The present disclosure generally relates to distillation columns, and in particular to configurations of dividing wall columns.
Thermal coupling links in distillation are known to reduce the overall costs of a configuration on a plant, owing to simultaneous reduction in capital and operating costs. Referring to
Despite its potential to significantly reduce the overall costs, the TC-TC configuration has seen limited industrial application. One reason for this is the operability issue that accompanies the TC-TC configuration. In
For further savings in plant space and capital costs, the TC-TC configuration can be incorporated into a single shell, popularly called the dividing wall column, as shown in
Although the dividing wall column was introduced by Wright as early as 1949, the first industrial application of this column did not happen until the late 1980s. Since then, the use of multicomponent dividing wall columns has seen a rapid increase in several industrial applications. Updates on the recent developments in dividing wall columns can be found in the works of Aspiron and Kaibel, Dejanovic et al. and Yildirim et al.
Though the TC-TC column of
Alternate dividing wall columns, as shown in
Disclosed herein is a method for separating feed stream containing a more volatile component, at least one intermediate volatile component and a less volatile component by feeding the feed to a distillation column containing one or more vertical partitions and is characterized by any one of the following embodiments.
In one embodiment (L-TC configuration): (i) a first vertical partition that starts at the top of the distillation column, continues and ends at a vertical location that is below the feed location to the distillation column and above the bottom of the column providing the zone Z1; (ii) the column is operated such that the feed is fed to an intermediate location of zone Z1 and (iii) at least one liquid stream, called the first intermediate stream, depleted in the less volatile component is withdrawn from an intermediate location of the first vertical partition's zone Z1 that is above the feed location and fed to an intermediate location of a second zone of the distillation column, and (iv) the column is operated such that at least one product stream enriched in the more volatile component is produced from a location in the first vertical partition's zone Z1 above the location from where the first intermediate stream is withdrawn, and (v) at least one product stream enriched in the more volatile component is recovered from the second zone at a location that is above the location where the first intermediate stream is fed; (vi) at least one product stream enriched in an intermediate volatile component is withdrawn from a zone which is different from zone Z1 and the withdrawal location of this stream is at an intermediate height of the column and, (vii) at least one product stream enriched in the less volatile component is withdrawn from a location in the distillation column below the bottom of the first vertical partition.
In another embodiment, (TC-L configuration): (i) a first vertical partition that starts at the bottom of the distillation column, continues and ends at a vertical location that is above the feed location to the distillation column and below the top of the column providing the zone Z1; (ii) the column is operated such that the feed is fed to an intermediate location of zone Z1 and (iii) at least one liquid stream, called the second intermediate stream, depleted in the more volatile component is withdrawn from an intermediate location of the first vertical partitions zone Z1 that is below the feed location and fed to an intermediate location of a second zone of the distillation column, and (iv) the column is operated such that at least one product stream enriched in the more volatile component is withdrawn from a location in the distillation column above the top of the first vertical partition, and (v) at least one product stream enriched in an intermediate volatile component is withdrawn from a zone which is different from zone Z1 and the withdrawal location of this stream is at an intermediate height of the column and, (vi) at least one product stream enriched in the less volatile component is produced from a location in the first vertical partition's zone Z1 below the location from where the second intermediate stream is withdrawn, and (vii) at least one product stream enriched in the less volatile component is recovered from the second zone at a location that is below the location where the second intermediate stream is fed.
In another embodiment, (L-L configuration): (i) a first vertical partition that starts at the top of the distillation column, continues and ends at the bottom of the distillation column providing the zone Z1; (ii) the column is operated such that the feed is fed to an intermediate location of zone Z1 and (iii) at least one liquid stream, called the first intermediate stream, depleted in the less volatile component is withdrawn from an intermediate location of the first vertical partition's zone Z1 that is above the feed location and fed to an intermediate location of a second zone of the distillation column, and (iv) at least one liquid stream, called the second intermediate stream, depleted in the more volatile component is withdrawn from an intermediate location of the first vertical partition's zone Z1 that is below the feed location and fed to an intermediate location of a second zone of the distillation column that is below where the first intermediate stream is fed, and (v) the column is operated such that at least one product stream enriched in the more volatile component is produced from a location in the first vertical partition's zone Z1 above the location from where the first intermediate stream is withdrawn, and (vi) at least one product stream enriched in the more volatile component is recovered from the second zone at a location that is above the location where the first intermediate stream is fed; (vii) at least one product stream enriched in an intermediate volatile component is withdrawn from a zone which is different from zone Z1 and the withdrawal location of this stream is at an intermediate height of the column and, (viii) at least one product stream enriched in the less volatile component is produced from a location in the first vertical partition's zone Z1 below the location from where the second intermediate stream is withdrawn, and (ix) at least one product stream enriched in the less volatile component is recovered from the second zone at a location that is below the location where the second intermediate stream is fed.
a is a schematic showing an operable version of the TC-TC configuration.
b is a schematic showing an operable version of the TC-TC configuration.
a is a schematic showing a dividing wall column.
b is a schematic showing a dividing wall column.
a shows the top view of the distillation column when the vertical partition is a dividing wall.
b shows show the top view of the distillation column when the vertical partition is a concentric cylinder.
c show the top view of a possible arbitrarily shaped vertical partition that could be used in a distillation column.
d shows the top view of two possible arbitrarily shaped vertical partition that could be used in a distillation column.
a, 6b, 6c, and 6d respectively show the front views of the distillation columns in
a is a schematic showing a possible distillation configuration.
b is a schematic showing a possible distillation configuration.
c is a schematic showing a possible distillation configuration.
a is a schematic showing a new, more operable dividing wall column version of the L-TC configuration.
b is a schematic showing a new, more operable dividing wall column version of the TC-L configuration.
c is a schematic showing a new, more operable dividing wall column version of the L-L configuration.
a is a schematic of a dividing wall column from
b is a schematic of a dividing wall column from
a is a schematic showing one possible arrangement of the L-TC column with one reboiler and condenser.
b is a schematic showing one possible arrangement of the TC-L column with one reboiler and condenser.
c is a schematic showing one possible arrangement of the L-L column with one reboiler and condenser.
a is a schematic showing an alternate arrangement for the L-TC column with one reboiler and condenser.
b is a schematic showing an alternate arrangement for the TC-L column with one reboiler and condenser.
c is a schematic showing an alternate arrangement for the L-L column with one reboiler and condenser.
a is a schematic showing that in the L-L column, if no liquid BC is transferred across the vertical partition, with only the liquid AB transfer, the column could produce B from the bottom of the vertical partition's zone Z2.
b is a schematic depicting a situation where liquid BC is transferred but no liquid AB is transferred, B could be produced from the top of the vertical partition's zone Z2 of the L-L column, leading to the operation similar to a side rectifier.
a is a schematic showing a thermally coupled four-component configuration.
b is a schematic showing a three-column configuration with all liquid transfers and only one vapor transfer between distillation columns.
a is a schematic showing a dividing wall version of the configuration in
b is a schematic of a simplified version of the dividing wall column in
a is a schematic showing a variant of the configurations in
b is a schematic showing a variant of the configurations in
c is a schematic showing a variant of the configurations in
d is a schematic showing a variant of the configurations in
a-19l show possible combinations of a situation from an intermediate location below the feed, the two possible submixture transfers are BCD or BC, implying that, for each of the three vertical partitioned columns, we have four possible combinations of the two submixtures.
a-20h are schematics showing the various operating modes of the L-L column to separate a quinary mixture.
a and 21b are schematics showing extensions to dividing wall columns of
For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended.
Presented herein are new dividing wall columns that are more operable than the TC-TC column and operate with approximately the same minimum heat duty as the TC-TC column (or configuration).
Following are brief definitions of key terms used in the present disclosure.
A, B, C, D, E denote components with volatilities decreasing in the same order that are present in a feed mixture ABCDE. A is the most volatile component and E is the least volatile component and B, C and D are components of intermediate volatility with B being more volatile than C, and C being more volatile than D. The feed mixture for separation using the invention described here may be from the group but are not limited to benzene/toluene/xylene mixtures, nitrogen/oxygen/argon mixtures, nitrogen/carbon mono-oxide/methane mixtures, combinations of three or more components from C1 to C5 alcohols, and hydrocarbon mixtures, the mentioned hydrocarbon mixtures could be any from the set of pentane/hexane/heptane, isopentane/pentane/hexane, butane/isopentane/pentane, isobutene/n-butane/gasoline, and combinations of at least three components from C1 to C10 hydrocarbons or C4 isomers. Further, the invention could be used to separate benzene from pyrolysis gasoline, C7+aromatics from C7+olefin/paraffin or for separations by distillation as described in References 23 to 42.
Streams are named according to the components they predominantly contain. For example BC is a stream that is primarily a mixture of components B and C, but may contain traces or acceptable concentrations of other components. Similarly, a product stream A may contain acceptable concentration of other components but will primarily be rich in A.
More volatile component means, for a given feed, any feasible stream that contains the most volatile component of the feed. For feed ABC, more volatile component implies any one of AB or A. For feed ABCD, more volatile component implies any one of ABC or AB or A. For feed ABCDE, more volatile component implies any one of ABCD or ABC or AB or A.
Intermediate volatile component means, for a given feed, any feasible stream that is lean in the most volatile and the least volatile components of the feed. For feed ABC, intermediate volatile component implies B. For feed ABCD, intermediate volatile component implies any one of BC or B or C. For feed ABCDE, intermediate volatile component implies any one of BCD or BC or CD or B or C or D.
Less volatile component means, for a given feed, any feasible stream that contains the least volatile component of the feed. For feed ABC, less volatile component implies any one of BC or C. For feed ABCD, less volatile component implies any one of BCD or CD or D. For feed ABCDE, less volatile component implies any one of BCDE or CDE or DE or E.
A stream enriched in the more volatile component (less volatile component) means, in such a stream, the ratio of the flow rate of the more volatile component (less volatile component) to the flow rate of the least volatile component (most volatile component) present in the feed is higher than the corresponding value for the feed.
A stream depleted in the more volatile component (less volatile component) means, in such a stream, the ratio of the flow rate of the more volatile component (less volatile component) to the flow rate of the least volatile component (most volatile component) present in the feed is lower than the corresponding value for the feed.
A stream enriched (depleted) in the intermediate volatile component means, in such a stream, at least one of the two ratios—the ratio of the flow rate in the stream of the intermediate volatile component, to the flow rate in the stream of the feed's least volatile component, or the ratio of the flow rate in the stream of the intermediate volatile component, to the flow rate in the stream of the feed's most volatile component, is higher (lower) than in the feed.
In general, depending on the context, a product stream enriched in the less volatile component may contain components in addition to the least volatile component, but these additional components are the ones whose volatility is adjacent to the least volatile component. For example, for a feed mixture ABCD, where D is the least volatile component, a stream enriched in the less volatile component may contain either one of the following: D, or CD, or BCD. Similarly, depending on the context, a stream enriched in the intermediate volatile component may contain one or more components of intermediate volatilities. For example, for the feed mixture ABCD, the stream enriched in the intermediate volatile component may be any one of the following: B, C, or BC. Likewise, depending on the context, a product stream enriched in the more volatile component may contain components in addition to the most volatile component, but these additional components are the ones whose volatility is adjacent to the most volatile component. For example, for a feed mixture ABCD, a stream enriched in the more volatile component may contain either one of the following: A, or AB, or ABC.
Vertical partition means, any physical separation that is used to prevent the exchange of mass between the two sides of the vertical partition inside the distillation column.
The shapes of the distillation columns shown in the figures are not to be construed as implying that only cylindrical distillation columns are possible. Rather, the distillation column's diameter may vary at any location along the height of the column. Similarly, partitions are a partition is any physical separation of any shape, which prevents the liquid and vapor of its two sides from mixing inside the distillation column.
Use of a vertical partition divides a column shell into a least two zones, each on either side of the vertical partition. In this case, the zone on any one side of the partition is the region between the vertical partition and the column shell on that side. A zone has separation stages for liquid-vapor contact. Thus, in
Generally, when it is said that a stream is withdrawn from a location in a column or a zone which is below the withdrawal or feed location of another stream, then it means that there is one or more separation stages between the two locations. Same is true when a stream is fed above a location where another stream is either fed or withdrawn. Similarly, when it is said that a stream is fed or withdrawn from an intermediate location of a zone or a distillation column, it is meant that there are one or more separation stages above as well as below the location under consideration. By separation stages, it is meant mass transfer contact devices such as trays, structured or random packing, etc.
A distillation column operated in an advantageous manner means, the operation of the distillation column accompanied by a reduction in total heat duty in the reboilers of the distillation column or attainment of desired product purities.
Cooling medium means, a stream of sufficiently low temperature used in a heat exchanger that allows heat exchange with a process stream to reduce the process stream's enthalpy content.
Heating medium means, a stream of sufficiently high temperature used in a heat exchanger that allows heat exchange with a process stream to increase the process stream's enthalpy content.
Streams of similar composition means, in such streams, the ratio of each component's flowrate in one stream to the total flowrate of that stream is similar to the corresponding values in every other stream.
Streams of dissimilar composition means, in such streams, the ratio of at least one component's flowrate in one stream to the total flowrate of that stream is not equal to the corresponding values for every other stream.
Distillation configurations with liquid transfers between distillation columns are easier to operate and control than configurations with vapor transfers between distillation columns. Based on this fact, for the distillation of a ternary mixture, Agrawal proposed the three configurations of
The low heat duty requirement of the L-TC configuration, for example, can be partially understood by the fact that, with the same vapor that enters distillation column 1 at the bottom, for separating feed ABC into AB and BC, some A is also distilled from the top of the first column. Hence, this quantity of A is absent from the system for separation in column 2, which potentially reduces the heat duty requirement of this column. A similar analysis can be extended to understand the low heat duty requirements of the TC-L and L-L configurations.
In
The L-TC column, like the TC-TC column, has one vapor split at the bottom of the vertical partition. However, the two condensers 103 at A in the L-TC column can be artificially used to create a desired pressure drop in zones Z1 and/or Z2 of the vertical partition. This can be achieved by either placing a valve in the piping before the condenser 103, or, by controlling the inlet temperature of the cooling medium within each of the condensing heat exchangers. For example, assume the condensing fluid in both the condensers 103 of the L-TC column to be pure benzene, the outlets to be pure saturated liquid benzene and an approach temperature of the pure saturated liquid benzene with respect to the cooling medium to be 10° C. in both condensers 103. At 1000 mm Hg, benzene condenses at approximately 90° C., which means the inlet cooling medium for both condensers 103 is at 80° C. However, if the inlet cooling medium temperature of one condenser 103 is raised by 10° C., to 90° C., maintaining the same approach temperature, benzene condenses at approximately 100° C., 1050 mm Hg in this condenser 103. Thus, this increase in pressure at the outlet saturated liquid benzene of this condenser 103 results in reduced pressure drop across the respective zone and hence, reduced split of vapor through the respective zone at the bottom of the partition. Simultaneously, the inlet temperature of the cooling medium in the other condenser 103 may also have to be appropriately modified for achieving desired vapor splits. Alternatively, the heat exchanger may be designed to be a submersible heat exchanger, whereby, submergence of the passage for the condensing fluid can be controlled to tailor the active area through which most of the heat transfer takes place. This will control the condensing temperature, and hence the pressure of the condensing fluid. The control of the pressure at the top of either of the zones Z1 or Z2 of the vertical partition will tailor the pressure drop across that zone, and hence the vapor flowrate through that zone. Thus, the L-TC column offers an indirect control on the vapor split at the bottom of the vertical partition.
Interestingly, the TC-L and L-L columns have no vapor splits. The two reboilers 101 at C can be used to operate each section in the two parallel zones, on either side of the vertical partition, at the desired L/V ratios. It is worth noting that, in the case of the L-L column, the two parallel zones can be operated like two independent distillation columns, which may give the configuration more flexibility and freedom to operate.
A dividing wall column somewhat similar to the L-L column in
The L-TC and TC-L columns use one more heat exchanger, and the L-L column uses two more than the TC-TC column. Arrangements can be made to each dividing wall column of
a and 12b and 12c show an alternate arrangement for the L-TC, TC-L and L-L columns with one reboiler 101 and condenser 103. In the L-TC column of
Under the assumptions of ideal mixtures and constant molar flow conditions, through modeling and extensive computation, we have observed that the total minimum vapor requirement for the TC-TC, L-TC, TC-L and L-L distillation columns are equal. It is also observed for a number of feed conditions that the range of ratio of splits of vapor in zones Z1 and Z2 of the vertical partition are also equal in all the four distillation columns.
There is yet another flexibility of the L-TC, TC-L and L-L columns of
New, More Operable n-Component Dividing Wall Columns:
Generally, the overall cost saving from dividing wall columns significantly increases with the number of components in the feed. In this section, it is demonstrated that the disclosed method can also be easily used to draw new more operable dividing wall columns for the distillation of feeds containing more than three components. The method is illustrated by drawing new, more operable, standalone dividing wall columns that separate a four-component feed into four pure products. The focus will be on the dividing wall columns derived from the fully thermally coupled configuration. Similar dividing wall columns for higher number of components can be easily drawn.
The fully thermally coupled four-component configuration is shown in
At least eighteen variants of the dividing wall column of
While we have shown the more operable dividing wall columns derived from the fully thermally coupled configuration, other such more operable dividing wall columns derived from the various well-known four component configurations can be drawn, which may offer other benefits. An example dividing wall column, similar in skeleton structure to the one in
In this work, we focused on the new, more operable dividing wall columns derived primarily from the fully thermally coupled multicomponent configurations. However, using the concept proposed by Agrawal, any thermal coupling link can be converted to a liquid only transfer. Such a liquid transfer can be incorporated in a dividing wall column as explained in this paper. Furthermore, our proposed method can also be easily applied to feeds containing more than four components.
Application of the New n-Component Dividing Wall Structures to Feeds with More than n-Components:
The disclosed new n-component skeleton dividing wall structures presented earlier can be easily adapted to separate a multicomponent feed containing more than n components. In such cases, product streams enriched in different components will be produced. However, the possible product streams and the number of operating modes increase rapidly with the number of components in the feed. Any of these operating modes can be included within a larger flowsheet that separates multicomponent mixtures into component product streams. We will first illustrate the adaptation of the various operating modes of the L-TC, TC-L and L-L columns, originally drawn for the distillation of a ternary feed, to a quaternary feed mixture, ABCD. Then, as a generalization of our approach, a quinary mixture will be distilled using one of our quaternary skeleton dividing wall structures.
The L-TC, TC-L and L-L columns have two submixture transfers from intermediate locations, one above the feed and the other below the feed (AB and BC in the earlier studied three-component case). When a quaternary feed mixture ABCD is distilled in these columns, there are two possible submixtures, ABC or AB, which could be transferred from an intermediate location above the feed. Similarly, from an intermediate location below the feed, the two possible submixture transfers are BCD or BC. This implies that, for each of the three vertical partitioned columns, we have four possible combinations of the two submixtures.
Some interesting observations can be made from
An interesting case emerges in
Based on the observations made for quaternary mixtures, the various operating modes of the L-L column to separate a quinary mixture are shown in
Those skilled in the art will recognize that numerous modifications can be made to the specific implementations described above. The implementations should not be limited to the particular limitations described. Other implementations may be possible.
The present U.S. patent application is related to and claims the priority benefit of U.S. Provisional Patent Application Ser. No. 61/896,122, filed Oct. 27, 2013, the contents of which is hereby incorporated by reference in its entirety into this disclosure.
Number | Date | Country | |
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61896122 | Oct 2013 | US |