Option For Energy Conversion Research Articles

Two-dimensional Be2P4 as a promising thermoelectric material and anode for Na/K-ion batteries.

Incredibly effective and flexible energy conversion and storage systems hold great promise for portable self-powered electronic devices. Owing to their large surface area, exceptional atomic structures, superior electrical conductivity and good mechanical flexibility, two-dimensional (2D) materials are recognized as an attractive option for energy conversion and storage application. In this work, we examined the stability, electronic, thermoelectric and electrochemical aspects of a novel 2D Be2P4 monolayer by adopting density functional theory (DFT). The Be2P4 monolayer exhibits a direct semiconductor gap of 0.9 eV (HSE06), large Young's modulus (∼198 GPa), high carrier mobility (∼104 cm2 V-1 s-1) and a low excitonic binding energy of 0.11 eV. Our calculated findings suggest that Be2P4 shows a lattice thermal conductivity of 1.02 W m K-1 at 700 K, resulting in moderate thermoelectric performance (ZT ∼ 0.7), encouraging its use in thermoelectric materials. In addition, a higher adsorption energy of -2.28 eV (-2.52 eV) and less diffusion barrier of 0.22 eV (0.17 eV) for Na(K)-ion batteries promote fast ion transport in the Be2P4 monolayer. This material also shows a high specific capacity and superior energy density of 8460 W h kg-1 (8883 W h kg-1) for Na(K)-ion batteries. Thus, our results offer insightful information for investigating potential thermoelectric and flexible anode materials based on the Be2P4 monolayer.

Energy from forest residues in Turkey: An environmental and economic life cycle assessment of different technologies

Forest residues, as cheap and abundant feedstock, can replace current fossil-energy sources, helping to reduce greenhouse gas (GHG) emissions and improve energy security. Given 27 % of total lands covered with forests, Turkey has a remarkable potential of forest residues from harvesting and industrial activities. This paper thus focuses on evaluating the life cycle environmental and economic sustainability of heat and electricity generation utilising forest residues in Turkey. Two types of forest residues (wood chips and wood pellets) and three energy conversion options are considered: direct combustion (heat only, electricity only and cogenerated heat and power (CHP)), gasification (for CHP) and co-firing with lignite. Results suggest that direct combustion of wood chips for cogeneration of heat and power has the lowest environmental impacts and levelised costs for both functional units (per MWh heat and per MWh electricity generation) considered. Compared to fossil-fuel sources, energy from forest residues has a potential to reduce the climate change impact as well as fossil-fuel, water and ozone depletion by >80 %. However, it also causes an increase in some other impacts, such as terrestrial ecotoxicity. The bioenergy plants have also lower levelised costs than electricity from the grid (except those using wood pellets and gasification regardless of the feedstock) and heat from natural gas. Electricity-only plants using wood chips achieve the lowest LCC, generating net profits. All biomass plants, except the pellet boiler, pay back in their lifetime; however, the economic feasibility of electricity-only and CHP plants is highly sensitive to subsidies for bioelectricity and efficient use of heat. Utilising the currently available forest residues in Turkey (5.7 Mt/yr) for energy provision could potentially reduce the national GHG emissions by 7.3 Mt/yr (1.5 %) and save $0.5 bn/yr (5 %) in avoided fossil-fuel import costs.

Seaweed Pellets as a Renewable Fuel Feedstock

Seaweed can be a desirable source of renewable energy or fuel after it has been processed by combustion, thermochemical conversion by gasification, pyrolysis, or hydrothermal liquefaction (HTL) or biochemical conversion routes like anaerobic digestion (AD). This work explores how well the measured properties of seaweed pellets match the specifications for the various fuel and energy conversion options listed. Blends of hay, wood chips, sawdust, and seaweed were pelletized. Eight pellet blends with dominant seaweed content and minimum acceptable mechanical strength and stability were produced and their physical and chemical properties were reported. The seaweed pellets had an energy content of around 14 MJ/kg, and each pellet could withstand almost 200 N of compression force. Their water content was around 5% or less and their ash content was around 20–34%. According to the results, a higher wood content increased the energy content of the pellets. Among those properties measured in this project, none of them contradicted the typical specifications of combustion, HTL, and AD. However, the low water content and low strength of some pellet types were unable to meet the specifications for certain types of gasification and pyrolysis.

The future of residue-based bioenergy for industrial use in Sub-Saharan Africa

Energy outlooks for Africa feature increased use of fossil fuels. However, they widely ignore that a transition from traditional to modern bioenergy can support the increasing commercial energy demand and offer a high level of flexibility and dispatchability. We use energy statistics, resource assessments and demand analysis to show how switching traditional biomass use to more sustainable technologies could practically eliminate unsustainable fuelwood use. Furthermore, mobilising agricultural and forestry residue for commercial use could grow a sustainable biomass industry and offset Africa's projected expansion of fossil fuels. The assessment focuses on feedstocks and potential energy conversion options for selected and most promising bioenergy pathways in Sub-Saharan Africa's growing and economically relevant industries: cement, agricultural processing, livestock, and horticulture. Examples of specific applications are given to support the high-level resource assessment and demand balances in these sectors. Our results indicate that 3317 PJ bioenergy could be utilised in Sub-Saharan Africa. Even with the calculated gap between biomass availability and biomass demand of 5559 PJ in future energy scenarios, bioenergy can contribute to sustainable energy supply and access in SSA. The sustainability mapping highlighted that bioenergy could deliver integral social and economic impacts because of the close integration with agriculture as the main livelihood supporting sector in SSA. Sustainability frameworks and governance structures must consider bioenergy beyond its cost and clean energy potential to maximise positive trade-offs.

Development of an ultra-low head siphon hydro turbine using computational fluid dynamics

Structural simplification and efficient hydraulic performance are key to effectively utilizing ultra-low head water power resources and reducing hydroelectric unit costs. In this study, a computational fluid dynamics (CFD) method was used to predict hydraulic performance of an axial turbine at the Gaoliangjian power station. CFD results agreed well with field test data. Using the same numerical method, a new siphon turbine was then designed based on the original distributor and turbine runner equipment. This study investigated the effect of different siphon outlet passage geometry parameters, runner blade shapes, and distributors on the hydraulic performance of the siphon turbine. The maximum hydraulic efficiency increased to 87.9% under a head of 2.87 m. Finally, the hydraulic performance of the turbine was compared for four different distributor designs after adding an intake sump at the turbine entrance. The bell-shaped distributor with four guide vanes resulted in the highest power output at the lowest head. Therefore, the siphon turbine is a good option for energy conversion in ultra-low water head settings.

Towards Circular Economy: Evaluation of Sewage Sludge Biogas Solutions

Today it is obvious that the existing linear model of the economy does not correlate with the principles of sustainable development. The circular economy model can replace the current linear economy whilst addressing the issues of environmental deterioration, social equity and long-term economic growth. In the context of effectively implementing circular economy objectives, particular importance should be attributed to wastewater treatment sludge management, due to the possibility of recovering valuable raw materials and using its energy potential. Anaerobic digestion is one of the methods of recovering energy from sewage sludge. The main goal of this study is to make a preliminary evaluation of possible sewage sludge biogas and biomethane solutions using a computation model called MCBioCH4 and compare its results with laboratory tests of sewage sludge fermentation from the northern wastewater treatment plant (WWTP) of Ekaterinburg (Russian Federation). Laboratory experiments were conducted to determine the volume and qualitative composition of biogas produced throughout anaerobic fermentation of raw materials coming from the WWTP. The specific productivity of samples ranged between 308.46 Nm3/tvs and 583.08 Nm3/tvs depending if mesophilic or thermophilic conditions were analyzed, or if the experiment was conducted with or without sludge pre-treatment. Output values from the laboratory were used as input for MCBioCH4 to calculate the flow of biogas or biomethane produced. For the case study of Ekaterinburg two possible energy conversion options were selected: B-H (biogas combustion with cogeneration of electrical and thermal energy) and M-T (biomethane to be used in transports). The results of the energy module showed a net energy content of the biogas between 6575 MWh/year and 7200 MWh/year. Both options yielded a favorable greenhouse gas (GHG) balance, meaning that avoided emissions are higher than produced emissions. The results discussion also showed that, in this case, the B-H option is preferable to the M-T option. The implementation of the biogas/biomethane energy conversion system in Ekaterinburg WWTP necessitates further investigations to clarify the remaining technical and economic aspects

Modeling of Bubbling Fluidized Bed Combustor Based on Biomass &Co-firing

As the rising demand of the fossil fuelsand their limited resources, the use of biomass fuels as energy resource in the thermal power plants is increasing popularly. The combustion of the biomass fuel with conventional combustion techniques is not suitable but the fluidized bed combustion (FBC) is one of the most promising energy conversion options available for the combustion of such low density fuel. The scope of this paper is to investigate the suitability of mathematical model of fluidized bed combustion based upon the bio-mass fuel &co-firing of bio-mass fuel with coal to predict and simulate the performance of 15 TPH plant situated at Ladhar paper mill, Nakodar and 75 TPH plant situated at Satia Paper Industry, ShriMuktsar Sahib, Punjab (India). The Ladhar paper mill runs at 100% bio-mass fuel &Satia paper industry plant runs on 85% husk with 15% coal to 100% husk. The model produces the relevant input/output parameter of bed such as fluidized velocity of air, combustion efficiency of boiler, the exit value of CO2 to the atmosphere etc. by the change in the supply of excess air to the boiler.

Potential sodium–CO2 interaction of a supercritical CO2 power conversion option coupled with an SFR: Basic nature and design issues

The supercritical CO2 Brayton cycle option for energy conversion in a sodium-cooled fast reactor (SFR) has recently received a great deal of attention due to highly reliable system design features that make it essentially free from risk of a sodium–water reaction in a traditional Rankine cycle power conversion. Although this novel approach will yield significant improvements in overall plant safety and energy utilization, it raises the risk of pressure boundary failure and consequent sodium–CO2 interaction. Since an understanding of the interaction mechanism is directly relevant to safety issues for the advanced SFR design, the kinetic behavior of sodium–CO2 interaction and its basic nature were investigated in this study. Experiments were performed for sodium temperatures ranging from 200 to 600°C. The results indicated that the reaction kinetics over the sodium temperature range of 300–550°C depends heavily on the temperature but is not sensitive to the velocity of CO2 flowing over the gas–liquid reacting interface explored in this study. The rate of the chemical reaction was determined by measuring the gas concentration of the CO/CO2 mixture, and a two-zone reaction model was proposed with a threshold temperature of 460°C. The kinetic parameters, i.e., the activation energies according to reaction zones, were obtained experimentally and the corresponding model parameters were identified. Finally, practical design and safety issues regarding a wastage scenario and the potential plugging of faulty heat exchanger channels were also addressed.

Carbon Mitigation and Economics for Energy Conversion When CO2 is Stored via Enhanced Oil Recovery

The carbon mitigation benefits and economics are described for alternative coal energy conversion options for which CO2 is captured and sold for enhanced oil recovery (EOR). Both the CO2 capture cost and internal rate of return on equity (IRRE) are considered as economic metrics. Post-combustion, oxycombustion, and pre-combustion capture options are considered for power generation, and pre-combustion capture options are also considered for making synthetic gasoline and for coproducing gasoline and electricity. In addition, coprocessing some biomass with coal is considered for plants coproducing gasoline and electricity.Findings for prospective crude oil prices are that: (i) the most profitable options using only coal are systems providing synthetic gasoline; (ii) systems coproducing electricity + gasoline are more profitable than any systems providing only electricity; (iii) options coprocessing some biomass will become the most profitable options at high GHG emission prices, and (iv) gasoline and coproduction plants, even sited remotely from CO2 EOR market opportunities, are likely to be competitive in EOR markets if an adequate CO2 pipeline infrastructure were in place; (v) coal/biomass systems coproducing gasoline + electricity are likely to be more profitable coal/biomass systems making gasoline for crude oil prices less than $75/barrel.

Effect of turbine section orientation on the performance characteristics of an oscillating water column device

Oscillating water column (OWC) devices are the most successful devices for extracting energy from ocean waves. In oscillating water column devices, the air turbine section is of either horizontal or vertical orientation. An experimental study is carried out to compare the airflow characteristics and turbine rpm in horizontal and vertical turbine sections of an oscillating water column device. Two OWC models, one with a horizontal duct connecting the turbine to the atmosphere and the other with a vertical duct, were tested at mean water depths of 230mm, 260mm and 290mm and at frequencies of 0.6Hz, 0.7Hz, 0.8Hz, 0.9Hz, 1.0Hz and 1.1Hz. Mean total pressure profiles were plotted just upstream and downstream of the turbine section for different cases, while instantaneous static and dynamic pressure measurements were performed to study their variations with time at these locations. A Savonius type rotor was used as a turbine and its rpm was measured and at the above depths and frequencies to compare the performance of the two OWC models. The OWC model with the horizontal turbine section showed better performance characteristics compared to the OWC with the vertical turbine section. RPM values were 20–30% greater in the horizontal turbine orientation compared to the vertical one. The successful use of a Savonius type rotor as a good and cost-effective option for energy conversion is emphasized in this work.

A dual representation for targeting process retrofit, application to a pulp and paper process

A method for the analysis of process energy requirements has been used to identify in an early design stage the potential process retrofit measures in an integrated pulp and paper mill. The minimum energy requirements (MER) of the process were computed by means of a dual representation that segregates the thermodynamic requirement of the process from its technological implementation. Energy and exergy recovery opportunities have been examined to improve the integration of the utility system to the process. An MILP optimisation targeting method has been applied to identify the best energy conversion options and to optimise the production of combined heat and power (CHP). Replacing the steam injections to mixing tanks by heat exchangers would decrease the MER by 10%, and increase the combined production of heat and power by a factor 1.7. Improving the exergy efficiency of the paper drying technology would be more difficult to implement, but the results indicate that this could bring an additional 12% gain of electricity cogenerated with no change to the MER.

PLASMA REACTORS AS AN ALTERNATIVE FOR THE CLASSIC TECHNOLOGIES - METHANE STEAM REFORMING WITH OXYGEN IN A MAGNETIC BLOW OUT GLIDARC REACTOR

One of the most viable near-term options for energy conversion involves the development of simple small-scale steam methane reformers to produce hydrogen at local fuel stations, or of the combined reformer-fuel cell systems for possible automotive applications. The present work deals with the study of methane steam reforming with oxygen in a new type of gliding arc reactor. The process is described in terms of methane conversion, reaction selectivity, and energy cost. The paper confirms previous conclusions on the reaction mechanism and reveals some specific aspects of the studied process.

Thermal Degradation of Rice Husks in an Oxygen Atmosphere

Of the various energy conversion options of rice husk, thermochemical conversion processes such as pyrolysis, combustion, and gasification offer the most efficient way to use rice husk. However, a knowledge of the thermal characteristics of rice husks is essential for the optimal design of these systems and for ensuring stringent emissions as well as high conversion efficiency. Thermogravimetric analysis is used to profile weight loss due to physical and chemical phenomena taking place in the sample while being subjected to high temperatures. This technique presents an ideal system to study thermal properties of carbonaceous materials. Evaluation of the thermogravimetric behavior of four rice husk varieties (Lemont, ROK 14, CP 4, and Pa Potho) at three heating rates (10, 20, and 50 C min) in an oxygen atmosphere is described. The thermal degradation rates, the initial degradation temperature, and the residual weight at 700 C were deter mined. These thermal degradation indices of rice husks are a function of tempera ture, heating rate, and the composition of the rice husks. The initial degradation temperature decreased while both the thermal degradation rate and the residual weight at 700 C increased when the heating rate was increased. The higher the cellulosic content of the rice husk, the higher the thermal degradation rate and the initial degradation temperature. Also, higher ash content in the rice husk resulted in higher residual weight at 700 C. Rice husk could be degraded to the extent of 73-80 %.