Clean Energy via Hydrothermal Gasification of Hydrocarbon Resources
Creators: name: Alshammari, Yousef
Publisher: name: Imperial College London
Year: 2013

description: Synthesis gas and clean hydrogen will become key components of the energy industry. Their production from fossil fuels is likely to be a major source of these energy vectors and chemical building blocks for many decades ahead. Currently all the hydrocarbon conversion steps are carried out above surface, starting from oil and gas extraction and transportation to dedicated plants, with any separated CO2 returned back to the fields. However, there are increasingly strong drivers to reduce the environmental impact of the oil processing industry, by e.g. minimising the “footprint” of such operations and leaving the undesirable and low- value material underground (CO2, heavy metals, sulphur). One novel approach, which could be key, would be the production of syngas or hydrogen via downhole hydrothermal processing/partial oxidation. This envisages using the sub-surface well system as a continuous processing and reactor network to carry out as much as possible of the required separations and conversions in the well system (underground) or close to it (at the wellhead). The goal is to radically reduce, by design, the overall environmental footprint (by minimising the number of species extracted other than final products, the number of external processing steps and the need for transport to/from the underground fields) while improving the overall economics of new fields and increasing the efficiency of recovery from conventional, mature reservoirs. This thesis presents research work on the hydrothermal gasification and partial oxidation of n-hexadecane, as a heavy hydrocarbon model, under potential downhole conditions. Thermodynamic analysis was carried out to predict equilibrium limits showing optimum conditions for maximising the theoretical yield of hydrogen under oxidative and non- oxidative hydrothermal conditions. This was followed by experimental analysis where hydrothermal gasification of n-hexadecane was conducted in high pressure flow reactor system. Conversion data at different residence times, and temperatures were used to determine the reaction kinetic data at sub- and supercritical water conditions. The new experimental system was modified for partial oxidation of n-hexadecane, to enable combined total decomposition of H2O2, in a separate reactor, with partial oxidation of n-hexadecane, in a gasification reactor. The experimental data were consolidated with the development of a new CFD model for supercritical water gasification of hexadecane, and it was also used to validate and tune our kinetic data obtained experimentally by taking into account the radial effects occurring from the laminar flow under the experimental conditions. Finally, a new subsurface georeactor system model was developed, using ASPEN HYSYS, which shows thermodynamically the optimal conditions for maximising the system’s energy efficiency showing potential conditions for maximising energy recovery with hydrogen cogeneration. These results are discussed with view of opening new routes for clean generation of hydrogen and synthesis gas via underground gasification of hydrocarbons.