400
Ind. Eng. Chem. Fundam., Voi. 18, No. 4, 1979
Gaseous Nitrogen Oxide Absorption in a Sieve-Plate Column Robert M. Counce' Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
Joseph J. Perona Department of Chemical Engineering, University of Tennessee, Knoxville, Tennessee 379 16
Nitrogen oxides were absorbed into dilute nitric acid in a three-stage sieve-plate column. The variables investigated were liquid flow rate, total gas flow rate, partial pressure of nitrogen oxide in the feed gas, acid molarity, and condensable gas (steam) flow rate. The results of the study indicate the importance of three mechanisms in the absorption of gaseous NO, compounds: (1) the absorption of N204, which results in the production of liquid "OB and "0,; (2) the dissociation of the liquid HNO, into HNO, and gaseous NO; and (3) the gas-phase oxidation of NO to NO2. An interesting aspect of this study was the detrimental effect that liquid nitrous acid has on nitrogen oxide removal efficiency. The removal efficiencies varied between 75 and 90%.
Introduction The removal of nitrogen oxides from gas streams is required in the aqueous reprocessing of nuclear fuels. It is important for NO, (NOz 2Nz0, NO) scrubbing equipment to provide (1)adequate gas-liquid contacting surface, (2) sufficient gas-phase residence time for the oxidation of NO to the more soluble NOz* (NOz + 2N204, a mixture of nitrogen dioxide and its equilibrium polymer, nitrogen tetroxide), and (3) relatively low column temperatures to facilitate these absorption and oxidation steps. Additionally, process equipment for use in a radioactive environment must be simple and easily maintained. Nitrogen oxide absorption studies were made using a tower fitted with sieve plates which provide high gas-liquid interfacial area for relatively low superficial gas velocities to aid in meeting requirements (1)and (2) (Counce and Perona, 1979). The column was designed to accommodate high liquid flow rates to remove heat generated in the absorption process, thus eliminating the usual cooling loads in the plate froth. The heat generated during the absorption process was removed from the liquor external to the column. The scrubber liquid was recirculated in order to produce an adequate-strength nitric acid for the liquid product. The gas mixture used in most of these studies was an air-nitrogen oxide-steam mixture. These experiments were conducted to study nitrogen oxide removal from gases containing large amounts of steam. However, the influence of steam on the tower performance appeared to be only on the first tray; otherwise, there is little difference in the results of experiments with and without steam. Experimental Apparatus and Procedure The flowsheet for the experiment is shown in Figure 1. The NO, scrubber is a three-stage sieve-plate column constructed of 0.076 m i.d. X 0.25 m long sections of Pyrex glass pipe. The plates and downcomers are constructed of stainless steel (Counce and Perona, 1979). The free area per plate, 0.670, is relatively low when compared with that of a typical sieve-plate column (Perry and Chilton, 1973). This is because the column was designed for high ratios of liquid flow rate to gas flow rate to facilitate the dissipation of the heat generated from the absorption reactions and the condensation of the steam;
+
+
0019-7874/79/1018-0400$01 .OO/O
the low gas velocity provides increased gas residence time in the column. Other equipment used in the experiment includes a scrubber liquid holdup tank, pump, rotameter, and heat exchanger; a gaseous NOz* supply system; and process air, steam, and water supply systems. The gas-handling equipment includes a N02*-air rotameter, an effluent gas holdup tank, an infrared analyzer to determine the concentrations of NO, in the feed and effluent gas streams, a calibration gas supply system, and an exhaust gas system. The system is normally operated by pumping the scrubber liquid from the scrubber liquid holdup tank and metering it through heat exchangers to the column. Upon leaving the column, the effluent liquid stream flows by gravity to the return tank. Gaseous NOz* is supplied to the system by vaporizing commercially obtained liquid NOz* in a temperature-regulated water bath. Process air is metered with the NOz* by a rotameter and is blended with steam in a common feed stream to the column. Steam flow is controlled by maintaining a constant differential pressure across a calibrated capillary tube. The system is allowed to reach steady-state conditions before data are taken. The system is considered to be at steady state when all gas and liquid flow rates, column temperatures, and NO, concentrations in the feed and effluent streams have shown no significant change over a 30-min interval. The gas stream is sampled before entering the column and on each stage. The gas-sample streams, with the exception of the feed stream, are passed through a sample holdup tank to provide sufficient time for the NO, gases to reach the NOz* state for analysis. The sample streams are then metered to an infrared analyzer (Lira Model 202), which is specific for NOz* and requires a gas with a known air-N02* content for the purpose of calibration. Samples of the scrubber liquid are taken when entering and leaving the column. These liquid samples are analyzed for HNO, and HNOz by standard techniques. Plate and column efficiencies are then calculated from the gas concentration differences. Theoretical The chemical reactions involved in the steady-state absorption of NO, compounds into water or dilute HNO, appear to be adequately represented as follows
0 1979 American Chemical Society
Ind. Eng. Chem. Fundam., Vol. 18, No. 4, 1979
* NzO,(g) NzO,(g) * NzOd(1)
2NOzk)
(1)
-
N204(l)+ HzO(l) HNOJ1) + HNOz(l) 3HN0,(1) e HzO(l) + HNO,(l) + 2NO(g)
-
(2) (3) (4)
2NO(d + 02(g) 2NOz(g) (5) where (g) and (1) indicate gas and liquid species, respectively. A review of the literature indicates that the following assumptions relative to the overall reactions may be made. 1. The NOz and N204 are in continuous gas-phase equilibrium (Bodenstein, 1922; Hoftyzer and Kwanten, 1972; Verhoek and Daniels, 1931). 2. Reaction of Nz04 and water proceeds by means of a fast pseudo-first-order liquid-phase reaction (Andrews and Hanson, 1961; Carberry, 1959; Caudle and Denbigh, 1953; Chilton and Knell, 1972; Corriveau, 1971; Dekker et al., 1959; Denbigh and Prince, 1947; Detournay and Jadot, 1973; Gerstacker, 1961; Hoftyzer and Kwanten, 1972; Koval and Peters, 1960; Kramers et al., 1961; Kameoka and Pigford, 1977; Moll, 1966;Peters and Holman, 1955; Peters et al., 1955; Sherwood et al., 1975; Wendel and Pigford, 1958). For NO2* partial pressures >0.01 atm, this is the predominant absorption reaction (Andrews and Hanson, 1961). 3. Liquid HNOz decomposes by eq 4 (Abel and Schmid, 1928a,b; Abel et al., 1928a,b; Abel and Schmid, 1929; Abel et al; 1930a,b). 4. Oxidation of gaseous NO occurs as an overall third-order gas-phase reaction (Ashmore et al., 1962; Bodenstein, 1918; Greig and Hall, 1967; Hasche and Patrick, 1925; Morrison et al., 1966; Treacy and Daniels, 1955). Experimental Data In general, two types of experimental results are reported here. A preliminary series of runs using a single plate were conducted to evaluate the effects on NOz* removal efficiency of varying partial pressures of NOz* and noncondensable gas flow rates, liquid flow rates, and steam flow rates. These experiments are reported in Table I. The bulk of the experimental work concerned the evaluation of the NO, removal efficiency of the described three-stage system a t design conditions. These studies are reported in Tables I1 and 111. The parameters studied using the three-stage system, as originally described, were the partial pressure of NO2* in the feed gas, the noncondensable gas flow rate, the scrubber liquid flow rate, the steam flow rate, sparging of the scrubber liquid prior to recycle, and the molarity of HNO, in the scrubber solution. Results and Discussion The partial pressure of NOz* in the feed and effluent gas streams during the single plate studies presented in Table I was determined by using the described gaseous NOz* analysis with N2 as the diluent gas. The absence of Oz prevented any oxidation of gaseous NO species to the NOz* state. Variation of the partial pressure of NO2* at a constant feed gas rate produced the results presented in Figure 2, where the NOz removal efficiency (Levenspiel, 1973) is defined as XNOP
=
1 - P N O ~ * o, u t / P ~ ~ ~in* , -k cpN02*, in/PNOz*,
401
(6)
out
As shown in Figure 2 for one gas rate and in Table I for several different gas rates, the NOz* removal efficiency increases with increasing partial pressures NOz*, reaching an approximately constant value for feed gas NOz* partial
-1 ROTllETER
W O L
0
VUVC
W
4'%*'2%
Figure 1. Flowsheet of equipment used in NO, scrubbing experiment. m3/sec
G = I86 x
80
L =I 75 x
i
IO-^ m%ec
T.292 K
X
50
40
c 000
005
010
015
PNo:,\N
020
025
C30
(atm)
Figure 2. Experimental NOz* absorption vs. the partial pressure of NOz* entering the tray at a total gas flow rate of 1.86 X lo-' m3/s in a single-plate column.
pressures greater than 0.05 atm. Also from Table I, the NO,* removal efficiency appears to be inversely proportional to some function of the feed gas flow rate. Some degree of direct proportionality to the liquid flow rate is also indicated. This is probably due to the increased froth height which produces higher gas-liquid interfacial area. The presence of steam produces an increase in NO2* removal efficiency with little proportionality to the steam flow rate. For the N2-NOz*-steam system, the NOz* absorption efficiency was directly proportional to some function of the liquid flow rate. The effect of steam on the NO2* absorption efficiency might be interpreted as a gas-liquid interfacial area effect. The removal of gaseous NO, compounds depends not only on the absorption of NOz* but on the dissociation of liquid HNOz producing gaseous NO and the subsequent oxidation of NO. Thus, the bulk of the experimental work was focused on obtaining experimental NO, removal efficiencies for the three-stage column using the system as
Ind. Eng. Chem. Fundam., Vol. 18, No. 4, 1979
402
IO0
100
0 90
0 90
0
OVERALL
080
so
0 70
0 70 0 60
0 60
K
0 050
z
X
0 050
X
z
0 40
X
0 40
fldG-*
0 30
PLATE 2
0.30
PLATE 3
0 20 0 10
0 20
0.oc
0 10 0 .oo
3 .O
20
IO
L ( mJ/s
4 . 0 a IO-'
I
loo
O'gOt
\
0.90
c
080 070
t
OVERALL
00 0" z
I
0.20
0.30
0.40
0.50
P N O ~ F E E D( a t m )
Figure 5. NO, removal in three-stage sieve-plate column for varied partial pressure of NOz* in feed gas.
Figure 3. NO, conversion in three-stage sieve-plate column for varied scrubber-liquid flow rates.
0.80
.
0.10
PLATE 1
I
I
I
I
IO
20
30
40
0.501
Figure 6. Overall NO, removal in three-stage sieve-plate column for varied acid molarity in scrubber liquid.
1
1
0.20 0.1 0
I
O.OOl
It5
20
2.5
3.0a
G h3/d
Figure 4. NO, removal in three-stage sieve-plate column for varied feed-gas flow rates.
described in the Experimental Section. Increasing the flow rate of the scrubber liquid decreases the internal column temperatures (Tables 11, 111; experiments: 50, 42, 48, 49). The decreased column temperatures result in higher overall NO, conversion, XNo,,as shown in Figure 3. The term XNO,is defined in an analogous way to XNO (eq 6). Within the column, t i e response to increased liquid flow rates is most apparent on the first plate, where the temperature decrease is most pronounced. The increased NO, conversion on the first plate seems to be the major factor in greater overall NO, conversion with increased liquid flow rates. This is consistent with the increase in absorption rates with increased partial pressures of Nz04. Also, the oxidation of NO is increased at reduced temperatures (Ashmore et al., 1962; Bodenstein, 1918; Greig and Hall, 1967; Hasche and Patrick, 1925; Treacy and Daniels, 1955). The effect of higher gas flow rates is a slight decrease in NO, conversion throughout the column (Tables 11,111; experiments: 62, 42, 60, 44). This is shown in Figure 4.
This effect is probably the result of a reduced gas residence time in the froth for absorption and in the gas spaces between the plates for NO oxidation, and higher column temperatures. The results of varied NO2*partial pressures in the gas feed stream are shown in Figure 5 (Tables 11, 111; experiments: 51,42,61). The increased conversion of NO, with higher NO2* partial pressures in the feed gas is consistent with increased absorption of NOz*and oxidation of NO due to higher driving force concentrations of NOz* and NO, respectively. The reversibility of the NOz* absorption reaction can be neglected at low H N 0 3 concentrations. However, the Henry's law constant for N204is a slight inverse function of the ionic strength (Hoftyzer and Kwanten, 1972). The decreased overall NO, absorption with increased acid molarity shown in Figure 6 (Tables 11, 111; experiments: 9, 10, 12, 11) is probably caused by a reduction in the respective solubilities of N2O4 with increased acid strengths. The effect of varying the ratio of the steam flow rate to the air and NOz* flow rate in the feed gas is shown in Figure 7 (Tables 11,111; experiments: 42,45,46,47). The increase in the steam concentration in the feed gas appears to increase NO, conversion up to -3.5 kg of steam/m3 of NOz*and air. Above this ratio, the increase in steam flow rate appears to decrease NO, conversion. This could be explained by the presence of steam enhancing the absorption of NO2* by increasing the gas-liquid interfacial area and reducing the oxidation rate of NO by increasing
Ind. Eng. Chem. Fundam., Vol. 18, No. 4, 1979
Table I. Steady-State NOT Scrubbing Data for a Single Sieve Plate and a Nonrecirculating Scrubber Liquida
run no. 55a 55b 55c 55d 55e 55f 5 5g 56a 56b 56c 56d 56e 56f 5% 57a 57b 57c 57d 57e 57f 57g 5 8a 58b 58c 5 8d 5 8e 58f 59a 59b 59c 59d 63a 63b 63c 63d 64a 64b 64c 64d 6 5a 65b 6 5c
pNOT,m%
PNOr,out,
TGjn,
TG out,
TL,
atm 0.026 0.051 0.106 0.161 0.207 0.267 0.330 0.035 0.053 0.107 0.167 0.187 0.260 0.330 0.020 0.044 0.101 0.161 0.216 0.279 0.312 0.015 0.050 0.107 0.165 0.211 0.260 0.163 0.163 0.163 0.163 0.152 0.145 0.151 0.151 0.165 0.166 0.163 0.166 0.14 1 0.152 0.151
at m 0.012 0.020 0.040 0.059 0.081 0.103 0.117 0.013 0.017 0.035 0.057 0.075 0.0 88 0.094 0.011 0.020 0.044 0.068 0.094 0.119 0.134 0.009 0.0 24 0.051 0.075 0.099 0.119 0.079 0.075 0.062 0.057 0.051 0.044 0.056 0.036 0.026 0.024 0.024 0.022 0.031 0.019 0.028
K
It
K
293 294 294 294 294 294 294 294 294 294 294 294 294 294 294 294 294 295 295 295 295 29 5 295 295 29 5 295 295 294 294 294 294 299 297 294 294 348 355 362 365 368 359 369
297 297 297 29 7 29 7 297 297 298 298 298 298 29 8 298 29 8 297 297 29 8 298 29 8 298 298 298 298 298 298 298 298 296 296 296 296 297 298 298 298 302 304 306 309 316 300 3 22
292 29 2 292 292 292 29 2 29 2 29 3 293 29 3 293 293 293 293 293 293 293 292 292 292 29 2 293 29 2 292 292 292 292 292 293 292 290 290 29 1 290 290 298 302 309 317 337 300 322
G, std m3/s 2.0 x 10-4 2.0 x 10-4 2.0 x 2.0 x 10-4 2.0 x 10-4 2.0 x 10-4 2.0 x 1.5 X 10“’ 1.5 x 10-4 1.5 X l o w 4 1.5 X 1.5 x 10-4 1.5 x 1.5 X 2.5 x 10-4 2.5 x 10-4 2.5 x 10-4 2.5 X 2.5 x 2.5 X 2.5 x 10-4 3.0 x 10-4 3.0 x 10-4 3.0 x 10-4 3.0 x 10-4 3.0 x 10-4 3.0 X 2.0 x 10-4 2.0 x 10-4 2.0 x 2.0 x 2.0 x 10-4 1.5 x 10-4 2.5 x 10-4 2.5 X 2.0 x 10-4 2.0 x 2.0 x 10-4 2.0 x 10-4 2.0 x 10-4 2.0 x 10-4 2.0 x
Fstem,
L,
kg/s
m3/s 1.75 X 1.75 X l o - ’ 1.75 X l o - ’ 1.75 x lo-’ 1.75 x 10-5 1.75 x lo-’ 1.75 x 1.75 x 10-5 1.75 X 1.75 x 10-5 1.75 X lo-’ 1.75 X lo-’ 1.75 x lo-’ 1.75 X 10.’ 1.75 X l o w 5 1.75 x 10-5 1.75 X 1.75 X l o - ’ 1.75 x 10-5 1.75 x l o - ’ 1.75 x 10-5 1.75 x 10-5 1.75 x lo-’ 1.75 x 10-5 1.75 X l o - ’ 1.75 X lo-’ 1.75 X lo-’ 0.44 x 10-5 0.88 x 10-5 2.60 x 3.50 x 10-5 1.75 X l o - ’ 1.31 x 10-5 2.19 x 2.19 x 10-5 1.75 x lo-’ 1.75 x 1.75 X lo-’ 1.75 x 10-5 0.44 x 3-50 x 10-5 0.86 x
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 1.67 X 3.67 x 10-4 7.83 x 10-4 11.83 x l o - + 7.83 x 7.83 X 7.83 x 10-4
Column pressure in all runs was 1.1 atm, loor
0.90 “0°
0“
0501
z
05 04 PLnTt
3
020
O‘O
t‘
0001
00
I
I
05 F,,,t,,(
,
I
10
5.10.~
kg/s)
Figure 7. NO, removal in three-stage sieve-plate column for varied steam flow rates in the feed gas.
the column operating temperature. An interesting experimental observation was the relationship between NO, conversion and HNOz liquid concentration. The attainment of steady-state operation appeared to be closely related to reaching a steady-state HNOz liquid concentration. This phenomenon was pre-
-
-
/o/6-0-
xNO:
0.55 0.62 0.65 0.66 0.65 0.67 0.72 0.63 0.68 0.69 0.69 0.64 0.71 0.73 0.45 0.56 0.59 0.61 0.61 0.64 0.64 0.43 0.52 0.55 0.58 0.58 0.60 0.55 0.58 0.66 0.68 0.70 0.72 0.66 0.66 0.86 0.87 0.81 0.88 0.80 0.89 0.84
403
404
Ind. Eng. Chem. Fundam., Vol. 18, No. 4, 1979
Table 11. Steady-State NO, Scrubbing Data for Recirculating Scrubber Liquid gas temp, K
NO, partial pressure, atm run no.
feed
stage 1
stage 2
stage 3
feed
9 10 11 12 13 15 16 17 18 19 20 31 32 42 44 45 46 47 48 49 50 51 52 53 54 60 61 62
0.308 0.312 0.299 0.295 0.273 0.341 0.310 0.293 0.332 0.0 0.310 0.341 0.352 0.306 0.295 0.301 0.301 0.031 0.350 0.301 0.312 0.145 0.21 5 0.317 0.321 0.293 0.400 0.308
0.106 0.114 0.114 0.110 0.012 0.128 0.141 0.100 0.103 0.0 0.117 0.125 0.117 0.141 0.136 0.150 0.125 0.143 0.141 0.107 0.171 0.066 0.127 0.183 0.132 0.129 0.174 0.114
0.067 0.068 0.073 0.068 0.073 0.073 0.084 0.057 0.057 0.0 0.066 0.079 0.070 0.088 0.09 5 0.097 0.088 0.097 0.090 0.069 0.112 0.048 0.110 0.123 0.101 0.079 0.101 0.068
0.051 0.053 0.058 0.053 0.062 0.051 0.070 0.040 0.042 0.0 0.042 0.057 0.051 0.062 0.066 0.084 0.070 0.068 0.068 0.051 0.075 0.040 0.105 0.103 0.07 9 0.057 0.070 0.050
352 353 353 351 353 353 298 352 351 351 351 348 348 364 365 299 357 368 363 363 367 362 298 299 365 366 366 357
stage 1 stage 2 314 312 312 309 312 313 302 312 312 303 316 307 308 320 320 303 311 322 315 317 333 317 300 303 317 317 315 336
306 305 304 305 305 305 303 304 304 299 305 300 300 307 308 306 306 308 307 305 310 304 300 307 306 306 305 313
liquid temp, K stage 3 305 303 304 304 303 304 305 303 303 299 303 299 299 305 306 299 305 305 305 304 305 303 301 309 305 303 303 300
stage 1 stage 2 310 310 310 310 310 312 297 310 309 310 309 305 305 320 320 298 310 331 313 309 337 318 298 298 318 310 311 310
29 8 297 291 297 29 7 29 7 29 7 297 29 7 29 7 297 29 2 292 20 8 29 8 297 298 299 29 9 29 8 299 298 29 7 297 296 298 29 I 297
stage 3 29 7 29 7 297 297 29 7 29 7 29 7 29 7 29 7 297 291 292 292 29 7 29 7 297 297 298 29 7 29 7 29 7 297 297 29 7 295 297 296 297
Table 111. Steady-State NO, Scrubbing Data (Total Pressure = 1.1atm in All Runs) ~~
~
recycle of liquid holdup steam feed air feed liquid feed gas from tank sparge run rate,a rate,a rate,a "02, HNO,, liquid holdup rate, no. kg/s x l o 3 m3/s x l o 4 m3/s x l o 4 M M tank m3/s x IO6 9 0.73 1.40 0.35 1.0 Yes 0.0 10 0.73 1.40 0.35 2.0 Yes 0.0 11 0.73 1.40 0.35 3.5 Yes 0.0 12 0.73 1.40 0.35 3.0 Yes 0.0 13 0.73 1.40 0.35 3.5 Yes 0.0 15 0.73 1.40 0.35 2.4 Yes 2.5 16 0.73 1.40 0.35 3.2 Yes 0.0 17 0.73 1.40 0.35 3.0 Yes 7.5 18 0.73 1.40 0.35 2.4 Yes 14.0 19 0.73 1.40 0.35 2.2 Yes 0.0 20 0.73 1.40 0.35 2.2 yes 2.5 0.0 31 0.73 1.40 0.35 0.45 1.3 no 32 0.73 1.40 0.35 0.39 1.7 no 2.5 42 0.70 1.40 0.17 0.25 2.3 no 0.0 44 1.08 2.10 0.26 0.20 1.6 no 0.0 45 0.00 1.40 0.18 0.28 2.7 no 0.0 46 0.35 1.40 0.18 0.18 3.0 no 0.0 47 1.09 1.40 0.18 0.18 2.8 no 0.0 48 0.67 1.40 0.26 0.30 2.6 no 0.0 49 0.67 1.40 0.35 2.0 no 0.0 50 0.67 1.40 0.09 0.20 2.4 no 0.0 0.0 51 0.67 1.70 0.18 0.21 2.0 no 52 0.00 1.80 0.18 2.1 no 0.0 53 0.00 2.16 0.26 0.20 3.0 no 0.0 54 0.85 1.80 0.22 0.20 3.0 no 0.0 60 0.83 1.80 0.22 0.19 1.5 no 0.0 61 0.65 1.24 0.17 0.28 2.4 no 0.0 62 0.36 1.22 0.13 0.27 2.4 no 0.0 a The tabulated numbers in the columns have been multiplied by the indicated factor.
and both reach a semi-steady state simultaneously. This relationship between NO, removal efficiency and HNOz concentration is shown in the data from an experimental run from start-up to steady state (Figure 8). Increasing the air sparge of the liquid holdup tank resulted in increased overall NO, conversion, as shown in Figure 9 (Tables 11,111; experiments: 16, 15, 17, 18). The air sparge of the liquid holdup tank probably drives the equilibrium
~~
liquid holdup vol., m3 x l o 2 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 2.51 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64
reaction of HNOz, eq 4, to the dissociation of HNOP This seems to be confirmed by comparing experiment 31 and experiment 32 (Table IV). The reduction of HNOp concentration in the liquid phase of experiment 32 vs. experiment 31 coincides with the air sparge of the liquid holdup tank and greater NO, conversion. The greater NO, conversion probably results from the increased liquid capacity for holding NO in the liquid phase as HN02.
Ind. Eng. Chem.
Fundam., Vol. 18, No.
4, 1979
405
Table IV. Data Showing the A p p r o a c h to Steady State for NO, S c r u b b i n g w i t h R e c i r c u l a t i n g S c r u b b e r Liquid
HNO,, M
partial pressure of NO,, atm
expt
time, s
feed
stage 1
stage 2
31
0 1800 3600 5400 7 200 9000 10800 12600 14400 16200 0 3600 5400 7200 9000 10800 12600 14400 16200 18000 19800
0.341 0.34 1 0.341 0.341 0.341 0.341 0.341 0.341 0.341 0.34 1 0.361 0.361 0.361 0.360 0.355 0.350 0.350 0.350 0.350 0.350 0.350
0.100
0.047
0.125 0.108
0.079 0.062
32
0.116
0.070
IO0
L
0OBO 70 0 0
50
100
ISOXIO-~
F i g u r e 9. Overall NO, removal in three-stage sieve-plate column for varied sparge rates of the holdup tank.
0.90 loo
I
0.80 .
o
\
*
OVERALL
0.70 . 0.60.
x0 z 0.50.
1 PLATE
1
0.40. PLATE 2
0.30 -
0.10
0.00
1
-
L 2.0
2.5
3.0 a IO-
G (rn 3 / s )
Figure 10. ExperimentalNO, conversion in a three-stage sieve-plate column for varied feed gas flow rates with no steam in the feed gas.
The results of two runs with no steam in the feed gas and a t different gas rates are shown in Figure 10 (Tables 11,111;experiments: 45, 53). The results are comparable in scrubber efficiency to experiments in which steam is present in the feed gas. The only noticeable difference is in the lower first plate efficiency for cases with no steam.
stage 3 0.0 23 0.024 0.036 0.04 1 0.044 0.051 0.053 0.057 0.059 0.059
0.04 0
0.04 2 0.044 0.048 0.051 0.050 0.051
feed liquid
effluent liquid
HNO,, M
0.02 0.09 0.23 0.30 0.35 0.29 0.44 0.46 0.46 0.45 0.02 0.06 0.15 0.18 0.28 0.32 0.32 0.33 0.33 0.40 0.38
0.02 0.22 0.25 0.30 0.31 0.43 0.46 0.47 0.43 0.46 0.02 0.08 0.16 0.18 0.31 0.34 0.36 0.38 0.38 0.42 0.39
1.01 0.94 0.95 0.98 1.02 1.10 1.12 1.18 1.23 1.31 1.67 1.60 1.56 1.59 1.58 1.60 1.64 1.62 1.70 1.70 1.78
Conclusions The following conclusions can be drawn from the results of this study. 1. The conversion of NO, varies directly with some function of the gas flow rate and the partial pressure of NO?*. 2.- The buildup of HNOz in the scrubber liquid results in a decrease in scrubbing efficiency. 3. These findings indicate that a method to destroy HNOz in the scrubber liquid before its recycle to the column will increase the system NO, removal efficiency. Acknowledgment This work was performed in the Chemical Technology Division under the ausr>ices of the Consolidated Fuel Reprocessing Program 01 the Oak Ridge National Laboratory. Nomenclature Fsteam = mass flow rate of steam, kg/s G = gas volumetric flow rate, m3/s G, = sparge gas volumetric flow rate, m3/s L = liquid volumetric flow rate, m3/s M, = molar concentration of component j , kg-mol/m3 NOz* = the sum of NOz + 2N20, NO, = a mixture of nitrogen oxides consisting of NOz + 2N204 + NO P, = partial pressure of gas component j , atm Pi,,,, = feed and effluent partial pressure of gas component j, atm T = temDerature, K = feed and effluent gas temperature, K TG,~,, 7 ' ~= liquid temperature, K Xj = removal efficiency of component j , amount of material absorbed per amount of material entering, 1- Pj,out/Pjb/(l + e PjoUt/Pjin), dimensionless e = fractional volumetric change due to bulk removal of gaseous components Literature Cited Abel, E., Schmid, H., Z.Phys. Chern., 132, 55 (1928a). Abel, E., Schmid, H., Z.Phys. Chem., 134, 279 (1928b). Abel, E., Schmid, E., Babad, s., 2.Phys. Chern., 136, 135 (1928a). Abel, E.. Schmid, E., Babad, S., Z.Phys. Chem., 136, 419 (1928b). Abel, E., Schmid, Z.Phys. Chern., 136, 430 (1929). Abel, E., Schmid, H., Stein, M., E/ektrochem., 36, 692 (1930a). Abel, E., Schmid, H., Roemer, E., Z.Phys. Chern., 136, 337 (1930b). Andrew, S.p., Hanson, D.. Chern. f n g . Sci., 14, 115 (1961). Ashmore, P. G., Bmett, M. G., Tyler, B. J., Trans. Faraday Soc., 58, 685 (1962). Bodenstein, M., E/ektrochem., 100, 68 (1922).
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Bodenstein, J., 2.Elektrochem., 24, 183 (1918). Carberry, J. J., Chem. Eng. Sci., 9, 189 (1959). Caudle, P. G., Denbigh, K. G., Trans. Faraday SOC.,49, 39 (1953). Chilton, T. H., Knell, E. W., PACHEC III, (1972). W i v e a u , C. E., Master's Thesis in Chemical Engineering, University of Califwnia, Berkeley, 1971. Counce, R. M., Perona, J. J., Ind. Eng. Chem. Process Des. Dev., 18. 562
(1979). Dekker, W. A,, Snoeck, E., Kramers, H., Chem. Eng. Sci., 11, 61 (1959). Denbigh, K. G., Prince, A. J., J . Chem. SOC., 53, 790 (1947). Detournay, J. P., Jadot, R. H., Chem. Eng. Sci., 28,2099 (1973). Gerstacker, Chem. Eng. Sci., 14, 124 (1961). Greig, J. D., Hall, P. G.. Trans. Faraday SOC.,63, 655 (1967). Hasche, R. L., Patrick, W. A., J . Am. Chem. SOC.,47, 1207 (1925). Hoftyzer, P. J., Kwanten, F. J. G., "Processes for Air Pollution Control", Chapter 58, 2nd ed, Chemical Rubber Co., New York, 1972. Kameoka, Y., Pigford, R. L., Ind. Eng. Chem. Fundam., 16, 163 (1977). Koval, E. S..Peters, M. S . , Ind. Eng. Chem., 52, 1011 (1960). Kramers, H., Blind, M. P. P., Snoeck, E., Chem. Eng. Sci., 14, 115 (1961). Levenspiel, O.,"Chemical Reaction Engineering", 2nd ed,p 72,Wiley, New York,
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Makhotkin, A. F., Shamsutdinov, A. M., KhimKhim. Teknol., XIX, 1411 (1976). Moll, M. J., Ph.D. Thesis, University of Washington, 1966. Morrison, M. E., Rinker, R. C., Corcoran, W. H., Ind. Eng. Chem. Fundam.,
5, 175 (1966). Perry, R. H., Chilton, C. H., "Chemical Engineers Handbook", 5th ed, p 18-7, McGraw-Hill, New York, 1973. Peters, M. S., Holman, J. L., Ind. Eng. Chem., 47,2536 (1955). Peters, M. S.,Ross, C. P., Klein, J. E., AICh€ J., 1, 105 (1955). Sherwood, T. K., Pigford, R. L., Wilke, C. R., "Mass Transfer", Chapter 8, McGraw-Hill, New York, 1975. Treacy, J. C., Daniels, F., J . Am. Chem. Soc., 77, 2033 (1955). Verhoek, F. H.,Daniels, F. J., J . Am. Chem. SOC.,5 3 , 1250 (1931). Wendel, M. M., Pigford, R. L., AIChE J., 4, 249 (1958).
Received f o r review February 12, 1979 Accepted May 4, 1979 This research was sponsored by the Nuclear Power Development Division, U S . Department of Energy under Contract W-7405eng-26 with the Union Carbide Corporation.
Absorption and Reaction of Acetylene in Aqueous Cuprous Chloride Slurries' S. S. Tamhankar and
R. V. Chaudhari'
National Chemical Laboratory, Pune 4 1 I 008, India
An experimental study on the absorption of acetylene in aqueous cuprous chloride slurry is reported. The results are interpreted based on the theories for gas absorption with reaction. It has been found that the reaction between dissolved acetylene and CuCl is instantaneous and occurs in the liquid film next to the gas-liquid interface. Effects of various parameters on the rate of absorption and shifts in the controlling regime are subsequently discussed.
Introduction Absorption of gases in slurries containing sparingly soluble solid particles is important in the removal of waste gases (Rochelle and King, 1977) and in the preparation of precipitated carbonates (Shreve, 1967). Traces of acetylene from ethylene or butadiene streams can be efficiently removed by absorbing in cuprous chloride suspensions (Mamalis, 1968). Also, acetylene reacts with cuprous chloride to form copper(1) acetylide complex, which is known to catalyze ethynylation reactions (Copenhaver and Bigelow, 1949). This kind of catalyst is employed in the commercial manufacture of 2-butyne-1,4-diol from acetylene and formaldehyde (Appleyard and Gartshore, 1946; NCL report, 1978). This suggests that the reaction is of potential importance in industry. Acetylene absorption in cuprous chloride solutions has been recently studied (Chaudhari and Gupte, 1978), but such studies in aqueous cuprous chloride slurries have not been reported in the literature. The latter system provides an interesting example of a reaction between simultaneously dissolving gas and a solid in a liquid medium. Such a system would involve various controlling regimes, such as gas-liquid and solid-liquid mass transfer, chemical reaction, and combinations. Only a few experimental studies have been reported on such systems (Bjerle et al., 1972; Juvekar and Sharma, 1973; Rochelle and King, 1977). NCL Communication Number 2314. 0019-7874/79/1018-0406$01.00/0
The objective of this work is to study the various controlling regimes in acetylene absorption in cuprous chloride slurries under different conditions. These results may be useful in the design of absorbers for acetylene removal as also the preparation of catalysts for ethynylation reactions.
Theory Gas absorption in a liquid containing sparingly soluble solid particles has been considered by Ramachandran and Sharma (1969) and later by Uchida and Wen (1977). The various possible regimes have been discussed by these authors. In the present case, let us assume the following reaction scheme for the reaction of acetylene and cuprous chloride in aqueous solution
CzH,(l) (A)
+ zCuCl(1) (B)
-
products
(3)
Depending on the mass transfer characteristics and the reaction rate constant, reaction 3 would occur in different regimes. An important consideration in gas absorption in slurries containing fine particles is whether solid dissolution in the liquid film next to the gas-liquid interface is important or not. When the particle size is large in comparison to the liquid film thickness (dp >> 8 ) or the concentration of the solid is relatively small, it is the case
0 1979 American Chemical
Society
