Ind. Eng. Chem. Res. 1996,34, 3083-3089
3083
Parametric Studies on COz Separation and Recovery by a Dual Reflux PSA Process Consisting of Both Rectifying and Stripping Sections Doudou Diagne Department of Industrial Science, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-I,Kumamoto 860, Japan
Motonobu Goto and Tsutomu Hirose* Department of Applied Chemistry, Kumamoto University, Kurokami 2-39-1, Kumamoto 860, Japan
Carbon dioxide separation and recovery from air-COz mixtures were carried out by means of a pressure swing adsorption process consisting of both rectifylng and stripping sections. Zeolite MS 13X was used as the adsorbent and parametric studies such as effects of feed inlet position, reflux ratio, gas flow rates, and pressure ratio on the enriched product concentration or recovery as well as lean product concentration were experimentally investigated. The concept of optimal feed inlet position and reflux ratio was discussed from a viewpoint of concentration distributions along each adsorbent bed. It is also found that a reduction of the gas flow rates, which allows longer residence time inside the column, improves sensibly the separation performance.
Introduction In the last three decades, we have witnessed tremendous progress in the development of pressure swing adsorption (PSA) technology, motivated by its low energy requirement and low capital investment cost. PSA technology is being widely used in industry for hydrogen purification, air separation, and various other separations. Excellent reviews of the state of the art of PSA have been made by Tondeur and Wankat (19851, Kawai (1986),Yang (19871, Suzuki (19901,and Ruthven et al., (1994). Recently, a worldwide preoccupation with solving the huge problem of the greenhouse effect has also made PSA a potential tool for the removal of C02 from flue or dense gases (Kumita et al., 1993;Komiyama and Fujitani, 1993; Kikkinides and Yang, 1993; Chue et al., 1995). Many sophisticated PSA processes or cycles can be used to remove or concentrate carbon dioxide. Concentrated C02 can be successfully used in various forms in the chemical and food industries in applications such as refrigeration equipment, fire extinguishers, carbonated beverages, and antioxidants during inert blanketing and so on. However, most of the processes are mainly operated with complicated cycles, with increasing numbers of adsorbers, and at a very high pressure ratio making them quite expensive for an environmental purpose. Obviously, the potential for high recovery of the product at low separation cost must remain the key driving force behind the growth in PSA technology too. In our previous works (Hirose, 1991; Diagne et al., 1994), we briefly described and experimentally demonstrated the applicability of a new PSA process with an intermediate feed inlet position and a dual reflux policy to the simultaneous removal and concentration of carbon dioxide from both dilute and dense systems. For this purpose, some improvements were made to the reflux policy as seen in symmetric single stage units (Mikami et al., 1989; Kanemaru and Nishino, 1990; Sircar, 1990) or in a multistage cross flow unit (Mersmann et al., 1983). The new PSA process belongs to an asymmetric two stages-in-series unit and operates with an intermediate feed inlet position and a dual reflux policy. The main objective was to show the advantage
that the minimum difference of pressure or pressure ratio could be decreased in this new process. Therefore, the objective of this paper is to carry on the development of this PSA process and to investigate the effects of various operating parameters on the separation performance. Since a huge number of theoretical studies and only few experimental works on PSA have been carried out up to now, this present paper is presented with emphasis on experimental results. Moreover, the concept of optimal values of the dimensionless feed inlet position and reflux ratio is interpreted by means of the concentration distributions of the C02 mole fraction along the adsorption column during variation of these two characteristic parameters.
Decomposition and Synthesis of the PSA Process Basic Configurations. The term “configuration” implies both flow sheet and process operating sequence (Tondeur and Wankat, 1985). Basic configurations can be found in the PSA purification unit and the PSA enriching unit. Both configurations are respectively designed to remove or concentrate one or many components from a binary or multicomponent feed gas. Hirose (1990) has proposed an interesting and useful tool for PSA process analysis which is adopted here to decompose the configuration diagram for purification and enriching purposes as shown in Figures 1 and 2 for typical examples of four-column PSA involving blowdown, equalization, reflux, and so on. Each adsorption column is represented by a parallelogram drawn in a plane in which the dotted area refers to the pressure history against the time axis scaled outwards. The process is sequenced in every step time in a circular permutation and counterclockwise direction according to the imposed steps. The more adsorbable component in the feed mixture (QF, XF)is concentrated or removed resulting in an enriched gas product or lean gas product. However, both configurations are subjected to thermodynamic limitations in the sense that, in Figure 1, the mole fraction of the solute from the bottom of the desorption
Q888-5885/95/2634-3Q83$Q9.Q0/0 1995 American Chemical Society
3084 Ind. Eng. Chem. Res., Vol. 34, No. 9, 1995 QE
&E
*l
-0 F
Figure 1. Basic configuration of PSA for removal purposes (stripping).
Figure 4. Schematic diagram of PSA with intermediate feed inlet position.
Figure 2. Basic configuration of PSA for enrichment purposes (enriching).
The feed position or fractional length of the rectifying section divides each column into rectifylng and stripping sections. The rectifying section will provide an enriched gas with a high enough concentration of solute while the stripping section will play the role of recovering the solute from the lean gas stream. Carbon dioxide is then separated from air in the sense that a lean gas product is alternatively and continuously produced at the bottom of one column and an enriched gas product a t the top of the other column. In the case of a high pressure feed configuration (Figure 41, parts of the lean and enriched gases are respectively recycled t o the bottom of one column and the top of the other column alternatively after vacuum and atmospheric compression resulting in a dual reflux ratio Rr and R,' which are related by
(1 + R,') = E.(&) QL where R,' is the enriching reflux ratio, Rr is the stripping reflux ratio, and QL,QEare, respectively, the flow rates of the lean and enriched gases which are continuously produced. The case of the low pressure feed configuration can be visualized similarly and the reflux ratio R, and R,' will be related by Figure 3. Configuration of PSA with intermediate feed inlet position (enriching and stripping).
column ( X E )cannot be enriched by a factor higher than the pressure ratio (palp,) while in Figure 2 the mole fraction of the solute from the top of the adsorption column ( X L )cannot be removed by a factor lower than the reciprocal of the pressure ratio (pd/pa). PSA with Rectifying and Stripping Sections. This type of PSA process was proposed to achieve simultaneously both removal and concentration and overcome the thermodynamic limitations which characterize the basic configurations illustrated by Figures 1 and 2. The configuration shown in Figure 3 results in a combination of the configuration of Figures 1 and 2 and consists basically of a complicated eight-column configuration. However when blowdown, equalization, and pressurization are omitted, the eight-column configuration can be simplified to the two-column foursection configuration schematically represented in Figure 4 for the case of a high pressure feed configuration.
R,' = (1 + RJ(B;) QL as cited in the previous paper (Diagne et al., 1994).
Experimental Section The high pressure feed configuration was adopted to develop the PSA experimental setup. A pair of 1 m long and 18 mm i.d. brass columns were packed with 300 g of zeolite 13X. Pure carbon dioxide from a COa cylinder was continuously mixed with dehumidified air from another PSA unit, and the mixture at atmospheric pressure was supplied as the feed gas at an intermediate axial position of the adsorption column receiving in its upper part a portion of the enriched gas produced at the top of the desorption column. The desorption column received in its lower part a portion of the lean gas produced at the bottom of the adsorption column. This portion of the lean gas was used as a regeneration
Ind. Eng. Chem. Res., Vol. 34,No. 9,1995 3085 Table 1. Experimental Conditions" Figure 5 6 7 8 9 10 11 12
QF
[Uminl
1.250 1.250 1.250 1.250 1.250 1.250 1.250 0.25-0.50
t, = 120 s and
QE
[Uminl
0.250 0.250 0.250 0.250 0.250 0.250 0.250 0.025-0.005
QL [Uminl 1.000 1.000 1.000 1.000 1.000 1.000 1.000 0.225-0.45
R,
XF
ZFIL
Pdpd
0.50 0.10 0.18-1.0 0.18-1.0 0.10 0.10 0.1-1.0 0.2 -4.4
0.20 0-0.20 0.20 0.20 0.20 0.20 0.20 0.20
0.50 0.50 0.50 0.50 0.1-0.9 0.3-0.9 0.1-0.9 0.5
1.64-12.50 1.64-12.50 2.94-4.76 2.94 1.64- 12.5 12.5 2.94 1.64
W = 300 g for all experiments.
gas in addition to an evacuation by a vacuum pump. The role of each column was switched every 2 min by means of a programmable controller. The gas concentrations as well as the concentration distributions along each adsorption column were continuously monitored by means of C 0 2 gas sensors in addition to a gas chromatograph equipped with automatic sampling devices. For the concentration distributions and in order to keep constant the overall process performance during the sampling procedure, very small and equal amounts of gas sample were continuously sent to the gas chromatograph by means of nine thin tubes easily connectable to the adsorption column at intervals of 10 cm. Therefore, for a given sampling point, the C02 concentration was measured at the middle of the adsorption step and almost corresponded to the volume-averaged mole fraction of CO2 during the whole adsorption step. The operating conditions for each experiment are summarized in Table 1. Some minor problems of data reproducibility can be encountered. These problems are due t o the cyclic nature of the PSA process and also to the frequent variations in feed gas temperature resulting in slight differences in the amount adsorbed and desorbed between experiments under the same operating conditions. Comparison of Three PSA Configurations. The new PSA process is derived from a simple combination of the two conventional processes mentioned above. Thus, prior to the parametric studies, a simple comparison between the three processes was carried out. Identical operating conditions, such as gas flow rates, feed concentration, half-cycle time, amount of adsorbent, and apparatus variables, such as column length and diameter, were fixed for each process, and the effects of the pressure ratio (Palp,) on the enriched gas as well as lean gas concentrations were investigated. Typical results are shown in Figure 5a for the enriched product and Figure 5b for the lean gas product. It can be seen in both figures that the efficiency of the new PSA process (intermediate feed) is far greater than that of the basic enriching and stripping PSA processes. Since the adsorption pressure was kept constant in each experiment, it is evident that the desorption or evacuation pressure which is the variable in the pressure ratio equation is very important for the separation. Since the adsorption isotherm of C02 onto zeolite 13X is of the Langmuir type, an increase in the pressure ratio results in an increase in the amount adsorbed. However, at a pressure ratio range where the COz concentration starts to level off as a consequence of the saturation of the solid adsorbent, a further decrease of the evacuation pressure or increase of the pressure ratio does not significantly improve the separation performance. At a low pressure ratio Palp, = 1.64-2.94,it can be seen for the new PSA process that the enrichment ratio which is the ratio of COZconcentration in the enriched
1.o
-2
-g
g
a) Enriched gas
0.90 0.80
Enriching 0.70
m
0.60
8
8 0.50 8"0.40
-
0.30
0.20 1
3
5
7
9
1
1
1
3
1
3
Pressure ratio , P,P, 0.20 *
-
b)Leangar
0.16
I
Xd
8
-
'S
0.12
E 8
p 0.080 8
Enriching
8"0.040 0.0 1
3
5
7
9
1
1
Pressure ratio , P,/P, Figure 5. Simple comparison between the new PSA process and conventional processes.
gas and feed gas is much higher than the pressure ratio. Thus, the new process is free from so-called thermodynamic limitations. Efficiency of the New PSA Process. The process efficiency can be represented by the plot of the COS concentration in the product gases against the C02 concentration in the feed gas. Figure 6 shows the process efficiency at various values of the pressure ratio and the feasibility of C02 separation and recovery by this PSA process. The curves were constructed from arbitrarily fixed values of the dimensionless feed inlet position (ZFIL),the reflux ratio (&I, the adsorption pressure (Pa),and the feed and product gas flow rates (QF, &E, and QL).Under the operating conditions given in Table 1, an evacuation pressure of 0.08 atm corresponding to a pressure ratio of 12.5(adsorption pressure Pa= 1atm) was necessary to obtain a concentration of CO2 greater than 0.94 in the enriched gas and less than 0.04 in the lean gas product with a fractional recovery of more than 0.94from a feed gas consisting of 20%C02.
3086 Ind. Eng. Chem. Res., Vol. 34, No. 9, 1995 1.o
o,90
-0- PalPd = 4.76
-+ PalPd = 2.94
0.40
0
0.05
0.1
0.15
0.2
0
0.2
C02concentration in feed, Xf 0.20
-
0.6
1
0.8
Figure 7. Effects of the reflux ratio and the pressure ratio on the enriched gas Concentration.
b) Lean gas
0.16
o
Y
*.d
.g
0.4
Reflux ratio, Rr [-]
0 0.8
0.12
Rr = 0.18 Rr = 0.30 Rr = 0.50
5
B3
0.6
0.080
8-0.040
0.4
0.2
0.0 0
0.05
0.1
0.15
0.2
C02 concentration in feed, Xf
Figure 6. Efficiency of the PSA process at various values of the pressure ratio.
These values of the enriched and lean gas concentrations as well as C 0 2 recovery should be much better with an appropriate combination of the operating parameters. Combined Effects of the Reflux Ratio and the Pressure Ratio. The objectives of these experiments were to confirm the existence of the effects of the reflux ratio on the concentration of the enriched and lean gases and t o extend the investigation at some values of the pressure ratio toward an optimization. The experiments were carried out with a set of fixed operating conditions given in Table 1. Typical results are shown in Figure 7 for the enriched gas. The importance of the desorption pressure or pressure ratio can be confirmed in this figure. Furthermore, it is interesting to see that the effects of the reflux ratio are very significant for both values of the pressure ratio, and optimal values of the reflux ratio between 0.3 and 0.7 were observed. Concentration Distributions and the Optimum Reflux Ratio. The existence of an optimal value of the reflux ratio R, can be interpreted by means of the concentration distributions along each adsorption bed. The results for various values of R, are presented in Figure 8 in which the CO2 concentration is plotted against the axial distance (ZfL)along the adsorption bed. Since measurement of the concentration was impossible a t the feed inlet position, the distribution in the neighborhood of the feed inlet was extrapolated from up- and downstream data. The feed is mixed with a stream of different concentration, and a concentration jump appears a t the feed inlet position as shown by the dotted lines.
0.0 0
0.2
0.4 0.6 Axial distance, ZIL
0.8
1
Figure 8. Concentration distributions at various values of the reflux ratio
At a low reflux ratio (R, = 0.181, the COz concentration decreases rapidly near the top of the rectifying section and then becomes almost constant from an axial distance ZIL = 0.2, including the entire zone of the stripping section (0.5 < Z / L < 1). As a consequence, the C 0 2 concentration in the enriched gas product (at Zf L = 0) becomes quite low while that in the lean gas (at Zf L = 1) undergoes a serious increase both resulting in a quite low performance. These results can be interpreted t o be a consequence of an incomplete regeneration of the adsorption column due to relatively low values of the reflux ratio. At a high reflux ratio (R, = 0.5 and 1.01, it can be seen that the C 0 2 wave front has deeply penetrated the bed over the entire zone of the stripping section although there is a slight variation of the COz concentration in the rectifying section (0 Z f L < 0.5). This results in a rapid decrease of the C 0 2 concentration in the stripping section. The shape of the concentration distributions implies that at a high reflux ratio, the stripping section is well regenerated while the rectifying section is not. During these experiments, the highest C 0 2 concentration in the enriched gas and the lowest COz concentration in the lean gas were observed at R, = 0.5 (Figure 7). However, when the reflux ratio tends to higher values, the residence time of the solute inside the column becomes shorter resulting in a relatively lower performance as in the case of R, = 1.0. From the shape of the concentration distributions and taking into account the COSconcentration in both the
1.0 0.90 c
A
.
1 I
Ind. Eng. Chem. Res., Vol. 34, No. 9, 1995 3087
0.80
XU
d
0.70
'U
s
8
8"
0.60
PjP, = 2.94
0.50 PjP, = 2.13
0.40
0.30
1'.
0.20
0
'
'
,, "
0.2
0.4
"
"
0.6
" '
I '
' ' 1
0.8
1
Dimensionless feed position ,Z N - 1 0.20
b) Leangos
P I P , = 1.64
4
PjP, = 4.76
0.050
0.0 0
0.2
0.4
0.6
1
0.8
Dimensionless feed position, ZJL
0.2
0.4
0.6
0.8
1
Axial distance, Z/L[-]
0.10
8"
0
[-I
Figure 9. Effects of the dimensionless feed position ZFIL on the product gas concentration at various pressure ratios.
enriched and lean gases, the optimum reflux ratio is located around R , = 0.5, values at which the COS concentration is expected t o decrease smoothly in the entire section of the column. From a viewpoint of optimization, further investigations employing both experiments and modeling are necessary for a wide range of pressure ratios and dimensionless feed inlet positions. Combined Effects of the Dimensionless Feed Inlet Position and the Pressure Ratio. As in the case of the reflux ratio, the effects of the dimensionless feed inlet position (ZFIL), Le., the fractional length of the rectifying section, were extended to a wide range of pressure ratios. The experiments were carried out with a low value of the reflux ratio (R,= 0.1) at which significant effects of zF/L on the concentration of the enriched gas as well as lean gas products were expected. Figure 9 is the plot of the C 0 2 concentration against the axial dimensionless feed inlet position ZdL. In the case of the enriched gas (Figure 9a) as well as the lean gas product (Figure 9b), it can be seen at any value of the pressure ratio that there exists an optimum dimensionless feed position. On the basis of COa concentration in both gases, the optimum feed inlet position was located for all curves between ZF/L= 0.4 and 0.6. At the highest pressure ratio (Pa/Pd = 12.51, the COz concentration a t the optimum feed inlet position was nearly equal t o 0.95 in the enriched gas and lower than 0.03 in the lean gas with a fractional recovery of 0.95. At a low pressure ratio, the C 0 2 concentration in both gases and the enriched product recovery can be im-
Figure 10. Concentration distributions a t various values of the feed inlet position.
proved by increasing the value of the reflux ratio as demonstrated in the above section. Concentration Distributions and the Optimum Feed Inlet Position. The concentration distributions measured a t Pa/Pd = 12.5 and at different values of the dimensionless feed inlet position are summarized in Figure 10 . From a feed inlet position zF/L = 0.7, the COZconcentration first decreases below the feed concentration XF= 0.20 in the rectifying section and then undergoes a sharp increase or "concentration change". Finally, it starts decreasing again in the stripping section. This increase or "concentration change" can be considered as a "perturbation" within the concentration distributions and is due to mixing problems which occur between the feed flux and the downstream flux available in the neighborhood of the feed inlet position. This phenomenon always resulted in lower performance, and this effect was more remarkable a t zF/L = 0.9. In the case Of ZF/L = 0.3, the mixing problem between different concentrations is significant again and the stripping section has to start with a much higher concentration than the feed. As a result, the optimum feed inlet position would correspond to a position at which there is neither a mixing problem nor a "perturbation" of the concentration distributions. At ZF/L= 0.6, the C 0 2 concentration near the feed inlet position becomes very close to that in the feed gas. A smooth decrease of the C 0 2 concentration characterized by a deep penetration of the C02 wave front over the entire section of the bed can be observed. Therefore, the optimum feed inlet position was located at ZF/L= 0.6 at which position the C02 in the feed gas was concentrated up to 0.95 while keeping the lean gas concentration under 0.03. In an analogy to distillation, a concentration distribution of the solute is built from the top t o the bottom of the column. Thus, in this PSA process as well as in distillation, the optimum feed inlet position will always correspond t o a position or stage where the concentration of the solute in the feed and that in the feeding position or stage are very close to avoid mixing problems. Combined Effects of the Reflux Ratio and the Dimensionless Feed Inlet Position. The main advantage of this PSA process is that the minimum difference of pressure or pressure ratio (Pa/Pd)can be sensibly reduced while keeping reasonable product concentrations and recovery. Therefore, it is interesting
3088 Ind. Eng. Chem. Res., Vol. 34,No. 9, 1995 1.0
1.O
i
I
5
0.18
= 0.3
PolPd = 1.64 2.IL IO.50
a) Enriched gas
= 0.51 = 0.71 =1
+Rr +Rr *Rr
= 0.1
+Rr *Rr -O-Rr
0.80
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0.70
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0.10
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-
7 0.08
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.s
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0.0
,
0.250
0.500
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, , o,;o., 0.450
,
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0.4
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-
0.04
0.00 0
0.2
0.4
0.6
0.8
1
Dimensionless feed position , Z P L[-]
0
0.2
0.4
0.6
0.8
1.0
1.2
RL Rr.Q,[Umin]
Figure 11. Combined effects of ZFIL and R, on the product concentration.
Figure 12, Effects of gas flow rates on product concentration a t Palp, = 1.64.
to investigate at a modest pressure ratio PJPa = 2.94 how both characteristic parameters, i.e., the dimensionless feed inlet position ZFIL and the reflux ratio Rr, would simultaneously affect the concentration of both the enriched and lean gases. The curves shown in Figure l l a (enriched product) and Figure llb (lean product) were obtained from fixed values of gas flow rates while the dimensionless feed position (ZFIL)and reflux ratio (R,)were alternatively varied, respectively, between zF/L = 0.1 and 0.9 and between R, = 0.1and 1. In Figure l l a , the optimum feed inlet position increases with increasing values of the reflux ratio and then decreases via the highest COz concentration at Rr = 0.5-0.7. In the case of the lean gas (Figure llb), the optimum feed inlet position was located between ZFIL = 0.4 and 0.6 at any value of the reflux ratio. These results imply that at Pa/Pd = 2.94, the optimal values of zF/L and R, at which the highest and lowest COz concentrations were obtained, respectively, in the enriched and lean gas products were located between zF/L = 0.4 and 0.6 and R, = 0.5 and 0.6. Therefore from a feed gas consisting of 20% COZ, the enriched gas concentration was around 0.80 and the lean gas concentration was lower than 0.05 both resulting in a fractional recovery higher than 0.80. The COz concentration in both products can be increased and reduced simultaneously by reducing the gas flow rates inside the adsorption and desorption columns. Effects of Gas Flow Rates. From the viewpoint of material balance (QF = QE + QL), changing the flow rates of the enriched or lean product will result in a
change of the feed gas flow rate. For these reasons, the overall effects of the gas flow rates on the enriched and lean gas concentrations were investigated by reducing the residence or contact time of the gas inside the column from run 1 to run 2. The experiments were carried out at a modest pressure ratio P#d = 1.64, at zF/L = 0.5, and at XF= 0.10. The results are shown in Figure 12 with experimental conditions for each run. In Figure 12, the abscissa corresponds to the flow rate of the recycled lean gas, RL = R r Q ~ Therefore, . instead of the reflux ratio Rr,RLwas used to keep the curves in the same range of variation and make the comparison easier. It can be seen that when the gas flow rates are reduced to half of their initial values from run 1to run 2, the COa concentration in the enriched gas doubled while that in the lean gas was reduced by a factor of 2. Optimal values of RL were observed between 0.4 and 0.6 Umin for all curves. For run 2, at the optimal values of RL and at a very modest pressure ratio PaIPa = 1.64, the feed gas consisting of 10% COz was simultaneously concentrated up to 80% and removed up to 2% with a fractional recovery of 80%. From the viewpoint of modeling, the above results can be described by a rate-controlling or equilibrium stage model. If we consider a rate-controlling model, since the cycle time is quite short, the process is far from reaching equilibrium and attaining a better degree of separation while a decrease in the gas flow rates will be caused by a large number of mass transfer units. Therefore, in such a case, the rate-controlling concept with a finite mass transfer coefficient will be the appropriate model to describe the process. If the
Ind. Eng. Chem. Res., Vol. 34, No. 9, 1995 3089 equilibrium stage model is considered for the analysis of the observed behavior, since decreasing the gas flow rates results in a short HETP, the number of equilibrium stages becomes larger resulting in a better fractionation. However, it is very premature to clarify which model offers a better description of the observed experimental behavior. Further studies involving the application of both models among others are necessary to analyze the process.
Concluding Remarks The practical feasibility of carbon dioxide separation and recovery from air-COz mixtures by means of a new PSA was demonstrated. Comparison between the new process and the conventional processes from which it was synthesized shows a large predominance of the former over the latter. Parametric studies of the new PSA process confirm the importance of the dimensionless feed inlet position (zF/L)and the reflux ratio (R,) which are the main characteristic parameters. Within the range of experimental conditions studied here, the optimum feed inlet position was almost located between ZdL= 0.4 and 0.6 and the optimum reflux ratio between R, = 0.3 and 0.6. Both results were consistent from a viewpoint of concentration distributions along each adsorption column. For an appropriate combination of the operating parameters, it was possible from a feed gas consisting of 20%C02 to obtain a 95% COz enriched gas and a less than 3% CO2 lean gas with 95% fractional recovery. At a lower pressure ratio, with increasing importance of zF/L and R,, it was also possible to concentrate and remove the C 0 2 simultaneously beyond a factor of the pressure ratio a situation unattainable in the conventional PSA processes.
Acknowledgment The research was financially supported by the Sasakawa Scientific Research Grant from the Japan Science Society.
Nomenclature L = column length, m P = pressure, atm Q = gas flow rate, N m3/min R , = stripping reflux ratio t, = half-cycle time, s W = mass of adsorbent, kg X = mole fraction 2 = axial distance, m Z F = feed inlet position, m Subscripts a = adsorption d = desorption
E = enriched gas F = feed gas L = lean gas R = rectifying section S = stripping section
Literature Cited Chue, K. T.; Kim, J. N.; Yoo, Y. J.; Cho, S. H.; Yang, R. T. Comparison of Activated Carbon and Zeolite 13X for COz Recovery from Flue Gas by Pressure Swing Adsorption. Znd. Eng. Chem. Res. 1995,34,591-598. Diagne, D.; Goto, M.; Hirose, T. New PSA Process with Intermediate Feed Inlet Position Operated with Dual Refluxes: Application to Carbon Dioxide Removal and Concentration. J . Chem. Eng. Jpn. 1994,27 (l),85. Hirose, T. Recent Developments in PSA . Proceedings of the 2nd Korea-Japan Symposium on Separation Technology, 1990, p 345. Hirose, T. A simple Design Method of a New PSA Process Consisting of Both Rectifying and Stripping Sections. Proceedings of the 2nd China-Japan-USA Symposium on Adsorption, 1991, p 123. Kanemaru, T.; Nishino, Ch. PSA Ho Koseino Tansan Gasu Bunri Purosesu no Kaihatsu. (Development of High Performance PSA Process for Carbon Dioxide Separation.) Kemikaru Enginiaringu 1990, 9,66. Kawai, T. Atsuryoku Suingu Kyuchaku Gijutsu Shusei (Monograph of PSA Technology). Kogyogtjutsukai 1986. Kikkinides, E. S.; Yang, R. T. Concentration and Recovery of COz from Flue Gas by Pressure Swing Adsorption. Znd. Eng. Chem. Res. 1993, 32, 2714. Komiyama, H.; Fujitani, T. A Comparative Study of Processes for Separating COz from Stack Gas in Terms of Energy Consumption. Kagaku Kogaku Ronbunshu 1993,19 (5), 818. Kumita, M.; Watanabe, F.; Hasatani, M. Separation of Carbon Dioxide by Pressure Swing Adsorption Using Granular Molecular Sieving Carbon. Kagaku Kogaku Ronbunshu 1993,19 (31, 314. Mersmann, A.; Munstermann, U.; Schadl, J. Trennen Von Gasgemischen Durch Adsorption. (Separation of Gas Mixtures by Adsorption.) Chem. Zng. Tech. 1983, 55 (61, 446. Mikami, K.; Ikumi, S.; Ibaraki, S. PSA System of Producing High Purity Nz Gas. Mitsui Zosen Giho 1989,137,44 (in Japanese). Ruthven, D. M.; Farooq, S.; Knaebel, K. S. Pressure Swing Adsorption; VCH Publishers: New York, 1994. Sircar, S. Production of Hydrogen and Ammonia Synthesis Gas by Pressure Swing Adsorption. Sep. Sci. Technol. 1990,25 (11, 121, 1087. Suzuki, M. Adsorption Engineering, Kodansha: Tokyo, 1990. Tondeur, D.; Wankat, P. C. Gas Purification by Pressure Swing Adsorption. Sep. Purif. Methods 1985, 14 (21, 157. Yang, R. T. Gas Separation by Adsorption Processes; Butterworth: Boston, 1987.
Received for review November 28, 1994 Revised manuscript received May 4,1995 Accepted May 31, 1995@
IE940700A
@
Abstract published in Advance ACS Abstracts, August 1,
1995.
