PhD defence: Osama Kabbashi Mohammed Ibrahim

Osama Kabbashi Mohammed Ibrahim is defending his thesis for the degree philosophiae doctor (PhD) at the University of South-Eastern Norway.

He has completed the PhD programme in Process-, energy- and automation engineering. The doctoral work has been carried out at the Faculty of Technology, Natural Sciences, and Maritime Sciences.

• Read the thesis here

Both the trial lecture and the PhD defence are open to the public. Immediately after the defence the doctoral programme will hold a small defence reception outside Auditorium A-271, approximately from 15:00-15:30.

Summary

Developing carbon capture and storage (CCS) technologies is crucial to reduce release of carbon dioxide. Transport of captured CO2 to the storage facility is an important step in the technological process. However, major safety concerns arise regarding an unintended release of liquid CO2 during transport. A rupture of a pressurized CO2 container results in depressurization and rapid phase transition with explosive evaporation. It could lead, under certain conditions, to boiling liquid expansion vapor explosion (BLEVE). BLEVE is one of the most severe explosions and could cause loss of life and significant material damage.

A deep understanding of explosion evaporation is necessary to improve vessel design, develop mitigation techniques, and prepare operational procedures to prevent such catastrophic scenarios. This research is within the safety of CO2 transport and storage facilities. It is a continuation of the prior research in the research group “Process safety, combustion and explosions” at USN to investigate the rapid phase change mechanisms and evaluate the hazards that arise during the accidental release of liquid CO2. The research expands former studies to cover the effect of a vessel's diverging cross-sectional geometry on the phase transition mechanism during sudden depressurization. In addition, it examines the evaporation wave characteristics during the release below the liquid level.

The study presents a new installation that comprises (1) a high-pressure divergent cross-section vessel sealed with (2) a double-membrane separated by a medium-pressure slip-on flange. Operational analyses based on the experimental results showed that increasing the medium-pressure section pressure is a more practical method to run CO2 depressurization tests on this installation. Results also showed that the evaporation wave velocity increased with decreasing cross-sectional area and increased liquid content in the vessel. The divergent cross-section has led to a more significant fluid expansion than the results obtained from previous experiments on a constant cross-sectional duct.

Investigating the blast wave effects during CO2 depressurization, overpressures, and the released multiphase flow evolution have been recorded during CO2 release through a polycarbonate tube. Results demonstrated that the rapid liquid evaporation has substantially influenced the peak and duration of overpressure positive phases and impulses. Additionally, the study examined the flying fragments' velocities and their kinetic energies based on the captured high-speed videos. Results also showed increased fragments' velocity and kinetic energy with increased liquid volume fraction. The fragments' velocities and kinetic energies from the experiments show that these fragments imply great danger.

Interpreting the pressure and temperature histories coincidentally with high-speed shadowgraph images was the basis for analyzing phase change during release from the bottom of a rectangular duct. The evaporation mechanism in these experiments contrasted with the previous top-release tests. The pressure records indicated faster evaporation during bottom-release tests than in top-release, and the shadowgraph images showed that the initial contact surface remained flattened, almost horizontally, for a relatively extended duration before breaking up. This behavior indicates that the headspace vapor has little influence on the initial evaporation. This will likely affect the blast strength and fragment formation in accidental events involving ruptures of vessels containing liquid CO2.