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 (1006735574) Gas Management Program University of Indonesia-2011

Sour Gas Processing Plant with Amine Unit

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

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

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

Absorber - Flash Column System 1180 psig 30 psig LCV

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.

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

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

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)

Event Tree of Loss-of-Level Accident

Event Tree Analysis - Quantification Net Frequency = sum of the frequencies of each state (shutdown, runaway, continue operation) Shutdown: 0.4455 + 0.003375 + 0.001125 = 0.45 occurrences/yr Runaway: 0.0495 + 0.000375 + 0.000125 = 0.05 occurrences/yr Continue Operation: 0.495 + 0.00375 + 0.00125 = 0.50 occurrences/yr

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.

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