No abstract

Summary Pipeline blockage is a major problem in gas production and transportation processes. Safety and economic costs of pipeline blockages are compelling the industry to design innovative means for early detection of partial blockages along pipe systems as a preventive measure. This paper presents a simple numerical model to be used for accurate blockage characterization in natural gas pipelines. The transport phenomenon is modeled with a quasi-1D set of partial differential equations for isothermal natural gas flow in pipes. The variable area formulation maintains the simplicity of a 1D formulation and yet allows for the complex geometries associated with natural gas pipeline blockages. Viscous effects are also included in the formulation of the governing equations, and a cubic equation of state is incorporated into the model to provide the quasi-compositional effect of real gases without the complexities of a fully compositional model. The generalized Newton-Raphson technique is used to solve the piece-wise finite-volume formulation iteratively as an optimization problem with pressure and velocity as perturbed variables. Reflected pressure waves observed at the pipe inlet node were analyzed for blockage characterization. It was observed that viscous losses have no effect on blockage length and location prediction accuracy, but has significant impact on the accuracy of blockage severity predictions.

Two-phase gas-solids transport models are widely utilized for process design and automation in a broad range of industrial applications. Some of these applications include proppant transport in gaseous fracking fluids, air/gas drilling hydraulics, coal-gasification reactors and food processing units. Systems automation and real time process optimization stand to benefit a great deal from availability of efficient and accurate theoretical models for operations data processing. However, modeling two-phase pneumatic transport systems accurately requires a comprehensive understanding of gas-solids flow behavior. In this study we discuss the prevailing flow conditions and present a low-fidelity two-fluid model equation for particulate transport. The model equations are formulated in a manner that ensures the physical flux term remains conservative despite the inclusion of solids normal stress through the empirical formula for modulus of elasticity. A new set of RoePike averages are presented for the resulting strictly hyperbolic flux term in the system of equations, which was used to develop a Roe-type approximate Riemann solver. The resulting scheme is stable regardless of the choice of flux-limiter. The model is evaluated by the prediction of experimental results from both pneumatic riser and air-drilling hydraulics systems. We demonstrate the effect and impact of numerical formulation and choice of numerical scheme on model predictions. We illustrate the capability of a low-fidelity one-dimensional two-fluid model in predicting relevant flow parameters in two-phase particulate systems accurately even under flow regimes involving counter-current flow.