Effect of stirring devices on the intensification of gas-fluid processes

Article abstract of DOI:10.1023/A:1012701829616

A comparative analysis is made of the operation of apparatus of rotary-pulsation and ejector types with self-suction turbine agitator. The dependence of the efficiency of operation on the output capacity and energy-related characteristics determining power consumption for agitation of gas-fluid mixtures were determined experimentally.

Full text of DOI:10.1023/A:1012701829616

Russian Journal of Applied Chemistry, Vol. 74, No. 3, 2001, pp. 461 465. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 3,
2001, pp. 451 455.
Original Russian Text Copyright
2001 by V. Ivanets, Al’brekht, G. Ivanets.
PROCESSES AND EQUIPMENT
OF CHEMICAL INDUSTRY
Effect of Stirring Devices on the Intensification
of Gas Fluid Processes
V. N. Ivanets, S. N. Al’brekht, and G. E. Ivanets
Kemerovo Technological Institute of Food Industry, Kemerovo, Russia
Received April 3, 2000; in final form, November 2000
Abstract A comparative analysis is made of the operation of apparatus of rotary-pulsation and ejector types
with self-suction turbine agitator. The dependence of the efficiency of operation on the output capacity and
energy-related characteristics determining power consumption for agitation of gas fluid mixtures were
determined experimentally.
One of the main parameters characterizing the effi-
ciency of a gas fluid apparatus is the phase surface
contact area. Present attempts to raise its value are
commonly associated with reducing the geometric
dimensions of gas bubbles by using, as a rule, various
bubbling and mechanical stirring devices [1 3]. How-
ever, gas fluid apparatus presently used in chemical
and other industries have a number of serious disad-
vantages and frequently fail to satisfy modern require-
ments to the output capacity, quality, and energy ex-
penditure per unit product. Therefore, development of
new absorber designs and improvement of the exist-
ing types of apparatus are, beyond any doubt, urgent
tasks. One of possible ways to solve this problem is to
provide intensive stirring ensuring a significant rise
in the phase boundary area and concentration of a
considerable amount of energy in small volumes. It is
known that the use of low-frequency (20 20000 Hz)
acoustic elastic vibrations allows in most cases a sub-
stantial intensification of the homogenization process.
In this case, such phenomena as cavitation, acoustic
pressure, and pulsing microflows occur in the medium
being treated, making higher the rate of physicochem-
ical processes in heterogeneous systems [3].
nitrosation of diphenylamine (DPA) in an organic
solvent (trichloroethylene, TCE, fluid phase) with a
mixture of nitrose gases, NO and NO (gas phase),
2
with the aim to develop a multifunction apparatus for
intensifying processes of absorption, homogenization,
and dispersion.
In the first stage, the influence exerted by the main
parameters (temperature, concentration, solubility of
the gas phase, its amount and means of delivery) on
the time of process completion was studied. For this
purpose, a laboratory rig was designed and fabricated.
The experiments were performed as follows. A pre-
treated 1.01 : 1 gas mixture of nitrogen oxides, NO +
NO , was fed through a rotameter into the reactor,
2
together with a 15% solution of DPA in TCE. The
temperature of the reaction mixture was monitored
with a thermocouple; its prescribed value was main-
tained with thermostat and supply lines for a cooling
3
3
agent. The reactor of volume 0.65 10
m
was
equipped with a mechanical agitator and a bubbling
device. Samples were taken at 30-s intervals and
analyzed for the content of DPA in solution by thin-
layer chromatography and spectrometry on an SF-46
instrument.
Acoustic vibrations are generated by means of hy-
drodynamic transmitters. In transmitters of this kind,
acoustic vibrations are generated by rotary-pulsation
devices. In view of their great potentiality, it may be
assumed that that use of gas fluid rotary-pulsation
apparatus (RPA) for performing absorption will allow
a substantial intensification of this process.
Originally, the effect of the nitrosing agent flow
rate on the time of complete DPA conversion was
studied. Analysis of the results furnished by mathe-
matical processing of experimental data shows that at
3
1
a gas phase flow rate exceeding 0.3 m h the time in
which the process is complete remains practically
unchanged. Therefore, in further experiments, the gas
phase flow rate was taken to be, in a certain excess,
The goal of this study was to analyze the efficiency
of conventional gas fluid apparatus (of ejector type
and with turbine agitator) and RPA for performing
3
1
0.35 m h . Then the dependence of the time of com-
plete DPA conversion on the process temperature was
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462
IVANETS et al.
Table 1. Time of process completion at varied flow rates
of the gas (Qg) and fluid (Qf) phases in the extractor
compared apparatus, and redox potentiometer for
determining the completion time of the chemical reac-
tion. The reaction mixture volume was constant
1
, min, at indicated Ql, m3 h
3
(0.018 m ) in all the experiments.
1
Qg, m3 h
As a criterion for comparing the operation of the
three apparatus served the efficiency
0.2
0.275
0.35
0.66
1
1.5
2
70
59
38
32
70
58
33
70
57
28.7
21.4
E = V /(N ),
(1)
3
where V is the reaction mixture volume (m ), N is the
power consumed for performing the process (W), and
is the process duration (min).
26.7
Table 2. Maximum output capacity Vl of ejector-type
apparatus at varied gas component flow rate Ql and work-
ing phase flow rate W
The power consumed for performing the process
consists of the following components:
1
1
Vl, m3 h , at indicated W, m3 s
N = N1 + N2 + N3 + N4 + N5,
1
Qg, m3 h
where N , N , N , N , and N are, respectively, the
1
2
3
4
5
10.46
14.38
18.3
powers consumed for stirring of the gas fluid system,
preparing the starting solution, cooling the oxidizing
agent, pumping the cooling agent to lower the tem-
perature of the reaction unit, and feeding the gas. The
N N values are approximately the same in perform-
ing the same process in apparatus of different types.
Therefore, they can be disregarded in comparing the
0.66
1
1.5
2
0.01543
0.0183
0.02842
0.03375
0.01543
0.01862
0.03273
0.04045
0.01543
0.1895
0.03763
0.05047
2
5
studied in the range 10 30 C with a step of 5 C. It
was found that the shortest time (1.5 min) is achieved
at a temperature of 20 2 C [4]. The dependences of
the process duration on the intensity of stirring and
method of gas phase feeding into the reactor (into the
over-solution space or through a bubbler situated at
the bottom) were studied. It was found that the time
of complete DPA conversion decreases with increas-
ing agitator speed. The minimum time corresponds to
efficiencies of the apparatus under study. The N
values were determined for each apparatus experi-
mentally.
1
In each experiment the duration of DPA nitrosation
is a function of the flow rates of fluid and gas phases
without taking into account conditions common to all
of the three apparatus studied. The ejector-type ap-
paratus comprises an ejector and a bottom reactor.
A chemical reaction occurs in the mixing chamber of
the ejector during motion of the fluid and gas phases,
with the fluid simultaneously saturated with dissolved
gas. The reaction continues in the lower part of the
reactor, but the amount of gas phase dissolved in
the fluid phase is smaller, compared with that in the
ejector. The residual kinetic energy of the jet goes
to agitation of the reaction mixture, which leads to
leveling of substance concentrations over the entire
volume. For the studied flow rate ranges for the fluid
1
an agitator rotation rate of 157 s . In this case, the
method by which the gas phase is fed has virtually no
effect on the time of process completion. Analysis of
experimental data shows that under the found optimal
conditions [temperature 20 2 C, atmospheric pres-
sure, nitrogen oxide mixture composition NO : NO =
2
(1.01 1.04) : 1, initial DPA concentration 15 wt %,
3
stirring intensity Re = 5 10 ] the DPA nitrosation
is kinetically controlled. Vigorous stirring eliminates
the effect of the mass exchange at the phase boundary
on the rate of the chemical reaction.
3
1
3
1
(0.2 0.35 m h ) and gas phases (0.66 2 m h ),
1
1
the minimum (10 m s ) and maximum (20 m s )
velocities of the fluid outflowing from the ejector
nozzle of diameter 2.6 10 m were taken according
After the basic process parameters were found, the
most efficient of the three kinds of gas fluid apparatus
(with ejector, with self-suction turbine agitator, and of
rotary-pulsation type) was determined. The DPA ni-
trosation was studied on a semicommercial installa-
tion comprising rotameters and control equipment
serving to vary the flow rates of components within
prescribed limits, reaction unit including one of the
3
to the known recommendations [5]. The obtained ex-
perimental data are presented in Table 1. Mathemati-
cal processing of these data for the batch mode yielded
the dependence
= 115.43
68.26Qg
32.22QgQl + 16.15Q2g. (2)
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 3 2001

EFFECT OF STIRRING DEVICES
In the continuous mode, the maximum output
463
5
P
10 , Pa
capacity V of the ejector-type apparatus was studied
l
experimentally at different velocities W of working
medium outflow from the nozzle and different gas
flow rates (Table 2). Analysis of the experimental
results shows that shorter time is achieved in the
1
batch mode at ejector flow velocity of 20 m s and
3
1
gas phase flow rate of 2 m h . In the continuous
mode, the maximum output capacity of the installa-
tion is achieved at the same flow rates.
1
Ql, m3 h
Fig. 1. Total loss of the pressure P of the working medium
in the circuit vs. the fluid phase flow rate Q .
The total hydraulic loss of pressure, P, in the
circulation circuit consists of losses in suction and
pumping lines and in the ejector itself. The working-
l
3
of the reaction mixture 0.018 m , and volume of
apparatus with STA 0.01 m . In the batch mode, the
time of process completion in the entire volume of
the reaction mixture was determined. The obtained
experimental data are presented in Table 3.
3
medium pressure at the nozzle outlet P = 0.1 MPa,
w
whereas the total loss of pressure in the circulation
circuit will be given, with account of the working-
medium pressure, by
The equation describing the time (min) of com-
plete conversion in relation to the flow rate of the gas
phase in an apparatus with STA has the form
P = Psuc
+
Ppump
+
Pej + Pw.
(3)
Figure 1 shows the dependence of P on the fluid
phase flow rate Q , described by the equation
= 9.9Q2g
43.02Qg + 66.3.
(7)
l
P = 8.02Q2l
1.256Ql + 1.97.
(4)
The self-suction turbine-type agitator used in the
experiments had the following characteristics: diam-
eter 0.1 m, number of blades 6, blade width 0.01 m.
In calculating the power consumed by the STA for
agitation of the gas fluid system, two circumstances
were taken into account: (1) the dynamic viscosity
coefficient of the main component was chosen as
With account of (4), the power consumed for pumping
the working medium through the circulation circuit is
given by
724.35Q2l 267.22Ql + 35.81
N =
,
(5)
Table 3. Process completion time for apparatus with
STA and RPA
where
= 0.55 is the pump efficiency.
With account of expressions (1), (2), and (5) and
V = 0.018 m , the formula for determining the effi-
ciency of ejector-type apparatus will have the form
1
, min, at indicated Qg, m3 h
3
Run
no.
1
1.25
1.5
1.75
2
E = [(73.17Q2l
26.99Ql + 3.6)(115.43
68.26Qg
(6)
Self-suction turbine agitator
1
32.22QgQl + 16.15Q2g)] .
1
2
3
33.04
33.07
33.04
28.44
28.34
28.42
24.34
24.33
24.39
21.47
21.34
21.42
19.94
19.83
19.96
Analysis of (6) shows that the highest efficiency is
achieved for apparatus of this type at a fluid phase
1
Average 33.05
28.4
24.35
21.41
19.91
nozzle velocity of 10.43 m s and gas phase flow rate
3
1
of 2 m h (Table 2).
Rotary-pulsation apparatus
In studying the operation of a self-suction turbine
agitator (STA), the gas phase was delivered, under the
action of the pumping effect created by the mixer, into
the central, hollow part of the rotating shaft and dis-
persed directly into the fluid phase. The flow rate of
1
2
3
32.53
32.56
32.56
26.05
26.03
26.04
21.71
21.68
21.72
18.24
18.27
18.23
16.57
16.59
16.61
3
1
the nitrose gases was varied between 1 and 2 m h .
Average 32.56
26.04
21.70
18.25
16.59
1
The rotation speed of the mixer was 110 s , volume
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 3 2001

464
IVANETS et al.
The rotary-pulsation apparatus operates as follows.
Table 4. Experimental values of power Ne
The fluid phase is fed into the working cavity via the
inlet pipe. Under the action of inertia forces created by
a rotating rotor it passes through rectangular slits in
the rotor and stator rings. With the shaft rotating, the
slits are periodically closed. In this zone of strong tur-
bulence, there exist pulsation forces and high velocity
gradients. The gas phase delivered via two pipes goes
through channels inside the stator teeth and arrives in
the space formed by slits in the rotor ring. During
rotor rotation, the outlet channels are periodically
closed at the same frequency, which favors fine dis-
persion of the gas phase.
1
Flow rate, m3 h
Ne, W
gas phase in RPA
fresh solution
1
0.03318
0.04147
0.04976
0.05916
0.06510
37.70
36.62
35.77
35.16
34.80
1.25
1.5
1.75
2
the key factor for a reaction mixture with gas satura-
Thus, to achieve complete interaction of the gas
and fluid phases, a unit volume of fluid is subjected to
multiple treatment in the active zone of the RPA. The
clearance between the rotor and stator teeth was 1
tion
< 0.3, and (2) the reaction mixture density
1
(kg m ) in the apparatus was calculated at gas
m
3
1
flow rates in the range from 1 to 2 m h by the
equation
4
1
10 m, and the speed of rotation, 314 s . The main
goal of the performed sets of experiments was to de-
termine the time of completion of diphenylamine
nitrosation in RPA at gas phase flow rates in the range
= 38.86Q2g
181.37Qg + 1327.8.
(8)
m
Under these conditions, the values of the centri-
fugal criterion Re are within (2.18 24) 10 . For the
turbine agitator of the given type [1], the power cri-
terion K remains constant (0.76) in the above range
of Re values. Then, use of the known formula [1] and
expression (8) gives a theoretical relation for deter-
mining the power consumption N (W) for agitation
with STA:
5
3
1
c
from 1 to 2 m h and reaction mixture volume of
3
0.001 m . The obtained experimental data are pre-
N
sented in Table 3.
c
The equation obtained by processing the data in
Table 3 has the form
t
= 12.37Q2g
53.02Qg + 73.16.
(12)
Nt = 0.041
= 1.59Q2g
7.43Qg + 54.4.
(9)
m
The power N consumed for agitation of the gas
e
fluid mixture in RPA was measured experimentally at
varied flow rates of the gas and fluid phases; the
averaged results are given in Table 4.
However, analysis of the experimental dependence
Ne = 1.68Q2g
8.9Qg + 56.1
(10)
The obtained experimental data are described by
the regression equation
shows that, with increasing flow rate of the gas com-
ponent, the experimental power values are somewhat
lower than the theoretical values, which is presumably
due to lower density of the reaction mixture near the
agitator.
Ne = 1.95Q2g
8.76Qg + 44.5.
(13)
Analysis of Eq. (13) clearly shows that the con-
sumed power decreases somewhat with increasing
flow rate of the gas phase, which is presumably due to
a decrease in the density of the gas fluid mixture in
the active zone of the apparatus.
With account of (7) and (10), the dependence of the
efficiency of a gas fluid apparatus with STA on the
flow rate of the gas component can be represented as
3
E = 1 10 (0.92Q4g
8.9Q3g + 58.3Q2g
The operation efficiency of an installation with
STA can be calculated using Eqs. (12) and (13). Then
the dependence of the RPA efficiency on the gas
phase flow rate has the form
1
166.78Qg + 206.56) .
(11)
Analysis of (11) shows that the efficiency of an
apparatus with STA grows with increasing flow rate
of the gas phase because of the decreasing power con-
sumed for agitation and shorter process duration.
An RPA of original design has been developed to in-
tensify gas fluid processes [5].
3
E = 1 10 (1.34Q4g
11.75Q3g + 64.34Q2g
1
166.75Qg + 181.1) .
(14)
To compare the efficiencies of the apparatus under
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 3 2001

EFFECT OF STIRRING DEVICES
study, the following parameter values are taken: for
465
1
E
106, m3 W 1 min
3
1
apparatus with ejector, Q = 2 m h , flow velocity
g
1
of the fluid phase 10.46 18.3 m s ; for apparatus
with STA and for RPA, Q = 1 2 m h , output
3
1
g
1
3
capacity 0.032 0.065 m h .
Graphical interpretation of the obtained relations
describing the dependence of the efficiency of the
apparatus on their output capacity is done in Fig. 2.
Analysis of the experimental data in Fig. 2 shows
that the apparatus with STA has much lower effi-
ciency than its competitors, becoming comparable
with an ejector-type apparatus only at an output capac-
1
Ql, m3 h
3
1
ity of 0.05 m h . In contrast to the apparatus under
consideration, the ejector-type apparatus shows high
efficiency only at low output capacities, and its effi-
ciency steeply decreases when this parameter grows.
Fig. 2. Efficiency E of an installation vs. its output capacity
Q. Apparatus: (1) with ejector, (2) with STA, and (3) of
rotary-pulsation type.
3
1
that the ejector-type apparatus is the most efficient
Already at an output capacity of 0.0425 m h it
becomes comparable in efficiency with RPA. An
undisputed leader in efficiency, beginning with output
3
1
at low output capacities (up to 0.042 m h ), and the
rotary-pulsation apparatus, at higher values of this
3
1
3
1
parameter (more than 0.045 m h ).
capacity of 0.045 m h , is RPA, and it is this ap-
paratus that should be used to perform the process
under consideration.
REFERENCES
The results obtained in studying the operation of a
semicommercial RPA in performing gas fluid proc-
esses were used to produce an intermediate, N-nitroso-
diphenylamine, in manufacture of an antioxidant for
1. Braginskii, B.P., Begachev, V.I., and Barabash, V.M.,
Peremeshivanie v zhidkikh sredakh: Fizicheskie osnovy
i inzhenernye metody rascheta (Agitation of Fluid
Media: Physical Foundations and Methods of Engineer-
ing Calculation), Leningrad: Khimiya, 1984.
1
rubber articles Diafen FP and commercial p-nitroso-
2
phenol.
2. Barabash, V.M. and Belevitskaya, M.A., Teor. Osn.
Khim. Tekhnol., 1995, vol. 29, no. 4, pp. 362 372.
3. Aksel’rod, Yu.V., Gazozhidkostnye khemosorbtsionnye
protsessy: Kinetika i modelirovanie (Gas Fluid Chemi-
sorption Processes: Kinetics and Modeling), Moscow:
Khimiya, 1989.
CONCLUSIONS
(1) The dependences of the time in which di-
phenylamine nitrosation is complete on the flow rates
of the gas and fluid phases were obtained for ap-
paratus with a self-suction turbine agitator and those
of rotary-pulsation and ejector types. Mathematical
models of the occurring processes were developed for
these cases. The power expenditure for agitation of
the gas fluid system under study was found for these
apparatus.
4. Ivanets, V.N. and Al’brekht, S.N., in KemTIPP 25 let:
dostizheniya, problemy, perspektivy: Sbornik nauch-
nykh trudov (25th Foundation Aniversary of Kemerovo
Technological Institute of Food Industry: Achieve-
ments, Problems, and Prospects: Coll. of Sci. Works),
Kemerovo, 1988, part 2, pp. 3 7.
5. Ivanets, G.E., Plotnikov, P.V., and Al’brekht, S.N., in
Tekhnologii i protsessy pishchevykh proizvodstv: Sbor-
nik nauchnykh trudov KemTIPP (Technologies and
Processes of Food Industry: Coll. of Sci. Works of
Kemerovo Technological Institute of Food Industry),
Kemerovo, 1999, pp. 133 134.
(2) The efficiencies as functions of the output
capacity were compared for apparatus with ejector or
self-suction turbine and apparatus of rotary-pulsation
type in performing a gas fluid process. It was found
1
2
Azot Joint-Stock Company, Kemerovo.
NVKh Khimtekh (Berezniki, Perm oblast).
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 3 2001