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[en] Highlights: • Hierarchical attribution management method is proposed for life cycle assessment. • Carbon footprint of the coal-to-methanol chain in China is at 2.971 t CO_2_,_e/t methanol. • Gasification and WGS unit are the main contributors for GHG generation in life cycle chain. • Methanol synthesis unit is a potential “carbon sink” for CO_2 utilization. • CCS is proved to be an effective method to reduce carbon footprint. - Abstract: Coal is considered as an abundant energy source in China and coal-to-methanol chain is an essential routing on account of methanol’s irreplaceable status in chemical industries. However, coal-based methanol production aroused controversy due to its intensive energy consumption and high greenhouse gas emission, compared with other processes by oil or natural gas. Carbon footprint is an improved indicator that evaluates both direct and indirect greenhouse gas emissions in the life cycle perspective and guides policymakers for better industry-chain planning. In this study we proposed the idea of hierarchical attribution management (HAM) to provide a classified method for evaluating carbon footprint of coal-to-methanol chain, combined with life cycle assessment (LCA) and the tool of ASPEN Plus. The results show that the life cycle carbon footprint was 2.971 t CO_2_,_e/t methanol. By the HAM, it’s concluded that methanol production process was the largest emission contributor in the defined life cycle system with a share of 92.86%, followed by coal mining process with 4.34%. Gasification unit and water-gas shift unit were two major greenhouse gas generators, accounting for 21.26% and 52.80% of life cycle emission, respectively, while methanol synthesis unit showed the potential for CO_2 utilization and emission reduction. Additionally, the results of sensitivity analysis showed that electricity emission factor with a sensitivity factor of 189.11 was the most extensive influence factor on life cycle emission due to its widest application. The discuss on effects of CCS on life cycle emission showed that carbon footprint approximately decreased by 64.9% when the methanol plant was retrofitted with CO_2 capture and compression, indicating that CCS is an effective way to alleviate global warming.
[en] Highlights: • A 62.7 kW PV plant is modelled for a demand of 175 kWh/d with 1% annual load growth. • The plant’s yield and losses are 1723 kWh/kW and 502 kWh/kW, respectively. • The plant’s maximum monthly mean efficiency is 13.85%. • Availability of 98.91–99.56% is achieved over the year. • The plant’s estimated life cycle emission rate is 50 gCO_2/kWh. - Abstract: This study presents detailed techno-economic and environmental impact assessment of a photovoltaic power system (PPS) for a small off-grid community. The PPS is designed to meet a community’s load demand of ∼63,900 kWh, with an annual load growth of 1% over a 25-year project lifespan. Its performance is assessed in terms of the power output, energy production, yield and losses, and the efficiency. Furthermore, detailed battery state of charge (SoC) and reliability analysis is presented. The paper uses the life cycle evaluation technique to analyse the system’s economic and environmental performances, using Bununu community in Bauchi State, Nigeria as a case study. Results show that the loss of energy probability and the availability of 0.44–1.09% and 98.91–99.56%, respectively, can be achieved with PPS sizes of 50–62.7 kW. In addition, the proposed PPS’s life cycle costs range from ∼48 to 49.5% of the values obtained for the diesel plant. The PPS’s life cycle emission rate is 50 gCO_2-eq/kWh, which is ∼7.9–8.7% of the diesel plant’s emission rates. The proposed PPS’s GWP ranges from 4307 to 5400 kgCO_2-eq. These outputs are evaluated by comparing them with some existing results in the literature, and can be useful for planning stand-alone PPS for remote locations around the world.
[en] Highlights: • Sensitivity analysis on system configuration of the AFC as a micro-CHP. • Flow rate in the secondary heating circuit can be used to control water management. • Part load behavior of fuel cells is compared to other micro-CHP technologies. • For future energy demand in buildings fuel cells have the best performance. - Abstract: Micro-cogeneration is an emerging technology to reduce the non-renewable energy demand in buildings and reduce peak load in the grid. Fuel cell based cogeneration (CHP) has interesting prospects for building applications, even at relatively low heat demand. This is due to their partial load behavior which is completely different, compared to other micro-CHP technologies. Within the fuel cell technologies suitable for small scale CHP or micro-CHP, the existing configuration of an alkaline fuel cell system is analyzed. This analysis is based on validated models and offers a control strategy to optimize both water management and energy performance of the alkaline fuel cell system. Finally, the model of the alkaline fuel cell system with optimized control strategy is used to compare its part load behavior to other micro-CHP technologies.
[en] Highlights: • Pyrolysis gases from waste plastics have the potential to replace natural gas (NG). • PVC HCl-scrubbed pyrolysis gas is a suitable fuel for US and Europe NG burners. • PS pyrolysis at 900 °C is a possible source for US NG burners but not for EU burners. • The least conforming pyrolysis gases for NG burners are PE, PP, and PET. • PE gases have potential to replace propane in terms of keeping burner power. - Abstract: The development of effective recycling methods for plastic wastes is critical in terms of resource security and environmental conservation. In this work, we focused on the gaseous pyrolysis products of plastic wastes as alternatives to natural gas (NG) and propane. The pyrolysis of polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and their mixtures was carried out under isothermal conditions at 500, 700, and 900 °C. The potential for replacing NG and propane with the pyrolysis gases was assessed by graphical interchangeability methods for the first time. The pyrolysis gas compositions obtained from the mixed plastics and HCl-scrubbed gas from the PVC were deemed suitable NG alternatives in Europe and the USA. In addition, PE and PP pyrolysis gases showed the potential for replacing propane in the USA, whereas gases from PET showed the least interchangeability. Thus, the graphical interchangeability methods are promising for evaluating the potential of plastic waste pyrolysis gases as alternatives to NG.
[en] Highlights: • We apply three different types of neural network for a hybrid system components modeling. • We vary the activation function, network structure and training testing ratio to find the most optimal combination. • We apply data-mining algorithm for parameter selection. • We choose the neural network with best performance to model the whole system. • The result shows a good agreement between predicted and measured value within ±10% error. - Abstract: In order to predict the performance of a hybrid ejector air conditioning system, neural network is chosen to model the proposed platform. First, three different types of neural networks, namely multi-layer perceptron (MLP), radial basis function (RBF) and support vector machine (SVM) are applied to model the component of a hybrid ejector air conditioning system. The MLP outperforms other two networks in this research and therefore it is selected to model the whole system. Since there is no formal criterion about input selection so far, a date-mining algorithm, boosting tree, is employed before system modeling to search the most significant parameters among the 19 input variables and the five most influential parameters of them are selected to be the final input of the system model. And the result shows a good agreement between predicted and measured value which indicates the excellent ability of MLP.
[en] Highlights: • A systematic approach for energy management of complex structures is proposed. • Technological systems of Leonardo da Vinci Airport of Rome are described. • A multi-year consumption analysis highlights the most energy-consuming sectors. • The “Smart Grid” prototype project inherent to T1 Terminal is presented. • Wind and photovoltaic plants are designed and discussed to test the smart storage. - Abstract: Because of the growing need for efficient energy production systems, energy policies promoted in recent years have also involved complex structures, like airports. This paper proposes the implementation of an energy management system for a very energy-consuming structure, composed of different power plants and many energy consumers: the Leonardo da Vinci International Airport of Rome. In this study, the examination of historical data related to airport electric power, thermal energy and fuel consumption is discussed, starting with the analysis of the production energy plants, mainly based on a combined heat and power system. Furthermore, pioneering solutions are proposed, not only to cover airport energy requirements, but also to test the safety and reliability of innovative load management systems. For this reason, the choice of the Leonardo da Vinci management company, oriented to install a smart storage in order to manage the bidirectional energy flows by consumers and producers, is justified. Such innovative energy procurement systems are examined, with the goal of achieving greater penetration of renewable sources: mini and micro wind power plants and high concentrator photovoltaic plants.
[en] Highlights: • Net Present Value varies from 437 to 624 € per kW installed. • Discounted Payback Time ranges from 4 years to 6 years. • Reduction of emissions of 21 tCO_2eq for each kW installed during the 20 years. • Break-even point of increase of self-consumption varies from 6% to 13%. • The opportunity to keep a 50% of fiscal deduction for 5 years. - Abstract: The installation of photovoltaic power plants in 2015 compared to 2014 registered a growth of 25.6%, reaching a cumulative power equal to 229 GW. In developed solar markets, as many European countries, the sector is pushed by the alignment between the electric power demanded and the one offered. Consequently, self-consumption makes consumers active players of the energy transition. Italy is evaluated as a case study in this paper, in fact is the first country in the world where solar energy contributes largely to the national energetic demand. This paper aims to evaluate photovoltaic systems in residential sector without subsidies. Economic and environmental results are proposed and the indicators used are Net Present Value, Discounted Payback Time and Reduction in the Emissions of Carbon Dioxide. Three sizes (3 kW, 6 kW and 20 kW) are evaluated. In addition, a sensitivity analysis of critical variables (investment cost, annual electricity purchase price, annual electricity sales price, opportunity cost, tax deduction unitary, period of fiscal deduction, average annual insolation and percentage of energy self-consumption) demonstrates the robustness of the economic results. Also for environmental evaluation, alternative scenarios are proposed varying the value of emissions released by source energy analysed (photovoltaic, coal, oil and gas). Economic and environmental results suggest that small-scale photovoltaic systems can support the transition towards a sustainable energy mix.
[en] Highlights: • A new retrofit design method based on multiobjective optimization is proposed. • Quantify if lower exergy destruction are cost effective in heat exchanger retrofit. • Water preheat operating costs lowered by 89% with 82% less exergy destruction. • Exergy analysis is used to evaluate energy demands, distribution and degradation. • Economic analysis based directly on equipment design optimization and installation. - Abstract: Reducing the energy consumption of a plant often conflicts with the investment required for heat recovery. This paper presents a design study of shell and tube heat exchanger and direct-contact heat exchanger in three retrofit configurations. Multiobjective optimizations are employed to find optimal solutions that increase exergy efficiency at justifiable costs. A numerical modelization of heat transfer equipements is developed using heat transfer, pressure drop and cost correlations from the open literature. In order to verify the capability of the proposed approach, a case study for heat recovery in a pulp and paper plant is presented. In which multiple structural modifications of existing heat recovery systems are proposed based on an analysis of the Grand Composite Curve pinch targeting method. Each proposed modification is subject to multiobjective optimization based on the fast non-dominant sorting genetic algorithm (NSGA-II). The case study’s results shows significant steam operation cost reduction of up to 89% reducing exergy destruction by 82%. It has also been shown that for some heat recovery modifications the most cost effective solution is close to the minimum exergy destruction solution subject to equipment design constraints.
[en] Highlights: • Process modelling and optimisation of an integrated marine MCFC system. • Component-level and spatially distributed exergy analysis and balances. • Optimal simple cycle MCFC system with 45.5% overall exergy efficiency. • Optimal combined cycle MCFC system with 60% overall exergy efficiency. • Combined cycle MCFC system yields 30% CO_2 relative emissions reduction. - Abstract: In this paper we present the exergy analysis and design optimisation of an integrated molten carbonate fuel cell (MCFC) system for marine applications, considering waste heat recovery options for additional power production. High temperature fuel cells are attractive solutions for marine energy systems, as they can significantly reduce gaseous emissions, increase efficiency and facilitate the introduction of more environmentally-friendly fuels, like LNG and biofuels. We consider an already installed MCFC system onboard a sea-going vessel, which has many tightly integrated sub-systems and components: fuel delivery and pre-reforming, internal reforming sections, electrochemical conversion, catalytic burner, air supply and high temperature exhaust gas. The high temperature exhaust gasses offer significant potential for heat recovery that can be directed into both covering the system’s auxiliary heat requirements and power production. Therefore, an integrated systems approach is employed to accurately identify the true sources of losses in the various components and to optimise the overall system with respect to its energy efficiency, taking into account the various trade-offs and subject to several constraints. Here, we present a four-step approach: a. dynamic process models development of simple and combined-cycle MCFC system; b. MCFC components and system models calibration via onboard MCFC measurements; c. exergy analysis, and d. optimisation of the simple and combined-cycle systems with respect to their exergetic performance. Our methodology is based on the thermofluid and chemical reactions modelling of each component, via our in-house ship machinery systems modelling framework, DNVGL COSSMOS. For the major system components spatially distributed exergy balances are considered in order to capture the coupling of the local process phenomena and exergy destruction with component design characteristics. Exhaust heat recovery is considered using a steam turbine combined-cycle module integrated with the rest of the MCFC system. Both the simple and combined cycle MCFC systems are optimised with respect to their overall exergetic efficiency subject to design, technical, operational and space constraints. The exergy analysis identified and ranked the sources of exergy destruction and the subsequent optimisation yielded significant improvement potential for both systems. The simple MCFC system optimisation yielded an exergy efficiency improvement of 7% with 5% more power produced. Heat recovery in the combined cycle MCFC resulted in 40% more power produced, with a 60% overall exergy efficiency (relative increase of 45%). Both MCFC systems outperform conventional dual-fuel engines with respect to efficiency, having also a positive impact on CO_2 emissions with a relative reduction of about 30%.
[en] Highlights: • Stable MWNTs and graphene nanofluids were used in a mechanical wet cooling tower. • Thermal and rheological properties of nanofluids were investigated. • Nanofluids enhanced the efficiency, cooling range and tower characteristic. • Water consumption reduced significantly for both MWNTs and graphene nanofluids. - Abstract: This study deals with an experimental investigation on the thermal performance of a mechanical wet cooling tower with counter flow arrangement by using multi-walled carbon nanotubes (MWNTs) and nanoporous graphene nanofluids. Stable nanofluids were prepared through two-step procedure by using water with properties taken from a working cooling tower in the South of Iran. Zeta potential revealed suitable stability of MWNTs and nanoporous graphene nanofluids. Thermal and rheological properties of the nanofluids were investigated. It was found that thermal conductivity increases by 20% and 16% at 45 °C for MWNTs and nanoporous graphene nanofluids, respectively. The increase in density and viscosity, particularly in low concentrations of nanoparticles, was insignificant enough for industrial applications. Moreover, it was found that by using nanofluids, efficiency, cooling range and tower characteristic (KaV/L) are enhanced in comparison to water. For instance, at inlet water temperature of 45 °C and water/air (L/G) flow ratio of 1.37, the cooling range increases by 40% and 67% for MWNTs and nanoporous graphene nanofluids (0.1 wt.%), respectively. On the other hand water consumption is reduces by 10% and 19% at inlet water temperature of 45 °C for MWNTs and nanoporous graphene nanofluids, respectively.