Solidification caused by under-cooling

Alhowaity, Awatif (2018) Solidification caused by under-cooling. Doctoral thesis, University of East Anglia.

Abstract

Many crude oils contain dissolved waxes that can cause significant problems,
such as blockage of pipeline, because of the precipitation and deposition of wax
particles during the production and transportation of the oil. The waxy oils
are transported through very long pipelines from warm natural reservoirs to
cooler conditions in the surrounding of the pipe. An important phenomenon
occurring during the under-cooling of the pipeline is the formation of solid
matter inside the pipe. The wax deposition is one of the most serious problems,
potentially restricting flow and plugging the pipe. Wax deposits begin to form
when the temperature is below the wax appearance temperature. We model
a particle's growth in the oil pipe once the temperature falls below the wax
appearance temperature. We determine the temperature distribution in the oil,
formulate and solve a self-similar problem of wax particle growth from a single
point. A corresponding initial boundary value problem is studied numerically
by a time-stepping numerical algorithm. The numerical algorithm is used
to compute the non-linear solution of an initial value problem of diffusion and
transport of wax towards the particle. The numerical solution is compared with
and validated against the self-similar solution derived for specific conditions.
Then the boundary value problem is formulated for the general case. A coupled
diffusion/flow problem of a single wax particle is formulated. An asymptotic
analysis is used to describe the motion and growth of the wax particle. At the
leading order, we consider a spherical wax particle and assume the velocity of
the particle to be close to the local velocity of the flow. The flow relative to
the wax particle is negligible in the leading order problem. In the first-order
correction problem, the wax particle is treated as spherical initially, and the
correction to the particle shape is caused by a small difference between the
wax particle speed and the speed of the local flow. We draw conclusions and
recommendation for further work at the end of this thesis.

Item Type: Thesis (Doctoral) Faculty of Science > School of Mathematics Jackie Webb 06 Aug 2018 10:41 06 Aug 2018 10:41 https://ueaeprints.uea.ac.uk/id/eprint/67960