Side Stripper Research Articles

Process Intensification for the Recovery of Hydrogen Cyanide in the Andrussow Process

AbstractThe aim of this work was to determine a cost‐optimal design of the distillation unit of the Andrussow process. For this purpose, a feed with a mass flow rate of 121 t h−1 and a concentration of ca. 2 wt % hydrogen cyanide (HCN) was considered. An approach for a cost‐optimal process intensification was developed with the goal to achieve the desired product qualities, while minimizing the organonitrile accumulation in the column. For this purpose, the simple distillation column of the established cost‐optimal design of the base case was extended to a configuration with a side stripper with taking into consideration heat integration in the process. It was found that this new configuration allows a much smaller accumulation of organonitriles in the main column; reducing thereby the operation issues of the process while decreasing considerably the total annual cost of the distillation unit by 61 % as compared to that of the base case design.

Novel design of lubricant-type vacuum distillation process for lube base oils production from hydrocracking tail oil

Dividing-wall columns (DWCs) are widely used in the separation of ternary mixtures, but rarely seen in the separation of petroleum fractions. This work develops two novel and energy-efficient designs of lubricant-type vacuum distillation process (LVDP) for the separation of hydroisomerization fractions (HIF) of a hydrocracking tail oil (HTO). First, the HTO hydroisomerization reaction is investigated in an experimental fixed-bed reactor to achieve the optimum liquid HIF by analyzing the impact of the operating conditions. A LVDP used for HIF separation is proposed and optimized. Subsequently, two thermal coupling intensified technologies, including side-stream (SC) and dividing-wall column (DWC), are combined with the LVDP to develop side-stream vacuum distillation process (SC-LVDP) and dividing-wall column vacuum distillation process (DWC-LVDP). The performance of LVDP, SC-LVDP, and DWC-LVDP are evaluated in terms of energy consumption, capital cost, total annual cost, product yields, and stripping steam consumption. The results demonstrates that the intensified processes, SC-LVDP and DWC-LVDP significantly decreases the energy consumption and capital cost compared with LVDP. DWC-LVDP further decreases in capital cost due to the removal of the side stripper and narrows the overlap between the third lube oils and fourth lube oils. This study attempts to combine DWC structure into the separation of petroleum fractions, and the proposed approach and the results presented provide an incentive for the industrial implementation of high-quality utilization of HTO through intensified LVDP.

Novel use of dividing wall columns for intensification multicomponent batch distillations

While the dividing wall columns for continuous distillations have become quite popular, we present the first detailed analysis of a dividing wall column for batch distillation. For a dividing wall side stripper batch distillation column, we present an operating sequence and its associated mathematical model. Since there are many operating parameter combinations possible for this column, selecting the right operating parameters according to product specifications is presented as an optimization problem. This new configuration's performance is compared with the conventional batch rectifier and the middle vessel columns using two case studies related to the separation of a ternary mixture. The new batch dividing wall column performance is significantly better than the rectifier or the middle vessel column. As the purity specifications increase, the percentage improvement in profit due to the batch dividing wall column compared to the rectifier and the middle vessel columns increases.

Comparative assessment of different intensified distillation schemes for the downstream separation in the oxidative coupling of methane (OCM) process

Downstream separation in the oxidative coupling of methane (OCM) is a major technical challenge limiting the industrial implementation of ethylene production from natural gas. This work focuses on the assessment of different thermally coupled cryogenic distillation schemes for the separation of OCM effluent gases. The composition of the feed gas was defined according to an experimentally validated OCM effluent stream, previously treated for H2O and CO2 removal, and containing N2, H2, CO, methane, ethane, and ethylene. The different separation schemes corresponded to conventional distillation trains using direct or indirect sequences at different pressures, configurations with side rectifier or side stripper, a dividing wall column (DWC), and a Kaibel column. All assessed alternatives incorporated the required propylene-ethylene-methane refrigeration cycle. Process simulations using validated models for physicochemical properties and phase equilibria calculations were implemented in Aspen Plus®. Optimization of the different distillation schemes was done using the total annual cost (TAC) as an objective function, employing different algorithms coded in Python® and directly linked into Aspen. Results indicate that the side rectifier scheme is the preferred configuration enabling >10% savings concerning the best conventional configuration. DWC and Kaibel schemes have major drawbacks that make them unsuitable for the studied process.

Control of a distillation column with side stripper and side rectifier

A recent paper developed a complex divided-wall column with two walls in a single vessel that was capable of separating a four-component mixture into four high-purity products. The walls created three internal sections in the middle of the column. One section was sealed at the bottom and had a small reboiler from which the lighter of the intermediate-boiling components was withdrawn. A second section was sealed at the top and had a small condenser and reflux drum from which the heavier of the intermediate components was withdrawn. The feed was introduced into the middle of the third section that was open at both ends. The top of this section was connected to the rectifying section of the vessel, which had a main condenser and reflux drum from which the lightest component was produced in the overhead distillate. This section was also open at the bottom and connected to the stripping section of the vessel, which had a main reboiler from which the heaviest component was produced as the bottoms.The purpose of this paper is to demonstrate that the process conceptual design and the practical plumbing is much more straightforward by using a conventional main column that has a side-stripper connected to the upper part of the column and a side-rectifier connected to the lower part of the column. Separating the functions into three vessels simplifies the design, has equivalent economics and improves the dynamic controllability.

Feasibility study on replacement of atmospheric distillation column with new sequences in a natural gas condensate refinery

The atmospheric distillation unit is the main separation unit in crude oil and natural gas condensate refineries. An atmospheric distillation column in a natural gas condensate unit usually consists of a single column with 3 pump-arounds and 2 side strippers. In this work a new column sequences have been synthesised for the first time using the modified separation matrix method and the results had been compared to other well-known configuration through economic, exergy and exergoeconomic analysis. The results illustrate that the conventional atmospheric distillation configuration has a medium performance compared to other sequences. As an example, comparing the results obtained from the direct sequence, to the conventional distillation sequence, leads in almost 30% less annual cost, 54% less exergy loss rate and 5% more exergoeconomic factor. However, the 84.87% exergoeconomic factor for the conventional configuration could justify the application of conventional sequence in the refinery.

Energy Consumption in Sharp and Non-Sharp Splits of Ideal Ternary Mixtures

Most of the distillation processes deal with multicomponent mixtures, existing a great quantity of distillation sequences for this process. The sharp splits available for an ideal ternary mixture are the direct and the inverse distillation sequence scheme in which the compounds are separated in two different columns. There are non-sharp splits in which all the compounds are separated in a single distillation column that can incorporate a side column. Unfortunately, to choose non-sharp splits schemes, there is no heuristic that can provide information about the recommended cases, e.g. a single distillation column in which the intermediate boiling compound is collected by a side stream at the required purity or by other possibilities, such as the use of a side stripper or a side rectifier. The literature about this subject is very scarce, and many times when the non-sharp splits are used, no comparison with the sharp split alternatives is provided. Therefore, the cases for which the literature suggests the use of side columns are further studied, e.g. BTX (Benzene, Toluene, Xylene) mixtures separation.For many case studies, the results obtained show that the energy savings achieved, due to the use of side columns, are not significantly higher than the best sharp split process schemes. However, these results do not discard that for some other situations; the side column could be the most advantageous case.Usually, it is considered that when the desired purity of the main product in a stream is reached, the impurities proportion do not affect significantly the energy consumption, and for most of the systems, this is true. However, for a mixture with a molar composition of 10 % isopentane, 10 % pentane and 80 % hexane (mol), when split in the respective compounds at a purity of 95 % (mol), very different energy requirements are depicted depending on the proportion of isopentane and hexane, present in the pentane stream obtained in a direct sequence process . The rigorous simulation results illustrate that almost 60% of the energy required to separate the above-mentioned mixture is saved when the pentane stream carries a mixture of isopentane and hexane. In addition, the environmental impact has been analyzed for each case studied, being reduced in the same way as the energy consumption does.

Energy saving in acetic acid process using an azeotropic distillation column with a side stripper

ABSTRACTDilute acetic acid is obtained primarily from fermentation and synthesis processes and cannot be produced by simple distillation due to relatively low volatility of acetic acid compared to water. Instead, an azeotropic distillation is applied to increase the concentration of dilute acetic acid. When acetic acid is extracted from a dilute aqueous solution using a solvent mixture of ester and alcohol, its recovery requires an energy-intensive azeotropic distillation. In the water stripping process that follows azeotropic distillation, two distillation columns handle the acetic acid and water mixture in similar composition. Therefore, the two columns can be combined as a side stripper connected to the azeotropic distillation column. The energy-saving effect is examined with the HYSYS (Aspentech Corporation) evaluation of the process. Compared to the conventional process, the modified process suggests 39% reduction in heating duty and 24% coolant savings. The economic analysis shows 32% decrease in investment and 36% utility savings. Based on heat utilization analysis, the thermodynamic efficiency is enhanced by 11%.

Thermodynamic and Exergy Analysis of Energy-Integrated Distillation Technologies Focusing on Dividing-Wall Columns with Upper and Lower Partitions

This study continues our research about dividing-wall distillation columns (DWCs) with upper and lower partitions (Ind. Eng. Chem. Res. 2016, 56, 952). Thermodynamic efficiencies and heat demands are investigated to offer a more complex point of view about distillation technologies. Rigorous simulations of nine distillation systems are completed, and the results are evaluated. Among the separation systems there are conventional direct and indirect distillation systems and energy-integrated ones, that is, DWCs with upper and lower partition, columns with side stripper or side rectifier, the fully thermally coupled distillation column, the sloppy system, and a direct sequence with backward heat integration are examined using three different alcohol mixtures. Results are obtained from rigorous simulations using exergy analysis. Thermodynamic efficiencies are in agreement with the expectations based on previous researches. On the basis of the thermodynamic efficiencies and heat demands the direct sequence wit...

Evaluation of various heat pump assisted direct, indirect, Petlyuk and side stripper sequences for three-product separations

In this paper, various configurations of vapor recompression and bottom flashing systems were developed. The systems were developed based on direct sequence, indirect sequence, Petlyuk and side stripper designs. This research was performed with three main aims. First aim was to investigate possibility of enhancing energy and economic performance of complex three-product distillation systems via implementation of vapor recompression and bottom flashing. Second aim was to shed light on differences in potentials of vapor recompression and bottom flashing systems in energy and costs savings of three-product distillation schemes. Third aim was to name the best configuration of three-product separation schemes from economic and energy points of view. Twelve configurations were designed. Energy and costs requirements of each configuration were evaluated and compared to each other. Based on the presented results, implementation of vapor recompression and bottom flashing systems can lead to better economic performance of complex three-product distillation systems. In case study presented in this work, application of vapor recompression and bottom flashing enhanced performance of direct sequence, indirect sequence, Petlyuk and side stripper designs. Equivalent work requirements of base direct sequence separation system was 5.59 MW. Based on the obtained results, considering energy requirements, Side stripper and Petlyuk arrangements are the best options for separation of the three-product system with equivalent work savings of 27.6 and 23.5%, respectively. Considering equivalent mechanical work of the systems, the highest savings was obtained in Side stripper with VRC heat pump (71.3% saving). It is shown that the most economically attractive configuration is Petlyuk with bottom flashing with total annual costs (TAC) saving of 43.4% (compared to 9.58 mUSD/year TAC of the base case), while the best performances of vapor recompression systems were obtained on Petlyuk and side stripper designs with TAC savings of 37.4 and 31.0%, respectively.

Optimisation of thermally coupled distillation sequences with side columns

An approach for the optimal design of thermally coupled distillation sequences (TCDS) with side columns is presented. Both systems with side strippers and side rectifiers are considered. The design task is formulated as a non-linear programming problem that uses shortcut methods for the thermally coupled systems. The application of the optimisation model provides the tray structure and operating conditions that minimise the total annual cost of the system, which includes capital investment and utilities costs. When the shortcut designs were validated through rigorous simulations, one major feature of the resulting TCDS structures was that they properly located the interconnecting tray for the thermal coupling, thus providing energy-efficient designs by minimising remixing effects. A comparison with reported results for the design of TCDS with side columns from the use of a mixed-integer non-linear programming model is also presented.

Study on Heat Integrated Azeotropic Distillation

In this paper, the design and optimization procedures of a heterogeneous heat integrated azeotropic distillation sequence with side stripper (HIADS-SS) for the purification of isopropanol are investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy consumption. The procedures are applied to the study of the separation of azeotropic mixtures using the two distillation sequences. In the HIADS-SS, the top end of the side stripper has both liquid and vapor exchange with the main column, which eliminates a condenser compared with the conventional heterogeneous azeotropic distillation sequence (CHADS). The results show that reductions in energy consumption can be obtained using the HIADS-SS.

Steady state analysis of snowball effects for reaction–separation–recycle systems with thermally coupled distillation sequences

It is known that the steady and dynamic characteristics of processes with recycles can be significantly different from those without recycle streams. Particular attention has been given to the reactor–separator–recycle (RSR) system; because of the existence of snowball effects, a small load change can translate into a large change in the recycle flowrate, which propagates throughout the whole system. Previous works have analyzed the influence of separators on snowball effects using flash units and conventional distillation columns. This work explores the existence of snowball effects in steady state conditions under the implementation of thermally coupled distillation sequences in RSR systems. In particular, the implementation of coupled systems with side columns (sequences with side rectifiers or side strippers) is considered. A simplified process for ethylbenzene production is taken as a basis, and the effects of implementing thermally coupled systems on snowball effects are compared to those generated by conventional distillation systems.

Graphical design and analysis of thermally coupled sidestream columns using column profile maps and temperature collocation

AbstractA systematical procedure is presented to design thermally coupled sidestream units like side rectifiers and side strippers are presented in this article. The method combines the column profile map technique to assess topological characteristics of the specific configuration with temperature collocation to rigorously ensure a realizable column design, without making assumptions with regard to the phase equilibrium or product specifications. The proposed methodology offers a unique graphical insight into the challenging problem of thermally coupled column synthesis. Techniques are presented for highlighting superior designs or eliminating inferior ones, based on vapor flow rate, number of stages, and thermodynamic efficiency. Design parameters such as the feed and side‐draw trays that may require insight or experience are products of the procedure. Design solutions obtained using this methodology can be used to initialize the state of the art process flow sheeting tool, AspenPlus™, which typically leads to fast convergence to the desired product purities without further adjustments. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Reducing Energy Consumption and CO2 Emissions in Thermally Coupled Azeotropic Distillation

AbstractThe design and optimization procedures of a heterogeneous thermally coupled azeotropic distillation sequence with a side stripper (TCADS‐SS) for the purification of isopropanol has been investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy consumption, which is related to the minimum CO2 emissions and the lowest total annual cost (TAC). The procedures are applied to the study of the separation of azeotropic mixtures using the two distillation sequences. In the TCADS‐SS, the top end of the side stripper has both liquid and vapor exchange with the main column, which eliminates a condenser in contrast with the conventional heterogeneous azeotropic distillation sequence (CHADS). The results show that not only reductions in energy consumption and CO2 emissions but also higher thermodynamic efficiency can be obtained for the TCADS‐SS.

Synthesis and heat integration of thermally coupled complex distillation system

Based on stochastic optimization strategy and pinch technique, a method is proposed for optimal synthesis and heat integration of thermally coupled complex distillation column systems comprising simple columns, complex columns with side rectifier and/or side stripper as well as partially or fully thermally coupled (Petlyuk) columns with pre-fractionators. Three example problems for five-component mixtures separation have been solved and the optimized parameters and economic benefits of different optimal schemes have been analyzed and compared. The results demonstrate that the annual total cost in energy consumption and investment can be effectively reduced by using the heat-integrated complex distillation configuration. The solutions of example problems also demonstrate that the proposed method is efficient for the heat-integrated complex distillation synthesis problem. Copyright © 2009 John Wiley & Sons, Ltd.

Synthesis of heat-integrated complex distillation systems via Genetic Programming

This paper addresses the application of Genetic Programming (GP) to the synthesis of heat-integrated complex distillation system and the flowsheet of complex separation can be expressed directly using GP's special hierarchical structure. A series of unique encoding method and solution strategy is proposed and some evolutionary factor is improved based on the domain knowledge of chemical engineering. A shortcut method is applied to calculate all required design parameters. Conventional and complex columns, thermally coupled (linked) side strippers and side rectifiers, fully thermally coupled columns as well as heat integration between any different columns are simultaneously considered. Two illustrating examples are presented to demonstrate the effective computational strategies.

Advanced fractionation technology for the oleochemical industry

AbstractSteadily increasing requirements on fractionation demands in the oleochemical industry require advanced separation technology. Today, often a distillation column has not only to process several different feeds, but also be able to produce two different products simultaneously. Divided wall columns have been proposed and used in the chemical industry, but there are, presently, few applications of divided wall columns in the oleochemical sector. The main reason prohibiting their use might be in the limited familiarity, higher requirements on operation, potential corrosion problems and last but not least, limited flexibility.Fractionation columns with added side stripper are a well‐proven way to satisfy increased demand of separation duties. The availability of second‐generation structured packing increases the efficiency and reduces pressure drops while making it possible to increase capacity and/or product purities. A lower pressure drop has a positive impact on the separation itself. Combining these effects with an increase in capacity will result in a synergy effect on the separation performance.The newly developed BXPlus structured packing is a powerful tool for advanced Glycerin separation, combining good wettability resulting in high efficiency with low‐pressure drop. New columns can be designed much more compactly. Revamps will improve both capacity and/or purity. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

Control of Thermally Coupled Distillation Arrangements with Dynamic Estimation of Load Disturbances

Because of their potential energy savings, thermally coupled distillation sequences provide interesting alternatives to the use of sequences based on conventional distillation columns. Three thermally coupled structures have been particularly analyzed for the separation of ternary mixtures: the sequence with a side rectifier, the sequence with a side stripper, and the Petlyuk column. Design methods have been developed for such sequences, but their dynamic and operational characteristics still require a wider understanding to promote their practical implementation. Previous works have shown that thermally coupled systems can provide suitable control properties; most of the studies on closed-loop control analysis of thermally coupled systems have been based on proportional−integral (PI) controllers. In this work, a PI controller with dynamic estimation of uncertainties is implemented for the control of the thermally coupled distillation arrangements. The controller comprises three feedback terms: proportional, integral, and quadratic actions. The last term provides a dynamic estimation of unknown load disturbances to improve the closed-loop performance. Comparison with the classical PI control law was carried out to analyze the performance of the proposed controller in facing unknown load disturbances in feed composition and set point changes. The results show that the implementation of the controller with dynamic estimation of uncertainties improved noticeably the closed-loop responses provided by the PI controller.

Thermodynamic Analysis of Thermally Coupled Distillation Sequences

Thermodynamic efficiency calculations have been performed for the separation of ternary and quaternary mixtures of hydrocarbons in both conventional and thermally coupled distillation sequences. When ternary mixtures were considered, energy savings achieved in the thermally coupled distillation sequences were between 10 and 30% in comparison to the two conventional distillation sequences. Regarding thermodynamic efficiency, thermally coupled distillation sequences presented the highest values in almost all of the cases considered. When the analysis was extended to the separation of quaternary mixtures, the thermally coupled distillation sequences show acceptable energy savings and the thermodynamic efficiency of a thermally coupled distillation sequence linked to a side stripper and a side rectifier was better than that obtained in the conventional distillation sequence; however, for the thermally coupled distillation with prefractionator (Petlyuk-type column), the second law efficiency was low when compared to that of the conventional distillation sequence for the separation of a quaternary mixture with a low content of intermediate components.