Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 4, 1979
Y = ratio of r , / R in an unreacted-core-shrinking particle Subscripts i = gaseous component j , k = reactions in solid and gas phase, respectively, see
definition in Appendix Literature Cited Anthony, D. B., Howard, J. E., AIChE J . , 22, 625 (1976). Anthony, D. B., Howard, J. B., Hottel, H. C., Meksner, H. P., Fuel, 55, 121 (1976). Eadzioch, S., Hawksley. P. B. W., Ind. Eng. Chem. Process L k s . Dev., 9, 521 (1970). Bissett, L. A., "An Engineering Assessment of Entrainment Gasitlcation", MERC/RI - 7812, Morgantown Energy Research Center, April 1978. Dobner, S., Modeling of Entrained Bed Gasification: The Issues", EPRI, Palo Alto, Calif.. Jan. 15, 1976. Evans, F. L., Jr., "Equipment Oesign Handbodc for Refineries and Chemical Phnts", Vol. 2, p 9, Gulf Publishing, Houston, Texas, 1971. Field, M. A., Gill, D. W., Morgan, B. E., Hawksley, P. B. W., "Combustion of Pulverized Coal", BCURA, Leatherhead, 1967. Hottel, H. C., Williams, G. C., Nerheim, N. M., Schneider, G. R., 10th International Symposium on Combustion, 111-121, 1965. Kane, R. S., McCailister, R. A,, AIChE J., 24, 55 (1978). Loison, R., Chauvin, R., Chem. Ind., 91, 269 (1964). Ludwig, E. E., "Applied Process Design for Chemical and Petrochemical Plants", Vol. 111, 1965. McAdams, W. H., "Heat Transmission", 3rd ed, Chapter 4, p 95, McGraw-Hill, New York, N.Y., 1954. Pitt, G. J., Fuel, 41, 267 (1962).
695
Robin, A. M., "Hydrogen Production from Coal Liquefaction Residues", EPRI Rpt., EPRI-AF-233 (Dec. 1976). Robin, A. M., "Gasification of Residual Materials from Coal Liquefaction", D.O.E. Quarterly Report, FE-2274-11 (Oct. 1977). Russel, W. B., Saville, D. A., Greene, M. I., 70th AIChE Annual Meeting, New York, N.Y., No. 101, Nov. 1977. Singh. C. P. P., Saraf, D. N.. Ind. Eng. Chem. Process Des. Dev., 16, 313 (1977). Suuberg, E. M., Peters, W. A., Howard, J. B., Ind. Eng. Chem. Process Des. Dev., 17. 37 (1978). Wen, C. Y., Bailie, R. C., Lin, C. Y., O'Brien, W. S., Adv. Chem. Ser., No. 131, 9 (1974). Wen, C. Y., Ind. Eng. Chem., 60, 32 (1968). Wen, C. Y., Fan, L. T., "Models for Flow Systems with Emphasis on Chemical Reactor Modeling", Chapter 7, Marcel Dekker, New York, N.Y., 1975. Wen, C. Y., "Optimization of Coal Gasification Processes", R D Report No. 66, Office of Coal Research, U S . Government, 1972. Wen, C. Y., Dutta, S., "Rate of Coal Pyrolysis and Gasification Reaction", chapter of the monograph "Coal Conversion Technology", Wen and Lee, Addison-Wesley, 1979. Wen, C. Y., Tone, S., ACS Symp. Ser., No. 72 (1978). Ubhayaker, S. K., Stickler, D. B., Gannon, R. E., Fuel. 56, 281 (1977). Zahradnik, R. L., Grace, R. J., Adv. Chem. Ser., No. 131, 126 (1974).
+
Received for review October 24, 1978 Accepted June 15, 1979 This work was supported by Contract E(49-18)2274for the United States Department of Energy.
A High-Temperature Pneumatic Transport Line Test Facility Wen-ching Yang," Walter G. Vaux, Dale L. Keairns, and Ted Vojnovich Research and Development Center, Westinghouse Electric Corporation, Pittsburgh, Pennsylvania 15235
Under the sponsorship of the Electric Power Research Institute, we constructed a high-temperature pneumatic transport line facility to test refractories under simulated high-temperature dilute-phase (high particle velocity and low particle concentration)erosion conditions. Two ambient temperature tests lasting 52 h and four high-temperature runs (640 to 925 O C ) lasting 85 h were conducted in the test facility. This paper describes the equipment, construction, operation, and capability of the facility and discusses briefly the test results. A companion paper presents the detailed data analysis and the development of a predictive model for refractory erosion.
Introduction
Because of the abundance of coal reserves in the United States, one of the alternatives for achieving energy selfsufficiency is to convert coal into a clean-burning fuel through coal gasification or by direct combustion with air in a fluidized bed for steam and power generation. The operating conditions in these processes of widely different design involve temperatures ranging from 500 to 1500 "C, pressures ranging from 0.1 to 10 MPa, reducing and oxidizing atmospheres, and a generally erosive and corrosive environment. Metal and refractory structurals and linings are used to construct the reaction vessels, transfer lines, valves, and cyclone separators. These materials must be able to withstand erosion and corrosion by particulateladen gas streams. An understanding of the erosion of these materials in the corrosive environment of coal conversion systems would be helpful in predicting expected life and in designing long-lived materials of construction for such systems. Westinghouse, funded by the Electric Power Research Institute, has concluded a two-year program to design refractory materials for use under erosion/corrosion 0019-7882/79/1118-0695$01.00/0
conditions at high temperature in coal-gasification and coal-combustion systems. Portions pertaining to the application of pneumatic transport principles are presented here. A vertical pneumatic transport line operating at atmospheric pressure and at temperatures up to 925" C was conceived as a test facility for erosion/corrosion studies of the refractories. A pneumatic transport line test facility possesses the following advantages: (1) A large number of test samples can be evaluated at each test. ( 2 ) The solid particle types, sizes, velocities, and concentrations can be easily controlled and changed. (3) The operating conditions are close to those in the transfer lines of commercial plants. (4)Reliability is high for long duration operation. ( 5 ) Actual components such as valves, cyclones, and elbows can be tested a t the same time. Pneumatic Transport L i n e Test Facility
A schematic of the test facility is presented in Figure 1;the test facility is also pictured in Figures 2 and 3 with labels identifying each major component. The detailed description for each major component follows. P n e u m a t i c T r a n s p o r t Tube. The main part of the test facility was the L-shaped pneumatic transport tube 0 1979 American
Chemical Society
696
Ind. Eng. Chem. Process Des. Dev., VOI. 18, No, 4, 1979 Exhausi to High-Temperature Flue
t
rSar Sample
Refractory W Lightweight Cartable ES -Refractory Specimens m
H
Figure 1. Impingement tube test facility. Figure 3. The burner (a) forms hot exhaust at 1260 "C. Granular solids are carried from the hopper (b) through the screw feeder (c) and fall into the stream of hot exhaust and are swept up the vertical tube (d).
Fp;um 2. T h e ~mpngrme.nileri ikdw a, ga- l,uner; b, solids screw feeder; e, [est m t i w * ; 11. cyclone; e, solidi r e < ~ v e r yline.
constructed from sections uf 34.3 cm i.d. steel (nominal 14-in., schedule 4U) pipes. There were two tee sertions making up the horizontal run, four 0.76-m acceleration sections, and five 0.30-m test sections in the vertical run. An elbow section on top of the column direcled the particulate-laden gas into a cyclone. Thc 0.76-m acceleration sectiuns were lined with Harhison-Walker Altec
high alumina tubes of dimensions 5 cm i.d. X 10 em 0.d. X 38 cm long to resist erosion in the acceleration region of the pneumatic impingement unit. The back-up insulation was provided by 13 cm of Harbison-Walker Lightweight Castahle ES. Every 0.30-m test section was originally designed to accept two refractory test specimens 5 cm i.d. X 10 cm 0.d. X 15 cm long. The test specimens were changed to 5 cm id. X 10 cm 0.d. X 4.4 cm high later. Four curved sections of Harbison-Walker Siltec, a claybonded silicon carbide refractory, 5 em i.d. X 10 cm 0.d. were used to form the 53-cm radius elbow backed by 13 cm of lightweight castable insulation. The sections were held together by 150 lb slip-on flanges. Flexitalic gaskets with 304 stainless steel backing were used between the flanges. The unit was supported at the bottom by a 5.1-cm steel plate insulated from the column itself by a 2.5 cm thick piece of transite. The platform and the total unit could be moved up and down by four 2-ton screw jacks with a travel distance of 15 cm to facilitate the removal of the test sections. The column was surrounded by a steel structure to prevent its lateral movement while allowing vertical growth during hot operation. One hole was provided in every flange to accept a thermocouple or pressure probe. All pressure probes led to a 6-tube manometer panel. Any blockage could be readily detected through the abnormal pressure drop. The metal surface was painted with Tempi1 temperaturesensitive paint to warn of the refractory breakdown. The test facility was scattered with thermocouples leading t o a 24-point recorder for monitoring both the inside and outside temperatures along the column. Solids Feeding Device. The solids feeding device was a screw feeder supplied by Acrison, Inc. with a 0.17 m3 hopper. The screw speed was controlled by a variable speed dc motor capable of a speed range of 30 t o 1 (or a
Ind. Eng. Chem. Process Des.
Dev., Vol. 18. NO. 4. 1979
697
Table I 100% Stoichiometric, excess air,
co, H,O
N, 0,
%
."
W," "
9.53 18.86 71.61
5.03 9.95 75.58 9.43
0
250% excess air, l"
2.94 5.82 77.40 13.84
120 to 4 output rpm range). The feeder was calibrated on site by collecting the solids delivered over a 10-min period at different control settings. Particulate Removal System. A cyclone made of 310 stainless steel by Fisher-Klosterman, Inc. was used t o remove the particles from the gas stream. The recovered particles were collected in a water-cooled 55-gal drum. The remaining particles in the gas stream were again cleaned in a knock-out drum before being vented through the high-temperature flue. N a t u r a l Gas Burner. The hot gas was provided by burning natural gas with a burner at the end of the horizontal leg (see Figures 1 and 3). The Series 4422 (Model 4422-4) XSA natural gas burner was supplied by the North American Manufacturing Co. This sealed-in nozzle-mix burner was stable with up to 2100% excess air, depending on the air pressure. The Honeywell flame safeguard is a UV system with Minipeeper ultraviolet flame detector, cabinet, and purge timer. A t ambient temperature the test environment was air; at elevated temperatures, the gas environment depended on the operating temperature and heat losses. Assuming no heat losses, a flue gas temperature of 760 "C (1400 "F) could be attained by complete combustion of natural gas (assuming 96% CH4, 3.2% N2,and 0.8% C0.J with 250% excess air. A flue gas temperature of 1204 "C (2200 "F) could be attained with 100% excess air. The gas environment under these two operating conditions was calculated and compared with that of stoichiometric combustion. (See Table I.) In the actual operation larger gas/air ratios were required because of heat losses and possibly incomplete combustion. The gas compositions would be slightly different from those shown; the actual gas composition, however, could be calculated from the actual flow rates of natural gas and air. The burner was selected t o permit modification for burning on the reducing side. Injection of water vapor and other corrosive compounds such as alkali metal and sulfur compounds into the combustion gas containing reducing
Figure 4. Refractory test samples to be located in the 0.30 m test sections.
gases would provide the corrosive condition similar to that in a coal gasification plant. High-Temperature Instrumentation. A platinumrhodium thermocouple was located between the gas bumer and the solids inlet point to measure the flue-gas temperature. The temperature was continuously recorded in a miniservo recorder (I31600 "C range) by Esterline Angus. Chromel-alumel thermocouples were located along the pneumatic transport line and a t each individual test section. The penetration of the thermocouples into the gas-solids stream could be adjusted individually. Thermocouples were also attached to the metal surfaces of the test facility and the cyclones. All temperatures were monitored continuously and automatically by a 24-point chart recorder with alarms. Experimental Conditions Two runs were performed a t ambient conditions, the first for 12 h and the second for 40 h. Ten 15 cm high hollow cylindrical specimens were evaluated in both runs. The specimens included four of the high-purity alumina castable A, three of the chrome castable C, and three of the lightweight castable F. The specimens were stacked in the five test sections in the order A-C-F-A-C-F-A-C-F-A. Four tests were completed at high temperatures ranging from 642 to 924 "C. In the first and second tests only hollow cylinder specimens were placed in the test section. In the third and fourth tests transverse bars spanning the
Table 11. Summary of Impingement Tube Test Facility Operating Conditions
run no.
ATP-1 ATP-1 HTP-1
HTP-2
calcd solid solid run gas loading, particle geometry of duration, temp' velocity, kg of solid/ velocity, specimens h av peak solid particles mis k g o f gas m/s hollow cylinders, 12 20 20 -18 mesh dead-burned dolomite 20.9 0.23 12.5 15.2 em high particles with a weight-mean average size of 500 ;m hollow cylinders, 40 20 20 20.9 0.23 12.5 15.2 cm high hoilowcylinders, 2.5 642 642 20.6 0.61 11.3 15.2 cm high hollowcylinders, 25 675 707 22.5 1.0 11.9 15.2 em hiah rings" and 32 715 740 23.5 1.13 12.5 couponsb ringsa 25 807 924 23.0 0.42-1.66 12.0 ~
HTP-3
HTP-4
Height of rings averaged approximately 4.45 cm (1.75 in.). 5.08 cm (0.5 in. X 2.0 in,).
a
X
Cross-sectional area of coupons in gas stream was 1.25 em
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Ind. Eng. Chem.
Process Des. Dev., Vol.
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Table In. Detailed Profiles of Test Section Temperature and Particle Velocities for Selected Time Intervals in Test Run HTP-4 test interval, 1977
T/C height above bottom of test section
solids feed temp rate range, "C
from 5/24 to 5/25
2000 0040
high 86 kg/h
lower 684-724
T/C temp, 'C particle velocity,
from 5/25 to 5/25
1430 2355
low 23 kg/h
higher 851-924
T/C temp, "C particlevelocity,
1 2 2 c m 152cm
Ocm
30cm
61cm
91cm
724 10.74
720 10.71
720 10.71
707 10.59
704 10.57
684 10.38
924 13.09
928 13.10
918 13.03
903 12.91
899 12.77
851 12.44
mIS
m/s Table IV. Summarg of Test Results in the Pneumatic Impingement Test Facility Using -18 x 0 Mesh Dead-Burned Dolomite Particles. The Test Was Run for 40 h at Room Temperature with a Solids Feeding of 90 Ih/h (Area of Cvlinder = 243.1 cm'l
refractory material A (alumina)
wt
position
loss, g
cm'
7. 0 4.0 38.0 10.0 2.0 88.0 8.0 3.0 46.0 1.0 6.5 3.0 57.3
2.60 1.38 26.69 3.71 0.69 68.75 2.96 1.03 35.94 0.37 2.41 1.03 44.8
top
C (chrome) F (lightweight) A
C F A C F A
av A C F
vol. loss
specimen
bottom
tube diameter were placed every 30 cm along the tube. The specimen configurations for all tests are summarized in Table 11. The arrangement of the test specimens is shown below. Arrangement of Test Specimens. The refractory test specimens used in the earlier tests are shown in Figure 4. Each 30.5 cm test section can accept two of these test specimens (5 cm i.d. X 10 cm 0.d. X 15 em long). The one on the left with the tongue was seated a t the bottom of the test section and the one on the right without the tongue was on top of it. After analyzing the initial test results, it wax decided that rings 4.4 cm high rather than 15 cm high cylinders should he used. This change allowed more samples to be tested in each run so that duplicates could be used and the weight losses were a larger percentage of the original sample weight. In addition to the ring samples, bar samples shown in Figure 5 were also positioned in each test section. The lower surfaces of the samples were sloped to provide different impingement angles toward the solids-carrying gas stream. Operating Conditions. The operating conditions for both the ambient and high-temperature tests are summarized in Table 11. The solid particles used in the tests are -1000 pm (-18 U.S.mesh) dead-burned dolomite with a weight-mean average particle size of 500 pm, Because of the heat losses through the column wall, the temperature at each test section was slightly different. The typical temperature profile in the five 30.5-cm test sections is presented in Table 111, along with the temperature effect on the solid particle velocity. The temperature difference between the top and the bottom test sections is usually around 50 O C . The change in solid particle velocity due t o the temperature change is less than 5%. Experimental Results Erosion Test Results. The results of the second cold flow run of 40 h duration are reported in Table IV in weight losses and volume losses per gram and per particle. The chrome castable C experienced the lowest erosion loss,
cm'/cm' 0.0107 0.0057 0.1221 0.0152 0.0028 0.2828 0.0122 0.0043 0.1478 0.0015 0,0099 0.0043 0.1842
vol. loss per gram, cm3/cmi/g
6.56 x 3.50 x 10-9 74.9 x 9.32 x 10-9 1.72 x 173.50 x 7.48 x 10.' 2.64 x 90.7 x 10-9 0.93 x 10-9 6.05 x 10-9 2.63 x 10-9 112.1 x 10-9
vol. loss
per particle,
m'/m'/particle 1.28 0.69 14.7 1.83 0.32 34.0 1.46 0.52 17.8 0.18 1.18 0.52 22.1
Figure 5. Kefractory bar for HI'Y-3 shown supported in a castable (F)ring specimen. The leading edge of the coupon was shaped for 309 impingement.
the lightweight castable F the highest erosion loss, and the alumina castable A slightly more than the chrome castable. The erosion mechanism observed in specimens tested in the impingement tube appears to have occurred by simultaneous preferential attack of the bonding phases and fine-grained matrix with some undercutting and attack of the larger aggregates. The presence of pores is also known to promote erosion. In Figures 6 and 7 the eroded surfaces of castable F and A parallel to the air flow are shown. The lightweight castable evidenced much more erosion than did the alumina castable, as indicated by weight loss measurements. In Figure 8 the erosion in the vicinity of a large aggregate is shown. The erosion pattern shows
Ind. Eng. Chem. Process Des. Dev., Vol. 18. No. 4, 1979 699
T
AIR F t O W
Figure 8. Erosion of lightweight castable F cylinder in the vicinity of an aggregate (arrow indicates direction of airflow). seccian
Figure 6. Erosion of lightweightcatable F cylinder in the test section of the pneumatic impingementtest facility after 48 h (arrow indicates direction of airflow).
&D
ID E
Fisure 7. Erosion of high-alumina castahle A cvlinder in the t e s t ~" section of the pneumaticlmpingementtest facility after 48 h (arrow indicates direction of airflow). ~~~~
~~~
~~~~
~~~~
erosion on either side of the aggregate with the erosion profde following aerodynamic lines. The aggregate appears t o have played an important role in resisting erosion. It is surmised that further erosion in the vicinity of aggregate would he controlled by the erosion of the aggregate protruding tip. As this tip eroded, the bonding phases and matrix in front of the aggregate would he cut hack until the aggregate was completely eroded away or until the aggregate was freed by breaking away or by some undercutting. It is also interesting to note the wide range of erosive particle velocities and impingement angles. The lower erosion observed in the vicinity of the large aggregates implies that large aggregates carefully sized and graded to achieve maximum packing density with the minimum amount of cement phase necessary t o achieve
-
50-601 Alumha
C.rt*b,e
6.5,
WM,
Calcined Pire clay iiggregare
Figure 9. High-temperature run 760 "C pneumatic impingement tube.
high bonding strength should improve erosion resistance. The alumina (A) and chrome (C) castables with their hard dense aggregates did demonstrate less erosion than the lightweight castable F, which has relatively softer aggregates. Photographs of the eroded surfaces of the specimens in high-temperature run HTP-3 are presented in Figures 9 and 10. The summary results of high-temperature test runs HTP-3 and HTP-4 are shown in Figure 11 and 12 with relative ranking of refractories tested. In test HTP-3 interaction among specimens was evident. Transverse ham protected a lee area of several square centimeters of the
700
Ind. Eng. Chem. F'rocess Des. Dev., Vol. 18, No. 4, 1979
Integrity of Test Particles. The capacity of the solid hopper in the present test facility is 0.17 m3. A t a solid delivery rate of 41 kg/h in runs ATP-1 and ATP-2, the solids in the hopper will run out in about 6 h. Thus, after every 6 h of operation, the solids must be transferred back to the hopper from the collection drum underneath the cyclone dip leg. During the two runs with a total operation time of 52 h, one solid sample was collected every 6 h from the collection drum to study the attrition and decrepitation of the dead-burned dolomite. Their respective particle size distributions during the operation are presented in Table V. No apparent attrition or decrepitation is noticed, taking into consideration the possible variation of solids samples.
Figure 10. High-temperature run 760 "C pneumatic impingement tube.
cylinders from erosion. Those cylindrical specimens that readily eroded exposed the annular edges of downstream specimens to direct impingement, causing accelerated erosion. The detailed information on the preparation of the test specimens, on the analysis of the test data, and on the development of a model for predicting refractory erosion can be found in the final report submitted to EPRI (Vojnovich et al., 1977) and in a companion paper (Vojnovich et al., 1979).
Discussion and Analysis of Particle Velocities The most important parameters in the analysis of teat results from the pneumatic transport test program are the solid particle velocities, solid particle concentrations, and impingement angles, a t sample specimen locations. The fact that the solid particles are usually irregular in shape, different in size, and numerous in the pneumatic transport line makes the determination of these parameters even more difficult. Pure theoretical analysis often introduces many arbitrary parameters that have t o he determined experimentally for each individual case and often does not lead to physical insight into the observed phenomena in the transport line. The most successful approaches so far are the semiempirical ones. The literature for both the vertical and horizontal pneumatic transport lines has been reviewed (Yang, 1977). Methods of calculating the particle acceleration length, particle velocity, particle concentration, and line performance are available (Yang, 1973,1974,1975; Yang et al., 1973; Yang and Keairns, 1976). The proposed correlations cited in these references have been tested with good engineering accuracy against a very wide range of literature data in terms of particle size, particle density, particle shape, and conveying conditions. These correlations are briefly described below and were used in the calculations. Estimation of Solid Particle Velocity. Starting with material and force balances in a differential section of pipe length, dL, Yang (1973; Yang et al., 1973) derived the
: -Caslabie
Average Erorion Lor$ per Particle
' -Piastir
Refractory
Description
M
85% Alumina
K
- F i r m Phos - Bonded Brick
S -Fired S n a p
1 1 0 - ~m ~ 3im2~~i
anking ~
FS
1O.DXLI
1
WZ Aiumma Brick - Mullite Bonded
FS
]O.Owa
2
P
70% Alumina Firebrick
FS
]am
3
0
90% Alumina - P h o i Bonded
P
10.2
4
L
405 Alumina Firebrick
FS
30.6
5
I
50% Alumina
- Fireciay Aggregates
C
30.7
6
E
60% Alumina .Fireclay Aggragalar
C
7 1 1
7
C
Chrome 146% Alumina 23% Chramiai
C
1
B
%%Alumina
C
1
1
.
9
9
H
4 % Alumina - Fused Aggregde~
C
I
1
.
9
10
G
83% s i c - CA Bonded
C
1
1
.
9
I1
J
Samear~wlh4%K~iin~ddiliver
C
A
4%Alumina -Tabular Alumina Aggregates
C
-
- Fine Tabular AiUrniM Aggrqaler
0
%%Alumina
- Coarse Tabular Alumina Aggregater
C
F
40% Alumina
- Lightweight Aggrqaler
C
1
8
8
12
12.6
I3
12.9
14
16.2
,' 148.9
E -
Figure 11. Relative ranging of refractories tested for erosion resistance at high temperature in the pneumatic impingement test facility. Run HTP-3.
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 4, 1979 701 P - Plastic FS - Fired Shape
Description
Refractory
M
85% Alumina-Fired Phos-Bonded Brick
K
W% Alumina
0
W% Alumina -
- CA
Brick
- Mullite Bond
Phos Bonded
FS
m3/m2/pi
lanking
I 0. 1
1
FS
2
P
3
G
83% S i c
L
40% Alumina Firebrick
FS
5
P
70% Alumina Firebrick
FS
6
A
96% Alumina - Tabular Aggregate
C
7
H
% % A l u m i n a - Fused Aggregates
C
Bonded
2. 1
C
- 23% Chromiai
C
Chrome 146% Alumina
I
50% Alumina
- Fireclay Aggregates
C
B
%%Alumina -FlneTabuiar A l u m i n a Aggregates
C
J
Sameas A With 4% Kaolin Addition
C
D
%% Alumina - Coarse Tabular Alumina Aggregates
C
E
6 0 % Alumina
- Fireclay Aggregates
C
C
40% Alumina - tiqhhveiqht A q q r w t e s
4
4. 3
F:.7 , 4.4
10. 3
8
9 10 11
u
M,:2 13 14
C
L1
197. 7
15
Figure 12. Relative ranking of refractories tested for erosion at high temperatures in the pneumatic impingement test facility. Run HTP-4.
equations for calculating the solid particle velocities in both the vertical and horizontal pneumatic conveying lines as follows vertical conveying
horizontal conveying
where (3) To solve for solid particle velocity from eq 1 and 2, a knowledge of solid friction factor, f p , is necessary. Yang (1974,1978a) proposed two empirical equations for both vertical and horizontal pneumatic conveyings. vertical conveying fp
= 0.0126- (1 t3
[
€1 (1 - 4-
1-0.979
(4)
and Jones (1950) and Mendies et al. (1974) for horizontal conveying were recently tested (Yang, 1977). The accuracy of the proposed equations is fairly convincing. Except for the Alundum particles of size 8390 pm in horizontal transport, the accuracy is within &30%. Estimation of Particle Acceleration Length. When particles travel from a horizontal to a vertical direction, the particles must be accelerated from essentially zero velocity to their final velocities. The distance required for this acceleration is important. If the test samples are located within the acceleration length, the particle velocities and the particle concentrations at the sample locations will be different from their final equilibrium values. The erosion characteristics will then be different for samples at different locations. It is preferable to locate all test samples outside this acceleration region so that the sample location can be eliminated as an additional variable. Yang and Keairns (1976) developed two equations for calculating the acceleration length in both the vertical and horizontal solids conveying lines. The lower limit of integration, Upl, in eq 6 and 7 is derived from eq 3 with an assumed voidage of 0.45, and the upper limit, Up?,is obtained from calculations performed in the last section. vertical conveying . hL =
horizontal convevinP: horizontal conveying Since the variables Up,e, and f p are interrelated, the trial and error solution is required to solve eq 1, 3, and 4 for vertical conveying and eq 2, 3, and 5 for horizontal conveying. The accuracy of the proposed equations has been tested previously (Yang, 1973; Yang et al., 1973) by comparing the experimental and calculated solid velocity for catalysts (Belden and Kassel, 1949; Hariu and Molstad, 1949), plastic particles, and Alundum (Hinkle, 1953). More data by Capes and Nakamura (19761, Lewis et al. (1949), and Mendies et al. (1974) for vertical conveying, and Hitchcock
4 The available literature acceleration data in both vertical and horizontal pneumatic transport were collected and compared with these proposed equations, and the accuracy was found to be &30% for more than 80% of the data. The type of materials included for comparison are PVC cubes to irregularly shaped coal to relatively spherical steel shot. The average particle size ranged from 2.56 pm to 1 2 700 pm; particle density from 1.05 to 7.51 g/cm3; tube
702
Ind. Eng. Chem. Process
Des. Dev., Vol. 18, No. 4,
1979
Table V. Summary of Particle Size Distribution for the Pneumatic Impingement Tests (Particles -18 X 0 Mesh Dead-Burned Dolomite) particle size distribution, mesh size accum. runno. run time, h 16 20 30 40 50 ATP-1 Oa 0.54 8.73 30.44 23.14 11.34 ATP-2
a
6 12 18 24 30 36 44 50 52
0.12 0.60 1.05 0.90 0.95 0.88 0.29 0.53 0.53
2.24 4.52 8.30 6.79 8.04 7.38 6.19 7.40 7.79
23.00 23.84 22.90 25.96 26.28 27.95 29.24 25.44 32.95
16.56 23.36 29.01 28.14 32.55 32.61 29.52 31.27 30.08
16.58 14.35 12.94 13.35 13.42 14.03 14.44 13.38 14.68
60 3.95 6.56 5.76 4.33 4.53 4.17 4.54 4.63 4.65 4.04
Pan 21.87 34.94 27.57 21.48 20.33 14.60 12.62 15.70 17.33 9.93
Original material.
i.d. from 3.2 to 12.7 cm; and conveying velocity from 8 to 44.5 m/s. The present operating conditions are within the range tested. Thus, similar accuracy in particle velocity and acceleration length calculations may be expected. Additional sources of error may come from: (1) the accuracy and stability of the screw conveyor metering the solids stream; (2) the change in gas temperature along the pneumatic transport line as it affects the actual gas velocity at each test section; (3) the loss of pipe smoothness as specimens erode, creating localized turbulence which is difficult to quantify. The mathematical model was only tested against data collected in smooth pipes; (4)the fact that pneumatic transport of particles of wide size distribution is not very well understood. The estimated particle velocity is the average particle velocity of the average size particles. Larger or smaller particles will travel at different velocities from that estimated. Segregation of particles in transport lines has also been reported (Nakamura and Capes, 1976; Yang, 1978b). I t is conceivable that at the top of the vertical leg where the test sections are located, the particle concentration of smaller particles may be larger than the mean concentration due to segregation; (5) the fact that when there are samples located across the gas-solids stream, the particles will be decelerated and reaccelerated. The interpretation of particle velocity after this disturbance is less certain. It is recommended that the subsequent cross samples be located as far apart as practical and that the samples be made as small as possible so that only a small fraction of the total solid particles will be affected. Conclusions There are a few limitations on the present pneumatic transport line test facility. Because of the small heat input into the reactor at an operating gas velocity of around 20 m/s, the heat losses through the reactor wall represent more than 30% of the total heat input. Heat transferred from the flue gas to the incoming cold solids takes an additional 10% (for solids/gas loading -1.0) or more, depending on the solids/gas loading ratio. The highest operating temperature at 20 m/s and solids/gas loading of 1.0 is -980 "C. This temperature limitation can be extended by increasing the heat input with increases in operating gas velocity, by preheating the solid particles, by decreasing the heat losses with decreases in particle concentration, and by insulating the reactor walls. The test duration at present is limited by the hopper capacity (0.17 m3). With a double-hopper arrangement the solids collected in the cyclone can be fed directly to a hopper immediately above the present feed hopper and thus increase the test duration indefinitely.
All the experiments performed so far have an oxidizing gas environment; the gas burner was selected to have the capability of producing a reducing gas environment as well. In this operating mode an afterburner may be needed for safety. Test specimens other than the refractories, such as metals, can be tested in the unit. Other high-temperature transport line components such as valves, cyclones, and elbows can also be evaluated in the test facility. More tests should be carried out to study the interactions between the test specimens. A preferred arrangement of the test specimens perhaps would be to locate the higher erosion-resistant specimens in the upstream side and to locate the lower resistant ones in the downstream. More fundamental studies should be performed to permit better estimation of particle velocity for particles of wide size distribution, of collision frequency with the test samples, and of impingement angles. Extrapolation of the erosion data obtained in this test facility to vessels of much larger diameter is not recommended. The mechanism of the surface loss of the castable material in large vessels is different. It is primarily due to thermal stress caused by expansion and contraction. Acknowledgment Financial support for this work from the Electric Power Research Institute is gratefully acknowledged. John Capozzi and Harry Sherwin ably constructed the facility and performed the tests. Nomenclature CDs = drag coefficient on a single particle d, = mean particle diameter, m D = inside diameter of conveying lines, m f = solid friction factor, fp = 4f, = solid flow rate per unit area, kg/m2 g = gravitational acceleration, m/sz U = particle acceleration length, m Uo = superficial fluid velocity based on empty-column cross section, m/s Uf = actual fluid velocity defined as Uo/c, m/s U = actual particle velocity, m/s Up, = lower and upper limits of integration, m/s U$ terminal velocity of a single particle, m/s W , = total solid flow rate, kg/h pf = fluid density, kg/m3 pp = particle density, kg/m3 p = fluid viscosity, kg/m s t = voidage in transporting lines Literature Cited
6
v"
Belden, D. H., Kassel, L. S., Ind. Eng. Chem., 41, 1174 (1949). Capes, C. E., Nakamura, K., Can. J . Chem. Eng., 51, 31 (1973). Hariu, 0.H., Molstad, M. C., Ind. Eng. Chem., 41, 1148 (1949). Hinkle. B. L., Ph.D Thesis, Georgia Institute of Technology, 1953. Hitchcock, J. A,, Jones, C., Brit. J . Appi. Phys., 8, 218 (1958).
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 4, 1979 Lewis, W. K., Gilliland, E. R., Bauer, W. C., Ind. Eng. Chem., 41, 1104 (1949). Mendies, P. J., Wheeldon, J. M., Williams, J. C., Proc. Pneumotransport. 2, No. 1 (1974). Nakamura, K., Capes, C. E., "Fluidization Technology", Vol. 11, pp 159-184, D. L. Keairns, Ed., Hemisphere Publishing Corp., 1976. Vojnovich, T., Keairns, D. L., Yang, W. C., Vaux, W. G., "Design of Refractories for Resistance to Huh Temperature Erosion/Cwosbn", Final Report submitted to Electric Power Research Institute under Contract No. RP625-1 (1977). Vojnovich, T., Keairns, D. L., Yang, W. C., Vaux. W. G., "Wear of Refractory Linings Under Dilute Phase Erosion/Corrosion Conditions", paper presented at the Coal Conversion Materials Conference, Berkeley, Calif., Jan 24-26, 1979.
703
Yang, W. C., Ind. Eng. Chem. Fundam., 12, 349 (1973). Yang, W. C., Keairns, D. L., Archer, D. H., Can. J . Chem. Eng., 51, 779 (1973). Yang, W. C., AIChE J.. 20(3), 605 (1974). Yang, W. C., AIChE J., 21(5), 1013 (1975). Yang, W. C., Keairns, D. L., Proc. Pneumotransport, 3, D7-89 (1976). Yang, W. C., J . Powder Bulk Solids Techno/., I,89 (1977). Yang, W. C., AIChE J.. 24(3), 548 (1978a). Yang, W. C., Proc. Pneumotransport, 4, 82-21 (1978b).
Receiued f o r reuieu' November 3, 1978 Accepted May 3, 1979
Theoretical Analysis of Reaction of Two Gases in a Catalytic Slurry Reactor' P. A. Ramachandran" and R. V. Chaudhari National Chemical Laboratory, Poona 4 7 1 008, India
The problem of reaction of two gases in a catalytic slurry reactor has been analyzed incorporating all the transport resistances. The concept of an overall effectiveness factor has been extended for this case and generalized equations have been developed for [ 1,1] and [ 1,0] order kinetics. The effect of gas-phase backmixing on the reactor performance has been discussed. Special features of [ 1,0] order kinetics have been pointed out. An application of the theory for [ 1,O] kinetics has been illustrated using SO2 oxidation in slurries of activated carbon.
Introduction In many industrial systems, two gases are contacted with a slurry and the reaction of the gases occurs on the active sites of the catalyst. A recent application is in the field of pollution control where pollutant gases such as SO2 (Komiyama and Smith, 1975) or H2S are oxidized in a slurry containing activated carbon as a catalyst. A process for hydrocarbon synthesis involves the reaction of CO and H2 in a slurry reactor in the presence of a suspended catalyst and this route appears to have some advantages over the conventional process (Kolbel and Ackermann, 1951; Schlesinger and Crowell, 1951). Other examples are oxidation of carbon monoxide in a slurry phase (Id0 et al., 19761, hydrogenation of olefins (Calderbank et al., 1963) and acetylene (Heck and Smith, 19701, oxidation of ethylene to ethylene oxide (Shingu, 1961) and hydroformylation of olefins using polymer bound catalysts (Pittman et al., 1975). Although the problem is important in several contexts, and some kinetic studies have been attempted, detailed analysis of the performance of slurry reactor incorporating the mass transfer effects of both the gases and intraparticle diffusion has not been published. A recent work in this direction is the work of Goto and Smith (1978), who have modelled the SO2 oxidation reaction system theoretically on the basis that the rate of reaction is independent of S O p concentration. The aim of this paper is to make a general theoretical analysis of the problem. Two types of kinetic schemes are analyzed-[ 1,1] order reaction and [1,0] order reaction. (The latter [1,0] has some special features necessitating a separate theoretical analysis.) Equations are derived to calculate the rate of reaction which incorporates the influence of all the transport resistances. The concept of an overall effectiveness factor is extended to a slurry reactor NCL Communication No. 2377, 0019-7882/79/1118-0703$01 .OO/O
and analytical equations are derived for calculation of this quantity. The application of the theory derived for [ 1,0] reaction is illustrated by an application to SOz oxidation in a slurry reactor. Overall Rate of Mass Transfer The reaction scheme considered is A + vB products
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Here A and B are two species present in the gas phase which dissolve in the liquid phase and react on the sites of the catalyst. Steady-state conditions are assumed to prevail. The mixing pattern of the gas phase in the reactor is assumed to be plug flow. The implications of this assumption will be examined later and the effects of gas backmixing will be discussed. It can be shown that the overall rate of transfer of A from the gas phase to the external surface of the catalyst can be expressed as
where
Equation 1 gives total rate of mass transfer from gas phase to the catalyst surface for the reactor and incorporates gas to liquid mass transfer, solid to liquid mass transfer, and also the effects due to the variation of gas phase concentration in the reactor. The latter (variation of gas phase concentration) does not appear to have been incorporated in most of the earlier analysis of slurry re0 1979
American Chemical Society
