hot plume dispersion from ground flares in … · hot plume dispersion from ground flares in an lng...

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:


CRISTINA ZULIANI

Loss prevention and Environment

department

Fano

SAIPEM S.p.A.

[email protected]


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


OUTLINE

Comparative study:



▫CFD model

▫Findings

▫Conclusions



Introduction – Flares in LNG plants

ALTERNATIVE

GROUND FLARE ELEVATED FLARE


Introduction – Ground Flares

Large dimensions

Hundreds of burners

Large amount of flue

gases generated


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


Objective

Plume temperature profile

Turbulence, etc.

Geometryand terraininteraction

Cross windeffects


Objective

Iso - surface temperature profile

Temperature slice profile

Measured temperature at target locations


OUTLINE

Comparative study:



▫CFD model

▫Findings

▫Conclusions



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


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%


Modelling approach

Complete mixing of flue gases and entrained air –

homogeneous emitting source

No combustion chemistry – 100% excess air

Flames entirely shielded – no radiation


OUTLINE

Comparative study:



▫CFD model

▫Findings

▫Conclusions



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)


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


OUTLINE

Comparative study:



▫CFD model

▫Findings

▫Conclusions



Findings – CASE 1 & 2

Temperature vertical profile at Gas Turbine

Ground flare

Gas TurbineW

Minor differences in the

maximum registered T (max

10°C)


position of the peak

temperature


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


Findings – Case 1 (W - 7m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view


Findings – Case 1

Iso-surface (70°C)

FLACS


Findings – Case 1

Velocity streamlines

FLACS


Findings – Case 1

Temperature slice - + 2°C contour above Tamb

FLACS FLUENT

@ ground


Findings – Case 1

Temperature slice - 70°C contours at centreline

FLACS FLUENT

No impact on personnel at GT area


Findings – Case 2 (W - 15m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view


Findings – Case 2


FLACS FLUENT

Equipment performance is affected

@ground

400m


Ground flare

Air coolers

NWFindings – Case 3 & 4

Temperature vertical profile at Air Coolers


maximum registered T –

Max 8°C (2%)


position of the peak

temperature


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


Findings – Case 3 (NW – 7m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view


Findings – Case 4 (NW – 15m/s)

Iso-surface (70°C)

FLACS

FLUENT

No impact on

personnel

Plan view Side view

Plan view Side view


Findings – Case 4


AC performance is affected

@22m

FLACS FLUENT

670m


OUTLINE

Comparative study:

— Introduction and objective

— Description of case study and modelling approach

— CFD model

— Findings

— Conclusions



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


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


OUTLINE

Comparative study:

— Introduction and objective

— Description of case study and modelling approach

— CFD model

— Findings

— Conclusions



Adjacent flare pits

What happens?

How does the relative distance affect the plume?


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


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



CASE 1 – 40m distance



CASE 1 – 80m distance



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



SINGLE PIT

TWO FLARE PITS

40m

TWO FLARE PITS

80m

Longer and wider

plume

Behaviour

comparable to a

single larger GF


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


[email protected]


Conclusions

Wind inlet boundary conditions:

FLUENT: ABL based on Richard and Hoxey

FLACS: ABL based on Monin and Obukhov

hot plume dispersion from ground flares in … · hot plume dispersion from ground flares in an lng...

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