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Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2018;140(7):071201-071201-9. doi:10.1115/1.4039023.

This study deals with thermodynamic analyses of an integrated wind thermal energy storage (WTES) system. The thermodynamic analyses of the proposed system are performed through energy and exergy approaches, and the energy and exergy efficiencies of the components in the system and overall system are determined and assessed. The magnitudes of irreversibilities are determined, and the impacts of different parameters on the performance of the system are identified. The overall energy and exergy efficiencies of the proposed system and its subsystems are computed as well. The energy and exergy efficiencies of the overall system are defined and obtained as 7.0% and 8.6%, respectively. WTES plants with combined molten salt energy storage application can run continuously, and can provide electrical power for both on-grid and off-grid systems. By converting the wind power into a permanent energy source, the WTES offers a practical solution that can meet the electrical demand of the regions where the climate conditions are feasible for consistent, environmentally benign and cost-effective electric power, and it can be considered as a potential energy solution.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):071202-071202-9. doi:10.1115/1.4039349.

Icing on wind turbines is a major problem in cold regions. To study blade icing, water droplet collection efficiency is calculated on the National Renewable Energy Laboratory (NREL) phase VI blade. First, water droplet conservation equations are embedded into ANSYS Fluent, and the results calculated by the Eulerian method are validated. For the two-dimensional (2D) airfoil, the peak collection efficiency error is 3.7%; for the three-dimensional (3D) blade, the peak collection efficiency error is 2.8%. Second, collection efficiency on the NREL phase VI blade is investigated. The results indicate that water droplets mainly impact on the blade leading edge, and the collection efficiency increases along the radial direction. Finally, the 3D rotating effect on collection efficiency is studied. The results demonstrate that, at a wind speed of 7 m/s, the 3D rotating effect has almost no influence on collection efficiency; however, the effect must be considered in water droplet collection at a wind speed of 10 m/s.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Conversion/Systems

J. Energy Resour. Technol. 2018;140(7):071601-071601-8. doi:10.1115/1.4039446.

For the application of waste heat recovery (WHR), supercritical CO2 (S-CO2) Brayton power cycles offer significant suitable advantages such as compactness, low capital cost, and applicability to a broad range of heat source temperatures. The current study is focused on thermodynamic modeling and optimization of recuperated (RC) and recuperated recompression (RRC) configurations of S-CO2 Brayton cycles for exhaust heat recovery from a next generation heavy duty simple cycle gas turbine using genetic algorithm (GA). This nongradient based algorithm yields a simultaneous optimization of key S-CO2 Brayton cycle decision variables such as turbine inlet temperature, pinch point temperature difference, compressor pressure ratio, and mass flow rate of CO2. The main goal of the optimization is to maximize power out of the exhaust stream which makes it single objective optimization. The optimization is based on thermodynamic analysis with suitable practical assumptions which can be varied according to the need of user. The optimal cycle design points are presented for both RC and RRC configurations and comparison of net power output is established for WHR. For the chosen exhaust gas mass flow rate, RRC cycle yields more power output than RC cycle. The main conclusion drawn from the current study is that the choice of best cycle for WHR actually depends heavily on mass flow rate of the exhaust gas. Further, the economic analysis of the more power producing RRC cycle is performed and cost comparison between the optimized RRC cycle and steam Rankine bottoming cycle is presented.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2018;140(7):072001-072001-6. doi:10.1115/1.4038964.

Mixing of fresh (river) water and salty water (seawater or saline brine) in a controlled environment produces an electrical energy known as salinity gradient energy (SGE). Two main conversion technologies of SGE are membrane-based processes: pressure retarded osmosis (PRO) and reverse electrodialysis (RED). Exergy calculations for a representative river-lake system are investigated using available data in the literature between 2000 and 2008 as a case study. An exergy analysis of an SGE system of sea-river is applied to calculate the maximum potential power for electricity generation. Seawater is taken as reference environment (global dead state) for calculating the exergy of fresh water since the sea is the final reservoir. Aqueous sodium chloride solution model is used to calculate the thermodynamic properties of seawater. This model does not consider seawater as an ideal solution and provides accurate thermodynamics properties of sodium chloride solution. The chemical exergy analysis considers sodium chloride (NaCl) as main salt in the water of this highly saline Lake with concentration of more than 200 g/L. The potential power of this system is between 150 and 329 MW depending on discharge of river and salinity gradient between the Lake and the River based on the exergy results. This result indicates a high potential for constructing power plant for SGE conversion. Semipermeable membranes with lifetime greater than 10 years and power density higher than 5 W/m2 would lead to faster development of this conversion technology.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072002-072002-9. doi:10.1115/1.4039267.

In the field of combustion, a special attention was given lately especially to the search for new, greener and more efficient fuels. Among them, hydrogen is intensely studied worldwide as a possible alternative fuel since new ways for producing and transporting it developed lately. Different studies are trying to confirm the possibility of the hydrogen transport using the existing natural gas distribution network, by mixing the two gases. Because the properties of the new mixture influence the combustion parameters, using the existing equipment would face new problems, like the risk of flashback, the effects of higher temperatures, and the modification of the flame front. Hence, new solutions are needed. In this context, this paper presents a newly developed and patented type of injector, designated for the combustion of the premixed hydrogen–methane fuel in various proportions. Based on the characteristics and dimensions of an existing combustion chamber of a gas turbine, different types of injectors were numerically simulated and compared. After the analysis of the results, the preliminary conclusions lead to a first swirl injector made from titanium alloy. The new type of swirled injector was tested on a cheap, simplified low pressure rig, designed to have similar dimensions to the initial combustion chamber, for preliminary validation of the main characteristics and of the stability of the new injector. The experiments indicated good lean blowout characteristics, and the promising results are encouraging for more future tests on a complex experimental setup, for optimizing the final solution.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072003-072003-9. doi:10.1115/1.4039096.

The paper presents a novel concept and method of coal combustion process analysis using flame scanners supervision system. The combustion process analysis and diagnostic has a crucial influence on boiler effectiveness, especially in high variance of load demand, which is nowadays a top challenge for coal-fired power plants. The first indicator of combustion inefficiency is flame stability, which can be observed as variation of flame intensity. Nowadays, there are no validated measuring methods dedicated for industrial usage, which are able to give complete information about flame condition. For this reason, the research activity was launched and focused on usage of commercial flame scanners for fast combustion analysis based on on-line flame parameters measuring. The analysis of combustion process was performed for 650 t/h live steam power boiler, which is supplied by five coal mill units. Each coal mill supplies four pulverized coal burners pulverized fuel ((PF) burners). The boiler start-up installation consists of 12 heavy oil burners placed in PF burners equipped with individual supervisory system based on Paragon 105f-1 flame scanners, which gave the possibility to observe and analyze the PF burner flame and oil burner flame individually. The research included numerous tests in which the combustion conditions inside the combustion chamber were changed. During stable load of selected mills, the primary air flow, secondary air dampers, air–coal mixture temperature, and balance were changed. The results of the changes were observed by flame scanners and the available optical parameters of the flame were analyzed: power spectral density, average amplitude (AA) of flame fluctuation, and flame temperature.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072004-072004-15. doi:10.1115/1.4039266.

The scaling concept is important, effective, and consistent in any application of science and engineering. Scaled physical models have inimitable advantages of finding all physical phenomena occurring in a specific process by transforming parameters into dimensionless numbers. This concept is applicable to thermal enhanced oil recovery (EOR) processes where continuous alteration (i.e., memory) of reservoir properties can be characterized by various dimensionless numbers. Memory is defined as the continuous time function or history dependency which leads to the nonlinearity and multiple solutions during modeling of the process. This study critically analyzed sets of dimensionless numbers proposed by Hossain and Abu-Khamsin in addition to Nusselt and Prandtl numbers. The numbers are also derived using inspectional and dimensional analysis (DA), while memory concept is used to develop some groups. In addition, this article presents relationships between different dimensionless numbers. Results show that proposed numbers are measures of thermal diffusivity and hydraulic diffusivity of a fluid in a porous media. This research confirms that the influence of total absolute thermal conductivities of the fluid and rock on the effective thermal conductivity of the fluid-saturated porous medium diminishes after a certain local Nusselt number of the system. Finally, the result confirms that the convective ability of the fluid-saturated porous medium is apparently more pronounced than its conductive ability. This study will help to better understand the modeling of the EOR process thus improving process design and performance prediction.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072005-072005-13. doi:10.1115/1.4039376.

The Goswami cycle is a cycle that combines an ammonia–water vapor absorption cycle and a Rankine cycle for cooling and mechanical power purposes by using thermal heat sources such as solar energy or geothermal steam. In this paper, a theoretical investigation was conducted to determine the performance outputs of the cycle, namely, net mechanical power, cooling, effective first law efficiency and exergy efficiency, for a boiler and an absorber temperature of 85 °C and 35 °C, respectively, and different boiler pressures and ammonia-water concentrations. In addition, an experimental investigation was carried out to verify the predicted trends of theoretical analysis and evaluate the performance of a modified scroll expander. The theoretical analysis showed that maximum effective first law and exergy efficiencies were 7.2% and 45%, respectively. The experimental tests showed that the scroll expander reached a 30–40% of efficiency when boiler temperature was 85 °C and rectifier temperature was 55 °C. Finally, it was obtained that superheated inlet conditions improved the efficiency of the modified expander.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072006-072006-8. doi:10.1115/1.4039323.

Hydrogen production via carbonaceous catalytic methane decomposition is a complex process with simultaneous reaction, catalyst deactivation, and carbon agglomeration. Conventional reaction and deactivation models do not predict the progress of reaction accurately. Thus, statistical modeling using the method of design of experiments (DoEs) was used to design, model, and analyze experiments of methane decomposition to determine the important factors that affect the rates of reaction and deactivation. A variety of statistical models were tested in order to identify the best one agreeing with the experimental data by analysis of variance (ANOVA). Statistical regression models for initial reaction rate, catalyst activity, deactivation rate, and carbon weight gain were developed. The results showed that a quadratic model predicted the experimental findings. The main factors affecting the dynamics of the methane decomposition reaction and the catalyst deactivation rates for this process are partial pressure of methane, reaction temperature, catalytic activity, and residence time.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2018;140(7):072201-072201-7. doi:10.1115/1.4039268.

In this paper, the effects of hydrothermal modification on sulfur-containing pollutants, such as sulfur dioxide (SO2) and carbonyl sulfide (COS), during coal pyrolysis and combustion, have been investigated. Three typical Chinese low-quality coals, Zhundong, Yimin, and Zhaotong coal (ZT), have been treated by hydrothermal modification at final modification temperatures of 200 °C, 250 °C, and 300 °C. Coal pyrolysis and combustion experiments using raw coal and modified coals were performed using a tube furnace. Results showed that SO2 and COS emission were suppressed after hydrothermal modification in the pyrolysis process. Lower emission of both SO2 and COS were also achieved when final hydrothermal modification was increased, this was attributed to the loss of aliphatic sulfur, e.g., sulfoxide, sulfone, and thiother, during the modification process. For ZT, hydrothermal modification also caused a delay in the release of sulfur-containing gases. In combustion experiments, hydrothermal modification reduced the SO2 emission for Yimin coal, but for ZT, the SO2 release amount almost doubled, and for Zhundong coal (ZD), it also increased, after hydrothermal modification. Hydrothermal modification also caused a delay in peak SO2 emission during the combustion of ZT; this is attributed to conversion of sulfur containing structures to stable aromatic compounds through hydrothermal modification.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072202-072202-7. doi:10.1115/1.4039322.

In spark ignition engines, gasoline direct injection (GDI) is surely the most attractive technology to achieve the demand of high energy efficiency by directly injecting fuel into combustion chamber. This work, as a preliminary study, investigates the effect of retarded injection timing on knock resistance and cycle-to-cycle variation in gasoline engine by experimental method. The retarded injection timing during compression stroke coupled with increased intake air temperature was employed to concentrate on suppressing knock occurrence with stable combustion. Based on the great advantage of injection timing retard on knock suppression, intake temperature was used in this work to reduce cycle-to-cycle variation. In addition, piezo-electrically actuated injector was employed. The results show that injection timing retard during compression stroke can significantly suppress the knock tendency, but combustion becomes unstable and cycle-to-cycle variation is larger than 10%. Thus, increasing intake temperature decreased the cycle-to-cycle variation but increased significantly the knock tendency, as expect. Meanwhile, rich fuel–air mixture in this work also had the same effect as intake temperature did. It can be concluded that retarded injection timing is of significant potential to suppress the knock in GDI engine, although the high intake temperature causes high probability of large knock occurrence. The percentages of knock at the spark timings of 24 °CA before top dead center (BTDC) and 26 °CA BTDC were significantly reduced from approximately 40% to 7% and from approximately 60% to 10%, respectively. Furthermore, the retarded injection timing not only reduced the probability of knock occurrence, but also decreased the knock intensity obviously.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072203-072203-10. doi:10.1115/1.4039445.

Two waste biomass materials, pine needle (PN) and corn stalk (CS), were pyrolyzed at different temperatures (200–900 °C). The organic functional groups and carbonaceous structure of the biomass chars were characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, respectively. The combustion characteristics and kinetics of biomass chars were investigated by thermogravimetric analysis (TGA). The content of carbon-, hydrogen-, and oxygen-containing functional groups in the biomass samples decreases with an increase in preparation temperature, leading to more aromatic macromolecular structure at elevated pyrolysis temperatures. With increasing pyrolysis temperature, the comprehensive combustibility index (S) of both chars related to combustion reactivity generally decreases especially for CS char because of the loss of active groups. However, the Raman spectra show that the degree of order decreases with increasing pyrolysis temperature from 400 to 700 °C because of the generation of isolated sp2 carbon.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2018;140(7):072901-072901-8. doi:10.1115/1.4039269.

In order to assess the critical sand deposition condition, a unique 4-in ID test facility was designed and constructed, which enables the pipe to be inclined 1.5 deg upward. Experiments were conducted with air–water-glass beads at low sand concentrations (< 10,000 ppm), and the air and water flow rates were selected to ensure stratified flow regime along the pipe. At constant superficial liquid velocity, the gas velocity was reduced to find the critical sand deposition velocity. Six sand flow regimes are identified, namely, fully dispersed solid flow, dilute solids at the wall, concentrated solids at the wall, moving dunes, stationary dunes, and stationary bed. The experimental results reveal that sand flow regimes under air–water stratified flow are strong functions of phase velocities, particle size, and particle concentration. Also, the results show that air–water flow regime plays an important role in particle transport; slug flow has high capability to transport particles at the pipe bottom, while the stratified flow has high risk of sand deposition. As long as the sand dunes are observed at the pipe bottom, the critical sand deposition velocities slightly increase with concentrations, while for stationary bed, the critical velocity increases exponentially with concentration.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072902-072902-6. doi:10.1115/1.4039319.

The application of water flooding is not successful for the development of low permeability reservoirs due to the fine pore sizes and the difficulty of water injection operation. CO2 can dissolve readily in crude oil and highly improve the mobility of crude oil, which makes CO2 flooding an effective way to the development of the ultralow-permeability reservoirs. The regularities of various CO2 displacement methods were studied via experiments implemented on cores from Chang 8 Formation of Honghe Oilfield. The results show that CO2 miscible displacement has the minimum displacement differential pressure and the maximum oil recovery; CO2-alternating-water miscible flooding has lower oil recovery, higher drive pressure, and relatively lower gas-oil ratio; water flooding has the minimum oil recovery and the maximum driving pressure. A large amount of oil still can be produced under a high gas-oil ratio condition through CO2 displacement method. This fact proves that the increase of gas-oil ratio is caused by the production of dissolved CO2 in oil rather than the free gas breakthrough. At the initial stage of CO2 injection, CO2 does not improve the oil recovery immediately. As the injection continues, the oil recovery can be improved rapidly. This phenomenon suggests that when CO2 displacement is performed at high water cut period, the water cut does not decrease immediately and will remain high for a period of time, then a rapid decline of water cut and increase of oil production can be observed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072903-072903-8. doi:10.1115/1.4039270.

Permeability is a key parameter related to any hydrocarbon reservoir characterization. Moreover, many petroleum engineering problems cannot be precisely answered without having accurate permeability value. Core analysis and well test techniques are the conventional methods to determine permeability. These methods are time-consuming and very expensive. Therefore, many researches have been introduced to identify the relationship between core permeability and well log data using artificial neural network (ANN). The objective of this research is to develop a new empirical correlation that can be used to determine the reservoir permeability of oil wells from well log data, namely, deep resistivity (RT), bulk density (RHOB), microspherical focused resistivity (RSFL), neutron porosity (NPHI), and gamma ray (GR). A self-adaptive differential evolution integrated with artificial neural network (SaDE-ANN) approach and evolutionary algorithm-based symbolic regression (EASR) techniques were used to develop the correlations based on 743 actual core permeability measurements and well log data. The obtained results showed that the developed correlations using SaDE-ANN models can be used to predict the reservoir permeability from well log data with a high accuracy (the mean square error (MSE) was 0.0638 and the correlation coefficient (CC) was 0.98). SaDE-ANN approach is more accurate than the EASR. The introduced technique and empirical correlations will assist the petroleum engineers to calculate the reservoir permeability as a function of the well log data. This is the first time to implement and apply SaDE-ANN approaches to estimate reservoir permeability from well log data (RSFL, RT, NPHI, RHOB, and GR). Therefore, it is a step forward to eliminate the required lab measurements for core permeability and discover the capabilities of optimization and artificial intelligence models as well as their application in permeability determination. Outcomes of this study could help petroleum engineers to have better understanding of reservoir performance when lab data are not available.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(7):072904-072904-7. doi:10.1115/1.4039316.

Well cements are an important aspect of wellbore integrity and recent investigations focus on describing the cement lifetime using, when possible, nondestructive tests like ultrasonic measurements. However, the original API and ASTM testing standards were based on destructive mechanical testing of cements, leading to the decision to investigate the backward and forward compatibility between ultrasonic measurements and mechanical testing, which makes the subject of this work. Ultrasonic cement measurement became a very popular method to assess the mechanical properties of the cement in a nondestructive manner. Since various measurement systems exist on the market, the development of an accurate reference data base that can be used to calibrate such measurements becomes very important. Two major systems have therefore been compared: the ultrasonic compressive strength, using the ultrasonic pulse velocity (UPV) principle, and the unconfined compressive strength (UCS), using the standard testing frame according to API and ASTM standards. The tests have been performed at different curing times, using both devices, on API Class G cements with bentonite and other additives. This paper presents the results of over 200 experiments that have displayed a different UPV response as a function of the additive content. Cement specific UPV versus UCS correlations were established. Thereby, a new level of accuracy was reached. Moreover, it was observed that after a given curing time, depending on the additive and its concentration, the UPV response is not as sensitive as the results yielded by the UCS method. The outcomes are an important step forward to improve and understand the wellbore integrity.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Transport/Pipelines/Multiphase Flow

J. Energy Resour. Technol. 2018;140(7):073001-073001-9. doi:10.1115/1.4039019.

The relieving system using the choke valve is applied to control the pressure in CO2 pipeline. However, the temperature of fluid would drop rapidly because of Joule–Thomson cooling (JTC), which may cause solid CO2 form and block the pipe. A three-dimensional (3D) computational fluid dynamic (CFD) model considering the phase transition and turbulence was developed to predict the fluid-particle flow and deposition characteristics. The Lagrangian method, Reynold's stress transport model (RSM) for turbulence, and stochastic tracking model (STM) were used. The results show that the model predictions were in good agreement with the experimental data published. The effects of particle size, flow velocity, and pipeline diameter were analyzed. It was found that the increase of the flow velocity would cause the decrease of particle deposition ratio and there existed the critical particle size that causes the deposition ratio maximum. It also presents the four types of particle motions corresponding to the four deposition regions. Moreover, the sudden expansion region is the easiest to be blocked by the particles. In addition, the Stokes number had an effect on the deposition ratio and it was recommended for Stokes number to avoid 3–8 St.

Commentary by Dr. Valentin Fuster

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