1. TUGAS K3 DALAM INDUSTRI KIMIA
Example of
EVENT TREE ANALYSIS
For Loss-of-Level Accident of Amine Absorber
TUGAS K3 DALAM INDUSTRI KIMIA
SITI SITAWATI
( )
Gas Management Program
University of Indonesia-2011

2. Sour Gas Processing Plant with Amine Unit

3. Sour Gas Processing Plant – Block Diagram
SULFUR RECOVERY
GAS METERING
STATION
WELL #1
FIRE WATER SYSTEM
HEAT ING MEDIUM
WATER TREATMENT
CLOSED DRAIN SYSTEM
INSTRUMENT AIR SYSTEM
FUTURE BOOSTER
COMPRESSOR
SALES GAS PIPELINE
WELLHEAD AREA
CENTRAL PROCESSING PLANT
UTILITIES
PRODUCED WATER TREATMENT
SEPA RATION
ACID GAS REMOVAL UNIT
DEHY-DRATION
FUEL GAS SYSTEM
INJECTION
WELL
POWER GENERATION SYSTEM
VENT
WASTE WATER TREATMENT SYSTEM
DEW POINT CONTROL
WELL #2
WELL #3
WELL #N
ACID GAS DISPOSAL
FLARE SYSTEM

4. Feed Gas & Sales Gas Composition
%-mole
Sales Gas
H2S
0.011
4 ppmv
CO2
29.56 5 N2
0.01
0.4 C1
69.86
91.6 C2
0.40
1.8 C3
0.065
0.7
C4+
0.119
5.5
Pressure, psig
1200
1150
Flow, MMscfd 93 55

5. Acid Gas Removal Unit – Amine Plant
1180 psig
LCV
30 psig

6. Absorber - Flash Column System
1180 psig
30 psig
LCV

7. Process Description of Amine Absorber
Sour gas containing 29% mole CO2 and 110 ppmv H2S is treated to meet sales gas specification by chemical solvent process in Amine Unit
CO2 & H2S are removed inside Amine Absorber, where lean amine and semi-lean solutions are contacted with incoming feed gas. Sweet gas is released from the top of the column.
Rich amine from Amine Absorber (1180 psig) is sent to Flash Column (30 psig) to release CO2 from amine solution by flashing/pressure reduction.
Amine Absorber level is controlled by LCV, which also functions to reduce pressure from 1180 psig to 30 psig.
Amine Absorber inlet and outlet lines are equipped with shutdown valves (SDV) to isolate the system in the event of upset/emergency cases.

8. Root Cause of Loss of Level Event
LCV failure due to cavitation damage
Absorber low level detected
Process control system activates SDV closing - failure
High pressure gas from Absorber blows by to low pressure Flash Column
Overpressure in Flash Column – PSV popping
Plant Shutdown

9. EVENT TREE ANALYSIS
One of probabilistic methods to show and quantify individual hardware component contribution to a failure of a process.
Include the effects of an event initiation followed by the impact of the safety systems.
Typical steps:
Identify an initiating event of interest
Identify the safety functions designed to deal with the initiating event
Construct the event tree
Describe the resulting accident event sequences

10. Event Tree Analysis - Assumptions
Loss of level event occurs once a year
Hardware safety functions fail 1% of the time they are placed in demand (0.01 failure/demand)
Operator notices low level 3 out of 4 times (0.25 failure/demand)
Operator is successful in closing SDV to keep absorber level 2 out of 4 times (0.5 failure/demand)
Operator is successful to shut down the system 9 out of 10 times (0.1 failure/demand)

11. Event Tree of Loss-of-Level Accident

12. Event Tree Analysis - Quantification
Net Frequency = sum of the frequencies of each state (shutdown, runaway, continue operation)
Shutdown:
= occurrences/yr
Runaway:
= occurrences/yr
Continue Operation:
= occurrences/yr

13. Event Tree Analysis - Interpretation
Dangerous runaway operation will occur on average 0.05 time/year or once every 20 years.
Net probability frequency is considered to be too high  requires reliable shutdown system.
Amine Plant shutdown will occur on average 0.45 time/year or once every 2.2 years.
Net probability frequency is considered to be too high  requires reliable level control system.
Amine Plant can continue operation by re-establishing level will occur on average 0.5 time/year or once every 2 years.
Net probability frequency is considered to be too high  requires highly reliable level control and shutdown systems.

14. Thank You