44
L. Lindmüller et al.
of the secondary particle properties is presented in the previous chapter by Skorych
et al. For flowsheet simulations of CLC, the oxidation state is usually described by
no more than 10 intervals, for calculation speed reasons. After a reduction of the OC,
the particles move from one oxidation class to the next lower one, or the next higher
one for OC oxidation.
2.3 Process Units
For flowsheet simulation, the process is subdivided into individual model units. In
the following section, the modeled units used for Chemical Looping Combustion are
described, which are fluidized bed reactors, loop seal and a cyclone unit.
2.3.1 Fluidized Bed Reactor Unit
Fluid Mechanics
For the fluidized bed reactor, a single module was developed, which can be used for a
CFB riser and a bubbling bed. The module is divided into two zones, a dense bottom
zone and a freeboard zone. The bottom zone consists of a suspension phase and a solid
free bubbles phase. In the freeboard zone, the solids concentration is exponentially
decreasing with the rector height [14]. Figure 3 (left) shows a typical solids concentration distribution over the fluidized bed reactor height. For all process conditions,
the presence of bubbles is assumed in the bottom zone. All fluid dynamic effects in
the model are assumed to be one dimensional. In the following the correlations used
for the description of the fluid mechanics are summarized. A more detailed description can be found in a publication by Werther and Wein [15]. The initial bubble size
d v,0 above the gas distributor is given by Davidson and Harrison [16]:
d v,0 = 1.3 ·
˙
V
2
or
g
0.2
(1)
With ˙
V or being the volumetric flow through a single orifice and the gravitational
acceleration g. With increasing height over the distributor, the bubble diameter d v is
described with:
d(d v )
dh
=
2ε b
9π
1/3
−
d v
3λu b
(2)
In the equation ε b describes the bubble volume fraction and λ the average bubble
lifetime. The formed bubbles rise with the velocity u b :
L. Lindmüller et al.
of the secondary particle properties is presented in the previous chapter by Skorych
et al. For flowsheet simulations of CLC, the oxidation state is usually described by
no more than 10 intervals, for calculation speed reasons. After a reduction of the OC,
the particles move from one oxidation class to the next lower one, or the next higher
one for OC oxidation.
2.3 Process Units
For flowsheet simulation, the process is subdivided into individual model units. In
the following section, the modeled units used for Chemical Looping Combustion are
described, which are fluidized bed reactors, loop seal and a cyclone unit.
2.3.1 Fluidized Bed Reactor Unit
Fluid Mechanics
For the fluidized bed reactor, a single module was developed, which can be used for a
CFB riser and a bubbling bed. The module is divided into two zones, a dense bottom
zone and a freeboard zone. The bottom zone consists of a suspension phase and a solid
free bubbles phase. In the freeboard zone, the solids concentration is exponentially
decreasing with the rector height [14]. Figure 3 (left) shows a typical solids concentration distribution over the fluidized bed reactor height. For all process conditions,
the presence of bubbles is assumed in the bottom zone. All fluid dynamic effects in
the model are assumed to be one dimensional. In the following the correlations used
for the description of the fluid mechanics are summarized. A more detailed description can be found in a publication by Werther and Wein [15]. The initial bubble size
d v,0 above the gas distributor is given by Davidson and Harrison [16]:
d v,0 = 1.3 ·
˙
V
2
or
g
0.2
(1)
With ˙
V or being the volumetric flow through a single orifice and the gravitational
acceleration g. With increasing height over the distributor, the bubble diameter d v is
described with:
d(d v )
dh
=
2ε b
9π
1/3
−
d v
3λu b
(2)
In the equation ε b describes the bubble volume fraction and λ the average bubble
lifetime. The formed bubbles rise with the velocity u b :