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The hydrogen carrier ammonia is considered a prominent carbon-free alternative fuel. This paper examines the impact of flue gas recirculation (FR) on combustion instability and emission behavior of premixed CH 4 /NH 3 /air swirl flame at different equivalence ratios (Φ) and ammonia mole fractions (χ NH 3 ). Experimental results show that FR is beneficial to suppressing the self-excited pulsating pressure and pulsating heat release rate of CH 4 /NH 3 /air flame, and the pulsating frequency decreases monotonically with the increase of FR. Under fuel-lean and stoichiometric conditions, FR is beneficial to suppressing NOx formation but will increase CO and NH 3 emissions. Under fuel-rich conditions, FR reduces CO emissions but increases NOx emissions. The NO emissions obtained from the chemical reactor network simulation are in qualitative agreement with the experimental results. The results show that the elementary reactions related to HNO and NHi radicals play a crucial role in the influence of FR on NO formation. • Flue gas recirculation (FR) suppresses combustion instability of CH 4 /NH 3 /air flame. • FR decreases NOx emission but increases CO emission under non-rich conditions. • FR increases NOx emission but decreases CO emission under fuel-rich conditions. • Chemical reactor network reveals the main reactions of FR affecting NO formation. [ABSTRACT FROM AUTHOR]

The paper develops a design feasibility study of a multi-tubular polytropic fixed bed reactor for the one-stage ethanol to 1,3-butadiene (ETB) process employing a modified MgO-SiO 2 catalyst. The analysis quantifies the effect of the internal diffusion on scaling up the catalyst activity and selectivity by considering a complex chemistry of seven parallel/series reactions described by detailed kinetic modelling. The efficient numerical solution takes advantage from the MATLAB™ function bvp5c. The simulation model allows scanning the catalytic process by profiles of species' concentrations, reaction rates and effectiveness factors, inside the catalyst particle and over the reactor. The butadiene yield is controlled by the accumulation in particle of ethanol and key intermediates, as acetaldehyde and crotonaldehyde, related to internal chemical reaction with diffusion and external mass and heat transport rates. The catalyst performance depends significantly on the pellet size that becomes optimization variable for catalyst selection and reactor design. Catalyst particles in the range 2 to 3 mm with tubes of to 25 to 40 mm diameters are the most efficient for achieving 80% butadiene carbon selectivity suitable for an industrial process. The modelling approach is generic for calculating the catalyst effectiveness and designing catalytic chemical reactors involving complex reactions. [Display omitted] • Design of multi-tubular reactor for one-stage bioethanol to 1,3-butadiene process, MgO/SiO 2 catalyst, particle modelling. • Generic method for computing porous catalyst effectiveness involving complex reactions by using MATLABTM bvp5c routine • Catalyst particles of 2 to 3 mm achieve 84 % carbon selectivity with 25 to 40 mm tube diameter at 1.5 bar and 390 °C. [ABSTRACT FROM AUTHOR]

This paper studies the problem of event-triggered impulsive tracking control (ETITC) for uncertain strict-feedback nonlinear systems (USFNSs). In contrast to existing impulsive control schemes, this paper incorporates the neural-network (NN)-based backstepping technique into impulsive control design, such that stronger nonlinearities and uncertainties are allowed to be included in the concerned systems. The proposed state-feedback ETITC scheme guarantees that all the signals of the closed-loop system are bounded and the tracking error ultimately converges to an adjustable bounded region, while also avoiding the Zeno behavior. In addition, by constructing a NN-based observer, this paper further develops an output-feedback ETITC scheme to extend its investigation to the scenario where full states are not available for impulsive control design. Finally, an illustrative example involving a chemical reactor system is presented to demonstrate the effectiveness of our control schemes. [ABSTRACT FROM AUTHOR]

Low-fidelity, cost-effective, physics-based models are useful for assessing the environmental performance of novel combustion systems, especially those utilizing alternative fuels, like hydrogen and ammonia. However, these models require calibration and quantification of their limitations to be reliable predictive tools. This paper presents a framework for calibrating a simplified Chemical Reactor Network model using higher-fidelity Computational Fluid Dynamics data from a micro-gas-turbine-like combustor fuelled with pure ammonia. A Bayesian inference strategy that explicitly accounts for model error is used to calibrate the most relevant CRN parameters based on NO emissions data from CFD simulations and to estimate the model's structural uncertainty. The calibrated CRN model accurately predicts NO emissions within the design space and can extrapolate reasonably well to conditions outside the calibration range. By utilizing this framework, low-fidelity models can be employed to explore various operating conditions during the preliminary design of innovative combustion systems. • Bayesian calibration with model error embedding of Chemical Reactor Network (CRN) parameters is performed. • 15 RANS simulations of an ammonia-fuelled, multi-stage, mGT-like combustor are used as higher-fidelity samples. • Polynomial Chaos Expansion is used for likelihood construction and global sensitivity analysis. • Calibration enables quantifying parametric and model-form uncertainties in the CRN predictions of NO. • CRN allows performing optimisation under uncertainty to minimise NO at the combustor outlet. [ABSTRACT FROM AUTHOR]

Fuel-air mixing strategy always plays an important role in NO x mitigation during ammonia/methane (NH 3 /CH 4) co-combustion. In this paper, a novel dual-annular bluff-body burner is employed to investigate the effects of fuel/air distribution on the flame stability and NO x emission of NH 3 /CH 4 flames. Both straight and swirl flames are studied over a wide range of four key operating parameters, i.e., the overall NH 3 thermal ratio (E N H 3 , o v e), the NH 3 thermal ratio (E N H 3 , p r i) and equivalence ratio (Φ pri) in the primary stream, and the swirl number (S w) in the secondary stream. First, flame stability over these operating parameters is investigated, where E N H 3 , o v e shows nonmonotonic impacts on the lean and rich blowout limits represented by Φ pri. Subsequently, an analysis of the Damköhler number (Da) helps reveal the underlying mechanism. The reaction and flow time scales are adjusted while operating the distribution of CH 4 and air in primary or secondary streams, thus altering the flame stability. Secondly, NO x emissions can be reduced by increasing E N H 3 , p r i and Φ pri. A minimize value of ∼400 ppm is obtained at relatively high Φ pri values (>1.4) for E N H 3 , o v e = 0.1 of both straight and swirl flames. Furthermore, OH*/NH 2 * chemiluminescence is measured to understand the kinetics of NO x formation. In straight flame, two NO x reduction mechanisms are revealed. While increasing operation parameters Φ pri and E N H 3 , p r i , OH inhibition mechanism is shown by lower OH* in the flame zone, and the NH 2 -induced reduction mechanism is marked by increasing NH 2 * content downstream. Subsequent chemical reactor network (CRN) analysis confirms that OH decrement and NH 2 increment contribute to NO reduction. For swirl flames, both OH* and NH 2 * distribute in the flame zone and decrease with Φ pri. When increasing Φ pri , a continuous decrease of NO x emission indicates that the effect of NH 2 on NO x reduction is suppressed compared to that of OH*. These findings suggest the feasibility of an enhanced fuel-nitrogen/hydrocarbon separation to further achieve effective NO x mitigation. [ABSTRACT FROM AUTHOR]

• Reactor and continuum models were used for calculations of an ammonia-fueled gas turbine combustion chamber. • A gas turbine combustion chamber with mixing of components in the pre-chamber has been developed. • The influence of combustion chamber parameters on ammonia burnout was investigated at a thermal power of 1 MW. • Ammonia combustion is ensured with reactant residence times not exceeding 0.025 s. • The use of a radial-axial swirler increased the stability of the combustion process. Achieving climate neutrality requires the use of alternative hydrogen carriers for energy purposes, with ammonia currently being considered. One potential application in the energy sector is gas turbine systems, for which combustion chambers need to be designed to efficiently combust ammonia within an airflow. This paper focuses on theoretical investigations of fuel combustion completeness and environmental cleanliness of a gas turbine combustion chamber with a thermal power output of 1.0 MW, operating on gaseous ammonia. A prospective scheme for organizing processes is proposed, based on pre-mixing ammonia with a portion of air in a special pre-chamber, the sequential introduction of the remaining air through a radial-axial swirler and a series of holes in the flame tube, ensuring stable fuel combustion. Two approaches were used for modeling combustion processes in such a combustion chamber: one based on chemical reactor theory and the other on three-dimensional hydrodynamic analysis. After conducting a detailed kinetic analysis, it was concluded that to maintain stable ammonia combustion while varying the air excess coefficient in the primary combustion zone from 1.4 to 2.0, the reactants need to remain in this zone for a duration exceeding 0.025 s. Based on these parameters, design schemes for two combustion chamber variants were developed, differing in combustion tube length and air distribution pattern, for operation with an ammonia flow rate of approximately 50 g/s and a pressure of 0.3 MPa, determining a gas outlet temperature of 1490 K. Three-dimensional calculations of aerodynamic flow structures, ammonia combustion, and formation of toxic components were conducted, revealing that the proposed process organization scheme ensures complete ammonia combustion and small nitrogen oxide emissions. These results have potential applications in the development of new gas turbine combustion chamber designs for decarbonized energy systems, including those integrated with solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

This paper puts forward an adaptive saturated threshold event-triggered control (STETC) scheme with global transient and steady-state performance assurance for nonlinear Markov jumping systems. Initially, the dead-zone model is characterized by an adaptive approximation model while integrating the property of the Nussbaum function. Then, an improved adaptive global preassigned performance control scheme is developed under the command-filtered backstepping control framework, where a second-order filter is employed to tackle the curse of dimensionality faced by the iterative derivation and a novel error compensation signal is constructed with consideration of the characteristics of dead-zone output and preassigned performance to eliminate the potential effects caused by filter errors. Drawing inspiration from the preceding ETC results, a STETC tactic fusing the dynamic parameter is proposed to economize the communication costs, and the control signal is encoded and decoded as 0 or 1 bits to decrease the bandwidth consumption simultaneously. The reported STETC method guarantees that overall signals in the closed-loop system keep bounded in probability while the tracking error rigorously evolves within the prescribed range without dependent on initial values. Ultimately, two illustrative examples are implemented to check the flexibility and practicality of the reported control solution. • Control design is flexible consuming less bandwidth resources in comparison to existing PPC and ETC. • Differential calculation of the virtual control signal avoid the curse of dimensionality. • Improved error compensated signal drastically eliminates the filter errors. • STETC method guarantees that overall signals keep bounded in probability. • The tracking error rigorously evolves within the prescribed range regardless of the initial value. [ABSTRACT FROM AUTHOR]

The ironmaking blast furnace (BF) is a counter-current chemical reactor. The porosity distribution of burden layers in BF plays an important role for the gas distribution and gas–solid two-phase interaction. In this research paper, to analyze how porosity distributions affect gas velocity, gas temperatures and reduction, the different porosity distributions were investigated using three distinct processes by numerical models. The results showed that the change of porosity along the radius direction had a more obvious effect than along the height direction. When the porosity is exponentially distributed, the gas velocity was allowed a great development, promoting the gas temperature and reduction. Besides, in the lower part (height = 1/3H), with increasing porosity, the gas velocity increases by 30% and reduction by 25%. In the middle part (height = 2/3H), the gas velocity is increased by 30%, the gas temperature is increased by 200 °C, and the reduction is increased by 20%. [Display omitted] • Studied the influence of several different porosity distributions on the reactions of blast furnaces • The variation of porosity along the radius direction has a significant impact on the gas velocity • The impact of porosity is mainly due to its rate of change rather than its size [ABSTRACT FROM AUTHOR]

[Display omitted] • Review of CFD simulations that model dry reforming of methane reaction. • Various types of reactors can be optimized through CFD for efficient DRM reaction. • CFD can help identify catalytic properties needed to suppress carbon deposition. • Challenges and potential research directions on CFD simulation of DRM are presented. Computational Fluid Dynamics (CFD) is a powerful tool for modeling chemical reactors. While limited literature is available on CFD simulation of Methane Dry Reforming (DRM), this reaction presents several environmental and economic advantages. Modeling DRM using CFD can provide insights for optimizing chemical reactors, evaluating catalysts interactions with surrounding reactive flow, improving properties of catalysts that are not yet well developed and determining optimum operating conditions for high process efficiency. This review paper provides a comprehensive overview of the current state-of-the-art in CFD modeling of DRM. After a brief description of the reaction thermodynamics, the kinetic models applied in CFD simulation for DRM and their limitations are covered along with an analysis of the governing equations employed. The review also tackles various catalysts and types of reactors employed for DRM simulation. It then identifies remaining challenges and potential research directions for more efficient hydrogen and syngas production using DRM. [ABSTRACT FROM AUTHOR]

• A phenomenological design approach is constructed for the design of CLC-PPBR at/above pilot scale. • Macroscopic behaviors of the heat/reaction front are introduced to depict the dynamic operation of the reactors. • Bed size must conform to certain limitations to fulfill reasonable operational stability and cost-effectiveness. • Effects among design parameters are studied to optimize the preliminary design scheme for the 1.5 MW th reactor. The parallel packed bed reactor (PPBR) is a promising route for industrial application of chemical looping combustion. This paper introduces a phenomenological approach for the rational design of PPBR, serving as a manner to efficiently obtain comprehensive design results. Based on the macroscopic propagation of heat and reaction fronts, it elucidates the dynamic heat/mass transfer within the bed. Subsequently, it is applied to design a 1.5 MW th reactor. The risk of carbon deposition in the bed is firstly investigated from a thermodynamic perspective. Then, the study reveals that the height-to-diameter ratio of the reactor must meet certain constraints to ensure stable and cost-effective operation, and these constraints are extended to the scale-up process. Sensitivity analysis is utilized to investigate the effect of key parameters on the design schemes and performance. Effects of particle size on intra-particle gas diffusion is analyzed. Finally, detailed design schemes and performance of the reactor are determined. [ABSTRACT FROM AUTHOR]

An accurate and self-consistent methodology for mass transport of multi-component mixtures in multi phase media is a necessity for a proper description of complex physical and chemical processes in reactors such as catalytic packed beds. In this regard, a novel methodology has been developed to describe and couple underlying transport phenomena in fluid and porous media as well as at the solid-fluid interface. The methodology is symmetric as it treats all components in a mixture equally. The Maxwell-Stefan equations are symmetrically formulated, discretized conservatively and coupled with a compressible flow solver for the fluid part. The Dusty Gas Model is applied inside porous media by developing a self-consistent and robust numerical formulation. A ghost-cell Immersed Boundary Method is used to capture the physics at the solid-fluid interface with the implementation of a novel symmetric non-singular mass flux formulation. Several test cases are established to demonstrate the accuracy and robustness of the newly developed symmetric methodology in this paper. These test cases can be used as benchmark for the future development of symmetric methodologies for multicomponent systems in multi phase media. • A novel computational methodology has been developed to couple transport phenomena in fluid-solid multicomponent media. • The developed methodology is symmetric as all components in a mixture are treated equally. • A symmetric and unconditional stable formulation for the Dusty Gas Model has been developed. • A novel non-singular mass flux formulation has been developed and embedded in the ghost-cell Immersed Boundary Method. • Several test cases are designed for verification and validation of the developed methodology. [ABSTRACT FROM AUTHOR]

In this paper, considering the uncertainties of the controller and the model, a non-fragile H ∞ control law is robustly developed for time-delay equations with additive uncertainty. Hence, exploiting the linear matrix inequality (LMI), the robust compensator design is translated to an LMI one. In a continuous - time delayed model, the stabilization around equilibrium points and the rejection of the exogenous disturbance are discussed via the non-fragile robust H ∞ controller. Such an aim is realized by checking the feasibility of the LMI. Then, through solving an LMI, the controller's parameters would be found and updated directly. To show the superiority of the tactic in process control, the reported strategy is employed in a two-stage chemical reactor. The figurative results along with the quantitative findings consistently disclose the advantages of the addressed controller over conventional techniques. • Both the closed-loop stabilization and the disturbance rejection are considered to design a non-fragile H ∞ controller in uncertain continuous-time delayed models. • The non-fragile robust H ∞ compensation is converted to the feasibility of an LMI. Then the controller's gains would be found from the LMI. • The addressed H ∞ controller is applied in two-stage chemical reactors. The results reflect the merits of the proposed scheme over the similar one. [ABSTRACT FROM AUTHOR]