WO2010151498A1

WO2010151498A1 - Non-vertical rotating distillation column

Info

Publication number: WO2010151498A1
Application number: PCT/US2010/039254
Authority: WO
Inventors: Michael Nixon; Michael W. Mccaw
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-06-25
Filing date: 2010-06-18
Publication date: 2010-12-29
Anticipated expiration: 2011-12-25

Abstract

A vertical packed distillation column of the prior art is inclined slightly above horizontal and slowly rotated to continuously distribute reflux fluid throughout packing in the column therein achieving a longer path of the reflux fluid through the packing that interacts with rising vapor in the column.

Description

NON-VERTICAL ROTATING DISTILLATION COLUMN

BACKGROUND Field of the Invention

This invention relates to distillation apparatuses and more specifically to a non-vertical rotating packed distillation column.

Background Distillation is a well-known process for separating two or more components of a liquid mixture based on different boiling points of the components. When a mixture of two or more liquids is boiled, more of the liquid with the lower boiling point vaporizes than does a liquid with a higher boiling point.

Thus the derived vapor has a higher concentration of the liquid with the lower point than does the liquid mixture. Further concentration occurs in successive cycles of distillation by condensing the vapor, which condensation, called reflux liquid, maintains the same ratio of the liquids as the vapor, and re-vaporizing it. After many distillation cycles, a maximum concentration is achieved when a constant concentration ratio of the liquids is obtained, which may be complete separation of the liquids or an azeotrope of the mixture.

Equipment to implement distillation includes a boiler to initially heat the mixture, a vertical distillation column in which the distillation cycles occur after receiving vapor from the boiler and a condenser for extracting the separated liquids in a final condensation. Two basic designs for distillation columns are in common use. The first employs a series of trays on which reflux liquid is temporarily received as the reflux liquid cascades from tray to tray down the distillation column, each tray representing a distillation cycle. Each tray includes holes known as bubble caps through which rising vapor enters the tray and condenses, passing through the reflux liquid on the tray and transferring its latent heat to the reflux liquid. The transferred heat revaporizes a portion of the reflux liquid and in doing so further concentrates it, which revaporized reflux liquid then rises to the next upper tray. The process continues with vapor that reaches the condenser at the top of the column being removed from the column. The second design increases the surface area for receiving reflux liquid and enhances the liquid- vapor heat exchange by filling the column with packing onto which descending reflux liquid temporarily collects and then drips off while providing sufficient free volume through which vapor may pass. As vapors rise through the column, they interface with the descending liquid condense, releasing latent heat. This heat revaporizes some fo the reflux liquid to produce an enriched vapor, and this ascends into interaction with reflux liquid higher in the column, this process being repeated up the column. It is clear then that a redistillation occurs throughout the packed column each time reflux liquid is vaporized. This design is known as a packed column. The efficiency of a distillation column is largely determined by factors affecting the transfer of latent heat delivered from the rising vapors to the reflux liquid. The most important factors then are first, the extent of reflux liquid surface area in direct contact with the rising vapor and second, the time that the reflux liquid is exposed to the vapor while it traverses the column. The tray design and the packed design address these factors differently but both are limited by the size of the column.

The object of this invention is to improve both the time the reflux liquid is exposed to the vapor and the surface area of the reflux liquid exposed to the vapor.

SUMMARY These objects are achieved in a same packed distillation column of the prior art that is inclined from vertical and rotated. Inclining the column results in several advantages. Reflux liquid moves through the liquid slower as the effective force of gravity along the longitudinal axis of the column is reduced by the sine of the angle of inclination from horizontal. The time that the reflux liquid is exposed in the column is thereby increased. However, in an inclined column the reflux liquid quickly accumulates and flows down a lower side of the column, which severely negatively affects the interface between the descending liquid and the rising vapors, which tend to proceed along an upper side of the column. This negative affect is obviated by rotating the column about its axis during distillation, which continuously distributes the liquid evenly through the body of the packing. Liquid on packing throughout the column packing is rotated in circular paths around the column axis. The liquid therefore travels in a helical path through the column. As liquid drips from the packing to lower packing the liquid is continuously redistributed throughout the packing, preventing liquid from streaming down the lower wall of the column. Vapor therefore interacts with all of the reflux liquid. It also prevents preferred flow paths and rapid down flow within the packing, known as avalanching, which occurs in conventional vertical packed columns when the column diameter exceeds a critical value, thus removing the restriction on column diameter required on vertical packed columns.

Benchmark tests of the inclined and rotated distillation packed column were conducted with a packed column four meter in length on an ethanol and water mixture on a ten percent alcohol by volume (abv) fermented wash added to the boiler without the usual step of stripping the wash to achieve a higher initial strength. The system was first run in a conventional vertical orientation. It was then run with a column inclination of 83 degrees from vertical (7 degrees from horizontal) and then 85 degrees from vertical. When the column was vertical the time to achieve equilibrium where no further concentration was achieved with 100% applied reflux was 30 minutes. The applied reflux was then reduced to zero and the product was drawn off. The concentration did not exceed 80% abv and concentration reduced as the test continued. When the same column was rotated at both 83 degrees and 85 degrees inclination from vertical, equilibrium was attained in both cases within five minutes, again under 100% applied reflux. When the applied reflux was reduced to zero and product drawn off, the concentration of the product was found to be 95-96% abv, which is the azeotrope for a water/ethanol mixture. This concentration was maintained throughout the test until almost all of the ethanol in the boiler was exhausted. These tests were repeated using a two meter long packed column with similar results, the only difference being that equilibrium when inclined took ten minutes to achieve but followed as before by delivery of the azeotrope concentration with no artificially added reflux returned to the column. It was thus confirmed that the non-vertical packed distillation column may be of a length required to obtain the azeotrope for a water/ethanol mixture, the length being less than that of a same packed distillation column disposed vertical and required to obtain an azeotrope mixture. Further tests showed that the operational stability of a slowly rotated packed column is maintained as the inclination from vertical is increased and efficiency increases until the column is almost horizontal, at which time the distillation efficiency is greatly increased.

There are other practical advantages achieved by the inclined column. The entire length of the column is readily available at ground level for operation, inspection, maintenance, and adjustment. The distillation apparatus is not restricted by considerations of height. In fact, as noted, a shorted column can be employed without reduced concentration and without significant loss of efficiency. Because streaming and avalanching does not occur the column may be any convenient size diameter with the length and diameter of the column determined by considerations other than operational efficiency.

It should be understood that although the apparatus was designed and tested for an ethanol/water mixture, the apparatus is applicable generally to separation of liquid mixtures by distillation. Any reference to an ethanol/water mixture should be understood to be representative of all such liquid mixtures, which mixtures are deemed included in the reference. Also, reference herein to an azeotrope mixture is not to be interpreted as limited to the azeotrope for an ethanol/water mixture. It is also recognized that complete separation (for all practical purposes) of the liquid components is achievable through distillation.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings identical reference numbers identify similar elements or function. The sized and relative positions of elements in the drawings and the shapes of various elements and angles are not necessarily drawn to scale. Some of the elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of elements as drawn are not necessarily intended to convey any information regarding the actual shape of particular elements and have been solely selected for ease of depiction and recognition in the drawings. FIG. 1 is a functional diagram of a typical bubble cap distillation apparatus of the prior art having a vertical distillation column. FIG. 2 is a functional diagram of a typical packed column distillation apparatus of the prior art having a vertical distillation column. FIG. 3 is a functional diagram of a distillation apparatus employing a distillation column inclined from vertical and rotated FIG. 4 is a diagram representing a helical path traversed by reflux fluid in the column of FIG. 3. FIG. 5 is a pictorial view of vapor rising and reflux liquid descending in packing in a distillation column. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, certain details are set forth in order to provide an understanding of the preferred embodiments However, one skiiied in the relevant art will recognize that embodiments may he practiced without one or more ot these details, or with other methods, components, materials, etc Also, weH-known structures and processes associated with distillation systems, such as energy sources, pumps pipes, heat exchangers, and typically related operations have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments However, these well- known structures and processes are deemed incorporated into the describe embodiments by this general reference Also, described features, structures or characteristics may be combined in any suitable manner m one or more embodiments. The present invention discloses a distilling apparatus 10 with a distillation column 12 filled, or partially filled, with packing 14 for use in distilling a feed liquid that comprises a mixture of at least two component liquids. As in the prior art, the packing 14 serves as a vapor-liquid contact apparatus in the column 12 that enables contact between vapors 18 rising in the column 12 and reflux liquid 20 descending in the column 12 through the packing 14. For all purposes herein, reference to packing 14 in the column 12 includes the column 12 being filled or partially filled with packing 14. Also as in prior art, when operated as a continuously fed still, such as a fuel ethanol still, steam is introduced through a sealed bearing 22 at the bottom of the rotating column 12 from a boiler 42. However, unlike prior art, the column 12 is elevated at a preferred angle A from horizontal, typically near horizontal and currently 7 degrees in present implementations, and rotated. It should be recognized that any non-vertical implementation derives the benefits described herein with benefits increasing with increasing inclination from vertical until nearly horizontal. Some elevation is required so vapor 18 rises through the column 12 and reflux liquid 20 descends through the column 12. As described above, as the column 12 is rotated the descending reflux liquid 20 is dispersed about the packing 14 and intersects the ascending vapor 18 as the vapor 18 passes through the packing 14 thereby achieving the required contact with the reflux liquid 20. As the reflux liquid 20 descends through the column 12 while the column 12 is rotated, the liquid traverses a helical path 24.

A column rotator 26 is connected to the distillation column 12 to slowly rotate the column 12 during distillation of the liquid mixture. The rotator 26 is typically an electric motor coupled to the column 12 through a speed reduction gear box 28 and a static sealed bearing 22. The rotating column 12 is maintained at the desired angle by any suitable means, such as by two or more support bearings 30 that may be mounted on adjustable tripods 31 or on adjustable brackets attached to a wall. A static tube 32 that passes through a static condenser assembly 34 at the top of the column 12 runs through the packing 14 down the axis 38 of the rotating column 12. The tube 32 delivers low concentrate alcohol wash through the static condenser assembly 34 along the tube 32 to the packing 14 on the axis 38 of the column 12 for continuous distillation. The wash in the tube 32 is heated as it passes through the tube 32 and when discharged to the packing 14 is immediately subjected to the distillation process. Wash that continues to descend through the packing 14 during the distillation process is mostly stripped of all alcohol and vaporized, leaving only a small amount of alcohol received into the boiler 42. That alcohol received into the boiler 42 is subjected to further boiling and is vaporized with any liquid discharge from the boiler overflow being virtually all water.

When operated in a batch mode, for example when the purpose is to produce potable alcohol, the static tube 32 and the boiler overflow are not utilized; the boiler 42 is filled with fermented wash 16 instead of water. In both the modes vapor 18 that arrives at the end of the column 12 is condensed by a static condenser assembly 34, typically comprising an inner cooling coil 44 and an outer cooling coil 46.

Initially, cooling water is passed through the inner coil 44 to condense all vapor 18 reaching the top of the column 12 and return it to the column 12 as liquid reflux, enabling the rotating column 12 to reach an equilibrium where the concentrations of the vapor 18 and the liquid reflux 20 remain the same at any given point along the column 12, increasing in concentration from the bottom end 22 at the boiler 42 to the top end at the static condenser assembly 34. When equilibrium has been achieved, cooling water is diverted from the inner cooling coil 44 to the outer coil 46. High concentration vapor 18 then passes the inner coil 44 without being condensed and is diverted back into an annulus formed by the rotating column 12 and a shroud 52 of the static condenser assembly 34 to be condensed by the outer cooling coil 46. The final product is discharged from the static condenser assembly 34 via a discharge tube 54 fitted to the static condenser assembly shroud 52.

Claims

1. A distillation apparatus comprising: a distillation column adapted for use in distilling a feed liquid that comprises a mixture of at least two component liquids, a column rotator adapted to rotate the distillation column during distillation of the liquid, a vapor-liquid contact apparatus in the column facilitating contact between vapor ascending in the column and reflux liquid descending in the column, wherein rotation of the column causes the descending reflux liquid to be dispersed about the vapor-liquid contact apparatus into intersection with the vapor ascending through the vapor-liquid contact apparatus.

2. The distillation apparatus of claim 1 wherein the distillation column is non-vertical.

3. The distillation apparatus of claim 1 wherein the vapor-liquid contact apparatus comprises packing in the distillation column.

4. The distillation apparatus of claim 3 wherein the distillation column is non-vertical.

5. The distillation apparatus of claim 4 wherein the distillation column is inclined slightly above horizontal.

6. The distillation apparatus of claim 5 wherein the column rotator rotates the column such that reflux liquid in the column traverses a generally helical path through the packing.

7. The distillation apparatus of claim 4 wherein the non-vertical packed distillation column is of length required to obtain a maximum separation of the component liquids.

8. The distillation apparatus of claim 7 wherein said length is less than that of a same packed distillation column disposed vertically that also obtains a maximum separation of the component liquids.

9. The distillation apparatus of claim 1 further comprising a tube through a rotation axis of the distillation column adapted to deliver low concentrate wash from a condenser at a distillation column top to the vapor-liquid contact apparatus along the axis where it is reintroduced to the column for continued distillation.

10. The distillation apparatus of claim 9 wherein the low concentrate wash in the tube is preheated as it passes through the tube.

11. A distillation apparatus comprising: a distillation column adapted for use in distilling a feed liquid, wherein the distillation column is non-vertical, a column rotator adapted to rotate the distillation column during distillation of the liquid, a vapor-liquid contact apparatus comprising packing in the distillation column facilitating contact between vapors ascending in the column and reflux liquid descending in the column.

12. The distillation apparatus of claim 11 wherein the distillation column is inclined slightly above horizontal.

13. The distillation apparatus of claim 12 wherein the distillation column is inclined from horizontal approximately 7 degrees.

14. The distillation apparatus of claim 11 further comprising a tube through a rotation axis of the distillation column adapted to deliver low concentrate wash through a condenser assembly at a distillation column top to the vapor-liquid contact apparatus along the axis where it is reintroduced to the column for continued distillation.

15. A process of distilling a feed liquid comprising a mixture of component liquids comprising the following steps: a) Providing the feed liquid to a non-vertical packed distillation column; b) Rotating the distillation column during distillation.

16. The process of claim 15 wherein the distillation column is elevated slightly above horizontal.

17. The process of claim 15 wherein the step of rotating the distillation column during distillation includes the step of causing reflux liquid to traverse a generally helical path through the distillation column during rotation.

18. The process of claim 15 wherein the non-vertical packed distillation column is of length required to obtain a maximum separation of the component liquids, said length being less than that of a same packed distillation column disposed vertically that also obtains a maximum separation of the component liquids.

19. The process of claim 15 further including the step of delivering low concentrate wash from a condenser at a distillation column top through a tube on a rotation axis of the distillation column to the packed distillation column intermediate the rotating distillation column where it is reintroduced to the column for continued distillation.

20. The process of claim 15 including the step of heating the low concentrate wash in the tube as it passes through the tube.