Showing papers on "Combustion published in 1994"

Evaluated Kinetic Data for Combustion Modeling: Supplement II

Abstract: This compilation updates and expands a previous evaluation of kinetic data on elementary, homogeneous, gas phase reactions of neutral species involved in combustion systems [J. Phys. Chem. Ref. Data 21, 411 (1992)]. The work has been carried out under the auspices of the European Community Energy Research and Development Program. Data sheets are presented for some 78 reactions and two tables in which preferred rate parameters are presented for reactions of ethyl, i‐propyl, t‐butyl, and allyl radicals are given. Each data sheet sets our relevant thermodynamic data, experimental kinetic data, references, and recommended rate parameters with their error limits. A table summarizing the recommended rate data is also given. The new reactions fall into two categories: first, to expand the previous compilation relating largely to the combustion in air of methane, ethane and aromatic compounds; and second, provide data for some of the key radicals involved in the combustion of higher alkanes.

Catalysis in thermal biomass conversion

Abstract: The potential offered by biomass and solid wastes for solving some of the world's energy problems is widely recognised. The energy in biomass may be realised either by direct use as in combustion, or by upgrading into a more valuable and usable fuel such as fuel gas, fuel oil, transport fuel or higher value products for the chemical industry. This paper is concerned with conversion and upgrading by thermochemical conversion. It briefly describes the technologies of gasification, pyrolysis and liquefaction of biomass with particular reference to the use of catalysts. In addition, the use of catalytic processes in upgrading primary products from thermochemical conversion to higher quality and value fuels and chemicals is included.

The evolution equation for the flame surface density in turbulent premixed combustion

Abstract: One basic effect of turbulence in turbulent premixed combustion is for the fluctuating velocity field to wrinkle the flame and greatly increase its surface area. In the flamelet theory, this effect is described by the flame surface density. An exact evolution equation for the flame surface density, called the Σ-equation, may be written, where basic physical mechanisms like production by hydrodynamic straining and destruction by propagation effects are described explicitly. Direct numerical simulation (DNS) is used in this paper to estimate the different terms appearing in the Σ-equation. The numerical configuration corresponds to three-dimensional premixed flames in isotropic turbulent flow. The simulations are performed for various mixture Lewis numbers in order to modify the strength and nature of the flame-flow coupling. The DNS-based analysis provides much information relevant to flamelet models. In particular, the flame surface density, and the source and sink terms for the flame surface density, are resolved spatially across the turbulent flame brush. The geometry as well as the dynamics of the flame differ quite significantly from one end of the reaction zone to the other. For instance, contrary to the intuitive idea that flame propagation effects merely counteract the wrinkling due to the turbulence, the role of flame propagation is not constant across the turbulent brush and switches from flame surface production at the front to flame surface dissipation at the back. Direct comparisons with flamelet models are also performed. The Bray-Moss-Libby assumption that the flame surface density is proportional to the flamelet crossing frequency, a quantity that can be measured in experiments, is found to be valid. Major uncertainties remain, however, over an appropriate description of the flamelet crossing frequency. In comparison, the coherent flame model of Marble & Broadwell achieves closure at the level of the Σ-equation and provides a more promising physically based description of the flame surface dynamics. Some areas where the model needs improvement are identified.

Horizontal well gravity drainage combustion process for oil recovery

Abstract: An in-situ combustion method is provided for the recovery of viscous oil from an oil-bearing reservoir. A linear array of vertical air injection wells is drilled into the reservoir; the wells are completed in the upper portion of the reservoir. One or more gas production wells are provided, remote from the row of injection wells, said gas production wells also being completed in the upper portion of the reservoir. A horizontal oil production well is completed in the bottom portion of the reservoir, aligned with and positioned in spaced relation beneath the vertical injection wells. The reservoir is prepared for ignition and combustion is initiated at each of the injection wells. A hot fluid-transmissive chamber is formed around each of the injection wells as combustion proceeds. Combustion gas communication is established with the gas production wells. Heated oil and water, produced by the combustion front in each hot chamber, drains under the effect of gravity and is produced from the horizontal production well. The main features of the process are the implementation of gravity drainage to a basal horizontal well in a combustion process and the splitting of liquid and gas production.

Sources of Combustion Irreversibility

Abstract: Approximately 1/3 of the useful energy of the fuel is destroyed during the combustion process used in electrical power generation. This study is an attempt to clarify and categorize the reasons for the exergy destruction taking place in combustion processes. The entropy production is separated into three subprocesses: (1) combined diffusion/fuel oxidation, (2) “internal thermal energy exchange” (heat transfer), and (3) the product constituent mixing process. Four plausible process paths are proposed and analyzed. The analyses are performed for two fuels: hydrogen and methane. The results disclose that the majority (about 3/4) of the exergy destruction occurs during the internal thermal energy exchange. The fuel oxidation, by itself, is relatively efficient, having an exergetic efficiency of typically 94% to 97%.

A Novel Combustor Based on Chemical-Looping Reactions and Its Reaction Kinetics

Abstract: A novel combustor based on controlled chemical-looping reactions without flame differs from the traditional combustor, in which the fuel is in direct contact with air. It allows CO2 to be easily recovered and promises advanced-level thermal efficiency for power generation. Promising results of laboratory experiments with the novel combustor are presented here. We found that NiO particles mixed with YSZ (yttria-stabilized zirconia) have very good properties with respect to oxidation rate, conversion, and physical strength. Especially, the rate of oxidation of Ni particles is increased significantly. The effects of YSZ content in the particle, the reaction temperature, the particle size, and the water vapor concentration were examined by studying the kinetic behavior of reactions. These promising results revealed high potential for applying chemical-looping combustion in a power-generation plant.

Trace gas emissions from biomass burning in tropical Australian savannas

Abstract: During the 1991 and 1992 dry seasons (April to October), we collected and analyzed over 100 samples of smoke from savanna fires at the Kapalga Research Station (12°S, 132°E) in Kakadu National Park, Northern Territory, Australia. Samples collected from the ground and from a light aircraft flying at 50–700 m above the fires were analyzed for CO2, CO, CH4, C2H2, C6H6, CH2O, CH3CHO, NOx (= NO + NO2), NH3, HCN, and CH3CN using gas phase Fourier transform infrared (FTIR) spectroscopy, matrix isolation FTIR spectroscopy, and chemiluminescence techniques. In addition, we made detailed analyses of the mass, carbon, and nitrogen loads of the prefire fuel and the postfire ash residue. Molar emission ratios relative to emitted CO2 and CO, and emission factors relative to the fuel carbon or nitrogen burned were determined for the measured trace gases. Over 96% of the fuel carbon burned was released to the atmosphere, predominantly as CO2 (87±3% of fuel C) and CO (7.8±2.3%). The mean ΔCO/ΔCO2 emission ratio of 9.0±2.6% indicates efficient combustion in these fires of grasses and other light fuels. The main nitrogen-based emissions we measured were NOx (21±8% of fuel N) and NH3 (23±13%). The combined emissions of NOx, NH3, N2O, CH3CN, and HCN accounted for only 51±17% of the fuel N released to the atmosphere during combustion. We use these measurements to estimate the annual emissions of several important trace gases from savanna burning in Australia.

Partially premixed turbulent flame propagation in jet flames

Abstract: Flamelet formulations for premixed and non-premixed combustion are combined in order to treat partiallypremixed combustion in the fast chemistry limit. The flamelet concept for non-premixed combustion is based on the equation for the mixture fraction Z (x, t ), while that for premixed combustion uses a field equation for the scalar field G (x, t ), whose level surfaces G=G 0 represent the flame surface. The laminar burning velocity appearing in this equation is assumed to depend on the local mixture fraction field Z (x, t ) and the scalar dissipation rate χ. The formulation is used to determine flame propagation and liftoff heights in turbulent jet diffusion flames of methane. The analysis is viewed as a first step to resolve the previous controversy about the stabilization mechanism—premixed flame propagation vs diffusion flame quenching—since both effects are found to be important and to influence the liftoff height.

Gas turbine combustor

Abstract: PURPOSE:To reduce a generation amount of NOx by controlling a combustor so as to obtain optimum air-fuel ratio in accordance with an operation condition of a gas turbine. CONSTITUTION:A plurality of fuel nozzles 1a, 1b, 1c and a bypass valve 14 for adjusting an amount of combustion air, supplied to a combustor 1 from an air compressor 3, are provided in the combustor 1. A gas turbine is provided with means 9, 17, 18 for adjusting the amount of combustion air while individually controlling a flow amount of fuel supplied to each fuel nozzle in accordance with an operation condition of the gas turbine with at least its rotational speed N, exhaust gas temperature Tex and a generator output Mw serving as parameters.

Method for removing carbon dioxide from combustion exhaust gas

Abstract: A method for removing carbon dioxide from a combustion exhaust gas under atmospheric pressure by the use of a mixed solution of a specific amine compound X having an alcoholic hydroxyl group and a primary amino group which is bonded to a tertiary carbon atom having two unsubstituted alkyl groups and another amine compound Y being a diaminotoluene (DAT) selected from the group consisting of 2,3-DAT, 2,4-DAT, 2,5-DAT, 2,6-DAT, 3,4-DAT and 3,5-DAT.

An improved liquefied natural gas fueled combined cycle power plant

Abstract: A process and system which improves the capacity and efficiency of a combined cycle power plant. An LNG supply system fuels the combined cycle plant. Gasified LNG in a combustor mixes with the air from the air compressor to provide the hot combustion gas for the gas turbine. The expanding LNG is used to chill a primary heat exchange fuid, e.g. water, which primary heat exchange fluid cools and densifies the intake air for the air compressor. Subsequently, the primary heat exchange fluid is used to condense the spent steam discharged from the steam turbine. The primary heat exchange fluid is then re-chilled and recycled to cool and densify the intake air.

Polymer combustion and flammability—Role of the condensed phase∘

Abstract: The combustion process of polymers is a complex coupling of energy feedback from a flame to thepolymer surface with gasification of the polymer to generate combustible degradation products. Although there are extensive studies of the effects of wind velocity, gas phase oxygen concentration, external thermal radiation, and gravity on the combustion of polymers, the effects of polymer characteristics on combustion and flammability are not nearly as well understood as those in the gas phase. At present, detailed governing equations for continuity, momentum, energy, and chemical species concentration in the gas phase can readily be written with appropriate boundary conditions, and their solutions can be derived for various cases. However, even those governing equations cannot be derived for the condensed phase without understanding of the governing chemical and physical processes that control the gasification of polymers. This paper concentrates on describing various observed phenomena in polymers (which have been often ignored or neglected) during their combustion, some or all of which might have significant effects on the burning rate and flammability properties. Because of a lack of understanding of the basic combustion mechanisms of polymers, theoretical models able to predict combustion phenomena and flammability properties are not available. In order to overcome this problem, global material characteristics are currently measured by well-defined test methods, and the results are used as inputs to fire growth models intended to predict behavior of the materials in specific fire scenarios. To improve the fire performance of polymers, a nonhalogenated char-forming flame-retardant approach is suggested, and its benefits are discussed.

Use of nitrogen from an air separation unit as gas turbine air compressor feed refrigerant to improve power output

Abstract: The present invention is an improvement to a process for the production of work to generate electricity or to drive a mechanical device using a gas turbine. In the process, feed air stream is compressed and combusted with a fuel gas to produce a combustion product. This combustion product is expanded in a gas turbine expander, thereby producing a hot exhaust gas and work. This produced work is used to generate electricity or to drive a mechanical device. The improvement to the process, which increases the work produced by the gas turbine expander, is characterized by cooling nitrogen product, produced by a cryogenic air separation unit to a subambient temperature and combining this subambient cooled, nitrogen product with the feed air stream prior to compression. The improvement of the present invention is particularly suited to the process, wherein at least a portion of the oxygen product produced by the cryogenic air separation unit is reacted with a carbonaceous feedstock in a gasification unit to produce the fuel gas, which is rich in carbon monoxide and hydrogen. The carbonaceous feedstock reacted in the gasifier unit can be coal, petroleum coke, tar sands bitumen, tar sand emulsion, municipal wastes, petroleum residua, waste oil or mixtures thereof.

Molecular combustion motors.

Abstract: We construct a molecular model of an internal combustion engine, by coupling a Brownian ratchet with an exothermic chemical cycle. We derive explicitly the thermodynamically allowed couplings, and show that almost every such coupling will result in motion. We compute from this formalism the maximal transmission efficiency of Brownian gears. Cells have a service infrastructure, just like cities have steam tunnels and subways and trucks delivering food to supermarkets. There are several related aspects to this infrastructure. Various substances have to be shipped from the place where they are produced to the place where they are needed. This involves transporting them both within regions of the cells and across regions [1,2]. Within a region, transport is achieved, for instance, through protein motors which walk on a complex and dynamic set of highways (the cytoskeleton), and can pull along vesicles containing those substances. The motors consume energy-carrying molecules (adenosine triphos-phate or ATP) to walk. These motors are extraordinarily tiny: the motor domain of kinesin is about 12 nm across, about 50 times smaller than the smallest transistor we can manufacture on microchips. Their length scale and energy scale reveal they are essentially Brownian machines, In this Letter, I will try to outline a mathematical framework with which one can describe how a Brownian machine can convert chemical energy into mechanical motion. A little over 30 years ago, Feynman described a Brow-nian motor which has been the basis of many models [3]. A paddle sits in a box with gas at a certain temper* ture and is subject to Brownian fluctuations. The paddle is coupled to a ratchet device which, supposedly, should \"rectify\" these fluctuations to provide motile power. The ratchet sits in a box at some other temperature and can itself random walk. Feynman shows that this contraption obeys precisely the formulas for a Carnot cycle, so it is a Brownian analog of a steam engine. Since then, several models formally related to the Feynrnan ratchet have been applied to microscopic systems. Fox described rotary molecular assemblers [4], Vale and Oosawa tried to use a Feynman ratchet to describe protein motors [5], Oster and co-workers studied polymerization ratchets [6,7], Simon et al. understood protein translocation across membranes [8], and Ajdari and Prost proposed a setup for high performance chromatography by showing that periodically turning a ratchetlike potential on and off will generate transport [9]. Recently I observed that a ratchet can …

A flat flame burner as calibration source for combustion research: Temperatures and species concentrations of premixed H2/air flames

Abstract: A commercially available flat flame burner with a sintered porous bronze disk was used to stabilize premixed H2/air flames at atmospheric pressure. Temperatures for various stoichiometries, flow rates, and heights above the burner disk have been measured by coherent anti‐Stokes Raman scattering with an accuracy of ≊2.5%. The corresponding exhaust gas compositions have been derived from equilibrium calculations. This burner together with the data presented in this article can be used for the verification or calibration of a variety of measuring techniques in combustion research.

Dual fuel ultra-low NOx combustor

Abstract: An ultra-low NOx gas turbine combustor having a dual fuel capability. The combustor has a pre-mixing zone and a downstream combustion zone. The pre-mixing zone has three concentric annular passages that surround a central diffusion-type dual fuel nozzle. A gas fuel manifold distributes gas fuel around the inner and outer passages. A plurality of dual fuel nozzles are disposed in the middle passage to distribute either gas or oil fuel around the middle passage. The distribution of fuel around the passages allows the formation of lean fuel/air ratios, thereby lowering NOx formation. In addition, swirl vanes are arrayed around the inner and outer passages and around each of the fuel nozzles. A step increase in the flow area in going from the pre-mixing zone to the combustion zone creates vortices that tend to anchor the flame.