The effect of varying ambient temperature on the boil-off gas rates during the isobaric storage of liquid ammonia

Abstract

A new transient 1-D model for the evaporation of liquid ammonia in a vertically orientated cylindrical storage tank exposed to variable ambient temperature has been developed. It considers radial heat transfer in the tank walls and vertical heat transfer from the superheated vapour towards the liquid. As a result of ambient temperature oscillations, daily boil-off gas rates vary, in a large-scale ammonia tank, up to 33.7% for the scenarios studied. The model elucidates the presence of two non-periodic transient periods: (i) a short period for the tank thermal conditioning and (ii) a more extended period for the onset of periodic liquid heat flux. The duration of each period is a strong function of the thermophysical properties and thickness of the composite wall. The model has been implemented in an open-source software optimised for the evaporation of refrigerated liquids, which allows for the simulation of many days of storage in less than a minute. This efficient and publicly available implementation facilitates the usage of the model to optimise the design and operation of refrigerated ammonia storage tanks.