Bypass Fractions Research Articles

Bypass pigging technology in improving pigging safety and efficiency: Principles, progress, and potentials

Bypass pigging is a promising strategy to improve pipeline flow assurance by eliminating pigging-generated slugs and reducing pig velocity. This paper provides a comprehensive analysis of the fundamentals, recent progress, and prospects of bypass pigging for enhancing pigging safety and efficiency in gas pipeline systems. A model of bypass pigging motion is developed based on momentum balance, incorporating key factors that affect performance. Recent studies of the influence of the bypass fraction, pressure drop coefficient, and friction force on pigging performance are discussed. The pressure drop coefficient, crucial for accurate dynamic pigging simulation, depends primarily on the pig bypass structure. The impact of variations in the bypass fraction on pig velocity, a significant factor affecting pigging performance, is analyzed. Higher bypass fractions lead to lower pig velocities, resulting in improved pigging efficiency. However, the risk of pig blockage increases owing to the decreased driving gas force at a higher bypass fraction. Therefore, the use of bypass pigs with anti-blocking capability is necessary to enhance overall flow assurance. The paper also highlights the quantifiable benefits of bypass pigging in reducing pig velocity and the pigging-generated slug volume. The prospects for further development of bypass pigging are also discussed. This study aims to comprehensively elucidate the bypass pigging strategy, promoting its wider implementation in natural gas pipelines to enhance pigging efficiency and safety.

Integrated synthesis and control of heat exchanger networks with dynamic flexibility consideration

• Dynamic flexible aspect is taken into account in early integration stage. • A sequential iterative algorithm for the problem solution is devised. • Stream matches, heat transfer areas and bypass fractions are optimized. • Results indicate considerable cost (−14.95%) and control performances (+61.83%). • Major advantages found for case studies with multiple disturbances. Flexible synthesis and control which can be both used to reduce the influences of disturbances on heat exchanger networks are often considered as two separate issues assisting network development at different stages. A proper integration of these separate yet connected tasks carries the promise of achieving superior designs. Currently, the study of integration of heat exchanger networks is still towards a sequential procedure consisting of initial flexible synthesis based on steady-state economic calculations followed by a controller. To overcome this challenge, based on the stage-wise superstructure, an optimization framework in this work is presented to address dynamic flexible synthesis and advanced control simultaneously for maximizing performance in face of disturbances. The framework is based on a sequential iterative procedure that decomposes the overall problem into two stages. The first stage is performed by the dynamic flexibility analysis where the design variables are chosen. In the second stage, the optimization variables are adjusted during the discrete time intervals on the realizations of the control actions and the variation ranges of outlet stream temperatures. The sequential iterative is to map the temperature regulations to the network configuration retrofits. The application to two case studies indicates that the proposed framework returns solutions which are considerably better all in terms of dynamic flexibility, economics and control performance than those published in literature. Compared to previous literature studies, the optimized solutions feature a total annual cost reduction up to 14.95%, a decrease in control action up to 48.58% and an increase in control performance up to 61.83%. Moreover, the application to two case studies indicates that allows solving a real-world problem with up to 26 hot streams and 29 cold streams (leading to models with a size of 523 binary variables and 1655 equations).

An improved solution to flow assurance in natural gas pipeline enabled by a novel self-regulated bypass pig prototype: An experimental and numerical study

Bypass pigging is an emerging strategy in effectively overcoming inherent issues of high pig speed and overflow of pigging-induced slug volume concomitantly caused by traditional pigging for natural gas pipelines, which is attracting wide attention for flow assurance in oil and gas industry. In view of most bypass pigs with simple bypass structures, the risk of pig stalling or pipeline blockage accidents can be encountered when suffering from increased resistance forces. Accordingly, a novel bypass pig prototype with a self-regulated module is proposed in this study as an improved solution to strengthening pigging safety, efficiency and flow assurance. A self-regulated, easily assembled bypass pig prototype was fabricated for experimental studies in a horizontal transparent gas pipeline system. The pressure mitigation and pig velocity characteristics were fully evaluated under varying bypass fractions. Specifically, when the bypass fraction increases from 0% to 3%, the average pig velocity can be reduced by 64.3–81.5% and pressure fluctuations are more stable. Besides, as an important structural parameter in affecting pig velocity and accuracy of dynamic pigging simulation, the pressure drop coefficient of gas through the bypass pig structure with an internal regulating valve was numerically studied. Compared to the common bypass pig with only a simple bypass port, the addition of the bypass regulating valve will notably increase the pressure drop coefficient. In particular, when the bypass fraction is increased to 7%, pressure drop coefficients for the bypass pig without or with an internal valve are 1.03 and 1.97, respectively, with the deviation of 90.9%. Finally, an optimal design scheme for bypass pigging operations was newly proposed to optimize bypass fractions in accordance with practical scenarios. This study can provide an effective pathway towards the implementation of self-regulated bypass pigging technology in substantially improving flow assurance of natural gas pipeline systems.

An experimental and modelling study of the Selective Non-Catalytic Reduction (SNCR) of NOx and NH3 in a cyclone reactor

The Selective Non-Catalytic Reduction process was investigated through experiments and modelling in a bench scale cyclone reactor. Outlet and internal profiles of NO and NH3 concentrations were measured at varying operating conditions. Cyclone inlet temperatures between 866 and 1023 °C were used, while the inlet NO concentration was kept at ~500 ppm. Gaseous ammonia was injected in the cyclone inlet, with nitrogen carrier gas. 60–69% NO reduction was achieved at inlet temperatures of 975–982 °C, and stoichiometric ratio NH3/NO β≈1.6, with no ammonia slip. The main reaction zone was the inlet and upper cyclone chamber. The experiments was modelled using simple and detailed kinetics combined with simple reactor models and a compartment model suggested in this work. The qualitative trends of NO reduction and ammonia slip were predicted by the models. However, the ammonia slip was significantly over-predicted in most cases. The outlet concentrations were insensitive to choice of reactor model, while sensitive to temperature and kinetics. The compartment model quantitatively reproduced the cyclones NO concentration profiles, through its simplified representation of the cyclone flow and temperature gradients, while the NH3 profiles were only qualitatively predicted. The choice of bypass fractions showed a large influence on the ammonia profiles.

Research on bypass pigging in offshore riser system to mitigate severe slugging

During pigging operations in offshore pipelines, severe slugging can block the pig or cause sudden velocity changes. Therefore, this paper proposed a method involving bypass pigs to mitigate the influence of severe slugging on the pigging process. The impact of different inlet mass flow rates and pig bypass fractions on the characteristic parameters, such as the pressure in the riser bottom, pig velocity, and liquid-phase distribution patterns, were analyzed by combining OLGA and CFD simulations. Furthermore, the accuracy of the simulations was verified by the comparisons of OLGA and CFD, as well as the transient indoor experiments. The results show that the bypass pig significantly reduces pressure fluctuations in the riser bottom and pig velocity in severe slugging conditions, compared with the conventional pig. Consequently, the bypass pig dissipates downstream liquid slugs, reducing the mass flow rate and liquid holdup in the riser outlet. In addition, an increase in bypass fraction reduces the pressure fluctuations in the riser bottom and pig velocity, increases the ability to dissipate the downstream liquid slug, and decreases the mass flow rate and liquid holdup in the riser outlet. Increasing the inlet mass flow rate improves the ability to dissipate the downstream liquid slug. However, the inlet mass flow rate has a lower mitigation effect on severe slugging than the bypass fraction.

Аналіз екологічної ефективності димових труб котелень за умов застосування теплоутилізаційних технологій

Виконано аналіз екологічної ефективності димових труб газоспоживальних котелень комунальної теплоенергетики за умов застосування сучасних теплоутилізаційних технологій з охолодженням відхідних димових газів нижче від температури роси водяної пари, що міститься в газах. У цих технологіях використовували теплоутилізатори, призначені для нагрівання зворотної тепломережної води котельні, та тепловий метод антикорозійного захисту газовідвідних трактів шляхом байпасування частини гарячих газів від котла повз зазначене теплоутилізаційне устаткування. Розглянуто одиночні димові труби різного типу під час виготовлення корпусу труби з антикорозійного матеріалу або під час монтування в цегляну (або іншу трубу з покращеними теплоізоляційними властивостями) газовідвідних стволів з цих матеріалів. Доліджено показники максимальних приземних концентрацій у навколишньому середовищі труби найшкідливіших викидів димових газів, таких як окиси вуглецю СО і азоту NOх залежно від режиму роботи котлів згідно з тепломережним графіком роботи котельні. Проаналізовано вплив використання теплоутилізаційних технологій та зазначеного теплового методу захисту димових труб на безпеку експлуатації газовідвідних трактів і на умови розсіювання шкідливих викидів. Показано, що в разі дотримання рекомендованих режимів роботи котлів зі зменшенням їх кількості згідно з тепломережним графіком роботи котельні й в разі застосування сучасних теплоутилізаційних технологій та димових труб з антикорозійних матеріалів реалізується розсіювання викидів СО та NOх у навколишньому середовищі згідно зі сучасними нормативними вимогами.

Coordination between bypass control and economic optimization for heat exchanger network

The bypass is widely used for optimizing the operation of heat exchanger network (HEN) to maintain the control requirements. More attention on the bypass control strategy has been paid to the control performance without considering the economics. However, the economic efficiency is quite important to the industry with energy intensive production as energy prices to rise. Therefore, both the control performance and the economic efficiency should be considered simultaneously during the life cycle of HEN. In this work, firstly we proposed a methodology for two-stage coordination of bypass control and economic optimization (CBCEO). Then the one-step coordination between bypass control and economic optimization is developed based on two-stage CBCEO. Secondly, the margin of HEN is commonly optimized and can be calculated by the variation of bypass fractions, which is regarded as the objective function in this work. Then non-square relative gain array is utilized to obtain optimization variables and the optimal control structure is established. Thirdly, an optimization algorithm combining external penalty function with pattern search is used to solve this dynamic optimization problem (DOP). Finally, two case studies indicated that the proposed CBCEO strategy can achieve the purpose of effective control and optimal economic at the same time.

Methodological framework for economical and controllable design of heat exchanger networks: Steady-state analysis, dynamic simulation, and optimization

The problem of interaction between economic design and control system design of heat exchanger networks (HENs) is addressed in this work. The controllability issues are incorporated in the classical design of HENs. A new methodological framework is proposed to account for both economics and controllability of HENs. Two classical design methods are employed, namely, Pinch and superstructure designs. Controllability measures such as relative gain array (RGA) and singular value decomposition (SVD) are used. The proposed framework also presents a bypass placement strategy for optimal control of the designed network. A case study is used to test the applicability of the framework and to assess both economics and controllability. The results indicate that the superstructure design is more economical and controllable compared to the Pinch design. The controllability of the designed HEN is evaluated using Aspen-HYSYS closed-loop dynamic simulator. In addition, a sensitivity analysis is performed to study the effect of bypass fractions on the total annualized cost and controllability of the designed HEN. The analysis shows that increasing any bypass fraction increases the total annualized cost. However, the trend with the total annualized cost was not observed with respect to the control effort manifested by minimizing the integral of the squared errors (ISE) between the controlled stream temperatures and their targets (set-points). An optimal ISE point is found at a certain bypass fraction, which does not correspond to the minimal total annualized cost. The bypass fractions are validated via open-loop simulation and the additional cooling and/or heating utility requirements, in order to meet the target temperatures, are optimized. The optimum bypass fraction, which minimizes the additional utilities, is found to be the same as the one determined by minimization of ISE.

MAJOR THERMAL-HYDRAULIC PHENOMENA FOUND DURING ATLAS LBLOCA REFLOOD TESTS FOR AN ADVANCED PRESSURIZED WATER REACTOR APR1400

A set of reflood tests has been performed using ATLAS, which is a thermal-hydraulic integral effect test facility for the pressurized water reactors of APR1400 and OPR1000. Several important phenomena were observed during the ATLAS LBLOCA reflood tests, including core quenching, down-comer boiling, ECC bypass, and steam binding. The present paper discusses those four topics based on the LB-CL-11 test, which is a best-estimate simulation of the LBLOCA reflood phase for APR1400 using ATLAS. Both homogeneous bottom quenching and inhomogeneous top quenching were observed for a uniform radial power profile during the LB-CL-11 test. From the observation of the down-comer boiling phenomena during the LB-CL-11 test, it was found that the measured void fraction in the lower down-comer region was relatively smaller than that estimated from the RELAP5 code, which predicted an unrealistically higher void generation and magnified the downcomer boiling effect for APR1400. The direct ECC bypass was the dominant ECC bypass mechanism throughout the test even though sweep-out occurred during the earlier period. The ECC bypass fractions were between 0.2 and 0.6 during the later test period. The steam binding phenomena was observed, and its effect on the collapsed water levels of the core and down-comer was discussed.

Two-Dimensional Modeling of the Direct ECC Bypass in the APR1400 Downcomer

In a nuclear reactor vessel downcomer incorporating the safety feature of direct vessel injection (DVI), the direct bypass of emergency core coolant (ECC) is activated during the reflood phase of a large-break loss-of-coolant accident due to momentum transfer between the downward liquid film and transverse gas. Direct ECC bypass is reportedly the major bypass mechanism of ECC, and various experiments have been performed to obtain detailed information about the ECC bypass in a DVI downcomer. In the present study, a model of the direct ECC bypass was developed based on two-dimensional two-fluid equations for the adiabatic two-phase flow to predict the ECC bypass flow rate. The direct ECC bypass fractions were calculated with various interfacial friction factor correlations, and the results were compared with the available experimental data. The values predicted by the current model showed reasonably good agreement with the experimental data at bypass fractions >40% when applying the interfacial friction factor model developed in a countercurrent flow condition. However, when the bypass fraction was <40%, models incorporating cocurrent annular flow provided better results than those with countercurrent flow. These results suggest that a transition occurs from a smooth film to a rough film as the gas flow rate increases, and hence, interfacial friction factor models that adequately incorporate this transition are necessary to predict the direct ECC bypass phenomenon.

Ethylene quench column optimal operation and controllability analysis

Abstract The operating conditions for a heat-integrated ethylene quench column are optimized and diagnosed for controllability and resiliency. Since a bank of seawater coolers largely meets the column's cooling duty requirements, the heat-exchanger by-pass flow fractions were optimized as a function of seawater temperature, using a specially adapted genetic algorithm. The controllability and resiliency of the quench column are studied and two alternative MIMO control configurations are investigated. Of particular interest was the impact of the nominal operating position of the bypass on disturbance rejection capacity. It was found that the resiliency of the column could be significantly enhanced by repositioning the nominal operating point of the main bypass valve and at the same time, the overall heat recovery in the seawater coolers could be enhanced, leading to significant savings in operating costs.

10.2172/1062632

This is the second in a series of reports on the response of a BWR/5 boiling water reactor to anticipated transients without reactor scram (ATWS) when operating in the expanded operating domain MELLLA+. In this report ATWS events initiated by a turbine trip are considered at two points in the fuel cycle: beginning of cycle (BOC) and peak excess reactivity (PHE, close to the middle of the cycle). The effect of the gap (between the fuel pellet and clad) conductance modeling, turbine bypass fractions, and initial core flow rates are evaluated.. Two limiting values of gas-gap conductance, the lowest value of 5,000 W/m2-K at BOC and the highest value of 161,000 W/m2-K at PHE, are compared with corresponding base cases which utilized the dynamic gas-gap model. Turbine bypass fractions analyzed are 10% and 25% at PHE and these two sensitivity cases are compared with the 100% bypass base case. The reduced core flow case at 75% of nominal core flow is analyzed at PHE and compared with the base case of 85% core flow. The simulations were carried out using the TRACE/PARCS code system and models developed for a previous study at three different times during a fuel cycle with all relevant BWR/5 systems. The modeling in the core is particularly detailed (four fuel rod types included in each fuel assembly and 382 thermal-hydraulic channels to represent all assemblies taking into account half-core symmetry) in order to capture the complex neutronic-thermal-hydraulic coupling during periods of instability. The study provides insights into reactor behavior during these events, including the impact of assumed operator actions on the oscillatory behavior due to reactor instabilities and on the eventual shutdown of the reactor. It shows the effect of gap conductance, turbine bypass fraction and initial flow rate. and #8195;

Predicting the migration rates of subaqueous dunes

In this paper we develop a simple, physically based method for predicting what fraction of sediment moving over the crests of dunes will bypass their lee faces. The bypass fraction is found by calculating a characteristic excursion length for every grain size making up a particular train of dunes. All particles with excursion lengths greater than the downstream span of the lee face of the average dune are assumed not to contribute to dune propagation. Bypass fractions based on distributions of excursion lengths account for the discrepancies between total sediment discharge and dune migration rate measured by Stein [1965] and Guy et al. [1966] in laboratory flumes, as well as by us in the North Loup River of Nebraska. Calculations and these data agree over sediment‐transporting conditions associated with the entire stability field for dunes composed of medium sand. The two laboratory studies show that commonly 30–60% of all sand moving over fully developed dunes is not deposited on slip faces. Measurements from the North Loup River reveal that of all sediment moving over the dune crests there, roughly 45% is not being captured on lee faces even though 99% of sediment is transported within 2 cm of the bed. The method developed herein successfully estimates measured values for the bypass fraction from 0 to 80%. Our analysis indicates that the division between grains that are deposited versus those that are bypassing falls within the range of sand sizes making up the suspended load at dune crests.

Optimal operation of heat exchanger networks based on structural information

A procedure for optimal operation of heat exchanger networks is discussed. For each possible bypass location, a change in the bypass fraction will have a monotonously increasing or decreasing effect on the outlet temperatures or utility duties. The signs of these are stored in two sign matrices which contain sufficient information to operate several classes of heat exchanger networks optimally, that is, to maintain the target temperatures while utility consumption at the same time is minimized. The method is used to pair inputs (bypass fractions) and outputs (target temperatures) in a decentralized control scheme with variable structure. Results based on simulations show that the method performs better, in terms of reduced utility consumption, than ordinary decentralized feed-back control.

Optimal design of controllable heat-exchanger networks under multi-directional resiliency-target constraints

Controllable design of heat exchanger networks is formulated as constrained nonlinear optimization problem. The objective of this new method is to find the individual exchanger areas and bypass fractions which minimize the total annualized cost (or the total area) of the given heat exchanger network structure and, at the same time, to satisfy all the target temperature constraints (hard or soft) for a set of disturbances predefined in all possible directions. This is achieved by solving only one constrained optimization problem which considers the exchanger model equations (heat transfer and mixing) and constraints (resiliency index, heat load and the minimum approach temperature) simultaneously for all possible predefined disturbance directions. With the proposed method, a retrofit design satisfying given set of resiliency-target constraints of a heat exchanger network at minimum cost is accomplished.