Investigation of deposits formation in steam superheaters during combustion of halloysite doped biomass

This paper presents the results from the experimental investigation of the impacts of mineral additive halloysite on reducing slag and corrosive deposits formation, commonly found in boilers fired with K-Cl enriched agricultural biomass. The selected three types of agricultural biomass doped with halloysite and one reference coal were fired under different thermal conditions simulated in two pulverized fuel reactors from University of Stuttgart (USTUTT) and Silesian University of Technology (SUT). During the appropriate tests performed at the reactor furnace temperatures ranged between 1200⁰C and 900⁰C, the uncooled and cooled ash deposits and fly ashes were collected to determine their mass, elemental composition and structure (by SEM/EDX analysis) to get better understanding of the additive impacts on deposit formation. Moreover, more fundamental additional tests with different additive/KCl mass ratios were carried out to investigate interactions between halloysite and KCl under varied temperature and residence time conditions. The positive impact of halloysite on the change of deposit structure was confirmed and the halloysite effects on deposit formation rate in a temperature window of 1200^o C-900^o C were discussed in comparison with the results obtained from the pure biomass and coal combustion tests.