3.2 Gefahrguttanks und Unfallmechanik
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The ongoing geo-political conflicts and the increasing need for the implementation of measures to improve the energetic system sustainability are increasing the importance of tanks for storing cryogenic fluids in the energy industry. The most common example of cryogenic tank applications is the transport of natural gas and hydrogen in their liquid form (LNG and LH2 respectively) for which, considering the same transport volume cryogenic storage ensures significantly higher transport capacities with respect storage based solely on overpressure.
A common feature of all cryogenic transported fluids is that their condition must be maintained minimizing heat leaks from the environment as much as possible. This is achieved by the implementation of thermal super Insulations (TSI) systems based on e. g. rock wool, perlites, microspheres, multilayer insulations (MLI), and vacuum which have proven to be effective in applications. However, due to the relatively short period of use in some applications, the small number of documented incidents, and the still few investigations carried out in the field, the exploitation of such systems in the cryogenic fluids transport sector still suffers from insufficient knowledge about the course and consequences of incidents. Accidents involving collisions, fires, and their combination are quite common in the transportation sector and may generate extraordinary loads on the tank and its insulation system, eventually leading to tank failure.
The present study focuses on the behavior of TSI systems in tanks when it is exposed to an external heat source representative of a hydrocarbon fire scenario. This may cause an increase of the heat flux into a tank by several orders of magnitude with respect to normal design conditions, thus inducing severe and in the TSI, causing the rapid release of flammable gas and even resulting in a Boiling Liquide Expanding Vapour Explosion (BLEVE).
To study such scenarios a test rig was developed at BAM that allows testing of TSI at industrial conditions and enables subsequent analysis of TSI samples. This test rig considers the typical double-walled design of tanks for cryogenic fluids with vacuum and an additional insulating material in the interspace. Adjustable electrical heating elements simulate the fire on one side of the double wall. This process allows the implementation of repeatable heat loads of up to 100 kW/m². The other side of the double wall is represented by a fluid-supported heat exchanger, which allows the simulation of cold or cryogenic conditions in the test rig, and to determine the heat flux transmitted through the double wall. Thus, the test rig allows thermal loading and performance analysis of TSI samples at the same time.
In the presentation, the results of diverse tested TSI systems will be presented and discussed. As a result of this study, the list of advantages and disadvantages for the choice of tested TSI expands. Within the test, all samples degraded as a consequence of a hydrocarbon fire-orientated thermal load. Strong differences in the behavior of the tested TSI systems over temperature, location, and time were observed. Additionally, the tested MLI insulations were significantly more resistant to their base materials. These results are relevant for the design, the definition of national and international regulations, the Risk assessment, and the development of safety concepts for cryogenic tanks.
The importance of tanks for storing cryogenic fluids in the energy industry is increasing because of ongoing political conflicts and the implementation of more environmentally friendly energy sources. Key representatives for the application of cryogenic tanks are natural gas in the form of Liquefied Natural Gas (LNG) and hydrogen, e. g. in the form of Liquefied Hydrogen (LH2), for which significantly higher transport capacities can be achieved with the same transport volume using cryogenic storages than with storages based solely on overpressure.
What applies to all cryogenic transported fluids in common is their condition that must be maintained. Hence heat flows into the preserved fluid must be minimized. Thermal super Insulations (TSI) based on e. g. multilayer insulations (MLI), perlites, and vacuum are utilized for this purpose and have already proven themselves in similar applications. However, for the use of tanks for cryogenic fluids in the transport sector, there is insufficient knowledge regarding the course and consequences of incidents, which is due to the still short period of use and the few documented incidents, hence few investigations carried out in this field. Typical scenarios in the transport sector represent car accidents with collisions, fires, and their combination, which are associated with extraordinary loads on the tank.
The focus of this study is to investigate the behavior of TSI as a result of their thermal exposure to a heat source representing a fire. It is worth mentioning that this could lead to an increase of the heat flux into a tank by several orders of magnitude, and to permanent damage of the TSI, ultimately rapid release of flammable gas as well as a Boiling Liquide Expanding Vapour Explosion (BLEVE). For this purpose, a high temperature thermal vacuum chamber (HTTVC) has been developed that allows thermal loading of MLI or perlites in a vacuum and simultaneous measurement of heat flow through this TSI. The HTTVC is designed to represent realistic insulation conditions and to withstand thermal loads from typical design fires.
The HTTVC was applied to investigate TSI based on MLI and vacuum. It is shown that the thermal stress caused permanent damage to the TSI, with shrinkage, phase change, pyrolysis, and condensation being significant damage mechanisms. The results are relevant for the evaluation of accident scenarios and can thus contribute to the improvement of TSI and the development of emergency measures for the protection of persons and infrastructures.
Hydrogen is among the most promising candidates to replace fossil fuels in the energy transition. Hydrogen-powered vehicles are already a reality, and their number is foreseen to increase considerably in the next decade. Among the possible solutions to store hydrogen in such vehicles, cryogenic tanks equipped with multi-layer insulation (MLI) appear to be one of the most effective to ensure high volumetric energy density. A potential loss of integrity of this kind of storage equipment might lead to severe consequences due to high flammability of hydrogen. This might occur, for instance, as a consequence of the exposure to an external source of heat such as a fire following a car accident. Real scale fire test results suggest that the super insulating performance of MLI systems may undergo severe degradation when this is subjected to high temperature, leaving the tank almost unprotected and leading to failure in a relatively short time. Characterizing this kind of accident scenario is crucial to ensure a safe design of storage tanks for Hydrogen-powered vehicles.
This presentation provides an overview of the ongoing research work on modelling MLI LH2 tanks exposed to fire. Lumped and computational fluid dynamic based models are presented, highlighting current gaps. The relevance of taking MLI degradation into account when simulating the pressure increase due to external fire exposure is here demonstrated through the analysis case studies.
We are interested in accidental fire impingement of HazMat pressure vessels. Want to develop improved models for predicting time to failure or empty (if PRV present). We are still trying to properly predict pressurization and time to first PRV activation due to liquid temperature stratification for a range of fire scenarios (Full and partial engulfing pool fire, jet fires, with roll over, with TP defects, etc.)
The interest in hydrogen-based green energy is increasing worldwide, and the same is true for hydrogen-powered vehicles. Among the possible solutions to store hydrogen in such vehicles, cryogenic tanks equipped with multi-layer insulation (MLI) are the most promising to increase the amount of energy stored per unit volume. However, MLI is affected by severe deterioration when exposed to an external source of heat such as a fire following a car accident, leaving the tank unprotected and leading to failure in a relatively short time. In this work, a one-dimensional model to evaluate MLI thermal degradation when a liquid hydrogen tank is exposed to fire is presented. The relevance of taking MLI degradation into account when simulating the pressure increase due to external fire exposure is here demonstrated through the analysis of several case studies. The results show that MLI systems performance depletes within a few minutes of exposure to hydrocarbon poolfire.
Liquefied Hydrogen (LH2) or Liquefied Natural Gas (LNG) establish themselves as important energy carriers in the transport sector. Its storage requires tanks with Thermal Super Insulations (TSI) to keep the transported fluid cold. The presentation includes 2 main topics of the department.
First TSI has proven itself in various applications over a long time, but not in the land transport sector, where accidents involving collisions, fires, and their combination are to be expected. To analyze fire scenarios a High-Temperature Thermal Vacuum Chamber (HTTVC) was developed that allows the thermal loading of thermal insulation material in a vacuum and measuring the heat flow through the TSI in parallel. Within this chamber, 5 samples were tested regarding 3 different types of MLI, rock wool, and perlites. In the presentation, the results are presented.
Second, the studying of accident scenarios enables the improvement of thermal superinsulation and to find novel insulation concepts. This is necessary for LH2 large-scale storages, for which state-of-the-art solutions are not suitable. Within the presentation, a novel insulation concept will be presented.
Liquid cargo has a significant impact on the interface wheel-track interaction. The sloshing affects the track-railcar's dynamic behavior. The effect is detectable at the track level and at the vehicle. Its characterization requires the combination of different techniques:
Empirical Mode Decomposition (EMD)
Time-Frequency Maps
Sloshing occurred when significant perturbations happened in the railcar:
The railcar entered a curve
Reduction in its travel speed
A railcar with a tank is a clear example of a multibody dynamic system with a nonlinear behavior.
Evaluate tank car PRV behavior under realistic fire conditions Subject 1/3 scale tank with full size PRV to engulfing pool fire Initial tests with water lading. Current tests with flammable lading (Ethanol). Document PRV performance with respect to opening pressure, reclosing, and evacuating the tank