Research

Jump to: Review

23 pages, 5514 KiB

Open AccessArticle

Performance Optimizations with Single-, Bi-, Tri-, and Quadru-Objective for Irreversible Atkinson Cycle with Nonlinear Variation of Working Fluid’s Specific Heat

by Shuangshuang Shi, Yanlin Ge, Lingen Chen and Huijun Feng

Energies 2021, 14(14), 4175; https://0-doi-org.brum.beds.ac.uk/10.3390/en14144175 - 10 Jul 2021

Cited by 29 | Viewed by 1792

Abstract

Considering nonlinear variation of working fluid’s specific heat with its temperature, finite-time thermodynamic theory is applied to analyze and optimize the characteristics of an irreversible Atkinson cycle. Through numerical calculations, performance relationships between cycle dimensionless power density versus compression ratio and dimensionless power [...] Read more.

Considering nonlinear variation of working fluid’s specific heat with its temperature, finite-time thermodynamic theory is applied to analyze and optimize the characteristics of an irreversible Atkinson cycle. Through numerical calculations, performance relationships between cycle dimensionless power density versus compression ratio and dimensionless power density versus thermal efficiency are obtained, respectively. When the design parameters take certain specific values, the performance differences of reversible, endoreversible and irreversible Atkinson cycles are compared. The maximum specific volume ratio, maximum pressure ratio, and thermal efficiency under the conditions of the maximum power output and maximum power density are compared. Based on NSGA-II, the single-, bi-, tri-, and quadru-objective optimizations are performed when the compression ratio is used as the optimization variable, and the cycle dimensionless power output, thermal efficiency, dimensionless ecological function, and dimensionless power density are used as the optimization objectives. The deviation indexes are obtained based on LINMAP, TOPSIS, and Shannon entropy solutions under different combinations of optimization objectives. By comparing the deviation indexes of bi-, tri- and quadru-objective optimization and the deviation indexes of single-objective optimizations based on maximum power output, maximum thermal efficiency, maximum ecological function and maximum power density, it is found that the deviation indexes of multi-objective optimization are smaller, and the solution of multi-objective optimization is desirable. The comparison results show that when the LINMAP solution is optimized with the dimensionless power output, thermal efficiency, and dimensionless power density as the objective functions, the deviation index is 0.1247, and this optimization objective combination is the most ideal. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Figure 1

18 pages, 6438 KiB

Open AccessArticle

Research and Development of the Oxy-Fuel Combustion Power Cycles with CO₂ Recirculation

by Andrey Rogalev, Nikolay Rogalev, Vladimir Kindra, Ivan Komarov and Olga Zlyvko

Energies 2021, 14(10), 2927; https://0-doi-org.brum.beds.ac.uk/10.3390/en14102927 - 18 May 2021

Cited by 27 | Viewed by 2672

Abstract

The transition to oxy-fuel combustion power cycles is a prospective way to decrease carbon dioxide emissions into the atmosphere from the energy sector. To identify which technology has the highest efficiency and the lowest emission level, a thermodynamic analysis of the semiclosed oxy-fuel [...] Read more.

The transition to oxy-fuel combustion power cycles is a prospective way to decrease carbon dioxide emissions into the atmosphere from the energy sector. To identify which technology has the highest efficiency and the lowest emission level, a thermodynamic analysis of the semiclosed oxy-fuel combustion combined cycle (SCOC-CC), the E-MATIANT cycle, and the Allam cycle was carried out. The modeling methodology has been described in detail, including the approaches to defining the working fluid properties, the mathematical models of the air separation unit, and the cooled gas turbine cycles’ calculation algorithms. The gas turbine inlet parameters were optimized using the developed modeling methodology for the three oxy-fuel combustion power cycles with CO₂ recirculation in the inlet temperature at a range of 1000 to 1700 °C. The effect of the coolant flow precooling was evaluated. It was found that a decrease in the coolant temperature could lead to an increase of the net efficiency up to 3.2% for the SCOC-CC cycle and up to 0.8% for the E-MATIANT cycle. The final comparison showed that the Allam cycle’s net efficiency is 5.6% higher compared to the SCOC-CC cycle, and 11.5% higher compared with the E-MATIANT cycle. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Figure 1

19 pages, 5528 KiB

Open AccessArticle

Impact of Water Temperature Changes on Water Loss Monitoring in Large District Heating Systems

by Olgierd Niemyjski and Ryszard Zwierzchowski

Energies 2021, 14(8), 2060; https://0-doi-org.brum.beds.ac.uk/10.3390/en14082060 - 08 Apr 2021

Cited by 1 | Viewed by 2302

Abstract

This paper explores how water temperature changes in a district heating system (DHS) impact the monitoring of water losses. Water volume in DHS is constantly monitored, recorded, and replenished. The leakage and failure status of the DHS is often monitored through measuring the [...] Read more.

This paper explores how water temperature changes in a district heating system (DHS) impact the monitoring of water losses. Water volume in DHS is constantly monitored, recorded, and replenished. The leakage and failure status of the DHS is often monitored through measuring the make-up water flow rate. In this paper, we present the methodology and a simplified model of the dynamics of the heating system operation, which was used to determine the profile of changes in the average temperature and density of water in the system. The mathematical model of the district heating network (DHN) was verified by comparing the results of simulation calculations, i.e., calculated values of the temperature of water returning to the heat source, with the measured values. Fluctuations in water temperature cause changes in the density and volume of water in the DHN, which affect the amount of water supplementing the system. This is particularly noticeable in a DHN with a large water volume. The study reports an analysis of measurement results of operating parameters of a major DHS in Poland (city of Szczecin). Hourly measurements were made of supply and return water temperature, water flow rate, and pressure throughout the whole of 2019. The water volume of the analyzed DHN is almost 42,000 m³ and the changes in water volume per hour are as high as 5 m³/h, representing 20–30% of the value of the make-up water flow rate. The analysis showed that systems for monitoring the tightness of the DHS and detecting failures, on the basis of measurements of the make-up water flow rate, should take into account the dynamics of water volume changes in the DHN. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Figure 1

24 pages, 3753 KiB

Open AccessArticle

Distributed Battery Energy Storage Co-Operation for Renewable Energy Sources Integration

by Hussein M. Abdeltawab and Yasser A. I. Mohamed

Energies 2020, 13(20), 5517; https://0-doi-org.brum.beds.ac.uk/10.3390/en13205517 - 21 Oct 2020

Cited by 4 | Viewed by 1982

Abstract

This paper presents a multiagent system (MAS) day-ahead co-operation framework between renewable energy resources (RESs) and Battery Energy Storage Systems (BESSs) owned by different stakeholders. BESSs offer their storage services to RESs by shifting RES power to sell it during profitable peak-hours (aka; [...] Read more.

This paper presents a multiagent system (MAS) day-ahead co-operation framework between renewable energy resources (RESs) and Battery Energy Storage Systems (BESSs) owned by different stakeholders. BESSs offer their storage services to RESs by shifting RES power to sell it during profitable peak-hours (aka; time-shifting). The MAS framework consists of three phases. Phase-one is a pre-auction phase that defines the maximum charging and discharging BESS power limits. These limits guarantee a reliable distribution system operation without violating the buses’ voltage limits or the ampacity of the branches. Phase-two is an auctioning phase between the BESS-agents and the RES-agents. Each agent has a different owner with a specific profit agenda and risk levels. The agent tries to maximize the profit potential of the owner. The agents use historical trade data and expected weather conditions to maximize profitability. Phase-three is called the post-auctioning phase, in which the agreement between the BESS- and RES-agents is finalized, and the agents are ready for another 3-phases trade. Case studies compare different auctioning strategies and prove the effectiveness of the proposed MAS system. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Figure 1

16 pages, 4105 KiB

Open AccessArticle

Optimization and Comparison of Two Combined Cycles Consisting of CO₂ and Organic Trans-Critical Cycle for Waste Heat Recovery

by Liya Ren and Huaixin Wang

Energies 2020, 13(3), 724; https://0-doi-org.brum.beds.ac.uk/10.3390/en13030724 - 07 Feb 2020

Cited by 4 | Viewed by 1932

Abstract

CO₂-based trans-critical and supercritical cycles have received more and more attention for power generation in many applications such as solar and nuclear energy due to the desirable thermal stability and properties of CO₂ and the high efficiency and compact size [...] Read more.

CO₂-based trans-critical and supercritical cycles have received more and more attention for power generation in many applications such as solar and nuclear energy due to the desirable thermal stability and properties of CO₂ and the high efficiency and compact size of the plant. In this study, two combined cycles driven by the flue gas exhausted from the LM2500+ gas turbine, CO₂-TC+OTC (organic trans-critical cycle) and CO₂-TC/OTC, which can achieve a good trade-off between thermal efficiency and utilization of the waste heat, are investigated. Parameters optimization is carried out by means of genetic algorithm to maximize the net power output of the combined cycle and the effects of the key parameters on the cycle performance are examined. Results show that the exergy efficiency of CO₂-TC+OTC is about 2% higher than that of CO₂-TC/OTC. In CO₂-TC+OTC, the recuperation process of CO₂ causes the largest exergy loss; in CO₂-TC/OTC, the largest exergy loss occurs in the heat recovery vapor generator, followed by the intermediate heat exchanger due to the larger variation of the specific heat capacity of CO₂ and organic fluid in the heat addition process. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Figure 1

51 pages, 9129 KiB

Open AccessArticle

Classification and Evaluation of Concepts for Improving the Performance of Applied Energy System Optimization Models

by Karl-Kiên Cao, Kai von Krbek, Manuel Wetzel, Felix Cebulla and Sebastian Schreck

Energies 2019, 12(24), 4656; https://0-doi-org.brum.beds.ac.uk/10.3390/en12244656 - 07 Dec 2019

Cited by 31 | Viewed by 4315

Abstract

Energy system optimization models used for capacity expansion and dispatch planning are established tools for decision-making support in both energy industry and energy politics. The ever-increasing complexity of the systems under consideration leads to an increase in mathematical problem size of the models. [...] Read more.

Energy system optimization models used for capacity expansion and dispatch planning are established tools for decision-making support in both energy industry and energy politics. The ever-increasing complexity of the systems under consideration leads to an increase in mathematical problem size of the models. This implies limitations of today’s common solution approaches especially with regard to required computing times. To tackle this challenge many model-based speed-up approaches exist which, however, are typically only demonstrated on small generic test cases. In addition, in applied energy systems analysis the effects of such approaches are often not well understood. The novelty of this study is the systematic evaluation of several model reduction and heuristic decomposition techniques for a large applied energy system model using real data and particularly focusing on reachable speed-up. The applied model is typically used for examining German energy scenarios and allows expansion of storage and electricity transmission capacities. We find that initial computing times of more than two days can be reduced up to a factor of ten while having acceptable loss of accuracy. Moreover, we explain what we mean by “effectiveness of model reduction” which limits the possible speed-up with shared memory computers used in this study. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Graphical abstract

22 pages, 7794 KiB

Open AccessFeature PaperArticle

Parametric Optimization and Thermodynamic Performance Comparison of Organic Trans-Critical Cycle, Steam Flash Cycle, and Steam Dual-Pressure Cycle for Waste Heat Recovery

by Liya Ren and Huaixin Wang

Energies 2019, 12(24), 4623; https://0-doi-org.brum.beds.ac.uk/10.3390/en12244623 - 05 Dec 2019

Cited by 5 | Viewed by 2749

Abstract

Compared with the basic organic and steam Rankine cycles, the organic trans-critical cycle (OTC), steam flash cycle (SFC) and steam dual-pressure cycle (SDC) can be regarded as the improved cycle configurations for the waste heat power recovery since they can achieve better temperature [...] Read more.

Compared with the basic organic and steam Rankine cycles, the organic trans-critical cycle (OTC), steam flash cycle (SFC) and steam dual-pressure cycle (SDC) can be regarded as the improved cycle configurations for the waste heat power recovery since they can achieve better temperature matching between the heat source and working fluid in the heat addition process. This study investigates and compares the thermodynamic performance of the OTC, SFC, and SDC based on the waste heat source from the cement kiln with an initial temperature of 320 °C and mass flow rate of 86.2 kg/s. The effects of the main parameters on the cycle performance are analyzed and the parameter optimization is performed with net power output as the objective function. Results indicate that the maximum net power output of SDC is slightly higher than that of SFC and the OTC using n-pentane provides a 19.74% increase in net power output over the SDC since it can achieve the higher use of waste heat and higher turbine efficiency. However, the turbine inlet temperature of the OTC is limited by the thermal stability of the organic working fluid, hence the SDC outputs more power than that of the OTC when the initial temperature of the exhaust gas exceeds 415 °C. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures

Figure 1

Review

Jump to: Research

22 pages, 2017 KiB

Open AccessReview

Review of Trends and Targets of Complex Systems for Power System Optimization

by Jan Vysocky and Stanislav Misak

Energies 2020, 13(5), 1079; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051079 - 01 Mar 2020

Cited by 2 | Viewed by 2683

Abstract

Optimization systems (OSs) allow operators of electrical power systems (PS) to optimally operate PSs and to also create optimal PS development plans. The inclusion of OSs in the PS is a big trend nowadays, and the demand for PS optimization tools and PS-OSs [...] Read more.

Optimization systems (OSs) allow operators of electrical power systems (PS) to optimally operate PSs and to also create optimal PS development plans. The inclusion of OSs in the PS is a big trend nowadays, and the demand for PS optimization tools and PS-OSs experts is growing. The aim of this review is to define the current dynamics and trends in PS optimization research and to present several papers that clearly and comprehensively describe PS OSs with characteristics corresponding to the identified current main trends in this research area. The current dynamics and trends of the research area were defined on the basis of the results of an analysis of the database of 255 PS-OS-presenting papers published from December 2015 to July 2019. Eleven main characteristics of the current PS OSs were identified. The results of the statistical analyses give four characteristics of PS OSs which are currently the most frequently presented in research papers: OSs for minimizing the price of electricity/OSs reducing PS operation costs, OSs for optimizing the operation of renewable energy sources, OSs for regulating the power consumption during the optimization process, and OSs for regulating the energy storage systems operation during the optimization process. Finally, individual identified characteristics of the current PS OSs are briefly described. In the analysis, all PS OSs presented in the observed time period were analyzed regardless of the part of the PS for which the operation was optimized by the PS OS, the voltage level of the optimized PS part, or the optimization goal of the PS OS. Full article

(This article belongs to the Special Issue Energy Complex System Simulation, Design, and Optimisation)

► Show Figures