lp dec3 full report

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TITAN CHEMICALS CORP. BHD. (222357-P)

SHORT ASSIGNMENT:

STUDY OF LP DEPROPANIZER (2T-360)

TEE CHEE KEONG

CHEMICAL ENGINEERING

UNIVERSITI TUNKU ABDUL RAHMAN

NOV 2010



ii

Table of Contents

No. Content Page No.

TABLE OF CONTENTSii

LIST OF TABLESiii

LIST OF FIGURESiv

1.1

1.2

1.3

SECTION 1: INTRODUCTION

Objective

Study Period

Structure of Tower

1

1

1

2.1

2.2

2.3

SECTION 2: TOWER DETAIL

Process Flow Description

Flow Controller and Analyzer

Design Mole Balance

2

4

4

3.1

3.2

3.3

3.4

3.5

3.6

3.7

SECTION 3: RESULTS

Plant Loads

Total Feed In

Total Flow Out

Deviation

Reflux Ratio

Top≤ C3 Composition

Top C4+ Composition

7

8

9

10

11

12

13

SECTION 4: DISCUSSIONS 14

SECTION 5: CONCLUSION 16



iii

LIST OF TABLES

TABLE TITLE PAGE

1 Structure of the tower 3



iv

LIST OF FIGURES

FIGURE TITLE PAGE

2.1 Process Flow Diagram 3

2.2 Flow Controller and Analyzer Diagram 5

2.3 Design Mole Balance Diagram (Case 1) 6

3.1.1 Graph of plant load before TA 7

3.1.2 Graph of plant load after TA 7

3.2.1 Graph of Total feed in before TA 8

3.2.2 Graph of Total feed in after TA 8

3.3.1 Graph of Total flow out before TA 9

3.3.2 Graph of Total flow out after TA 9

3.4.1 Graph of Deviation before TA 10

3.4.2 Graph of Deviation after TA 10

3.5.1 Graph of Reflux Ratio before TA 11

3.5.2 Graph of Reflux Ratio after TA 11

3.6.1 Graph of Top ≤C3% before TA 12

3.6.2 Graph of Top ≤C3% after TA 12

3.7.1 Graph of Top C4+% before TA 13

3.7.2 Graph of Top C4+% after TA 13



SECTION 1: INTRODUCTION

LP depropanizer is a distillation column in cracker plant which separate C3 and C4. Therefore,

the incoming feed will be separated as a top vapor which is rich in C3, and a bottom liquid of

essentially C4 and heavier components. Partial reflux system where portion of C3 reflux back to

the tower to increase C3 composition in the top stream. The bottom stream is sent to debutanizer

to recover C4 from heavier components.

1.1 Objective

To compare the flow, reflux ratio and the performance of the LP depropanizer before and after

the turnaround project on October 2010.

1.2 Study Period

Before Turnaround – 24, 25, 26 August 2010

After Turnaround – 16, 17, 18 November 2010

1.3 Structure

Table 1: Structures of the tower

TrayAmount 67

Type Sieve type with 1 pass

Dimension 48.175m (Height) × 22.6m (Diameter)

InsulationCold Insulation from top to tray 28

Hot Insulation from tray 28 to bottom

1



SECTION 2: TOWER DETAIL

2.1 Process Flow Description

(Refer to the Fig 2.1 process flow diagram)

1. Main liquid feed from the bottom of the HP depropanizer (2T-365) is cooled by cooling water

in LP depropanizer feed cooler (2E-368) and then enter the LP depropanizer at tray 21.

2. Another feed from the bottom of the propylene stripper (2T-530) enters the column at tray 10.

3. The operating temperature of the LP depropanizer column is controlled to be higher at the

bottom so that C3 or lighter components would vaporize up, and lower temperature at the

bottom so that C4 or heavier components would condense down. Therefore the C3 will go up

and exit as top vapor and C4 will go down and exit as bottom liquid.

4. The condensing duty for the column is provided by the LP depropanizer condenser (2E-359)

using 7°C propylene refrigerant, which totally condenses the overhead vapor into liquid.

5. The liquid is collected in the reflux drum (2V-366). Part of the liquid is pumped back the top

of the LP depropanizer as reflux, through the pumps (2P-360A/S) to reduce the C4 amount in

the top stream.

6. The remaining liquid is pumped forward to the C3 hydrogenation system via the C3

hydrogenation feed pumps (2P-361A/S). This liquid consists of mainly C3.

7. The reboil duty for the column is provided by the LP depropanizer reboiler (2E-360) using

133°C quench oil, which heat up part of the bottom stream into vapor and send back to the

bottom of the LP depropanizer.

8. The bottom liquid product is essentially C4 and heavier components. This stream is then

transferred to the debutanizer (2T-560).

2



Step number: Referred to the process description

Fig 2.1: Process Flow Diagram

3

2T-360

LP DeC3

C4+ Liquid

To 2T-560

Debutanizer

BTM from

2T-530

C3 Vapor

2E-359

2P-360A/S

C3R

2V-366 To C3

Hydrogenation

2E-368

BTM from

2T-365

HP DeC3

CW

QO

2E-360A/S



2.2 Flow Controller and Analyzer

(Refer to Fig 2.2 flow controller and analyzer diagram)

2.2.1 Flow Controllers

1. Flow controller (2FC-3701) regulates the flow of quench oil to the reboiler (2E-

360), reset by the temperature controller (2TC-3704), which used to maintain the

cut point temperature on tray 50.

2. Flow controller (2FC-5303) measures the flow rate of the reflux at the top.

3. Flow controller (2FC-3702) regulates the bottom flow from the LP depropanizer,

which is reset by the column bottom level controller (2LC-3702), to maintaincertain liquid level in the column.

4. Flow controller (2FC-3703) regulates the flow of reflux back to the top of the

column.

5. Flow controller (2FC-3704) regulates the flow to top C3 liquid flow to the C3

hydrogenation system, reset by the reflux drum level controller (LC-3705).

2.2.2 Analyzer

1. Analyzer (2AI-36021) checks on the composition of the main feed from 2T-365.

2. Analyzer (2AI-36012) checks on the top vapor composition.

3. Analyzer (2AI-36022) checks on the bottom liquid composition.

2.3 Design Mole Balance

(Refer to Fig 2.3 design mole balance diagram)

This is the mole balance calculated based on case 1 (fully naphtha feed) used to compare the

actual flow, reflux ratio and performance of the tower.

4



Controllers: FC – Flow Controller

AI - Analyzer

Fig 2.2: Flow Controller and Analyzer Diagram

5

2T-360LP DeC

3

BTM from

2T-530

2FC-

53032AI-

36012

2FC-

3704

2FC-

3703

C3 Vapor

2E-359

2P-360A/S

C3R

2V-366 To C3

Hydrogenation

QO

2E-360A/S

2E-368

BTM from2T-365

HP DeC3

CW

2FC-

3604

2AI-

36021

C4+ Liquid

To 2T-560

Debutanizer

2FC-

3702

2AI-

36022



QO

Fig 2.3: Design Mole Balance Diagram (Case 1)

6

2E-360A/S

Total: 158508 kg/h

Legends:

Total – Total molar flow rate

≤C3 – C3 and lighter componentsmolar flow rate

C4+ – C4 and heavier componentsmolar flow rate

Reflux Ratio = = 2.088

Yield (C3) = = 99.81%

Yield (C4) = = 99.51%

Total: 3154.27 kg/h

≤C3: 2264.39 kg/h

C4+: 889.89 kg/hBTM from

2T-530

To 2T-560

Debutanizer Total: 22335.54 kg/h

≤C3: 15.63 kg/h

C4+: 22319.92 kg/h

2E-368

BTM from

2T-365

HP DeC3

CW

Total: 27597.60 kg/h

≤C3: 6056.60 kg/h

C4+: 21541.00 kg/h

2T-360LP DeC

3

2E-359

2P-360A/S

To C3

Hydrogenation

C3R

2V-366

Total: 8416.37 kg/h

≤C3: 8305.36 kg/h

C4+: 111.01 kg/h

Total: 25990 kg/h

Total: 17573.63 kg/h



SECTION 3: RESULTS

3.1 Plant Loads

Plant loads is the percentage of naphtha feed into the furnace decided by maximum naphtha feed based on 100% naphtha feed design.

Plant Load Before TA

0

10

20

30

40

50

60

70

80

90

100

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

P e r c e n t a g e %

plantload2

Plant Load After TA

0

10

20

30

40

50

60

70

80

90

100

11/16/201

0 0:00:00

11/16/201

0 12:00:00

11/17/201

0 0:00:00

11/17/201

0 12:00:00

11/18/201

0 0:00:00

11/18/201

0 12:00:00

11/19/201

0 0:00:00

Time

P e r c e n t a g e %

plantload2

Fig 3.1.1: Graph of plant load before TA Fig 3.1.2: Graph of plant load after TA

By comparing the two graphs above, obviously the plant load after the turnaround was much higher. This may be due to the change in

feed where feedstock used was naphtha and LPG before turnaround, and fully naphtha after turnaround.

The plant load is higher after turnaround because of 100% naphtha feed.

7



3.2 Total Feed In

Total feed in is the summation of the flows of main feed from the bottom of 2T-365, and from the bottom of 2T-530

Total In = 2FC-3604 + 2FC-5303

Total In Before TA

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

F l o w

R a t e ( k g / h r )

Actual

Design

Total In After TA

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

11/16/201

0 0:00:00

11/16/201

0 12:00:00

11/17/201

0 0:00:00

11/17/201

0 12:00:00

11/18/201

0 0:00:00

11/18/201

0 12:00:00

11/19/201

0 0:00:00

Time

F l o w R a t e ( k g / h r )

Actual

Design

Fig 3.2.1: Graph of Total feed in before TA Fig 3.2.2: Graph of Total feed in after TA

By comparing the two graphs above, although the total amount of feed flow after the turnaround was fluctuating due to instability, but

the value is almost the same to the feed flow before turnaround.

The feed flow rate has not much different before and after turnaround.

8



3.3 Total Flow Out

Total flow out is the summation of the top product that is going to C3 hydrogenation and the bottom liquid flow.

Total Flow Out = 2FC-3702 + 2FC-3704

Total Out Before TA

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

F l o w

R a t e ( k g / h r )

Actual

Design

Total Out After TA

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

11/16/201

0 0:00:00

11/16/201

0 12:00:00

11/17/201

0 0:00:00

11/17/201

0 12:00:00

11/18/201

0 0:00:00

11/18/201

0 12:00:00

11/19/201

0 0:00:00

Time

F l o w

R a t e ( k g / h r )

Actual

Design

Fig 3.3.1: Graph of Total flow out before TA Fig 3.3.2: Graph of Total flow out after TA

By comparing the two graphs above, although the total amount flow out from the tower after the turnaround was fluctuating due to

instability, but the value is almost the same to the total flow out before turnaround.

The amount of flow out from tower has not much different before and after turnaround.

9



3.4 Deviation

Deviation is the difference between Total In and Total Out

Deviation = Total In - Total Out

Deviation Before TA

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

30000

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

F l o w

R a t e ( k g / h r )

Actual

Deviation After TA

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

30000

11/16/201

0 0:00:00

11/16/201

0 12:00:00

11/17/201

0 0:00:00

11/17/201

0 12:00:00

11/18/201

0 0:00:00

11/18/201

0 12:00:00

11/19/201

0 0:00:00

Time

F l o w

R a t e ( k g / h r )

Actual

Fig 3.4.1: Graph of Deviation before TA Fig 3.4.2: Graph of Deviation after TA

By comparing the two graphs above, although the amount of deviation after the turnaround was fluctuating due to instability, but the

value is almost the same to the amount of deviation before turnaround.

From the comparison, the amount of deviation has not much different before and after turnaround.

10



3.5 Reflux Ratio

Reflux ratio is a ratio that the amount of top product reflux back to tower divided by the amount of top product sent to the next stage.

Reflux Ratio = 2FC-3703 / 2FC-3704

Reflux Ratio Before TA

0.00

1.00

2.00

3.00

4.00

5.00

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

R e f l u x R a t i o

Actual

Design

Reflux ratio After TA

0.00

1.00

2.00

3.00

4.00

5.00

11/16/2010

0:00:00

11/16/2010

12:00:00

11/17/2010

0:00:00

11/17/2010

12:00:00

11/18/2010

0:00:00

11/18/2010

12:00:00

11/19/2010

0:00:00

Time

R e f l u x R a t i o

Actual

Design

Fig 3.5.1: Graph of Reflux Ratio before TA Fig 3.5.2: Graph of Reflux Ratio after TA

By comparing the two graphs above, obviously the reflux ratio after the turnaround is lower than that before turnaround. This reflux

ratio can be controlled by the Boardman by controlling the amount of top product flowing to the C3 hydrogenation, higher reflux ratio

helps to get higher purity product.

Therefore, the reflux ratio is lower after the turnaround.

11



3.6 Top ≤ C3 composition

Top ≤ C3 composition is the molar percentage of C3 and lighter components in the top stream

Top Composition (≤C3) Before TA

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

m o l %

Actual

Design

Top Composition (≤C3) After TA

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

11/16/201

0 0:00:00

11/16/201

0 12:00:00

11/17/201

0 0:00:00

11/17/201

0 12:00:00

11/18/201

0 0:00:00

11/18/201

0 12:00:00

11/19/201

0 0:00:00

Time

m o l %

Actual

Design

Fig 3.6.1: Graph of Top ≤C3% before TA Fig 3.6.2: Graph of Top ≤C3% after TA

By comparing the two graphs above, obviously the percentage of ≤ C3 in top stream became lower after turnaround. Besides, the C3

composition before turnaround not so fluctuate compares to after turnaround which is fluctuate within 70% to 90%.

The percentage of C3 in top stream is lower after the turnaround.

12



3.7 Top C4+ Composition

Top C4+ composition is the molar percentage of C4 and heavier components in the top stream

Top C4+ Composition Before TA

0

1

2

3

4

5

6

8/24/2010

0:00:00

8/24/2010

12:00:00

8/25/2010

0:00:00

8/25/2010

12:00:00

8/26/2010

0:00:00

8/26/2010

12:00:00

8/27/2010

0:00:00

Time

m o l %

Actual

Design

Top C4+ Co mposition After TA

0

1

2

3

4

5

6

11/16/2010

0:00:00

11/16/2010

12:00:00

11/17/2010

0:00:00

11/17/2010

12:00:00

11/18/2010

0:00:00

11/18/2010

12:00:00

11/19/2010

0:00:00

Time

m o l %

Actual

Design

Fig 3.7.1: Graph of Top C4+% before TA Fig 3.7.2: Graph of Top C4+% after TA

By comparing the two graphs above, although the top C4+ molar percentage after the turnaround was fluctuating due to instability, but

the average value is almost the same to the top C4+ molar percentage before turnaround. Besides, the C3 composition before

turnaround not so fluctuate compares to after turnaround which is fluctuate within 70% to 90%.

The average top C4 + molar percentage has not much different before and after turnaround.

13



SECTION 4: DISCUSSION

By comparing the actual flows to the design flows, most of the actual flows are closed to

the design flow, except for the Total In Flow. The Total In is about 3500 kg/h higher than the

design feed flow, due to the high flow of main feed from the bottom of HP depropanizer (2T-

365). For the reflux ratio, the actual reflux ratio is closed to the design one before turnaround but

lower to the design after turnaround. For the analyzer part, both the C3≤ and C4+ percentage in

the top stream showing under performance of tower if compared to the design.

From the comparison of Total In and Total Out flows, deviation keeps happening for the

tower no matter before or after turnaround which does not happen in the design condition. This

shows that certain amount of stream has been “missing” from the tower. This may be due to the

following reasons:

1. Sent for flaring or blowdown. However, this reason is not appropriate since the flaring

amount is only little when the plant is running in normal condition.

2. Inaccuracy of the flow indicator. This is reasonable to explain the missing of the flow.

Example like the inaccuracy of flow indicator for the main feed from 2T-365, this could

explain the increase of about 3500kg/h flow compared to the design value.

3. Accumulation in the tower. The product is kept in the tower to maintain the operation

parameter, causes the deviation to occur.

14



Besides that, there are a few parameters founded that change after the turnaround:

1. The plant load has been increased. Plant load is the percentage of naphtha feed into the

plant compared to the amount of naphtha feed in the design (100%). This may be due to

the change in feed condition whereby naphtha was mixed with certain amount of LPG as

feed before turnaround, but used fully naphtha after turnaround. Therefore the plant load

used has been increased after turnaround.

2. The reflux ratio has been reduced. Reflux ratio is a ratio that the amount of top product

reflux back to tower divided by the amount of top product sent to the next stage. This

reflux ratio can be controlled by the Boardman by controlling the amount of top productflowing to the C3 hydrogenation, higher reflux ratio helps to get higher purity product.

3. The percentage of C3 in top stream has been reduced. This shows that the under

performance of the tower after the turnaround. This might be due to the decrease of reflux

ratio, or the change on the plant load.

15



SECTION 5: CONCLUSION

In a conclusion, LP depropanizer (2T-360is under performance compare to the design value after

the turnaround. However, the cracker plant is not so stable at the investigation period. Therefore,

a further study should be performed once the cracker plant becomes more stable.

16

lp dec3 full report

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