Basic engineering design of flares on oil platforms using computational fluid dynamics

Transcription

1 Basic engineering design of flares on oil platforms using computational fluid dynamics Mauro C. B. Dolinsky, D.Sc PETROBRAS/CENPES Marcos Antonio P. Amaral, M.Sc PETROBRAS/CENPES Paulo Roberto Pagot, D.Sc PETROBRAS/CENPES

2 PRESENTATION TOPICS Company Overview; Problem Description; Methodology; Results; Conclusion and next steps.

3 Petrobras Business Plan Company Overview (US$ 220,6 billions) 27,4% (US$ 64,8 bi) E&P 62,3% (US$ 147,5 bi)

4 Company Overview

5 Company Overview Cenpes CENPES Original Expansion Total Constructed area m m m 2 Total area m m m Laboratories Equipments Investiment US$700 million

6 Problem Description The basic engineering design on a flare project is responsible for determining tower height as well as additional protection at tower surface. The radiation behaviour around the structure is used to stablish the safe distance of the flame to personel at the process unit.

7 Problem Description Temperature profile at tower surface indicates the necessity of additional protection (special painting and/or heat shield).

8 Problem Description The main objective of this study is to develop a CFD methodology analysys to be used as a tool for basic design of flares.

9 Methodology Assumptions The 3D model was simplified; Pipe burner type; Annular air flare Solar radiaton (789 W/m 2 ); Steel emissivity 0.7 Wind temperature 30 C Wind speed: Calm condition, 0.5 m/s Mean 6 m/s Maximum 13 m/s

10 Methodology Gas composition Emergency Low Pressure (continuous) High Pressure Low Pressure Composition H2O 1,36 0,05 1,36 N2 0,01 1,34 0,01 H2S 0,00 0,00 0,00 CO2 3,78 9,46 3,78 Metane 7,83 68,81 7,83 Etane 12,52 9,86 12,52 Propane 27,75 6,11 27,75 ISO-butane 7,97 1,19 7,97 n-butane 16,63 2,14 16,63 ISO-pentane 4,76 0,42 4,76 n-pentane 5,95 0,45 5,95 Hexane 11,43 0,13 11,43

11 Methodology Pipe definition Unit High pressure flare Low pressure flare Flare type - Pipe Pipe Position - Vertical Vertical Lenght [m] 3,0 3,0 Number Unidade 1,0 1,0 Diameter [mm] 800,0 250,0 Gas speed [m/s] 130,1 76,2

12 Methodology Tetrahedrical mesh preliminary analysys 2.2x10 6 cells second phase 3.3 x 10 6 refined at wall structure Emergency continuous Assist Air Turbulence: k-ω + SST

13 Methodology Models Combustion: Eddy Dissipation Model Soot: Moss brokes Soot precursor Low pressure Emergency Initial analysis C 3 H 8 CH 4 Case 1 C 3 H 8 C 3 H 8 Case 2 C 4 H 10 C 4 H 10 Radiation: Discrete Ordinates (DO) with solar radiation; Weighted Sum of Gray Gas Model (WSGGM)

14 Results Flame profile (isometric) Calculated adiabatic temperature 2350C 0,5 m/s 6 m/s 13 m/s

15 Results Flame profile Emergency (isometric) Calculated adiabatic temperature 2460C 0,5 m/s 6 m/s 13 m/s

16 Results Visible flame (1350K) 0,5m/s 6 m/s 13 m/s

17 Results Visible flame - Emergency (1350K) 0,5 m/s 6 m/s 13 m/s

18 Results Soot 0,5 m/s 6 m/s 13 m/s

19 Results Soot - Emergency 0,5 m/s 6 m/s 13 m/s

20 Results Incident radiation - Compare to API recommended practice (1577 w/m 2 ) for continuous exposition to check tower height 0,5 m/s 6 m/s 13 m/s

21 Results Incident radiation - Compare to API recommended practice (4730 w/m 2 ) for human exposure at emergency conditions 0,5 m/s 6 m/s 13 m/s

22 Results Wall temperature (Low pressure) 0,5 m/s 6 m/s 13 m/s

23 Results Wall temperature (Emergency) 0,5 m/s 6 m/s 13 m/s

24 Results Convective heat transfer coeficient 45 Low pressure 45 Emergency Calculated convective heat transfer coefficient (W/m2K) Simulated convective heat transfer coefficient (W/m2K) Calculated convective heat transfer coefficient (W/m2K) Simulated convective heat transfer coefficient (W/m2K) ,5m/s 6m/s 13m/s 0 0,5m/s 6m/s 13m/s

25 Conclusion and next steps CFD methodology is usefull for basic engineering design of flares; Results indicate that at wind speed increase, the flame is bent which increase temperature at the strucure; Thermal balance shows that thermal radiation contributes more on heating the structure than the convective wind on refreshment of the structure;

26 Conclusion and next steps Evaluation of full structure; Evaluation of simplified structure (no wall at the top);

27 Conclusion and next steps Evaluation of low pressure and emergency as separated structures; Remove assist air on pipe. Emergency continuous Assist Air Evaluate other models.