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Abstract This paper presents a numerical study of the particle cluster behavior in a riser/downer reactor by means of combined computational fluid dynamics (CFD) and discrete element method (DEM), in which the motion of discrete particles is obtained by solving Newton's equations of motion and the flow of continuum gas by the Navier–Stokes equations. It is shown that the existence of particle clusters, unique to the solid flow behavior in such a reactor, can be predicted from this first principle approach. The results demonstrate that there are two types of clusters in a riser and downer: one is in the near wall region where the velocities of particles are low; the other is in the center region where the velocities of particles are high. While the extent of particle aggregation appears to be similar, the duration time for the first type in a downer is shorter than in a riser. Furthermore, it is demonstrated that the formation of clusters is affected by a range of variables related to operational conditions, particle properties, and bed properties and geometry. The increase of solid volume fraction, sliding and rolling friction between particles or between particles and wall, or damping coefficient can enhance the formation of clusters. The use of multi-sized particles can also promote the formation of clusters. But the increase of gas velocity or use of a wider bed can suppress the formation of clusters. The van der Waals force may enhance the formation of clusters when solid concentration is high but suppress the formation of clusters near the wall region when solid concentration is low.

Abstract Plug flow attracts continuous interest due to its advantages of low particle attrition, low pipeline wear and low energy consumption. A novel non-mechanical draft tube type feeder (DTF) has been proposed in our previous work for vertical plug conveying of coarse particles. Detailed particle motion behaviors and plug formation mechanisms in the draft tube type feeder are investigated by the combined approach of Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) in the present study. The CFD-DEM method based on local averaging of granular matter is used to deal with fluid cell sizes smaller than particle sizes under the specific conditions. The applicability of the model is verified by comparing the calculated results with the experimental results of vertical plug formation of 6 mm glass beads in a draft tube type feeder, in terms of plug flow pattern, pressure drop and solid mass flow rate. Detailed analysis of the particle entrainment in feeder container, flow properties at riser inlet and natural plug formation in riser are then carried out. It is found that both gas and particle flows result in entrainment effect on particles, respectively, through fluid-particle and particle-particle interactions. The linear increase of solid mass flow rate with superficial gas velocity is closely related to the linear increase of particle vertical velocity at riser inlet. Plug formation is achieved in a natural way, which shows the features of self-organization phenomenon. Particle concentration is a key parameter in this self-organization process. This study provides some insights into the natural plug formation of coarse particles in a non-mechanical feeder. The model should be useful to study the gas-solid flow of coarse particles in a confined domain with complex geometry, where the fluid cell size may be smaller than the particle size.

This paper presents a method for harmoniously coordinating roles between generators and faster-acting energy storage systems (ESSs), e.g. batteries, to improve their frequency response and regulation services to the grid, particularly at the high wind penetration. The paper theoretically demonstrates that the proposed droop with the state of charge (SOC) feedback (DaSOF) provides a unified frequency control framework for distributed and energy-constrained ESS, seamlessly fitting the conventional primary and secondary frequency control practice. The ESS autonomously takes charge of high-frequency components of a frequency deviation and thus complements the frequency controls of the incumbent generators. By securing the SOC of the ESS at the desired level, the method provides the capability to provide other ancillary services from the energy constrained ESS. These coordinated roles are represented and validated through time and frequency domain analyses. Rigorous case studies using DIgSILENT/PowerFactory demonstrate the efficacy of the proposed method to support the high level of variable renewable energy, which should help improve the value of operating the ESS and scale up renewable energy.

Abstract This paper presents a new approach to the extraction of a single-diode five-parameter model and its performance evaluation. The proposed model can analytically describe the current–voltage (I–V) and power–voltage (P–V) characteristics of a photovoltaic (PV) module in different conditions. The PV parameters mainly identify the accuracy of any PV model. Different evaluation criteria have been used in this study. All benchmark used to compare current results accuracy with literature studies outcomes. In addition, the performance of the five parameters tested. Results of PV parameters performance showed clear improvements, which are evident in the I–V and P–V characteristics. Consequently, the proposed model introduces five accurate and flexible parameters, compared to legacy work. The extracted parameters are based on nine coefficients. Results also show the effect of the five parameters on maximum power point (MPP), short circuit current (Isc), and open circuit voltage (Voc). Furthermore, a brief review on the PV parameter extraction methods and its accuracy level has been completed.

MOFs derived ZnCo–Fe nanocages are synthesized by a self-templated approach showing the remarkable performance for OER catalysts.

To reduce the costs of controlling emissions from coal-fired power stations, we propose an advanced and effective process of combined SO2 removal and NH3 recycling, which can be integrated with the aqueous NH3-based CO2 capture process to simultaneously achieve SO2 and CO2 removal, NH3 recycling and flue gas cooling in one process. A rigorous, rate-based model for an NH3–CO2–SO2–H2O system was developed and used to simulate the proposed process. The model was thermodynamically and kinetically validated by experimental results from the open literature and pilot-plant trials, respectively. Under typical flue gas conditions, the proposed process has SO2 removal and NH3 reuse efficiencies of >99.9%. The process is strongly adaptable to different scenarios such as high SO2 levels in flue gas, high NH3 levels from the CO2 absorber and high flue gas temperatures, and has a low energy requirement. Because the process simplifies flue gas desulphurisation and resolves the problems of NH3 loss and SO2 removal, it could significantly reduce the cost of CO2 and SO2 capture by aqueous NH3.

The CO2 permeability of fractured coal is of great significance to both coalbed gas extraction and CO2 storage in coal seams, but the effects of high confining pressure, high injection pressure and elevated temperature on the CO2 permeability of fractured coal with different fracture extents have not been investigated thoroughly. In this paper, the CO2 permeability of fractured coals sampled from a Pingdingshan coal mine in China and artificially fractured to a certain extent is investigated through undrained triaxial tests. The CO2 permeability is measured under the confining pressure with a range of 10–25 MPa, injection pressure with a range of 6–12 MPa and elevated temperature with a range of 25–70°C. A mechanistic model is then proposed to characterize the CO2 permeability of the fractured coals. The effects of thermal expansion, temperature-induced reduction of adsorption capacity, and thermal micro-cracking on the CO2 permeability are explored. The test results show that the CO2 permeability of naturally fractured coal saliently increases with increasing injection pressure. The increase of confining pressure reduces the permeability of both naturally fractured coal and secondarily fractured coal. It is also observed that initial fracturing by external loads can enhance the permeability, but further fracturing reduces the permeability. The CO2 permeability decreases with the elevation of temperature if the temperature is lower than 44°C, but the permeability increases with temperature once the temperature is beyond 44°C. The mechanistic model well describes these compaction mechanisms induced by confining pressure, injection pressure and the complex effects induced by elevated temperature.

AbstractBACKGROUNDThe current study investigated the co‐pyrolysis nature of biomasses, gas yields, kinetics and thermodynamics of Chroococcus sp. (CC), digested municipal solid waste (DMSW) and their mixtures using thermogravimetric analysis and mass spectrometry.RESULTSThermogravimetric/differential thermogravimetric analysis indicated three major weight loss stages: dehydration (50–150 °C), thermal degradation of structural components (150–550 °C) and char decomposition (550–800 °C). The gases released during the process mainly contained CO, CH4, CO2 and H2 as main components. Also, with an increase in the composition of CC, the hydrogen yields were noticed to increase. Model‐free isoconversional methods, the Kissinger–Akahira–Sunose and Friedman methods, were considered to identify the activation energy. The kinetic results showed that an increase in the percentage of CC in the mixture lowered the activation energy. The activation energies recorded for CC, DMSW, CD‐1, ‐2 and ‐3 were 282.11, 202.55, 210.54, 145.46 and 139.98 kJ mol−1, respectively.CONCLUSIONSThermodynamic and kinetic analysis for CC, DMSW and their mixtures can be effectively used for reactor design and process optimization for similar types of waste materials. © 2021 Society of Chemical Industry (SCI).