Combustion Experiments Research Articles

Reservoir Properties Alteration in Carbonate Rocks after In-Situ Combustion

Summary This study summarizes the work conducted as a part of laboratory modeling of in-situ combustion (ISC) experiments on cores from carbonate heavy oil fields. Porosity, permeability, fluid saturation, thermal, and geochemical properties are crucial characteristics of the target field defining the performance of the combustion technology. Here, we report the changes in reservoir properties, porous structure, and mineral composition of the rock samples induced by the thermal exposure and registered by a set of standard and advanced experimental techniques. Most combustion tests are conducted on the crushed core pack, which does not accurately represent the reservoir properties. In this paper, we present the results of three combustion tube tests (classic ISC and consecutive hot-water treatment ISC) involving actual field core samples. Gas porosimetry, nuclear magnetic resonance (NMR), and microcomputed tomography (μCT) revealed an increase in total porosity and pore size distribution and enabled visualizing the changes in the porous core structure at nano- and microlevels. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated the change in mineral composition and lithological texture as a result of dolomite decomposition; Rock-Eval pyrolysis and elemental analysis were utilized to confirm the changes in the rock matrix. Optical scanning registered the changes in thermal conductivity (TC) of samples, which is important for numerical modeling of the combustion process. The proposed core analysis has proved its efficiency in providing a complete petrophysical description of the core of a heavy oil carbonate reservoir in the framework of evaluation of the ISC application for dolomite-rich carbonates and demonstrated the different responses of rock to the ISC technology.

Role of carbide slag addition on NO emission characteristics during coal combustion

This work presents an experimental study on the NO emission characteristics of coal combustion with carbide slag addition. Combustion experiments were carried out in a fixed-bed reactor to investigate the effects of Ca/S molar ratio, oxygen concentration and reaction temperature on the transformation of fuel nitrogen to NO emission. Further, a pilot test was performed in a 30 kW CFB reactor to study the influence of carbide slag on the NO emission. Experimental results show that using carbide slag and a high Ca/S molar ratio promoted the fuel-N/NO conversion rate. The main contribution to the fuel-N/NO conversion rate increment was the catalytic role of carbide slag in the char-N/NO conversion process. The promotion effect of carbide slag on fuel-N/NO conversion was weakened at a higher temperature and lower O2 concentration. The pilot test results verified that using carbide slag promoted NO emission. Based on the test results, the fuel-N conversion route and the NO formation process during coal combustion with carbide slag addition were presented.

Emission characteristics and formation pathways of carbonyl compounds from the combustion of biomass and their cellulose, hemicellulose, and lignin at different temperatures and oxygen concentrations

Carbonyl compounds are important precursors of free radicals, ozone (O3), and secondary organic aerosols (SOA) in the atmosphere. Biomass burning is an important source of carbonyl compounds. To explore the formation pathway of carbonyl compounds from biomass burning and the effects of fuel composition and burning conditions, this study performed tube-furnace combustion experiments using three biomass types (rice straw, pine, and poplar) and their three component extracts (cellulose, hemicellulose, and lignin) at seven ignition temperatures (300–900 °C, 100 °C gradient) and two oxygen concentrations (21% and 10.5%). The results showed that the average emission factors of carbonyl compounds (EFCC) from rice straw, pine, and poplar were 2.28 ± 1.72, 3.09 ± 2.98, and 2.90 ± 2.78 g/kg, respectively. EFCC were significantly higher (5.37 ± 0.25 g/kg) in lower temperature (300–500 °C) stage than in higher temperature (0.55 ± 0.03 g/kg). Furthermore, oxygen reduction promoted the emission of carbonyl compounds, increasing the EFCC by 21.6% on average. The average EFCC for the three components of biomass decreased in the order of cellulose (3.78 ± 3.90 g/kg), hemicellulose (2.90 ± 2.60 g/kg) and lignin (1.98 ± 1.72 g/kg), and their CCs profiles were also different. Cellulose and hemicellulose produced more formaldehyde and acetaldehyde than lignin, contributing 71.1 ± 12.6%, 69.0 ± 4.4% and 62.4 ± 15.5% in CCs, respectively. Acetone was mainly produced by the combustion of hemicellulose and lignin. Aromatic aldehydes were mainly produced by lignin burning, and also were significantly affected by temperature, the proportion under higher temperature is 2.7 times that under lower temperature. The EFCC values by weighted average calculation from the three components were good matched with those of parent fuels (r = 0.98), while the fitting results for those species such as aromatic aldehydes were relatively weak (r = 0.66), showing that there are different formation pathways and sensitivity to fuel composition and burning condition among different CCs.

Visualization research on ash deposition characteristics of Zhundong coal in a vertical liquid slagging cyclone furnace

A 300 kW vertical liquid slagging cyclone furnace is built for the combustion experiment of Hami coal(HM), a kind of Zhundong coal. The sampling probe and CCD camera are used to monitor the growth process of deposition in the furnace online. In addition, the slags at various positions of the furnace are collected and analyzed to study the metal migration law and slagging characteristics of HM during combustion in the furnace. The results show that compared with the traditional furnace, deposition thickness on the probe of the liquid slagging cyclone furnace is much smaller. The stable thickness of the deposition on probes 1 and 2 is 0.85 mm and 3.30 mm respectively. Fe2O3 shows enrichment in liquid slag. The alkali metals in the gas phase condensed on the low-temperature surface of the sampling probe and existed in the initial layer of the deposition. The SO3 reacts with alkaline oxides at low temperature to form viscous compounds such as Na2SO4 and CaSO4. Due to the fast cooling rate, almost no diffraction peaks can be observed in the XRD curves of the liquid slag and glass filaments, which indicates that the material is a completely amorphous solid.

Retention of As during coal combustion: Devolatilization and char combustion

The retention of arsenic (As) during coal combustion facilitates As emission control. A fixed-bed experimental system was used to conduct devolatilization and char combustion experiments at 1100–1300 °C using three types of coal. Both processes contributed to the As release. As in coal was bound to carbonate, oxide, sulfide, and aluminosilicate (Als-As). During devolatilization, carbonate- and oxide-bound As and Als-As remained stable, while sulfide-bound As was completely decomposed. The gaseous As was partially retained as Char-As. During char combustion, Char-As was oxidized to As2O3, which was partially retained by minerals. Carbonate- and oxide-bound As reacted with silicon (Si) and aluminum (Al) to produce Als-As, which was the main As form in ash. As retention was significantly inhibited by the destruction of the lattice structure. As retention by char during devolatilization and minerals during char combustion promoted As enrichment in solid products and its removal.

Essence of Thermal Analysis to Assess Biodiesel Combustion Performance

The combustion phenomena are always complex in nature due to the involvement of complex series and parallel reactions. There are various methods that are involved in analyzing combustion phenomena. Viscosity is the first and foremost factor that acts as the DNA of fuel. By evaluating the viscosity, it is possible initially to understand the combustion phenomena. Thermophysical and transport properties are helpful during the intensification of the combustion process. Combustion experiments are economically infeasible and time-consuming processes. Combustion simulations demand excellent computational facilities with detailed knowledge of chemical kinetics. So far, the majority of researchers have focused on analyzing coal combustion phenomena, whereas less work has been carried out on liquid fuels, especially biodiesel combustion analysis. Traditional engine testing provides only performance parameters, and it fails to have oversight of the thermodynamic aspects. The application of thermal analysis methods in combustion research is useful in the design, modeling, and operation of the systems. Such investigations are carried out extensively in the combustor, engine, and process industries. The use of differential scanning calorimetry (DSC) and thermogravimetry (TG) to assess the properties of biofuels has been attracting researchers in recent years. The main objective of this paper is to discuss the application of TGA and DSC to analyze heat flow, enthalpy, thermal stability, and combustion indexes. Moreover, this paper reviews some of the other aspects of the kinetics of combustion, transport properties’ evaluation, and combustion simulations for biodiesels and their blends. TG curves indicate two phases of decomposition for diesel and three phases for biofuel. The B-20 blend’s (20% biodiesel and 80% diesel) performance was found to be similar to that of diesel with the combustion index and intensity of combustion nearly comparable with diesel. It is thermally more stable with a high offset temperature, confirming a longer combustion duration. A case study reported in this work showed diesel and B20 JOME degradation start from 40 °C, whereas jatropha oil methyl ester (JOME) degradation starts from 140 °C. JOME presents more decomposition steps with high decomposition temperatures, indicative of more stable compound formation due to the oxidation process. The peak temperature of combustion for diesel, JOME, and B20 JOME are 250.4 °C, 292.1 °C, and 266.5 °C, respectively. The ignition index for the B-20 blend is 73.73% more than that of diesel. The combustion index for the B20 blend is 37.81% higher than diesel. The B20 blend exhibits high enthalpy, better thermal stability, and a reduced peak temperature of combustion with an improved combustion index and intensity of combustion nearly comparable to diesel.

Using active subspace-based similarity analysis for design of combustion experiments

Experimental data under a wide range of conditions are essential for the optimization of combustion kinetic models. However, some laboratory measurements under given conditions may not be conducted due to the constraint of existing techniques. It is thus needed to employ the experimental data obtained under alternate conditions to improve the model predictions for the desired conditions. In this work, an active subspace-based similarity analysis is proposed as an experimental design method to find substitutes for experiments (or measurements) that are difficult to conduct. The eigenvalues and eigenvectors of the matrix that contains the gradient information of a model output with respect to inputs (matrix C of the active subspace) are used to calculate the cosine-based similarity of key reactions of two model targets. The method is demonstrated in three combustion systems, i.e., ignition of hydrogen/oxygen mixture, premixed flame of the dimethyl ether (DME), and C2H6/O2 systems in different reactors. The results show that if the similarity coefficient is large, the key reactions for the two model targets are similar, and the measurement of one target can improve the model prediction of the other target. In addition to designing experimental targets or conditions with strong constraint effects beforehand, this method can also be used to classify potential experimental targets/conditions.

Experimental and numerical investigations on NOx formation and reduction mechanisms of pulverized-coal stereo-staged combustion

With the gradual increase of intermittent renewable energy, the coal-fired power generating units must provide flexible peak shaving capabilities. However, the new requirement comes with increasing challenges for the pulverized coal utility boilers, as it tends to have lower combustion efficiency and higher NOx emission at extremely low loads. Accordingly, this work aims at coupling the NOx formation and reduction mechanisms with computational fluid dynamic simulation to thoroughly explore the technology for NOx abatement. The effect of the different primary air equivalence ratios on the Whitehaven bituminous combustion was experimentally and numerically studied. The combustion experiments were performed in a down-fired facility. Moreover, the numerical model validated well with the experimental results. The results reveal that, by reducing the primary air equivalence ratio, the combustion efficiency of pulverized coal stereo-staged combustion increased. Furthermore, the formation and reduction rate of fuel-NOx by HCN decreased but those by NH3 slightly increased. In addition, the fuel-NOx reaction rates from char-nitrogen decreased. The NH3 was oxidized to NOx, while HCN mainly played the role of reducing NOx. The primary air equivalence ratio of 0.24–0.28 was found to be the optimal range for the pulverized coal stereo-staged combustion technology.

Experimental investigation on spontaneous combustion oxidation characteristics and stages of coal with different metamorphic degrees.

Coal spontaneous combustion (CSC) is a major disaster threatening coal mine safety; therefore, the investigation of coal spontaneous combustion and oxidation characteristics has been a hot topic in the long term. In this paper, the experimental temperature programmed system is used to carry out the simulation experiment of coal spontaneous combustion and oxidation of three kinds of coal with different metamorphic degrees under three oxygen concentrations (9%, 15%, 21%). The effects of metamorphic degree and oxygen concentration on coal oxidation characteristics were analyzed, and the variation laws of crossing point temperature, three characteristic point temperature, and apparent activation energy were qualitatively discussed. Finally, coal oxidation reaction stages were evaluated and divided. The results show that the concentrations of CO and C2H4 are negatively correlated with the degree of deterioration but increase with the increase of oxygen concentration. High metamorphic coal corresponds to high crossing point temperature (CPT). The average error between the CPT value calculated from the BM empirical correlation and the experimental data is very small, which is 6.42%. The higher the metamorphic degree of coal, the higher the three characteristic temperature points (critical temperature, xerochasy temperature, and activity temperature). The oxidation process of the three coal samples is divided into four stages: surface oxidation, oxidation self-heating, accelerated oxidation, and deep oxidation. The apparent activation energy of each stage exhibits significant variability, with varying patterns displayed with the degree of metamorphism.

Active Control of Fuel Position in Opposed-Flow Strand Burner Experiments

ABSTRACT This paper describes a new active method of controlling the position of the burning surface of a solid fuel strand in an opposed-flow burner experiment. This method is designed to avoid biases to the combustion process introduced by retaining wires and to avoid experimental delays caused by wire failures. Regression rates are presented for hydroxyl-terminated polybutadiene fuel strands burning in various oxidizer streams. The active control method uses a control loop composed of a diode laser, a photodiode, and a stepper motor. For comparison, tests were also performed using the commonly used passive control method of spring-loading the fuel against a retaining wire. This active control method can only be used at high values of oxidizer mass flux; at low mass flux, soot accumulation obstructs the laser beam. In passive control tests, the retaining wire conducts heat from the flame into the fuel and increases regression rate. The presence of the wire also modifies the extinction limits of the flame. A model was developed for regression rate as a function of oxidizer mass flux, oxidizer composition, and retaining wire diameter. This model can be used to correct future regression rate data for the bias introduced by retaining wires.

Experimental study on combustion characteristics of fire in data room

Through the combustion experiments on the cables and servers in a data room, the combustion characteristic parameters of the materials were obtained, and the materials were analyzed and evaluated from the aspects of heat release rate, gas concentration, flue gas temperature, and so on. The results show that network cable and electric cable can be ignited during the cable combustion test. In the overall fire combustion experiment of single server and the server group with three cabinets, the fire process is divided into three stages: initial growth stage, stable combustion stage, and combustion attenuation stage. The heat release rate, flue gas temperature, and CO2 concentration of the overall experiment have three peaks, respectively, 58, 98, and 134 kW; 100°C, 152°C, and 232°C; 1314, 2514, and 2988 ppm. The research results can provide some reference for design of fire protection system in data rooms.

Experimental and Numerical Simulation Analyses of Flame Spread Behaviour over Wood Treated with Flame Retardant in Ancient Buildings of Fuling Mausoleum, China

AbstractTo protect ancient buildings from fire, prevent the occurrences of fire, and minimise the losses caused by fire to the maximum extent possible, this study combined experimental measurements and numerical simulations to analyse the flame spread behaviour over wood treated with flame retardants. First, some wood blocks were treated with a nitrogen and phosphorus (water-based) flame retardant, and then a smoke combustion experiment was performed to test the smoke density. Scanning electron microscopy was also employed to observe the flame retardant effect. Next, a fire dynamic simulation software was used to simulate and analyse the results of the flame spread behaviour over the yellow pine collected from the Long’en Hall of Fuling Mausoleum, that was treated with flame retardants. The results showed the variation trend of the fire site’s heat release rate (HRR) over time to be consistent with the movement of fire spread after its occurrence. Compared with pristine wood, the flame retardant-treated wood exhibited a HRR reduction of 53.1%. The addition of flame retardants also reduced the concentration of the released smoke and CO2 gas, decreased the temperature of the fire site, and enhanced visibility.

Oxyfuel combustion experiments to reduce CO2 emissions in the cement production process

Oxyfuel combustion experiments to reduce CO₂ emissions in the cement production process

Application of experiments and density function theory on the formation mechanism of NH3 during O2/Ar and O2/H2O combustion process of demineralized coals

Understanding the formation mechanism of NH3 during the pulverized coal combustion process is a feasible approach to reducing NOx emissions. In this study, the emission characteristics of NH3 during the O2/Ar and O2/H2O combustion processes were investigated by the isothermal combustion experiments and the Density Functional Theory (DFT) method. The experimental results demonstrated that H2O accelerated the conversion of HCN to NH3, and the positive effects of H2O were applied to all kinds of coal-based fuels. The DFT calculations deeply revealed the formation mechanism of NH3 through the homogeneous conversion of HCN and the heterogeneous hydrogenation of coal-N. The hydrogenation of coal-N is the primary source of NH3 emissions during O2/Ar combustion. During O2/H2O combustion process, the heterogeneous generation of NH3 was modified by the synergetic effects of O2 and H2O, and the additional H2O strengthened the proportion of the homogeneous reaction. The homogeneous conversion of HCN was the main NH3 formation pathway. This study is prone to coupling the experiments and quantum chemistry to deeply reveal the formation mechanisms of NH3 during O2/Ar and O2/H2O combustion processes, providing a relatively complete pathway for the emissions of NH3.

Experimental and numerical study of soot volume fraction and number density in laminar co-flow diffusion flames of n-decane/n-butanol blends

Normal decane was selected as a surrogate fuel for RP-3 aviation fuel, and soot formation characteristics and effects of n-decane (D) /n-butanol (B) cofiring were investigated experimentally and numerically. Combustion experiments of six n-decane/n-butanol blends (i.e., D100, D80, D60, D40, D20, D00, indicating the volumetric fraction of n-butanol in blends) were performed on co-flow diffusion flames. The volume fraction and morphological characteristics of soot at different heights of the flame axis were obtained using thermophoretic sampling and transmission electron microscopy analysis. A newly developed n-decane/n-butanol/PAH kinetic model consisted of 73 species and 275 reactions were further applied to model the soot formation process and ascertain the effects of n-butanol blending. Experimental and simulation results showed that soot loading (soot volume fraction and number density) decreased with increasing n-butanol blending ratios. Chemical kinetic analysis suggested that n-butanol addition decreased the rate of the HACA reaction as a result of a reduction of C2H2 and C2H3 (+M) ⇄ C2H2 + H (+M), ultimately leading to a reduction of soot loading.

Lagrangian coherent structures in flow past a backward-facing step

This paper investigates flow past a backward-facing step (BFS) in a duct at Reynolds number $Re = 5080$ based on step height, mean inflow velocity and fluid kinematic viscosity. The flow configuration matches a combustion experiment conducted by Pitz and Daily in 1983. High-resolution velocity fields are obtained in OpenFOAM by direct numerical simulation, and the flow field analysed by Lagrangian approaches. Trajectories of fluid particles in areas of interest are obtained by high-order numerical integration, and used to compute finite-time Lyapunov exponents (FTLEs) and polar rotation angles. Lagrangian coherent structures (LCSs) are extracted using geodesic theory, including hyperbolic LCSs and elliptic LCSs. We use complementary qualitative and quantitative LCS analyses to uncover the underlying flow structures. Notably, we find that a flow pathway in which fluid particles rarely diverge from adjacent particles is opened and closed by FTLE ridges determined by the periodic shedding of vortices from the BFS. Two dominant vortices with significant Lagrangian coherence, generated respectively by the separated boundary layer and shear layer, are self-sustaining and of comparable strength. Hyperbolic repelling LCSs act as transport barriers between the pathway and cores of the coherent vortices, thus playing a major part in the fluid entrainment process. Interactions between these different geometric regions partitioned by LCSs lead to intrinsic complexity in the BFS flow.

Comparative Study of In-Situ Combustion Tests on Consolidated and Crushed Cores

Summary A significant amount of oil is contained in carbonate reservoirs, but only half of that oil can be produced by secondary enhanced oil recovery (EOR) methods. However, substantial improvements were made in EOR techniques and the prediction of carbonate reservoir performance within the last decades. Nevertheless, existing flow-simulation computer programs failed to provide a reliable prediction of such reservoirs due to their high heterogeneity and the reactivity of the rock. Potentially, in-situ combustion (ISC) is considered effective in developing heavy oils in carbonate reservoirs. The combustion reactions between crude oil and heterogeneous rock matrices introduce additional complexity to the simulation process. Also, most of the laboratory experiments studying the reaction kinetics of the ISC process are performed on the crushed core. However, to minimize the risks, improve the control of the process, and overcome upscaling issues, physical simulation must be carried out under conditions as close to the reservoir as possible. Consolidated core material in combustion tube (CT) experiments is desirable for better simulating some reservoir conditions with synthetic packs and for the cases when actual preserved reservoir core material may be available. Studying the relative effects of porosity and packing properties (specific surface area, sand grain distribution, and cementation) on the fuel is essential to evaluating the process under actual field conditions. This work presents a set of medium-pressure CT (MPCT) tests on crushed and consolidated cores and analyzes the differences, limitations, and performances of both approaches. Two MPCT tests were performed to evaluate the ISC feasibility on the heavy-oil carbonate reservoir with an initial oil saturation level of 0.38 to 0.50. According to previously published experimental results, such oil saturation levels can help avoid oil banking. Both experiments were conducted at reservoir conditions to consider the phase behavior at elevated pressures and temperatures. The method used in this research allows approbation of the methodology of ISC tests using consolidated core at high pressure, ensuring pack and process integrity during the experiment. The influence of consolidated core caused by significantly lower porosity and more uniform porous media elements than those made with unconsolidated material on combustion performance was assessed. Valuable data for different variations of combustion experiments were generated. This work compared two tests and presented the combustion parameters for a stabilized combustion period, such as fuel and air requirements, recovery efficiency, front velocity, and composition of produced gases. The research intends to demonstrate the potential application problems and address issues that might arise during ISC application on target reservoirs, including the higher air flux required for lower porosity of consolidated core samples. The experimental results performed under conditions closest to reservoir conditions are essential for further predictions and affect the ISC performance during pilot tests.

Experimental study and modelling of pressurized oxy-coal combustion: Effect of devolatilization conditions on the physical structure and combustion characteristics of char particles

Pressurized oxy-coal combustion has been regarded as a promising carbon capture and storage (CCS) technology, and the combustion characteristics of char particles under pressurized oxy-fuel combustion conditions have been extensively investigated. However, most previous studies used the char samples prepared under the atmospheric N2 condition rather than under the pressurized CO2 condition, which may lead to the misunderstanding of the combustion characteristics. In this study, the effects of devolatilization atmosphere and pressure on the physical structure of char particles were experimentally investigated. The char particles produced under different devolatilization conditions were then used for the oxy-char combustion experiments conducted in a fluidized bed with the operating pressure between 0.1 and 0.5 MPa. In view of the limitations of the experiment, an experimental verified particle-scale char combustion model was further used for predicting the char particle’s combustion reactivity and temperature, and the influence of physical structure on the combustion characteristics was analyzed. The results obtained from the experiments demonstrated that higher devolatilization pressure led to larger mean pore sizes and specific surface areas of char particles. The char particles obtained with CO2 atmosphere had larger specific surface areas but smaller mean pore sizes than those obtained with N2 atmosphere. Besides, increasing devolatilization pressure resulted in shorter burnout times of char particles. The simulation results showed that using the char samples prepared under the atmospheric N2 condition for the pressurized oxy-fuel combustion experiments led to the underestimations of char combustion reactivity and peak temperature.

High frequency Rayleigh scattering measurements of density fluctuations in high-pressure premixed combustion

Measuring physical flow properties, such as density and temperature, at high frequency in high temperature and pressure environments is very challenging. Rapid fluctuations of these properties often have an impact on combustion efficiency and stability. We hereby attempt to measure density fluctuations in high-pressure premixed combustion using high temporal resolution laser Rayleigh scattering. The Rayleigh scattering intensity was assessed by counting individual photons due to the low signal to noise ratio. The measurement system was first verified at various air pressures without combustion. Combustion experiments were then conducted at four different pressures, from 1 to 7 bar. The density fluctuations increased with pressure, but the dominant fluctuation frequency decreased. Proper orthogonal decomposition analysis of high-speed schlieren images of the flame front was used to verify the results.

Modification of a 240 kWth grate incineration system for oxyfuel combustion of wood chips

The objective of this work is the application of the oxyfuel combustion technology for grate incineration systems to increase the CO2 concentration in the flue gas for higher efficiency when processing the gas for storage or utilization. Therefore, an experimental 240 kWth moving grate combustion facility has been modified to allow the investigation of the combustion behavior under various oxyfuel conditions. Subsequent to the modification, combustion experiments with dried wood chips under air and several oxyfuel atmospheres have been performed. During oxyfuel operation, the oxygen concentration in the gas supply streams towards the furnace has been set to 30 vol.-% dry with recycled flue gas being the rest of the gas composition. The oxygen distribution between primary and secondary zone has been varied (30%/70%, 40%/60%). Additionally, one case with increased oxygen concentration in the primary zone (40 vol.-% dry) has been investigated. The results show that oxyfuel grate incineration of the given fuel in this setup is feasible. However, the combustion behavior differs significantly between air and oxyfuel conditions in the investigated cases. The CO2 concentration in the dry flue gas could be increased to around 73 vol.-% with 5.7 vol.-% excess O2. Compared to the reference air cases the emission rates of CO were also increased during oxyfuel operation. However, it seems manageable given enough excess oxygen (∼7 vol.-% dry). Although the temperature at the end of the furnace is comparable among the cases, oxyfuel combustion leads to lower maximum temperatures along the combustion chamber. Differences between 150 °C and 200 °C have been measured among corresponding air and oxyfuel cases. Also, the temperatures of the grate and inside the fuel bed are reduced during oxyfuel operation even in the case with increased O2 concentration leading to the impression that the thermal strain on the grate is lower compared to air operation with the same fuel throughput.