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minimum explosion concentration (MEC) and limiting oxygen concentration (LOC) in our recent works. This work further studies the reasonability and reliability of the alternative method experimentally and theoretically. Six different dust samples were tested via a 20-L spherical explosion chamber. The experimental results showed that the data of MEC and LOC determined by using the alternative and the standardized methods are in good agreement. The minimum flame propagation velocity (Sf) and the corresponding maximum combustion duration time (tc) were found at its MEC and LOC, suggesting that the theoretical analysis can well explain all the experimental data. It is the first time to study the theoretical basis of the explosion criterion, thus helping to improve our understandings of dust explosion characteristics, and to amend the explosion criterion in future test standards.
Major accidents in the process industry often lead to the release of light or dense gases, which can mean a thread to employees, local residents or to the environment. Possible scenarios are therefore analyzed and evaluated in advance for approval issues. There is a trend, where simple empirical models are being replaced with more complex numerical models. Gaussian dispersion models or models based on dimensional analysis approaches are for example, increasingly replaced by CFD simulations. The main reason for this is the potentially higher accuracy. However, usually scenarios using sharp parameter values are calculated, since comprehensive consideration of parameter distributions via Monte Carlo or Latin Hypercube Sampling fails due to the numerical effort. This includes the risk that the influence of uncertainties on the simulation results is not taken into account. Response surface methods offer an alternative, with which the CFD problem can be mapped onto an algebraic surrogate model. If this is sufficiently precise, parameter sampling can also be carried out with the surrogate as well, as shown in some publications. Previous investigations only demonstrated the basic principle using trivial dispersion models. In this paper two realistic CFD simulations from the plant safety area are considered: VOC emissions from a storage tank and near-ground dense gas emissions. The entire procedure of response surface determination and parameter studies was automated and parallelized for high-performance-computing, and is carried out on the underlying CFD grids. For the CFD simulations as well as for all visualizations, the commercial software ANSYS CFX and the open source software OpenFOAM were used. The aim of this paper is to demonstrate the method using industry-relevant applications as well as to show how this can be used in practical engineering applications. The quality of surrogate modeling, the numerical effort and advantages that can result from the procedure are discussed as well as advantages which may result from taking parameter uncertainties into account in safety studies.
There is no applicable existing standard for the determination of safety characteristics for hybrid mixtures. While developing a new standard in a joint research project in Germany first results from parameter studies led to a standard procedure that can be adopted by laboratories that are already testing dusts in the so called 20L-sphere with as little additional effort as necessary. In fact, one of the main objectives of this research project was to keep modifications and adjustments from the generally accepted dust testing procedures as easy and minimal as possible so as to limit potential deviations from one laboratory to another.
In this first round robin test on hybrid mixtures ever, with methane as gas component and a specific corn starch as dust sample, the practicality of the whole procedure, the scattering of the results and the deviation between the testing apparatuses is investigated. This paper summarizes the experimental procedure adopted and objectives of the first round-robin phase involving three of the four original German companies, plus volunteering laboratories from Australia, Belgium, Czech Republic, France, Poland and P.R. China. The results will have an impact on the new standard and may lead to robust data for later simulation purposes.
Bei Geräten und Maschinen zur bestimmungsgemäßen Verwendung in explosionsgefährdeten Bereichen muss in der europäischen Union eine Zündgefahrenbewertung durchgeführt werden. Dabei müssen unter anderem die Gefahren von nichtelektrischen Zündquellen betrachtet werden, zu denen auch die mechanischen Schlagvorgänge gehören.
Bei Schlagvorgängen kommt es infolge des Zusammenstoßes zweier Werkstücke zu einer Umwandlung der kinetischen Energie. Dabei erhöht sich die Temperatur der Werkstoffe an der Kontaktstelle und es kommt unter Umständen zu einem Abtrennvorgang kleiner Partikel erhöhter Temperatur. Sowohl die heißen Kontaktstellen als auch die abgetrennten Partikel können eine wirksame Zündquelle für ein explosionsfähiges Gasgemisch darstellen. Zur Festlegung von Grenzwerten wurden in der Norm DIN EN ISO 80079-36:2016 die Gasgemische anhand ihrer Explosionsgruppe klassifiziert und zu jeder Gruppe die maximale Energie des Schlagvorgangs festgelegt, unter derer die Entstehung einer wirksamen Zündquelle als unwahrscheinlich angenommen werden kann.
Performance of the standardized testing method for detonation fl ame arresters at increased pressure
(2022)
Detonation flame arresters are typically used as autonomous protection systems in industrial applications to prevent potential hazards associated with flammable and/ or explosive chemicals. To verify and examine the suitability of detonation flame arresters, a testing method originating from the DIN EN ISO 16852 standard is used, which is mainly designed for atmospheric conditions.
In order to optimize the production capabilities, numerous industrial processes are taking place at pressures, temperatures, or oxygen concentrations beyond the ambient range, i.e. at non-atmospheric conditions and information on the performance of the regulated testing method are therefore required when the standard testing protocols are modified with regard to pressure, temperature or oxidizer.
The main objective of this study is to develop an improved testing method for detonation flame arresters, which offers a higher reproducibility and moreover, an applicability under non-atmospheric conditions. Therefore, an interlaboratory comparison on the performance of in-line flame arresters for stable and unstable detonations is jointly conducted by the project partners (PTB, BAM, Braunschweiger Flammenfilter GmbH and IBExU GmbH). The experiments are performed according to the testing method regulated in the DIN EN ISO 16852 standard for different pressures before ignition and different explosion groups. The experimental data is analyzed in detail to further optimize the test method and to thus achieve an improved reproducibility of detonation tests at high pressures, especially regarding the deflagration to detonation transition.
Potential ambiguities of the standardized testing method that might lead to the differing results at the different institutes are identified from the interlaboratory comparison and the test method is modified accordingly. Based on these results, an improved testing method for detonation flame arresters will be developed, which will ensure a greater safety at process plants while handling combustibles.
The evaluation of thermal properties is probably an underrated tool for the onsite health monitoring of concrete structures. The photothermal approach offers a possibility to realize a real onsite measurement. This contribution presents the application of the photothermal approach under lab conditions on three different concrete types. The obtained results were compared with those of a commercial device based on the Transient Plane Source (TPS) method. Both agreed well within the estimated uncertainty ranges and therefore demonstrate the applicability of the photothermal method for this kind of investigations. First results of a concrete sample with different water contents support the potential of this method for the characterization of concrete in general.
The poor thermal conductivity of MH beds limits hydrogen absorption in metal hydride (MH) reactors for thermochemical heat storage. The compaction of MH powder with expanded natural graphite (ENG) is an efficient and cost-effective approach for the heat transfer enhancement of MH beds. However, the addition of ENG reduces the hydrogen storage density of the compacted composites. How to optimize the allocation of a limited amount of ENG in the MH bed has not been studied. In this study, a multilayer MH bed configuration with an ENG grade content was adopted to improve the heat transfer performance of an MH reactor for thermochemical heat storage. The effect of the ENG content gradient on the performance of the MH reactor was investigated using a mathematical model of the MH reactor. Furthermore, an optimization method based on the entransy dissipation extremum principle (EDEP) was proposed to optimize the ENG distribution in magnesium hydride (MgH2)-ENG compacts. The results showed that a larger ENG content gradient resulted in faster hydrogen absorption and better heat-discharge performance. Compared with a configuration with a uniform ENG content, the optimized configuration based on the EDEP exhibited a shorter reaction time, more uniform bed temperature distribution, and 15.33% higher gravimetric exergy-output rate. In addition, the number of optimization iterations had little effect on the optimal results, which could be obtained by implementing only one optimization iteration. The optimization results showed that more ENG should be allocated to the internal layer of the MgH2-ENG compact. The compacts were divided into three layers, and the ENG content of each layer was calculated according to the optimized configuration based on the EDEP. The optimization method proposed in this study can be applied to optimize
MIKE III apparatus tests were conducted to investigate the minimum ignition energy (MIE) of coal dusts in air and O2/CO2 atmospheres with and without small amount of CH4/H2. The O2 mole fraction (XO2) in the gas mixtures varied from 21% to 50% with the CH4/H2 mole fraction from 0 to 2%. Experimental result showed that MIE of coal dusts significantly decreases even by three orders of magnitude in mJ with increasing XO2 and the addition of CH4/H2. Compared with CH4, H2 had a relatively strong promotion effect on the spark ignition of coal dusts. The inhibiting effect of CO2 was found to be much stronger than N2, but this inhibiting effect of CO2 could be eliminated by 9% increment of XO2. The effect on MIE of coal dusts thus followed by the order: 9% increment of XO2 > CO2 replacing N2 > 2% CH4 or H2 addition. Moreover, two empirical models were used to estimate the MIE of hybrid dust-gas mixture (HMIE), and the results showed that calculated data can well reflect the promoting effect of elevated XO2 and flammable gas addition, and the inhibiting effect of inert gas
Im Projekt InnoBOSK wurden insgesamt vier wissenschaftlich basierte Bedarfserhebungsworkshops durchgeführt. Die Workshops hatten jeweils thematische Schwerpunkte und wurden mit Vertretern unterschiedlicher BOS (Behörden und Organisationen mit Sicherheitsaufgaben) durchgeführt.
In der vorliegenden Arbeit werden die erhobenen Bedarfe ausgewertet.