Dust and Hybrid Explosibility in a 1 Meter Cubed Spherical Chamber - Summary

Dust and Hybrid Explosibility in a 1 m3 Spherical Chamber – Summary

1-Sentence-Summary: Turbulence and ignition energy show different effects on dust, gas, and hybrid mixture explosion in the 1-m3 chamber.

Authors: K. Chatrathi

Read in: Three Minutes

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Dust and Hybrid Explosibility in a 1 Meter Cubed Spherical Chamber - Summary

The current author performs explosion testing of dust, gas, and hybrid mixtures in a spherical 1-m3 chamber. For dusts, lycopodium, cornstarch, Pittsburgh coal, and calcium stearate are tested. Propane gas and mixtures of propane gas and cornstarch are also explored. For each test maximum pressure, maximum rate of pressure rise, and initial rate of pressure rise are reported.

The turbulence level in the chamber is varied by changing the ignition delay time. Delay times of 550, 700, and 850 ms are tested. Two chemical ignitors totaling 10 kJ are used for the dust explosion tests, while the propane explosions are tested with both chemical ignitors and fuse wire ignition.

Three of the main findings from this paper are:

  1. Turbulence level has a large effect on dust and gas explosion severity
  2. Initial rate of pressure rise does not correlate to maximum rate of pressure rise for dust or hybrid explosion
  3. Hybrid explosion showed higher maximum rate of pressure rise than the fuels individually

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: Turbulence level alters dust and gas explosion severity

The effect of turbulence level was explored for dust and gas explosion. Increasing the the ignition delay from 550 to 850 ms caused a 0.5 bar decrease in maximum pressure and 40-60% decrease in maximum rate of pressure rise for dust explosion.

Turbulence was included for propane explosion by running the injection system without dust and then igniting at 550 ms delay. The turbulent flame propagation resulted in a maximum rate of pressure rise of 485 bar/s compared to 200 bar/s for quiescent conditions. The authors express a need to better characterize the turbulence level in industrial equipment and laboratory equipment alike. This will allow better comparison between practical industrial situations and experimental testing.

One last comment on explosion severity is that ignition energy did not have an impact on maximum rate of pressure rise for propane gas explosion. Tests were not completed shown in this work but the ignition energy typically increases the rate of pressure rise for dust explosion. These considerations likely have important implications for hybrid explosion results and further demonstrate a need to better characterize typically industry hazards compared to standardized testing.

Finding #2: Initial rates of pressure rise should be considered for dust or hybrid explosion protection design

The authors propose that the initial rate of pressure rise may be more important to explosion protection than the maximum. The thought process is that suppression or venting systems will terminate the explosion before the maximum is reached. At the start of the paper, the authors propose the question: “Is the initial rate of rise proportional to the maximum rate of rise?” to determine if the initial rates can be correlated to the maximum.

The experimental results show that there is a correlation between initial and maximum rate of pressure rise for gas explosion. One practical difficulty is that changes in ignition energy do not impact the maximum rate of pressure rise, but do change the initial rate. This may be due to initial over reaction or over driving caused by the strong ignitors.

The experimental results also show that the initial and maximum rates are not correlated for dust or hybrid explosion. For dust explosion initial rates change from 10 to 45 bar/s when maximum rates change from 50 to 150. However, beyond maximums of 150 bar/s the initial rates tend to stay constant around 45 bar/s. For hybrid explosion a piece wise correlation between initial and maximum rate is seen, but no comments can be made on estimating one from the other.

Finding #3: Hybrid explosions were more severe than dust and gas alone

The hybrid explosion tests were completed at a single ignition delay (550 ms) and using 10 kJ ignition energy. Similar to the work of Dufaud, 2008 and Dufaud, 2009 and “more than additive” effects were seen for the hybrid mixture. The maximum hybrid deflagration rate was 630 bar/s compared to 500 bar/s for propane and 242 bar/s for cornstarch alone.

Minimum explosible concentrations were also measured for hybrid mixtures of propane and cornstarch. In general the flammability limits agree well with the predictions of Le Chatelier’s Law. Other hybrid explosion literature have provided various competing results in this area (e.g., Pilao et al., 2006 and Sanchirico et al., 2011). Future posts will provide more in-depth review of the ignition limits of hybrid mixtures for other works (e.g., Jiang, et al. 2014 and Jiang, et al. 2015).

My Personal Take-Aways From
“Dust and Hybrid Explosibility in a 1 m3 Spherical Chamber”

This paper presents very good experimental data for dust, gas, and hybrid explosion in the 1-m3 chamber. It would be useful for anyone designing safety methodologies for these systems in industry. The comments on understanding the impact of turbulence and ignition sources in the system under analysis are also important to consider.

It is interesting that the current authors found “more than additive” effects for hybrid explosion. Previous work showing this effect (e.g., Dufaud, 2008 and Dufaud, 2009) were completed in the smaller 20-L chamber with 10 kJ ignition energy. The results from this paper suggest that these synergistic effects may be chemical in nature and not due of overdriving in the smaller chamber.

Full Citation:

  • K. Chatrathi, “Dust and hybrid explosibility in a 1 m$^{3}$ spherical chamber,” Process saftey progress, vol. 13, pp. 183-189, 1994.
    [Bibtex]
    @ARTICLE{Chatrathi1994,
    title={Dust and hybrid explosibility in a 1 m$^{3}$ spherical chamber},
    author={Chatrathi, K.},
    journal={Process Saftey Progress},
    volume={13},
    pages={183--189},
    year={1994},
    link ={http://onlinelibrary.wiley.com/doi/10.1002/prs.680130403/abstract},
    summary = {http://www.mydustexplosionresearch.com/dust-and-hybrid-explosibility-in-a-1-m3-spherical-chamber-summary},
    }

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