Restart Process Research Articles

Flow prediction analysis of shutdown and restart for off-station pipeline based on flow assurance and energy-saving

Abstract Due to unforeseen operation errors or natural disasters, off-station pipelines may undergo emergency shutdown operations, necessitating a focus on flow assurance during the shutdown and restart process. Moreover, energy saving and emission reduction have become the focal points in the transformation of oilfield enterprises. This paper formulates a method for predicting the flow status during shutdown and restart of off-station pipelines based on the liquid conservation law, and the characteristic equations are solved by the characteristic line method. A comparative analysis is conducted on the operation rules of shutdown and restart for oil-water mixing transportation and dewatering processes under different water cuts. A typical off-station pipeline in a transfer station is selected as the case study object. The results indicate that due to the lower station heating required for the oil-water mixing transportation process, this process saves 44.3% of costs compared to the dewatering process. As the water cut increases, operation costs decrease and then increase, with the total cost of the 50% water cut scheme being the most economical. This study provides a reference for the safe operation and energy-saving management of off-station pipelines in the future.

Analysis of CCER Policy Application in the New Energy Vehicle Industry

As China's economy is booming, the issue of carbon emissions is becoming increasingly prominent. In terms of policy, China has established a domestic CCER mechanism to improve the carbon trading market, and the future development of CCER policy has received much attention, but there are still deficiencies in synergistic development with specific industrial sectors. This paper explains the CCER restart process based on the progressive policy model, through the analysis of energy type suitability, the future development path of new energy vehicles, and the existing CCER methodology, combined with the example of the development of new energy vehicle industry in Guiyang City, Guizhou Province, effectively demonstrates the suitability of new energy automobile industry and renewable energy CCER projects, and explores the combination of the two. It also explores the path of "light storage, charging and discharging", and then puts forward the following suggestions for CCER policy development: improve the policy content and strengthen the policy synergy.

Water-in-Oil Emulsion Temporal and Spatial Evolution at Static Conditions and Its Impact on Pipeline Restart

Summary Understanding emulsion evolution at static conditions is crucial for production operations, such as pipeline operations during the shut-in and restart process and separator optimal design. This study experimentally investigated the temporal and spatial evolution of water-in-oil emulsion properties under static conditions. Numerical simulations were conducted to study their impacts on pipeline restart operations. The experiments were conducted in graduated glass cylinders, with mineral oil and tap water as the testing fluids and Span® 80 as the surfactant. Different water cuts, mixing speeds, and surfactant concentrations were investigated. Along with idle time at static conditions, the mixture demonstrated two layers, namely an upper oil layer and a lower emulsion layer, except for the lowest surfactant concentration that gave a third additional free-water layer at the bottom. Experimental results showed a dramatic increase in viscosity in the emulsion layer with time and depth, which was closely related to the increase in the water volumetric fraction. The increase rate slowed down and plateaued out with time. The increase rate is also related to water cut, mixing speed, and surfactant concentration. Experimental results also show that the relationships between the viscosity and water cut for separated emulsion follow the master curve of viscosity and water cut for homogeneous emulsion. This suggests that one can estimate the viscosity using the master curve given the water volumetric fraction. The numerical simulation was conducted for pipelines with a valley configuration and with the fluid properties obtained from the experimental measurements. It demonstrates that a higher pressure is required to restart the flow to the original flow rate. It also shows that the flow rate may not be able to resume its original value given the same pressure boundaries due to the accumulation of dense emulsion layers in the horizontal and upward inclined sections. For example, for a 16-m pipe, the flow cannot be restarted given the same inlet pressure (100 Pa). It can only resume 4.6% of the original flow rate when the pressure is elevated to 300 Pa.

Renewable energy powered membrane technology: Impact of intermittency on membrane integrity

Directly coupled photovoltaic-powered nanofiltration/reverse osmosis is a sustainable and cost-effective solution to brackish water desalination in remote areas. Intermittent operation of the system may cause physical membrane damage and loss of membrane integrity. The potential causes of integrity loss during intermittency include the sudden spontaneous restart process, frequent shut-down events, and osmotic backwash (OB) cleaning with controlled permeate backpressure. A bench-scale crossflow system powered by a solar array simulator was used to perform periodic fluctuation on filtration experiments that in this case cause intermittency. A wide range of feed pressure increase rates (0.17 to 2 bar/s) during the start-up process, up to 1000 shut-down events, and additional permeate backpressure up to 4 bar to enhance OB were applied. Results show that no significant membrane performance deterioration was observed at the highest feed pressure increase rate (2 bar/s), and when the shut-down event number increased to 1000 implying the robustness of NF/RO membranes and spontaneous OB cleaning. When increasing permeate backpressure to 2–4 bar to enhance the OB process, membrane integrity loss of both membranes was observed. This demonstrates the reliability and robustness towards fluctuations, intermittency, and spontaneous OB cleaning in a directly coupled photovoltaic-powered nanofiltration/reverse osmosis system if permeate backwash is avoided.

Comparison of the unstart/restart processes of a two-dimensional twin-duct supersonic inlet induced by the plug throttling and thermal choking at the sideslip state

It is of great significance to study the hysteresis phenomenon in the unstart/restart process of supersonic inlets for restart control in the practical operation of ramjet engines. In this paper, the unsteady numerical simulations are conducted for the unstart/restart processes of a ramjet engine with a two-dimensional twin-duct inlet configuration under asymmetric incoming-flow conditions (Ma0 = 2.6,β = 2°), and the unstart/restart characteristics of the inlet caused by the plug throttling and the thermal choking are compared and analyzed. The results show that from the perspective of source incentives, the hysteresis loop of the restart process of the leeward inlet caused by the thermal choking is larger than that of the restart process of the leeward inlet caused by the plug throttling, which indicates that it is difficult to verify the restart performance of the ramjet with the two-dimensional twin-duct inlet configuration in the actual operating process by the inlet's plug-throttling experiment in the conventional wind tunnel. In addition, in the practical operations, the increase of fuel gas causes the transition of the leeward inlet to the unstart state, and part of the fuel gas reacts and combusts stably on the external compression surface of the leeward inlet, which easily leads to the burning of the inlet if there is without any special thermal protection.

Fluid-Solid Reaction in Porous Media as a Chaotic Restart Process.

Chemical and biological reactions at fluid-solid interfaces are central to a broad range of porous material applications and research. Pore-scale solute transport limitations can reduce reaction rates, with marked consequences for a wide spectrum of natural and engineered processes. Recent advances show that chaotic mixing occurs spontaneously in porous media, but its impact on surface reactions is unknown. We show that pore-scale chaotic mixing significantly increases reaction efficiency compared to nonchaotic flows. We find that reaction rates are well described in terms of diffusive first-passage times of reactants to the solid interface subjected to a stochastic restart process resulting from Lagrangian chaos. Under chaotic mixing, the shear layer at no-slip interfaces sets the restart rate and leads to a characteristic scaling of reaction efficiency with Péclet number, in excellent agreement with numerical simulations. Reaction rates are insensitive to the flow topology as long as flow is chaotic, suggesting the relevance of this process to a broad range of porous materials.

Experimental study on the restart of heavy oil-water core annular flow in a horizontal pipe

An experimental campaign is conducted to investigate the pressure drop during the restart of a heavy oil-water core-annular flow (CAF) from a stratified configuration in a polyvinyl chloride (PVC) horizontal pipe. The evolution characteristic of restart pressure drop along time is explored, and the effects of various factors including oil holdup (0.26-0.76), oil viscosity (1.0553-3.02 Pa·s), standstill period (0.5 & 1.0 h) and water cleaning superficial velocity (0.25-1.01 m/s) on maximum restart pressure drop are emphatically investigated. The results demonstrate that the restart process can be divided into decay and steady two stages. The maximum restart pressure drop generally increases along with the increase of oil holdup, oil viscosity, standstill period and water cleaning superficial velocity. Moreover, of all the measured variables, oil holdup and water cleaning superficial velocity have a significant influence on maximum restart pressure drop. The results obtained can provide a theoretical reference and practical guidance for the development of appropriate restart schemes for on-site shutdown pipelines.

GPU-accelerated transient thermo-hydraulic simulation of weakly compressible restart flow of a non-Newtonian fluid in a long-buried hot oil pipeline

For the complex transient thermo-hydraulic restart process of a long-buried hot oil pipeline, it takes a long time to solve the restart simulation model, which cannot meet the requirements of rapid restart prediction and assessment. The modern GPU is specialized for compute-intensive and massively parallel computation, and it has great potential to accelerate transient thermo-hydraulic restart simulation. According to the computational characteristics of restart model solutions, four types of GPU parallel strategies, from the mapping of grids to the convergence judgment of the discrete equation solution, are combined to accelerate the whole process of a transient thermo-hydraulic restart simulation. The results indicate that the total computation time of the transient thermo-hydraulic simulation is reduced from 185.4 min to 8.8 min, corresponding to an acceleration rate of 21.1, which exhibits a good acceleration effect for a single GPU and is beneficial to the rapid assessment of restart schemes. Based on the GPU-accelerated numerical results, the complex transient thermo-hydraulic restart process with the changing soil temperature field, the non-Newtonian thixotropic behavior of crude oil and flow pattern evolution, is investigated. The analysis reveals that the dominant influencing factors of the restart process vary with the restart time, and the flow pattern evolution plays an important role in the thermo-hydraulic characteristics of the restart process.

Study on fault mechanism of LCC HVDC large disturbances under cloud-to-ground lightning with long continuous current

The safe and stable operation of the line commutated converter high voltage direct current (LCCHVDC) system is of great significance to the reliability of electricity supply. In order to clearly reveal the mechanism of LCCHVDC large disturbance fault under the Cloud-to-Ground (C-G) lightning with long continuous current, the HVDC-lightning simulation model considering long continuous current, actual control and protection systems is proposed. The effect of long continuous current on traveling wave protection is analyzed. Transient processes including commutation failure (CF), fault restart and blocking of the DC system under the lighting with long continuous current are simulated. The reasons for CF of LCCHVDC system caused by long continuous current are analyzed, and the influence of long continuous current amplitude and duration on fault restart process is studied. Results show that the long continuous current has little influence on the response characteristics of travelling wave protection, but during the regulation process of control system under lightning disturbance, the DC current control regulation quantity will increase due to the presence of long continuous current. If the amplitude of long continuous current exceeds 80 A, the CF will occur in the DC system. If the duration of long continuous current exceeds the deionization time, the line will fail to restart, and the line can be successfully restarted only if the long continuous current is over before the voltage begins to rise.

Rad52’s DNA annealing activity drives template switching associated with restarted DNA replication

It is thought that many of the simple and complex genomic rearrangements associated with congenital diseases and cancers stem from mistakes made during the restart of collapsed replication forks by recombination enzymes. It is hypothesised that this recombination-mediated restart process transitions from a relatively accurate initiation phase to a less accurate elongation phase characterised by extensive template switching between homologous, homeologous and microhomologous DNA sequences. Using an experimental system in fission yeast, where fork collapse is triggered by a site-specific replication barrier, we show that ectopic recombination, associated with the initiation of recombination-dependent replication (RDR), is driven mainly by the Rad51 recombinase, whereas template switching, during the elongation phase of RDR, relies more on DNA annealing by Rad52. This finding provides both evidence and a mechanistic basis for the transition hypothesis.

A nonlinear creep damage model for gelled waxy crude

Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure, to describe the process completely and accurately is the basis of numerical simulation of restart process of the pipeline. The creep and yield behaviors of two gelled waxy crudes were investigated experimentally under different constant applied stresses. The results clearly show that the creep process of waxy crude is related to the applied stress and time. The greater the applied stress, and the longer the loaded time, the more obvious the nonlinear features. Based on the fractional calculus theory, a fractional viscous element was developed to describe the decelerated and steady creep process of gelled waxy crude. On the basis of the damage theory, an elastic damage element was proposed to describe the accelerated creep after the yielding. According to the idea of mechanical analogy, a nonlinear creep model was established by a fractional viscous element, an elastic damaged element, and an elastic element in series, which can accurately describe the whole creep and yielding process of gelled waxy crude.

Numerical study of gelation and flow restart in a waxy crude oil riser

Precipitation of paraffin wax during crude oil transportation in low ambient temperature presents many technological challenges in petroleum industries. During a complete shutdown, the precipitation intensifies to form a gel-like structure which usually demands high restart pressure during flow restart operation. Numerical simulations are performed to investigate the gelation process in the shutdown pipeline and subsequent non-isothermal flow start-up operation in a heterogeneously gelled pipeline. A Finite volume method is used to solve the mass, momentum and energy conservation-based governing equations over an orthogonal static grid setup. The gelation model utilizes a modified Eyring-based viscosity model to account for temperature-dependent changes in gel strength. On the other hand, the flow restart process follows the deformation and temperature-dependent shear-thinning based rheological model. The pipeline under consideration in the present work is vertical, replicating flow in risers. Our gelation model considers natural convection-driven flow inside the pipeline, which incites the hot oil in the core to mix with cooler fluid at the wall. The gelation is achieved through cooling the static crude oil in the pipeline for different timespans varying from 3 h to 15 h. The gelation stage ends up producing spatial heterogeneity in gel strength. Such heterogeneity leads to weaker gel structure in the core causing early flow restart due to cohesive failure of the gel medium at some interior radial location. Hence, it can be concluded that depending on the cooling stage, the heterogeneous gel with a weaker gel in the pipe core can restart faster than when the pipeline is filled with the gel having an equivalent average temperature. The findings provide realistic insights into the mechanism of gel failure in the pipeline, and the knowledge can be utilized to develop a better flow assurance strategy.

Improved Adaptive Time Step Method for Natural Gas Pipeline Transient Simulation

As the natural gas pipeline network becomes larger and more complicated, a stricter requirement of computation efficiency for the large and complicated network transient simulation should be proposed. The adaptive time step method has been widely used in the transient simulation of natural gas pipeline networks as a significant way to improve computation efficiency. However, the trial calculation process, which is the most time-consuming process in time step adjustment, was used to adjust the time step in these methods, reducing the efficiency of time step adjustment. In order to reduce the number of trial calculations, and improve the calculation efficiency, an improved adaptive time step method is proposed, which proposes the concept of energy number and judges the energy number of the boundary conditions after judging whether the variation of the pipeline state is tolerable. A comparison between the adaptive time step method and the improved adaptive time step method in the restart process of natural gas pipelines and an actual operation of the XB section in China shows the accuracy, effect, and efficiency of the improved adaptive time step method. The results show that with the same accuracy, 27% fewer trial calculation processes and 24.95% fewer time levels are needed in the improved time step method.

Biased random walk with restart for essential proteins prediction

Predicting essential proteins is crucial for discovering the process of cellular organization and viability. We propose biased random walk with restart algorithm for essential proteins prediction, called BRWR. Firstly, the common process of practice walk often sets the probability of particles transferring to adjacent nodes to be equal, neglecting the influence of the similarity structure on the transition probability. To address this problem, we redefine a novel transition probability matrix by integrating the gene express similarity and subcellular location similarity. The particles can obtain biased transferring probabilities to perform random walk so as to further exploit biological properties embedded in the network structure. Secondly, we use gene ontology (GO) terms score and subcellular score to calculate the initial probability vector of the random walk with restart. Finally, when the biased random walk with restart process reaches steady state, the protein importance score is obtained. In order to demonstrate superiority of BRWR, we conduct experiments on the YHQ, BioGRID, Krogan and Gavin PPI networks. The results show that the method BRWR is superior to other state-of-the-art methods in essential proteins recognition performance. Especially, compared with the contrast methods, the improvements of BRWR in terms of the ACC results range in 1.4%–5.7%, 1.3%–11.9%, 2.4%–8.8%, and 0.8%–14.2%, respectively. Therefore, BRWR is effective and reasonable.

Study on the time and duration of restart on the AC/DC interconnected system based on dynamic energy

Concerning the difficulty in determining the restart strategy for AC/DC interconnected systems, this paper proposes a method of calculating the optimal restart strategy for AC/DC interconnected systems based on dynamic energy. First, a dynamic energy function that characterises the stability of system is constructed. Then, the analytical expressions of the dynamic energy function are calculated separately for the deionisation stage, the restart stage, and the alpha retard stage of the entire restart process. On this basis, the variation rate of the system dynamic energy is defined as the energy accumulation rate, which quantifies the accumulation or consumption of dynamic energy during the restart process, and facilitates detailed analysis of the effects of the restart time and restart duration on the stability of system. Then, a method to calculate the optimal restart time is proposed with the goal of minimising the dynamic energy accumulated in the system. Finally, hardware-in-the-loop tests are carried out on the RT-LAB platform for simulation verification. The experimental results show that the dynamic energy function constructed in this paper can reflect the stability of system. Using the proposed optimal restart strategy can reduce the accumulation of dynamic energy and improve the stability of system.

Discovery of Synergistic Drug Combinations for Colorectal Cancer Driven by Tumor Barcode Derived from Metabolomics "Big Data".

The accumulation of cancer metabolomics data in the past decade provides exceptional opportunities for deeper investigations into cancer metabolism. However, integrating a large amount of heterogeneous metabolomics data to draw a full picture of the metabolic reprogramming and to discover oncometabolites of certain cancers remains challenging. In this study, a tumor barcode constructed based upon existing metabolomics “big data” using the Bayesian vote-counting method is proposed to identify oncometabolites in colorectal cancer (CRC). Specifically, a panel of oncometabolites of CRC was generated from 39 clinical studies with 3202 blood samples (1332 CRC vs. 1870 controls) and 990 tissue samples (495 CRC vs. 495 controls). Next, an oncometabolite-protein network was constructed by combining the tumor barcode and its involved proteins/enzymes. The effect of anti-cancer drugs or drug combinations was then mapped into this network by the random walk with restart process. Utilizing this network, potential Irinotecan (CPT-11)-sensitizing agents for CRC treatment were discovered by random forest and Xgboost. Finally, a compound named MK-2206 was highlighted and its synergy with CPT-11 was validated on two CRC cell lines. To summarize, we demonstrate in the present study that the metabolomics “big data”-based tumor barcodes and the subsequent network analyses are potentially useful for drug combination discovery or drug repositioning.

Experimental investigations of hypersonic inlet unstart/restart process and hysteresis phenomenon caused by angle of attack

In this study, the unstart/restart process of a hypersonic inlet caused by the angle of attack (AOA) is experimentally performed at a Mach number of 5.0, and the unsteady flow characteristics during the test are investigated. The flow characteristics are simultaneously recorded using high-frequency pressure measurement and high-speed schlieren imaging. The results show that the inlet enters the unstarting state at AOA = 8.4° but restarts at AOA = 0.3°, exhibiting an obvious hysteresis phenomenon. During the unstart process, the forebody shock gradually approaches the body and then impinges on the inside of the cowl with the increasing angle of attack, indicating that the inlet works under an overrated mode. As the angle of attack increases further, the airflow chokes, and a high-pressure zone is first formed in the exit of the duct. Then, the high-pressure signal propagates upstream in the duct, leading to the emergence of an inlet unstart. When the inlet enters the unstarted pattern, a typical local unstarted flow field is formed. Low-amplitude oscillations occur in the internal contraction region, but further propagation to the isolator is weak. During the restart process, when the angle of attack decreases from 3.2° to 0.3°, two kinds of big buzz patterns, namely, intermittent high-amplitude oscillation and periodic high-amplitude oscillation, appear successively. The intermittent high-amplitude oscillation is characterized by the intermittent occurrence of a high-amplitude oscillation after the low-amplitude oscillations for a random length of time. In the periodic high-amplitude oscillation, the separation bubble is repeatedly disgorged and swallowed, resulting in a dominant fluctuation frequency in the entire duct. Furthermore, as the angle of attack decreases, the dominant frequency gradually rises from 280 Hz to 339 Hz. This work provides new insights into the flow evolutions and unsteady behaviors of hypersonic inlet unstart/restart owing to the AOA and provides potential applications on the detection and prediction of hypersonic inlet unstart/restart.

Anomaly detection for wind turbine damaged due to lightning strike

The development of wind energy is now underway globally as a renewable source and has attracted much attention as a cost-effective power generation method. However, blade damage caused by lightning strikes on wind turbines has occurred in Japan, and there is pressure to take measures to mitigate this problem. When blade lightning damage occurs, the damage is magnified by the continued rotation of the damaged blades. To stop the wind turbines before this secondary damage occurs, wind farms, in the regions of Japan vulnerable to winter lightning, are required to introduce lightning detection systems. Typically, the wind turbine stops automatically due to lightning detection and is restarted after the soundness of the blades is confirmed by visual inspection. However, it is often difficult to check the soundness of the blade visually due to bad weather, and the resulting delay in the restart process prolongs the downtime and reduces the availability of the wind turbine. In this paper, we report the results of using a machine learning model and supervisory control and data acquisition system data to check the soundness of the blades after a lightning strike to enable operations to resume sooner, thereby increasing up-time.

Improving local search for the weighted sum coloring problem using the branch-and-bound algorithm

The weighted sum coloring problem (WSCP) is an extension of the weighted vertex coloring problem and sum coloring problem, and has important applications in the batch scheduling of distributed systems. Compared to the weighted vertex coloring problem and sum coloring problem, where extensive methods have been proposed for efficiently solving graphs in the real world, fewer solvers have been developed for WSCP, especially no practical complete algorithm is available for solving WSCP. This paper is devoted to design branch-and-bound strategies for solving WSCP, including a branching heuristic rule, a lower bound based on weighted clique partitioning, and a branching search framework for searching all possible coloring solutions. As a result, a new branch-and-bound algorithm BABWSCP is proposed. We also design a novel combination method for improving the local search using complete algorithm in the restart process for WSCP. Consequently, a new local search algorithm named BABLS is designed. Experimental results show that our branch-and-bound strategies are effective, and BABLS almost always outperforms the state-of-the-art WSCP solvers for the benchmarks studied in previous works.

Study on Restart Safety of Waxy Crude Pipelines Based on Reliability Principle under Constant Flow.

The restart process of waxy crude pipelines is an unsteady thermo-hydraulic coupling process, which mainly includes two modes of the constant flow and constant pressure in industry. However, some parameters involved in the restart process have obvious uncertainties, such as the operating parameters, physical parameters of crude oil, environmental parameters, and pipeline parameters, resulting in the traditional deterministic method that cannot scientifically describe the safety of the pipeline restart process. To do this, this study introduces the reliability-based limit state method and interference principle into the safety evaluation of waxy crude pipelines during the restart process. Considering the random fluctuation characteristics of the mentioned parameters, the restart physical process, the flow and heat transfer mathematical model, and the restart failure limit state function were established. On this basis, the failure probability during the restart process for one waxy crude pipeline under constant flow was determined. This research has realized the quantitative evaluation of restart safety of waxy crude pipelines.