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- 2 Prozess- und Anlagensicherheit (14) (entfernen)
For hazard assessment purposes, the dispersion of gases in complex urban areas is often a scenario to be considered. However, predicting the dispersion of heavy gases is still a challenge. In Germany, the VDI Guideline 3783, Part 1 and 2 is widely used for gas dispersion modelling. Whilst Part 1 uses a gauss model for calculating the dispersion of light or neutrally buoyant gases, Part 2 uses wind tunnel experiments to evaluate the heavier-than-air gas dispersion in generic built up areas. In practice, with this guideline, it is often not possible to adequately represent the existing obstacle configuration. To overcome this limitation, computational fluid dynamics (CFD) methods could be used. Whilst CFD models can represent obstacles in the dispersion area correctly, actual publications show that there is still further research needed to simulate the atmospheric flow and the heavy gas dispersion. This paper presents a modified k-ε-turbulence model that was developed in OpenFOAM v5.0 (England, London, The OpenFOAM Foundation Ltd Incorporated) to enhance the simulation of the atmospheric wind field and the heavy gas dispersion in built-up areas. Wind tunnel measurements for the dispersion of neutrally buoyant and heavy gases in built-up environments were used to evaluate the model. As a result, requirements for the simulation of the gas dispersion under atmospheric conditions have been identified and the model showed an overall good performance in predicting the experimental values.
Schäden an Rohrleitungen können zu hohen Umweltbelastungen und wirtschaftlichen Schäden führen. Um die dauerhafte Verfügbarkeit der Infrastruktur zu gewährleisten, wird im Rahmen des Projekts AGIFAMOR an der Bundesanstalt für Materialforschung und -prüfung (BAM) erprobt, inwiefern das Verfahren der verteilten akustischen faseroptischen Sensorik (Distributed acoustic sensing - DAS) zur kontinuierlichen Überwachung von Rohrleitungen verwendet werden kann. Neben der DAS werden erprobte Verfahren der zerstörungsfreien
Prüfung wie Schallemissionsanalyse (SEA) und Beschleunigungssensoren eingesetzt. An dieser Stelle soll detailliert auf die unterschiedlichen Messverfahren und deren spezifischen Einsatz im Rahmen des Projektes eingegangen werden.
Schäden an Rohrleitungen können zu hohen Umweltbelastungen und wirtschaftlichen Schäden führen. Um die dauerhafte Verfügbarkeit der Infrastruktur zu gewährleisten, wird im Rahmen des Projekts AGIFAMOR an der Bundesanstalt für Materialforschung und -prüfung (BAM) erprobt, inwiefern das Verfahren der verteilten akustischen faseroptischen Sensorik (Distributed acoustic sensing – DAS) zur kontinuierlichen Überwachung von Rohrleitungen eingesetzt werden kann. Neben der DAS werden erprobte Verfahren der zerstörungsfreien Prüfung wie Schallemissionsanalyse (SEA) und Beschleunigungssensoren eingesetzt. An dieser Stelle soll detailliert auf die Hauptschadensursachen an Rohrleitungen, den Versuchsstand zur mechanischen Belastung von Rohren sowie die Möglichkeiten zu Untersuchungen im Realmaßstab eingegangen werden.
CFD simulations of near-ground gas dispersion depend significantly on the accuracy of the wind field. When simulating wind fields with conventional RANS turbulence models, the velocity and turbulence profiles specified as inlet boundary conditions change rapidly in the approach flow region. As a result, when hazardous materials are released, the extent of hazardous areas is calculated based on an approach flow that differs significantly from the boundary conditions defined. To solve this problem, a turbulence model with consistent boundary conditions was developed to ensure a horizontally homogeneous approach flow. Instead of the logarithmic vertical velocity profile, a power law is used to overcome the problem that with the logarithmic profile, negative velocities would be calculated for heights within the roughness length. With this, the problem that the distance of the wall-adjacent cell midpoint has to be higher than the roughness length is solved, so that a high grid resolution can be ensured even in the near-ground region which is required to simulate
gas dispersion. The evaluation of the developed CFD model using the German guideline VDI 3783/9 and wind tunnel experiments with realistic obstacle configurations showed a good agreement between the calculated and the measured values and the ability to achieve a horizontally homogenous approach flow.
Bei Störfallauswirkungsbetrachtungen an Biogasanlagen muss das Versagen der Folienabdeckung der Gärbehälter untersucht werden.
Hierbei sind insbesondere Risse in derselben hinsichtlich des austretenden Massenstromes an Biogas zu bewerten, ebenso wie der durch eine Zündung resultierende Flammenstrahl. Zurzeit existieren für Biogasfolien keine Erkenntnisse zu realistischen Ausflussziffern für die Massenstromberechnung. Die Anwendbarkeit verfügbarer Modelle zur Berechnung der Wärmestrahlung ist ebenso bisher ungeklärt. Um diese Fragestellungen zu untersuchen, wurden in der BAM Versuche an einem 80 m3 Biogassack durchgeführt.
A steel pipeline segment of 2.5 m length was subjected to quasi-static four-point bending load in three steps for studying the initial cracking and damage accumulation based on the Acoustic Emission (AE) technique and by the direct current potential drop (DCPD) technique. For the latter, a new post-test analysis method was established.
AE is found more sensitive to crack initiation than DCPD. Formation of mesoscopic and macroscopic cracks as well as their closure and the resulting friction generate weighted peak frequencies below 400 kHz, whereas microscopic cracking produces AE with broad band spectra identifiable by weighted peak frequencies above 400 kHz. Critical states alike the maximum load level and the leak opening were accompanied by peak amplitudes above 85 dBAE. This rather fundamental study provides a data base for possibly developing advanced strategies of detection and alarm systems based on acoustic monitoring of pipelines, or at least, steel structures.
In the presented work, the potential of fiber-optic distributed acoustic sensing (DAS) for detection of small gas pipeline leaks (<1%) is investigated. Helical wrapping of the sensing fiber directly around the pipeline is used to increase the system sensitivity for detection of weak leak-induced vibrations. DAS measurements are supplemented with reference accelerometer data to facilitate analysis and interpretation of recorded vibration signals. The results reveal that a DAS system using direct fiber application approach is capable of detecting pipeline natural vibrations excited by the broadband noise generated by the leaking medium. In the performed experiment, pipeline vibration modes with acceleration magnitudes down to single ug were detected. Simple leak detection approach based on spectral integration of time-averaged DAS signals in frequency domain was proposed. Potential benefits and limitations of the presented monitoring Approach were discussed with respect to its practical applicability. We demonstrated that the approached is potentially capable of detection and localization of gas pipeline leaks with leak rates down to 0.1% of the pipeline flow volume and might be of interest for monitoring of short- and medium-length gas pipelines.
Large-scale experiments have been performed to investigate the possible consequences of realistic amounts of liquified hydrogen (LH2) encountering water. The experiments aimed at simulating an accidental release of LH2 onto water, for instance during the fuelling of a ship. For liquified natural gas (LNG), it has been demonstrated that physical explosions may occur when it is spilled onto water. These phenomena are referred as rapid phase transitions (RPTs). It cannot be excluded that RPTs are also possible in the case of LH2. The tests were performed at the Test Site Technical Safety of the Bundesanstalt für Materialforschung und –prüfung (BAM) in Horstwalde, Germany. The tests were performed in a 10 m x 10 x 1.5 m basin filled with water. LH2 releases of up to about 1 kg/s were established releasing directly from a trailer carrying LH2. The releases occurred from a height of 50 cm above the water surface pointing downwards, 30 cm under the water surface pointing downwards and 30 cm under the water surface pointed along the water surface. All release configurations resulted in a very chaotic LH2-water mixing zone, causing considerable evaporation and resulting in minor over pressures. No RPTs were observed. The main phenomenon to be observed is, however, an ignition of the released gas cloud resulting in significant blast wave overpressures and heat radiation to the surroundings. The ignition occurred in all under-water releases and in about 90 % of the releases above the water surface.
In case of a vehicle fire, an installed LPG (liquefied petroleum gas) tank with a malfunctioning safety device poses severe hazards. To investigate the consequences in case of tank failure, we conducted 16 tests with toroidal shaped LPG vehicle tanks. Three tanks were used for a Hydraulic Burst Test under standard conditions. Another three tanks were equipped with a statutory safety device and were subjected to a gasoline pool fire. The safety device prevented tank failure, as intended. To generate a statistically valid dataset on tank failure, ten tanks without safety devices were exposed to a gasoline pool fire. Five tanks were filled to a level of 20 %; the re-maining five were filled to a level of 100 %. In order to gain information on the heating process, three tem-perature readings at the tank surface, and three nearby flame temperatures were recorded. At distances of l = (7; 9; 11) m to the tank, the overpressure of the shock wave induced by the tank failure and the unsteady tem-peratures were measured. All ten tanks failed within a time of t < 5 min in a BLEVE (boiling liquid expanding vapor explosion). Seven of these resulted directly in a catastrophic failure. The other three resulted in partial failure followed by catastrophic failure. A near field overpressure at a distance of l = 7 m of up to p = 0.27 bar was measured. All ten tests showed massive fragmentation of the tank mantle. In total, 50 fragments were found. These 50 fragments make-up 88.6 % of the original tank mass. Each fragment was georeferenced and weighed. Fragment throwing distances of l > 250 m occurred. For the tanks with a fill level of 20 %, the average number of fragments was twice as high as it was for the tanks that were filled completely.
Compressed natural gas (CNG) is a widely used automotive fuel in a variety of countries. In case of a vehicle fire where the safety device also malfunctions, a failure of the CNG automotive cylinder could occur. Such a cylinder failure is associated with severe hazards for the surrounding environment. Firstly, a comprehensive analysis is given below, summarizing various accidents involving CNG automotive cylinders and their consequences. In an extensive experimental program, 21 CNG automotive cylinders with no safety device were tested. Of the 21, burst tests were carried out on 5 Type III and 5 Type IV cylinders. Furthermore, fire tests with 8 Type III and 3 Type IV cylinders were conducted. Apart from cylinder pressure, inner temperature and cylinder mantle temperature, the periphery consequences, such as nearfield blast pressure and fragmentation are documented. The maximum measured overpressure due to a Type III cylinder failure was p = 0.41 bar. Each traceable fragment was georeferenced. All-in-all, fragment throw distances of d > 300 m could be observed. As one key result, it can be stated that the tested Type IV CNG cylinders showed less critical failure behavior then the Type III cylinders under fire impingement.