Thermal Runaway Chemical Reaction Hazards

Fig ure 12-5. A typioal ourve of heat rate versus temperature. 

The fraction of heat required to heat up the vessel, rather than its contents, depends on the heat capacity of the vessel (i.e., how much 

Wrong kinetic assumption. Too high feed rate. 

Too low temperature. Incorrect initiation. Insufficient mixing. Impurities (inhibitors). 

Low heat transfer capacity. Too much thermal insulation. 

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Barton, J. A. and Nolan, P. F. Incidents in the Chemical Industry due to Thermal-runaway Chemical Reactions, Hazards X Process... 

Mix, K. K., "The Use of Advanced DTA Methods for the Evaluation of Thermal Instability, Hazard Evaluation, and Process Design," in Proceedings Runaway Chemical Reaction Hazards Symposium, IBC, London, England (1987). 

Historical perspective An analysis of thermal runaways in the United Kingdom (Barton and Nolan, Incidents in the Chemical Industry due to Thermal Bunaway Chemical Reactions, Hazards X Process Safety in Fine and Specialty Chemical Plants, IChem 115 3-18) indicated that such incidents occur because of the following general causes ... 

Controlling legionella m nursing and residential care homes Chemical reaction hazards and the risk of thermal runaway... 

Chemical Reaction Hazards and the Risk of Thermal Runaway HSE Reviewed only... 

Chemical reaction hazards are associated with thermal runaway, which begins when the heat generated by a reaction exceeds the heat which can be removed to the surroundings. The surplus heat increases the temperature of the reaction mass, which causes the reaction rate to increase and in turn accelerates the rate of heat production. Thermal runaway occurs because, as the temperature rises, the rate of heat loss to the surroundings increases linearly with temperature, but the rate of reaction — and so the rate of heat generation — increases exponentially. Therefore, thermal runaway can start slowly but then accelerate, until eventually it can lead to an explosion. 

Health and Safety Executive, United Kingdom. Chemical Reaction Hazards and the Risk of Thermal Runaway available at http //www.hse.gov.uk/pubns/indg254.htm (accessed March 19, 2009). 

Safety. The MR is much safer than the MASR. (1) The reaction zone contains a much smaller amount of the reaction mixture (hazardous material), which always enhances process safety. (2) In case of pump failure, the reaction automatically stops since the liquid falls down from the reaction zone. (3) There is no need to filter the monolithic catalyst after the reaction has been completed. Filtration of the fine catalysts particles used in slurry reactors is a troublesome and time-consuming operation. Moreover, metallic catalysts used in fine chemicals manufacture are pyrophoric, which makes this operation risky. In a slurry reactor there is a risk of thermal runaways. (4) If the cooling capacity is insufficient (e.g. by a mechanical failure) a temperature increase can lead to an increase in reaction, and thus heat generation rate. 

Chemical reactivity has many different names, such as reactive materials, runaway reaction hazards, instability, thermal sensitivity, and incompatibility. Flammability, toxicity, and corrosion are also forms of reactivity. Since these topics are addressed elsewhere, our focus here will be on those reactions that fall outside the normal definitions of flammable or toxic and that generally occur far more rapidly than corrosion. 

Of the 167 incidents, 36 percent are attributed to chemical incompatibility, 35 percent to runaway reactions, and 10 percent to impact or thermally sensitive materials. The hazard is unknown for 19 percent of the incidents. 

In reviewing the hazard associated with a chemical process, one of the hazards which should be considered is that of a potential runaway reaction. If either the desired chemical reaction or an undesired reaction (e.g., a side reaction or the unintended decomposition of a product) produces more heat than can be dissipated, the heat will accumulate in the system. This can lead to the thermal runaway. If the exothermic reaction(s) is accompanied by significant pressure generation, the runaway reaction can lead to rupture of the reaction vessel. 

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