Acknowledgement to Reviewers of Journal of Energy and Power Technology in 2021

The editors of Journal of Energy and Power Technology would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2021. We greatly appreciate the contribution of expert reviewers, which is crucial to the journal's editorial process. We aim to recognize reviewer contributions through several mechanisms, of which the annual publication of reviewer names is one. Reviewers receive a voucher entitling them to a discount on their next LIDSEN publication and can download a certificate of recognition directly from our submission system. Additionally, reviewers can sign up to the service Publons (https://publons.com) to receive recognition. Of course, in these initiatives we are careful not to compromise reviewer confidentiality. Many reviewers see their work as a voluntary and often unseen part of their role as researchers. We are grateful to the time reviewers donate to our journals and the contribution they make.

Acknowledgement to Reviewers of Journal of Energy and Power Technology in 2021

The editors of Journal of Energy and Power Technology would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2021. We greatly appreciate the contribution of expert reviewers, which is crucial to the journal's editorial process. We aim to recognize reviewer contributions through several mechanisms, of which the annual publication of reviewer names is one. Reviewers receive a voucher entitling them to a discount on their next LIDSEN publication and can download a certificate of recognition directly from our submission system. Additionally, reviewers can sign up to the service Publons (https://publons.com) to receive recognition. Of course, in these initiatives we are careful not to compromise reviewer confidentiality. Many reviewers see their work as a voluntary and often unseen part of their role as researchers. We are grateful to the time reviewers donate to our journals and the contribution they make.

Harvesting the Potential of CO2 before it is Injected into Geological Reservoirs

To store CO2 in geological reservoirs, expansion valves have been used to intentionally release supercritical CO2 from high-pressure containers at a source point to lower-pressure pipelines and transport to a selected injection site. Using expansion valves, however, has some shortcomings: (i) the fluid potential, in the form of kinetic energy and pressure which can produce mechanical work or electricity, is wasted, and (ii) due to the Joule-Thomson cooling effect, the reduction in the temperature of the released CO2 stream might be so dramatic that it can induce thermal contraction of the injection well causing fracture instability in the storage formation. To avoid these problems, it has been suggested that before injection, CO2, should be heated to a temperature slightly higher than that of the reservoir. However, heating could increase the cost of CO2 injection. This work explores the use of a Tesla Turbine, instead of an expansion valve, to harvest the potential of CO2, in the form of its pressure and kinetics, to generate mechanical work when it is released from a high-pressure container to a lower-pressure transport pipeline. The goal is to avoid throttling losses and to produce useful power because of the expansion process. In addition, due to the friction between the gas and the turbine disks, the expanded gas temperature reduction is not as dramatic as in the case when an expansion valve is used. Thus, as far as CO2 injection is concerned, the need for preheating can be minimized.

The Drag Forces on a Taylor Bubble Rising Steadily in Vertical Pipes

By the adoption of a drag-buoyancy equality model, analytical solutions were obtained for the drag coefficients (CD) of Taylor bubbles rising steadily in pipes. The obtained solutions were functions of the geometry of the Taylor bubble and the gas volume fraction. The solutions were applicable at a wide range of Capillary numbers. The solution was validated by comparison with experimental data of other investigators. All derived drag formulas were subject to the condition that Bond number >4, for air-water systems.

Reactor Design for Biogas Production-A Short Review

Biogas is an alternative to gaseous biofuels and is produced by the decomposition of biomass from substances such as animal waste, sewage sludge, and industrial effluents. Biogas is composed of methane, carbon dioxide, nitrogen, hydrogen, hydrogen sulfide, and oxygen. The anaerobic production of biogas can be made cheaper by designing a high throughput reactor and operating procedures. The parameters such as substrate type, particle size, temperature, pH, carbon/nitrogen (C/N) ratio, and inoculum concentration play a major role in the design of reactors to produce biogas. Multistage systems, batch, continuous one-stage systems, and continuous two-stage systems are the types of digesters used in the industry for biogas production. A comprehensive review of reactor design for biogas production is presented in the manuscript.

Effect of Mineral Additives on Fusion Behavior of Agricultural Residue Ashes during Combustion or Co-combustion with Lignite

In this work, the ash fusibility behaviour of selected agricultural residues and their blends with lignite was studied, by carrying out chemical, mineralogical, fusibility and thermogravimetric analyses and calculating slagging/fouling indicators for predicting deposition tendencies in boilers. Two additives, bauxite, and clinochlore, were used at varying amounts to reduce ash melting, followed by examining their anti-fusion mechanisms. Initial deformation and softening temperatures of biomass materials were low for combustion processes operating above 900 °C due to their high concentration in K, Na, and P compounds. When the additives were mixed with raw fuels or lignite/biomass blends, the initial deformation of ashes started at temperatures up to 340 °C higher, whereas the fluid temperature in most cases exceeded 1500 °C. Bauxite was more effective than clinochlore. The positive impact of additives was attributed to the mineralogical transformations during ashing to phases with a high melting point through reactions with K, Na-bearing minerals, or CaO of fuel ashes.

Variable Speed Diesel Electric Generators: Technologies, Benefits, Limitations, Impact on Greenhouse Gases Emissions and Fuel Efficiency

A substantial share of the electric energy is generated with synchronous generators that provide sustained alternating current (AC) voltage and frequency energy to regional and national power systems, which subsequently transport and distribute it to diverse users. In an attempt to reduce environmental effects, electric energy markets have recently become more open, resulting in more flexible distributed electric power systems. In such distributed systems, stability, quick and efficient delivery, and control of electric power require some degree of power electronics control to allow for lower power in the electric generators to tap the primary fuel energy potential better and increase efficiency and stability. This is how variable-speed electric generators (VSEG) recently came into play, up to the 400-megavolt ampere (MVA)/ unit size, and which have been at work since 1996. This paper provides coverage of variable-speed electric diesel generators (VSDEG) in distributed generation and their impacts on fuel efficiency and greenhouse gases (GHG). It discusses permanent-magnet-(PM) synchronous generators, solutions based on power electronics such as diesel-driven wound-rotor-induction generator, doubly-fed-induction generator (DFIG), rotating stator generator, and the application of continuously variable transmission to a VSEG. The benefits and limitations of the selected technologies are also presented. The list of references given at the end of the paper should offer aids for students and researchers working in this field.

Potential of Coupling Heavy Metal (HM) Phytoremediation by Bioenergy Plants and Their Associated HM-Adapted Rhizosphere Microbiota (Arbuscular Mycorrhizal Fungi and Plant Growth Promoting Microbes) for Bioenergy Production

There is growing concern for the contamination of our soils and waters worldwide with heavy metals (HMs), as a result of indiscriminate use of agrochemicals for feeding growing population which require optimal use of resources and sustainable agricultural strategies. This can be simultaneously achieved by using microbes as bio-fertilizers, bio-protectants, and bio-stimulants, and suitable phytoremediation- plant capable of removing heavy metals contaminants from contaminated sites. There is a growing need to adopt such environmentally safe, attractive, and economical techniques that can remove most HMs contaminants as well as yield high biomass for bioenergy production. Phytoremediation and the microbes associated with the roots and inhabiting rhizospheres of the plants used for this purpose, has emerged as an alternative strategy. This article reviews the principles and application of this strategy, and provides an overview of the use of fast growing, non-food bioenergy plants, like Vetiver grass and industrial hemp, and their root-associated microbiota such as Arbuscular Mycorrhizal Fungi (AMF), Mycorrhiza Helping Bacteria (MHB), and Plant–Growth–Promoting-Rhizobia (PGPR) that can both tolerate and immobilize HMs in the roots, i.e. sequestrate contaminant HMs thereby protecting plants from metal toxicity. This mini-review also focuses on other phytoextraction strategies involving rhizosphere microbes, such as (1) inoculating plants used for phytoremediation of HMs contaminated soil and water with rhizobial microflora, and (2) managing their population in the rhizospheres by using a consortium of site specific AMF, PGPR, and MHB, and N-fixing rhizobia as biofertilizers to Phyto-remediate derelict contaminated sites. Various crop management strategies such as Crop Sequencing and Intercropping or Co-cropping of, for example, mycorrhizal and non-mycorrhizal crops, or leguminous and non-leguminous crops, etc., can be employed for improved plant growth. Another possible strategy to exploit soil microbes is to employ pre-cropping with mycotrophic crops to exploit AMF for mycorrhizo-remediation strategy.

Aqueous Lithium--Air Batteries with High Power Density at Room Temperature under Air Atmosphere

Rechargeable batteries with higher energy and power density exceeding the performance of the currently available lithium-ion batteries are suitable for application as the power source in electric vehicles (EVs). Aqueous lithium-air batteries are candidates for various EV applications due to their high energy density of 1910 Wh kg-1. The present study reports a rechargeable aqueous lithium-air battery with high power density at room temperature. The battery cell comprised a lithium anode, a non-aqueous anode electrolyte, a water-stable lithium-ion-conducting NASICON type separator, an aqueous catholyte, and an air electrode. The non-aqueous electrolyte served as an interlayer between the lithium anode and the solid electrolyte because the solid electrolyte in contact with lithium was unstable. The mixed separator comprised a Kimwipe paper and a Celgard polypropylene membrane for the interlayer electrolyte, which was used for preventing the formation of lithium dendrites at a high current density. The proposed aqueous lithium-air battery was successfully cycled at 2 mA cm-2 for 6 h at room temperature under an air atmosphere.

A Review on High-Capacity and High-Voltage Cathodes for Next-Generation Lithium-ion Batteries

lithium-ion battery (LIB) is at the forefront of energy research. Over four decades of research and development have led electric mobility to a reality. Numerous materials capable of storing lithium reversibly, either as an anode or as a cathode, are reported on a daily basis. But very few among them, such as LiCoO2, lithium nickel manganese cobalt oxide (Li-NMC) variants (LiNi0.33Mn0.33Co0.33O2, LiNi0.5Mn0.3Co0.2O2, LiNi0.6Mn0.2Co0.2O2, and LiNi0.8Mn0.1Co0.1O2), LiNi0.8Co0.15Al0.05O2, LiFePO4, graphite, and Li4Ti5O12 are successful at commercial scale. Future energy requirements demand a push in the energy density of LIBs to meet the criteria of electric aviation, power trains, stationary grids, etc. All these applications have different needs which cannot be satisfied by a particular set of materials. Therefore, various materials need to be utilized in widespread fields of battery applications in the near future. This review discusses potential cathode materials that show a capacity of ≥ 250 mAh g-1 (Li-rich oxides, conversion materials, etc.) or average voltage of ≥ 4 V vs. Li+/Li (polyanionic materials, spinel oxides, etc.). Failure mechanisms, challenges, and way-outs to overcome all the issues are put forward to determine commercial viability.