[ safety ]
Fig . 1 : Design requirements for a non-combustible fire barrier around a hydrogen storage tank 4
far less volume of inert gas to be stored at the facility .
When the system is being taken offline for maintenance or decommissioning , the system should be purged with an inert gas ( e . g ., nitrogen ) after depressurization such that the final mixture in the system is non-flammable . 4 This can be done by purging the system with 5 vessel volumes of inert gas ( to reduce the hydrogen concentration to below 1 %) or by continuous purging until appropriate concentration is confirmed with the use of a hydrogen detector designed for use with an inert gas background . 7
Containment area
A gaseous hydrogen storage tank or vessel can be installed in a variety of ways , each with benefits and drawbacks . Common to an industrial setting would be an aboveground outdoor bulk storage tank . ‘ Aboveground ’ identifies the setting for fixed-installation vertical or horizontal tanks above or below grade with no backfill . ‘ Outdoor ’ defines the tank area without overhead cover . An overhead cover is permissible so long as less than 25 % of the perimeter is enclosed by walls ; this is classified as weather protection . An area with overhead cover and greater than 25 % of the perimeter enclosed by walls would qualify the containment area as ‘ indoor ’. ‘ Bulk ’ identifies the quantity of stored gaseous hydrogen being greater than 141.6 Nm 3 ( 5000 scf ). 4
" WARNING : HYDROGEN – FLAMABLE GAS – NO SMOKING – NO OPEN FLAMES ”
Requirements for indoor storage areas differ vastly and are dependent on the volume and pressure of hydrogen being stored , the nature of its use , and the size and design of the indoor structure . Details regarding indoor storage will not be covered in this article ( for details , the reader can refer to NFPA 2 and NFPA 55 ).
Fig . 2 : Bollards protecting a compressed gas storage tank from potential vehicular damage 9
14 Hydrogen Tech World | Issue 8 | February 2023