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Renewable energies became more and more important in the last years. The production of biogas using agricultural waste and the use of wind and solar energy in combination with water electrolysis is one way to substitute natural gas. Therefore the number of biogas plants is growing very fast in Germany. In the meantime, the operation of such plants is responsible for a significant number of accidents. New safety regulations on biogas plants and a short statistical summary of accidents in Germany are presented in the first part of this presentation. The main focus of the paper is the principle hazards arising from the substances and materials in biogas and hybrid power plants. Primarily, these are the hazards of fire and explosion induced by flammable methane gas. However, further hazards are the dangers of asphyxiation and poisoning by gases such as carbon dioxide, hydrogen sulphide and ammonia. Furthermore, hydrogen is produced by water electrolysis in hybrid power plants and mixed with bio methane in some cases. In order to prevent explosions when handling biogas and hydrogen it is necessary to know the explosion limits of gas and gas mixtures in mixture with air. However, biogas from agricultural plants can vary significantly in its composition. Therefore, for each gas composition the explosion limits would have to be determined. This would require a considerable amount of time and effort. Due to this fact, the explosion limits of biogas are frequently referred to only by the methane fraction of the gas mixture in the safety-relevant literature. In reality as biogas can consist of methane, carbon dioxide and further residual gases the explosion limits are generally over or underestimated. A calculation method for explosion limits was developed by means of explosion diagrams to avoid such errors. In a last topic methods are shown for the calculation of gas spreading in case of leakages in gas buffers for risk evaluation and land use planning. For this purpose the German directive VDI 3783 was evaluated.
Land-use planning
(2007)
Heavy gases in large quantities are used worldwide in various industries. Past incidents, such as the liquefied gas disaster in Viareggio (2009) have shown that these materials are difficult to handle in a safe manner. According to the German Hazardous Incident Ordinance (StörfallVO 2000 - 12. BIMSchV), plant operators with extended responsibilities must produce a report in which they verify that , in the event of an unintentional gas release, the surrounding area will not be aversely affected. Essential elements of this report are calculations of both the released mass flow and the gas dispersion. Using models such as the VDI guideline 3783 (state of the art in Germany) plant operators are able to predict the characteristics of likely gas dispersions. The presented experimental investigations were carried out at the BAM better understand heavy gas dispersion with high gas concentrations in the air (≥ 1 Vol.-%), as well as concentrations with approximately neutral density characteristics (≤ 3000ppm) in order to test the accuracy of the VDI guideline. The starting point for experimental trials was the heavy gas releases resulting from pipeline, vessel or standard gas bottle leaks, with mass flows of between 20 and 100 g s-1. Investigations on the gas-phase release process focused on the unsteady mass flow associated with releases from standard gas bottles. The experimental results will be used as comparative parameters for future simulations. The goal of these simulations is to develop a model with which calculation of the unsteady mass flow, based on the material characteristics for any gas, is possible.
Safety criteria for the transport of hydrogen in permanently mounted composite pressure vessels
(2020)
The recent growth of the net of hydrogen fuelling stations increases the demands to transport compressed hydrogen on road by battery vehicles or tube-trailers, both in composite pressure vessels. As a transport regulation, the ADR is applicable in Europe and adjoined regions, and is used for national transport in the EU. This regulation provides requirements based on the behaviour of each individual pressure vessel, regardless of the pressure of the transported hydrogen and relevant consequences resulting from generally possible worst case scenarios such as sudden rupture. In 2012, the BAM (German Federal Institute for Materials Research and Testing) introduced consequence-dependent requirements and established them in national transport requirements concerning the “UN service life checks” etc. to consider the transported volume and pressure of gases. This results in a requirement that becomes more restrictive as the product of pressure and volume increases. In the studies presented here, the safety measures for hydrogen road transport are identified and reviewed through a number of safety measures from countries including Japan, the USA and China. Subsequently, the failure consequences of using trailer vehicles, the related risk and the chance are evaluated. A benefit-related risk criterion is suggested to add to regulations and to be defined as a safety goal in standards for hydrogen transport vehicles and for mounted pressure vessels. Finally, an idea is given for generating probabilistic safety data and for highly efficient evaluation without a significant increase of effort.
Propane/air deflagrations and CTA measurements of turbulence inducing elements in closed pipes
(2008)
The current paper presents experimental investigations on several influence parameters of deflagrations in long closed pipes. The experiments were carried out with different propane/air mixtures, various length-to-diameter ratios (up to L/D=143, D=0.159 m) and miscellaneous initial pressures. Maximum values of explosion pressures and flame speeds were found at stoichiometric propane/air compositions. With increasing L/D, the explosion pressures decreased while higher flame speeds were determined. In addition, elevated initial pressures led to rising explosion pressures. Furthermore, it is well known that turbulence inducing elements in pipes, ducts or vessels enhance the heat and mass transfer during reactive flows. This may lead to a significant acceleration of ongoing gaseous reactions and could finally cause a deflagration to detonation transition (DDT) aligned with much higher pressures and flame speeds. Therefore, constant temperature anemometry (CTA) measurements were carried out to describe the influence of frequently used flange assemblies and baffles on the velocity and turbulence distributions of air flows in steel pipes similar to those in the explosion measurements. The experiments showed that in contrast to flange assemblies, baffles caused a significant increase of the turbulence intensity in pipe flows.
15 identical off-the-shelf propane cylinders (m = 11 kg liquid propane) were underfired. The infrared Radiation of the Explosion, that occurred in the aftermath of the vessel failure, was recorded using four bolometers. These measurements are compared with an estimation of the Maximum intensity gained by an Analysis of the Video data, an Extended Version of the Stefan-Boltzmann law and a BLEVE model.