During high-temperature combustion of coal, biomass, and municipal waste, ash particles can agglomerate and adhere to the internal surfaces of the plant under high-temperature conditions, resulting in a decrease in operating efficiency. It is known that the presence of small amounts of Na and K in the ash can facilitate adhesion; however, mechanistic details of the process are unclear. In this paper, a synthetic ash strategy consisting of a base material of SiO2 involving controlled additions of simple chemical components is proposed as a novel and convenient way to investigate adhesion. The synthetic ash consisted of SiO2 as the base material, and trace amounts of Na or K were added as target elements to examine their potential role in facilitating the adhesion process. It became clear that small amounts of Na and K increased the propensity for adhesiveness at high temperatures. The effect of the addition of Al2O3 nanoparticles to the synthetic ashes, which was expected to prevent adhesion, was also investigated. Therefore, it was found that the effect of Al2O3 would depend on the elements, which may increase the adhesiveness. It is projected that the present research can contribute to stable operation of many types of combustion plants.

Energy recovery from various fuels with high efficiency is an important objective to realize sustainable energy conversion systems. During the combustion process, ash particles are produced that can form aggregates inside of combustion plants, which inhibit stable and effective plant operation. This is a serious problem for plant operation, and the control of ash particle aggregation under high-temperature conditions is an important objective. In this research, a method to effectively suppress the adhesiveness of particles at high temperatures is proposed based on a synthetic ash strategy. Synthetic ashes were prepared from a base material with sodium (Na) or potassium (K) as target elements to induce adhesiveness. The base material included both silicon (Si) and aluminum (Al). The tensile strengths of powder beds of the prepared synthetic ash with various alkali concentrations were measured at high temperatures, by which it was confirmed that Na could induce higher adhesiveness than K at low alkali concentrations. This difference was ascribed to the presence of Al. The role of Al in particle adhesiveness was clarified by control of the Al concentration through the addition of aluminum oxide (Al 2 O 3 ) nanoparticles, and the ratio of alkali to Al (Na/Al or K/Al) had an effect on particle adhesiveness at high temperatures, that is, the particle adhesiveness could be suppressed by a decrease of these ratios.

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