HOT PLUME DISPERSION FROM GROUND FLARES IN … · HOT PLUME DISPERSION FROM GROUND FLARES IN AN LNG...

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FLUG Meeting – Bergen 1st June 2016

COMPARATIVE STUDY FLACS vs FLUENT

Cristina Zuliani, SAIPEM S.p.a

HOT PLUME DISPERSION FROM

GROUND FLARES IN AN LNG

PLANT:

FLUG Meeting – Bergen 1st June 2016

CRISTINA ZULIANI

Loss prevention and Environment

department

Fano

SAIPEM S.p.A.

cristina.zuliani@saipem.com

FLUG Meeting – Bergen 1st June 2016

COMPARATIVE STUDY FLACS vs FLUENT

Cristina Zuliani, SAIPEM S.p.a

HOT PLUME DISPERSION FROM

GROUND FLARES IN AN LNG

PLANT:

4FLUG Meeting – Bergen 1st June 2016

OUTLINE

Comparative study:

▫ Introduction and objective

▫Description of case study and modelling approach

▫CFD model

▫Findings

▫Conclusions

Effect of adjacent flare pits operations

5FLUG Meeting – Bergen 1st June 2016

OUTLINE

Comparative study:

▫ Introduction and objective

▫Description of case study and modelling approach

▫CFD model

▫Findings

▫Conclusions

Effect of adjacent flare pits operations

6FLUG Meeting – Bergen 1st June 2016

Introduction – Flares in LNG plants

ALTERNATIVE

GROUND FLARE ELEVATED FLARE

7FLUG Meeting – Bergen 1st June 2016

Introduction – Ground Flares

Large dimensions

Hundreds of burners

Large amount of flue

gases generated

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Introduction – Ground Flares

Safety Concerns

Pollutant emissions

Heat generated

High temperature gases

impacting on:

Personnel on elevated

structures

Equipment performance

(i.e. air coolers)

Equipment/buildings/

structures

9FLUG Meeting – Bergen 1st June 2016

Objective

Plume temperature profile

Turbulence, etc.

Geometryand terraininteraction

Cross windeffects

10FLUG Meeting – Bergen 1st June 2016

Objective

Iso - surface temperature profile

Temperature slice profile

Measured temperature at target locations

11FLUG Meeting – Bergen 1st June 2016

OUTLINE

Comparative study:

▫ Introduction and objective

▫Description of case study and modelling approach

▫CFD model

▫Findings

▫Conclusions

Effect of adjacent flare pits operations

12FLUG Meeting – Bergen 1st June 2016

Case Study – Ground flare LNG plant

Ground flare

400m

520m

670m

Gas Turbine

Air coolers

Targets:

Gas turbine

Air coolers

Criteria:

Personnel: 70°C

Equipment

performance: +2°C

increase above Tamb

W

NW

13FLUG Meeting – Bergen 1st June 2016

Case study - Scenarios

Case ID

Prevailing wind direction

from

Wind velocity

[m/s]

1 W 7

2 W 15

3 N-W 7

4 N-W 15

Constant variables

Ambient

Temperature [°C]33

Flue gas flow rate

[t/h]74870

Flue gas

temperature [°C]1195

Composition

(vol %)

N2 – 75%

O2 – 10%

CO2 – 5%

H2O – 10%

14FLUG Meeting – Bergen 1st June 2016

Modelling approach

Complete mixing of flue gases and entrained air –

homogeneous emitting source

No combustion chemistry – 100% excess air

Flames entirely shielded – no radiation

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OUTLINE

Comparative study:

▫ Introduction and objective

▫Description of case study and modelling approach

▫CFD model

▫Findings

▫Conclusions

Effect of adjacent flare pits operations

16FLUG Meeting – Bergen 1st June 2016

CFD Model set up – FLUENT v.12

Domain (LxWxH) 1100x1100x700m

Unstructured hexahedral grid

Turbulence sub-model: RNG k-

epsilon model

Boundary conditions:

Velocity inlet (Inlet, Top)

Pressure outlet (Outlet, left and

right side)

Wall (Ground)

17FLUG Meeting – Bergen 1st June 2016

CFD Model set up – FLACS v.10.2

Domain (LxWxH)

1500x1500x600m

Cartesian grid – refined around

the leak

Dispersion and ventilation – New

species

Wind & nozzle boundary

conditions

Area leak: Rectangular – uniform

18FLUG Meeting – Bergen 1st June 2016

OUTLINE

Comparative study:

▫ Introduction and objective

▫Description of case study and modelling approach

▫CFD model

▫Findings

▫Conclusions

Effect of adjacent flare pits operations

19FLUG Meeting – Bergen 1st June 2016

Findings – CASE 1 & 2

Temperature vertical profile at Gas Turbine

Ground flare

Gas TurbineW

Minor differences in the

maximum registered T (max

10°C)

Minor differences in the

position of the peak

temperature

Minor differences in the

registered T at target

height (22m) – Max 5%

0

50

100

150

200

250

300

350

400

450

500

306 311 316 321 326 331 336 341 346 351 356

Heig

ht

(m)

Temperature (K)

W 7ms (FLACS) W 7ms (FLUENT) W 15ms (FLACS) W 15ms (FLUENT)

H=22m

20FLUG Meeting – Bergen 1st June 2016

Findings – Case 1 (W - 7m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view

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Findings – Case 1

Iso-surface (70°C)

FLACS

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Findings – Case 1

Velocity streamlines

FLACS

23FLUG Meeting – Bergen 1st June 2016

Findings – Case 1

Temperature slice - + 2°C contour above Tamb

FLACS FLUENT

@ ground

24FLUG Meeting – Bergen 1st June 2016

Findings – Case 1

Temperature slice - 70°C contours at centreline

FLACS FLUENT

No impact on personnel at GT area

25FLUG Meeting – Bergen 1st June 2016

Findings – Case 2 (W - 15m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view

26FLUG Meeting – Bergen 1st June 2016

Findings – Case 2

Temperature slice - + 2°C contour above Tamb

FLACS FLUENT

Equipment performance is affected

@ground

400m

27FLUG Meeting – Bergen 1st June 2016

Ground flare

Air coolers

NWFindings – Case 3 & 4

Temperature vertical profile at Air Coolers

Minor differences in the

maximum registered T –

Max 8°C (2%)

Minor differences in the

position of the peak

temperature

Minor differences in the

registered T at target

height (22m) – Max 1%

0

100

200

300

400

500

600

700

306 308 310 312 314 316 318 320 322 324 326

Heig

ht

(m)

Temperature (K)

NW 7ms (FLACS) NW 7ms (FLUENT)

NW 15 ms (FLACS) NW 15ms (FLUENT)

H=22m

28FLUG Meeting – Bergen 1st June 2016

Findings – Case 3 (NW – 7m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view

29FLUG Meeting – Bergen 1st June 2016

Findings – Case 4 (NW – 15m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view

30FLUG Meeting – Bergen 1st June 2016

Findings – Case 4

Temperature slice - + 2°C contour above Tamb

AC performance is affected

@22m

FLACS FLUENT

670m

31FLUG Meeting – Bergen 1st June 2016

OUTLINE

Comparative study:

— Introduction and objective

— Description of case study and modelling approach

— CFD model

— Findings

— Conclusions

Effect of adjacent flare pits operations

32FLUG Meeting – Bergen 1st June 2016

Conclusions

FLACS confirms the same conclusions of the study

performed with FLUENT:

Performance of target equipment may be affected

No impact on personnel

Main differences:

FLACS - slightly higher maximum plume T (max 5%)

FLACS - slightly shorter extension of the 70°C iso-surface

FLACS - less evident plume bifurcation behaviour for the low wind

scenarios

33FLUG Meeting – Bergen 1st June 2016

Conclusions

Turbulence model: strength of buoyancy production in

the transport equation of the turbulence dissipation rate is

different;

More turbulence in FLACS – More mixing – shorter high T plumes

Inlet wind turbulence conditions; this is responsible

for the length of the plume, in particular at large distances

downwind;

Grid resolution effects in the far field. Effect of grid

stretching in FLACS

FLACS

FLUENT

𝐶3𝜀𝐹𝐿𝐴𝐶𝑆 = 1 − 𝐶3𝜀𝐹𝐿𝑈𝐸𝑁𝑇

Buoyancy production definition

34FLUG Meeting – Bergen 1st June 2016

OUTLINE

Comparative study:

— Introduction and objective

— Description of case study and modelling approach

— CFD model

— Findings

— Conclusions

Effect of adjacent flare pits operations

35FLUG Meeting – Bergen 1st June 2016

Adjacent flare pits

What happens?

How does the relative distance affect the plume?

36FLUG Meeting – Bergen 1st June 2016

Adjacent flare pits – Scenarios

Case ID

Prevailing wind direction

from

Wind velocity

[m/s]

1 W 7

2 W 15

3 N-W 7

4 N-W 15

Distance

40mDistance

80m

37FLUG Meeting – Bergen 1st June 2016

Findings – Adjacent flare pits – CASE 1

SINGLE PIT

TWO FLARE PITS

40m

TWO FLARE PITS

80m

Significant interaction

at 40m distance:

Longer and wider

plume

Behaviour

comparable to a

single larger GF

Reduced interaction

at 80m distance

38FLUG Meeting – Bergen 1st June 2016

Findings – Adjacent flare pits – CASE 1

CASE 1 – 40m distance

39FLUG Meeting – Bergen 1st June 2016

Findings – Adjacent flare pits – CASE 1

CASE 1 – 80m distance

40FLUG Meeting – Bergen 1st June 2016

Findings – Adjacent flare pits – CASE 2

SINGLE PIT

TWO FLARE PITS

40m

TWO FLARE PITS

80m

Significant interaction

at 40m distance:

Longer and wider

plume

Behaviour

comparable to a

single larger GF

No interaction at 80m

distance

41FLUG Meeting – Bergen 1st June 2016

Findings – Adjacent flare pits – CASE 3

SINGLE PIT

TWO FLARE PITS

40m

TWO FLARE PITS

80m

Longer and wider

plume

Behaviour

comparable to a

single larger GF

42FLUG Meeting – Bergen 1st June 2016

Findings – Adjacent flare pits – CASE 4

SINGLE PIT

TWO FLARE PITS

40m

TWO FLARE PITS

80m

Longer and wider

plume

Behaviour

comparable to a

single larger GF

43FLUG Meeting – Bergen 1st June 2016

Conclusions - Adjacent flare pits

Plume interaction can be significant and alter

conclusions of the analysis:

Adjacent flare pits with limited separation distance behave as a

single larger flare pit

Separation distance between flare pits is an important

design parameter and needs to be investigated with

sensitivity analysis

44FLUG Meeting – Bergen 1st June 2016

cristina.zuliani@saipem.com

45FLUG Meeting – Bergen 1st June 2016

Conclusions

Wind inlet boundary conditions:

FLUENT: ABL based on Richard and Hoxey

FLACS: ABL based on Monin and Obukhov

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