This paper describes a new mathematical model of the fluid dynamic processes in a high recirculation airlift reactor. The model was created to provide information to assist in the design of a reactor, in particular considering the selection of parameters to adjust in order to achieve a steady state solution. The modelling of two phase-flow of air and water in small scale airlift bio-reactors is considered. This modelling was applied to the high recirculation airlift reactor process. A new computer simulation was created and a test program performed to evaluate the models used. The results of this evaluation are presented. The evaluation showed that variation of the superficial gas velocity or the simultaneous variation of the downcomer and riser diameters could be used to produce a steady-state design solution.
Large-scale High Recirculation Airlift Reactors have been used to treat biodegradable waste waters since the mid nineteen seventies. The system is particularly attractive for situations where the land to locate wastewater works is restricted. Little is known, however, about the fluid dynamics of the gas-liquid mixture flowing around the reactor. This makes the determination of air injection rates difficult if effluent quality and dynamic stability are to be maintained. When the air injected is not sufficient to maintain stable operation the reactor contents may reverse violently resulting in down time, failure to achieve target discharge quality and possible damage to the reactor itself. As a result many reactor installations operate at air injection rates above those necessary for the biological processes. The extra air injected results in higher capital and process costs. This paper considers the effect of air injection rates on the hydrodynamic stability of Airlift Reactors and a two-phase model is proposed to predict stable operation at a reduced air injection rate. Results are presented which show the effect of reactor design on stability.
Under the current market environment, deep water projects are required to evolve a more robust cost solution to remain competitive within the industry portfolio, ensuring safety as priority. With such market drivers in place, this paper details the engineering behind the development of a single flowline concept that ties-in to an existing production system for a GoM deep water development and the associated challenging flow assurance aspects of that design.
The development is a fast track project (approximately 1.5 year from concept to first-oil) that leverages existing subsea infrastructure. The flowline length is over 10,000 ft at water depths exceeding 5,000 ft and will tie-in to a current flow loop dead leg of more than 7 miles in length. Success of the project will set a trend and allow development for future projects, i.e. infrastructure led solutions utilizing single flowlines with rapid delivery and increased financial returns.
To meet economics and schedule, the tie-in is a flexible flowline, which implies limitation in the amount of insulation that can be added to the system; in addition the reservoir temperature is relatively low. These challenges constrain the operating envelop, limited by thermal performance.
Traditional hydrate strategies such as dead oil displacement are not possible for a single leg spur line and continuous hydrate inhibition is not feasible from an OPEX aspect. Therefore a novel hydrate management strategy leveraging existing infrastructure is deployed. The development behind the hydrate and other flow assurance strategies is presented in this paper, as well as the realization of those strategies through to operation.
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