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Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2019;141(10):102001-102001-11. doi:10.1115/1.4043391.

This study presents a train of thought and method for flue gas energy utilization management by connecting an optimized supercritical carbon dioxide (S-CO2) Brayton cycle with a selected steam/water Rankine cycle to recover the turbine exhaust gas heat with promising flue gas coupling capacity. Better performance over the currently used steam/water bottoming cycle is expected to be obtained by the combined bottoming cycle after the S-CO2 cycle is coupled with the high-temperature flue gas. The performances of several S-CO2 cycles are compared, and the selected steam/water cycle is maintained with constant flue gas inlet temperature to properly utilize the low-temperature flue gas. Aspen Plus is used for simulating the cycle performances and the flue gas heat duty. Results show that the recompression S-CO2 cycle with the reheating process is most recommended to be used in the combined bottoming cycle within the research scope. The suggested combined bottoming cycle may outperform most of the triple reheat steam/water cycles for the turbine exhaust temperature in the range of 602–640 °C. Subsequently, it is found that the intercooling process is not suggested if another heat recovery cycle is connected. Moreover, the specific work of the suggested S-CO2 cycles is calculated, and the bottoming cycle with the preheating cycle with the reheating process is found to be more compact than any other combined bottoming cycles.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102002-102002-14. doi:10.1115/1.4043436.

Simulations of natural gas pipeline transients provide an insight into a pipeline capacity to deliver gas to consumers or to accumulate gas from source wells during various abnormal conditions and under variable consumption rates. This information is used for the control of gas pressure and for planning repairs in a timely manner. Therefore, a numerical model and a computer code have been developed for the simulation of natural gas transients in pipelines. The developed approach is validated by simulations of test cases from the open literature. Detailed analyses of both slow and fast gas flow transients are presented. Afterward, the code is applied to the simulation of transients in a long natural gas transmission pipeline. The simulated scenarios cover common operating conditions and abrupt disturbances. The simulations of the abnormal conditions show a significant accumulation capacity and inertia of the gas within the pipeline, which enables gas packing and consumers supply during the day time period. Since the numerical results are obtained under isothermal gas transient conditions, an analytical method for the evaluation of the difference between isothermal and nonisothermal predictions is derived. It is concluded that the nonisothermal transient effects can be neglected in engineering predictions of natural gas packing in long pipelines during several hours. The prescribed isothermal temperature should be a few degrees higher than the soil temperature due to the heat generation by friction on the pipelines wall and heat transfer from the gas to the surrounding soil.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2019;141(10):102201-102201-8. doi:10.1115/1.4043393.

Engine knock remains one of the major barriers to further improve the thermal efficiency of spark-ignition (SI) engines. SI engine is usually operated at knock-limited spark advance (KLSA) to achieve possibly maximum efficiency with given engine hardware and fuel properties. Co-optimization of fuels and engines is promising to improve engine efficiency, and predictive computational fluid dynamics (CFD) models can be used to facilitate this process. However, cyclic variability of SI engine demands that multicycle results are required to capture the extreme conditions. In addition, Mach Courant–Friedrichs–Lewy (CFL) number of 1 is desired to accurately predict the knock intensity (KI), resulting in unaffordable computational cost. In this study, a new approach to numerically predict KLSA using large Mach CFL of 50 with ten consecutive cycle simulation is proposed. This approach is validated against the experimental data for a boosted SI engine at multiple loads and spark timings with good agreements in terms of cylinder pressure, combustion phasing, and cyclic variation. Engine knock is predicted with early spark timing, indicated by significant pressure oscillation and end-gas heat release. Maximum amplitude of pressure oscillation analysis is performed to quantify the KI, and the slope change point in KI extrema is used to indicate the KLSA accurately. Using a smaller Mach CFL number of 5 also results in the same conclusions, thus demonstrating that this approach is insensitive to the Mach CFL number. The use of large Mach CFL number allows us to achieve fast turn-around time for multicycle engine CFD simulations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102202-102202-9. doi:10.1115/1.4043437.

The investigated combustor employs injection of liquid fuel (ethanol) into the strong cross-flow of air using a round tube to achieve effective fuel atomization in non-premixed mode of operation. The reverse-flow configuration (air injection from the exit end) allows effective internal product gas recirculation and stabilization of the reaction zone. This apparently suppresses near-stoichiometric reactions and hot spot regions resulting in low pollutant (NOx and CO) emissions in the non-premixed mode. The combustor was tested at thermal intensity variation from 19 to 39 MW/m3 atm with direct injection (DI) of liquid fuel in cross-flow of air injection with two fuel injection diameters of 0.5 mm (D1) and 0.8 mm (D2). The combustion process was found to be stable with NOx emissions of 8 ppm (for D1) and 9 ppm (for D2), the CO emissions were 90 ppm for D1 and 120 ppm for D2, at an equivalence ratio (ϕ) of 0.7. Macroscopic spray properties of the fuel jet in cross-flow were investigated using high-speed imaging techniques in unconfined and nonreacting conditions. It was found that the fuel jet in smaller fuel injection diameter (D1) case penetrated farther than that in D2 case due to higher fuel injection momentum, thus possibly resulting in a finer spray and better fuel-oxidizer mixing, and in turn leading to lower CO and NOx emissions in the D1 case as compared with the D2 case.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102203-102203-9. doi:10.1115/1.4043390.

Miscibility of methanol in mineral diesel and stability of methanol–diesel blends are the main obstacles faced in the utilization of methanol in compression ignition engines. In this experimental study, combustion, performance, emissions, and particulate characteristics of a single-cylinder engine fueled with MD10 (10% v/v methanol blended with 90% v/v mineral diesel) and MD15 (15% v/v methanol blended with 85% v/v mineral diesel) are compared with baseline mineral diesel using a fuel additive (1-dodecanol). The results indicated that methanol blending with mineral diesel resulted in superior combustion, performance, and emission characteristics compared with baseline mineral diesel. MD15 emitted lesser number of particulates and NOx emissions compared with MD10 and mineral diesel. This investigation demonstrated that methanol–diesel blends stabilized using suitable additives can resolve several issues of diesel engines, improve their thermal efficiency, and reduce NOx and particulate emissions simultaneously.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102204-102204-13. doi:10.1115/1.4043553.

This experimental study endeavors to investigate the evolution of microexplosion phenomenon of water in biodiesel emulsion droplets with the base fuel (B5) containing 95% diesel and 5% of palm oil methyl ester (POME). Parameters such as water content varied from 9%, 12%, and 15%, surfactant dosages of 5%, 10%, and 15% and the hydrophilic–lipophilic balance (HLB) values of 6, 7, 8, and 9 were varied to study its impact on microexplosion phenomenon. Three different sizes of emulsion droplets of approximately Ø2.8 mm, Ø2.2 mm, and Ø0.3 mm were visualized for the evolution of microexplosion phenomenon under the Leidenfrost effect using hot plate as a heat source. The evolution of microexplosion phenomenon of parent droplets, puffing behavior, and waiting time was visualized with high-resolution images. It was observed that the coalescence process was the dominating factor in inducing the microexplosion, and the coalescence process can either be advanced or be delayed by the surfactant dosage. The waiting time for the microexplosion was found to be influenced by the surfactant dosage and the droplet size. The rate of phase change of emulsions and puffing was found to be influenced by the surfactant dosage. By analyzing the postbehavior of the child droplets formed after the microexplosion of the parent droplet, it was observed that the child droplets undergo a series of puffing process and eventually microexplosion phenomenon also. The size of the parent droplets has a significant influence on the size of the child droplet.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102205-102205-8. doi:10.1115/1.4043634.

Low-energy and volumetric density of biomass has been a major challenge, hindering its large-scale utilization as a bioenergy resource. Torrefaction is a thermochemical pretreatment process that can significantly enhance the properties of biomass as a fuel by increasing the heating value and thermal stability of biomass materials. Densification of biomass by pelleting can greatly increase the volumetric density of biomass to improve its handling efficiency. Currently, torrefaction and pelleting are processed separately. So far, there has been little success in dovetailing torrefaction and pelleting, which only requires a single material loading to produce torrefied pellets. Synchronized ultrasonic torrefaction and pelleting has been developed to address this challenge. Synchronized ultrasonic torrefaction and pelleting can produce pellets of high energy and volumetric density in a single step, which tremendously reduces the time and energy consumption compared to that required by the prevailing multistep method. This novel fuel upgrading process can increase the biomass temperature to 473–573 K within tens of seconds to create torrefaction. Studying the temperature distribution is crucial to understand the fuel upgrading mechanism since pellet energy density, thermal stability, volumetric density, and durability are all highly related to temperature. A rheological model was established to instantiate biomass behaviors when undergoing various ultrasonic vibration conditions. Process parameters including ultrasonic amplitude, ultrasonic frequency, and pelleting time were studied to show their effects on temperature at different locations in a pellet. Results indicated that the volumetric heat generation rate was greatly affected by both ultrasonic amplitude and frequency. This model can help to understand the fuel upgrading mechanism in synchronized ultrasonic torrefaction and pelleting and also to give guidelines for process optimization to produce high-quality fuel pellets.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2019;141(10):102901-102901-9. doi:10.1115/1.4043338.

Annulus pressure buildup (APB) is still a serious problem in offshore gas wells, which threatens the safety of wells for the entire phases of drilling, completion, and production. The existing methods for mitigating APB are technically complex and highly costly. Setting top of cement (TOC) below the outer casing shoe to mitigate APB is easy to implement and can significantly reduce costs. However, there are no unified methods of determining TOC for this purpose. Nevertheless, existing petroleum standards give ambiguous regulations on the setting of TOC. This article brings a new and cheap method of mitigating APB by determining best TOC settings using a mathematical model for calculating APB from both annulus fluid expansion (AFE) and sustained casing pressure (SCP). Field data from gas well X are inputted to the model to describe how it serves this purpose. Calculation results for well X show that setting TOC's above and below the upper casing shoes for production and intermediate casings annuli, respectively, can greatly avoid the problem of APB and the costs associated with the existing mitigation methods. This technique can be used to other wells following the same procedures. The developed model reduced greatly the ambiguity of TOC determination as it helps to get the clear TOC combinations that control APB at the lowest cost of well construction while maintaining good and safe well operation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102902-102902-11. doi:10.1115/1.4043388.

A new drilling method called coiled-tubing partial underbalanced drilling (CT-PUBD) was proposed in this paper. The method is not only able to enhance rate of penetration (ROP) just like the conventional underbalanced drilling technology but can also maintain borehole stability in the upper formation. In the new method, the wellbore pressure system is divided into two parts by a packer: (1) normal pressure system in the upper formation used to balance formation pressure and maintain borehole stability and (2) an underbalanced pressure system in the annulus near the bit used to enhance ROP. Because the pressure system and the circulation system are different, the cuttings transportation process of the method is different from the conventional way. Therefore, it is essential to study how to carry cuttings away efficiently. The flow field and cuttings distribution in the annulus near the bit were analyzed by computational fluid dynamic (CFD) methods. Cuttings transportation trajectory, velocity distribution, and cuttings concentration distribution were obtained under different holes’ parameters of the backflow device (including holes number, diameter, distance, and angle) and different drilling fluid viscosities. The results show that these parameters all have influence on cuttings carrying efficiency, and the most influential parameters are viscosity, angle, and diameter. According to the result of an orthogonal test, a suitable combination of the holes’ parameters was obtained. In the combination, the value of holes number, diameter, distance, and angle is 4, 50 mm, 300 mm, and 120 deg, respectively. This paper provides a theoretical basis for an optimization design of the new method.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102903-102903-6. doi:10.1115/1.4043392.

An integrated technique has been developed to experimentally and numerically evaluate water control and production increase in a tight gas formation with polymer. Experimentally, polymer has been appropriately selected and formulated to form a preferentially blocking membrane on the surface of pore and throat in core plugs collected from a tight gas reservoir. The unsteady-state experiments at high temperatures and confining pressures are then conducted to not only measure gas and water relative permeability but also to evaluate the performance of water control and gas production with and without such formulated polymers. The inlet and outlet pressure of the coreholder and flow rates of water and gas are measured throughout the displacement experiments. Theoretically, numerical simulations have been performed to history match the coreflooding experiments and then extended to evaluate well performance in gas fields with and without polymer treatment. Due to the good agreement between the simulated relative permeability and the measured values, the formulated polymer is found to simultaneously control water and increase gas production. Also, it is found from simulation that, after 10 years of production, gas wells after polymer injection show a higher recovery of 10.8% with a lower water-to-gas ratio and a higher formation pressure.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102904-102904-8. doi:10.1115/1.4043435.

The influence of shale anisotropy and orientation on shale drilling performance was studied with an instrumented laboratory drilling rig with a 38.1-mm dual-cutter polycrystalline diamond compact (PDC) bit, operating at a nominally fixed rotational speed with a constant rate of flow of drilling fluid—water. However, the rate of rotation (rpm) was affected by the weight on bit (WOB), as was the torque (TRQ) produced. The WOB also affected the depth of cut (DOC). All these variables, WOB, rpm, TRQ, and DOC, were monitored dynamically, for example, rpm with a resolution of one-third of a revolution (samples at time intervals of 0.07 s.) The shale studied was from Newfoundland and was compared with similar tests on granite, also from a local site. Similar tests were also conducted on the concrete made with fine aggregate, used as “rock-like material” (RLM). The shale samples were embedded (laterally confined) in the concrete while drilled in directions perpendicular, parallel, and at 45 deg orientations to bedding planes. Cores were produced from all three materials in several directions for the determination of oriented physical properties derived from ultrasonic testing and oriented unconfined compressive strength (OUCS). In the case of shale, directions were set relative to the bedding. In this study, both primary (or compression) velocity Vp and shear ultrasonic velocity Vs were found to vary with orientation on the local shale samples cored parallel to bedding planes, while Vp and Vs varied, but only slightly, with orientation in tests on granite and RLM. The OUCS data for shale, published elsewhere, support the OUCS theory of this work. The OUCS is high perpendicular and parallel to shale bedding, and is low oblique to shale bedding. Correlations were found between the test parameters determined from the drilling tests on local shale. As expected, ROP, DOC, and TRQ increase with increasing WOB, while there are inverse relationships between ROP, DOC, and TRQ with rpm on the other hand. All these parameters vary with orientation to the bedding plane.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102905-102905-6. doi:10.1115/1.4043612.

The well clean-up process involves the removal of impermeable filter cake from the formation face. This process is essential to allow the formation fluids to flow from the reservoir to the wellbore. Different types of drilling fluids such as oil- and water-based drilling fluids are used to drill oil and gas wells. These drilling fluids are weighted with different weighting materials such as bentonite, calcium carbonate, and barite. The filter cake that forms on the formation face consists mainly of the drilling fluid weighting materials (around 90%), and the rest is other additives such as polymers or oil in the case of oil-base drilling fluids. The process of filter cake removal is very complicated because it involves more than one stage due to the compatibility issues of the fluids used to remove the filter cake. Different formulations were used to remove different types of filter cake, but the problem with these methods is the removal efficiency or the compatibility. In this paper, a new method was developed to remove different types of filter cakes and to clean-up oil and gas wells after drilling operations. Thermochemical fluids that consist of two inert salts when mixed together will generate very high pressure and high temperature in addition to hot water and hot nitrogen. These fluids are sodium nitrate and ammonium chloride. The filter cake was formed using barite and calcite water- and oil-based drilling fluids at high pressure and high temperature. The removal process started by injecting 500 ml of the two salts and left for different time periods from 6 to 24 h. The results of this study showed that the newly developed method of thermochemical removed the filter cake after 6 h with a removal efficiency of 89 wt% for the barite filter cake in the water-based drilling fluid. The mechanisms of removal using the combined solution of thermochemical fluid and ethylenediamine tetra-acetic acid (EDTA) chelating agent were explained by the generation of a strong pressure pulse that disturbed the filter cake and the generation of the high temperature that enhanced the barite dissolution and polymer degradation. This solution for filter cake removal works for reservoir temperatures greater than 100 °C.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(10):102906-102906-10. doi:10.1115/1.4043635.

T-junctions have been applied in water-control structures. A comprehensive understanding of shunt characteristics can contribute to the optimal design of T-junctions. In this work, we seek to understand the shunt ratio of fluids with different viscosities in a T-junction and to achieve a greater shunt ratio. The computational fluid dynamics (CFD) approach is applied to study the influence of the properties, such as the fluid viscosity, the branch angle, the channel shape, and the flow rate, on the shunt ratio in a T-junction. The viscosity of oil can be divided into three intervals, and the optimal angles of the T-junction are different in each interval. For the fluid viscosity in the 1–20 cP range, the optimal branch angle is in the 45–60 deg range. For the fluid viscosity in the 20–65 cP range, the branch angle should be designed to be 45 deg. For the viscosity greater than 65 cP, the branch angle should be designed to be 75 deg. The appearance of the eddy and secondary flow will reduce the flow. The secondary flow and eddy intensity on the branch increase with increasing angle. The secondary flow intensity of the main channel decreases gradually with the increase in the angle. This study provides an important guidance for the design of automatic water control valve tools.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Energy Resour. Technol. 2019;141(10):104501-104501-10. doi:10.1115/1.4043389.

In this paper, energy- and exergy-based analysis is used to analyze a factory with high energy demand for the production of aluminum discs. The analysis is focused on heat processes that take place in a melting furnace, a casting machine, a heat treatment oven, and a drying oven. Energy and exergy efficiencies are computed to assess the room for the improvement of the energy efficiency processes. The analysis shows that a large amount of energy is lost due to heat losses to the environment, and solutions for reducing energy demand and emissions have been identified. Instead of changing the equipment of a factory, significant improvements and consequent reduction of fossil fuels consumption can be obtained by increasing the thermal insulation of some components and by means of waste heat recovery performed by heat exchangers, with a consequent energy demand reduction of 15%.

Commentary by Dr. Valentin Fuster

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