3 Dynamics of Spray Granulation in Continuously …
103
The control algorithm for the Sauter diameter in Fig. 24 is a simple linear proportional controller. It was shown that additional integral action is destabilizing and
should therefore be avoided for this process. It was shown that the simple proportional controller works very well for small disturbances. For larger disturbances,
however, more advanced, model-based control concepts are required as proposed for
example in Refs. [66–69].
Besides particle size, particle morphology, in particular particle porosity, is of
major interest in many applications. Therefore, automatic adjustment of particle
porosity by feedback control was studied in Neugebauer et al. [54]. Problem here
is, that porosity cannot be controlled directly, due to a lack of available online measurement information. However, as discussed in Sect. 4, particle porosity depends
directly on the drying potential which is related to the thermal conditions. The thermal conditions can be measured online easily. Therefore, the drying potential is taken
as controlled variable for porosity control and the inlet temperature of the fluidization
gas is taken as manipulated variable. For this control configuration a simple single
loop PI controller was designed and tested using the model. For this, the plant model
was extended to account for the influence of porosity on the milling of oversized
particles, which is crucial for the stability of the particle size distribution.
Results taken from Neugebauer et al. [54] are shown in Fig.25. The solid line
represents a scenario where only porosity control is applied, whereas the red dashed
line is for simultaneous porosity and d 32 control. In all cases, bed mass control as
described above was applied. At time t sp in Fig. 25 the reference value of the particle
porosity was changed from p,I to p,I I and at time t dist a step disturbance of the
moisture content of the inlet gas from 6 to 15 g/kg dry air was introduced.
p,I
0.41
p,II
0.44
p [−]
particle porosity
1.00
1.06
d32,ref
d
32 [mm]
Sauter diameter
0
5
1 0
2 0
2 4
70
75
80
t sp
t dist
process time t [h]
θ
f,in [
◦
C]
fluid temperature
0
5
10
20
24
0.80
0.85
0.90
t sp
t dist
process time t [h]
μ
mill,0 [mm]
particle milling
Fig. 25 Porosity control with (dashed red line) and without d 32 control (solid line)
103
The control algorithm for the Sauter diameter in Fig. 24 is a simple linear proportional controller. It was shown that additional integral action is destabilizing and
should therefore be avoided for this process. It was shown that the simple proportional controller works very well for small disturbances. For larger disturbances,
however, more advanced, model-based control concepts are required as proposed for
example in Refs. [66–69].
Besides particle size, particle morphology, in particular particle porosity, is of
major interest in many applications. Therefore, automatic adjustment of particle
porosity by feedback control was studied in Neugebauer et al. [54]. Problem here
is, that porosity cannot be controlled directly, due to a lack of available online measurement information. However, as discussed in Sect. 4, particle porosity depends
directly on the drying potential which is related to the thermal conditions. The thermal conditions can be measured online easily. Therefore, the drying potential is taken
as controlled variable for porosity control and the inlet temperature of the fluidization
gas is taken as manipulated variable. For this control configuration a simple single
loop PI controller was designed and tested using the model. For this, the plant model
was extended to account for the influence of porosity on the milling of oversized
particles, which is crucial for the stability of the particle size distribution.
Results taken from Neugebauer et al. [54] are shown in Fig.25. The solid line
represents a scenario where only porosity control is applied, whereas the red dashed
line is for simultaneous porosity and d 32 control. In all cases, bed mass control as
described above was applied. At time t sp in Fig. 25 the reference value of the particle
porosity was changed from p,I to p,I I and at time t dist a step disturbance of the
moisture content of the inlet gas from 6 to 15 g/kg dry air was introduced.
p,I
0.41
p,II
0.44
p [−]
particle porosity
1.00
1.06
d32,ref
d
32 [mm]
Sauter diameter
0
5
1 0
2 0
2 4
70
75
80
t sp
t dist
process time t [h]
θ
f,in [
◦
C]
fluid temperature
0
5
10
20
24
0.80
0.85
0.90
t sp
t dist
process time t [h]
μ
mill,0 [mm]
particle milling
Fig. 25 Porosity control with (dashed red line) and without d 32 control (solid line)