Modelling of gas decompression process for CO2 transmission pipeline (original) (raw)
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Chemical Engineering Research & Design, 2020
Pressurized liquefied gases such as carbon dioxide are transported at a pressure above their saturation pressure. Therefore, if a pipeline transporting this substance ruptures, an abrupt expansion occurs, causing the flashing of the fluid. Computational tools that predict how fast a depressurization develops, help to assess the consequences of potential pipeline rupture scenarios. This paper describes the development of a 2-D full-bore rupture decompression model to simulate the transient depressurization of a pipeline transporting pure liquefied CO 2 , using ANSYS Fluent as CFD software. The scope of work focuses on incorporating non-equilibrium phase transition, while addressing the calculation of properties for metastable liquid. Additionally, it includes the comparison of model predictions when implementing two thermodynamic approaches: the Peng-Robinson Equation of State (EoS), and correlations developed in this work based on the Span-Wagner EoS. It was found that the thermodynamic approach is deemed to have a predominant effect on the arrival time of the decompression wave front at different locations along the computational domain, while the mass transfer coefficient in the source terms (C) governs the phase transition and the pressure plateau representing this phenomenon.
Industrial & Engineering Chemistry Research
Decompression of CO 2 pipelines is studied both experimentally and numerically to provide a partially validated model as the basis for the prediction of the hazards associated with CO 2 solid formation. The pipeline decompression experiments, performed using a fully instrumented 36.7 m long and 50 mm internal diameter test pipe up to a maximum pressure of 45 bar, incorporating discharge orifice diameters of 4 and 6 mm, reveal the stabilisation of pressure and temperature near the CO 2 triple point. Also, video recordings of the decompression flow in the reinforced transparent section of the steel pipe show that initial stratification of the constituent liquid and vapour phases is followed by rapid CO 2 solid formation and accumulation in the pipe. To aid the prediction of hazards associated with solids formation in pipelines, a homogeneous equilibrium pipeline decompression model is developed accounting for the pertinent physical properties of CO 2 in the liquid, vapour and solid states. The model is validated against the experimental data, showing ability to accurately predict the measured pressure and temperature variations with time along the pipe, as well as the time and amount of the solid CO 2 formed upon decompression across the triple point.
Industrial & Engineering Chemistry Research, 2018
Decompression of CO2 pipelines is studied both experimentally and numerically to provide a validated model as the basis for the prediction of the hazards associated with CO2 solid formation. The pipeline decompression experiments, performed using a fully instrumented 36.7 m long and 50 mm internal diameter test pipe up to a maximum pressure of 45 bar, incorporating discharge orifice diameters of 4 and 6 mm, reveal the stabilisation of pressure and temperature near the CO2 triple point. Also, video recordings of the decompression flow in the reinforced transparent section of the steel pipe show that initial stratification of the constituent liquid and vapour phases is followed by rapid CO2 solid formation and accumulation in the pipe. To aid the prediction of hazards associated with solids formation in pipelines, a homogeneous equilibrium pipeline decompression model is developed accounting for the pertinent physical properties of CO2 in the liquid, vapour and solid states. The model is validated against the experimental data, showing ability to accurately predict the measured pressure and temperature variations with time along the pipe, as well as the time and amount of the solid CO2 formed upon decompression across the triple point.
Energy, 2020
The design of safe and cost-efficient CO 2-transportation systems is an integral part of CO 2 capture and storage (CCS) deployment. To achieve this, accurate transient flow models capturing the occurrence of gas, liquid and solid CO 2 are needed. These in turn rely on experimental validation. In this work, we present a new experimental facility designed to capture pressure and temperature during the depressurization of CO 2 and CO 2-rich mixtures in a tube at high spatial and temporal resolution. Experiments with pure CO 2 starting from both gaseous and dense (liquid) states are presented, and a reference experiment with N 2 is included. The experimental results for both pressure and temperature are analysed by comparison with predictions by a homogeneous equilibrium model. Emphasis is put on the decompression-wave speed, of particular relevance for running-ductile fracture in CO 2-transportation pipelines. We observe good agreement with predicted decompression-wave speeds in the single-phase region, and fair agreement for two-phase flows when the calculations are based on the assumption of equilibrium. However, the observed 'pressure plateau', a key factor in the prediction of running-ductile fracture, can be significantly lower than that calculated assuming equilibrium.
Chemical Engineering Transactions, 2016
The problem of a reliable simulation of relief condition of a fluid (flow rate, pressure and temperature) is a preliminary and fundamental step to the calculation of dispersion effects. The evaluation of the mass discharged from pipelines in cases of leaks or abnormal operating conditions is largely based on the use of commercial simulators for safety analysis like PHAST or more specialized codes developed for oil&gas transportation such as OLGA and Ledaflow. However all these codes use a simplified thermodynamic approach since physical and transport properties are calculated on the basis of fixed fluid compositions and stored in tables. To avoid these limitations vapour-liquid equilibrium and fluid dynamics equations should be coupled and solved at the same time. This paper presents the implementation of two-fluid model fluid dynamics equations in a process simulator (XPSIM) providing an integrated tool which allows the simulation of vapour-liquid flows taking into account also the...
Process simulation of impurity impacts on CO2 fluids flowing in pipelines
Journal of Cleaner Production, 2019
Captured carbon dioxide flowing in pipelines is impure. The impurities contained in the carbon dioxide fluid impact on the properties of the fluid. The impact of each impurity has not been adequately studied and fully understood. In this study, binary mixtures containing carbon dioxide and one impurity, at the maximum permitted concentration, flowing in pipelines are studied to understand their impact on pipeline performance. A hypothetical 70 km uninsulated pipeline is assumed and simulated using Aspen HYSYS (v.10) and gPROMS (v.5.1.1). The mass flow rate is 2,200,600 kg/h; the internal and external diameters are 0.711 m and 0.785 m. 15 MPa and 9 MPa were assumed as inlet and minimum pressures and 33 o C as the inlet temperature, to ensure that the fluid remain in the dense (subcritical or supercritical) phase. Each binary fluid is studied at the maximum allowable concentration and deviations from pure carbon dioxide at the same conditions is determined. These deviations were graded to rank the impurities in order of the degree of impact on each parameter. All impurities had at least one negative impact on carbon dioxide fluid flow. Nitrogen with the highest concentration (10-mol %) had the worst impact on pressure loss (in horizontal pipeline), density, and critical pressure. Hydrogen sulphide (with 1.5-mol %) had the least impact, hardly changing the thermodynamic properties of pure carbon dioxide.
A homogeneous relaxation flow model for the full bore rupture of dense phase CO2 pipelines
International Journal of Greenhouse Gas Control, 2013
The development of an homogeneous relaxation flow model for simulating the discharge behaviour following the full bore rupture of dense phase CO 2 pipelines is presented. Delayed liquid-vapour transition during the decompression process is accounted for using an empirically derived equation for the relaxation time to thermodynamic equilibrium. The flow model's robustness is successfully demonstrated based on a series of hypothetical shock tube tests. Model validation on the other hand is performed by comparison of the predictions against experimental data obtained for the full bore rupture of realistic scale CO 2 pipelines. Within the ranges investigated, it is found that although delayed phase transition effects have negligible impact on the pipeline decompression rate, ignoring such phenomena results in underestimating the transient discharge rate. This is important since the latter governs the minimum safety distances to CO 2 pipelines and emergency response planning in the unlikely event of pipeline failure.
The Journal of Supercritical Fluids, 2014
Transport of carbon dioxide is an essential feature of Carbon Capture and Storage. Power plants and industrial production plants-large point sources of CO 2-are often situated far away from storage locations, thus it is necessary to transport the resulting CO 2-rich streams from the point of capture to the storage/utilization site. The CO 2 quality required for transport may influence the choice of the capture technology and impose limits on the performance requirements. In order to design CO 2 transport networks, it is important to have an accurate knowledge of the thermodynamic properties of CO 2-rich mixtures containing small amounts of impurities. However, a suitable equation of state under the appropriate conditions for pipeline transport has not been clearly defined yet and different options may be used for different applications. For a quick evaluation of transport options, simple cubic EOS may be sufficient, but for accurate measurements of CO 2 flows needed for fiscal purposes more accurate non-analytical EOS may be required. In this paper the results of different EOS, including both cubic equations and non-analytical equations, have been compared with P-ρ-T experimental data of binary mixtures of carbon dioxide with nitrogen, oxygen and argon obtained by the authors at the Energy and Environmental Laboratory of Piacenza (LEAP). Moreover a refitting of the mixture binary interaction parameters has been carried out for analysed EOS. The Lee-Kesler-Plöcker, the Perturbated-Chain SAFT equations and the GERG model showed good prediction of the density of CO 2-mixtures in the conditions typical of pipeline transport: "dense" liquid phase (P above the critical pressure and T below the critical temperature) and CO 2 molar concentration greater than 95%. Finally, the application of EOS to CO 2 transport simulations and pipeline design has been performed in order to find the best configuration of pipelines on the basis of geometrical characteristics and operating conditions.