Riser Section Research Articles

Hydrogen permeation behavior of X80 pipeline steel under alternating wet-dry environment in the South China Sea

The riser sections of offshore pipelines are subject to cathodic potentials, alternating wet-dry (AWD) cycles and stresses in the service environment. The hydrogen permeation of X80 offshore pipeline with different cathodic potentials, dry/wet ratios, and constant tensile stress in AWD environment were investigated by the self made experimental equipment, which includes the three modules, i.e., the constant stress loading, the two-component cell hydrogen permeation, and AWD environment. Results showed that hydrogen permeation current fluctuates with the AWD, which is different from that in the bulk solution. In one AWD cycle, the permeation increases in the wetting stage and decreases in the dry stage. The smaller the dry/wet ratio, the longer the hydrogen permeation current keeps high level which is caused by the dense corrosion product layer. The hydrogen permeation currents in the elastic stress are greater than those in the plastic deformation, and unstressed conditions is the smallest.

Modeling and Simulation of a Multizone Circulating Reactor for Polyethylene Production with Internal Cooling.

Polyolefins play a role in industries and are typically manufactured using two types of reactors: high-pressure tubular reactors and fluidized bed reactors. An innovative technology called the Multizone Circulating reactor (MZCR) has emerged, which introduces an innovative approach with interconnected polymerization zones creating a continuous loop of polymer flow. This study focuses on modeling and simulating ethylene gas phase polymerization within the MZCR in the presence of internal cooling to gain insights into its behavior. To achieve this, a comprehensive computational fluid dynamics (CFD) simulation was developed. It considered momentum, material, and energy balance aspects. The model equations were solved using the finite difference method in COMSOL Multiphysics version 6.1. The investigation primarily focused on studying the impact of incorporating a cooler into the riser section on the temperature profile within the reactor and ethylene conversion. The presence of this cooler resulted in a reduction in temperature change along the riser from approximately 8.0 °C to 4.0 °C. Moreover, it led to an increase of 7%, in ethylene single-pass conversion.

Evolution of mixing length empirical equation for recouping of heat from industrial waste flue gases using air‐quarry dust/iron ore

AbstractIndustry processes require large amounts of energy inputs and often generate high temperatures exit gases that can potentially serve as secondary sources of energy. Waste heat recovery offers an opportunity for energy conservation that deserves more attention in the current global effort. Recovery of such waste heat can result in substantial reductions in net energy demand. Based on these objectives, this report describes the result of an experimental study that used solid particles in a vertical riser to recover gas energy from hot air through co‐current contact with solid particles. To study the hydrodynamic aspects of the riser section, this study utilized a fabricated experimental apparatus similar to the vertical duct used in the cement industry. The purpose of this study is to collect hydrodynamic data because there is limited information available about these aspects in the literature. A metallic fluid particle heat exchanger has been investigated through experiments. Various sizes of quarry dust and iron ore particles are studied in the present study. An empirical correlation is used to fit the mixing length (LA) determined at different parametric levels (gas velocity, particle size, solid feed rate, and solid density). Experimental correspondence for mixing length or LA is given as . The constructed experimental setup demonstrates a suspension preheater (SP) used in modern cement plants, but the correlation can be extended to a variety of other industries where waste heat recovery is feasible.

Flow distribution analysis of a novel fcc system through experiment study and atomic model

As the largest palm oil producer in the world, Indonesia has a promising potential to produce green fuel through the Fluid Catalytic Cracking (FCC) process. A novel FCC configuration, FCC Proto X 3, which combines a riser reactor and downer reactor in the system, has been developed. However, several valves including in the FCC system remain a black box to the flow distribution in the system. The objective of this paper is to investigate the effect of the valve setting variation on the airflow distribution of the FCC system. The methodology uses experiment and acausal modeling. The effect of valve setting variation on pressure and average velocity of the airflow has been investigated. The experiment is conducted under cold test conditions, while the acausal model of the FCC system is built by using OpenModelica. It is obtained that valve 2 which controls the flow at the channel toward the regenerator is essential due to its role in controlling the air supply combustion process in the regenerator and driving the spent catalyst particles to the regenerator. Valve 3 is responsible for controlling the flow toward the riser reactor directly. Later, it is responsible for supplying the lifting fluid to support the catalytic cracking reaction at the riser sections. Valve 4 contributes to controlling the lifting fluid to the downer reactor. It will also be responsible for supplying thermal energy from the high-temperature particle catalyst to the reactor. When all valves toward the regenerator and reactor are 100 % open, the measured average velocity at the flue gas outlet and the product outlet are 8.04 m/s and 5.775 m/s respectively. The result shows that the airflow at the FCC system tends to flow through the regenerator. The atomic model estimation also shows a similar trend to the experiment result

State estimation and slug flow control of subsea production systems

The simulation and control of the severe slugging flow in the subsea multiphase pipeline is the focus of research in the production and exploitation of oil companies. Severe slug flow results in severe fluctuations of pressure and flow rate at both the wells end and the receiving host processing facilities, causing safety and shutdown risks. To prevent the severe slugging flow regime in multiphase transport pipelines, an ODE model is established by using the mass conservation law for individual phases in the pipeline and the riser sections. Then, the proposed model is compared to the results from the OLGA simulation. A comparative study of different slugging flow control solutions is conducted. Extended Kalman Filter (EKF), Back Propagation Neural Network (BPNN) and EKF&BPNN are used for state estimation and combined with PI controller. The EKF and BPNN are good nonlinear filters. However, when the nominal choke opening is increased, they work unsatisfying. The EKF&BPNN observer shows slightly better results than EKF and BPNN when the system has high input disturbance.

Wave Effects on Vortex-Induced Vibrations of a Top-Tensioned Riser

Abstract Offshore drilling risers and many production risers are top-tensioned risers (TTRs), connecting the vessel and seabed via joints. External loads such as currents, waves, and vessel motions introduce cyclic loads and motions on riser sections and associated components, such as universal joint, flex joints, and well head at the bottom, which may shorten the service life due to accumulated fatigue damage. Dynamic responses under combined currents and waves are more complicated than vortex-induced vibrations (VIVs) caused by pure currents, and it is not fully understood. Several model test campaigns on TTR have been carried out at SINTEF Ocean (former MARINTEK) during the past decades. Currents, waves, and vessel motions were modeled, and the riser model responses were measured. In this study, selected cases from such model tests are analyzed, and used to validate a semi-empirical time domain VIV prediction tool—VIVANA-TD. A better understanding of the dynamic responses of TTR under combined currents and waves has been achieved. By comparing the results from numerical simulation using VIVANA-TD and model test measurements, validity and limitation of the time domain tool have been investigated. Important features that need to be considered are discussed. The experience gained from the present study establishes a good basis for VIV and wave load prediction of full-scale TTRs under combined currents and waves where the uncertainty of combined wave and VIV prediction is further reduced.

Effect of bed material size on gas-solid flow characteristics in a CFB at low solid recirculation rates

The gas–solid flow characteristics greatly influence the heat transfer, combustion and pollutant formation processes in a circulating fluidized bed (CFB) boiler. The effects of particle size on the gas–solid flow characteristics, including flow structure, axial pressure and bed density profiles were studied in a two-dimensional CFB cold apparatus under low solid circulation rates (Gs’s). At the same time, an optical fiber probe was used to assess the particle size effect on the formation of particle clusters and their properties under different operating conditions. Results revealed that when the averaged size of bed materials decreased from ∼200 μm to ∼100 μm, at the same operating condition, the bottom dense bed became remarkably higher, and the upper dilute zone had stronger pressure fluctuation, more even axial and horizontal particle distributions, and higher solid density. Gs was more sensitive to the variation of the superficial gas velocity than the bed inventory. In addition, the standard deviation and power spectrum density of instantaneous pressure decreased in the dense bed and increased in the dilute zone. The particle velocity was slightly lower in the lower section of the riser but noticeably greater in the upper riser section. In addition, the clusters formed more frequently and lasted significantly longer. The study showed that flow characteristics in the bed qualitatively changed from that of Type B particles to that Type A particles in the Geldart’s classification, even at a small Gs, and previous studies with Type B particles could very likely not apply in the CFB boilers operating with fine bed materials.

Developing a Zigzag-baffled column photobioreactor to increase mass-transfer, CO2 fixation and biomass yield during A. platensis cultivation

The present work aims to evaluate performance of a novel zigzag-flow column photobioreactor (ZZ-flow PBR) designed to achieve a high biomass during A. platensis cultivation. The ZZ-flow PBR was installed with four optimized zigzag baffle structures mounted over its outer (riser) section. The optimum parameters (w = 18 and h= 5 cm) for each zigzag baffle structure generated zigzag flow patterns throughout microalgae solution, which decreased mixing time (MT) by 51.1% but increased mass transfer coefficient (MTC) by 58.2% as compared with traditional PBR. The solution followed zigzag path along the baffles to facilitate frequent movement of microalgae cells across the PBR, where overall photochemical efficiency φPSII and Fv/Fm increased by 21.4% and 12.4%, respectively. The intracellular photosynthesis promoted electron transfer rate (ETR) by16.6% and chlorophyll a content by 8.3%, resulting in an increased biomass yield and CO2 fixation by 28.8% and 36.3%, respectively, relative to conventional column PBR.

Experimental study of the hydraulic jump phenomenon induced by the downstream riser structure in a pipeline–riser system

• The interface wave in the horizontal section before the riser was studied by an ECVT. • Flow regime transition boundaries shift to lower velocities due to the riser. • The period of hydraulic jump is consistent with that of severe slugging flow. • The hydraulic jump upstream is mainly caused by pressure fluctuations of the riser. This paper describes experiments conducted on the gas–liquid two-phase flow characteristics in a pipeline-riser system under 1 MPa. The hydraulic jump phenomenon (HJP) in the upstream horizontal section was quantitatively studied using electrical capacitance volume tomography (ECVT). Flow regime transition boundaries were shifted to lower gas and liquid velocities due to the impact of the riser at the end of the horizontal pipe. The HJP’s period is consistent with that of severe slugging flow; additionally, the liquid slug production and the gas–liquid eruption stages always occur before the HJP in the upstream horizontal section. The Pearson correlation coefficient between the HJP upstream and the pressure fluctuations in the three main structures (horizontal, downward, and riser sections), the period consistency, and the sequential relationship between them were analyzed to verify that the pressure fluctuations in the downstream riser were the main cause of the HJP upstream.

Circulating fluidized bed reactors – Experimental optimization of loopseal aeration and parametric study using CPFD simulations

Circulating fluidized bed (CFB) technology has diverse applications from process industry to energy generation. Experimental studies were performed in a CFB to analyse the effect of loopseal aeration for the rate of particle circulation, which is a crucial process parameter. The experimental data were used to re-evaluate the performance of optimized particle modeling parameters in computational particle fluid dynamic (CPFD) simulations. Two sand particle sizes of 850–1000 μm and 1000–1180 μm were used in the experiments with varying loopseal aeration. The experiments could conclude that the rate of circulation is possible to improve greatly by slight reduction of the particle size. The aeration at the standpipe of the loopseal showed a higher contribution for the circulation than bottom aeration. CPFD simulations could capture exact rate of particle circulation and the core-annulus structure in the riser section. Subsequently, the duly validated CPFD model was used to analyse the particle residence time, effects of particle inventory and the riser aeration.

Tailoring the Local Design of Deep Water Composite Risers to Minimise Structural Weight

Following the rising technological advancements on composite marine structures, there is a corresponding surge in the demand for its deployment as ocean engineering applications. The push for exploration activities in deep waters necessitates the need for composite marine structures to reduce structural payload and lessen weights/loads on platform decks. This gain is achieved by its high strength–stiffness modulus and light-in-weight attributes, enabling easier marine/offshore operations. Thus, the development of composite marine risers considers critical composite characteristics to optimize marine risers’ design. Hence, an in-depth study on composite production risers (CPR) is quite pertinent in applying composite materials to deep water applications. Two riser sections of 3 m and 5 m were investigated under a 2030 m water depth environment to minimise structural weight. ANSYS Composites ACP was utilized for the CPR’s finite element model (FEM) under different load conditions. The choice of the material, the fibre orientation, and the lay-up configurations utilised in the modelling technique have been reported. In addition, the behaviour of the composite risers’ layers under four loadings has been investigated under marine conditions. Recommendations were made for the composite tubular structure. Results on stresses and weight savings were obtained from different composite riser configurations. The recommended composite riser design that showed the best performance is AS4/PEEK utilising PEEK liner, however more work is suggested using global design loadings on the CPR.

A Review of Modelling of the FCC Unit—Part II: The Regenerator

Heavy petroleum industries, including the Fluid Catalytic Cracking (FCC) unit, are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The FCC unit’s regenerator is where these emissions originate mostly, meaning the operation of FCC regenerators has come under scrutiny in recent years due to the global mitigation efforts against climate change, affecting both current operations and the future of the FCC unit. As a result, it is more important than ever to develop models that are accurate and reliable at predicting emissions of various greenhouse gases to keep up with new reporting guidelines that will help optimise the unit for increased coke conversion and lower operating costs. Part 1 of this paper was dedicated to reviewing the riser section of the FCC unit. Part 2 reviews traditional modelling methodologies used in modelling and simulating the FCC regenerator. Hydrodynamics and kinetics of the regenerator are discussed in terms of experimental data and modelling. Modelling of constitutive parts that are important to the FCC unit, such as gas–solid cyclones and catalyst transport lines, are also considered. This review then identifies areas where the current generation of models of the regenerator can be improved for the future. Parts 1 and 2 are such that a comprehensive review of the literature on modelling the FCC unit is presented, showing the guidance and framework followed in building models for the unit.

Computational fluid dynamics simulation of internally circulating fluidized bed reactor for dry reforming of methane

Internally circulating fluidized bed reactor (ICFB) is the reactor that combines the conventional circulating fluidized bed (CFB) reactor system, including riser, downer, loop seal and cyclones, into a single compact reactor column. The ICFB reactor column is separated into two sections (riser and downer) by baffles and is linked together via connecting ports. The solid particles are circulated in the ICFB reactor by unequal fluidizing velocities in the riser and downer sections. The solid particles in the downer section are operated with low fluidizing velocity in the bubbling fluidization regime. In the riser section, the solid particles are transferred to the downer section because of the high fluidizing velocity. In this study, the carbon dioxide reforming or dry reforming reaction of methane was investigated. Dry reforming is a reaction between carbon dioxide and methane, which are the major greenhouse gases, for producing syngas, hydrogen and carbon monoxide. The hydrodynamics and dry reforming reaction with different reactor designs were explored using two-dimensional Eulerian–Eulerian computational fluid dynamics simulation (CFD). The ICFB reactor with no elevation gas distributor, 90 cm of draft tube height, 2 cm of loop-seal length and 1 cm of gas outlet diameter gave the highest methane conversion of 15.4%. The analysis of variance (ANOVA) indicated that the length of loop-seal and the gas outlet diameter gave substantial negative and positive effects on methane conversion, respectively. The interaction between length of loop-seal and gas outlet diameter also had a significant effect on the methane conversion. Although the ICFB reactor in this study gave the methane conversion slightly lower than referenced literature conventional CFB reactor, the ICFB reactor is the reactor that can reduce construction cost and simplify complex reactor operation.

Parametric analysis for free standing riser by a new calculation procedure

A new calculation procedure for the structural analysis of a free standing riser system is presented. The riser model includes a flexible jumper section and rigid riser section as two single continuous segments, which are coupled at the buoyancy can to form the overall riser static model. The equilibrium equations of the flexible jumper and rigid riser are established based on Minimum Total Potential Energy Principle. At each equilibrium configuration, the elastic potential energy of the system will be always equal to the sum of the potential energy caused by the external forces. The coupled equations are numerically solved by finite difference method, using Newton-Raphson technique in an iterative manner. This calculation procedure is evaluated by convergence analysis and the results validated by comparisons with well established commercial code. Parametric studies consider platform span, flexible jumper length, buoyancy force, buoyancy can depth and ocean current velocity effects to evaluate aspects related to simplicity, flexibility and robustness of the proposed methodology. The solution works as an expeditious alternative to enhance efficiency of the numerical calculations used in deep water riser design applications.

Effects of drag and subgrid-scale turbulence modeling on gas–solid hydrodynamics of a pilot-scale circulating fluidized bed

Large eddy simulation is performed on a circulating fluidized bed (CFB) based on an Eulerian-Eulerian approach. The riser of the CFB has two axial sections of different diameters joined by a diffuser. The effects of drag and subgrid-scale models are examined on hydrodynamic parameters, such as solids volume fraction (εs), solids circulation rate (Gs), and full loop pressure profiles. A hybrid energy minimization multi-scale (EMMS) drag model is applied that combines EMMS drag models for the bubbling and the fast fluidized bed regimes. Experiments are conducted on a pilot-scale CFB model, and numerical results are validated against the experimental measurements of pressure and Gs. The change in the riser diameter has a significant influence on axial- and radial profiles of εs, particularly in the upper riser section. The hybrid EMMS drag model and the sgs-TKE turbulence model give the best agreement to the experimental data.

Floating catenary riser system concept for brownfield application

The expansion of a deepwater brownfield may become necessary to increase the production of hydrocarbons. Such expansion often requires the installation of additional risers to the existing floating production platform. However, the seabed footprint of the existing facilities may be congested with existing subsea pipelines and structures. Tying back of risers such as steel catenary riser (SCR) to the floating platform becomes challenging. Floating catenary riser (FCR) is a novel riser solution with floating bends or ‘waves’ close to the seabed. The FCR is engineered to extend its touch down point (TDP) far beyond the nominal TDP of the SCR and away from the congested seabed footprint. The riser sections before the nominal SCR TDP is configured to float by installing buoyancy modules. The multiple wave buoyant sections also provide the FCR with the capability to decouple its touch down zone (TDZ) from the floating platform motion. This can result in a significant reduction in the stress and fatigue damage around the riser TDP. Presented in this paper are the FCR configuration development and global responses to vessel offsets, current drag load impact, combined load, and wave fatigue loads, simulated to demonstrate the FCR feasibility.

A Study of Fast Front Transients of an HVDC Mixed Transmission Line Exposed to Bipolar Lightning Strokes

Bipolar lightning strokes are associated with multiple polarity electrical discharge with no current intervals in between, making their behavior quite peculiar. This work presents a fast front analysis of a mixed high voltage direct current (HVDC) transmission link, evaluating the factors that influence the line transients due to shielding failures and backflashovers (BFOs), considering both overvoltage and repeated polarity reversal at the cable sending terminal. The research process includes a detailed modeling of a bipolar lightning stroke, frequency-dependent HVDC overhead, and underground transmission line sections. Noticeable findings include the occurrence of only a positive polarity insulator BFO for the adjacent and subsequent tower, despite the dual polarity of the lightning stroke with relatively small values for the lightning parameters. The influence of traveling waves on the insulator flashover performance of the line with varying parameters (such as the riser section length, the tower grounding impedance, and the location of the lightning stroke) is recorded and explained.

Development of an analytical model for predicting the wet collapse pressure of curved flexible risers

Flexible risers are designed with strong anti-collapse capacities which enable them to operate in deep-water reservoirs. However, this anti-collapse capacity is susceptible to the pipe curvature in the flooded annulus condition. For the curved riser sections within the touch-down zone, significant reduction of collapse capacity can occur once their external sheaths are worn out by the seabed, resulting in the so-called “wet collapse”. Mostly, wet collapse studies of curved flexible risers are performed through costly numerical simulations since there are no alternative analytical approaches. In view of it, this work presents an analytical model for predicting the wet collapse pressure of curved flexible risers. The analytical model is developed based on a spring-supported arch model that from our previous work, which is able to take the curvature-induced factors into account. With the stability theories of arched structures, the wet collapse pressure of curved flexible risers can be solved. To verify this analytical model, 3D full FE models are employed. The critical collapse pressures predicted by these two kinds of approach are in good agreement, indicating this proposed analytical model can be an useful tool to facilitate the collapse analysis in pipe design stage.

Effect of heater and condenser orientations on fluid flow behaviour in a two-phase natural circulation loop

A Numerical investigation on the influence of heater and condenser orientation and its location on steady state performance of a Two Phase Natural Circulation Loop (TPNCL) is presented. In the present study, four possible orientations are considered in TPNCL namely, Vertical Heater and Vertical Condenser (VHVC), Vertical Heater and Horizontal Condenser (VHHC), Horizontal Heater and Horizontal Condenser (HHHC) and Horizontal Heater and Vertical Condenser (HHVC). An in house MATLAB code is developed to solve the systems of equations. Homogeneous equilibrium model (HEM) is used in two phase regions. It is observed that steady state mass flow rate of the loop is significantly influenced by the developed pressure gradient in the riser and downcomer sections, as well as available vapour quality in the riser section. Moreover, it is also noticed that condenser position and orientation significantly effects the thermo-hydraulic characteristic of loop compared with heater orientation.

Experimental investigation on vortex-induced vibration of variable diameter riser with uniform flow

Diameter design of the riser is a very important link in offshore riser engineering, which will affect a series of parameter changes of the riser. In this paper, the riser is a variable-diameter riser with different cross-sections spliced by riser sections with diameters of 18, 25, and 30. In the wave-flow combined flume, dynamic response parameters such as strain-time history curve and root-mean-square of dimensionless strain were obtained by changing the outflow velocity and diameter of the riser, the effect of variable diameter on vortex-induced vibration of the riser was studied in detail. The results show that the vibration amplitude of the variable diameter riser varies with the axial position of the riser, but the frequency is dominated by the excitation of the thickest section riser; the variable diameter riser is always dominated by the first-order frequency in the outflow velocity range, and the relationship between the in-line and the cross-flow dominant frequency is always 2 times. With the increase of the flow velocity, the root mean square value of strain increases steadily.