Quicker Approach to Staggered Blowdown Presentation Final
- 2. C t tContents What is Blowdown/Depressurizationp When Staggered Blowdown is Required Conventional Approach to Staggered Blowdown Case Study Case Study Methodology of Quicker Approach Conclusion 2
- 3. Wh t i Bl dWhat is Blowdown What is Blowdown/Depressurizationp Blowdown is to depressurize a high pressure system, containing hydrocarbon/toxic gases, to a low pressure level to reduce the risk of rupture/burst in case of fire or any other emergency.p / y g y How Blowdown is carried out Th bj ti f Bl d i t d i th t f it d i The objective of Blowdown is to depressurize the system from its design pressure to 700 kPa(g) or 50% of the system design pressure, whichever is lower, in 15 minutes. How Blowdown is Activated Upon detection of Fire/Gas or any other demand scenario the blowdown valve is opened either automatically or by a push button by operator to activate the blowdown. When Blowdown is Required Blowdown is required when operating pressure > 1700 kPa(g). 3
- 4. Wh t i Bl dWhat is Blowdown 4
- 5. Wh t i Bl dWhat is Blowdown 5
- 6. Wh St d Bl d i R i d Staggered Blowdown is required: When Staggered Blowdown is Required gg q Simultaneous Blowdown load >> largest relief load Design of flare system for simultaneous blowdown is impractical/uneconomical. Staggered blowdown system shall be designed to restrict the flare system design capacity (green fields) For brown field projects staggered blowdown is an essential requirement when the relief/blowdown load is added into existing flare system. 6
- 7. C ti l A h t St d Bl d Zonal Blowdown Approach Conventional Approach to Staggered Blowdown pp The conventional approach is to divide the blowdown loads into zones and carryout the blowdown zone by zone. Zones can be made: based on physical separation of units. b bi i th bl d l d f dj t it t k th t t l l by combining the blowdown loads of adjacent units to make the total zonal blowdown load equal to flare capacity. Z b Ph i l S i Zones by Physical Separation Make zones by physical segregation based on allowable radiation criteria from one zone to another. M ffi i f d bl d More efficient way of staggered blowdown. Effective for relatively smaller facilities. 7
- 8. C ti l A h t St d Bl d Zones By Blowdown Load Conventional Approach to Staggered Blowdown y Zones can be made on blowdown loads analysis. Adjacent units loads shall be combined to make a reasonable total which will be the j flare capacity. Flare capacity shall be carefully selected taking into account the relief valve p y y g capacities for largest individual relief and simultaneous relief. 8
- 9. C St d Project: Rabab Harweel Integrated Project (High Sour. H2S 6% ‐ 20%) Case Study j g j ( g ) Simultaneous Blowdown Load: 90 MMSCMD (million standard cubic meters/day) Flare Capacity: 16.55 MMSCMD 3.13 MMSCMD is reserved for relief valve from trunk lines. Effective Flare Capacity: 13 42 MMSCMDEffective Flare Capacity: 13.42 MMSCMD Combined Blowdown load is about 6 times the flare capacity. Developing an effective staggered blowdown sequence is a challenge due to very large combined blowdown load compared to the flare capacity. 9
- 10. C St d C ti l A h Making zones based on physical segregation of the units yield numerous Case Study: Conventional Approach g p y g g y zones and each zone capacity was significantly less than the effective flare system capacity. Therefore, zones were made based on blowdown loads analysis. d h t t li t l MMSCMD 7 zones were made each totaling to nearly 13.42 MMSCMD. Adding relief valve load of trunkline to each zone’s blowdown load make each zone’s total load equal to flare system capacity. Then under a plant wide blowdown situation, such as instrument air failure or p , power failure, all the zones shall blowdown one by one. Last zone start to blowdown at 84 minutes Last zone start to blowdown at 84 minutes. 10
- 11. C St d C ti l A hCase Study: Conventional Approach 11
- 12. C St d C ti l A h Long depressuring time Increased Risk Case Study: Conventional Approach g p g Exceeds UPS backup time facility cannot be safely blowdown Possible Solution Increase flare capacity More cost ($$$) 12
- 13. C St d Q i k A h The idea of the quicker approach lies in the fact that the peak depressuring Case Study: Quicker Approach q pp p p g rate occurs in the beginning of the blowdown and then depletes exponentially. Depressuring rate drops to half of the peak rate in less than four (4) minutes. 13
- 14. C St d Q i k A h This method utilizes the maximum use of flare header capacity. Case Study: Quicker Approach p y Units to blowdown are prioritize. Preferential units blowdown first, followed by other units in order of priority. The moment the capacity becomes available in the header, next blowdown is kicked in. The last unit starts to blowdown at 45 minutes. About half of the blowdown time calculated by conventional zonal blowdown About half of the blowdown time calculated by conventional zonal blowdown approach (84 minutes). 14
- 15. C St d Q i k A hCase Study: Quicker Approach 15
- 16. M th d l f Q i k A h Blowdown load of each processing unit in the facility is listed below: Methodology of Quicker Approach p g y Unit Name Peak Depressring Rate (MMSCMD) Unit Name Peak Depressring Rate (MMSCMD) Inlet Separator A 5 48 Dehydration Unit‐2 1 09Inlet Separator A 5.48 Dehydration Unit 2 1.09 Inlet Separator B 5.48 HP Acid Gas Compressor‐1 0.54 Inlet Separator C 1.23 HP Acid Gas Compressor‐2 0.54 Test Separator 0.53 LP Acid Gas Compressor‐1 0.11 Condensate Stabilizer Unit 2.21 LP Acid Gas Compressor‐2 0.11 Flash Gas Compressor 1 Piping segment‐1 10.46 Trunk Line 3.13 Piping segment‐2 2.51 Sweetening Unit‐1 5.42 Piping segment‐3 3.02 Sweetening Unit‐2 5.42 Piping segment‐4 1.24 Export Gas Compressors 2.48 Piping segment‐5 2.95 Dew Point Control Unit 7 31 Piping segment 6 3 18Dew Point Control Unit 7.31 Piping segment‐6 3.18 Reinjection Compressor‐1 5.67 Seal Gas Compressor 0.18 Reinjection Compressor‐2 5.67 Seal Gas Buffer Vessel 6.53 Reinjection Compressor‐3 5.72 Fuel Gas Unit 1.71Reinjection Compressor 3 5.72 Fuel Gas Unit 1.71 Dehydration Unit‐1 2.15 Total 93.06 16
- 17. M th d l f Q i k A h At zero time, when the plant wide depressurization is activated by ESD system, the first set of Methodology of Quicker Approach units, summing up to flare capacity, will starts to blowdown (peak‐1). after 2.17 minutes the blowdown load has dropped to 10.18 MMSCMD. Table‐01 shows that blowdown load of Reinjection compressor‐1 and HP Acid Gas Compressor 2 is 6 21 MMSCMD which can be safely started to blowdownCompressor‐2 is 6.21 MMSCMD which can be safely started to blowdown. At 2.17 minutes, blowdown of Reinjection compressor‐1of Reinjection compressor‐1 and HP Acid Gas Comp.‐2 is started which raise the total blowdown load to total blowdown load to 16.4 MMSCMD (peak‐2). Similarly, after 4.5 minutes, y, 4 5 , the blowdown rate falls to 10.81 MMSCMD and from table‐01, Inlet Separator‐A can be started to blowdown safely (peak‐3). 17
- 18. ESD S t D i f Q i k A h Several Staggered Blowdown Sequences may need to be developed. ESD System Design for Quicker Approach gg q y p Fire detection in each area of the facility will need a separate staggered blowdown sequence as the area under fire shall be the first unit in the sequence blowdown sequence as the area under fire shall be the first unit in the sequence to blowdown. I f d f il i i i t t i f il l t In case of common mode failure scenarios i.e. instrument air failure or plant wide power failure, set of preferential units shall blowdown first. Thus, the ESD system shall be provided with several staggered blowdown sequences to deal with different emergency situations. 18
- 19. C l i Quicker approach reduces the total blowdown time by about 50%. Conclusion Q pp y 5 Reduced risk & hazard to personal and environment. Do not need flare capacity enhancement. Save capital cost ($$$). Total blowdown time is within the UPS backup time Total blowdown time is within the UPS backup time Facility can be safely blowdown. 19
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