Gas Combustion Research Articles

Automated process control in electric arc furnaces in the aspect of digital twin technology

An approach to managing the main modes of smelting steel in heavy-duty electric arc furnaces (EAF) using digital twin technology was defined and formulated. It was noted, that the existing power regulators do not have the function of balancing the effective power of phases and, accordingly, electric arcs because they are focused on working with a certain average value of the signal. It is proposed to use the analysis of dynamic characteristics based on instantaneous values of input parameters instead of operating ones, as it’s usually implemented in most devices. This allows us to obtain more accurate data on the arc state and reduce the amount of time and computing power required to obtain a result and form recommendations. Based on the data obtained as a result of long - term observations of the heavy-duty EAF-135 operation, the relationship of the constant component of the arc voltage (CCAV) with the metal oxidation is shown. An example of its use as a criterion for controlling the melting oxidative stage is given. This reduces the consumption of electrochemical sensors for each melting in the case of serial metal production. Based on the recorded data, it is possible to timely determine the unevenness of the arc power release between the furnace electrodes and issue recommendations on gas burners operation regulating to equalize the rate of scrap melting at electrodes with less power release. The authors propose the idea of using digital twins based on models of the active power distribution across the melting bath zones and dependence of metal oxidation on oxygen blowing for monitoring and controlling the electric mode and the oxygen blast mode at the oxidative stage of the melting process. Simplified schemes of these twins are given.

Hydrogen blending with natural gas for combustion efficiency improvement toward decarbonisation of power plants

Abstract The 12th Malaysia Plan highlighted Malaysia’s commitment to reduce Greenhouse Gas (GHG) emissions by 45% based on Gross Domestic Product (GDP) in 2030 and reach net zero by 2050. To achieve this target, Malaysia has to decarbonise the energy sector as it is the primary emission source, contributing up to 75% of GHG emissions in Malaysia. Hydrogen fuel is getting much attention globally, and it has been said that it can be a new renewable energy source to replace fossil fuels. Hydrogen combustion is clean and only produces water and energy. However, several studies have identified that hydrogen combustion could produce NOx, which is more harmful to the environment than CO2. Studies on hydrogen application in the energy sector in Malaysia are limited, and the implementation of total hydrogen fuel in power plants may not happen shortly. Hence, a fundamental study was proposed on co-firing hydrogen and natural gas fuel. This study aimed to examine co-firing characteristics such as temperature, pressure, and air-to-fuel ratio on GHG emission and energy release to find the optimum natural gas-to-hydrogen ratio. The model was developed using Aspen Plus, and hydrogen-natural gas blend percentages varied from 0% to 30%. The findings showed that increased operating temperature led to higher NOx formation, while varying pressures did not impact the CO2 and NOx formation. The pure natural gas combustion system was more sensitive towards air-to-fuel ratio changes, and an increase in air-to-fuel ratio to 1.5 led to 160% higher NOx formation due to an increase in nitrogen content. The combustion of the hydrogen blend led to lower CO2 formation but higher NOx formation. Lastly, the energy released by the hydrogen blending system was lower due to the formation of water that absorbed the heat released by the combustion.

Efficient natural gas combustion and NOx reduction: A novel application of simultaneous over-fire air (OFA) and flue gas recirculation (FGR) in a 250 MW opposed firing steam power plant boiler

OFAGR, as a new controllable technology, combines over-fire air (OFA) and flue gas recirculation (FGR) systems for modifying combustion characteristics and enhancing boiler efficiency. It also reduces NOx generation considerably. The effects of OFA and FGR on the combustion are reported for coal-fired boilers, however, no reference was found for the application of OFAGR, especially in boilers with natural gas fuel so far. Furthermore, the method of adjusting the ratio of OFA and FGR in OFAGR nozzles to achieve the required combustion modification is not investigated and this fact should be even covered for different types of boilers. For analysis of complicated combustive mixed fuel (natural gas) and air in furnace, computational fluid dynamics (CFD) simulated the flow by the use of Eddy-Dissipation Concept (EDC) and developing reactions by Jones-Lindstedt mechanism. Simulation results are validated by the measured boiler operation data for a 250 MW steam power plant boiler. The staged combustion in each burner is modeled by considering three inlet air flows (primary, secondary, and tertiary) with swirl. The effects of different ratios of OFA and FGR streams on characteristics of combustion and NOx production are investigated. The combustion efficiency, temperature profile, distribution of species, and the transferred heat flux to water-walls are computed, and analyzed. Results showed injecting only OFA from OFAGR nozzles, reduced NOx generation up to 55.4 % but lowered the furnace efficiency from 95.3 % to 93.1 %. When the OFAGR stream contained 25 % FGR and 75 % OFA (case study 2), an ideal state existed for increasing the combustion efficiency from 95.3 % to 96.0 % and NOx reduction by 58 %. Increasing the share of FGR in the OFAGR stream by more than 25 % improved the NOx reduction but reduced the combustion efficiency from 95.3 % due to the drop in the usable absorption heat of the boiler. Calculations showed that the OFAGR injection stream containing 64.1 % OFA and 35.9 % FGR reduced NOx formation from 274 to 112 ppm without losing furnace efficiency.

A New Air-Assisted Flare Tip Design for Managing Gas Flare Emissions (CFD Analysis)

Recently, flares have been considered as a major source of air pollution from the petroleum refining industry. The United Nations has instigated an international effort related to the management of flare emissions to reduce the global warming impact related to flaring. Eliminating or removing the need for gas flares is difficult because these devices are generally used as safety devices to allow the combustion of flammable gases in a controlled fashion which supports safe operation. However, reducing flaring is generally possible using well-designed, efficiently operated flare equipment. In general, flare performance can be enhanced following the API-521 methodology and using assist-media including air and steam to achieve smokeless operation. This present work will discuss flare emissions in the petroleum refining industry and a method to manage flare emissions. Moreover, this work will discuss flare combustion efficiency (CE) and destruction and removal efficiency (DRE) in terms of efficient flare operation. This work uses actual operating flare data, published previously, which will be used in this work together with the CFD Code C3d. This code, developed at the USDOE Sandia National Laboratory, is based on a standard LES methodology to conduct transient flare analysis and is used to simulate flare operation to estimate flame shape and emissions produced. In this work, a new air-assisted flare tip design which uses the Coanda effect to improve flare operation was analyzed. This new flare design reduces the emission rate and demonstrates the design’s effectiveness. The analysis considers a flare 39″ high and 6″ diameter in the center of a 4m x 4m x 4m domain. Boundary conditions assume no cross wind and an ambient temperature of 300 K. The initial condition is a hydrostatic pressure profile across the computational domain. In the air-assist simulation, stoichiometric ratio will be a variable, and therefore, more than one case was considered.

Effects of space-confined ratio on the MILD combustion of coke oven gas

The objective of this study is to investigate the effects of the spatial structure on MILD combustion characteristics of coke oven gas via numerical simulation. The space-confined ratio, defined as the ratio of the furnace height to the longest diagonal of the transverse section, is used to characterize the variation in spatial structure. An experimental study in a long-narrow confined furnace (LNCF) was initially conducted to investigate the conditions for achieving MILD combustion. Subsequently, the effects of spatial structure on MILD combustion characteristics were thoroughly investigated through numerical simulation by altering the space-confined ratio of the LNCF. The experimental results show that the transition from conventional combustion to MILD combustion is achieved at a dilution rate of 50 %, which improves the temperature uniformity and reduces the NO emission by 96.5 % to 3 ppm. The numerical results show that reducing the space-confined ratio enhances the flue gas internal recirculation and the temperature uniformity, especially the maximum temperature is significantly reduced. Moreover, reducing the space-confined ratio achieves nearly zero NO emissions, but an excessively space-confined ratio may result in incomplete combustion, consequently causing a significant rise in CO emissions. To guarantee complete combustion, the optimal furnace structure is achieved at a space-confined ratio of 6.4, ensuring not only temperature uniformity but also ultra-low emissions of NO and CO. Therefore, this study provides a theoretical and practical foundation for the ultra-low emission of pollutants in space-confined combustion systems.

Investigation of the heating characteristics of turbulent non-premixed gas combustion in the industrial-scale walking beam type reheating furnace

Oxygen-enriched combustion is widely used in industrial furnaces. To elucidate the multi-physics properties of reheating process, this study numerically explores the flow and combustion characteristics of syngas oxygen enrichment combustion in an industrial-scale walking beam type reheating furnace. The findings demonstrate that gas flow patterns at the furnace inlet primarily encompass the billet periphery, enhancing heat transfer efficiency. Oxygen-enriched combustion achieves lower temperature differences, higher heating temperature and CO2 emissions. Additionally, increasing levels of oxygen enrichment correlates with elevated temperatures, though the increments diminish progressively. Specifically, temperatures at the outlet of the preheating section range from 1100 K to 1200 K, with the middle region of the heating section displaying slightly lower temperatures compared to the areas adjacent to the burner. High temperature zones are primarily concentrated around the burners in soaking and heating sections. In terms of heating temperature and thermal uniformity, 30 % oxygen-enriched condition yields superior performance, evidenced by higher heating temperatures and reduced temperature differentials. Moreover, oxygen-enriched combustion enlarges CO2 emissions, with a 124.5 % enhancement observed. The lowest NO emission content at the outlet occurs during combustion with 21 vol% air and 45 vol% oxygen enrichment, however, these values remain relatively high. The insights derived from this study provide a foundational framework and guiding principles for furnace design and optimization of multi-gradient oxy-enriched combustion.

Numerical simulation and optimization of gas premixing structures for tail gas incinerators

It is a common practice for chemical refinery tail gases to be treated in an incinerator and then released into the atmosphere. However, tail gas combustion is a key component in ensuring that the treatment process meets the relevant standards. In this paper, a vertical tail gas incinerator gas premixing structure design is proposed, aiming to improve the gas mixing effect. Based on the basic structure of the right-hand gas distribution pipe and the single-layer fan mixer at the throat, three new structures are proposed. The five new gas-premixing structures were combined into eight new structures. A series of numerical simulations were performed for one prototype premixed structure and five new premixed structures, respectively. The gas premixing structures were screened, evaluated, and optimized using gas mixing inhomogeneity and pressure loss as control parameters. Finally, the premixing structure with the best combination for the mixing unit was selected. This study is of great significance for improving the effectiveness of tail gas incineration in chemical refineries and protecting the ecological environment.

Industrial Decarbonization through Blended Combustion of Natural Gas and Hydrogen

The transition to cleaner energy sources, particularly in hard-to-abate industrial sectors, often requires the gradual integration of new technologies. Hydrogen, crucial for decarbonization, is explored as a fuel in blended combustions. Blending or replacing fuels impacts combustion stability and heat transfer rates due to differing densities. An extensive literature review examines blended combustion, focusing on hydrogen/methane mixtures. While industrial burners claim to accommodate up to 20% hydrogen, theoretical support is lacking. A novel thermodynamic analysis methodology is introduced, evaluating methane/hydrogen combustion using the Wobbe index. The findings highlight practical limitations beyond 25% hydrogen volume, necessitating a shift to “totally hydrogen” combustion. Blended combustion can be proposed as a medium-term strategy, acknowledging hydrogen’s limited penetration. Higher percentages require burner and infrastructure redesign.

Energy production from landfill gas, emissions and pollution indicators–Opportunities and barriers to implementing circular economy

The goal of this research was to test the air emissions resulting from landfill gas combustion in a 250-kW cogeneration unit, in the context of pollutant emission due to the produced electricity. The test results mainly revealed emissions of carbon dioxide, sulfur dioxide, nitrogen oxides, carbon oxides, and dust. The volume of emissions of individual pollutants was compared with the emission values reported from the emission balancing database. The highest emission burdens concerned the production of one MWh of electricity for carbon dioxide 579.80 kgCO2∙MWh−1, carbon monoxide 2.57 kgCO2∙MWh−1, and nitrogen oxides 1.77 kgNOx∙MWh−1. It is worth noting that small cogeneration installations are not covered by emission standards and so they are not equipped with a device for reducing gaseous and particulate pollution. The tests revealed a difference between the actual emissions from the tested installation and the values reported to the national database. The innovation of this study is that it demonstrates the real emission burden of renewable energy in the context of sustainable development. The results can be used as input material for discussion to apply gaseous and particulate pollution reduction systems for cogeneration installations powered by landfill gas, including various types of biogases.

Experimental Investigation of Sulfur and Nitrogen Oxide Emissions and Corrosion Propensity During the Combustion of Coals and Biomass Fuels

ABSTRACT The increasing use of biomass in Indonesian coal-fired power plants, mainly through co-firing, presents challenges due to different fuel characteristics, which can affect gas emissions, ash deposition, and combustion efficiency. This study assesses flue gas emissions (SO2 and NOx) and corrosion tendencies of various biomass types and coal. The study begins with characteristic testing and ash analysis of coal and biomass samples, including proximate, ultimate, and calorific value analyses, to determine their suitability as fuels. Preliminary calculations predict flue gas emissions and ash deposit formation, followed by laboratory-scale combustion experiments using a DTF to assess flue gas and ash deposit characteristics. The results show that sulfur in biomass is converted to the gas phase up to 99%, while in coal, it is converted up to 95% at high temperatures. NOx levels are primarily affected by the nitrogen contents of the fuels; for instance, Coal-B at 0.88 wt% produces less NOx than solid recovered fuel (SRF) and refused derived fuel (RDF) with 1.73 wt% and 1.51 wt%, respectively, yet still generates higher emissions than the other three biomass types. In general, wood chips (WC), rise husk (RH), and palm kernel shell (PKS) emit 30–80% less flue gas compared to coal. However, ash deposition results indicate that PKS, SRF, and RDF exhibit corrosion tendencies due to the dominance of albite (NaAlSi3O8) in the mineral phase. Additionally, the high chlorine content in SRF (0.544 wt%) and RDF (0.224 wt%) leads to the formation of sticky ash deposits, which potentially impact heat transfer surfaces. These findings contribute to identifying suitable biomass types for both co-firing or dedicated combustion in coal-fired power plants.

Distributed Regime and Swirler Effects on Methane and Coke Oven Gas Combustion Characteristics

Distributed Regime and Swirler Effects on Methane and Coke Oven Gas Combustion Characteristics

Investigating the Impact of Steam Enhancement on Combustion in a Swirl-Assisted Jet-Stabilized Gas Turbine Combustor

Abstract A newly developed gas turbine combustor system based on the swirl-assisted jet-stabilized concept using Jet A-1 and natural gas as reference fuel is tested under wet conditions to evaluate its combustion characteristics in the presence of steam. The effect of steam injection into the gas turbine combustor under both spray and superheated liquid fuel injection conditions is studied experimentally on an atmospheric test rig. To evaluate the effect of steam injection on combustion performance, the water-to-gas ratio (WGR) is varied from 0 to 32%. With increasing WGR = 0 to 16% and at stoichiometric condition, NOx reductions of -82% to -100% were observed during Jet A-1 and natural gas combustion, respectively. It is shown that the reduction of the combustion zone temperature due to the steam acting as a heat sink is the main cause of the NOx decrease. The operating range of the burner remained fairly constant for Jet A-1 until WGR = 20%, while it decreased significantly with increasing WGR for natural gas combustion. While the effect of the WGR on CO was modest, the greatest effect of the WGR was on the heat release zone intensity at a constant air to fuel ratio. In reducing the NOx levels of Jet A-1 and natural gas combustion, both thermal and chemical effects of steam injection were observed. However, steam acting as a heat sink and lowering the flame temperature, thereby reducing the thermal NO formation rate, was the dominant factor in NOx reduction.

Fine particulate matter from burning oil and gas and neurological symptoms among oil spill cleanup workers

Fine particulate matter from burning oil and gas and neurological symptoms among oil spill cleanup workers

A comprehensive investigation on flame flickering characteristics of premixed conical flame at different inclination angles

To thoroughly investigate how the inclination angle affects the flickering of premixed conical flames, a series of experiments and simulations were carried out. Propane-air conical flames were established on a Bunsen burner, and various inclination angles were tested, resulting in a wide range of flame flickering frequency data. The findings revealed that the further the inclination angle deviates from 0°, the lower the flickering frequency. Consequently, an empirical correlation that factors in the inclination angle was developed. To gain a more comprehensive understanding of the flame flickering behavior under different gas inclination angles, researchers utilized Particle Image Velocimetry (PIV) and numerical simulation to visualize the velocity fields of a typical flame. The results demonstrated that deviated inclination angles not only alter the shear strength between the burnt gas and surrounding gas but also significantly change the flame flickering mode. These factors lead to various Kelvin-Helmholtz instability patterns and vortex shedding modes, ultimately impacting flickering frequency.

Experimental Study of Natural Gas and Hydrogen Co-Firing Characteristics Using Different Types of Single Nozzles of F-Class Practical Gas Turbine Combustors

Abstract Recent research on co-firing natural gas and hydrogen, a carbon-free clean fuel, aims to reduce greenhouse gas emissions from aging gas turbine power generation, a key energy issue. This approach can enhance old gas turbines and increase the proportion of combined cycle power plant utilization as coal-fired power plants in Korea gradually shut down. This study seeks optimal operating conditions for mixed fuels without modifying the F-class gas turbine combustor. Experiments were conducted using four different types of fuel nozzles (F-Class DLN combustors) under varying loads and co-firing rates. The test used actual machine operating conditions from 30% to 100% thermal load, with hydrogen co-fired with natural gas up to 70% at each load. OH high-speed imaging and an OH-PLIF technique analyzed flame structure and characteristics. Dynamic pressure was measured to check combustion instability, and exhaust gas emissions were evaluated for combustion characteristics. Key findings include critical co-firing rates for each nozzle based on NOx emission levels and combustion dynamics. As the hydrogen co-firing rate increased, flame length decreased, and NOx levels rose rapidly beyond 30%vol. Dynamic pressure oscillations showed no significant variations compared to natural gas combustion. This study successfully derived a characteristic operation map for a single nozzle based on the hydrogen co-firing rate.

Boosting the photocatalytic performance of swiftly produced carbon nitride: Impact of cyano group and oxygen doping within the matrix

We present a significant advancement in the synthesis of carbon nitride framework (CN) using a rapid electric bunsen burner (EBB) method, achieving notable outcomes within a mere 10-min timeframe. The resulting material, designated as U10, exhibits amplified porosity and a semi-scrolling structure with a thickness measuring at 2.1 nm. In comparison to conventionally synthesized urea-derived carbon nitride (UCN) through a box furnace, the U10 demonstrates significantly heightened photocatalytic activity in both hydrogen (H2) production and the removal of organic dye (methylene blue) from aqueous solutions. To ensure the robustness and reliability of this synthetic approach, two additional precursors were subjected to testing, and their rates of H2 production were analyzed. The exceptional photocatalytic performance of the U10 material arises from its distinctive structural attributes and the synergistic influences of oxygen doping (O-doping) and the cyano (-CΞN) functional group, which are introduced during the rapid synthesis strategy. This innovative and streamlined strategy for synthesizing CN not only conserves energy and time but also significantly reduces production costs, rendering it a feasible method for the large-scale production of carbon nitride material.

Important contributions of natural gas combustion to atmospheric nitrate aerosols in China: Insights from stable nitrogen isotopes

Important contributions of natural gas combustion to atmospheric nitrate aerosols in China: Insights from stable nitrogen isotopes

Numerical Study on Optimization of Combustion Cycle Parameters and Exhaust Gas Emissions in Marine Dual-Fuel Engines by Adjusting Ammonia Injection Phases

Decarbonizing maritime transport hinges on transitioning oil-fueled ships (98.4% of the fleet) to renewable and low-carbon fuel types. This shift is crucial for meeting the greenhouse gas (GHG) reduction targets set by the IMO and the EU, with the aim of achieving climate neutrality by 2050. Ammonia, which does not contain carbon atoms that generate CO2, is considered one of the effective solutions for decarbonization in the medium and long term. However, the concurrent increase in nitrogen oxide (NOx) emissions during the ammonia combustion cycle, subject to strict regulation by the MARPOL 73/78 convention, necessitates implementing solutions to reduce them through optimizing the combustion cycle. This publication presents a numerical study on the optimization of diesel and ammonia injection phases in a ship’s medium-speed engine, Wartsila 6L46. The study investigates the exhaust gas emissions and combustion cycle parameters through a high-pressure injection strategy. At an identified 7° CAD injection phase distance between diesel and ammonia, along with an optimal dual-fuel start of injection 10° CAD before TDC, a reduction of 47% in greenhouse gas emissions (GHG = CO2 + CH4 + N2O) was achieved compared to the diesel combustion cycle. This result aligns with the GHG reduction target set by both the IMO and the EU for 2030. Additionally, during the investigation of the thermodynamic combustion characteristics of the cycle, a comparative reduction in NOx of 4.6% was realized. This reduction is linked to the DeNOx process, where the decrease in NOx is offset by an increase in N2O. However, the optimized ammonia combustion cycle results in significant emissions of unburnt NH3, reaching 1.5 g/kWh. In summary, optimizing the combustion cycle of dual ammonia and diesel fuel is essential for achieving efficient and reliable engine performance. Balancing combustion efficiency with emission levels of greenhouse gases, unburned NH3, and NOx is crucial. For the Wartsila 6L46 marine diesel engine, the recommended injection phasing is A710/D717, with a 7° CAD between injection phases.

Numerical Investigation and Simulation of Hydrogen Blending into Natural Gas Combustion

Numerical Investigation and Simulation of Hydrogen Blending into Natural Gas Combustion

Study on radiation heat transfer characteristics of aeroengine combustion chamber

The thermal radiation of gaseous combustion products in an aero-engine combustion chamber has obvious non-ash-body characteristics. In this paper, based on the OpenFOAM platform, a numerical study on multi-field coupled turbulence-combustion-radiation radiative heat transfer was carried out for a certain type of aero-engine combustion chamber using the mean weighted sum of grey gas (WSGG) gas radiation model, which can accurately describe the non-ash characteristics of the gas. The results show that the radiation heat transfer characteristics are influenced by several factors such as equivalent ratio, combustion pressure and wall emissivity, among which the equivalent ratio is dominant. Increasing the equivalence ratio from 0.11 to 0.4 resulted in a 189% increase in average incident radiation at the combustion chamber wall and a 233% increase in average incident radiation at the exit. Increasing the equivalent ratio, combustion pressure or wall emissivity will increase the average radiation intensity in the combustion chamber and the inhomogeneity of radiation distribution at the exit of the combustion chamber. The radial radiation distribution factor (RRDF) also increases with the increase of equivalent ratio, combustion pressure and wall emissivity.