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Page 1: Cracked Gas Compressor

Ethylene Unit Cracked Gas CompressorCase Studies on Fouling

Visagaran Visvalingam - Presenter

Cyron Anthony Soyza

Sew Nyit Tong

Karl Kolmetz

Page 2: Cracked Gas Compressor

Outlines

? Overview of Equipment and Setup

? CGC Fouling Experiences

? Identification of Turbine Fouling

? Impacts of Compressor-Turbine fouling

? Turnaround Inspections

? Countermeasures for Fouling Control

? Future Improvements

? Conclusions

Page 3: Cracked Gas Compressor

Overview of Equipment & Setup

• CGC is a five stages centrifugal compressor

• Caustic wash and drying are facilitated between 4th

and 5th stage

• 5th stage is a heat pump for DeC3 system where C4

and heavier are removed

• CGC is driven by a SHP steam turbine

• Turbine extracts HP steam while condensing is

controlled by CGC power demand

Page 4: Cracked Gas Compressor

Compressor System Flow Diagram

Cracked Gas

Caustic& Dryers

Stage 1 Stage 2 Stage 3 Stage 4

Stage 5

ToRecoverySection

HP DeC3

Acetylene Converters

Wash Oils

Page 5: Cracked Gas Compressor

Diffusers

BalanceLine

Wheels

Inlet Vanes

Compressor Overview

Page 6: Cracked Gas Compressor

Fouling Phenomenon - What,Why and How

• Organic : Free radicalmechanism catalyzed byperoxides, transition metals andheat

• Inorganic : Quench watercarryover

• Organic or inorganic depositsdehydrogenate over timeleaving behind

InitiateInitiate

PropagatePropagate

TerminateTerminate

R-H

• R • H

• ROO

heat

O2

ROOH + •R

R-H

•R•R +

Page 7: Cracked Gas Compressor

CGC Fouling Experiences

£ Polytropic efficiencies dropped

£ Discharge temperatures increased

£ Inter-cooler pressure drops increased

£ Governor valve opening maximum

£ Turbine steam rate increased

£ Max continuos speed not sustainable

Page 8: Cracked Gas Compressor

CGC Polytropic Efficiency

50

55

60

65

70

75

80

85

90

23/4/9628/6/9625/11/9630/4/9729/9/97

23/12/9721/5/9816/9/9805/12/9823/3/9916/07/9907/10/9925/12/9902/01/0006/03/0003/05/0010/07/0007/09/0004/11/0012/12/0005/01/01

Eff

icie

ncy

(%)

2nd stg Polly. Eff 3rd stg Polly. Eff 4th stg Polly. Eff 5th stg Polly. Eff

AFTER TURNAROUND

96

AFTER TURNAROUND

99

TURNAROUND 2001

Page 9: Cracked Gas Compressor

Compressor Delta T

30

35

40

45

50

55

60

65

70

23/4

/96

28/6

/96

25/1

1/96

30/4

/97

29/9

/97

23/1

2/97

21/5

/98

16/9

/98

05/1

2/98

23/3

/99

16/0

7/99

07/1

0/99

25/1

2/99

02/0

1/00

06/0

3/00

03/0

5/00

10/0

7/00

07/0

9/00

04/1

1/00

Stage 1 delta T Stage 2 delta T Stage 3 delta T Stage 4 delta T

AFTER TURNAROUND

96

AFTER TURNAROUND

99TURNAROUND

2001

Page 10: Cracked Gas Compressor

Identification of Turbine Fouling

? Unable to maintain speed at max steam flow

? HP and LP valve fully open

? Backpressure from LP turbine

HPValve

SHP

LPValve

P1 P2

HP SteamExtraction

ExhaustSteam

HP Casing LP Casing

Page 11: Cracked Gas Compressor

Causes of Turbine Fouling

• BFW quality upset

– High Sodium / Silica due to capacity overrun orimproper regeneration of demin train

• Water Carry-over

– Steam drum level control high

• Steam contamination

– Attemporating water

high in sodium or silica

Water level

Page 12: Cracked Gas Compressor

Impacts of Compressor-TurbineFouling

£ Throughput limited due to maximum driver governorvalve opening

£ Increased suction pressure

£ Energy inefficient due to higher steam rate

£ Short run length, 3 years down for cleaning

Page 13: Cracked Gas Compressor

Turnaround Inspections

• Inspection done during TA99 and TA 2001

• 1st and 5th stage - relatively clean

• 2nd, 3rd & 4th stage - heavily fouled

• Polymer deposits and most samples were organic

component

• Inter-coolers fouled with polymers and tars

• Discharge piping layered with polymer

Page 14: Cracked Gas Compressor

CGC Inspection- TA99 & TA2001

Summary of the Inspection Findings

Suct/Dischpiping

Impeller/Diffuser

Volute

1st stage

2nd stage

3rd stage

4th stage

5th stage

Turbine

Page 15: Cracked Gas Compressor

1st Discharge1st Discharge 2nd Discharge2nd Discharge 4th Discharge4th Discharge3rd Discharge3rd Discharge

1st to 4th Stage Discharge Condition during Turnaround 2000/011st to 4th Stage Discharge Condition during Turnaround 2000/01

Page 16: Cracked Gas Compressor

RotorRotor CasingCasing

Page 17: Cracked Gas Compressor

2nd stage intercooler bundle Bundle entrance

Polymer laced inlet pipeline Inlet to intercooler

Page 18: Cracked Gas Compressor

Turnaround inspections - CGC Turbine

Page 19: Cracked Gas Compressor

Countermeasures for Fouling Control• Compressor wash oil review

¤ Feed points available at the suction piping¤ Injection spray atomizers enhance distribution¤ Increased wash oil injection rate to 3-4% vol.¤ Quality monitoring - existent gums¤ Quantity monitoring - dP

• Antifoulant Injection

¤ Trial run at the 4th stage - worst case

• Improved BFW quality¤ Proper Demin regeneration and lower steam drum level

Page 20: Cracked Gas Compressor

Compressor Wash Oil Review

? 1st to 3rd stage - HPG + C5

? 4th stage - HPG

? Specific gravity - 0.77-0.80

? Aromatic content - 65 %

? Existent gums - < 5mg/100ml

? Distillation D-86

– IBP - 70 oC

– End point - 185 oC

Page 21: Cracked Gas Compressor

Anti-foulant Injection

• Trail run at 4th stage

• Start of run - 9 May 02

• Co-injection with the existing wash oil

• Injection rate at 2-5 ppm by weight

• Monitoring parameters :− Polytropic Efficiency− Suction / Discharge Temperatures− Pressure Drop Across Inter-cooler− Steam Consumption− Vibrations

Page 22: Cracked Gas Compressor

Antifoulant Trial Run

Cracked Gas

Caustic& Dryers

Stage 1 Stage 2 Stage 3 Stage 4

Stage 5To

RecoverySection

HP DeC3

Acetylene Converters

Wash Oils

Antifoulant : 2-5ppm wt based on the4th stage charge rate

Page 23: Cracked Gas Compressor

• Polytropic efficiency improved - 4-5%

• Comp discharge temperature reduced - 3-4oC

• Delta T reduced

• Pressure drop across inter-cooler maintained

• Vibration normal

Antifoulant Trial Run Findings

Page 24: Cracked Gas Compressor

4th Stage Polytropic Efficiency and Delta T

65

66

67

68

69

70

71

72

73

74

75

76

05-0

1-02

15-0

1-02

25-0

1-02

04-0

2-02

14-0

2-02

24-0

2-02

06-0

3-02

16-0

3-02

26-0

3-02

05-0

4-02

15-0

4-02

25-0

4-02

05-0

5-02

15-0

5-02

25-0

5-02

04-0

6-02

14-0

6-02

4th

Sta

ge P

olyt

ropi

c E

ffici

ency

, %

51

52

53

54

55

56

57

58

59

60

61

Com

pres

sor D

elta

T, d

egC

Efficiency (%) DT

Dosage 2ppm Dosage 3-4 ppm

Page 25: Cracked Gas Compressor

4th Stage Polytropic Efficiency and Delta T

C-300 Efficiency

60

62

64

66

68

70

72

74

76

78

80

31-Mar-02

05-Apr-02

10-Apr-02

15-Apr-02

20-Apr-02

25-Apr-02

30-Apr-02

05-May-02

10-May-02

15-May-02

20-May-02

25-May-02

30-May-02

04-Jun-02

09-Jun-02

14-Jun-02

19-Jun-02

24-Jun-02

Eff

, %

2nd stage

4th stage

Ave eff = 1st to 3rd stage

Page 26: Cracked Gas Compressor

Future Improvements� Wash oil quality

– C8+ High aromatics, low gums & higher FBP

– Intermittent or Continuos - 0.5% wg

– High volume flush - 2% wg

� Wash oil and Antifoulant injection to casing– Revamp or TA modification

� Wash water injection– max 1% throughput to minimize rotor erosion

� Inter-coolers– Antifoulant injection facilities for online cleaning

� High efficiency 3D impeller blades (new service)– More efficient and larger gas passage

Page 27: Cracked Gas Compressor

Conclusions

? A review of equipment and maintenance records areessential to each producer

? Part of this review should include turbine andcompressor fouling

? Adequate wash oil selection and antifoulant injectionenables cracker extension of cracked gas compressorrun lengths by reducing the amount of polymerfouling.

? Any review should also include future optimizations

Page 28: Cracked Gas Compressor

Thank You

Q & A