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[en] Highlights: • Three novel schemes about integrating solar energy into the boiler are proposed. • Solar-coal hybrid system under fuel saving mode and power boosting mode are studied. • Sankey diagram is used to analyze the exergy destruction of key components. - Abstract: A Solar Tower Aided Coal-fired Power (STACP) system utilizes a solar tower coupled to a conventional coal-fired power system to reduce pollutants, greenhouse gas emissions and the investment of solar energy facilities. This paper examines three different schemes for integrating solar energy into a conventional boiler. For each scheme, an energy and exergy analysis of a 600 MWe supercritical coal-fired power system is combined with 53 MWth of solar energy in both a fuel saving mode and a power boosting mode. The results show that, for all these integration schemes, the boiler’s efficiency and system’s efficiency are reduced. However, the standard coal consumption rate is lower in comparison to conventional power plants and the standard coal consumption rate in the fuel saving mode is lower than that in the power boosting mode for all three schemes. Comprehensively considering both the standard coal consumption rate and efficiency, the scheme that uses solar energy to heat superheat steam and subcooled feed-water is the best integration option. Compared with a coal-fired only system, the saved standard coal consumption rate of the above mentioned scheme in fuel saving mode and power boosting mode can reach up to 11.15 g/kWh and 11.11 g/kWh, respectively. Exergy analysis shows, for STACP system, exergy losses of boiler and solar field contribute over 88% of whole system’s exergy loss.
[en] Highlights: • Novel optimization method for off-grid renewable installations is presented. • Results are compared with an installed PV-battery system. • At least 9.7% reduction in the lifetime cost of the system is achieved. • Sensitivity analysis is performed to consider Li-ion battery price uncertainties. - Abstract: This paper proposes a new methodology to find the most economic system configuration and energy management strategy for Li-ion battery based off-grid renewable energy systems. A system level macroscopic model and a microscopic battery lifetime prediction model are incorporated into the optimization framework to simulate hourly performance of the system. Due to the computational efficiency of the model, optimization is carried out using enumerative method (evaluating all the possible combinations of components and control strategies) to ensure finding the global optimum solution of the problem. To investigate the effectiveness of the proposed methodology, the optimization results are compared with a baseline scenario which is an installed PV-battery system to provide electricity for an isolated house situated near Zaragoza, Spain. Results indicate that the optimized scenario leads to 9.7% reduction in the levelized cost of energy and 48.6% improvement in the battery service period in comparison with the baseline scenario. Moreover, by considering a 0.5% unmet load, the economic feasibility of the system and the battery longevity are enhanced to 14.6% and 78.4%, respectively. Finally, to evaluate the effect of battery unit price and future trends on the optimization results, sensitivity analysis is performed.
[en] Highlights: • A data-driven system approach was developed for visualization analysis. • A transport biofuel technological paradigm (TBTP) is proposed. • Further electric energy trends were discovered through a DAS trend analysis. • Indirect e-bio fuel cell and direct bioelectricity assist in electric energy conversion. • The paradigm shift exits the biofuel paradigm to a bio-electric energy paradigm. - Abstract: The continuing dependence on fossil fuels and the rising energy use in the transport sector have resulted in increased research into viable transport biofuels to mitigate climate change and improve energy security. As transport biofuels now only have a small share of the transport sector energy supply and the complexity in providing the fuels because of issues related to available land and food security, this paper develops conversion path solutions for transport biofuel development based on a technological paradigm study. A data-driven approaches system (DAS) that combines visualization analyses with technological paradigm theory is proposed to reveal the key areas and trends in transport biofuels. Timeline, timezones, and cluster visualizations identified the transport biofuel technological paradigm (TBTP) from current transport biofuel developments; a pre-shift phase (including TBTP competition and TBTP diffusion) and a shift phase (TBTP shift), which respectively relate to conventional biofuels, advanced biofuels, and biofuel cells. However, from further DAS trend analyses and the practical findings, electric energy trends were revealed, indicating that there was a paradigm shift from the biofuel paradigm to a bio-electric energy paradigm. From the developed bio-electric energy framework, both indirect and direct methods were found to have led to an this electric energy conversion to an e-bio fuel cell vehicle for fuel cell electric vehicles (FCEV) and bioelectricity for electric vehicles (EV), both of which can contribute to a low-carbon, sustainable transportation future.
[en] Highlights: • The SOFC-PEMFC hybrid system coupled with TSA technology is proposed and modeled. • The novel hybrid system presents a higher efficiency than the single FC systems. • WGS reaction heat can be recycled for driving TSA reaction to improve efficiency. • Using TSA instead of PSA improves efficiency without increasing exergy destruction. - Abstract: A novel hybrid system fueled with natural gas (NG), consisting of solid oxide fuel cell (SOFC), proton exchange membrane fuel cell (PEMFC) and gas processing (GP) subsystem for H2 production and purification, is proposed and modeled in this paper. The combination of water gas shift (WGS) and thermal swing adsorption (TSA) methods is adopted to convert the syngas from the SOFC into H2 with high purity for subsequent use as a fuel in PEMFC for additional power generation. The parametric and exergy analyses show that the proposed hybrid system can achieve high energy conversion efficiency of approximately 64% and exergy efficiency of 61%, which are higher than some other fuel cell systems, such as reformer-PEMFC, standalone SOFC, SOFC-engine/gas turbine and SOFC-chemical looping hydrogen production. The waste heat recovery for driving the TSA reaction and the H2 recirculation for the PEMFC are found to improve the net electricity efficiency by 3.24% and 6.33%, respectively. In addition, using TSA method instead of the traditional pressure swing adsorption (PSA) could improve the efficiency of the SOFC-PEMFC hybrid system without increasing the exergy destruction. These results reveal that the novel hybrid system is a promising energy conversion system with high efficiency.
[en] Highlights: • The mathematical model of combined heat and power plant operation is developed. • Energy flows in various modes of CHP operation are compared. • Effect of the increased CO2 emission price on CHP probability is studied. • Economic analysis of CHP operation in different modes is performed. - Abstract: This paper presents mathematical modeling and economic analysis of a medium size combined heat and power (CHP) operation, installed in Poland. The plant is equipped with steam boilers, extraction condensing turbine, and the grade type water boilers. The paper determines the most efficient mode of CHP operations. The economic efficiency analysis is performed for transient seasons, characterized by low demands for heating, which obliged production units to operate out of its nominal conditions at a lower efficiency. The developed method is also suitable for analyzing complex power plants, with a few energy equipments. The developed mathematical model for simulating CHP performance gives the possibility to select the boiler type, and assess the probability and efficiency of each configuration. The dedicated tool calculates the selected operation mode, heating power demand, and enables models comparison. The algorithm includes real equipment operational parameters, technical limitations, actual energy prices and costs regarding energy law acts. The performed analysis is up-to-date, due to a few aspects: permanently increased fossil fuels costs, low electric energy prices, growing costs of CO2 emission allowances, and high electricity production cost on turbine’s condensing section at steam parameters of T = 435 °C and p = 34 bar. A detailed cost analysis is performed on each product separately: thermal energy, electric energy from cogeneration and electric energy from condensation, during every hour, frequently. The calculation is carried every an hour for a period of 24 h, the energy balance is ensured during the calculation. The most important result of this study is a comparison of CHP to water boiler operation profitability, also including the net profit comparison. Furthermore, the cost of the CO2 emission is studied, for the production profitability in two scenarios, as the price increases from 7 EUR/tone to 15 EUR/tone and 30 EUR/tone.
[en] Highlights: • A novel cogeneration heating system with full waste heat recovery is proposed. • Optimization direction of integration is revealed for waste heat recovery system. • Thermodynamic perfection, energy consumption and economy are analyzed intensively. • Total exergy efficiency of the novel system increases by 6.1–14.1% • Both the heating energy consumption and the unit heating cost are evidently reduced. - Abstract: In order to utilize the condensed waste heat of multi turbine units of cogeneration plant efficiently and simultaneously, a novel cogeneration heating system is proposed. Comparative analyses are made among the conventional cogeneration heating system, the absorption heat pump cogeneration heating system, the high backpressure cogeneration heating system and the novel cogeneration heating system from the aspects of thermodynamics, energy consumption and economy. The research objects are 2 × 300 MW water-cooling turbine units. The aim of the work is to point out the optimization direction of system integration for the novel cogeneration heating system by the thermodynamic analysis, and to reveal the actual heating energy consumption and the unit heating cost of the systems based on the method of equivalent electricity of heating. The study results show that the novel cogeneration heating system reasonably matches the extraction steam, the exhaust steam and the heating network water with each other at different energy levels. Therefore, it has evident advantages in the aspects of the thermodynamic perfection, the actual heating energy consumption and the economy. Compared with other systems, the novel cogeneration heating system increases the total exergy efficiency by 6.1–14.1%, reduces the equivalent electricity of heating by 11.1–29.4% and reduces the unit heating cost by 8.7–23.9%.
[en] Highlights: • The built environment is facing an energy challenge due to an aging population. • Benefits of poly-generation for houses inhabited by elderly people were analysed. • Results show 26% reduction in CO2 emissions and 80% savings in the energy bill. • Potential 8% reduction in CO2 emissions of the national residential sector by 2037. - Abstract: The increasing number of elderly people (over 65 years of age), long-term home care policies and the generally higher energy demand of houses inhabited by elderly people will pose an energy challenge for the built environment. The paper analyses the benefits of poly-generation technologies, focusing on the case of hard to heat homes in Northern Ireland. The energy consumption of a test house that is representative of 28% of Northern Ireland housing stock and of a house with elderly inhabitants has been monitored without any intervention. An optimization procedure has been developed to identify the optimal mix of poly-generation technologies. The technologies considered are micro-combined heat and power, heat pump and photovoltaic systems with possible integration of thermal energy storage systems. Six scenarios based on different energy tariffs and technology incentives have been presented. In the best case scenario, the combination of photovoltaic, heat pump and thermal energy storage provides 26% reduction in carbon dioxide emissions and 80% savings in the energy bill compared to standard energy generation. The investment required would be in the order of £11,000. In Northern Ireland, 307,000 households (79.1% more than in 2012) will have elderly inhabitants by 2037. The adoption of poly-generation technologies in the older housing stock could lead to 8% reduction of carbon dioxide emissions of the entire residential sector, with 150 GWh increase in the electricity generation from renewable energy without affecting the electricity distribution network.
[en] Highlights: • Allocation factors are calculated for CHP units using different methodologies. • Allocation factors are used in multi-energy systems to obtain performance indicators. • The choice of the methodology has a significant impact on the results. • For most methodologies the allocation factors are influenced by external parameters. • The methodology defined by European Union shows potential problems. - Abstract: The planning and operation of multi-generation units needs to be properly addressed, to guarantee a correct assessment of their performance with respect to standard energy generation units. Performance indicators are defined to compare energy conversion units, and in presence of multiple outputs an allocation methodology is required. There is currently no single method to allocate input resources and impacts in cogeneration and multi-generation systems, as the number of aspects that are involved leads to different approaches. Each method provides specific advantages related to the target for which it has been defined, but attention must be paid on the entire range of boundary conditions that could affect the results. This paper evaluates the current methodologies for allocation factors calculation in Combined Heat and Power plants, to present an indication of the strengths and the limits of each approach. The methods are applied to multiple case studies, by considering the operation data from existing natural gas plants of different size, technology and conversion efficiency. The use of real data allows to consider actual situations in which the choice of the method could lead to different indications. The results show the significant variability of the allocation factors, the main drivers being the choice of the methodology itself, the conversion technology and the reference efficiency values that are set for separate production of heat and power. A discussion is proposed on the importance of defining proper methods and reference parameters, with particular attention to the applications for which the allocation factors need to be calculated and the potential effects on energy policies and regulations.
[en] Highlights: • Organic Rankine cycle for waste heat recovery at low temperature (• Effect of composition of working fluids on the process parameters was investigated. • Butanes and their mixtures showed better results than pentanes. • Significant reduction in the carbon dioxide emissions was achieved. - Abstract: This paper summarizes the results of a study aimed at using isobutane, butane, isopentane and pentane as working fluid of an organic Rankine cycle utilizing heat of an air cooler. Ranking of different working fluids based on the maximum achievable power output, cycle efficiency, heat recovery, required heat exchanger area, attainable CO2 emission reduction, and payback period was performed. By applying pure components, the extractable turbine power varied in the range of 452–678 kW and the CO2 emission reduction potential was in the range of 723–1085 t/y in which isobutane provided the best results. Economic calculation involving both the capital and operating expenditures was conducted, which showed that the estimated payback periods were between 3.4 and 4.6 years with the best result of butane. The results of calculations that were obtained by using working fluids composed from pairs of light hydrocarbons showed that the extractable turbine power was higher for mixtures of butanes than those for butanes/pentanes and pentane mixtures. Based on the payback period, the hydrocarbon mixtures were composed from isobutane/butane in 25:75 and 50:50, and butane/pentane in 75:25 mass ratios that can be applied as favourable working fluids.
[en] Highlights: • A novel system for the hydrogen production utilizing steel furnace waste heat. • Heat source is integrated with the thermochemical copper-chlorine (Cu-Cl) cycle. • Energetic and exergetic performance assessment of the integrated system. • The overall energy and exergy efficiencies are 38.2% and 39.8% respectively. - Abstract: A novel integrated system for the production of hydrogen at a high pressure utilizing steel furnace waste heat is presented and analyzed in this paper. The system utilizes a hybrid thermochemical copper-chlorine (Cu-Cl) cycle. This study integrates the industrial waste heat source with the thermochemical Cu-Cl cycle combined with a hydrogen compression system. The electrical energy required by the system is provided by a supporting Rankine cycle. The hydrogen compression system compresses hydrogen to a pressure of 750 bars. The integrated system is simulated with Aspen Plus software. Energy and exergy analyses are performed for the integrated system. Results from the simulations are presented and discussed. The overall energy efficiency is 38.2% and overall exergy efficiency is found to be 39.8%.