Characterization of mineral matter particles in gasification and combustion processes. (15th July 2015) - Thiel, Christopher
Highlights: Method to collect particle samples from combustion and gasification processes. Characterization of mineral matter particles depending on process conditions. Information on the deposition probability of mineral matter particles. Information on the precipitation of volatile mineral matter species. Abstract: Slagging and fouling mechanisms in high temperature solid fuel conversion processes are usually related to the presence of mineral components in the fuel. These mineral components can be extraneous particles or organically bound to the fuel. Both types will be released during the combustion or gasification process. The released mineral particles are diverse and can undergo certain transformation mechanisms along the flue gas path. Common fuel investigation methods rely on bulk ash analysis and other methods that do not take into account the process parameters. It is difficult to predict the deposition and also corrosion behavior of a certain fuel with these laboratory methods alone. An approach with more information about the actual particle situation and where the actual process parameters can be reproduced would be preferable. One way to make the released mineral particles visible, depending on temperature and concentration, is the so called Particle-Wire-Mesh method. Flue gas is extracted from the process through a wire-mesh formed by twilled Dutch weave. The twilled Dutch weave serves as a filter, i.e. particles that are contained in the flue gas will deposit in the pockets or on the wires of the weave. This weave also serves as the sample holder for SEM and EDS analyses. With these analyses the particles can be made visible in the same form as they are extracted from the process. The particles can then be characterized in terms of size, shape, and elemental composition. Size and shape give information about whether the particle has possibly been fused during the combustion process (spherical particles) or not (regularly shaped particles with sharp edges). The location where a particle is found on the wire-mesh can typically be either the wire itself or the pocket. It indicates whether the particle has a probability to stick on furnace walls and heat exchanger surfaces and form a deposit. In order to be found on the wires a particle has to have a sticky surface or impact at a surface that is sticky itself. Particles that are found in the pockets are not sticky. The Particle-Wire-Mesh method of collecting particle samples gives the opportunity to characterize a certain fuel toward the behavior of its mineral content. The metal weave makes it possible to differentiate between single particles. Together with extracting particle samples at different locations in the process, to get the influence of different temperatures, this results in a detailed image of the different species contained in the mineral matter of the fuel.