Dust/Gas Mixtures Explosion Regimes - Summary

Dust/Gas Mixtures Explosion Regimes – Summary

1-Sentence-Summary: Addition of methane gas to niacin dust results in increased explosion violence and can be characterized by five explosion regimes based on concentration: dust-driven explosion, gas-driven explosion, dual-fuel explosion, synergic explosion, and no explosion.

Authors: A. Garcia-Agreda, A. Di Benedetto, P. Russo, E. Salzano, and R. Sanchirico

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Dust/Gas Mixtures Explosion Regimes - Summary

The authors of this paper perform experimental explosion testing on mixtures of methane gas and niacin dust (also named nicotinic acid or vitamin B3). The dust concentrations range from 30 to 250 g/m3 and the gas concentrations from 1 to 10% by volume. The dust particle size is characterized as having a percentile mean diameter of 32 µm, surface weighted mean diameter of 14.4 µm, and a volume weighted mean diameter of 41.4 µm.

The explosion tests are completed in a 20-L chamber with a weak spark ignition. The testing equipment is modified to remove the spark delay so the mixture is ignited directly after the dust is dispersed into the chamber.

In the article the authors give maximum pressure and maximum rate of pressure rise as a function of dust and gas concentration. Maximum pressure results are compared with CEA equilibrium calculations. A final explosion regime diagram is given based on maximum rate of pressure rise of the hybrid mixtures and is divided into five explosion regimes.

Three of the main findings from this paper are:

  1. Hybrid mixtures explode more violently than either component at the same concentration, but not as violently as the gas at its stoichiometric concentration
  2. Hybrid explosions can be divided into five explosion regimes depending on the flammability criteria of the two fuels individually
  3. The flammability of niacin/methane mixtures agrees with Le Chatelier’s Law as the flame temperatures of the fuel are similar

The following sections outline the main findings in more detail. The interested reader is encouraged to view the complete article at the link provided below.

Finding #1: Hybrid mixtures below the stochiometric gas concentration explode more violently than the fuels individually

In general the addition of methane gas to niacin dust increased maximum pressure and rate of pressure rise. The increase in maximum pressure ranged from 1.2 times to 1.5 times depending on the initial dust concentration. The increase in maximum rate of pressure rise ranged from 3 to 6 times when the dust was above its minimal explosible concentration alone.

The effects of the methane gas were even more prominent at lower dust concentrations. At the minimal explosive concentration the maximum rate of pressure rise increased from 20 to 470 bar-m/s with the addition of 6% methane gas (its lower flammability limit). Non-explosible concentrations of dust were also made explosible from the addition of methane below its flammability limit.

Finding #2: Hybrid explosions can be divided into five categories based on the fuel concentrations

The authors demonstrate that maximum pressure and maximum rate of pressure rise behave differently depending on the concentrations of the two fuels. In their work they give the maximum rate of pressure rise on a 2D plot with the dust and gas concentration as the two axes. They then divide the dust/gas plane into five different explosion regimes:

  1. Dust-driven explosion – above the dust MEC and below the gas LFL
  2. Gas-driven explosion – above the gas LFL and below the dust MEC
  3. Dual-fuel explosion – above the dust MEC and the gas LFL
  4. Syngeric explosion – below the dust MEC and gas LFL but still explosible
  5. No explosion – mixtures which do not explode in the experimental test

The authors suggest that hybrid explosion effects are largest in the synergic regime where either fuel cannot expload without the other. Along the dust MEC and gas LFL pressure rise rate enhancement effects are also very large. In the dust-driven regime the effect of gas addition is smaller and decreases with increasing dust concentration. In the gas-driven regime the dust acts as both a heat sink and a fuel source but still leads to increase pressure rise. Both fuels are expected to contribute in the dual-fuel regime although it is not explored extensively in this work. The mixtures resulting in the worst case scenarios appear to be along a stochiometric line drawn on the dust/gas plane.

Finding #3: Explosion limits of methane/niacin mixtures agree with Le Chatelier’s Law

The last main finding in this work is that the hybrid mixtures appear to agree with Le Chatelier’s Law of linear mixing. Other studies have presented differing findings in this regard depending on the mixtures tested. Future posts will focus on the flammability limits of hybrid mixtures more thoroughly but the interested reader is encouraged to see the articles from Landman, 1995, Amyotte et al., 1993, Sanchirico et al., 2011, Jiang, et al., 2014, and Jiang, et al., 2015. The current authors suggest that niacin and methane have similar flame temperatures and that this is why Le Chatelier’s Law applies for these experiments.

My Personal Take-Aways From
“Dust/Gas Mixtures Explosion Regimes”

This paper gives some very good data for hybrid mixtures and demonstrates a useful technical for categorizing hybrid explosions. Use of combustion or explosion regime diagrams has been successful elsewhere in the literature (e.g., see my post on turbulent flame structures or Chapters 5 and 6 in Kuo, 2012) and it is encouraging to see this approach evolving for hybrid mixtures.

Like other articles in this field the dust used in this paper is relevant to the pharmaceutical industries. See the pharmaceutical tag for an up-to-date list paper summaries. The current authors have also developed theoretical models of dust combustion and explosion which have been applied to hybrid mixtures (e.g., See Russo et al., 2012). Later studies have also extended to the concept of explosion regime diagrams to other mixtures (See Sanchirico et al., 2011)

Full Citation:

  • A. Garcia-Agreda, A. Di Benedetto, P. Russo, E. Salzano, and R. Sanchirico, “Dust/gas mixtures explosion regimes,” Powder technology, vol. 205, pp. 81-86, 2011.
    [Bibtex]
    @ARTICLE{Garcia-Agreda2011,
    title={Dust/gas mixtures explosion regimes},
    author={Garcia-Agreda, A. and Di Benedetto, A. and Russo, P. and Salzano, E. and Sanchirico, R.},
    journal={Powder Technology},
    volume={205},
    pages={81--86},
    year={2011},
    link={http://www.sciencedirect.com/science/article/pii/S0032591010004705},
    summary={http://www.mydustexplosionresearch.com/dust-gas-mixtures-explosion-regimes-summary},
    }

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