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Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2018;140(11):112001-112001-10. doi:10.1115/1.4038117.

The paper presents the possibilities of the use of a high-temperature gas-cooled nuclear reactor for energy purposes in the hydrogen and electricity production process. The system provides heat for a thermochemical sulfur–iodine cycle producing hydrogen and generates electricity. Its structure and electricity generation capacity are conditioned by the demand for heat and the levels of temperature required at the sulfur–iodine cycle individual stages. In the three structures under analysis, electricity is generated in a gas turbine system and steam systems (steam, low-boiling fluids). The impact of helium parameters in a two-stage compression system with interstage cooling on power efficiency of the analyzed structures of cogeneration systems and on total power efficiency of the systems is investigated assuming that both hydrogen and electricity are produced. Thermodynamic analyses are conducted using the EBSILON Professional program. The aim of the analyses is to determine the optimum structure of the system and parameters of the mediums in terms of power efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112002-112002-8. doi:10.1115/1.4040403.

We have investigated a novel gas/solid contacting configuration for chemical looping combustion (CLC) with potential operating benefits. CLC configurations are typically able to achieve high fuel conversion efficiencies at the expense of high operating costs and low system reliability. The spouted fluid bed (SB) was identified as an improved reactor configuration for CLC, since it typically exhibits high heat transfer rates and offers the ability to use lower gas flows for material movement compared to bubbling beds (BB). Multiphase Flow with Interphase eXchanges (MFIX) software was used to establish a spouted fluid bed reactor design. An experimental setup was built to supplement the model. The experimental setup was also modified for testing under high temperature, reacting conditions (1073–1273 K). The setup was operated in either a spouted fluid bed or a bubbling bed regime to compare the performance attributes of each. Results for the reactor configurations are presented for CLC using a mixture of carbon monoxide and hydrogen as fuel. Compared to the bubbling bed, the spouted fluid bed reactor achieved an equivalent or better fuel conversion at a lower pressure drop over the material bed. The spouted fluid bed design represents a viable configuration to improve gas/solid contacting for efficient fuel conversion, lower energy requirements for material movement and increase operational robustness for CLC. The research laid the groundwork for future research into a multi-phase reacting flow CLC system. The system will be developed from computational fluid dynamic modeling and pilot-scale testing to expedite the development of CLC technologies.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112003-112003-11. doi:10.1115/1.4040202.

Biomass torrefaction is a mild pyrolysis thermal treatment process carried out at temperatures between 200 and 300 °C under inert conditions to improve fuel properties of parent biomass. Torrefaction yields a higher energy per unit mass product but releases noncondensable and condensable gases, signifying energy and mass losses. The condensable gases (volatiles) can result in tar formation on condensing, hence, system blockage. Fortunately, the hydrocarbon composition of volatiles represents a possible auxiliary energy source for feedstock drying and/or torrefaction process. The present study designed a low-pressure volatile burner for torrefaction of pine wood chips and investigated energy recovery from volatiles through clean co-combustion with natural gas (NG). The research studied the effects of torrefaction pretreatment temperatures on the amount of energy recovered for various combustion air flow rates. For all test conditions, blue flames and low emissions at the combustor exit consistently signified clean and complete premixed combustion. Torrefaction temperature at 283–292 °C had relatively low volatile energy recovery, mainly attributed to higher moisture content evolution and low molecular weight of volatiles evolved. At the lowest torrefaction pretreatment temperature, small amount of volatiles was generated with more energy recovered. Energy conservation evaluation on the torrefaction reactor indicated that about 27% of total energy carried by the exiting volatiles and gases has been recovered by the co-fire of NG and volatiles at the lowest temperature, while around 19% of the total energy was recovered at the intermediate and highest torrefaction temperatures, respectively. The energy recovered represents about 23–45% of the energy associated with NG combustion in the internal burner of the torrefaction reactor, signifying that the volatiles energy can supplement significant amount of the energy required for torrefaction.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112004-112004-11. doi:10.1115/1.4040193.

High energy penalty and cost are major obstacles in the widespread use of CO2 capture techniques for reducing CO2 emissions. Chemical looping combustion (CLC) is an innovative means of achieving CO2 capture with less cost and low energy penalty. This paper conducts a detailed techno-economic analysis of a natural gas-fired CLC-based power plant. The power plant capacity is 1000 MWth gross power on a lower heating value basis. The analysis was done using Aspen Plus. The cost analysis was done by considering the plant location to be in the United Arab Emirates. The plant performance was analyzed by using the cost of equipment, cost of electricity, payback period, and the cost of capture. The performance of the CLC system was also compared with a conventional natural gas combined cycle plant of the same capacity integrated with post combustion CO2 capture technology. The analysis shows that the CLC system had a plant efficiency of 55.6%, electricity cost of 5.5 cents/kWh, payback time of 3.77 years, and the CO2 capture cost of $27.5/ton. In comparison, a similar natural gas combined cycle (NGCC) power plant with CO2 capture had an efficiency of 50.6%, cost of electricity of 6.1 cents/kWh, payback period of 4.57 years, and the capture cost of $42.9/ton. This analysis shows the economic advantage of the CLC integrated power plants.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112005-112005-11. doi:10.1115/1.4040194.

The fundamental challenge in the synthesis/design optimization of energy systems is the definition of system configuration and design parameters. The traditional way to operate is to follow the previous experience, starting from the existing design solutions. A more advanced strategy consists in the preliminary identification of a superstructure that should include all the possible solutions to the synthesis/design optimization problem and in the selection of the system configuration starting from this superstructure through a design parameter optimization. This top–down approach cannot guarantee that all possible configurations could be predicted in advance and that all the configurations derived from the superstructure are feasible. To solve the general problem of the synthesis/design of complex energy systems, a new bottom–up methodology has been recently proposed by the authors, based on the original idea that the fundamental nucleus in the construction of any energy system configuration is the elementary thermodynamic cycle, composed only by the compression, heat transfer with hot and cold sources and expansion processes. So, any configuration can be built by generating, according to a rigorous set of rules, all the combinations of the elementary thermodynamic cycles operated by different working fluids that can be identified within the system, and selecting the best resulting configuration through an optimization procedure. In this paper, the main concepts and features of the methodology are deeply investigated to show, through different applications, how an artificial intelligence can generate system configurations of various complexity using preset logical rules without any “ad hoc” expertise.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112006-112006-13. doi:10.1115/1.4040195.

Cooling the air before entering the compressor of a gas turbine of combined cycle power plants is an effective method to boost the output power of the combined cycles in hot regions. This paper presents a comparative analysis for the effect of different air cooling technologies on increasing the output power of a combined cycle. It also presents a novel system of cooling the gas turbine inlet air using a solar-assisted absorption chiller. The effect of ambient air temperature and relative humidity on the output power is investigated and reported. The study revealed that at the design hour under the hot weather conditions, the total net power output of the plant drops from 268 MW to 226 MW at 48 °C (15.5% drop). The increase in the power output using fogging and evaporative cooling is less than that obtained with chillers since their ability to cool down the air is limited by the wet-bulb temperature. Integrating conventional and solar-assisted absorption chillers increased the net power output of the combined cycle by about 35 MW and 38 MW, respectively. Average and hourly performance during typical days have been conducted and presented. The plants without air inlet cooling system show higher carbon emissions (0.73 kg CO2/kWh) compared to the plant integrated with conventional and solar-assisted absorption chillers (0.509 kg CO2/kWh) and (0.508 kg CO2/kWh), respectively. Also, integrating a conventional absorption chiller shows the lowest capital cost and levelized electricity cost (LEC).

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2018;140(11):112201-112201-9. doi:10.1115/1.4040380.

The present study surveys the effects on performance and emission parameters of a partially modified single cylinder direct injection (DI) diesel engine fueled with diesohol blends under varying compressed natural gas (CNG) flowrates in dual fuel mode. Based on experimental data, an artificial intelligence (AI) specialized artificial neural network (ANN) model have been developed for predicting the output parameters, viz. brake thermal efficiency (Bth), brake-specific energy consumption (BSEC) along with emission characteristics such as oxides of nitrogen (NOx), unburned hydrocarbon (UBHC), carbon dioxide (CO2), and carbon monoxide (CO) emissions. Engine load, Ethanol share, and CNG strategies have been used as input parameters for the model. Among the tested models, the Levenberg–Marquardt feed-forward back propagation with three input neurons or nodes, two hidden layers with ten neurons in each layer and six output neurons, and tansig-purelin activation function have been found to the optimal model topology for the diesohol–CNG platforms. The statistical results acquired from the optimal network topology such as correlation coefficient (0.992–0.999), mean square error (MSE) (0.0001–0.0009), and mean absolute percentage error (MAPE) (0.09–2.41%) along with Nash–Sutcliffe coefficient of efficiency (NSE), Kling–Gupta efficiency (KGE), mean square relative error, and model uncertainty established itself as a real-time robust type machine learning tool under diesohol–CNG paradigms. The study also incorporated a special type of measure, namely Pearson's Chi-square test or goodness of fit, which brings up the model validation to a higher level.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112202-112202-7. doi:10.1115/1.4040381.

We provide the first demonstration of an acousto-optically modulated quantum cascade laser (AOM QCL) system as a diagnostic for combustion by measuring nitric oxide (NO), a highly regulated emission produced in gas turbines. The system provides time-resolved broadband spectral measurements of the present gas species via a single line of sight measurement, offering advantages over widely used narrowband absorption spectroscopy (e.g., the potential for simultaneous multispecies measurements using a single laser) and considerably faster (>15 kHz rates and potentially up to MHz) than sampling techniques, which employ fourier transform infrared (FTIR) or GC/MS. The developed AOM QCL system yields fast tunable output covering a spectral range of 1725–1930 cm−1 with a linewidth of 10–15 cm−1. For the demonstration experiment, the AOM QCL system has been used to obtain time-resolved spectral measurements of NO formation during the shock heating of mixture of a 10% nitrous oxide (N2O) in a balance of argon over a temperature range of 1245–2517 K and a pressure range of 3.6–5.8 atm. Results were in good agreement with chemical kinetic simulations. The system shows revolutionary promise for making simultaneous time-resolved measurements of multiple species concentrations and temperature with a single line of sight measurement.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2018;140(11):112901-112901-7. doi:10.1115/1.4040378.

In this study, we analyzed the flow-back resistance of slick water fracturing fluid in shale reservoirs. The flow-back resistance mainly includes capillary force, Van der Waals (VDW) force, hydrogen bond force, and hydration stress. Shale of Lower Silurian Longmaxi Formation (LSLF) was used to study its wettability, hydration stress, and permeability change with time of slick water treatment. The results reveal that wettability of LSLF shale was more oil-wet before immersion, while it becomes more water-wet after immersion. The hydration stress of the shale increased with increasing immersion time. The permeability decreased first, then recovered with increasing immersion time. The major reason for permeability recovery is that the capillary effect (wettability) and the shale hydration make macrocracks extension and expansion and hydration-induced fractures formation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(11):112902-112902-8. doi:10.1115/1.4040205.

The CO2 foam generated by the conventional surfactants usually does not show long-term stability due to the substantial solubility and diffusivity of CO2 in water. Silica nanoparticles with different wettability and high adsorption energy on the gas–water interface can be used as a stabilizer to enhance the stability of the CO2 foam. In this study, nine kinds of nonionic amine surfactants were employed to generate the CO2 foam, while three kinds of silica nanoparticles were selected and added to improve the CO2 foam stability. The influences of various factors, including pressure, temperature, pH, surfactant, and nanoparticle, on the CO2 foam stability have been investigated. The experimental results show that without nanoparticles, the CO2 foam stability decreases with the increase of the number of EO groups in the ethoxylated amine surfactant, especially under high-temperature and high-pressure (HTHP) conditions. In general, the nanoparticles with a low concentration (<0.5 wt %) have little influence on the CO2 foam stability, but when the concentration of nanoparticle is enhanced high enough (1.0 wt %), the CO2 foam stability can be improved significantly. In particular, by adding 1.0 wt % nanoparticle of QS-150 to 0.5 wt % surfactant of C18N(EO)2/10, the CO2 foam stability has been increased 5–6 times, while the volume of generated CO2 foam has been increased by 17–31%. Therefore, in this study, the synergetic mechanisms between the amine surfactants and the silica nanoparticles to generate and stabilize CO2 foam have been identified.

Commentary by Dr. Valentin Fuster

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