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)

Simulation and optimisation of industrial steam reformers. Development of models for both primary and secondary steam reformers and implementation of optimisation to improve both the performance of existing equipment and the design of future equipment.

Traditionally the reactor is recognised as the `heart' of a chemical process system and hence the focus on this part of the system is usually quite detailed. Steam reforming, however, due to the `building block' nature of its reaction products is unusual and generally is perceived as a `utility' to other reaction processes and hence the focus is drawn " towards the 'main' reaction processes of the system. Additionally as a `mature' process, steam reforming is often treated as sufficiently defined for the requirements within the overall chemical process. For both primary and secondary steam reformers several models of varying complexity were developed which allowed assessment of issues raised about previous models and model improvements; drawing on the advancements in modelling that have not only allowed the possibility of increasing the scope of simulations but also increased confidence in the simulation results. Despite the complex nature of the steam reforming systems, a surprisingly simplistic model is demonstrated to perform well, however, to improve on existing designs and maximise the capability of current designs it is shown that more complex models are required. After model development the natural course is to optimisation. This is a powerful tool which must be used carefully as significant issues remain around its employment. Despite the remaining concerns, some simple optimisation cases showed the potential of the models developed in this work and although not exhaustive demonstrated the benefits of optimisation

Alternative sustainable routes to methanol production: techno-economic and environmental assessment

open

Exploiting the potential of chemical looping processes for industrial decarbonization and waste to energy conversion. Process design and experimental evaluations

The impact of anthropogenic activities on the environment is leading to climate changes and exceptional meteorological phenomena all over the world. To address this negative trend, the scientific community agrees that the environmental impact from fossil fuels-based power production must be mitigated by the integration with alternative and sustainable technologies, such as renewable energy. However, the time required for the complete development and diffusion of such technology poses the urgency of finding a midterm solution to significantly reduce CO2 emissions. Carbon capture, utilization, and storage (CCUS) technologies represent an interesting option to mitigate CO2 emissions. CCUS involves (among other possible applications) the separation of the CO2 content from industrial off-gases, its transport and storage or its reconversion to a chemical/fuel. Chemical looping can be considered as an oxyfuel combustion where the oxygen supply comes from the lattice oxygen atoms of a solid. It is based on gas-solid reactions where a solid also known as oxygen carrier, generally a metal oxide, undergoes successive reduction and oxidation steps. In the reduction step, normally occurring at high temperatures (700-1000 °C), the oxygen carrier interacts with a reducing agent, such as coal, natural gas, syngas etc. and loses part of its oxygen atoms. By controlling the degree of reduction of the oxygen carrier is thus possible to achieve a complete oxidation of the reducing agent (the fuel) to CO2 and H2O (chemical looping combustion) or a partial oxidation to a syngas (chemical looping reforming and gasification). In these latter case, the introduction of external CO2 and H2O can be of help to support the reforming or gasification processes. The oxygen carrier in the reduced phase is then sent to an air reactor, where it reacquires the oxygen atoms by an exothermic reaction with air. This process presents several advantages according to the specific application. In chemical looping combustion, intrinsic separation of N2 and CO2 is achieved, because the two streams are involved in two different reaction steps. This largely simplifies the CO2 separation effort for storage or utilization purposes. On the other hand, in chemical looping reforming it is possible to achieve autothermal operation thanks to the exothermicity of the oxidation step in the air reactor, as well as high reforming efficiencies. Similarly, in chemical looping gasification the resulting syngas is characterized by no N2 dilution, lower tar release and possibility of autothermal operation. These benefits enhance the energy efficiency of the process, leading to a better energy utilisation. In this work, strategies for the decarbonisation and circularity of the industrial and power sector are proposed based on the synthesis of hydrogen and hydrogen-derived fuels. In particular, the potential of chemical looping technology is deeply studied aiming at exploiting its ability to reconvert or valorise CO2 or waste streams to a syngas and then to a liquid fuel/chemical, such as methanol or ammonia. This task is carried out through modelling and experimental evaluations. The modelling activities mainly concern design of process schemes involving the chemical looping section for waste or CO2 reconversion and the liquid fuel synthesis section. The experimental evaluations are focused on two crucial that have been limitedly discussed in the literature: the thermochemical syngas production step by oxidation with CO2 and H2O streams, the effect of high-pressure operation on the redox abilities of a typical iron and nickel-based oxygen carrier. In Chapter 1, a general overview on the main research developments on chemical looping technology is provided. A section is reserved for each chemical looping variant, i.e. combustion, reforming and gasification, and a general description of each process is provided along with the summary of the main research achievements. Subsequently, the technology is divided by application in power production and chemicals production. Main findings from techno-economic assessment and process designs are discussed in comparison with benchmark technologies and other clean pathways. In Chapter 2 steel mills are taken as an example of the hard-to-abate industry. A H2-based decarbonization strategy is proposed and assessed by Aspen Plus simulation. The strategy starts from an initial configuration that is characterized by a typical blast furnace-basic oxygen furnace steel mill and consider the introduction of direct reduction – electric arc furnace lines, that are more efficient and involve natural gas as reducing agent rather than coke. Sensitivity analyses are carried out to assess the effect of the introduction of H2/CH4 blendings in the direct reduction plant and of the utilization of scrap material in the electric arc furnace. The impact of each configuration on the CO2 emissions and the energy flows of the plant is assessed by mass and energy balances. The results indicate a promising decarbonization potential of the introduced technologies but require large investments to increase the renewable sources penetration in the energy mix and large availability of H2. Therefore, alternative pathways for an earlier decarbonization of hard-to-abate industries and for large scale syngas/H2 production need to be considered. In Chapter 3, a novel process scheme is proposed involving chemical looping for syngas production. The CO2 content in blast furnace gases is separated with a calcium looping cycle and subsequently injected with H2O into the oxidation reactor of a chemical looping cycle. Assuming an inlet stream of pure CO2, mass balances on the chemical looping plant are carried out to compare the performance of nickel ferrites and iron oxides in terms of required oxygen carrier flow rate to process 1 t/h of CO2. Computational fluid dynamics simulations with integrated reaction kinetics are then carried out to validate the assumptions on the oxygen carrier conversion and syngas compositions. In Chapter 4 and 5, experimental evaluations are carried out on two crucial aspects for the successful operation of a chemical looping plant aiming at syngas production. In Chapter 4, the syngas productivity by CO2 and H2O splitting over a Fe bed is investigated. This is a very important step, and the effect of various parameters was considered. Firstly, the CO2 splitting is analysed for different temperatures with an inlet flow rate of 1 NL/min to ensure a substantial dissociation of the CO2. Subsequently, combined streams of CO2 and H2O are evolved in the reactor. The effect of the total flow rate, reactants molar ratio and bed height is investigated and from the results, the optimal syngas composition is identified. SEM and XRD are used to assess the morphological evolution and the phase changes of the material during the test. On the contrary, in Chapter 5 the effect of high-pressure operation on the redox abilities of two NiFe aluminates is assessed. The aluminates present similar Fe loadings, but different Ni loadings. High pressure operation is crucial for the development of this technology because it facilitates downstream processing of the syngas to liquid fuels. For a comparative analysis, preliminary tests at low pressure are carried out at three temperatures. Subsequently, the effect of reactants flow rate, temperature, total pressure, gas composition is analysed at high pressure conditions. Finally, long term tests are performed both at ambient and high-pressure conditions. Material characterization by SEM, XRD and H2-TPR is used to support the comparative analysis. In Chapter 6, a techno-economic analysis on a process scheme encompassing methanol and ammonia production from chemical looping gases is carried out. Chemical looping hydrogen production is a very versatile technology and allows for the combined production of power and H2 or syngas. With proper calibration of the flow rates, a stream of high purity N2 can also be obtained at the air reactor outlet and used for ammonia synthesis. Back up with an alkaline electrolyser is considered for the supply of the required amount of hydrogen. Sensitivity analyses are carried out on the chemical looping plant to evaluate the effect of fuel flow rate, steam flow rate, and oxygen carrier inlet temperature to the fuel reactor. Subsequently, a techno-economic analysis is carried out evaluating several parameters among which: the specific CO2 emissions, the energy intensity, and the levelized cost of methanol and ammonia. Finally, a comparison with benchmark technologies and other clean alternatives is presented. In this way, the benefits as well as the drawbacks of chemical looping in terms of environmental and economic parameters are assessed and the missing elements to reach industrial competitivity are clarified

Clean Energy via Hydrothermal Gasification of Hydrocarbon Resources

Synthesis gas and clean hydrogen will become key components of the energy industry. Their production from fossil fuels is likely to be a major source of these energy vectors and chemical building blocks for many decades ahead. Currently all the hydrocarbon conversion steps are carried out above surface, starting from oil and gas extraction and transportation to dedicated plants, with any separated CO2 returned back to the fields. However, there are increasingly strong drivers to reduce the environmental impact of the oil processing industry, by e.g. minimising the “footprint” of such operations and leaving the undesirable and low- value material underground (CO2, heavy metals, sulphur). One novel approach, which could be key, would be the production of syngas or hydrogen via downhole hydrothermal processing/partial oxidation. This envisages using the sub-surface well system as a continuous processing and reactor network to carry out as much as possible of the required separations and conversions in the well system (underground) or close to it (at the wellhead). The goal is to radically reduce, by design, the overall environmental footprint (by minimising the number of species extracted other than final products, the number of external processing steps and the need for transport to/from the underground fields) while improving the overall economics of new fields and increasing the efficiency of recovery from conventional, mature reservoirs. This thesis presents research work on the hydrothermal gasification and partial oxidation of n-hexadecane, as a heavy hydrocarbon model, under potential downhole conditions. Thermodynamic analysis was carried out to predict equilibrium limits showing optimum conditions for maximising the theoretical yield of hydrogen under oxidative and non- oxidative hydrothermal conditions. This was followed by experimental analysis where hydrothermal gasification of n-hexadecane was conducted in high pressure flow reactor system. Conversion data at different residence times, and temperatures were used to determine the reaction kinetic data at sub- and supercritical water conditions. The new experimental system was modified for partial oxidation of n-hexadecane, to enable combined total decomposition of H2O2, in a separate reactor, with partial oxidation of n-hexadecane, in a gasification reactor. The experimental data were consolidated with the development of a new CFD model for supercritical water gasification of hexadecane, and it was also used to validate and tune our kinetic data obtained experimentally by taking into account the radial effects occurring from the laminar flow under the experimental conditions. Finally, a new subsurface georeactor system model was developed, using ASPEN HYSYS, which shows thermodynamically the optimal conditions for maximising the system’s energy efficiency showing potential conditions for maximising energy recovery with hydrogen cogeneration. These results are discussed with view of opening new routes for clean generation of hydrogen and synthesis gas via underground gasification of hydrocarbons.Open Acces

Gaur egungo hidrogeno-ekoizpena: metanoaren ur-lurrun bidezko erreformatzea

In our society, hydrogen is an increasingly important source of energy. Among all the production techniques, methane steam reforming is the most widely used. This process is based on the following steps: natural gas cleaning, heating process, reforming furnace, water-steam conversion and hydrogen separation; the most significant being the reforming furnace. However, this technique has several challenges related to the emitted CO2, the design of the catalysts and the energy consumption. This paper presents a general description of the methane steam reforming process, providing an overview of the combustion chamber, catalysts, thermal efficiency and modelling of the reforming furnace.; Gure gizartean, gero eta garrantzi handiagoa duen energia-iturria da hidrogenoa. Ekoizpen-teknika guztien artean, metanoaren ur-lurrun bidezko erreformatzea da erabiliena. Prozesua honako urrats hauetan oinarritzen da: gas naturalaren garbiketa, beroketa-prozesua, labe erreformatzailea, ur-lurrunaren bihurketa eta hidrogenoaren bereizketa; horien artean, labe erreformatzailea da elementurik garrantzitsuena. Dena den, teknika honek hainbat erronka ditu, isuritako CO2-ari, katalizatzaileen diseinuari eta energia-kontsumoari lotutakoak. Dokumentu honetan, metanoaren lurrun-bidezko erreformatze-prozesuaren deskribapen orokorra aurkezten da, errekuntza-ganberaren, katalizatzaileen, eraginkortasun termikoaren eta labe erreformatzailearen modelizazioaren nondik norakoak azalduz

Advances in Hydrogen Energy

This book, which is a reprint of articles published in the Special Issue "Advances in Hydrogen Energy" in Energies, seeks to contribute to disseminating the most recent advancements in the field of hydrogen energy. It does so by presenting scientific works from around the world covering both modeling and experimental analysis. The focus is placed on research covering all aspects of the hydrogen energy, from production to storage and final use, including the development of other easy to transport and versatile hydrogen-based energy carriers via the power-to-x (PtX) route, such as ammonia and methanol.Hydrogen energy research and development has attracted growing attention as one of the key solutions for clean future energy systems. In order to reduce greenhouse gas emissions, governments across the world are developing ambitious policies to support hydrogen technology, and an increasing level of funding has been allocated for projects of research, development, and demonstration of these technologies. At the same time, the private sector is capitalizing on the opportunity with larger investments in hydrogen technology solutions.While intense research activities have been dedicated to this field, several issues require further research prior to achieving full commercialization of hydrogen technology solutions. This book addresses some of these issues by presenting detailed models to optimize design strategies and operating conditions for the entire hydrogen value chain, covering production via electrolysis, storage and use in different types of fuel cells and in different forms of energy carriers

Gasification for Practical Applications

Although there were many books and papers that deal with gasification, there has been only a few practical book explaining the technology in actual application and the market situation in reality. Gasification is a key technology in converting coal, biomass, and wastes to useful high-value products. Until renewable energy can provide affordable energy hopefully by the year 2030, gasification can bridge the transition period by providing the clean liquid fuels, gas, and chemicals from the low grade feedstock. Gasification still needs many upgrades and technology breakthroughs. It remains in the niche market, not fully competitive in the major market of electricity generation, chemicals, and liquid fuels that are supplied from relatively cheap fossil fuels. The book provides the practical information for researchers and graduate students who want to review the current situation, to upgrade, and to bring in a new idea to the conventional gasification technologies

A mechanistic analysis of particle flow in a multiphase chemical looping reactor with theories of contact mechanics

Understanding particle dynamics and their characteristics is essential to the operation, design, and optimization of chemical looping reactors. The chemical looping dry reforming (CLDR) process is a novel hydrogen production process in which methane and carbon dioxide mixture is converted into syngas in a cyclic oxidation-reduction reaction in the presence of an oxygen carrier. This paper presents a three-dimensional computational fluid dynamic model to study the fluid flow pattern in a chemical looping dry reforming methane (CLDRM) reactor. The numerical analysis was applied through Eulerian and Lagrangian approaches. This multiphase model design comprises a dual circulating fluidized bed consisting of a high-velocity air reactor (AR) with a high-velocity riser, a cyclone chamber (CC), a fluidizing bed fuel reactor (FR), and a connecting loop, which closes the loop between AR and FR. Analysis of gas-solid hydrodynamics in CLDRM was performed to understand the particles distribution, volume fraction, flow pattern, velocity and circulation between the AR and FR. The evolution of particle flow circulation rate was carefully analyzed to understand the particle material rebalance and the transfer of solid particles between reactors operating on different velocities. The results showed that the CLDR system experiences a pressure imbalance between the reduction and oxidation zones, which causes solid particles to undergo a highly intricate and turbulent pulse flow. This results in periodic bursts of pulses that lead to the intermittent transportation of particles ― in the form of particle clusters― from high-pressure areas to regions with lower pressure. This paper discusses the impacts of velocity and geometric modifications on the distribution of the particles. The results showed that the fluidized beds exhibited a periodic pulse pattern with various phenomena occurring in a millisecond, and it was concluded that an air velocity of 3.2 m/sec, fuel mass flow rate of 0.0025 kg/sec, and connection loop diameter of 25 mm were ideal operating parameters