Abstract
The paper presents results of investigations on KCl interaction with halloysite under high temperature conditions. Halloysite is an aluminosilicate that can be used as a fuel additive to prevent chlorine corrosion and formation of low melting corrosive deposits during combustion of biomass. It is claimed that an increase of the emission of gaseous chlorine as HCl(g) and decrease of chlorine share in the ash as result of KCl and halloysite interaction should be expected. During presented tests the mixtures of KCl and halloysite with different ratios were thermally decomposed in a muffle furnace at high temperatures of 900°C and 1100°C. Then, the analyses of potassium and chlorine contents in the formed solid residues were determined. Besides, it has been proved that halloysite addition changes the ash deposit structure as well as increases the ash fusion temperatures. This was supported by performing phase equilibrium calculations for the investigated different halloysite/KCl mixtures. The positive effects of halloysite on potassium capture while reducing chlorine content in solid residue to prevent formation of corrosive deposits have been confirmed.
Highlights
Biomass is considered to be a “difficult” fuel due to its physical and chemical properties
Analyzing the impact of KCl on slag formation of halloysite, an increase of halloysite/KCl ratio led to shifting the maximum slag levels to higher temperatures, which corresponds to the measured ash flow temperatures of investigated halloysite/KCl mixtures
Based on the carried out phase equilibrium calculations, it could be observed that for the ratio of halloysite/KCl=20, the KCl was completely removed from the system, resulting in formation of KAlSi3O8(s) and HCl(g), and increasing slightly the slag % in temperature range of 900oC -1200oC, whilst shifting the complete ash melting to the higher temperature far above 1500oC
Summary
Biomass is considered to be a “difficult” fuel due to its physical and chemical properties. The increased presence of alkali salts in biomass may lead to formation of low melting alkali chloride deposits which can significantly increase corrosion rates of boiler heat exchange surfaces, The interaction of alkali elements with aluminosilicates, quartz may decrease (for low (Al2O3+SiO2)/K2O ratios) the melting temperature of ash particles and cause increased slagging and fouling. In order to prevent chlorine inducted corrosion and ash deposition in biomass-fired boilers selected fuel additives can be used. In general they can be classified in two groups [2,3,6]: a) Additives which influence gas K-S-Cl chemistry and aerosols formation. The results obtained will provide better knowledge on halloysite behavior under high temperature conditions and will help to optimize additive dosage when utilizing high chlorine content agricultural biomass
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