SwePub - search: L773:2050 0505

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1.	Anees, Hafiz Muhammad, et al. (author) A mathematical model-based approach for DC multi-microgrid performance evaluations considering intermittent distributed energy resources, energy storage, multiple load classes, and system components variations 2021 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 9, s. 1919-1934 Journal article (peer-reviewed)abstract The efficiency of DC microgrid needs investigation from a smart grid perspective, since their spread has expected to prevail in comparison with AC counterparts. Furthermore, there is a need to address the limitations (majorly to cater the intermittency of distributed energy resources (DERs) as well as the time dependency of systematic parameters etc.) in previous model and propose a new mathematical model to evaluate system efficiency for given parameters and scenarios. The core focus of current study aims at formulation of an improved (composite) mathematical model, that is capable of bridging issues and serve as a tool to address requirements of future DC systems including microgrids (MGs) and multi-microgrids (MMGs). This research work offers such a mathematical model that consists of 3D matrices based on newly derived set of discrete time dependent equations, which evaluates the system efficiency of residential DC-MMGs. Each DC-MG is embedded with intermittent DERs, storage, components (with efficiency variations), and multi-class load (with discrete time dependency), for evaluation across worst, normal, and best scenarios. A comprehensive sensitivity analysis across various cases and respective scenarios are also presented to evaluate overall system performance. Also, the impacts of system parameters on various system variables, states, and overall system efficiency have presented in this paper.
2.	Arababadi, Reza, et al. (author) Building stock energy modeling : Feasibility study on selection of important input parameters using stepwise regression 2021 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 9:2, s. 284-296 Journal article (peer-reviewed)abstract Building energy assessment is essential to accomplish the sustainable energy targets of new and present buildings. Retrofitting of the existing buildings by assessing them through energy models is the most prominent method. Studies revealed that there is still blank information about the building stocks, and these affect the valuation of building energy efficiency policies. Literature also recommends that the existing energy models are too complex and unreliable to predict the energy use. Reliability of such energy models would improve through a better alignment of the input parameters and the model assumptions. The authors hypothesized that the reliability of models would be improved through identification of the most relevant energy use parameters for the building stocks in different regions and models. One of the most commonly accepted methods for detecting the most dominant input parameters is sensitivity analysis, though its shortcomings include the need for a large number of data samples and long computing time. In this research, the Energy, Carbon, and Cost Assessment for Buildings Stocks (ECCABS) model is adopted to identify the most important parameters of the presented model. The research team uses the model that has been validated by studies conducted for the UK building stock. Moreover, by assessing the feasibility study with the stepwise regression to identify the significant input parameters have been discussed. Results show that stepwise regression method could produce the same results compared to sensitivity analysis. This paper also indicates that stepwise regression is considerably faster and less computationally intensive compared to common sensitivity analysis methods.
3.	Beheshtinia, Mohammad Ali, et al. (author) Energy‐efficient and sustainable supply chain in the manufacturing industry 2023 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 11:1, s. 357-382 Journal article (peer-reviewed)abstract This study aims at reducing energy consumption in supply chain networks by providing optimal integrated production and transportation scheduling. The considered supply chain consists of one main manufacturing center, multiple production units (i.e., suppliers), and multiple heterogeneous vehicles as the transportation fleet. To schedule this complex supply chain network in an energy-efficient way, several decisions should be made concerning the assignment of orders to suppliers and determining their production sequence, splitting orders, assigning orders to vehicles, and assigning delivery priority to orders. To cope with the problem, a mixed-integer linear programming model is presented. Due to the complexity of the problem, a novel development of the genetic algorithm named the Multiple Reference Group Genetic Algorithm (MRGGA) is also proposed. Four objectives are considered to be optimized to meet both suitability and energy-efficiency aspects in the supply chain network. These optimization objectives are to minimize the total orders' delivery times to the manufacturing center, fuel consumption by the vehicles, energy consumption at supplies, and maximize orders' quality. To analyze the performance of the proposed algorithm, a real case and a set of generated instances are solved. The results obtained by the proposed algorithm are compared with an existing genetic algorithm in the literature. Moreover, the results are also compared with the optimal solutions obtained from the mathematical model for small-size problems. The results of the comparisons show the efficiency of the proposed MRGGA in finding energy-efficient solutions for the considered supply chain network.
4.	Beheshtinia, Mohammad Ali, et al. (author) Identifying and prioritizing marketing strategies for the building energy management systems using a hybrid fuzzy MCDM technique 2023 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 11:11, s. 4324-4348 Journal article (peer-reviewed)abstract Preventing energy waste in residential and office buildings has emerged as a critical issue in both developed and developing countries over recent decades. The growing demand for oil and energy reserves has amplified the urgency of this concern. The deployment of building energy management systems (BEMSs) can lead to timely responses to changes in environmental conditions, the prevention of energy wastage, a reduction in CO2 emissions, and an increase in the longevity of building equipment. Despite the undeniable benefits of BEMSs, their market size remains small, creating challenges for providers in reaching potential customers. This research seeks to identify and prioritize the marketing strategies for BEMSs. A case study was conducted, employing the “Strengths, Weaknesses, Opportunities, and Threats” analysis as a tool for identifying marketing strategies related to BEMSs. This method resulted in the identification of 18 distinct marketing strategies. These strategies were subsequently prioritized using a novel fuzzy multicriteria decision-making technique, VIkor-topSIS, considering six specific criteria. The findings of the study suggested a hierarchical influence of six criteria on the BEMS market, arranged in the following order of significance: effectiveness, cost, attainability, complexity, timing, and popularity. Furthermore, the top three marketing strategies for BEMSs were found to be internet advertising strategies, discounts to consumers, and online sales. The analysis of the results has also offered valuable insights into the strengths and weaknesses of the studied BEMS provider, as well as the opportunities and threats present within the BEMS market.
5.	Bokinge, Pontus, et al. (author) Renewable OME from biomass and electricity—Evaluating carbon footprint and energy performance 2020 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 8:7, s. 2587-2598 Journal article (peer-reviewed)abstract Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. Renewable drop-in fuels provide a short- to medium-term solution to decreasing carbon dioxide emissions from the transport sector. Polyoxymethylene ethers (OME) are among interesting candidates with production pathways both from biomass (bio-OME) as well as electricity and CO2 (e-OME) proposed. In the present study, both bio- and e-OME production via methanol are assessed for energy performance and carbon footprint. Process integration methods are applied to evaluate synergies from colocating methanol production with further conversion to OME. Even a hybrid process, combing bio- and e-OME production is evaluated. The energy efficiency of bio-OME is considerably higher than for the e-OME pathway, and colocation synergies are more evident for bio-OME. Carbon footprint is evaluated according to EUs recast Renewable Energy Directive (RED II). If renewable electricity and natural gas are used for power and heat supply, respectively, results indicate that all pathways may be counted toward the renewable fuel targets under RED II. The largest emissions reduction is 92.8% for colocated hybrid-OME production. Carbon footprints of e- and hybrid-OME are highly sensitive to the carbon intensity of electricity, and the carbon intensity of the heat supply has a major impact on results for all pathways except colocated bio- and hybrid-OME.
6.	Eberhard, A., et al. (author) Renewable energy auctions in South Africa outshine feed-in tariffs 2016 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 4:3, s. 190-193 Journal article (peer-reviewed)abstract South Africa's Renewable Energy Independent Power Producer Procurement Program has run four competitive tenders/auctions since 2011, which have seen US$19 billion in private investment, and electricity prices of wind power falling by 46% and solar PV electricity prices by 71%, in nominal terms. Competitive tenders were introduced after an unsuccessful attempt to implement feed-in tariffs. The tenders incorporated standard, nonnegotiable contract documents, including 20-year Power Purchase Agreements and an Implementation Agreement whereby the Government of South Africa back-stops IPP payments by the national utility, Eskom. All of these projects have reached financial close to date and some are already delivering power to the grid. The financing success has been due in part to the requirements for commercial banks to undertake a thorough due diligence of projects prior to bids being offered. The details of the policy package described may be useful for other policy makers in countries developing policies for renewable energy deployment.
7.	Eboh, Francis Chinweuba, et al. (author) Estimating the specific chemical exergy of municipal solid waste 2016 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 4:3, s. 217-231 Journal article (peer-reviewed)
8.	Eboh, Francis Chinweuba, et al. (author) Estimating the specific exergy of municipal solid waste 2016 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 4:3, s. 217-231 Journal article (peer-reviewed)abstract A new model for predicting the specific chemical exergy of municipal solid waste (MSW) is presented; the model is based on the content of carbon, hydrogen, oxygen, nitrogen, sulfur, and chlorine on a dry ash-free basis (daf). The proposed model was obtained from estimations of the higher heating value (HHV) and standard entropy of MSW using statistical analysis. The ultimate analysis of 56 different parts of MSW was used for the derivation of the HHV expression. In addition, 30 extra parts were used for validation. One hundred and seventeen relevant organic substances that represented the main constituents in MSW were used for derivation of the standard entropy of solid waste. The substances were divided into different waste fractions, and the standard entropies of each waste fraction and for the complete mixture were calculated. The specific chemical exergy of inorganic matter in the waste was also investigated by considering the inorganic compounds in the ash. However, as a result of the extremely low value calculated, the exergy of inorganic matter was ignored. The results obtained from the HHV model show a good correlation with the measured values and are comparable with other recent and previous models. The correlation of the standard entropy of the complete waste mixture is less accurate than the correlations of each individual waste fraction. However, the correlations give similar results for the specific chemical exergy, indicating that HHV has a greater impact when estimating the specific exergy of solid waste than entropy.
9.	Engström, Jens, et al. (author) Energy absorption from parks of point-absorbing wave energy converters in the Swedish exclusive economic zone 2020 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 8:1, s. 38-49 Journal article (peer-reviewed)abstract In a future energy system based on renewable energy sources, wave energy will most likely play a role due to its high energy potential and low intermittency. The power production from parks of wave energy converters of point absorber type has been extensively studied. This is also the case for the wave energy resource at many coastal areas around the globe. Wave energy has not yet reached a commercial level, and a large variety of technologies exist; therefore, an established method to calculate the technical potential for wave energy has still not been established. To estimate the technical potential of wave energy conversion, some approximations inevitably need to be taken due to the systems high complexity. In this study, a detailed mapping of the wave climate and simulation of large arrays of hydrodynamically cross‐coupled wave energy converters are combined to calculate the technical potential for wave energy conversion in the Swedish exclusive economic zone. A 16‐year wave data set distributed in a 1.1 km × 1.1 km grid is used to calculate the absorbed energy from a park of 200 generic point absorbers. The areas with best potential have an average annual energy absorption of 16 GWh for the selected wave energy park adapted to 1 km2 when using a constant damping, while the theoretical upper bound is 63 GWh for the same area.
10.	Eriksson, Matias, et al. (author) Oxyfuel combustion in rotary kiln lime production 2014 In: Energy Science & Engineering. - : Wiley-Blackwell. - 2050-0505. ; 2:4, s. 204-215 Journal article (peer-reviewed)abstract The purpose of this article is to study the impact of oxyfuel combustion applied to a rotary kiln producing lime. Aspects of interest are product quality, energy efficiency, stack gas composition, carbon dioxide emissions, and possible benefits related to carbon dioxide capture. The method used is based on multicomponent chemical equilibrium calculations to predict process conditions. A generic model of a rotary kiln for lime production was validated against operational data and literature. This predicting simulation tool is used to calculate chemical compositions for different recirculation cases. The results show that an oxyfuel process could produce a high-quality lime product. The new process would operate at a lower specific energy consumption thus having also a reduced specific carbon dioxide emission per ton of product ratio. Through some processing, the stack gas from the new process could be suitable for carbon dioxide transport and storage or utilization. The main conclusion of this paper is that lime production with an oxyfuel process is feasible but still needs further study.
11.	Eriksson, Sandra, et al. (author) Tip Speed ratio control of a 200 kW VAWT with synchronous generator and variable DC voltage 2013 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 1:3, s. 135-143 Journal article (peer-reviewed)abstract A novel control method for a fixed-pitch variable speed wind turbine is introduced and experimental results are presented. The measured absorbed power and rotational speed, together with a look-up table for the aerodynamic efficiency, are used to estimate the wind speed reaching the turbine as well as the tip speed ratio. Thereby, the control is independent on wind speed measurements and the wind turbine itself is used as an anemometer. Tip speed ratio control is implemented by comparing the estimated tip speed ratio to a reference value and adjusting the DC voltage level accordingly. Tip speed ratio control benefits from that the aerodynamic efficiency hardly varies with changing tip speed ratio when close to its optimum value. Experimental results from a 200 kW vertical axis wind turbine are presented. The voltage from the permanent magnet generator is passively rectified and the alternating DC voltage is then inverted, filtered, transformed, and grid connected. The estimated wind speed is compared with the measured wind speed. The absorbed power when tip speed ratio control has been implemented is shown. It is concluded that the presented control method works and some future improvements are discussed.
12.	Gladis, Arne, et al. (author) Influence of different SSF conditions on ethanol production from corn stover at high solids loadings 2015 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 3:5, s. 481-489 Journal article (peer-reviewed)abstract In this study, three different kinds of simultaneous saccharification and fermentation (SSF) of washed pretreated corn stover with water-insoluble solids (WIS) content of 20% were investigated to find which one resulted in highest ethanol yield at high-solids loadings. The different methods were batch SSF, prehydrolysis followed by batch SSF and fed-batch SSF. Batch-SSF resulted in an ethanol yield of 75–76% and an ethanol concentration of 53 g/L. Prehydrolysis prior to batch SSF did not improve the ethanol yield compared with batch SSF. Fed-batch SSF, on the other hand, increased the yield, independent of the feeding conditions used (79–81%, 57–60 g/L). If the initial amount of solids during fed-batch SSF was lowered, the yield could be improved to some extent. When decreasing the enzyme dosage, the greatest decrease in yield was seen in the fed-batch mode (75%), while lower or the same yield was seen in batch mode with and without prehydrolysis (73%). This resulted in similar ethanol yields in all methods. However, the residence time to achieve the final ethanol yield was shorter using fed-batch. This shows that fed-batch can be a better alternative also at a lower enzyme loading.
13.	Gosens, Jorrit, 1980, et al. (author) China's next renewable energy revolution: goals and mechanisms in the 13th Five Year Plan for energy 2017 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 5:3, s. 141-155 Journal article (peer-reviewed)abstract Over the past few months, China has published its development plans for the 13th Five Year Plan [FYP] period [2016–2020] for energy, and separately for the electricity sector, renewable energy, hydro, wind, solar, and biomass energy. Here, we review these policies, as well as a number of key supporting policy documents that aim at increased renewable energy use in China. Presuming that China will not overshoot its growth targets for wind and PV, annual additions over the 13th FYP period will average 16 GW for wind and 13.5 GW for PV, well below the growth levels seen in recent years. The key to success in China's continued transition to renewable energy, however, does not lie in such capacity additions alone. At least as important will be the efforts at improving grid interconnectedness, flexibility of generating capacity and the grid, market mechanisms that will reduce and spread electricity demand, and better enable renewables to compete, and efforts at increasing the level of consumption of the renewable power generated.
14.	Hussain, Arif, et al. (author) Methoxy-methylheptane as a cleaner fuel additive : An energy- and cost-efficient enhancement for separation and purification units 2021 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; :9, s. 1632-1646 Journal article (peer-reviewed)abstract Environmental protection agencies have begun imposing stringent regulations on the existing refineries to control the levels of gasoline additives. In this context, a novel compound, 2-methoxy-2-methylheptane (MMH), had drawn attention as fuel additive for cleaner combustion. The conventional process of MMH production features three distillation columns in a direct sequence. These columns are used to maintain the required product purities and to utilize the unreacted reactants through recycling streams. The distillation system of the existing MMH plant can afford significant energy savings, leading to a reduction in the total annual costs (TAC). The aim of this investigation is to demonstrate that the reported conventional process can be significantly enhanced by modifying the design and operational parameters and by replacing two distillation columns with an intensified dividing wall column (DWC) configuration. The DWC design is further optimized using several algorithms such as the modified coordinate method (MCD), robust particle swarm paradigm (PSP), and firefly (FF) with nonlinear constraints. Compared to conventional process, the optimized DWC resulted in 24% and 11.5% savings in the plant operating and total annual costs, respectively.
15.	Kiessling, Anders (author) Low-grade heat recycling for system synergies between waste heat and food production, a case study at the European Spallation Source 2016 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 4, s. 153-165 Journal article (peer-reviewed)abstract At present food production depends almost exclusively on direct use of stored energy sources, may perhaps they be nuclear-, petroleum-, or biobased. Arable land, artificial fertilizers, and fresh water resources are the base for our present food systems, but are limited. At the same time, energy resources in the form of waste heat are available in ample quantities. The European Spallation Source (ESS) will require approximately 270 GWh of power per year to operate, power that ultimately is converted to heat. This multidisciplinary case study details an alternative food production cooling chain, using low-grade surplus heat, and involving fermentation, aquaculture, nutrient recapture, and greenhouse horticulture including both use of low-grade surplus heat and recycling of society's organic waste that is converted to animal feed and fertilizer. The study indicates that by combining the use of surplus energy with harvest of society's organic side flows, for example, food waste and aquatic-based cash crops, sustainable food systems are possible at a level of significance also for global food security. The effects of the proposed heat reuse model are discussed in a system perspective and in the context of the UNSCD indicator framework. The potential sustainability benefits of such an effort are shown to be substantial and multifaceted.
16.	Kåberger, Tomas, 1961 (author) A new era of renewable power plants? 2017 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 5:1, s. 4-4 Journal article (other academic/artistic)
17.	Kåberger, Tomas, 1961 (author) Combining science and engineering for global health and prosperity 2016 In: Energy Science & Engineering. - 2050-0505. ; 4:1, s. 3- Journal article (other academic/artistic)
18.	Kåberger, Tomas, 1961 (author) The new power supply! 2018 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 6:1, s. 4-4 Journal article (other academic/artistic)
19.	Li, Nan, et al. (author) Study of the influence of the characteristics of loose residual coal on the spontaneous combustion of coal gob 2020 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 8:3, s. 689-701 Journal article (peer-reviewed)abstract Mine fires are becoming a serious issue as the intensity of mining increases, especially in deep mines. Loose coal gob has a hidden ignition location and a high possibility of spontaneous combustion, which makes fire prevention difficult. Therefore, based on the theory of gas seepage and the characteristics of loose coal, a model of air leakage and spontaneous combustion in gob is established in this paper. Using working face #10414 in the Yangliu coal mine as an example, the relationship between the three spontaneous coal combustion (CSC) zones and the three stress zones is analyzed and verified by combining a FLAC3D simulation with field monitoring. In addition, the influence of advancing speed on the CSC is discussed, and suggestions for fire prevention are presented. The results show that the variation in the calorific value of the CSC with increasing degree of looseness of the residual coal in the gob forms an arch‐shape. There is a one‐to‐one relationship between the distribution of the three stress zones and the three CSC zones. In addition, as the advancing speed increases, the contact time between the loose coal body and the air decreases and the possibility of CSC decreases. This study provides a scientific basis for fire prevention and control in mines.
20.	Norwood, Zack, 1979, et al. (author) Testing of the Katrix rotary lobe expander for distributed concentrating solar combined heat and power systems 2014 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 2:2, s. 61-76 Journal article (peer-reviewed)abstract In this article, we present performance results and analysis of a novel rotary lobe expander device. This is part of a larger research effort into the analysis and design of a small-scale solar system that would compete with available distributed technologies for heat and electricity generation. To choose an appropriate working fluid and components for a distributed concentrating solar combined heat and power (DCS-CHP) system, we compared many different working fluids, collectors, and expander choices. Of the expanders analyzed, including piston expanders, radial inflow turbines, Tesla turbines, screw expanders, and scroll expanders, the rotary lobe expander shows the greatest promise in small-scale power applications due to its high efficiency in expanding fluids over large pressure ratios and its low cost to manufacture. This article focuses on testing of a prototype small-scale expander that was chosen because, to date, no suitable commercial product of less than 10 kW has been found for this application. Initial testing was completed with air to get results that should be indicative of future testing with steam. The test system consists of a compressed air expander (a prototype designed by Katrix, Inc. of Australia) connected to an induction motor driven by a variable frequency drive (VFD) that enables expander testing at varying shaft speeds. Results of the expander testing are reported isentropic efficiencies of 22–25%, thermomechanical efficiencies of 80–95%, and pressure ratios of 6–11 at the tested speeds. Despite mixed results from this particular expander, future refinements could lead to a new class of expanders with low cost and high performance for use in solar combined heat and power and waste-heat recovery.
21.	Poulikidou, Sofia, 1984, et al. (author) Lifecycle energy and greenhouse gas emissions analysis of biomass-based 2-ethylhexanol as an alternative transportation fuel 2019 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 7:3, s. 851-867 Journal article (peer-reviewed)abstract This study investigates the environmental performance of 2-ethylhexanol (2-EH), as a potential drop-in transport fuel alternative. Three different biomass-based production pathways are evaluated and compared using life cycle assessment (LCA) methodology. The environmental impact of 2-EH is assessed in terms of cumulative energy demand (CED) and global warming potential (GWP). Among the three alternative pathways, 2-EH produced via syngas results in the lowest primary energy demand and GHG emissions under the baseline assumptions of this work. The two biochemical production pathways (via ethanol and butanol) exhibit higher CED and GWP during biomass conversion steps mainly due to process materials and chemicals used. Process specifications such as transport distance to production facility or the fate of the obtained by-products are shown to influence the overall environmental impact of the fuel for all studied pathways. The use phase performance of 2-EH was also considered in this work, as part of a 100% renewable blend and was compared to existing fossil and renewable fuels. The studied blend has the potential to reduce GHG emissions by more than 85% compared to fossil diesel while when certain production pathways are followed, it exhibits lower GWP than renewable fuels already in the market such as ethanol blends and biodiesel. 2-EH can therefore provide a competitive alternative to fossil transport fuels increasing the share of renewable content in the current vehicle fleet, thus enhancing the efforts for a sustainable transport sector.
22.	Queiroz, Marcus Vinicius Almeida, et al. (author) Experimental comparison between R134a/R744 and R438A/R744 (drop-in) cascade refrigeration systems based on energy consumption and greenhouse gases emissions 2021 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 9:12, s. 2281-2297 Journal article (peer-reviewed)abstract This experimental study evaluates the energy performance and climatic changes of a cascade cooling system operating with the R134a/R744 pairs (cooling capacity of 4.5-6 kW) and R438A/R744. In both cases, the low-temperature refrigerant, R744, operated under subcritical conditions. The experimental apparatus basically consists of two vapor-compression cycles coupled by a plate cascade condenser. Two operational variables, from R744 cycle, were controlled: the degree-of-superheat and the compressor frequency. The experiment was initially assembled to pair R134a/R744. Subsequently, the R134a refrigerant charge in the high-temperature cycle was replaced by R438A, on a drop-in basis. The two systems, R134a/R744 and R438A/R744, were compared for similar cooling capacities and cold chamber air temperatures. Results showed that the energy consumption of the high-temperature compressor, operating with R438A, was higher than R134a for all tests. As a result, the COP values for R438A/R744 were 30% lower than those for R134a/R744. The greenhouse gases emissions of the two systems were evaluated using the total equivalent warming impact factor, TEWI, whose value for the R438A/R744 pair was approximately 29.5% higher, compared with R134a/R744. Since R438A was originally designed to substitute R22, a few comparative tests were carried out with the latter, always with R744 as the low-temperature cycle working fluid.
23.	Qyyum, Muhammad Abdul, et al. (author) Weed colonization-based performance improvement opportunities in dual-mixed refrigerant natural gas liquefaction process 2021 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 9:2, s. 297-312 Journal article (peer-reviewed)abstract Dual-mixed refrigerant (DMR) process is a promising candidate for liquefying the natural gas (LNG) at onshore as well as offshore sites, thanks to its higher liquefaction capacity and flexibility in using full gas turbines. DMR involves two mixed refrigerant cycles to perform precooling and subcooling of natural gas (NG), and these refrigerant compositions need constant tweaking to match the ever-changing NG cooling curve, as it is obtained from different gas fields. Mismatching of cooling curves often results in suboptimal operation, which ultimately leads to an increase in the overall energy consumption. Thus, this study is aimed at making DMR liquefaction operation close to optimal using the invasive-weed paradigm. At first, the decision variables for performance improvement were determined using degrees of freedom analysis then through invasive-weed paradigm the best set of parameters that results in minimal overall energy consumption were obtained. For the given set of conditions, it was found that after optimization, the DMR process can produce LNG using 16.2% less compression power compared to the published optimized DMR process. Taking into account the higher sensitivity of the DMR process against NG feed conditions, the IWO approach was also examined to find the multiple optimal solutions corresponding to different sets of feed conditions. The thermodynamic evaluation revealed that the mixed refrigerant involves in NG subcooling and interstage coolers have the highest level of exergy destruction. After successful performance improvement of the DMR process, it is also found that still, 62% improvement potential (based on avoidable/unavoidable exergy destruction analysis) is available in the DMR process that can be attained through either sole optimization or optimal retrofitting/revamping.
24.	Sabzpoushan, S., et al. (author) Nonisothermal two-phase modeling of the effect of linear nonuniform catalyst layer on polymer electrolyte membrane fuel cell performance 2020 In: Energy Science & Engineering. - : John Wiley and Sons Ltd. - 2050-0505. ; 8:10, s. 3575-3587 Journal article (peer-reviewed)abstract In this research, it is investigated to numerically evaluate the performance of a polymer electrolyte membrane fuel cell (PEMFC). The performance is investigated through the nonuniformity gradient loading at the catalyst layer (CL) of the considered PEMFC. Computational fluid dynamics is used to simulate a 2D domain in which a steady-state laminar compressible flow in two-phase for the PEMFC has been considered. In this case, a particular nonuniform variation inside the CL along the channel is assumed. The nonuniform gradient is created using a nonisothermal domain to predict the flooding effects on the performance of the PEMFC. The computational domain is considered as the cathode of PEMFC, which is divided into three regions: a gas channel, a gas diffusion layer, and a CL. The loading variation inside the catalyst is defined as a constant slope along the channel. In order to find the optimum slope, different slope angles are analyzed. The results point out that the nonuniform loading distribution of the catalyst (platinum) along the channel could improve the fuel cell performance up to 1.6% and 5% for power density and voltage generation, respectively. It is inferred that it is better to use more catalyst in the final section of the channel if the performance is the main concern.
25.	Sjökvist, Stefan, et al. (author) Study of demagnetization risk for a 12 kW direct driven permanent magnet synchronous generator for wind power 2013 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 1:3, s. 128-134 Journal article (peer-reviewed)abstract One of the main aspects when designing a permanent magnet (PM) generator is to choose suitable PMs, both in terms of achieving the required flux in the generator but also of withstanding high demagnetizing fields, that is, having sufficiently high coercivity. If the coercivity is too low, the magnets are at risk of demagnetizing, fully or partially, at the event of a short circuit and/or an increase in temperature. This study aims to determine the risk of demagnetization for a 12 kW direct driven permanent magnet synchronous generator. Furthermore, as the prices on PMs have increased drastically the last few years the possibility to use smaller and/or cheaper PMs of different grades has been investigated. A new proprietary finite element method (FEM) model has been developed, which is also presented. The study is based on simulations from this FEM model and is focused on NdFeB magnets. Results show that the reference magnet can withstand a two-phase short circuit at both the temperatures tested and in both geometries. The use of cheaper magnets, smaller air gap and in the event of a two-phase short circuit often results in partial irreversible demagnetization. However, magnets with lower coercivity are easier demagnetized.
26.	Stotsky, Alexander, 1960, et al. (author) An overview of proactive wind turbine control 2013 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 1:1, s. 2-11 Journal article (peer-reviewed)abstract Recent achievements in the proactive turbine control, based on the upwind speed measurements, are described in a unified framework (as an extension of the tutorial [1]), that in turn represents a systematic view of the control activity carried out within the Swedish Wind Power Technology Center (SWPTC). A new turbine control problem statement with constraints on blade loads is reviewed. This problem statement allows the design of a new class of simultaneous speed and pitch control strategies based on the preview measurements and look-ahead calculations. A generation of a piecewise constant desired pitch angle profile which is calculated using the turbine load prediction is reviewed in this article as one of the most promising approaches. This in turn allows the reduction of the pitch actuation and the design of the collective pitch control strategy with the maximum possible actuation rate. Two turbine speed control strategies based on one-mass and two-mass models of the drivetrain are also described in this article. The strategies are compared to the existing drivetrain controller. Moreover, postprocessing technique that can be used for estimation of the turbine parameters with improved performance is also discussed. Postprocessing-based estimation of the turbine inertia moment is given as an example. All the results are illustrated by simulations with a wind speed record from the Hönö turbine, located outside of Gothenburg, Sweden. Recent achievements in the proactive turbine control, based on the upwind speed measurements are described in a unified framework that in turn represents a systematic view of the control activity carried out within the Swedish Wind Power Technology Center (SWPTC).
27.	Stotsky, Alexander, 1960 (author) Blade root moment sensor failure detection based on multibeam LIDAR for fault-tolerant individual pitch control of wind turbines 2014 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 2:3, s. 107-115 Journal article (peer-reviewed)abstract Detection of blade root moment sensor failures is an important problem for fault-tolerant individual pitch control, which plays a key role in reduction of uneven blade loads of large wind turbines. A new method for detection of blade root moment sensor failures which is based on variations induced by a vertical wind shear is described in this paper. The detection is associated with monitoring of statistical properties of the difference between amplitudes of the first harmonic of the blade load, which is calculated in two different ways. The first method is based on processing of the load sensor signal, which contains a number of harmonics. The first harmonic is recovered via least squares estimation of the blade load signal with harmonic regressor and strictly diagonally dominant (SDD) information matrix. The second method is a model-based method of estimation of the first harmonic, which relies on the blade load model and upwind speed measurements provided by multibeam Light Detection and Ranging (LIDAR). This is a new application for future LIDAR-enabled wind turbine technologies. Moreover, adaptation of the load model in a uniform wind field is proposed. This adaptation improves accuracy of the load estimation and hence the performance of the blade load sensor failure detection method.
28.	Taqvi, Syed Ali Ammar, et al. (author) Simultaneous fault diagnosis based on multiple kernel support vector machine in nonlinear dynamic distillation column 2022 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 10:3, s. 814-839 Journal article (peer-reviewed)abstract Although numerous works have been done, most of the studies in fault diagnosis are limited to single fault type at a time. Majority of the works reported in the literature do not extend the diagnosis of the root cause of the fault for simultaneous faults specifically in the distillation column. However, an industrial system is susceptible to more than one fault at a time, which may or may not be interrelated. These faults not only reduce the diagnosis performance but also increase the computational complexity of the diagnosis algorithm. In this work, therefore, a multiple kernel support vector machine (MK-SVM) algorithm is proposed to diagnose simultaneous faults in the distillation column. In the developed MK-SVM algorithm, multilabel approach based on various kernel functions has been utilized for the classification of simultaneous faults. Dynamic simulation of a pilot-scale distillation column using Aspen Plus(R) is used for generating data in normal and faulty operation. Eight different fault types are considered, including valve sticking at reflux and reboiler, tray upsets, loss of feed flow, feed composition, and feed temperature changes. In the classification of simultaneous faults, a combination of two, three, and four faults is introduced for the performance evaluation of the proposed MK-SVM algorithm. The result showed that the proposed MK-SVM has a high fault detection rate (FDR) of 99.51% and a very low misclassification rate (MR) of 0.49%. The MK-SVM-based classification is better with the F1 score of >97% for all combinations of faults. Moreover, it is observed that the proposed MK-SVM shows better fault diagnosis for single, multiple, and simultaneous faults as compared to other established machine-learning algorithms.
29.	Thunman, Henrik, 1970, et al. (author) Advanced biofuel production via gasification – lessons learned from 200 man-years of research activity with Chalmers’ research gasifier and the GoBiGas demonstration plant. 2018 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 6:1, s. 6-34 Journal article (peer-reviewed)abstract This paper presents the main experiences gained and conclusions drawn from the demonstration of a first-of-its-kind wood-based biomethane production plant (20-MW capacity, 150 dry tonnes of biomass/day) and 10 years of operation of the 2–4-MW (10–20 dry tonnes of biomass/day) research gasifier at Chalmers University of Technology in Sweden. Based on the experience gained, an elaborated outline for commercialization of the technology for a wide spectrum of applications and end products is defined. The main findings are related to the use of biomass ash constituents as a catalyst for the process and the application of coated heat exchangers, such that regular fluidized bed boilers can be retrofitted to become biomass gasifiers. Among the recirculation of the ash streams within the process, presence of the alkali salt in the system is identified as highly important for control of the tar species. Combined with new insights on fuel feeding and reactor design, these two major findings form the basis for a comprehensive process layout that can support a gradual transformation of existing boilers in district heating networks and in pulp, paper and saw mills, and it facilitates the exploitation of existing oil refineries and petrochemical plants for large-scale production of renewable fuels, chemicals, and materials from biomass and wastes. The potential for electrification of those process layouts are also discussed. The commercialization route represents an example of how biomass conversion develops and integrates with existing industrial and energy infrastructures to form highly effective systems that deliver a wide range of end products. Illustrating the potential, the existing fluidized bed boilers in Sweden alone represent a jet fuel production capacity that corresponds to 10% of current global consumption.
30.	Thunman, Henrik, 1970, et al. (author) Economic assessment of advanced biofuel production via gasification using cost data from the GoBiGas plant 2019 In: Energy Science and Engineering. - : Wiley. - 2050-0505. ; 7:1, s. 217-229 Journal article (peer-reviewed)abstract This paper describes an economic analysis of the GoBiGas plant, which is a first-of-its-kind industrial installation for advanced biofuel production (ABP) via gasification, in which woody biomass is converted to biomethane. A previous technical evaluation of the demonstration unit confirmed that it is technically feasible to construct advanced biofuel production plants, using commercially available and widely used components. Thus, significant cost reductions for equipment cannot be expected as a consequence of learning effects. However, the equipment itself accounted for <20% of the total investment cost at GoBiGas and there exists the potential to reduce the production cost through learning how to assemble the process and reduce project-specific costs. The analysis shows that a plant with capacity of 200 MW of biomethane is an attractive scale for future stand-alone ABP plants with respect to limiting the production cost. For a 200-MW ABP plant operated using forest residues as fuel, the production cost for biomethane is estimated at approximately 600 SEK/MWh, (60€/MWh, 75US$/MWh), which is equivalent to 5.4 SEK/liter gasoline [0.54 €/liter, or 2.5USD per gallon (9.9 SEK/€, 8 SEK/USD)], where the feedstock accounts for about 36% of the production cost. The most significant uncertainty factors pertaining to the estimated production costs are expected to relate to: trade conditions; the location of the installation; and the local price of feedstock. Thus, there is some potential for implementing cost-competitive ABP systems of smaller capacity if low-grade feedstocks (eg, waste-derived woody biomass) can be utilized, and/or if the unit can be integrated with the already existing infrastructure.
31.	Ul Haq, Sheikh Ehsan, et al. (author) Multistage carbon dioxide compressor efficiency enhancement using waste heat powered absorption chillers 2021 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 9:9, s. 1373-1384 Journal article (peer-reviewed)abstract The performance of a multistage centrifugal compressor is highly influenced by the ambient conditions, especially during the summer seasons; their capacity shrinks and thus the power requirement for compression will increase. The prime cause of these constraints is the interstage cooling limitations. This study simulates various suction conditions of a multistage compressor on Aspen HYSYS (R) and suggests its debottlenecking by making the suction temperatures comparable to winter seasons. This is achieved by installing an additional exchanger at the downstream of each interstage cooler, cooling down the gas further by using absorption refrigeration chillers. These chillers are powered up by the waste heat recovered from the exhaust steam coming from the prime mover, steam turbine, of the same compressor. This modification will save a considerable amount of power (663 kW), net savings (Gross Savings - OPEX: 72 289 $/y), and reduce the carbon footprint (954 ton/y) of the overall process.
32.	Wang, Yabo, et al. (author) Potential environmental benefits of integrating flue gas quench in biomass/waste-fueled CHP plants 2021 In: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 9:2, s. 189-199 Journal article (peer-reviewed)abstract Due to stricter regulations, large biomass/waste incineration power plants are expected to reduce (i) pollutant emissions through water (such as organic compounds dissolved in the discharge water), (ii) the withdrawal of external freshwater, and (iii) the disturbance to the natural water by increasing the water recycle and internal reuse. To address such challenges, flue gas quench (FGQ) is playing a vital role that links flue gas (FG) cleaning and wastewater treatment. In this study, a detailed analysis based on the material and energy balance is performed regarding the pollutant distribution in the flue gas and the wastewater within a combined heat and power (CHP) plant. The real data from the reference CHP plant were used; and results show that the utilization of FGQ can result in less wastewater discharge (about 73 tonnes/d) together with less pollutant concentration to the municipal wastewater treatment plant, as compared to the system with only flue gas condenser but without FGQ. The integration of FGQ also results in less burden on the external freshwater use by increasing the amount of clean water for internal use (about 57 tonnes per day). In addition, the integration of FGQ can offer a potential annual energy saving of about 13.1 MWh in the municipal wastewater treatment plant due to the less wastewater coming from the CHP plant.
33.	Yanti, Hari, et al. (author) Effect of ester compounds on biogas production : beneficial or detrimental? 2014 In: Energy Science & Engineering. - : Wiley. - 2050-0505. ; 2:1, s. 22-30 Journal article (peer-reviewed)abstract Esters are major flavor compounds in fruits, which are produced in high volume. The widespread availability of these compounds in nature attracts interest on their behavior in anaerobic digestion in waste and wastewater treatments. The aim of this work was to study the effects of various esters at different concentrations in anaerobic digestion followed by determination of their minimum inhibitory concentration (MIC), and to study the effect of chain length of functional group and alkyl chain of ester on methane production. Addition of methyl butanoate, ethyl butanoate, ethyl hexanoate, and hexyl acetate at concentration up to 5 g L−1 increased methane production, while their higher concentrations inhibited the digestion process. The MIC values for these esters were between 5 and 20 g L−1. Except hexyl acetate, the esters at concentration 5 g L−1 could act as sole carbon source during digestion. For ethyl esters, increasing number of carbon in functional group decreased methane production. For acetate esters, alkyl chain longer than butyl inhibited methane production. Effect of ester on methane production is concentration-dependent.

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