An Experimental Study on the Influence of the Particle Size of Chemically Active Inhibitors in Turbulent Combustion
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Accidental gas leaks pose a great danger in the process industries. To reduce the consequences, should such a gas leak ignite, mitigating measures are needed. One such measure, involving the introduction of water deluge upon confirmed gas detection, has been successfully applied on larger offshore production platforms. The use of water deluge is a promising effort, but due to the large amounts of water needed, it is ill-suited for inland facilities. A possible alternative, involving chemically active inhibitors, has been investigated by Total Petrochemicals and GexCon AS in the recent years. The concept is to use pressurized containers to release chemically active inhibitors into a detected gas leak. Since combustion consists of chain-reactions involving radicals it is possible to slow the combustion, or even quench it, by using inhibitors that react with those same radicals. To verify the potential of this concept, laboratory and large-scale experiments were conducted at GexCon AS. A wide variety of potential inhibitors were tested on a variety of combustible hydrocarbon-air mixtures. It was found that potassium carbonate had the highest general effect. When added at concentrations of up to 50g/m3, it led to a drastic reduction of the laminar burning velocity for most of the combustible mixtures tested. At higher inhibitor concentrations, the added effect varied depending on the type of fuel and the equivalence ratio tested. There was however, no investigation into the possible effect of the inhibitor particle size. Due to the larger surface area to mass ratio, and the increased rate of particle decomposition as it is exposed to heat, smaller particles should be more efficient at inhibiting combustion. This tendency has been seen in experiments involving laminar combustion, but has yet to be confirmed for turbulent combustion. The aim of this thesis is therefore to investigate the influence of particle size in the chemically active inhibitor, potassium carbonate. Three parameters commonly used to describe the violence of explosions are examined using a 20 liter USBM vessel. The particle size, concentration of inhibitor, and equivalence ratio of the combustible mixture are varied. The parameters examined are the maximum pressure, the maximum rate of pressure rise and the calculated laminar burning velocity, of the explosion. The research was conducted at the laboratories of the University of Bergen and at GexCon AS. Funding for the project was provided by the University of Bergen, GexCon AS and Total Petrochemicals. The overall conclusion from the conducted experiments is that the particle size of the chemically active inhibitor, potassium carbonate, influences its ability to function as an inhibitor in turbulent combustion. It was also discovered that the grinding effect caused, as the potassium carbonate is dispersed from the reservoir in the 20 liter USBM vessel, is concentration dependent. Neither observation has been found in other scientific literature.