Steam Leakage Research Articles

High-pressure core meltdown and hydrogen generation during In-vessel and Ex-vessel phases of VVER-1000 nuclear reactor and effect of heat structures

Following unprecedented Fukushima Daiichi severe accident, which significantly amplify the production of hydrogen and the associated risk of explosions, particularly in accidents like station blackout (SBO) that jeopardize containment integrity and reactor safety, a thorough investigation and comprehension of the phenomenon known as high-pressure melt ejection (HPME) are necessary. This study examines how the SBO accident develops without operator intervention or access to emergency diesel generators through full nuclear power plant simulation, including containment, core, primary, and secondary circuits. Accurate time step selection is crucial for the simulation to produce reliable results for high-pressure melt ejection processes. While the process is faster and easier under Low Pressure Melt Ejection (LPME) conditions, time step tuning can significantly lengthen the (HPME) simulation (approximately one month for each scenario). After thorough examinations and analysis of various simulation findings, three cases were evaluated for the ex-vessel phase, illustrating the most likely scenarios of high-pressure molten material splashing into the cavity. The findings demonstrate that during the in-vessel phase, 578 kg of hydrogen is created. Additionally, during the ex-vessel phase, there is a significant increase in the containment’s temperature and pressure due to the high-temperature hydrogen and significant water and steam leakage. The temperature and pressure inside the containment rise well above the safety criteria due to the leakage of 1529 kg of hydrogen from the cavity and lead to hydrogen explosion due to MELCOR message. The calculated amount of hydrogen gas is within the explosion limit range of 18.3% to 59% of the containment atmospheric pressure volume. Moreover, the height and diameter of the cavity alter due to the direct heating and corrosion of the cavity walls, ultimately compromising the integrity of the plant in the alpha mode. Based on the results obtained, it can be seen that if a large portion of the molten material is deposited on the concrete surface (case III) instead of dispersed in the cavity atmosphere (case I), the rate of hydrogen production and therefore the total amount of hydrogen (and its related energy) produced will be increased and could lead to deflagration to detonation situation.

Detecting Steam Leakage in Nuclear Power Systems Based on the Improved Background Subtraction Method

As a key system in nuclear power plants, nuclear power systems contain high-temperature, high-pressure water media. A steam leak, if it occurs, can at minimum cause system functional loss and at worst lead to casualties. Therefore, it is urgent to carry out steam leakage detection work for high-temperature, high-pressure loop systems. Currently, steam leaks are primarily detected through visual monitoring and pressure gauges. However, if there is a minor leak under high system pressure, the slight decrease in pressure may not be enough to alert the operators, leading to a delay in detecting the steam leak. Thus, this detection method has certain drawbacks. In view of these issues, this paper introduces computer vision technology to monitor the high-temperature, high-pressure loop system and proposes the use of an improved background subtraction method to detect steam leaks in the loop system. The results show the following advantages of this method: (1) It can effectively identify steam leaks at an early stage; (2) it overcomes the difficulty of determining the threshold value for the binarization of grayscale images in traditional background subtraction methods; (3) it eliminates the noise impact brought by the binarization of grayscale images in existing improved background subtraction methods. The introduction of this method provides a new approach for detecting steam leaks in high-temperature, high-pressure loop systems and can be effectively applied in engineering fields. It also offers reference value for the detection of high-temperature, high-pressure media leaks in other fields.

Experience sharing on abnormal handling during operation of 350MW DC boiler after major overhaul

Recently, during the commissioning period of a 350MW DC boiler in a certain power plant, multiple abnormal situations occurred, which are relatively rare. For example, in normal operation, when the oil pressure of the supply fan suddenly rises to 10MPa full range, the moving blades of the supply fan cannot be adjusted, resulting in an automatic decrease in fan output, negative pressure fluctuations, and a decrease in unit load; Oil leakage in the control oil pipe of the air supply fan, causing a decrease in system oil pressure; A large amount of steam leakage occurs in the water valve of the warm valve; Leakage and other issues with the cooling water control valve of the superheater. Serious impact on the safe operation of the unit. Through summary and analysis, the root cause problem was ultimately discovered and thoroughly solved. This article mainly summarizes the analysis of abnormal causes and the sharing of experience in the handling process.

Enhancing Energy Efficiency in a Palestinian Dairy Factory Utilizing RETScreen Expert

This paper delves into the intricacies of optimizing energy utilization within a dairy manufacturing facility situated in Palestine through the utilization of RETScreen Expert. An exhaustive energy audit is undertaken to meticulously scrutinize and comprehend the existing energy landscape within the dairy factory. This investigation is specifically oriented towards the evaluation of seven distinct energy efficiency strategies, encompassing aspects such as lighting enhancements, insulation upgrades, the maintenance of steam traps, mitigation of steam leaks, harnessing heat recovery mechanisms, and the installation of a solar water heating system. The study extends its purview to encompass environmental concerns, encompassing the estimation of CO2 emissions, and conducts a comprehensive assessment of the economic feasibility associated with these proposed measures. The findings of this investigation unequivocally reveal the substantial potential for diminishing energy consumption and curtailing CO2 emissions, alongside the concurrent enhancement of economic viability through the judicious implementation of the aforementioned energy efficiency initiatives. In essence, this scholarly work serves as a valuable resource, shedding light on the advantageous outcomes achieved by the incorporation of energy efficiency measures within industrial frameworks. It underscores the imperative of a holistic approach, where both environmental and economic dimensions are harmoniously considered in the decision-making processes pertaining to energy-related initiatives.

Energy audit and associated carbon footprint estimation for a Meta Abo brewery

Industrial development in Ethiopia is rapidly increasing, leading to a growing gap between energy supply and demand. To address this, efficient energy utilization in existing industries is crucial. Energy audits identify energy losses and recommend saving measures. Therefore, this study evaluates energy efficiency through an audit and estimates greenhouse gas emissions for a Meta Abo brewery. The indirect method of energy audit and the greenhouse gas protocol of carbon footprint estimation were used to evaluate the energy efficiency and carbon emissions of Meta Abo brewery. The boiler efficiency for Bono Energia and Cochran boilers was found to be 79.2% and 80.9%, respectively. Poor insulation caused an estimated annual fuel loss of 35,350 l (638,768 Ethiopian birr) for steam pipes, while steam leakage resulted in a loss of 31,614 l (571,265 Ethiopian birr). The factory's high electricity expense was attributed to a diesel generator consuming 6000 l/d. Greenhouse gas emissions raised from 9156 to 22,697 tons of CO2 equivalent between 2014 and 2018. Implementing the proposed energy-saving measures could save 20.4 TJ of thermal and electrical energy annually, costing approximately 8.5 million Ethiopian birr, and reduce boiler emissions by 455 tons of CO2 equivalent. Therefore, implementation of these measures is recommended.

Experimental study on acoustic signal characteristic analysis and time delay estimation of pipeline leakage in boilers

Acoustic signal detection technology has significant advantages in detecting the leakage and bursting of heat exchange pipes in boilers. To address the current lack of sound signal data for steam medium leakages and the problem of large errors in the complex sound field environment of power plants, we performed an innovative experimental comparative analysis of leakage acoustic signals under a dual medium of compressed air and steam to provide a reference for detecting leakage acoustic signals. During the experiment, the time and frequency domains were analyzed by changing the pressure of the leakage pipeline and aperture of the leakage hole, and the spectrogram and power spectrum of the leakage acoustic signal were obtained using fast Fourier transform and autocorrelation analysis. The results showed that the signal value of the leakage medium increased with increasing pipeline pressure and leakage aperture and that the energy of the steam leakage acoustic signal was greater than that of compressed air under the same pressure and aperture because of its larger specific heat capacity. In addition, the complete empirical mode decomposition of adaptive noise (CEEMDAN) algorithm was introduced into the denoising decomposition of the leakage sound signal in the furnace, and the average error of the time delay value of the leakage acoustic signal calculated using the CEEMDAN algorithm was observed to be within 5%.

Dynamic process simulation of a 780 MW combined cycle power plant during shutdown procedure

The share of variable renewables in power generation is increasing due to the push to reduce emissions, and the flexibility of conventional power plants has become a major concern. There are many ways to increase the flexibility of existing power plants and implement a more flexible system for the future, such as a fast start-up procedure and higher load change rates. In this study, a 2D dynamic process simulation model of a reference combined cycle power plant is presented to increase the flexibility of cyclic operation by investigating, for the first time in the literature, the shutdown procedure using APROS software. The 780 MWel Tambak Lorok reference combined cycle power plant consists of the GE 9HA.02 heavy-duty gas turbine and a three-stage horizontal heat recovery steam generator with reheat. Several steps were considered to improve the accuracy of the developed dynamic process simulation model, including varying the steam leakage to the atmosphere to control how much thermal energy remains in the heat recovery steam generator, changing the shape loss coefficients of the tubes to achieve higher or lower recirculation, and decoupling the reheater and the intermediate pressure drum. The developed model is validated with real data from three different combined cycle power plants in different countries with various capacities. The comparison shows that the developed dynamic simulation model can accurately represent the real behaviour of natural convection in the heat recovery steam generator. The main outcome was to provide detailed information on the shutdown procedure of large-scale combined cycle power plants, addressing the aspect of the development of new start-up strategies to reduce the time required for the start-up procedure.

Study on flow characteristics of leakage in the last stage inner blade tip clearance of steam turbine

Internal steam leakage in steam turbines from the high-pressure side to the low-pressure side through clearances causes loss, resulting in reduced efficiency and potentially compromising the safe operation of the turbine. Therefore, a comprehensive understanding of the flow characteristics of leakage through blade tip clearances is crucial to improve the efficiency of steam turbines. In this paper, the last stage blades of the low-pressure cylinder of a certain 600 MW ultra-supercritical steam turbine unit were studied. A wet steam flow model and a turbulence model were established, and the flow characteristics of the last stage under different inlet parameters, outlet parameters, and tip clearance sizes were analyzed. The results showed that an increase in the clearance size affects the inlet and outlet steam angles of the rotor blades, with significant changes occurring near the blade tip. The main flow velocity inside the rotor blade channel fluctuates violently starting from the 70% axial position. The high entropy region is located near the exit flow region of the rotor blade, with its range expanding as the clearance size increases. The entropy change is significant at 60% blade height and above, with more intense changes occurring in the blade tip area. The relative leakage amount and efficiency change uniformly with clearance variation. Generally, for every 0.1% increase in clearance height, the relative leakage amount increases by ∼0.31%–0.42%, and the stage efficiency decreases by 0.34%–0.44%. The results of this study can provide a theoretical basis and guidance for improving the flow efficiency of steam turbines.

Analyzing reactor water level measurements in the Fukushima Daiichi 1 accident

Measuring the water level in the Fukushima Daiichi reactors was based on measuring the pressure difference between two pipes, connected to the reactor at different elevations and filled with water. Boiling of the water in the measurement system distorted the measurements. The water level readings during the unit 1 accident were analyzed with the MELCOR code. The behavior of the measurement system can be reproduced by assuming a small leak of superheated steam from a steam line to the drywell before 6.5 h after the earthquake. This confirms earlier conclusions of a Japanese accident investigation committee and analyses performed by TEPCO. The steam leak did not have any significant effect on the cesium release to the environment.

Energy Utilization and Saving Opportunities in Process Industries: Case Study of Textile Manufacturing Industry in Kenya

The industrial sector is seriously threatened by high energy costs brought on by inefficient energy use. Energy, together with labor and raw materials, make up the majority of production costs in the textile industry. As a result, the only real way for the textile industry to turn a profit and maintain its competitiveness is to reduce its energy costs through energy conservation measures and energy management strategies. The main objective of the study was to investigate energy utilization in textile manufacturing plant and identify energy saving and conservation measures that help reduce energy costs. In the current work, energy investigation was carried out to determine performance of high energy consuming utility systems and equipment such as compressed air systems, boilers, motors, lighting systems and steam distribution systems. Boiler flue gas analysis test, air compressor air leak test, heat loss analysis for steam distribution system, motor load assessment and load variation trends in air compressor were done. Energy utilization analysis showed that high electricity consumption occurs in spinning (48%), followed by weaving (26%) and wet processing (22%). Statistical analysis of energy consumption in spinning, weaving and wet processing showed linear relationship between production and energy consumption with correlation coefficients (R2) of 0.782, 0.708 and 0.637 respectively which reveals that there continues to be a large potential of energy efficiency across all the major textile manufacturing processes in the plant. The study found potential savings in electric energy to be approximately 367,784 kWh/year, wood fuel savings 1,219 tones/year and furnace oil savings to be 22,275 L/year. The results displayed 31.6% overall energy cost saving potential with an average simple payback period of 0.5 years on the investigated high energy consuming utility systems and equipment. In conclusion, significant energy savings in the sector might be attained by implementing free or inexpensive investments including sealing air and steam leaks, insulating bare pipes, and properly drying wood fuel.

Determination of steam leaks through faulty labyrinth seals of a steam turbine

BACKGROUND: When calculating the axial force acting on the thrust bearing of a steam turbine, when calculating the dimensions of the unloading piston, when calculating the efficiency of the turbine stages, it is necessary to determine the amount of steam leakage through its diaphragm and end seals. Existing methods make it possible to calculate leaks only through serviceable, undamaged labyrinth seals of several standard designs. However, during the operation of steam turbines, due to off-design axial and radial displacements of the rotor, labyrinth seals are often damaged - deformed, crushed or broken.
 AIMS: The purpose of the study is to develop a method for calculating leaks using direct CFD modeling in serviceable and damaged seals with typical failures, verify the simulation results by comparison with known methods and experimental data, and determine critical steam leaks through faulty labyrinth turbine seals.
 MATERIALS AND METHODS: A method for calculating the steam flow rate through serviceable and faulty labyrinth seals of a steam turbine using the capabilities of modern CFD methods is proposed and verified. The computational domain of modeling the front-end seal of the turbine, the features of setting the boundary conditions, the adaptive computational grid, and the numerical mathematical model used are described.
 RESULTS: The results of a numerical study of steam leakage through serviceable and damaged labyrinth end seals of the turbine are presented: with bent ridges in the seals, with partial or complete absence of ridges. The operation of the front-end seal of the turbine was simulated with several typical failures. It is shown that partial damage to the ridges of the front-end seal of the turbine, which is often encountered during operation, leads to a significant increase in steam leakage. It has been established that with significant damage to the ridges, an increase in steam leakage can lead to the exhaustion of the capacity of the steam pressure regulator in the seal, which leads to a malfunction of the turbine thrust bearing unloading system.
 CONCLUSIONS: The proposed technique and the results obtained can be used to calculate steam leakage through serviceable and faulty diaphragm and end labyrinth seals of turbines, when calculating the value of the axial force acting on the turbine thrust bearing in variable operating modes, the technique is useful in assessing the efficiency of the thrust bearing unloading system.

슈라우드 접촉에 따른 증기터빈 블레이드의 진동모드 해석과 실험적 검증

An integral shrouded blade with a gas turbine dovetail that is robust against the stress of the dovetail has been applied in large steam turbines to achieve high efficiency by minimizing the steam leakage of the tip. Further, the natural frequency of the blade has been calculated with high accuracy considering the contact condition of the shrouded blade for the avoidance design of resonance. This paper compares the analysis and measurement results for the shrouded blade with a gas turbine dovetail. To realize a valid analysis model, a full-scaled mock-up with blades and a rotor was manufactured and assembled, and a spin test was conducted in balancing shop up to 120 % overspeed of the rated speed. The spin test procedure was described, and a Campbell diagram was obtained as the test result. The FE model and boundary conditions of the shrouded blade were observed to agree well with the measured Campbell diagram. The model is expected to be applicable for the vibration design of the shrouded blade for gas turbine blades and steam turbines.

ANALISA ALIRAN MASSA UAP PADA KATUP KONTROL UREA (UREA GLOBE CONTROL VALVE) DI UNIT PRODUKSI UREA PABRIK 1B PT. PETROKIMIA GRESIK

In a process, industrial plants have several tools that require steam to help run the processing of a material. For the heating process, PT. Petrokimia Gresik requires steam. Sometimes the steam leak during the process, which reduces the productivity of this industry. For that reason, the purpose of this calculation is to find out the steam loss during the process, especially in the urea globe control valve (PV-723, PV-726, PV-735). The result shows that the upstream pressure and temperature at PV-723 are 21 kg /cm2G and 307 oC, upstream pressure and temperature in PV-726 are 5 kg / cm2G and 158 oC, upstream pressure and temperature on PV-735 of 2.5 kg / cm2G and 138 oC. For downstream pressure on all valves is 1.03323 kg/cm2G. The obtained mass flow (F) in each valve is 0.514 tons / hr, 0.86 tons / hr and 1,902 tons / hr. The value of the input mass balance of steam in the system is 82.70 tons/hour and the overall output is74.11 tons/hour. Therefore, the total steam loss in PV-723, PV-726, and PV-735 is around 8.59 tons/hour which means there is some leak during the process that needs to do further investigation.

Numerical analysis of axial flow cyclone for steam and droplets separation in saturated steam turbine

ABSTRACT In this paper, an axial flow cyclone separator is employed to separate the droplets entrained in saturated steam turbine. The Eulerian–Eulerian approach and the Reynolds stress model are combined in numerical simulation. Then, the effects from the vane exit angle and the length of separation section on the separation performance are investigated, respectively. The distributions of pressure and velocity in the cyclone are presented in detail to describe the characteristics of flow field. The results demonstrate that the separation efficiency could be effectively elevated to 95% either by reducing vane exit angle or by increasing the inlet-velocity. In addition, the promotion brought by reducing the vane exit angle is larger than that of increasing inlet-velocity once comprehensively assessing pressure drop and separation efficiency. Furthermore, it is found that the designed the length of separation section should not be too short to reduce the steam leakage ratio, considering that the steam is flowed into the saturated steam turbine. The leakage ratio would decrease by 15% as the aspect ratio of separation section increases from 1.5 to 3.5. The improvement of separation efficiency can effectively reduce the damage of the steam turbine and improve its operational safety.

Characterization and identification of static and dynamic hammer tail characteristics in infrared temperature field of leaking steam

Characterization and identification of static and dynamic hammer tail characteristics in infrared temperature field of leaking steam

Improved performance of corrugated metal gaskets in boiler’s piping system through multilayered coating

The corrugated metal gasket is still in the early stages of development. However, gasket contact flanges with a high surface roughness (more than 3.5 µm) leak and require a lot of force to tighten. A nickel or copper-coated corrugated metal gasket was designed. A water pressure test was used to measure leaks, and the results revealed that nickel or copper-covered gaskets performed better. The effect of high temperature has not been explored in this study, which only reveals high pressure. The goal of this study is to use copper and nickel coatings to improve the performance of corrugated metal gaskets. Copper or nickel infiltrates the pipe flange's rough surface, preventing leaking. The purpose of this study is to investigate the performance of a coated corrugated metal gasket in a boiler system, which has high temperature and pressure. Corrugated metal gaskets were formed using a cold forming process. The gasket material was SUS304, which is copper or nickel-plated through electroplating. The gasket was installed in a series of pipes in the boiler that flows water at high temperature and pressure. The water leak was trickling on white paper that had been placed beneath the gasket. Even small water leaks are detected on white paper. The thermal camera can detect vapor leaks. The results of the studies reveal that the coated corrugated metal gasket's performance was improved, as seen by the reduction in leakage. At the highest pressure of 7 bar and the lowest tightening force of 40 kN, neither gasket leaked. This result is different from standard corrugated metal gaskets, where at the same pressure and temperature, steam and water leaks are observed. Both copper and nickel-plating types can be used to coat corrugated metal gaskets made of SUS304.

Tightness problems at the flange connection in transient temperature and high pressure condition

The main goal of the article is to study, analyze and explain the most apparent cause of transient steam leakage from a high pressure turbine stage body. The analyses focus on transient heat transfer on the metal-metal flange connection of an external turbine casing and start-up tests. The coupled effect of thermal expansions and their impact on the residual bolt pretension force was analyzed in detail using FE models. Series of experiments were performed to confirm the results obtained by numerical calculation. The conclusion provided in this article can be used to improve the design of the flange connection working in variable temperature conditions.

Discussion on calculation method of natural frequency of flue design in thermal power plant based on temperature field simulation

The vibration of the boiler tail flue not only leads to tearing and steam leakage at the welding point between the superheater and manhole, but also makes the acoustic soot blower in the tail flue basically unable to be put into operation, which seriously affects the safe operation of the unit. In order to reduce the size of external reinforcing ribs, the minimum number of internal struts should be used in large section flue. By means of temperature field simulation, the author adds a flow guide device at the junction of the down flue and the horizontal flue to forcibly guide the flue gas to the convection heat exchange area. The simulation results show that the vertical velocity field distribution of the horizontal flue tends to be uniform after adding the diversion device. Measures should be taken to prevent the vibration of the inner strut, such as selecting the inner strut with appropriate specifications; Install fins on the inner strut; Change the natural frequency of the inner strut; Select appropriate flue gas flow rate, etc.

Hydrogen sensors for comprehensive detection of steam leak in sodium-cooled fast reactors

A comprehensive hydrogen detection system is developed to track steam leak into sodium by monitoring hydrogen in liquid sodium and in argon cover gas simultaneously and its performance is demonstrated. A fraction of hydrogen, generated from steam leaks, gets dissolved in liquid sodium while the other enters the cover gas and its relative distribution depends on the sodium temperature. Detectors for hydrogen in sodium and argon cover gas are deployed to track the hydrogen in liquid sodium and in cover gas to assess the extent of the steam leak.

Assessment of the thermal outcome during steam-pulse ablation for sheep tissue

Thermal ablation has attracted attention as a minimally invasive tissue ablation treatment. Steam flow was recently introduced as a novel ablation procedure. This work aimed to assess the applicability of pulsated steam flow for tumor ablation. Ex vivo ablation was performed using liver, muscle, and fat tissues of sheep. Three experimental protocols of pulse number were administered to these tissues, while computational simulation was conducted according to the ex vivo tests for each tissue. Real-time measurements of temperature revealed heat propagation during and subsequent to ablation. The peak temperature was achieved after ablation. The time to reach the peak (highest temperature) increased with the distance from the thermal sensor to the steam needle according to thermal conductivity, except for steam leakage along to gap between the tissue and blood vessel. A cross-section of the ablated specimen clearly revealed the boundaries of cell defects. The ablated area was droplet shaped up to the steam needle. Computational simulations revealed that the ablated area was consistent with the area with the highest temperature. Though several limitations still remain such as no blood circulation, pulsated steam flow can ablate diverse animal tissues.