The present work uses a quasi-stationary model for predicting hydrate dispersion formations in slug flows. The approach couples a kinetic model for the hydrate formation rate with a model for the unit cell geometry. The mass balance takes into account the phases' consumption rates, while the energy balance, the heat generation due to the exothermic nature of hydrate formation. Simulations for long pipelines were carried out, with boundary conditions similar to those found in offshore scenarios. Results are presented in such a way that the hydrate formation effects on slug flow hydrodynamics and heat transfer can be understood.
Hydrates are crystals formed by the trapping of gas molecules inside of cages formed of hydrogen bonded water molecules (1). Whenever natural gas and water mixtures flow through pipelines at high pressures, hydrates may form: on the pipe wall, where the temperature gradient is higher and the wall imperfections trigger the nucleation process; or in the gas-water interface, where there is a more effective contact between the phases (2). In either case, the hydrate formation may change the flow hydrodynamics and heat transfer, by reducing the flow cross sectional area and creating an insulating hydrate layer, in the first case; by precipitating solid particles and forming a dispersion flow, in the second case (3). In both situations, pipe blockage may happen if hydrate formation is out of control, being by a complete obstruction of the cross sectional area or by hydrate particles' agglomeration and plug formation (2).