Oxygen-enriched Combustion Research Articles

Lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched premixed combustion mode

Compared with pure NH3 fuel, the lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched combustion mode have been identified quantitatively. Furthermore, the effects of the H2 addition on the NO productions of premixed oxygen-enriched NH3–H2 flames are studied numerically, while the major reactions responsible for the variation of total NO are identified. Results show that the H2 addition is eligible to reduce the NO emissions of the oxygen-enriched NH3 combustion if the laminar burning velocity is fixed to a larger value (>23 cm/s). The quantitative equations are obtained to determine the optimum oxygen-enriched conditions of the NH3–H2 mixture, aiming to achieve lower NO emission and similar or improved combustion stability compared to pure NH3 fuel by restricting the minimum and maximum O2 percentages for the NH3–H2 mixtures. Based on the rate of production (ROP) analysis, for the oxygen-enriched NH3–H2 combustion, R144 (HNO + H<=>H2+NO) is consistently the most significant NO production reaction, while R85 (NH + NO<=>N2O + H) and R91 (N + NO<=>O + N2) play significant roles in the NO consumption. When the laminar burning velocity (SL) is kept to a lower value, the increased total NO of the oxygen-enriched NH3 flames with the H2 addition is ascribed to more efficient suppressions on the NO consumption reactions of R85, R91 and R77 (NH2+NO<=>NNH + OH). In contrast, thanks to the extra impact of the higher O2 percentage on the H/O/OH radical pool at larger SL, the NO production reactions begin to suffer stronger suppressions of the H2 addition, resulting in the reduced total NO of NH3–H2 mixtures. Furthermore, R144 is identified as the key reaction influencing the variation trend of total NO at both lower and higher SL values.

Study on Oxygen-Enriched Combustion Characteristics of Blast Furnace Gas Boiler

ABSTRACT To study the dynamic characteristics of OEC (oxygen-enriched combustion) in a BFG (blast furnace gas) boiler, the BFG boiler of an iron and steel enterprise is taken as the research object, and a thermal test bed for OEC of BFG is set up, and a thermodynamic simulation model of the BFG boiler is constructed based on the heat loss of chemical incomplete combustion obtained from thermal test, using MSP (Multi-Subject Simulation Platform). The effects of OC (oxygen concentration) and the position of oxygen entering the furnace chamber on the key parameters of the OEC process of the BFG boiler under different working conditions were analyzed. The results showed that the excess air coefficient of 1.2 and exhaust temperature of 120°C was kept constant during the thermal test. With a fuel volume of 2.4 Nm3/h, for example, after the OC was increased from 21% to 40%, the combustion flame temperature in the furnace was increased by about 34°C, the heat loss due to unburned gas was reduced by 0.21%, and the boiler efficiency was increased by 1.38%. In the dynamic model, at the instant when the OC is changed, the disturbance of the whole system is relatively large, and the FAT (furnace average temperature) outlet, the pressure of the steam ladle, and the MST (main steam temperature) will have a step change, and then gradually level off again. With the increase of OC, the combustion reaction is more and more intense, the steam side of the heat transfer process is strengthened, the boiler efficiency is improved, and the FAT chamber outlet, the steam ladle pressure and the MST after OEC in different ways of oxygen entry into the furnace chamber will be longer and longer to reach a stable value. The results of the study can provide a reference for the OEC operation of BFG boilers.

Experimental and numerical study on the combustion characteristic of H2 and CH4 in oxygen-enriched environment

Oxygen-enriched combustion could rise the hazard of unexpected fire and explosion in industry. This study experimentally and numerically analyzed the combustion characteristic of H2 and CH4 in oxygen-enriched environment (Ω = 21%–100 %). For H2 at Φ = 1 and Ω = 100 %, the maximum explosion pressure and maximum pressure rise rate were about 3.89 MPa and 1259.2 MPa/s. For CH4, these values were about 4.77 MPa and 6279.4 MPa/s. The upper flammability limit of gases increased sharply with the increase of Ω, however, the lower flammability limit was almost unchanged. Besides, the increasing of Ω also could result in the rising of aforementioned combustion parameters. The sensitivity of burning velocity was also analyzed. For H2 flame at Φ = 0.8, R35 could slow down burning velocity when Ω = 21 %, but promote it when Ω = 30 % and 70 %. For CH4 flame at Φ = 1.4, the sensitivity coefficients of R11, R35, R43 and R84 changed from negative to positive when Ω increased from 21 % - 30 %–70 % - 100 %. It was concluded that the oxygen concentration not only affect the inert gas but also affect the reaction kinetic of flame.

Optimal allocation method of oxygen enriched combustion-carbon capture low-carbon integrated energy system considering uncertainty of carbon-source-load

In the context of green grid, it is crucial to enhance the low-carbon transformation of integrated energy systems. To improve the degree of low-carbon in these systems, this paper proposes an optimal allocation method of oxygen enriched combustion-carbon capture low-carbon integrated energy system considering the uncertainty of carbon-source-load. Firstly, this paper provides an analysis of uncertainties of carbon-source-load and uses budget uncertainty sets to model the three uncertain parameters. Secondly, in the integrated energy system, the by-product O2 of hydrogen production by electrocution and the oxygen storage device are used to provide oxygen-enriched combustion conditions for the gas turbine to reduce the CO2 generated in the combustion process. At the same time, the carbon capture device is used to collect CO2, and the oxygen enriched combustion-carbon capture integrated energy system is formed. Finally, an improved multi-populations quantum-behaved particle swarm optimization algorithm is proposed to solve the proposed model. This method considers the uncertainty of carbon emission intensity, which makes the optimal allocation of integrated energy system more inclined to low-carbon rather than economic. In addition, in terms of model structure, this method integrates oxygen enriched combustion-carbon capture into the integrated energy system to form a low-carbon model, which directly improves the low-carbon performance of the system. The simulation results show that the carbon emission of the proposed method is reduced by 38.8 % compared with other methods.

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.

A device for dynamic testing of the refractory ceramic resistance to biomass ash

The corrosive effects of biomass ash on refractory materials in combustion chambers pose challenges. Development of new castable refractory materials which are more resistant to corrosion requires tests that accurately reflect the conditions occurring in real devices. This article describes the Computational Fluid Dynamics (CFD) design and construction of a device for evaluating the corrosion of refractory materials in dynamic regime. The device allows to simulate combustion chamber conditions accurately, to regulate an injection of corrosive medium on the tested material surface under the specified conditions (temperature, time, and flow). In the present investigation the conventional refractory material was exposed to attack of biomass ash at the temperature of 1300 °C for 3 h to test the functionality of the device. A burner with technology oxygen–enriched combustion was used to heat the device. The corrosion tests were conducted in accordance with the standard P CEN/TS 15,418 and the standard STN EN ISO 21404. The operational state required for corrosion tests at 1300 °C was achieved within 1.12 h. The extent of refractory material degradation in the dynamic corrosion regime was evaluated using electron microscopy-energy dispersive spectroscopy (EM-EDS) and compared with the results of a static crucible test (3 h at 1300 °C). The dynamic test provided sufficient information on the interactions of corrosion medium with the refractories. Its main advantages are the maintenance of non-equilibrium conditions by controlled deposition of the corrosion medium in quantity from 1 to −100 g/h, fast heating rate to operating temperature (20 °C/min), and the possibility of conditions variability during tests (temperature, ox-red. atmosphere, fuel gas flow etc.).

Low-Carbon Economic Dispatch of Virtual Power Plants Considering the Combined Operation of Oxygen-Enriched Combustion and Power-to-Ammonia

In order to achieve sustainable development, China has proposed to “strive to peak carbon dioxide emissions by 2030 and strive to achieve carbon neutrality by 2060”. Virtual power plants (VPPs) are an effective means to achieve carbon neutrality goals. In order to improve the economy and low-carbon performance of virtual power plants, this paper proposes a low-carbon economic optimization dispatching model considering the combined operation of oxygen-enriched combustion (OEC) and electricity-to-ammonia (P2A). Firstly, the mechanism of the combined operation of OEC and P2A is proposed. The oxygen-enriched combustion technology can reduce the carbon emissions of the system and enhance the flexibility of the system operation; P2A can effectively consume renewable energy and improve the energy utilization rate. The by-product of the P2A process, oxygen, is the raw material needed for oxygen-enriched combustion, which reflects the complementary nature of the OEC and P2A.Then, an optimal dispatching model is established with the objective function of minimizing the total cost. Finally, the validity of the proposed model is verified by comparing and analyzing the simulation results of five different models. After the introduction of the combined operation of OEC and P2A, the total cost of the system decreases by 10.95%, and the carbon emission decreases by 34.79%.

A co-doped strategy for simultaneously improving oxygen permeability and stability of BaCoO3-δ ceramic membrane

Perovskite-type oxygen transport membrane (OTM) has considerable potential in the application of oxygen-enriched combustion, which can prepare low-cost, low-energy, and high-purity oxygen. BaCoO3-δ-based OTM, as a promising candidate, possesses high oxygen permeability, but poor stability limits its application. In this study, the strategy of Y3+ and W6+ co-doping BaCo0·8Y0.2-xWxO3-δ (BCYW-x) was proposed firstly to control the trade-off effect between oxygen permeability and stability by considering the radius and valence of ions. Y3+ and W6+ co-doping stabilize the perovskite cubic structure to room temperature of the BCYW-x, and the average bond energy of metal-oxygen increases with W6+ doping, enhancing the structure stability. Although oxygen vacancy concentration and critical radius decrease, the migration of oxygen ions is accelerated with the increase of W6+ content at high temperatures. The BCYW-0.1 shows the exceptional oxygen permeation flux of 1.90 mL･cm−2･min−1 at 900 °C and stably operates at 900 °C and 800 °C. Furthermore, the kinetic model calculation indicates that the permeation resistance decreases because of the acceleration of the oxygen surface exchange reaction as W6+ doping, contributing to the oxygen permeation process. This study provides a feasible and effective co-doping strategy to improve the oxygen permeability and stability of perovskite OTMs simultaneously.

Multiplicative effects of co-incineration of sewage sludge and wasted oyster shells in air, CO2, and steam atmospheres on P speciation and bioavailability and metal ecotoxicity

The study was aimed at the reutilization of oyster shells (OS) as a calcium-based additive to turn sewage sludge ash into phosphate fertilizer, employing the oxygen-enriched combustion technology. This process transformed all non-apatite inorganic phosphorus into apatite phosphorus with the incorporation of a 7.5% Ca-based additive. OS demonstrated comparable effectiveness to CaO in catalyzing this transformation in the oxygen-steam atmosphere. The amount of OS added and the atmosphere type significantly influenced the P bioavailability of sewage sludge ash. The oxygen-steam atmosphere, with its increased water vapor concentration, facilitated the decomposition of CaCO3 and initiated reactions with calcium phosphate to form hydroxyapatite, thus substantially enhancing P bioavailability. The oxygen-steam atmosphere increased not only metal volatilization but also the ecological toxicity of residual metals, particularly Pb, mainly in the form of F2. Excessive OS addition appeared to elevate the toxicity of Cr. Therefore, additional strategies for metal removal or passivation are needed to improve the safety of sewage sludge ash with high metal content.

NOx emissions during oxygen-enriched combustion of sewage sludge and corresponding hydrochar

This study proposed an oxygen-enriched combustion technology for the resource utilization of hydrochar prepared from sewage sludge (SS) through hydrothermal carbonization (HTC). However, its application potential relies heavily on NOx emissions. To investigate NOx emissions during oxygen-enriched combustion of hydrochars prepared at different temperatures (200 °C, 240 °C, and 280 °C), real-time NOx concentrations were recorded under varying conditions, including different carrier gases (N2 and CO2), temperatures (600 °C, 800 °C, and 1000 °C), and oxygen concentrations (20 %, 30 %, and 40 %). In comparison to air combustion processes, the NOx emissions during the devolatilization stage were considerably depressed in oxygen-enriched combustion. A high concentration of CO2 inhibited NH3 production and HCN oxidation, and generated increased amounts of CO to facilitate NOx reduction. Elevated temperatures also reduced the NOx release during the oxygen-enriched combustion of SS and hydrochar, as the accelerated oxygen consumption weakened the oxidation reactions of HCN and NH3; the enhanced reduction reaction rate and increased CO production also promoted NOx reduction. Elevated oxygen concentrations, however, promoted NOx release owing to the increased NH3 and HCN oxidation by an increased number of oxidizing groups. Additionally, the reduction of reducing gases and rapid char combustion hindered NOx reduction. The NOx-N conversion of the hydrochars was much lower than that of SS under different conditions. HTC effectively reduced the nitrogen content of SS, with nitrogen in HC-280 existing as stable heterocyclic -N. HC-280 showed significantly less nitrogen conversion at low temperatures (9.03 % reduction at 600 °C) and high oxygen concentrations (2.01 % reduction at 40 % O2) compared to SS, highlighting the potential of combining HTC and oxygen-enriched combustion.

Coupled Oxygen-Enriched Combustion in Cement Industry CO2 Capture System: Process Modeling and Exergy Analysis

The cement industry is regarded as one of the primary producers of world carbon emissions; hence, lowering its carbon emissions is vital for fostering the development of a low-carbon economy. Carbon capture, utilization, and storage (CCUS) technologies play significant roles in sectors dominated by fossil energy. This study aimed to address issues such as high exhaust gas volume, low CO2 concentration, high pollutant content, and difficulty in carbon capture during cement production by combining traditional cement production processes with cryogenic air separation technology and CO2 purification and compression technology. Aspen Plus® was used to create the production model in its entirety, and a sensitivity analysis was conducted on pertinent production parameters. The findings demonstrate that linking the oxygen-enriched combustion process with the cement manufacturing process may decrease the exhaust gas flow by 54.62%, raise the CO2 mass fraction to 94.83%, cut coal usage by 30%, and considerably enhance energy utilization efficiency. An exergy analysis showed that the exergy efficiency of the complete kiln system was risen by 17.56% compared to typical manufacturing procedures. However, the cryogenic air separation system had a relatively low exergy efficiency in the subsidiary subsystems, while the clinker cooling system and flue gas circulation system suffered significant exergy efficiency losses. The rotary kiln system, which is the main source of the exergy losses, also had low exergy efficiency in the traditional production process.

Experimental and numerical investigation of methane combustion in a HCCI engine under enriched oxygen conditions

The challenge in the energy transition lies in the intermittent nature of renewable energy, requiring the development of effective storage methods. E-fuels are considered a promising solution, with potential applications to Homogeneous Charge Compression Ignition (HCCI) engines known for their high thermal efficiency and low nitrogen oxide emissions. However, HCCI engines face limitations such as low power density and a narrow operating range. To overcome these issues, oxygen-enriched combustion is proposed, aiming at enhancing the mixture reactivity and expanding the operating range by decreasing the intake temperature. As the potential of the expansion of the operating range has never been investigated, we performed an experimental campaign using a methane-fuelled HCCI engine at variable oxygen fractions in the oxidizer. To further elucidate the effects of oxy-fuel combustion, we also performed a kinetic analysis of the reactions driving the combustion behaviour. It has been experimentally found that increasing the oxygen content in the mixture, up to 90%, has a significant potential to decrease the needed intake temperature (up to 70 °C) of the charge to keep the Maximum Pressure Rise Rate (MPRR) below the safety threshold of 8 bar/CAD. Despite the notable IMEP increase achieved, operating the engine at high oxygen content presents significant technical challenges. Therefore, to make HCCI engines competitive with other combustion modes, it is essential to combine oxygen enrichment with additional power density enhancement techniques. The kinetic analysis has highlighted that the mixture is less sensitive to intake temperature changes at higher oxygen percentages (above 50%) and that the rates of the main reactions involved in methane and OH consumption are highly enhanced by oxygen addition.

Numerical simulation of oxygen-enriched combustion in a precalciner using coal gangue-blended pulverized fuel

This study emphasizes the potential role of coal gangue as an alternative fuel and oxygen-enriched combustion technology within TTF precalciners(Twin-Tank Furnace) in mitigating carbon emissions from cement production. The research primarily unfolds in two segments. Initially, the investigation addresses the influence of blending varying proportions of coal gangue under an air atmosphere on the internal temperature field and raw material decomposition components within the precalciner, aiming to discern the optimal blending ratio. Subsequently, the study simulates combustion under different oxygen-enriched atmospheres at the ideal coal-gangue blending ratio, establishing the combustion patterns under these conditions. Although the mixed fuel prompts symmetry in the flow field and temperature field, the distinct combustion characteristics of coal gangue and coal powder-following a 20% coal gangue blend-lead to an accelerated mainstream velocity and abbreviated fuel residence time. Consequently, the exit temperature and CO2 concentration diminish with increasing blending content, reaching an optimal raw material decomposition rate of 91.12% within the precalciner when blended with 20% coal gangue. Furthermore, in oxygen-enriched combustion, as the oxygen content escalates, both the average temperature at the precalciner's exit and the raw material decomposition rate witness an upsurge, whereas the average CO2 concentration at the outlet experiences a decline.

REDUCING THE СО2 ATMOSPHERIC EMISSION BY NATURAL GAS “OXY-FUEL COMBUSTION”, AS A MEANS OF PREVENTION THE GREENHOUSE IMPACT

At present, the relation to the fuel-energy complex as the main source of climatic changes of a planetary scale (global warming) has been formed. In view of the corresponding forecasts related to the greenhouse effect, mostly associated with emissions of carbon-containing combustion products (carbonization of the environment), the following ways of countering the climate threat are considered the last time: a — rejection of use of the organic fuel with a gradual transfer to using (burning) of carbon-free fuels (primarily hydrogen and hydrogen-containing mixtures); b — increasing an efficiency of use the organic fuel, first of all is the natural gas, which can provide a 2-times (sometimes more) reduction of total CO2 emissions in the industry; c — reducing the consumption of C-containing technological substances in the treatment of thermal and chemical-thermal processing of metallic materials (steel); d — ferrous recycling and maximum scrap using by iron and steel production. In the paper under consideration the methodology, based upon application the specific greenhouse (CʺСO2) and harmful (CʺNOx) substances issue per unit of useful energy as the determinative parameters, has been advanced for the first time from the standpoint of environment’s decarbonization and pollution. The proper solution for lowering СО2 issue is especially suitable by provision the high temperature processes with utilization the systems of gently oxygen-enriched combustion air. In contrast to traditional assessment of harmful (primarily NOx) and greenhouse (СО2) emissions per unit of generated or supplied energy (the corresponding indicators are C'NOx and C'СO2), application of more adequate values have been proposed by performing the relevant calculations per unit of useful energy Quse. The proper values of relevant indicators CʺNOx and CʺСO2 are objective characteristics by option the most suitable composition of fuel-oxidant mixture. This is approach makes the decisive solution by conditions of mutual substitution the fuels with purpose of account the energy utilization of exhaust gases. Thermodynamic principles and a methodology for calculation the relevant indicators of pollution the exhaust gases CʺNOx and CʺСO2 have been developed. Numerical calculations have been performed and the values of specific emissions of CʺNOx and CʺСO2 have been and determined in dependence on degree of enrichment an oxidizing air-oxidant with oxygen [O2], % (vol.), by account the operating temperature of the process. The possibility of reducing the CʺСO2 emissions by 2 to 3 times or more compared to natural gas with atmospheric air burning has been established even by the cases of a slight (till 30 % vol.) enrichment of the air with oxygen. Bibl. 33, Fig. 11, Tab. 1.

Exergy, energy, economy analysis and multi-objective optimization of a comprehensive energy utilization system for LNG-powered ships based on zero-carbon emissions

To realize efficient utilization of energy in LNG-powered ships and zero-carbon emissions, a comprehensive energy utilization system based on zero-carbon emissions for LNG-powered ships is proposed in this study coupling the full utilization of LNG cold energy and flue gas waste heat with the carbon capture technology of oxygen-enriched combustion with the LNG dual-fuel-powered bulk carrier as the object as well. By system modeling, the system is analyzed using the thermoeconomic method and the operating parameters are studied. The results demonstrate the selection of the working fluid combinations and the settings of the operating parameters of equipment affect the system's thermodynamic and economic performance. Based on the parameters analysis, a multi-objective genetic algorithm is adopted for optimization. The optimization results indicate that 51.71 % exergy efficiency and 511 kW net output power are achieved under the zero-carbon emissions condition, while the initial investment cost and cost of power generation are 6.33·106$ and 0.0869$/kWh, which indicate the system is of excellent environmental and economic benefits.

Economical Configuration of Oxygen-Enriched Air Production Process Using Polysulfone-Based Composite Membranes

Oxygen-enriched combustion technology is an emerging incineration method suitable for waste treatment. In this study, we investigated an economical modular configuration method for oxygen-enriched air production using gas separation membrane technology. Various module configurations were examined based on input pressure, gas temperature, sweep, and multistage module arrangement, and an optimal economically viable configuration was proposed. Using a polysulfone-based polymer membrane module, oxygen-enriched air with an oxygen concentration of 40–65% was produced. Even in cases of low input pressures achieved using a vacuum pump at the permeate side, oxygen-enriched air with concentrations &gt;40% was achieved, with an approximately 20% increase in the permeation flow rate. As the permeation rate increased with increasing temperature, the oxygen recovery efficiency decreased. When the membrane area was increased, the corresponding increase in the input pressure did not result in a proportional increase in the permeation rate compared with single-module setups. Through multistage module arrangements, oxygen-enriched air with a maximum oxygen concentration of 66% was produced. By employing sweep that recirculated a portion of input air to the permeate side, the production of oxygen-enriched air was enhanced by approximately 38%. Therefore, the proposed process involving low input pressure, vacuum pumps, and sweeping was optimal for oxygen-enriched air production.

Inhibition effect and mechanism of CF3CHCl2 on methane flame in oxygen-enriched environment

In oxygen-enriched environment (oxygen concentration above 21%), flammable materials become even more flammable with higher net heat release rate, burning velocity and combustion intensity. Unfortunately, most investigations concentrated on the characteristics and mechanisms of oxygen-enriched combustion, the methods to control or weaken their perniciousness of oxygen-enriched fire have been rarely reported. CF3CHCl2 (HCFC-123, R123) has been demonstrated excellent inhibition performance for oxygen-normal combustion in the fire suppression experiment, was considered as the potential fire extinguishing agents of aircraft cargo. This study performed the comparison between the inhibition performance and kinetic mechanism of CF3CHCl2 for the CH4-N2-O2 (21% of O2) flame and the flames enriched up to 23.1%, 25.2%, 27.3% of oxygen with constant-volume combustion chamber and numerical prediction. Even for the oxygen-enriched flames, CF3CHCl2 showed substantial inhibition effect on the burning velocities and adiabatic flame temperature. The chain-radicals production/consumption rate and normalized sensitivity coefficients were investigated to analyze the in-depth inhibition mechanisms of CF3CHCl2 for oxygen-enriched flames. The mechanism analysis found that the inhibition effect of CF3CHCl2 and relevant halogenated species on oxygen-enriched flame are smaller than that in normal flame.

Optimal metal immobilization of oxygen-enriched co-combustion of Zn/Cd hyperaccumulator and textile dyeing sludge with natural or modified kaolin

Eco-friendly disposal of post-harvest and metal-enriched hyperaccumulator biomass is critical for the industrialization of phytoremediation. The addition of Al/Si-based materials, such as sludge and natural mineral additives, is intended to solve the issue of HM metal stabilization in the oxygen-enriched combustion of hyperaccumulator and slow down ash sintering. This study aimed to quantify and reveal the effects of 10% kaolin or modified kaolin on the oxygen-enriched (co-)combustions of Sedum alfredii Hance (SAH) and textile dyeing sludge (TDS) and their combustion kinetics, metal enrichment rates, and immobilization/stabilization mechanisms. The activation energies for the (co-)combustions of SAH and SAH mixed with 10% additives (ST31) were estimated at 75.84–260.97 kJ/mol and 65.58–327.59 kJ/mol, respectively. The (co-)combustion mechanism model was complex, including phase boundary, diffusion, and chemical reaction order. The co-combustion of SAH with 10% modified kaolin increased Cd and Zn immobilization by approximately 66.6% and 3.2%, respectively, compared with the theoretical data at 550 °C. The co-combustion of ST31 with 10% modified kaolin increased Cd immobilization by approximately 160.9% compared with the theoretical data at 750 °C. Obtained via thermal-acid modified treatment, modified kaolin increased the immobilization efficiencies of Zn and Cd through aluminosilicate reactions to form the stable structures (Ca–Zn–Si, Ca–Zn–Al, K–Zn–Si, Zn–Al, Zn–Si, Cd–Al, and Cd–Si) as well as physical absorption. According to the combination of the experimental, multi-objective optimization, and simulation results, SAH mixed 10% modified kaolin at 550 °C and ST31 mixed with 10% modified kaolin at 750 °C were the ideal co-combustion environment. This study can provide new insights into how to best reduce the environmental risks of the hyperaccumulator disposals through the oxygen-enriched combustion technology.

Effect of oxygen enrichment on methane ignition

Oxygen-enriched combustion has attracted interest in the energy sector due to its increased thermal efficiency and low carbon capture cost compared to ‘air’ combustion. Experimental data on the ignition of oxygen-enriched mixtures are limited in literature. In this work, ignition delay times (IDTs) of various methane/oxygen mixtures diluted in argon/nitrogen were measured using a low- and a high-pressure shock tube over a temperature range of 1200 – 1700 K, three pressures of 1, 10, and 20 bar and an equivalence ratio range of 0.21 - 4. The oxygen mole fraction in the mixtures was varied from 19% (‘air’) to 90.5%, and dilution levels from 71% to zero. The reported IDTs were extracted from pressure and OH* emission profiles. To the best of our knowledge, this is the first comprehensive IDT study on the effect of oxygen enrichment on methane ignition. High-speed imaging experiments were performed to determine the possible presence of non-ideal ignition in these unconventional mixtures. The Bifurcation Damköhler number was found to be a good indicator of non-ideal ignition observed in some imaging experiments. Measured IDTs were compared with the predictions of AramcoMech 3.0 model as well as with GRIMech 3.0 and NUIGMech 1.1 for few cases. In general, AramcoMech 3.0 overestimated IDTs for the investigated methane mixtures. Brute force sensitivity analyses were conducted with AramcoMech 3.0 to identify reactions with a strong influence on IDT prediction for the investigated mixtures. Minor modifications were made to AramcoMech 3.0 resulting in improved predictions of ignition behavior in oxygen-enriched methane mixtures.

A Review of Current Advances in Ammonia Combustion from the Fundamentals to Applications in Internal Combustion Engines

The energy transition from hydrocarbon-based energy sources to renewable and carbon-free energy sources such as wind, solar and hydrogen is facing increasing demands. The decarbonization of global transportation could come true via applying carbon-free fuel such as ammonia, especially for internal combustion engines (ICEs). Although ammonia has advantages of high hydrogen content, high octane number and safety in storage, it is uninflammable with low laminar burning velocity, thus limiting its direct usage in ICEs. The purpose of this review paper is to provide previous studies and current research on the current technical advances emerging in assisted combustion of ammonia. The limitation of ammonia utilization in ICEs, such as large minimum ignition energy, lower flame speed and more NOx emission with unburned NH3, could be solved by oxygen-enriched combustion, ammonia–hydrogen mixed combustion and plasma-assisted combustion (PAC). In dual-fuel or oxygen-enriched NH3 combustion, accelerated flame propagation speeds are driven by abundant radicals such as H and OH; however, NOx emission should be paid special attention. Furthermore, dissociating NH3 in situ hydrogen by non-noble metal catalysts or plasma has the potential to replace dual-fuel systems. PAC is able to change classical ignition and extinction S-curves to monotonic stretching, which makes low-temperature ignition possible while leading moderate NOx emissions. In this review, the underlying fundamental mechanism under these technologies are introduced in detail, providing new insight into overcoming the bottleneck of applying ammonia in ICEs. Finally, the feasibility of ammonia processing as an ICE power source for transport and usage highlights it as an appealing choice for the link between carbon-free energy and power demand.