TABLE OF CONTENTS S. Sivaraman, Exxon Research & Engineering Co., Florham Park, N.J.
Nomographs, based on the guidelines presented in American Petroleum Institute (API) Publication No. 2519, have been constructed to estimate the average evaporation loss from internal floating-roof tanks. Loss determined from the charts can be used to evaluate the economics of seal conversion and to reconcile refinery, petrochemical plant, and storage terminal losses.
The losses represent average standing losses only. They do not cover losses associated with the movement of product into or out of the tank.
The average standing evaporation loss from an internal floating-roof tank depends on:
Vapor pressure of the product
Type and condition of roof seal
Tank diameter
Type of fixed roof support
The nomographs (Figures 1-4) can estimate evaporation loss for product true vapor pressures (TVP) ranging from 1.5 to 14 psia, the most commonly used seals for average and tight fit conditions, tank diameters ranging from 50-250 ft, welded and bolted designs, and both self-supporting and column-supported fixed roof designs. The charts are purposely limited to tank diameters 250 ft and less, because internal floating-roof tanks are generally below this diameter.
Typical values of the deck fitting loss factors presented as a function of tank diameters in the API Publication 2519 have been used in the preparation of these nomographs. In addition, for the calculations of the evaporation loss for the bolted deck design, a typical deck seam loss factor value of 0.2 has been assumed.
