Experimental Study on the Bubble Formation Mechanism during the Sintering of Coal and Biomass Ash Blends

Abstract

This paper presents an experimental study on bubble formation in the process of sintering of Zhundong coal and corn stalk (CS) ash blends in a horizontal chamber furnace. The effect of the blend ratio of biomass ash was investigated. Bubble parameters, such as number, area, and porosity, were measured on the basis of a metalloscope equipped with a charge-coupled device camera and digital image processing technique. After sintering experiments, ash and condensed matter in the bubbles were sampled and analyzed by X-ray diffraction. In addition, a chemical equilibrium calculation was conducted to reveal the influence of biomass ash on the formation of bubbles. The experimental results show that a 50% CS blend has the greatest melting degree and the formation time of bubbles is earlier than other cases, while a low ratio of CS ash has limited influence on bubble formation and mineral composition. The formation mechanism of bubbles is proposed on the basis of the results. The condensed matter in the bubbles mainly contains NaCl, CaSO4, and KCl. The results indicate that chlorine promotes the transformation of alkali metals to gaseous phase. The chemical equilibrium calculation verified the experimental results.

Experimental Study of the Pore Structure during Coal and Biomass Ash Sintering Based on X-ray CT Technology

“…29−32 Zheng et al 33 deduced that the pores in the melting slag reduced the thermal conductivity while the thickness of the sintered layer decreased with an increase in the number of bubbles. Zhou et al 34 measured the bubble parameters for coal and biomass co-combustion with a metalloscope. Pang et al 35 calculated the porosity of fusion ashes from biomass and coal based on scanning electron microscopy (SEM) analysis by an imaging technique.…”

“…To manage a co-fired boiler and prevent severe ash-related problems, an increasing number of scholars have recently studied the ash sintering characteristics of coal and biomass. − Scholars reported that a porous structure was produced during the sintering of ash deposits, which affected the thermal conductivity, hindered the heat transfer in the furnace and reduced the service life of the equipment. − Zheng et al deduced that the pores in the melting slag reduced the thermal conductivity while the thickness of the sintered layer decreased with an increase in the number of bubbles. Zhou et al measured the bubble parameters for coal and biomass co-combustion with a metalloscope. Pang et al calculated the porosity of fusion ashes from biomass and coal based on scanning electron microscopy (SEM) analysis by an imaging technique.…”