Combustion Furnace Research Articles

Impacts of scattering of non-gray gas particulate mixtures on radiative heat transfer and mid-infrared image temperature in a 2D oxy-coal combustion furnace

Impacts of scattering of non-gray gas particulate mixtures on radiative heat transfer and mid-infrared image temperature in a 2D oxy-coal combustion furnace

The Impact of Hydrogen on Flame Characteristics and Pollutant Emissions in Natural Gas Industrial Combustion Systems

To improve energy savings and emission reduction in industrial heating furnaces, this study investigated the impact of various molar fractions of hydrogen on natural gas combustion and compared the results of the Non-Premixed Combustion Model with the Eddy Dissipation Combustion Model. Initially, natural gas combustion in an industrial heating furnace was investigated experimentally, and these results were used as boundary conditions for CFD simulations. The diffusion flame and combustion characteristics of natural gas were simulated using both the non-premixed combustion model and the Eddy Dissipation Combustion Model. The results indicated that the Non-Premixed Combustion Model provided simulations more consistent with experimental data, within acceptable error margins, thus validating the accuracy of the numerical simulations. Additionally, to analyze the impact of hydrogen doping on the performance of an industrial gas heater, four gas mixtures with varying hydrogen contents (15% H2, 30% H2, 45% H2, and 60% H2) were studied while maintaining constant fuel inlet temperature and flow rate. The results demonstrate that the Non-Premixed Combustion Model more accurately simulates complex flue gas flow and chemical reactions during combustion. Moreover, hydrogen-doped natural gas significantly reduces CO and CO2 emissions compared to pure natural gas combustion. Specifically, at 60% hydrogen content, CO and CO2 levels decrease by 70% and 37.5%, respectively, while NO emissions increase proportionally; at this hydrogen content, NO concentration in the furnace chamber rises by 155%.

Experimental study on the effects of co-firing mode and air staging on the ultra-low load combustion assisted by water electrolysis gas (HHO) in a pulverized coal furnace

Developing zero-carbon fuel (H2/NH3) co-firing technology with pulverized coal can improve the low-load flame instability and pollutant emissions of boilers during peak shaving. In this study, we propose to assist the low-load combustion of coal powder furnaces with the safer water electrolysis gas (HHO). To further optimize the combustion strategy, a one-dimensional furnace combustion system coupled with an HHO gas generation and transportation system was used to investigate the effects of injection methods and air staging on the flue gas emission and auxiliary combustion characteristics of the lignite load reduction process and ultra-low load. The results indicate that reducing the coal combustion load achieves carbon reduction and reduces actual CO2 emissions. The excess air coefficient increases, resulting in higher NOX and lower CO emissions. Air staging can control NOX and CO emissions during load shedding, with a 40.49 % reduction in NOX at 30 % load. Under ultra-low load, HHO-assisted combustion increases the oxygen concentration in the furnace, increasing NOX emissions, while SO2 decreases and then increases. However, the effect of HHO gas premixed mode (PM) on NOX generation is weaker than that of staged mode (SM). As the flow rate of HHO increases, HHO-SM promotes the conversion of CO to CO2 and reduces CO emissions, while CO emissions under PM remain at ∼10 ppm. Both HHO injection methods exhibit assisted combustion effects for ultra-low load operation. Due to the different effects of the two on the recirculation zone inside the combustion, the auxiliary combustion effect of PM is superior than that of SM. At 1800L/h HHO, the decrease in combustion instability coefficient (βT) of PM is 57.14 %, higher than that of SM. Air staging is beneficial for stable combustion under ultra-low load, but it can affect the auxiliary combustion of HHO gas. Under ultra-low load HHO co-firing conditions, 11%-OFA can also control NOX and CO emissions.

A new denitrification strategy based on high-temperature catalytic coatings Y2O3-BaO-ZrO2 without using ammonia in a lab-scale natural gas combustion furnace

Catalytic decomposition of NO at high temperatures without the use of ammonia, offers an eco-friendly and sustainable solution for denitrification in industrial combustion or heating processes. To simulate a complex combustion flue gas, we designed a lab-scale natural gas industrial combustion furnace specifically for assessing the impacts of Y2O3-BaO-ZrO2 catalyst coated on SiC plates on NO emissions. Various factors including the plate number, excess air ratio, combustion power, and coating position were considered. Results demonstrated that arranging the Y2O3-BaO-ZrO2 coated plates shifted the high-temperature zone of the furnace downstream. When the excess air ratio was below 1.05, the catalytic coating significantly reduced NO emission concentration at the furnace outlet by over 40 %. However, this reduction coincided with a substantial presence of unburned CO in flue gases. Placing the coated SiC plates in the constant temperature zone of 1100–1200 °C within the middle of furnace offered significant advantages in NO removal, particularly as the combustion power increased. Based on a 60-h durability evaluation of Y2O3-BaO-ZrO2 coating, the observed good high-temperature thermal and chemical stabilities further enhanced the coating’s potential for industrial application. The possible mechanism of the reduction NO by CO over coating surfaces were analyzed by in situ optical measurements. After calculation, using 12 kg Y2O3-BaO-ZrO2 catalysts might decrease at least 642 kg of ammonia consumption under ideal conditions, and significantly reduce the investment cost on existing flue gas denitrification equipment. Therefore, the investigated technology is a green and sustainable denitrification strategy, which would potentially provide a novel approach towards attaining ultra-low NO emissions.

Pyrolysis behaviour and synergistic effect in co-pyrolysis of wheat straw and polyethylene terephthalate: A study on product distribution and oil characterization

Renewable lignocellulosic biomass is a favorable energy resource since its co-pyrolysis with hydrogen-rich plastics can produce high-yield and high-quality biofuel. In contrast to earlier co-pyrolysis research that concentrated on increasing product yield, this study comprehends the synergistic effects of two distinct feedstocks that were not considered earlier. This work focuses on co-pyrolyzing wheat straw (WS) with non-reusable polyethylene terephthalate (PET) for the production of pyrolysis oil. WS and PET were blended in different ratios (100/0, 80/20, 60/40, 40/60, 20/80, and 0/100), and pyrolysis experiments were conducted in a fixed-bed reactor under different temperatures to assess their synergistic effect on oil yield. Synergy rates of up to 7.78 % were achieved on yield for the blends of plastic and biomass at a temperature of 500 °C. In comparison to individual biomass or plastics, co-pyrolyzing PET-biomass blends demonstrated good process interaction and promoted the yields of value-added products. The heating value of the pyrolysis oils was in the range of 16.45–28.64 MJ/kg, which depends on the amount of plastic present in the feedstock. The physical analysis of the oils shows that they can be used for heat production by direct combustion in boilers or furnaces. The correlation between WS and PET was validated with the aid of Fourier transform infrared spectroscopy (FT-IR) and gas chromatography-mass spectrometry (GC-MS) analysis. The GC-MS result demonstrated the presence of different compounds such as O-H compounds, esters, carbonyl group elements, acids, hydrocarbons, aromatics, and nitrogenated compounds in the pyrolysis oil, which differed based on the proportions of PET in the feedstock. The increased hydrocarbon and reduced oxygen percentages in the pyrolysis oil were implicitly caused by enhanced hydrocarbon pool mechanisms, in which the breakdown of PET may be supplied as a hydrogen donor. Overall, waste lignocellulosic biomass and plastics can be used to produce biofuels, which helps reduce the amount of solid waste that ends up in landfills. This study also revealed that future research should be focused on the reaction mechanisms of WS and PET co-pyrolysis in order to examine the synergistic interactions.

Novel hollow-electrode glow discharge mass spectrometry for the quantitative analysis of protein content in food.

Protein content in food is an important indicator of nutritional value and food safety. Therefore, it is of great significance to accurately detect protein content in food. In this work, a combustion furnace and novel hollow-electrode glow discharge ion source-quadrupole mass spectrometry (HGD-MS) were designed, which were used to construct a "combustion furnace + mass spectrometry" experimental platform to detect the protein content in food. Five food standard samples were selected for the analysis. The food samples were combusted in the combustion furnace at a high temperature (1300 °C) in an oxygen-rich environment. The gas products were passed into the novel hollow electrode glow discharge ion source-quadrupole mass spectrometer. A standard curve of y = 635.06x + 11 082, R2 = 0.9994 was plotted by detecting the NO+ ion intensity at a relative standard deviation (RSD) of 1.8% to 5.7%. Using the same method, food samples no. 6 and 7 were combusted and NO+ ion intensity was measured to verify the accuracy of the quantitation curve. Subsequently, the protein content was determined using a nitrogen-to-protein conversion factor of 6.25. This method provides a rapid, accurate, and environmentally friendly approach for determining protein content in food.

Accurate and rapid reactive flow simulations using dynamic load balancing and sparse analytical Jacobian approach

The present study introduces a rapid and accurate customized solver on the OpenFOAM platform for large-scale industrial computations. Specifically, a sparse analytical Jacobian approach utilizing the SpeedCHEM library was implemented to enhance the efficiency of the ordinary differential equation solver. The dynamic load balancing code was used to distribute computational workloads uniformly across multiple processes. Optimization continued with open multi-processing to improve parallel computing efficiency and the local time stepping scheme to maximize individual cell time steps. The effectiveness and robustness of the customized solver were first validated using Sandia flames D–F as benchmarks. The results showed that the customized solver exhibited better strong scaling characteristics and led to a speed increase of up to 30 times for two-dimensional Sandia flame D calculations. The numerical predictions for temperature and species distribution closely matched the experimental trends, confirming the accuracy of the solver. Subsequently, a three-dimensional numerical study on a 10 kW ammonia co-combustion furnace was conducted, exploring the performance of the solver in large-scale reactive simulations. Results analysis indicated that the acceleration capability was reduced due to increased communication overhead between processors, achieving up to 7.06 times speed-up. However, as the size of the reaction mechanism increases, better acceleration capabilities can be demonstrated. The numerical predictions could closely replicate experimental trends, effectively predicting NO emission trends within the combustion furnace. This study offers one viable solution for rapid and accurate calculations in the OpenFOAM platform, which could be applied in the subsequent ammonia industrial combustion processes.

Carbon monoxide (CO) and particulate matter (PM) emissions during the combustion of wood pellets in a small-scale combustion unit – Influence of aluminum-(silicate-)based fuel additivation

The additivation of solid biofuels has proven to be an effective method for reducing total particulate matter (TPM) and carbon monoxide (CO) emissions, as well as for reducing ash-related problems related to, e.g., fouling and slagging. During the combustion with additives, potassium (K) released from the solid biofuels is bound into temperature-stable compounds, thus preventing the formation of inorganic (i.e., K-based) TPM. Simultaneously by reducing K in the gas phase, the inhibition of gas-phase oxidation (e.g., CO oxidation) due to interference of K within the existing radical pool is hindered. Particularly kaolin, an aluminum-silicate-based additive has proven effective in reducing not only TPM but also CO emissions. The mitigation effects on CO emissions have previously been reported mostly in a subordinate role and explanations are given in the form of hypotheses. In this study, seven additives (i.e., kaolin, kaolinite, meta-kaolinite, aluminum hydroxide, muscovite, muscovite coated with titanium dioxide and kalsilite, each at 0.3 wt%a.r.) were investigated during wood pellet combustion in a small-scale furnace (7.8 kW). For both CO and TPM emissions, kaolin proved to be most effective (i.e., −52% CO, −49% TPM), followed by muscovite, kaolinite, TiO2 coated muscovite, aluminum hydroxide, and meta-kaolinite.

Influences of ultra-low load operation strategies on performance of a 300 MW subcritical bituminous coal boiler

To reveal the operational characteristics of subcritical boilers under ultra-low loads, numerical simulations were conducted based on a 300 MW subcritical bituminous coal boiler. The impacts of boiler load and low-load operation strategies on coal combustion behavior, heat transfer process, and NOx emission were thoroughly examined. Results indicate that acceptable aerodynamic and temperature fields can still be formed at 25 % ultra-low load, but the boiler performance is significantly reduced, with the maximum cross-sectional average combustion temperature being reduced by 225.98 K compared with the full-load condition. At 25 % load, the use of only two layers of burners results in a substantial increase in NOx emission from 290.32 mg/m3 to 445.56 mg/m3. The position of in-service burners affects the region where the intense coal combustion and heat release process occurs, and using the middle three layers of burners helps to maintain heat absorption by the suspended heating surfaces and to minimize NOx emissions. Furthermore, increasing primary air velocity at ultra-low loads can promote coal combustion and heat transfer processes in the lower furnace, but increase NOx emission by 14.23 % when primary air velocity is increased from 14.90 m/s to 23.00 m/s at 25 % load. These findings provide valuable insights for optimizing the ultra-low load operation of subcritical boilers engaged in deep peak-shaving processes under the carbon neutrality goal.

Effect of coal suspension concentration and gas-air medium temperature on liquid droplets collisions

Relevance. Understanding the mechanisms of liquid droplets interaction with each other is important for many industrial and technical applications related to solving a range of problems like slag removal in a high-temperature environment, obtaining components of the desired fraction in the food industry, etc. Aim. Establishment of the main patterns of suspension droplets interaction in a gas-air environment with temperature variation. Methods. Using shadow high-speed video recording, the main patterns of the binary collision of suspensions droplets were determined. The paper introduces the results of experimental studies of the characteristics of collisions of droplets of coal-water suspensions in a gas-air environment with a temperature of 90–120°C. Parameters of the generated droplets: radius 1.0–2.2 mm, velocity 0.5–2.0 m/s. Results and conclusions. The authors have determined the modes of collision of droplets of suspensions (coagulation and separation) and the main characteristics of secondary fragments and constructed the maps of the modes of interaction of drops of suspensions with each other when varying the concentration of solid particles in the suspension, the temperature of the gas-air environment and the time the target drop spent in a gas-air environment with an elevated temperature. The conditions were established for the coagulation of droplets, as well as their intensive secondary grinding to intensify their drying, ignition and combustion in boiler furnaces. It was established that an increase in the temperature of the gas-air environment leads to a significant change in the size and properties of droplets, as well as to the occurrence of oscillatory phenomena in the system. It is substantiated that collision of droplets of suspensions in a gas-air environment with elevated temperature is complex and multi-parametric. Its characteristics depend on a combination of factors (surface tension and liquid viscosity, size and shape of droplets, speed of their movement, density and viscosity of gas-air environment). The authors obtained mathematical expressions to describe the boundaries of the modes of the studied processes and schemes for using the results obtained in order to increase the efficiency of the corresponding technological processes.

GPU-powered CFD-DEM framework for modelling large-scale gas–solid reacting flows (GPU- rCFD-DEM) and an industry application

The coupling of CFD (computational fluid dynamics) and DEM (discrete element method) is extensively used for simulating gas–solid reacting flows in various industrial processes, while its high computational cost limits its industry applications, especially large-scale systems with a large number of particles and complex geometries. This paper reports a robust highly efficient GPU (graphics processing unit) − powered CFD-DEM coupling approach that is, for the first time, capable of simulating large-scale gas–solid reacting flow systems with complex geometries (GPU- rCFD-DEM). The fluid flow calculations are performed using CPU parallelization, while the particle flow simulations leverage GPU parallelization, and the coupling calculations between CFD and DEM are fully implemented on GPU. The model includes advanced coupling strategies to enhance numerical stability, especially when handling complex geometries with unstructured CFD meshes. The developed model is validated through experimental measurements and its computational performance is evaluated by comparison with previous GPU-based simulations. It shows good agreement with the experiments and superior performance compared to the traditional coupling method. The model is then applied to simulate raceway dynamics and coke combustion in an industrial-scale blast furnace, showcasing its effectiveness in handling complex geometries and a huge number of particles in gas–solid reacting flows. This work provides an efficient and robust solution for numerically simulating industrial applications of gas–solid reacting flow systems.

Effects of carbonization on the structure and sorption properties of coffee grounds for Pb(II) and Ni(II) in various metal systems

Two biochars (i.e., Mu@CG and Tu@CG) derived from waste coffee grounds (CG) were prepared and muffle furnace (Mu) and tube furnace (Tu) were utilized to inspect the impact of carbonization process. It indicated that the specific surface area of Mu@CG could reach 124.26 m2/g, which was 37 times higher than that of Tu@CG (3.288 m2/g). Sorption experiments revealed that the optimal conditions were 55 °C, pH= 4, time= 10 h, and concentration was 80 mg/L for both combustion furnaces. Specifically, Mu@CG exhibited larger pore size (3.42 nm) than Tu@CG (0.015 nm), suggesting that Mu can increase the pore size of CG. The sorption of Pb(II) and Ni(II) on Mu@CG and Tu@CG followed pseudo-1st-order kinetic model. The Langmuir qm value of Mu@CG for Pb(II) was 67.037 mg/g. While, the cycle times of Mu@CG for Pb(II) and Ni(II) can be arrived at 5 times and HCl is an ideal de-sorbent for the regeneration of Mu@CG for Pb(II) and Ni(II). Further, the negative ∆G and positive ∆H data confirmed that Pb(II) and Ni(II) sorption on Mu@CG and Tu@CG were spontaneous and endothermic processes. Based on these findings, it can be concluded that for CG pyrolysis, muffle furnace will be one of the most favorable manners.

Co-combustion of municipal sewage sludge and food wastes-derived anerobic digestates: Combustion characteristics, HCl/NO/SO2 emission and ash behaviors

Co-combustion of sewage sludge (SS) and food wastes-derived anerobic digestate (AD) is a promising way of waste-to-energy. Therefore, it is crucial to examine their combustion performance, ash behaviors, and gaseous pollutants emissions during the combustion of AD-SS blends using a thermogravimetric analyzer and a tube furnace combustion system. Results show that obvious interactions between AD and SS are observed in their co-combustion process. In terms of comprehensive combustion index, co-combustion can improve their combustion performance with the decrement of burnout temperature and enhanced combustion reactivity. Higher blending ratio of AD favors the increment of their ash fusion temperature, i.e., from 1109 to 1403 °C for deformation temperature due to the formation of high melting point minerals (i.e., Ca9Fe(PO4)7, 2CaO·Al2O3·SiO2). Significant in-situ reduction of NO and HCl as well as self-desulfurization is observed during the combustion of AD-SS blends. Compared to the theoretical values, the emission amount of HCl, NO, and SO2 is reduced by 0.13, 1.39, and 0.35 mg·g−1, respectively at 850 °C and blending ratio of AD to SS = 0.75:0.25. These phenomena are associated with the reducing environment and reducing substances by their high volatiles as well as the abundant minerals such as CaCO3 and Fe2O3 in AD and SS. However, high combustion temperature is unfavorable for chlorine fixation. This work provides a better understanding of their thermal behaviors, ash characteristics, and gaseous pollutants emission characteristics to realize their stable and clean incineration.

Numerical simulation of hydrogen co-firing distribution on combustion characteristics and NOx release in a 660 MW power plant boiler

The article discussed the influence on furnace temperature distributions, combustion characteristics, and NOx release when hydrogen, coal, and sludge co-firing in a 660 MW power plant boiler by CFD. Non-premixed combustion model was chosen as the gas combustion model. As the height of the hydrogen injection position rises, the temperature difference in the main combustion region decreases from 297.22 K to 94.72 K. The co-combustion of hydrogen inhibits solid fuels' combustion. As hydrogen nozzles' height decreases, the NOx mass at the furnace outlet increases from 98.41 % to 160.38 %. When the excess air coefficient changes from 1.15 to 1.35, the temperature in the main combustion region significantly increases, while the temperature in the upper furnace decreases, and the heat flux of the main combustion region increases by 11.10 %, the heat flux of the total furnace decreases by 1.39 %, the NOx mass at the furnace outlet increases by 31.67 %. The optimum co-combustion method is injecting the hydrogen from the top hydrogen nozzles and the excess air coefficient is 1.15, the overall impact on the furnace is minimal in this way. The fundamental reason hydrogen affects co-combustion is the fuel characteristics’ difference between hydrogen and solid fuels.

Experimental study on combustion characteristics of a 40 MW pulverized coal boiler based on a new low NOx burner with preheating function

In this study, a novel low NOx burner is proposed and tested on a 40 MW pilot pulverized coal combustion system, aiming to experimentally investigate the impact of preheating temperature, air ratio distribution, and thermal power on furnace combustion characteristics. The experimental results demonstrate that the pulverized coal could be preheated stably above 700 °C in the designed burner. Furthermore, an increase in preheating temperature from 500 °C to 750 °C corresponds to a proportional rise in the total volume fraction of combustible pyrolysis gases released from pulverized coal, ranging from 18.34 % to 22.85 %. Consequently, the release and combustion of pyrolysis gases effectively improve the combustion characteristics within the boiler furnace and lead to reduced NOx emissions at the furnace outlet. When the thermal power is increased from 22.5 MW to 37.5 MW, the NOx emissions at the furnace output range from 46.8 mg/Nm3 to 98.3 mg/Nm3 (at 9 % O2). Under a specific thermal power of 25MWth, the boiler furnace output NOx emissions are reduced to 47.9 mg/Nm3 (@9 % O2) without any additional NOx reduction equipment. These findings offer valuable insights for advancing cleaner and more efficient low-NOx pulverized coal combustion technology.

Simulation of the work of glass furnaces with the purpose of searching for reserves and increase their efficiency

The object of research is the operation of a glass furnace. The work involved modeling the operation of a glass furnace by changing the technical and economic indicators of its operation in order to optimize the technological processes of manufacturing glass products, increase the energy efficiency of the process, and reduce the ecological burden on the environment. Glass furnaces are complex heat engineering units that require a large amount of energy to operate. Therefore, increasing their effectiveness is the main task of our research. In the work, computer modeling of thermal processes in the furnace was carried out, heat balances were calculated and analyzed, and the performance of the furnace was analyzed after changing and improving the technological regimes of combustion processes, glass boiling and furnace construction. Studies have shown that in order to increase the technical and economic performance of glass furnaces, it is advisable to conduct additional thermal insulation of the furnace enclosures. The thermal insulation of the vault increases the efficiency of the furnace by 2–3 %, and the thermal insulation of the remaining areas of the furnace in total allows to increase the efficiency of the heating unit up to 3 %. Such measures improve the sanitary and technical working conditions of the staff in the machine-bath shop. Studies have shown that additional heating of the air used for burning fuel significantly increases the efficiency of the furnace. Thus, an increase in air temperature by 100 °C increases the efficiency of the furnace by approximately 2.5 %. However, such a measure is possible with a corresponding increase in the volume of regenerator nozzles. A significant increase in the efficiency of the furnace was achieved when additional electric heating was installed. This allows to reduce the total energy costs, and at the same time, the introduction of every 10 % of additional electric heating increases the efficiency of the furnace by up to 3 % and improves the quality of the glass mass. Such additional heating can be recommended in the amount of 20–30 % of the total heat consumption for the operation of the furnace. The analysis of the obtained results showed a fairly good convergence of the results, which indicates the acceptable adequacy of the models. The obtained process simulation results allow choosing the optimal design and operation parameters of the glass furnace. The results of the work can be used in practice for the design of efficient glass furnaces of various purposes and performance.

Numerical simulation of the effect of coaxial and cross-axis injection modes on pulverized coal combustion in the raceway of blast furnace tuyere

The aim of this study is to investigate the influence of the angle of the pulverized coal (PC) injection lance on the combustion characteristics of fuel in the raceway of blast furnace tuyeres. Using FLUENT software, a Euler-Lagrange three-dimensional numerical model was constructed to analyze the influence of different positions of blast furnace tuyere coal powder injection lance (coaxial and cross-axis) on key parameters such as temperature distribution, gas flow, and combustion efficiency. The results demonstrate that adjusting the angle of the injection lance significantly modifies the average and peak temperatures in the raceway, while the composition of gas components remains relatively stable. When the injection lance angle is 10°, the average temperature and peak temperature in the raceway are 2294 K and 2747 K, respectively. When the injection lance angle is 12°, the combustion efficiency of the PC reaches 80.8%. This study reveals the significant impact of the injection lance angle on the combustion process. Especially at an angle of 12°, the combustion efficiency of the blast furnace significantly improves. With coaxial injection, the combustion rate increases as the distance between the injection lance tip and the tuyere increases. This paper is instructive for the optimization of the blast furnace combustion system, which improve fuel utilization efficiency and reduce environmental emissions. This paper provides practical recommendations for adjusting blast furnace operational parameters, offering insights for achieving more efficient and environmentally friendly industrial production.

Nitrogen and Sulfur Oxides Emissions from Fuel Oil Combustion in Industrial Steel Reheat Furnace

Many industrial heating operations still use fueloil for combustion instead of the cleaner gaseous fuels. Inthe steel industry, large furnaces referred to as reheat furnaces are used to heat steel stocks to rolling temperaturesusing normally fuel oil for combustion. The combustionproducts of flue gases consist of mainly carbon dioxide,water vapor and traced of other oxides such as nitrogen andsulfur oxides. These oxides are of a concern to theenvironment and should be minimized as much as possible.Experiments were carried out on a steel billet reheatfurnace in which air/fuel ratios are varied while the nitrogenoxide content is being monitored using furnace instruments.These variations in air/fuel ratios for combustion are foundto affect the concentration of nitrogen oxides in the flue gaswhere higher air/fuel ratios promoted the formation ofhigher nitrogen oxides during combustion. The sulfurdioxide content in the flue gas was calculated based onactual measurements of air and fuel rates to the furnace andfound to be minimal in the flue gas.

Comparative analysis of combustion characteristics and economy between air assisted combustion and oxy-fuel combustion in glass furnaces

The oxy-fuel combustion is an effective means to improve the high energy consumption, pollution, and economic cost of glass furnaces. In this paper, the combustion characteristics in the flame spaces of traditional natural gas/air assisted combustion glass furnace (GF-NAC) and reformed natural gas/oxy-fuel combustion glass furnace (GF-NOC) are analyzed and compared by means of numerical calculation. More importantly, a systematic quantitative comparative analysis is conducted on the economic performance of the two glass furnaces from the perspectives of fixed and operating costs. The results show that enhanced combustion performance of GF-NOC over GF-NAC is found with flames being extended across the entire width of the furnace in GF-NOC. A more uniform temperature distribution within the furnace is consequently accomplished in GF-NOC. The flame center temperature, the average furnace temperature, and the average glass surface temperature in GF-NOC are increased by 7.42 %, 1.17 %, and 7.96 %, respectively, compared to GF-NAC. Furthermore, a reduction in gas velocity by 50 % at the arch in GF-NOC is observed to mitigate the erosive effects of high-temperature gas flows on the furnace crown. According to the service life of glass furnace of 15 years, the GF-NOC can save 420 M (million yuan) (12.8 %) compared to the GF-NAC. Although the fixed cost of GF-NOC is 9.82 M (5.43 %) higher than that of GF-NAC due to the expenditure on oxygen production equipment, the difference is offset by operating costs. Compared to GF-NAC, GF-NOC can save operating costs of 28.7 M (15.87 %) per year.

3D numerical study of NH3/H2 MILD combustion in a reversed flow MILD combustion furnace

Combustion of fuels to generate energy is essential for numerous residential and industrial human endeavors. In contrast to fossil fuels, the demand for carbon-free fuels such as ammonia and hydrogen to meet climate commitments is rapidly growing. This study conducts a numerical investigation of NH3/H2 MILD combustion. A three-dimensional CFD simulation model of a 90-degree sector of a reversed flow MILD combustion furnace is presented. The SAGE detailed chemical kinetics solver featuring the CEU-NH3 mechanism is employed with dynamic mechanism reduction for computational efficiency. The effects of varying the hydrogen mole fraction in the inlet fuel mixture from 0 to 50 % on the thermal characteristics, reaction zone, and emissions are investigated. The findings show that temperature homogeneity, assessed through temperature uniformity parameters and standard deviation, reveals a diminishing trend in temperature homogeneity with increased hydrogen concentration. The boundaries of the reaction zone are determined according to the NNH and N mole fractions, and both criteria are approximately identical. All the investigated cases match the MILD combustion definition; however, the cases with H2 concentrations ranging from 10 to 40 % fall under the MILD-like combustion regime. Emissions analysis shows that for all investigated cases, the ammonia slip emissions and the exhaust N2O emissions are below 1 and 0.5 ppm, respectively. The NOx emissions are found to increase abruptly with increasing hydrogen concentration from 0 to 35 % and subsequently undergo minor fluctuations.