Parametric study of chemical looping combustion for tri‐generation of hydrogen,heat, and electrical power with CO2 capture

In this article, a novel cycle configuration has been studied, termed the extended chemical looping combustion integrated in a steam‐injected gas turbine cycle. The products of this system are hydrogen, heat, and electrical power. Furthermore, the system inherently separates the CO₂ and hydrogen that is produced during the combustion. The core process is an extended chemical looping combustion (exCLC) process which is based on classical chemical looping combustion (CLC). In classical CLC, a solid oxygen carrier circulates between two fluidized bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO₂ separation occurs. In exCLC the oxygen carrier circulates along with a carbon carrier between three fluidized bed reactors, one to oxidize the oxygen carrier, one to produces and separate the hydrogen, and one to regenerate the carbon carrier. The impacts of process parameters, such as flowrates and temperatures have been studied on the efficiencies of producing electrical power, hydrogen, and district heating and on the degree of capturing CO₂. The result shows that this process has the potential to achieve a thermal efficiency of 54% while 96% of the CO₂ is captured and compressed to 110 bar. Copyright © 2005 John Wiley & Sons, Ltd.     

Simultaneous production of two types of synthesis gas by steam and tri‐reforming of methane using an integrated thermally coupled reactor: mathematical modeling

In this work, tri‐reforming and steam reforming processes have been coupled thermally together in a reactor for production of two types of synthesis gases. A multitubular reactor with 184 two‐concentric‐tubes has been proposed for coupling reactions of tri‐reforming and steam reforming of methane. Tri‐reforming reactions occur in outer tube side of the two‐concentric‐tube reactor and generate the needed energy for inner tube side, where steam reforming process is taking place. The cocurrent mode is investigated, and the simulation results of steam reforming side of the reactor are compared with corresponding predictions for thermally coupled steam reformer and also conventional fixed‐bed steam reformer reactor operated at the same feed conditions. This reactor produces two types of syngas with different H₂/CO ratios. Results revealed that H₂/CO ratio at the output of steam and tri‐reforming sides reached to 1.1 and 9.2, respectively. In this configuration, steam reforming reaction is proceeded by excess generated heat from tri‐reforming reaction instead of huge fired‐furnace in conventional steam reformer. Elimination of a low performance fired‐furnace and replacing it with a high performance reactor causes a reduction in full consumption with production of a new type of synthesis gas. The reactor performance is analyzed on the basis of methane conversion and hydrogen yield in both sides and is investigated numerically for various inlet temperature and molar flow rate of tri‐reforming side. A mathematical heterogeneous model is used to simulate both sides of the reactor. The optimum operating parameters for tri‐reforming side in thermally coupled tri‐reformer and steam reformer reactor are methane feed rate and temperature equal to 9264.4 kmol h^?1 and 1100 K, respectively. By increasing the feed flow rate of tri‐reforming side from 28,120 to 140,600 kmol h^?1, methane conversion and H₂ yield at the output of steam reforming side enhanced about 63.4% and 55.2%, respectively. Also by increasing the inlet temperature of tri‐reforming side from 900 to 1300 K, CH₄ conversion and H₂ yield at the output of steam reforming side enhanced about 82.5% and 71.5%, respectively. The results showed that methane conversion at the output of steam and tri‐reforming sides reached to 26.5% and 94%, respectively with the feed temperature of 1100 K of tri‐reforming side. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental and modeling studies of a multi‐tailpipe on a pulse combustor system

The effect of a multi‐tailpipe structure on a pulse combustor with an exhaust decoupler and a vent pipe is investigated. A nonlinear theoretical model is established, and corresponding experiments are made to verify the theoretical model. The results show that the multi‐tailpipe structure has two effects: It enhances the exhaust gas resistance and decreases exhaust gas velocity in the tailpipe; it also expands the tailpipe heat dissipation area and increases the heat loss. The amplitude of pressure fluctuations in the combustion chamber and exhaust decoupler is determined by competition between the strengthening effect of tailpipe resistance and the weakening effect of heat loss from the tailpipe. Frequency and pressure characteristics are dominated by tailpipe resistance and tailpipe heat loss. The working region is divided into three parts for different structure parameters: low frequency inphase zone, unstable zone, and high‐frequency antiphase zone. Tailpipe resistance only affects the unstable zone, and the necessary value of tailpipe friction exists to minimize the unstable zone. Heat loss from the tailpipe can reduce the unstable zone and cause it to squeeze the inphase zone, resulting in shrinkage of the inphase zone. Copyright © 2016 John Wiley & Sons, Ltd.     

Towards maximising the integration of renewable energy hybrid distributed generations for small signal stability enhancement: A review

Integrating renewable energy hybrid distributed generation (REHDG) into distribution network systems (DNSs) has become increasingly important because of various technical, economic, and environmental advantages accruing from it. However, the output power of REHDGs from photovoltaic (PV) and wind is highly variable because of its dependency on intermittent parameters such as solar irradiance, temperature, and wind speed. Such variability of generated power from large-scale REHDGs or load introduces small signal instabilities (oscillations). Meanwhile, different locations of integration and sizes of REHDGs in the DNS affect the system oscillation modes by either improving or depriving the small-signal stability (SSS) of the network. Consequently, a significant number of research has been conducted on the planning of optimal allocation of REHDGs in DNS. In this regard, this paper reviews the existing planning models, optimisation techniques, and resources' uncertainty modelling employed in REHDGs allocations in terms of their capability in obtaining optimal solutions and enhancing SSS of the system. Planning models with optimisation algorithms are evaluated for modelling renewable resource uncertainties and curtailing SSS variables. Research works on planning of optimal allocation of these generations attain minimum cost, but were unable to satisfy the SSS requirements of the system. The existing models for the planning and design of optimal timing, sizing, and placement of REHDGs will need to be improved to optimally allocate REHDGs and satisfy the SSS of the DNS after the integration.     

Entropy generation in an asymmetrically cooled slab with temperature‐dependent internal heat generation

The paper presents an entropy generation analysis for steady conduction in a slab with temperature‐dependent volumetric internal heat generation. The slab experiences asymmetric convective cooling on its two faces. The exact analytical solution for the temperature distribution is used to compute dimensionless local and total entropy generation rates in the slab. The total entropy generation rate depends on five dimensionless parameters: reference heat generation temperature Q, the heat generation–temperature variation parameter a, the temperature asymmetry parameter λ, and Biot numbers Bi₁ and Bi₂. Graphs illustrating the effect of these five parameters on the local and total entropy generation rates are presented and discussed. It is found that the total entropy generation in the slab can be minimized with a suitable choice of the cooling parameters. The paper corrects the flawed entropy results published recently. The present results for the special case of uniform internal heat generation confirm the results presented in a 2003 paper. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20404     

Wind turbines and seismic hazard: a state‐of‐the‐art review

Wind energy is a rapidly growing field of renewable energy, and as such, intensive scientific and societal interest has been already attracted. Research on wind turbine structures has been mostly focused on the structural analysis, design and/or assessment of wind turbines mainly against normal (environmental) exposures while, so far, only marginal attention has been spent on considering extreme natural hazards that threat the reliability of the lifetime‐oriented wind turbine's performance. Especially, recent installations of numerous wind turbines in earthquake prone areas worldwide (e.g., China, USA, India, Southern Europe and East Asia) highlight the necessity for thorough consideration of the seismic implications on these energy harnessing systems. Along these lines, this state‐of‐the‐art paper presents a comparative survey of the published research relevant to the seismic analysis, design and assessment of wind turbines. Based on numerical simulation, either deterministic or probabilistic approaches are reviewed, because they have been adopted to investigate the sensitivity of wind turbines' structural capacity and reliability in earthquake‐induced loading. The relevance of seismic hazard for wind turbines is further enlightened by available experimental studies, being also comprehensively reported through this paper. The main contribution of the study presented herein is to identify the key factors for wind turbines' seismic performance, while important milestones for ongoing and future advancement are emphasized. Copyright © 2016 John Wiley & Sons, Ltd.     

A comprehensive state‐of‐the‐art survey on power generation expansion planning with intermittent renewable energy source and energy storage

Generation expansion planning (GEP) is a power plant mix problem that identifies what, where, when, and how new generating facilities should be installed and when old units be retired over a specific planning horizon. GEP ensures that the quantity of electricity generated matches the electricity demand throughout the planning horizon. This kind of planning is of importance because most production and service delivery is dependent on availability of electricity. Over the years, the traditional GEP approaches have evolved to produce more realistic models and new solution algorithms. For example, with the agitation for green environment, the inclusion of renewable energy plants and energy storage in the traditional GEP model is gradually gaining attention. In this regards, a handful of research has been conducted to identify the optimal expansion plans based on various energy‐related perspectives. The appraisal and classification of studies under these topics are necessary to provide insights for further works in GEP studies. This article therefore presents a comprehensive up‐to‐date review of GEP studies. Result from the survey shows that the integration of demand side management, energy storage systems (ESSs), and short‐term operational characteristics of power plants in GEP models can significantly improve flexibility of power system networks and cause a change in energy production and the optimal capacity mix. Furthermore, this article was able to identify that to effectively integrate ESS into the generation expansion plan, a high temporal resolution dimension is essential. It also provides a policy discussion with regard to the implementation of GEP. This survey provides a broad background to explore new research areas in order to improve the presently available GEP models.     

Performance evaluation of a mercury‐steam combined–energy‐generation system (MES)

In this study, exergy and thermo‐ecology–based performance analyses of a mercury‐steam combined–energy‐generation system are comprehensively presented. Performance characteristics such as net‐power output, net‐power density, exergy efficiency, exergy destruction, and ecological coefficient of performance have been obtained by developing a novel numerical model. The impacts of the pressures of open feed water heater and steam turbines, temperatures of mercury boiler, and mercury turbines on the performance characteristics have been investigated. The results indicated that the performance characteristics of the system have been remarkably affected by the pressure and temperature variations of the system components.     

Zero non‐detection zone assessment for anti‐islanding protection in rotating machines based distributed generation system

The challenges for a reliable operation of electrical power system have increased due to the presence of multi‐distributed generation units (DGs) in the distribution systems in order to meet the increase of the load demand. Detection of unintentional islanding situation is very important as non‐detection of islanding situation could result in a cascaded failure of the system. If the islanding situation remains undetected, the instability in the islanded part can lead to a complete failure of the electrical power system. This paper introduces a new passive scheme for islanding detection, which is suitable for multi‐distributed generation units based on rotating machines. The proposed method is based on the measurements of the system voltage and frequency to compute two indices called the islanding index and harmonics index. The islanding index is the main index used to discriminate and identify the islanding situation. However, the harmonics index in conjunction with a strategy called speed reduction strategy assists the islanding index to discriminate between islanding situation in case of a close power match and system disturbances. The simulation studies were conducted in MATLAB/SIMULINK environment, and various cases have been considered, such as normal operation, islanding operation, sudden load change, DG tripping, separation of some DG units, faults, etc. The novelty of the proposed strategy is that it provides fast detection and has zero nondetection zone compared with the existing detection methods. Moreover, the proposed strategy has no effect on the power quality, and the maximum detection time is almost 350 ms at a close power match. The results indicate that the proposed scheme is successful in discrimination of the islanding conditions from other grid disturbances, revealing its great potential to be able to detect islanding events. Finally, the proposed method is applied only for rotating machine based DGs, such as wind turbines. Wind farms' power generation system based on doubly‐fed induction generators is introduced in this paper as an example of DGs units.     

Zn‐Al hydrotalcite‐derived CoxZnyAlOz catalysts for hydrogen generation by auto‐thermal reforming of acetic acid

Auto‐thermal reforming (ATR) of acetic acid (HAc) is considered as a promising route for hydrogen generation from renewable resources, while oxidation, coking, and sintering need to be addressed for durable catalysts in ATR. In the current work, Zn‐Al hydrotalcite‐derived Co_xZn_yAlO_z catalysts were prepared by co‐precipitation and evaluated in a fixed‐bed tubular quartz continuous‐flow reactor. The Co_0.70Zn_3.30AlO_{5.5 ± δ} catalyst presented a HAc conversation near 100% and a stable hydrogen yield near 3.01 mol‐H₂/mol‐HAc. The characterization results of XRD, H₂‐TPR, BET, SEM, XPS, and TG indicated that the hydrotalcite structure was obtained via co‐precipitation method; over the hydrotalcite‐derived mixed oxides, (a) the specific surface area was increased with high dispersion of Co, (b) the phases of ZnO with spinel of ZnAl₂O₄,CoAl₂O₄, Co₃O₄, and ZnCo₂O₄ were beneficial to improve resistance to coking and oxidation, and (c) the relative stability of Co species over ZnO and spinel phases helps to suppress sintering. Meanwhile, ratio of O/C and temperatures near 0.28 and 650 °C, respectively, were also evaluated and proposed as optimized conditions for hydrogen generation, and the durable Co_0.70Zn_3.30AlO_{5.5 ± δ} catalyst produced a rate of 114.9 mmol‐H₂/s/g‐catalyst in a 15‐hour ATR test, showing promising potential for hydrogen generation.     

Power characteristics of a fuel cell micro‐grid with wind power generation

An independent micro‐grid connected with renewable energy has the potential to reduce energy costs, and reduce the amount of greenhouse gas discharge. However, the frequency and voltage of a micro‐grid may not be stable over a long time due to the input of unstable renewable energy, and changes in short‐period power load that are difficult to predict. Thus, when planning the installation of a micro‐grid, it is necessary to investigate the dynamic characteristics of the power. About the micro‐grid composed from 10 houses, a 2.5 kW proton exchange membrane fuel cell is installed in one building, and it is assumed that this fuel cell operated corresponding to a base load. A 1 kW PEM‐FC is installed in other seven houses, in addition a 1.5 kW wind turbine generator is installed. The micro‐grid to investigate connects these generating equipments, and supplies the power to each house. The dynamic characteristics of this micro‐grid were investigated in numerical analysis, and the cost of fuel consumption and efficiency was also calculated. Moreover, the stabilization time of the micro‐grid and its dynamic characteristics accompanied by wind‐power generation and fluctuation of the power load were studied. Copyright © 2007 John Wiley & Sons, Ltd.     

Distributed generation hybrid AC/DC microgrid protection: A critical review on issues,strategies, and future directions

The integration of distributed energy resources (DERs) with conventional systems emerges as an intelligent solution for providing uninterrupted and secure power even at times of high load demand. Better load management with a mature fault handling mechanism makes AC a viable option which has an efficiency of 78.24%. In contrast with less power loss and slightly better efficiency of 84.6%, DC microgrid is a reliable option in a low power environment. In order to accommodate all operating conditions and load types, a hybrid system can be designed with a theoretical efficiency of more than 90%. Bidirectional power flows, low inertia, the transition between different modes of operations are the challenges for the protection of alternating current (AC) and direct current (DC) microgrid systems. Power balance fluctuation, absence of zero-crossing currents, selection of suitable grounding, and coordination between different rating devices restrict the hybrid system to achieve the said efficiency constantly. This paper reviews in detail of existing protection along with grid-connected algorithms for both modes of operation. Finally, the limitation, major hurdles, and future course of action for a reliable, efficient, and secure hybrid grid system are figured out.     

Hydrogen generation from photocatalytic hydrolysis of alkali‐metal borohydrides

The controllable photocatalytic hydrolysis of alkali‐metal borohydrides is studied for hydrogen generation in this work. The results indicate that the photocatalysis of P25 TiO₂ controllably promotes the hydrogen generation rates from alkali‐metal borohydride hydrolysis. Its apparent activation energy is calculated to be reduced from 57.20 to 53.86 kJ mol^?1. This is due to the mechanism of photocatalytic hydrolysis: holes (h⁺) react with BH₄‐ and OH^? to form H₂ and B(OH)₄‐, meanwhile electrons (e^?) react with H⁺ to from H₂. In addition, Ti³⁺‐doped TiO₂ with a crystalline‐disordered core‐shell structure can be generated during the photocatalytic hydrolysis process. The consumption of e^? is identified as the rate‐limiting step in photocatalytic hydrolysis process. Copyright © 2017 John Wiley & Sons, Ltd.     

Insight into the effect of In addition on hydrogen generation behavior and hydrolysis mechanism of Al‐based ternary alloys in distilled water—A new active Al‐Ga‐In hydrolysis hydrogen generation alloy

(Al2Ga)‐xIn (x = 0, 2, 4, 6, 8 wt%) ternary aluminum (Al) alloys with different weight ratio of In for hydrolysis H₂ generation were prepared by melting‐casting technique. The phase compositions and microstructures of Al‐rich alloys were investigated by X‐ray diffraction (XRD) and high resolution scanning electron microscope (HR‐SEM) equipped with an energy dispersive spectrometer (EDS). The effect of In addition ratio on microstructures and H₂ generation performance were investigated, and the hydrolysis mechanism for Al‐Ga‐In ternary Al‐based alloys has been proposed. Al phase as matrix phase in the Al‐Ga‐In ternary alloy mainly determines the hydrolysis behavior, and the second phase In strongly promotes the hydrolysis process. The increase of In content can accelerate the H₂ generation rate as well as the final capacity and generation yield in neutral water. The generation yields for (Al2Ga)‐x In (x = 2, 4, 6, 8 wt%) alloys at 50°C are 0.56, 0.59, 0.62, and 0.66, respectively. The raising hydrolysis temperature can elevate the initial hydrolysis rate, final H₂ generation capacity, and yield. The H₂ generation capacities of (Al2Ga)‐8In alloy at 50°C, 60°C, and 70°C are 262, 290, and 779 mL·g^?1, respectively.     

Investigation on a low‐melting‐point gallium alloy MHD power generator

A magnetic hydrodynamic (MHD) power generator using an electro‐conductive low‐melting‐point gallium alloy is introduced. An experimental setup is designed and established to investigate its performance with aids of numerical simulations. Theoretical derivations based on Faraday Law are also presented as a theoretical foundation of the present study. It is found that the electric output increases with flow velocity, magnetic strength and electric conductivity, and the theoretical predictions and numerical results are in good agreement with the experimentally measured data. It is understood that in order to obtain a practical power generation, priority should be put on increasing fluid flow velocity and magnetic field strength. The present MHD power generation system has shown to be operated reliably in a long time at room temperature and could be used as a micro‐distributed energy supply system for domestic use in the future. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental‐ and numerical‐simulation research on the inner–secondary‐air ratio in a 600‐MWe down‐fired boiler

Using a phase Doppler‐anemometer measurement system, the cold gas/particle‐airflow behavior in a 1:40 scale‐model furnace was assessed to study the influences of adjusting the inner–secondary‐air ratio in a 600‐MW_e multi‐injection and multistaging down‐fired boiler. Numerical simulations were also conducted to verify the results of the modeling trials and to provide heat‐state information. The results demonstrate that reducing the inner–secondary‐air ratio from 19.66% to 7.66% gradually enhances the downward velocity decay of the gas/particle airflow, while the inner secondary‐air downward‐entraining effect on the fuel‐rich flow is weakened. Lowering the inner–secondary‐air ratio greatly inhibits the decay of the near burner–particle volume flux. In addition, the fuel rich–flow ignition distance is reduced, from 1.02 to 0.87 m. A lower inner–secondary‐air ratio is harmful to restrain early NO_x formation. Reducing the ratio also causes the fuel‐rich flow to turn upwards ahead, while the penetration depth of this flow gradually decreases and the maximum temperature in the hopper region falls from 1900 to 1800 K. On the basis of these data, an optimal inner–secondary‐air ratio of 13.66% is recommended.     

Investigation of the distributed generation penetration in a medium voltage power distribution network

This paper investigates the results of the distributed generation penetration in a weak medium voltage power distribution network. The connected distributed generation resources are in their entirety small hydroelectric plants. Their locations are predetermined. Specifically, the influence of distributed generation on the network branch currents and voltage profile as well as on the short‐circuit level at the medium voltage busbars of the infeeding substation are examined using a commercial‐grade software package. The arising problems are explored and alternative technical solutions to deal with them are proposed. Finally, an initial proposal for an optimum distributed generation penetration in the predetermined network positions is given. A real‐world study case, rather than a simplified academic network, is selected to be analysed in order to specify, as accurately as possible, the arising practical problems and to use this experience in the future in the development of a fast and reliable method for the determination of optimal distributed generation allocation in random network positions. Copyright © 2009 John Wiley & Sons, Ltd.     

Catalytic effect of EG and MoS2 on hydrolysis hydrogen generation behavior of high‐energy ball‐milled Mg‐10wt.%Ni alloys in NaCl solution—A powerful strategy for superior hydrogen generation performance

In this study, the metallurgical melting Mg‐10wt.%Ni (Mg10Ni) alloy is firstly modified by high‐energy ball milling (HEBM) and then surface catalysts expanded graphite (EG) or MoS₂ or EG‐MoS₂ are introduced to prepare Mg10Ni‐M (M = EG, MoS₂, and EG‐MoS₂) composites. The effects of surface catalysts on hydrolysis hydrogen generation of HEBM Mg10Ni alloy are comprehensively investigated. Their kinetics, rate‐limiting steps, and apparent activation energies are investigated by fitting the hydrolysis curves at different temperatures. The results indicate that the total hydrogen generation capacities of prepared Mg10Ni‐M (M = EG, MoS₂, and EG‐MoS₂) composites are 200, 170, 674, and 720 mL·g^?1 within 1 minute at 291 K. The capacity and yield of Mg10Ni are 500 mL·g^?1 and 56% within 15 minutes. The surface catalysts EG or MoS₂ or EG‐MoS₂ can distinctly elevate the initial H₂ produce rate and promote the complete hydrolysis process. The highest capacity and generation yield within 15 minutes are 740.8 mL·g^?1 and 91% obtained by HEBM Mg10Ni‐EG‐MoS₂ composite at 291 K. The surface catalysis can promote high generation yield of Mg10Ni alloy in a short time.     

Entropy generation in an unsteady Eyring‐Powell hybrid nanofluid flow over a permeable surface: A Lie group analysis

In thermal processes, the choice of the thermofluid plays an essential role in minimizing entropy generation and thereby improving thermal efficiency. In this study, entropy generation in a viscous hybrid nanofluid described by the Eyring‐Powell model is investigated. The model accounts for the effect of the nanoparticle volume fraction and viscous dissipation on an Eyring‐Powell Cu‐Al₂O₃/ethylene glycol nanofluid. A similarity solution to the time‐dependent model is found using the Lie group symmetry technique. The bivariate spectral quasi‐linearization method is used for the solution of the self‐similar transport equations. We analyze the effects of the nanoparticle volume fraction, suction/injection, and viscous dissipation on the fluid properties. The skin friction and Nusselt number are determined. A comparison between the Nusselt number of a regular nanofluid and a hybrid nanofluid shows that the hybrid nanofluid has better thermal characteristics compared with the regular nanofluid. The findings show that a decrease in the nanoparticle volume fraction and Eckert number minimizes entropy generation in the system.     

Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines

In this study, an innovative concept for load reduction on the two‐bladed Skywind 3.4 MW prototype is presented. The load reduction system consists of a flexible coupling between the hub mount, carrying the drive train components including the hub assembly, and a nacelle carrier supported by the yaw bearing. This paper intends to assess the impact of introducing a flexible hub connection on the system dynamics and the aero‐elastic response to aerodynamic load imbalances. In order to limit the rotational joint motion, a cardanic spring‐damper element is introduced between the hub mount and the nacelle carrier flange, which affects the system response and the loads. A parameter variation of the stiffness and damping of the connecting spring‐damper element has been performed in the multi‐body simulation solver Simpack. A deterministic, vertically sheared wind field is applied to induce a periodic aerodynamic imbalance on the rotor. The aero‐structural load reduction mechanisms of the coupled system are thereby identified. It is shown that the fatigue loads on the blades and the turbine support structure are reduced significantly. For a very low structural coupling, however, the corresponding rotational deflections of the hub mount exceed the design limit of operation. The analysis of the interaction between the hub mount motion and the blade aerodynamics in a transient inflow environment indicates a reduction of the angle of attack amplitudes and the corresponding fluctuations of the blade loading. Hence, it can be concluded that load reduction is achieved by a combination of reduced structural coupling and a mitigation of aerodynamic load imbalances. Copyright © 2016 John Wiley & Sons, Ltd.