Scheduled Shutdown Research Articles

Impact of the Delay Period between Electrochemical Hydrogen Charging and Tensile Testing on the Mechanical Properties of Mild Steel

With escalating global regulatory pressure for countries to adhere to emission laws, repurposing existing natural gas pipelines for hydrogen-based commodities stands to be an economical solution. However, the effects of hydrogen embrittlement must be thoroughly considered for this application to avoid the unexpected catastrophic failure of these pipelines. The literature proposes several physicochemical embrittlement models. This paper reports one aspect of hydrogen embrittlement that remains to be quantified: the recovery of ductility (embrittlement) of mild steel specimens subjected to artificially accelerated hydrogen absorption via electrochemical charging as a function of time. The effects of charging duration and particularly the delay period between charging and mechanical tensile testing were investigated. Unsurprisingly, longer charging time shows a greater loss of elongation; however, a more extensive recovery of ductility correlated with longer charging time in the first few days after charging. The data also show that while the uncharged mild steel met all minimum required values for strength and elongation for the specified grade, there was a substantial variability in the elongation to failure. The same trends in variability of elongation translated to the hydrogen-charged specimens. Due to this extensive variability, failure to meet the elongation specification of the grade is reported based on the worst-case scenario obtained for a given set of samples for each exposure condition. These results have practical implications for the monitoring and testing of infrastructure exposed to hydrogen, particularly as this relates to industry planned operational shutdown schedules.

Predictive maintenance system for high-end equipment in nuclear power plant under limited degradation knowledge

To ensure the safe operation of high-end equipment, the three-stage maintenance strategy comprising unplanned shutdown, temporary shutdown, and scheduled shutdown is currently employed in nuclear power plants. However, this strategy hinders the acquisition of degradation knowledge (run-to-failure data or degradation mechanism), thereby impeding the application of traditional predictive maintenance systems. Hence, the responsibility for determining the maintenance stage primarily lies with experienced field engineers, and an incorrect decision could potentially result in an unplanned shutdown. To this challenge, we integrate the three-stage maintenance strategy and prognosis methods to form a predictive maintenance system for nuclear power plants. The system framework is first established, and prognosis methods, including sensor selection, degradation trend prediction for short-term prognosis, and remaining useful life (RUL) prediction for long-term prognosis, are then developed under limited degradation knowledge. Finally, the system is deployed in the circulating water pump of a nuclear power plant utilizing an Internet of Things (IoT) architecture. An industry case study verifies that the proposed system can provide decision-making support and further achieve predictive maintenance for high-end equipment in nuclear power plants.

Alternative Approaches for Real-time Monitoring of the Effectiveness of Hydrogenerator Heat Exchangers

Heat exchangers require periodic maintenance. Offline cleaning scheduled shutdowns are usually needed to restore the exchanger effectiveness, drastically reduced when fouling accumulation occurs. An online real-time alternative for monitoring the effectiveness of exchanger (during a period of eleven months of continuous operation) and an adapted version of the ε-NTU method to calculate its effectiveness are discussed. The experimental difficulties of measuring the mass flow rate and the hot air temperature at the exit of the exchanger is examined. Detailed analysis confirmed that the outlet temperature of the hot fluid could introduce errors of up to 30% in the calculation of the exchanger effectiveness. A skillful treatment of the energy balance is proposed to address the issue. The associated uncertainties are estimated by two independent approaches, the so-called classic method, i.e., the Guide to the Expression of Uncertainty in Measurement and the Monte Carlo method. Both confirmed that measurements of the air outlet temperature accounts for more than 50% of the uncertainty associated with the calculation of the exchanger effectiveness. It is suggested that the conventional method (based on measurements of the outlet air temperature) is not suitable for traditional everyday practices to monitor the effectiveness of the heat exchangers of hydrogenerators.

The role of electricity market design for energy storage in cost-efficient decarbonization

The role of electricity market design for energy storage in cost-efficient decarbonization

Shutdown safety analysis of megawatt-class space gas-cooled reactor system

Among the numerous space nuclear power sources, high temperature gas-cooled reactor with closed Brayton cycle has the advantages of both high power and high energy conversion efficiency. An Open-grid MEgawatt Gas-cooled spAce nuclear reactor (OMEGA) is investigated. Furthermore, a system Transient Analysis code of scheduled Shutdown and emergency Shutdown (TASS) is developed, including core, turbine-generator-compressor, regenerator, condenser, heat pipe radiator and other modules. TASS was verified by comparing prediction value with designed value, and transient performances of system shutdown were simulated. Over the course of shutdown, emissivity of fuel cladding is closely related to cladding peak temperature. Firstly, there is no overlay coating on fuel cladding whose emissivity equals to 0.18, the peak temperature of fuel cladding during scheduled shutdown and emergency shutdown reaches melting point at 7.8 h and 3.6 h respectively. Secondly, there is overlay coating on fuel cladding and emissivity is increased to 0.80. Radiation heat transfer can be greatly enhanced, and peak temperature of fuel pellet and cladding do not exceed the melting point of relevant material, which reflects the importance of fuel cladding surface processing. This paper provides a valuable analysis support for the design of megawatt-class space gas-cooled reactor system.

Ultrasonic Transducers for In-Service Inspection and Continuous Monitoring in High-Temperature Environments.

The inspection of structures operating at high temperatures is a major challenge in a variety of industries, including the energy and petrochemical industries. Operators are typically performing nondestructive evaluations using ultrasound to monitor component thicknesses during scheduled shutdowns, thereby ensuring safe operation of their plants. However, despite being costly, this calendar-based approach may lead to undetected corrosion, which can potentially result in catastrophic failures. There is therefore a need for ultrasonic transducers designed to withstand permanent exposure to high temperatures, so as to continuously monitor the remnant thicknesses of structures in real time. This paper discusses the design of a heat-resistant ultrasonic transducer based on a piezoelectric element. The piezoelectric material, the electrodes, the backing layer, the wires and the casing are presented in detail from the acoustic and thermal expansion point of view. Four transducers optimized for 3 MHz were manufactured and tested to destruction in different conditions: (1) 72-h temperature steps from room temperature to 750 ∘C, (2) thermal cycles from room temperature to 500 ∘C and (3) 60 days of continuous operation at >550 ∘C. The paper discusses the results, as well as the effect of temperature over time on the properties of the transducer.

Air Quality Impact Estimation Due to Uncontrolled Emissions from Capuava Petrochemical Complex in the Metropolitan Area of São Paulo (MASP), Brazil

In the second quarter of 2021, the companies at the Capuava Petrochemical Complex (CPC, Santo André, Brazil) carried out a 50-day scheduled shutdown for the maintenance and installation of new industrial equipment. This process resulted in severe uncontrolled emissions of particulate matter (PM) and volatile organic compounds (VOCs) in a densely populated residential area (~3400 inhabitants/km2). VOCs can be emitted directly into the atmosphere in urban areas by vehicle exhausts, fuel evaporation, solvent use, emissions of natural gas, and industrial processes. PM is emitted by vehicle exhausts, mainly those powered by diesel, industrial processes, and re-suspended soil dust, in addition to that produced in the atmosphere by photochemical reactions. Our statistical analyses compared the previous (2017–2020) and subsequent (2021–2022) periods from this episode (April–May 2021) from the official air quality monitoring network of the PM10, benzene, and toluene hourly data to improve the proportion of this period of uncontrolled emissions. Near-field simulations were also performed to evaluate the dispersion of pollutants of industrial origin, applying the Gaussian plume model AERMOD (steady-state plume model), estimating the concentrations of VOC and particulate matter (PM10) in which the population was exposed in the region surrounding the CPC. The results comparing the four previous years showed an increase in the mean concentrations by a factor of 2 for PM10, benzene, and toluene, reaching maximum values during the episode of 174 µg m−3 (PM10), 79.1 µg m−3 (benzene), and 58.7 µg m−3 (toluene). Meanwhile, these higher concentrations continued to be observed after the episode, but their variation cannot be fully explained yet. However, it is worth highlighting that this corresponds to the post-pandemic period and the 2022 data also correspond to the period from January to June, that is, they do not represent the annual variation. A linear correlation indicated that CPC could have been responsible for more than 60% of benzene measured at the Capuava Air Quality Station (AQS). However, the PM10 behavior was not fully explained by the model. AERMOD showed that the VOC plume had the potential to reach a large part of Mauá and Santo André municipalities, with the potential to affect the health of more than 1 million inhabitants.

Prediction of the Time to Failure of Boiler Tubes Flawed With Localized Erosion

AbstractA failure mechanism prevalent with boiler tubes operating in harsh environmental conditions is localized erosion. The consequence of the erosion mechanism is a substantial reduction of the tube thickness, ultimately leading to plastic collapse and consequently rupturing of the tubes. Locating and repairing all the affected tubes within the boiler are time consuming and expensive. It will be worthwhile to rank all the identified flaws so that critical flaws that cannot survive till the next scheduled shutdown are prioritized for repair. Consequently, nonlinear structural analysis was conducted on various boiler tubes that failed by localized erosion. The tubes had a wide range of localized erosion flaws that required a detailed assessment technique. The failure was evaluated numerically using various stress and strain-based failure criteria as well as performing the American Petroleum Institute and the American Society of Mechanical Engineers (API-ASME) fitness-for-service (FFS) assessment on the tubes. A projected time to failure (Pt) for each tube based on the various criteria used in this study was determined. This enabled the ranking of the flawed tubes based on the priority of their repair. The outcome of this study demonstrates the potential for a tool which will enable industry users to prioritize the replacement or repair of critically flawed tubes and avert replacing tubes that are still safe for future operation.

Хищные птицы и ветроэнергетика в Казахстане: какие перспективы для орлов?

Хищные птицы и ветроэнергетика в Казахстане: какие перспективы для орлов?

Investigations on Caesium Dispersion and Molybdenum Coating on SPIDER Components

SPIDER is the 100 keV full-size Negative Ion Source prototype of the ITER Neutral Beam Injector, operating at Consorzio RFX in Padova, Italy. The largest Negative Ion Source in the world, SPIDER generates an RF driven plasma from which Deuterium or Hydrogen negative ions are produced and extracted. At the end of 2021, a scheduled long-term shutdown started to introduce major modifications and improvements aiming to solve issues and drawbacks identified during the first three years of SPIDER operations. The first action of the shutdown period was the disassembly and characterization of the SPIDER beam source after removal from the vacuum vessel and its placement inside the clean room. Each component was carefully assessed and catalogued, following a documented procedure. Some source components, i.e., the Plasma Grid, Extraction Grid and Bias Plate, revealed the presence of different and non-uniform red, white and green coatings that might be correlated to back-streaming positive ions impinging on grid surfaces, electrical discharges and caesium evaporation. Thus, several analyses have been carried out to understand the nature of such coatings, with the study still ongoing. The evidence of caesium evaporation and deposition on molybdenum-coated SPIDER components, such as the formation of oxides and hydroxides, is demonstrated through surface characterization analyses with the use of the Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS).

A Framework for In-Service Life Extension of Hydroelectric Generation Assets

Abstract The integrity assessment of aged or worn out large electromechanical equipment units, such as in hydroelectric generators, for possible life extension has been identified as a growing challenge in the electrical power generation industry worldwide. Although the available recommended practices provide a general assessment process, it is necessary to have more detailed guidelines. This can be achieved by adding relevant theories and models which can capture time-dependent equipment unit degradation more precisely. Seeking to fulfill this gap, this work aims to present a framework that combines several techniques of data analysis, reliability, and decision-making to support engineers, operators, and managers in the often-complex decision process, regarding whether or not to extend the time in service of an equipment or system, thus postponing the moment of a scheduled maintenance shutdown. To demonstrate the application of the proposed framework, a case study is presented considering simulated scenarios based on data and information from a real Hydroelectric Power Plant. The results show how the reliability of the components and the remaining useful life of those in fault can impact the decision-making regarding the in-service life extension of a system.

Optimal unit-commitment generation scheduling using genetic algorithm: A case study of a 10-generator power system network

Generation Scheduling is a complex optimisation problem. The aim is to get an optimal combination of generating units for optimal operation. In this paper, Genetic Algorithm (GA) is presented as a viable optimisation tool to solve a fuel cost-based unit-commitment problem. The power system network adopted for the study is a 10-generator network. The prime objective here is to prepare the best economic start-up and shutdown schedules of the generators which meets the forecasted load demand plus reserve for a particular time interval while at the same time satisfying various system constraints. The implementation was done with the GA Toolbox in MATLAB 2018a. Results obtained were compared to the ones obtained with Lagrangian Relaxation optimisation technique and the comparison shows that Genetic Algorithm led to a slight reduction in fuel cost by ₦ 522,452.20 for the 24-hour period.

An approach for stiction compensation in industrial process control valves

In the process industry, control valve stiction causes oscillations in the control loop, and this results in deterioration of control performance. Therefore, the sticking control valves are repaired during a scheduled plant shutdown maintenance. Until such permanent solutions are used, it is expected that the oscillations can be reduced with a low-cost approach; PID control parameter re-tuning is a suitable approach in this case. This study involves a method of compensating for control valve stiction. In particular, it aims to improve the control performance by tuning the parameters of normal PID controllers. We propose a method to search for the optimal PID parameter values based on control simulation using a stiction model. First, the stiction model and the process model are identified. Next, simulation is performed using a combination of the stiction model, process model and PID controller. Finally, the PID parameter values are optimized based on the assessment.

Estimation of Shutdown Schedule to Remove Fouling Layers of Heat Exchangers Using Risk-Based Inspection (RBI)

Oil and Gas plants consist of a set of heat exchangers, which are used in recovering the waste heat from product streams to preheat the oil. The heat transfer coefficient of exchangers declines considerably during the operation period due to fouling. Fouling in heat exchangers is a complex phenomenon due to the acceleration of many layers of chemical substances across tubes of heat exchangers resulting from chemical reactions and surface roughness. In this paper, the fouling process was determined as a critical failure in the heat exchanger. Failure is an accelerated fouling layer across the heat exchanger tubes, which can be the reason for the clogging of tubes. Hence, a risk assessment was conducted using the Risk-Based Inspection (RBI) approach to estimate the probability of fouling in heat exchangers. The results showed that the RBI approach can be used successfully to predict the suitable time to shut down the plant and conduct the fouling cleaning process.

Experimental characterization of hydrate formation in non-emulsifying systems upon shut-in and restart conditions

In offshore oil production, scheduled or emergency shutdowns of the production system may occur due to maintenance, equipment failure, production issues, and weather-related events. During the shut-in, the fluids may enter into the hydrate zone because of the thermal energy transfer to the cold ocean waters, increasing the risk of hydrate formation during the shut-in period and upon the restart of the production system. This work is focused on identifying some parameters that influence the hydrate formation in shut-in and restart conditions. Using a rock-flow cell with visual capabilities, the hydrate formation and the phenomena involved upon the restart were investigated. The main results of the experiments showed that the high shear conditions applied at the restart promoted water dispersion into the oil phase and contributed to the dispersion of hydrates. In addition, the low shear rate favored the formation of hydrate deposits while hydrate agglomerate was formed at high shear rate. Besides the shear rate, the subcooling proved to be an important parameter that favors the hydrate formation under sheared conditions. Conditions with high subcooling and low water cut promoted the formation of small hydrate particles (~2 mm) that can be dispersed in the oil-phase even without the anti-agglomerant. A high subcooling promoted the formation of “dry” hydrates, preventing the particles to stick with each other (agglomerates). The results indicated that subcooling is an important parameter to ensure a safe restart in the pipeline. Lastly, the addition of an anti-agglomerant reduced the water–oil interfacial tension, which promoted the water/hydrate dispersion; the effectiveness of the anti-agglomerant was clearly affected by the shear and the water cut.

Day-Ahead and Intra-Day Collaborative Optimized Operation among Multiple Energy Stations

An integrated energy system (IES) shows great potential in reducing the terminal energy supply cost and improving energy efficiency, but the operation scheduling of an IES, especially integrated with inter-connected multiple energy stations, is rather complex since it is affected by various factors. Toward a comprehensive operation scheduling of multiple energy stations, in this paper, a day-ahead and intra-day collaborative operation model is proposed. The targeted IES consists of electricity, gas, and thermal systems. First, the energy flow and equipment composition of the IES are analyzed, and a detailed operation model of combined equipment and networks is established. Then, with the objective of minimizing the total expected operation cost, a robust optimization of day-ahead and intra-day scheduling for energy stations is constructed subject to equipment operation constraints, network constraints, and so on. The day-ahead operation provides start-up and shut-down scheduling of units, and in the operating day, the intra-day rolling operation optimizes the power output of equipment and demand response with newly evolved forecasting information. The photovoltaic (PV) uncertainty and electric load demand response are also incorporated into the optimization model. Eventually, with the piecewise linearization method, the formulated optimization model is converted to a mixed-integer linear programming model, which can be solved using off-the-shelf solvers. A case study on an IES with five energy stations verifies the effectiveness of the proposed day-ahead and intra-day collaborative robust operation strategy.

Failure analysis in heat exchanger tubes from the top system of the regeneration tower of the hydrotreatment unit in an oil refinery: a case study

ABSTRACT This paper presents a failure analysis performed on tubes of a heat exchanger. Heat exchangers are among the most common equipment in an oil refining industry, as heat transfer is one of the most important and common processes in chemical and petrochemical industries. The equipment analyzed was the condenser of the top system of the diethanolamine regeneration tower of the naphtha hydrotreating unit of an oil refinery. The tubular bundle consists of 78 tubes in the ASTM A213 Grade 316L specification, with 19.05 mm in diameter and 1.65 mm in wall thickness. The tubes are subjected to the aqueous flow of H2S and diethanolamine on the outside and cooling water on the inside. After a scheduled general shutdown in July 2011, after six years of continuous operation, the loss of thickness in several tubes was observed. The result of the failure analysis indicated that, through visual inspection, the corrosive process occurred from outside to inside the tubes. The eddy current test indicated an active corrosive process with a corrosion rate of 0.16775 mm / year. The ultrasonic inspection performed through the internal rotating inspection system (IRIS) confirmed the loss of thickness and the presence of perforated tubes, with consequent loss of containment. Amine corrosion in the presence of H2S was identified as the basic failure mechanism, aggravated by DEA concentration higher than 20 wt.% in the analyzed equipment. In October 2019, the tubes of this exchanger were replaced and the proposed solution to mitigate the problem was to dilute the solution with washing water, to obtain amine solution concentrations below 5% by mass in the beam tubes of the heat exchanger.

Дополнительные способы повышения энергоэффективности нефтепроводного транспорта

The challenges of increasing the energy efficiency of the economy as a whole and of certain production sectors in particular are a priority both in our country and abroad. As part of the energy policy of the Russian Federation to reduce the specific energy intensity of enterprises in the oil transportation system, Transneft PJSC developed and implements the energy saving and energy efficiency improvement Program. The application of energy-saving technologies allowed the company to significantly reduce operating costs and emissions of harmful substances. At the same time, further reduction of energy costs is complicated for objective reasons. The objective of this article is to present additional methods to improve the energy efficiency of oil transportation by the example of the organizational structure of Transneft. Possibilities to reduce energy costs in the organization of the operating services, planning and execution of work to eliminate defects and preparatory work for the scheduled shutdown of the pipeline, the use of pumping equipment, including pumps with variable speed drive, the use of various pipelines layouts, changing the volume of oil entering the pipeline system and increase its viscosity.

Simulation approach and code functionality assessment using deterministic and Monte Carlo codes system for U-235 core-follow depletion calculation

Improving the performance of reactor simulation codes and adequately predicting the fuel composition are crucial to increase the accuracy of simulations and the quality of the analysis. McMaster Nuclear Reactor (MNR) follows a strict daily operational and shutdown schedule, except for Sundays. This results in a buildup of neutron poison during the reactor shutdown and hence the Control Rods (CRs) are extracted in the time of the reactor startup. Therefore, tracking MNR core composition using faithful Control Rods (CRs) positions data to estimate the axial fuel inventory profile is not yet established. In this study, nodal diffusion (OSCAR-4) and Monte Carlo (Serpent-2) simulations codes were employed. This study investigates: (1) code-to-code differences in the multiplication factor (keff) and in the axial fuel inventory considering the same burnup step sizes and total energy release with all CRs out; (2) for long cycles of core calculation, Monte Carlo stochastic code is computationally expensive, therefore an adequate temporal discretization steps are studied and identified. The keff values for the fresh reactor when all rods are out is: 1.1339 and 1.1283, and the results at the end of the burnup calculation is: 1.0101 and 1.0049, for Serpent-2 and OSCAR-4, respectively. In addition, the findings showed that averaging the CRs travel distance, for calculation the fuel inventory, can provide results similar to those with most tracked CRs motion.

Assessment of WWER-1000 Core Baffle Form Alteration during Operation

The paper illustrates the results of the computer assessment of the form alteration in WWER-1000 core baffle obtained via the solution to the coupled thermoelastoplastic task considering the strains of irradiation growth and creep. In the modeling of the contact conditions, the temperature redistribution is considered due to the incompliance of the coolant flow in the contact zone between the core baffle and in-vessel core barrel with the design conditions. The modern approaches to the modeling of strains of the irradiation growth and irradiation creep in austenite steels are used in the space-limited environment under neutron exposure and elevated temperature. The finite element analysis involves the mixed scheme of the finite element method, which allows determination of the stress-strain state with high accuracy. The calculations are performed in the two-dimensional statement for the cross-section of the core baffle with the maximum damaging dose and irradiation temperature under the condition of the generalized plane strain. The results of the calculations are presented for full-scale reactor operation and scheduled shutdown to recharge the fuel cluster at the end of core life. The data on the distribution and value of the gap between the core baffle and barrel, as well as the spacer grids of the edge fuel assemblies and reactor core baffle edges, have been obtained from the median values of the dose dependence on swelling at different temperatures in Kh18N10T austenite steel.