A comparative evaluation of economic efficiency was performed for native polyculture microalgae oil production in an oxidation ditch (OD) process wastewater treatment plant (WWTP). A cost function was developed for the process. The operational cost per 1 m3 of wastewater (w.w.) was 1.34 $/m3-w.w. in the existing scenario, 1.29 $/m3-w.w. in algal scenario A (no cost for CO2 and waste heat) and 1.36 $/m3-w.w. in algal scenario B (no cost for CO2). The conditions were set as follows: hydraulic retention time (HRT): 4 days, microalgal productivity: 0.148 g/L and daily treatment volume: 81.6 m3-w.w./d. The cost differences were related to the increase in polymer flocculants for algae separation (+0.23 $/m3-w.w), carbon credits from CO2 absorption (−0.01 $/m3-w.w), the sales of biocrude (−0.04 $/m3-w.w) and sludge disposal (−0.18 $/m3-w.w). Hence, the introduction of the algae scenario was the same cost-effective as the existing scenario. Microalgae oil production in an OD process WWTP can s... [more]

Cable lines are one of the basic components of power systems. Medium and high voltage cables mainly comprise a metallic sheath, which is concentric to the main core conductor. There are several operating schemes of such cable lines, which differ in the place of earthing of sheaths and the possible use of the sheaths and/or conductors crossing. The sheaths cross-bonding is typically done in two places of one cable line section, and it allows to reduce power losses. Nevertheless, the use of incomplete sheaths crossing—only in one place on cable route may have economic justification. The paper presents an incomplete sheaths cross-bonding analysis of an existing medium voltage cable line. The results obtained by the mathematical model are validated by measurements taken on 30 October 2019 on an existing cable line. Measurements recorded on a real object for various systems of crossing sheaths are presented. The influence of incorrect sheaths crossing on the measured quantities was shown. I... [more]

Attenuation of solar radiation between the receiver and the heliostat field in concentrated solar power (CSP) tower plants can reduce the overall system performance significantly. The attenuation varies strongly with time and the average attenuation at different sites might also vary strongly from each other. If no site specific attenuation data is available, the optimal plant design cannot be determined and rough estimations of the attenuation effect are required leading to high uncertainties of yield analysis calculations. The attenuation is caused mainly by water vapor content and aerosol particles in the lower atmospheric layer above ground. Although several on-site measurement systems have been developed during recent years, attenuation data sets are usually not available to be included during the plant project development. An Atmospheric Attenuation (AATTENUATION) model to derive the atmospheric transmittance between a heliostat and receiver on the basis of common direct normal i... [more]

As one of the machines widely used in mining, a semi-autogenous grinding (SAG) mill can significantly improve the roughing efficiency of rock. But the SAG mill still faces the obstacles of significant energy consumption and empirical operation parameters. In order to obtain the optimal operation parameters of a SAG mill, in this paper, the discrete element method (DEM) is used to simulate the breakage process of the particles by controlling three parameters, i.e., the mill speed ratio, the mill fill level ratio, and the steel ball ratio. This method simulates the particles size, mill power, and qualified particles quality of crushed particle, which reveal the grinding strength and energy consumption of the SAG mill. In this paper, the grinding changes of a SAG mill under different parameter conditions are explored. Firstly, an experiment on the influence of a single parameter change on the mill’s operation is set up, and then the influence of three parameter changes on the mill’s opera... [more]

Belt conveyor (BC) transportation systems are considered to be the most effective for handling large volumes of bulk material. With regards to the rules of sustainable development, the improvement of belt conveyor technology is, in many cases, focused on environmental issues, which include the idea of energy usage optimization. The key issue in an energy-efficient transportation system is reducing the value of specific energy consumption (SEC) by increasing conveyor capacity whilst decreasing belt conveyor motion resistance. The main idea of this paper is to conduct an analysis of the modernization of existing belt conveyor transportation systems operated in open-pit lignite mines, in order to achieve relatively small electric energy consumption for a considered transportation task. The first part of the paper investigates the relationship between a conveyor’s SEC and material flow rate for various conveyor design parameters. Then, based on multi-parameter simulations, an analysis of e... [more]

Shale formations are attractive prospects due to their potential in oil and gas production. Some of the largest shale formations in the mainland US, such as the Tuscaloosa Marine Shale (TMS), have reserves estimated to be around 7 billion barrels. Despite their huge potential, shale formations present major concerns for drilling operators. These prospects have unique challenges because of all their alteration and incompatibility issues with drilling and completion fluids. Most shale formations undergo numerous chemical and physical alterations, making their interaction with the drilling and completion fluid systems very complex to understand. In this study, a high-pressure, high-temperature (HPHT) drilling simulator was used to mimic real time drilling operations to investigate the performance of inhibitive drilling fluid systems in two major shale formations (Eagle Ford Shale and Tuscaloosa Marine Shale). A series of drilling experiments using the drilling simulator and clay swelling... [more]

In this paper, a superconducting fault current limiting breaker (SFCLB) using flux coupling with a tap changer is suggested and its effective fault current limiting and breaking characteristics due to the winding method using its tap changer are analyzed. The suggested SFCLB using flux coupling, which consists of the SFCLB using flux coupling with a tap changer, mechanical switch and driving coil, can perform the circuit-breaking function without external driving power after the fault current limiting operation. To examine the suggested SFCLB’s operation, the small scale SFCLB using flux coupling was fabricated and alternative current (AC) short-circuit experiments due to the winding method using the tap changer of the SFCLB were executed. From the experimental results, a lower fault current limiting rate and faster breaking time in the case of a SFCLB with a series connection could be obtained compared to one with a parallel connection.

This paper presents a novel analysis methodology to detect degradation in electrical contacts, with the main goal of implanting a predictive maintenance procedure for sectionalizing switches, circuit breakers, and current transformers in bays of electric transmission and distribution substations. The main feature of the proposed methodology is that it will produce a predictive failure indication for the system under operation, based on the spectral analysis of the load current that is flowing through the bay’s components, using a defined relationship similar to the signal-to-noise ratio (SNR) used in data communication. A highlight of using the proposed methodology is that it is not necessary to make new investments in measurement devices, as the already-existing oscillography measurement infrastructure is enough. By implementing the diagnostic system proposed here, electrical utilities will have a modern tool for monitoring their electrical installations, supporting the implementation... [more]

This in situ study presents an analysis of the wear of mobile contacts of switching in an automatic line voltage regulator, regarding the surface wear of the contacts. It is interesting to analyze the contacts of this equipment due to the friction and wear generated during the contact change, in order to predict and contain mechanical operation failures. The contacts were evaluated for mass loss, profilometry, and analysis in a scanning electron microscope, after remaining in operation in the regulator for about one year and switching the contacts almost 2500 times. This study aims to evaluate the performance of the contacts, in terms of surface wear, correlating the number of switching and the effects generated on the contacts in terms of loss of mass and surface damage. With the results obtained, it is possible to conclude that with each switching maneuver the mobile contact loses about 0.002895% of its initial mass. In addition, there was a change in the topography of the sample, as... [more]

With increasing demands for cleaning and purification of water, wastewater treatment plants (WWTP) require their most efficient operation. The operators are thus obliged to constantly review the efficiency of the processing units and technological equipment of WWTPs and seek opportunities for improvements. To increase the efficiency of particular equipment, the important parameters to be used for the intensification must be correctly selected. A common WWTP consists of different types of processing units, where the basic parameters can be changed to achieve the highest efficiency (i.e., maximum output with minimum energy consumption) in the WWTP. However, due to many possible technologies in the wastewater treatment process, the combinations of processing units can be complex. In such cases, the efficiency assessment can be misleading if only basic parameters were accessed. Moreover, single-unit intensification can potentially improve the efficiency of the unit itself but cannot guaran... [more]

The Air-conditioning System (ACS), used in office buildings in the hot summer and cold winter zone of China, are always operate intermittently. The dynamic thermal behaviors of building walls with real climate conditions may be different from those with only the representative day’s climate conditions, due to the time varying nature of the climate, which will lead to the variation of the ACS loads. A numerical calculation was performed to analyze the effects of insulation form on heat behavior of external walls and ACS loads. The results indicate that cooling transmission load with inside insulation reaches its maximum value when the solar-air temperature in daytime is the highest, while that with outside insulation occurs at the time when the air temperature at night is the highest during summer. Heating transmission load for the wall with external and internal insulation both peaks in the day with lowest mean outdoor temperature during the last non-working period. Inside insulation c... [more]

Implemented in road transport enterprises (RTEs) on a large scale, telematics systems are dedicated both to the particular aspects of their operation and to the integrated fields of the total operational functioning of such entities. Hence, a research problem can be defined as the identification of their efficiency levels in the context of operational activities undertaken by RTEs (including more holistic effects, e.g., lowering fuel/energy consumption and negative environmental impacts). Current research studies refer to the efficiency of some particular modules, but there have not been any publications focused on describing the efficiency of telematics systems in a more integrated (holistic) way, due to the lack of a universal tool that could be applied to provide this type of measurement. In this paper, an attempt at filling the identified cognitive gap is presented through empirical research analysing the original matrix developed by the authors that refers to the efficiency rates... [more]

In this study, a multifunctional air and water source heat pump system was developed with a parallel refrigerant piping arrangement, which possessed six operational functions: space cooling (SC), space heating (SH), water heating (WH), water cooling (WC) and two composite operational modes. The two composite operational modes were the SC/WH mode and the SH/WH mode. The performance of the multifuctional heat pump system under different ambient conditions was investigated based on the testing standards of CNS 14464 and CNS 15466. In this study, the effect of the direct water heating (DWH) and circulating water heating (CWH) methods on the performance was investigated. It was found that the water heating performance of the system by the DWH method is better than that of the system by the CWH method. The water heating capacity and COPw,h of the DWH method can be improvement by 2.6% to 22.1% and 2.9% to 50.8%, respectively. Moreover, this study developed a refrigerant pressure balance metho... [more]

This paper builds an optimal carbon-energy combined-flow (OCECF) model to optimize the carbon emission and energy losses of power grids simultaneously. A novel multi-agent cooperative reduced-dimension Q(λ) (MCR-Q(λ)) is proposed for solving the model. Firstly, on the basis of the traditional single-objective Q(λ) algorithm, the solution space is reduced effectively to shrink the size of Q-value matrices. Then, based on the concept of ant cooperative cooperation, multi-agents are used to update the Q-value matrices iteratively, which can significantly improve the updating rate. The simulation in the IEEE 118-bus system indicates that the proposed technique can decrease the convergence speed by hundreds of times as compared with conventional Q(λ), keeping high global stability, which is very suitable for dynamic OCECF in a large and complex power grid compared with other algorithms.

Contemporary distributions are now going to underground their overhead distribution lines due to techno-social reasons. Reliability and loss reduction are the two prime objectives for distribution system operation. Since failure rates of ungrounded cables are the function of Joules heating besides their physical lengths, the reliability evaluation of undergrounded distribution systems needs to be reviewed. This paper suggested a suitable modification in existing reliability indices in order to make them more appropriate for underground distribution systems. A multi-objective network reconfiguration problem is formulated to enhance the reliability and performance of distribution systems while duly addressing the variability and uncertainty in load demand and power generation from renewables. The application results on a standard test bench shift the paradigm of the well-known conflicting nature of reliability and network performance indices defined for overhead distribution systems.

The widespread adoption of electric vehicles (EVs) has entailed the need for the parking lot operators to satisfy the charging and discharging requirements of all the EV owners during their parking duration. Meanwhile, the operational constraints of the power grids limit the amount of simultaneous charging and discharging of all EVs. This affects the EV owner’s quality of experience (QoE) and thereby reducing the quality of performance (QoP) for the parking lot operators. The QoE represents a certain percentage of the EV battery required for its next trip distance; whereas, the QoP refers to the ratio of EVs with satisfied QoE to the total number of EVs during the operational hours of the parking lot. This paper proposes a two-stage fuzzy logic inference based algorithm (TSFLIA) to schedule the charging and discharging operations of EVs in such a way that maximizes the QoP for the parking lot operators under the operational constraints of the power grid. The first stage fuzzy inference... [more]

This article presents a methodology for optimizing the operation of parallel pumping stations in an open-channel water transfer system. A mathematical model was established for the minimum power with constraints on water level, flow rate and pump unit performance, and related factors. In the objective function, energy consumption of relevant equipment or facilities, such as main pump units, power transmission and transformation equipment, and auxiliary equipment, was considered comprehensively. The model was decomposed to two layers for solving. In the first layer, by using discharge distribution ratio as a variable, the flow rate and water level of the two water channels could be determined by employing the dichotomy approach (DA), and were calculated according to the principle of energy conservation, considering energy loss caused by hydraulic leakage and evaporation losses. In the second layer, the number of running pumps and the flow rate of a single pump were obtained by simulated... [more]

Natural disturbances are common in Canadian boreal managed forests. For example, during and after insect epidemics, foresters must deal with significant amounts of degraded or dead wood that cannot be processed into sawn timber or pulp. Bioenergy could be an alternative pathway for this wood. A case study in Quebec (Canada) was used to evaluate the profitability of pellet production for bioenergy using degraded trees from insect epidemics. A bioenergy scenario was simulated in which degraded trees were harvested for bioenergy alongside sound wood for timber and pulp. This scenario was compared to a reference scenario in which degraded trees were left on cutovers. Using wood pellets as a case study, the results showed that at current market prices, harvesting degraded trees for pellet production is not as profitable as leaving them in the forest. Nevertheless, the overall forest operations for procuring wood for timber and pulp were still profitable, even with very high degradation leve... [more]

Lignocellulosic biomass is used in various industries and its procurement involves a set of operations that are mainly done using equipment powered by internal combustion engines. The sustainability of forest operations may be characterized by balancing their energy inputs with those typically embodied in their outputted products. Forest tending operations are problematic because most of them cannot output marketable products while the data on their energy inputs are important for the forest management. Six of the most commonly used brushcutters equipped successively with discs and knives were tested to provide part of the data needed to run an energy analysis and to be able to characterize the energy inputs in release cutting operations by implementing the Gross Energy Requirements method. Fuel burning was found to have the greatest contribution (83−92%) in the total energy inputs (0.8−1.2 GJ/ha) of the studied operations and it was highly dependent on the efficiency of operations. Mo... [more]

This paper presents an on-line diagnosis method for large photovoltaic (PV) power plants by using a machine learning algorithm. Most renewable energy output power is decreased due to the lack of management tools and the skills of maintenance engineers. Additionally, many photovoltaic power plants have a long down-time due to the absence of a monitoring system and their distance from the city. The IEC 61724-1 standard is a Performance Ratio (PR) index that evaluates the PV power plant performance and reliability. However, the PR index has a low recognition rate of the fault state in conditions of low irradiation and bad weather. This paper presents a weather-corrected index, linear regression method, temperature correction equation, estimation error matrix, clearness index and proposed variable index, as well as a one-class Support Vector Machine (SVM) method and a kernel technique to classify the fault state and anomaly output power of PV plants.

A multi-agent architecture for a Non-Intrusive Load Monitoring (NILM) solution is presented and evaluated. The underlying rationale for such an architecture is that each agent (load event detection, feature extraction, and classification) outperforms others of the same type in particular scenarios; hence, by combining the expertise of these agents, the system presents an improved performance. Known NILM algorithms, as well as new algorithms, proposed by the authors, were individually evaluated and compared. The proposed architecture considers a NILM system composed of Load Monitoring Modules (LMM) that report to a Center of Operations, required in larger facilities. For the purposed of evaluating and comparing performance, five load event detect agents, five feature extraction agents, and five classification agents were studied so that the best combinations of agents could be implemented in LMMs. To evaluate the proposed system, the COOLL and the LIT-Dataset were used. Performance impr... [more]

Building energy performance benchmarking increases awareness and enables stakeholders to make better informed decisions for designing, operating, and renovating sustainable buildings. In the era of nearly zero energy buildings, the embodied energy along with operational energy use are essential for evaluating the environmental impacts and building performance throughout their lifecycle. Key metrics and baselines for the embodied energy intensity in representative Hellenic houses are presented in this paper. The method is set up to progressively cover all types of buildings. The lifecycle analysis was performed using the well-established SimaPro software package and the EcoInvent lifecycle inventory database, complemented with national data from short energy audits carried out in Greece. The operational energy intensity was estimated using the national calculation engine for assessing the building’s energy performance and the predictions were adapted to obtain more realistic estimates.... [more]

One of the ways to sustain development is striving for energy efficiency. This is the purpose of directive 2012/27/EU on energy efficiency, which aims at explaining and promoting energy−saving and ecological solutions that allow increasing the output of consumed energy. Several years after implementation, it is possible to assess the directive’s usefulness and completeness in a few areas of the economy, in particular in the operation of enterprises, which substantially contribute to the global energy consumption. Therefore, the purpose of the study was defined as an assessment of the execution of the concept of energy efficiency in business operations in EU countries, in accordance with the assumptions of directive 2012/27/EU. The collected raw data were derived from surveys gathered in the process of public consultations of the European Commission regard directive 2012/27/EU on energy efficiency. Resulting observations were analysed using the basic methods of descriptive statistics, a... [more]

This article presents a comparative experimental evaluation of some power calculation methods used for three-phase and single-phase systems. In order to make the comparison, methods based on three reference frames, the natural one, αβ and dq, are considered. This paper addresses the experimental comparison for single-phase systems facing sinusoidal and non-sinusoidal waveforms in both linear and non-linear loads. The results are obtained from an experimental platform consisting of a controlled voltage inverter and an acquisition system based on a TMS320F28335, where the power calculation algorithms are implemented. The experimental comparison of the different methods for active and reactive power calculation is made in terms of accuracy and processing time in digital implementation.

Compared with conventional forward converters, active clamp forward (ACF) converters have many advantages, including lower voltage stress on the primary power devices, the ability to switch at zero voltage, reduced EMI and duty cycle operation above 50%. Thus, it has been the most popular solution for the low bus voltage applications, such as 48 V and 28 V. However, because of the poor performance of Si MOSFETs, the efficiency of active clamp forward converters is difficult to further improved. Focusing on the bus voltage of 28 V with 18~36 V voltage range application, the Gallium Nitride high electron-mobility transistors (GaN HEMT) with ultralow on-resistance, low parasitic capacitances, and no reverse recovery, is incorporated into active clamp forward converters for achieving higher efficiency and power density, in this paper. Meanwhile, the comparative analysis is performed for Si MOSFET and GaN HEMT. In order to demonstrate the feasibility and validity of the proposed solution an... [more]