One problem in coal gasification
is the release of alkali species,
which can cause fouling and corrosion. Depending on their composition,
slags have a high potential for alkali retention. Therefore, the vapor
pressures of alkali species (Na, K) over four real solidified gasifier
slag samples were determined over the temperature range 1134 to 1591
K by Knudsen effusion mass spectrometry (KEMS). In addition, the residues
from the KEMS investigations were studied by X-ray diffraction (XRD)
and scanning electron microscope/energy dispersive X-ray (SEM/EDX)
to determine the phase composition of the samples and map the alkali
distribution. A strong correlation between the composition of the
slags in terms of amount of acidic oxides (SiO2, Al2O3) and basic oxides (CaO, FeO) and the volatility
was determined. The volatility results showed that higher acidic oxide
content leads to higher alkali retention capability. The XRD and SEM/EDX
analysis of the KEMS residues showed that an anorthite type phase
contains more Na than all the other phases in the equilibrium.
A compact version of a gasifier realised by integrating the fluidised bed steam gasification of biomass and the hot gas cleaning and conditioning system into one reactor vessel was the aim of the 'UNIQUE' project. Hot gas filtration systems are designed to protect the gas turbine or fuel cell from erosion and particle contamination, clean the process gases for production of synthetic fuels and indirectly improve efficiency and decrease maintenance. Knowledge of critical points of the porous ceramic filter elements is essential for the successful operation of the hot gas filtration. The corrosion behaviour of ceramic filter materials in contact with different biomass ashes under simulated gasification conditions was investigated for aluminium oxide, based SiC with mullite filter layer and mullite based filter candles. Analyses by energy dispersive X-ray spectroscopy show the influence of potassium on filter candle materials.
This
work focused on the release of alkali metals (K and Na) and non-metals
(S, Cl, and P) during high-temperature gasification of dried distillers
grains with solubles. The release experiments were performed at 600–1400
°C in a flow channel reactor. Hot-gas analysis was performed
by a molecular beam mass spectrometer. The underlying release mechanisms
are discussed with dependence upon the temperature.
Alkali release and behaviour of coal slags are among the main problems in the high temperature coal conversion processes. Therefore, the thermodynamic properties of slags and the related synthetic oxide systems are important. This article gives several examples of vaporisation investigations on coal slags and synthetic oxide systems by KEMS performed in our lab in the recent years.
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