420
Ind. Eng. Chem. Process Des. Dev. 1980, 19, 420-426
*
a
Izr
TI
u
-
Figure 17. A cascade refrigeration system.
the cycles together to form an MRC system. There are, however, some significant differences between the two systems that hinder the applicability of this approach. First, because of the impurities in the coldest refrigerant at the coldest level after lumping the cycles, the temperature at that level will be higher than before lumping and thus cannot meet the coldest temperature requirement. Similarly, the temperature requirements of the colder levels will not be met while the temperature requirements of the warmer levels will be overly met. To avoid lowering the pressure and the possibility of going below the pressure limits of some of the refrigerants, a margin of say, 10 K below the temperature required by the heat sources must be provided for the colder levels in the cascade design. This provision, however, is contradictory to heuristics l a to ICoutlined earlier and thus invalidates the optimality of the cascade system. Another drawback is that in order to equalize the inlet temperatures of the three compressors in the cascade system so that they can be lumped into one, the amounts of superheat in the colder refrigerants are
excessively high and this again runs counter to the experience in optimal cascade system design. Despite these drawbacks the approach of lumping pure refrigerant cycles to form an MRC system does provide a feasible design for which further improvement can be made and is therefore worth exploring. Nomenclature E = parameter used in eq 4 C = individual equipment cost, $ C, = heat capacity, cal/g-mol K f = relative cost of material (carbon steel = 1.0) g = refrigerant flow, g-mol/s H = enthalpy, cal/g-mol k = compression ratio N = number of temperature levels P = pressure, N/m2 Q = amount of heat transferred, cal/g-mol R = gas constant, 1.987 cal/g-mol K S = cost parameter T = temperature, K x = coefficient of cost function y = exponent of cost function Greek Letters 17 =
compressor efficiency
X = operating enthalpy range, cal/g-mol
Literature Cited Barnes, F. J., King, C. J., Ind. Eng. Chem. Process Des. Dev., 13, 421-433 (1974). Cheng, W. E., Ph.D. Thesis, Northwestern University, Evanston, Ill., 1979. Cheng, W. B., Mah. R. S. H., Cornpot. Chem. Eng., 2, 133-142 (1978). Hendry, J. E., Rudd, D. F., Seader, J. D., AIChE J . , 18, 1-15 (1973). King, C. J., AIChE Monogr. Ser., 70(8), 3-31 (1976). Reid, R. C., Prausnitz, J. M., Sherwood, T. K., "The Properties of Gases and Liquids", 3rd ed, McGraw-Hill, New York, 1977. Soave, G., Chem. Eng. Sci., 27, 1191-1203 (1972).
Received for review August 23, 1979 Accepted March 31, 1980
The authors wish to acknowledge the support of this work in the form of a fellowship to W. B. Cheng from the AMOCO Foundation.
Nonisothermal Determination of the Intrinsic Kinetics of Oil Generation from Oil Shale S.-M. Shih and H. Y. Sohn' Departments of Metallurgy and Metallurgical Engineering and of Mining and Fuels Engineering, University of Utah, Salt Lake City, Utah 84 112
nonisothermal technique using various heating rates has been applied to the determination of the intrinsic kinetics of oil generation from oil shale. From an engineering standpoint the rate of oil generation c a n adequately be described by overall first-order kinetics with a constant activation energy of 199 kJ/mol. Various methods are applied to the determination of the kinetics parameters. The relative merits of these methods are discussed. The results are compared with data reported in the literature. The nonisothermal technique has the advantages of short experimental time and the elimination of difficulties due to the initial heat-up period accompanying the isothermal experiments. A
Introduction The kinetics of the decomposition of kerogen in oil shale, which is the precursor of oil, has been studied by a number of investigators (Hubbard and Robinson, 1950; Allred, 0196-4305/80/1119-0420$01.00/0
1966; Weitkamp and Gutberlet, 1970; Braun and Rothman, 1975; Johnson et al., 1975; Campbell et al., 1978). The complex nature of kerogen and its decomposition reaction has complicated the interpretation of data and led to
e 1980 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 421
various postulates for the decomposition mechanisms. Hubbard and Robinson (1950) treated the kinetics using a mechanism consisting of two first-order steps for the decomposition of kerogen to bitumen which subsequently decomposes to oil, gas, and carbon residue. Allred (1966) proposed the decomposition reactions to take place in three stages with different rate constants. Weitkamp and Gutberlet (1970) found the kinetics to be a diffusion-limited first-order reaction complicated by the possibility of bond-breaking steps. Most previous investigations were carried out under isothermal conditions. For the determination of intrinsic decomposition rates, isothermal experiments are prone to error because of the difficulty of accounting for the reaction taking place during the heat-up period (Braun and Rothman, 1975). Other experiments have been carried out using thermogravimetric analysis which relies on weight change. In this case the interpretation is complicated by the weight loss due to the evolution of noncondensable gases and water in addition to the product of interest-oil. From the engineering standpoint of oil shale retorting, the rate of oil production is the important aspect of kerogen decomposition. Recently, Campbell et al. (1978) have used a nonisothermal method for studying the kinetics of oil shale retorting. They heated oil shale at a linear heating rate of 0.033 K/s. The volume of oil generated was measured directly, and the data were interpreted based on global first-order kinetics. The nonisothermal method has the advantages of a shorter experimental time required and the elimination of difficulties due to the initial heat-up period accompanying the isothermal experiments. Furthermore, nonisothermal heating simulates more closely the actual temperature history encountered in the situ and the above-ground retorting of oil shale. Kerogen in oil shale is a complex heterogeneous mixture of organic compounds and the oil product is formed by many different reactions involving these components. For this reason a global first.-order expression greatly simplifies the representation of the decomposition rate, if it gives a reliable result for most engineering purposes. Campbell et al. (1978) recognized this in their work. However, they used only one heating rate for their experiments. In view of the presence of many different precursor compounds in oil shale kerogen, more reliable data can be obtained by using different heating rates (Flynn and Wall, 1966). The analysis of nonisothermal kinetics under different heating rates can be made using a number of different procedures-direct Arrhenius plot, integral method, differential method, etc. In this paper we present the results of applying these techniques to the analysis of experimental data for the intrinsic rate of oil generation from oil shale kerogen obtained under nonisothermal conditions using different heating rates. The use of different heating rates, believed to be the first time as far as the decompositon of kerogen is concerned, has severid distinct advantages in terms of the determination of rate parameters in addition to the above-mentioned reason. This will be discussed subsequen tly. Experimental Section Oil shale used in this >workwas obtained from the Anvil Points Mine in Colorado. Its Fisher Assay grade was 164.5 f 4 mL/kg (39.4 f 0.9 1J.S. gal/short ton). It was ground and sieved to a size range of -8 to +48 mesh. A schematic diagram of the apparatus used for the decomposition experiments is given in Figure l. The retort chamber was a 5 in. long stainless steel cylinder with 1.25 in. i.d. A fine-mesh steel filter was placed at the bottom.
-
Thermocouples
1
Nitrogen
temperature
Furnace
recorder
Retort Assembly
programmable c co on n tt rr o o ll ll e e rr
IT1
I Power
Oil Shale Sample Aluminum Aluminum R Ro od d
'l'j-
S t e e l Fllter I
Line Insulation Plug
I
I
Oil Coliection Tubes
Ice-Salt Bath
Figure 1. Schematic diagram of oil shale retorting apparatus.
Lids were attached at the ends. The top lid accommodated the inlet of sweeping nitrogen flow and a thermowell. An aluminum rod of 0.5 in. diameter was attached to it. Oil shale sample was placed in the annular space. The rod served the purpose of maintaining uniform temperature throughout the packed oil shale sample by reducing its thickenss and also improving heat conduction into the middle of the column. Uniformity of temperature was considerably improved by the presence of the rod. From the normal position of the thermocouple midway between the inner and outer surface of the annulus and between the top and the bottom ends, the maximum temperature difference was about f7.5 K radially and less than 1.5 K longitudinally at 0.0968 K/s heating rate, the highest value used in this work. At slower heating rates, temperature was more uniform. About 80 g of oil shale sample was charged in the retort and heated a t linear heating rates of 0.0154-0.0958 K/s while maintaining a stream of nitrogen a t about 60 mL/ min. The flow rate of nitrogen was high enough for the swift removal of oil vapor but low enough for the efficient condensation of vapor product. The liquid holdup between the retort and the oil collection tubes was negligible because the line was kept hot and its length short. The complete decomposition of kerogen normally occurred before the temperature reached about 780 K. The oil vapor produced flowed out through an outlet tube. A three-way valve was connected to the outlet tube so that the oil vapor can be condensed and measured at small time intervals. The oil was collected in two 15-mL centrifuge tubes connected in series and immersed in an ice-salt bath. One tube collected most of the product, the second serving as a check for a complete recovery. The condensed product containing oil and water was warmed to room temperature before the oil volume was read. Results and Discussion The cumulative oil volume produced is shown as a function of temperature in Figure 2. The instantaneous rate of oil generation is plotted in Figure 3. The rate curves were obtained by first plotting the average rate AV/At against the arithmetic average temperature for the period in which the volume increment was collected and then drawing smooth curves through the points. Both the
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980
422
T(KI 750
725
700
675
650
I
I
TEMPERATURE ( K l
Figure 2. Cumulative oil yield vs. temperature plots at different heating rates.
;; 24 0)
1
I I
0 A 0
0
I
0 0154
ii
I
I
K/S
00337 K / s 00764 K / s 00956 K / S
0
0
rn
\
0
00
200"
-0 \
>
V
I
14
15
IOOO/T ( K - ' l
Figure 4. Friedman's procedure for the determination of kinetics parameters using data obtained a t different heating rates.
time t and Vo is the total volume of oil produced from 1 g of oil shale. With this, eq 1 can be rewritten as
16
-
-
w
2
13
Taking logarithms of eq 2 gives
0
12-
a
U J 3 0
:
a Iz a
IUJ
f
-
A
In
0
A
8O
-
O
n
A
A 0
A
4 -
-
O $000 O
6 10
(LE) Vo dt = In A + n In
A
S
€40
I
I
670
700
-
A OOO
A A
1
730
760
-
7 90
TEMPERATURE ( K )
Figure 3. Instantaneous oil production rates at different heating rates.
cumulative volume and the instantaneous rate data were used in determining various kinetic parameters using different procedures as discussed below. 1. Analysis Using Friedman's Procedure. The experimental data were first analyzed following the treatment of Friedman (1965). The following kinetics equation was assumed to hold for the overall pyrolysis reaction of oil shale
where x is the extent of conversion of organic matter, A is the preexponential factor for the rate constant, E is the activation energy of reaction (J/mol), R is the gas constant (8.313J/mol.K), and n is the reaction order. The amount of organic matter is usually difficult to follow by measurement. If one assumes that the stoichiometry of the reaction to form oil remains constant during the process, then x can be expressed as V/ Vo in which V (cm3/g) is the volume of oil produced from one gram of oil shale up to
Nine values of V/ Vo were selected, ranging from 0.1 to 0.9, at equal intervals. The values of (l/Vo)(dV/dt) and T were determined for each V/ V, value of each heating rate. Plots of In [(l/Vo)(dV/dt)]vs. 1/T are shown for different values of V/ Vo in Figure 4. The slope of each line gives the value of - E / R , while the intercept is equal to A(l V/ Vo)". As can be seen here, the activation energy can be determined without the knowledge of the form of the rate dependence on conversion. This is a distinct advantage made possible by the availability of experimental data obtained using various heating rates. The values of E and In [A(1 - V/Vo)"] are plotted as functions of V/ Vo in Figure 5. The activation energy is rather constant during the reaction despite the heterogeneity of the organic material being decomposed. The range of variation that is associated with each point represents the probable error of the points based on the least-squares treatment. The values of 90% conversion are quite uncertain, probably due to the difficulty associated with obtaining accurate values of dV/dt near the completion of the reaction. The trends in the values of E and In [A(1 - V/Vo)"], however, are identical; thus it appears that the kinetics of the overall process are consistent. The average value of E is 218.72 kJ/mol. Experimental parameters and the values of activation energy were substituted in eq 3 to give 36 values of In [A(1 V/V0)"). Average values of In [A(1- V/Vo)"] are plotted as a function of In (1- V/ Vo) in Figure 6. A reasonably good straight line is obtained over the entire range of conversion, indicating that the reaction order remains quite constant. Based on the curve, n = 1.1and A = 2.26 X l O I 3 S-1.
Ind. Eng. Chern. Process Des. Dev., Vol. 19, No. 3, 1980 423 Table I. Kinetic Parameters Calculated by Different Methods
E, kJ/mol
A , s-'
Arrhenius heating Friedman's plot rate, K/s procedure method
integral differential method method
0.0154 0.0337 0.0764 0.0958 overalla
184.00 180.77 194.43 182.40 199.46
185.84 192.53 196.84 175.84 197.25
218.'72
183.28 195.06 197.52 174.35 178.69
Friedman's procedure
Arrhenius plot method
2.26 X
6.72 X 2.53 X 5.60 X 1.63 X 5.63 x
lOI3
integral method
10" 10"
10" 10'O 10"
differential method
4.81 X 3.26 X 3.78 X 4.98 X
10" 10" 10" 10"
4.13 X 3.74 X 6.24 X 1.25 X
8.25
10"
2.50
X
X
10" 10" 10" 10" 10"
The overall values; are those obtained using the data for the four heating rates simultaneously, rather than simply averaging the values for each heating rate.
31
27
260
23
240
21
c
;
-24
-20
-I 6
-I 2
-0 8
-04
0
In ( 1 - V/ Vo I
Figure 6. Determination of the preexponential factor and the reaction order.
reaction order to be unity. Thus, the rate expression can now be written as
-_ d V = k(1 - V/Vo)
I20
0
01
0 2
0 3
0 4
0 5
0 6
0 7
0 8
0 9
IO
v/ vo Figure 5. Kinetics parameters as functions of conversion.
Small deviation from the straight line is observed for the abscissa values above -0.36 corresponding to the conversion below 0.3. This corresponds closely to the overall conversion at which Allred (1966) inferred, based on the data of Hubbard and Rob:inson (1950),that the decomposition of kerogen to bitumen which is an intermediate species was complete. Since we used a single overall rate expression in this analysis it is reasonable to expect some variations in rate parameters in the early stage of decomposition during which the intermediate bitumen is formed. From the above analysis it is concluded that the decomposition rate can be described by eq 2 with the average values of parameters A , E , and n as 1 d_V _ = 2.26 X Vo d t
(
1 --V ")'
(
exp - 2 6 y )
(s-9
(2) The value of Vo depends on the grade of the oil shale sample. 2. Overall First-Order Kinetics-Direct Arrhenius Plot Method. Since the reaction order is close to unity it would be advanta.geous to simplify the kinetics to first-order kinetics. This would greatly simplify the subsequent use of the rate expression in the modeling oil shale retorting in a rubblized bed. It will also facilitate the comparison of our experimental results with those of previous investigators,,most of whom a priori assumed the
(4) Vo dt where k = Ae-E/RTis the reaction-rate constant. The values of k for the individual runs were calculated based on eq 4 by dividing experimental values of (l/Vo)(dV/dt) by [ l - (V/Vo)]. Arrhenius plots of the four runs at different heating rates are shown in Figure 7. The curves lie close to each other indicating that the heating rate has little effect on the kinetics of kerogen decomposition, which in turn indicates again that the reaction can adequately be described by an overall single-step mechanism. The lines were obtained by the least-square treatment of the data. The values of E and A for each heating rate are listed in Table I. The values of E and A obtained using all data points simultaneously are 197.25 kJ/mol and 5.63 X 10" s-l, respectively. 3. Overall First-Order Kinetics-Integral Method. This method estimates the values of E and A of a reaction from the overall conversion vs. temperature curves. Since the heating rate is linear d- T =c dt where C is the heating rate (K/s). Substituting eq 5 into eq 4, rearranging and integrating, we get
where To is the initial temperature. Integration of eq 6 gives
424
Ind. Eng. Chern. Process Des. Dev., Vol. 19, No. 3, 1980 T (KI 50
T
725
700
67 5
I
I
I
0-
A
--
- 1 5 1 800
650 I
0 15 .0. .4
7 5I 0
I
I
K/s
(K)
700 I
650 I
-
0
~
--
A
0,0337 K / s
0
----
0
I
0.0154K/s 0 0337 K/s 00764 K / s 00958 K / s
- 1 p 5
IO3
-22
IOOO/T ( K - ' I
-23
Figure 7. The direct Arrhenius-plot method for the determination of kinetics parameters.
Here we made use of the fact that To is chosen low and the rate at this temperature is negligible; therefore, the lower limit can be replaced by zero. The exponential integral Ei(-E/RT) can be approximated by
Ei(-&)
(E/Rv2 -e 1 ( E/RT+ -
= E/RT
-
2!
l!
-
...)
I
I
I
1.46
1.54
1.62
I
I
1.22
1.30
1.38
IOOO/T(K-')
Figure 8. The integral method for the determination of kinetics parameters. T (Kl 700
(8)
650
0 A
0
0
If the first three terms of the approximation are used, eq 7 become
0 0154 K / s 00337 K / S 00764 K / s 00758 K / s
4
Dividing both sides of eq 9 by RTZ(1 - 2 R T / E ) / C and taking the logarithm, we get ln[
- C l n ( 1 - V / V o ~ ] -1n RTZ
(
I--2
3 ; = I nA --- E E RT
(10) The values of E and A can be obtained by repeated least-squares fit of eq 10 to the experimental data. By first using an approximate E in the left-hand side of eq 10, one can plot the left-hand side of eq 10 as a linear function of 1 / T and obtain -EIR from the slope and A I E from the intercept. The value of E thus obtained is used in the values of the left-hand side and successively a more accurate value of E is obtained until no improvement in the value of E takes place. Final plots for the four runs are shown in Figure 8. The E's and A's derived from this method are listed in Table I. Figure 9 shows the leastsquares fit of eq 10 to all of the data. The overall values of E and A thus obtained are 199.46 kJ/mol and 8.25 X 10l1 s-l, respectively. From eq 10, V can be obtained as
- 23
I
I 2 2
I30
I
138
IOOO/T
I46
I I54
'
I
I
162
(K-II
Figure 9. Determination of the overall values of kinetics parameters using the integral method.
The calculated cummulative oil volume vs. temperature curves using the overall values of E and A are compared with experimental data in Figure 10. 4. Overall First-Order Kinetics-Differential Method. This method determines the values of E and A from
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 425 I
0 16
I
0
--- --- -
1 0-
-
0,0337 K / s 0.0764 K / S 0.0958 K / s
-
A--
0
-
-
>
I
I -
-B
0.17154 K / s
0 14
I
.- _ _ _ - -
00s
-
0 06
-
0.04
-
0 02
-
0 -----
00154 K/s 00337 K/S 00764 K/s 00958 K/J
20
-1
0 0
'? 0
'm
I
0
-610
640
670
700
TEMPERATURE
730
760
790
(K)
Figure 10. Comparison between experimental data and curves calculated using the overall kinetics parameters determined by applying the integral methlod.
0
-
0 10154 K / s
TEMPERATURE
0 0764 K / s
(K)
Figure 12. Comparison of instantaneous rate data with curves calculated using the kinetics parameters from the integral method.
instantaneous rates as measured in our experiments. Although we used small time increments, the rates we measured are based on the average of true instantaneous rates over the time interval. Therefore, the kinetics parameters obtained using the integral method are recommended as the best values determined from our experimental data. The expression using an overall single first-order reaction for the oil production from kerogen decompositon becomes
L
n
-1 dV - 8.25 Vod T 610
640
670
700
TEMPERATURE
730
760
790
(K)
Figure 11. Results of the differential method.
the instantaneous rate vs. temperature curves. Substituting eq 11 into eq 4 gives
The values of E and A can be obtained by fitting eq 12 to the experimental data, using the repeated least-squares treatment. Specifical.ly, one treats eq 12 to have two independent variables, 1 / T and P e - E ' R T ( l - 2 R T I E ) I C . The second variable 1.s calculated using an approximate E in the first step. Once an approximate E is obtained from least-squares treatment, Pe-E'RT(1 - 2 R T / E ) / C is redetermined using the new value of E and successively a more accurate value of E is obtained. The individual values of E and A derived from this method are listed in Table I. The overall values of E and A were calculated by using the data for all runs. The rates calculated using the overall values of E and A are shown in Figure 11. 5. Overall First-Order Kinetics-Recommended Kinetics Parameters. As can be seen from the above analyses summarized in Table I, different procedures give somewhat different activation energies and associated preexponential factors. We believe that the data in terms of the cumulative oil volume are more reliable than the
X
lo1'( 1 -
E)
ex,(-
y)
(5-l)
(4') The instantaneous rate computed using the recommended values of kinetics parameter in eq 12 is shown in Figure 12. The agreement with experimental data is still satisfactory. General Discussion Among the various procedures tested, the treatment of Friedman is the most comprehensive. This method yields simultaneously the reaction order, the activation energy, and the preexponentid factor. It has the additional advantage of enabling the computation of activation energy without any knowledge of the rate dependence on conversion. Furthermore, for complex chemical reactions with different mechanisms at various stages of reaction, this method will yield these kinetic parameters as functions of conversion. This was shown to be unnecessary in the case of kerogen decompositon. The reaction order determined from this procedure was close to unity and thus overall first-order kinetics can be assumed for the oil generation from oil shale kerogen. As discussed earlier, the integral method is likely to be the most reliable for the determination of overall values of the kinetics parameter. However, the direct Arrhenius plot method which uses both the cumulative oil volume and the instantaneous rate data is the simplest and involves the least amount of effort, while yielding results which are in close agreement with those obtained using the integral method. The integral method can be simplified for reactions with a large activation energy in which case the
426
Ind. Eng. Chem. Process Des. Dev. 1980, 19, 426-431 T (K) 750
-I
700
725
650
675
625
Campbell et al. (1978) obtained their result by treating their experimental data at a single heating rate of 0.033 K/s using the differential method. The results of Braun and Rothman (1975) are for the oil generation step and are based on an analysis of the isothermal data of Hubbard and Robinson (1950). Johnson et al. (1975) compiled the overall initial first-order rate constants obtained for different shales by many investigators. A direct comparison of their rate constant with the other three is not meaningful because the latter are based on the whole range of conversion whereas the former is based on only the initial stage. There exists good agreement among the data based on an overall first-order reaction for the entire range of conversion. Our activation energy is seen to be close to the average value of all other data. We recommend a global first-order rate expression given in eq 4 for an engineering calculation of the rate of oil generation from oil shale.
Acknowledgment The authors are thankful to Dr. J. J. Duvall of Laramie Energy Technology Center for providing oil shale and for many helful discussions during the course of this work. Messrs. I. C. Lee and S. Rizvi assisted in experimental work, which is acknowledged with thanks.
Literature Cited I
I
1
I 15
14
16
IOOO/T (K-')
Figure 13. Comparison of rate constants obtained by various investigators.
second term in eq 10 becomes negligible (E >> ZRT), or by using T corresponding to 50% conversion in that term. In either case iteration becomes unnecessary. The differential method is less accurate for the reason mentioned earlier. Furthermore, the procedure is rather involved. In Figure 13, our recommended rate constant is compared with rate constants reported by other investigators.
Allred, V. D., Chem. Eng. frog., 62, 5 5 (1966). Braun, R. L., Rothman, A. J., Fuel, 54, 129 (1975). Campbell, J. H., Kosklnas, G. H.,Stout, N. D., Fuel, 57, 372 (1978). Flynn, J. H., Wall, L. A., J. Res. Natl. Bur. Stand., 70A, 487 (1966). Frleman, H. L., J. Polym. Sci., C6, 183 (1965). Hubbard, A. B., Roblnson, W. E.,Rept. Invest. U . S . Bur. Mines, 4744 (1950). Johnson, W. F., Walton, D. K., Keller, H. H.,Couch, E. J., Proc. 8th Oil Shale Symp., Quart. Colorado School Mines, 70(30), 237 (1975). Weitkamp, A. W., Gutberlet, L. C., Ind. Eng. Chem. Process Des. Dev., 9, 386 (1970). Received for review A u g u s t 20, 1979 Accepted February 26, 1980
This work was s u p p o r t e d by DOE AS03-78ET13095.
under Contract
No. DE-
A Mathematical Model for Nitrogen Oxide Absorption in a Sieve-Plate Column Robert M. Counce" Consolidated Fuel Reprocessing Program, Oak Ridge National Laboratory, Oak Ridge. Tennessee 3 7830
Joseph J. Perona Department of Chemical Engineering, University of Tennessee, Knoxviiie, Tennessee 3 79 16
A mathematical model was developed for a sieve-plate column utilizing kinetic and equilibrium constants from the literature. The model adequately represents the effects of gas and liquid flow rates and feed gas composition on conversion as determined experimentally in a three-plate column. The concentration of HN02 in the scrubber liquid was shown to affect conversion strongly.
Introduction The removal of nitrogen oxides from gas streams is required in many industrial processes. It is desirable for NO, (NO2 + ZNz04+ NO) scrubbing equipment to provide (1)
adequate gas-liquid contacting surface, (2) sufficient gas-phase residence time for the oxidation of nitric oxide species to the more soluble N02*.(N02+ ZNz04,a mixture of nitrogen dioxide and its equilibrium polymer, nitrogen
0196-4305/80/1119-0426$01.00/00 1980 American Chemical Society
