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Review Article

J. Energy Resour. Technol. 2018;141(2):020801-020801-5. doi:10.1115/1.4041288.

The rate-controlled constrained-equilibrium (RCCE), a model order reduction method, assumes that the nonequilibrium states of a system can be described by a sequence of constrained-equilibrium kinetically controlled by relatively a small number of constraints within acceptable accuracies. The full chemical composition at each constrained-equilibrium state is obtained by maximizing (or minimizing) the appropriate thermodynamic quantities, e.g., entropy (or Gibbs functions) subject to the instantaneous values of the constraints. Regardless of the nature of the kinetic constraints, RCCE always guarantees correct final equilibrium state. Ignition delay times measured in shock tube experiments with low initial temperatures are significantly shorter than the values obtained by constant volume models. Low initial temperatures and thus longer shock tube test times cause nonideal heat transfer and fluid flow effects such as boundary layer growth and shock wave attenuation to gradually increase the pressure (and simultaneously increase the temperature) before ignition. To account for these effects, in this paper, the RCCE prescribed enthalpy and pressure (prescribed h/p) model has been further developed and has been applied to methane shock tube ignition delay time simulation using GRI-Mech 3.0. Excellent agreement between RCCE predictions and shock tube experimental data was achieved.

Commentary by Dr. Valentin Fuster

Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2018;141(2):021201-021201-13. doi:10.1115/1.4041409.

This paper presents the results of a thermo-economic analysis of integrating solar tower (ST) with heat and power cogeneration plants that is progressively being installed to produce heat and electricity to operate absorption refrigeration systems or steam for industrial processes. The annual performance of an integrated solar-tower gas-turbine-cogeneration power plant (ISTGCPP) with different sizes of gas turbine and solar collector's area have been examined and presented. Thermoflex + PEACE software's were used to thermodynamically and economically assess different integration configurations of the ISTGCPP. The optimal integrated solar field size has been identified and the pertinent reduction in CO2 emissions due to integrating the ST system is estimated. For the considered cogeneration plant (that is required to produce 81.44 kg/s of steam at 394 °C and 45.88 bars), the study revealed that (ISTGCPP) with gas turbine of electric power generation capacity less than 50 MWe capacities have more economic feasibility for integrating solar energy. The levelized electricity cost (LEC) for the (ISTGCPP) varied between $0.067 and $0.069/kWh for gas turbine of electric power generation capacity less than 50 MWe. Moreover, the study demonstrated that (ISTGCPP) has more economic feasibility than a stand-alone ST power plant; the LEC for ISTGCPP is reduced by 50–60% relative to the stand-alone ST power plant. Moreover, a conceptual procedure to identify the optimal configuration of the ISTGCPP has been developed and presented in this paper.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Storage/Systems

J. Energy Resour. Technol. 2018;141(2):021901-021901-11. doi:10.1115/1.4041381.

Power-to-gas to energy systems are of increasing interest for low carbon fuels production and as a low-cost grid-balancing solution for renewables penetration. However, such gas generation systems are typically focused on hydrogen production, which has compatibility issues with the existing natural gas pipeline infrastructures. This study presents a power-to-synthetic natural gas (SNG) plant design and a techno-economic analysis of its performance for producing SNG by reacting renewably generated hydrogen from low-temperature electrolysis with captured carbon dioxide. The study presents a “bulk” methanation process that is unique due to the high concentration of carbon oxides and hydrogen. Carbon dioxide, as the only carbon feedstock, has much different reaction characteristics than carbon monoxide. Thermodynamic and kinetic considerations of the methanation reaction are explored to design a system of multistaged reactors for the conversion of hydrogen and carbon dioxide to SNG. Heat recuperation from the methanation reaction is accomplished using organic Rankine cycle (ORC) units to generate electricity. The product SNG has a Wobbe index of 47.5 MJ/m3 and the overall plant efficiency (H2/CO2 to SNG) is shown to be 78.1% LHV (83.2% HHV). The nominal production cost for SNG is estimated at 132 $/MWh (38.8 $/MMBTU) with 3 $/kg hydrogen and a 65% capacity factor. At U.S. DOE target hydrogen production costs (2.2 $/kg), SNG cost is estimated to be as low as 97.6 $/MWh (28.6 $/MMBtu or 1.46 $/kgSNG).

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2018;141(2):022001-022001-11. doi:10.1115/1.4041286.

Control quality of an once-through boiler’s water-fuel ratio (WFR) and main-steam temperature are heavily influenced by the control quality of the once-through boiler’s intermediate point enthalpy (IPE), and it is also related to the economic and stable operation of the a once-through boiler. In order to control the IPE in a better way and to increase boiler efficiency, an improved model of IPE control system was built in this paper, matlab/simulink is used to build the IPE control system model based on a 600 MW supercritical unit, and the mechanism model of the control object is built in the same time. The feedforward of the feed-water temperature is brought to this model to increase the control rate. The control method of amendments to the amount of coal and the control method of amendments to the amount of feed-water are combined by the means of fuzzy control to solve the problem of the contradiction of the responding speed of the IPE and the separation interface’s stability of the steam-water separator. The simulation results show that the improved control method has better control effect and higher boiler efficiency was obtained as well.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022002-022002-11. doi:10.1115/1.4041287.

Energy hubs is an integrated system which is capable of transporting, transforming, and storing several types of energy. A number of hubs can be combined as a network and achieve higher efficiency by exchanging information and energy with each other. A decision-making framework for optimal integration of independent small-scale distributed energy systems and traditional large scale combined heating and power (CHP) plants is presented, and an energy supply system with renewable energy resources in Shanghai is cited as a case study. A performance simulation model of this energy network is proposed based on energy hub concept and energy flow between its elements. Furthermore, a novel optimization method named Whales optimization algorithm (WOA) is presented for 24 h operational optimization. A case study is undertaken on a seven-node energy system, including four energy hubs and three load hubs. The results of the case study show that the proposed model and optimization method can improve energy utilization efficiency and reduce system operating costs, even under a system contingency condition.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022003-022003-11. doi:10.1115/1.4041408.

Based on previous experiment result, an assumption is made to explain the abnormal head degradation in the first stage of an electrical submersible pump (ESP): the bubbles' breaking up and coalescence effect with compressibility is the main reason of this phenomenon. To investigate the head degradation problem inside the ESP, a series of numerical simulations are performed on the first stage of the split-vane impeller pump commonly employed for gas handling purpose. These three-dimensional transient Eulerian multiphase simulations are divided into two groups: one group with the traditional fixed bubble size method and the other with the ANSYS population balancing model (PBM) allowing the bubbles to break up and coalesce. The simulation result with the changing bubble size matches well with the experiment data, which supports the previous assumption. The flow field based on PBM simulation is visualized and analyzed. Also the separation of phases is discovered with large volume of gas accumulating at the suction side of the impeller trailing blades, which is also supported by experimental observation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022004-022004-8. doi:10.1115/1.4041722.

Wave rotor with pressure exchange function can be attempted to improve refrigeration performance. The objective of this paper is to verify the feasibility of the method by thermodynamic and experimental analysis. First, a refrigeration process which contains wave rotor pressurization was established. Then, a thermodynamic model which reflects the refrigeration process was designed. The thermal performance was researched under various key parameters. Finally, based on the novel wave rotor refrigeration platform, the experimental work was carried out, and the effects of main parameters of the device were systematically studied. The results showed that it was feasible to enhance the coefficient of performance (COP) by using pressure exchange characteristic of wave rotor. The COP could be improved substantially at relatively small expansion ratio. Under the design point, more than half of the pressure energy could be restored. The performance curve of the novel equipment was also obtained. Enhancing the isentropic efficiency of expansion is the effective means to improve the COP and σ of the system. This paper was designed in a way that contained a novel equipment to enhance the COP of wave rotor refrigeration.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2018;141(2):022201-022201-14. doi:10.1115/1.4040580.

Direct injection spark ignition or gasoline direct injection (GDI) engines are superior in terms of relatively higher thermal efficiency and power output compared to multipoint port fuel injection engines and direct injection diesel engines. In this study, a 500 cc single cylinder GDI engine was used for experiments. Three gasohol blends (15% (v/v) ethanol/methanol/butanol with 85% (v/v) gasoline) were chosen for this experimental study and were characterized to determine their important fuel properties. For particulate investigations, exhaust particles were collected on a quartz filter paper using a partial flow dilution tunnel. Comparative investigations for particulate mass emissions, trace metal concentrations, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) analyses, and high-resolution transmission electron microscopy (HR-TEM) imaging of the particulate samples collected from different test fuels at different engine loads were performed. For majority of the experimental conditions, gasohols showed relatively lower trace metal concentration in particulates compared to gasoline. HR-TEM images showed that higher engine loads and presence of oxygen in the test fuels increased the soot reactivity. Multicore shells like structures were visible in the HR-TEM images due to growth of nuclei, and rapid soot formation due to relatively higher temperature and pressure environment of the engine combustion chamber. Researches world-over are trying to reduce particulate emissions from GDI engines; however there is a vast research gap for such investigations related to gasohol fueled GDI engines. This paper critically assesses and highlights comparative morphological characteristics of gasohol fueled GDI engine.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022202-022202-9. doi:10.1115/1.4041405.

In this work, numerical investigations of methane catalytic combustion in the opposed counter-flow microcombustor are conducted under various inlet velocities, equivalence ratios, and geometric parameters. The results indicate that the high temperature zone is mainly located at the front and middle parts of the reaction zone. With the increase of inlet velocity, both methane conversion and exhaust gas temperature decrease, while the methane concentration in the downstream area increases. Its maximum velocity limit is 2.9 m/s. Moreover, temperature step zones of opposed counter-flow are obviously located at the front and middle parts with different equivalence ratios. The combustion efficiency decreases slowly with the increase of equivalence ratios. More importantly, critical values about the geometric parameters are determined for keeping better thermal performance. It is concluded that inlet velocity limit and methane conversion rate can be significantly increased and the temperature distribution is more uniform via reducing inlet width L2 and inlet height H, increasing the length of the downstream parts L1 and the downstream entrance length L3. In general, the opposed counter-flow microcombustor with optimized structure has better combustion stability. This design offers another way for developing the opposed counter-flow microcombustor.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022203-022203-6. doi:10.1115/1.4041407.

After coal seam mining, the residual coal is soaked with the accumulated water in goaf, and its spontaneous combustion characteristics were changed after air-dried. To study the reoxidation characteristics of soaked and air-dried coal, temperature-programmed experiments were carried out, and the cross point temperatures and index gases were investigated. Results showed that the cross point temperature of raw coal (146.3 °C) was reduced to 137.1 °C after it was pre-oxidized at 90 °C. The cross point temperature of water-soaked, and air-dried coal (96 h) was 122.5 °C, while the cross point temperature of water-soaked, air-dried (96 h) and pre-oxidized (90 °C) coal was 111.5 °C. Although CO was produced in the initial slow oxidation phase, it was found that C2H4 and C3H8 were not generated. In the rapid oxidation stage, different pretreatments affected the gas generation and the overall oxidative degree was consistent with the cross point temperature. The generation temperature and the concentration of C2H4 and C3H8 were decreased after the coal was water-soaked, air-dried, and pre-oxidized. Furthermore, the high-energy chemicals and functional groups were studied, which could be used to explain the physical experiment oxidation characteristics of different coals.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022204-022204-8. doi:10.1115/1.4041289.

The rate-controlled constrained-equilibrium (RCCE), a model order reduction method, has been further developed to simulate the combustion of propane/oxygen mixture diluted with nitrogen or argon. The RCCE method assumes that the nonequilibrium states of a system can be described by a sequence of constrained-equilibrium states subject to a small number of constraints. The developed new RCCE approach is applied to the oxidation of propane in a constant volume, constant internal energy system over a wide range of initial temperatures and pressures. The USC-Mech II (109 species and 781 reactions, without nitrogen chemistry) is chosen as chemical kinetic mechanism for propane oxidation for both detailed kinetic model (DKM) and RCCE method. The derivation for constraints of propane/oxygen mixture starts from the eight universal constraints for carbon-fuel oxidation. The universal constraints are the elements (C, H, O), number of moles, free valence, free oxygen, fuel, and fuel radicals. The full set of constraints contains eight universal constraints and seven additional constraints. The results of RCCE method are compared with the results of DKM to verify the effectiveness of constraints and the efficiency of RCCE. The RCCE results show good agreement with DKM results under different initial temperature and pressures, and RCCE also reduces at least 60% CPU time. Further validation is made by comparing the experimental data; RCCE shows good agreement with shock tube experimental data.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022205-022205-10. doi:10.1115/1.4041316.

Laminar burning speed and ignition delay time behavior of iso-octane at the presence of two different biofuels, ethanol and 2,5 dimethyl furan (DMF), was studied in this work. Biofuels are considered as a better alternative source of fossil fuels. There is a potentiality that combustion characteristics of iso-octane can be improved using biofuels as an oxygenated additive. In this study, three different blending ratios of 5%, 25%, and 50% of ethanol/iso-octane and DMF/iso-octane were investigated. For laminar burning speed calculation, equivalence ratio of 0.6–1.4 was considered. Ignition delay time was measured under temperature ranges from 650 K to 1100 K. Two different mechanisms were considered in numerical calculation. These mechanisms were validated by comparing the results of pure fuels with wide range of experimental and numerical data. The characteristic change of iso-octane with the presence of additives was observed by comparing the results with pure fuel. Significant change was observed on behavior of iso-octane at 50% blending ratio. A comparison was also done on the effect of two different additives. It has found that addition of DMF brings significant changes on iso-octane characteristics comparing to ethanol.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022206-022206-12. doi:10.1115/1.4041412.

Biomass has been considered as a valuable alternative fuel recently. A fundamental property of biomass/air flame, laminar burning speed, is measured in this research. Experiments have been made in a cylindrical combustion vessel with two end windows. Central ignition has been used to start the combustion process. A high-speed CMOS camera capable of taking pictures of 40,000 frames per second has been used to study morphology of flame front. Flames are initially smooth, and as pressure and flame radius increase, cracks and cells appear on the flame surface. In this paper, experimental results have only been reported for smooth flames. A multishell thermodynamic model to measure laminar burning speed of biomass/air mixture with varying CO2 concentrations (0%–60%), based on the pressure rise data collected from a cylindrical chamber during combustion, has been developed in this paper. Burning speed has been only reported for flame radii larger than 4 cm in radius in order to have negligible stretch effect. Power law correlations, to predict burning speed of biomass/air mixtures, based on the measured burning speeds, have been developed for a range of temperatures of 300–661 K, pressures of 0.5–6.9 atmospheres, equivalence ratios of 0.8–1.2, and CO2 concentrations 0%–60%. Moreover, the measured laminar burning speeds have been compared with simulation results using a one-dimensional steady-state laminar premixed flame program with GRI-Mech 3.0 mechanism and other available data from literatures. Comparison with existing data has been excellent.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022207-022207-6. doi:10.1115/1.4041468.

The present work explored the constitution of the calorific values of biomass fuels and the mechanism by which basic chemical compositions affect the fuel calorific data. For the first time, an energy conversion model was developed for the functional groups stored in biomass fuels by combustion. Validation of the model was performed by testing with various types of substances. By analyzing the effect of mass increase of individual chemical species on the amount of heat released by a fuel, it was confirmed that for ligno-cellulosic fuels, the species containing C–H, C–C and C=C bonds positively affect the fuel calorific values, whereas the species containing O–H, C–N, C–O, and C=O bonds have negative role in the increase of the fuel calorific values. A ratio parameter was then developed to quantitatively evaluate the potential of individual chemical bonds to contribute to the calorific values of biomass fuels, which well explained the existing techniques for treating biomass as fuels. The outcomes of this work serve as a theoretical basis for improving the efficiency in energy utilization of biomass fuels.

Topics: Fuels , Biomass , Combustion , Heat
Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2018;141(2):022901-022901-9. doi:10.1115/1.4041406.

The iterative ensemble smoother (IES) algorithm has been extensively used to implicitly and inversely determine model parameters by assimilating measured/reference production profiles. The performance of the IES algorithms is usually challenged due to the simultaneous assimilation of all production data and the multiple iterations required for handling the inherent nonlinearity between production profiles and model parameters. In this paper, a modified IES algorithm has been proposed and validated to improve the efficiency and accuracy of the IES algorithm with the standard test model (i.e., PUNQ-S3 model). More specifically, a recursive approach is utilized to optimize the screening process of damping factor for improving the efficiency of the IES algorithm without compromising of history matching performance because an inappropriate damping factor potentially yields more iterations and significantly increased computational expenses. In addition, a normalization method is proposed to revamp the sensitivity matrix by minimizing the data heterogeneity associated with the model parameter matrix and production data matrix in updating processes of the IES algorithm. The coefficients of relative permeability and capillary pressure are included in the model parameter matrix that is to be iteratively estimated by assimilating the reference production data (i.e., well bottomhole pressure (WBHP), gas-oil ratio, and water cut) of five production wells. Three scenarios are designed to separately demonstrate the competence of the modified IES algorithm by comparing the objective function reduction, history-matched production profile convergence, model parameters variance reduction, and the relative permeability and capillary pressure of each scenario. It has been found from the PUNQ-S3 model that the computational expenses can be reduced by 50% while comparing the modified and original IES algorithm. Also, the enlarged objective function reduction, improved history-matched production profile, and decreased model parameter variance have been achieved by using the modified IES algorithm, resulting in a further reduced deviation between the reference and the estimated relative permeability and capillary pressure in comparison to those obtained from the original IES algorithm. Consequently, the modified IES algorithm integrated with the recursive approach and normalization method has been substantiated to be robust and pragmatic for improving the performance of the IES algorithms in terms of reducing the computational expenses and improving the accuracy.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022902-022902-17. doi:10.1115/1.4041410.

In this paper, a pragmatic and consistent framework has been developed and validated to accurately predict reservoir performance in tight sandstone reservoirs by coupling the dynamic capillary pressure with gas production models. Theoretically, the concept of pseudo-mobile water saturation, which is defined as the water saturation between irreducible water saturation and cutoff water saturation, is proposed to couple dynamic capillary pressure and stress-induced permeability to form an equation matrix that is solved by using the implicit pressure and explicit saturations (IMPES) method. Compared with the conventional methods, the newly developed model predicts a lower cumulative gas production but a higher reservoir pressure and a higher flowing bottomhole pressure at the end of the stable period. Physically, a higher gas production rate induces a greater dynamic capillary pressure, while both cutoff water saturation and stress-induced permeability impose a similar impact on the dynamic capillary pressure, though the corresponding degrees are varied. Due to the dynamic capillary pressure, pseudo-mobile water saturation controlled by the displacement pressure drop also affects the gas production. The higher the gas production rate is, the greater the effect of dynamic capillary pressure on the cumulative gas production, formation pressure, and flowing bottomhole pressure will be. By taking the dynamic capillary pressure into account, it can be more accurate to predict the performance of a gas reservoir and the length of stable production period, allowing for making more reasonable development schemes and thus improving the gas recovery in a tight sandstone reservoir.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;141(2):022903-022903-9. doi:10.1115/1.4041741.

The development process of a dipping gas reservoir with an aquifer considering stress sensitivity is complex. With gas development, formation pressure decreases, stress-sensitive effect decreases permeability and porosity, and formation water could flow into the development gas well and gather in the wellbore. The accumulation of water may lead to a lower gas rate. Simultaneously, the gravity action of fluid caused by formation dip angle affects gas well productivity. However, few studies have investigated a deliverability model for a water-producing gas well with a dipping gas reservoir considering stress sensitivity. For this reason, it is important to determine the relationships between gas well productivity and stress sensitivity, formation angle, and water production. In this research, a new mathematical model of deliverability was developed for a water-producing gas well with a dipping gas reservoir considering stress sensitivity. Additionally, a new equation was developed for gas well productivity. By analyzing a typical dipping gas reservoir with an aquifer, the level of influence on gas well productivity was determined for stress sensitivity, formation angle, and water–gas ratio (WGR). The work defined the relationships between gas well productivity and stress sensitivity, formation angle, and WGR. The results indicate that deliverability increases with an increase in formation angle, and growth rate hits its limit at an angle of 40 deg. Due to the influence of formation angle, fluid gravity leads to production pressure differences in gas wells. When bottom-hole flow pressure equaled formation pressure, gas well production was not 0 × 104 m3/d, the angle was large, and gas well production was greater. Deliverability and stress sensitivity hold a linear relationship: the stronger the stress sensitivity, the lower the deliverability of the gas well, with the stress sensitivity index from 0 to 0.06 MPa−1 and the deliverability decrease rate at 37.2%. Deliverability and WGR hold an exponential relationship: when WGR increased from 0.5 to 15.0 m3/104 m3, the deliverability decrease rate was 71.8%. The model and the equations can be used to predict gas deliverability in a dipping gas reservoir with an aquifer considering stress sensitivity. It can also be used to guide the development process for a dipping gas reservoir with an aquifer.

Commentary by Dr. Valentin Fuster

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