Liquefied Natural Gas Tanks Without Bottom Fill

Overview

Main Objective

This project will evaluate the operation of LNG tanks without bottom fill capabilities and determine the process means that will allow such operation can be performed safely. The safety evaluation of tanks without bottom fill will be performed using Computational Fluid Dynamics tools and will be demonstrated separately for two case studies consistent with typical U.S. LNG tank installations. The scope of the project is to define requirements and safe limits of operation for LNG tanks without bottom fill.

Public Abstract

Project Description: This project will review typical design and operating conditions of flat-bottomed LNG storage tanks of different capacity and for different types of facilities, to define ranges of conditions for which top filling of the tanks can safely be performed. The project will rely upon experience and expertise from tank manufacturers, designers and plant operators to identify the process means (e.g., operating parameters, instrumentation, control systems) that can mitigate LNG stratification inside the tank and allow the safe operation of LNG tanks without bottom fill capabilities. The limits of operation for top-filled LNG tanks will then be demonstrated quantitatively by means of Computational Fluid Dynamics (CFD) modeling, by evaluating two case studies, including a large, export-scale tank (e.g., 160,000 m3) and a smaller, peakshaver-scale tank (e.g., 40,000 m3).

Anticipated Results: Identification of process means that could be used to mitigate LNG stratification inside an LNG tank, in the absence of bottom-fill capabilities, in order to satisfy the requirement in NFPA 59A. Evaluation of the operation of LNG tanks without bottom fill capabilities and determine the process means that will allow such operation can be performed safely. Define requirements and safe limits of operation for LNG tanks without bottom fill.

Potential Impact on Safety: NFPA 59A requires that all LNG tank systems be designed for both top and bottom filling unless other process means are provided to mitigate stratification. The purpose of this requirement is to provide LNG plant operators with the flexibility to introduce LNG at either location, to preserve stable stratification and minimize the potential for rollover of the LNG column inside the tank. These operation requirements will mitigate LNG stratification inside an LNG tank, in the absence of bottom-fill capabilities, in order to satisfy the requirement in NFPA 59A.