Note: Descriptions are shown in the official language in which they were submitted.
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LOW ENERGY DISTILLATION SYSTEM AND METHOD
FIELD
[0001] The presently disclosed subject matter relates to energy efficient
distillation systems
and methods, including energy efficient distillation systems and methods for
use in
petrochemical refining operations or the like.
BACKGROUND
[0002] Refining and chemical plants consume large amounts of energy. In a
typical refinery
about 10% of the energy content of crude oil is spent in refining the crude to
various
finished products. Large amounts of energy are directed to bringing liquid and
semi-liquid
feeds to near their boiling point in order to stage vapor-liquid equilibrium
separations.
Distillation technology that requires less energy would significantly improve
the overall
energy efficiency of refineries and chemical plants.
[0003] In conventional distillation, the waste heat at the condenser at the
top of the
distillation tower is not recovered. This results in a very low energy
efficiency (e.g.,
exergetic efficiency of less than 10%). Heat Integrated Distillation Columns
(HIDiC) have
been disclosed previously, but have not been commercialized to date. Either a
shell and tube
type configuration, or distillation columns with two concentric trays, with
the rectifier
section inside the stripper section, are generally described. Since HIDiC
configurations
proposed in academic literature generally use lateral placement of the
rectifier and stripper
sections, hurdles include complex heat transfer arrangements and the need for
dual, side-by-
side columns that would be required for heat integration increasing the
footprint of the
operation. Such arrangements may not be practical for retrofitting existing
columns.
[0004] Figure 1 depicts a conventional distillation operation 1000. A
condenser 1010,
located on top of the column 1020, removes heat from the vapor-rich process
stream 1030 to
produce a liquid product stream 1040 rich in a higher volatile ("lighter")
product. The
condenser also produces a reflux stream 1050 employed to improve the quality
of the vapor-
liquid staged separation process. The heat removed at the condenser is not
recovered, but is
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discharged to the cooling water or air, thereby resulting in a low energy
efficiency of
distillation. The Second Law Thermodynamic Efficiency, also referred to as
Exergy
efficiency, in a distillation column is generally less than 10%. The Exergy
efficiency
defines how efficient the system is relative to a thermodynamically perfect
system
performing the same operation starting with same input feeds and producing the
same
product streams
[0005] As can be seen in Figure 1, the rectifier section 1060 is located, in
vertical proximity,
above the stripping section 1070 in a conventional distillation column.
[0006] The column shown in Figure 1 is also provided with a reboiler 1080
which receives a
feed rich in less-volatile ("heavier") components, in which heat is employed
to vaporize
more volatile components. Heavier liquid products remaining after the input of
heat are
withdrawn from the column 1090, while some heavier vaporized product 1100 is
recycled
back to the column to improve the quality of the separation.
[0007] Figure 2 depicts a HIDiC unit operation 2000 described in J. of Chem.
Tech. and
Biotech., 78:241-248 (2003), which is hereby incorporated by reference in its
entirety.
Unlike the distillation column of Figure 1 where the rectifier section 1060 is
located above
the stripper section 1070, the rectifier and the stripper sections 2060 and
2030, respectively,
in Figure 2 are located in a lateral position with additional provision for
heat transfer from
the rectifier to the stripper sections. A compressor 2010 is employed to
compress the vapor
from the stream 2020 exiting the stripping section 2030, which is the section
defined by area
below the feed 2040. The compression results in a higher temperature in the
rectifier section
2060, which is generally the column 2080 shown on the right of Figure 2. A
valve 2090 is
provided to control the flow of the stream 2100 exiting the bottom of the
rectifying section
to a location in close proximity to the feed. The upper portion of the second
column 2080
yields a vapor-rich stream 2110 which is directed to a condenser 2120 that
yield a low
volatile product 2130 and a reflux stream 2140, which is returned to the
rectifier section
2060.
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[0008] Upon transfer of heat from the rectifier section 2060 to the stripper
section 2030, the
stream 2100 providing liquid reflux functionality between the rectification
and stripping
sections is generated. The "reflux ratio" of the stream 2100 providing liquid
reflux
functionality is set by the column heat balance with proximate control based
on level in the
rectification section bottoms by valve 2090.
[0009] Another proposed HIDiC operation 3000 is depicted in Figure 3, which is
taken from
Z. Olujic et al., Energy 31:3083-3096 (2006), and hereby incorporated by
reference in its
entirety.
[0010] Figure 3, illustrates a concentric tray design with the stripping
section located outside
of the rectifier section, with heat transfer panels 3030 placed in between
trays. Lateral heat
transfer occurs between two parallel or concentric columns, which can be
provided by, for
example, an inner rectifying section 3010 surrounded by an outer stripping
section 3020.
[0011] Figure 4, from U.S. Patent No. 4,234,391, hereby incorporated by
reference in its
entirety, depicts a conceptual design 4000 in which heat pipes 4010 transfer
heat from a
rectifier section 4040 to a stripping section 4030, which are separated by a
partition 4020.
The heat pipes are in a lateral position, as shown in Figure 4. Such HIDiC
designs have not
been commercialized to date.
[0012] Thus, there remains a need and desire to improve energy efficiency of
distillation
operations, particularly within refineries and chemical plants. There also
remains a need for
HIDiC designs that can be easily retrofitted to existing distillation column
infrastructure.
SUMMARY
[0013] One aspect of the presently disclosed subject matter provides a
distillation system for
separating at least two components of a multi-component fluid feed. The system
includes a
stripper section including (i) an inlet to receive a feed of fluid containing
at least two
components, (ii) a compressor in fluid communication with a more volatile
portion of the
fluid within the stripper section to provide an output feed, and (iii) a
reboiler to receive a
heating fluid and in fluid communication with a less volatile portion of fluid
within the
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stripper section. The distillation system also includes a rectifier section
aligned vertically
with and disposed below the stripper section, the rectifier section to receive
the output feed
from the compressor and further including (i) a condenser to receive a cooling
fluid and in
fluid communication with a more volatile portion of the output feed from the
compressor,
the condenser including an exit to remove at least one component from the more
volatile
portion of the output feed, and (ii) an outlet to recycle a less volatile
portion of the output
feed from the compressor for recycle back to the stripper section.
[0014] Another aspect of the presently disclosed subject matter provides a
distillation
method for separating at least two components of a multi-component fluid feed.
The
method includes introducing a feed of fluid containing at least two components
to a stripper
section, the stripper section including (i) an inlet to receive the feed of
the fluid, (ii) a
compressor in fluid communication with a more volatile portion of the fluid
within the
stripper section to provide an output feed, and (iii) a reboiler to receive a
heating fluid and in
fluid communication with a less volatile portion of fluid within the stripper
section. The
distillation method also includes directing the output feed from the
compressor to a rectifier
section aligned vertically with and disposed below the stripper section, the
rectifier section
including (i) a condenser to receive a cooling fluid and in fluid
communication with a more
volatile portion of the output feed from the compressor, the condenser
including an exit to
remove at least one component from the more volatile portion of the output
feed, and (ii) an
outlet to recycle a less volatile portion of the output feed from the
compressor to the stripper
section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will now be described in conjunction with the
accompanying drawings
in which:
[0016] FIG. 1 is a schematic view of a conventional distillation column with a
rectifying
section located above the stripping section, in which energy removed at the
condenser is not
recovered.
[0017] FIG. 2 is a schematic view of a conventional HIDiC concept.
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[0018] FIG. 3 is a schematic view of a concentric HIDiC design with heat
transfer from the
inner rectifier to outer stripper section.
[0019] FIG. 4 is a schematic view of a HIDiC design with heat pipes for heat
transfer from
the rectifier section to the stripper section in lateral positions.
[0020] FIG. 5 is a schematic view of a representative embodiment of the
distillation system
of the presently disclosed subject matter.
[0021] FIG. 6 is a schematic view of another representative embodiment of the
distillation
system of the presently disclosed subject matter.
DETAILED DESCRIPTION
[0022] The following definitions are provided for purpose of illustration and
not limitation.
[0023] The Exergy efficiency defines how efficient the separation is relative
to a
thermodynamically perfect system. The Exergy of each stream is the theoretical
maximum
amount of work it can produce, determined by taking it through a series of
reversible steps
to bring it into equilibrium with ambient surrounding. The increase in Exergy
content of the
products versus the feed inputs represents the minimum amount of work needed.
The
Exergy efficiency is defined as the ratio of this minimum amount of work
divided by the
total Exergy expended in actually doing the separation
[0024] As used herein, the term "produced in an industrial scale" refers to a
production
scheme in which end products are produced on a continuous basis (with the
exception of
necessary outages for plant maintenance) over an extended period of time
(e.g., over at least
a week, or a month, or a year) with the expectation of generating revenues
from the sale or
distribution of the end product. Production at an industrial scale is
distinguished from
laboratory or pilot plant settings which are typically maintained only for the
limited period
of the experiment or investigation, and are conducted for research purposes
and not with the
expectation of generating revenue from the sale or distribution of end
products.
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[0025] In accordance with the presently disclosed subject matter, a
distillation system is
provided for separating at least two components of a multi-component fluid
feed. The
distillation system includes a stripper section including (i) an inlet to
receive a feed of fluid
containing at least two components, (ii) a compressor in fluid communication
with a more
volatile portion of the fluid within the stripper section to provide an output
feed, and (iii) a
reboiler to receive a heating fluid and in fluid communication with a less
volatile portion of
fluid within the stripper section. The distillation system also includes a
rectifier section
aligned vertically with and disposed below the stripper section, the rectifier
section to
receive the output feed from the compressor and further including (i) a
condenser to receive
a cooling fluid and in fluid communication with a more volatile portion of the
output feed
from the compressor, the condenser including an exit to remove at least one
component from
the more volatile portion of the output feed, and (ii) an outlet to recycle a
less volatile
portion of the output feed from the compressor for recycle back to the
stripper section.
[0026] In accordance with another aspect of the presently disclosed subject
matter, a
distillation method is provided for separating at least two components of a
multi-component
fluid feed. The distillation method includes introducing a feed of fluid
containing at least
two components to a stripper section, the stripper section including (i) an
inlet to receive the
feed of the fluid, (ii) a compressor in fluid communication with a more
volatile portion of
the fluid within the stripper section to provide an output feed, and (iii) a
reboiler to receive a
heating fluid and in fluid communication with a less volatile portion of fluid
within the
stripper section. The distillation method also includes directing the output
feed from the
compressor to a rectifier section aligned vertically with and disposed below
the stripper
section, the rectifier section including (i) a condenser to receive a cooling
fluid and in fluid
communication with a more volatile portion of the output feed from the
compressor, the
condenser including an exit to remove at least one component from the more
volatile portion
of the output feed, and (ii) an outlet to recycle a less volatile portion of
the output feed from
the compressor to the stripper section.
[0027] The method and system disclosed herein will be described in conjunction
with each
other for understanding and enablement.
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[0028] For purposes of illustration and not limitation, reference is made to
the embodiment
of Figure 5, in which the stripper section 5250 and the rectifier section 5500
are contained
within a single, at least partially enclosed, structure 5010. A multi-
component liquid feed
5100 is introduced above the feed tray or stage 5120 of the distillation
column 5010 at a
temperature near the boiling point of the feed composition. In a preferred
embodiment, the
feed to the distillation system is primarily hydrocarbons, although any multi-
component feed
can be separated using the presently disclosed methods and systems.
[0029] As the feed is introduced to the column, liquid portions rich in less
volatile
components flow down the column, and gaseous portions rich in more volatile
components
of the feed flow up toward a gas compressor 5150. A partition 5200 is provided
to prevent
the liquid portions rich in heavier components of the feed from traveling
further down the
column into the rectifier section 5500. The section between the feed and the
partition
constitute the stripping or stripper section 5250 of the distillation column.
[0030] A reboiler 5300, which is supplied with a source of steam or other
heating fluid,
inputs heat to the column and yields a bottoms product, 5350, rich in less
volatile
("heavier") products and a stream, 5400 that is returned to the stripping
section 5250.
[0031] Compressed vapors 5450 exiting the compressor 5150 are directed to the
bottom of
the rectifier section 5500. The compression of the gases results in a higher
temperature in
the rectifier section 5500 as compared to the stripper section 5250, which
consists of the
section of the column below the partition 5200. Thus, in one embodiment, the
rectifier
section 5500 is operated at a higher average temperature than the stripper
section 5250.
[0032] In this particular embodiment, liquid components 5600 are drawn from
the bottom of
the column and introduced into the stripper section 5250 in the feed 5100 or
to the feed tray
5120 by means of, for example, a throttle valve or pump 5650. A condenser 5700
is
provided at the top of the rectifying section, which receives a supply of
cooling water and
yields a product, 5750, rich in lighter products and a reflux stream, 5800
which is redirected
to the column into the rectifying section. The composition exiting the
condenser can
include, or consist of primarily the light, low boiling components of the feed
5100.
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[0033] In one embodiment, end products derived from the methods and systems
of the
presently disclosed subject matter are produced in an industrial scale.
[0034] As noted above, the rectifier section 5500 in operated at a higher
temperature than
the stripping section 5250. Having the stripper section 5250 located, in
vertical proximity,
above the rectifier section 5500 allows the use of one or more heat pipes 5850
to transfer
heat from the rectifier section 5500 to the stripper section 5250 and reduce
the heat load on
the reboiler. Thus, in one embodiment of the presently disclosed subject
matter, the system
includes at least one heat pipe traversing between at least a portion of the
rectifier section
and at least a portion of the stripper section to transfer heat from the
rectifier section to the
stripper section.
[0035] The heat duty of the condenser 5700 as well as the reboiler 5300 is
significantly
reduced and a significantly higher energy efficiency is achieved. Essentially,
the liquid
reflux in the rectifier is generated not only by any heat removal at condenser
but by transfer
of heat from the rectifier section to the stripper section.
[0036] The heat pipe 5850 can be oriented substantially perpendicular to a
base of the
rectifier section, as shown in Figure 5, to direct condensate inside the heat
pipe 5800 to the
rectifier section via gravity. The system 5000 can be further provided with at
least one
hollow distillation tray 5900, 5950 located at least one end of the heat pipe.
Alternatively,
as shown in Figure 5, the system can include, for example, two hollow
distillation trays
5900, 5950 that are located on both ends of the heat pipe. The hollow
distillation trays
5900, 5950 can be further provided with fins (not shown) to enhance the heat
transfer area to
and from the heat pipe.
[0037] Condensate inside the heat pipe returns by gravity to the hotter
rectifier section 5500
at the bottom. Gravity driven heat pipes have a larger carrying capacity, as
compared to
wick driven heat pipes such as the heat pipes shown in Figure 4.
[0038] It should be noted that the features summarized in Figure 5 are
according to only
one, non-limiting embodiment. For example, solely for purposes of clarity,
only one heat
pipe is shown in Figure 5. In other embodiments, multiple heat pipes are
provided from
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several or all of the stages (e.g., trays) of the distillation operation, more
particularly, from
stages of the rectifier section to corresponding trays of the stripper
section. Furthermore,
multiple heat pipes can be used even between a single set of trays. The use of
one or more
heat pipes is well within the scope of the present invention.
[0039] The compression provided by the compressor 5150 results in a higher
temperature in
the rectifier section 5500. Heat is transferred from the rectifier section
5500 to the stripping
section 5250 via one or more heat pipes. This heat transfer reduces and/or
eliminates the
heat discharged at the condenser. Furthermore, the heat duty of the reboiler
5300 at the
bottom of the stripping section 5250 is reduced, thus resulting in an overall
improvement in
exergetic efficiency (e.g., up to and exceeding 50%).
[0040] The heat pipe in the rectification section 5950 acts as an inter-
condenser, with the
heat pipe in the stripping section 5900 acting as an inter-reboiler. The
working fluid inside
the heat pipe 5850 condenses in the stripping section 5900 and vaporizes in
the rectification
section 5950, which transfers heat from the rectifier section to the stripper
selection. When
this heat transfer occurs, process liquid (the material being distilled) in
the stripping section
is vaporized and process vapor in the rectification section is condensed.
Based on the design
of the representative embodiment shown in Figure 5 or Figure 6, the stream
providing liquid
reflux functionality is formed as the heat pipe working fluid condenses in
going from the
warmer rectifier section to the cooler stripper section, and the working fluid
flows back to
the rectifier section via gravity. The amount of heat pipe heat transfer is
set by the design of
the heat pipe including the choice of working fluid, the temperature
differential, the working
fluid pressure level, the physical layout including surface area of both heat
transfer sections
and the gravity driving force. The heat pipe design determines the amount of
inter-
condenser generated reflux and inter-reboiler generated vaporization.
[0041] While the presently disclosed subject matter has been described, merely
for purposes
of convenience, in terms of a trayed distillation column, it is equally
applicable to a packed
tower. For example, packed towers can be preferred due to pressure drop
considerations in
situations involving debottlenecking of distillation units. Also packed towers
may offer
more capacity to compensate for the lost area if the heat pipe is installed
internal to the
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column. A packed rectification section with a lower pressure drop will also
allow a lower
compression ratio for the compression of the stripper section overhead to feed
the
rectification section. Heat pipes can be used, for example, to transfer heat
from different
sections of the rectifier to corresponding sections of the stripper. A
corresponding section
would be a section that maintains the same delta temperature between the
rectification
section inter-condenser and the stripping section inter-reboiler. This means
that an upper
inter-condenser would transfer heat to an upper inter-reboiler and a lower
inter-condenser
would transfer heat to a lower inter reboiler as shown in the system 6000 in
Figure 6. These
heat pipes can have, according to one non-limiting embodiment, heat exchangers
with
radially extending fins on both ends of the heat pipe.
[0042] The presently disclosed subject matter, such as the embodiment shown in
Figure 5 or
Figure 6, provides a more practical column configuration where, unlike
conventional
distillation, the rectifier section is vertically below the stripper section.
Heat transport from
the rectifier section 6500 to the stripper section 6250 can be achieved using
one or more heat
pipes, and the heat is transferred mostly in the axial direction. The vertical
configuration
allows gravitational force to return the condensate in the heat pipe from the
stripper section
to the rectifier section below. Heat integration is achieved in a single
column, making it
easier to retrofit existing columns and reducing the plot area that would be
needed for a
second column. Figure 6 illustrates an embodiment of the present invention
using external
heat pipes in a thermo siphon orientation with a vapor riser 6851 and liquid
return 6852,
which allows the heat pipe working fluid to segregate and help avoid flooding.
The riser
6851 and the return 6852 are operatively coupled to internal heat transfer
surfaces 6853.
The internal heat transfer surfaces 6853 can be a hollow distillation tray, a
structural packing
in a plate or frame type configuration or any other suitable heat transfer
device that promotes
heat transfer without restricting column capacity. The same concept can also
be achieved
with external heat pipe with a single connection with countercurrent vapor and
liquid flow
provided the heat pipe is sized adequately to avoid flooding.
[0043] Operating conditions for the systems and methods of the presently
disclosed subject
matter can be determined by a person of ordinary skill in the art. Further
insight can be
CA 02813892 2013-04-05
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obtained from, for example, Internal heat integration - the key to an energy-
conserving
distillation column. Z. Olujic, F. Fakhri, A de Rijke, F de Graauw and PJ
Jansens, J of
Chemical Technology and Biotechnology, 78, page 241-248 (online 2003);
Internal versus
External Heat Integration. Operational and Economic Analysis. J. P. Schmal, H.
J. Van Der
Kooi, A. De. Rijke, Z. Olujic and P. J. Jansens, Trans IChemE, Part A,
Chemical
Engineering Research and Design, 2006, 84, page 374-380; A new approach to the
design of
internally heat integrated tray distillation columns. M. Gadalla, Z. Olujic,
A. de Rijke and J.
P. Jansens, European Symposium on Computer Aided Process Engineering, 15: 805-
810; A
thermo-hydraulic approach to conceptual design of an internally heat-
integrated distillation
column (i-HIDiC), M. Gadalla, L. Jimenez, Z. Olujic and P. J. Jansens,
Computers and
Chemical Engineering (2006), doi : 10.1016/j . comp chemeng .2006.11 .006; and
Conceptual
design of an internally heat integrated propylene-propane splitter, Z. Olujic,
L.Sun, A. de
Rijke, P. J. Jansens, Energy 31(2006) 3083-3096. Each of these references is
hereby
incorporated by reference in their entirety.
* * *
[0044] The present invention is not to be limited in scope by the specific
embodiments
described herein. Indeed, various modifications of the invention in addition
to those
described herein will become apparent to those skilled in the art from the
foregoing
description and the accompanying figures. Such modifications are intended to
fall within
the scope of the appended claims.
[0045] It is further to be understood that all values are approximate, and are
provided for
description.
[0046] Patents, patent applications, publications, product descriptions, and
protocols are
cited throughout this application, the disclosures of each is incorporated
herein by reference
in its entirety for all purposes.
* * *
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