Title of Invention

"AN APPARATUS FOR DISTRIBUTING DOWNFLOWING LIQUID IN A PACKED COLUMN"

Abstract An apparatus for distributing downflowing liquid on a packed bed in a vapour-liquid contacting column is disclosed. The apparatus comprising of at least a predistributor unit (12), a plurality of lower distributor troughs (13) and connected to said predistributor unit (12) through connecting pipes (14), a feed pipe (6) connected to said predistributor unit (12) to allow said liquid to enter said predistributor unit (12) for initial distribution and thereafter enter the lower distribution troughs (13) through connecting pipes (14), said distributor unit (12) consisting of a main chamber (15) with a bottom plate (16), a perforated chamber (17) connected to the bottom plate (16), primary drip tubes (18) connected to the bottom plate (16) outside the perforated chamber (17), said primary drip tubes (18) extending above and below the bottom plate (16), said primary drip tubes (18) being connected to said connecting pipes (14) below the bottom plate (16).
Full Text A LIQUID DISTRIBUTOR FOR PACKED COLUMN
Field of invention
The present invention relates to an improved two stage liquid distributor for packed
columns
Background of the Invention
Liquid distributor is an integral part the packed column. Performance of packed column depends largely on the efficiency of the liquid distributor. Following aspects are important for designing liquid distributor:
- Number of pour points per unit area Turndown of liquid rate Minimum liquid flow rate Resistance to fouling
For new generation random and structured packing, high pour point density improves the performance. To economise the design and engineering as well to fulfill the process requirement high turndown distributors are important. For systems operating under vacuum, distributors are required to handle low liquid load. Resistance to fouling offers wider range of applicability reduces maintenance requirements.
The invention relates to an improved design of liquid distributor, which offers high pour point density, handles low liquid load, operates at high turndown ratio and is resistant to fouling. Prior Knowledge
Packed columns are used for vapor-liquid contacting in various operations, such as distillation, fractionation, absorption, stripping and heat exchange. Packings are either random packings or structured packings. The columns are usually operated with counter-current flows of liquid and gas. Different applications indicate the use of differing packing arrangements and differing means of distributing the liquid onto the packing. For example, columns with one packed bed require one device for distributing the liquid onto the packing. In these columns the device is mounted above the packed bed and is known as a liquid distributor. Column having more than one packed bed require additional distributing devices, which are positioned between the packed sections. The additional distributing devices are known as liquid redistributors.
Two general types of conventional liquid distributors are commercially available. The first is the orifice type, which is characterised by head-driven flow through orifices,

tubes, or nozzles, located in the bottom of a pan, trough, or pipe. Examples of this include distributors having orifice plates, perforated pipes, or spray nozzles. Other conventional liquid distributors are of the overflow weir type. These distributors are characterized by flow through weirs cut into the tops or sides of tubes fitted in the bottom of a pan, or weirs cut into the wall of troughs laid out in a ladder pattern. Liquid from distributor falls onto the packing in the column and vapor entering the bottom of the column rises up through the packing, where it contacts the downflowing liquid. Drawbacks connected with hitherto Known Processes/Devices
A number of problems are encountered in the use of these known distributing devices. First of all, the function of the distributors and redistributors in vapor-liquid contact operations is to ensure uniform liquid distribution across the cross-section of the tower. Uneven liquid distribution is referred to as maldistribution. Maldistribution results in a reduced transfer of mass and/or heat between the vapor and liquid phases, which consequently can result in poor separation of components in the column. Maidistribution is a particularly common problem when the conventionally used distributors are used in packed columns having large diameters. The problem is particularly acute in operations such as vacuum fractionation where the liquid loading per cross-sectional area of the column is low. In the larger columns the longer span of the weir-type or orifice-type system makes it much more difficult to maintain uniform level throughout, particularly since most distributor systems are not precisely level even when first installed. Later, with prolonged operation, the distributors become even further out of level. In a system, which is not level, the liquid collects at the lower end of the trough or tube and the higher end is thus starved for liquid.
A second problem encountered is that of fouling. While this is generally not a problem with the weir-type devices, it can present major difficulties in an orifice-type system. This is particularly so in processes such as vacuum fractionation and other operations, which require a low flow rate of liquid and orifices are made very small to maintain high pour point density. Solids in the liquid often plug these orifices, requiring time consuming and expensive servicing, and resulting in poor operation while plugged.
Finally there is often a problem in efficient use of space. The turndown/turnup ratio i.e., the ratio between the minimum and maximum liquid flow rates necessitates additional liquid head. The head required at maximum flow is equal to the head at minimum flow multiplied by the square of the turndown/turnup ratio. Thus, for example, if a 2 inch head is to be maintained at minimum flow and there is a turndown/turnup ratio of

3: 1, the head required at maximum flow would be 18 inches. However, because of this relationship serious problems arise particularly as to the redistributors, since in a packed column even relatively small reductions in packed space can significantly reduce column efficiency, and it is not always possible to simply enlarge the column. Solutions or improvements to some of the above noted problems have been provided by the invention described in U.S. Pat. No. 4,472,325, U.S. Pat. No. 4,808,350 and U.S. Pat. No. 5,061,407. Objects of the invention
The main objective of the invention is to provide a novel design method for liquid distributor for use in packed columns. The improved design of liquid distributor offers high pour point density, handles low liquid load, operates at high turndown ratio and is resistant to fouling. Summary of Invention
The present invention is an improvement in the liquid distributor for distributing downflowing liquid on packing in a vapor-liquid contacting column. Principally the apparatus distributes liquid in two stages and accordingly it comprises of one predistributor unit and a number of lower distributor troughs.
The predistributor unit is a rectangular open-top chamber with a bottom plate and sidewalls. Another smaller rectangular chamber made of perforated vertical walls is welded at the centre of the bigger chamber. The downflowing liquid enters the smaller perforated chamber and flows to the bigger chamber through the perforated walls and thereby the paniculate matters, present in the liquid which are responsible for fouling get arrested in the smaller chamber. A number of drip tubes are fitted in annular portion of the two chambers. These are primary drip tubes. The primary drip tubes are tubular members, which are welded to the plate and extend above and below the plate. Above the plate the drip tubes are vertical and below the plate these are partly vertical and partly angled depending on the location of lower distributor troughs to which these are connected. Above the plate each primary drip tube has one orifice at lower level and two vertical slots near the top end. The predistributor unit is mounted horizontally inside the column above the packed bed, such that it is oriented above the lower distributor troughs. Each one of the primary drip tubes is in liquid connection with one of the lower distributor troughs, wherein the downflowing liquid enters the predistributor unit, flows downwardly through the primary drip tubes therein into the lower distributor troughs, and then flows downwardly onto the packed bed.
The downflowing liquid is distributed uniformly across the packed bed through the drip tubes in the lower distributor troughs. These are secondary drip tubes. Each primary drip tube is connected to one lower distributor trough. Each lower distributor trough comprises of a bottom plate and vertical wall members, the wall members are welded along the edge of the bottom plate to form an open-top chamber. At the centre of each chamber there is circular receiving pan welded to the bottom plate. The receiving pan has a number of equispaced circular holes in its vertical wall. Each primary drip tube from the predistributor is extended inside the receiving pan. In the lower distributor troughs, a number of secondary drip tubes are installed. These drip tubes are either mounted on outer surface of the vertical walls or welded to the bottom plates. These drip tubes are tubular members of triangular cross-section, which extend above and below the plate. Above the plate the drip tubes are vertical and below the plate these are made partly vertical and partly angled in order to maintain uniform distribution of drip points over the packed bed. The secondary drip tube with triangular cross-section is made of a strip of flat plate on which a 90°-angle piece is welded. For the wall mounted drip tubes, the strips of flat plate are replaced by wall members of the lower distributor troughs. Above the plate each secondary drip tube has a triangular notch at lower level and an orifice at upper level. Each secondary drip tube is extended to a predefined location such that the distribution of drip points follows a certain pattern and is uniform over the packed bed. The lower distributor troughs are sized in such a way that the intermediate gaps provide the space for vapour to rise
Thus, the apparatus for distributing downflowing liquid on a packed bed in a vapour-liquid contacting column consists of one predistributor unit and a number of lower distributor troughs. The liquid is fed to the predistributor unit through a feed pipe. After primary distribution in the predistributor unit, the liquid flows down to the lower distributor troughs through the connecting pipes. The final distribution of liquid on the packed bed is achieved in the lower distributor troughs. The lower distributor troughs are uniquely positioned on a support grid at the lowest level above the packed bed. The primary distributor unit is supported on the lower troughs using support cleats. The support grid with lower troughs and predistributor unit on it hangs from a retainer grid by a number of tie rods. The retainer grid rests on a support ring welded to the column wall. The whole assembly of the liquid distributor is positioned in such a way inside a column that it receives liquid at a single point from the feed pipe and distribute it uniformly over
the entire cross-section of the packed bed through a large number of drip points, oriented
in a specific regular pattern.
The predistributor unit consists of a main chamber, a perforated chamber and a number of primary drip tubes. The perforated chamber, placed at the centre of the main chamber receives liquid from the feed pipe. As the liquid flows out of the perforated chamber through the perforations any dirty material contained in the feed liquid gets trapped inside the chamber and only the clean liquid flows to the primary drip tubes. This eliminates the possibility of choking of primary drip tube orifices. The flow through the perforations also dampens the turbulence in liquid and the primary drip tubes receive calm liquid with nearly constant level. This improves the distribution quality of primary drip tubes.
The primary drip tubes in the predistributor unit have orifices through which the liquid flows under normal operating conditions. The governing equation for liquid flow through orifice is : q = C.a(2gh)05 , where q is the flow through orifice, C is orifice coefficient, a is area of orifice, h is liquid head above orifice and g is acceleration due to gravity. The orifice is, therefore less sensitive to level fluctuation and gives a very good uniform distribution. Since in the present distributor primary distribution is through orifices, the uniformity of distribution is very good at this level.
In the present apparatus each primary distribution point is connected to a number of secondary distribution points and the ratio of primary to secondary distribution points is a design variable and cane be fixed according to the quality of distribution required. For low liquid rate less number of primary drip tubes are designed to have orifices of reasonably big size to avoid choking. The ratio of primary to secondary distribution points is then adjusted to get the number of secondary distribution points according to the distribution need. By this two tier design adjustment it is possible to handle even very low liquid rate without compromising in distribution requirement. Since uniform distribution is achieved at the predistrubutor level, even there is certain degree of non-uniformity in distribution from the lower distributor troughs, it is confined to that particular trough only and overall uniformity of distribution does not get affected.
The primary drip tubes can also handle additional liquid load under abnormal operating conditions. Excess liquid, which orifices cannot handle, flows through rectangular slots in primary drip tubes. This enables the present liquid distributor to handle wide variation in liquid load.
The lower distributor troughs receive liquid from the predistributor unit through the connecting pipes. The liquid enters the trough the receiving pan. As the liquid flows out of the pan through the oblong openings, the turbulence in liquid is dampened. This eliminates the fluctuation of level in the trough and better distribution quality is achieved through the secondary drip tubes.
The liquid flows through the triangular notches in secondary drip tubes. The governing equation for liquid flow through orifice is : q = C.tan(Φ/2)(2g)0.5h2.5, where q is the flow through triangular notch, C is dimensionless coefficient, Φ is angle at the bottom of the notch, h is liquid level in the notch and g is acceleration due to gravity. The triangular notch can handle wide range of liquid rates and thereby provides large turndown ratio. Whatever variation in liquid load the lower distributor troughs receive, the triangular notches can handle that, maintaining reasonably good quality of distribution. In case the liquid load is more than the operating range of notches, it flows through the orifices above the notches in secondary drip tubes.
Triangular notches are sensitive to fluctuation in liquid level. In case of level fluctuation in lower distributor troughs, the distribution quality is likely to suffer. But since uniform distribution is achieved as predistributor level, the deterioration in distribution quality from a lower distributor trough remains confined to the area of packed bed covered by that trough and overall distribution does not get affected.
Accordingly, the present invention provides an apparatus for distributing downflowing liquid on a packed bed in a vapour-liquid contacting comprising of at least a predistributor unit, a plurality of lower distributor troughs and connected to said predistributor unit through connecting pipes, a feed pipe connected to said predistributor unit to allow said liquid to enter said predistributor unit for initial distribution and thereafter enter the lower distribution troughs through connecting pipes, said distributor unit consisting of a main chamber with a bottom plate, a perforated chamber connected to the bottom plate, primary drip tubes connected to the bottom plate outside the perforated chamber, said primary drip tubes extending above and below the bottom plate, said primary drip tubes being connected to said connecting pipes below the bottom plate. Description of the accompanying drawings
Figure-1 shows column configuration where the location of liquid distributor is shown relative to packed bed and other column internals.
Figure-2 shows the overall assembly of the distributor components inside a column.
Figure-3 shows the relative positions of the predistributor unit and the lower distributor trough.
Figure-4a shows the details of predistributor unit along with the perforated chamber and the primary drip tubes.
Figure-4b shows the details of primary drip tubes.
Figure-5a shows the details of lower distributor trough with receiving pan and secondary drip tubes.
Figure-5b shows the details of secondary drip tubes (type-I). Figure-Sc shows the secondary drip tubes (type-II) Detailed Description
Figure-1 shows the overall assembly of the liquid distributor (1). The distributor (1) is installed in a column (2), above a bed (3) of random or structured packing. During normal operation, gas enters the column through the inlet (4) and flows through the packed bed (3) and the distributor (1) to the outlet (5). Liquid flows from a feed pipe (6) to the distributor (1), through the distributor (1) to the packed bed (3) and through the bed (3) to the liquid outlet (7).
Inside a column (2), the distributor (1) is supported on a support grid (8). The support grid (8) is supported from the retainer grid (9) by a number of tie rods (10). The support grid (9) is fixed to a support ring (11), which is welded to the column (2).
Figure-2 shows the overall assembly of the distributor (1). The distributor consists of predistributor unit (12), lower distributor troughs (13) and the connecting pipes (14). The liquid from the feed pipe (6) enters the predistributor unit (12). After initial distribution the liquid enters the lower distribution troughs (13) through connecting pipes (14). From the lower distributor troughs the liquid is distributed over the packed bed (3)
Figure-3 shows the relative positions of the predistributor unit (12), the lower distributor trough (13) and the connecting pipe (14). The predistributor unit (12) is located above the lower distributor troughs (13). The predistributor (12) receives liquid from the feed pipe (6) and distribute it to the lower distributor troughs (13) through the connecting pipes (14). There is one predistributor unit (12) in the liquid distributor (1). The number of lower distributor troughs (13) is equal to the number of primary distribution points in predistributor unit (12) and each lower distributor trough is connected to each primary distribution point by one connecting pipe (14).
The details of the primary distributor unit (12) are shown in Figure-4a. The primary distributor unit consists of a main chamber made of four side walls (15) and one
bottom plate (16). At the centre of the predistributor unit (12) a perforated chamber (17) is welded to the bottom plate (16). Primary drip tubes (18) are welded to the bottom plate
(16) outside the perforated chamber (17). The primary drip tubes (18) are extended above
and below the bottom plate (16) but above the bottom plate (16) the height of drip tubes
(18) is less than the height of the side walls (15). Below the bottom plate (16) the drip
tubes (18) are connected to the connecting pipes (14).
Figure-4b shows the details of the primary distributor tubes (18). The portion of the primary drip tube (18) above the bottom plate (16) of the predistributor unit (12) has one round orifice (19) and two rectangular slots (20). The round orifice (19) is closer to the bottom plate (16) and the rectangular slots (20) are at the top edge of the primary drip tube (18). The portion of the primary drip tube (18) below the bottom plate (16) is extended to a certain length and is then connected to the connecting pipe (14).
The perforated chamber (17) inside the predisributor unit receives liquid from feed pipe (6). The perforated chamber (17) removes dirt from the liquid and dampens the turbulence in liquid. The liquid flows through the perforations of the perforated chamber
(17) and then flows through the round orifice (19) of primary drip tubes (18) under normal
operating condition. In case the liquid rate is higher than the design range, it flows
additionally through the rectangular slots (20). The liquid is then passed into the
connecting pipe (14) and flow down to the lower distributor troughs (13).
Figure-5a shows the details of lower distributor trough (13). The lower distributor trough (13) consists of side walls (21) and bottom plate (22). At the centre of the trough (13) there is a receiving pan (23) and the connecting pipe (14) terminates inside the receiving pan (23). The receiving pan is a small pipe piece welded to the bottom plate (22) and has oblong openings (31) at the bottom. On the walls of the trough (21) there are a number of triangular notches (24) and corresponding to each notch (24) there is one circular orifice (25). The notches (24) are nearer to the bottom plate and the holes (25) are nearer to the top edge of the walls (21).
Figure-5b shows the details of the secondary drip tubes (type-I) (26). Outside the side walls (21) the notches (24) and the orifices (25) are covered by a triangular channel (27). The channel (27) is extended below the bottom plate (22). Below the bottom plate (22) the open end of the channel (27) is covered by a narrow plate (28). The channel (27) and the plate (28) together form the wall mounted secondary drip tube (type-I) (26).
Figure-Sc shows the details of secondary drip tubes (type-II) (29). A triangular channel (27) is welded on a narrow plate (30) to form the secondary drip tube (type-II)
(29). On the metal plate (30) a triangular notch (24) and a circular orifice (25) are created. The tube (29) is welded to the bottom plate (22). The portion of the tube (29) above the bottom plate (22) has the notch (24) and the orifice (25). The tube (29) is also extended below the bottom plate (22).
The liquid from the predistributor unit (12) flows down to the receiving pan (23) of the lower distributor trough (13) through the primary drip tube (18) and the connecting pipe (14). The receiving pan dampens the liquid turbulence and the liquid flows out of the receiving pan (23) through the oblong openings (31). Under normal operating condition, the liquid flows through the triangular notches (24) of secondary drip tubes : type-I (26) and type-II (29) and gets distributed over the packed bed (3). As such the triangular notch 24) can handle large variation in liquid load. In case the liquid load is even higher, it flows additionally through the orifices (25).













We claim:
1. An apparatus for distributing downflowing liquid on a packed bed in a vapour-liquid contacting comprising of at least a predistributor unit (12), a plurality of lower distributor troughs (13) and connected to said predistributor unit (12) through connecting pipe (14), a feed pipe (6) connected to said predistributor unit (12) to allow said liquid to enter said predistributor unit (12) for initial distribution and thereafter enter the lower distribution troughs (13) through connecting pipes (14), characterized in that said predistributor unit (12) consists of a main chamber (15) with a bottom plate (16), a perforated chamber (17) connected to the bottom plate (16), primary drip tubes (18) connected to the bottom plate (16) outside the perforated chamber (17), said primary drip tubes (18) extending above and below the bottom plate (16), said primary drip tubes (18) being connected to said connecting pipes (14) below the bottom plate (16).
2. An apparatus as claimed in claim 1 wherein said primary distributor unit consists of a main chamber made of four side walls (15) and one bottom plate (16).
3. An apparatus as claimed in claim 1 wherein a perforated chamber (17) is connected to the bottom plate (16) at the center of said predistributor unit (12).
4. An apparatus as claimed in claim 3 wherein said primary drip tubes (18) are connected to the bottom plate (16) outside the perforated chamber (17).
5. An apparatus as claimed in claim 4 wherein said primary drip tubes (18) extend above and below said bottom plate (16) but above the bottom plate (16) the height of said drip tubes (18) is less than the height of said side walls (15).
6. An apparatus as claimed in any one preceding claim wherein below the bottom plate (16) the said drip tubes (18) are connected to said connecting pipes (14).
7. An apparatus as claimed in any preceding claim wherein portion of the primary drip tube (18) above the bottom plate (16) of the predistributor unit (12) has one round orifice (19) and two rectangular slots (20).
8. An apparatus as claimed in claim 7 wherein said round orifice (19) is closer to the bottom plate (16) and the rectangular slots (20) are at the top edge of the primary drip tube (18).
9. An apparatus as claimed in claim 8 wherein the portion is primary drip tube (18) below the bottom plate (16) extends to a certain length and is then connected to the connecting pipe (14).
10. An apparatus as claimed in any preceding claim wherein said lower distributor trough (13) consists of side walls (21) and bottom plate (22).
11. An apparatus as claimed any preceding claim wherein at the center of said trough (13) there is a receiving pan (23), said connecting pipe (14) terminating inside said receiving pan (23).
12. An apparatus as claimed in claim 11 wherein said receiving pan comprises of a small pipe piece welded to the bottom plate (22) and has oblong openings (31) at the bottom.
13. An apparatus as claimed in any preceding claim wherein on the walls of the through (21) there are a number of triangular notches (24) and corresponding to each notch (24) there is one circular orifice (25).
14. An apparatus as claimed in claim 13 wherein said notches (24) are nearer to the bottom plate and said holes (25) are nearer to the top edge of the walls (21).
15. An apparatus as claimed in any preceding claim wherein outside the side walls (21) the notches (24) and the orifices (25) are covered by a triangular channel
(27).
16. An apparatus as claimed in claim 15 wherein said channel (27) extends below the bottom plate (22).
17. An apparatus as claimed in claim 16 wherein below the bottom plate (22) the open end of the channel (27) is covered by a narrow plate (28), the channel (27) and the plate (28) together forming the wall mounted secondary drip tube (type-I) (26).
18. An apparatus as claimed in any preceding claim wherein a triangular channel (27) is welded on narrow plate (30) to form the secondary drip tube (type-II) (29).
19. An apparatus as claimed in claim 19 wherein on the metal plate (30) a triangular notch (24) and a circular orifice (25) are created.
20. An apparatus as claimed in claim 18 or 19 wherein the tube (29) is welded to the bottom plate (22), the portion of the tube (29) above the bottom plate (22) has the notch (24) and the orifice (25), sad tube (29) also extending below said bottom plate (22).
21. An apparatus for distributing downflowing liquid on a packed bed in a vapourliquid contacting substantially as herein described with reference to the accompanying drawings.

Documents:

118-DEL-2002-Abstract-(08-06-2010).pdf

118-del-2002-abstract.pdf

118-DEL-2002-Claims-(08-06-2010)].pdf

118-del-2002-claims.pdf

118-DEL-2002-Correspondence-Others-(07-05-2010).pdf

118-DEL-2002-Correspondence-Others-(08-06-2010).pdf

118-del-2002-correspondence-others.pdf

118-del-2002-correspondence-po.pdf

118-del-2002-description (complete).pdf

118-del-2002-description (provisional).pdf

118-del-2002-drawings.pdf

118-DEL-2002-Form-1-(07-05-2010).pdf

118-DEL-2002-Form-1-(08-06-2010).pdf

118-del-2002-form-1.pdf

118-del-2002-form-18.pdf

118-DEL-2002-Form-2-(08-06-2010).pdf

118-del-2002-form-2.pdf

118-del-2002-form-3.pdf

118-del-2002-form-4.pdf

118-del-2002-form-5.pdf

118-DEL-2002-GPA-(07-05-2010).pdf

118-DEL-2002-Petition-137-(07-05-2010).pdf


Patent Number 241534
Indian Patent Application Number 118/DEL/2002
PG Journal Number 29/2010
Publication Date 16-Jul-2010
Grant Date 12-Jul-2010
Date of Filing 15-Feb-2002
Name of Patentee ENGINEERS INDIA LIMITED
Applicant Address ENGINEERS INDIA BHAWAN, 1, BHIKAJI CAMA PLACE, R K PURAM, RING ROAD, NEW DELHI 110066
Inventors:
# Inventor's Name Inventor's Address
1 BANIK, SUKUMAR, R&D CENTER EIL, SECTOR 16 GURGAON-122001 HARYANA
2 SARKAR TARUN KUMAR R&D CENTER EIL, SECTOR 16 GURGAON-122001 HARYANA
3 BHASKAR, THALLAPALLI R&D CENTER EIL, SECTOR 16 GURGAON-122001 HARYANA
4 MAJUMDAR KAUSHIK, R&D CENTER EIL, SECTOR 16 GURGAON-122001 HARYANA
PCT International Classification Number B05B 7/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA