Gas–particle equilibrium of alkali metal compounds studied in an aerosol test reactor
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Alkalimetalliyhdisteiden kaasu–hiukkastasapainon tutkiminen aerosolitestireaktorissa
The research topic of this thesis is inorganic gases from combustion that form particles via gas-to-particle conversion. The particles formed in gas-to-particle conversion have an effect on fouling of the super heaters and corrosion in boilers. These are the main reasons for unscheduled shutdowns and tube failure. Aerosol particlesformed from inorganic gases are challenging to study in boiler conditions. To be able to measure the particles formed via gas-to-particle conversion, the related processes need to be isolated from the boiler to a smaller and easily controllable environment. The experiments of this thesis were conducted in laboratory environment. The most important facilities used were high-temperature chambers, particle sampling and particle instruments. The ﬁrst high-temperature chamber is used for the vaporization of the reactants, and the latter is used to achieve the gas-to-particle equilibrium. Water solution of solid reactants is fed to the chamber in order to control the amount of reactants. In addition, different gases are fed to the chamber. The reactants used in this thesis were selected from black liquor recovery boiler process. Black liquor composition is highly affected by the quality of the wood used in pulping, and that is why the reactant concentrations should be controllable. Black liquor consists mainly of sodium and sulphur but also of chloride from the wood. The chloride has been observed to be problematic since it causes corrosion in recovery boilers. A sample was taken from the second high-temperature chamber by diluting it in three steps before the particle measurement equipment. The measurement results show two mode particle size distributions. Results indicate that one of the mode is formed in high-temperature conditions and the other in the dilution. It was discovered that alkali sulphate formation is the key component of the particle formation in the second high-temperature chamber. Indirect references of alkali chloride formation are observed by studying the nucleation mode. The nucleation mode particle number is decreased when temperature of the second high-temperature chamber is lowered because more alkali chloride compounds is transferred to the particle phase already in high temperature conditions.