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Evaluation of gas—solid flow behavior using a voidage meter
Powder
Short
Technology.
34
(1983)
109 - 111
109
Communication
Evaluation of Gas-Solid a Voidage Meter
Flow Behavior using
G. E. KLINZING ChcmicaI/Petrole~rn~ sits of Pittsburgh.
F .ginccring Depnrtmsnt. Uni~crPiitsburgh. PA 15261 (U.S.A.)
and M. P. MATHUR Li.S_Department of Energy. Pittsburgh Energy nology Center. Pittsbu@. PA 15236 (US_A.) [Received June 2.1952;
Tcch-
in revised form July 29.1982)
The existence of clusters of particles as an equilibrium condition in gas-solid transport has been documented or inferred in a number of papers [l - 43 _ Some theoretical analysis has shown that even in the dilute phase regime the condition of a uniform dispersion of particulates in a flowing system is unstable [ 5]_ Esperimental analysis of such clusters is a difficult task. One would have to observe these clusters of particles under in situ conditions. Probably high-speed photography and microscopic analysis would be required. Recently, some experiments were conducted under a variety of loading conditions from 0 to 200 kg of solid/kg of gas for the pneumatic transport of fine coal (Dp - 100 pm). This system employed an Auburn meter to monitor the voidage of the flow. The Auburn meter measures the average dielectric constant of the flowing media by applying a potential to a rapidly changing sequence of perpendicular electrodes placed around the circumference of the meter- The meter has the same diameter as the flow sys’&m and as such does not obstruct the flow. In our study, the meter was placed on the vertical section of the test unit, as shown in Fig. 1. A 0.0095 m diameter line was employed with Montana Rosebud coal having an average weight diameter of 60 pm. The influence of the bends before and after the meter were felt to be minimal, since both bends have a 0.82 pm radius and are far removed from the meter. The output voltage from the Auburn meter is usually averaged over a period of 50 to 120 s and recorded on 0032-5910/83/0000-00001503.00
Fig. 1. Schematic of the coal flow test loop facility. 0.0095
m diameter pipe.
--Ii20
msec
Fig. 2. Output signal from the Auburn Monitor.
a data-acquisition system_ In this study. the instantaneous voltage output of the meter was recorded on a strip chart. Figure 2 shows a typical instantaneous output signal trace. As the loading of solids was changed, the signal level and amplitude of the fluctuations noticeably varied. The frequencies observed by the Auburn meter response are much larger than any fluctuations introduced in the gas and solid injection systems. Khile visual observation of the clusters was not made, the frequencies of the fluctuations seem to point to the cluster phenomena observed by Yerushalmi @ Elscvier SequoialPrinted
in The Setherlnnds
110
[2]. In order to analyze this output signal in more detail, a high-speed FM tape recorder was connected to the Auburn meter output signal. Once the signal was recorded, a Hewlett Packard 302A wave analyzer was emplcyed to break the signal down into component frequencies and amplitudes. The signal was then analyzed to obtain characteristics of the flow.
Analysis The tests analyzed were carried out under a variety of operating conditions_ Table 1 summarizes these conditions. The loadings varied from 23 to 124 kg of coal/kg of gas. The higher loading conditions are most probably in the dense phase flow regime. By use of the wave analyzer, a frequency spectrum was constructed for each condition. Is typical frequency spectrum is shown in Fig. 3. It was noteworthy that the frequency at which the maximum amplitude occurred was approsimately the same for each test. Using standard turbulence theory, the data have been analyzed to find the length scale of the turbulence-like signal seen in Fig. 2. This has been done in an effort to infer possible cluster sizes for the flowing particles. Using the concept that the reciprocal frequency gives a time constant, the length scale of the signal can be shown as
(1) For the test conditions considered here, u = 35 m/s and f = 6-72 k Hz; h is found to be abotlt 0.50 cm. The superficial gas velocity remained relatively constant for all tests conducted. This length scale of 0.5 cm can be inferred to be of the order of magnitude of the flowing cluster of particles_ This inference can be made, since the Auburn meter will respond to changes in density of the flowing material. A cluster of particles is naturally more dense than a homogeneously distributed group of particles. The Auburn meter, which determines the average instantaneous voidage in the vertical test line, can be employed to find this cluster size. It is interesting to compare these findings on length scale to the cluster sizes found by Yerushahni (23 in his analysis of ‘fast fluidization’. Yerushalmi showed that a cluster diameter could be derived by equat-
TABLE
1
Experimental
test conditions Loading
Test
Solid
number
flowrate (kg/s)
(kg of coail
1 2 3 4 5 6 7
0.052 0.098 0.121 0.099 0.160 0.185 0.194
43.9 86.1 109.7 85.6 134.4 167.3 173.0
kg of gas)
6600
6700 FREQUENCY,
LHZ
Fig. 3. Frequency spectrum of the Auburn loading 57.5 (kg of coal/kg of gas)_
signal;
ing the drag force across the bed to the static pressure drop. Under a variety of conditions with 60 pm diameter catalyst particles, cluster diameters from O-1 to 4.5 cm were measured, and voidages ranged from 0.98 to 0.75. The length scale obtained by analysis of the unsteady signal from the Auburn meter measuring point voidages gives a value that in the range found by Yerushalmi. Each of the tests conducted had a run time of 30 min under steady conditions. The signal from the Auburn Monitor was consistent over this time range; analysis of the signal is therefore felt to be representative of a significant macro-steady condition.
111 In addition to the length scale calculated above, the frequency spectrum from each test as shown in Fig. 3 was integrated over frequency to form the power spectral density function
s’
= j-F(w)
dw
(2)
0
d This function was plotted as a function of solids loading (Fig. 4). One sees first that the function decreases with increased loading, which indicates a more uniform flow. As the loading further increases, the function rises again, achieving a masimum at a loading of 110 kg of coal/kg of gas. This maximum, or tendency to unsteadiness, is conjectured to be the transition into the slugging, or choking, region of flow. After passing the maximum, the flow at higher loading settles down to a more homogeneous, steady dense-flow behavior_ This higher loading regime beyond choking is sometimes termed estrusion flow_ The Auburn voidage meter is felt to give an indication of some of the details of gas-solid flow structure over a wide range of solid loadings_ While clusters were not usually observed in this opaque experimental arrangement, their existence is based on conjecture_ However, with the visual observation of Yerushalmi and theories of Grace and Tuot [5] and Rlatsen 143, the drawing of such an inference appears probable.
Disclaimer This report was prepared as a account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, appar-
w-----
*
80
LOADlHG
[kg of cd
Fig. 1. Power spectral density ing (kg of coal/kg of gas).
160
120 ,LQ
of QCS]
function
CS. solid
load-
atus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors espressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. The flow-monitoring devices tested in this program were selected based on their unique features and their potential for providing satisfactory performance in the intended application. Other monitoring devices with similar capabilities may be available commercially_
References 1
F. Decamps,
TechnoL. 2
3
G_ Dumont
5 (19711i2)
J_ Yerushalmi, 69th cago. IL, (1976). H. Arastoopour and
and W. Goossens. Powder 299. Annual AIChE Ileefinp. Chi-
D. Gidaspoa, Powder Technol. . -3-3 (1979) 77. 1 J. Matsen, 74th Annual _-lIChE Meeting. _\reu.Orleans, LA (1981). 5 J. R. Grace and J. Tuot, Trans. Inst. Chem. Engrs.. 57 (1979) 4.
Short
Technology.
34
(1983)
109 - 111
109
Communication
Evaluation of Gas-Solid a Voidage Meter
Flow Behavior using
G. E. KLINZING ChcmicaI/Petrole~rn~ sits of Pittsburgh.
F .ginccring Depnrtmsnt. Uni~crPiitsburgh. PA 15261 (U.S.A.)
and M. P. MATHUR Li.S_Department of Energy. Pittsburgh Energy nology Center. Pittsbu@. PA 15236 (US_A.) [Received June 2.1952;
Tcch-
in revised form July 29.1982)
The existence of clusters of particles as an equilibrium condition in gas-solid transport has been documented or inferred in a number of papers [l - 43 _ Some theoretical analysis has shown that even in the dilute phase regime the condition of a uniform dispersion of particulates in a flowing system is unstable [ 5]_ Esperimental analysis of such clusters is a difficult task. One would have to observe these clusters of particles under in situ conditions. Probably high-speed photography and microscopic analysis would be required. Recently, some experiments were conducted under a variety of loading conditions from 0 to 200 kg of solid/kg of gas for the pneumatic transport of fine coal (Dp - 100 pm). This system employed an Auburn meter to monitor the voidage of the flow. The Auburn meter measures the average dielectric constant of the flowing media by applying a potential to a rapidly changing sequence of perpendicular electrodes placed around the circumference of the meter- The meter has the same diameter as the flow sys’&m and as such does not obstruct the flow. In our study, the meter was placed on the vertical section of the test unit, as shown in Fig. 1. A 0.0095 m diameter line was employed with Montana Rosebud coal having an average weight diameter of 60 pm. The influence of the bends before and after the meter were felt to be minimal, since both bends have a 0.82 pm radius and are far removed from the meter. The output voltage from the Auburn meter is usually averaged over a period of 50 to 120 s and recorded on 0032-5910/83/0000-00001503.00
Fig. 1. Schematic of the coal flow test loop facility. 0.0095
m diameter pipe.
--Ii20
msec
Fig. 2. Output signal from the Auburn Monitor.
a data-acquisition system_ In this study. the instantaneous voltage output of the meter was recorded on a strip chart. Figure 2 shows a typical instantaneous output signal trace. As the loading of solids was changed, the signal level and amplitude of the fluctuations noticeably varied. The frequencies observed by the Auburn meter response are much larger than any fluctuations introduced in the gas and solid injection systems. Khile visual observation of the clusters was not made, the frequencies of the fluctuations seem to point to the cluster phenomena observed by Yerushalmi @ Elscvier SequoialPrinted
in The Setherlnnds
110
[2]. In order to analyze this output signal in more detail, a high-speed FM tape recorder was connected to the Auburn meter output signal. Once the signal was recorded, a Hewlett Packard 302A wave analyzer was emplcyed to break the signal down into component frequencies and amplitudes. The signal was then analyzed to obtain characteristics of the flow.
Analysis The tests analyzed were carried out under a variety of operating conditions_ Table 1 summarizes these conditions. The loadings varied from 23 to 124 kg of coal/kg of gas. The higher loading conditions are most probably in the dense phase flow regime. By use of the wave analyzer, a frequency spectrum was constructed for each condition. Is typical frequency spectrum is shown in Fig. 3. It was noteworthy that the frequency at which the maximum amplitude occurred was approsimately the same for each test. Using standard turbulence theory, the data have been analyzed to find the length scale of the turbulence-like signal seen in Fig. 2. This has been done in an effort to infer possible cluster sizes for the flowing particles. Using the concept that the reciprocal frequency gives a time constant, the length scale of the signal can be shown as
(1) For the test conditions considered here, u = 35 m/s and f = 6-72 k Hz; h is found to be abotlt 0.50 cm. The superficial gas velocity remained relatively constant for all tests conducted. This length scale of 0.5 cm can be inferred to be of the order of magnitude of the flowing cluster of particles_ This inference can be made, since the Auburn meter will respond to changes in density of the flowing material. A cluster of particles is naturally more dense than a homogeneously distributed group of particles. The Auburn meter, which determines the average instantaneous voidage in the vertical test line, can be employed to find this cluster size. It is interesting to compare these findings on length scale to the cluster sizes found by Yerushahni (23 in his analysis of ‘fast fluidization’. Yerushalmi showed that a cluster diameter could be derived by equat-
TABLE
1
Experimental
test conditions Loading
Test
Solid
number
flowrate (kg/s)
(kg of coail
1 2 3 4 5 6 7
0.052 0.098 0.121 0.099 0.160 0.185 0.194
43.9 86.1 109.7 85.6 134.4 167.3 173.0
kg of gas)
6600
6700 FREQUENCY,
LHZ
Fig. 3. Frequency spectrum of the Auburn loading 57.5 (kg of coal/kg of gas)_
signal;
ing the drag force across the bed to the static pressure drop. Under a variety of conditions with 60 pm diameter catalyst particles, cluster diameters from O-1 to 4.5 cm were measured, and voidages ranged from 0.98 to 0.75. The length scale obtained by analysis of the unsteady signal from the Auburn meter measuring point voidages gives a value that in the range found by Yerushalmi. Each of the tests conducted had a run time of 30 min under steady conditions. The signal from the Auburn Monitor was consistent over this time range; analysis of the signal is therefore felt to be representative of a significant macro-steady condition.
111 In addition to the length scale calculated above, the frequency spectrum from each test as shown in Fig. 3 was integrated over frequency to form the power spectral density function
s’
= j-F(w)
dw
(2)
0
d This function was plotted as a function of solids loading (Fig. 4). One sees first that the function decreases with increased loading, which indicates a more uniform flow. As the loading further increases, the function rises again, achieving a masimum at a loading of 110 kg of coal/kg of gas. This maximum, or tendency to unsteadiness, is conjectured to be the transition into the slugging, or choking, region of flow. After passing the maximum, the flow at higher loading settles down to a more homogeneous, steady dense-flow behavior_ This higher loading regime beyond choking is sometimes termed estrusion flow_ The Auburn voidage meter is felt to give an indication of some of the details of gas-solid flow structure over a wide range of solid loadings_ While clusters were not usually observed in this opaque experimental arrangement, their existence is based on conjecture_ However, with the visual observation of Yerushalmi and theories of Grace and Tuot [5] and Rlatsen 143, the drawing of such an inference appears probable.
Disclaimer This report was prepared as a account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, appar-
w-----
*
80
LOADlHG
[kg of cd
Fig. 1. Power spectral density ing (kg of coal/kg of gas).
160
120 ,LQ
of QCS]
function
CS. solid
load-
atus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors espressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. The flow-monitoring devices tested in this program were selected based on their unique features and their potential for providing satisfactory performance in the intended application. Other monitoring devices with similar capabilities may be available commercially_
References 1
F. Decamps,
TechnoL. 2
3
G_ Dumont
5 (19711i2)
J_ Yerushalmi, 69th cago. IL, (1976). H. Arastoopour and
and W. Goossens. Powder 299. Annual AIChE Ileefinp. Chi-
D. Gidaspoa, Powder Technol. . -3-3 (1979) 77. 1 J. Matsen, 74th Annual _-lIChE Meeting. _\reu.Orleans, LA (1981). 5 J. R. Grace and J. Tuot, Trans. Inst. Chem. Engrs.. 57 (1979) 4.