(378am) Research of the Vertical Falling Film Behavior in the Scrubbing-Cooling Tube

Research on the vertical falling film
behavior in the scrubbing-cooling tube

Yifei Wang*, Xin Peng, Liucheng Yan , 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

Being a part of the opposed
muti-burner (OMB) gasifier, the scrubbing-cooling chamber is used to cool,
humidify and scrub the high temperature raw syngas. The chamber mainly consists
of a scrubbing-cooling ring, a scrubbing-cooling tube, a liquid pool and a
bubble bed. The cooling water flows through the ring and forms vertical liquid
film inside the tube. The liquid film protects the wall of the tube from the
high temperature syngas and slag. Most of the falling film studies are carried
out in micro-scale tube with small liquid Reynolds number. The research here
focuses on the study of both of the velocity and thickness
distribution of falling liquid film under relatively large Reynolds number which
is closed to actual industrial condition.

An Ultrasound Doppler Velocimetry was
employed to measure the velocity and thickness distribution of falling liquid
film and the liquid Reynolds number ranged from 1.0×10⁴ to 3.1×10⁴.
A 3D numerical model of the scrubbing-cooling tube was established and the simulation
results were in good agreement with the experimental data as shown in Fig. 1. The
average liquid film thickness became largest at the 0 circumferential position
while a part of the liquid was separated from the local liquid film and dripped
in the gas core when Reynolds number was larger than 1.5×10⁴ as
shown in Fig. 2-3. In the lower section of the tube, the circumferential liquid
film thickness distributed more evenly. With the increase of Reynolds number, both
of the thickness and velocity of global liquid film increased and the thickness
distribution became unevener. Under the effect of gravity, the liquid film
velocity increased with the increasing flow distance at small Reynolds numbers
while decreasing at large Reynolds numbers due to the resistance.

Keywords: falling film, film velocity and thickness, numerical
simulation, large Reynolds numbers, Ultrasound Doppler Velocimetry

Fig.
1 Comparison of liquid film velocity distribution between simulated and
experimental data

Fig. 2 Liquid film
thickness distribution at different Reynolds numbers

Fig.
3 Phase contour graph of the outlet of the tube