Not to forget: The high quality of Speakers as well as the wide range of Delegates from different Countries and all kinds of Industries lead to a perfect platform for Networking and Exchange of Ideas and Experiences.
Not to forget: The high quality of Speakers as well as the wide range of Delegates from different Countries and all kinds of Industries lead to a perfect platform for Networking and Exchange of Ideas and Experiences.
Mr. Price talks about the following:
A significant number of power generation projects adopting co-firing with Biomass are on the increase with schemes often requiring very large storage areas, often with silo’s | storage capacities in excess of 10,000 m³ and in some cases exceeding 100,000 m³. International standards for explosion relief design (NFPA, EN, VDI) have largely been developed for conventional bulk material handling silo volumes of less than 10,000 m³ with empirical calculations being used to determine the suitable vent areas in m² required to achieve explosion protection in the event of an internal incipient explosion.
Such methods are often not suitable for these massive bulk Biomass stores and if used would impose excessive very conservative explosion protection requirements with significant economic penalties. Using a probabilistic approach analysis of potential dust cloud dispersion within the storage volume assisted by modelling using validated dust explosion CFD codes provides a more realistic design approach to establish a suitable basis of safety using significantly less explosion relief area whilst still demonstrating ALARP. The paper demonstrates how validated CFD can be an effective tool to assist value engineering for an example study in which vent relief design calculations are performed both empirically and using the proposed probabilistic approach assisted with CFD modelling to protect a silo in excess of 100,000m³ for a typical Biomass dust explosion risk. Other examples of where CFD for modelling dust explosions to develop a realistic protection concept that demonstrates ALARP are also presented.
Prevention and mitigation measures are based on the knowledge of flammability (Minimum Ignition Energy, MIE; Minimum Ignition Temperature, MIT; Minimum Explosible Concentration, MEC; Limiting Oxygen Concentration, LOC) and explosion (Maximum Explosion Pressure, PMAX; Deflagration Index, KSt) parameters for dust/air and/or dust-gas/air mixtures. Experimental measurements of PMAX, KSt and MEC are performed in spherical vessels (20 L sphere and/or 1 m³ sphere, (ASTM E 1226 protocol, ASTM, 2003). A well-established procedure is followed that is based on injecting the dust in the vessel, initially pre-evacuated at 0.4 bar, through a valve connecting a container loaded with dust and pressurized with 21.0 bar of compressed air. At the bottom side of the sphere, a rebound nozzle is placed to allow dispersion of the dust/air mixture inside the vessel. In order to ensure accuracy in measurement, pre-ignition turbulence and uniform dust concentration should be guaranteed. Valeria Di Sarli, Paola Russo, Roberto Sanchirico and Almerinda Di Benedetto have developed a three-dimensional CFD model to describe the turbulent flow field induced by dust feeding and dispersion within the 20 L explosion vessel and the associated effects on the distribution of dust concentration. The developed CFD model was validated against measurements of time histories of pressure and root mean square velocity available in the literature (such as Pu YK, Jarosinski J, Johnson VG, Kauffman CW. The Combustion Institute. 1990: 843-849; van der Wel PGJ, van Veen JPW, Lemkowitz SM, Scarlett B, van Wingerden, CJM., Powder Technology. 1992; 71: 207-215; Dahoe AE, Cant RS, Scarlett B. Flow, Turbulence and Combustion. 2001; 67: 159-184; Hauert F, Vogl A, Radandt S.; In Proceedings of the 6th International Colloquium on Dust Explosions, Shenyang, PRC. 1994.). Simulation results show the presence of multiple turbulent vortex structures which generate dead volumes for the dust. The dust concentration has been also evaluated at different dust nominal concentration and size.
CEN bodies produced a significant number of standards explaining how safety devices should be tested so as to be EN certified. However, if the real applications are considered from the physical point of view, it appears sometimes that the prescription of the tests are far from the real situation or that the experimental conditions would not permit to tackle the most dangerous situation. A discussion is proposed and a vision is proposed to try and surpass these limitations.
Dr. Johannes Lottermann is Senior Consultant Explosion Protection in a leading position at REMBE®. Based in Germany most of the time you won´t find him there as he serves his customers in large scale projects all around the globe. He is member of several technical committees such as the VDI, VDSI and governmental expert groups. REMBE® is founding member of IND EX®. How do you protect an explosion prone dust collector? Based on the zoning you´ll choose the appropriate (electrical and mechanical) equipment of each category and mount it. With regard to your ignition hazard analysis you will then put explosion vents or suppression on the dust collector as external ignition sources from upstream units might not be safely prevented. With all respect: Isn´t it over-engineering to apply both: Fully comprehensive prevention on an already protected filter as the cause for an explosion is highly likely the external spark or hot particle and not a non-explosion-proof rotary valve or level sensor? The lecture of Dr. Lottermann will lead through this controversial discussion and enable you to really understand the ATEX-requirements – your benefit will be cost savings in your daily business acting still absolutely in compliance with the explosion safety related rulebooks.
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