The world is currently witnessing a rapid increase in sewage sludge (SS) production, due to the increased demand for wastewater treatment. Therefore, SS management is crucial for the economic and environmental sustainability of wastewater treatment plants. The recovery of nutrients from SS has been identified as a fundamental step to enable the transition from a linear to a circular economy, turning SS into an economic and sustainable source of materials. SS is often treated via anaerobic digestion, to pursue energy recovery via biogas generation. Anaerobically digested sewage sludge (ADS) is a valuable source of organic matter and nutrients, and significant advances have been made in recent years in methods and technologies for nutrient recovery from ADS. The purpose of this study is to provide a comprehensive overview, describing the advantages and drawbacks of the available and emerging technologies for recovery of nitrogen (N), phosphorus (P), and potassium (K) from ADS. This work... [more]

The article is a synthetic review of contemporary wind energy issues. It was created on the basis of a survey of literature from the last two years, with mainly review articles. This work is intended to be a source of information for a wide group of scientists and students from various fields. The aim is to interest them in a wide range of topics related to wind energy and wind turbines. This may allow for the selection of an area and the undertaking of research in this interesting and future-oriented field.

Decarbonizing the global power sector is a key requirement to fight climate change. Consequently, the deployment of renewable energy (RE) technologies, notably solar photovoltaic (PV), is proceeding rapidly in many regions. However, in many of these regions, the evening peak is predominantly being served by fossil-fired generators. Furthermore, as the evening peak is projected to increase in the coming years, there are plans to install more fossil-fired peaking generators. A cleaner alternative is to enable solar PV plants to provide clean power after sunset by pairing them with large-scale lithium-ion batteries to provide evening peak generation. In this work, we performed a techno-economic analysis of a solar PV plus battery (PVB) power plant using the island of Mauritius as a case study. We assessed the impacts of the battery size, inverter loading ratio (ILR), tracking type, and curtailment on the levelized cost of electricity (LCOE). The main results show that the LCOE of utility-... [more]

The anxiety of driving range and inconvenience of battery recharging has placed high requirements on the energy efficiency of electric vehicles. To reduce driving-wheel slip energy consumption while cornering, a torque vectoring control strategy for a rear-wheel independent-drive (RWID) electric vehicle is proposed. First, the longitudinal linear stiffness of each driving wheel is estimated by using the approach of recursive least squares. Then, an initial differential torque is calculated for reducing their overall tire slippage energy dissipation. However, before the differential torque is applied to the two side of driving wheels, an acceleration slip regulation (ASR) is introduced into the overall control strategy to avoid entering into the tire adhesion saturation region resulting in excessive slip. Finally, the simulations of typical manoeuvring conditions are performed to verify the veracity of the estimated tire longitudinal linear stiffness and effectiveness of the torque vect... [more]

The ambitious target of net-zero emission by 2050 has been aggressively driving the renewable energy sector in many countries. Leading the race of renewable energy sources is solar energy, the fastest growing energy source at present. The solar industry has witnessed more growth in the last decade than it has in the past 40 years, owing to its technological advancements, plummeting costs, and lucrative incentives. The United States is one of the largest producers of solar power in the world and has been a pioneer in solar adoption, with major projects across different technologies, mainly photovoltaic, concentrated solar power, and solar heating and cooling, but is expanding towards floating PV, solar combined with storage, and hybrid power plants. Although the United States has tremendous potential for exploiting solar resources, there is a scarcity of research that details the U.S. solar energy scenario. This paper provides a comprehensive review of solar energy in the U.S., highligh... [more]

This paper introduces and investigates a new design method that employs both teeth arrangement and pole−slot combination to reduce the detent force of permanent magnet linear synchronous motors (PMLSMs) for precision position control. The proposed topology is a 10-pole, 12-slot-based PMLSM comprising two sections that significantly reduce the detent force without implementing a skewing design. It was analytically and experimentally confirmed that the proposed design effectively reduces detent force with a negligible sacrifice of mover length. The general characteristics and servo performance of the proposed PMLSM were experimentally examined and then discussed.

Rice grain arsenic (As) is a major pathway of human dietary As exposure. This study was conducted to reduce rice grain As concentration through microwave (MW) and biochar soil treatment. Collected soils were spiked to five levels of As concentration (As-0, As-20, As-40, As-60, and As-80 mg kg−1) prior to applying three levels of biochar (BC-0, BC-10, and BC-20 t ha−1) and three levels of MW treatment (MW-0, MW-3, and MW-6 min). The results revealed that MW soil treatment alleviates As phytotoxicity as rice plant growth and grain yield increase significantly and facilitate less grain As concentration compared with the control. For instance, the highest grain As concentration (912.90 µg kg−1) was recorded in the control while it was significantly lower (442.40 µg kg−1) in the MW-6 treatment at As-80. Although the BC-10 treatment had some positive effects, unexpectedly, BC-20 had a negative effect on plant growth, grain yield, and grain As concentration. The combination of BC-10 and MW-6... [more]

The energy sector is the epitome of Industry 4.0; therefore, it should be developed in line with the Industry 4.0 implementation framework and be managed according to the guidelines dedicated to knowledge-based enterprises. Under this model of evolution, the layers surrounding the technological aspects are first, knowledge management (in particular, its transfer), and then people, and culture. This study addresses two of the three identified levels by attempting to verify the organizational culture that supports professional knowledge transfer as the leading factor in effective specialist knowledge exchange in the energy sector. Recently, this sector has become highly dependent on IT solutions as the main factor for its development and security. A key role in this respect is played by IT professionals, whose attitudes and employee behavior are critical to the stability, efficiency, effectiveness, and security of IT systems in the energy companies. The purpose of this paper is to propos... [more]

An online parameter estimation methodology using the d-axis current injection, which can estimate the distorted voltage of the current-controlled voltage source inverter (CCVSI), the varying dq-axis inductances, and the rotor flux, is proposed in this study for interior permanent magnet synchronous motor (IPMSM) drives in the constant torque region. First, a d-axis current injection-based parameter estimation methodology considering the nonlinearity of a CCVSI is proposed. Then, during current injection, a simple linear model is developed to model the cross- and self-saturation of the dq-axis inductances. Since the d-axis unsaturated inductance is difficult to obtain by merely using the recursive least square (RLS) method, a novel tuning method for the d-axis unsaturated inductance is proposed by using the theory of the maximum torque per ampere (MTPA) with the combination of the RLS method. Moreover, to improve the bandwidth of the current loop, an intelligent proportional-integral-de... [more]

The increasingly frequent use of electric drives is a new direction of development in personal transport. Sometimes these drives take over the work of human muscles, and sometimes they only support them. This is particularly evident in means of transport such as bicycles and scooters, but also in transporting people with disabilities. This study questions whether this is the only right development direction, and explores the possibility of developing means of transport for the more effective use of human muscles by proposing new structural solutions. We identified that such an action favors the minimization of the environmental load generated by technical facilities and, at the same time, may be a response to social needs resulting from the principles of sustainable development. This paper presents the operation principle of the innovative Wheelchair Cam-thread Drive (WCD), followed by field tests, laboratory measurements and biomechanical analyses of the WCD, comparing it with a typic... [more]

The impact of rock minerals on the performance of in situ combustion (ISC) techniques for enhanced oil recovery (EOR) is very important. This work is aimed at investigating the influence of carbonate rocks (dolomite and calcite) on heavy oil oxidation by Thermogravimetry−Fourier-Transform-Infrared (TG-FT-IR) coupled analysis. Two heavy oils with 19.70° and 14.10° API were investigated. Kinetic analysis was performed using TG data by differential and integral isoconversional methods. From TG-DTG curves, three reaction stages, i.e., low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO), were defined for both two heavy oil samples, and their reaction mechanism was explained combining the FT-IR data. After the addition of calcite or dolomite, three reaction stages became two with the disappearance of FD, and a significant shift of reaction stages into lower temperatures was also observed. These significant changes in oxidation behavior are because calc... [more]

As a promising renewable fuel, biodiesel has gained worldwide attention to replace fossil-derived mineral diesel due to the threats concerning the depletion of fossil reserves and ecological constraints. Biodiesel production via transesterification involves using homogeneous, heterogeneous and enzymatic catalysts to speed up the reaction. The usage of heterogeneous catalysts over homogeneous catalysts are considered more advantageous and cost-effective. Therefore, several heterogeneous catalysts have been developed from variable sources to make the overall production process economical. After achieving optimum performance of these catalysts and chemical processes, the research has been directed in other perspectives, such as the application of non-conventional methods such as microwave, ultrasonic, plasma heating etc, aiming to enhance the efficiency of the overall process. This mini review is targeted to focus on the research carried out up to this date on microwave-supported heteroge... [more]

This paper presents a method for shaft position estimation of a synchronous motor with permanent magnets. Zero speed and very low speed range are considered. The method uses the analysis of high-frequency currents induced by the introduction of additional voltage in the control path in the stationary coordinate system associated with the stator. An artificial neural network estimates the sine and cosine values necessary in the Park’s transformation units. This method can achieve satisfactory accuracy in the case of low asymmetry of inductance in the direct and quadrature axes of the coordinate system associated with the rotor. The TensorFlow/Keras package was used for artificial network calculations and the scikit-learn package for preprocessing. Aggregating the outputs of several artificial neural networks provides an opportunity to reduce the resultant estimation error. The use of as few as four networks has enabled the error to be reduced by approximately 20% compared to a single ex... [more]

Climate change is changing global weather patterns, with an increase in droughts expected to impact crop yields due to water scarcity. Crops can be provided with water via underground pumping systems to mitigate water shortages. However, the energy required to pump water tends to be expensive and hazardous to the environment. This paper explores different sites in Sudan to assess the crop water requirements as the first stage of developing renewable energy sources based on water pumping systems. The crop water requirements are calculated for different crops using the CROPWAT and CLIMWAT simulation tools from the Food and Agriculture Organization (FAO) of the United Nations. Further, the crop water requirements are translated into electrical energy requirements. Accurate calculations of the energy needed will help in developing cost-effective energy systems that can help in improving yields and reducing carbon emissions. The results suggest that the northern regions tend to have higher... [more]

Concentrating photovoltaic-thermal (CPVT) collectors have to face the challenge of contrary temperature requirements in the single receiver parts. The PV cells require low temperatures to achieve high efficiency, whereas the thermal part should generate high temperatures for providing industrial heat. The approach of “Spectral Splitting” can offer a solution for compact CPVT receivers; however, a clear quantification of the expected conversion efficiency is difficult. Therefore, this paper describes a modelling methodology for obtaining electrical and thermal performance parameters for a Spectral Splitting configuration using semiconductor-doped glass combined with appropriate heat transfer fluid. The PV technologies c-Si, CIGS and CdTe are considered. The presented model yields distinct results for maximising the electrical efficiency, calculates the reduction in waste heat dissipation within the cells and assesses the impacts of concentration factor and cell temperature. An optimised... [more]

An inertial response emulated control strategy of doubly-fed induction generators (DFIGs) is able to arrest their frequency decline following a severe frequency event. Nevertheless, the control coefficient is unchanged, so as to limit the benefit potentiality of improving the inertial response capability for various disturbances and provide less of a benefit for boosting the frequency nadir. This paper addresses an enhanced inertial response emulated control scheme for a DFIG to improve the maximum frequency deviation and maximum rate of change of frequency for various disturbances. To this end, the control coefficient is coupled with the system frequency deviation so as to regulate the control coefficient according to the system frequency deviation (i.e., sizes of the disturbance). Results clearly indicate that the proposed inertial response emulated control strategy provides better performance in terms of improving the maximum rate of change of frequency and maximum frequency deviati... [more]

The by-product gases from the blast furnace and converter of an integrated steelworks highly contribute to today’s global CO2 emissions. Therefore, the steel industry is working on solutions to utilise these gases as a carbon source for product synthesis in order to reduce the amount of CO2 that is released into the environment. One possibility is the conversion of CO2 and CO to synthetic natural gas through methanation. This process is currently extensively researched, as the synthetic natural gas can be directly utilised in the integrated steelworks again, substituting for natural gas. This work addresses the in situ methanation of real steelworks gases in a lab-scaled, three-stage reactor setup, whereby the by-product gases are directly bottled at an integrated steel plant during normal operation, and are not further treated, i.e., by a CO2 separation step. Therefore, high shares of nitrogen are present in the feed gas for the methanation. Furthermore, due to the catalyst poisons pr... [more]

Stratified air distribution systems are commonly used in large space buildings. The research on the airflow organization of stratified air conditioners is deficient in terms of the analysis of multivariable factors. Moreover, studies on the coupled operation of stratified air conditioners and natural ventilation are few. In this paper, taking a Shanghai Airport Terminal departure hall for the study, air distribution and thermal comfort of the cross-section at a height of 1.6 m are simulated and compared under different working conditions, and the effect of natural ventilation coupling operation is studied. The results show that the air distribution is the most uniform and the thermal comfort is the best (predicted mean vote is 0.428, predicted percentage of dissatisfaction is 15.2%) when the working conditions are 5.9% air supply speed, 11 °C cooling temperature difference and 0° air supply angle. With the coupled operation of natural ventilation, the thermal comfort can be improved fr... [more]

In the current study, the electrical responses of a thermoelectric (TE) module and a photovoltaic (PV) cell are investigated in three different systems, namely, a PV-only system, TE-only system, and hybrid TE-PV system with a beam splitter (TE-PV-BS), under variable solar irradiations demonstrating partly cloudy weather conditions. To enhance the deployment of solar energy, a predesigned beam splitter combined with the amorphous silicon TE and PV system is used in the experiments. The impact of the spectral beam splitting technology on the conversion performance of the TE module and PV cell in the hybrid system is studied and compared to the performance of the TE-only and PV-only systems. The electrical output parameters of the TE module and PV cell are obtained for the studied systems, and they are discussed in detail. The results of this work show that the power generated by the PV cell has a stepwise fluctuation similar to the variation in the concentrated solar radiation. Affected... [more]

The main goal of this work is the evaluation of the energy saving achievable in railway drive when using the coasting technique extensively, with reference to a practical case of the Italian railway network taken as an example. This technique consists in exploiting the kinetic energy accumulated by the running train whenever possible. To implement a driving style on purpose, the only driver contribution is not enough; indeed, it is necessary to provide an embedded automatic calculation control system. In the paper, an algorithm has been developed to evaluate the energy absorption of railway locomotives during the normal service and validated on a real railway line. The proposed hardware and software system could be implemented aboard the train, allowing motion data processing in real-time. Speed, time intervals and power absorption for a given path are calculated; then, the best coasting parameters are estimated to maximize the energy savings. In particular, the case study presented in... [more]

People are the main reason for the deterioration of indoor air quality (IAQ) due to the continuous physiological metabolism processes in their bodies, including respiration. We present results from an investigation of the influence of indoor air temperature on the concentration of exhaled carbon dioxide (CO2). The investigation was preconditioned by previous findings on the effect of air temperature on human metabolism. However, our literature survey showed a lack of studies on the influence of the indoor air temperature on the exhaled CO2 (or metabolic CO2), which leads to the novelty of our results. Our experiments had two phases: measurement in a university classroom with an installed heating, ventilation, and air-conditioning (HVAC) system during regular classes and measurement in a specially designed small climate chamber, where the time variations of the CO2 concentrations, together with some physiological parameters, were measured. Two indoor air temperatures were set: 23 °C and... [more]

In this study, we have proposed a novel current injection determination method that improves the voltage unbalance based on the unbalanced line impedance in a distribution network with a large-capacity PV system. An increase in the unbalance of the distribution line voltage was observed owing to a large-scale reverse power flow. To visualize this phenomenon, the P-V curves were derived for each phase to indicate the increase in the voltage unbalance with respect to the reverse power flow. Based on the derived P-V curves, the effect of a current unbalance on the voltage unbalance was investigated. It was clarified that there is a current unbalance that can improve the voltage unbalance even if the line impedance is unbalanced. In other words, the current unbalance that can theoretically make the voltage unbalance zero could be expressed in terms of the symmetrical components of unbalanced line impedance. As an application of the proposed method, the effect of the mitigation of voltage u... [more]

Manufacturing offers substantial opportunities for economic growth after COVID-19, as long as it delivers competitively priced goods while simultaneously reducing pressure on the environment. In this study, we present the methodological feasibility of the joint application of life cycle assessment (LCA) and data envelopment analysis (DEA) for assessing eco-efficiency at the sector level. We employ this methodology to assess the environmental profiles of manufacturing in Poland in relation to their gross value added, and subsequently calculate the improvement targets for the eco-inefficient manufacturing industries. The study reveals that only the chemical industry is relatively eco-efficient, whereas the remaining industries have considerable room for improvement due to their very low eco-efficiency, and thus should follow the best practices established by the chemical industry. Although there are always individual paths for manufacturing industries to achieve the decoupling of economi... [more]

It is of great significance to ascertain the mechanical characteristics and deformation laws of tectonic coal that is under complex stress conditions for safe production, but the targeted research in this area is still insufficient at present. This paper performed triaxial tests under cyclic multi-level loading at different rates by using an MTS-815 Rock Mechanics Testing System. The strain characteristics, elastic modulus and energy evolution were obtained in order to explore the effects of the mechanism of loading rate on the evolution of deformation and energy parameters of tectonic coal. The results showed that the irreversible strain and plastic energy increased exponentially with the increase in the deviatoric stress, but the growth rate decreased with the increase in loading rate. Furthermore, the elastic strain increased linearly and the growth rate was essentially unaffected by the loading rate. During the compaction stage, the variation of each parameter was not sensitive to... [more]

An opportunity to decarbonise the offshore oil and gas sector lies in the integration of renewable energy sources with energy storage in a hybrid energy system (HES). Such concept enables maximising the exploitation of carbon-free renewable power, while minimising the emissions associated with conventional power generation systems such as gas turbines. Offshore plants, in addition to electrical and mechanical power, also require process heat for their operation. Solutions that provide low-emission heat in parallel to power are necessary to reach a very high degree of decarbonisation. This paper investigates different options to supply process heat in offshore HES, while the electric power is mostly covered by a wind turbine. All HES configurations include energy storage in the form of hydrogen tied to proton exchange membrane (PEM) electrolysers and fuel cells stacks. As a basis for comparison, a standard configuration relying solely on a gas turbine and a waste heat recovery unit is c... [more]