Optimized CFD modelling and validation of radiation section of an industrial top-fired steam methane reforming furnace

[EN]The present study proposes an optimized computational fluid dynamics (CFD) modelling framework to provide a complete and accurate representation of combustion and heat transfer phenomena in the radiation section of an industrial top-fired steam methane reforming (SMR) furnace containing 64 reforming tubes, 30 burners and 3 flue-gas tunnels. The framework combines fully-coupled appropriate furnace-side models with a 1-D reforming process-side model. Experimental measurements are conducted in terms of outlet temperatures at the flue-gas tunnels, point-wise temperature distributions at the panel walls, and inside the reforming tube collectors which are placed at the refinery plant of Petronor. The final results are compared with the experimental data for validation purpose. The proposed fully coupled 3-D CFD modeling framework, which utilizes a detailed chemical-kinetic combustion mechanism, reproduces well basic flow features including pre-mixed combustion process, downward movement of flue-gas in association with large recirculation zones, radiative heat transfer to the reforming tubes, composition profiles along the reaction core of the reforming tubes, temperature non-uniformities, and fluctuating characteristics of heat flux. The reported non-uniform heat and temperature distributions might be optimized by means of the operating parameters in order to avoid a negative impact on furnace balancing and performance.This research is partially funded by Basque Industry 4.0 pro-gramme of Basque Government (BI00024/2019) and University-Company-Society 2019 call of UPV/EHU (US19/13) . Open access funding is provided by the University of the Basque Country (UPV/EHU)

Experimental Insights into the Coupling of Methane Combustion and Steam Reforming in a Catalytic Plate Reactor in Transient Mode

The microstructured reactor concept is very promising technology to develop a compact reformer for distributed hydrogen generation. In this work, a catalytic plate reactor (CPR) is developed and investigated for the coupling of methane combustion (MC) and methane steam reforming (MSR) over Pt/Al2O3-coated microchannels in cocurrent and counter-current modes in transient experiments during start-up. A three-dimensional (3D) computational fluid dynamics (CFD) simulation shows uniform velocity and pressure distribution profiles in microchannels. For a channel velocity from 5.1 to 57.3 m/s in the combustor, the oxidation of methane is complete and self-sustainable without explosion, blow-off, or extinction; nevertheless, flashbacks are observed in counter-current mode. In the reformer, the maximum methane conversion is 84.9% in cocurrent mode, slightly higher than that of 80.2% in counter-current mode at a residence time of 33 ms, but at the cost of three times higher energy input in the combustor operating at ∼1000 °C. Nitric oxide (NO) is not identified in combustion products, but nitrous oxide (N2O) is a function of coupling mode and forms significantly in cocurrent mode. This research would be helpful to establish the start-up strategy and environmental impact of compact reformers on a small scale

Comparison of Catalyst Geometries using Computational Fluid Dynamics for Methane Steam Reforming

Steam methane reforming is a widely-used process to convert methane into syngas. A conventional steam reformer consists of fixed-bed reactor tubes filled with supported nickel catalyst particles. This project proposed recommendations for better catalyst designs. Computational fluid dynamics was used to compare the effect of different multi-holed cylindrical catalyst geometries on heat transfer, pressure drop, and methane conversion under typical reforming conditions. The geometries modeled were 1-hole, 3-hole, 4-hole, 4-hole with vertical grooves, and 6-hole cylinders. It was concluded that the 4-hole with grooves offered a uniform particle temperature distribution, high reaction rate, and had a significantly larger void fraction, allowing a higher mass flow rate for a set pressure drop

Integrated Steam Reforming/Catalytic Combustion Annular Microchannel Reactor for Hydrogen Production

The overall goal of this dissertation work is the development of an annular microchannel reactor (AMR) that couples methane steam reforming and catalytic combustion of methane to produce hydrogen and/or synthesis gas achieving breakthroughs in heat transfer rates and methane reforming capacities. This is accomplished through reaction engineering design analysis and CFD models, validated by experimental data provided by our industrial collaborator, Power+Energy, Inc. The initial goal was to produce a CFD model that could verify experimental results provided by Power+Energy, Inc enabling the rapid design of an AMR prototype. Once the CFD model was verified, a manufacturable design produced higher power densities than competitive planar technology and competitive overall thermal efficiencies. The next goal was to establish that catalytic combustion of methane is a viable means of providing the heat duty necessary to sustain isothermal operation of the AMR and to match AMR heat duty profiles, established previously. Catalytic combustion of methane will supply sufficient heat flux to the AMR, but there will be axial mismatch in the heat duty profiles resulting in temperature deviations, investigated later using a coupled geometry. The next goal was to investigate the potential of an unconventional catalyst design space wherein catalyst efficiency is maintained, while thermal efficiency is increased due to the thickening of the catalyst coating. 1-D analysis show that the catalyst coating could be thicker than the catalyst efficiency “rule of thumb,” while maintaining high thermal efficiencies for the methane steam reforming conditions used. For the 2-D analysis, the AMR geometry is used and shows that the catalyst coating could be increased as much as three fold with minimal losses to catalyst efficiency while maintaining high thermal efficiencies. The final goal was to couple the models presented previously using isolated geometries, while including a finite thermally conductive wall. The objective was to show the effects of heat flux mismatch and prove that the temperature deviations seen when comparing the AMR and combustion results, will be less severe than suggested by the 1-D conduction model indicates due to multi-directional heat conduction within the volume-separating wall. Temperature deviations occurring from the heat flux mismatches still occur; however, the previous performance prediction are proven incorrect. The separated models over predict the methane capacity needed for the combustion chamber, subsequently under predicting thermal efficiency and combustion heat utilization. Additionally, the temperature deviations present allow for higher hydrogen yield than originally predicted. An asymmetric design is introduced that attempts to better match the drastic heat flux in the begging of the steam reforming reaction. This asymmetric design allows for high heat flux into the AMR tube, but generates hotspots. These hotspots are then investigated with the intent of mitigation. The objective was to add catalyst to the inner tube of the AMR, which would then act as a reactive heat sink subsequently reducing the magnitude and size of the hotspot. Nine different catalyst additions are investigated in a case study surrounding the lowest flowrate indicates that any catalyst addition will reduce the hotspot to a manageable size and temperature

Predicting Alarm And Safety System Performance Using Simulation

Safety is paramount to the chemical process industries. Because many processes operate at high temperatures and/or pressures, involving hazardous chemicals at high concentrations, the potential for accidents involving adverse human health and/or environmental impacts is significant. Thanks to research and operational efforts, both academically and industrially, the occurrences of such incidents are rare. However, disastrous events in the chemical manufacturing industry are still of relevant concern and garner further attention – the Deepwater Horizon incident (2010) and the Texas City refinery explosion (2005) being two recent examples. Many techniques have been developed to understand, quantify, and predict alarm and safety system failures. In practice, hazards are identified using Hazard and Operability (HAZOP) analysis, and a network of independently-acting safety systems works to maintain the probabilities of such events below a Safety Integrity Level (SIL). The network of safety systems is studied with Layer of Protection Analysis (LOPA), which uses failure probability estimates for individual subsystems to project the failures of entire safety system networks. With few alarm and safety system activations over the lifetime of a chemical process, particularly the critical last-line-of-defense systems, the failure probabilities of these systems are difficult to estimate. Statistical techniques have been developed, attempting to decrease the variances of such predictions despite few supporting data. This thesis develops methods to estimate the failure probabilities of rarely activated alarm and safety systems using process and operator models, enhanced by process, alarm, and operator data. Two repeated simulation techniques are explored involving informed prior distributions and transition path sampling. Both use dynamic process models, based upon first-principles, along with process, alarm, and operator data, to better understand and quantify the probability of alarm and safety system failures and the special-cause events leading to those failures. In the informed prior distribution technique, process and alarm data are analyzed to extract information regarding operator behavior, which is used to develop models for repeated simulation. With alarm and safety system failure probabilities estimated for specific special-cause events, near-miss alarm data are used, in real-time, to enhance the predictions. The transition path sampling method was originally developed by the molecular simulation community to understand better rare molecular events. Herein, important modifications are introduced for application to understand better how rare safety incidents evolve from rare special-cause events. This method uses random perturbations to identify likely trajectories leading to system failures – providing a basis for potential alarm and safety system design

Catalytic Reforming of Higher Hydrocarbon Fuels to Hydrogen: Process Investigations with Regard to Auxiliary Power Units

This thesis discusses the investigation of the catalytic partial oxidation on rhodium-coated honeycomb catalysts with respect to the conversion of a model surrogate fuel and commercial diesel fuel into hydrogen for the use in auxiliary power units. Furthermore, the influence of simulated tail-gas recycling was investigated

Reaction and Transport in Industrial-Scale Packed Bed Steam Reforming of Glycerol

The ubiquity of biodiesel production, which generates 10% glycerol as a by-product, has led to an abundance of glycerol waste and a reduction of value. Steam reforming presents an alternative to optimize the use of glycerol by converting it to hydrogen. The present study simulated the process in COMSOL Multiphysics using a bimetallic Ni–Co/Al2O3 catalyst in a packed bed reactor. The model was developed to simultaneously analyze the kinetics and thermodynamics of the system on an industrial scale, allowing for recommendations regarding process and reactor design. After comparing the process to methane steam reforming, it was found that glycerol steam reforming in a packed bed reactor is a feasible solution for the transformation of waste into a clean sustainable commodity

Mathematical modelling of a low-temperature hydrogen production process with In Situ CO2 capture

Imperial Users onl