Superheated liquids, hazards

So far the emphasis has been on substituting hazardous materials or using less, i.e., intensification. Let us now consider use of hazardous materials under less hazardous conditions, i.e. at less extreme temperatures or pressures or as a vapor rather than superheated liquid or diluted, in other words, attenuation. ... 

R = 8.3145 kJ-K 1-kmol 1 and T is the reactor temperature (K). T is also the supply temperature of A whose yet unknown inventory mA is in the form of a superheated liquid. The total amount of B to be produced is 1000 kmol. T and mA are to be selected with the additional consideration of safety. The normal boiling point of A is 70°C, its latent heat of vaporization is 25,000 kJ-kmol-1, the liquid specific heat capacity is 140 kJ-kmol K 1, and its heat of combustion is 2.5 x 106 k.bkrnol. The residence time of the reactor is 1 min, and the safety is measured in terms of fire and explosion hazards on the basis of the theoretical combustion energy resulting form catastrophic failure of the equipment. 

Johnson, D. W. 1991. Prediction of Aerosol Formation from the Release of Pressurized, Superheated Liquids to the Atmosphere, in Proceedings of International Conference and Workshop on Modeling and Mitigating the Consequences of Accidental Releases of Hazardous Materials, New Orleans, May 20-24, American Institute of Chemical Engineers, New York, pp. 1-34. 

If for any reason, the BOR falls below the total heat in-leak, the thermal energy flow into and out of the liquid is not balanced and the surplus energy flow is stored in the liquid as superheat or thermal overfill. This surplus energy remains in the liquid and builds up with time. It can only be released by evaporation of some of the now superheated liquid via one of the unstable evaporation phenomena described below. These uncontrolled evaporation phenomena constitute a hazard which increases with time, and with the scale of the storage container and with the volume of liquid being stored. 

A Boiling Liquid Expanding Vapour Explosion, or BLEVE, is an industrial event related to the laboratory bump occasioned when the inadequately mixed bottom of a vessel of liquid becomes superheated, then explosively boils. In the industrial version, rupture of a pressurised container is usually involved. Although strictly speaking a non-reactive physical hazard, chemical fires and explosions, with fatalities, often follow. Means of estimating risk and prevention, with a fist of incidents are given[l], A more ferocious version, the Boiling Liquid Compressed Bubble... 

Pitch. Pitch used to be stored in solid form at the tar distillery in open bays, from which it was removed by small explosive charges. Loading of the lump pitch by mechanical shovel created a dust hazard both at the tar installation and at the customers, where the lumps had to be ground before use. In the 1990s, pitch is stored in tanks heated by superheated steam or circulating hot-oil coils and transported in liquid form in insulated rail, road tankers, or ships. When transport as a hot liquid is not feasible, not acceptable by the customer, or for small amounts, the pitch is converted into a dust-free particulate form, ie, short rods termed pencils, pastilles, or flakes. 

Casal, J., and Salla, J. (2006) Using liquid superheating for a quick estimation of overpressure in BLEVEs and similar explosions, Journal of Hazardous Materials A137, 1321-1327. 

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