(457e) Local Flow Regimes and Bubble Size Distributions in the Scrubbing-Cooling Chamber containing Dilute Fiber Suspensions of an Entrained-Flow Gasifier

Xin Peng, Yifei Wang*, Zongyao Wei, Guangsuo Yu, Fuchen Wang

Key Laboratory of Coal Gasification and Energy Chemical Engineering of the Ministry of Education, East China University of Science and Technology, Shanghai 200237, PR China

Large-scale coal gasification is the key technology for clean and efficient coal utilization. The entrained-flow gasifier, the mainstream technology for the development of coal gasification, has a high gasification temperature and pressure, can be used for large-scale production and is widely adaptable for many coal types^[1]. In an opposed multi-burner (OMB) gasifier, the scrubbing-cooling chamber which plays an important role in the washing and cooling of high-temperature crude coal gas, is composed of a spray bed and an annular bubbling bed^[2]. Top-submerged and annular bubbling structures are adopted in the scrubbing-cooling chamber in which flow regimes are different from those of a conventional bubble column. Hardly any studies are carried out on the bubble size distributions in the scrubbing-cooling chamber, especially in the bubbling bed containing solid phase. This study here focuses on both of the local flow regimes and bubble size distributions in a scrubbing-cooling chamber containing dilute fiber suspensions.

A dual-tip conductivity probe was used to measure local radial gas holdups and bubble chord lengths to study the local flow regimes and bubble size distributions in a scrubbing-cooling chamber cold model apparatus. The results showed that the cross-section averaging gas holdups with different fiber volume fractions and aspect ratios could be estimated within errors of ±10% using the modified Kataoka-Ishii^[3] bubbly flow semi-empirical correlation at superficial gas velocities ranging from 0.074 m/s to 0.37 m/s. Local flow regime map^[4] plotted by local gas holdups and dimensionless bubble chord lengths showed that an obvious bubbly flow formed near the inner wall of the liquid bath due to the effect of wall shear stress, while a cap-bubbly flow formed in other annulus regions due to the emergence of cap bubbles. Chord length distributions were transformed into bubble size distributions by decomposing the measured chord length distributions and estimating the bubble shape factors^[5]. Bubble size was categorized into two types—small spherical and large non-spherical bubbles—depending on if the equivalent bubble diameter was smaller or larger than 2 mm^[6]. Liquid turbulence, shear stress between the fluid and the wall and liquid backmixing were enhanced by increasing the superficial gas velocity, which affected the size distributions of rising and descending bubbles as well as that of bubble populations.

Figure 1. Comparison of experimental data with bubbly flow semi-empirical correlation at different experimental conditions

Figure 2. Local flow regime map at different experimental conditions

Figure 3. Rising bubble size distributions in different regions at different superficial gas velocities (c_s = 0.01 %, a_r = 20)

Figure 4. Descending bubble size distributions in different regions at different superficial gas velocities (c_s = 0.01 %, a_r = 20)

Figure 5. Total bubble size distributions in different regions at different superficial gas velocities (c_s = 0.01 %, a_r = 20)

Keywords: scrubbing-cooling chamber, dual-tip conductivity probe, gas holdup, local flow regime, chord length, bubble size distribution.

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[2] Yu, Z.H., Yu, G.S., Gong, X., et al., inventors, 2011. East China University of Science and Technology, assignee. Multi-burner gasification reactor for gasification of slurry or pulverized hydrocarbon feed materials and industry applications thereof. US patent 7, 862, 632 B2.

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[5] Hoang, N.H., Euh, D.J., Yun, B.J., Song, C.H., 2015. A new method of relating a chord length distribution to a bubble size distribution for vertical bubbly flows. Int. J. Multiphase Flow 71, 23-31.

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