For full version of the thesis visit http://www.openthesis.org/documents/Gas-Flare-Stack-Process-603486.html and https://www.grin.com/document/387426

1. GAS FLARE STACK PROCESS
Shad B. Ibrahim
Mohammed A. Abdulkadir
Rabar M. Mahmood

2. CONTENT
› Introduction
› What is Flaring ?
› Flare Stack Classification
› Flare Process Components
› Design Calculation
› Cost Estimations
› Inspection, Safety And Recovery
› Gas Flare Implications
› References 2

3. INTRODUCTION
› The flare is the last line of defense in the safe emergency
release system in a refinery or chemical plant.
› It provides a means of safe disposal of the vapor streams
from its facilities, by burning them under controlled
conditions.
› With obeying the environmental regulation (EPA) of
pollution control and public relations requirements.
3

4. WHAT IS FLARING ?
› High-temperature oxidation process used to burn
combustible components (mostly hydrocarbons) of
waste gases from industrial operations.
› Natural gas, propane, ethylene, propylene, butadiene and
butane constitute over 95 % of the waste gases flared.
› C3H8 +5O2 → 3 CO2 + 4H2O.
4

5. FLARE STACK CLASSIFICATION
Flares
Height of
the flare
Elevated
Self Supported Stack
Guy Wired Supported
Stack
Derrick Supported
Stacks
Demountable Derrick
Supported Stacks
Ground
Open
Enclosed
Method to
enhance
mixing at
flare
Steam-Assisted
Air-Assisted
Non-Assisted
Pressure Assisted
5

6. FLARE PROCESS COMPONENTS
1
• Knock-out Drum
2
• Liquid Seal
3
• Flare Stack
4
• Gas Seal
5 •Burner Tip
6 •Pilot Burners
7 •Steam Jets
8 •Controls
6

7. FLARE STACK PROCESS (P&ID DRAWING)
7

8. DESIGN PROCEDURE AND CALCULATION
Parameters Value
Material Flowing Hydrocarbon Vapors
Flow rate 45 360 kg/h
Average Molecular Weight 46.1
Flowing Temperature 760 °R = 300 °F = 148.8 °C
Heat of Combustion 11 950 kcal/kg
Ratio of Specific Heats (γ = CP/CV) 1.1
Flowing Pressure at tip 1.03 kgf/cm2/a
Design Wind Velocity 33 km/h = 9.14 m/s
Hydrocarbon Vapor Density 1.33 kg/m3
› 𝑆𝑜𝑛𝑖𝑐 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 67.97 [
𝑘∗𝑅
𝑀𝑊
]0.5
= 289.55 𝑚/𝑠
› 𝐹𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 =
𝐹
𝑘𝑔
ℎ
ρ 𝑘𝑔
𝑚3 3600
𝑠
ℎ
= 9.43 𝑚3/𝑠
› 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝑔𝑎𝑠 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 289.55 0.2 = 57.91 𝑚/𝑠
› 𝐴𝑟𝑒𝑎 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 =
9.43 𝑚3/𝑠
57.91 𝑚/𝑠
= 0.1627 𝑚2
› Basis: Design for velocity of Mach number = 0.2
› 𝑑2
= 0.21 𝑚2
› 𝑑 = 0.45 𝑚
8

9. Figure 1: Flame Length vs Heat Release.
Flame Length
› 𝑄 = 𝐹
𝐾𝑔
ℎ
𝐻
𝐾𝑐𝑎𝑙
ℎ
= 54 107 𝐾𝑐𝑎𝑙
ℎ
= 6.2 ∗ 105 𝑘𝑊
› Figure 1: 𝐿 = 51.8 𝑚
9

10. Figure 2: Flame Distortion due to Lateral Wind.
›
𝑈 𝑤
𝑈 𝑜
= 0.158
› Figure 2:
›
∑∆𝑦
∑𝐿
= 0.35 m,
›
∑∆𝑥
∑𝐿
= 0.85 𝑚
› ∆𝑦 = 18.13 𝑚
› ∆𝑥 = 44.0 𝑚
Flame Distortion caused
by Wind
10

11. Flare Height
› Design basis: 𝐹 = 0.3, 𝑄 = (0.54)
(109
) 𝑘𝑐𝑎𝑙/ℎ
𝐾 = 5424 𝑘𝑐𝑎𝑙 / 𝑚 2/ ℎ 45.72m from
flare stack
› 𝐷 =
𝐹 𝑄
4 3.14 𝐾
=
39.0 𝑚
› 𝑅’ = 𝑅 − 1
2 𝑥 = 23.70 𝑚
› 𝐷2 = 𝑅′2 + 𝐻′2 so 𝐻′ = 30 𝑚
› 𝐻 = 𝐻 + 1
2 (𝑦) = 21.0 𝑚
Figure 3: Dimensional References for Sizing a Flare Stack 11

12. COST ESTIMATIONS
› In which 𝐷 = 0.46 m = 17.71 in, 𝐿 = 21 m = 68.89 ft
𝐶 𝐹 $ = (78.0 + 9.14 𝐷 + 0.749 𝐿)2 = 84 953.6 $
› In which 𝑑 = 1𝑚 = 39 𝑖𝑛, ℎ = 3𝑑 = 117 𝑖𝑛, 𝑡 = 0.37 𝑖𝑛
𝐶 𝑘 $ = 14.2 [𝑑𝑡 ℎ + 0.812 𝑑 ]0.737
= 1699.54 $
› 𝐶 𝑝 $ = 127 𝐷1.22
= 127(17.71)1.22
= 4232.8 $
› Total auxiliary equipment cost
𝐶 𝑘 $ + 𝐶 𝑝 $ = 5932.34 $
12

13. Item Cost ($)
Direct Costs
Purchased Equipment cost
Flare System 84 953.6
Auxiliary 5 932.34
Sum of A 90 885.94
Instrumentation (0.10 A) 9 088.59
Sales Taxes (0.03A) 2 726.57
Freight (0.05 A) 4 544.29
PEC = B 107 245.39
Direct Installation Costs
Foundation and Supports
(0.12 B)
12 869.44
Handling and Erection (0.40
B)
42 898.15
Electrical (0.01 B) 1 072.45
Piping (0.02 B) 2 144.90
Item Cost ($)
Installation (0.01 B) 1 072.45
Painting (0.01 B) 1 072.45
Total 61 129.84
Site Preparation 10 000
Facilities and Buildings 15 000
Total Direct Costs 𝟗𝟔 𝟏𝟐𝟗. 𝟖𝟒
Indirect Annual Costs
Engineering (0.10 B) 10 724.53
Construction & Field Expenses
(0.10 B)
10 724.53
Contractor Fees (0.10 B) 10 724.53
Start-up (0.01 B) 1 072.45
Performance Test (0.01 B) 1 072.45
Contingencies (0.15 B) 16 086.80
Total Indirect Costs 50 405.29
Total Capital Investment 146 535.13

14. INSPECTION, SAFETY AND RECOVERY
› Maintenance
› Spare Parts
› Malfunctions
› Operator Training
Inspection
› Emergency
planning
› Maintenance
› Ventilation
› Noise
Safety Recovery
› Collection,
compression
› Gas-to-liquid
› Generating
electricity
14

15. Mechanism Symptom Correction
Over
Pressurization Relief valves open Set valves to correct
position
Cross and open
connections.
Back fire Verify connection and
valve position
Burner fouling Flame out Clean burner tips more
frequently
15

16. GAS FLARE IMPLICATIONS
› Climate Change
› Acid Rain
› Agriculture
› Thermal Emission
› Luminosity
› Noise Pollution
› Radiation
› Adverse Effects
› Hematological
Effects
› Economic
› Pollution
› Social
Environmental Health Other
16

17. Gas Flaring Constituent Gas Composition Gas
Min.
Flaring
Max.
%
Average
Methane CH4 7.17 82.0 43.6
Ethane C2H6 0.55 13.1 3.66
Propane C3H8 2.04 64.2 20.3
n-Butane C4H10 0.199 28.3 2.78
Isobutane C4H10 1.33 57.6 14.3
n-Pentane C4H10 0.008 3.39 0.266
Isopentane C5H12 0.096 4.71 0.530
Neo-Pentane C5H10 0.000 0.342 0.017
n-Hexane C6H14 0.026 3.53 0.635
Ethylene C2H4 0.081 3.20 1.05
Propylene C3H6 0.000 42.5 2.73
1-Butene C4H8 0.000 014.7 0.696
Carbon Monoxide CO 0.000 0.932 0.186
Carbon Dioxide C02 0.023 2.85 0.713
Hydrogen Sulfide H2S 0.000 3.80 0.256
Hydrogen H2 0.000 37.6 5.54
Oxygen O2 0.019 5.43 0.357
Nitrogen N2 0.073 32.2 1.30
Water H2O 0.000 14.7 1.14
17

18. REFERENCES
› A L Ling, July 2007. FLARE SELECTION AND SIZING (ENGINEERING DESIGN
GUIDELINE), Johor Bahru: KLM Technology Group.
› Leslie B. Evans, William M. Vatavuk, Diana K. Stone, Susan K. Lynch, Richard F.
Pandullo, September 2000. VOC Destruction Controls, North Carolina, Durham:
Office of Air Quality Planning and Standards, U.S Environmental Protection
Agency.
› Ludwig, Ernest E., 1999. APPLIED PROCESS DESIGN FOR CHEMICAL AND
PETROCHEMICAL PLANTS, Volume 1, Third Edition, United States of America:
Gulf Publishing Company.
› Charles E. Baukal, JR., 2014. The John Zink Hamworthy Combustion Handbook,
Second Edition: Volume 3 – Applications, Boca Raton, Fort Lauderdale, USA:
Taylor & Fransic Group LLC.
› Nicholas P. Cheremisinoff, Apr 1, 2013. INDUSTRIAL GAS FLARING PRACTICES,
New Jersey USA: John Wiley & Sons Cooperation
18

19. THANK YOU
19