1,721,037 research outputs found
Heat market for interconnected multi-energy microgrids: A distributed optimization approach
No full textThermal networks, part of heat-and-power multi-energy microgrids, may face capacity issues, generation and distribution ones, either due to the increase in the requested demand or capacity underused, which is sized for peak hours. Under-capacity issues may be addressed with generation and pipeline capacity expansion, resulting in considerable capital costs and extra maintenance costs. In the case of over-capacity, better usage of the existing assets may bring further revenues and increase the multi-energy microgrid’s overall energy efficiency. In the electricity sector, it is being considered the interconnection of microgrids via the distribution system network, since microgrids can operate in both islanded and network-connected modes. In this work, in a similar fashion, we propose the interconnection of adjacent thermal networks enabling direct heat trading among them to increase the micro-grids’ supply flexibility, help meeting demand peaks, and reduce operational costs. Examples of integrated heat-and-power microgrids that could benefit from thermal interconnections are industrial parks, university campuses, hospitals, and even residential complexes with a shared heat generator.
This paper presents a market model for the optimal heat transfer between thermally interconnected heat-and-power microgrids. The resulting model is a convex quadratic programming model that enables the derivation of heat transfer prices that guarantee a competitive equilibrium. Furthermore, we performed numerical tests to explore the impact of connection topology, thermal power transfer capacity, and interconnection efficiency on transferred energy and prices
Double loop circulating fluidized bed reactor system for two reaction processes, based on pneumatically controlled divided loop-seals and bottom extraction/lift
No full textMany industrial processes are based on two reactions: a primary one related to the achievement of the main process objective and a secondary one which is necessary to continuously run the process. Those reactions can be performed continuously by means of two interconnected fluidized beds. The proposed design consists of two interconnected circulating fluidized beds (CFB). Both reactors can be operated in fast fluidization regime improving the particles' gas contact and reducing the reactor's system volume. The two CFBs are interconnected by means of pneumatically controlled divided loop-seals and a bottom extraction/lift. The divided loop-seals can re-circulate back to the reactor of origin part of the entrained solids; this implies that the amount of exchanged solids can be controlled and uncoupled from the amount of entrained solids. The bottom extraction/lift compensates the lower entrainment capability of the reactor with less fluidizing gas availability. An intense hydrodynamic test campaign has been performed with a full scale cold flow model. The design has proven to be reliable offering a stable operational window. Some interesting dependencies of the entrained solids flux have been found: from the cyclone pressure drop and the superficial gas velocity. The divided loop-seal allowed a stable internal recirculation of the entrained solids, up to 50%, without affecting the reactors' hydrodynamics. Such system could work effectively by controlling the pressures in correspondence of the points where the loop-seals return legs merge with the reactors. In this way gas backflows and particle losses through the cyclones are avoided.A safe operational procedure of the pneumatically controlled double loop CFB has been defined by means of a combined usage of the two key components: the bottom extraction/lift and the pneumatically controlled divided loop-seals. Design improvements were also identified. © 2013 Elsevier B.V
Two-stage MINLP algorithm for the optimal synthesis and design of networks of CHP units
Get PDFThis paper proposes a Mixed Integer Non Linear Programming (MINLP) model and two-stage optimization algorithm for determining the most profitable synthesis and design of Combined Heat and Power units within a district heating network with heat storage while taking into account the optimal scheduling of the units over the year. A two-stage algorithm for tackling the challenging MINLP problem is devised: at the upper level the selection and sizing of the units is optimized by means of specifically selected evolutionary algorithms, while at the lower level the operational scheduling problem is linearized and optimized with a commercial Mixed Integer Linear Programing solver. Three different approaches, based on two different evolutionary algorithms and discrete variable relaxation, are devised and compared to tackle the upper level problem. Moreover a bounding technique is proposed to limit the computational time required to solve the lower-level problem. The overall algorithm is tested on an industrial scale problem to find the two system designs leading to the minimum energy consumption and the minimum total annual cost. Computational results indicate that the continuous relaxation of the plant sizes significantly helps to improve the convergence rate of the tested evolutionary algorithm and to find improved solutions. For the considered test case, the design optimized for the minimum energy consumption allows to save 64% of primary energy compared to the minimum total annual cost solution, but with a 28% higher total annual cost
Towards future infrastructures for sustainable multi-energy systems: a review
Get PDFReviewTowards future infrastructures for sustainable multi-energy systems:A reviewElisa Guelpaa,*, Aldo Bischib, Vittorio Verdaa, Michael Chertkovb,c, Henrik LunddaPolitecnico di Torino, Energy Department, ItalybSkolkovo Institute of Science and Technology, Center for Energy Science and Technology, RussiacLos Alamos National Laboratory, Physics of Condensed Matter and Complex Systems, USAdAalborg University, Department of Planning, Denmarkarticle infoArticle history:Received 12 December 2018Received in revised form6 May 2019Accepted 8 May 2019Available online 9 May 2019Keywords:Energy infrastructureSmart energy systemsSmart gridHybrid energy systemsDistrict heatingGas gridabstractIntegration of different energy infrastructures (heat, electricity and gas vectors) offers great potential forbetter managing energy sources, reducing consumption and waste as well as enabling a higher share ofrenewables, lower environmental impact and lower costs. This paper aims at reviewing the state-of-the-art energy system infrastructures in order to provide a comprehensive overview of technologies, oper-ational strategies, modelling aspects and the trends towards integration of heat, electricity and gasinfrastructures.Various technological domains are taken into account, ranging from energy distribution networks(thermal, electric and gas), components for the energy vector conversion (e.g. combined heat and power,power to heat, power to gas, etc.) and energy storage. Furthermore, the aspects related to smart man-agement in energy systems are investigated, such as integration of renewable energy sources and energyrecovery systems
Chemical Looping Reactor System Design: Double Loop Circulating Fluidized Bed (DLCFB)
Get PDFChemical looping combustion (CLC) is continuously gaining more importance among the carbon capture and storage (CCS) technologies. It is an unmixed combustion process which takes place in two steps. An effective way to realize CLC is to use two interconnected fluidized beds and a metallic powder circulating among them, acting as oxygen carrier. The metallic powder oxidizes at high temperature in one of the two reactors, the air reactor (AR). It reacts in a highly exothermic reaction with the oxygen of the injected fluidizing air. Afterwards the particles are sent to the other reactor where the fuel is injected, the fuel reactor (FR). There, they transport heat and oxygen necessary for the reaction with the injected fuel to take place. At high temperatures, the particle’s oxygen reacts with the fuel producing CO2 and steam, and the particles are ready to start the loop again. The overall reaction, the sum of the enthalpy changes of the oxygen carrier oxidation and reduction reactions, is the same as for the conventional combustion.
Two are the key features, which make CLC promising both for costs and capture efficiency. First, the high inherent irreversibility of the conventional combustion is avoided because the energy is utilized stepwise. Second, the CO2 is intrinsically separated within the process; so there is in principle no need either of extra carbon capture devices or of expensive air separation units to produce oxygen for oxy-combustion.
A lot of effort is taking place worldwide on the development of new chemical looping oxygen carrier particles, reactor systems and processes. The current work is focused on the reactor system: a new design is presented, for the construction of an atmospheric 150kWth prototype working with gaseous fuel and possibly with inexpensive oxygen carriers derived from industrial by-products or natural minerals. It consists of two circulating fluidized beds capable to operate in fast fluidization regime; this will increase the particles concentration in the upper section of the reactors, thus the gas solids contact. They are interconnected by means of two pneumatically controlled divided loop-seals and a bottom extraction/lift. The system is designed to be as compact as possible, to help up-scaling and enclosure into a pressurized vessel, aiming pressurization in a second phase. In addition several industrial solutions have been utilized, from highly loaded cyclones to several levels of secondary air injections.
The divided loop-seals are capable to internally re-circulate part of the entrained solids, uncoupling the solids entrainment from the solids exchange. This will provide a better control on the process increasing its flexibility and helping to fulfil downstream requirements. No mechanical valves are utilized, but gas injections. The bottom extraction compensates the lower entrainment of the FR which has less fluidizing gas availability and smaller cross section than the AR. The lift allows adjusting the reactors bottom inventories, thus the pressures in the bottom sections of the reactors. In this way the divided loop-seals are not exposed to large pressure unbalances and the whole system is hydrodynamically more robust.
The proposed design was finally validated by means of a full scale cold flow model (CFM), without chemical reactions. A thorough evaluation of the scaling state-of-the-art in fluidization engineering has been done; two are the approaches. One consists of building a small scale model which resembles the hydrodynamics of the bigger hot setup, by keeping constant a set of dimensionless numbers. The other is based on the construction of a full scale model, being careful to be in the same fluidization regime and to utilize particles with the same fluidization properties as the hot setup. In this way the surface to volume ratio is kept the same as that one of the hot rig. The idea presented in this work combines those two strategies, building a full scale CFM. In this way, it can be used for the hot rig design debugging and it is at the same time the hydrodynamic small scale model of a ten times larger industrial application.
The adopted scaling strategy and design brought to the construction of one of the world biggest and more complex fluidized bed cold flow model reactor systems. The air and fuel reactor have a height of 5 m and a diameter of respectively 0.230 and 0.144 m. The selected particles are fine and heavy being classifiable as high density Geldart A; there is almost no published literature regarding those particles utilization in circulating fluidized beds.
Extensive test campaigns have been performed to hydrodynamically validate the proposed designs. It was possible to understand and evaluate the operational window, the sensitivity to the input parameters and the key design details performance. Control strategies were qualitatively developed. The presented double loop architecture design showed good stability and flexibility at the same time, so that can also suit the requirements of other chemical processes based on two complementary reactions taking place simultaneously and continuously.PhD i energi- og prosessteknikkPhD in Energy and Process Engineerin
Mixed Integer Linear Program model for optimized scheduling of a vanadium redox flow battery with variable efficiencies, capacity fade, and electrolyte maintenance
Get PDFRedox Flow Batteries are a promising option for large-scale stationary energy
storage. The vanadium redox flow battery is the most widely commercialized
system thanks to its chemical stability and performance. This work aims to
optimize the scheduling of a vanadium flow battery that stores energy produced
by a renewable power plant, keeping into account a thorough characterization of
the battery performance, with variable efficiencies and capacity fade effects.
A detailed characterization of the battery performance improves the calculation
of the optimal number of cycles and revenue associated with the battery use if
compared to the results obtained using simpler models, which take into account
constant efficiencies and no capacity fade effects. The presented problem is
nonlinear due to the functions of the battery efficiency, which depend upon
charging and discharging powers and state of charge with nonlinear, non-convex
correlations. The problem is linearized using convex hulls. The optimization
program also calculates the progressive battery capacity fade due to undesired
secondary electrochemical reactions and the economic impact of capacity
restoration through periodic maintenance. The final problem is solved as a
Mixed-Integer Linear Program (MILP) to guarantee the global optimality of the
linearized problem. The proposed optimization model has been applied to two
different case studies: a case of energy arbitrage and a case of load-shifting.
The optimization results have been compared to those obtained with constant
battery efficiency models, which do not consider the capacity fade effects.
Results show that simpler models overestimate the optimal number of cycles of
the battery and the revenue by up to 15% if they do not take into account the
degradation model of the battery, and respectively up to 32% and 42% if they
also assume constant efficiency for the battery.Comment: Journal of Energy Storage, Volume 59, March 2023, 10650
A Rolling-Horizon MILP Optimization Method for the Operational Scheduling of Tri-generation Systems with Incentives
No full textHydrodynamic viability of chemical looping processes by means of cold flow model investigation
No full textSINTEF Energy Research and the Norwegian University of Science and Technology - NTNU have proposed a 150kWthreactor system design aiming at further development of chemical looping processes. It consists of a double loop circulating fluidized bed, meant to be used as a platform to study atmospheric chemical looping combustion configurations, as well as other possible chemical looping processes e.g. gas turbine combustion and reforming. The hydrodynamic viability of the design needs to be tested by means of a cold flow model, operated without chemical reactions. An evaluation of the state of the art within cold flow model testing was done. It led to the choice of building a full scale (i.e. 1:1) cold model of the 150kWthhot rig design, in order to reduce wall-effects which have considerably larger influence at smaller reactor diameters than on larger ones. The cold flow model was extensively tested and experimental results are presented. The aimed design condition, mirroring a chemical looping combustion process adapted to steam generation, was achieved successfully and in a stable way. The performance of the reactor system was further tested in off-design conditions to define operational guidelines for the hot operation. In addition, attempts were done to resemble other chemical looping processes, getting some understanding of how the reactor system may perform and consequently providing solid hydrodynamic bases to improve the design for those applications. In all cases, stable operational sets were found in order to satisfy the cold flow model hydrodynamic requirements consistently with the actual high temperature processes. © 2011 Elsevier Ltd
Techno-economic analysis of a novel solar-driven PEMEC-SOFC-based multi-generation system coupled parabolic trough photovoltaic thermal collector and thermal energy storage
No full textThe present study proposes a novel multi-generation system with a solar-driven proton exchange membrane electrolysis cell, and a solid-oxide fuel cell coupled with a parabolic trough photovoltaic thermal collector and thermal energy storage. Surplus solar electricity is stored as high-pressure green hydrogen, and then a hydrogen-fueled solid-oxide fuel cell is employed to meet the electricity demand at night. The solar heat and other waste heat are stored in a thermal energy storage unit and then utilized to produce cooling/heating and domestic hot water. Multicriteria analyses of thermodynamic and economic performances are conducted to evaluate the techno-economic feasibility of the system, and the characteristics under variable operating conditions are also investigated. The results illustrate that the energy efficiency and exergy efficiency of the parabolic trough photovoltaic thermal collector may reach 80.7 % and 33.8 %, respectively, and the solar electricity of the parabolic trough photovoltaic thermal collector is continuously supplied to the user for 14 h and 9 h under typical cooling mode and heating mode, respectively. The net present value, simple payback period, and dynamic payback period reach 45.78 M/kWh shows the excellent economic superiority
Modeling production and energy needs of a vertical farm
No full textVertical farming represents a promising practice in the agricultural field with clear advantages in water savings and no need for pesticides, but it generally requires a relevant amount of energy in terms of lighting and internal conditioning. For this reason, the trade-off between yield and energy consumption needs to be evaluated. In order to do so, in this study, a transient model capable of evaluating both energy consumption and plant production as a function of internal temperature and light intensity was developed. Plant growth is a function of internal environment parameters as well as energy consumption. In the model both these two aspects were accounted for: building physics behavior (0D model including wall inertia and resistance thermal bridges and external ambient conditions in terms of air temperature, humidity and solar irradiation), conditioning plant (air treatment unit and internal heating/cooling units) and plant growth as a function of internal conditions. The model was realized in Simcenter AMESim, a multiphysics software allowing the development of 0D and 1D models of various physical systems. Results showed the production capacity of the vertical farm for two sizes of buildings and for various combinations of internal temperatures and light intensity, thus energy consumption. The study is performed for Boston (USA), representative of a humid continental climate, densely populated town with a high cost of life
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