Density wave amplification in hydraulic transport pipelines forms a high risk to operational continuity, as density waves can lead to system blockages or centrifugal pump drive failures. Recent experimental research, in pipelines which contain long vertical sections, has shown that density waves can amplify at velocities far exceeding the deposit limit velocity, previously thought to be a limiting condition for amplification. The typical design methodology of hydraulic transport pipelines is based on a steady-state philosophy, which assumes that the mixture velocity and sediment concentration are constant in time and space. However, these variations can lead to the amplification of density waves. This article discusses the cause of a new type of density wave amplification mechanism, which is related to slurry dynamics in a pipeline containing vertical sections. This research also presents a 1D Driftflux CFD model which models the aforementioned slurry dynamics and can predict density wave amplification.

The hydraulic transport of sediments in sediment–water multiphase mixtures is an important process in nature and many industrial applications. The flows are characterized by complex transient phenomena, in which the overall system scale and the particle scale are equally important. Experimental research into dense mixture flows is focused on measurement of flowrates, differential pressures and concentrations of the suspended sediments. Concentration measurements are especially challenging in the case of coarse particles (beyond millimeter size scale) flowing in dense mixtures, limiting the range of available sensors for accurately measuring the in-situ solids concentrations. For the investigation of transient processes, a quick sensor response is required, which makes concentration measurement based on mixture conductivity an interesting option. This study is focused on combined concentration and pressure measurements in dense sediment–water mixtures with coarse particles in a vertically oriented closed conduit, using differential pressure sensors over the vertical segments and conductivity probes for measuring the mixture concentration. We experimentally investigated the dispersion process of an initially densely packed batch of sand and gravel by measuring the concentration on different segments of the conduit, resulting in data on mixture wall shear stresses for different sand and gravel mixtures and data of attenuation of concentration gradients in vertical upward and downward flow, in the conduit horizontal top section and in the centrifugal pump. We describe in the detail the sensor calibration and data processing method, giving a best practice for the use of conductivity concentration sensors in dense coarse particle mixtures, and we suggest a novel method for analysis of density wave amplification and attenuation based on concentration measurements in general, which allows for the detailed analysis of transient multiphase flow phenomena at pipe system component level.

Polymetallic nodules provide an alternative source of valuable metals. Nodules from the seabed of the Clarion Clipperton Zone (CCZ), a prospective mining area, are typically abundant at depths of around 5 ​km. Mining these nodules comprises excavation or pick-up of nodules and hydraulic transport of nodules from the seafloor to the surface. The particle size distribution of the nodules, an important design parameter, will change during transport under influence of different processes. One of these processes is impact fragmentation, especially occurring in centrifugal pumps. Recent research has led to improved understanding of impact fragmentation of polymetallic nodules, but quantification of the degradation process still is an open question due to scarcity of breakage data. In this paper we present a detailed analysis of nodule strengths and stresses occurring during impact and we propose an impact fragmentation model based on limited breakage data. The model is compared with the experiments and we comment on application of this model in engineering practice.

The mining of polymetallic nodules from the seafloor at depths down to 6000m requires the excavation of nodules with a seafloor mining tool, the transport of nodules as a slurry through a jumper hose connecting the mining tool to a vertical hydraulic transport system and the transport of the nodules through the vertical lifting pipe. We focus on a concept with conventional hydraulic transport, using a series of centrifugal pump booster stations. The nodules will be transported in different flow regimes, ranging from a sliding bed (in the jumper hose) to a homogeneous suspension (vertical flow). Each regime gives rise to degradation of the nodules in a different way. It is important to understand the degradation mechanisms in detail in order to predict the particle size distribution of the slurry leaving the riser. This particle size distribution is a key design parameter for design of processing equipment and for environmental impact assessment. In this article we present the results of experimental work on abrasive wear (particle-wall interaction) and attrition (particle-particle interaction) of polymetallic nodules from the Clarion Clipperton Zone and we discuss its applicability to engineering practice.

During hydraulic transport for deep sea mining, polymetallic nodules are transported in various ascending inclined pipes located at the sea floor. These inclined pipes can constantly change their angle of inclination due to moving excavation equipment attached to these pipes. Flow assurance during transport requires a safe transport velocity which takes into account all inclination angles. A study was conducted into safe transport velocities of slurries composed of gravel sized material in ascending inclined pipes. Experimental research was conducted with 4.6, 6.3 and 12 mm diameter gravel in a 100 mm experimental flow loop up to an inclination angle of 52 degrees. Measured parameters include pressure losses, mixture velocity, delivered concentration, deposit limit velocity and velocity profiles from high speed camera footage. During this research, various literature sources have been studied for definitions and models of transition velocities between safe and unsafe transport. These definitions and models are discussed in terms of their relevance for coarse slurries. With these definitions in mind and with the experimental data a recommendation is given for a transportation velocity of coarse slurries in inclined pipes.