Special Issue "Selected Papers from SDEWES 2018 Conferences on Sustainable Development of Energy, Water and Environment Systems"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 December 2018).

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A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Neven Duić
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Guest Editor
Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Lučićeva 5, HR-10000 Zagreb, Croatia
Interests: energy planning of energy systems with high penetration of renewables; sustainable communities; energy policy; energy economics; mitigation of climate change; energy efficiency and combustion engineering
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Prof. Dr. Mário Costa †
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Guest Editor
Prof. Dr. Qiuwang Wang
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Guest Editor
Key Laboratory of Thermo-Fluid Science and Engineering (Ministry of Education), Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China
Interests: heat transfer enhancement and its applications to engineering problems; high-temperature heat transfer and fluid flow; transport phenomena in porous media; numerical simulation; prediction and optimization
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Prof. Dr. Francesco Calise
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Guest Editor
Department of Industrial Engineering, University of Naples Federico II, 80125 Naples, Italy
Interests: fuel cells; advanced optimization techniques; solar thermal systems; concentrating photovoltaic/thermal photovoltaic systems; energy saving in buildings; solar heating and cooling; organic Rankine cycles; geothermal energy; dynamic simulations of energy systems; renewable polygeneration systems
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Prof. Dr. Poul Alberg Østergaard
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Guest Editor
Department of Planning, Aalborg University, 9000 Aalborg, Denmark
Interests: energy systems; energy scenarios; renewable energy system integration; energy and development; environmental impacts from energy development
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Special Issue Information

Dear Colleagues,

One of the main issues of the coming decades is the need to improve efficiencies by integrating various life supporting systems, using waste from one as a resource in another, in the exact moment when it is beneficial to all, integrating electricity, heating, cooling, transport, water, buildings, waste, wastewater, industry, forestry, and agriculture systems. Sustainability is also a perfect field for the interdisciplinary and multi-cultural evaluation of complex systems. The SDEWES conferences have become a significant venue for researchers in those areas to meet and originate, discuss, share, and disseminate new ideas.

Energy has been and is the key-factor in human development. However, it is also one of the main—if not the main—human environmental fingerprints. Even with the significant attention paid to the importance and merits of sustainable energy supply over the past several decades, there are still significant gaps to be filled with respect to how to design and implement technically optimal energy systems at the lowest costs.

This Special Issue aims to provide an important contribution by presenting state-of-the-art knowledge with sustainable energy supply solutions ranging from the technical analyses of energy components on both supply and demand sides to energy scenarios and pathways. This Special Issue particularly welcomes SDEWES papers that address the energy system without traditional sector boundaries between electricity, heating, cooling, transportation, and industrial demands, and rather considers the integration and synergies between these sectors.

Three conferences on the Sustainable Development of Energy, Water and Environment Systems (SDEWES Conferences) were held in 2018: the 1st Latin American SDEWES in Rio de Janeiro, Brazil in January, the 3rd Southeast European SDEWES in Novi Sad, Serbia in July, and the 13th SDEWES in Palermo, Italy in October, were dedicated to the improvement and dissemination of knowledge on methods, policies, and technologies for increasing the sustainability of development by de-coupling growth from natural resources and replacing them with knowledge-based economy, taking into account economic, environmental, and social pillars.

Prof. Dr. Neven Duić
Prof. Dr. Mário Costa
Prof. Dr. Qiuwang Wang
Prof. Dr. Francesco Calise
Prof. Dr. Poul Alberg Østergaard
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • sustainability comparisons and measurements
  • smart energy systems
  • energy policy
  • water–energy nexus
  • energy system analysis
  • renewable energy resources
  • primary energy resources
  • renewable electricity generation systems
  • thermal power plants
  • district heating and/or cooling
  • advanced sustainable energy conversion systems
  • renewable heat systems
  • biofuels and biorefineries
  • alternative fuels
  • hybrid and electric vehicles
  • water treatment for drinking water
  • modelling for pollution avoidance and energy efficiency
  • cogeneration, trigeneration, polygeneration
  • energy storage
  • electricity transmission and distribution
  • gas security of supply
  • energy efficiency in industry and mining
  • energy-efficient appliances
  • energy efficiency in buildings
  • energy markets

Published Papers (24 papers)

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Open AccessFeature PaperReview
Toward an Efficient and Sustainable Use of Energy in Industries and Cities
Energies 2019, 12(16), 3150; https://doi.org/10.3390/en12163150 - 16 Aug 2019
Cited by 2
Abstract
Several countries have recently realized that the present development paradigm is not sustainable from an environmental and energy point of view. The growing awareness of the population regarding environmental issues is pushing governments worldwide more and more to promote policies aiming at limiting [...] Read more.
Several countries have recently realized that the present development paradigm is not sustainable from an environmental and energy point of view. The growing awareness of the population regarding environmental issues is pushing governments worldwide more and more to promote policies aiming at limiting harmful effects of human development. In particular, the rapid increase of the global temperature, especially in the polar regions, and the management of human wastes, mainly plastic in seas, are some of the main points to be addressed by these novel policies. Several actions must be implemented in order to limit such issues. Unfortunately, the recent COP 24 Conference was not successful, but hopefully an agreement will be established in 2020 at the COP 26 Conference. The effort performed by policymakers must be mandatorily supported by the scientific community. In this framework, this paper aims at showing that countries worldwide are trying to negotiate an agreement to increase energy efficiency and reduce greenhouse gas (GHG) emissions. In addition, in this paper all the researchers reported can provide quantitative measures of the actions to be implemented in order to address a sustainable and efficient use of energy. Here, innovations in terms of novel efficient and environmentally friendly technologies mainly based on renewable energy sources have been also investigated. The study also highlights different sectors that have been involved for this aim, such as energy conversion systems, urban areas, mobility, sustainability, water management, social aspects, etc. In this framework, specific conferences are periodically organized in order to provide a forum for discussion regarding these topics. In this area the Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference is the most ordinary conference. The 13th Sustainable Development of Energy, Water and Environment Systems Conference was held in Palermo, Italy in 2018. The current Special Issue of Energies, precisely dedicated to the 13th SDEWES Conference, is based on three main topics: energy policy and energy efficiency in urban areas, energy efficiency in industry and biomass and other miscellaneous energy systems. Full article
Open AccessArticle
Renewable Energy Generation Scenarios Using 3D Urban Modeling Tools—Methodology for Heat Pump and Co-Generation Systems with Case Study Application
Energies 2019, 12(3), 403; https://doi.org/10.3390/en12030403 - 28 Jan 2019
Cited by 6
Abstract
In the paper, a method was developed to automatically dimensionalize and calculate central energy generation and supply scenarios with a district heating system for cities based on 3D building models in the CityGML format and their simulated heat demand. In addition, the roof [...] Read more.
In the paper, a method was developed to automatically dimensionalize and calculate central energy generation and supply scenarios with a district heating system for cities based on 3D building models in the CityGML format and their simulated heat demand. In addition, the roof geometry of every individual building is used to model photovoltaic energy generation potential. Two types of supply systems, namely a central heat pump (HP) system and a large co-generation (combined heat and power-CHP) system (both with a central storage and district distribution system), are modeled to supply the heat demand of the area under investigation. Both energy generation models are applied to a case study town of 1610 buildings. For the HP scenario, it can be shown that the case study town’s heat demand can be covered by a monovalent, low-temperature system with storage, but that the PV only contributes 15% to the HP electricity requirement. For the CHP scenario, only 61% of the heat demand can be covered by the CHP, as it was designed for a minimum of 4000 operating hours. Both the PV and the CHP excess electricity are fully injected into the grid. As a result, the primary energy comparison of both systems strongly depends on the chosen primary energy factors (PEF): with given German regulations the CHP system performs better than the HP system, as the grid-injected electricity has a PEF of 2.8. In the future, with increasingly lower PEFs for electricity, the situation reverses, and HPs perform better, especially if the CHP continues to use natural gas. Even when renewable gas from a power to gas (P2G) process is used for the CHP, the primary energy balance of the HP system is better, because of high conversion losses in the P2G process. Full article
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Open AccessArticle
District Cooling Versus Individual Cooling in Urban Energy Systems: The Impact of District Energy Share in Cities on the Optimal Storage Sizing
Energies 2019, 12(3), 407; https://doi.org/10.3390/en12030407 - 28 Jan 2019
Cited by 5
Abstract
The energy transition of future urban energy systems is still the subject of an ongoing debate. District energy supply can play an important role in reducing the total socio-economic costs of energy systems and primary energy supply. Although lots of research was done [...] Read more.
The energy transition of future urban energy systems is still the subject of an ongoing debate. District energy supply can play an important role in reducing the total socio-economic costs of energy systems and primary energy supply. Although lots of research was done on integrated modelling including district heating, there is a lack of research on integrated energy modelling including district cooling. This paper addressed the latter gap using linear continuous optimization model of the whole energy system, using Singapore for a case study. Results showed that optimal district cooling share was 30% of the total cooling energy demand for both developed scenarios, one that took into account spatial constraints for photovoltaics installation and the other one that did not. In the scenario that took into account existing spatial constraints for installations, optimal capacities of methane and thermal energy storage types were much larger than capacities of grid battery storage, battery storage in vehicles and hydrogen storage. Grid battery storage correlated with photovoltaics capacity installed in the energy system. Furthermore, it was shown that successful representation of long-term storage solutions in urban energy models reduced the total socio-economic costs of the energy system for 4.1%. Full article
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Open AccessArticle
Fuel Switch to LNG in Heavy Truck Traffic
Energies 2019, 12(3), 515; https://doi.org/10.3390/en12030515 - 06 Feb 2019
Cited by 8
Abstract
Liquefied natural gas (LNG) use as a fuel in road and maritime traffic has increased rapidly, and it is slowly entering railroad traffic as well. The trend was pushed by the state administrations of mainly EU countries and international organizations seeing LNG as [...] Read more.
Liquefied natural gas (LNG) use as a fuel in road and maritime traffic has increased rapidly, and it is slowly entering railroad traffic as well. The trend was pushed by the state administrations of mainly EU countries and international organizations seeing LNG as a cost-effective and environmentally friendly alternative to diesel. Different infrastructural projects for the widespread use of LNG in transport have been launched around the world. The main goal of this paper was to analyze use of LNG as a fuel for heavy trucks. Different aspects of LNG chain were analyzed along with economical and ecological benefits of LNG application. Filling stations network for LNG were described for the purpose of comparative analysis of diesel and LNG heavy trucks. Conclusion has shown that using LNG as propellant fuel has numerous advantages over the use of conventional fuels. The higher initial investment of the LNG road vehicles could be amortized in their lifetime use, and in the long-term they are more affordable than the classic diesel vehicles. In addition to cost-effectiveness, LNG road vehicles reduce CO2 emissions. Therefore, the environmental goals in transport, not only of the member states but worldwide, could not be met without LNG in heavy truck traffic. Full article
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Open AccessArticle
Synthesis and Optimal Operation of Smart Microgrids Serving a Cluster of Buildings on a Campus with Centralized and Distributed Hybrid Renewable Energy Units
Energies 2019, 12(4), 745; https://doi.org/10.3390/en12040745 - 23 Feb 2019
Cited by 9
Abstract
Micro-district heating networks based on cogeneration plants and renewable energy technologies are considered efficient, viable and environmentally-friendly solutions to realizing smart multi-energy microgrids. Nonetheless, the energy production from renewable sources is intermittent and stochastic, and cogeneration units are characterized by fixed power-to-heat ratios, [...] Read more.
Micro-district heating networks based on cogeneration plants and renewable energy technologies are considered efficient, viable and environmentally-friendly solutions to realizing smart multi-energy microgrids. Nonetheless, the energy production from renewable sources is intermittent and stochastic, and cogeneration units are characterized by fixed power-to-heat ratios, which are incompatible with fluctuating thermal and electric demands. These drawbacks can be partially overcome by smart operational controls that are capable of maximizing the energy system performance. Moreover, electrically driven heat pumps may add flexibility to the system, by shifting thermal loads into electric loads. In this paper, a novel configuration for smart multi-energy microgrids, which combines centralized and distributed energy units is proposed. A centralized cogeneration system, consisting of an internal combustion engine is connected to a micro-district heating network. Distributed electric heat pumps assist the thermal production at the building level, giving operational flexibility to the system and supporting the integration of renewable energy technologies, i.e., wind turbines, photovoltaic panels, and solar thermal collectors. The proposed configuration was tested in a hypothetical case study, namely, a University Campus located in Trieste, Italy. The system operation is based on a cost-optimal control strategy and the effect of the size of the cogeneration unit and heat pumps was investigated. A comparison with a conventional configuration, without distributed heat pumps, was also performed. The results show that the proposed configuration outperformed the conventional one, leading to a total-cost saving of around 8%, a carbon emission reduction of 11%, and a primary energy saving of 8%. Full article
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Open AccessArticle
Covenant of Mayors: Local Energy Generation, Methodology, Policies and Good Practice Examples
Energies 2019, 12(6), 985; https://doi.org/10.3390/en12060985 - 13 Mar 2019
Cited by 5
Abstract
Local authorities and cities are at the forefront of driving the energy transition, which plays a crucial role in mitigating the effects of climate change. The greenhouse gas emissions in cities, due to energy consumption, are placed into two categories: direct emissions generated [...] Read more.
Local authorities and cities are at the forefront of driving the energy transition, which plays a crucial role in mitigating the effects of climate change. The greenhouse gas emissions in cities, due to energy consumption, are placed into two categories: direct emissions generated from the combustion of fossil fuels mainly in buildings and transport sectors, and indirect emissions from grid-supplied energy, such as electricity and district heating and/or cooling. While there is extensive literature focused on direct greenhouse gas emissions accounting in cities’ inventories, research has focused to a lesser extent on allocation methods of indirect emissions from grid-supplied energy. The present paper provides an updated definition for the concept of local energy generation within the Covenant of Mayors initiative and proposes a new methodology for indirect emission accounting in cities’ greenhouse gas emission inventories. In addition, a broader policy framework in which local action is taken is discussed based on the European Union energy and climate policies, and over 80 exemplary Covenant of Mayors good practices are identified across the technology areas of local energy generation and four modes of urban climate governance. The contributions of the paper demonstrate that local authorities have the capacity to support and mobilize action for local energy generation investments through the multiple modes of urban climate governance to update and strengthen climate action Full article
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Open AccessArticle
Sustainable Zoning, Land-Use Allocation and Facility Location Optimisation in Smart Cities
Energies 2019, 12(7), 1318; https://doi.org/10.3390/en12071318 - 05 Apr 2019
Cited by 3
Abstract
Many cities around the world are facing immense pressure due to the expediting growth rates in urban population levels. The notion of ‘smart cities’ has been proposed as a solution to enhance the sustainability of cities through effective urban management of governance, energy [...] Read more.
Many cities around the world are facing immense pressure due to the expediting growth rates in urban population levels. The notion of ‘smart cities’ has been proposed as a solution to enhance the sustainability of cities through effective urban management of governance, energy and transportation. The research presented herein examines the applicability of a mathematical framework to enhance the sustainability of decisions involved in zoning, land-use allocation and facility location within smart cities. In particular, a mathematical optimisation framework is proposed, which links through with other platforms in city settings, for optimising the zoning, land-use allocation, location of new buildings and the investment decisions made regarding infrastructure works in smart cities. Multiple objective functions are formulated to optimise social, economic and environmental considerations in the urban space. The impact on underlying traffic of location choices made for the newly introduced buildings is accounted for through optimised assignment of traffic to the underlying network. A case example on urban planning and infrastructure development within a smart city is used to demonstrate the applicability of the proposed method. Full article
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Open AccessArticle
Energy Embedded in Food Loss Management and in the Production of Uneaten Food: Seeking a Sustainable Pathway
Energies 2019, 12(4), 767; https://doi.org/10.3390/en12040767 - 25 Feb 2019
Cited by 7
Abstract
Recently, important efforts have been made to define food loss management strategies. Most strategies have mainly been focused on mass and energy recovery through mixed food loss in centralised recovery models. This work aims to highlight the need to address a decentralised food [...] Read more.
Recently, important efforts have been made to define food loss management strategies. Most strategies have mainly been focused on mass and energy recovery through mixed food loss in centralised recovery models. This work aims to highlight the need to address a decentralised food loss management, in order to manage the different fractions and on each of the different stages of the food supply chain. For this purpose, an energy flow analysis is made, through the calculation of the primary energy demand of four stages and 11 food categories of the Spanish food supply chain in 2015. The energy efficiency assessment is conducted under a resource use perspective, using the energy return on investment (EROI) ratio, and a circular economy perspective, developing an Energy return on investment – Circular economy index (EROIce), based on a food waste-to-energy-to-food approach. Results suggest that the embodied energy loss consist of 17% of the total primary energy demand, and related to the food categories, the vegetarian diet appears to be the most efficient, followed by the pescetarian diet. Comparing food energy loss values with the estimated energy provided for one consumer, it is highlighted the fact that the food energy loss generated by two to three persons amounts to one person's total daily intake. Moreover, cereals is the category responsible for the highest percentage on the total food energy loss (44%); following by meat, fish and seafood and vegetables. When the results of food energy loss and embodied energy loss are related, it is observed that categories such as meat and fish and seafood have a very high primary energy demand to produce less food, besides that the parts of the food supply chain with more energy recovery potential are the beginning and the end. Finally, the EROIce analysis shows that in the categories of meat, fish and seafood and cereals, anaerobic digestion and composting is the best option for energy recovery. From the results, it is discussed the possibility to developed local digesters at the beginning and end of the food supply chain, as well as to developed double digesters installations for hydrogen recovery from cereals loss, and methane recovery from mixed food loss. Full article
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Open AccessArticle
Environmental Performance of Effluent Conditioning Systems for Reuse in Oil Refining Plants: A Case Study in Brazil
Energies 2019, 12(2), 326; https://doi.org/10.3390/en12020326 - 21 Jan 2019
Cited by 2
Abstract
This study aims to evaluate the environmental and energy effects of the reuse of 1.0 m³ of water in a cooling tower obtained from an oil refinery effluent. An arrangement comprising reverse osmosis (RO), evaporation (EV), and crystallization (CR) was created for water [...] Read more.
This study aims to evaluate the environmental and energy effects of the reuse of 1.0 m³ of water in a cooling tower obtained from an oil refinery effluent. An arrangement comprising reverse osmosis (RO), evaporation (EV), and crystallization (CR) was created for water desalination. Six process routes were evaluated; for this purpose, each of them was converted into an specific scenario of analysis: S1: pre-treatment with Ethylenediaminetetraacetic acid (EDTA) + RO + EV (multi-effect distillation) + CR; S2: S1 with pre-treatment by BaSO4; S3: with Ca(OH)2/CaCO3/HCl; S4: S3 with waste heat to supply the thermal demand of EV; S5: S3 with steam recompression in EV; and, S6: S3 with HNO3 in place of HCl. The analysis was carried out by attributional LCA for primary energy demand (PED) and global warming (GW) impacts. The comparison was carried out for a reference flow (RF) of: add 1.0 m3 of reused water to a cooling tower with quality to proper functioning of this equipment. S4 presented the best performance among the analyzed possibilities (PED: 11.9 MJ/RF; and GW: 720 gCO2,eq/RF). However, dependence on other refinery sectors makes it inadvisable as a regular treatment option. Thus, S5 appears as the lowest impact scenario in the series (PED: 17.2 MJ/RF; and GW: 1.24 kgCO2,eq/RF), given the pre-treatment technique of RO-fed effluent, and the exclusive use of steam recompression to meet total EV energy demands. Finally, an intrinsic correlation was identified between RO water recovery efficiency and the accumulated PED and GW impacts on the arrangements that operate with heat and electricity. Full article
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Open AccessArticle
High-Efficiency Cogeneration Systems: The Case of the Paper Industry in Italy
Energies 2019, 12(3), 335; https://doi.org/10.3390/en12030335 - 22 Jan 2019
Cited by 6
Abstract
In January 2011, the introduction of high-efficiency cogeneration in Europe radically modified the incentive scheme for combined heat and power (CHP) plants. Since then, the techno-economic feasibility of new cogeneration plants in different areas of application (industry, service, residential, etc.), along with the [...] Read more.
In January 2011, the introduction of high-efficiency cogeneration in Europe radically modified the incentive scheme for combined heat and power (CHP) plants. Since then, the techno-economic feasibility of new cogeneration plants in different areas of application (industry, service, residential, etc.), along with the definition of their optimal operation, have inevitably undergone a radical change. In particular, with reference to the Italian case and according to the most recent ministerial guidelines following the new EU regulation, in the event that cogeneration power plants do not reach an established value in terms of overall efficiency, their operation has to be split into a CHP and a non-CHP portion with incentives proportional to the energy quantities pertaining to the CHP portion only. In the framework of high-efficiency cogeneration, the present study compares different CHP solutions to be coupled with the paper industry that, among all the industrial processes, appears to be the best suited for cogeneration applications. With reference to this particular industrial reality, energy, environmental, and economic performance parameters have been defined, analysed, and compared with the help of GateCycle software. Among the proposed CHP alternatives, results show that gas turbines are the most appropriate technology for paper industry processes. Full article
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Open AccessArticle
Numerical Simulation and Optimization of Waste Heat Recovery in a Sinter Vertical Tank
Energies 2019, 12(3), 385; https://doi.org/10.3390/en12030385 - 25 Jan 2019
Cited by 3
Abstract
In this paper, a two-dimensional steady model is established to investigate the gas-solid heat transfer in a sinter vertical tank based on the porous media theory and the local thermal non-equilibrium model. The influences of the air flow rate, sinter flow rate, and [...] Read more.
In this paper, a two-dimensional steady model is established to investigate the gas-solid heat transfer in a sinter vertical tank based on the porous media theory and the local thermal non-equilibrium model. The influences of the air flow rate, sinter flow rate, and sinter particle diameter on the gas-solid heat transfer process are investigated numerically. In addition, exergy destruction minimization is used as a new principle for heat transfer enhancement. Furthermore, a multi-objective genetic algorithm based on a Back Propagation (BP) neural network is applied to obtain a combination of each parameter for a more comprehensive performance, with the exergy destruction caused by heat transfer and the one caused by fluid flow as the two objectives. The results show that the heat dissipation and power consumption both gradually increase with an increase of the air mass flow rate. Additionally, the increase of the sinter flow rate results in a decrease of the heat dissipation and an increase of the power consumption. In addition, both heat dissipation and power consumption gradually decrease with an increase of the sinter particle diameter. For the given structure of the vertical tank, the optimal operating parameters are 2.99 kg/s, 0.61 kg/s, and 32.8 mm for the air flow rate, sinter flow rate, and sinter diameter, respectively. Full article
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Open AccessArticle
Development of an Exergy-Rational Method and Optimum Control Algorithm for the Best Utilization of the Flue Gas Heat in Coal-Fired Power Plant Stacks
Energies 2019, 12(4), 760; https://doi.org/10.3390/en12040760 - 25 Feb 2019
Cited by 1
Abstract
Waste heat that is available in the flue gas of power plant stacks is a potential source of useful thermal power. In reclaiming and utilizing this waste heat without compromising plant efficiency, stacks usually need to be equipped with forced-draught fans in order [...] Read more.
Waste heat that is available in the flue gas of power plant stacks is a potential source of useful thermal power. In reclaiming and utilizing this waste heat without compromising plant efficiency, stacks usually need to be equipped with forced-draught fans in order to compensate for the decrease in natural draught while stack gas is cooled. In addition, pumps are used to circulate the heat transfer fluid. All of these parasitic operations require electrical power. Electrical power has unit exergy of almost 1 W/W. On the contrary, the thermal power exergy that is claimed from the low-enthalpy flue gas has much lower unit exergy. Therefore, from an exergetic point of view, the additional electrical exergy that is required to drive pumps and fans must not exceed the thermal exergy claimed. Based on the First-Law of Thermodynamics, the net energy that is saved may be positive with an apparently high coefficient of performance; however, the same generally does not hold true for the Second-Law. This is a matter of determining the optimum amount of heat to be claimed and the most rational method of utilizing this heat for maximum net exergy gain from the process, under variable outdoor conditions and the plant operations. The four main methods were compared. These are (a) electricity generation by thermoelectric generators, electricity generation with an Organic-Rankine Cycle with (b) or without (c) a heat pump, and (d) the direct use of the thermal exergy that is gained in a district energy system. The comparison of these methods shows that exergy-rationality is the best for method (b). A new analytical optimization algorithm and the exergy-based optimum control strategy were developed, which determine the optimum pump flow rate of the heat recovery system and then calculate how much forced-draft fan power is required in the stack at dynamic operating conditions. Robust design metrics were established to maximize the net exergy gain, including an exergy-based coefficient of performance. Parametric studies indicate that the exergetic approach provides a better insight by showing that the amount of heat that can be optimally recovered is much different than the values given by classical economic and energy efficiency considerations. A case study was performed for method (d), which shows that, without any exergy rationality-based control algorithm and design method, the flue gas heat recovery may not be feasible in district energy systems or any other methods of utilization of the heat recovered. The study has implications in the field, since most of the waste heat recovery units in industrial applications, which are designed based on the First-Law of Thermodynamics, result in exergy loss instead of exergy gain, and are therefore responsible for more carbon dioxide emissions. These applications must be retrofitted with new exergy-based controllers for variable speed pumps and fans with optimally selected capacities. Full article
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Open AccessArticle
Numerical Study on Heat Transfer Performance in Packed Bed
Energies 2019, 12(3), 414; https://doi.org/10.3390/en12030414 - 28 Jan 2019
Cited by 5
Abstract
Packed beds are widely used in industries and it is of great significance to enhance the heat transfer between gas and solid states inside the bed. In this paper, numerical simulation method is adopted to investigate the heat transfer principle in the bed [...] Read more.
Packed beds are widely used in industries and it is of great significance to enhance the heat transfer between gas and solid states inside the bed. In this paper, numerical simulation method is adopted to investigate the heat transfer principle in the bed at particle scale, and to develop the direct enhanced heat transfer methods in packed beds. The gas is treated as continuous phase and solved by Computational Fluid Dynamics (CFD), while the particles are treated as discrete phase and solved by the Discrete Element Method (DEM); taking entransy dissipation to evaluate the heat transfer process. Considering the overall performance and entransy dissipation, the results show that, compared with the uniform particle size distribution, radial distribution of multiparticle size can effectively improve the heat transfer performance because it optimizes the velocity and temperature field, reduces the equivalent thermal resistance of convection heat transfer process, and the temperature of outlet gas increases significantly, which indicates the heat quality of the gas has been greatly improved. The increase in distribution thickness obviously enhances heat transfer performance without reducing the equivalent thermal resistance in the bed. The result is of great importance for guiding practical engineering applications. Full article
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Open AccessArticle
Temperature Disturbance Management in a Heat Exchanger Network for Maximum Energy Recovery Considering Economic Analysis
Energies 2019, 12(4), 594; https://doi.org/10.3390/en12040594 - 13 Feb 2019
Cited by 6
Abstract
The design of heat exchanger networks (HEN) in the process industry has largely focused on minimisation of operating and capital costs using techniques such as pinch analysis or mathematical modelling. Aspects of operability and flexibility, including issues of disturbances affecting downstream processes during [...] Read more.
The design of heat exchanger networks (HEN) in the process industry has largely focused on minimisation of operating and capital costs using techniques such as pinch analysis or mathematical modelling. Aspects of operability and flexibility, including issues of disturbances affecting downstream processes during the operation of highly integrated HEN, still need development. This work presents a methodology to manage temperature disturbances in a HEN design to achieve maximum heat recovery, considering the impact of supply temperature fluctuations on utility consumption, heat exchanger sizing, bypass placement and economic performance. Key observations have been made and new heuristics are proposed to guide heat exchanger sizing to consider disturbances and bypass placement for cases above and below the HEN pinch point. Application of the methodology on two case studies shows that the impact of supply temperature fluctuations on downstream heat exchangers can be reduced through instant propagation of the disturbances to heaters or coolers. Where possible, the disturbances have been capitalised upon for additional heat recovery using the pinch analysis plus-minus principle as a guide. Results of the case study show that the HEN with maximum HE area yields economic savings of up to 15% per year relative to the HEN with a nominal HE area. Full article
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Open AccessArticle
Techno-Economic Assessment of Turboexpander Application at Natural Gas Regulation Stations
Energies 2019, 12(4), 755; https://doi.org/10.3390/en12040755 - 24 Feb 2019
Cited by 4
Abstract
During the natural gas pipeline transportation process, gas stream pressure is reduced at natural gas regulation stations (GRS). Natural gas pressure reduction is accompanied by energy dissipation which results in irreversible exergy losses in the gas stream. Energy loss depends on the thermodynamic [...] Read more.
During the natural gas pipeline transportation process, gas stream pressure is reduced at natural gas regulation stations (GRS). Natural gas pressure reduction is accompanied by energy dissipation which results in irreversible exergy losses in the gas stream. Energy loss depends on the thermodynamic parameters of the natural gas stream on inlet and outlet gas pressure regulation and metering stations. Recovered energy can be used for electricity generation when the pressure regulator is replaced with an expander to drive electric energy generation. To ensure the correct operation of the system, the natural gas stream should be heated, on inlet to expander. This temperature should be higher than the gas stream during choking in the pressure regulator. The purpose of this research was to investigate GRS operational parameters which influence the efficiency of the gas expansion process and to determine selection criteria for a cost-effective application of turboexpanders at selected GRS, instead of pressure regulators. The main novelty presented in this paper shows investigation on discounted payback period (DPP) equation which depends on the annual average natural gas flow rate through the analyzed GRS, average annual level of gas expansion, average annual natural gas purchase price, average annual produced electrical energy sale price and CAPEX. Full article
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Open AccessArticle
A New Method of Selecting the Airlift Pump Optimum Efficiency at Low Submergence Ratios with the Use of Image Analysis
Energies 2019, 12(4), 735; https://doi.org/10.3390/en12040735 - 22 Feb 2019
Cited by 3
Abstract
This paper presents experimental studies on the optimization of two-phase fluid flow in an airlift pump. Airlift pumps, also known as mammoth pumps, are devices applied for vertical transport of liquids with the use of gas. Their operating principle involves the existence of [...] Read more.
This paper presents experimental studies on the optimization of two-phase fluid flow in an airlift pump. Airlift pumps, also known as mammoth pumps, are devices applied for vertical transport of liquids with the use of gas. Their operating principle involves the existence of a density gradient. This paper reports the results of experimental studies into the hydrodynamic effects of the airlift pump. The studies involved optical imaging of two-phase gas-liquid flow in a riser pipe. The visualization was performed with high-speed visualization techniques. The studies used a transparent model of airlift pump with a rectangular cross-section of the riser. The assessment of the airlift pump operation is based on the image grey-level analysis to provide the identification of two-phase flow regimes. The scope of the study also involved the determination of void fraction and pressure drops. The tests were carried out in a channel with dimensions 35 × 20 × 2045 mm with the gas flux range 0.2–15.0 m3/h. For the assessment of the two-phase flow pattern Probability Density Function (PDF) was applied. On the basis of the obtained results, a new method for selecting the optimum operating regime of airlift pump was derived. This method provides the finding of stability and efficiency of liquid transport. It can also be applied to determine the correlation between the total lifting efficiency and the required gas flux for proper operation of the airlift pump. Full article
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Open AccessArticle
A New Method Based on Thermal Response Tests for Determining Effective Thermal Conductivity and Borehole Resistivity for Borehole Heat Exchangers
Energies 2019, 12(6), 1072; https://doi.org/10.3390/en12061072 - 20 Mar 2019
Cited by 4
Abstract
Research on borehole heat exchangers is described on the development of a method for the determination, based on thermal response tests, of the effective thermal conductivity and the thermal resistivity for borehole heat exchangers. This advance is important, because underground thermal energy storage [...] Read more.
Research on borehole heat exchangers is described on the development of a method for the determination, based on thermal response tests, of the effective thermal conductivity and the thermal resistivity for borehole heat exchangers. This advance is important, because underground thermal energy storage increasingly consists of systems with a large number of borehole heat exchangers, and their effective thermal conductivities and thermal resistivities are significant parameters in the performance of the system (whether it contains a single borehole or a field of boreholes). Borehole thermal energy storages provide a particularly beneficial method for using ground energy as a clean thermal energy supply. This benefit is especially relevant in cities with significant smog in winter. Here, the authors describe, in detail, the development of a formula that is a basis for the thermal response test that is derived from Fourier’s Law, utilizing a new way of describing the basic parameters of the thermal response test, i.e., the effective thermal conductivity and the thermal resistivity. The new method is based on the resistivity equation, for which a solution giving a linear regression with zero directional coefficient is found. Experimental tests were performed and analyzed in support of the theory, with an emphasis on the interpretation differences that stem from the scope of the test. Full article
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Open AccessArticle
Hydraulic Experiments on a Small-Scale Wave Energy Converter with an Unconventional Dummy Pto
Energies 2019, 12(7), 1218; https://doi.org/10.3390/en12071218 - 29 Mar 2019
Cited by 2
Abstract
This paper investigates on a Wave Energy Converter (WEC) named Energy & Protection, 4th generation (EP4). The WEC couples the energy harvesting function with the purpose of protecting the coast from erosion. It is formed by a flap rolling with a single degree [...] Read more.
This paper investigates on a Wave Energy Converter (WEC) named Energy & Protection, 4th generation (EP4). The WEC couples the energy harvesting function with the purpose of protecting the coast from erosion. It is formed by a flap rolling with a single degree of freedom around a lower hinge. Small-scale tests were carried out in the wave flume of the maritime group of Padua University, aiming at the evaluation of the device efficiency. The test peculiarity is represented by the system used to simulate the Power Take Off (PTO). Such dummy PTO permits a free rotation of two degrees before engaging the shaft, allowing the flap to gain some inertia, and then applying a constant resistive moment. The EP4 was observed to reach a 35% efficiency, under short regular waves. The effects, in terms of coastal protection, are small but not negligible, at least for the shortest waves. Full article
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Open AccessArticle
Torrefaction as a Valorization Method Used Prior to the Gasification of Sewage Sludge
Energies 2019, 12(1), 175; https://doi.org/10.3390/en12010175 - 06 Jan 2019
Cited by 10
Abstract
The gasification and torrefaction of sewage sludge have the potential to make the thermal utilization of sewage sludge fully sustainable, thus limiting the use of expensive fossil fuels in the process. This includes sustainability in terms of electricity consumption. Although a great deal [...] Read more.
The gasification and torrefaction of sewage sludge have the potential to make the thermal utilization of sewage sludge fully sustainable, thus limiting the use of expensive fossil fuels in the process. This includes sustainability in terms of electricity consumption. Although a great deal of work has been performed so far regarding the gasification of sewage sludge and some investigations have been performed in the area of its torrefaction, there is still a gap in terms of the influence of the torrefaction of the sewage sludge on its subsequent gasification. This study presents the results from the torrefaction tests, performed on a pilot scale reactor, as well as two consecutive steam gasification tests, performed in an allothermal fixed bed gasifier, in order to determine if torrefaction can be deemed as a primary method of the reduction of tar content for the producer gas, from the aforementioned gasification process. A comparative analysis is performed based on the results obtained during both tests, with special emphasis on the concentrations of condensable compounds (tars). The obtained results show that the torrefaction of sewage sludge, performed prior to gasification, can indeed have a positive influence on the gas quality. This is beneficial especially in terms of the content of heavy tars with melting points above 40 °C. Full article
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Open AccessArticle
Modelling of the Biomass mCHP Unit for Power Peak Shaving in the Local Electrical Grid
Energies 2019, 12(3), 458; https://doi.org/10.3390/en12030458 - 31 Jan 2019
Cited by 5
Abstract
In the article, the method and algorithm for a control strategy of the operation of a micro combined heat and power (mCHP) unit and for reducing the power consumption peaks (peak shaving) are proposed and analyzed. Two scenarios of the mCHP’s operation, namely [...] Read more.
In the article, the method and algorithm for a control strategy of the operation of a micro combined heat and power (mCHP) unit and for reducing the power consumption peaks (peak shaving) are proposed and analyzed. Two scenarios of the mCHP’s operation, namely with and without the control strategy, are discussed. For calculation purposes, a boiler fired with wood pellets coupled with a Stirling engine, manufactured by ÖkoFEN, was used. These results were used to analyze two scenarios of the control strategy. In this study, the operation of mCHP was simulated using the energyPRO software. The application of this control strategy to dispersed mCHP systems allows for a very effective “peak shaving” in the local power grid. The results of calculation using the new algorithm show that the electricity generated by the mCHP system covers the total demand for power during the morning peak and reduces the evening peak by up to 71%. The application of this method also allows for a better reduction of the load of conventional grids, substations, and other equipment. Full article
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Open AccessArticle
Impact of Nanoadditives on the Performance and Combustion Characteristics of Neat Jatropha Biodiesel
Energies 2019, 12(5), 921; https://doi.org/10.3390/en12050921 - 10 Mar 2019
Cited by 5
Abstract
Jatropha biodiesel was produced from neat jatropha oil using both esterification and transesterification processes. The free fatty acid value content of neat jatropha oil was reduced to approximately 2% from 12% through esterification. Aluminium oxide (Al2O3) and cerium oxide [...] Read more.
Jatropha biodiesel was produced from neat jatropha oil using both esterification and transesterification processes. The free fatty acid value content of neat jatropha oil was reduced to approximately 2% from 12% through esterification. Aluminium oxide (Al2O3) and cerium oxide (CeO2) nanoparticles were added separately to jatropha biodiesel in doses of 100 ppm and 50 ppm. The heating value, acid number, density, flash point temperature and kinematic viscosity of the nanoadditive fuel samples were measured and compared with the corresponding properties of neat fossil diesel and neat jatropha biodiesel. Jatropha biodiesel with 100 ppm Al2O3 nanoparticle (J100A100) was selected for engine testing due to its higher heating value and successful amalgamation of the Al2O3 nanoparticles used. The brake thermal efficiency of J100A100 fuel was about 3% higher than for neat fossil diesel, and was quite similar to that of neat jatropha biodiesel. At full load, the brake specific energy consumption of J100A100 fuel was found to be 4% higher and 6% lower than the corresponding values obtained for neat jatropha biodiesel and neat fossil diesel fuels respectively. The NOx emission was found to be 4% lower with J100A100 fuel when compared to jatropha biodiesel. The unburnt hydrocarbon and smoke emissions were decreased significantly when J100A100 fuel was used instead of neat jatropha biodiesel or neat fossil diesel fuels. Combustion characteristics showed that in almost all loads, J100A100 fuel had a higher total heat release than the reference fuels. At full load, the J100A100 fuel produced similar peak in-cylinder pressures when compared to neat fossil diesel and neat jatropha biodiesel fuels. The study concluded that J100A100 fuel produced better combustion and emission characteristics than neat jatropha biodiesel. Full article
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Open AccessArticle
Techno-Economic Assessment of Bio-Energy with Carbon Capture and Storage Systems in a Typical Sugarcane Mill in Brazil
Energies 2019, 12(6), 1129; https://doi.org/10.3390/en12061129 - 22 Mar 2019
Cited by 6
Abstract
For significantly reducing greenhouse gas emissions, those from electricity generation should be negative by the end of the century. In this sense, bio-energy with carbon capture and storage (BECCS) technology in sugarcane mills could be crucial. This paper presents a technical and economic [...] Read more.
For significantly reducing greenhouse gas emissions, those from electricity generation should be negative by the end of the century. In this sense, bio-energy with carbon capture and storage (BECCS) technology in sugarcane mills could be crucial. This paper presents a technical and economic assessment of BECCS systems in a typical Brazilian sugarcane mill, considering the adoption of advanced—although commercial—steam cogeneration systems. The technical results are based on computational simulations, considering CO2 capture both from fermentation (released during ethanol production) and due to biomass combustion. The post combustion capture technology based on amine was considered integrated to the mill and to the cogeneration system. A range of energy requirements and costs were taken from the literature, and different milling capacities and capturing rates were considered. Results show that CO2 capture from both flows is technically feasible. Capturing CO2 from fermentation is the alternative that should be prioritized as energy requirements for capturing from combustion are meaningful, with high impacts on surplus electricity. In the reference case, the cost of avoided CO2 emissions was estimated at 62 €/t CO2, and this can be reduced to 59 €/t CO2 in case of more efficient technologies, or even to 48 €/t CO2 in case of larger plants. Full article
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Open AccessArticle
Assessment of the Energy Potential of Chicken Manure in Poland
Energies 2019, 12(7), 1244; https://doi.org/10.3390/en12071244 - 01 Apr 2019
Cited by 9
Abstract
Animal waste, including chicken manure, is a category of biomass considered for application in the energy industry. Poland is leading poultry producer in Europe, with a chicken population assessed at over 176 million animals. This paper aims to determine the theoretical and technical [...] Read more.
Animal waste, including chicken manure, is a category of biomass considered for application in the energy industry. Poland is leading poultry producer in Europe, with a chicken population assessed at over 176 million animals. This paper aims to determine the theoretical and technical energy potential of chicken manure in Poland. The volume of chicken manure was assessed as 4.49 million tons per year considering three particular poultry rearing systems. The physicochemical properties of examined manure specimens indicate considerable conformity with the data reported in the literature. The results of proximate and ultimate analyses confirm a considerable effect of the rearing system on the energy parameters of the manure. The heating value of the chicken manure was calculated for the high moisture material in the condition as received from the farms. The value of annual theoretical energy potential in Poland was found to be equal to around 40.38 PJ. Annual technical potential of chicken biomass determined for four different energy conversion paths occurred significantly smaller then theoretical and has the value from 9.01 PJ to 27.3 PJ. The bigger energy degradation was found for heat and electricity production via anaerobic digestion path, while fluidized bed combustion occurred the most efficient scenario. Full article
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Open AccessArticle
Thermodynamic and Technical Issues of Hydrogen and Methane-Hydrogen Mixtures Pipeline Transmission
Energies 2019, 12(3), 569; https://doi.org/10.3390/en12030569 - 12 Feb 2019
Cited by 7
Abstract
The use of hydrogen as a non-emission energy carrier is important for the innovative development of the power-generation industry. Transmission pipelines are the most efficient and economic method of transporting large quantities of hydrogen in a number of variants. A comprehensive hydraulic analysis [...] Read more.
The use of hydrogen as a non-emission energy carrier is important for the innovative development of the power-generation industry. Transmission pipelines are the most efficient and economic method of transporting large quantities of hydrogen in a number of variants. A comprehensive hydraulic analysis of hydrogen transmission at a mass flow rate of 0.3 to 3.0 kg/s (volume flow rates from 12,000 Nm3/h to 120,000 Nm3/h) was performed. The methodology was based on flow simulation in a pipeline for assumed boundary conditions as well as modeling of fluid thermodynamic parameters for pure hydrogen and its mixtures with methane. The assumed outlet pressure was 24 bar (g). The pipeline diameter and required inlet pressure were calculated for these parameters. The change in temperature was analyzed as a function of the pipeline length for a given real heat transfer model; the assumed temperatures were 5 and 25 C. The impact of hydrogen on natural gas transmission is another important issue. The performed analysis revealed that the maximum participation of hydrogen in natural gas should not exceed 15%–20%, or it has a negative impact on natural gas quality. In the case of a mixture of 85% methane and 15% hydrogen, the required outlet pressure is 10% lower than for pure methane. The obtained results present various possibilities of pipeline transmission of hydrogen at large distances. Moreover, the changes in basic thermodynamic parameters have been presented as a function of pipeline length for the adopted assumptions. Full article
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