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Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2017;140(5):051201-051201-17. doi:10.1115/1.4037813.

The splitter blades are very common to use for centrifugal compressor impellers to improve the compressor performance and manufacturing capability. In this study, a low-flow single-stage centrifugal compressor with a vaneless diffuser was used to investigate the location effects of the impeller splitter between two main blades. It is demonstrated that the splitter position provides an opportunity to improve the compressor performance and reduce the operational cost. The splitter location optimizations were performed numerically, and the optimal splitter location was identified. A prototype was built for the impeller with optimal splitter position. The performance tests were performed, and test results are compared with numerical analyses. The studies indicated that splitter positions have impacts on the compressor stage performances. The studies showed that the traditional splitter located in the middle of the two main blades is not the optimal location for aerodynamic performance. The splitter location optimization provided the opportunity to improve the centrifugal compressor performance further.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(5):051202-051202-13. doi:10.1115/1.4038119.

A fast-growing worldwide interest is directed toward green energies. Due to the huge costs of wind farms establishment, the location for wind farms should be carefully determined to achieve the optimum return of investment. Consequently, researches have been conducted to investigate land suitability prior to wind plants development. The generated data from the sensors detecting a potential land can be very huge, fast in generation, heterogeneous, and incomplete, which become seriously difficult to process using traditional approaches. In this paper, we propose Trio-V Wind Analyzer (WA) that handles data volume, variety, and veracity to identify the most suitable location for wind energy development in any study area using a modified version of multicriteria evaluation (MCE). It utilizes principal component analysis (PCA) and our proposed Double-Reduction Optimum Apriori (DROA) to analyze most of the environmental, physical, and economical criteria. In addition, Trio-V WA recommends the suitable turbines and proposes the adequate turbines’ layout distribution, predicting the expected power generated based on the recommended turbine’s specifications using a regression technique. Thus, Trio-V WA provides an integral system of land evaluation for potential investment in wind farms. Experiments indicate 80% and 95% average accuracy for land suitability degree and power prediction, respectively, with efficient performance.

Topics: Turbines , Wind , Wind farms , Design
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(5):051203-051203-6. doi:10.1115/1.4038485.

This paper aims to increase the efficiency of the maximum power point tracking (MPPT) methods by using an integral sliding mode voltage regulator (ISMVR). The ISMVR is applied to one of the frequently used MPPT methods called as tip speed ratio (TSR). The proposed method presents a fast and robust tracking capability. Also, there is no need to know about the parameters of the generator in order to generate the control signal. The ISMVR presents considerably simple control structure due to the fact that the authors used only the boost converter (BC) and controller parameters for the control signal. Additionally, the performances of the proposed improved TSR-MPPT method based on ISMVR are compared to the TSR-MPPT method based on conventional sliding mode voltage regulator (CSMVR) under the same conditions. The dynamic performance, robustness, and fast approximation of the offered method are proved with the simulations.

Commentary by Dr. Valentin Fuster

Research Papers: Energy From Biomass

J. Energy Resour. Technol. 2017;140(5):051801-051801-9. doi:10.1115/1.4038313.

Chlorine plays an important role in the slagging and corrosion of boilers that burn high-chlorine content biomass. This research investigated the emissions of hydrogen chloride (HCl) gas from combustion of biomass in a fixed bed, as functions of the mass air flow rate through the bed and of the moisture content of the fuel. The biomass burned was corn straw, either raw or torrefied. Results showed that increasing the air flow rate through the bed increased the release of HCl gas, as a result of enhanced combustion intensity and associated enhanced heat release rates. When the airflow through the bed was increased by a factor of six, the amount of fuel-bound chlorine converted to HCl nearly tripled. Upon completion of combustion, most of the chlorine remained in the biomass ashes, with the exception of the highest air flow case where the fraction of chlorine released in HCl equaled that captured in the ashes. HCl emissions from torrefied biomass were found to be lower than those from raw biomass. Finally, drying the biomass proved to be beneficial in drastically curtailing the generation of HCl gas.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2017;140(5):052001-052001-15. doi:10.1115/1.4038236.

Boiler's efficiency is one of the important performance indicators of boiler. To keep track of operation cost, efficiency needs to be calculated with adequate accuracy by employing effective mathematical tools. In this work, a new modification in conventional mathematical formulation of efficiency is presented based on time-varying efficiency using time-varying operational variables of boiler. This modification was accomplished using indirect method of efficiency by applying experimental data of variables for certain time span. Moreover a second-order dynamic model of flue gas temperature (FGT) has been derived to construct the mathematical formulation of efficiency only in terms of available inputs. The resulting input–output-based model proved to be in quite agreement with efficiency calculated from experimental data. After modeling, influence of variations in air to fuel ratio (AFR) and fuel flow rate (FFR) upon efficiency has been discussed and it has been shown that time-varying efficiency covers deeper aspect of dynamic relation between efficiency and other input of boiler especially AFR and FFR. Moreover, it has been established that efficiency interacts with the dynamics of boiler, and in this respect, a dynamic relation between combustion process and boiler dynamics has been constructed via efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(5):052002-052002-13. doi:10.1115/1.4037369.

This paper presents the approach of thermoeconomic analysis of centralized cold generation in trigeneration system integrated with steam-powered absorption chillers (ACs). The analysis was conducted for real back-pressure combined heat and power (CHP) unit BC-50 and single-effect absorption refrigerators using water and lithium bromide as the working fluids. It has been assumed that the heating medium supplied to the chiller generator is technological steam from the existing steam bleeding. The calculations take into account changes of energy demand for heating and cooling for each month of the year. Mathematical simulation models of cogeneration and trigeneration systems have been developed with the commercial program for power plant simulation EBSILON Professional. System effects of heat and electricity cogeneration and cogeneration with additional cold production have been calculated compared to separate production of heat, electricity, and cold (replaced heating plant and power unit). The effect of trigeneration has been assessed quantitatively by the coefficient of the increasing cogeneration effects, which has been calculated as a ratio of chemical energy savings of fuels to the demand for heat by the consumers in the cases of trigeneration and cogeneration. This paper includes also analysis of economic effectiveness of a trigeneration system with ACs for cold agent production. The results of economic calculations show that an acceptable payback period of approximately 13 yr for a CHP and absorption system may be achieved. Discounted payback (DPB) is equal to the half of assumed operating time of the system. Sensitivity analysis shows that the most important impact on profitability is the selling price of cold and the purchase of fuel—hard coal.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2017;140(5):052201-052201-9. doi:10.1115/1.4038376.

The rate-controlled constrained-equilibrium (RCCE) model reduction scheme for chemical kinetics provides acceptable accuracies in predicting hydrocarbon ignition delays by solving a smaller number of differential equations than the number of species in the underlying detailed kinetic model (DKM). To yield good approximations, the method requires accurate identification of the rate controlling constraints. Until recently, a drawback of the RCCE scheme has been the absence of a systematic procedure capable of identifying optimal constraints for a given range of thermodynamic conditions and a required level of approximation. A recent methodology has proposed for such identification an algorithm based on a simple algebraic analysis of the results of a preliminary simulation of the underlying DKM, focused on the degrees of disequilibrium (DoD) of the individual chemical reactions. It is based on computing an approximate singular value decomposition of the actual degrees of disequilibrium (ASVDADD) obtained from the DKM simulation. The effectiveness and robustness of the method have been demonstrated for methane/oxygen ignition by considering a C1/H/O (29 species/133 reactions) submechanism of the GRI-Mech 3.0 scheme and comparing the results of a DKM simulation with those of RCCE simulations based on increasing numbers of ASVDADD constraints. Here, we demonstrate the new method for shock-tube ignition of a natural gas/air mixture, with higher hydrocarbons approximately represented by propane according to the full (53 species/325 reactions) GRI-Mech 3.0 scheme including NOx formation.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2017;140(5):052901-052901-7. doi:10.1115/1.4038405.

Thermal–chemical flooding (TCF) is an effective alternative to enhance heavy oil recovery after steam injection. In this paper, single and parallel sand-pack flooding experiments were carried out to investigate the oil displacement ability of thermal–chemical composed of steam, nitrogen (N2), and viscosity breaker (VB), considering multiple factors such as residual oil saturation (Sorw) postwater flood, scheme switch time, and permeability contrast. The results of single sand-pack experiments indicated that compared with steam flooding (SF), steam-nitrogen flooding, and steam-VB flooding, TCF had the best displacement efficiency, which was 11.7% higher than that of pure SF. The more serious of water-flooded degree, the poorer of TCF effect. The improvement effect of TCF almost lost as water saturation reached 80%. Moreover, the earlier TCF was transferred from steam injection, the higher oil recovery was obtained. The parallel sand-pack experiments suggested that TCF had good adaptability to reservoir heterogeneity. Emulsions generated after thermal–chemical injection diverted the following compound fluid turning to the low-permeable tube (LPT) due to its capturing and blocking ability. The expansion of N2 and the disturbance of VB promoted oil recovery in both tubes. As reservoir heterogeneity became more serious, namely, permeability contrast was more than 6 in this study, the improvement effect became weaker due to earlier steam channeling in the high-permeable tube (HPT).

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(5):052902-052902-8. doi:10.1115/1.4038381.

Lost circulation is a serious problem which always exists in the petroleum industry. Wellbore strengthening by lost circulation materials (LCMs) is a commonly applied method for mitigating lost circulation. This paper presents a hydraulic fracturing apparatus to investigate the effect of material type, concentration, and particle size distribution (PSD) of LCMs on wellbore strengthening behavior. In addition, the characteristics of pressure curves in the fracturing process are analyzed in detail. The results showed that the fracture pressure of the artificial core can be increased by LCMs, and there exists an optimum concentration of LCMs for the maximum wellbore strengthening effect. The LCMs with wide PSD can significantly increase the fracture pressure. However, some LCMs cannot increase or even decrease the fracture pressure; this is resulting from the LCMs with relatively single PSD that makes the quality of mud cake worse. The representative pressure curve in the fracturing process by drilling fluids with LCMs was divided into five parts: the initial cake formation stage, elastic plastic deformation stage, crack stability development stage, crack instability development stage, and unstable plugging stage. The actual fracturing curves were divided into four typical types due to missing of some stages compared with the representative pressure curve. In order to strengthen the wellbore in effective, good LCMs should be chosen to improve the maximum pressure in the elastic plastic deformation stage, extend the stable time of pressure bearing in the crack stability development stage, and control the crack instability development stage.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(5):052903-052903-9. doi:10.1115/1.4038382.

This study investigates the effect of using date seed-based additive on the performance of water-based drilling fluids (WBDFs). Specifically, the effects of date pit (DP) fat content, particle size, and DP loading on the drilling fluids density, rheological properties, filtration properties, and thermal stability were investigated. The results showed that dispersion of particles less than 75 μm DP into the WBDFs enhanced the rheological as well as fluid loss control properties. Optimum fluid loss and filter cake thickness can be achieved by addition of 15–20 wt % DP loading to drilling fluid formulation.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(5):052904-052904-15. doi:10.1115/1.4038386.

A power-law mixing rule has been developed to determine apparent diffusion coefficient of a binary gas mixture on the basis of molecular diffusion coefficients for pure gases in heavy oil. Diffusion coefficient of a pure gas under different pressures and different temperatures is predicted on the basis of the Hayduk and Cheng's equation incorporating the principle of corresponding states for one-dimensional gas diffusion in heavy oil such as the diffusion in a pressure–volume–temperature (PVT) cell. Meanwhile, a specific surface area term is added to the generated equation for three-dimensional gas diffusion in heavy oil such as the diffusion in a pendant drop. In this study, the newly developed correlations are used to reproduce the measured diffusion coefficients for pure gases diffusing in three different heavy oils, i.e., two Lloydminster heavy oils and a Cactus Lake heavy oil. Then, such predicted pure gas diffusion coefficients are adjusted based on reduced pressure, reduced temperature, and equilibrium ratio to determine apparent diffusion coefficient for a gas mixture in heavy oil, where the equilibrium ratios for hydrocarbon gases and CO2 are determined by using the equilibrium ratio charts and Standing's equations, respectively. It has been found for various gas mixtures in two different Lloydminster heavy oils that the newly developed empirical mixing rule is able to reproduce the apparent diffusion coefficient for binary gas mixtures in heavy oil with a good accuracy. For the pure gas diffusion in heavy oil, the absolute average relative deviations (AARDs) for diffusion systems with two different Lloydminster heavy oils and a Cactus Lake heavy oil are calculated to be 2.54%, 14.79%, and 6.36%, respectively. Meanwhile, for the binary gas mixture diffusion in heavy oil, the AARDs for diffusion systems with two different Lloydminster heavy oils are found to be 3.56% and 6.86%, respectively.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Energy Resour. Technol. 2017;140(5):054501-054501-6. doi:10.1115/1.4038465.

Blooey line is a discharge pipe, used to conduct gas to keep drilling rock dust and cuttings away from the drilling rig, reducing the fire hazard and transporting the cuttings to a suitable distance from the well. In this paper, the blooey line's flow capacity and erosion mechanism have been investigated by numerical and experimental method. The model of blooey line, which is commonly used in Sichuan district, China, is established by using a computational fluid dynamics (CFD) method. And, the distribution of pressure field and velocity field in the blooey line are investigated by the CFD model. And, the effect of gas flow rate on impact force and erosion is also discussed. Compared with the simulation results, an experimental apparatus of the blooey line has been conducted under the mechanical similarity principle. The impact force and pressure on the elbows are measured under different gas flow rates. The numerical simulation and experimental method proposed in this paper can provide a reference for layout optimization and flow capacity calculation of blooey line in gas drilling.

Commentary by Dr. Valentin Fuster

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