(111d) Prevention and Mitigation of Polyethylene and Hydrocarbon/Polyethylene Explosions

The objective of the current work is to gain a better understanding of the effects of dust particle size and hydrocarbon (i.e. flammable gas) admixture on the likelihood and severity of dust explosions. From a fundamental perspective, these effects are relatively well-known and have been the subject of investigation worldwide. The unique feature of the current work is an emphasis on the inherent safety principle of moderation and the concept of explosibility boundaries [1]. The practical application of this research is in the development of appropriate strategies for the prevention and mitigation of polyethylene explosions and hydrocarbon/ polyethylene hybrid mixture explosions. The industrial focus is on a commercial fluidized-bed polyethylene reactor and associated process and storage units.

The work involves both experimental and modeling approaches. The experimental work is being conducted with a Siwek 20-L explosion chamber, MIKE 3 apparatus, and BAM oven. The explosibility parameters being investigated include: (i) maximum explosion pressure, Pmax, (ii) size-normalized maximum rate of pressure rise, KSt, (iii) minimum explosible concentration, MEC, (iv) minimum ignition energy, MIE, and (v) minimum ignition temperature, MIT. The system under consideration is high-density polyethylene (HDPE) powder and hydrocarbon gas (ethylene, hexane and propane). The test matrix consists of several particle size distributions and flammable gas concentrations.

At the time of writing, testing has been completed for polyethylene and ethylene/ polyethylene mixtures. The polyethylene dust explosion results show distinct explosibility boundaries for the various explosion parameters being examined. For example, the coarser samples display limited reactivity from all perspectives; the finer dust samples, however, attain a plateau in some parameters (e.g. Pmax of ~7 bar(g) at volume mean diameters of 146, 48 and 29 µm), but not for others (e.g. increasing KSt values of 78, 104 and 137 bar?m/s for volume mean diameters of 146, 48 and 29 µm, respectively). There are clear implications of these data for industrial safety, which will be explained in the symposium paper along with a report and interpretation of all dust and hybrid mixture explosion test data.

The modeling work is being conducted with a thermo-kinetic model [2] to predict Pmax, KSt, and MEC for the HDPE and hydrocarbon/HDPE samples being investigated experimentally. Preliminary model results for the KSt parameter have shown good agreement with our currently available HDPE data. These results, and those to be determined in upcoming testing, will be discussed in the symposium paper.

1. Amyotte, P.R., Pegg, M.J. and Khan, F.I., Application of Inherent Safety Principles to Dust Explosion Prevention and Mitigation, 12th Int. Symp. on Loss Prevention and Safety Promotion in the Process Ind., IChemE Symposium Series No. 153, Edinburgh, UK (May 22-24, 2007).

2. Di Benedetto, A. and Russo, P., Thermo-kinetic Modelling of Dust Explosions, Journal of Loss Prevention in the Process Industries, 20, 303-309 (2007).