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TECHNICAL PAPERS

J. Energy Resour. Technol. 2003;125(3):161-168. doi:10.1115/1.1580847.

Hilly-terrain pipelines consist of interconnected horizontal, uphill and downhill sections. Slug flow experiences a transition from one state to another as the pipe inclination angle changes. Normally, slugs dissipate if the upward inclination becomes smaller or the downward inclination becomes larger, and slug generation occurs vice versa. Appropriate prediction of the slug characteristics is crucial for the design of pipeline and downstream facilities. In this study, slug dissipation and generation in a valley pipeline configuration (horizontal-downhill-uphill-horizontal) were modeled by use of the method proposed by Zhang et al. The method was developed from the unsteady continuity and momentum equations for two-phase slug flow by considering the entire film zone as the control volume. Computed results are compared with experimental measurements at different air-mineral oil flow rate combinations. Good agreement is observed for the change of slug body length to slug unit length ratio.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):169-176. doi:10.1115/1.1595111.

During drilling operations, the mud filtrate interacts with the pore fluid around the wellbore and changes pore pressure by capillary and chemical potential effects. Thus the change in pore pressure around borehole becomes time-dependent, particularly in extremely low permeability shaley formations. In this paper, the change in pore pressure due to capillary and chemical potential effects are investigated experimentally. Analytical models are also developed based on the experimental results. A wellbore stability analysis model incorporating the time-dependent change in pore pressure is applied to a vertical well in a shale formation under normal fault stress regime.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):177-182. doi:10.1115/1.1586935.

This investigation is directly relevant to various applications associated with the safety aspects of underbalanced drilling operations where de-oxygenated air may be co-injected with oil-based drilling fluid. However, de-oxygenated air often still contains up to 5% oxygen by volume. This residual oxygen can react with oil during the drilling process, thereby forming potentially hazardous oxidized hydrocarbons and compromising the safety of drilling operations. This article examines the conditions and processes by which oxidation reactions occur and may be helpful in reducing risk in drilling operations. This project characterizes the oxidation behavior of several oils and a typical oil-based drilling fluid at atmospheric and elevated pressures using thermogravimetry (TG) and pressurized differential scanning calorimetry (PDSC). Tests performed on mineral matrix (core) from the oil reservoirs showed no reactivity in both inert and oxidizing atmospheres. In an inert atmosphere, tests on all hydrocarbon samples showed only vaporization, no reactivity. In an oxidizing environment, the tests on hydrocarbons showed several oxidation regions. The presence of core had no effect on the behavior of the hydrocarbons tested in an inert atmosphere but accelerated the higher temperature oxidation reactions of the oil samples. The oil-based drilling fluid exhibited the opposite effect—the presence of core material retarded the oxidation reactions. This is perhaps due to the presence of an oxygen scavenger reacting with oxygen-containing clays present in the mineral matrix. In all tests performed on mixtures of hydrocarbon and core in oxidizing atmospheres, elevated pressures resulted in acceleration of the lower and higher temperature reaction regions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):183-189. doi:10.1115/1.1591203.

A new ground resistance was developed for use in existing vertical bore heat exchanger (VBHEx) design algorithms. The new ground resistance accounts for the added heat transfer mode of convection due to groundwater flow by using as its foundation the solution for a moving line heat source. The combined ground resistance is presented in terms of the dimensionless Fourier and Peclet parameters. Results show that significant convection heat transfer may occur within a variety of hydrogeological regimes, particularly when the Peclet number is larger than 0.01. Since the new model captures the influence of groundwater flow, the resulting ground resistance differs markedly from the conduction-only ground resistance currently used in many vertical borehole heat exchanger design algorithms.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):190-198. doi:10.1115/1.1591204.

Solid/liquid phase change process has received great attention for its capability to obtain high energy storage efficiency. In order to analyze these systems, undergoing a solid/liquid phase change, in many situations the heat transfer process can be considered conduction-dominated. However, in the past years, it has been shown that natural convection in the liquid phase can significantly influence the phase change process in terms of temperature distributions, interface displacement and energy storage. In this paper, a procedure to analyze systems undergoing liquid/solid phase change in presence of natural convection in the liquid phase based on the utilisation of a commercial computer code (FLUENT), has been developed. This procedure is applied to the study of a cylinder cavity heated from above and filled with a phase change material. It was found that when the coupling with the environment, even if small, is considered, natural convection in the liquid phase occurs. The numerical results are then compared with available experimental data. The analysis shows that the agreement between numerical and experimental results is significantly improved when the results are obtained considering the presence of circulation in the liquid phase instead of considering the process only conduction-dominated. Furthermore, some interesting features of the flow field are presented and discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):199-207. doi:10.1115/1.1595670.

In a refinery distillation plant, there are many components of interest to be analyzed thermodynamically, e.g., the crude oil heating furnace, the distillation column and a network of heat exchangers. Previous studies showed that the highest exergy losses occur when there is a heat transfer process especially in the crude oil heating furnace where high quality fuel is used to heat the crude oil, which is a low quality duty, beside the high temperature difference. Therefore, it is proposed in this work to perform distillation in two stages rather than one to reduce heat duty of the heating furnace and thus reducing irreversible losses. In this paper, energy and exergy analyses of a traditional one-stage crude oil distillation unit and a newly proposed two-stage crude oil distillation unit are conducted to study energy and exergy efficiencies of these units and determine the exergy losses. The results are compared for both one- and two-stage distillation units. In this regard, a commercial software package, SimSci/PRO II program is used to carry out both energy and exergy calculations. It is found that the overall exergy efficiencies for single- and two-stage distillation units are 14.0% and 31.5%, respectively. The proposed two-stage distillation unit shows 43.8% decrease in the overall exergy losses and 125% increase in the overall exergy efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):208-220. doi:10.1115/1.1595112.

Residential combined heat and power (CHP) systems using fuel cell technology can provide both electricity and heat and can substantially reduce the energy and environmental impact associated with residential applications. The energy, environmental, and economic characteristics of fuel cell CHP systems are investigated for single-family residential applications. Hourly energy use profiles for electricity and thermal energy are determined for typical residential applications. A mathematical model of a residential fuel cell based CHP system is developed. The CHP system incorporates a fuel cell system to supply electricity and thermal energy, a vapor compression heat pump to provide cooling in the summer and heating in the winter, and a thermal storage tank to help match the available thermal energy to the thermal energy needs. The performance of the system is evaluated for different climates. Results from the study include an evaluation of the major design parameters of the system, load duration curves, an evaluation of the effect of climate on energy use characteristics, an assessment of the reduction in emissions, and a comparison of the life cycle cost of the fuel cell based CHP system to the life cycle costs of conventional residential energy systems. The results suggest that the fuel cell CHP system provides substantial energy and environmental benefits but that the cost of the fuel cell sub-system must be reduced to roughly $500/kWe before the system can be economically justified.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):221-227. doi:10.1115/1.1595110.

A combined power and cooling cycle is being investigated. The cycle is a combination of the Rankine cycle and an absorption refrigeration cycle. Evaluating the efficiency of this cycle is made difficult by the fact that there are two different simultaneous outputs, namely power and refrigeration. An efficiency expression has to appropriately weigh the cooling component in order to allow comparison of this cycle with other cycles. This paper develops several expressions for the first law, second law and exergy efficiency definitions for the combined cycle based on existing definitions in the literature. Some of the developed equations have been recommended for use over others, depending on the comparison being made. Finally, some of these definitions have been applied to the cycle and the performance of the cycle optimized for maximum efficiency. A Generalized Reduced Gradient (GRG) method was used to perform the optimization. The results of these optimizations are presented and discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2003;125(3):228-237. doi:10.1115/1.1577601.

This paper presents the potential for energy savings in various capacity sponge iron plants by estimating heat transfer rates using stabilized and optimized temperature data within the rotary kiln/reactor. Air jet seal instead of mechanical seal arrangements at specific locations in the rotary kiln and cooler are proposed and this is shown to reduce the power consumption and the size of the centralized grease lubricating system. The paper proposes atomized water spray on the post combustion chamber instead of larger droplets to reduce the size of the water handling system, thereby saving energy. The paper also suggests optimization of the performance of a pneumatic coal injector by optimizing coal and air quantities.

Commentary by Dr. Valentin Fuster

TECHNOLOGY OVERVIEW

J. Energy Resour. Technol. 2003;125(3):238-248. doi:10.1115/1.1586306.

Each year, the oil industry generates millions of barrels of wastes that need to be properly managed. For many years, most oil field wastes were disposed of at a significant cost. However, over the past decade, the industry has developed many processes and technologies to minimize the generation of wastes and to more safely and economically dispose of the waste that is generated. Many companies follow a three-tiered waste management approach. First, companies try to minimize waste generation when possible. Next, they try to find ways to reuse or recycle the wastes that are generated. Finally, the wastes that cannot be reused or recycled must be disposed of. Argonne National Laboratory (Argonne) has evaluated the feasibility of various oil field waste management technologies for the U.S. Department of Energy. This paper describes four of the technologies Argonne has reviewed. In the area of waste minimization, the industry has developed synthetic-based drilling muds (SBMs) that have the desired drilling properties of oil-based muds without the accompanying adverse environmental impacts. Use of SBMs avoids significant air pollution from work boats hauling offshore cuttings to shore for disposal and provides more efficient drilling than can be achieved with water-based muds. Downhole oil/water separators have been developed to separate produced water from oil at the bottom of wells. The produced water is directly injected to an underground formation without ever being lifted to the surface, thereby avoiding potential for groundwater or soil contamination. In the area of reuse/recycle, Argonne has worked with Southeastern Louisiana University and industry to develop a process to use treated drill cuttings to restore wetlands in coastal Louisiana. Finally, in an example of treatment and disposal, Argonne has conducted a series of four baseline studies to characterize the use of salt caverns for safe and economic disposal of oil field wastes.

Commentary by Dr. Valentin Fuster

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