm for thermally thick biomass particle during high-temperature pyrolysis is established by using reactive molecular dynamics (MD) and computational fluid dynamics (CFD) methods. The temperature gradient inside the particle is computed with a heat transfer equation, and a multiphase flow algorithm is used to simulate the advection/diffusion both inside and outside the particle. Besides, to simulate the influence of intraparticle temperature gradient on the primary pyrolysis yields, a multistep kinetic scheme is used. Moreover, a new tar decomposition model is developed by reactive molecular dynamic simulations where every primary tar species in the multistep kinetic scheme cracks under high temperature. The integrated pyrolysis model is evaluated against a pyrolysis experiment of a centimeter-sized beech wood particle at 800–1050 °C. The simulation results show a remarkable improvement in both light gas and tar yields compared with a simplified tar cracking model. Meanwhile, the MD tar cracking model also gives a more reasonable prediction of the species yield history, which avoids the appearance of unrealistically high peak values at the initial stage of pyrolysis. Based on the new results, the different roles of secondary tar cracking inside and outside the particle are studied. Finally, the model is also used to assess the influence of tar residence time and several other factors impacting the pyrolysis.

Soot generation is an important problem in high-temperature biomass gasification, which results in both air pollution and the contamination of gasification equipment. Due to the complex nature of biomass materials and the soot formation process, it is still a challenge to fully understand and describe the mechanisms of tar evolution and soot generation at the reactor scale. This knowledge gap thus motivates the development of a comprehensive computational fluid dynamics (CFD) soot formation algorithm for biomass gasification, where the soot precursor is modeled using a component-based pyrolysis framework to distinguish cellulose, hemicellulose and lignin. The model is first validated with pyrolysis experiments from different research groups, after which the soot generation during biomass steam gasification in a drop-tube furnace is studied under different operating temperatures (900–1200 °C) and steam/biomass ratios. Compared with the predictions based on a detailed tar conversion model, the current algorithm captures the soot generation more reasonably although a simplified tar model is used. Besides, the influence of biomass lignin content and the impact of tar and soot consumptions on the soot yield is quantitatively studied. Moreover, the impact of surface growth on soot formation is also discussed. The current work demonstrates the feasibility of the coupled multiphase flow algorithm in the prediction of soot formation during biomass gasification with strong heat/mass transfer effects. In conclusion, the model is thus a useful tool for the analysis and optimization of industrial-scaled biomass gasification. © 2021 The Author(s)

A detailed but still central processing unit (CPU)-efficient bed model for grate-fired combustion of biomass and waste is developed. Simulations of wood chip combustion are performed, and the results are compared to experiments. The so-called layer model is used to track the development of the thermally thick representative fuel particles in the bed. As an efficient way of handling a large number of physical fuel particles, each representative fuel particle represents a number of physical particles with the exact same properties. The motion of the fuel bed is handled in a way that requires negligible CPU power, while for wastes and other fuels with less defined shapes and structure, it still yields accuracy similar to the much more CPU-intensive collision-based models. In this work, the bed model is coupled with ANSYS Fluent and used to simulate one of the test campaigns performed at the grate-fired pilot unit at the University of Stuttgart. It is found that for the test campaign of interest, burning wood chips, the fuel bed is ignited from below, and it is explained how this is due to the thermal properties of the grate and how important the numerical handling of the grate is for an accurate prediction of the bed behavior.

Our earlier study showed significant differences in average particle velocity between simulation and experimental results for devolatilizing biomass particles in an idealised entrained flow reactor [N. Guo et al., Fuel, 2020]. This indicates that the simulations do not accurately describe the physicochemical transformations and fluid dynamic processes during devolatilization. This article investigates the reasons for these discrepancies using time-resolved analyses of the experimental data and complementary modelling work. The experiments were conducted in a downdraft drop-tube furnace with optical access, which uses a fuel-rich flat flame (CH4[sbnd]O2[sbnd]CO2) to heat the particles. Gas flow was characterized using particle image velocimetry, equilibrium calculations and thermocouple measurements. High-speed images of devolatilizing Norway spruce (Picea Abies) particles were captured and analysed using time-resolved particle tracking velocimetry methods. The data were used to estimate the balance of forces and fuel conversion. Thrust and “rocket-like” motions were frequently observed, followed by quick entrainment in the gas flow. Rocketing particles were, on average, smaller, more spherical and converted faster than their non-rocketing counterparts. These differences in conversion behaviour could be captured by a particle-size dependent, 0-D devolatilization model, corrected for non-isothermal effects. The results from this investigation can provide a basis for future modelling and simulation work relevant for pulverized firing technologies. © 2021 The Author(s)

The conversion of woody biomass is studied by means of a layer-based model for thermally-thick biomass particles (Thunman et al. 2002, Ström et al. 2013). The model implementation is successfully validated against experiments that study particle conversion in a drop tube reactor. After this validation step, this work focuses on the well-known problem of grid dependence of two-phase numerical simulations using the standard Euler–Lagrange (EL) framework. This issue is addressed and quantified by comparing EL data that models the particle boundary layers to corresponding simulations which fully resolve these boundary layers (fully-resolved, FR, simulations). A comparison methodology for the conceptually different FR and EL approaches by extracting the heat transfer coefficient from the detailed FR simulations is proposed and confirms that the EL results are strongly grid-dependent. This issue is overcome by applying a set of coarse-graining methods for the EL framework. Two coarse-graining methods are evaluated, a previously suggested diffusion-based method (DBM) and a new approach based on moving averages referred to as MAM. It is shown that both DBM and MAM can successfully recover the detailed FR data for pure particle heating for a case where the grid size is half the particle diameter, i.e. when the standard EL method fails. Both coarse-graining methods also give improved results for an EL simulation that considers the more complex combined physics of particle heating, drying and devolatilisation, given that the CG model parameters that scale the corresponding CG interaction volumes are sufficiently large. Based on the available FR data, recommended model parameter ranges for DBM and MAM are provided as a function of normalised boundary layer thickness. The novel MAM approach is shown to be significantly more efficient than the DBM and therefore suitable for future EL simulations with multiple particles. 

Denne studien belyser ulike aspekter ved personsikkerheten ved brann i tunnel og svarer ut konkrete spørsmål omkring temaet.

Oppdragsgiver er Bane NOR. Prosjektet har fått innspill fra en arbeidsgruppe som er koordinert og ledet av hhv. KS Bedrift og Bane NOR – med fagressurser fra Vestfold Interkommunale Brannvesen IKS (VIB), Bergen brannvesen (BB), Oslo brann- og redningsetat (OBRE), Bane NOR, operatørselskaper (Vy og Flytoget), Direktoratet for samfunnssikkerhet og beredskap (DSB) og Statens havarikommisjon for transport (SHT).

Rapporten er delt inn i to hoveddeler. Del 1 omhandler kartlegging av relevante forskningsprosjekt, dimensjonerende brannscenarier og røykkontroll, se sammendrag og forslag til veien videre i underkapittel 3.5. Del 2 omhandler kartlegging av kunnskap om menneskelig atferd i forbindelse med tunnelbrann, se sammendrag og forslag til veien videre i underkapittel 4.5. Denne delen er utarbeidet av Lunds Tekniska Högskola og WSP Sverige, og er følgelig på svensk.

This study evaluates venting from lithium-ion batteries in homes and is commissioned by the Norwegian Directorate for Civil Protection (DSB) and the Norwegian Building Authority (DiBK). The main objective is to study the extent to which venting from a battery in a dwelling can pose a risk for people, focusing on the consequences associated with venting. The Norwegian fire statistics database BRIS was used to identify relevant scenarios. Based on these scenarios, a total of nine numerical simulations of gas dispersion in a generic dwelling were carried out. Boundary conditions, such as gas quantity and composition, were based on a literature study. The simulations were used to evaluate the potential for accumulation of an explosive gas mixture, exposure to toxicity-related gases (both asphyxiants and irritants) and the possibility of detection of carbon monoxide (CO). Electric car batteries, electric bikes, electric scooters, electric hoverboards and larger, stationary battery energy storage systems are found to be the lithium-ion batteries with the highest energy content, which are most common in homes. Other electrical appliances – consumer products make up a larger share in the fire statistics, but these have a lower energy content and thus less potential to pose a major risk for people. Electric cars that are charged in the garage and larger batteries used for energy storage contain the most energy and therefore have the potential for the most severe consequences. However, these batteries are not stored or charged/discharged in living areas, while electric bikes/ scooters/ balancing boards are often stored and charged in the living room, hallway and bedroom. Electric bikes and similar batteries are also subjected to more mechanical and thermal loads compared with battery energy storage systems. It is therefore assumed that the frequency of incidents involving these batteries will be larger than the frequency of incidents involving battery energy storage systems. Therefore, the simulations in this study focused on venting from an electric bike battery (from a single cell and from an entire pack) in the hallway to a generic dwelling. A quantitative risk analysis of the risk associated with electric bike batteries compared with the risk associated with battery energy storage systems was not carried out. Lithium-ion batteries undergoing a thermal event typically emits 1-3 litres of gas per ampere-hour (Ah) at 26 °C and 3.7 volts (V), depending on battery chemistry and state of charge (SOC). Venting from lithium-ion batteries contains carbon dioxide, flammable components such as carbon monoxide, various hydrocarbons, methanol and hydrogen, as well as toxic components such as hydrogen fluoride, hydrogen chloride and hydrogen cyanide. The relatively large proportion of flammable gases (e.g. around 30% hydrogen) makes venting from lithium-ion batteries an explosion hazard. Although batteries with a low state of charge emit less gas than batteries with a high state of charge, the risk of explosion of batteries with a low state of charge may be larger, since the likelihood of late ignition is larger. There are many different types of lithium-ion batteries on the market and several methods for battery safety tests. Today, there is no unified, public system or database with an overview of data for venting from thermal events in lithium-ion batteries. Such a system would be useful, to cover knowledge gaps and to provide data that can be used in risk evaluations. The results show that the largest amount of flammable gas mixture, 26 litres, was accumulated by venting from a 400 watt-hour (Wh) electric bike battery pack, which was placed on a shelf in a small hallway of 3.5 square meters. When the thermal event was limited to a single battery cell, 3.6 litres of flammable gas were formed. Moreover, the results show that the location of the battery plays an important role in the accumulation of flammable gas. When the battery is stored in a partially enclosed area, such as a shelf, the gas can accumulate. The results also show that, especially for venting from a battery pack, it is best to store the batteries in large and wellventilated rooms. No explosion risk analysis was performed related to the accumulated flammable gas clouds. Fire gases from lithium-ion battery fires are generally not significantly more toxic compared with comparable plastic fires, but have the potential for low concentrations of more harmful gases, such as hydrogen fluoride (HF), to be released. The results of the simulations carried out in this study show that the limits for health-hazardous or fatal gas concentrations are exceeded by a thermal event in a lithium-ion battery. Toxic gases can have an asphyxiating and an irritating effect on humans. The results show that the critical value of irritating gases obtained before the limit value of asphyxiating gases. Hydrogen chloride (HCl) and hydrogen fluoride (HF) reached most rapidly health-hazardous or fatal gas concentrations, and these gases also spread most in the room. Furthermore, the results show that risks for people associated with exposure to toxic gases are primarily relevant when the entire battery pack is involved in the thermal event. When the thermal event is limited to a single cell, the simulations show that critical gas concentrations are reached only nearby the battery. If, on the other hand, a thermal event spreads to the entire battery pack, it leads to critical levels of toxic gases throughout the room after about 1 minute for a small room (3.5 m2 ), and in the entire upper half of a large room (43.5 m2 ) after about 4 minutes. To reduce the risk of toxic gas venting, the same measures are recommended as for the reduction of the risk of accumulated flammable gas. Larger lithium-ion batteries should be charged and stored in well-ventilated rooms that are not living areas or part of the escape route, ideally in external buildings. This is consistent with NELFO's recommendations for battery energy storage systems in residential buildings. However, costs/ benefits must be considered, especially for electric bikes and smaller batteries containing less energy than battery energy storage systems. Furthermore, closed doors are good physical barriers to prevent or delay gas and smoke spread in the dwelling. Another important barrier recommended to reduce the risk associated with venting from or fire in a lithium-ion battery is early detection. It is especially important since a thermal runaway develops very quickly, compared with, for example, a fire that starts as a smouldering fire. In this study, only a coarse analysis of the possibility of early detection of increased concentration of carbon monoxide was carried out. The results suggest that combination detectors near the battery may be a good measure to ensure early detection. Recommendations for further work identified in this study are the validation of the simulations by conducting battery fire tests of relevant electric bike batteries and conducting large-scale experiments for validation of gas dispersion and detection. It is also recommended to evaluate the potential overpressure that a delayed ignition (explosion) of gas can generate. Furthermore, it should be considered conducting a similar study for battery energy storage systems or other scenarios with significantly higher energy content than electric bike batteries.

Ventilation conditions are an essential factor in the development of car park fires. This study investigates if larger open wall areas can affect fires in naturally ventilated car parks such that a reduction of the fire resistance of the main load-bearing system is warranted. A set of ten fire simulations with different wind conditions (direction and force) were carried out. Two generic car parks were examined, one with a 21 % open area fraction and one with a 41 % open area fraction. A simplified structural analysis for all scenarios was, furthermore, conducted to investigate the effect of different open area fractions on the collapse time of individual steel beams. The results of this study indicate that the fire resistance of the main load-bearing structure should not be reduced from R30 or R60 to R15, even if the wall surfaces have a larger open area fraction.

The incineration of municipal solid waste (MSW) is an attractive technology to generate thermal energy and reduce landfill waste volume. To optimize primary measures to ensure low emission formation during combustion, numerical models that account for varying waste streams and their impact on nitrogen oxide (NOx) formation are needed. In this work, the representation of the fuel by surrogate species is adopted from liquid fuel and biomass combustion and applied to solid waste devolatilization and combustion. A surrogate formulation including biomass components, protein, inorganics, and plastic species is proposed, and a comprehensive description of the heterogeneous and homogeneous reactions is developed. The presented work combines and extends available schemes from the literature for woody and algae biomass, coal, and plastic pyrolysis. The focus is set on the prediction of fuel NOx and its precursors, including cyclic nitrogen-containing hydrocarbons. Additionally, the interaction of NOx with sulfur and chloride species is accounted for, which are typically released during the devolatilization of MSW. The model allows for predicting thermogravimetric analysis measurement of waste fractions and different waste mixtures. The proposed kinetic mechanism well reproduces NOx formation from ammonia and hydrogen cyanide and its reduction under selective non-catalytic reduction conditions. The chemical model is successfully applied to predict the released gas composition along a grate-fired fuel bed using a stochastic reactor network. © 2021 The Authors.

Biomass devolatilization and incineration in grate-fired plants are characterized by heterogeneous fuel mixtures, often incompletely mixed, dynamical processes in the fuel bed and on the particle scale, as well as heterogeneous and homogeneous chemistry. This makes modeling using detailed kinetics favorable but computationally expensive. Therefore, a computationally efficient model based on zero-dimensional stochastic reactors and reduced chemistry schemes, consisting of 83 gas-phase species and 18 species for surface reactions, is developed. Each reactor is enabled to account for the three phases: the solid phase, pore gas surrounding the solid, and the bulk gas. The stochastic reactors are connected to build a reactor network that represents the fuel bed in grate-fired furnaces. The use of stochastic reactors allows us to account for incompletely mixed fuel feeds, distributions of local temperature and local equivalence ratio within each reactor and the fuel bed. This allows us to predict the released gases and emission precursors more accurately than if a homogeneous reactor network approach was employed. The model approach is demonstrated by predicting pyrolysis conditions and two fuel beds of grate-fired plants from the literature. The developed approach can predict global operating parameters, such as the fuel bed length, species release to the freeboard, and species distributions within the fuel bed to a high degree of accuracy when compared to experiments. © 2020 American Chemical Society

Modern buildings are being built with increasingly complex technical installations and energy systems. The introduction of renewable energy production, like photovoltaic (PV) panels on building roofs and facades and an increasing number of connected electric appliances, changes the way the electric power is distributed from production to end-user. The difference in production and demand for energy over time also gives incentives for installing energy storage systems. Electric energy can be stored in batteries, transferred into hydrogen gas via electrolysis or stored as thermal energy for use later. The current work presents an overview of an ongoing study in the Fire Research and Innovation Centre (FRIC), on fire safety implications related to implementing new technology for energy storage and production. The focus is on the built environment such as dwellings and office buildings situated in the Nordic countries. This study builds on previous studies of related topics

This paper investigates fire safety in semi-automatic parking facilities (garages). A semi-automatic parking facility is a parking facility where larger or smaller areas have a system for automatic car stacking or close parking of cars on the same level. The paper is based on a project initiated to increase the knowledge about semi-automatic parking facilities and fire safety in these facilities. Information about semi-automatic parking facilities in Norway and abroad was collected through surveys, interviews, and literature studies.

The number of installed photovoltaic (PV) modules has increased significantly over the last years, and using available building surfaces to generate electricity by integrating PV modules in the construction is an attractive option. Building integrated photovoltaics (BIPV) or other vented claddings can spread fires rapidly to large parts of a building if the fire is allowed to propagate. To investigate this hazard, a large-scale SP FIRE 105 façade fire test was conducted. A façade measuring 4000 mm × 6000 mm covered with BIPV modules was exposed to flames that represent the fire plume from a window in a room at flashover. The results from the test show that critical failures, like falling objects and vertical flame propagation, can be expected in such constructions. These results highlight the importance of details in mounting of BIPV-façades and to require proper documentation from relevant fire tests of such systems. Small-scale cone calorimeter tests were conducted on the studied BIPV module to provide material properties of the combustible parts of the installation. These aspects should be considered when planning new or when retrofitting façades, to prevent escalation of fires. The results presented are, however, only valid for the configuration that was tested. Other BIPV-façades should also be investigated to study how these constructions can be built safely in the future with regard to critical details.

Lithium-ion batteries have been widely employed as the principal power source in electric vehicles and other storage systems. However, some critical issues in a battery pack still exist, such as thermal failures on initial cells that impact the temperatures of the surrounding cells. Such cascading failures may significantly affect battery performance and safety. Thermal barriers, as one kind of safety barrier, are therefore installed to prevent failure propagations. This paper focuses on the situation when the temperature of battery cell increases, but the battery pack still can be used in a degradation mode since the barriers are against cascading failures. An approach is proposed to analyze how the deployment and performance of thermal barriers in a battery pack determine their capabilities against cascading failures. The approach includes thermal propagation models associated with the simulations, degradation models, reliability analysis, and barrier analysis. Its application is illustrated with a practical case study. The battery reliabilities are sensitive to many factors of the barriers, such as temperature differences, failed cells, and performance coefficient. The barriers between parallel cells are found to be more effective in mitigating failure propagation. Such findings can be beneficial for barrier optimization and reliability improvement of battery packs. © 2022 The Authors

A three-dimensional reactive multi-phase particle-in-cell (MP-PIC) model is employed to investigate biomass combustion and gasification in fluidized bed furnaces. The MP-PIC model considered here is based on a coarse grain method (CGM) which clusters fuel and sand particles into parcels. CGM is computationally efficient, however, it can cause numerical instability if the clustered parcels are passing through small computational cells, resulting in over-loading of solid particles in the cells. To overcome this problem, in this study, a distribution kernel method (DKM) is proposed and implemented in an open-source CFD code, OpenFOAM. In DKM, a redistribution procedure is employed to spread the solid volume and source terms of the particles in the parcel to the domain in which the particles are clustered. The numerical stiffness problem caused by the CGM clustering can be remedied by this method. Validation of the model was performed using data from different lab-scale reactors. The model was shown to be able to capture the transient heat transfer process in a lab-scale bubbling fluidized bed reactor under varying fluidization velocities and loads of sand. Then, the model was used to study the combustion/gasification process in a bubbling fluidized bed reactor under varying ambient temperatures, equivalent air ratios, and steam-to-biomass ratios. The performance of DKM was shown to improve the accuracy and the robustness of the model. © 2021 The Author(s)

In the multi-scale modeling of a dense particle system, the particle phase and the gas phase can be modeled on vastly different scales. The coupling between the two models has a critical influence on the predictions obtained from the combined framework but can be accomplished in a variety of ways under different assumptions. In this work, a transient 3D model using a new coupling approach for fixed-bed combustion of biomass is presented. The developed model is formulated as an Eulerian-Lagrangian framework. A particle grid, generated based on the fluid grid, is applied as a transfer grid, and a diffusion operation is implemented to smooth the interactions between the gas phase and the particles. The interactions between gas and solid phases as well as the radiative heat transfer between particles are considered. The particle motion is resolved by the soft-sphere model, whereas the conversion is calculated based on a thermally thick particle model. All sub-models are optimized to enhance computational efficiency. The 3D model is validated by comparing the simulations with laboratory-scale experiments for a fixed-bed operated in counter-current combustion mode. The key simulation parameters are configured by sensitivity analysis. The simulation results are in good agreement with the experimental measurements, and the combustion regimes with different air inlet conditions are well captured. The coupling effects are discussed in detail. The particle grid size influences the prediction of the transient results, and the interplay between the heat transfer mechanisms inside the fixed-bed and the coupling scheme is thoroughly analyzed. Both inter-particle radiation and gas-to-particle convection play essential roles in the heat transfer inside the fuel bed, while the inter-particle heat conduction can be neglected. © 2021 The Authors

In CFD-DEM (computational fluid dynamics-discrete element method) simulations particles are considered Lagrangian point particles. The details of the flow near the particle surface are therefore not fully resolved. When the particle scale is larger than the resolved flow scale, the coupling between the CFD model and the DEM model is critical. An effective coupling scheme should minimize the risk of artificial influences on the results from choices of numerical parameters in implementations and consider efficiency and robustness. In this work, a novel coupling method is developed. The method includes both the smoothing of the particle data and the sampling of the gas phase quantities. The smoothing employs the diffusion-based method. The gas sampling method can reconstruct the filtered fluid quantities at the particle center. The sampling method is developed based on the diffusion-based method with higher efficiency. The new method avoids mesh searching and it can be easily implemented in parallel computing. The developed method is validated by the simulation of a forced convection experiment for a fixed bed with steel spheres. With the well-posed grid-independent coupling scheme, the simulation results are in good agreement with the experimental measurements. The coupling effects and the computational cost are discussed in detail. 

Solid fuel conversion in a fixed-bed is a challenging modelling task due to different time and length scales and the importance of heat transfer mechanisms. The current study aims to propose a novel model that can capture all the main features of the conversion of fuel bed while maintaining a moderate computational cost. The model is based on the commonly applied porous media approach, which describes the solid phase using an Eulerian framework. A layered particle submodel with four types of solids, wet wood, dry wood, char, and ash, is implemented to account for different conversion stages. At each computational cell, a matrix is used to record the information on all the properties of the four types of solids, including the number and volume of particles. The model allows the exchange of particles between cells, thus capable of simulating the motion of the fuel bed during conversion, such as bed collapsing. In addition, the new model can efficiently calculate heat transfer between particles and particles and fluid in each computational cell. The proposed model is validated against a series of experiments on biomass conversion in a rectangular fixed-bed combustor operated in a counter-current mode with various air supply rates. Good agreement with experiments was found even at the limited combustion regime. With the overall low computational cost generated by the bed model, the proposed model framework has the potential to efficiently simulate a wide range of solid fuel conversion processes at a large scale, not only in fixed-beds but also in moving beds and rotary kilns. 

Soot generation is a challenging issue in high-temperature biomass gasification, which reduces the biomass conversion rate and leads to contamination of the reactor. To provide new means and insights to optimize gasification processes, the soot generation during biomass gasification in a cyclone reactor is studied here by establishing a novel biomass gasification and soot formation model to improve the accuracy attainable in numerical predictions of spatio-temporal soot evolution. The new method is validated by comparing it with gasification experiments in two reactor configurations. A good performance in capturing the overall soot generation and light gas yield of the current model is obtained in the simulations of an entrained flow reactor compared with experimental data. Besides, the biomass gasification behavior in this entrained flow reactor is systematically studied by reviewing the tar, precursor, and soot mass fraction evolution in the reactor under different steam/carbon ratios, gasification temperatures, and air excess ratios with the new model. Furthermore, the influence of varying air equivalence ratios, the operation temperature and the fuel moisture on the soot generation in a cyclone gasifier, as well as the ability of the proposed model to reflect such influences, are also discussed. Numerical simulations demonstrate the existence of an optimal operation condition for the cyclone gasifier in terms of the soot generation. The current work thus provides a useful tool for analyzing the mechanism of soot formation at the reactor scale. 

The present research focuses on the synergistic source control of particulate matter (PM) and NOx formation from pulverized coal combustion. Comparative experiments of preheating-combustion and conventional combustion were conducted in a lab-scale high-temperature preheating-combustion furnace, and PM10 and NO were measured by an electrical low pressure impactor and a flue gas analyzer, respectively. The results of the experiment indicate that preheating-combustion has a significant reduction in PM10 (especially PM0.3 up to 37.51 %) and NO, which can achieve the synergistic control of PM10 and NO source emissions during the combustion process. The fragmentation in preheating-combustion was weaker compared to the conventional combustion. Meanwhile, the relatively weak preheating-combustion coal char oxidation reaction leads to a decrease in ultrafine mode PM yielded due to the inhibition on vaporization of mineral inclusions. The PM0.3/PM1 mass ratio of the preheating-combustion has a decreasing trend, implying an elevated yield of PM0.3-1 and a shift of the average PM1 particle size toward a larger particle size. Higher preheating temperature (Tp) presented the potential to further reduce NO formation, and the NO reduction efficiency increased from 46.59 % to 56.60 % when the Tp was increased from 1200 K to 1600 K. All our preliminary results throw light on the nature of synergistic source control of preheating-combustion PM and NO formation.