Vapor Recovery Units for Petrols in Germany – Process Technology from the Point of View of Explosion Protection

It is a requirement of environmental protection that the vapor/air mixtures formed during the storage, transport and refilling of petrols be collected and that the vapor contained in these mixtures be recovered. By vapor balancing within the distribution chain, the vapor/air mixtures are returned to the distribution depots where they are intermediately stored in vapor tanks, if need be, and processed in vapor recovery and exhaust air cleaning units. The more comprehensive the technical measures of discharging, conveying or processing the vapor/air mixtures of flammable liquids, the greater the problems of explosion protection. In this contribution, petrol will serve as an example to present and elucidate the explosion protection measures to be taken in exhaust air cleaning or vapor recovery units.     

Ethanol-containing automotive fuels – a safety concept for petrol stations in Germany

Due to the promotion of renewable energy sources, the demand for ethanol/automotive fuels has increased, whereby the ethanol is produced from biomass. As these fuels are flammable liquids, explosion protection concepts are needed for their transport, use and storage and for the operation of petrol stations. Safety characteristics are the basis of such concepts. Since the data for ethanol, on the one hand, and for automotive petrol, on the other hand, differ considerably, the relevant data for the ethanol/automotive petrol mixtures have to be determined and the existing explosion protection concepts will possibly have to be limited or modified. For this reason the correlations between the necessary safety characteristics – flashpoint, boiling point, auto-ignition temperature, maximum experimental safe gap, upper explosion point – and the mixing ratio of ethanol and automotive fuel have been investigated. Based on the results of this investigations, those concentration limits are elaborated for which the existing safety concepts remain valid. For mixtures with an ethanol content going beyond such limits, suitable safety measures and requirements regarding explosion-protected equipment are derived. The changes that are necessary with respect to the safety concept of petrol stations when ethanol/automotive petrol mixtures are offered instead of or in addition to pure petrol are explained.     

Heat transfer to liquids and suspensions in agitated narrow vessels

The knowledge of the heat transfer coefficient on the inner side of a heated vessel wall is of the utmost importance for the design of agitated vessels. In the case of large Reynolds numbers, the heat transfer is mainly determined by these numbers whereas, with small Reynolds numbers, the heat transfer is better described by considering the Grashof number. Investigations of heat transfer in agitated narrow vessels have shown that the height/diameter ratio exerts virtually no influence on the heat transfer when multi-impeller stirrers are used. The heat transfer to stirred suspensions can be described by relationships valid for liquids if the characteristic data of the liquid are replaced by those of the suspension and when the solids volume concentration is also taken into account. This relationship allows the heat transfer coefficient to be calculated for given solids volume concentrations of up to 60%.