Roof Tanks Research Articles

Surface cover method to reduce evaporation rate of crude oil

One of the problems that commonly found in petroleum industry is related to the evaporation of crude oil during storage. Hence the purpose of this study is to find lower-cost method to reduce crude oil evaporation. The method has the same principle as floating roof tank, but instead of surface covered by metal, low-density chemical substances, i.e., polyurethane foam and ethylene vinyl acetate foam (EVA mat), was used to cover the surface of crude oil. In comparison with EVA mat, polyurethane foam gave lower percentage of reduced crude oil evaporation. Increasing the thickness of the additive to 3 cm was found to be the best parameter to reduce the evaporation of crude oil. At temperatures of 40, 45, and 50°C, 3 cm thickness of polyurethane foam was able to reduce the evaporation of crude oil by 81.6 - 91.7%, 75.9 - 87.3%, and 74.2% - 86.6%, respectively. At temperatures of 40, 45, and 50°C, 3 cm thickness of EVA mat can reduce the evaporation of crude oil by 68.6 - 78.1%, 56.8 - 60.9%, and 42.4 - 49.6%, respectively.

Seismic Analysis of Steel Cylindrical Liquid Storage Tank Using Coupled Acoustic-Structural Finite Element Method For Fluid-Structure Interaction

A seismic analysis of ground-supported, three-dimensional (3-D) rigid-base steel cylindrical liquid storage tank is investigated, using a coupled acoustic-structural finite element (FE) method for fluid-structure interaction (FSI). In this method, the contained liquid in the tank is modelled using acoustic elements and the cylindrical tank is modelled using shell elements. The impulsive and convective terms are estimated separately by using the appropriate boundary conditions on the free surface of the liquid. The convergence and validation studies of the proposed FE model are conducted by comparing the results reported in the literature. The parametric studies are performed for rigid and flexible tanks for the varying slenderness of the open roof tanks. The sloshing displacement and base shear time history responses are evaluated for the 3-D tanks subjected to harmonic unidirectional ground motions. Further, the results are compared with the commonly used two and three lumped-mass models of the tank. Moreover, the seismic response quantities of the tank subjected simultaneously to the bi-directional horizontal components of earthquake ground motion are also investigated using the 3-D FE model, and the response quantities are compared with the lumped-mass models. The results obtained from the 3-D FE model and lumped-mass model are in close agreement. The average percentage difference in the 3-D FE and lumped-mass models for maximum sloshing displacement prediction is 15 percent to 20 percent and that for the base shear is about 4 to 10 percent, in the case of the uni-directional harmonic ground motions. It is concluded that the sloshing displacement is not affected by the tank flexibility, but the impulsive hydrodynamic pressure and the impulsive component of the base shear increases with the tank flexibility.

Assessment of the amount of hydrocarbon emissions to the atmosphere during handling and storage of diesel fuel in fixed roof tanks

Assessment of the amount of hydrocarbon emissions to the atmosphere during handling and storage of diesel fuel in fixed roof tanks

Quantitative risk assessment of emissions from external floating roof tanks during normal operation and in case of damages using Bayesian Networks

In this paper, events resulting in an increased or critical emission of volatile organic compounds from external floating roof tanks containing crude and mineral oils with high vapor pressure, e.g. gasoline or naphtha, are investigated. Here normal operations and deviations from normal operations such as tank revision procedures and damages to pipes, seals or deck fittings are included. To record emission-relevant events or damages, a comprehensive literature survey, a Germany-wide survey of companies which use external floating roof tanks and an expert survey were carried out. In addition, the probability of the occurrence of emissions-relevant events was determined and used for risk assessment based on Bayesian networks. This is a well-known method of quantitative risk analysis illustrating and describing causal dependencies. The aim of this work is to show which chains of events can lead to increased or critical emissions of volatile organic compounds. Furthermore, the available data in the literature will be extended by the damage and event rates determined in this work.

Failure analysis of an exploded large-capacity liquid storage tank using finite element analysis

In case of liquid storage tank has been designed regardless of international standards and there is little interest with its operating conditions, it may lead to fully or partially failure. This paper has studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis (FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation between weld electrode size and tank diameter at each type of weld electrode to determine the main framework of roof to top shell welding process. Also, to develop a relation between tank diameter and maximum stresses that resulted at every amount of vapor pressure according to maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through the circumference welding path. The results of analysis allowed us to redesign the tank according to API 650 and to express the recommendations for toluene storage tanks operation.

Современные методы монтажа плавающих крыш резервуаров вертикальных стальных и контроль их выполнения

Современные методы монтажа плавающих крыш резервуаров вертикальных стальных и контроль их выполнения

Современные конструкции уплотняющих затворов плавающих крыш вертикальных стальных резервуаров

Современные конструкции уплотняющих затворов плавающих крыш вертикальных стальных резервуаров

Analysis of the peak vertical displacement of liquid surface due to sloshing

When a tank containing liquid vibrates, the liquid exerts hydrodynamic effects on the solid domain of a tank. In the case of roof tanks, a large sloshing wave will impact the wall or roof of the tanks and may cause extensive damage or failure of the tanks. This paper provides the theoretical background of simplified seismic analysis of liquid storage cylindrical ground -supported tanks, and it documents the seismic effect of input motions characteristics on fluid sloshing behaviour.

Failure Analysis of an Exploded Large-Capacity Liquid Storage Tank Using Finite Element Analysis

In case of liquid storage tank has been designed regardless of international standards and there is little interest with its operating conditions, it may lead to fully or partially failure. This paper has studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis (FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation between weld electrode size and tank diameter at each type of weld electrode to determine the main framework of roof to top shell welding process. Also, to develop a relation between tank diameter and maximum stresses that resulted at every amount of vapor pressure according to maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through the circumference welding path. The results of analysis allowed us to redesign the tank according to API 650 and to express the recommendations for toluene storage tanks operation.

Experimental measurement of initial evaporation mass flows from gasoline spills and comparison with empirical models

AbstractIn this paper, we investigate the evaporation mass flow originating from spills of gasoline. Large spills of gasoline may form during partial or complete roof sinkings or in the case of perforations at various deck fittings at external floating roof tanks used for the storage. Additionally, spills may form in the retention area in the case of leakages at pipes or at the hull. The aim is to predict the order of magnitude of real‐scale evaporation mass flow. The determined evaporation mass flows will be used in a related project as input values for subsequent dispersion modeling in the vicinity of the tanks. This is relevant for questions of fire and explosion protection as well as for environmental protection aspects in tank farms or refineries, which use external floating roof tanks. The measurements presented in this paper were compared with predictions by empirical models and investigations of evaporations from small floor spills, round‐bottom flask, or from Petri dishes published in the literature. The main goal of this paper is to test the applicability of empirical models to provide reasonable evaporation mass flows as input for CFD dispersion simulations.

Hydroelastic modeling and active control of transient sloshing in a three dimensional rectangular floating roof tank

Partly filled rectangular containers are widely used for liquid transportation and storage in many industrial and civil applications. Undesirable liquid sloshing in these structures can highly degrade their reliable and safe operations. This paper presents a rigorous 3D hydro-elasto-dynamic analysis for suppression of transient liquid sloshing in a rigid-walled rectangular parallelepiped container that is equipped with a smart piezo-sandwich free-floating rectangular panel. The problem formulation is based on the linear water wave theory, the thin piezo-sandwich floating plate model, the pertinent structure/liquid compatibility condition, and the active damping control strategy. The controller gain parameters are systematically tuned using a standard MOPSO algorithm with conflicting objective functions. The key hydro-electro-elastic response parameters are calculated and discussed for three different external excitations, namely, a bidirectional seismic event, an oblique planar base acceleration, and a distributed impulsive floating roof excitation. Effectiveness of proposed active floating panel control configuration in remarkable suppression of the main hydro-elastic parameters is established, essentially regardless of liquid depth and loading configuration. Limiting cases are considered and validity of model is demonstrated against available data as well as by comparison with the results of a general finite element package.

Evaluation on thermal and mechanical performance of the hot tank in the two-tank molten salt heat storage system

A few tank failure accidents in the concentrated solar power plant have occurred in recent years, resulting in huge economic losses. In the present study, thermal and mechanical performance of the molten salt (60% NaNO3 and 40% KNO3) heat storage tank were studied. A coupled thermal performance evaluation model was proposed to evaluate heat losses and temperature distributions of the tank. The finite element method was then adopted to investigate the mechanical performances of the tank under different working conditions. The results indicated that the radiation in the inner air space of the tank made the temperature of the tank roof equal to that of the salt, so the temperatures of the tank wall remained constant at different salt levels. This eventually led to a constant heat loss of the tank at different salt levels. The temperature of the tank foundation was very high and greatly non-uniform, so a cooling system for the tank foundation was necessary for the safety of the tank operation, and the flow direction of the cooling air should be from the tank center to the outer part for obtaining a uniform temperature in the radial direction of the tank. With a rigid tank foundation, the range of the total stress is about 100 MPa for a daily charging/discharging cycle operation which may result in the fatigue in the tank shell. Lower foundation stiffness reduces the total stress range which in turn reduces thermal fatigue, but the stiffness of the ring wall and the tank foundation fillers should be above 30 MPa/m and 5 MPa/m respectively for a safe settlement and stress state. The thermal deformation in the tank is very high (e.g. 113.6 mm for the hot tank in the Solar Two system), and a small restriction of thermal deformation can lead to extremely high thermal stress which is detrimental for the safety of an operating tank, so any restriction in the thermal deformation should not be allowed.

Effect of transient temperature on 304 stainless steel LPG tank structure using numerical simulation approach

The use of numerical simulation approach to investigate the effect of transient boundary temperature on an LPG tank structure was investigated. Here, both transient thermal and structural system were coupled in ANSYS software version 19.2 to create an interaction between the thermal and mechanical load on the tank structure. The focus of this paper is to identify stress hotspot which may eventually lead to stress-corrosion using a non-linear solver. Literature has proven that temperature gradient acting on a material is a possible cause for failure in most engineering structures due to stress induced corrosion. In this study the effect of a time dependent change in the temperature of the material (304 stainless steel) was investigated. The temperature was set to increase from cryogenic to 30 °C, and the pressure which represents mechanical load was also implemented at the wall boundary. Results obtained showed that stress was concentrated at the principal plane connecting the tank roof to the cylindrical structure. However, a failure analysis was conducted were the mechanical load was increased to 3 × 1043 Pa. It was found that the material failed after 1,000,000 s time steps and the tensile yield strength obtained from the stress–strain curve was lower than the material standard value. This can be explained with the concept that the action of temperature disrupted the material microstructure, hence, reduced the material stiffness to fracture. The stress–strain curve was validated with the standard plot for the 304 stainless steel material type.

Analysis on the Influence Factors of Propellant Tank Stress

The propellant tank is a vital structure for the liquid rocket, and the analysis of influence factors to the propellant tank stress can provide a significant reference to design the propellant tank. Through establishing the ellipsoid cylindrical tank model, the meridian stress and hoop stress distributions of tank roof, cylinder and bottom are analysed. And then the equivalent stress is defined based on the material strength theory. According to the parameters of a certain type tank, the equivalent stresses of tank roof, cylinder and bottom are worked out with different ellipsoidal norms, overload factors, tank radiuses and internal pressurizations, the effects of these influence factors on the tank stress are analysed, and the change laws of tank roof, cylinder and bottom equivalent stresses are determined to provide a reference for the design of propellant tank.

Study on the Influence of Frangible Roof Performance of Tank Explosion Under Multi-field Coupling

Taking the 3000-m3 vertical vault storage tank as the research object, the finite element calculation method is used to calculate the pressure and temperature of the fluid during the explosion of the tank. By calculating the structural response of storage tank using multi-field coupling method, the distribution of stress and the deformation of tank are obtained. The tank frangible roof performance influenced by explosion load in different working conditions is analyzed. The results show that the failure pressures of the tank roof are the same in empty-tank, half-tank and full-tank conditions, and the damage pressure of the tank shell and bottom gradually increases with the storage liquid level. Temperature also affects the failure pressure at different locations. At the same location, the higher the temperature, the lower the failure pressure. When the tank is empty, the failure times of the roof and the bottom are almost the same, the failure time of tank shell is obviously earlier than that of other locations. The intensity ratio k is less than 1.5, which means the tank does not have frangible roof performance. For the liquid level of half tank and full tank, no matter where the explosion point is, the failure pressure at the roof-to-shell location is smaller than other locations, and the failure time at the roof-to-shell location is obviously earlier than other locations. The intensity ratio k is bigger than 2.5, which means the tank have frangible roof performance.

An optimal design model for the wall thickness of the propellant tank

The propellant tank is a vital part for the liquid rocket, and the optimal design of the propellant tank is a significant research to develop the heavy rocket. This paper aims at providing an optimal design model for tank wall thickness. Through establishing the tank mathematical model, analyzing the stress distributions of tank, and defining the equivalent stress of tank, the wall thickness parameters of tank roof, cylinder, and bottom are obtained. The effects of tank parameters on the wall thickness are analyzed to determine the distribution rules of tank roof, cylinder, and bottom wall thickness parameters. Combined with the safety factor that is defined as the ratio of the material's ultimate stress to the maximum equivalent stress, the optimal design model with invariable tank roof and bottom wall thicknesses and variable tank cylinder wall thickness is established. Finally, the optimal design model is verified by comparing the optimal tank with the original tank. The results show that the optimal design model can effectively decrease the mass of the tank and improve the stress distribution of the tank.

Safety assessment of Generation III nuclear power plant buildings subjected to commercial aircraft crash Part II: Structural damage and vibrations

Abstract Investigations of the commercial aircraft impact effect on nuclear island infrastructures have been drawing extensive attention, and this paper aims to perform the safety assessment of Generation III nuclear power plant (NPP) buildings subjected to typical commercial aircrafts crash. At present Part II, based on the verified finite element (FE) models of aircrafts Airbus A320 and A380, as well as the NPP containment and auxiliary buildings in Part I of this paper, the whole collision process is reproduced numerically by adopting the coupled missile-target interaction approach with the finite element code LS-DYNA. The impact induced damage of NPP plant under four impact locations of containment (cylinder, air intake, conical roof and PCS water tank) and two impact locations of auxiliary buildings (exterior wall and roof of spent fuel pool room) are evaluated. Furthermore, by considering the inner structures in the containment and raft foundation of NPP, the structural vibration analyses are conducted under two impact locations (middle height of cylinder, main control room in the auxiliary buildings). It indicates that, within the discussed scenarios, NPP structures can withstand the impact of both two aircrafts, while the functionality of internal equipment on higher floors will be affected to some extent under impact induced vibrations, and A380 aircraft will cause more serious structural damage and vibrations than A320 aircraft. The present work can provide helpful references to assess the safety of the structures and inner equipment of NPP plant under commercial aircraft impact.

ABOUT CHANGE OF THE LEVEL OF OIL IN THE STORAGE FLOATING-ROOF TANKTHROUGH ATMOSPHERIC BURNERS

The authors analyze the main tendencies in the reconstruction and development of tank farms of the main oil transportation system in Ukraine, namely the use of large-volume tanks with a floating roof. The authors consider one of the reasons that can complicate the operation of such tanks that is the presence of liquid (in the form of rain) or solid (snow and ice) atmospheric precipitation on it, which leads to the additional immersion of the floating roof of the tank into oil. The literature on the exploitation of floating roof tanks has been analyzed and it is found out that there are practically no data of measurements on the basis of which it is possible to estimate the influence of liquid atmospheric precipitation on the depth of immersion of tank floating roofs. The article shows the topicality of the issue from the point of view of commodity-transport operations on oil metering. The authors show the results of measuring the oil levels in the tank with regular appliances in the presence and absence of rainwater on the floating roof (after drainage of the latter through the drainage system) and the results of their treatment in order to determine the difference in the accounted oil mass in the tank caused by the accumulation of water on the roof, taking into account oil physical properties and the data of processing of the gauge tables of the tank. The results of natural measurements are analyzed and a simplified method of calculating the depth of immersion of a roof in the presence of additional loads on it in the form of atmospheric precipitation is developed. The oil level in the tank was determined using a standard system of the ENRAF type, and the determination of oil volumes was done using the gauge table of the tank. Based on physical regularities, the authors derive theoretical dependencies to determine the amount of atmospheric moisture on the floating roof depending on the volume (changes of the oil levels) of water on it. It is shown how to calculate the minimum amount of atmospheric water on the roof, which leads to the need to introduce corrections while determining the mass of oil in the tank using a static volume-mass method. This research has proved the necessity of introducing corrections while determining the level of oil in the tanks with floating roofs when there is atmospheric precipitation on the roof.

Numerical simulation and applications of equivalent film thickness in oil evaporation loss evaluation of internal floating-roof tank

Internal floating-roof tank (IFRT) is widely used to store light oil products, but there exist oil evaporation from the rim gap of the floating deck and oil vapor diffusion into the atmosphere from several vents on the tank wall or tank roof. Based on the single-film mass transfer theory and the wind tunnel experiments, the equivalent film thickness (δE) and the relevant evaporation rate model was proposed and numerically verified. The airflow speed, concentration and the evaporation loss rate in/from the tank were calculated using the model, and the influence of vent locations, the rim gap locations and the seal tightness of the annular rim gap on the loss rate was analyzed. The results show that when the floating deck elevates, the ambient wind speeds up, or the change of the vent locations from the roof to the wall, δE decreases; the relationship of δE with the oil type or the ambient temperature is not obvious; the effect of the seal tightness to the entire/partial rim gap on the loss rates is obvious. The results further reveal the interior mechanism of the vapor-air mass transfer and can provide important theoretical support for the design, management and improvement of IFRT.

Numerical and Experimental Evaluation of Sloshing Wave Force Caused by Dynamic Loads in Liquid Tanks

Proper evaluation of forces exerted on a solid boundary by liquid sloshing is difficult. If the free board in a liquid storage tank is insufficient, the sloshing waves caused by seismic excitation will collide with the tank roof and may cause major damage. The current study investigated the sloshing wave impact force (SWIF) in full-scale liquid storage tanks using numerical simulation based on the lattice Boltzmann method (LBM). Several shaking table tests have been conducted on a small-scale rectangular tank to validate the numerical model. The results of a standard dam break test have been used to express the validity of the proposed numerical model. This comparison confirms the validity of the numerical strategy for simulating the effect of sloshing. After validating the numerical model, it has been applied to a practical parametric study of SWIF in full-scale liquid tanks. The results of numerical simulation indicate that the simplified method recommended by related codes and standards for calculating SWIF in liquid tanks significantly underestimates the sloshing force. This confirms that the dynamic nature of sloshing should be considered in the design process of liquid storage tanks.