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

Abstract

This paper explores the evolution of pore structure parameters during Zhundong coal and biomass ash sintering at 1473 K. Additionally, the influences of blending biomass ash with different proportions are determined. The pore parameters, including the porosity, diameter, number, and frequency of the equivalent diameter, were processed by reconstructing and processing three-dimensional (3D) data on the basis of X-ray computed microtomography (XCT). The maximum porosities for the cases of pure coal and mixture of 10% biomass and 50% biomass during sintering are determined to be 46.6, 42.6, and 24.0%, respectively, while the frequencies of small pores (<0.2 mm) in the coal ash samples are lower than those in the other cases. In addition, the mineralogical phase transformation during sintering is identified by X-ray diffraction analysis. The condensate in the pores mainly comprises NaCl, CaSO 4 , and KCl, which indicates that the volatilization of alkali metals and the formation and gasification of anhydrite occur throughout the sintering process.

Experimental study on flow properties of coal ash slag based on the image measurement method

“…The holes on the ash surface are formed by thermal expansion and volatilization of alkali metal salts. With further sintering, the pore structure decreases with the formation of the molten phase 28,38 . The samples containing MS ash have a smoother surface with some spherical protrusions, which are related to the production of molten mineral components in the ash 39 .…”

“…According to ASTME1755-01, all ash was obtained by ashing in a muffle furnace at 550 C for 10 h until the weight was constant. 29 According to our previous work, 28 The purpose of this study is to investigate the flow characteristics of the ash mixture of ZD coal and MS. Three MS ash mixing ratios were selected: 10, 20, and 50 wt%. The mixing ratios mentioned above are based on coal ash.…”

“…According to ASTME1755‐01, all ash was obtained by ashing in a muffle furnace at 550°C for 10 h until the weight was constant 29 . According to our previous work, 28 the fuel properties of raw materials are listed in Table 1. It can be seen from Table 1 that ZD coal ash has high contents of Na 2 O (7.60%), Al 2 O 3 (14.50%), and Cl (10.72%).…”

“…With further sintering, the pore structure decreases with the formation of the molten phase. 28,38 The samples containing MS ash have a smoother surface with some spherical protrusions, which are related to the production of molten mineral components in the ash. 39 Figure 11 shows the surface morphology of the samples at 1180 C. The results show that the increase in temperature promotes the melting of the ash samples, which is manifested as the surface of the sample becomes denser and smoother.…”

“…Co-firing of coal and biomass is considered to be effective in reducing CO 2 emissions. Considering that maize is widely planted in China, there have been many studies on the melting characteristics and pore structure characteristics of ZD and MS mixed ash, [26][27][28] but few researches have investigated its flow characteristics at high temperature. The aim of this paper is to investigate the effect of maize straw (MS) ash on the flow properties of Zhundong coal ash.…”