66
X. Li et al.
When the tangential liquid flow rate is much larger than the axial figure, small
A/T, the flow pattern of gas–liquid two-phase flow is hollow tapered type, as shown
in Fig. 2a with the A/T at 0.1. Meanwhile, the gas flow rate is controlled at 150m
3 /h
and the total liquid flow rate is set as 0.62m
3 /h. Due to the large spray angle, the
liquid spins counterclockwise and hits the wall of tube, creating a small foaming
zone. After reaching the top, one part of the liquid flows down along the wall and
the other part flows down along the center of the tube for the secondary downstream
washing of the gas. Therefore, the pressure loss of gas for hollow tapered flow is
large.
Foaming flow formed, as shown in Fig. 2b, when the axial flow rate was increased.
The top of the foaming layer is turbulent strongly under the action of inertia force
and intensive collision of high-speed airflow, and is broken into many tiny drops.
The mass transfer between gas and liquid is further enhanced due to the continuous
renewal of gas- liquid interface. The foaming zone covers a large area and liquid film
thickness increases, which improves the removal efficiency of fine particles in flue
gas.
The gas–liquid two-phase flow will alter to the annular flow when the axial and
tangential liquid flow ratio reaches 2.5 (shown in Fig. 2c). The trajectory height of the
liquid phase is significantly higher than that of the foaming type, and the top liquid
phase is broken into large droplets. However, due to the reduction of tangential flow,
the coverage area of the liquid is significantly reduced. In addition, there is a gap
between the center of the annular flow and the side wall of the washing tube, which
results in that most airflow takes a shortcut and greatly reduces the dust removal
efficiency.
When the axial flow continues to increase, the liquid column is reached when
the A/T is 4.0, as shown in Fig. 2d. The liquid flow is straight up in a column and
flows through the entire reverse spray section. After reaching the top, the liquid flow
spreads out in all directions and then flows down along the axis. The spray angle of
the liquid column type is very small, and the covering area of the liquid column flow
is also small, so the contact condition between the gas–liquid phases is poor.
Hydrodynamics of Gas–Liquid Two-Phase Flow with A/T
Pressure Drop of Gas Phase
Changing the axial and tangential liquid flow ratio of the nozzle can alter the flow
patterns of gas–liquid two-phase flow. As the liquid spray angle increases, the
covering area of liquid phase increases, so the contact surface and the collision
strength between gas and liquid increase, leading to an increment in the pressure
drop for gas phase. A significant downward trend for pressure drop with the increase
of the A/T can be found in Fig. 3. Moreover, when the A/T is less than 2.0, the
downward trend is more obvious, mainly because the gas–liquid flow patterns are
foaming type or hollow tapered flow. With the increase of the A/T, the liquid covering
X. Li et al.
When the tangential liquid flow rate is much larger than the axial figure, small
A/T, the flow pattern of gas–liquid two-phase flow is hollow tapered type, as shown
in Fig. 2a with the A/T at 0.1. Meanwhile, the gas flow rate is controlled at 150m
3 /h
and the total liquid flow rate is set as 0.62m
3 /h. Due to the large spray angle, the
liquid spins counterclockwise and hits the wall of tube, creating a small foaming
zone. After reaching the top, one part of the liquid flows down along the wall and
the other part flows down along the center of the tube for the secondary downstream
washing of the gas. Therefore, the pressure loss of gas for hollow tapered flow is
large.
Foaming flow formed, as shown in Fig. 2b, when the axial flow rate was increased.
The top of the foaming layer is turbulent strongly under the action of inertia force
and intensive collision of high-speed airflow, and is broken into many tiny drops.
The mass transfer between gas and liquid is further enhanced due to the continuous
renewal of gas- liquid interface. The foaming zone covers a large area and liquid film
thickness increases, which improves the removal efficiency of fine particles in flue
gas.
The gas–liquid two-phase flow will alter to the annular flow when the axial and
tangential liquid flow ratio reaches 2.5 (shown in Fig. 2c). The trajectory height of the
liquid phase is significantly higher than that of the foaming type, and the top liquid
phase is broken into large droplets. However, due to the reduction of tangential flow,
the coverage area of the liquid is significantly reduced. In addition, there is a gap
between the center of the annular flow and the side wall of the washing tube, which
results in that most airflow takes a shortcut and greatly reduces the dust removal
efficiency.
When the axial flow continues to increase, the liquid column is reached when
the A/T is 4.0, as shown in Fig. 2d. The liquid flow is straight up in a column and
flows through the entire reverse spray section. After reaching the top, the liquid flow
spreads out in all directions and then flows down along the axis. The spray angle of
the liquid column type is very small, and the covering area of the liquid column flow
is also small, so the contact condition between the gas–liquid phases is poor.
Hydrodynamics of Gas–Liquid Two-Phase Flow with A/T
Pressure Drop of Gas Phase
Changing the axial and tangential liquid flow ratio of the nozzle can alter the flow
patterns of gas–liquid two-phase flow. As the liquid spray angle increases, the
covering area of liquid phase increases, so the contact surface and the collision
strength between gas and liquid increase, leading to an increment in the pressure
drop for gas phase. A significant downward trend for pressure drop with the increase
of the A/T can be found in Fig. 3. Moreover, when the A/T is less than 2.0, the
downward trend is more obvious, mainly because the gas–liquid flow patterns are
foaming type or hollow tapered flow. With the increase of the A/T, the liquid covering