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### Research Papers: Combustion of Waste/Fluidized Bed

J. Energy Resour. Technol. 2008;130(2):021401-021401-4. doi:10.1115/1.2906118.

Samples from four different parts of the peat deposits in the Yeniçağa (Bolu, Turkey) region were pyrolyzed in a fix-bed pipe type furnace at a heating rate of $2°C∕min$ and at a temperature of $600°C$. The analyses for the structure of the liquid products obtained were performed by elemental analysis, $H1-NMR$ spectroscopy and Fourier transform infrared spectroscopy. The structure of the solid products was determined by proximate and ultimate analyses, while the composition of gas products was found by gas chromatography.

Commentary by Dr. Valentin Fuster

### Research Papers: Environmental Aspect of Energy Sources

J. Energy Resour. Technol. 2008;130(2):022101-022101-10. doi:10.1115/1.2906112.

Exploration and production (E&P) waste generated by the petroleum industry in Croatia from two central oilfield pits (COPs) was investigated in order to (1) examine materials for waste treatment that can preferentially sorb organic contaminants and, in that way, improve the process of stabilization/solidification (S/S), and (2) find field-acceptable methods to reduce the amount of waste to be treated with S/S or some other method. Composite samples from COP Vinkovci were treated in the laboratory with different materials or with combinations of several materials: (a) Cement, (b) organophilic clay, (c) calcined moler clay, (d) $lime+organophilic$$clay+bentonite$, (e) $cement+organophilic$$clay+bentonite$, (f) $lime+calcined$ moler clay, and (g) $cement+calcined$ moler clay. A sample of E&P waste treated with lime was used for comparison of results. The most successful treatment for the majority of inorganic and organic pollutants was treatment with organophilic clay. Samples treated with organophilic clay release 63 times less total oils, 67 times less mineral oils, 798 times less naphthalene, and 136 times less lead to distilled water than the sample treated with lime. The next most successful material is calcined moler clay. The results clearly show that reduction in hydrocarbon content using some of the field-acceptable methods and detailed chemical analysis of remaining organic and inorganic pollutants must be implemented before selecting the most appropriate method for treatment of technological waste in petroleum industry. A composite sample from COP Žutica was treated in the laboratory using a four-step procedure involving boiling water, condensate, and organophilic clay. Organophilic clay was used because of its ability to sorb hydrophobic pollutants. In the leachate of an E&P waste sample, the lowest values for the majority of inorganic and organic pollutants were observed following the fourth step (treatment with organophilic clay). This is also manifested in the lowest indicator of total discharge (ITD%) values for the fourth treatment step. Considering the concentrations of analyzed parameters in leachates and their ITD% values, the biggest effect for the majority of inorganic and organic pollutants was achieved between the first and the second treatment step. This suggests that treatment with boiling water is the most effective treatment for the majority of inorganic and organic pollutants. Concentrations of benzene, ethylbenzene, toluene, and xylene (BETX) in distilled-water leachate generally increase after each succeeding treatment step. This shows that BETX is added to the E&P waste through condensate addition in the third treatment step.

Commentary by Dr. Valentin Fuster

### Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2008;130(2):022201-022201-7. doi:10.1115/1.2906123.

Intense energy security debates amidst the ever increasing demand for energy in the US have provided sufficient impetus to investigate alternative and sustainable energy sources to the current fossil fuel economy. This paper presents the advanced (injection) low pilot ignition natural gas (ALPING) engine as a viable, efficient, and low emission alternative to conventional diesel engines, and discusses further efficiency improvements to the base ALPING engine using organic rankine cycles (ORC) as bottoming cycles. The ALPING engine uses advance injection ($50–60deg$ BTDC) of very small diesel pilots in the compression stroke to compression ignite a premixed natural gas-air mixture. It is believed that the advanced injection of the higher cetane diesel fuel leads to longer in-cylinder residence times for the diesel droplets, thereby resulting in distributed ignition at multiple spatial locations, followed by lean combustion of the higher octane natural gas fuel via localized flame propagation. The multiple ignition centers result in faster combustion rates and higher fuel conversion efficiencies. The lean combustion of natural gas leads to reduction in local temperatures that result in reduced oxides of nitrogen $(NOx)$ emissions, since $NOx$ emissions scale with local temperatures. In addition, the lean premixed combustion of natural gas is expected to produce very little particulate matter emissions (not measured). Representative base line ALPING ($60deg$ BTDC pilot injection timing) (without the ORC) half load ($1700rpm$, $21kW$) operation efficiencies reported in this study are about 35% while the corresponding $NOx$ emission is about $0.02g∕kWh$, which is much lower than EPA 2007 Tier 4 Bin 5 heavy-duty diesel engine statutes of $0.2g∕kWh$. Furthermore, the possibility of improving fuel conversion efficiency at half load operation with ORCs using “dry fluids” is discussed. Dry organic fluids, due to their lower critical points, make excellent choices for waste heat recovery Rankine cycles. Moreover, previous studies indicate that dry fluids are more preferable compared to wet fluids because the need to superheat the fluid to extract work from the turbine is eliminated. The calculations show that ORC—turbocompounding results in fuel conversion efficiency improvements of the order of 10% while maintaining the essential low $NOx$ characteristics of ALPING combustion.

Commentary by Dr. Valentin Fuster

### Research Papers: Heat Energy Generation/Storage/Transfer

J. Energy Resour. Technol. 2008;130(2):022401-022401-11. doi:10.1115/1.2906034.

A thermodynamic performance analysis was performed on a novel cooling and power cycle that combines a semiclosed gas turbine called the high-pressure regenerative turbine engine (HPRTE) with an absorption refrigeration unit. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration cycle, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration depending on ambient conditions. Two cases were considered: a small engine with a nominal power output of $100kW$ and a large engine with a nominal power output of $40MW$. The cycle was modeled using traditional one-dimensional steady-state thermodynamics, with state-of-the-art polytropic efficiencies and pressure drops for the turbomachinery and heat exchangers, and curve fits for properties of the LiBr-water mixture and the combustion products. The small engine was shown to operate with a thermal efficiency approaching 43% while producing 50% as much $5°C$ refrigeration as its nominal power output (roughly $50tons$) at $30°C$ ambient conditions. The large engine was shown to operate with a thermal efficiency approaching 62% while producing 25% as much $5°C$ refrigeration as its nominal power output (roughly $20,000tons$) at $30°C$ ambient conditions. Thermal efficiency stayed relatively constant with respect to ambient temperature for both the large and small engines. It decreased by only 3–4% as the ambient temperature was increased from $10°Cto35°C$ in each case. The amount of external refrigeration produced by the engine sharply decreased in both engines at around $35°C$, eventually reaching zero at roughly $45°C$ in each case for $5°C$ refrigeration. However, the evaporator temperature could be raised to $10°C$ (or higher) to produce external refrigeration in ambient temperatures as high as $50°C$.

Commentary by Dr. Valentin Fuster

### Research Papers: Geothermal Energy

J. Energy Resour. Technol. 2008;130(2):022301-022301-11. doi:10.1115/1.2906108.

The purpose of this study is to investigate how the heat exchanger inventory allocation plays a role in maximizing the thermal performance of a two-stage refrigeration system with two evaporators. First, the system is modeled as a Carnot refrigerator and a particular heat transfer parameter is kept constant as the heat exchanger allocation parameter is allowed to vary. The value of the heat exchanger allocation parameter corresponding to the maximum coefficient of performance (COP) is noted. The results are compared to those of a non-Carnot refrigerator with isentropic and nonisentropic compression. It is found that the Carnot refrigerator can be used to predict the value of the heat exchanger allocation parameter where the maximum COP occurs for a non-Carnot refrigerator. In order to improve the accuracy of that prediction, the predicted value of the heat exchanger allocation parameter has to be inputted into the set of equations used for the non-Carnot refrigerator. This study is useful in designing a low-cost, high-performance refrigeration system.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2008;130(2):022302-022302-7. doi:10.1115/1.2932945.

This study deals with a monitoring and assessment of energetic and exergetic analysis of Salihli Geothermal District Heating System (SGDHS) in Manisa, Turkey. In the analysis, actual system yearly average data of latest heating season are used to assess the district heating system exergetic performance. New exergetic model is improved and compared with old exergetic model results throughout the SGDHS. The new exergy losses occur particularly due to the fluid flow, taking place in the reinjection of thermal water (e.g., geothermal fluid), pumps, and the heat exchanger, as well as the natural direct discharge of the system.

Commentary by Dr. Valentin Fuster

### Research Papers: Petroleum Transport/Pipelines/Multiphase Flow

J. Energy Resour. Technol. 2008;130(2):023001-023001-10. doi:10.1115/1.2824284.

Erosion damage in the pipe wall due to solid particle impact can cause severe problems in fluid handling industries. Repeated impact of the suspended small solid particles to the inner wall of process equipment and piping removes material from the metal surface. The reduced wall thickness of high pressure equipment and piping can no longer withstand the operating pressure that they were originally designed for and may cause premature failure of the system components. This results in production downtime, safety, and environmental hazards with significant loss to the industry and economy. Prediction of erosion in single-phase flow with sand is a difficult problem due to the effect of different parameters and their interactions that cause erosion. The complexity of the problem increases significantly in multiphase flow where the spatial distribution of the liquid and gas phases and their corresponding velocities change continuously. Most of the currently available erosion prediction models are developed for single-phase flow using empirical data with limited accuracy. A mechanistic model has been developed for predicting erosion in elbows in annular multiphase flow (gas-liquid-solid) considering the effects of particle velocities in gas and liquid phases of the flow. Local fluid phase velocities in multiphase flow are used to calculate erosion rates. The effects of erosion due to impacts of solid particles entrained in the liquid and gas phases are computed separately to determine the total erosion rate. Erosion experiments were conducted to evaluate the model predictions. Comparing the model predicted erosion rates with experimental erosion data showed reasonably good agreement validating the model.

Commentary by Dr. Valentin Fuster

### Research Papers: Hydrogen Energy

J. Energy Resour. Technol. 2008;130(2):022601-022601-10. doi:10.1115/1.2906114.

A one-dimensional transient model of a tubular solid oxide fuel cell stack is proposed in this paper. The model developed in the virtual test bed (VTB ) computational environment is capable of dynamic system simulation. This model is based on the electrochemical and thermal modeling, accounting for the voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. The temperature, the current density, and the gas concentration distribution along the axial direction of the cell are presented. The dynamic behavior of electrical characteristics and temperature under the variable load is simulated and analyzed. For easy implementation in the VTB platform, the nonlinear governing equations are discretized in resistive companion form. The developed model is validated with experimental results and can be used for dynamic performance evaluation and design optimization of the cell under variable operating conditions and geometric condition.

Commentary by Dr. Valentin Fuster