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

Abstract

During sewage treatment, phosphorus (P) is concentrated in sewage sludge, and the sludge is incinerated to produce P-concentrated ash particles. The P-containing ash particles possess high adhesiveness at high temperatures, which can cause problems for the incineration plants. Phosphorus is considered a key element for inducing ash particles adhesiveness; however, the mechanistic details remain unclear. The present study clarified the role of P in particle adhesion at high temperatures using synthetic ashes, which consist of P and Si. The tensile strength of synthetic ash powder beds was quantified using a specially developed device that could estimate adhesiveness of particles at high temperatures. Since synthetic ash has few components compared to incineration ashes collected from commercial incineration plants, evaluating the role of P is easier. Iron (Fe)-containing chemical species are used for water treatment as chemical conditioners, and Fe also is concentrated with P in the sludge-incinerated ashes. To determine the interactions between Fe and P, iron oxide nanoparticles were added to P-containing synthetic ashes and their adhesiveness was evaluated. A small addition of iron oxide nanoparticles significantly decreased the adhesiveness of P-containing synthetic ashes at high temperatures, information that can help to control adhesiveness of sewage sludge-incinerated ashes.

Role of Al-Based Additives in Controlling Ash Adhesion

“…2,3 Numerous additives have been developed for this purpose. 3,12−25 In previous reports, 12,13 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.…”

“…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 .…”

“…However, with the expansion of biomass fuel utilization, a wide variety of ashes are produced, ,,− requiring adhesion suppression techniques that are effective irrespective of the ash composition. 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 .…”

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

“…Synthetic ash was prepared according to the reported method herein. ,, In brief, silica microparticles were used as carriers, whose surfaces were coated with sodium or potassium. The oxalate salts were used as the sodium or potassium sources and were mixed with silica microparticles in deionized water.…”

Phosphorus-Related Ash Chemistry at High Temperatures: Role of Aluminum on Particle Adhesion

“…We have prepared synthetic ashes composed of P and SiO 2 (P-SiO 2 ), and studied their adhesion behavior related to phosphorus (Figure 1b). 28,36 It was found that the tensile strength of P-SiO 2 increased proportionally with increasing P concentration. It was indicated that high concentration of phosphorus in ash can cause trouble in thermochemical conversion plants.…”