CHARACTERIZATION OF TURBULENT REGIME BEHAVIOR IN THE DILUTE ZONE OF A CIRCULATING FLUIDIZED BED RISER

This study consists in characterizing the solid phase behavior in the dilute region of a circulating fluidized bed riser (CFB) for the turbulent regime (i.e. for superficial gas velocities U

Carbon Capture Utilization and Storage in Methanol Production Using a Dry Reforming-Based Chemical Looping Technology

This further investigates the concept of gas switching dry reforming (GSDR) that efficiently converts the two major greenhouse gases (CO2 and CH4) into a valuable product (syngas) for gas-to-liquid (GTL) syntheses. The proposed GSDR is based on chemical looping technology but avoids external circulation of solids (metal oxides) by alternating the supply of reducing and oxidizing gas into a single fluidized bed reactor to achieve redox cycles. Each cycle consists of three steps where a metal oxide/catalyst is first reduced using GTL off-gases to produce CO2 (and steam) that is supplied to the next reforming step to produce syngas for GTL processes. The metal oxide is then reoxidized in the third step associated with heat generation (through the exothermic oxidation reaction of the metal oxide and air) to provide the heat needed for the endothermic dry methane reforming step. Experimental demonstrations have shown that a syngas H2/CO molar ratio between 1 and 2 suitable for methanol production could be achieved. A further demonstration shows that pressure has negative effects on gas conversion. Following the successful experimental campaign, process simulations were completed using ASPEN to show how the GSDR process can be integrated into a methanol (MeOH) production plant.publishedVersio

Blue, green, and turquoise pathways for minimizing hydrogen production costs from steam methane reforming with CO2 capture

Rising climate change ambitions require large-scale clean hydrogen production in the near term. “Blue” hydrogen from conventional steam methane reforming (SMR) with pre-combustion CO2 capture can fulfil this role. This study therefore presents techno-economic assessments of a range of SMR process configurations to minimize hydrogen production costs. Results showed that pre-combustion capture can avoid up to 80% of CO2 emissions cheaply at 35 €/ton, but the final 20% of CO2 capture is much more expensive at a marginal CO2 avoidance cost around 150 €/ton. Thus, post-combustion CO2 capture should be a better solution for avoiding the final 20% of CO2. Furthermore, an advanced heat integration scheme that recovers most of the steam condensation enthalpy before the CO2 capture unit can reduce hydrogen production costs by about 6%. Two hybrid hydrogen production options were also assessed. First, a “blue-green” hydrogen plant that uses clean electricity to heat the reformer achieved similar hydrogen production costs to the pure blue configuration. Second, a “blue-turquoise” configuration that replaces the pre-reformer with molten salt pyrolysis for converting higher hydrocarbons to a pure carbon product can significantly reduce costs if carbon has a similar value to hydrogen. In conclusion, conventional pre-combustion CO2 capture from SMR is confirmed as a good solution for kickstarting the hydrogen economy, and it can be tailored to various market conditions with respect to CO2, electricity, and pure carbon prices.publishedVersio

Evaluation of the minimum fluidization velocity at elevated temperature and pressure through experiments and modelling

The minimum fluidization velocity is an important measure used in the design and scale-up of fluidized beds. Due to its importance, a large number of experiments over a wide range of operating conditions have focused on this property. Despite this attention, the amount of data where the combined effect of elevated temperature and pressure on the minimum fluidization velocity was investigated is still limited. In this study the minimum fluidization velocity is determined experimentally in a lab-scale fluidized bed reactor designed for use at elevated temperature and pressure. A central composite design (CCD) is used to design experiments where different operating parameters are varied over a wide range. This includes different particle sizes, pressures up to 5bar and temperatures up to 550°C. The collected data provides the basis for existing correlations, such as that given by Bi and Grace (1), to be evaluated at elevated temperature and pressure and allows for detecting any systematic deviations from the experimental data. In addition to the experiments, the minimum fluidization velocity and the voidage at minimum fluidization is calculated numerically over the CCD using computational. Several different drag models are evaluated, allowing their relative performances to be assessed and any weaknesses to be identified. Recommendations are made for drag model selection in pressurized fluidized bed reactors. 1. H.T. Bi and J.R. Grace. Flow regime diagrams for gas-solid fluidization and upward transport. Int. J. Multiphase Flow, 21: 1229-1236, 1995. Please click Additional Files below to see the full abstract

The swing adsorption reactor cluster for post-combustion CO2 capture from cement plants

The swing adsorption reactor cluster is a promising new method for post-combustion CO2 capture using a synergistic combination of temperature and pressure swings. The pressure swing is carried out by a vacuum pump and allows for 90% CO2 capture using only a small temperature swing, which is carried out by a heat pump. The small temperature swing allows the heat pump to transfer heat from carbonation to regeneration at a very high efficiency, minimizing the energy penalty. When applied to a cement plant, the energy penalty reduces further relative to a coal power plant that has a lower CO2 content in the flue gas. Higher CO2 concentrations allow a given CO2 capture ratio to be achieved with a smaller temperature swing, thus further improving the heat pump efficiency. As a result of the high heat pump efficiency and of the limited amount of waste heat available, heat integration with the cement plant yielded negligible efficiency gains. A swing adsorption reactor cluster post-combustion CO2 capture facility can therefore be constructed independently from the cement plant, making it attractive for retrofits. The specific energy consumption for CO2 avoidance of the process was determined as 2.04 MJLHV/kgCO2 when using electricity from the average European power mix, which is lower than all competing technologies recently assessed in the literature aside from oxyfuel CO2 capture. Primary energy consumption will continue to decline as the electricity sector decarbonizes, increasing the attractiveness of the swing adsorption reactor cluster over coming decades.publishedVersio

Economic assessment of the swing adsorption reactor cluster for CO2 capture from cement production

Cement production is responsible for about 8% of global CO2 emissions. Most of these emissions originate from the process itself and thus cannot be avoided via clean energy, leaving CO2 capture as the only viable solution. This study investigates the prospects of decarbonizing the cement industry via the swing adsorption reactor cluster (SARC) – a new post-combustion CO2 capture technology that requires no integration with the host process, consumes only electrical energy and shows a competitive energy penalty. SARC operates by synergistically combining a temperature swing using a heat pump and a vacuum swing using a vacuum pump. In the present study, the SARC concept is evaluated economically and compared to several benchmarks. SARC achieves CO2 avoidance costs of €52/ton in the base case, which is higher than oxyfuel combustion, similar to calcium looping and lower than four other technology options. SARC can approach the cost of oxyfuel combustion with more optimistic assumptions regarding economies of scale, particularly for the vacuum pump. The local electricity mix is another important factor because SARC, as an electricity consumer, becomes more attractive when the price and CO2 intensity of electricity is low. Furthermore, the simplicity of retrofitting existing cement plants with the SARC process becomes increasingly valuable when rapid CO2 emissions reductions are targeted. SARC is therefore well positioned for a global decarbonization effort aiming to limit global warming well below 2 °C.publishedVersio

An Assessment of the Ability of the TFM Approach to Predict Gas Mixing in a Pseudo-2D Bubbling Fluidized Bed

2D and 3D simulations of gas species diffusion in a pseudo-2D bubbling fluidized bed were carried out and compared to experimental measurements. Tracer gas concentration and solids velocity profiles measured throughout the bed showed great deviations of the 2D simulations due to negligence of the friction on the large front and back walls of the pseudo-2D unit and the inability to resolve gas species gradients across the thickness of the bed. 3D simulations circumvent these limitations and result in much more reasonable comparisons with experimental data. A clear lack of gas species diffusion was observed, however, and this was attributed to the negligence of particle-induced diffusion of gas species within the bed. Further work is recommended to investigate the modelling of particle-induced gas species diffusion in fluidized bed reactors

Optimal particle parameters for CLC and CLR processes - predictions by intra-particle transport models and experimental validation

Validated models for predicting oxidation and reduction kinetics of multi-component porous particles in chemical looping combustion (CLC) and chemical looping reforming (CLR) processes are of key importance to identify the rate limiting step in these processes. Since particle properties (i.e., their composition, porosity, pore size, grain size, etc.) can be adjusted by modern synthesis techniques, there is an open question on the optimal set of these properties that would lead to the most economic process. We introduce a general open-source simulation environment, called ParScale that can be used to simulate models relevant for CLC and CLR processes, and hence can be used for their optimization. Most important, ParScale features a generalized one-dimensional spherical discretization which enables the user to predict an arbitrary number of reactions within non-isothermal porous particles consisting of multiple solid (reactive or inert) species. We perform an optimization study (constrained by typical process requirements like the maximum reaction time) for an isothermal first-order reaction, as well as for an n-th order reaction typical for hematite reduction. Finally, materials consisting of active nanoparticles embedded in a matrix of a different composition are synthesized and analyzed

Carbon-negative hydrogen from biomass using gas switching integrated gasification: Techno-economic assessment

Ambitious decarbonization pathways to limit the global temperature rise to well below 2 °C will require large-scale CO2 removal from the atmosphere. One promising avenue for achieving this goal is hydrogen production from biomass with CO2 capture. The present study investigates the techno-economic prospects of a novel biomass-to-hydrogen process configuration based on the gas switching integrated gasification (GSIG) concept. GSIG applies the gas switching combustion principle to indirectly combust off-gas fuel from the pressure swing adsorption unit in tubular reactors integrated into the gasifier to improve efficiency and CO2 capture. In this study, these efficiency gains facilitated a 5% reduction in the levelized cost of hydrogen (LCOH) relative to conventional O2-blown fluidized bed gasification with pre-combustion CO2 capture, even though the larger and more complex gasifier cancelled out the capital cost savings from avoiding the air separation and CO2 capture units. The economic assessment also demonstrated that advanced gas treatment using a tar cracker instead of a direct water wash can further reduce the LCOH by 12% and that the CO2 prices in excess of 100 €/ton, consistent with ambitious decarbonization pathways, will make this negative-emission technology economically highly attractive. Based on these results, further research into the GSIG concept to facilitate more efficient utilization of limited biomass resources can be recommended.publishedVersio

Analyse de la structure de l’écoulement gaz-particules dans un lit fluidisé circulant par la PIV

Une étude expérimentale de l'écoulement gaz-particules dans une colonne à lit fluidisé circulant a été réalisé à l'aide de la technique de mesure PIV (Particle Imaging Velocimetry). Les vitesses axiales moyennes des particules et leurs écarts types ont été relevés sur trois hauteurs de la colonne de 0,5 m de diamètre et de 5 m de hauteur, et sont comparés aux résultats obtenus antérieurement à l'aide de la technique LDV (Laser Doppler Velocimetry) sur une colonne de même rapport d'aspect H/D. Ils sont en bon accord qualitatif. La technique de la PIV a mis en évidence l'existence de la structure coeur-anneau (flux de solide montant au centre et un autre descendant prés de la paroi) caractérisant l'écoulement dans le lit fluidisé circulant, avec une diminution de l'épaisseur de la zone annulaire en fonction de la hauteur. Ensuite, les vitesses axiales et transversales moyennes des particules et leurs écarts types ont été relevés et analysés pour une hauteur relative z/H = 0.35 et ceci pour trois masses chargées en particules, respectivement de 10, 25 et 40 kg. Ces résultats ont montré l'existence d'une zone de transfert de matière entre le coeur et l'anneau, où son épaisseur croît avec la masse chargée. Une augmentation en valeur absolue de vitesses axiales moyennes des particules est observée à la paroi en fonction de la masse chargée