Explosion protection with metal dust fuels

Abstract

Metal dust eqlosions have unique deflagration characteristics in comparison to organic fuels, and that can make them more difJi'cult to control. neflame temperature of some metals dusts can exceed 3,500" K, more than 1,000" K higher than an organic,flame. This can result in high explosionpressures, Pmax Also, thepressure rate of rise, K as well as the flame speed, can greatly exceed that found wzth organic fuels. All of these contribute to making explosion protection more difficult.Successful explosion protection lies in the speed of the system as well as its effectiveness. Detection and activation processes, as well as the mechanical response of the components, determine the overall speed. The effectiveness, for example, of suppression lies in the ability of the agent to stop the flame from propagating.?his paper reviews the potential effectiveness of explosion protection techniques (containment, suppression, venting and isolation) in metal dust explosions, and the limits associated with each technique. Experimental results will show that metal dust explosions can be controlled when the explosion protection techniques are properly applied. ma?

Dust explosions–Cases, causes, consequences, and control

“…Attempts to develop inertant dusts which can go on with the main material through the process have been made; for example Mintz et al [131] have patented a system which uses finely powdered refractories like MgO to completely inert highly explosible dusts such as a 50:50 Al-Mg alloy. [132] Metal dusts suspended in air during operations like grinding pose explosion hazard which can be mitigated by the use of wet grinding or the collection of the grinded dust by a wet medium. In the manufacturing of metal powders such as aluminum or magnesium, the process of inerting technique may be employed to reduce the oxygen concentration present at the process site.…”

A Review of the Fire and Explosion Hazards of Particulates

“…Since chemical reaction rates tend to increase exponentially with increasing temperature, substances with high adiabatic flame temperatures also tend to have higher laminar burning velocities and flame speeds, and thus higher rates of pressure increase, (dP/dt) max . Finely divided reactive metals such as aluminum and magnesium have particularly high heats of combustion, thus high adiabatic flame temperatures (up to nearly 3600 K 20) ), and thus high maximum explosion pressures (typically around 12 bara) and high K St values (well above 300 bar m/s).…”

Suppression of metal dust deflagrations

“…K St values found for these two dusts were quite different. K St (and P max to a lesser extent) (Going and Snoeys, 2002). also varied drastically between the 20L sphere tests and the 1 m 3 vessel tests (Table 5), by more than a factor 2.…”

“…This paper provides an overview of past (Going and Snoeys, 2002) and more recent (Taveau et al, 2013) suppression tests with metal dusts. Parameters such as explosibility characteristics (K St , P max ), dust concentration, vessel volume, suppressant type/ concentration, number and size of containers, and detector activation pressure were varied to determine their influence on suppression effectiveness.…”