New column configurations for pressure swing batch distillation II. Rigorous simulation calculations

The pressure swing distillation in different batch column configurations is investigated by rigorous simulation calculations. The calculations are made by a professional flow-sheet simulator for the separation of a minimum (ethanol–toluene) and a maximum boiling (water– ethylene-diamine) azeotropic mixture. Besides studying the well known configurations (rectifier, stripper) we also investigate two novel configurations such as double column batch rectifier and double column batch stripper. The alternate application of a batch rectifier and a batch stripper is also studied. The different column configurations are compared

Entrainer selection for pressure swing batch distillation

The feasibility of the separation of binary homoazeotropes with pressure swing batch distillation by the application of an entrainer is studied. The feasibility studies are based on the assumption of maximal separation and on the analysis of batch distillation/stripping regions and the vessel path in the residue curve map of the ternary mixture. The following configurations are investigated: batch rectifier, batch stripper, double column batch rectifier and double column batch stripper. Rules for the selection of an entrainer are suggested

Generalised model for heteroazeotropic batch distillation with variable decanter hold-up

A general model of batch heteroazeotropic distillation is proposed. Both liquid phases present in the decanter can be refluxed or withdrawn as distillate, their hold-up can be increased, decreased or kept constant, as well. By assuming maximal separation, that is, that the composition of the condensate always equals to that of the heteroazeotrope, the still path equation was derived. The still path directions are determined for all the 16 possible operational policies. It is possible to steer the still path in a desired direction by changing the operational parameters, which allows the recovery of a pure component in the still. The still path directions are validated by rigorous simulations for three policies not published yet using the mixture water – formaldehyde – propyl formate. From the 16 operational policies, 11 can be considered as useful in practice. To demonstrate the advantage of using a non-traditional policy, the separation of the mixture aniline – ethylene glycol – water was investigated, as well. By using a non-traditional operational policy with hold-up reduction in the decanter a higher purity of ethylene glycol was obtained in the still

New double column system for heteroazeotropic batch distillation

A new double column system (DCS) operated in closed mode is suggested for heterogeneous batch distillation. This configuration is investigated by feasibility studies based on the assumption of maximal separation and is compared with the traditional batch rectifier (BR). We study the configurations also by dynamic simulation based on a detailed model using a professional simulator. For the new configuration the minimal duration of the process is determined. The influence of the most important operational parameters is studied. The calculations and the simulations are performed for a binary (n-butanol–water) and for a ternary heteroazeotropic mixture (isopropanol–water + benzene as entrainer). One of the advantages of the DCS is that distillation of binary and ternary systems is performed in only one step. Furthermore the recovery of components is usually higher and the amount of byproducts is lower

Separation of ternary homoazeotropic mixture by pressure swing distillation

The separation of a ternary mixture (n-pentane-acetone-cyclo-hexane) with two binary minimum azeotropes is studied by feasibility studies and rigorous simulation calculations. By the feasibility studies based on the analysis of the vessel paths in the residue curve maps at the two different pressures (PI, PII) the separation steps are determined for the two configurations studied (batch stripper (BS), double column batch stripper (DCBS)). The rigorous calculations are performed by the CCDColumn professional dynamic flow-sheet simulator. For the DCBS two operational policies are compared

Új szakaszos heteroazeotróp rektifikáló rendszer vizsgálata részletes modellezéssel | Rigorous simulation of a new batch heteroazeotropic distillation configuration

A megvalósíthatósági vizsgálatok kedvező eredményei alapján az új kétoszlopos szakaszos heteroazeotróp desztillációs konfigurációra dinamikus szimulátorral részletes modellező számításokat is végzünk. Az új konfiguráció teljesítményét összehasonlítjuk a hagyományos szakaszos rektifikálóéval. Meghatározzuk az új konfiguráció minimális üzemidejét. Megvizsgáljuk a legfontosabb működési paraméterek hatását. A szimulációs számításokat egy binér (n-butanol – víz) és egy terner (izopropil-alkohol – víz + benzol) heteroazeotróp elegyre végezzük el. | On the basis of the favourable results of the feasibility studies performed for the new double-column batch heteroazeotropic distillation configuration we investigated this configuration also by rigorous simulation using the dynamic simulator of CHEMCAD (program CC-DCOLUMN). The column sections were modelled by the module DYNAMIC COLUMN, the reboilers and decanter by the DYNAMIC VESSEL, respectively (Fig. 1). The following simplifying assumptions were applied: - theoretical trays, - constant volumetric liquid holdup on the trays, - negligible vapour holdup, - negligible duration of pumping of the distillate from the product tank to the reboiler between the two steps (BR). We compared the performance of the new configuration with that of the conventional batch rectifier (BR). The total number of trays and and the total heat duty of the two columns of the new configuration was taken equal to those of the BR. For the new configuration we determined the minimal operational time (in the case where both products reach the purity prescribed at the same time). We varied the division of the total number of trays, total amount of feed, total heat duty, as well as the amount of the entrainer (in the case of the ternary mixture). The simulations were performed for a binary (n-butanol - water) and for a ternary heteroazeotropic mixture (isopropyl-alcohol – water + benzene). By the binary mixture we investigated the cases when the mixture contains one of the components in such amount that the mixture is homogeneous and also the heterogeneous case. In Fig. 2 the evolution of liquid compositions in the reboilers is shown for both configurations for the ternary mixture. The new configuration – in accordance with the results of feasibility studies – proved competitive with the BR: it gave slightly better results for the ternary mixture and similar results for the binary mixture, respectively

Új kétoszlopos szakaszos nyomásváltó rektifikáló rendszer üzemeltetése és szabályzása

When operating the DCBS (and DCBR) configuration(s) the liquid composition of the common vessel of the two columns must be kept between the two azeotropic compositions with affecting the flow rates of the two products. These can be varied by changing the reboil ratio and/or ratio of division of the liquid flow leaving the common vessel. The goals of this paper: -to propose and study a simple control scheme with PID parameters (providing good quality of control) for the new configuration, -investigation of the influence of the liquid division ratio, -determination of optimal value of liquid division ratio (providing the prescribed separation with minimal specific energy consumption). The calculations were made for a minimum (n-pentane - acetone) azeotropic mixture by using a professional dynamic simulator (CCDCOLUMN). By the aid of a PID controller we modified the flow rate of the bottom products (affecting the reboil ratios of the columns). We investigated the action of the control loops and the system for two different set points. In the first case the composition of the bottom products, in the second one – most common in the industry- the bottom temperatures were kept constant

Terner elegyek szakaszos nyomásváltó desztillációs elválaszthatóságának vizsgálata

Homoazeotropot tartalmazó terner elegyek nyomásváltó szakaszos desztillációval (NYVSZD) történő szétválaszthatóságát tanulmányozzuk megvalósíthatósági vizsgálatokkal. A maradékgörbe térképeket elemezzük. Meghatározzuk a megvalósítható tartomány(oka)t - ahonnan a terner elegy komponenseit tisztán visszanyerhetjük (legalább egy nyomásváltó lépést alkalmazva) - és az egyes kolonna konfigurációknál (egy és két oszlopos szakaszos sztripper és/vagy rektifikáló) alkalmazandó műveleti lépéseket. A leggyakoribb típusú, minimális azeotropot tartalmazó elegyeken mutatjuk be az eljárást

Batch heteroazeotropic distillation in a new Generalised Double-Column System

We study the separation of the minimum homoazeotrope isopropanol - water by applying cyclohexane and n-hexane as entrainer in a new Generalised Double-Column batch heteroazeotropic distillation System (GDCS). First its feasibility is studied by a simplified method then we do sensitivity analysis by rigorous simulation. The minimum duration is determined for the GDCS and for the original DCS, and their performances are compared. Due to its higher number of degrees of freedom the GDCS provides a more flexible operation than the DCS. In each case we obtained shorter process durations and lower energy demands by the GDCS than by the DCS