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[en] The techno-economics of biomass gasification systems for the production of Fischer-Tropsch (FT) based liquid fuels are analysed by estimating the overall mass and energy conversion of biomass to liquid (BTL) fuel. The investigation of BTL systems for 1000 kg/h biomass gasification system and an expected liquid hydrocarbon output of 1500 tonnes are estimated. The cost analysis, based on the annualized life cycle of the systems, includes a steam-oxygen based biomass gasification plant paired with the FT unit. The gasifier considered in this analysis is the downdraft reactor design, operating on oxygen-steam gasifying medium at an equivalence ratio of 0.1 and a steam-to-biomass ratio in the range of 0.8–1.2 to generate syngas with H2/CO ratio of 2.1:1, ideally suitable for the cobalt based fixed bed FT reactor. The mass and energy balance reveal that for a once-through FT reactor configuration, substantial energy exists in the gas phase, which includes C1-C5 hydrocarbons and unconverted syngas. The study suggests that the product gas be utilized in an IC engine and converted to electricity, for in-house power demands and for the sale of excess electricity to the grid. The analysis indicates a market competitive liquid fuel production with CO conversion greater than 60%, at a cost ranging from INR 35–40/litre (0.5–0.6 USD/litre) alongside electricity as a major co-product in the BTL system. This study examines the economics of building economically affordable and environmentally favourable BTL systems of smaller throughputs with particular reference to India. - Highlights: • Investigation on 1000 kg/h, O2-steam biomass gasifier & cobalt catalyzed FT system. • ALC based cost analysis of FT-BTL system to estimate its economic sustainability. • CO conversion should be >60% for market competitive liquid fuel production. • Liquid fuel produced at INR 39.1/l & INR 35.9/l with CO conversion of 65.6% and 73.1%. • Electricity generated as co-product from product gases of once-through FT reactor.
[en] The Korean government has given efforts to reduce green-house gas emissions. In order to avoid the monolithic system that only focuses on reducing the emission without considering operational environments of firms, the government should encourage respective firms to improve their energy efficiency which wastes less energy but produces maximum economic revenue. This paper employed a DEA (Data Envelopment Analysis) model to measure energy efficiency of energy intensive manufacturing firms in Korea. Identifying and comparing the difference in efficiency score by using the simplified single-stage DEA model is not sufficient to give governments and firms meaningful policy implications related to energy efficiency improvement. To compensate for this insufficiency, this study extended the single-stage model into a two-stage model that includes two efficiency measures: pure energy efficiency which is only for energy-related process and economy efficiency which is for the pursuit of profit, to reach the improvement of total energy efficiency. By using the two-stage DEA model, it has identified that the difference from overall energy efficiency is not caused by pure energy efficiency but rather by economy efficiency. In addition, this paper statistically analyzed the effects of environmental variables such as firm size, possession of certified management systems and emission type. - Highlights: • We develop DEA mathematical models for measuring energy efficiency. • The two-stage DEA model includes pure energy efficiency and economy efficiency. • We statistically validates the effects of environmental variables on efficiency. • Overall energy efficiency is more sensitive to pure energy efficiency. • A firm in different conditions has different possibilities to improve its efficiency.
[en] This paper presents an optimal planning and scheduling on energy storage systems (ESSs) for congestion management in electric power systems including renewable energy resources. The proposed problem finds optimal capacity and charging-discharging regime of ESSs. The storage units are optimally charged and discharged to tackle the uncertainty related to wind-solar units as well as relief congestion in the lines. Output power of solar and wind units is modeled by Gaussian probability distribution function (PDF) and Monte-Carlo simulation (MCS) is applied to tackle the uncertainty. Simulation results demonstrate that the proposed planning can manage congestion of the network efficiently while dealing with wind and solar resources uncertainties. - Highlights: • Congestion management is addressed through energy storage planning. • Uncertainty of wind and solar units is considered. • Monte-Carlo simulation is carried out to deal with the uncertainty. • Scenario based stochastic planning is applied to solve the problem. • The planning can tackle the uncertainties and manage congestion of the network.
[en] With the limiting supply of fossil fuel and the beneficial impact of technological innovation on renewable energy costs, PV power generation is increasingly considered a promising way to generate renewable power. Under the support of the national emerging industry, China's PV industry has experienced a dramatic development over recent years, catapulting into a vital position in the world PV market. The newly installed PV capacity has led to cost reductions. This paper chooses the methodology of techno-economic evaluation to analyze current market application of residential PV power generation, including grid-connected and off-grid systems. One of the main innovations is choosing five Chinese cities in different areas of solar radiation as research objects, which enables regional differentiation in calculating levelized cost of energy (LCOE). The results show that grid-connected PV systems with 3 kW PV modules can meet the electric demand of a 60–90 m2 residential building. The capacity of off-grid systems are 5–10 kW, which is determined by local solar radiation. By incorporating a learning curve, we forecast that off-grid PV systems for each of the five cities will reach grid parity over the next several decades. The estimation is used to offer policy recommendations for PV market diffusion in China. - Highlights: • Grid-connected and off-grid PV systems are examined by techno-economic evaluation. • The levelized cost of energy (LCOE) of PV systems is calculated for five regions. • The grid parity of PV power generation in China is estimated using learning curves. • Grid parity varies across regions based on solar radiation and electricity prices. • Policy implications are given to promote market deployment of China's PV industry.
[en] In this study, an inexact two-stage stochastic fuzzy programming (ITSFP) is developed for regional power generation planning with considering the intermittency and fuzziness of renewable energy power output. ITSFP incorporates interval-parameter programming (IPP), two-stage stochastic programming (TSP), and fuzzy credibility constrained programming (FCCP) within a general optimization framework which can tackle uncertainties expressed as intervals, probability distributions, and fuzzy sets. The developed method is applied to a regional electric power system over a one-day optimization horizon coupled with air pollution control. The power generation schemes, imported electricity, and system cost under various environmental goals and risk preferences are analyzed. The obtained results indicate that the model can provide a linkage between predefined electric power generation schedule and the relevant economic implications, as well as more reasonable decision alternatives for decision makers by loosening system constraints at specified confidence level. Besides, the fuzziness of forecast error corresponding to the variability of renewable energy resources could be effectively reflected. Moreover, the results are useful for addressing the trade-off between system economy and system risk. - Highlights: • An inexact stochastic-fuzzy programming is proposed for generation scheduling. • Uncertainties are expressed as intervals, probability distributions and fuzzy sets. • Power generation schemes, imported electricity, and system cost are analyzed. • Alternative solutions associated with different confidence levels are obtained. • Tradeoffs between system economic and reliability risk could be evaluated.
[en] This paper analyses practical procedures for the virtual recognition of CHP (Combined Heat and Power) and non-CHP parts of the plant, and for determining their efficiencies and other parameters required by the regulator. The division of the plant into CHP and non-CHP parts is done on the basis of standard measurements carried out in practice, and the correct thermodynamic energy balance. The Energy efficiency of the CHP part is equal to a pre-set value and that of the non-CHP part is lower than this value. Instead of the Primary Energy Saving (PES) indicator, which compares the efficiency of a CHP plant with a classical plant for the production of heat energy and electricity, here we are analyzing a method that recognizes only the part of the CHP plant that fulfills the preset value of high-efficiency cogeneration. This value is prescribed by the national regulator and depends on the type and age of the plant, operating conditions, etc. Practical calculation procedures rely primarily on rules that are used in the EU (European Union). The impact of a changeable practical operating mode and the sensitivity of the referred efficiency to the attractiveness of cogeneration is particularly evaluated. - Highlights: • Calculation procedures for complex cogeneration schemes are demonstrated. • Power loss coefficient is calculated simply based on standard industrial measurements. • Adjusting thresholds in EU Directives can be a powerful tool for creating energy policy. • The calculation is demonstrated for real CCGT plant calculation.
[en] The environmental control system of an aircraft is a complex energy intensive system and the most important non-propellant consumer of energy among all aircraft systems. Considering the highly competitive market for conventional aircraft, meaningful analysis methods for evaluation during conceptual design of ECS and effective modelling and simulation tools became more important. Hence, this paper focuses on energy and exergy analyses applied to the conventional aircraft environmental control system combined with the model-based design approach. The reported results are related to the different analysis methods for aircraft environmental control systems and cover the model-based design approach. The exergy method is applied to a model of a conventional air generation unit of a commercial aircraft. This model was developed using a model-based design framework. Within this framework, the exergy analysis was performed for four phases of a standard flight mission: Take-off, cruise, landing and taxi. The results obtained from the detailed exergy analysis show highly varying performances for the components at the different simulation cases. The exergy efficiencies range from 1% to 88%. A discussion about the special requirements for aircraft environmental control system analysis methods concludes the paper. - Highlights: • Exergy methods are applied to an aircraft environmental control system (ECS). • Integration of exergy analysis to a model-based design environment is presented. • Simulation and analysis are performed for different operation conditions. • The high interactivity of an aircraft ECS is emphasized by this analysis.
[en] An industrial ammonia synthesis loop is a complex interconnected system. With the synthesis reactor operated at high-pressure levels and with synthesis gas made of hydrogen and nitrogen, a highly efficient process design is necessary in order to meet the requirements in terms of cost-efficiency and environmental impact. The evaluation and optimization of different designs in the process synthesis phase are generally done by considering mass and energy balances. However, the conclusions drawn from such an analysis can be misleading and provide, if any, little useful information with respect to system improvement. In order to address these issues, an exergy analysis is used to identify the real thermodynamic inefficiencies of a system and its components. Furthermore, a subsequently conducted advanced exergy analysis provides the means to determine the structural interactions within a system and the thermodynamic improvement potential of its components. In this context, two different ammonia synthesis loop configurations are analyzed. The first concept consists of a three-staged adiabatic reactor with intermediate quench cooling, whereas the second design features a cooled reactor. - Highlights: • The information provided by thermodynamic, exergetic and advanced exergetic analyses is evaluated and compared. • Advanced exergetic analysis identifies the main design aspects and their impact for the ammonia synthesis loop. • Reactor design is the key decision variable for the thermodynamic efficiency of the synthesis loop. • Means for further system improvement are identified.
[en] Due to the limited energy resources and isolated power system network, an energy security (ES) which reflects such factors as a stable energy supply, energy efficiency, and environmental protection has significance in Korea in terms of sustainable development. This study evaluated the ES in South Korea for fuel options in power generation sector (coal, nuclear, natural gas, oil, and renewables) focusing on indicators of supply reliability, economy of electricity generation, environmental sustainability, and technology complementarity. The ES indicators suggested in this study are anticipated to contribute to establishing an ES policy based on a comprehensive understanding of the ES status in South Korea. In the future, it will be necessary to establish specific scenarios for holding out regional conflicts and post-2020 climate change conventions and conduct realistic and dynamic analyses. In addition, it is essential to draw comprehensive indicators by incorporating the results from individual indicators and produce policy data regarding the priority of energy sources in terms of ES in general. This study has an unusual position in the aspect of the quantitative analysis contribution to the ES of various energy sources by the microscopic parameters together with the time series changes of ES. - Highlights: • A model that contributes to national energy security by energy source is proposed. • Renewables, shown improve gradually, are beneficial in SS, EC and IO indicators. • Nuclear, shown improve gradually too, is beneficial in GH and TC indicators. • Fossil fuels such as LNG and coal have been improved in terms of indicators GH and SA. • This model is expected in finding out the security enhancement factor by energy source.
[en] Current district heating systems based on natural gas-fired boilers have lower primary energy efficiency due to its higher-temperature exhaust flue gas, and it cannot meet high-density heat load demand by the existing primary heating network. A new district heating system based on natural gas-fired boilers with absorption heat exchangers is presented to increase its primary energy efficiency and meet high-density heat load demand. In this new district heating system, absorption heat exchangers installed in heating substations could greatly decrease return water temperature of the primary heating network. The lower temperature return water could be used to cool exhaust flue gas and increase heat transmission capacity of the existing primary heating network. This new district heating system was analyzed by thermodynamics and economics. Results show that its primary energy efficiency and heat transmission capacity of the primary heating network are increased by about 11% and 47% respectively. When the heat transmission distance of the primary heating network is over 2.6 km, the new district heating system has better thermodynamic performance, economic benefit and environmental benefit, therefore, it would be a better choice for district heating systems based on natural gas-fired boilers with longer heat transmission distance of the primary heating network. - Highlights: • Absorption heat exchanger could decrease return water temperature greatly. • Lower-temperature return water could increase primary energy efficiency by about 11%. • Heating cost of new district heating system is reduced by 1.2–2.4 ¥/(m2 a). • New district heating system has better economic benefits and higher energy efficiency. • New district heating system is suitable for longer heat transmission distance.