Stripping Section Research Articles

98/00684 Optimization of specific rate of heat pumping in combined heat pump cycles

Although the ideal heat-integrated distillation column (ideal HIDiC) is much more thermodynamically efficient than its conventional analogues, its applications in the chemical and petrochemical process industries have been restrained due to the great difficulties and complexities in the design and implementation of internal heat integration between the rectifying section and the stripping section. For the avoidance of these difficulties and complexities, a novel simplified configuration for the ideal HIDiC, termed the SIHIDiC, is proposed and studied in this paper. Only three internal heat exchangers are used to approximate the internal heat integration, and their locations and sizes are key decision variables for process synthesis and design and should be considered to enhance thermodynamic efficiency in process development. A simple stepwise procedure is thus derived for process synthesis and design, and the SIHIDiC is then evaluated through intensive comparison with conventional distillation columns and the ideal HIDiC in terms of the separations of ethylene/ethane and benzene/toluene binary mixtures. The results obtained indicate that the SIHIDiC could be an excellent candidate to approximate the ideal HIDiC with reduced capital investment and somewhat similar (if not smaller) operating cost. The SIHIDiC offers essentially a much simpler way than the current available methods to design and implement the concept of the ideal HIDiC into separation processes.

Dual Composition Control in a Novel Batch Distillation Column

The newly emerging batch column called the middle vessel column presents the problem of dual composition control similar to the continuous distillation column. The degree of interaction between the two composition control loops can be assessed using the relative gain array technique. This paper presents the RGA analysis for the middle vessel column dual composition control problem. The analysis shows that the interaction between the two loops for this new column is mostly negligible due to the large time constant of the middle vessel. Furthermore, with the middle vessel column, there is a greater likelihood of reducing the interaction between control loops by varying the parameter q‘ (the ratio of the vapor rate in the rectification section of the column to the vapor rate in the stripping section of the column).

Analysis of dielectric E-plane waveguides and design of filters

A small-size waveguide made of high-permittivity ceramic is analyzed. The propagation constants are calculated approximately by an approach where the electromagnetic fields outside the waveguide are fully taken into consideration. The analysis values agree well with the experimental values. The constants of equivalent circuit for the metallic strip section are obtained by using a separate model for the analysis of the structure. Based on these results, bandpass filters (BPF's) are designed and fabricated. The fabricated BPF's have better transmission and reflection characteristics than those designed on the basis of a trough-guide model.

Improving copper cathode production efficiency: One company’s experience

Through the last three decades, improvements and modifications at Onahama Smelting and Refining Company’s tankhouse and stripper section have resulted in reduced labor and maintenance costs, more effective blank handling, stabilized operation in the stripper, and increased copper productivity. This article recounts some significant technological developments toward the attainment of these results.

Effect of two‐pass trays on distillation efficiencies

AbstractTwo important structural factors that affect distillation efficiencies, the outlet weir heigh and the liquid flowpath length, are investigated. Performance and efficiency data of an industrial scale i‐butane/n‐butane distillation column equipped with two‐pass trays are used as a basis for the calculations. A mathematical development for a new method for predicting the numbers of vapor and liquid phase transfer units is given. This method together with some other NTU calculation methods is used to assess the effect of the outlet weir height on efficiencies. The effect of outlet weir height on the Murphree tray efficiencies is investigated using the observed point efficiencies and different point efficiency to the Murphree tray efficiency relation methods. The effect of varying liquid flowpath lengths on efficiencies is studied by calculating the Murphree tray efficiencies for one‐pass and two‐pass trays. The results obtained using the NTU calculation method presented in this study show that a certain outlet weir height point efficiency reaches its maximum. Most of the other methods give opposite results giving a minimum for point efficiency at a certain outlet weir length. The results also show that the Murphree tray efficiencies for one‐pass trays are higher than for two‐pass trays. Obviously, this is caused by the longer liquid flowpath length of one‐pass trays. The Murphree tray efficiencies are also calculated for an industrial‐scale MTBE purification column. The column is equipped with two‐pass trays in the stripping section and with one‐pass trays in the rectifying section. The Murphree tray efficiencies of one‐pass trays are considerably higher than the two‐pass tray Murphree tray efficiencies.

Design of integrated compensated baluns

Rigorous analytical design equations for general integrated compensated baluns (Marchand baluns) have been derived based on the mode parameters of the associated coupled strip sections. It is shown that a third-order balun is realizable with the use of two equal sections of coupled lines. Example components using planar as well as multilayer MMIC technology have been designed with the method presented here. Simulated results obtained by approximate TEM analysis as well as those generated with a 2.5D EM full-wave simulator show good broadband performance. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 14, 75–81, 1997

Improved Operational Policies for Batch Extractive Distillation Columns

We and others (Hasebe et al., 1992; Meski et al., 1993; Davidyan et al., 1994) have previously developed insights into batch distillation when using a “middle vessel” batch column. We extended earlier work on reachable product regions for continuous columns to this and other batch column configurations. Our work also examined the use of a continuously flowing extractive agent to facilitate the separation of azeotropic mixtures. A middle vessel batch column has both an enriching and stripping section and thus both a distillate and bottoms product. In many ways it is just like a traditional continuous column, but we feed it by charging a middle tray having a very large holdup (a pot or still) with the initial feed. Our work compared running this column with running a batch rectifier for an azeotropic mixture when using an extractive agent. We showed that both are often able in theory to recover all of the distillate component in relatively pure form, with the middle vessel accomplishing this by “steering” t...

Determining Appropriate Configuration of Ideal Heat Integrated Distillation Columns(HIDiC).

The major concern in developing various kinds of heat integrated distillation columns is the strong interaction and high sensitivity resulting from heat integration (Takamatsu, 1996), which could drastically deteriorate system potential performance. Hence, it is of great importance to design processes so as to make these undesired properties as small as possible, namely to increase system dynamic resilience. As for the ideal heat integrated distillation column (HIDiC), we already know that its symmetrical specifications, such as equal feed split, middle feed location and same structures between rectifying and stripping sections, are the main reasons for strong interaction between top and bottom control loops (Huang et al, 1996). In order to make the ideal HIDiC have higher dynamic resilience, these kinds of symmetrical specifications should be deleted. A previous work (Huang et al, 1996) already explored how to improve the system resilience through appropriately assigning feed thermal condition q and feed location under general configuration of the ideal HIDiC. As to the effects of symmetrical structure between rectifying and stripping sections, its effects are still not clear. In this work we will concentrate on this problem by studying three possible configurations of the ideal HIDiC. Both time and frequency domain techniques have been employed to assess the potential effects of system configuration towards system performances, and the results obtained are further evaluated through rigorous nonlinear closed-loop simulation.

Development and Testing of Srex Flowsheets for Treatment of Idaho Chemical Processing Plant Sodium-Bearing Waste Using Centrifugal Contactors

Laboratory experimentation has indicated that the SREX process is effective for partitioning 90Sr from acidic radioactive waste solutions located at the Idaho Chemical Processing Plant. A baseline flowsheet has been proposed for the treatment of sodiumbearing waste (SBW) which includes extraction of strontium from liquid SBW into the SREX solvent (0.15 M 4′,4′ (5′)-di-(tert-butyldicyclohexo)-18-crown-6 and 1.2 M TBP in Isopar L®), a 0.01 M nitric acid strip section to back-extract components from the loaded solvent, and a 2.0 M HNO3 solvent acidification section to equilibrate the solvent with HNO3 prior to recycle to the extraction section. The flowsheet was designed to provide a decontamination factor (DF) of >103 which will reduce the 90Sr activity in the waste solution to below the NRC Class A LLW limit of 0.04 Ci 90Sr/m3. SREX flowsheet testing was performed using sixteen stages of 5.5-cm diameter centrifugal contactors. The behavior of stable Sr and other components which are potentially extracted by the SREX solvent were evaluated. Specifically, the behavior of the matrix components including Pb, K, Hg, Na, Ca, Zr, and Fe was studied. The described flowsheet achieved 99.98% Sr removal (DF=4250) with one cycle of SREX. Potassium and Zr were partially extracted into the SREX solvent with 35% and 21%, respectively, exiting in the strip product. Sodium, Ca, and Fe were essentially inextractable. Lead was determined to extract and accumulate in the SREX solvent and in the strip section. As a result, a Pb precipitate formed in the strip stages of the contactors. Mercury was also determined to extract and accumulate in the SREX solvent.

Simulation and Thermal Integration SRV in Extractive Distillation Column.

The present work aims at studying the application of the thermal integration Secondary Reflux and Vaporization (SRV) in extractive distillation. This technique is based on heat exchange between the rectifying and stripping sections, using the natural temperature difference between these two sections of the extractive distillation column for an ethanol/water/ethylene glycol mixture. The calculated results are compared with those relative to extractive distillation for an acetone/methanol/water mixture. A substantial reduction in the energy consumption is observed when comparing integrated columns with conventional ones.

Equations of strip equilibrium during asymmetrical flat rolling

The paper presents the equations of equilibrium of a flat rolled strip, generalized for non-symmetrical conditions in the roll-gap and for the cases of forces and moments operating on the strip sections beyond the roll-gap. The dependencies and assumptions imposed here are complete, which enables using them, e.g. to establish, simplified relationships useful for analytical solutions. In the discussion, the limitations of the solutions presented are indicated and the problems demanding further research defined.

Prefractionation to reduce energy consumption in distillation without changing utility temperatures

AbstractDistillation systems composed of a prefractionator and a main column are introduced. The columns operate at different pressures, but the temperatures of the utilities are the same as for a single column performing the same separation. The energy integration of the columns is realized by condensing a vapor overhead from the prefractionator in an intermediate reboiler located in the stripping section of the main column or by boiling a bottoms liquid from the prefractionator in an intermediate condenser placed in the rectifying section of the main column.Analysis is performed to determine feasible regions of operational parameters and to minimize vapor flows. A detailed simulation example of the benzene–toluene separation shows that for certain feed compositions it is possible to reduce energy requirements of a conventional binary distillation column by almost one‐third using this new distillation system. This savings is achieved without any change in the temperature of the utilities used.

Fascial Sling Correction of Kinked Efferent Limb in Patients With Continent Diversion and Catheterization Difficulty

Purpose We determined the efficacy of using a rectus fascial sling to revise an angulated efferent limb in patients with continent urinary diversion and difficulty with intermittent catheterization. Materials and Methods Two spinal cord injured women who underwent modified Indiana pouch urinary diversion required revision of each efferent limb because of difficulty with catheterization. A strip section of anterior rectus sheath was harvested and used to fix the efferent limb in position, assuring freedom from angulation and facilitating catheterization. Results Both patients remained continent for more than 2 years postoperatively and neither had further difficulties with catheterization or required additional surgery. Conclusions Use of the rectus fascial sling in continent urinary diversion enables fixation of the efferent limb to facilitate catheterization and enchance continence.

Dynamics of ideal heat integrated distillation columns.

An ideal heat integrated distillation column (HIDiC), which has neither a reboiler nor a condenser, was studied based on its non-linear and linearized dynamic models. It was found that heat integration between rectifying and stripping sections does not lead to an unstable plant. Moreover, the thermal interaction appears to be relatively stronger at low pressure difference than that at high pressure difference.Strong gain directionality has been found in the ideal HIDiC, where the pressure difference and feed thermal condition correspond to low and high gain direction respectively. With proper design of the process, thermal interaction, affects the system time constant only to a limited extent, and intensifies the interaction within a dual point composition control scheme. In fact, the degree of coupling between top and bottom control loops is governed by feed thermal condition since it is in line with high gain direction and can simultaneously introduce changes of both internal and external flows.

Numerical analysis of a dual refluxed PSA process during simultaneous removal and concentration of carbon dioxide dilute gas from air

The simultaneous removal and concentration of carbon dioxide present in ambient air were carried out by a dual refluxed Pressure Swing Adsorption (PSA) process with intermediate feed inlet position. The feed inlet position divides each column into rectifying and stripping sections from which enriched and lean gases can be simultaneously produced. A simple isothermal model with negligible axial dispersion and pressure drops through the PSA beds was developed to investigate the effects of various combinations of the operating variables and to analyze semi-quantitatively the effects of the main characteristic parameters such as the dimensionless feed inlet position (ZR/LT) and the stripping-reflux ratio (Rr). A good agreement between the model prediction and the experimental results was obtained. Moreover, an optimum feed inlet position was found and it corresponded to a position where the carbon dioxide mole ratio in the feed flux and that in the upstream flux leaving the stripping section were equal. The carbon dioxide mole ratio in the enriched product (YE) as well as that in the lean product (YL) were strongly dependent on the ratio of feed/enriched product flow rates (QF/QE) and the ratio of feed/lean product flow rates (QF/QL). Although the pressure ratio (Pa/Pd) was crucially important for the separation performance, a smaller value of Rr was sufficient to reach a performance which is unattainable in conventional PSA processes.

Evolution of Pinch-Point Zones in Multicomponent Distillation Columns. 1. Rectifying Section

The principles concerning the evolution of pinch-point zones with variation of the reflux ratio in the rectifying section of a multicomponent distillation column with an infinite number of stages are presented in this work. Analytical formulas are obtained for calculating the pinch-point zones as well as the distillate exactly. It has been found that the evolution of pinch-point zones in the stripping section is much similar to the evolution of pinch-point zones in the rectifying section. Based on these new findings, a new method for calculating the minimum reflux ratio of multicomponent continuous distillation, as well as a new shortcut method for the design calculation of a batch distillation process, can be developed.

On the Use of Intermediate Reboilers in the Rectifying Section and Condensers in the Stripping Section of a Distillation Column

Advantages of an intermediate reboiler in the stripping section of a distillation column and an intermediate condenser in the rectifying section are well-known. For highly nonideal mixtures the distillation process can be improved by placing an intermediate reboiler in the rectifying section of the column or an intermediate condenser in the stripping section, which is counterintuitive. In consequence the more expensive heating utility used in the bottom reboiler can be partially replaced with a less expensive heating medium (at a lower temperature) used in the intermediate reboiler. Similarly, a portion of the condensing duty from the top condenser can be replaced with the less expensive condensing duty (at a higher temperature) in the intermediate condenser. This placement of reboilers (condensers) can be used to reduce the total number of stages in the distillation column with a lower (higher) level of utility. Operating and capital costs of the distillation process with an intermediate heat exchanger can be lower than those for a classic column. A simple method providing valuable insights on the possible placement of intermediate heat exchangers along the column is proposed. It is based on calculations of the vapor flow along the height of a reversible, binary distillation column performing the equivalent separation task.

A numerical consideration on dynamic modeling and control of ideal heat integrated distillation columns.

In this paper, an ideal heat integrated distillation column (HIDiC), which has neither a reboiler nor condenser, is considered. A dynamic model, capable of doing both static and dynamic simulations of the ideal HIDiC is derived. Based on this model, the system properties and control feasibility are studied. It is found that the ideal HIDiC could be regulated quite well with manipulation of feed thermal condition and the pressure of either rectifying or stripping section. The efficient way to control its top and bottom product qualities is to use composition inferential systems to realize direct composition control.

Synthesis of Distillation Column Configurations for a Multicomponent Separation

Thermally linked distillation column configurations to separate near-ideal multicomponent mixtures containing four or more components are discussed. It is shown that for sharp separation of an n-component mixture using only one reboiler and one condenser the minimum number of rectifying and stripping sections needed is 4n − 6. A stepwise procedure is proposed to obtain such distillation configurations, and a series of observations are presented which make the task of generating these configurations a little easier. It is found that, for n ≥ 4, some of these distillation configurations are missing from the known superstructures in the literature. An alternative method is proposed to obtain an n-component superstructure. The resulting superstructure has all the earlier known configurations embedded within it and contains the substructures incorporating the missing configurations. This provides a more complete superstructure for the optimization task.

Extending Continuous Conventional and Extractive Distillation Feasibility Insights to Batch Distillation

Researchers have begun to study a batch column with simultaneous top and bottom products, sometimes called a middle vessel column. The column is similar to a continuous column in that it has both a rectifying and a stripping section. However, instead of a feed tray, the middle vessel column has a tray with a large holdup that acts like the still pot. Using ternary diagrams, the authors show that one can identify the feasible products and possible column profile regions for the batch rectifier, the stripper, and the middle vessel columns using methods developed for continuous distillation. Using insights developed for continuous distillation, they also compare extractive distillation using the batch rectifier and middle vessel column and show that these columns can theoretically recover all of the pure distillate product from an azeotropic feed. However, the batch rectifier requires a still pot of infinite size. It is possible to steer the still pot composition i the middle vessel column by adjusting column parameters such as the product and extractive agent flow rates. Theoretically, it thus becomes possible to recover all of the distillate product without the need for an infinite still pot.