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Article

J. Energy Resour. Technol. 2001;123(1):1. doi:10.1115/1.1355245.
Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS

J. Energy Resour. Technol. 2000;123(1):4-9. doi:10.1115/1.1348270.

The U.S. Department of Energy is partnering with industry to develop advanced coal-fired electric power plants that are substantially cleaner, more efficient, and less costly than current plants. Low-emission boiler systems (LEBS) and high-performance power systems (HIPPS) are based, respectively, on the direct firing of pulverized coal and the indirectly fired combined cycle. LEBS uses a low-NOx slagging combustion system that has been shown in pilot-scale tests to emit less than 86 g/GJ (0.2 lb/106 Btu) of NOx. Additional NOx removal is provided by a moving bed copper oxide flue gas cleanup system, which also removes 97–99 percent of sulfur oxides. Stack levels of NOx can be reduced to below 9 g/GJ (0.02 lb/106 Btu). Construction of an 80 MWe LEBS proof-of-concept plant is scheduled to begin in the spring of 1999. Engineering development of two different HIPPS configurations is continuing. Recent tests of a radiant air heater, a key component of HIPPS, have indicated the soundness of the design for air temperatures to 1150°C. LEBS and HIPPS applications include both new power plants and repowering/upgrading existing plants.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):10-14. doi:10.1115/1.1345891.

It is important and necessary to develop a new technology for CO2 capture with less or even no energy penalty to make a breakthrough in greenhouse gas abatement. Towards this objective, we have proposed a novel gas turbine power plant, which is not only to capture CO2 in the stage of combustion, but also to increase thermal efficiency of the power plant. The chemical-looping combustor in the proposed system consists of a fuel reactor (fuel reacts with metal oxide) and an air reactor (the resulting metal reacts with oxygen in air). This new system requires no additional energy consumption for CO2 separation (i.e., no energy penalty) and no CO2 separation equipment. Here, we have identified several breakthrough points in the proposed system and summarized promising results from experimental investigation on the chemical-looping combustion.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):15-20. doi:10.1115/1.1345732.

A LCA (life cycle assessment) scheme for any industrial activity system is introduced to estimate the quantitative load on the environment with the aid of the NETS (numerical environment total standard) method proposed by the authors as a numerical measure. Two kinds of environmental loads respecting fossil fuel depletion as input resources to the system and global warming due to CO2 emission as output are taken into account in the present eco-criterion, in which the total eco-load (EcL) value is calculated from the summation of respective environmental load factors on the whole process in a life cycle of the system. This NETS method is applied to eco-management co-generation systems, in which a computer-aided output navigator proceeds the LCA estimation with ICON and Q&A communication. An operation scheme most friendly to the environment with a minimum EcL value, i.e., an eco-operation scheme, is derived from the optimization theory.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):21-26. doi:10.1115/1.1345701.

Measurements of CO2 gasification kinetics of coal chars at temperatures of 1273–1873 K were conducted by using a bench-scale fluidized bed reactor (FBR) made of alumina. The gasification rates of chars carbonized under both rapid heating and slow heating conditions were measured using a high-volatile bituminous coal and a medium-volatile bituminous coal. The significant difference in reactivity between rapid heating chars and slow heating chars, and the decrease of char reactivity at high temperature were discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):27-31. doi:10.1115/1.1347988.

A biocoalbriquette, a new artificial solid fuel, is manufactured by a mixture of coal and biomass under a high-compression pressure. The combustion characteristics of biocoalbriquettes were investigated in this study experimentally and numerically. The combustion process of biocoalbriquettes appears in two stages: the volatile combustion stage followed by the char combustion stage. It was found that the volatile combustion happens over the whole pellet of biocoalbriquette, whereas the char combustion proceeds in a shrinking-core mode. A volume model and a shrinking-core reaction model were introduced and modified here to simulate the two stages of combustion process. The simulation results are found to be consistent with the experimental results.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):32-38. doi:10.1115/1.1347989.

Pyrolysis and ignition characteristics of pulverized coals were examined under similar burning conditions to those of industrial burners. In the early stage, fine particles (less than 37 μm) were mainly pyrolyzed by convective heat transfer from surrounding gas. The coals ignited when pyrolyzed volatile matter mixed with surrounding air and formed a combustible mixture. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. The effects of radiant heat transfer were strong for intermediate-size particles (37–74 μm). Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. The calculated results agreed with experimental ones obtained from both laboratory-scale and semi-industrial-scale burners.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):39-43. doi:10.1115/1.1345523.

This paper describes some of the recent work carried out in our laboratory regarding the effects of novel nitrogen compounds in gasoline and diesel fuel on ignition quality and on pollutant emissions. Emphasis is given in studying chemical structures that can be derived from biomass (renewable raw materials). Our approach was to investigate chemical structures that can be derived from biomass, by studying the performance of possible gasoline and diesel extenders as gaged by ignition quality, and also by testing their effectiveness in reducing exhaust emissions under various operating conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):44-49. doi:10.1115/1.1345893.

Fundamental characteristics of the catalytic combustion of vaporized kerosene spray were experimentally investigated. This study is a part of the development of a ceramic gas turbine engine for automobiles. Kerosene was used as a test fuel and its spray was injected from a swirl atomizer into a hot air stream. The inlet air temperature was elevated up to 900 K to vaporize the kerosene spray. Premixed gas of air and kerosene vapor was introduced into the catalyst. The total equivalence ratio was controlled from ϕ=0.18–0.32. The palladium catalyst was supported on a cordierite honeycomb monolith. Catalytic combustion phenomena were categorized in three typical states: (a) state of partial reaction in the catalytic monolith, (b) state of homogeneous reaction in the monolith, (c) state of homogeneous reaction with a blue flame supposed on the monolith. A parabolic shape blue flame in the state of (c) appeared downstream of the monolith. This flame was very stable and its temperature was relatively low compared with conventional premixed flames of hydrocarbon fuel because the equivalence ratio was much lower than those of premixed flames. The distance from the monolith to the ignition point of this flame became short with a rise of the inlet air temperature, even if the volumetric airflow rate increased with the air temperature. Spontaneous emission spectra of radiation from the blue flame were measured. Strong spectral peaks of OH, CH, and CO+ radicals were observed in the spectra. This spectral structure was quite different from that of a blue flame of premixed propane.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):50-58. doi:10.1115/1.1345731.

Stabilization of the combustion of natural gas in high-temperature processes by using the auto-ignition of the fuel when mixed with highly preheated air is well known and has found application on many occasions. Reasonably strong internal flue gas recirculation not only reduces nitric oxides emissions and increases convective heat transfer rates, but reduces local flame temperatures such that the flames become almost invisible for a human eye. This combustion regime is called flameless oxidation. Gasunie’s interest in this technique of flameless oxidation has two aspects. First, it must be clear which geometrical restrictions and flow conditions/disturbances in the oven or furnace have to be taken into account. Secondly, the use of this principle requires the auto-ignition of the fuel. This raises the question as to the stability of the combustion at or near the limits for auto-ignition. The study which is presented here reports on the stability of the oxidation process at these limiting conditions. These conditions are minimum load to the combustion system and minimum temperature in a combustion chamber. The stability has been determined using some “burner”/furnace combinations in which the distance between nozzles for air and natural gas have been varied.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):59-63. doi:10.1115/1.1348015.

Planar imaging of laser-induced fluorescence of CH radical is made to examine combustion processes in a valveless pulse combustor. An excimer-pumped dye laser tuned to a wavelength of 387 nm is used to excite the R1(N=6) line of (0,0) band of the B2Σ−X2Π system of CH radical, and an image-intensified CCD camera system is used to detect the (0,1) band emission at around 435 nm. According to the CH-LIF images, it is found that the progress in combustion during a pulsation period is expressed by the enlargement and breakup of the earlobe-shaped flame front along the outline of a pair of large-scale eddies of fresh mixture.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):64-69. doi:10.1115/1.1347990.

This paper describes high-temperature reliability, particularly creep and creep rupture behavior of three engineering ceramics—silicon nitride, silicon carbide, and alumina-based silicon-carbide-particulate ceramics—which are considered the most potential candidates for the use of blades of high-efficiency ceramic gas turbine. The structural reliability of silicon nitride is very often limited due to the softening of glassy phases formed at grain boundaries. On the other hand, silicon carbide, which generally does not contain glassy phase at the grain boundaries, shows excellent creep resistance even at very high temperatures. Finally, it is shown that creep resistance of alumina can be markedly improved by dispersing nano-sized silicon carbide particles into the grain boundary.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):70-75. doi:10.1115/1.1345892.

Relevant to the self-propagating high-temperature synthesis (SHS) process, an analytical study has been made to investigate dependence of its flame initiation on system parameters, such as operating and physicochemical parameters, in order to obtain ignition energy. Use has been made of the heterogeneous theory which can satisfactorily account for the premixed mode of the bulk flame propagation supported by the nonpremixed mode of particle consumption. It is found that the ignition energy strongly depends on not only heat loss, but also particle size of the higher melting-point metal, which has not been captured in the homogeneous theory.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):76-80. doi:10.1115/1.1346681.

A process has been developed to detoxify the waste magnesia-chromia bricks containing sexivalent chromium and recover valuable materials with arc plasma treatment. Especially magnesium and chromium, which are the major compounds of the waste bricks, could be separately recovered by carbothermic reduction with addition of iron. From the viewpoint of environmental protection and saving resources, such recovery processes are expected to be commercialized.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):81-91. doi:10.1115/1.1348336.

A computational model of a power plant steam condenser which incorporates the effects of air in-leakage and removal on the performance of the condenser is reported. The condenser interior space is modeled as a porous medium. A quasi-three-dimensional approach is taken in which the steady-state steady-flow conservation equations for the steam-air mixture mass, momentum, thermal energy, and air mass fraction are solved for a series of two-dimensional grids perpendicular to the circulating water flow direction. The air removal system is explicitly modeled. The computational model is used to calculate the performance of the steam condenser of a 750-MWe unit at 100 percent load. Some of the calculated variables are compared with measurements obtained in the condenser. The effects of changing various operating parameters on the condenser performance at 100 percent load are also studied.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2000;123(1):92-99. doi:10.1115/1.1349117.

The capacity control of a vapor-compression refrigeration system is investigated for three different capacity control schemes. In a hot-gas by-pass control scheme, the refrigerant is by-passed from the compressor and injected back into the suction line to decrease the cooling capacity, whereas in cylinder-unloading scheme, one or more cylinders are unloaded to decrease the refrigerant mass flow rate in the system, which decreases the cooling capacity. However, in suction gas throttling, the suction gas throttled at the inlet of the compressor, decreases the refrigerant mass flow rate, and hence a corresponding decrease in the system capacity. These schemes are investigated for HFC-134a by considering finite size of the components that are used in the refrigeration systems. The models consider the finite-temperature difference in the heat exchangers, thus allowing the variations in the condenser and evaporator temperatures with respect to capacity and external fluid inlet temperatures. A comparative study is performed among these schemes in terms of the system coefficient of performance (COP), the operating temperatures, and percentage of refrigerant mass fraction as a function of the percentage of full-load system capacity.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEF

J. Energy Resour. Technol. 2000;123(1):100-103. doi:10.1115/1.1348271.

This study experimentally investigates the effect of circuitry on the refrigerant-side pressure drops of plate finned tube evaporators. Experiments were performed with countercross, parallel-cross, and z-shape arrangements. The results showed that the parallel-cross-flow circuit gives a lower pressure drop than other arrangements. Generally, the refrigerant-side pressure drops increase with air frontal velocities. However, for G=200 kg/m2⋅s and parallel flow, the pressure drops decrease with increase of air frontal velocity. This unusual characteristic is most likely related to the flow pattern transition when subjected to heat addition.

Commentary by Dr. Valentin Fuster

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