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RAMBOLL OIL & GAS
PROCESS DESIGN – CAN WE
CHANGE MINDSET?
Anders Andreasen, Chief Consultant
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
INTRODUCTION AND OUTLINE
• Dynamic flare system
modelling
• Fire PSV’s: Sizing challenges /
Added safety?
• Process optimisation through
response surface methodology
Background:
2002
M.Sc. Chem. Eng. Aalborg University
Esbjerg: Heterogeneous catalysis and
kinetic modelling
2005
Ph.d. Chem. Eng. Technical University of
Denmark/Risø National Laboratory:
Energy storage in light metal hydrides.
2005-2012
Senior Research Engineer in Process
Development, MAN Diesel and Turbo,
Copenhagen. Research in engine
performance, combustion, emission
reduction technology.
2012-?
Chief Consultant, Process Department,
Ramboll Oil & Gas Esbjerg.
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
DYNAMIC FLARE SYSTEM MODELLING
OUTLINE
• Basic flare system introduction
• Key flare system process design criteria
• Current state of flare system modelling
• Advantages by dynamic flare modelling
• Preliminary dynamic simulation results
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
DYNAMIC FLARE SYSTEM MODELLING
FLARE SYSTEM INTRODUCTION
http://kolmetz.com/pdf/EDG/ENGINEERING%20DESIGN%20GUIDELINE-%20Flare%20Rev1.1.pdf
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
FLARE SYSTEM/BLOW-DOWN PURPOSE
NORSOK S-001: “The purpose of the BD (depressurisation) and flare/vent
system is during an accidental event or emergency situation to
• in the event of a fire to reduce the pressure in process segments to
reduced the risk of rupture and escalation,
• reduce the leak rate and leak duration and thereby ignition probability,
• in some cases avoid leakage at process upsets, e.g. in case of loss of
compressor seal oil/seal gas, “
API 521/ISO 23251
The purpose of the disposal system is to conduct the relieved fluid where it can be
safely discharged.
The primary function of a flare is to use combustion to convert flammable, toxic, or
corrosive vapours to less objectionable compounds
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
FLARE SYSTEM KEY DESIGN CRITERIA
• Velocity
• API 512: Mach 0.5 – Flare stack
• NORSOK Mach 0.6 – Header
• NORSOK Mach 0.7 – Tail pipe
• Pressure:
• Design pressure not to be exceeded by static pressure
• Temperature: Joule-Thompson effect
• Flow induced vibration and noise
• Stress: ρv2 < 200.000 kg/(m s2)
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
FLARE SYSTEM MODELLING – CURRENT
STATE
• State-state network solvers are used as an industry accepted
method for flare system rating and analysis
• Peak rates are considered only
• “Danger” of new design of flare systems is too large
(heavy/expensive)
• Debottlenecking on existing flare systems is made difficult when
adding new relief/blow-down source due to tie-in of additional
production
• Software: AspenTech Flare System Analyser, Honeywell UniSim
Flare.
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
FLARE SYSTEM MODELLING – CURRENT
STATE
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
DYNAMIC FLARE MODELLING
STATE OF THE ART
• Flare system load is generally not a steady-state phenomenon
• By dynamic modeling a number of effects can be taken into
account:
• Line packing
• Staggered opening of flow sources
• Flaring into ”empty” system
• Dynamic modelling may ensure a better utilisation of flare system
and avoid costly rebuild during revamp.
• Ramboll has experience with using dynamic Hysys for this
purpose.
• Aspentech is planning a dynamic version of flare system analyzer.
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
DYNAMIC FLARE SIMULATION EXAMPLE
• Part of HP flare system modelled in HYSYS
• A total of 16 BDV’s/flow sources modelled
• Hold-up volume of tail-pipes, sub-headers, headers and flare drum
BDV’s
Sub headers
Flare stack
Main header
Flare drum
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
DYNAMIC FLARE SIMULATION RESULTS
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
FIRE PSV’S
• What is a (fire) PSV?
• Why do we have fire PSV’s installed?
• Fire PSV simulations, a case study
• Alternative?
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
To flare
Image source http://www.enggcyclopedia.com/2011/04/typicalpid-arrangement-3-phase-separator-vessels/
WHAT IS A FIRE PSV?
Usually sized for pool fire with:
• Liquid expansion
• Gas expansion
• Two-phase evaporation
Image source: API 520
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
WHY HAVE FIRE RELIEF?
• According to codes such as API 521, API 14C PSV’s shall be
installed to protect equipment in case of a fire (ASME
requirement).
• PED is more performance based than ASME
• It has been recognised by the industry that fire PSV may not
prevent overpressure rupture in a fire and in some cases the PSV
may not even open.
• Still fire PSV’s are installed, but they should not be considered
primary protection against overpressure in a fire.
• Primary protection is Blowdown, PFP and deluge.
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
WHY HAVE FIRE RELIEF?
• To relieve generated vapour in a controlled manner
• Buy time to control / contain fire
• Prevent catastrophic vessel failure which can lead to
•
E.g. BLEVE (Boiling Liquid Expanding Vapour Cloud Explosion)
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION
• Calculate pressure in the system
• Temperature in all fluid phases
• Fluid composition in each phase
• Flow rate through orifice
• Liquid levels
• Temperature in metal
• Heat transfer at all interphases
• Stress calculations
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION CASES
• Large jet fire at unwetted part of vessel
• Small jet fire at unwetted part of vessel
• Pool fire exposing wetted part of vessel
• Pool fire exposing unwetted part of vessel
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION – LARGE
JET FIRE AT UNWETTED PART OF VESSEL
With PSV:
Without PSV:
Rupture!
Rupture!
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION – SMALL
JET FIRE AT UNWETTED PART OF VESSEL
Rupture!
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION – POOL
FIRE EXPOSING WETTED PART OF VESSEL
With PSV:
Without PSV:
Rupture!
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION – POOL
FIRE EXPOSING UNWETTED PART OF VESSEL
Without PSV:
With PSV:
Rupture!
Rupture!
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
VESSFIRE FIRE PSV SIMULATION – SUMMARY
Fire PSV does not prevent or significantly delay stress rupture except
for pool fire engulfing wetted part of a vessel.
For small jet fires the PSV will not even open before stress rupture.
If possible avoid installing fire PSV if it has no safety benefit as the
device itself introduces risk e.g. leak source, maintenance etc.
Rely instead on blowdown, PFP and deluge
Blowdown reduces inventory pressure and stress below PSV set
pressure!
Consider installing redundant blowdown where one BDV is activated by
fussible plugs
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
ALTERNATIVE TO FIRE PSV’S
To flare
•
Increased reliability of blowdown
•
Pressure relief not limited by set
pressure
Alternatively each BDV could have
its own orifice resulting in extremely
fast depressurisation of vessel
exposed to fire. However exceeding
design pressure of disposal system
will not be allowed whereas
exceedance of nominal flare
capacity is less critical.
S
BDV 2
ESD2
BDV 1
Pressure system
Consider lowering set points of fire
PSVs below design pressure if
operation pressure is significantly
below design pressure.
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
• Defining the optimisation problem
• Process optimisation by trial-and-error or one factor at a time
• Introduction to response surface methodology (RSM)
• Results of RSM and constrained multi-objective optimisation
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
Image source: http://www.mdpi.com/molecules/molecules-19-00067/article_deploy/html/images/molecules-19-00067-g001-1024.png
PROCESS OPTIMIZATION PROVIDED BY
RESPONSE SURFACE METHODOLOGY
OPTIMISATION PROBLEM – AN EXAMPLE
• NGL mitigation in off-shore oil and gas separation plant
• NGL can be exported mainly in gas or mainly in oil or both
• Oil and gas export specifications may act as constraints and may
be difficult/impossible to comply with simultaneously. In this
example not all export specifications can be met simultaneously.
• Power consumption minimisation is pivotal – space, weight, CO2
emissions, loss of revenue
NGL
Source: Natural Gas Liquids - Supply Outlook 2008-2015, International Energy Agency, April 2010
Source: Energinet.dk and
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
X1
X5
X4
X2
Y2
X3
Y1
PARAMETERS
X1
Booster pressure
X2
Pressure after
expander
X3
Separator pressure
X4
NGL reboiler temperature
Y3
OBJECTIVES
Y1
Oil export RVP
Y2 (Multiple)
X5
Gas Export Quality (see table)
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
Dehydration inlet
UNIVERSITY ESBJERG
2014/08/19
temperature
Y3
Total power consumption
PROCESS OPTIMISATION CHALLENGES
• Identification of important parameters/sensitivity. Process
intuition.
• Optimisation by trial-and-error:
• May result in many simulation/experiments for even a hand full of
independent variables
• Constraints are difficult to handle
• Little leaning
• One factor at a time (OFAT)/line search.
• Key sensitivities may be identified
• Interaction effects are not handled/considered
• General: Global optimum may not be found!
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
RESPONSE SURFACE METHODOLOGY
“COOKBOOK”
1. Generate a design of experiment probing the expected
parameter space (constraints in independent variables –
physical, practical etc.)
2. Perform the corresponding (simulation) experiments
3. For each dependent variable, Yi, generate a linear regression
model as a function of independent variables, Xj’s.
4. Check for linear regression assumption violations, lack-of-fit etc.
(normal residuals, “random residuals”, outliers with influence etc.)
5. Perform regression model selection (repeat 3-5)
6. Validate models (is often forgotten) outside training set
7. Optimize
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
EXPERIMENTAL DESIGN AND MODEL
SELECTION
• Full factorial (too many combinations): 5 parameters 3 levels =>
35 = 243 simulation runs/experiments
• Fractional factorial, reduced number of runs
• Central composite designs, face centered (three level): 44 runs
• Optimal designs
Model selection:
Remove terms in the
model which does not
improve the model fit
significantly
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
RESPONSE SURFACE MODEL RESULTS
R2=0.999
R2=0.997
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
RESPONSE SURFACE MODEL RESULTS
VALIDATION OUTSIDE “TRAINING SET”
All parameters (x) at +0.5 level
Python/HYSYS variable values = (40, 30, 2.4, 92.5, 32.5)
Python results:
HYSYS results with same x:
Wobbe: 57.20436
Wobbe:
56.83
SG:
0.675825
SG:
0.6709
HHV:
43.87115
HHV:
44.1
Dew:
-17.6542
Dew:
-17.61
RVP:
13.90993
RVP:
13.78
NGL:
2195.493
NGL:
2147.246
Power:
8072.93
Power:
8063
Error % Error # diff.
-0.65443
-0.37436
-0.72868 -0.004924605
0.521641
0.22885
-0.25028
0.044185
-0.93405
-0.129925
-2.19755 -48.247075
-0.123
-9.929659
All parameters (x) at -0.5 level
Python/HYSYS variable values = (30, 20, 2.2, 87.5, 27.5)
Python results:
HYSYS results with same x:
Wobbe: 56.49708
Wobbe:
56.18
SG:
0.655582
SG:
0.6516
HHV:
42.7474
HHV:
42.96
Dew:
-30.4695
Dew:
-30.11
RVP:
15.31608
RVP:
15.44
NGL:
2554.945
NGL:
2558.873
Power:
9310.954
Power:
9308
Error % Error # diff.
-0.56123
-0.31708
-0.60739 -0.003981955
0.497352
0.212605
-1.17972
0.359455
0.809117
0.123925
0.15374
3.927975
-0.03173
-2.954481
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
OPTIMIZATION SETUP
• Optimisation 1 – Live Oil: Minimize power, while meeting Wobbe
Index criterion, dew point, HHV.
• Optimisation 2: As optimization 1, without Wobbe Index criterion
• Optimisation 3 – Rich gas: Minimize power, RVP below
specification, dew point.
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
OPTIMIZATION RESULTS
• Optimisation 1 (Wobbe Index below max. limit):
HYSYS Results
(validation):
Optimisation Results:
Power
consumption
Dew
8841
-36.13
Power
consumption
Dew
Wobbe
56.2
Wobbe
HHV
42.3
HHV
SG
0.647
SG
RVP
17.05
RVP
Variables found:
P Expander
T Reboiler
rd
P3
Error %:
Error #
difference:
8832
-0.10
-9
-36.05
-0.22
0.08
55.9
-0.54
-0.3
42.47
0.40
0.17
0.6433
-0.57
-0.0037
17.02
-0.18
-0.03
Variables from optim.:
26.95
15
P Expander
T Reboiler
rd
26.95
15
Sep.
2.5
P3
Sep.
2.5
P Booster
85
P Booster
85
T TEG
25
T TEG
25
Optimisation by
N/A
expander
pressure only:
N/A
9807
N/A kW
N/A
Multiparameter
N/A
optimisation is pivotal!
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
OPTIMIZATION RESULTS
• Optimisation 2 (no Wobbe/HHV constraint):
HYSYS Results
(validation):
Optimization Results:
Error %:
Error #
difference:
7017
0.13
9
Power
consumption
7008
Power
consumption
Dew
-6.23
Dew
-5.428
-12.87
0.802
Wobbe
57.87
Wobbe
57.58
-0.50
-0.29
HHV
45.15
HHV
45.43
0.62
0.28
SG
0.697
SG
0.6933
-0.53
-0.0037
RVP
12.45
RVP
12.53
0.64
-0.08
Variables found:
Variables from optim:
P Expander
45
P Expander
45
T Reboiler
15
T Reboiler
15
rd
P3
rd
Sep.
2.5
P3
Sep.
2.5
P Booster
85
P Booster
85
T TEG
35
T TEG
35
HYSYS built-in optimisation
N/A
results:
N/A
N/A
1. 7700
kW (middle level
N/A
initial
N/A guess
2. 7400 kW (high level
initial guess)
2. 7020 (low initial guess)
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
OPTIMIZATION RESULTS
• Optimisation 3 (RVP below max. limit):
HYSYS Results
(validation):
Optimisation Results:
Error %:
Error #
difference:
7084
-0.63
-45
Power
consumption
7129
Power
consumption
Dew
-6.03
Dew
-5.439
-10.58
0.638
Wobbe
57.88
Wobbe
57.57
-0.54
-0.31
HHV
45.18
HHV
45.41
0.51
0.23
0.6931
-0.63
-0.0044
12.02
0.17
0.02
SG
0.6975
RVP
12.00
SG
RVP
Variables from optim:
Variables found:
P Expander
45
P Expander
45
N/A
T Reboiler
35
T Reboiler
35
N/A
2.45
N/A
rd
P3
Sep.
2.45
rd
P3
Sep.
P Booster
85
P Booster
85
N/A
T TEG
35
T TEG
35
N/A
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
OPTIMIZATION RESULTS - SUMMARY
• Generally the regression models perform very well and match the simulated
data from HYSYS
• Validated outside “training set”
• The optima found by optimisation are validated against corresponding
HYSYS simulation
• Rich gas i.e. live oil export is more energy efficient than exporting stabilised
oil. Power reduced by ~20%. On-shore handling not accounted for.
• Optimisation method with RSM seems more robust than HYSYS built-in
optimiser
• The methods hold promise for “production” usage
• Future extension to include uncertainty analysis, Monte Carlo methods etc.
• Model to include weight and cost for early phase studies
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19
THANK YOU FOR YOUR
ATTENTION. QUESTIONS?
Acknowledgments
Casper Nielsen, former intern/bachelor student, for providing a firm
implementation of the flare system in HYSYS.
Kasper Rønn Rasmussen, current intern, for conducting the RSM,
DOE and optimization study
Carsten Stegelmann, Chief Consultant, for providing material on
fire PSV’s
OFFSHORE OIL AND GAS SEMINAR 18 - 22 AUGUST 2014 AT AALBORG
UNIVERSITY ESBJERG
2014/08/19