Controlling particle adhesion of synthetic and sewage sludge ashes in high temperature combustion using metal oxide nanoparticles

Role of Al-Based Additives in Controlling Ash Adhesion

“…In particular, we have previously found that increasing the porosity effectively decreases the tensile strength at high temperatures. [20][21][22]26,27 In the present study, controlling adhesion via both chemical reaction and controlling porosity was expected. In the following sections, we analyze the causes of this phenomenon and investigate the mechanisms underlying the reduction in powder-bed strength in detail.…”

“…To reduce the adhesion of ash, which has a complex and variable composition, selecting an appropriate chemical additive that is both chemically effective and has a physical effect that is independent of its chemical composition is critical. 22 In a previous study, 21 we achieved a suitable physical effect by incorporating nanoparticles into ash; the nanoparticles efficiently inhibited adhesion by increasing the porosity. However, nanoparticles are expensive, and economic efficiency is imperative for large-scale plant use.…”

“…However, nanoparticles are expensive, and economic efficiency is imperative for large-scale plant use. Previous studies − have suggested that Al 2 O 3 is effective in inhibiting the adhesion of alkali-metal derivatives.…”

“…Therefore, we have established a method based on physical effects. ,, Here, a “physical effect” refers to a reduction of the adhesion points between particles and to the total adhesion force as a result of increasing the porosity between ash particles. To reduce the adhesion of ash, which has a complex and variable composition, selecting an appropriate chemical additive that is both chemically effective and has a physical effect that is independent of its chemical composition is critical . In a previous study, we achieved a suitable physical effect by incorporating nanoparticles into ash; the nanoparticles efficiently inhibited adhesion by increasing the porosity.…”

“…Alkali metals in ash can react with SiO 2 and Al 2 O 3 , which are the main components of ash and bed materials in a fluidized bed furnace. , As a result, compounds with a melting point lower than those of SiO 2 and Al 2 O 3 form and subsequently melt at the operating temperatures. These compounds form “liquid bridges” between ash particles and act as adhesives, thereby inducing adhesion. ,− Techniques to suppress this adhesion include using additives to alter the composition of the ash and increase its melting point through chemical effects. , Numerous additives have been developed for this purpose. ,− In previous reports, , we demonstrated the chemical efficacy of Al on the suppression of particle adhesion induced by alkali metals such as Na and K using coal ash and synthetic ashes containing alkali metals. Particle adhesion was quantified as the tensile strength of the powder bed using a previously developed device to measure the strength .…”