Thermal Runaway Essay

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1. Thermal runway reactions An exothermic reaction can lead to thermal runaway, which begins when the heat produced by the reaction exceeds the heat removed. The surplus heat raises the temperature of the reaction mass, which causes the rate of reaction to increase. This in turn accelerates the rate of heat production. An approximate rule of thumb suggests that reaction rate - and hence the rate of heat generation - doubles with every 10°C rise in temperature. Thermal runaway can occur because, as the temperature increases, the rate at which heat is removed increases linearly but the rate at which heat is produced increases exponentially. Once control of the reaction is lost, temperature can rise rapidly leaving little time for correction. The reaction vessel may be at risk from over-pressurisation due to violent boiling or rapid gas generation. The elevated temperatures may initiate secondary, more hazardous runaways or decompositions. Thermal runaway reactions are characterised by progressive increases in the rate of heat generation, temperature and pressure [Nolan, 1987]. Heat generation increases exponentially with the increase in temperature and may occur due many factors, including lack of process control, lack of cooling etc. The increase in pressure may occur due to vaporisation of some of the components in the reaction mass and/or decomposition of some of the gaseous products at the elevated temperatures. Thermal runaway reactions occur when the heat generated by a reaction exceeds the heat removal caused by the available cooling capacity. Thermal runaway reactions occur in the following sequence: heat is accumulated leading to a gradual rise in the temperature of the reaction mass; this causes an increase to the rate of reaction and subsequently accelerates the rate of heat generation.
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