Structured packing element and a mass and heat transfer process using such packing element

The present invention provides for a structured packing element, the element being corrugated with corrugations which form alternating peaks and troughs across the element, the corrugations having a longitudinal axis, the element having plural portions of first fluting at an angle between 0.degree. and 180.degree. to the longitudinal axis of the corrugations and plural portions of second fluting at an angle between 0.degree. and 180.degree. to the longitudinal axis of the corrugations, the fluting of the first portions being at an angle greater than zero to the fluting of the second portions, the respective first and second portions alternating both laterally and longitudinally of the element with respect to each other. The element preferably has a plurality of holes through the element. The foregoing structured packing is suited for use in processes requiring a contact device for accomplishing mass and/or heat transfer. The foregoing structured packing is particularly suited for a cryogenic air separation process comprising contacting vapor and liquid countercurrently in at least one distillation column containing at least one mass transfer zone wherein liquid-vapor contact is established by at least one structured packing element.

FIELD OF THE INVENTION 
The present invention relates to structured packing. The structured packing 
has particular application in exchange columns, especially in cryogenic 
air separation processes, though it may also be used in heat exchangers 
for example. 
BACKGROUND OF THE INVENTION 
In many processes, such as distillation or direct contact cooling, it is 
advantageous to use structured packing to promote heat and mass transfer 
between liquid and vapor streams which flow countercurrently to each other 
inside a column. Structured packing offers the benefit of high efficiency 
for heat and mass transfer combined with low pressure drop, when it is 
compared with dumped or random packing or with distillation trays. The 
most commonly used structured packing consists of corrugated sheets of 
metal or plastics foil or corrugated mesh cloths stacked vertically. These 
foils have various forms of apertures and/or surface roughening features 
aimed at improving the heat and mass transfer efficiency. While there are 
many types of structured packing described in the prior art, some of which 
are discussed below, they have evolved from a variety of applications and 
most have not been developed or optimized specifically for cryogenic 
separation processes, such as those used for separating the components of 
air. 
U.S. Pat. No. 4,296,050 (Meier) describes the use of the combination of 
apertures with fluting or grooves in a structured packing. The fluting 
runs at an angle of 15.degree.-90.degree. to the vertical, in a direction 
generally opposed to that of the corrugations, which run at an angle of 
15.degree.-60.degree. to the vertical. The wavelength of the fluting is in 
the range of 0.3 to 3.0 mm. The packing has widespread application in a 
variety of heat and mass transfer processes. 
U.S. Pat. No. 4,186,159 (Huber) discloses a structured packing having 
alternating bands of fluted and unfluted (plain) regions which run 
horizontally across the packing when it is viewed in its intended 
orientation within the column. The extent of these bands is at least 5 mm. 
The open area is specified to be 5-20%. 
U.S. Pat. No. 4,455,339 (Meier) describes the use of alternating corrugated 
and uncorrugated portions within each sheet of structured packing. The 
liquid acceleration, which would occur in the uncorrugated portions, is 
claimed to improve mass transfer performance. 
U.S. Pat. No. 4,597,916 and U.S. Pat. No. 4,604,247 (Chen et al.) describe 
the use of crisscrossing patterns produced by expanded metal. They also 
show the use of perforations in combination with the crisscrossing 
patterns or horizontal slits. The use of perforated sheets alternating 
with corrugated sheets, both with a variety of holes and features, is also 
disclosed. 
EP-A-337150 (Lockett et al.) describes the use of especially deep fluting 
which is said to improve the mass transfer performance due to increased 
liquid hold up and better spreading. 
U.S. Pat. No. 4,981,621 (Pluss) describes the use of crisscrossing texture 
without holes, which improve the liquid spreading. 
U.S. Pat. No. 5,132,056 (Lockett et al.) describes the use of edge 
modification to improve wetting, especially under turndown conditions. 
U.S. Pat. No. 5,454,988 (Maeda) discloses the use of special fluting in a 
corrugated packing with no holes. The fluting generally runs in a 
horizontal direction and is more square-wave like than sine-wave like in 
cross-section. The fluting also has a meandering flow path for laterally 
spreading liquid. 
It is also well-known in the prior art that mesh type packing helps spread 
liquid efficiently and gives good mass transfer performance, but mesh type 
of packing is much more expensive than most of the foil type packing 
described above. 
An object of the present invention is to provide a specific structure that 
shows high performance characteristics for cryogenic applications such as 
those used in air separation. 
A further object of the present invention is to generalize the specific 
structure such that it also shows a high performance in other, and 
preferably all, heat and mass transfer applications. 
SUMMARY OF THE INVENTION 
According to a first aspect of the present invention, there is provided a 
structured packing element, the element being corrugated with corrugations 
which form alternating peaks and troughs across the element, the 
corrugations having a longitudinal axis, the element having plural 
portions of first fluting at an angle between 0.degree. and 180.degree. to 
the longitudinal axis of the corrugations and plural portions of second 
fluting at an angle between 0.degree. and 180.degree. to the longitudinal 
axis of the corrugations, the fluting of the first portions being at an 
angle greater than zero to the fluting of the second portions, the 
respective first and second portions alternating both laterally and 
longitudinally of the element with respect to each other. 
The element preferably has a plurality of holes through the element. The 
open area of the element may be in the range of 5 to 20%, and preferably 
in the range of 8% to 12%, of the total area of the element. 
Said portions may be quadrangles. Said portions are preferably square. 
The angle between the fluting of the first portions and the fluting of the 
second portions of the developed element as seen in elevation is 
preferably in the range of 30.degree. to 150.degree. , more preferably in 
the range of 80.degree. to 100.degree. , and most preferably substantially 
90.degree. . 
According to a second aspect of the present invention, there is provided an 
exchange column for exchanging heat and/or mass between a first phase and 
a second phase, the exchanger comprising a plurality of packing elements, 
each element being corrugated with corrugations which form alternating 
peaks and troughs across the element, the corrugations having a 
longitudinal axis, each element being corrugated with corrugations which 
form alternating peaks and troughs across the element, the corrugations 
having a longitudinal axis, the element having plural portions of first 
fluting at an angle between 0.degree. and 180.degree. to the longitudinal 
axis of the corrugations and plural portions of second fluting at an angle 
between 0.degree. and 180.degree. to the longitudinal axis of the 
corrugations, the fluting of the first portions being at an angle greater 
than zero to the fluting of the second portions, the respective first and 
second portions alternating both laterally and longitudinally of the 
element with respect to each other. 
The elements may be packed substantially vertically with the first fluting 
forming an angle of between 0.degree. and 45.degree. , preferably between 
0.degree. and 30.degree. and more preferably between 0.degree. and 
10.degree. , with the horizontal. The second fluting may form an angle 
substantially between 0.degree. and 45.degree. , preferably between 
0.degree. and 30.degree. and more preferably between 0.degree. and 
10.degree. , with the vertical. Most preferably, the elements are packed 
substantially vertically, the first fluting being substantially horizontal 
and the second fluting being substantially vertical. 
The longitudinal axis of the corrugations may be at an angle substantially 
between 20.degree. and 70.degree. , preferably between 30.degree. and 
60.degree. and most preferably at an angle of substantially 45.degree. 
with the horizontal. 
Each element in the exchanger may have a plurality of holes through the 
element. 
In another aspect, the invention also provides a process for cryogenic air 
separation comprising contacting vapor and liquid countercurrently in at 
least one distillation column containing at least one mass transfer zone 
wherein liquid-vapor contact is established by at least one structured 
packing element, the element being corrugated with corrugations which form 
alternating peaks and troughs across the element, the corrugations having 
a longitudinal axis, the element having plural portions of first fluting 
at an angle between 0.degree. and 180.degree. to the longitudinal axis of 
the corrugations and plural portions of second fluting at an angle between 
0.degree. and 180.degree. to the longitudinal axis of the corrugations, 
the fluting of the first portions being at an angle greater than zero to 
the fluting of the second portions, the respective first and second 
portions alternating both laterally and longitudinally of the element with 
respect to each other. 
The present invention provides a corrugated structured packing element that 
shows high performance characteristics for heat and mass transfer 
applications. 
In use, in a preferred embodiment, the adjacent sheets of the packing 
elements are stacked vertically, the corrugations running in a 
crisscrossing and opposing fashion; the sheets of the packing elements 
build up a layer which covers a cylindrical section of a packed tower, 
which itself is configured as a tall vertical cylinder; the many layers 
that constitute the packed section of a given column or tower are rotated 
relative to one another about the column axis which is generally vertical; 
and, vapor and liquid are fed via distributors and preferably flow in 
roughly countercurrent directions.

DETAILED DESCRIPTION OF THE INVENTION 
In the drawings, generally only a representative portion of a packing 
element 1 is shown. 
The element 1 is a sheet-like structure and is provided with regularly 
spaced, relatively deep, corrugations 2 which form peaks 3 and troughs 4 
in the element 1. It will be appreciated that a peak viewed from one side 
of the element 1 will be a trough when viewed from the other side of the 
element 1 and vice versa. In use in a cryogenic air separation tower for 
example, the element 1 is packed vertically as shown in FIGS. 1 and 2 and 
as will be discussed further below. The corrugations 2 are substantially 
parallel and have a longitudinal axis 21 which is at an angle 8 to the 
horizontal. The corrugations 2 are generally sinusoidal. However, 
different profiles for the corrugations 2 are possible, such as, for 
example, pleated, square wave, triangular wave, and sawtooth wave, or the 
corrugations may be composed of elliptical or parabolic profiled segments, 
for example. 
The element 1 is provided with a particular surface texture which improves 
the performance of the element compared to the known packing elements. In 
particular, the element 1 has alternating portions of what shall be termed 
herein "fluting", the fluting providing a bidirectional surface texture in 
which there are portions of generally horizontal fluting 5 and portions of 
generally vertical fluting 6 in the vertically packed corrugated element 
1. The fluting 5,6 is formed by relatively fine grooves 7,8 or corrugation 
or striation of the surface of the element 1 in a manner which in itself 
is known, e.g. by stamping or rolling with a suitable die. 
As will be seen from the drawings, the portions 5,6 of horizontal and 
vertical fluting alternate both laterally and longitudinally of the sheet 
element 1 and the respective portions are preferably square. Thus, each 
square portion of horizontal fluting 5 is surrounded on each side by 
square portions of vertical fluting 6 and vice versa. This gives the 
surface of the element 1 an appearance which is similar to a basket weave. 
It will be appreciated that the portions of horizontal and vertical 
fluting 5,6 need not be square and may be rectangular instead, for 
example. 
The element 1 is provided with a plurality of through holes 9 in an array 
across the element 1. The through holes 9 may be in a regular array or may 
be distributed randomly across the element 1. 
Below is discussed some possible ranges of dimensions for the element 1 and 
its component features. 
The surface area density of the element 1 is preferably in the range of 
250-1500 m.sup.2 /m.sup.3 with a most preferred range of 500-1000 m.sup.2 
/m.sup.3. This can be realized through many different combinations of P, H 
and r, P being the "wavelength" or peak-to-peak separation of the 
corrugations 2, H being the amplitude or peak-to-peak height of the peaks 
3, and r being the radius of curvature of a peak 3. 
The corrugations 2 run in a generally sinusoidal wave pattern. The 
corrugations can be manufactured with curved peaks 3 and straight portions 
in between the peaks 3. The ratio of the corrugation wavelength to the 
corrugation radius of curvature is in the range of 5-30, with a preferred 
range of 10-25. 
The thickness of the sheet is preferably in the range of 0.05-1.0 mm with a 
most preferred range of 0.10-0.25 mm. 
The open area of the element 1 is preferably in the range of 5-20%, with a 
most preferred range of 8-12%, of the total area of the element 1. 
The holes 9 in the packing are circles with a diameter in the range of 1-5 
mm, with a preferred range of 2-4 mm. Alternatively, the holes in the 
packing are not circular, but their equivalent diameters--calculated as 
four times the area divided by the perimeter--are in the range mentioned 
above for circular holes. 
The width of the portions 5,6 of horizontal and vertical fine grooves 7,8 
are in the range of 2 to 20 mm each, with a preferred range of 5-10 mm. 
The portions 5,6 need not be square and may be rectangular. 
The wavelength of the fine grooves 7,8 of the surface texture forming the 
portions of horizontal and vertical fluting 5,6 is in the range of 0.5-5 
mm with a preferred range of 1-3 mm. The pitches or wavelength in the 
horizontal and vertical portions 5,6 can be different. 
The peak-to-peak height of the surface texture is in the range of 0.25-1.20 
mm with a preferred range of 0.25-0.50 mm. The peak-to-peak height can be 
different in the horizontal and vertical portions 5,6. 
The corrugation angle with the horizontal (.theta. in FIG. 1) is in the 
range of 20.degree.-70.degree. with a preferred range of 
30.degree.-60.degree. and is most preferably 45.degree. . 
The included surface texture angle of the developed element 1 is in the 
range of 30.degree.-150.degree. with a preferred range of 
80.degree.-100.degree. , and most preferably 90.degree. . 
The three features of the corrugations, holes and surface texture are 
arranged in such a manner that repeating patterns do not occur. Successive 
corrugations look different and the combinations are random. This is 
preferred. Alternatively, the three features of the corrugations, holes 
and surface texture are arranged in such a manner that repeating patterns 
do occur. Successive corrugations look similar, with the patterns 
repeating after one or more corrugations. 
The material of the packing element 1 is stainless steel, monel, brass, 
aluminum, copper or their alloys or plastics, or any other suitable 
material. 
The corrugations 2 and surface texture or fluting 5,6,7,8 are generally 
manufactured by a process such as rolling or pressing which determines the 
exact nature of the waves of each feature produced. They are generally 
sinusoidal in nature, but they need not be exactly sinusoidal. 
Alternatively, the surface texture may be produced by other well-known 
manufacturing techniques such as milling, cutting or grinding. 
The structured packing element 1 of the present invention can be used in a 
mass and/or heat transfer process such as distillation or direct contact 
cooling. A section of a column or tower is packed with the segments of the 
element, stacked vertically and with means to distribute liquid uniformly 
from above and vapor or gas uniformly from below. The liquid and vapor or 
gas flow under the influence of gravity in roughly countercurrent 
directions to each other. In many cases, it is advantageous to use a 
column with its axis along the vertical direction, but the present packing 
element 1 may also be used where the column axis is not vertical, but is 
instead in a horizontal or some other intermediate orientation. However, 
the relationship between the packing layers, the liquid and vapor flow, 
and the distributors would have to be maintained as before. 
Specifically, it is advantageous to use the present packing element 1 for a 
gas-liquid or vapor-liquid contacting device, for which the ability to wet 
the packing and to spread and remix the liquid are critical. 
More specifically, it is advantageous to use the present packing element 1 
for separation processes that employ cryogenic distillation. Examples of 
cryogenic distillation include separation of the components of air by 
using one or more contacting devices such as columns. The current packing 
element 1 may be used in one or more sections of these contacting devices. 
Also, it is advantageous to use the present packing element 1 for direct 
contact cooling applications. An example of this process is a tower that 
cools hot or warm air with cooler water, by direct contact between the 
phases wherein both heat and mass transfer take place. The element 1, 
though without through holes 9, may also be used in a heat exchanger in 
which the hot and cold phases exchange heat without coming into contact 
with each other. 
The present invention also includes a process for exchanging mass and/or 
heat between two liquids, comprising contacting said liquids in at least 
one exchange column wherein liquid-liquid contact is established by at 
least one structured packing element, the element being corrugated with 
corrugations which form alternating peaks and troughs across the element, 
the corrugations having a longitudinal axis, the element having plural 
portions of first fluting at an angle between 0.degree. and 180.degree. to 
the longitudinal axis of the corrugations and plural portions of second 
fluting at an angle between 0.degree. and 180.degree. to the longitudinal 
axis of the corrugations, the fluting of the first portions being at an 
angle greater than zero to the fluting of the second portions, the 
respective first and second portions alternating both laterally and 
longitudinally of the element with respect to each other, wherein one of 
said liquids preferentially wets said packing element. Said liquids may 
flow co-currently or counter-currently in the exchange column. 
The present invention has been described with particular reference to the 
examples illustrated. However, it will be appreciated that variations and 
modifications may be made to the example described within the scope of the 
present invention.