Ethylene Unit Cracked Gas CompressorCase Studies on Fouling

Visagaran Visvalingam - Presenter

Cyron Anthony Soyza

Sew Nyit Tong

Karl Kolmetz

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

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

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

Diffusers

BalanceLine

Wheels

Inlet Vanes

Compressor Overview

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

RR +

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

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

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

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

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

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

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

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

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

RotorRotor CasingCasing

2nd stage intercooler bundle Bundle entrance

Polymer laced inlet pipeline Inlet to intercooler

Turnaround inspections - CGC Turbine

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

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

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

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

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

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

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

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

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

Thank You

Q & A

Ethylene Unit Cracked Gas Compressor Case Studies on FoulingOutlinesOverview of Equipment & SetupCompressor System Flow DiagramFouling Phenomenon - What,Why and HowCGC Fouling ExperiencesCGC Polytropic EfficiencyCompressor Delta TIdentification of Turbine FoulingCauses of Turbine FoulingImpacts of Compressor-Turbine FoulingTurnaround InspectionsCGC Inspection- TA99 & TA2001Countermeasures for Fouling ControlCompressor Wash Oil ReviewAnti-foulant InjectionAntifoulant Trial RunAntifoulant Trial Run Findings4th Stage Polytropic Efficiency and Delta T4th Stage Polytropic Efficiency and Delta TFuture ImprovementsConclusionsThank You Q & A