dc.description.abstract | The growing population of the world places an enormous demand for energy in some
form or the other. Essentially, this means that the struggle to hunt and retrieve fossil fuels
has to continue for the smooth functioning of the world. Since the early 1900’s when drilling
for oil and gas started moving away from shores to some remote locations that we are at
today, the size and complexity of machinery and the interconnected systems have grown
exponentially. Despite investing enormous time, effort and money into implementing technically
advanced and innovative barrier systems to prevent Hydrocarbon (HC) leaks on
offshore installations in the Norwegian Continental Shelf (NCS), the statistics still stands
far from the target zero. Hence, the efforts towards minimizing the number of leaks can
never be ceased due to the catastrophic nature of its potential consequences to humans,
environment, asset or the reputation of a firm.
This master’s thesis features one such effort to visualize the effectiveness of some
barrier functions proposed in Modelling Instantaneous Risk for Major Accident Prevention
(MIRMAP) report. Some of the most critical barrier systems are incorporated into
the chosen generic module, which is then subjected to numerous gas leak simulations using
the latest version of the software, Kameleon FireEx - Risk and Barrier Management
(KFX-RBM), a Computational Fluid Dynamics (CFD) based simulation tool. A base case
scenario is a set-up using the chosen module with a 100% functional gas detection system,
Emergency Shutdown (ESD) system, with no temporary weather cladding attached and
closed fire-proof doors. This set-up is subjected to simulation with six different leak rates,
four different wind speeds and two different wind directions. The results of this being a
base for comparison, simulations are carried out with partially isolated gas detection system,
presuming on-going hot works in the near vicinity with a temporary weather cladding
and with fireproof doors left in open position. The variations in the total ignition probability
of the module compared to the base case would be the main objective of this thesis.
As additional objectives, since the barrier systems could be directly or indirectly influenced
by humans, an attempt is made by simulating the base case with a practically
acceptable delay in manual activation of the shutdown. Furthermore, to reduce the simulation
time, numerous simulations are run to arrive at the optimal grid resolution and courant
number with the quality of results remaining undiminished.
The case with delayed shutdown due to manual activation of ESD depicted the highest
influence to the complementary cumulative frequencies, followed by the case simulated
with a temporary weather cladding erected on one of the open ends of the module, with
second highest influence. The comparison of the two base case simulations with different
leak scenarios (direction and location), revealed that the release point and release direction
can significantly influence the probabilities of ignition, either positively or negatively. The
simulations that were carried out to optimize the grid resolution resulted in a significant
reduction of simulation time with a grid resolution of 125000, while the quality of the results
was undiminished. Further analysis by extracting the highest and the least release
rates separately resulted in an insight that the grid resolution is a function of release rate. | |