A theoretical and experimental study of biomass gasification

The modeling of large-scale gasifiers requires fundamental understanding of gasification of single char particles. In this work, the gasification rate of a singe char particle in an CO2-CO-N2 is investigated by means of (i) construction of a simple numerical model, (ii) material investigation of char and (iii) gasification experiments in a grid reactor. The numerical model indicates the existence of a reaction controlled limit and a diffusion controlled limit. The limiting cases can be discerned experimentally by increasing the partial pressure of nitrogen in the mixture, while keeping the other partial pressures constant. Material investigation of char particles indicates that they can be considered to be non-porous. Preliminary grid reactor experiments indicate that it is possible to test the results of the model experimentally and to verify whether the char is nonporous

Emission spectroscopy of a surface wave sustained N-2-H-2 discharge

An experimental investigation on the degree of molecular dissociation in a surface wave-driven discharge (¿/2p=2.45 GHz) operating in N2–H2 mixture at pressure p=(66.5–266 Pa) is performed by means of optical emission spectroscopy. The dissociation degree of nitrogen molecules [N(4S)]/[N2] increases with the amount of hydrogen (up to 50%) in the mixture in correlation with the increase in electron temperature, when the electron density and the pressure are kept nearly constant. The relative number of hydrogen atoms keeps approximately constant with increasing H2 percentage (between 10% and 50%) in the mixture. The degree of molecular dissociation decreases along the plasma column length following the decrease in the electron density

Modelling NOx-formation for application in a biomass combustion furnace

To optimize the design for biomass combustion furnaces for NOx-emission reduction, numerical models can be used. In these models, the Eddy Dissipation Concept and the PDF-flamelet approach can be applied to describe the interaction between the chemistry and the turbulence. As a first step in comparing these models for a grate furnace, they are tested for a flame from the literature (Sandia Flame D). In the calculations, only the kinetics for methane combustion without N-chemistry are used. The N-chemistry will be added in later stage. The predictions of the models agree qualitatively well with the measurements. Some deviations that are observed are related to the settings of the boundary conditions for the fuel inlet stream. Quantitatively, the two models are quite close, but deviatesignificantly from the measurements. The boundary conditions have to be improved to draw definitive conclusions

Modelling NOx-formation for application in a biomass combustion furnace

To optimize the design for biomass combustion furnaces for NOx-emission reduction, numerical models can be used. In these models, the Eddy Dissipation Concept and the PDF-flamelet approach can be applied to describe the interaction between the chemistry and the turbulence. As a first step in comparing these models for a grate furnace, they are tested for a flame from the literature (Sandia Flame D). In the calculations, only the kinetics for methane combustion without N-chemistry are used. The N-chemistry will be added in later stage. The predictions of the models agree qualitatively well with the measurements. Some deviations that are observed are related to the settings of the boundary conditions for the fuel inlet stream. Quantitatively, the two models are quite close, but deviatesignificantly from the measurements. The boundary conditions have to be improved to draw definitive conclusions

A flamelet-PDF approach for the modeling of combustion, and NOx formation in a biomass grate furnace

A flamelet-PDF approach is used to derive a model for the combustion and NOx formation in a biomass grate furnace. The model reduces the detailed combustion chemistry using the flamelet generated manifoldmethod. The species mass fractions and temperature become functions of the mixture fraction and a reaction progress variable. They are tabulated in look-up tables in a pre-processing step to speed up the numerical calculations. The turbulence-chemistry interaction is described by an assumed shape PDF approach. Transport equations are solved for mean and variance of mixture fraction and progress variable and the mean NO mass fraction. The model is validated by comparing model predictions with measurements for a partially premixed flame: Sandia Flame D. Good agreement between predictions and experimental data is found. The model is also applied to a 2D biomass grate furnace. Preliminary results are presented