Distillation Column Case Study

8/16/2019 Distillation Column Case Study

1/26

HYDRAULIC STUDY OF ULE

FRACTIONATION PLANT DISTILLATION

COLUMNS (GLP-2) UNDER OPERATIONAL

OCC SCENARIO

With the commissioning of the Occidente CryogenicComplex (OCC), the Ulé Fractionation Plant (GLP-2) willreceive from the extraction train of this complex, NGL atdifferent conditions of composition (Lean, Average andRich NGL), which generates the necessity of definingthe highest NGL feed flow rate that plant can handle.

From this point of view, it is required a hydraulic capacity

study of each column in order to avoid operationalproblems such as flooding or weeping, and therebyensure optimal operation of fractionation columns, meetquality product requirements demanded by the clientand ensure the operational availability of fractionationtowers.

Feed flowrates for each of the evaluated scenarios are27.5 MBPD of Lean NGL, 42.8 MBPD of Average NGLand 34.55 MBPD of Rich NGL.

!"#"

Autor: MSc. Roberto Paz

Gerencia de Procesamiento de Gas Occidente


2/26

!

Hydraulic Study Of Ule Fractionation Plant Distillation Columns (Glp-2)Under Operational Occ Scenario


RESUMEN

Ulé fractionation plant is located on “Intercomunal” Avenue, “Sector La Vaca”,

Simón Bolívar Municipality in Zulia State. Its function is to split the NGL comingfrom Tia Juana 2 and 3 plants in propane, butanes mixture (n-butane and i-

butane) and natural gasoline (C5 +).

With the commissioning of the Occidente Cryogenic Complex (OCC), the Ulé

Fractionation Plant (GLP-2) will receive from the extraction train of this complex,

NGL at different conditions of composition (Lean, Average and Rich NGL),

which generates the necessity of defining the highest NGL feed flow rate that

plant can handle.

That is why, it is required a hydraulic capacity study of each column in order to

avoid operational problems such as flooding or weeping, and thereby ensure

optimal operation of fractionation columns, meet quality product requirements

demanded by the client and ensure the operational availability of fractionation

towers.

To achieve this objective, there were applied several assessments or

sensitivities at different feed rates to GLP-2 by using Aspen Hysys 2006process simulator to find the maximum power of fractionation columns, under

different scenarios of OCC feed.

From sensitivities results, it was obtained that the maximum feed flow rates for

each of the evaluated scenarios for GLP-2 towers (under different OCC feeding

scenarios) are 27.5 MBPD of Lean NGL, 42.8 MBPD of Average NGL and

34.55 MBPD of Rich NGL, without occurring hydraulic problems in fractionating

columns.

INTRODUCCION

Ulé Fractionation Plant is comprised by plants GLP-1, 2 and 3. It is currently

operating the GLP-2 plant with a capacity by design of 46.0 MBPD of NGL from

Tia Juana 2 and 3 plants, producing: propane, butanes mixture and natural

gasoline. At present, GLP-2 processes about 16.0 MBPD as average.


3/26

$



GLP-2 train consists of a depropanizer column (D8-504 or T5-B), a debutanizer

column (D8-506 or T6-B), propane and butane condensers (D6-501 and D6-502

respectively), two feed drums (D8-501 A / B), two reflux drums (D8-505 and D8-507) and two reboilers (D2-504 and D2-506).

The propane production of the ULE facility is intended to meet local demand

using up to 85% for that purpose, moreover, 12% of the propane production is

sent back to the Tia Juana II and III to be used in the Mechanical Refrigeration

System and the remaining production is exported to international markets.

Due to future changes in the feeding of natural gas liquids (NGL) coming from

Occidente Cryogenic Complex (OCC) to LPG Ulé in terms of its compositionand feed flow, it is required a hydraulic capacity study of each column in order

to avoid operational problems such as flooding or weeping, and thereby ensure

optimal operation of fractionation columns, meet quality product requirements

demanded by the client and ensure the operational availability of fractionation

towers, after OCC commissioning.

PROBLEM STATEMENT

On April 29, 1958, Ulé Fractionation Plant started operations with CreolePetroleum Corporation Company. After the nationalization period in 1975, Ulé

became as part of the assets of the Venezuelan oil industry and began its

operations with the company LAGOVEN S.A. After the unification of the

Venezuelan oil subsidiary in 1997, the Ulé Fractionation Plant is transferred to

PDVSA Gas, as part of the Western Gas Processing Management.

With the commissioning of Western Cryogenic Complex, the extraction process

will have the capacity to process 950 MMSCFD of gas which will produce 58.88MBPD of natural gas liquids (Average NGL).

The OCC inlet gas to be processed (extraction process), comes from various

production blocks or zones in the region, resulting in different compositions,

which are mentioned hereunder:

Lean Gas (2.2 GPM).


4/26

%



Average Gas (2.6 GPM).

Rich Gas (3.26 GPM).

From these compositions, it will be obtained different qualities of the liquids

extracted in the CCO that are classified as Lean NGL, Average NGL and Rich

NGL, depending on the composition of the gas fed.

The liquids extracted from gas will be distributed on the normal OCC operating

scenario (two trains for extraction process and one train for fractionation

process) to the different fractionation trains of the West division as follows:

35.0 MBPD for the new OCC fractionation train.

18.0 MBPD for Ulé Fractionation Plant.

5.88 MBPD for Bajo Grande fractionation Plant and additionally 3.42MBPD of stabilized condensates.

Since the NGL composition that will be fed to the Ulé Fractionation Plant with

the OCC commissioning varies regarding the design composition of GLP-2

Plant, and to define the distribution scenario of the NGL production from the

OCC extraction train in case of maintenance in the fractionation train of thiscomplex, and that production would be distributed to the Ulé and Bajo Grande

fractionation plants, it is necessary to evaluate the hydraulic behaviour of each

fractionation tower internals in order to identify the maximum volumes that can

be processed, which will allow to avoid operational issues such as flooding or

weeping, guarantying the continuous and optimum plant operation, meet quality

product requirements and ensure the operational availability of fractionation

train, after OCC commissioning.


5/26

&



OBJETIVES

MAIN OBJECTIVE

To evaluate the process hydraulic capacity of Ué Fractionation Plant under thescenario of future feeding from Occidente Cryogenic Complex, in order to meet

the quality requirements of fractionated products and ensure operational

continuity of fractionation towers with the OCC commissioning.

SPECIFIC OBJECTIVES

• To evaluate the hydraulic capacity of depropanizer and debutanizer

towers (D8-504 and D8-506) of GLP-2 under OCC feed scenario.• To find the maximum flow feed rate to GLP-2 fractionation towers under

different OCC feeding scenarios.

BASES AND ASSUMPTIONS

The bases and assumptions used during the study development are:

• To obtain the stream process physical - chemical parameters were used

process simulator Aspen Hysys 2006.

• The hydraulic evaluation of each GLP-2 fractionation towers was

performed using Aspen Hysys 2006 simulation software, through the

“Tray sizing” tool.

• The considered NGL feed flows (minimum and maximum) for GLP-2

fractionation towers hydraulic evaluation were ranged from 10.0 to 42.0

MBPD.

• The different NGL compositions (Lean, Average and Rich) from OCC

Extraction Plant used for the sensitivities or hydraulic evaluations are as

follow. (Source: Doc. 8922Y-000-PP-202 Rev. 0, Bases de Diseño

Bloque I y II FEED 98% (OCC Project):


6/26

'



Components

Lean NGL

(% Molar)

Average NGL

(% Molar)

Rich NGL

(% Molar)

Ethane 0.53 0.58 0.59

Propane 52.97 58.37 58.63

i-Butane 10.16 9.00 9.77

n-Butane 17.36 16.18 17.97

i-Pentane 5.69 5.40 5.18

n-Pentane 5.49 5.47 5.06

n-Hexane 4.49 3.29 2.17n-Heptane 2.70 1.23 0.47

n-Octane 0.62 0.28 0.06

n-Nonane 0.0 0.16 0.04

n-Decane 0.0 0.03 -0.06

n-Undecane 0.0 0.0 0.06

Table 1: NGL Molar Percentage from OCC

• According to SIALAB reports, quality specifications that fractionated

products such as propane and butane mixture must comply, are:

Propane Product (Depropanizer Column Top)

Component % Molar

Methane Max. 0.5

Ethane Max. 5.1

Propane Min. 90.0

i-Butane Max. 1.82

n-Butane Max. 0.28

Table 2: Maximum and minimum quality values for Depropanizer Column Top


7/26

(



Butane Mixture (Debutanizer Column Top)

Component % Molar

Propane Máx. 2.5

i-Pentane Máx. 1.4

n-Pentane Máx. 0.35

Table 3: Maximum and minimum quality values for Debutanizer Column Top

• The natural gasoline must comply with a maximum Reid Vapor Pressure

(RVP) of 15.0 psia.

• The technical specifications of the internal fractionation GLP-2 columns

were taken from the manual “CREOLE PETROLEUM CORPORATION

LPG EXPANSION PROJECT ULE FRACTIONATION PLANT

PROCESS DESIGN SPECIFICATIONS”.

• The behaviour of a distillation column is efficient in a range of 40 to 90%

of flooding, according to Process Design PDVSA Manual, PDVSA MDP-

04-CF-14 (Tray efficiency).

• The downcomer inlet velocity should be limited to a maximum of 0.15

m/s (0.5 ft/s). For foaming systems, lower inlet velocities should be used

(in the order of 0.06 m/s (0.2 ft/s)). The maximum outlet velocity for

sloped or stepped downcomers should be twice the inlet velocity or 0.6

ft/s (0.18 m/s), whichever is less, according to the PDVSA Process

Design Manual, PDVSA MDP-04-CF-12 (Valve Tray Type).

• The final dry tray pressure drop will generally fall in the range of 1 to 4 in.

(25 to 100 mm) of hot liquid, according to PDVSA Design Manual,

PDVSA MDP-04-CF-12 (Valve Tray Type).

• The following tables show some hydraulic parameters for fractionation

towers, to take into account according to PDVSA Design Manual,

PDVSA MDP-04-CF-12 (Valve Tray Type).


8/26

)



• In the next chart it can see the recommended residence time in thedowncomers, depending on the hydrocarbon molecular weight. (AppliedProcess Design for Chemical and Petrochemical Plants, E.

Ludwing).


9/26

*



- NGL FEED

- PROCESS DATA

- HYSYS SIMULATOR

- PRESSURE DROP

- FLOODING FACTOR %

- DOWNCOMER VELOCITY

- RESIDENCE TIME

- OPERATIONAL PARAMETER ANALYSIS

- SYSTEM MODIFICATION PROPOSAL

+ , - . , + / 01 2 - , / 3 4

5 - 2 / 6 - , / 3 4

+ /012-,/34 3 7 8 8 3

3 9 : . - , / 3 4 - 2 8 3 4 6 /, / 3 4 +

8 3 4 5 : . ; : <

2 3 = : . / 4 ; 4; 2

7 2 3 = 7 : : 6

. - , :

8 3 0 9 2 >


10/26

#"



1,5000

1,5500

1,6000

1,6500

1,7000

1,7500

1,8000

1,8500

0 5 10 15 20 25 30 35 40

Tray Number

D r y

L i q u

i d P r e s s u r e

D r o p

( i n )

Lean NGL

Average NGL

Rich NGL

Figure 1: Pressure Drop in Tray Section of D8-504

1,5000

1,5500

1,6000

1,6500

1,7000

1,7500

1,8000

1,8500

0 5 10 15 20 25 30 35 40

Tray Number

D r y

L i q u

i d P r e s s u r e

D r o p

( i n )

Lean NGL

Average NGL

Rich NGL


0,0000

1,0000

2,0000

3,0000

4,0000

5,0000

6,0000

7,0000

0 5 10 15 20 25 30

Tray Number

D r y L i q

u i d P r e s s u r e D r o p ( i n )

Lean NGL

Average NGL

Rich NGL


0,0000

1,0000

2,0000

3,0000

4,0000

5,0000

6,0000

7,0000

0 5 10 15 20 25 30

Tray Number

D r y L i q

u i d P r e s s u r e D r o p ( i n )

Lean NGL

Average NGL

Rich NGL


In Figure 1, the pressure drop in the internal section of the depropanizer tower

(D8-504) is within the PDVSA established range in its standard MDP-04-CF-12

(valve trays type), from 1.0 to 4.0 inches of hot liquid. The range of pressure

drops varies from 1.5 to 1.83 inches.

For the debutanizer tower D8-506, Figure 2 shows the variation of dry tray

pressure drop for 42.0 MBPD of Lean, Average and Rich NGL.


11/26

##



35,00

40,00

45,00

50,00

55,00

60,00

65,00

70,00

0 5 10 15 20 25 30 35 40

Tray Number

F l o o

d i n g

F a c

t o r

%

Lean NGL

Average NGL

Rich NGL

Figure 3: Flooding Factor for Column D8-504

35,00

40,00

45,00

50,00

55,00

60,00

65,00

70,00

0 5 10 15 20 25 30 35 40

Tray Number

F l o o

d i n g

F a c

t o r

%

Lean NGL

Average NGL

Rich NGL


For the debutanizer tower (D8-506), the pressure drop along the internal

section, Figure 2 shows that only the scenario with Average NGL feed is within

the limits described in the PDVSA standard, these values are in a range of 1.3to 3.0 inches.

While the other two feeding schemes (Lean and Rich NGL) exceed the values

of pressure drop in trays sections from the top and bottom in the column, in the

case of Lean NGL for example, only the first two internal (trays) are among the

values described by the standard (3.71 - 3.94 inches of liquid) and the middle

part of trays below the feed tray (tray 19).

The top column internal values range from 4.0 to 6.0 inches of liquid. The RichNGL ranges between 2.5 and 4.5 inches of liquid, so it neither complies with the

PDVSA standard MDP-04-CF-12 (valve tray type).

Flooding Factor.

Figures 3 and 4 show the flooding factors of GLP-2 fractionation columns for the

different scenarios evaluated in this study.


12/26

#!



30,00

40,00

50,00

60,00

70,00

80,00

90,00

100,00

110,00

120,00

0 5 10 15 20 25 30

Tray Numbe r

F l o o d i n g F a c t o r %

Lean NGL

Average NGL

Rich NGL


30,00

40,00

50,00

60,00

70,00

80,00

90,00

100,00

110,00

120,00

0 5 10 15 20 25 30

Tray Numbe r

F l o o d i n g F a c t o r %

Lean NGL

Average NGL

Rich NGL


On Figure 3 it is shown that the flooding factor of the depropanizer column for

the evaluated scenarios has an efficient behavior, according to the standards

PDVSA MDP-04-CF-14 (Tray Efficiency) and PDVSA MDP-04-CF-12 (Valve

Tray), which states that a flooding factor range between 40% and 90% is an

efficient behavior for a column. The reported values are between 43% and 63%

for Rich, Lean and Average NGL.

Regarding the debutanizer columns, Figure 4 shows that only the Average NGL

scenario complies with the standards having a range of 53% to 73% of flooding,

the rest of the feed scenarios show a flooding factor that exceeds the standard

all along column internals. For the Rich NGL scenario the section of the column

below the feed tray has flooding factor ranging from 80% to 74%, whereas the

section above ranges from 90% to 82%. For the Lean NGL case, the wholecolumn is flooded 95% to 113%.

Downcomer velocity.

Figures 5 and 6 show the downcomer velocities for the GLP-2 fractionation

columns for the different composition scenarios evaluated in this study.


13/26

#$



0,2000

0,2500

0,3000

0,3500

0,4000

0,4500

0,5000

0,5500

0,6000

0,6500

0 5 10 15 20 25 30

Tray Number

D o w n c o m e r V e l o c i t y ( f t / s )

Lean NGL

Average NGL

Rich NGL

Figure 6: Downcomer Velocities for Column D8-506

0,2000

0,2500

0,3000

0,3500

0,4000

0,4500

0,5000

0,5500

0,6000

0,6500

0 5 10 15 20 25 30

Tray Number


Lean NGL

Average NGL

Rich NGL


In figure 5, it can be seen that downcomer velocity ranges from 0.21 to 0.67 ft/s

which indicates that velocities in the bottom section would be exceeded in the

bottom section of the depropanizer (D8-504) for the three feed scenarios of the

CCO. According to the standard PDVSA MDP-04-CF-12 (Valve Trays) the

downcomer entrance velocity should be limited to 0.15 m/s (0.5 ft/s) maximum.

The top section of the column complies with the standard (0.41 ft/s).

0,2000

0,3000

0,4000

0,5000

0,6000

0,7000

0,8000

0 5 10 15 20 25 30 35 40

Tray Number

D o w n c o m e r

V e

l o c

i t y

( f t / s )

Lean NGL

Average NGL

Rich NGL


0,2000

0,3000

0,4000

0,5000

0,6000

0,7000

0,8000

0 5 10 15 20 25 30 35 40

Tray Number

D o w n c o m e r

V e

l o c

i t y

( f t / s )

Lean NGL

Average NGL

Rich NGL



14/26

#%



1,7000

1,9000

2,1000

2,3000

2,5000

2,7000

2,9000

0 5 10 15 20 25 30

Tray Number

R e s i d e n c e T i m e

( s ) Lean NGL

Average NGLRich NGL

Figure 7: Residence Time on Tray for Section for Column D8-504

1,7000

1,9000

2,1000

2,3000

2,5000

2,7000

2,9000

0 5 10 15 20 25 30

Tray Number

R e s i d e n c e T i m e

( s ) Lean NGL

Average NGLRich NGL



1,0000

1,5000

2,0000

2,5000

3,0000

3,5000

4,0000

0 5 10 15 20 25 30 35 40

Tray Number

R e s i d e n c e T i m e ( s )

Lean NGL

Average NGL

Rich NGL


1,0000

1,5000

2,0000

2,5000

3,0000

3,5000

4,0000

0 5 10 15 20 25 30 35 40

Tray Number


Lean NGL

Average NGL

Rich NGL

In the debutanizer column (D8-506), downcomer velocites, Figure 6, displays

velocities ranging from 0.63 to 0.25 ft/s. These high velocities are found in the

bottom of the column, being the case of the Lean NGL scenario for which theywere found. According to the results, downcomer velocities only comply for the

Rich and Average scenarios.

Residence Time.

Figures 7 and 8 show the residence time of the tray sections of the

depropanizer column (D8-504), in the case where 42.0 MBPD of NGL are

processed for the different compositions scenarios from the CCO (Lean,

Average and Rich NGL) and for the debutanizer column D8-506.


15/26

#&



Assuming that hydrocarbon fractionating in the GLP-2 columns has a medium

molecular weight at the bottom and light at the top, in figure 7 can be seen that

the residence time on the internals of the depropanizer column is in the range of1.13-1.26 seconds in the bottom section, this lowering of the residence time is

due to multiple Flow Paths (4). Regarding the top section it can be mentioned

that the residence time is 3.2 – 3.6 seconds.

According to recommendations from Applied Process Design for Chemical and

Petrochemical Plants (E. Ludwig), the residence time in the downcomer of a

column should be approximately 4 seconds for medium molecular weight

hydrocarbons and 3 seconds for light molecular weight hydrocarbons. In Figure

9, the debutanizer column has a residence time oscillating between top and

bottom from 1.9 to 2.8 seconds.

• Maximum Allowable Feed Flow Rate to the GLP-2 columns under different

CCO Feed Scenarios.

Dry Liquid Pressure Drop.

In Figures 9 and 10 show the dry liquid pressure drop in the tray section for the

depropanizer (D8-504) and debutanizer (D8-506) columns; for the case whereNGL feeds are processed depending of the maximum allowed capacity of the

distillation columns, considering the different composition schemes for the CCO

(Lean, Average and Rich NGL).

Hydraulic evaluation to find the maximum feed rate to the fractionation columns

of GLP-2 under the different CCO Feed scenarios without hydraulic problems

occurring in the fractionation columns, it is found that for each evaluated

scenario are 27.5 MBPD for the Lean NGL Case, 42.8 MBPD for the AverageNGL Case and 34.55 MBPD for the Rich NGL Case.


16/26

#'



1,4000

1,4500

1,5000

1,5500

1,6000

1,6500

1,7000

1,7500

1,8000

1,8500

0 5 10 15 20 25 30 35 40

Tray Number

D r y L i q u i d P r e s s u r e D r o p ( i n

Lean NGL 27,5 MBPD

Average NGL 42,8 MBPD

Rich NGL 34,55 MBPD

Figure 9: Pressure Drop on Tray Section D8-504

1,4000

1,4500

1,5000

1,5500

1,6000

1,6500

1,7000

1,7500

1,8000

1,8500

0 5 10 15 20 25 30 35 40

Tray Number

D r y L i q u i d P r e s s u r e D r o p ( i n

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


1,0000

1,5000

2,0000

2,5000

3,0000

0 5 10 15 20 25 30

Tray Number

D r y

L i q u

i d P r e s s u r e

D r o p

( i n

)

Lean NGL 27,5 MBPD


Rich NGL 34,55


1,0000

1,5000

2,0000

2,5000

3,0000

0 5 10 15 20 25 30

Tray Number

D r y

L i q u

i d P r e s s u r e

D r o p

( i n

)

Lean NGL 27,5 MBPD


Rich NGL 34,55


On Figure 9 can be seen the pressure drop on the internals of the depropanizer

column (D8-504) for different flow rates and feed compositions, each of the

scenarios is under the ranges established on the standard PDVSA MDP-04-CF-

12 (Valve Trays). The highest range of pressure drop was found for the

Average NGL scenario since is the one with the highest feed rate. In this case,

the pressure drop is 1.68 to 1.8 in.


17/26

#(



25,00

30,00

35,00

40,00

45,00

50,00

55,00

60,00

65,00

0 5 10 15 20 25 30 35 40

Tray Number

F l o o d i n g F a c t o r

Lean NGL 27,5 MBPD Average NGL 42,8 MBPD

Rich NGL 34,55 MBPD

Figure 11: Flooding Factor of Column D8-506

25,00

30,00

35,00

40,00

45,00

50,00

55,00

60,00

65,00

0 5 10 15 20 25 30 35 40

Tray Number

F l o o d i n g F a c t o r

Lean NGL 27,5 MBPD Average NGL 42,8 MBPD

Rich NGL 34,55 MBPD


50,00

55,00

60,00

65,00

70,00

75,00

80,00

0 5 10 15 20 25 30

Tray Number

F l o o d i n g F a c

t o r ( % )

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


50,00

55,00

60,00

65,00

70,00

75,00

80,00

0 5 10 15 20 25 30

Tray Number

F l o o d i n g F a c

t o r ( % )

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


On Figure 10 are shown the debutanizer (D8-506) pressure drop for each of the

flow rate and composition scenarios, the highest pressure drops on the internals

of the debutanizer column were found for the Rich NGL case since it has thegreatest amount heavy ends on the feed stream. The range of the pressure

drops found was 1.79 to 3.02 in

Flooding Factor.

Figures 11 and 12 show the flooding factors of the GLP-2 columns for the

different feed scenarios evaluated in the study.


18/26

#)



Figure 11 shows the Flooding Factors for the evaluated scenarios for the

depropanizer column. The highest flooding factor is found for the Average NGL

composition in a range of 57 to 62%, in this case the behavior is consideredefficient, according to the standards PDVSA MDP-04-CF-14 (Tray Efficiency)

and PDVSA MDP-04-CF-12 (Valve Trays), which indicates that a range form 40

to 90% of flooding factors is considered efficient for a column.

While the Lean NGL feed case shows an inefficient behavior with a range from

35.7 to 39.4% in the bottom sections and part of the top sections of the column,

due to the low contents of heavy ends in the column feed. Although other

authors recommend an efficiency range for a fractionation column between 10

to 90% (A Working Guide to Process Equipment, N. Lieberman), the

authors of this work consider that low efficiency during operation of a

fractionation column could lead to weeping and flooding.

On Figure 12, it can be seen that the scenario that presents the highest flooding

factor is the Rich NGL case, and thus having the highest efficiency value, which

were found in the range of 65.9 to 76.2%.

Downcomer Velocity.

Figures 13 and 14 show the estimated downcomer velocities for the GLP2

fractionation columns.

On Figure 13, it can be seen that downcomer velocity for the different evaluated

cases are in a range from 0.65 to 0.24 ft/s for a Average NGL feed, which

indicates that velocity values in the bottom section of the depropanizer column

(D8-504), would exceed the recommended values of the standard PDVSA

MDP-04-CF-12 (Valve Trays) which states a maximum of 0.5 ft/s. The

velocities in the top sections were found to be according to the standard.


19/26

#*



0,1000

0,2000

0,3000

0,4000

0,5000

0,6000

0,7000

0,8000

0 5 10 15 20 25 30 35 40

Tray Number


Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD

Figure 13: Downcomer Velocity Column D8-504

0,1000

0,2000

0,3000

0,4000

0,5000

0,6000

0,7000

0,8000

0 5 10 15 20 25 30 35 40

Tray Number


Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


0,2300

0,2500

0,2700

0,2900

0,3100

0,3300

0,3500

0,3700

0,3900

0,4100

0,4300

0 5 10 15 20 25 30

Tray Number

D o w n c o m e r V e l o c

i t y ( f t / s )

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


0,2300

0,2500

0,2700

0,2900

0,3100

0,3300

0,3500

0,3700

0,3900

0,4100

0,4300

0 5 10 15 20 25 30

Tray Number

D o w n c o m e r V e l o c

i t y ( f t / s )

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


Regarding downcomer velocities on the debutanizer column (D8-506), Figure

14 shows that the highest velocities were reached under the Rich OCC feed

scenario ranging from 0.40 to 0.23 ft/s. These high downcomer velocities could

lead to liquid carryover and tray flooding.


20/26

!"



1,0000

1,5000

2,0000

2,5000

3,0000

3,5000

4,0000

4,5000

5,0000

0 5 10 15 20 25 30 35 40

Tray Number

R e s

i d e n c e

T i m e

( s )

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD

Figure 15: Residence Time on Trays Section Column D8-504

1,0000

1,5000

2,0000

2,5000

3,0000

3,5000

4,0000

4,5000

5,0000

0 5 10 15 20 25 30 35 40

Tray Number

R e s

i d e n c e

T i m e

( s )

Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


1,9000

2,0000

2,1000

2,2000

2,3000

2,4000

2,5000

2,6000

2,7000

2,8000

2,9000

0 5 10 15 20 25 30

Tray Number


Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


1,9000

2,0000

2,1000

2,2000

2,3000

2,4000

2,5000

2,6000

2,7000

2,8000

2,9000

0 5 10 15 20 25 30

Tray Number


Lean NGL 27,5 MBPD


Rich NGL 34,55 MBPD


Residence Time.

Figures 15 and 16 show the residence time for each tray on the evaluated

columns.

On Figure 15 can be seen that the residence time on the internals of the

depropanizer column for the different evaluated scenarios. The residence time

ranges from 1.4 to 1.7 seconds in the bottom section, while in the top section it

ranges from 4.55 to 4.3 seconds. From the three evaluated scenarios, the

highest residence time values were found for Lean Feed case. On Figure 16, it


21/26

!#



can be seen that the debutanizer column has residence time oscillating from

bottom to top section 1.9 to 2.8 seconds for the Average NGL Feed case.

• Top Product Quality of the Depropanizer Column (D8-504).

On table 4 are presented the product qualities of the column D8-504

(depropanizer) of GLP-2, for each of the cases studied (Lean, Average and

Rich NGL):

ANALYZED STREAMS

Component Quality Plan Lean NGL Average NGL Rich NGL

Ethane (%Molar)Máx. 5.1 0.98 0.77 0.98

Propane(%Molar) Min. 90 97.46 97.64 97.44i-Butane(%Molar) Máx. 1.82 1.43 1.43 1.43n-Butane(%Molar) Máx. 0.28 0.13 0.15 0.15

Table 4: D8-504 Propane Product Molar Porcentages

• Topa and Bottom Product Quality of the Debutanizer Column (D8-506). On

tables 5 and 6 are shown the qualities of the top and bottom products of the

column D8-506 (debutanizer) of GLP-2, it can also be seen that the Reid Vapor

Pressure (RVP) of the non-stabilized of the Gasoline Stream.

ANALYZED STREAMS

Component Quality Plan Lean NGL Average NGL Rich NGL

Propane (%Molar) Máx. 2.5 0.34 0.33 0.29i-Butane(%Molar) Min. 10 34.34 33.12 32.61n-Butane(%Molar) Min. 30 63.28 65.41 65.42i-Pentane (%Molar) Máx. 1.4 1.9 0.99 1.53n-Pentane(%Molar) Máx. 0.35 0.15 0.15 0.15

Table 5: D8-506 Butane Mixture Molar Percentages


22/26

!!



ANALYZED STREAMS

Property Quality Plan Lean NGL AverageNGL

Rich NGL

RVP (psia) Máx. 15.0 11.72 13.32 14.8

Table 6: D8-506 Non-stabilized Gasoline Reid Vapor Pressure

When comparing the maximum and minimum values of the molar percentages

of the contaminant components of the top of the depropanizer (ethane, i-butane

and n-butane) and the debutanizer (propane, i-pentane and n-pentane) columns

of GLP-2 (D8-504 and D8-506) to the values found on the different CCO feed

simulations, the Propane Product Stream (top of D8-504) is within plant design

specifications regarding methane content (0.0% molar Lean, Average, and

Rich NGL), ethane (0.98 – 0.77 – 0.98% molar Lean, Average and Rich NGL), i-

butane (1.43% molar for the three scenarios) and n-butane (0.13 – 0.15 –

0.15% molar Lean, Average and Rich NGL).

Regarding top product quality for the debutanizer column (D8-506), the butane

mixture also complies with plant design specifications, propane (0.34 – 0.33 –

0.29% molar Lean, Average and Rich NGL), n-pentane (0.15% for the three

scenarios). It must be noted that i-pentane content in the butane mixture has a

molar concentration of 1.9 – 0.99 and 1.53%, that complies with quality

specifications of the Lean NGL GLP-2 feed scenario.


23/26

!$



CONCLUSIONS

• Top and bottom product quality of the depropanizer (D8-504) and

debutanizer (D8-506) columns of GLP-2 comply with SIALAB specificationsfor the evaluated NGL compositions.

• For the 42.0 MBPD NGL form the CCO scenario (Lean, Average and Rich),

the depropanizer column (D8-504) complies with recommendations of the

standard PDVSA MDP-04-CF-12 (Valve Trays), regarding tray pressure

drop of 1.0 to 4.0 in of liquid.

• Accordingly, for the feed scenario of 42.0 MBPD of OCC NGL, the

debutanizer column (D8-506), the pressure drop along column internals areonly standard allowable values for the Average NGL case, these values

ranged from 1.3 to 3.0 in

• It was observed that the flooding factors of the depropanizer column (D8-

504) for the evaluated scenarios display an efficient behavior according the

standards PDVSA MDP-04-CF-14 (Tray Efficiency) and PDVSA MDP-04-

CF-12 (Valve Trays), which indicates that a range of 40 to 90% of flooding

for a column is considered efficient column behavior (42.0 MBPD of NGL

fractionation scenario).

• For the debutanizer column (D8-506), only the Average NGL scenario

complies with the standards having a flooding factor ranging from 53 to 73%

(42.0 MBPD of NGL fractionation scenario).

• Downcomer velocities were found to range from 0.21 to 0.67 ft/s, this

indicates that velocities on the bottom section of the depropanizer column

(D8-504) for the three feed scenarios would exceed standards

recommendations. According to standard PDVSA MDP-04-CF-12 (Valve

Trays) the downcomer entrance velocity should be limited to maximum of

0.15 m/s (0.5 ft/s). The top section of the column was found to comply to

standard (42.0 MBPD of NGL fractionation scenario).

• Downcomer velocities on the debutanizer columna (D8-506) were found to

range from 0.63 to 0.25 ft/s. These high velocities were found on the


24/26

!%



bottom section of the column for the Lean NGL case (42.0 MBPD of NGL

fractionation scenario).

• Residence time of the internals of the depropanizer column (D8-504)ranged from 1.13 to 1.26 seconds on the bottom sections, this residence

time distribution is due to presence of multiple Flow Paths (4). The top

section of the column has a residence time ranging from 3.2 to 3.6 seconds

(42.0 MBPD of NGL fractionation scenario).

• The debutanizer column (D8-506) has a residence time oscillation on the

bottom and top sections from 1.9 to 2.8 seconds (42.0 MBPD of NGL

fractionation scenario).• The maximum feed rate to the GLP-2 fractionation columns for the different

CCO feed scenarios without having column hydraulic problems were found

to be 27.5 MBPD for the Lean NGL case, 42.8 MBPD for the Average NGL

case and 34.55 MBPD for the Rich NGL Case.

• Pressure drop on the internals of the depropanizer column (D8-504) for the

different feed rates and compositions evaluated comply with the standard

PDVSA MDP-04-CF-12 (Valve Trays). The highest pressure drop rangewas found for the Average NGL feed scenario since it has the highest feed

rate. The values found for the pressure drop ranged from 1.68 to 1.8 in.

• For the debutanizer column (D8-506), the pressure drop was evaluated for

the different scenarios of flowrate and feed composition and the highest

were found for the Rich NGL case since it has the greates amount of heavy-

ends content on the feed. The found pressure drop ranged from 1.79 to

3.02 in.

• The highest flooding factors of the depropanizer column (D8-504) ranged

from 57 to 62% for the Average NGL case. For the Lean NGL case, the

flooding factor as an inefficient behavior having a range from 35.7 to 39.4%

all along the bottom section and part of the top section of the column.

• For the debutanizer column, D8-506, the highest flooding factors were

found for the Rich NGL case. This case was the one with highest efficiency

on which the flooding factor were found to range from 65.9 to 76.2%.


25/26

!&



• Downcomer velocities for the different cases evaluated ranged from 0.65 to

0.24 ft/s for an Average NGL feed composition; this indicates that

downcomer velocities on the bottom section of the depropanizer column(D8-504) would exceed recommended values. The top section of the

column velocity values comply with the standards.

• For the debutanizer column (D8-506) the downcomer velocities were found

to reach a maximum for the Rich NGL scenario, on which the velocities

ranged from 0.40 to 0.23 ft/s.

• Residence time of the internals of the depropanizer column (D8-504)

ranged from 1.4 to 1.7 seconds for the bottom section. For the top section,this parameter was found to range from 4.55 to 4.3 seconds. From the

three evaluated scenarios the highest reported values were found of the

Lean NGL feed.

• The debutanizer column (D8-506) has a residence time oscillating from top

to bottom section 1.9 to 2.8 seconds for the Average LGN feed.


26/26

!'



REFERENCES

• CREOLE PETROLEUM CORPORATION LPG EXPANSION PROJECT

ULE FRACTIONATION PLANT PROCESS DESIGN SPECIFICATIONS.• MANUAL DE DISEÑO DE PROCESOS DE PDVSA, PDVSA MDP-04-CF-

14 (EFICIENCIA DE PLATOS).

• MANUAL DE DISEÑO DE PROCESOS DE PDVSA, PDVSA MDP-04-CF-

12 (PLATOS TIPO VÁLVULA).

• APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL

PLANTS, E. LUDWING.

• A WORKING GUIDE TO PROCESS EQUIPMENT, N. LIEBERMAN.

Documents

Distillation Column Case Study