Oxy-fuel combustion of pulverized coal: Characterization, fundamentals, stabilization and CFD modeling

Localized fluid flow measurements with an He-Ne laser spectrometer

The cycle of nitrogen oxides in the troposphere is discussed from both global and regional perspectives. Global sources for NO(x) are estimated to be of magnitude 50 (+ or - 25) x 10 to the 12th gm N/yr. Nitrogen oxides are derived from combustion of fossil fuels (40 percent) and biomass burning (25 percent) with the balance from lightning and microbial activity in soils. Estimates for the rate of removal of NOx based on recent atmospheric and precipitation chemistry data are consistent with global source strengths derived here. Industrial and agricultural activities provide approximately two thirds of the global source for NOx. In North America, sources from combustion of fossil fuels exceed natural sources by a factor of 3-13. Wet deposition removes about one third of the combustion source of NOx over North America, while dry deposition removes a similar amount. The balance is exported from the continent. Deposition of nitrate in precipitation over eastern Canada and the western Atlantic is clearly influenced by sources of NOx in the eastern United States.

Nitrogen oxides in the troposphere: Global and regional budgets

Modeling of nitrogen oxides formation and destruction in combustion systems

Large-eddy simulation (LES) was used to study mixing of turbulent, coannular jets discharging into a sudden expansion. This geometry resembles that of a coaxial jet-combustor, and the goal of the calculation was to gain some insight into the phenomena leading to lean blow-out (LBO) in such combustion devices. This is a first step in a series of calculations, where the focus is on the fluid dynamical aspects of the mixing process in the combustion chamber. The effects of swirl, chemical reactions and heat release were not taken into account. Mixing of fuel and oxidizer was studied by tracking a passive scalar introduced in the central jet. The dynamic subgrid-scale (DM) model was used to model both the subgrid-scale stresses and the subgrid-scale scalar flux. The Reynolds number was 38000, based on the bulk velocity and diameter of the combustion chamber. Mean velocities and Reynolds stresses are in good agreement with experimental data. Animated results clearly show that intermittent pockets of fuel-rich fluid (from the central jet) are able to cross the annular jet, virtually undiluted, into the recirculation zone. Most of the fuel-rich fluid is, however, entrained into the recirculation zone near the instantaneous reattachment point. Fuel trapped in the recirculation zone is, for the most part, entrained back into the step shear layer close to the base of the burner.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112096002479

Large-eddy simulation of turbulent confined coannular jets

A detailed mathematical model is used to predict local and effluent properties within an axisymmetric, entrained-flow gasifier. Laboratory experiments were conducted to provide local properties for four coal types from a gasifier operating at near-atmospheric pressure. Effects of selected model parameters and test variables were examined and compared with measurements in most cases. The comparison of predictions and measurements provides the first evaluation of capabilities and limitations of a comprehensive model for entrained-flow gasifiers.

Measurement and prediction of entrained-flow gasification processes.

Pulverized-coal combustion research at Brigham Young University

Effect of coal type on entrained gasification

Near-exit measurements of NO, HCN, NH;1 and coal burnout an: reported for a highmoisture,subbituminous pulverized coal fired with air in a laboratory combustor. Test variableswere coal moisture level, stoichiometric ratio and swirl number for the secondary inlet air stream.Data arc also reported for the undried coal wherein gas-char samples were obtained from throughoutthe combustor. Concentrations of major gas species, clcmcn tal composition of the char, gasmixture fraction and N-pollutant concentrations are reported. Effects of coal moisture on burnoutwere negligible and only small decreases in NO levels wereobserved when coal was dried. Resultscan be used for evaluation of predictive models.

Effect of Coal Moisture on Burnout and Nitrogen Oxide Formation

The objective of this study was to determine the mixing characteristics of two-phase, confined, coaxial jets. Gas composition, gas velocity, and particle mass flux radial profiles were obtained at different axial stations using 20% by weight of 6 or 30 μm spherical aluminum particles in the primary stream. Additional tests were conducted without particles. Radial profiles for gas composition, velocity, and particle flux were correlated using the principle of similarity. In the gas phase, mass mixed more rapidly than momentum, and the 6 μm particles mixed less rapidly than mass or momentum. Systems with low primary density and low secondary velocity mixed most rapidly. An implicit numerical model was developed to predict the rate of mixing of the gas/particle mixture. The model included coupled dynamic and thermal nonequilibrium effects between the gas and solid phases. Comparisons of model predictions and experimental results were good.

Paul O. Hedman

Papers

Measurement and prediction of entrained-flow gasification processes.

Pulverized-coal combustion research at Brigham Young University

Effect of coal type on entrained gasification

Effect of Coal Moisture on Burnout and Nitrogen Oxide Formation

Particle‐gas dispersion effects in confined coaxial jets