Article pubs.acs.org/est
Amine Modeling for CO2 Capture: Internals Selection Prakash Karpe† and Clint P. Aichele*,‡ †
Phillips 66, Post Office Box 4428, Houston, Texas 77210, United States School of Chemical Engineering, Oklahoma State University, 423 Engineering North, Stillwater, Oklahoma 74078, United States
‡
S Supporting Information *
ABSTRACT: Traditionally, trays have been the mass-transfer device of choice in amine absorption units. However, the need to process large volumes of flue gas to capture CO2 and the resultant high costs of multiple trains of large trayed columns have prompted process licensors and vendors to investigate alternative mass-transfer devices. These alternatives include third-generation random packings and structured packings. Nevertheless, clear-cut guidelines for selection of packings for amine units are lacking. This paper provides well-defined guidelines and a consistent framework for the choice of mass-transfer devices for amine absorbers and regenerators. This work emphasizes the role played by the flow parameter, a measure of column liquid loading and pressure, in the type of packing selected. In addition, this paper demonstrates the significant economic advantage of packings over trays in terms of capital costs (CAPEX) and operating costs (OPEX).
1. INTRODUCTION Removing CO2 from flue gases by chemical solvents, such as amines, is the most promising technology choice currently available. Several factors reinforce the viability of aqueous amine absorption, including the capacity to handle large volumes of flue gas and wide ranges of CO2 concentrations. Additional factors include a tolerance for the presence of oxygen (O2) in small concentrations, operability at low temperatures and pressures, and the long history of operating experience. A typical amine unit, as shown in Figure 1, consists of an absorber and a regenerator. In the absorber, lean amine reacts with CO2 that is in the flue gas. The rich amine exits the bottom of the absorber, and it is pumped to the regenerator, where heat is supplied to dissociate CO2 from the amine. A pure CO2 stream is sent to the compression unit, and the regenerated lean amine is pumped back to the absorber. To achieve effective mass transfer in the absorber and regenerator, a mass-transfer device for contacting the vapor and liquid phases is used. Traditionally, trays have been the masstransfer device of choice in amine units. This is because amine units have been small in size, there has been a wealth of experience regarding the design and operation of trayed columns, and the steady-state modeling approach based on the equilibrium stage concept was found to be adequate. However, the need to process large volumes of flue gas to capture CO2 and the resultant high capital costs (CAPEX) and operating costs (OPEX) have prompted process licensors and vendors to investigate use of alternative mass-transfer devices, such as third-generation random packings (RPs) and structured packings (SPs). © 2013 American Chemical Society
The change from trays to packings is now possible because of the availability of high-performance packings, experimental data for mass transfer in packed beds, and rigorous rate-based modeling of reactive separation processes. Several recent publications have tried to address the use of packings in amine absorbers and regenerators through experimentation and modeling.1−5 Menon et al.6 and Weiland et al.7 have compared various packings for post-combustion capture of CO2 by amines. While this is a welcome trend, a careful review of the literature revealed that clear guidelines for selection of appropriate mass-transfer devices for amine units are lacking. This paper provides a brief theoretical background about column internals selection, well-defined guidelines for column internals selection, and a consistent framework for the choice of mass-transfer devices for amine absorbers and regenerators. The directional impact on costs, both CAPEX and OPEX, is demonstrated with a few examples.
2. MODELING BACKGROUND 2.1. Foaming. Amine−water systems are known to have a high foaming tendency. Trays typically operate in regimes where vapor disperses in liquid-forming droplets. On the other hand, packings generate thin films instead of droplets for mass and heat transfer. As a result, packings are less prone to foaming Received: Revised: Accepted: Published: 3926
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Figure 1. Typical amine unit for CO2 capture.
than trays. On trays, the presence of foam can lead to premature jet flood as well as premature down-comer flood.8 2.1.1. Tray Sizing Criteria for Amine Systems. To compensate for the loss of capacity, derating factors and empirical criteria are applied to tray sizing. The recommended procedure is to rate the trays using the normal procedure of tray sizing, which is based on estimating percent flood and then dividing the results by a derating factor called the system factor (SF). As the foaming tendency increases, the SF decreases. New trays are typically sized for design percent flood (jet flood) of 70−80%. This work uses 80% design flood for trays with an appropriate SF value (see Table 1).8
Table 2. Pressure Drop (in. of H2O/ft) for Absorbers and Regenerators
derating factor
amine absorber amine regenerator
0.8 0.85
amine systems
0.25−0.4 0.25−0.4
0.25 0.3
by (a) the choice of the mass-transfer device, (b) the absorber diameter, and (c) the number of equilibrium stages. Trays have the highest pressure drop per foot of column height, followed by random packings, while structured packings have the least pressure drop. The pressure drop in the packed bed and on trays reduces with an increase in the tower diameter. While this directionally reduces the blower CAPEX and OPEX, the absorber CAPEX increases. The final characteristic that affects pressure drop, number of equilibrium stages, is discussed in more detail in the following section. 2.3. Estimation of Height Equivalent to a Theoretical Plate (HETP) for Packings. A significant amount of published data and correlations are available for estimating HETP for both random and structured packings for a wide variety of applications.8 HETP provides an estimate of the distance between equilibrium stages. Kister proposed the following rule of thumb for HETP, and it has been found adequate for most applications, including random packings8
Table 1. Tray Derating Criteria for Columns in Amine Systems column type
nonfoaming systems absorber regenerator
2.1.2. Packed Tower Sizing Criteria for Amine Systems. Two criteria are normally preferred for sizing of packed columns: flood point and pressure drop. Fair and Bravo9 define flood point as “the region of rapidly increasing pressure drop with simultaneous loss of efficiency”. In this study, 80% flood is used as the design criterion. Table 2 recommends maximum design pressure drops for absorbers and regenerators with random packings.8 Criteria given in Table 2 will also be used for structured packings. 2.2. Pressure Drop. One of the important cost factors is pressure drop per packing height that can be saved inside the amine absorber. The flue gas is typically available at atmospheric pressure; therefore, the absorber needs to be operated as close to atmospheric pressure as possible to minimize the flue gas blower size and power (CAPEX and OPEX). The total pressure drop in the absorber is influenced
HETP = 1200/a p + 4
(1) 2
where ap is the packing surface area per unit volume (ft /ft3) and HETP is expressed in inches. Equation 1 should be used with caution, and whenever possible, the results should be checked against published data. Emerging HETP correlations are being developed that attempt to account for the complexities of these systems through the incorporation of chemical reactions.10 Amine systems preclude the exclusive use of the previously described criteria for three primary reasons: (1) the majority of 3927
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Table 4, one can conclude that, at FP > 0.3, the use of SPs should be avoided and trays or RPs should be used instead. 2.5. Comparison of Costs. The two major CAPEX items influenced by the type of mass-transfer device used are the absorber and the regenerator. In addition, for low-pressure amine systems, the flue gas blower cost is also influenced by the absorber mass-transfer device. This is not an issue in highpressure amine systems. Excluding CO2 compression, the two major components of OPEX are the blower power for lowpressure amine systems and reboiler duty. However, for fixed lean and rich amine loadings (mol of CO2/mol of amine) and percent CO2 recovery, regenerator reboiler duty is independent of the type of mass-transfer internal used in the absorber and the regenerator. Low-pressure steam was assumed for all cases for regenerator operating cost estimates. Equipment cost estimates were based on preliminary quotes from vendors.
amine systems use trays for mass transfer, and as a result, insufficient efficiency data are available for packings; (2) amine capture of CO2 involves reactive distillation for which the conventional HETP correlations cannot be used; and (3) in some cases, the viscosity and surface tension of amine solutions fall outside the limits of these correlations. This study proposes the use of SF for derating HETP for amine systems. Therefore, for amine systems, eq 1 can be rewritten as HETP = (1200/a p + 4)/SF
(2)
where the appropriate system factor, SF, is used from Table 1. 2.4. Comparison of Trays, Random Packing, and Structured Packing Performance C-Factor and Flow Parameter (FP). Two parameters that are commonly used for rating trays and packings are the C-factor and the flow parameter, FP.8 The C-factor is a measure of the vapor handling capacity of a mass-transfer device and is defined as C‐factor = (V /A s)[ρG /(ρL − ρG )]0.5
3. RESULTS AND DISCUSSION This paper discusses three cases, two from published literature14,15 and one from an internal ConocoPhillips study, as listed in Table 5. These cases employ 30 wt %
(3)
where V is volumetric flow rate of gas, As is the cross-sectional area of the packing or active area of the tray, and ρL and ρG are densities of liquid and gas, respectively. The FP has often been used to correlate the effects of the liquid rate and operating pressure on capacity and efficiency of trays and packings and is defined as FP = (L /G)(ρG /ρL )0.5
Table 5. Summary of Cases
(4)
where L and G are mass flow rates of liquid and gas, respectively. FP increases with both the liquid rate and gas density (or operating pressure). Note that FP is a dimensionless number, while the C-factor has the unit of linear velocity. Table 3 presents the typical performance of mass-transfer devices in distillation columns.11,12
type of mass-transfer device random packing
structured packing
0.03− 0.35 3−15
0.03−0.35
0.01−0.45
1.0−2.0
0.01−1.0
24−70
18−66
4−33
trays
capacity (C-factor, ft/s) pressure drop (mmHg per theoretical stage) mass-transfer efficiency (HETP, in.)
Kister et al.11 and Bravo13 have studied the dependence of the capacity and efficiency of trays and packings upon the FP, and their findings are summarized in Table 4. The rapid decline in the capacity and efficiency of structured packings is due to their hypersensitivity to maldistribution in this region. From Table 4. Impact of the Flow Parameter on the Performance of Mass-Transfer Devices flow parameter
capacity
efficiency
0.02−0.1 0.1−0.3 0.3−0.5 0.5
SPs 30−40% greater equivalent SPs steepest decline RPs greatest
SPs 50% greater SPs 50−20% greater SPs steepest decline RPs greatest
reference
gas rate (MMSCFD)
1 2 3
Fisher et al.15 internal Weiland et al.14
426 per train 113 112
monoethanolamine (MEA) to absorb CO2 from different sources. The cases are modeled using AMSIM, a nonequilibrium stage-based software for modeling amines in Aspen HYSYS. The AMSIM-based models in this study were tuned carefully to match the original conditions and results, thereby ensuring that the HETP estimations are as reliable as possible. The models were also verified using Protreat, a ratebased modeling software.16 Rating calculations (percent flood and pressure drop) for trays and packings were performed using the corresponding vendor software. For example, for packings manufactured by Koch-Glitsch, KG-Tower (version 4.0) was used,17 while for those from Sulzer, SulCol (version 2.0.8) was used.18 3.1. Case 1. Key model input parameters and results for this case are summarized in Table 6. This case was based on a U.S. Department of Energy (DOE)−National Energy Technology Laboratory (NETL) study for the capture of CO2 from flue gas at a 500 MW coal-fired power plant using 30 wt % MEA. The stage-based modeling approach worked reasonably well for both packings and trays in this case. HETP for RPs and SPs were estimated using the rule of thumb proposed in eq 2 combined with SF values from Table 1. Note that the low FP value of 0.12 allows use of SP (Mellapak 250.X in this example) in the absorber, while its high value of 0.69 precludes its use in the regenerator. As illustrated in Table 6, the use of SP in the absorber and RP in the regenerator results in the lowest CAPEX and OPEX. The major CAPEX reduction comes from the fact that, for trays, two absorbers and two regenerators are needed instead of one each for packings. This is because the trays have 4 passes and their size is limited by down-comer choke flood. This example also underscores the disadvantage of using trays in low-pressure absorbers because they cause highpressure drop in the column. This leads to a significant increase
Table 3. Typical Performance of Mass-Transfer Devices in Distillation Columns
characteristic
cases
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Table 6. Key Model Input Parameters and Results for Case 1 1 of 4 trains
operating conditions
flue gas rate (Ibmols/h) lean amine rate (USGPM) CO2 in flue gas (mol frac) MEA in lean amine (wt %) percent CO2 captured (%) lean loading (mol/mol) rich loading (mol/mol)
46753 10457 0.1233 30 90 0.28 0.48 absorber
column top pressure (psia) flow parameter mass-transfer device type number of stages/trays HETP (trays spacing, in.) ΔP (in. of H2O/ft) [mmHg/tray] total ΔP (psi) practical HETPP,P (in.) column height (ft) column diameter (ft) percent CAPEX reduction (columns) (%)a blower ΔP (psi) blower power (hp) (efficiency = 75%) percent CAPEX reduction (blower) (%)b percent OPEX reduction (blower) (%)
trays 4-p float valve 15 24 [6.6] 2.0 28 2 × 33 2.6 4710
regenerator
14.7 0.12 random packings
27.9 0.69 structured packings
trays
random packings
CMR no. 2 15 39 0.5 0.9 42.9 53.6 33 26 1.5 2785 27 41
Flexipac 250.X 15 25 0.17 0.2 27.5 34.4 29.5 47 0.8 1510.0 49 68
4-p float valve 10 24 [7] 1.4
CMR no. 2 10 36.7 0.5 0.6 40.4 33.6 20 27
18.0 2 × 20
a
A power factor of 0.6 based on the column weight is used for estimating the installed cost. bA power factor of 0.6 based on the blower hp is used for estimating CAPEX.
in blower CAPEX and OPEX compared to random and structured packings. As seen in Table 6, structured packing is clearly the masstransfer device of choice in low-pressure absorbers. Despite this economic advantage of SPs over RPs, some designers recommend the use of only RPs in amine absorbers in flue gas service, citing the concern for severe fouling if SPs are used. The concern of fouling and plugging structured packing in the absorber can be addressed by (a) properly designing the wet gas scrubber and the knock-out drum and (b) installing proper safeguards, such as interlocks in the pretreatment plant to prevent carryover of particulate matter and corrosive pollutants (e.g., SOx). It should be noted that the estimated ΔP values for both columns exceed the recommended values (Table 2) of 0.25 in. of H2O/ft for the absorber and 0.3 in. of H2O/ft for the regenerator. 3.2. Case 2. Key model input parameters and results for case 2 are summarized in Table 7. This case is based on an internal study performed for capturing CO2 from flue gas using 30 wt % MEA. On the basis of the estimated values of FPs, SP (Mellapak 250.X) was chosen for the absorber and RP (I-Ring40) was chosen for the regenerator. Modeling was performed using both stage- and rate-based approaches. Both modeling approaches yielded similar results. HETPs for packings were estimated using eq 2 and SF values from Table 1. The use of SP in the absorber and RP in the regenerator leads to the lowest costs, in both CAPEX and OPEX. The reduction in the blower CAPEX (26%) and OPEX (91%) when SP is used in the absorber instead of trays is quite dramatic. This reduction is due to the significant differences in the pressure drops, as shown in Table 7. 3.3. Case 3. Key model input parameters and results are summarized in Table 8. This case is based on data from an
actual plant capturing CO2 (17.3%) from a stream containing predominantly H2 (58.7%) and N2 (20.2%) using 30 wt % MEA. The relatively high absorber pressure is equal to 369.3 psia and is packed with number 2 Cascade Mini Rings (CMR) random packing. Note that the estimated high value of FP (1.52) precludes the use of structured packing in the absorber. The treated gas at the top of the absorber had a tight specification of 5 ppm CO2. The original case was modeled using the rate-based approach, and it was duplicated for this study using the stage-based approach. Use of fewer stages (or trays) in the model could not meet the tight CO2 specification on the treated gas, while a further increase in the number of stages had a negligible impact on the CO2 specification. HETP was back-calculated to be 15.7 in. from the packing height of 31.5 ft and 24 stages. This matches well with the data published in the literature.19 However, calculation of HETP using eq 2 and SF equal to 0.8 yields a value of 42.9 in. If this value, combined with 24 stages, is used to estimate the column height, then it will result in a column almost 3 times taller than the actual. This case, therefore, emphasizes the importance of exercising caution in using the stage-based modeling approach combined with HETP estimation for packed columns in amine plants. The stage-based modeling approach, however, works well with trays. As seen in Table 8, use of 24 trays instead of packing in the column will yield the same performance. However, the use of random packing results in a smaller column than trays (34.5 × 9.5 ft for packing versus 46 × 12 ft for trays), leading to lower CAPEX (27% reduction). It is worthwhile to note that, in this example, the trays have 4 passes and their size is limited by down-comer choke flood, while the packed column has extra capacity available (operating ΔP of 0.17 in. of H2O/ft versus the recommended maximum of 0.25 in. of H2O/ft). This could 3929
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Table 7. Key Model Input Parameters and Results for Case 2 single train
absorber column top pressure (psia) flow parameter
type number of stages/trays HETP (trays spacing, in.) ΔP (in. of H2O/ft) [mmHg/tray] total ΔP (psi) practical HETPP,P (in.) column height (ft) column diameter (ft) percent CAPEX reduction (columns) (%)a blower ΔP (psi) blower power (hp) (efficiency = 65%) percent CAPEX reduction (blower) (%)b percent OPEX reduction (blower) (%)
trays 4-p float valve 26 24
operating conditions
operating conditions
flue gas rate (Ibmols/h) lean amine rate (USGPM) CO2 in flue gas (mol frac) MEA in lean amine (wt %) percent CO2 captured lean loading (mol/mol) rich loading (mol/mol)
mass-transfer device
random packings
14.7 0.16 structured packings
27.9 0.66 trays
16 38
7 35
[6.9]
0.24
0.25
[8]
0.2
3.5
0.9 41.8 55.7 22 −7
0.2 27.5 36.7 18.0 26
1.1
0.13 38.5 22.5 13 24
1.0 453
0.3 138.0
52
76
71
91
3.6 1542
14.0 20
12244 2822 0.1734 30 10 0.182 0.48 absorber
column top pressure (psia) flow parameter mass-transfer device
random packings
4-p float valve 8 24
IR40
flue gas rate (Ibmols/h) lean amine rate (USGPM) CO2 in flue gas (mol frac) MEA in lean amine (wt %) CO2 in sweet gas (ppm) lean loading (mol/mol) rich loading (mol/mol)
12440 3616 0.155 30 90 0.286 0.462 regenerator
Mellapak 250.X 16 25
50 22
Table 8. Key Model Input Parameters and Results for Case 3
type number of stages/trays HETP (trays spacing, in.) ΔP (in. of H2O/ft) [mmHg/tray] total ΔP (psi) practical HETPP,P (in.) column height (ft) column diameter (ft) percent CAPEX reduction (%)a
IR40
trays 4-p float valve 24 24 [9] 3.5 46 12
369 1.52 random packings CMR no. 2 24 15.7 0.17 0.2 17.27 34.5 9.5 27
a
A power factor of 0.6 based on the column weight is used for estimating the installed cost.
a
A power factor of 0.6 based on the column weight is used for estimating the installed cost. bA power factor of 0.6 based on the blower hp is used for estimating CAPEX.
result in a further reduction in the packed column size and, therefore, the installed cost. 3.4. Summary of Performance and Cost. Figure 2 summarizes the flow parameter performance for the three cases. The flow parameter in the absorber for case 3 was high because of the elevated pressure. Data were not available for the regenerator for case 3. The flow parameters for cases 1 and 2 are similar, and they indicate the need for structured packing in the absorber and random packing in the regenerator. Figure 3 shows the HETP comparison for the three cases. For comparative purposes, the equivalent HETP for trays is shown. For case 3, the rule-of-thumb approximation of HETP leads to an overprediction of the tower height by a factor of 3. A detailed comparison of absorber CAPEX reductions is shown in Figure 4. Both the column and blower CAPEX for structured packing are reduced more than random packing relative to trays. For case 3, there is clearly a CAPEX advantage to use random packing in the absorber. For the regenerator, there is approximately a 25% column CAPEX incentive to use random packing over trays for cases 1 and 2. The absorber blower represents the greatest potential for absorber OPEX reductions. Figure 5 shows that both random packing and structured packing are advantageous over trays in terms of reducing the blower OPEX. However, because of the
Figure 2. Summary of the flow parameter for each case. Note that regenerator information was not available for case 3.
reduced pressure drop, structured packing has the greatest advantage, which is as great as 91% for case 2. This paper provides well-defined guidelines and a consistent framework for the choice of mass-transfer devices for amine absorbers and regenerators. This work emphasizes the role played by the flow parameter, a measure of column liquid loading and pressure, in the type of packing selected. In addition, this paper illustrates the significant economic advantage of packings over trays in terms of capital costs (CAPEX) and operating costs (OPEX). The total savings for amine plants in CAPEX (absorber, regenerator, and blower) can vary from 25 to 48% when packings are used instead of trays. Use of packings in low-pressure amine absorbers can realize a significant reduction in blower operating cost because of the pressure drop reduction in the absorber. On the basis of the above criteria, the primary choice of mass-transfer device for low-pressure amine absorbers should be structured packings. Random packings should be used in amine 3930
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Figure 5. Comparison of absorber OPEX reductions realized because of structured packing. Figure 3. HETP comparison for the three cases. Note that the rule-ofthumb approximation overpredicts the absorber height requirement for case 3.
■
ASSOCIATED CONTENT
■
AUTHOR INFORMATION
S Supporting Information *
System factor (SF), flow parameter (FP), C-factor, and HETP definitions. This material is available free of charge via the Internet at http://pubs.acs.org.
regenerators and high-pressure absorbers, where flow parameters are high. Use of process-modeling software for column rating (estimation of capacity, diameter, and pressure drop) is recommended only for preliminary estimations. Rigorous rating calculations should be performed using tray and packing vendors’ software. Appropriate derating criteria, as proposed in this report, should be employed to account for the presence of foaming in amine contactors. Preliminary estimation of the packing height can be performed with reasonable accuracy in most low-pressure amine absorbers and regenerators using the rule of thumb proposed in this report for HETP. However, rate-based modeling software should be used to perform final process design and optimization.
Corresponding Author
*Telephone: (405) 744-9110. Fax: (405) 744-6338. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
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Figure 4. Comparison of absorber equipment CAPEX reductions. 3931
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(2) Zhao, G.; Zhang, D.; Chen, J. Acid gas removal using packed columns. Proceedings of the 82nd Annual GPA Convention; San Antonio, TX, March 9−12, 2003. (3) Sivasubramanian, M. S.; Weiland, R. H.; Dingman, J. C. Packed amine absorber simulation tracks plant performance. Proceedings of the 82nd Annual GPA Convention; San Antonio, TX, March 9−12, 2003. (4) Weiland, R. H.; Dingman, J. C. How to increase CO2 slip. Proceedings of the 51st Laurence Reid Gas Conditioning Conference; Norman, OK, Feb 25−28, 2001. (5) Weiland, R. H.; Hatcher, N. A.; Nava, J. L. AMP for carbon capture? Proceedings of the 60th Laurance Reid Gas Conditioning Conference; Oklahoma City, OK, Feb 21−24, 2010. (6) Menon, A.; Duss, M.; Bachmann, C. Post-combustion capture of CO2. Pet. Technol. Q. 2009, Q2, 115−121. (7) Weiland, R. H.; Oettler, B.; Ender, C.; Dingman, J. C. Selective amine treating using trays, structured packing, and random packing. Proceedings of the International Conference on Distillation and Absorption; Baden-Baden, Germany, Sept 30−Oct 2, 2002. (8) Kister, H. Z. Distillation Design; McGraw-Hill: Boston, MA, 1992. (9) Fair, J. R.; Bravo, J. L. I. Prediction of mass transfer efficiencies and pressure drop for structured tower packings in vapor/liquid service. Inst. Chem. Eng. Symp. Ser. 1987, 104, A183. (10) Hanley, B.; Chen, C. New mass transfer correlations for packed towers. AIChE J. 2012, 58, 132−152. (11) Kister, H. Z.; Larson, K. F.; Yanagi, T. How do trays and packings stack up? Chem. Eng. Prog. 1994, 90 (2), 23. (12) Chen, G. K. Packed column internals. Chem. Eng. 1984, 40. (13) Bravo, J. L. Select structured packings or trays? Chem. Eng. Prog. 1997, 93 (7), 36−41. (14) Sivasubramanian, M. S.; Weiland, R. H.; Dingman, J. C. Packed amine absorber simulation tracks plant performance. Proceedings of the 82nd Annual GPA Convention; San Antonio, TX, March 9−12, 2003. (15) Fisher, K.; Beitler, C.; Rueter, C.; Searcy, K.; Rochelle, G.; Jassim, M. Integrating MEA regeneration with CO2 compression and peaking to reduce CO2 capture costs. DOE and NETL Report; National Energy Technology Laboratory (NETL), U.S. Department of Energy (DOE): Pittsburgh, PA, June 9, 2005. (16) Optimized Gas Treating, Inc. http://www.ogtrt.com (accessed Sept 16, 2012). (17) Koch-Glitsch. http://www.koch-glitsch.com/default.aspx (accessed Sept 16, 2012). (18) Sulzer Chemtech, Ltd. http://www.sulzer.com (accessed Sept 16, 2012). (19) Wagner, I.; Stichlmair, J.; Fair, J. R. Mass transfer in beds of modern, high-efficiency random packings. Ind. Eng. Chem. Res. 1997, 36 (1), 227−237.
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