Performance of Appended Wire Mesh Packing in Sieve Tray Distillation Column of Ethanol-Water System

Transcription

1 Modern Alied Science; Vol. 9, No. 7; 015 ISSN E-ISSN Published by Canadian Center of Science and Education Performance of Aended Wire Mesh Packing in Sieve Tray Distillation Column of Ethanol-Water System Fadlilatul Taufany 1, Nonot Soewarno 1, Melvina Eliana Sutanto 1 & Indi Raisa Girsang 1 1 Deartment of Chemical Engineering, Seuluh Noember Institute of Technology, Indonesia Corresondence: Fadlilatul Taufany, Deartment of Chemical Engineering, Seuluh Noember Institute of Technology, Surabaya, 60111, Indonesia. taufany99@yahoo.com Received: May 4, 015 Acceted: June 5, 015 Online Published: June 30, 015 doi: /mas.v9n7148 UR: htt://dx.doi.org/ /mas.v9n7148 Abstract For the searation rocess in liquid-liquid mixture such as ethanol-water mixture, a sieve tray distillation column is an alternatif for affordable rocess and maintenance. However to date, this sieve tray system is still currently having a lower Murhee efficiency and smaller interfacial area, as comared to other tray system, that is, either a bubble ca or valve tray. Therefore it is of imortant to otimize the erformance of sieve tray distillation by means of adding the wire mesh acking on that tray, as being the aim of the resent study. This study is conducted by using a batch sieve tray distillation system, where the wire mesh acking is added on the third tray that is calculated from the to of the column, to avoid flooding inside the column. Here the resulting fermented molasses of containing a 10% volume of ethanol is used as a mixture distillation feed. The height of the wire mesh acking being studied is varied as 5 cm, 3 cm, and cm. Our results showed that the Murhee efficiency obtained by the variation of the acking height of 5 cm, 3 cm, cm and without acking were 73.5%, 66.7%, 56.86%, and 46.7% resectively, and were increased by subsequent level of the acking height. The corresonding hydrodynamic roerties of this aended acking sieve tray distillation by means of the interfacial area were cm /cm 3, 0.48 cm /cm 3, and 0.3 cm /cm 3, while its ressure dro measured from the water manometer height were cm H O/m, 30 cm H O/m, 10 cm H O/m for the acking height of 5 cm, 3 cm, cm height, resectively. The increasing of the erformance of aended acking sieve tray distillation by means of the Murhee efficiency is exlained by the increasing of the interfacial area for vaour-liquid than the tray itself. This reliminary study is exected to be a ioneer study of strategy to increase the erformance of conventional sieve tray distillation that is known as a kind of affordable distillation rocess. Keywords: sieve tray distillation, wire mesh acking, ethanol-water, Murhee efficiency 1. Introduction Distillation is rime method that is commonly used in industrial searation rocess. In a distillation searation rocess, there are various tyes of trays that can be utilized, namely sieve tray, valve tray and bubble ca tray. Among these trays, sieve tray has received interest from both the scientific and industrial communities, due to its affordable in cost and simlicity in design (GÓrak, A., & Olujić, Ž., 014). Although sieve tray is of significance, the rationale design in its tray efficiency is an ongoing challenge. This challenge is generally correlated to the small interfacial area and oor tray efficiency resulted from the contact of vaour-liquid (Zuiderweg, F. J., 198). Much effort has been devoted to answer this challenge, including the design of small hole size in sieve tray in order to roduce small bubbles with large interfacial area, thus could imrove the vaor-liquid contact and increase tray efficiency (Bain, J., & Van Winkle, M., 1961; Smith, B. D., 1963). However, this effort still struggles to fully meet the feasibility in economic asect. In contrast to the above sieve tray distillation column, a acked distillation column has a larger interfacial area, higher efficiency, less ressure dro, and suitable for corrosive substances. But it is not suitable for low flow rates liquid. (Sagnolo, D. A., & Chuang, K. T., 1984) are the ioneer to reveal on the ossibility of combining sieve tray column with acking. To be recise, they incororated a knitted mesh acking with bed size of 5 mm on the trays for the roduction of Girdler-Sulfide heavy water at the oerating ressure and temerature of.17 MPa and 3 C, resectively, where they found increasing tray efficiency by 3-0%. In articular methanol-water searation rocess, (Salem, A., & Alsaygh, A. A., 1988) reorted that the incororation of 115 mm bed of stacked stainless steel acking on the trays increased the tray efficiency by 1%. Similar system of 148

2 Modern Alied Science Vol. 9, No. 7; 015 methanol-water mixture was also subjected into a acked sieve tray distillation column, where a knitted mesh acking was being articularly used by Chen, G. X., et al. In their study, the Murhree tray efficiency was found to be increased, in the range of 40-50%. (Kachur, P. J., et. al. 004), studied the structured acking tray as an alternative for dual flow tray. They found that the structured acking tray was able to rovide 44% imrovement in caacity comared to that from dual-flow sieve tray using high liquid density systems. It also had found that its efficiency is 100% greater than the dual-flow sieve tray. (Xu, Z. P., et al., 1996) redicted the tray efficiency in relation with the addition of mesh acking in their modeling study. Similar to that of reorted exerimental studies, they found that the addition of mesh acking on the tray significantly increased its tray efficiency. Here the addition of acking will lead to the increase in interfacial area and vaor-liquid contact time. However, this henomenon must be validated by the exerimental studies. To the best of our knowledge, the exerimental studies on validating the factors of acking on the interfacial area in sieve-tray distillation column and its corresonding efficiency have not been reorted yet. Therefore, it encourages us to conduct an exerimental based study with the aim to comrehend the addition of wire mesh acking with various heights on the resulting tray efficiency, and to validate the roosed factors that are resonsible for the mechanism, i.e. interfacial area.. Method In the resent study, a sieve tray distillation column is modified by adding the wire mesh by means of increasing the vaor-liquid contact area in sieve tray column, thus increasing tray efficiency is exected. Here the height of wire mesh acking is varied as 5 cm, 3 cm, cm, while its void fraction and wide area are conditioned as 0.94 and 0.5 cm, resectively. The exeriment was carried out in batch system at a standard temerature and ressure condition. Ethanol and water mixture containing 10% mass of ethanol is used as feed. The wire mesh acking of having that 0.94 void fraction is only alied on the 3 rd tray to avoid weeing and flooding. The effects of the addition of wire mesh acking and its different in heights, on the resulting single tray efficiency or known as Murhee efficiency, will be the focus of this study. In a relation with Fig 1 of the schematic diagram of the exerimental aaratus, the rocedure is started with closing the valve and turn on the water condensor. By using batch system, E-101 is initially filled with the mixture until it reached 80% the tank volume, and then is turned on. In the control anel B-101, the boiler temerature is set u at 110 C and from the TC3 reading was exected in 76.8 C or less. This is exected to revent water imurities in the distillate and liquid-vaour samling. As the design sieve tray column has columns, thus P-101 is needed to um the liquid from bottom C-10 to to C-101. Until the first dro of distillate begins to form and constant, some samles are taken from GV-106 for measuring ethanol-water concentration using alcohol meter. Then, full closed GV-106 for total reflux ratio and P-10 is turned on. Aarently, y n, y n+1 and x n are required for calculating Murhee efficiency, and to do that, which some amount of samle is taken from V-10, V-103, and V-104. Figure 1. Schematic diagram of acked sieve trays for distillation column 149

3 Modern Alied Science Vol. 9, No. 7; 015 Figure. Snashot hotos of a single sieve tray without acking 4,5 cm 5,87 cm Figure 3. Wire mesh acking Table 1. Detail dimensions of the columns and test No. Parameter Dimension Detail Dimension 1 Column diameter 5.87 cm Tray Sacing 30 cm 3 Hole diameter mm 4 Column height.5 m 5 Number of tray 16 6 Tray tye Sieve Tray 7 Weir height 5 cm Here the interfacial area of acking is calculated from ste consecutive equations, i.e. equation 1 and, as follows. First, secific surface area of acking is calculated by the relationshi with the relative volatility, density of both vaor and liquid. α ( a e ) ρ G a + ρ where α relative volativity, ρ G density vaor ( kg/m 3 ), ρ density liqud ( kg/m 3 ), and a secific surface area of acking (cm /cm 3 ). After obtaining the secific surface area of acking, look for the interfacial area obtained by the following equation (McCabe, W.. et al., 001, Van Winkle, M., 1967): 0.5 (1) σ aw a 1 ex 1,45 Re Fr We σ C With Re, We, and Fr are described as follows. Re G a μ 0.75 () (3) We a 150 G σ ρ (4)

4 Modern Alied Science Vol. 9, No. 7; 015 a G Fr g ρ (5) where a w Wetted (interfacial) surface area of acking (m), Re Reynolds number for liquid, Fr Froude number for liquid, We Weber number for liquid, G iquid mass flow (kg/h.m), S Surface tension (N/m), µ Viscosity of liquid (kg/m.s), a Secific surface of acking (cm /cm 3 ), and g Gravity acceleration. Based on the data of interfacial area, the vaor velocity in each acking height can be the obtained. Several calculation stes must be carried out, first ste is to calculate effective article diameter by assuming that the shae factor of articular acking is 0.87 (based on shae factor of cylinder acking. D 6 ϕ a S v (6) Second ste is to substitute the obtained effective article diameter, the viscosity and density of vaor, the measured ressure dro, the void fraction and height of the acking, into the Ergun equation, to obtain vaor velocity by trial method (Geankolis, C. J., 1993). 150μυ Δ 1 ε 1.75ρυ Δ 1 ε Δ + (7) 3 3 D ε D ε where a v Interfacial area (cm /cm 3 ), Φ S Shae factor, P Pressure dro (N/m ), µ Viscosity of vaor (kg/m.s), v Vaor velocity (m/s), Packing height (m), ε Void fraction 3. Results and Discussion Figure 4 shows the effects of acking heights on their corresonding interfacial areas. As can be seen from this figure, the interfacial area were found to be cm /cm 3, 0.48 cm /cm 3, and 0.3 cm /cm 3 for the acking height of 5 cm, 3 cm, cm height, resectively. The increasing of interfacial area is affected by the increasing of acking height, with higher acking height tend to have better liquid-vaor contact. This can be exlained by the fact that resence of mesh-acked tray would tend to generate uniform smaller bubbles comared to that of from sieve tray only, which is usually followed by an increase in interfacial area. (Chen, G. X., et al., 199). 6 ( ) ( ) Packing height (cm) a W (cm /cm 3 ) Figure 4. Interfacial area with different height Figure 5 shows the effects of acking heights on their corresonding Murhee efficiencies. To obtain the Murhee efficiency itself, the samles from yn, yn+1 and xn must be taken. Here the yn is mole fraction of more volatile comonent from vaor stream above the tray while for that of yn+1 is from below the tray. The yn* is mole fraction of the vaour stream above the tray, which is in equilibrium with its liquid stream (Perry, R., et al., 1997). Using the ethanol-water equilibrium curve, the yn* is obtained from the data of xn, which is measured from the exeriment. In detailed observation in this figure, the Murhee efficiency (EMV) is found to be increased by the increase in acking height. To be secific, EMV of 47 % is obtained from tray without acking; while the EMV of 74 % is obtained from tray with 5 cm acking height, which means there is an increase in 151

5 Modern Alied Science Vol. 9, No. 7; 015 efficiency of 58 % from 47 %. EMV of 66 % is obtained from tray with 3 cm acking height, which means there is an increased efficiency of 4 % from 47 %. For the smallest acking with cm height of having EMV of 57 %, it is found that an increased EMV of % from 47 %. In general, overall Murhee efficiency increased in between 1-57 % comared to that of without acking. This increase in Murhee efficiency can be exlained by the fact that the addition of acking enhances the contat between liquid-vaor, as exlained in Figure 4. Also, the froth with smaller bubble size tends to have a higher surface tension (Sagnolo, D. A., et al., 1984) E MV (%) Packing height (cm) Figure 5. EMV(%) result from different acking height (cm) ΔP/Δz (cm H O/m) vaor velocity (m/s) Packing Height (cm) 0.00 Figure 6. Measured ΔP/ΔZ (cm HO/m) and vaor velocity (m/s) from different acking height (cm) From Figure.6 exlained that ressure dro measured from the water manomater height were cm H O/m, 30 cm H O/m, 10 cm H O/m for the acking height of 5 cm, 3 cm, cm height, resectively. This indicates that the mass transfer effciency is very high in the acking zone because of the large interfacial area. Pressure dro increased along with the increasing interfacial area (Chen, G. X., et al., 199). Nevertheless, significant difference in ressure dro is shown for acking with cm and 3 cm height, as exlained before in Figure.4, where it can be correlated by the gradient in interfacial area. According to Chen, G. X., et al., the resence of mesh acking in sieve tray column showed a lower weeing and entrainment effects, 15

6 Modern Alied Science Vol. 9, No. 7; 015 yet showed a higher froth and ressure dro effects. The effects of entrainment and weeing could be suressed because of the resence of mesh acking could break u the vaor into smaller size and stabilize the bubbles, thus in effect the vaor could flow through to the next tray. If some liquid also brought by the vaor through the next tray, this would decrease the Murhee efficiency. Higher froth height would revents the liquid to fall through the next below tray, and thus could lower the weeing effect. Figure 6 also exlained the correlation between acking height and vaor velocity. According to Ergun equation (Geankolis, C. J., 1993) that is alicable in low, intermediate, and high Reynolds numbers, the vaor velocity were found to 0.63 m/s, 3.8 m/s, 4.76 m/s for the acking height of 5 cm, 3 cm, cm height, resectively. This means the increase in acking height will result in decrease in vaor velocity. This finding is consistent with the revious discussion on interfacial area (see discussion on Figure 4). The increase in acking height will tend to imrove the liquid-vaor contact, by making a uniform and stable small bubbles result. This will also result in increase in froth height and residence time, thus it gives an increase in ressure dro. Acknowledgments The authors would like to thank the Seuluh Noember Institute of Technology (ITS) and the Indonesian Directorate General of Higher Education (DIKTI) for the financial suorts, under the financial scheme of BOPTN ITS with contract number of /IT.7/PN.01.00/014 and /IT.11/PN.08/015. References Bain, J., & M. Van Winkle. (1961). A Study of Entrainment, Perforated Plate Column-Air-Water System. AIChE, 7(3), htt://dx.doi.org/10.100/aic Chen, G. X., Afacan, A., Xu, C., & Chuang, K. T. (1990). Performance of Combined Mesh Packing and Sieve Tray in Distillation. The Canadian Journal of Chemical Engineering, 68(3), htt://dx.doi.org/10.100/cjce Chen, G. X., Chuang, K. T., Chien, C., & Ye, Y. (199). Mass Transfer and Hydraulic of Packed Sieve Tray. Gas Searation and Purification, 6(4), htt://dx.doi.org/ / (9)8004-d Geankolis, C. J. (1993). Transort Processes and Unit Oerations (3rd ed.). America: Prentice-Hall, Inc. GÓrak, A., & Olujić, Ž. (014). Distillation: Equiment and Processes. Oxford, UK: Academic Press Kachur, P. J., Afacan, A., & Chuang, K. T. (004). Use of Structured Packing As a Dualflow Tray in Distillation. Chemical Engineering Research and Design, 8(A7), htt://dx.doi.org/10.105/ McCabe, W.., Smith, J. C., & Harriot, P. (001). Unit Oerations of Chemical Engineering (6 th Edition). New York: McGraw-Hill Book Comany Perry, R., & Chilton, C. (1997). Chemical Engineer s Handbook (6th ed.). New York: Mc. Graw Hill Book Comany, Inc. Salem, A., & Alsaygh, A. A. (1988). Better Sieve Tray Add Packing. Hydrocarbon Processing, 67(5), G-H. Smith, B. D. (1963). Design of Equilibrium Stage Proceses. New York: McGraw-Hill Book Comany. Sagnolo, D. A., & Chuang, K. T. (1984). Imroving Sieve Tray Performance with Knitted Mesh Packing. Industrial & Engineering Chemistry Process Design and Develoment, 3(3), htt://dx.doi.org/10.101/i0006a06 Van Winkle, M. (1967). Distillation. New York: McGraw-Hill Book Comany. Xu, Z. P., Afacan, A., K. T., & Chuang, K. T. (1996). Prediction of Packed Sieve Tray Efficiency in Distillation. Chemical Engineering Research and Design, 74(8), htt://dx.doi.org/10.105/ Zuiderweg, F. I. (198). Sieve Trays: A View on the state of the art. Chemical Engineering Science, 37(10), htt://dx.doi.org/doi: / (8) Coyrights Coyright for this article is retained by the author(s), with first ublication rights granted to the journal. This is an oen-access article distributed under the terms and conditions of the Creative Commons Attribution license (htt://creativecommons.org/licenses/by/3.0/). 153