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Pressurised sand filters used in drip irrigation need periodic backwashing to flush the contaminant particles out of the porous media. This process consumes high amounts of energy and water. The selection of more efficient backwashing operational conditions requires accurate information of the pressure drop and the bed expansion, the latter being not measured in commercial filters. An experimental study with a scaled filter that used a window to observe the bed expansion was conducted with three porous media types (glass microspheres and two silica sands), two packed media bed heights (200 mm and 300 mm) and four nozzles (one commercial and three prototypes). The 24 combinations of the filter experimental configuration were investigated for different superficial velocities. Both data and video recordings for all the 705 tests conducted were carefully analysed to obtain mean values and standard deviations of the height of the expanded bed. The behaviour of the fluidised bed dynamics was characterised. Results indicated that the nozzle design had a strong influence on the pressure drop, and, in consequence, on the power required for backwashing. It also had an observable impact on the fluidised bed dynamics although its effect on determining the overall height of the expanded bed was limited, this being more dependent on the type of the porous media. The most effective combination in terms of energy efficiency and porosity of the expanded bed was obtained with microspheres, though its retention efficiency might be questionable from the literature review, and the frustoconical nozzle geometry. • Video and data recordings of 705 backwashing tests were analysed. • The nozzle design plays a main role on the total pressure drop. • The nozzle design influences the fluidised bed dynamics. • The height of the expanded bed is mostly dependent on the media type. [ABSTRACT FROM AUTHOR]

In this study, a binary fluidised bed made out of quartz sand and cenospheres for the biomass combustion process was created. Materials were fluidised with air to achieve a vertical density profile (from 0.5 g/cm³ to 1.1 g/cm³) resulting from grains segregation. The density profile was selected to ensure optimal control over the location of the combusted fuel particle. This involved positioning the process as close to the bottom sieve as possible. Fluidised bed combustion was carried out at temperatures of 600 °C, 700 °C, 820 °C and 870 °C using straw, willow and sawmill pellets as fuels. Qualitative and quantitative analysis of flue gases was performed using an FTIR spectrometer. Over 90 % carbon conversion from the biomass to carbon dioxide was achieved at 700 °C. At 820 °C and 870 °C, 100 % of biomass carbon left the reactor as CO2. The composition of organic compounds in the process products remained low, reaching a maximum of 3.0 % wt. at 600 °C. To gain further insights into the processes occurring in the immediate vicinity of biomass samples, a complementary TGA/FTIR analysis was conducted. This aimed to clarify the impact of the biomass particle decomposition stage in the fluidised bed combustion process. The proposed mechanism for biomass combustion in the binary fluidised bed contains the particle decomposition stage and the subsequent stage resulting from the coalescence of bubbles containing flammable components and bubbles containing oxidiser. [ABSTRACT FROM AUTHOR]

Thermochemical energy storage (TCES) presents a promising method for energy storage due to its high storage density and capacity for long-term storage. A combination of TCES and district heating networks exhibits an appealing alternative to natural gas boilers, particularly through the utilisation of industrial waste heat to achieve the UK government's target of Net Zero by 2050. The most pivotal aspects of TCES design are the selected materials, reactor configuration, and heat transfer efficiency. Among the array of potential reactors, the fluidised bed emerges as a novel solution due to its ability to bypass traditional design limitations; the fluidised nature of these reactors provides high heat transfer coefficients, improved mixing and uniformity, and greater fluid-particle contact. This research endeavours to assess the enhancement of thermochemical fluidised bed systems through material characterisation and development techniques, alongside the optimisation of heat transfer. The analysis underscores the appeal of calcium and magnesium hydroxides for TCES, particularly when providing a buffer between medium-grade waste heat supply and district heat demand. Enhancement techniques such as doping and nanomaterial/composite coating are also explored, which are found to improve agglomeration, flowability, and operating conditions of the hydroxide systems. Furthermore, the optimisation of heat transfer prompted an evaluation of heat exchanger configurations and heat transfer fluids. Helical coil heat exchangers are predominantly favoured over alternative configurations, while various heat transfer fluids are considered advantageous depending on TCES material selection. In particular, water and synthetic liquids are compared according to their thermal efficiencies and performances at elevated operating temperatures. [ABSTRACT FROM AUTHOR]

The UK has no established process for recycling waste glass fibre-reinforced thermosets that are widely used within wind blade structures. Consequently, these materials are typically disposed of in landfills or undergo energy recovery in waste facilities. This study investigates the carbon footprint of the fluidised bed process for recycling glass fibre composite waste, considering the present and future scenarios of composite waste management in the UK. The impact was compared to conventional disposal routes and other prominent recycling technologies, such as cement kiln co-processing and mechanical recycling, by developing energy and material flow models for each waste treatment strategy. Variables, such as the type of waste, the quantity of recycling facilities in the UK, and waste haulage distance, were examined to inform the lowest impact deployment of recycling technologies. Cement kiln co-processing, mechanical, and fluidised bed recycling technologies reduced the global warming potential of processing wind blade waste compared with conventional disposal routes, with impacts of −0.25, −1.25, and −0.57 kg CO2e/kg GRP waste, respectively. Mechanical recycling had the lowest global warming potential resulting from low greenhouse gas emissions associated with the process itself and potentially high offsets by replacing glass fibre in the production of moulding compound. Composite wind turbine blade waste was found to be a particularly promising feedstock for the fluidised bed process due to relatively low resin content diminishing direct greenhouse gas emissions during thermal decomposition, as well as high material recovery offsets due to the high glass fibre content of this waste stream. [ABSTRACT FROM AUTHOR]

Nowadays, naval propellers are made in Ni-Al or Mn-Al bronzes, which are affected by high cavitation erosion. In this study, the possibility of adopting 6xxx alloy with different superficial treatments obtained through fluidised beds and laser surface texturing was investigated. 6xxx alloy series is known for its versatility due to an excellent mix of mechanical and physical properties, combined with ease of processing, welding, and good chemical resistance; however, its main drawback is low resistance to cavitation erosion. In this study, a total of 4 different surface treatments were produced and characterized such as fluidised bed coatings (Al2O3, S280) and laser textured samples (0–30% overlap). Moreover, the effect of a heat-treatment was evaluated for each kind of specimen analysed. The study was divided into two steps: in the first phase, the samples were morphologically and mechanically characterised through roughness measurements, micro-hardness, scratch, wear, and wettability tests. Successively, a modified ASTM-G32-10 standard was adopted to assess the cavitation erosion resistance; in particular, for each sample, mass and volume loss were analysed and compared to the as-built sample. Results showed a drastic reduction of the wear evaluated through pin-on-disk tests with the application of the high hardness coatings (Al2O3, S280) while a reduction of the cavitation erosion volume of about 20% lower was obtained through the best laser texturing treatment. [ABSTRACT FROM AUTHOR]

Thermochemical energy storage (TCES) presents a promising method for energy storage due to its high storage density and capacity for long-term storage. A combination of TCES and district heating networks exhibits an appealing alternative to natural gas boilers, particularly through the utilisation of industrial waste heat to achieve the UK government’s target of Net Zero by 2050. The most pivotal aspects of TCES design are the selected materials, reactor configuration, and heat transfer efficiency. Among the array of potential reactors, the fluidised bed emerges as a novel solution due to its ability to bypass traditional design limitations; the fluidised nature of these reactors provides high heat transfer coefficients, improved mixing and uniformity, and greater fluid-particle contact. This research endeavours to assess the enhancement of thermochemical fluidised bed systems through material characterisation and development techniques, alongside the optimisation of heat transfer. The analysis underscores the appeal of calcium and magnesium hydroxides for TCES, particularly when providing a buffer between medium-grade waste heat supply and district heat demand. Enhancement techniques such as doping and nanomaterial/composite coating are also explored, which are found to improve agglomeration, flowability, and operating conditions of the hydroxide systems. Furthermore, the optimisation of heat transfer prompted an evaluation of heat exchanger configurations and heat transfer fluids. Helical coil heat exchangers are predominantly favoured over alternative configurations, while various heat transfer fluids are considered advantageous depending on TCES material selection. In particular, water and synthetic liquids are compared according to their thermal efficiencies and performances at elevated operating temperatures.

The article includes the study and reconstruction of a fluid bed device with the purpose of separating the granular material from the grinding process of rapid antigen tests. The following techniques were performed, with the purpose of characterisation of the ground particles: sieve analysis, X-ray fluorescence spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. The paper includes experimental testing of a simplified separation process with zeolite spheres and paper strips, supported by a numerical model. The flow conditions' impact on the behaviour and interactions of particles of the considered problem were simulated using coupled computational fluid dynamics (CFD) and the discrete element method (DEM) approach. The separation process of zeolite spheres and paper strips was found to be efficient. The simulation results showed the appropriate behaviour of the particles during the process. We explained the results' deviations, and we also presented the shortcomings and possible improvements. Further research is required to define the adequacy of the process, while using actual ground material of rapid antigen tests. [ABSTRACT FROM AUTHOR]

This research work deals with the application of the calcium looping concept for thermochemical energy storage. Experiments were carried out in a lab-scale fluidised bed reactor, which was electrically heated. An Italian limestone (98.5% CaCO3, 420–590 μm) was present in the bed alone, or in combination with silica sand/silicon carbide (this last material was chosen as per its high absorption capacity in the solar spectrum). Calcium looping tests (20 calcination/carbonation cycles) were carried out under operating conditions resembling the "closed-loop" scheme (calcination at 950 °C, carbonation at 850 °C, fluidising atmosphere composed of pure CO2 in both cases). Carbonation degree, particle size distribution, and particle bulk density were measured as cycles progressed, together with the application of a model equation to relate carbonation degree to the number of cycles. Mutual relationships between the nature of the bed material and possible interactions, the degree of CaO carbonation, the generation of fragments, and changes in particle density and porosity are critically discussed. An investigation of the segregation behaviour of the bed material has been carried out through tests in a devoted fluidisation column, equipped with a needle-type capacitive probe (to measure solid concentration). [ABSTRACT FROM AUTHOR]

The heat transfer in the combustion chamber (freeboard) of a fluidised bed combustor is of critical importance, due to the need for thermal efficiency, the possible environmental impacts, and the increasing costs of fuel and electricity. In this study, an artificial neural network model was used to analyse the heat transfer in a bubbling fluidised bed combustion system. The heat transfer of the system was investigated using temperature measurements of the combustion chamber and side wall of a 0.3 MWe fluidised bed combustor, the fly ash contents (%) of 40 types of coal, the gas absorption coefficients (CO2 and H2O vapour), and the enthalpy of the flue gas. The whole system was analysed using a backpropagation algorithm (10 hidden layers with 10 neurons). It was found that the most important factor when calculating the heat transfer in the combustion chamber was the height of the chamber, and the influence of the flue gas enthalpy and the ash particle content on the heat transfer accounted for 4% and 8.6%, respectively. The accuracy of the results from the proposed multilayer perceptron algorithm is high, and analyses could be performed for different values of the input data.

The sustainable fulfilment of world energy demand should be based on the diversification of the energetic portfolio and, at the same time, on the decrease of the use of fossil fuels in favour of renewable energy sources. This perspective review article focuses its attention on a particular source of renewable energy, i.e. biomass. As non‐fossil materials of natural origin, biomasses are formed by storing, in the noble and stable form of chemical bonds, solar energy. Gasification has been here chosen as biomass thermoconversion route: general concepts and history, chemical reactions and uses of syn‐gas, and the role of tar, are addressed. Fluidised beds are discussed as reactors to carry out biomass gasification, also considering that a new approach based on dual interconnected fluidised bed schemes can realise the concept of sorption‐enhanced gasification (to increase H2 productivity). Syn‐gas and tar characteristics are presented and, finally, an original case study concerning the fluidised bed gasification of civil and industrial sludges is presented. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

To improve the recovery rate of clean coal, a liquid–solid fluidised bed is typically used to process coarse coal slime of 0.25–1.5 mm. In this paper, a combination of experimental measurements and computational fluid dynamics (CFD) simulations was used. The fluidisation behaviour of four groups of coarse coal particles with different sizes and densities in a fluidised bed with rectangular cross-section was investigated. The Euler–Euler method, shear stress transport k–ω turbulence model, kinetic theory of granular flow (KTGF) and modified Gidaspow drag model were used for CFD simulations. The experiment and CFD simulation results showed that when J L /U mf was greater than 1, the expansion ratio of the fluidised bed of coarse coal particles varied as a power function of the J L /U mf value. The bed expansion ratio model developed by Tripathy et al. in a fluidised bed with a circular cross-section was also applicable to a fluidised bed with a rectangular cross-section. The pressure drop data at different heights indicated that the measured values showed a linear pattern with the measured height. This indicated that when J L /U mf was greater than 1, the coarse coal particles showed a uniform fluidisation characteristic. After choosing appropriate initial conditions and models, the CFD simulation agreed well with the experimental data. The experimental data and simulation results can deepen the understanding of liquid–solid fluidised beds of coarse coal particles, which is beneficial to improve the fluidisation quality of the fluidised bed and further improve the separation effect. [Display omitted] • Coarse coal particle fluidisation is investigated by experimental and CFD approach. • Bed expansion ratio varies as a power function of the J L /U mf value greater than 1. • The pressure drop at different levels is linearly related to the measured height. • The bed expansion ratio model is applied to the rectangular fluidised bed. [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative model is developed by integrating reacting flow CFD models and a process controller. • The collaborative model proves its versatility by stabilising the OC circulation of CLC systems. • The optimal effectiveness of the controller is determined by testing under three intervals. • The model can be used in process optimisation of CLC in clean combustion or solid waste conversion. Chemical reactors usually feature complex internal reacting flows, and they are usually equipped with process controllers to stabilise their operations, especially for highly dynamic reactors including chemical looping combustion/conversion (CLC). However, their dynamic internal states are not well understood due to the lack of reliable research tools. In this work, for the first time, an innovative numerical collaborative model is developed to describe the reacting flow details and simulate the response to a process controller. The collaborative model is applied to a fuel reactor (FR) in a CLC to demonstrate its effectiveness. The detailed internal flow patterns in the FR are obtained and described by the three-phase reacting flow CFD model, and the circulating rate of oxygen carrier (OC) is controlled and optimised by the fuzzy logic controller (FLC). The controller is designed to operate at varying control time intervals, 1 s, 2 s, and 5 s, to study the optimal frequency for data sampling and feedback. The efficiency of the controller to the FR is tested in terms of OC circulation, gas components and the general performance of the reactor. The results show that the stability of OC circulating rate and performance are effectively improved by the process controller; among the three control intervals, the 2 s interval shows the highest feasibility and capability of maintaining stable OC circulation and CO 2 yield in the FR. Quantitatively, compared to the base case without a controller, the range of OC circulating rates has been narrowed from [0.014, 0.534] to [0.018, 0.385] in control case A, [0.075, 0.342] in control case B, and [0.004, 0.530] in control case C. Meanwhile, the CO 2 yield increased from 86.93 % in the base case to 87.98 % in control case A, 88.16 % in control case B, but decreased to 85.4 % in control case C due to poor controlling performance. The combustion efficiency increased from 84.20 % in the base case to 84.87 % in control case A, 86.22 % in control case B, and 85.88 % in control case C. Among all control cases, control case B presents the narrowest data range and highest efficiency, indicating optimal control performance in improving OC circulation stability. The deviation of OC circulating rate values decreases from 0.123 to 0.058, and the CO 2 yield increases from 86.93 % to 88.16 % in control case B with a 2 s interval. This work provides a new cost-effective tool for real-time simulating and controlling the reacting flow system including CLC for clean combustion and solid wastes conversion. [ABSTRACT FROM AUTHOR]

This research work deals with the application of the calcium looping concept for thermochemical energy storage. Experiments were carried out in a lab-scale fluidised bed reactor, which was electrically heated. An Italian limestone (98.5% CaCO3, 420–590 μm) was present in the bed alone, or in combination with silica sand/silicon carbide (this last material was chosen as per its high absorption capacity in the solar spectrum). Calcium looping tests (20 calcination/carbonation cycles) were carried out under operating conditions resembling the “closed-loop” scheme (calcination at 950 °C, carbonation at 850 °C, fluidising atmosphere composed of pure CO2 in both cases). Carbonation degree, particle size distribution, and particle bulk density were measured as cycles progressed, together with the application of a model equation to relate carbonation degree to the number of cycles. Mutual relationships between the nature of the bed material and possible interactions, the degree of CaO carbonation, the generation of fragments, and changes in particle density and porosity are critically discussed. An investigation of the segregation behaviour of the bed material has been carried out through tests in a devoted fluidisation column, equipped with a needle-type capacitive probe (to measure solid concentration).

Production of syngas from the gasification of a biomass is attracting attention with an eye to the concepts of circularity, sustainability, and recent needs, triggered by socio-political events, to increase the level of self-sufficiency of energy sources for a given community. This manuscript reports on the gasification of spruce wood chips in a demonstration fluidised bed gasifier (1.5 MWth, height of 5.40 m, internal diameter of 1.2 m), with 0.2–0.4 mm olivine inventory (1000 kg). Gasification was carried out in air, at four different values of equivalence ratio (from 27% to 36%). The bed was fluidised at about 0.6 m/s, and the bed temperature resulted in the range of about 960–1030 °C as a function of the different tests. A mass flow rate of biomass in the range of about 360–480 kg/h (as a function of the different tests) was fed to the fluidised bed gasifier. Syngas lower heating value, specific mass and energetic yield, and chemical composition, were reported along with data on the production of elutriated fines. Moreover, tar compounds were collected, quantified and chemically speciated. The effect of the equivalence ratio on the main process parameter was critically discussed, proposing useful analytical relationships for the prediction of syngas lower heating value, tar mass flow rate and chemical composition. [ABSTRACT FROM AUTHOR]

• Simultaneous production of hydrogen and separable solid carbon from CH 4 was demonstrated in a fluidised bed. • Carbon types including CNTs, CNOs, carbon sheets, and amorphous carbon were observed. • Multiple carbon formation mechanisms were responsible for carbon growth. • High U/U mf allowed better separation of carbon from the main catalytic particles. • Lattice oxygen in the NiO/Ca 2 Fe 2 O 5 /CaO particles promoted the production of hydrogen and carbon growth. This work investigated the possibility of simultaneous production of hydrogen/syngas and separable solid carbon in a fluidised bed by using CH 4 -CO 2 cycles and exploring the carbon growth over solid catalytic particles of NiO/Ca 2 Fe 2 O 5 /CaO. This two-stage process included i) stage I: H 2 -rich gas and carbon were simultaneously generated from the interaction between CH 4 and NiO/Ca 2 Fe 2 O 5 /CaO particles; and ii) stage II: the reduced/carbon-deposited particles were regenerated in CO 2. Following our previous successful demonstration of the process for stable hydrogen production over cycles, this study focused on the formation of solid carbon and aimed at understanding its growth mechanism as well as demonstrating the potential of using fluidisation as a means of automatic carbon separation. By tracking the carbon growth history and the change in phases of the reacted NiO/Ca 2 Fe 2 O 5 /CaO particles at temperatures from 700 to 900 °C, we discovered the formation of various forms of nano-structured carbon from CH 4 conversion (e.g. partial oxidation, pyrolysis). These include carbon nanotubes (CNTs), carbon graphite sheets, carbon onions (CNOs), and carbon fibres. Amorphous carbon was also observed, particularly in the initial stage of CH 4 conversion. Higher temperatures like 800 °C and 900 °C gave faster kinetics of CH 4 conversion and more formation of solid carbon. Fe 3 C phase was observed on the reduced catalytic particles and could act as an intermediate phase or carbon sink for carbon growth. The results suggested that other mechanisms for carbon deposition, such as directly over Fe sites, may also exist. Fluidisation with a higher U/U mf ratio separated more carbon-rich fines from the bulk catalytic particles in the fluidised bed. Fluidising with air at 700 °C effectively removed amorphous carbon on the reacted catalytic particles, whilst structured carbon remained. Full separation and purification to obtain pure carbon require furthers optimisation of e.g. fluidisation parameters and material design. [ABSTRACT FROM AUTHOR]

• Heating uniformity is a major challenge to scale-up of microwave processes. • Novel hybrid convective-microwave heated toroidal fluidised bed reactor presented. • Rapid uniform volumetric heating of process material is achieved. • Robustness, scalability and high-temperature operability built in reactor concept. • Flexible platform technology for development of sustainable processes. Challenges exist to implementing high-temperature microwave processes with changing dielectric properties that achieve uniform processing. This paper presents a new high-temperature hybrid microwave processing system which overcomes these challenges in a robust, scalable way, integrating a slotted waveguide ring microwave feed into a toroidal fluidised bed reactor and maintaining its fluidisation behaviour. The prototype operates at a frequency of 2450 MHz with a maximum power of 10 kW and within a temperature range of 50–300 °C, though it is scalable to industrial levels. Electromagnetic simulations of the system were experimentally validated using a range of agri-crop feedstocks. Hydrodynamic and thermodynamic reactor characterisation was performed, and treatment performance was quantified regarding surface bed temperature variation. Excellent treatment uniformities were found under microwave and hybrid regimes, with a temperature coefficient of variation (CoV) across the bed's surface below 2 %, an order of magnitude better than existing microwave processes, generally regarded as highly uniform with CoV of approximately 20 %. The integration of microwaves and toroidal fluidised beds, without exposed moving parts, potentially unlocks a range of applications previously inaccessible to microwave technology or fluidised bed technologies on their own. Future work involves process development, techno-economic studies, and large-scale pilot trials. [Display omitted] [ABSTRACT FROM AUTHOR]

• The physical principles and typical challenges of acoustic techniques applied to fluid-particle systems are explained. • Signal processing for obtaining velocity profiles, solid volume fractions, and PSD of the dispersed phases are discussed. • Acoustic-based methods can advance the fundamental understanding of fluid-particle flows. • Ultrasound techniques can be further applied to three phase flows, bubbly flows and liquid-liquid or liquid gas flows. Acoustic methods applied to opaque systems have attracted the attention of researchers in fluid mechanics. In particular, owing to their ability to characterise in real-time, non-transparent and highly concentrated fluid-particle systems, they have been applied to the study of complex multiphase flows such as fluidised beds. This paper gives an overview of the physical principles and typical challenges of ultrasound and acoustic emission AE methods when applied to fluid-particle systems. The principles of ultrasound imaging are explained first. The measurement techniques and signal processing methodologies for obtaining velocity profiles, size distribution of the dispersed phases, and solid volume fraction are then discussed. The techniques are based on the measurement of attenuation, sound speed, frequency shift, and transit time of the propagated sound wave. A description of the acoustic emission technique and applications to fluid-particle systems are then discussed. Finally, extensions and future opportunities of the acoustic techniques are presented. [ABSTRACT FROM AUTHOR]

Continuous manufacturing in the pharmaceutical industry has been gaining traction in the past few years. To fully understand and optimise continuous manufacturing processes it is important not only to focus on the single units which act as building blocks but also to understand how the parameters in different units affect and interact each other and the final product. In this study, the drying behaviour of granules in a segmented fluidised bed dryer was studied. Granules were produced in a twin screw granulator, forming part of a continuous powder to table line (Consigma-25). The temperature readings and the moisture content were recorded during the drying process of granules produced with different amounts of liquid binder. From the temperature profiles, it was possible to create a method able to detect when the drying process loses efficiency (the drying rate drops) and therefore predict the optimal drying time at different conditions. The method was validated via online Near Infra Red (NIR) moisture measurements to detect the moisture content of the granules during the drying, and was compared to the available fixed drying time and temperature controlled end of drying methods. The method was successful in targeting a specific moisture content and could be used to locate the optimal drying temperature for a target moisture content in the future. The moisture content during the filling of the dryer was also recorded and provided further insight into the drying behaviour of the granules in the segmented dryer; this characteristic behaviour could later be used to detect problems during the filling time. The drying rate was also calculated making it possible to predict the optimal drying time at different operating conditions in the granulator and to assess the impact on drying of the different liquid to solid ratio used. Drying is an important part of the continuous powder to tablet process in the Consigma-25. A method using the derivative of the fluidised bed cell temperature was designed to detect when the drying rate is reduced significantly causing inefficient drying. The method was also able to target a consistent moisture content across different L/S used in the twin screw granulator feeding the dryer. [Display omitted] • Continuous fluidised bed dryer NIR curve during continuous filling and drying. • Different control system for determination of end of drying compared. • Different L/S ratios utilised in the fluidised bed to improve the understanding of its effect. [ABSTRACT FROM AUTHOR]

The aim of this study was to model the drying kinetics of microwave and fluidised bed of parchment coffee beans (Coffea arabica L.) using a semi-theoretical approach. A completely randomized design with six treatments: three with microwave drying (MD) and the rest with microwave fluidised bed drying (MFBD) was carried out. The drying curves were established until reaching a final moisture content between 10 and 12 % w.b. Results indicated that the drying time decreased as the microwave power level increased. When MFBD was used, drying times increased approximately 4-fold compared to MD treatments. The values of effective diffusivity for coffee beans treated with MD and MFBD ranged from 0.913 to1.72x10-9 m².s-1 and from 0.23 to 0.42x10-9 m².s-1, respectively. Although all the models presented high goodness of fit, the two-term model presented the highest R² (>0.98) and lowest RMSE (0.0128-0.0285). In general, all models adequately fit the experimental data, so they can be used to predict the drying kinetics, therefore they could be very useful in equipment design and optimization of the coffee drying process. [ABSTRACT FROM AUTHOR]

Low-temperature thermochemical energy storage (TCES) with composites 'salt in porous matrix' (CSPMs) is widely recognized as a sustainable and efficient solution for harnessing low-grade heat and off-peak electricity. However, many high-performance CSPMs described in the literature have been produced in powder form with particle sizes below 50 μm, which makes them unsuitable for direct use in conventional fixed-bed or fluidised-bed systems. Fluidised-bed systems, highly regarded for their rapid heat and mass transfer advantages, have been extensively used in high-temperature TCES. However, their potential for low-temperature TCES applications remains unexplored due to the lack of suitable thermochemical sorption materials. In this work, we aim to investigate the feasibility of fluidised-bed TCES systems for low-temperature TCES applications using the self-developed fluidisable and high-performance CSPMs. A series of CSPMs were prepared using a commercial mesoporous silica (CMS) as the host matrix and CaCl 2 , MgSO 4 and MgBr 2 as the salts, with the same salt loading level of 50 wt% and particle size range of 150–300 μm. A lab-scale fluidised-bed TCES system was constructed for a comprehensive assessment of the material properties, including minimum fluidisation velocity (u mf), water adsorption capacity, temperature lift, and energy storage density (ESD). The results show that the salt/CMS composite powders can be easily fluidised with a u mf of approximately 0.01 m/s and provide efficient solid mixing during bubbling fluidisation. Among the tested CSPMs, the CaCl 2 /CMS composite shows the best heat-discharging performance. Specifically, the CaCl 2 /CMS composite, when hydrated at 30 °C and 60% relative humidity, has a ESD of 1508 kJ/kg (equivalent to 264 kWh/m3) and provides a maximum bed temperature of 58 °C. In addition, it exhibits excellent stability for use in the fluidised-bed system, with similar fluidisation characteristics and ESDs after multiple cycles of heat charging and discharging processes. This work is believed to inspire future research on the development of CSPM powders. • A salt-composite-based fluidised bed system was developed for low temperature TCES. • CMS-based salt composites exhibited good fluidisability with a low u mf of around 0.01 m/s. • CaCl 2 /CMS composite attained a high ESD of 1508 kJ/kg when hydrated under 30 °C and 60% RH. • CaCl 2 /CMS composites demonstrated good cyclic stability in the fluidised bed system. [ABSTRACT FROM AUTHOR]

Numerical simulation of large-scale fluidized beds presents significant challenges for both scaling up the simulations and evaluating their performance, as full-scale computational fluid dynamics (CFD) simulations incur substantial computational time and cost. To overcome these challenges, we propose a novel approach that combines CFD simulations with data-driven deep-learning models to predict complex hydrodynamics. In this study, we trained two machine learning (ML) algorithms, namely the Long Short-Term Memory (LSTM) and Gated Recurrent Unit (GRU), using spatiotemporal data obtained from CFD simulations. Impressively, the trained models accurately predicted future events for successive time steps, exhibiting excellent agreement for mean voidage, gas velocity, and particle velocity. Among the models utilized, LSTM outperformed the other. This demonstrated its superior ability to capture spatiotemporal CFD data while requiring less computational time and power. The trained models provide a reliable means to extrapolate desirable mean particle velocity and voidage values within fluidized beds. These findings hold promising opportunities for enhancing the design and operation of gas-solid fluidized bed reactors, potentially leading to a significant reduction of up to 57–68% in simulation time. [Display omitted] • ML models demonstrate potential for effective prediction of FB hydrodynamics. • CFD-based RNN models (LSTM, GRU) were developed for large range of datasets. • Limited data enabled promising predictions of solid velocity and volume fraction. • LSTM excelled over GRU, effective computation cost and time. [ABSTRACT FROM AUTHOR]

The two-fluid simulation of a fluidised bed of non-adhesive particles, in which particles are represented as a continuous medium, requires a model for the pressure associated with particle contacts. While closures may be derived in the framework of the kinetic theory of granular flow for short-duration contacts, the frictional pressure associated with enduring particle contacts is generally modelled with an empirical closure involving several free parameters. This article proposes to use the experimental transition between the fluidised-bed and fixed-bed regimes in the determination of these parameters. The prediction of the minimum fluidisation velocity is shown to be governed by the frictional parameters, with either a discrete-element method or a two-fluid model. The shape of the particles, proxied by a sphericity coefficient, also influences the minimum fluidisation velocity. Such dependences of the model prediction can be used to select relevant frictional parameters, by comparison with experimental data or CFD-DEM simulation results. • The minimum fluidisation velocity is governed by particle friction in CFD-DEM. • The frictional-pressure model determines the minimum fluidisation velocity in TFM. • Relevant frictional-pressure parameters follow from the defluidisation process. • The shape of the particles also influences the parameters selection. [Display omitted] [ABSTRACT FROM AUTHOR]

Production of syngas from the gasification of a biomass is attracting attention with an eye to the concepts of circularity, sustainability, and recent needs, triggered by socio-political events, to increase the level of self-sufficiency of energy sources for a given community. This manuscript reports on the gasification of spruce wood chips in a demonstration fluidised bed gasifier (1.5 MWth, height of 5.40 m, internal diameter of 1.2 m), with 0.2–0.4 mm olivine inventory (1000 kg). Gasification was carried out in air, at four different values of equivalence ratio (from 27% to 36%). The bed was fluidised at about 0.6 m/s, and the bed temperature resulted in the range of about 960–1030 °C as a function of the different tests. A mass flow rate of biomass in the range of about 360–480 kg/h (as a function of the different tests) was fed to the fluidised bed gasifier. Syngas lower heating value, specific mass and energetic yield, and chemical composition, were reported along with data on the production of elutriated fines. Moreover, tar compounds were collected, quantified and chemically speciated. The effect of the equivalence ratio on the main process parameter was critically discussed, proposing useful analytical relationships for the prediction of syngas lower heating value, tar mass flow rate and chemical composition.

The dataset presented in this article is the supplementary data for the research article titled “The pyrolysis and combustion of polyoxymethylene in a fluidised bed with the possibility of incorporating CO2” [1], in which possible paths of polyoxymethylene conversion in the fluidised bed made from cenospheres and by means of various fluidising gases (air, N2, CO2) were tested. The use of CO2 as fluidising gas was particularly interesting because above 600°C its incorporation into process products (i.e. CO-rich flue gas) was observed. The gaseous products were detected using Fourier Transform Infrared Spectroscopy (FTIR, Gasmet DX-4000) at intervals of a few seconds. The data on the concentration changes over time will allow to evaluate and verificate of new kinetic models of polyoxymethylene degradation with the possibility of incorporating CO2.

The dataset presented in this article is the supplementary data for the research article by Żukowski and Berkowicz (doi:10.1016/j.combustflame.2019.05.024) [1], in which for the first time the inert and catalytic cenospheres were used as the fluidised bed material, giving the possibility to burn liquids inside the fluidised bed without the need for using specialised dosing systems. The instantaneous concentrations of the gaseous products during the combustion of glycerol samples were detected using Fourier Transform Infrared Spectroscopy (FTIR, Gasmet DX-4000). The accurate composition at the outlet of the reactor makes it possible to evaluate and verify new kinetic models of the glycerol combustion in the fluidised bed. It also will be helpful in creating new simplified models. The data presented here is essential for the evaluation of CFD combustion models which have to include accurate kinetic data.

The drying of biomass particles is an important industrial process where heat and mass transfer simultaneously occur. Following on from our previous work on convective heat transfer, here we report experimental results obtained by analysing the mass transfer between the gas and the surface of the wood particles, during drying in a mechanically stirred fluidised bed. It is assumed that, during the constant drying rate period, the moisture concentration of the gas on the surface of the particle is constant. The results have allowed us to obtain a correlation between the Sherwood number and the Reynolds number in the range of Re p between 102 and 257; the proposed correlation Sh gp = Sh gp (Re p) predicts the surface mass transfer coefficient with an average deviation of 30% in relation to experimental data. • Experimental results on mass transfer between the gas and wood particles. • Convective mass transfer coefficient for the drying of forest biomass particles. • The experiences were carried out in a in a mechanically stirred fluidised bed dryer. • Mass transfer coefficient varied between 6 × 10−3 and 20 × 10−3 m s−1. • A correlation between the Sherwood number and the Reynolds number is proposed. [ABSTRACT FROM AUTHOR]

Particle dispersion behaviour in a solid liquid fluidised system leads to interesting outcomes such as mixing and segregation which are often quantified by an empirical dispersion coefficient. The present study aims at providing a better estimation of particle dispersion behaviour from a fundamental definition analogous to diffusion coefficient. By tracking a tracer particle using high speed image analysis, fluctuating velocity components (V i /) were determined in a solid-liquid fluidised bed comprising glass particles (d S = 8 mm, ρ S = 2230 kg m−3) and water as a fluidising medium. Both inter-particle and particle-wall collisions were determined from the time varying jerk data. The particle mean-free path (λ) was then estimated as a distance between two successive peaks in the jerk profile. Finally, dispersion efficient D was computed based on the product of λ and V. Estimated dispersion coefficients were compared with the available correlations and reasonable agreement was obtained. Unlabelled Image • High speed imaging used to determine particle motion in a liquid fluidised bed. • Particle velocity and speed follow a Normal and Maxwellian distribution. • Mean free path determined from successive peaks in time varying jerk profile. • Measured mean free path decreases with increasing solid fraction. • Dispersion coefficient quantified from the product of mean free path and velocity. [ABSTRACT FROM AUTHOR]

Fluidised bed technology is a very common industrial process and has a wide range of applications in process engineering. Though indirectly, a common way to infer the end product uniformity is through investigating the solid residence time distribution (RTD) in the system. A good understanding of the particle RTD is crucial for the proper design, optimisation, and scale-up of a fluidisation process. Flexible ribbon particles have a very different flow behaviour in a fluidised bed compared to that of spheres which in turn influences the RTD of the particles. However, this issue is still not very well addressed to date. In this paper, a double chain model is adopted to model cut tobacco strips in a fluidised bed riser. The spring constants of this chain model are calibrated, and the model is validated against experimental datum. Finally, the particle RTD as a function of different process parameters is investigated. Unlabelled Image • Spring constants of the double chain model is calibrated. • Residence time distribution of flexible ribbon particles is validated against experimental datum. • Flexible ribbon particle in the riser is shown vividly. • Axial and radial residence time distribution of this special particle is discussed. [ABSTRACT FROM AUTHOR]

The influence of distributor design, including orifice size, number and positioning, on the behaviour of a gas-fluidised granular bed has been studied experimentally. The use of Positron Emission Particle Tracking (PEPT) to non-invasively probe the system's three-dimensional dynamics has allowed the extent of (de)fluidisation and the homogeneity of particle distribution to be quantitatively characterised. While increasing the number of orifices demonstrates a clear, positive influence on both fluidisation quality and homogeneity, the data obtained suggest that the orifice size and positioning play a more complex role. Unlabelled Image • Influence of distributor orifice size, number and position on fluidised bed dynamics investigated. • Positron emission particle tracking used to quantify extent of defluidisation and bed homogeneity. • Increasing orifice number found to increase both fluidisation quality and bed homogeneity. • Changing orifice size at fixed orifice number found to have little impact on fluidisaion. [ABSTRACT FROM AUTHOR]

A stochastic model is presented of two coupled fluidised-bed reactors with a steady circulation of particles between them. The particles undergo reaction in each fluidised bed. The model uniquely accounts for the full conversion history of particles as they are circulated. Chemical looping combustion (CLC) is an example of such a process. We have previously used the model, in a general form, to understand the sensitivity of a CLC process to factors such as the nature of the gas-solid reactions or the residence time distribution of the particles in the reactors. To demonstrate that the stochastic model is also valuable for simulating and optimising specific configurations of CLC, it is applied in this paper to simulate CLC with methane as the fuel gas, conducted in a laboratory-scale circulating fluidised bed. Under the operating conditions of the circulating fluidised bed, it was found that the oxidation and reduction reactions were limited by the intrinsic chemical kinetics of the oxygen carrier particles. It was possible to conduct experiments in a packed bed reactor for reduction and a thermogravimetric analyser for oxidation where the reaction was also limited by the intrinsic chemical kinetics. This enabled a single particle model, for inclusion in the stochastic model, to be developed independently of the experiments in the circulating fluidised bed. The resulting stochastic model was able to simulate the performance of the circulating fluidised bed with reasonable accuracy. Unlabelled Image • Stochastic approach to model reactor-regenerator systems developed. • Model uniquely accounts for the full conversion history of particles. • Applied to simulate a specific configuration of chemical looping combustion. • Able to simulate process with reasonable accuracy. [ABSTRACT FROM AUTHOR]

The evolution of the volume of a fluidized bed solid–gas over time is measured by the oscillation of its surface. It is assumed that the system is governed by the pressure gradient between the plenum and the surface; the latter is considered as the reference. The surface oscillation is measured with a laterally located CCD video camera such that it monitors the flattest portion of the surface and records its coordinates. Simultaneously obtain all the phenomena that regulate the hydrodynamics of the bed, the entering bubbles, coalesce, split, increase their volume adiabatically, and explode on the surface. The gas flow and the weight of fluidized material are studied. The time series of the surface oscillation is analysed in the frequency domain and the phase space. The frequencies obtained are approximately between 0.6 Hz and 1.8 Hz. The entropy values behaves linearly proportional to the total number of bubbles. The volume fluctuation of the bed is the fingerprint that identifies all the phenomena that. occur in it. Unlabelled Image • The volume fluctuation of the bed is the fingerprint that identifies all the phenomena • that occur in it. • Detection of periodic and chaotic phenomena. • Bubble expansion confers the well-known non-linearity of the phenomenon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cable plastic, a mix of PE, XLPE and PVC, cannot be mechanically recycled. • Cable plastic steam cracking was evaluated as recycling option in an industrial scale. • Steam cracking of cable plastic shows the production of olefins and benzene. The use of plastic materials in a circular way requires a technology that can treat any plastic waste and produce the same quality of product as the original. Cable plastic residue from metal recycling of electric wires is composed of cross-linked polyethene (XLPE) and PVC, which is a mixture that cannot be mechanically recycled today. Through thermochemical processes, polymer chains are broken into syngas and monomers, which can be further used in the chemical industry. However, feedstock recycling of such a mixture (XLPE, PVC) has been scarcely studied on an industrial scale. Here, the steam cracking of cable plastic was studied in an industrial fluidised bed, aiming to convert cable plastics into valuable products. Two process temperatures were tested: 730 °C and 800 °C. The results show that the products consist of 27–31 wt% ethylene and propylene, 5–16% wt.% other linear hydrocarbons, and more than 10 wt% benzene. Therefore, 40%–60% of the products are high-value chemicals that could be recovered via steam cracking of cable plastic. [ABSTRACT FROM AUTHOR]

This paper explores the effectiveness of metal recovery and values of gaseous emissions during thermal e-waste processing followed by magnetic separation. The thermal process of conversion of this kind of waste is difficult due to the uncertainty of the operation when compared to the processing of homogeneous materials. This is due to their complex and heterogeneous structure. The adoption of the fluidized bed reactor makes the process feasible, stabilizing it significantly and limiting emissions of harmful gases. Mobile cellphones were used as the raw input material of 450 g total mass. During the thermal transformation, the exhaust gases such as: CO, CO2, NOx, SO2, HCI, HBr, HCN, NH3, phenol, hydrocarbons, HF and COCI2 were analysed. The thermal treatment resulted in 333.6 g of solids in the fluidized bed. They were fragmented into grains smaller than 1 mm and 0.5 mm. The process of magnetic enrichment was used next on grains greater than 1 mm and smaller than 0.5 mm. The process was carried out using a neodymium magnet for particles >1 mm and a plate electromagnetic separator (powered by a three-phase current) together with a 1-disc tape-type separator, which was used for particles

A sorption-enhanced methanation concept has been recently presented, which is based on the employment of a sorbent able to capture in situ the H2O produced during the methanation reaction, in order to shift the equilibrium towards the formation of methane. In this work CaO, derived from natural limestone, was tested as a possible sorbent material for H2O capture in a novel configuration based on the concept of chemical looping in dual interconnected fluidized bed systems. The lab-scale experimental campaign was focused on the study of the sorbent performance in terms of hydration and dehydration cycles at different operating conditions relevant for catalytic methanation. The effect of temperature on the sorbent performance, as well the presence of CO2 in the reaction environment, were investigated. The results showed that CaO has good capacity to capture and release steam in the temperature range of interest. Unfortunately, even at the lowest temperatures tested, the sorbent is affected by the presence of CO2 that worsen its performance in terms of H2O capture capacity. [ABSTRACT FROM AUTHOR]

A fluidised bed of low-density (<0.9 g/cm3) hollow microspheres (cenospheres) was used for the combustion of selected liquid and solid fuels. It was proven that with such a fluidised bed, these materials burned inside the bed, not on its surface. For the purpose of some experiments the cenospheres with a nanometric, catalytic layer of iron oxide was prepared by original method using fluidised bed and Fe(CO) 5 as a Fe 2 O 3 precursor. The combustion was examined in the temperature range of 400–700 °C. When the inert fluidised bed was heated to 700 °C, ∼90% of the carbon of the degraded samples reacted to CO 2 (93% for paraffin wax, and 84% for paraffin oil and glycerol). When the process was performed in the catalytic bed, ∼90% of the conversion to CO 2 of the carbon contained in glycerol and paraffin fuels was achieved at 500 °C. The acoustic analysis confirmed that combustion takes place either just in the bubbles (inert bed) or both on the surface of particles and in the bubbles (catalytic bed). The analysis of acoustic signals showed that the explosions occurring in the bed do not form a deterministic pattern. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Lime added to biomass as a countermeasure to agglomeration in BFB combustion. • Defluidisation time extensively prolonged for biomass fuels with lime addition. • Reduced K/Ca ratio in ash leads to smaller agglomerates & less sand cracking. • Fe precipitates from sand & reacts with molten ash, accelerating agglomeration. • Lime addition to fuels hinders the acceleration caused by Fe precipitation. Abstract The unique fuel flexibility of fluidised bed system facilitates the combustion of low quality solid fuels such as agricultural residues, but may suffer from serious bed agglomeration problems especially when operating at the high end of the typical fluidised bed combustion temperature range (800–900 °C). In this study, a 1.5 wt% lime addition to biomass fuels was investigated as a countermeasure to agglomeration for the combustion of pelletised wheat straw and miscanthus in a 20 kW bubbling fluidised bed (BFB) combustor using quartz sand as the bed material. Comparing to the widely studied agglomeration countermeasures such as bed additives and alternatives, the lime addition to fuel can provide a continuous on-site agglomeration counter action. Without lime addition, defluidisation as a result of bed agglomeration occurred once the bed temperature reached 860 °C and 877 °C for miscanthus and wheat straw respectively. However, with the lime addition, stable combustion could be achieved at 900 °C for both fuels with a substantially prolonged operation time. The obtained agglomerates were characterised using CAMSIZER, XRD and SEM/EDX and the results showed that the presence of lime in the fuel could significantly reduce the agglomerates size by forming high melting point calcium silicates/phosphates which hinder the K-rich molten substance attachment and result in heterogeneous coating layers in the agglomerates. The results of this study clearly indicate that using lime as fuel additive can realise the combustion of the problematic non-woody biomass fuels by considerably reducing the bed agglomeration propensity in practical fluidised bed combustion plants. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CFD-DEM simulations of spherocylindrical particles in a fluidised bed. • Explore the effect of varying hydrodynamic force conditions. • Lift and torque correlations derived from recent DNS simulations are used. • Lift has considerable influence on the velocity of particles parallel to fluid flow. • Inclusion of hydrodynamic torque greatly affects preferred orientation of particles. Abstract The aim of many industrial processes is to manipulate solid particle aggregates within gas suspensions. Prime examples of such processes include fluidised bed reactors, cyclone separators, and dust collectors. In recent years, fluidised bed reactors have been used in the gasification of biomass particles. When fluidised, these particles are subject to various hydrodynamic forces such as drag, lift and torque due to interactions with the fluid. Computational approaches, which can be used to replicate laboratory and industrial scale processes, offer a crucial method for the study of reactor design and for the formulation of optimal operating procedures. Until now, many computer models have assumed particles to be spherical whereas, in reality, biomass feedstocks typically consist of non-spherical particles. While lift and torque are of minimal importance for spherical particles, non-spherical particles experience varying lift force and torque conditions, depending on particle orientation relative to the direction of the fluid velocity. In this study, we present a numerical investigation on the effect of different lift force and torque correlations on fluidised spherocylindrical particles. We find that lift force has a significant influence on particle velocities parallel to the direction of gravity. On the other hand, particle orientation is dependent on hydrodynamic torque. Results from this numerical study provide new insight with regards to the dynamics of non-spherical particles that can be of paramount importance for industrial processes involving non-spherical particles. [ABSTRACT FROM AUTHOR]

Highlights • Several improvements to drag closures in filtered Two Fluid Models are proposed. • Resolved data reveals the importance of developing anisotropic drag closures. • A formulation based on the drift velocity accounts for anisotropy in a natural way. • A non-linearity correction and meso-scale interphase force closure are also required. • Improvements are demonstrated via verification against resolved simulation data. Abstract Over the past decade, filtered Two Fluid Models (fTFMs) have emerged as a promising approach for enabling fluidized bed simulations at industrially relevant scales. In these models, the filtered drag force is considered to be the most important quantity that requires closure. To date, such closures have typically relied on an isotropic interphase momentum exchange coefficient by applying a drag correction factor to the microscopic drag closures commonly used in resolved simulations. In the present study, both isotropic and anisotropic closures are developed for predicting the filtered interphase forces. The relative performance of these two approaches is then evaluated by means of an a priori assessment, considering data obtained from simulations in which all flow variables are resolved, which were also used for closure derivation. Also, an a posteriori assessment, which compares coarse grid simulation results to a benchmark resolved simulation of a bubbling fluidized bed, is presented. The primary conclusion from the present study is that it is essential to account for the anisotropy of the filtered momentum exchange coefficient. It is shown that this can be done by employing a drift velocity formulation of the filtered drag force and by considering a gravitational contribution that only acts in the vertical direction. Furthermore, it is found that for the large computational grid sizes that are typically required in industrial scale fluidized bed simulations, a closure for the meso-scale interphase force is essential. Finally, also for coarse grids, a non-linearity correction factor, which accounts for assumptions in deriving the drift velocity-based form of the filtered drag force, requires closure. The present study therefore highlights multiple avenues for improving drag closures used in fTFMs. Hence, these results may critically strengthen the predictive capabilities of fTFMs, as well as guide future modelling efforts. [ABSTRACT FROM AUTHOR]

Highlights • Filtered Two Fluid Model closures for solids stresses are thoroughly investigated. • Meso-scale solids stresses dominate, but other stresses feature at smaller filter sizes. • The established Boussinesq-based meso-scale stress modelling approach performs poorly. • Novel anisotropic closure proposed for individual meso-scale stress tensor components. • Verification cases illustrate clear improvements in accuracy and grid independence. Abstract Models for predicting flows in large scale fluidized beds, such as filtered Two Fluid Models (fTFMs), must account for meso-scale phenomena that manifest spontaneously in sedimenting gas-particle suspensions. Next to the closures for interphase momentum exchange, the filtered solids stresses also require closure in such models. A budget analysis reveals that, for large filter sizes, the meso-scale solids stresses, which arise due to the particles’ sub-grid velocity fluctuations, are the most important contribution to these stresses. Previously, closures for meso-scale stresses have commonly adopted a Boussinesq approach where (i) a filtered solids pressure is used to close the mean normal stress, and (ii) a filtered solids viscosity is modelled to close the deviatoric stress components. The present study highlights that such a Boussinesq approach fails to accurately predict the forces arising from the meso-scale stresses. This is primarily due to the fundamental inability of a viscosity-based formulation to approximate deviatoric stress components in sedimenting gas-particle suspensions. The present study proposes a novel anisotropic approach in which both normal (i.e., diagonal) and shear (i.e., off-diagonal) stress components are modelled individually. The proposed anisotropic closure explains resolved stress data significantly more reliably (i.e., with a correlation coefficient of R 2 ≈ 0.62) compared to a conventional Boussinesq-based approach (R 2 ≈ - 0.65) using a single model equation. Finally, these findings are confirmed by evaluating different stress closures in fTFM simulations of bubbling and turbulent fluidization. These simulations indicate that the novel anisotropic stress closure leads to improved model generality and better grid independence. Most important, it is found that a classical Boussinesq-based closure leads to worse predictions compared to a complete neglect of meso-scale solids stresses. Thereby, the present study underlines that it is essential to account for anisotropy when closing the meso-scale solids stress in fTFMs. [ABSTRACT FROM AUTHOR]

Highlights • Detailed costs analysis of Power-to-Gas processes with biogas conducted. • Main cost impact caused by electrolysis, biogas costs and electricity consumption. • Fixed bed reactors are two time more expensive than fluidised bed reactors. • Power-to-Gas processes can be profitable until electricity prices of 5.3–6.0 Ct € /kWh el. • The most feasible process contains a fluidised bed methanation and a membrane with 22.7 Ct € /kWh new production costs. Abstract Six different processes for the direct methanation of biogas for biomethane production were evaluated regarding their economically optimised operating conditions, their absolute costs and profitability. Detailed process simulations turned out to be important to obtain a solid process design so that a realistic cost estimate is possible. This is necessary since the stated costs in literature vary by a factor of 10 due to the shortage of simulation details. In addition, cost data for the methanation from recent literature are often under-estimated due to the lack of a required second upgrading step (post-upgrading) to reach the demanded gas grid specifications and of additional process equipment. A fixed bed methanation reactor is two times more expensive than a bubbling fluidised bed reactor but due to the dominant share of costs of the electrolysis, costs differences between the whole processes of 5% are less pronounced. It turned out that a gas separation membrane and a second fixed bed, as a post-upgrading step, are equally expensive. However, a gas separation membrane seems to be technically more robust. Biomethane production costs of 10.2 Ct € /kWh total for processes containing a fluidised bed and of 10.7 Ct € /kWh total for processes containing a main fixed bed are obtained. As a consequence, the corresponding processes are profitable until an electricity price of 6.0 Ct € /kWh el and 5.3 Ct € /kWh el without considering the extra revenues from process heat and oxygen. Furthermore, the profitability of the processes increases with the methane content in the biogas. Considering extra revenues and a concentration increase of 10% for methane in the biogas, the maximum electricity price for a profitable process increases by 3 Ct € /kWh el. [ABSTRACT FROM AUTHOR]

In this paper we apply, for the first time, positron emission particle tracking (PEPT) to a fluidised bed in which gas is injected through a nozzle-type distributor. The detailed, three-dimensional data obtained provide direct insight into how the angle of the orifices through which gas is injected affects the fluidisation, mixing, and flow patterns observed within the bed. Our results show that the fastest and most consistent recirculation of material – an indicator of good mixing – as well as the most complete fluidisation may be achieved by using a nozzle with horizontal- or near-horizontal outlets. • The effect of nozzle design on fluidised bed dynamics was explored. • Detailed three-dimensional data were acquired via positron emission particle tracking. • Angle of nozzle outlets has strong influence on both fluidisation and mixing. • Optimal flow pattern and mixing achieved with downward-facing nozzles. [ABSTRACT FROM AUTHOR]