Char Oxidation Research Articles

Unveiling the role of oxygen in ammonia coal combustion: A DFT study on NOx emission mechanism

Ammonia-coal combustion mitigates CO2 emissions, yet nitrogen oxide emissions and char nitrogen oxidation mechanisms require further study. Our research employs density functional theory to explore coal char interactions with NO, NH3, and the impact of hydroxyls (–OH) and oxygen on reduction–oxidation processes. Findings indicate oxygen aids in forming hydroxyls on coal char, facilitating NO to NO2 conversion, lowering the activation energy for ammonia-coal oxidation to NO2. Oxygen also promotes char nitrogen oxidation to NO, reducing its activation energy. In NH3/coal/O2 systems, NH3 oxidation initiates NO formation. With the increase of the temperature, the reduction rate of NO by ammonia is always higher than the production rate of NO.

A char removal protocol to visualize fiber cross‐sections of carbon/epoxy composites subjected to flame

AbstractPost‐crash fires obscure or destroy critical fracture surfaces needed to determine the origin of aircraft structural failures. Our goal is to eliminate combustion residue from carbon fiber‐reinforced polymer composites to enable fractographic examination during aviation accident investigations. In this work, combustion residues were removed from burned Hexcel SGP370‐8H/8552 woven‐fabric carbon/epoxy specimens by nitric/sulfuric acid oxidations. Scanning electron microscopy identified various types of char obscuring the fiber ends. For char removal, the burned specimens were immersed in a nitric acid/sulfuric acid/water solution (0.18 wt.%, 96.25 wt.%, 3.57 wt.%) at elevated temperatures (75–150°C). Higher temperatures enhanced nitric acid decomposition in this highly acidic, low‐water environment, accelerating char oxidation and progressively enhancing the extent of char removal. At lower temperatures (T < 100°C), char deposits were partially oxidized after 60 mins. At 125 and 150°C, the char was removed within 30 mins of immersion. The epoxy matrix both chemically decomposed and oxidized and the char oxidized during these oxidation treatments. Gas evolution and soluble products dissolved in the HNO3/H2SO4 media. The damage morphology created by the sawing action on the fiber ends, created before flame exposure, remained clearly visible after the acid oxidations. This occurs because oxidation rates at the carbon fiber ends are much slower than the char oxidation in these acid treatments. If the acid treatment temperature raised above 185°C, then this sawing‐induced fiber damage morphology will also be destroyed. This preliminary understanding can be applied to develop a comprehensive forensic analysis procedure for post‐crash fire investigations.Highlights Flame exposure of sawed specimen cross‐sections leads to char formation, obscuring fiber damage morphologies. HNO3/H2SO4 oxidations at elevated temperatures (75–150°C) resulted in char removal from fiber ends. Higher temperatures (T = 125 and 150°C) accelerated char oxidation. The sawing of carbon/epoxy composites caused extensive fiber damage and ply delamination. Residual decomposed resin matrix and char oxidized faster than the carbon fibers and the fiber sawing‐induced fiber damage morphologies created before flame exposure and were preserved after char removal.

Deactivation of chromated copper arsenate as a catalyst in smouldering of wood

Chromated copper arsenate (CCA) is a preservative treatment that enhances the biodegradation resistance of wood, essential for prolonging the service life of exterior infrastructure. However, the susceptibility of CCA-treated wood to smouldering combustion presents a significant challenge, as the metals present in the CCA catalyze the smouldering. In this work, we examined the oxidative behaviour of char produced from CCA-treated wood through dynamic thermogravimetric analysis. There was a gradual decrease in the catalytic activity of the CCA as temperature increased, particularly above 400 °C. At this stage, lignin undergoes secondary pyrolysis, and thermal decomposition of CCA complexes occurs. The thermal decomposition of CCA-treated wood at temperatures above 650 °C was similar to that of untreated wood, indicating the possible deactivation of the CCA. The agglomeration of species containing Cu or Cr above 650 °C might be responsible for the deactivation. This process is influenced by simultaneous lignin pyrolysis and decomposition of CCA complexes, which are also likely contributors to the loss of CCA's catalytic activity. This research introduced a novel experimental approach to assess the catalytic effects of CCA on char oxidation at elevated temperatures, offering valuable insights into CCA deactivation and its implications for fire safety. It also contributes to the development of potential modifications to CCA formulations aimed to reduce smouldering in wildfire-prone regions.

Efficient and low-NOx combustion in a grate-fired boiler by feeding biomass non-uniformly along grate width: An integrated modeling study with experimental validation

The distribution of air flows and fuel feeds are two crucial operational parameters determining the high-efficiency combustion and low-nitrogen emissions in biomass-fired grate boilers. However, current optimizations primarily focus on air distribution, with limited attention given to fuel feeds optimization. In this study, a three-dimensional integrated model was developed in FLUENT platform for simulating a grate-fired boiler with four feed inlets, in which the DPM model was adopted to track particle information in detail, and the Ergun model was used to account for the flow resistance generated by the thick packed bed, implemented in the form of a UDF code. The reliability of the model was validated through comprehensive on-site experimental data. It was found that key parameters such as temperature and ignition front of char are non-uniformly distributed along the width of the four grates. Specifically, a significant lag in volatiles release and char oxidation occurs near the water-cooled wall on both sides. On this basis, the optimization strategies on improving efficient and low-NOx combustion were proposed by redistributing the biomass fuel from near the sidewalls to the middle sections, and the optimal non-uniform feeding mode along the grate width was found. Results demonstrate that when the mass ratio of fuel between the middle and side grates is 0.30 to 0.20, yielding a maximum overall char burnout ratio of 84.74%. Additionally, the concentration of NO decreases from 163.2 mg/m3 of uniform feeding mode to 149.4 mg/m3 (at 11% O2). These predictions will provide reliable theoretical guidance for enhancing boiler efficiency and reducing NOx emissions in grate-fired boilers.

Numerical analysis of the ignition and gas-phase flame evolution of pulverized coal based on online experimental diagnostics

A transient ignition model employing a reduced chemical mechanism was developed to investigate the ignition characteristics and the gas-phase flame evolution of pulverized coal particles. The chemical percolation devolatilization (CPD) model was chosen to simulate the devolatilization process, and its accuracy was validated using a high-temperature entrained-flow reactor. Additionally, a novel method was introduced to cross-validate the single-particle simulation results with real-time OH-PLIF experimental measurements of particle streams, particularly at a large particle spacing ratio. The ignition mode was determined using the ignition delay time and volatile burnout time. Results show that as the oxygen volume fraction increases from 5% to 50% at a temperature of 1800 K, the ignition mode transitions from homogeneous ignition (GI) to heterogeneous ignition (HI). Notably, the same ignition mode was observed regardless of whether GI was defined using gas-phase temperature or OH levels. In the homo-heterogeneous ignition mode, the gas-phase flame intensity, characterized by OH levels, increases rapidly, then decreases, and re-increases slightly. The sequence of gas-phase reactions initiates with volatile combustion, followed by the co-combustion of residual volatiles and newly generated CO, and culminates in the combustion of CO itself. Online experimental findings confirmed that CO originates from char oxidation. Throughout this process, the gas-phase flame front extends outward until the volatiles are consumed.

Experimental and numerical investigation on the combustion behavior of densified wood: Differences among wood species and impact of char oxidation

Densified wood (DW) is a novel structural material with promissing application potential in construction industry due to its excellent mechanical performance. However, it could also be a disastrous fuel contributing to the development of fires. This work experimentally and numerically investigated the combustion behavior of DW. The differences among wood species (fir, pine and oak) and their char oxidation impacts are emphasized. The experimental results indicate that DW has a 44.7 K lower pyrolysis peak temperature on average, a 32.2 % lower peak mass loss rate, and a 8 % higher residual mass ratio than natural wood (NW) in N2 due to the delignification process. The hemicellulose and cellulose pyrolysis are endothermic in N2 but exothermic in air. Wood pyrolysis has an additional char oxidation reaction in air. The higher density of DW leads to longer times for ignition and flaming combustion. DW presents a higher heat release rate and average 4.7 MJ kg−1 higher effective heat of combustion of char. Two parallel pyrolysis reaction schemes based on ambiance are proposed, which well-predict the microscale characterizations but fail to represent the combustion behavior. An optimized mode was developed by adding a continuous char oxidation reaction to the N2 reaction scheme, which best predicts the combustion behaviors.

Effect of the wood species on the fire behavior in vertical orientation

The objective of this study was to investigate the parameters controlling auto-ignition, degradation and auto-extinction of wood. For this purpose an extensive set of experiments was conducted varying extrinsic parameters such as external heat-flux but also the type of wood. Varying the wood species allowed to explore the role of thermal properties and wood composition. Seven wood samples were tested, some light and some heavy, both hardwood and softwood. The experimental setup was based on a double-cone calorimeter, which allowed to accurately change the imposed heat flux at a predefined moment. More than 600 tests were carried out in a vertical orientation, allowing a statistical analysis. For each test, mass loss, surface temperature and in-depth temperature of the samples were measured using a precision scale, an infrared camera and thin wire thermocouples embedded using a special machining, respectively. The auto-ignition study showed that the time to auto-ignition increases linearly with density. Despite a wide range of these times to ignition, the surface temperatures at ignition were in the same order of magnitude for all species considered: between 450 and 700 °C for auto-ignition before 2 min and between 700 and 800 °C for auto-ignition after 2 min. The onset of char oxidation was observed at low heat fluxes. It occurs at different times depending on the wood species, but at similar surface temperatures, between 380 and 400 °C. The sliding double heating cone made it possible to identify the criteria for auto-extinction: the heat flux for auto-extinction can vary from 40 to 55 kW.m−2 depending on the wood species, and a linear correlation was found between the mass loss rate at extinction and the initial density of each sample studied. The study highlights the dominant role of density for auto-ignition and auto-extinction.

An integrated model for flexible simulation of biomass combustion in a travelling grate-fired boiler

Grate-fired boiler is of considerable interest for burning biomass owing to its reduced sensitivity to variations in fuel composition and size. However, grate-fired technology exhibits unsatisfactory performance in terms of combustion efficiency, contaminant emissions, and flame stability. CFD modelling can provide reasonable optimizations to overcome these drawbacks and ultimately achieve clean and efficient energy production. Conventional approach simulates the fuel-bed and freeboard combustion separately using an in- and over-bed coupling procedure, where data of the gases leaving from the packed-bed top and the radiative heat flux emitted by the high-temperature flame onto the bed cannot be interacted in real-time. This may cause distinct deviations in the calculations. In this paper, a three-dimensional (3D) full-scale integrated model is developed for the simulation of grate-fired boiler, in which the intensive combustion of both the freeboard and fuel-bed is solved in one scheme using the Eulerian-Lagrangian method. The gas phase is considered as a continuous medium and calculated by the Eulerian model, while the solid particles are considered as a discrete phase and tracked via the Lagrangian method. The reliability of the model is well verified through various field measurements and observations. Results shows that the key parameters are non-uniformly distributed along the grate width, i.e., the aerodynamic and combustion environment is poor at the vicinity of water-cooled walls compared with that at the furnace center. This results in a significant lag in volatile gases release and char oxidation near the water-cooled wall on both sides, which finally causes obvious differences in the distribution of temperature and species. For instance, the peak of CO concentration at the center is 12.6 % at 3.3m from the feed entrance, while that near the water-cooled wall is 8.6 % around 3.5m. The char burnout ratio in the bottom ash can be accurately calculated by this model, with a negligible relative error between the simulation of 81.97 % and the measurement of 82.50 %. It also provides a novel method for the calculation of fly ash particles by using size-grouped and non-spherical particles. Small-size particles in the vicinity of the feed inlet, as well as a part of the particles burning at the end of the grate are entrained into the freeboard by the primary air supplied beneath the grate and the high-momentum secondary air on the bed top. This model can provide valuable theoretical guidance for optimizing the refined distribution of fuel and air in grate-fired power plants and mitigating irregular deposition (corrosion) on heat exchangers and water-cooled walls caused by fly ash.

Thermal behaviors of coal particles in an impinging entrained-flow gasifier: Char oxidation

The thermal behaviors of high-temperature particle (HTP) and low-temperature particle (LTP) are investigated based on the bench-scale impinging entrained-flow coal-water slurry (CWS) gasification experimental platform with a modified visualization system. The size and velocity distribution of both particles, and the evolution of HTP are analyzed through the algorithmic and precise processing of the image sequences. In addition, in-situ temperature diagnosis of the particles during the reaction process were realized. The typical evolution process and the temperature of HTP in char oxidation stage are obtained. The results show that the concentration of HTP in the gasifier is greater than LTP, but the particle size is relatively small. Particles moving at the low speed (0–2 m/s) account for the largest proportion of both HTP and LTP. The char oxidation process lasts over 300 ms and can be divided into three reaction stages. During the reaction, the peak temperature at the center of the particle can reach more than 2000 K. The average temperature of the particles gradually increased, reaching a peak in reaction stage II (1500 K) followed by a gradual decrease. The particle temperature is affected by O/C and is prone to experience swelling and bubbling phenomena during char oxidation.

Experimental and theoretical study on the smoldering combustion of size-fractioned forest duff particles

Smoldering combustion process has been suggested as a new method potentially useful in the treatment of biosolids. Natural forest duff (FD) often consists of organic fuel layers with varying particle sizes, yet the influence of the size-fractioned particles on the smoldering combustion dynamics in terms of the heat and mass transfer is not well understood. In this study, the oxidative pyrolysis and smoldering behavior of FD samples with four particle sizes (0 < d1 ≤ 0.425 mm, 0.425 < d2 ≤ 1 mm, 1 < d3 ≤ 2 mm, 2 < d4 ≤ 4 mm) were experimentally and theoretically investigated. Micro-scale thermo-gravimetric (TG) analysis, and a four-step kinetic model incorporating water evaporation, FD pyrolysis, FD oxidation and char oxidation showed that the activation energy of the FD pyrolysis and the ash content are negatively correlated, while the activation energy of the char oxidation increases from 87.26 kJ mol−1 to 119.22 kJ mol−1 with the particle size increasing from d1 to d4. Furthermore, the order of the combustion performance of the FD samples is shown as d1<d2<d4<d3. A series of laboratory-scale smoldering experiments revealed that the peak smoldering temperature increases with the fuel depth while the horizontal spread rate decreases with the fuel depth. Both the peak mass loss rate and the smoldering duration presented a reverse order (d1>d2>d4>d3) of the combustion performance found in the TG tests. A simplified heat transfer analysis qualitatively revealed the beneficial effects of the size-fractioned particles on the smoldering spread rate, while a mass transfer analysis revealed the favorable and adverse influences of the particle size on the kinetic-controlled and diffusion-controlled char oxidation rate, respectively. These findings verify that particle sizes alter the FD physicochemical properties (e.g., specific surface area, bulk density, porosity, permeability, chemical components, and lower calorific value), which in return impact the chemical kinetics, heat and mass transfer process in smoldering combustion. This work provides new insights into the effects of the size-fractioned particles on smoldering combustion, ultimately improving the fundamental understanding for optimizing particle sizes for energy conversion and usage.

Effect of oxy-fuel combustion with different O2/CO2 fractions on the pulverized coal combustion mechanism and heat transfer characteristics in rotary kilns: A numerical simulation study

Oxy-fuel combustion combined with carbon capture and storage is the most effective and direct technology to achieve carbon neutrality in cement industry. In this work, numerical simulation was employed to investigate the effects of air combustion and oxy-fuel combustion with different O2/CO2 fractions on the airflow field, temperature field, pulverized coal combustion mechanism, heat transfer characteristics and NOx distribution in rotary kiln. The results show that the airflow field under different conditions has no significant change. When transitioning from the air condition to the oxy-fuel condition, the ignition point of pulverized coal extends backward by approximately 0.2 m. The maximum temperature decreases from 2306 K to 2052 K, and the temperature becomes more uniform. As the oxygen concentration in the primary air increases, both the maximum and average temperatures gradually rise, and the flame length shortens from 25.4 m to 24.16 m. In the rotary kiln, the locations of char oxidation and gasification reactions differ, but these reaction locations remain consistent under different conditions. Under oxy-fuel conditions, the oxidation rate and oxidation proportion of char decrease, while the gasification rate and gasification proportion of char increase, resulting in a shortening of the burnout distance of coal from 34.5 m to 31.3 m. With increasing oxygen concentration in the primary air, the rates of char oxidation and gasification gradually rise, further shortening the burnout distance. The decrease in temperature at the front end of the rotary kiln under oxy-fuel conditions reduces the total heat transfer in the burning zone by 15 %. When the oxygen content of the primary air is 70 %, it ensures stable calcination of clinker. Additionally, under oxy-fuel conditions, the NOx generation is significantly reduced. With the increase of oxygen concentration in the primary air, the NOx concentration at the outlet decreases slightly from 451 ppm to 406 ppm, due to the increase in kiln temperature that favors the reduction of fuel NOx.

Computational study on the glowing combustion of a wooden ember landing on a non-reacting substrate

Despite the increasing frequency in spot ignition by embers in wildfires, research on the multiple physicochemical processes intrinsic to ember combustion is limited. In this study, a two-dimensional computational model was proposed to study the glowing combustion of a wooden ember. A global char oxidation reaction was used to represent the glowing combustion of the ember. A parametric study showed that the porosity, heat of reaction, and oxygen concentration were the most influential parameters on the ember combustion. Then, the model was compared to a series of bench-scale experiments in terms of glowing time and thermal response of a non-reacting substrate when exposed to a hot ember. The simulation results showed that ember combustion was mostly diffusion-controlled rather than kinetic-controlled. Thus, given the ember diversities in spotting fire, modelers should pay more attention to the difference in the physical properties instead of the kinetics between ember species.

Firebrand burning under wind: an experimental study

Background Spot fires play a significant role in the rapid spread of wildland and wildland–urban interface fires. Aims This paper presents an experimental and modelling study on the flaming and smouldering burning of wood firebrands under forced convection. Methods The firebrand burning experiments were conducted with different wind speeds and firebrand sizes. Key results The burning rate of firebrands under forced convection is quantified by wood pyrolysis rate, char oxidation rate and a convective term. The firebrand projected area is correlated with firebrand diameter, char density, wind speed, and flaming or smouldering burning. A surface temperature model is derived in terms of condensed-phase energy conservation. We finally establish a simplified firebrand transport model based on the burning rate, projected area and surface temperature of firebrands. Conclusion The mass loss due to wood pyrolysis is much greater than that due to char oxidation in self-sustaining burning. The burning rate is proportional to U1/2, where U is wind speed. The projected area for flaming firebrands decreases more rapidly than that for smouldering ones. The firebrand surface temperature is mainly determined by radiation. Implications Knowledge about firebrand burning characteristics is essential for predicting the flight distance and trajectory in firebrand transport.

Thermal Decomposition and Combustion Analysis of Malaysian Peat Soil Samples Using Coats Redfern Model-free Method

This research investigates the thermal decomposition behaviour of Malaysian peat soil through thermogravimetric analysis at varying heating rates. The study aims to analyse the thermal kinetics of decomposition for distinct peat soil types under inert and oxidative atmospheres while considering the role of available oxygen. The investigation encompasses virgin and agricultural peat, employing a non-isothermal thermogravimetric analysis technique to evaluate thermal decomposition characteristics and compute kinetic parameters using the Coats Redfern model-free approach. The pyrolysis profiles reveal three primary stages: moisture evaporation (30–180°C), organic component decomposition (200–500°C), and mineral decomposition (600–800°C). Virgin peat experiences a 43% mass loss during pyrolysis, while agricultural peat shows a 46% mass loss, emphasising insights into thermal behaviour and consistent decomposition patterns across peat types. Combustion profiles exhibit three main stages: dehydration (30–180°C), oxidative pyrolysis transforming organic matter into volatiles and char (200–300°C), and subsequent char oxidation (300–500°C). The study determines average activation energy trends, measuring 14.87 kJ/mol for virgin peat and 5.37 kJ/mol for agricultural peat under an inert atmosphere, and 28.89 kJ/mol for virgin peat and 36.66 kJ/mol for agricultural peat under an oxidative atmosphere. The research introduces an innovative two-step reaction model elucidating peat thermal decomposition kinetics (excluding dehydration), including a discussion on the impact of oxygen availability on kinetic parameters. These findings essential peat fire smouldering modelling, contributing to peat combustion behaviour for effective strategies to reduce peat fire risks.

Simulations of flaming combustion and flaming-to-smoldering transition in wildland fire spread at flame scale

Our objective in the present study is to provide basic insights into the coupling between external-gas and solid biomass vegetation processes that control the dynamics of flame spread in wildland fire problems. We focus on a modeling approach that resolves processes occurring at vegetation and flame scales, i.e., the formation of flammable vapors due to the thermal degradation of the solid biomass, the subsequent combustion in ambient air, the thermal feedback to the biomass through radiative and convective heat transfer, and the possible transition from flaming combustion (taking place outside of the solid biomass) to smoldering combustion (taking place inside the solid biomass). The capability uses a multiphase combustion framework and treats external-gas processes through a Large Eddy Simulation solver and solid biomass processes through a discrete particle model. The discrete particle model adopts a one-dimensional porous medium formulation, includes descriptions of drying, thermal pyrolysis, oxidative pyrolysis, and char oxidation, as well as a description of the external-gas-to-solid-biomass diffusion of oxygen mass; the discrete particle model thereby provides a treatment of in-depth oxidative processes and allows the simulation of smoldering combustion. The modeling capability is applied to the simulation of fire spread across a surrogate biomass vegetation bed corresponding to a discrete array of cylindrical-shaped, vertically-oriented, pine wood sticks, characterized by a monomodal size distribution, in horizontal flat terrain and under wind-aided conditions. The numerical results demonstrate that the model can simulate successful flaming-to-smoldering transition followed by complete biomass consumption.Novelty and Significance statement:• A new computational model is proposed to simulate wildland fire behavior at high levels of resolution capable of capturing vegetation- and flame-scale phenomena.• Solid biomass vegetation processes are treated using a discrete particle model that features a porous medium formulation and includes a description of in-depth oxygen mass diffusion, and exothermic oxidative pyrolysis and char oxidation reactions.• The computational model is shown to be capable of simulating the transition from flaming to smoldering combustion, often observed in wildland fire spread problems.

Measurement of Char Oxidation Rate of Larch Glue Laminated Timber

Measurement of Char Oxidation Rate of Larch Glue Laminated Timber

Transition from smouldering to flaming combustion of pine needle fuel beds under natural convection

Smouldering transition to flaming combustion (StF) of forest fuels can rekindle wildfires, possibly causing the suppression effort to be useless or the firefighters to be stuck in danger. However, the StF mechanism of forest fuels remains to be elucidated. In this work, the StF of pine needle fuel beds with different bulk densities was investigated experimentally. Two modes of transition are identified: Middle- and Trailing-StF, which occur at the middle and trailing edges of the char region in the fuel bed, respectively. The conditions for the occurrence of both modes include (1) the length of the char region exceeding a critical value and (2) a hot glowing area (strong secondary char oxidation area) appearing before StF. An overhang structure is also necessary to induce Trailing-StF. These conditions are interpreted in terms of the permeability of fuel beds, which affects the diffusion and convection supply of oxygen for smouldering. Middle-StF occurs due to sufficient oxygen diffusion and convection supply in the middle of the char region with large pores. In Trailing-StF, the overhang structure forms a region with high permeability, which significantly enhances the convection mass flow rate of oxygen and provides a favorable space for the accumulation of mixed combustible gases. The oxygen mass flow rate leading to both StF modes is in the order of 10−2 g/s.

Experimental exploration of potassium compounds in the vicinity of a burning biomass pellet: From near-surface to downstream

The concentrations of gas-phase potassium hydroxide (KOH), potassium chloride (KCl) and atomic potassium (K(g)) were quantitatively measured from the near-surface to downstream area of burning pinewood pellets by a newly developed photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) technique to reveal the original form of the released potassium. The novel arrangement of the PF-TDLAS system enabled a spatial resolution of ∼1 mm3, which made it possible to obtain temporal release profiles of K(g)/KOH/KCl at different heights above the burning pellet surface. Surface temperature and mass loss of the wood pellet as well as the gas temperature at measurement points were measured simultaneously. During the devolatilization stage, the release of all three potassium species was observed, with each of them accounting for ∼1/3; while in char oxidation stage, the release of KOH was dominant, but the release intensity was strongly influenced by the local oxygen content. The results from different measurement heights showed there was a notable difference in potassium release profiles of different potassium species over the near-surface area, where the detected potassium forms were the best representative of the originally released forms of potassium. For a period of time during the devolatilization stage, only K(g) was detected in the near-surface area, and the concentration was significantly lower than the downstream area where KOH and KCl coexisted. This suggested that a large amount of potassium might leave the pellet as organic-K, which cannot be detected by the PF-TDLAS method. During char oxidation stage, the total potassium concentration at the near-surface area was also lower than the downstream area, but it was due to the lack of oxygen at the measurement position. A potassium release mechanism during the devolatilization stage of biomass combustion was proposed based on the experimental measurements, and the results also indicated the importance of spatially resolved measurement.

Synergistic reduction on PM and NO source emissions during preheating-combustion of pulverized coal

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.

Modeling of wood crib fires using a detailed pyrolysis model

Wood is a widely used energy source but is dangerous in the case of fires. In this study, a detailed pyrolysis model was used to analyze wood fires. Cellulose, active cellulose, hemicellulose, lignin, char, ash, moisture, and air were the wood components that were considered in this study. Seven flammable gaseous species (cellulose gas, hemicellulose gas, lignin gas, propane, char gas, oxidized product 1, and oxidized product 2) were considered in the detailed pyrolysis model. The wood fire model, using a detailed pyrolysis model, predicted the heat release rate and mass loss rate of the wood close to those of a cone calorimetry experiment, particularly for high external heat fluxes (35, 50, and 65 kW/m2). The wood crib fire was analyzed with a detailed pyrolysis model and the heat release rate (HRR)-based model, and the simulation results were compared with experimental results. The HRR-based fire model could not capture the experimentally measured HRR curves. The wood fire model based on the detailed pyrolysis model was able to predict the flaming stage of the wood crib fire. However, the total heat release was predicted to be lower than that in the experiment, and the fire could not be sustained at the stage where heat release due to char oxidation occurred.