hot plume dispersion from ground flares in … · hot plume dispersion from ground flares in an lng...
TRANSCRIPT
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.
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
8FLUG Meeting – Bergen 1st June 2016
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
15FLUG 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
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
21FLUG Meeting – Bergen 1st June 2016
Findings – Case 1
Iso-surface (70°C)
FLACS
22FLUG Meeting – Bergen 1st June 2016
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
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