Mechanistic Determination of the Role of Aluminum in Particle Adhesiveness at High Temperatures Induced by Sodium and Potassium Using a Synthetic Ash Strategy

Abstract

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.

Role of Phosphorus and Iron in Particle Adhesiveness at High Temperatures Using Synthetic Ashes

“…A device to evaluate the adhesiveness of particles at high temperatures was developed previously and could measure the adhesiveness of many types of particulate materials, including combustion and incineration ashes. − An analysis of various ashes revealed that P, Na, and K in ashes increased adhesiveness at high temperatures. − For sewage sludge incinerated ashes, which contained P at high concentrations, adhesiveness began to increase near 600 °C, a temperature that is lower than that of coal ashes. , This observation indicated that the adhesiveness of ashes that contain P easily adhere inside the incineration machinery. These provided a promising method for quantifying the adhesiveness of P-containing ashes at high temperatures.…”

“…Because the chemical components of ashes are complex, the detailed roles of the different elements in adhesiveness are unclear. To clarify the effect of each element in ash on adhesiveness, a strategy using synthetic ash was developed to understand the role of an element in adhesiveness at high temperatures. , Synthetic ashes consist of base particulate materials that are stable and target elements that induce adhesiveness at high temperatures. In a simple synthetic ash system, the role of target elements in adhesiveness can be determined.…”

“…A previous study focused on Na and K as target elements and examined the mechanistic details of adhesiveness induced by these elements. The role of coexisting Al also was studied with synthetic ashes, and the information obtained can help to develop methods to prevent adhesiveness . Therefore, a synthetic ash strategy is a good tool for understanding the increase in adhesiveness induced by various elements and the role of coexisting elements at high temperatures.…”

“…The role of coexisting Al also was studied with synthetic ashes, and the information obtained can help to develop methods to prevent adhesiveness. 45 Therefore, a synthetic ash strategy is a good tool for understanding the increase in adhesiveness induced by various elements and the role of coexisting elements at high temperatures. This strategy has the potential for gaining an understanding of the role of P and coexisting Fe in adhesiveness and was used in the present study (Figure 1b).…”

Shear Strength Testing of Synthetic Ash: The Role of Surface vs Interparticle Adhesions

“…We have been engaging in research on fly ash deposition using a tensile strength tester (Figure ). − The tester can directly measure the tensile strength of fly ash powder beds that are closely related to the interparticle adhesion. Most importantly, the tester can predict fly ash deposition that occurs at temperatures significantly lower than the ash melting point, where no significant liquid (slag) phase formation is expected.…”