(162b) Lng Vapor Dispersion Research Needs

This paper reviews atmospheric dispersion model application to LNG vapor dispersion and suggests current research needs. The ?dense gas? question has been resolved for practical application, but there is still great confusion about the differences between the positive safety benefits of natural gas ?lighter than air? behavior and the dense gas behavior of (cold) LNG vapor. Furthermore, current lumped parameter models cannot cope with complex effects of obstacles-to-the wind (or vapor) flow, but such effects can be of determining importance, as in the case of LNG spills into impoundments or diked areas. The LNG vapor rate (and concentration in admixture with air) overflowing the impoundment/dike are the proper source terms (input) to the dispersion model. Although complex three-dimensional computational fluid dynamics (CFD) models have been developed and approved (FEM3A) by the federal regulations for such uses, little or no use has been made of them to date. Perhaps most importantly, serious inconsistencies have appeared in the prescription of spill scenarios that must be considered ? the so called ?design spills?. Thus, while the methods for predicting atmospheric dispersion of LNG vapor has been vastly improved in the last three decades, current application of this technology lags far behind ? perhaps most importantly in the determination of the source terms that must be specified for the dispersion models. Common sense alone indicates that if the (LNG vapor) input term is reduced to a small value, the exclusion zone extent is consequently reduced to a small value as well. Failure to follow well defined specification of design spills and to correctly describe the source inputs from such design spills for input to dispersion models is key to meeting the requirements of the National Environmental Policy Act as well as the specific requirements of the LNG regulations.