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This study reviews the advancements in nickel-based catalysts for carbon dioxide methanation, a key process for reducing greenhouse gas emissions and supporting renewable energy. It explores the development of Ni-based catalysts, focusing on innovations in catalyst composition, structure, and operating conditions that address challenges like deactivation and low efficiency. This review presents a comprehensive analysis of the factors influencing catalytic performance, including the effects of supports, promoters, and structured catalysts, as well as environmental impacts such as energy use and greenhouse gas emissions. By comparing different catalysts and highlighting the benefits of structured catalysts like foams and monoliths, this work provides a new perspective on enhancing methane production efficiency. Key factors influencing catalyst activity are discussed, including basicity, bimetallic structures, particle size, feed gas composition (O 2 , H 2 O, SO x and NO x), and the impact of contaminants (siloxanes, NH 3 , and halogenated compounds). The study addresses deactivation mechanisms, such as carbon deposition and sulfur poisoning, and proposes mitigation strategies. The review also discusses the Life Cycle Assessment (LCA) of Ni-based catalysts, demonstrating their potential to minimize environmental impacts. This comprehensive approach offers valuable insights for advancing CO 2 methanation technology, contributing to sustainable energy production and aligning with global emissions targets and sustainable development goals. [Display omitted] • Review of Ni-based catalysts' advancements for efficient CO 2 methanation processes. • Analysis of supports, promoters, and structured catalysts enhancing Ni-based performance. • Impact of feed gases and contaminants on Ni-based catalyst performance and deactivation. • Environmental impacts and Life Cycle Assessment of Ni-based catalysts in CO 2 methanation. • Challenges and future research directions for optimizing Ni-based catalysts in sustainable energy. [ABSTRACT FROM AUTHOR]

This research evaluated the operational conditions for a diesel engine with high compression ratio (CR) converted to spark ignition (SI), under stable combustion conditions close to the knocking threshold. The main fuel used in the engine was biogas, which was blended with natural gas, propane, and hydrogen. The engine limit to test the maximum output power was using the knocking threshold; just below the knocking threshold, the output power and generating efficiency are the highest for each blend. Leaner mixtures increased the engine knocking tendency because the required increase in the % throttle reduced the pressure drop at the inlet stroke and increased the mixture pressure at the end of the compression stroke, which finally reduced the ignition delay time of the end gas and increased the knocking tendency of the engine for all the blends. Therefore, the output power should be decreased to operate the engine below to the knocking threshold. Purified biogas achieved the highest output power and generating efficiency compared with the other blends and the original diesel operation; this blend was operated with five equivalence ratios. Purified biogas exhibits an optimal balance between knocking resistance, low heating value, flame speed, and energy density. [ABSTRACT FROM AUTHOR]

Highlights • Self-recuperative burner simulation with variable air preheating temperature was made. • A new methodology to calculate solid and gas radiation in reheating furnaces form CFD simulation was presented. • The heat transfer on billets increases as a result of the use of self-recuperative burners. • The heat recovery increase the process efficiency but reduces the billet temperature homogeneity, due to furnace design. Abstract The present study presents a numerical simulation of the effects of using self-recuperative burners on the performance of a walking-beam reheating furnace. The study was done using CFD (Computational Fluid Dynamics) simulations where a low computational cost method was implemented to simulate the billet heating as a steady state system. The preheating temperature of the air was defined as a function of the air mass flow and the flue gas temperature in each burner, using a UDF (User-Defined Function). The results of the billet heating profile were validated with experimental measurements in a furnace not utilizing heat recovery and showed good agreement with a maximum deviation of 54 K. Efficiency was found to increase from 32.7% to 48.5% with the use of self-recuperative burners. This result was reflected in a fuel consumption decrease of 31.3%, or an increase in furnace production of 51.3%. The heat transfer in the furnace and the billet heating characteristic were analyzed, which were observed to have changed with the different burners. This effect was lesser when the thermal input was decreased, and greater when the production was increased or when both remain constant. With and without heat recovery, radiation represents about 90% of the total heat flux on the billets. Due to the importance of radiation, solid and gas radiation were also analyzed. An improvement upon a methodology found in the literature was proposed. Using this new methodology it was found that, for the furnace evaluated, around 25% of the radiation absorbed by the billets comes from the flue gases. The effect of defined a constant billet emissivity on the results of the simulation was also discussed. [ABSTRACT FROM AUTHOR]

Abstract This work presents the strategies applied to improve the performance of a spark ignition (SI) biogas engine. A diesel engine with a high compression ratio (CR) was converted to SI to be fueled with gaseous fuels. Biogas was used as the main fuel to increase knocking resistance of the blends. Biogas was blended with natural gas, propane, and hydrogen to improve fuel combustion properties. The spark timing (ST) was adjusted for optimum generating efficiencies close to the knocking threshold. The engine was operated on each blend at the maximum output power under stable combustion conditions. The maximum output power was measured at partial throttle limited by engine knocking threshold. The use of biogas in the engine resulted in a power derating of 6.25% compared with the original diesel engine (8 kW @ 1800 rpm). 50% biogas + 50% natural gas was the blend with the highest output power (8.66 kW @1800 rpm) and the highest generating efficiency (29.8%); this blend indeed got better results than the blends enriched with propane and hydrogen. Tests conditions were selected to achieve an average knocking peak pressure between 0.3 and 0.5 bar and COV of IMEP lower than 4% using 200 consecutive cycles as reference. With the blends of biogas, propane, and hydrogen, the output power obtained was just over 8 kW whereas the blends of biogas, natural gas, and hydrogen the output power were close to 8.6 kW. Moreover, a new approach to evaluate the maximum output power in gas engines is proposed, which does not depend on the engine % throttle but on the limit defined by the knocking threshold and cyclic variations. Highlights • Different strategies were applied to improve the performance of a spark ignition (SI) engine. • A diesel engine converted to SI was used to measure the maximum output power to gaseous fuel blends. • Biogas was blended with natural gas, propane and hydrogen to improve fuel combustion properties. • The output power and generating efficiency were higher than the original diesel engine operation. • Purified biogas got the highest output power due to balance of knocking resistance and energy density. [ABSTRACT FROM AUTHOR]

The cement industry is one of the world’s largest energy consumers. In this work, a walk-through study of representative cement companies was carried out to characterize the energy profile of the cement industry in Colombia, with emphasis on evaluating the degree of obsolescence of the technology used in the processes, as well as identifying the main barriers that prevent the adaptation of more efficient technologies. Perception-surveys were performed among the energy managers to determine the barriers that hinder the implementation of energy efficiency measures. A factor that quantifies the influence of each type of barrier was defined according to the results of the survey. The results show that the Colombian cement industry has a specific energy consumption that is competitive with the largest cement producers in the world, while the technological obsolescence found is at a medium - low level. Furthermore, the main barrier to the penetration of energy efficiency technologies and measures is identified as the hidden costs associated with the implementation of these technologies. Finally, some conventional and emerging technologies are proposed to improve the efficiency of thermal energy use in the processes studied. [ABSTRACT FROM AUTHOR]

The present study evaluated numerically and experimentally in a 20 kW furnace (using natural gas as fuel and with an equivalent ratio of 1.2) the stability of the flameless combustion regime due to the fluctuation of the thermal load through the use of different air flow (43 scfm, 63 scfm y 83 scfm) and an Air-Helium mixture (Air 82.02 scfm and Helium 7.06 scfm); the last one it was used to evaluate the behavior of the system in the face of an increase in the load fluid specific heat capacity. The study was divided in two parts, numerical simulation and experimental phase. From the numerical simulation was calculated the temperature profile, CO profile, the recycle ratio Kv and the mass of flue gases recirculated. In the experimental phase the temperature profiles obtained showed a decrease in the temperature of the combustion chamber as the load air flow increased however, this decrease did not affect the thermal uniformity inside of the furnace. Furthermore the useful efficiency showed an increase when went over from a load air of 43 scfm to 63 scfm, followed by a decrease of it with the other load flows. [ABSTRACT FROM AUTHOR]

Methane number (MN) and the critical compression ratio (CCR) measurements for twelve blends of biogas with methane or propane and hydrogen additions were taken in a Cooperative Fuel Research (CFR) F2 model engine according to the standard. In addition, CHEMKIN simulations of MN and the CCR were performed on these blends at similar conditions to the CFR F2 engine operation. Eight chemical kinetics mechanisms were used; it was concluded that the best mechanism to simulate the CCR is USCII, and the best mechanism to simulate MN is San Diego. In almost all blends that include propane, the best mechanism to predict the CCR and MN is Butane. It was not possible to find an optimal mechanism for all gaseous blends to simulate the CCR and MN. Experimentally, three blends of biogas were found with methane or propane and hydrogen additions with an MN of 100, with the intention to find blends of alternative and conventional fuels to interchange with methane from the viewpoint of knock resistance. For two blends, tests were carried out while changing the equivalence ratio and inlet pressure to evaluate their effect on knocking, measured with the CCR. A correlation between MN and the CCR is presented utilizing data from current and past tests performed at Colorado State University. The MN and CCR characterize the knocking tendency for each blend and indicate the maximal compression ratio to spark ignition engines; a higher CCR will lead to higher thermal efficiencies. These proposed blends use mostly biogas with a high percentage of inert gas, with favorable combustion properties including relatively large energy densities, low heating values, laminar flame speeds and low adiabatic flame temperatures. Blends of biogas with conventional fuels allow desirable combustion characteristics and high resistance to knocking. [ABSTRACT FROM AUTHOR]

This paper presents a study of CH 4 /Air/H 2 /O 2 premixed laminar flames using a ratio of H 2 /O 2 equal to 2/1. This gas mixture represents the products of the electrolysis of water. To date, only numerical analysis has been carried out on these kinds of blends and using H 2 /O 2 percentages of only up to 10% by volume. Furthermore, there have been no reports of experimental analysis or possible flame instabilities associated with the enrichment of the mix with H 2 /O 2 . In this study, the effect of adding water electrolysis products on the laminar burning velocity and stability of lean premixed methane/air flames is studied for different percentages of H 2 /O 2 (10 and 25) in the lean combustion regime, which is relevant for most engineering applications. The results show that a higher addition of H 2 /O 2 to methane increases the laminar burning velocity. In particular, at Φ = 0.75, intrinsic instabilities are observed for mixtures with 25% of H 2 /O 2 in methane. With the addition of H 2 /O 2 , the laminar flame thickness decreases and the growth rate increases. Hence, the addition of H 2 /O 2 to a premixed natural gas flame enhances the hydrodynamic instabilities. [ABSTRACT FROM AUTHOR]

The primary objective of this work is to study the combustion of an equimolar mixture of methane and syngas (CH 4 –SG ) in a ceramic surface-stabilized combustion burner. We examine the effects of the fuel composition, the air-to-fuel ratio and the thermal input on the flame stability, the radiation efficiency and the pollutant emissions (CO and NOx). In this study, we evaluate a syngas with a high hydrogen content that is similar to those obtained by coal gasification (50–60% H 2 ) using Sasol/Lurgi gasification technology and biomass gasification, for example. To determine the effect of the air-to-fuel ratio ( λ ), the burner performance is analyzed at λ = 1.4 and λ = 1.1. Some studies have reported optimal operating conditions for λ = 1.4, whereas for hydrocarbons, the proximity to stoichiometric conditions at the λ = 1.1 air-to-fuel ratio produces the highest possible laminar burning velocity and flame temperature. The thermal inputs evaluated in this study correspond to three values (1.0, 1.8, and 2.5 kW) found in household appliances and for cooking appliances in particular. The results for this experimental burner design indicate that the macroscopic flame shape for an equimolar CH 4 –SG mixture is approximately the same as that for CH 4 . Moreover, the pollutant concentrations in the flue gas are generally below 85 ppm for CO and 15 ppm for NOx. However, the thermal input and the air-to-fuel ratio significantly affect the flame structure, the radiation efficiency and the pollutant emissions. [ABSTRACT FROM AUTHOR]

Abstract: Numerical and experimental measurements of the laminar burning velocities of biogas (66% CH4 – 34% CO2) and a biogas/propane/hydrogen mixture (50% biogas – 40% C3H8 – 10% H2) were made with normal and oxygen-enriched air while varying the air/fuel ratio. GRI-Mech 3.0 and C1–C3 reaction mechanisms were used to perform numerical simulations. Schlieren images of laminar premixed flames were used to determine laminar burning velocities at 25 °C and 849 mbar. The mixture's laminar burning velocity was found to be higher to that of pure biogas due to the addition of propane and hydrogen. An increase in the laminar burning velocities of both fuels is reported by enriching air with oxygen, a phenomenon that is explained by the increased reactivity of the mixture. Additionally, an analysis of interchangeability based on both the Wobbe Index and the laminar burning velocity between methane and a biogas/propane/hydrogen mixture is presented in order to consider this mixture as a substitute for natural gas. It was found that the variations of these properties between the fuels did not exceed 10%, enabling interchangeability. [Copyright &y& Elsevier]

Abstract: The effect of oxygen enriched air was tested for a diesel-biogas dual fuel engine. The operation and performance characteristics, such as thermal efficiency, pollutant emissions and combustion parameters were determined. Experiments have been carried out with a stationary compression ignition (CI) engine coupled with a generator in dual mode using a typical biogas composition of 60 vol. %CH4 and 40% vol. %CO2. For every engine load evaluated, the oxygen concentration in the intake air engine was varied from 21% to 27% O2 v/v. Ignition delay time and methane emissions were decreased when using oxygen enriched air with respect to normal air (21%O2), whereas the thermal efficiency was increased. [Copyright &y& Elsevier]

A methodology to design flameless combustion heating equipment is presented. The design of flameless combustion devices requires an appropriate methodology to guarantee the necessary conditions to obtain this combustion mode. Nevertheless, such methodologies are not available in the scientific literature. For this, a combination of dynamic scaling, based on air/gas impulse ratio, and numerical simulation with FLUENT® has been employed to get suitable geometric configurations and dimensions for discharging fuel and comburent air. The proposed methodology has been applied to the design of a 20 kW experimental furnace using natural gas as fuel. The validity of the methodology has been verified with stable flameless combustion operation in the furnace. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen addition to methane will have an important role to reach a fully developed hydrogen economy. The effects of this addition on the flame structure and CO emissions were evaluated in two different atmospheric burners. Four fuels with the following composition were used: 100%CH4, 2%H2+98%CH4, 6%H2+94%CH4 and 15%H2+85%CH4. In a single-port atmospheric burner, a decreasing trend in the height of the blue cone with hydrogen addition was determined. The increase in the laminar burning velocity was identified as the main effect on the behavior of this parameter. In a drilled-port atmospheric burner, a significant reduction in CO emissions with hydrogen addition was achieved under two operating conditions: (1) keeping the primary air ratio constant and (2) keeping the primary air ratio and the thermal input constant. The results obtained were consistent with previous experimental studies. This reduction is attributed to a higher concentration of OH radicals as a result of hydrogen addition. [Copyright &y& Elsevier]

Turbulent burning velocity is one of the most relevant parameters to characterize the premixed turbulent flames. Different correlation has been proposed to estimate this parameter. However, most of them have been obtained using experimental data at atmospheric pressure or higher. The present study is focused on obtaining a correlation for the turbulent burning velocity using data at sub-atmospheric pressure. The turbulent burning velocity was experimentally calculated using the burner method, where turbulent premix flames are generated in a Bunsen burner. Stoichiometric and lean conditions were evaluated at a pressure of 0.85 atm and 0.98 atm, whereas the turbulence intensity was varied for each condition. Perforated plates and a hot-wire anemometer were used to generate and measure the turbulence intensity. Schlieren images were used to obtain the average angle of the flame and calculate the turbulent burning velocity. Experiments and theory show that the turbulent deflagration rate decrease as pressure decrease. The turbulent deflagration speed decreased by up to 16 % at 0.85 atm concerning atmospheric conditions for the same turbulence intensity, discharge velocity, and ambient temperature, according to the experimental results. The comparison among the experimental results at sub-atmospheric conditions and the correlations reported in the literature exposes prediction issues because most of them are fitted using data at atmospheric conditions. A general correlation is raised between turbulent burning velocity (ST), laminar burning velocity (SL) and turbulence intensity (u′) proposed from the experimental data. This correlation has the form ST/SL ∝α [ur/SL]n. For sub-atmospheric and atmospheric conditions, the coefficients were determined. [ABSTRACT FROM AUTHOR]

• Oxygen-enriched air significantly influences RTB performance. • The thermal efficiency of the recuperator averages 76.3%. • Numerical simulations provide reliable results for combustion and heat transfer processes. • Optimization of RTB design and operation is necessary when considering oxygen enrichment. The effect of oxygen enrichment on the performance of a self-recuperative radiant tube burner (RTB) was evaluated. Reynolds-Averaged Navier Stock (RANS) Fluid Dynamic Simulations (CFD) are performed on a non-recirculating radian tube burner with fuel-oxidant mixing and primary combustion reactions occurring inside a combustion chamber rather than in the radiant tube. The radiant tube burner is intended for drying applications with an operating surface temperature of around 950 K. Oxygen concentrations in the oxidant ranging from pure air to pure oxygen are evaluated, and the effect of oxygen enrichment on the flame structure, heat transfer, and burner performance is analyzed. The recuperative part of the RTB was also included in the analysis. The effect of O 2 content, flue gas temperature, and mass flow rate on the performance of the heat exchanger is evaluated, and a correlation to describe the oxidant preheat temperature is calibrated with the data from the simulations. Oxygen enrichment significantly impacts the performance of the self-recuperative radiant tube burner. The mean radiant tube temperature and the radiation efficiency rise with increasing oxygen enrichment until it reaches a peak value around 40% O 2 for the burner evaluated; beyond this value, the efficiency of the RTB begins to decline. The same oxygen enrichment gives the higher energy recovery ratio in the heat exchanger at flow rates corresponding to constant reference thermal power. The position of the flame and the interplay between the variations in specific heat, emissivity, temperature, and flow rate of the gases explain these results. [ABSTRACT FROM AUTHOR]

This research involves a knocking effect analysis of the operation and performance of a spark ignition engine with high compression ratio using a blend of 50% biogas with 50% natural gas. A diesel engine was converted to spark ignition mode. During testing, the output power, equivalence ratio, fuel blend composition and engine speed were kept constant while the spark timing was modified. Three knock intensities were evaluated using three different spark timing to evaluate the combustion parameters and engine performance. Eighteen tests were developed for repeatability analysis. A knocking analysis compare the engine performance with negligible and low knocking intensities. The knocking effect was analyzed with respect to instantaneous pressure in the combustion chamber, heat release rate, crank angle location for mass burned, combustion duration, coefficient of variation of indicated mean effective pressure, knock peak pressure, specific fuel consumption, thermal efficiency, and emissions. The thermal efficiency reached was 28.76% with an output power of 7.5 kW. High values of efficiency result from high CR and high output power, close to the knocking threshold. A knock peak pressure in the range between 0.3 and 0.5 bar averaged over 200 cycles is established as the knocking threshold. [ABSTRACT FROM AUTHOR]

The primary objective of this work is to study the blending of natural gas in equimolar proportions with three high hydrogen content syngases in a radiant porous media burner. We examined the effects of the composition of the syngases, the fuel-to-air ratio and the thermal input on the flame stability, the radiation efficiency and the pollutant emissions (CO and NOx). In this study, we emulated the syngases with H 2 –CO mixtures, in which the H 2 to CO ratio was varied between 1.5 and 3. Additionally, pure natural gas was also used as a base fuel for comparison. The thermal inputs evaluated in this study correspond to two values (300 and 500 kW/m2) found in practical applications. The results indicate that the thermal input and the fuel-to-air ratio significantly influenced the temperature profile in the radiant porous media burner, the radiation efficiency, and the pollutant emissions. On the other hand, contrary to what was observed in other studies for lower hydrogen concentrations, we found that substituting natural gas with high hydrogen content syngases (up to 50%) affected the flame stability limits. Significant differences were also observed for the radiation efficiencies and pollutant emissions. [ABSTRACT FROM AUTHOR]

The present paper analyzes experimentally the morphology of a set of non-premixed diffusion reactions of hydrogen enriched natural gas (NG). For the analysis the H 2 content was varied from 0 to 100 vol.-% and the mixture issues in a co-flow at variable preheating temperatures, from ambient conditions of 25 °C and up to 400 °C. For the various NG-H 2 blends the thermal power input was held constant at 0.8 kW. For processing the images, a bitmap filter was used to isolate visible flame height, visible width variations, and soot free length fraction (SFLF). The results show that visible flame height always decreases when increasing H 2 content in NG at any preheating temperature. The effects of air preheating summarize as follows: for NG enriched up to 75 vol.-% H 2 , the visible flame height reduces when increasing the air preheating temperature from 25 °C to 200 °C, then at 300 °C the visible flame height increases when rising the air temperature up to 400 °C. For the 100% H 2 non-premixed flame the visible height presents a linear trend to increase as air temperature rises. Roper's theory for non-premixed flames in circular ports correlates reaction length to air preheating temperature and fuel composition variations, however those trends neglect buoyancy and diffusion phenomena, which results in significant error on predicting the effects of hydrogen addition to NG on the reaction length. A modified correlation is proposed to predict accurately the effects of air preheating and H 2 fraction on visible flame height. Finally, a multidimensional scaling analysis shows that hydrogen addition up to 50 vol.-% does not modifies the visible flame morphology significantly when compared to pure NG. • Adding H 2 up to 50 v% to NG does not significantly change the flame shape. • NG-H 2 non-premixed flame length has a parabolic trend with air preheating. • Air preheating and hydrogen addition make non-premixed flames shorter and thinner. • The soot free length fraction decreases when increasing air preheating temperature. • Accurate correlation for predicting visible flame height of NG-H 2 blends. [ABSTRACT FROM AUTHOR]

The present work numerically and experimentally studies the mixture of 30% syngas and 70% natural gas (SG-NG), by volume, and compares performance to pure natural gas (NG). The experimental measurements were carried out in a semi-industrial regenerative furnace originally designed for pure natural gas. A 25 kW thermal input and a 1.2 excess air ratio were maintained throughout. Temperatures and species were measured inside the combustion chamber. The effect of the syngas on the reaction zone location was determined by imaging spontaneous chemiluminescence. The effect of preheating was also studied for the SG-NG mixture. CFD modeling was used to analyze the effects on recirculation patterns. SG-NG exhibited an average temperature decrease of 6% compared to NG, due to the greater recirculation and increased CO 2 in the flue gases. The species uniformity remained consistent, while the thermal uniformity factor (RTU) decreased by 10.5%, indicating greater uniformity. NOx emissions decreased by almost 50% for the SG-NG mixture. The addition of syngas improved the reactivity and displaced the reaction zone upstream. Without preheating, the recirculation and the reactant dilution decrease, generating a disturbance in the thermal uniformity (RTU increase by 65%) and the reaction zone was displaced downstream. • Stable flameless combustion remains whit a 30% syngas addition to natural gas. • Syngas addition changes the kinetic pathways at flameless combustion conditions. • NOx decreases when syngas is added to natural gas at a flameless combustion regime. • Higher recirculation and lower temperatures were observed when syngas was added. • The syngas addition improved the reactivity and displaced the reaction zone upstream. [ABSTRACT FROM AUTHOR]

In this paper, we present a methodology for calculating the thermal efficiency of a pot on an electric stove using numerical simulations in ANSYS FLUENT®. The system domain was divided into three subsystems: electrical resistors, the air volume inside the resistors, and the pot. It was determined that the heat transfer to the pot was mainly caused by conduction between the heating element and the pot surface, representing 85.7% of the total energy going into the system. Heat transfer by convection and radiation represented 13% and 1.3% of the total incoming energy, respectively. A method to set the initial value of the contact resistance between the electrical resistance and the pot based on experimental tests is also presented. This initial contact resistance value is a key parameter for the correct simulation of the system. The numerical simulations and experimental tests corresponded well with one another, with a difference of no more than 15% for all geometries analyzed. Finally, a substantial stove improvement is proposed. The enhancement consists of the suppression of the circulating currents that are formed inside the stove by adding an insulating material. With this improvement, the heat losses to the surroundings were reduced from 15.19% to 6.64%. And therefore, a potential reduction of the cost of living is possible in the main urban centers of Colombia. [ABSTRACT FROM AUTHOR]

Clay drying is one of the most important steps in the construction materials industry. Due to its high-energy requirement, clay drying is one of the most energy-consuming processes contributing to greenhouse gas emissions, motivating the search for strategies to increase the energy efficiency of the process. The process involves several operating variables whose historical records can generate a large amount of data, which can be organized and analyzed efficiently using data mining techniques (DMT). In this paper, the performance variables of a material-industry rotary dryer were identified and analyzed. A cluster analysis was performed using the Ward's classification method with 1729 operating data, identifying the kind of materials processed and the operating configurations. A linear regression model was constructed using the RRELIEFF feature selection algorithm in Orange: Data Mining Toolbox in Python. The main thermal-energy-consumption variables were the production rate, power, inlet gas temperature, and product moisture delta. These four variables represent the dryer's specific energy consumption index ( I c ) more suitably than the classic Energy Vs Production model. Consequently, it was established that a global-aeration-factor reduction could improve the process efficiency by 7% to 10% at the average production rate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combination of flameless combustion, oxygen enrichment and regenerative heat recovery. [•] No previous studies with enrichment up to 35% with regenerative flameless burners. [•] NO x emissions were below 5ppm and efficiency increased 5% for enrichments of 30%. [•] The energy recovery ratio of regenerators remained above 80% for all enrichments. [•] Air excess and ejection pressure level must be adjusted to optimized system operation. [Copyright &y& Elsevier]

Abstract: An experimental and numerical study on laminar burning velocities of hydrogen/air flames was performed at low pressure, room temperature, and different equivalence ratios. Flames were generated using a small contoured slot-type nozzle burner (5 mm × 13.8  mm). Measurements of laminar burning velocity were conducted using the angle method combined with Schlieren photography. Numerical calculations were also conducted using existing detailed reaction mechanisms and transport properties. Additionally, an analysis of the intrinsic flame instabilities of hydrogen/air flames at low pressure was performed. Results show that the behavior of the laminar burning velocity is not regular when decreasing pressure and that it depends on the equivalence ratio range. The behavior of the laminar burning velocity with decreasing pressure can be reasonably predicted using existing reaction mechanisms; however changes in the magnitude of the laminar burning velocity are underestimated. Finally, it has been found experimentally and proved analytically that the intrinsic flame instabilities are reduced when decreasing the pressure at sub-atmospheric conditions. [Copyright &y& Elsevier]

Abstract: The effects of low pressure on the laminar burning velocity and flame stability of H2/CO mixtures and equimolar H2/CO mixtures diluted with N2 and CO2 were studied experimentally and theoretically. Experiments were conducted at real sub-atmospheric conditions in three places located at high altitudes 500m.a.s.l. (0.947atm), 1550m.a.s.l. (0.838atm), and 2300m.a.s.l. (0.767atm). Flames were generated using contoured slot-type nozzle burners and Schlieren images were used to determine the laminar burning velocity with the angle method. The behavior of the laminar burning velocity at low pressures depends on the equivalence ratio considered; it decreases at lean and very rich equivalence ratios when pressure is increased. However, a contrary behavior was obtained at equivalence ratios corresponding to the highest values of the laminar burning velocity, where it increases as pressure increases. Numerical calculations were also conducted using a detailed reaction mechanism, and these do not reproduce the behavior obtained experimentally; a sensitivity analysis was carried out to examine the differences found. At lean equivalence ratios, flame instabilities were observed for all the syngas mixtures. The range of equivalence ratios where flames are stable increases at lower pressures. This behavior is due to the increase of the flame thickness, which considerably reduces the hydrodynamic instabilities in the flame front. [Copyright &y& Elsevier]

Abstract: Experimental measurement of the laminar burning velocities of H2/CO/air mixtures and equimolar H2/CO mixtures diluted with N2 and CO2 up to 60% and 20% by volume, respectively, were conducted at different equivalence ratios and conditions near to the sea level, 0.95 atm and 303 ± 2 K. Flames were generated using contoured slot-type nozzle burners and Schlieren images were used to determine the laminar burning velocity with the angle method. Numerical calculations were also conducted using the most recent detailed reaction mechanisms for comparison with the present experimental results. Additionally, a study was conducted to analyze the flame stability phenomenology that was found in the present experiments. The increase in the N2 and CO2 dilution fractions considerably reduced the laminar burning velocity due to the decrease in heat release and increase in heat capacity. At the same dilution fractions this effect was higher for the case of CO2 due to its higher heat capacity and dissociation effects during combustion. Flame instabilities were observed at lean conditions. While the presence of CO in the fuel mixture tends to stabilize the flame, H2 has a destabilizing effect which is the most dominant. A higher N2 and CO2 dilution fraction increased the range of equivalence ratios where unstable flames were obtained due to the increase in the thermal-diffusive instabilities. [Copyright &y& Elsevier]

The analysis of combustion products inside flames reaction zones and combustion chambers requires special equipment and methods of sampling compared to measurements made in chimneys. For example, non-intrusive experimental devices, such as laser techniques, or intrusive ones, such as sampling probes, should be used in zones where a flame is present. The use of the first ones means high costs, while the second ones must guarantee that the combustion reactions do not continue inside the sample probe; otherwise significant errors occur in the species measurements. To identify whether there are thermal and chemical kinetic effects that produce differences in the major species measurement, this paper presents a comparison of sampling results inside the reaction zone of a partially premixed flame when two types of sample probes are used: one with a sonic neck and a convective cooling of the sample, and another made just of a straight stainless steel tube. The results show that when using a straight tube there are errors in CO2 and CO measurements up to 7.0%, and errors in O2 measurements above 14%. [ABSTRACT FROM AUTHOR]

The increase in pollutant emissions has generated the development of clean technologies and encouraged the use of alternative fuels like syngas. Flameless combustion is one of the most promising clean technologies due to lower pollutants emissions and high thermal efficiency. In the present study, regenerative furnace simulation under flameless combustion was carried out using a fuel mixture of 70% natural gas and 30% syngas with high H2 content (in vol.); by mean of CFD approach. A symmetrical mesh with 405,632 hexahedral cells was used in the calculations. The κ-ε standard, discrete ordinates and Eddy Dissipation Concept models were used for physical phenomena of turbulence, radiation and turbulence - chemistry interaction, respectively. The combustion chambers thermal uniformity factor was 0.3 and 0.1 for vertical and horizontal planes, respectively. The results confirm that it is possible to achieve the flameless combustion regime in a regenerative furnace using the addition of syngas, preserving the temperature and reaction zone uniformity. [ABSTRACT FROM AUTHOR]

The global energy demand enhances the environmental and operational benefits of natural gas as an energy alternative, due to its composition, mainly methane (CH4), it has low polluting emissions and benefits in energy and combustion systems. In the present work, the laminar burning velocity of methane was determined numerically and experimentally at two pressure conditions, 0.85 atm and 0.98 atm, corresponding to the city of Medellín and Caucasia, respectively, located in Colombia. The environmental conditions were 0.85 atm, 0.98 atm, and 295 ± 1 K. The simulations and experimental measurements were carried out for different equivalence relations. Experimental laminar burning velocities were determined using the burner method and spontaneous chemiluminescence technique, flames were generated using burners with contoured rectangular ports to maintain laminar Reynolds numbers for the equivalence ratios under study and to reduce the effects of stretch and curvature in the direction of the burner's axis. In general, the laminar burning velocity fits well with the numerical results. With the results obtained, a correlation is proposed that relates the laminar burning velocity with the effects of pressure, in the form SL = aPb, where a and b are model constants. Sensitivity analysis was performed using the GRI-Mech 3.0 mechanism which showed that the most sensitive reaction was H+O2 = O+OH (R38). Additionally, it was found that the reactions H+CH3 (+M) = CH4 (+M) (R52), 2CH3 (+M) = C2H6 (+M) (R158), and O+CH3 = H+CH2O (R10) dominate the consumption of CH3 which is an important radical in the oxidation of methane, this analysis is carried out for equivalence ratios of 0.8 and 1.0, and atmospheric pressures of 0.85 atm and 0.98 atm. [ABSTRACT FROM AUTHOR]

• A significant difference in the reaction zone is observed comparing the combustion models. • The skeletal kinetic mechanisms used with the EDC model adequately describe the evaluated system. • The burner geometry was responsible for the small difference in the RT temperature prediction between combustion models. • The 2-D axisymmetric simulation gives good results as compared with the 3-D simulation. This work presents the computational fluid dynamic (CFD) simulation of a single-ended non-recirculating radiant tube burner (RTB). In the RTB evaluated, the mixing and main combustion reactions take place inside a combustion chamber, which differs from most of the RTB configurations found in the literature. The eddy-dissipation-concept (EDC) model and the Steady-Diffusion-Flamelet (SDF) model were compared to contrast their performance in the studied burner. Five chemical kinetic mechanisms were evaluated with the two combustion models. The chemical equilibrium approach with a PDF tabulation was also included. The CFD simulations were made using an axisymmetric two-dimensional (2-D) computational domain. The performance of the CFD simulation was evaluated by comparing its predicted outer radiant tube (RT) temperature with experimental measurements. Temperature and mole fraction of CO and OH were also compared between models and kinetic mechanisms. A third model, the Flamelet Generated Manifold (FGM), was subsequently included in the analysis, due to its capability to describe partially premixed combustion. Finally, the results of the 2-D simulation were contrasted with a three-dimensional (3-D) simulation, determining the effect of geometry simplification and confirming the suitability of 2-D CFD models in the studied case. [ABSTRACT FROM AUTHOR]

A characterization of the energy profile of certain ceramic industry enterprises in Colombia was carried out. An emphasis was placed on the barriers that prevent the implementation of energy efficiency actions, the degree of obsolescence of their production equipment, and the potential for energy efficiency savings. The barrier with the greatest impact in this sector was found to be hidden costs , followed by corporate values . There was a positive correlation between the potential savings and the degree of equipment obsolescence and the total barrier factor to the implementation of energy efficiency measures. Finally, it was concluded that the creation of programs that allow for more certainty in the appropriation of new technologies could help to overcome the barriers in Colombia's ceramic industry. [ABSTRACT FROM AUTHOR]

The present work studies the effect of reagent preheat temperature on methanation while maintaining the initial temperature of the catalytic bed constant. An adiabatic packed bed reactor was used with 193 g of commercial 10% Ni/Al 2 O 3 catalyst. The tested preheat temperatures were 25 °C, 100 °C, 180 °C, and 280 °C, while the initial catalytic bed temperature was 280 °C. Two tests were performed in which the effect of preheat temperature was evaluated: the first comparing gas hourly space velocities (GHSVs) of 935 h−1 and 1559 h−1, and the second comparing gauge pressures of 0 bar, 1 bar, and 4 bar. Similar behavior was observed for the temperature inside the reactor and final CO 2 conversion for preheating temperatures of 100 °C, 180 °C, and 280 °C at a gauge pressure of 0 bar. However, at this pressure, conversion was considerably reduced for the preheat temperature of 25 °C, due to a large part of the catalytic bed serving to preheat the reactants to the minimum reaction temperature. This effect can be partially attenuated by decreasing the GHSV, due to the increased residence time. Finally, increased pressure significantly improved the final CO 2 conversion for all preheating temperatures (T in), and attenuates the effect of T in. These results show that certain operating conditions do not require as high a reactant preheat temperature for methanation, which offers energy savings in certain processes such as power-to-gas (P2G), where the hydrogen is produced from electrolysis and can leave the process at a lower temperature than that required for methanation. • Under high pressure, no high reactant preheating temperature is required in a methanation reaction. • The CO2 conversion is highly dependent on preheating temperature in atmospheric methanation reaction. • CO production is highly dependent on the reactant preheating temperature under low pressures. [ABSTRACT FROM AUTHOR]

• Effect of atmospheric humidity on premixed combustion was studied. • Coupling between the pressure and the heat release rate at same frequency. • The presence of water in the reaction zone modifies the flame structure of methane. • The lower the carbon content, the lower the combustion instability under wet conditions. Combustion instabilities are an undesired phenomenon in premix burners, leading to vibrations and potential flame problems such as lift-off or flashback. The combustion stability in a premix burner is highly sensitive to fuel composition and local environmental conditions. Consequently, this work presents the effect of air humidity and fuel composition on the degree of combustion instability in a swirl stabilized premix burner at atmospheric pressure, initiating in both unstable and stable states. The experimental setup consists of a swirl stabilized 20 kW burner with a square combustion section of 100 mm × 100 mm, with optical access to the reaction zone on three sides. Three types of fuel were evaluated: methane (CH 4), CUSIANA (85% CH 4 ; 10% C 2 H 6 ; 5% C 3 H 8), and propane (C 3 H 8). Atmospheric humidity was emulated over a range from 0% to 5%, molar basis, the high point corresponding to the greatest atmospheric humidity. The degree of burner instability was characterized by the standard deviation of the pressure signal. It was found that atmospheric humidity can reduce combustion instability, affecting methane more significantly than propane at low air preheat temperature (315 K); at high preheat temperature, the water content was found to have no effect on combustion instability. The flame structure, i.e. shape and size, was similar for all fuel types at the same adiabatic flame and air preheat temperatures. Under unstable operating conditions, a similar flame shape and area of oscillation were found with the same resonant frequencies. This indicates that the variables characterizing thermoacoustic instability maintain similar values or proportions, regardless of the fuel type. [ABSTRACT FROM AUTHOR]