Background for the research
Researching the influence of sustained tilt on the mass transfer of CO2 in a packed column, the basics of the floating production systems are going to be considered. One of the unit operations onboard floating systems is the gas-liquid contacting columns used to strip gases such as CO2 and H2S from natural gas. To follow the projects, the large tilting column is going to be used to measure the mass transfer of CO2 and N2 from the air using a suitable liquid solvent. The current literature review will be focused on the board floating system, on mass transfer of CO2 in a packed column, and other variables connected to the field of discussion.
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The background for the project became the research conducted by White, Kalbassi, Waldie, and Wilson (2009) who managed to design a structured packing that is used “in a vapor/liquid contact column operating in locations where environmental conditions adversely affect the steady-state operation of the column to reduce maldistribution of liquid in the column under motion” (p. 2). The main importance of the invention is that it may be practically used offshore where “tilt of the column out of vertical alignment due to the rolling motion of the platform can significantly affect the efficiency of the column” (White et al, 2009, p. 2).
As far back as 1991, Coker managed to notice the advantage of packed towers over trayed towers. The main function of these two kinds of towers is similar, still, a great difference is observed in their performance due to “the percentage opening of each phase-contacting device” (Coker, 1991, p. 93). Being more specific, the same study indicates the following more effective features of the packed towers over the trays. Packed towers better cope with viscosity, they are more combinable, they possess a high capacity of foaming system, they are more advantaged at lower pressure and time residence. Moreover, the study offers the program “TOWER”, effective in identifying the size of the packed power for changing pressure, and presents an example on how to use implement it in practice (Coker, 1991, p. 94).
Furthermore, the research conducted in the sphere of the widespread floating production systems is of great value. Westwood and Wingrove (2000) gathered and analyzed the information dealing with the current stick of the floating production systems. According to the got results, 119 units of the floating production systems were available in the world by 2000. As far as they could judge, the basic scheme of the systems used in the world was considered that made it possible to predict the perspective of the sphere development. The main limitation of the analysis is that the authors do not stress whether the trayed or packed towers were used. Nevertheless, it is stated that due to the use of pipeline-export and production infrastructure, the number of floating production systems is low in the USA Gulf of Mexico (Westwood & Wingrove, 2000, p.60).
Types of packing
There are two different types of packing, random packing and structured. Sillla (2003) tried to make it clear the difference between these two types of packing. It was stated that the random packing is “loaded into the separator by first filling the separator with water, then, the packing is gradually loaded into the separator’ after settling the packing will assume random positions within the column” (Silla, 2003, p. 316). The main purpose of the water in this construction is to prevent the fragile packing break. The structured packing is different from the random one by the place of the packing. The location of packing in the structured packing is defined. The same is mentioned in the book by Couper, Penney, Fair & Walas (2009). Still, they not just identified the functional difference of these two types of packing columns, but also tried to point out some specific characteristics inherent in them. The authors stated that being less costing and the performing functions being more researched, structured packing is used more frequently and managed to replace trays and random packing. After all, the choice of the type of packing depends on different variables; it may be “pressure drop, mass transfer efficiency, and cost” (Couper et al, 2009, p. 455).
To understand the difference between the structured and random packings on the practical example, Kaushik et al (2005) conducted an experiment that allowed evaluating different packings in a lube extraction system. Thus, the research tried to comprise the most important information on the new generation packings, the experiment embraced just berl saddle and random packing. Still, the results of the experiments conducted are extremely important for our study as they show that it is possible to “reduce solvent treat rates and provide higher yield for the same quality” (Kaushik et al, 2005, p. 442) via using different types of packings.
Habaki et al (2007) focused their research on the Super Mini Ring that is considered to be one of the types of novel packing within the packing columns. The main purpose of the study is to measure the level of absorbed CO2 in the Super Mini Ring. The results of the experiment conducted while the research are important as they show that the novel packing “offers higher absorption performance relative to pal rings due its smaller pressure drop and larger specific surface area” (Habaki et al, 2007, p. 712). It is obvious that Super Mini Ring performs strong potential and can be resulted as the main predeterminer for reducing the pal ring column by 20% (Habaki et al, 2007, p. 2008).
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Rejl, Linek, Moucha, and Valenz (2009) researched gathering and analyzing the methods used for “measurement of mass-transfer characteristics” (p. 695). The authors accomplished a deep analysis on the methods that are used for now and tried via analyzing them to create a standardized measure of the mass transfer of CO2 and/or N2. The two main procedures were mentioned as the standards for the measurement, “absorption systems with mass-transfer resistance limited to the liquid phase” for kLa and the absorption of SO2 in NaOH in kGa. Thus, it may be concluded that the research managed to prove that to increase the effectiveness of the measurement, it is better to use the gas and other liquid substance from the packing directly. The previously used methods that sampled the gas from the top and bottom are not effective and should be substituted with the more actual (Rejl et al, 2009, p. 703).
The research conducted by Stemmet et al (2008) was aimed to quantify “hydrodynamic parameters (frictional pressure drop and liquid holdup) and the gas-liquid mass transfer coefficient for co-current two-phase flow through these solid foam packings for conditions when the viscosity of the liquid has been increased” (Stemmet et al, 2008, p. 1095). Conducting research, the authors implemented the following technique, they increased the viscidity and at the same time decreased the tension of the liquid surface. Here are the results that were got, the liquid holdup grew in the upflow regime, “the gas-liquid mass transfer coefficient” was affected, as well as the energy dissipation happened “to be equal to the frictional pressure drop” (Stemmet et al, 2008, p. 1105).
Similar research on the standardization methods for measuring the mass transfer was conducted as far back as 2007 when Hoffmann et al (2007) wanted to create the standard measurement methods for absorption on the example on the random packing. In the process of study, the author and conductors of the experiment noticed that the literature sources devoted to the determination of the “mass transfer parameters for absorption systems” (Hoffmann et al, 2007, p. 40) are rather controversial and false. Conductive experiments in practice, the research showed that the calculations and practical results do not coincide. Thus, it was concluded that there is a sharp necessity in the standardization of the procedure for the estimation of mass transfer parameters that are to be used in the absorption system (Hoffmann et al, 2007, p. 40).
Dil’man et al (2005) focus their experiment on the problem of packed column’s mass-transfer efficiency in different situations. The authors researched two different transformations. First, the experiment took place in catalytic distillation, and the second experiment was conducted in multicomponent distillation. Both experiments used the chemically reactive mixture “that is uncomplicated by chemical transformations” (Dil’man et al, 2005, p. 453). Comparing the results of these two experiments, Dil’man et al (2005) concluded that the catalytic method of acquiring the necessary products provides purer results. It should be noted that before conducting practical experiments, the calculation was accomplished and the results of theoretical and practical implementation of the hypothesis coincided. Researching the same conditions and in the same equipment, 60 cm high packed column, it was proved that using catalytic distillation is more effective and gives much better results (Dil’man et al, 2005, p.461).
The research conducted by Manduca, González, and Elman (2003) represents us with the results that “the main mass transfer resistance is in the liquid phase and that the external area and amount of catalyst of the packing enhance the vapor-liquid mass-transfer rate” (Manduca, González & Elman, 2003, p. 3535). The 1-in diameter column was taken for the research. It was filled with bale packing and “CO2 was absorbed from the air using an aqueous solution of mono-ethanol-amine” (Manduca, González & Elman, 2003, p. 3536). The data for the research was collected experimentally and different mass transfer models were used for comparison. To predict the volumetric mass-transfer coefficients, the following models were compared, the model of Subawalla et al, the model of Bravo and Fair, the model of Onda et al, and the model of Zheng and Xu (Manduca, González & Elman, 2003, p. 3540).
Pavlenko et al (2009) conducted the research directed on the identification of the affecting of the separation efficacy of a binary freon mixture using intentional unfair dispensing over a structured packing. The experiment was accomplished in that “the rotation angle of structured packed layers has a significant effect on the efficiency of mixture separation in the case of maldistribution” (Pavlenko et al, 2009, p. 1). In detail, the unbalanced distribution in the structured packing initially leads to the disbalance inside and to the reduction of the Freon mixture efficiency. The effect of the rotation angle in this situation influences the mixture separation efficiency proportionally, “A decrease in the layer rotation angle for a maldistribution over the packing leads to a significant decrease in the mixture separation efficiency” (Pavlenko et al, 2009, p. 8).
Dohi, Takahashi, Minekawa & Kawase (2006) conducted the related research. They were aimed to consider “gas holdups and volumetric mass transfer coefficients in stirred tanks” (Dohi et al, 2006, p. 689) and their empirical correlations via identifying “gas-liquid mass transfer characteristics of large-scale impellers” (Dohi et al, 2006, p. 689). They studied the Maxblend and Full zone impellers’ performances in the situation of gas dispersion and small-scale impellers. Both larger-scale and small-scale impellers implement similar characteristics, of gas scattering and transmission of gas-liquid mass. On the assumption of these results it is possible to notice that for the same value of impeller speed, the energy effectiveness is the same within both larger-scale and small-scale impellers.
Gas and liquid influence on the packed column functioning
Alix and Raynal (2008) considered the opportunities to improve the industrial gas/liquid contractors which are usually used “for distillation or post-combustion capture of C02” (p. 585). For accomplishing successful research, the liquid hold-up and distribution were measured for the following packing, random and structured. The main results achieved via the research are as follows, the high capacity packings used for the research showed the same good effect while liquid distribution. Thus, they may be used at the same volume. The current research opened several problems that should be considered. First, further research should be conducted within the same conditions but changing some physical characteristics of the experiment, “by varying liquid properties and increasing superficial gas velocity” (Alix & Raynal, 2008, p. 591). Still, due to the research, it is possible to evaluate the effect that is provided on the liquid hold-up from “the liquid flow rate and the liquid viscosity” (Alix & Raynal, 2008, p. 585).
Two different processes influence the work of packed columns greatly. The article ‘Tilt-compliant column’ (1999) mentions title and motion as well as gas and liquid flow. Title and motion are the factors that make it difficult to provide a correct work performance for a column on floating factors. Owing to this, the gas and liquid flow problem appear. The problem can be decided via promoting several steps. First of all, if the column is tilted, the liquid flow should be transferred to the lower side. The helical element of the column helps to bear the construction at the 900 angles with the axis 250. Due to such construction, liquid substances usually flow “parallel to the column’s central axis” (‘Tilt-compliant column’, 1999, p. 46). Thus, the angle of the packed column is important as it helps to coordinate the gas and liquid flows while the packed column’s motion.
Alekseenko et al (2007) measured the thickness “of a liquid film on geometrically complex surfaces inside a distillation column with a structured packing and countercurrent flow of gas and liquid” (p. 417). The main purpose of the study was to measure the differences that may occur in the liquid and gas substances that could be stirred up by the pressure drop in the column. It is significant to notice that the center of the experiment was “standard Koch 1Y corrugated packing (435 m2/m3) with a double-corrugated structure” (Alekseenko et al, 2007, p. 417). The column comprised of two, three, of four packing plates that were brought together via stacks. Furthermore, the angle of the rotating stacks of the columns was 900. The other technical characteristics of the experiment are as follows, the size of the plates was similar, 0.195×0.2 m2. Each stack consisted of 30 such plates, and “the angle between the adjacent edges of the plate was 90°” (Alekseenko et al, 2007, p. 417). Moreover, 14 mm was the plates’ scope of rough corrugations, while the scope of the smooth horizontal surface was 1.85 mm. The angle of the edges on the plates was 450. Each plate had more than 470 openings 3 mm each. One of the peculiarities of the research was the electrochemical refinement of the corrugated plates (Alekseenko et al, 2007, p. 418).
The effective area of packings
Kolev, Nakov, Ljutzkanov, and Kolev (2009) tested packing with the purpose to identify the most effective area of a metal Raschig Super-Ring. It is significant to notice that the research was conducted for the first time as nobody expressed the desire to research the topic before. The authors took six different sizes of the tested equipment (from 80 to 250 m2/m3). The main results of their research are as follows, the authors managed to conclude that “at the high liquid superficial velocity the effective area of the investigated packings is higher than their specific area” (Kolev et al, 2009, p. 429). The authors used the zero angle for the wettability and it is significant to take it into account while applying the results of the research in practice.
Similar research is described in the study presented by the same authors, Nakov, Kolev, Ljutzkanov, and Kolev (2007), but the main purpose of the experiment conducted is different. In the mentioned case, the authors wanted to check and compare the effective area of the metal and plastic packings to consider which one is greater. When in use, the research showed that metal effective area is greater than plastic one due to several issues (Nakov et al, 2007).
Olutoye and Eterigho (2008) designed a gas absorption column model for the CO2-NaOH system. The main peculiarity of the study is that the model is created for functioning in the unsteady state condition. The results of the research are significant as considering the “values of the carbon dioxide concentrations in caustic soda can be predicted” (Olutoye & Eterigho, 2008, p. 113) the study gives way for conducting further research of the outlet of the concentration of the CO2 in the air. The study is extremely useful if to relate it to our research that is connected with the measurement of the mass transfer of carbon dioxide or nitrogen gas from air (Olutoye & Eterigho, 2008, p. 113). Thus, the model used in the study can be used in our research; still, some limitations and differences should be considered beforehand.
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Alix, P & Raynal, L 2008, ‘Liquid distribution and liquid hold-up in modern high capacity packings’, Chemical Engineering Research & Design, vol. 86, iss. 6, pp. 585-591.
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