In my third LNG project, I had a chance to meet two different LNG storage tank vendors. One vendor produce vacuum insulated storage tank (pressurized type) and the other one produce flat bottom storage tank (atmospheric type).
During the meeting I got several terms of LNG flat bottom storage tank types, such as single containment tank, double containment tank, and full containment tank. What was that?
In this post I want to share you different types of LNG flat bottom storage tank and its special features.
Single Containment Tank
Typical feature of single containment storage tank is primary liquid containment open-top inner tank, a carbon steel primary vapor containing outer tank, and earthen dike for secondary containment.
Peru LNG selected single containment flat bottom tank due to site remoteness and enough space is available to provide secondary containment thus comply with regulations and represented safe design of installation.
Double Containment Tank
Double containment tanks are similar to single containment tanks except that outer tank is capable of containing liquid spill in the event of a breach in the inner tank wall. The tank design has a freestanding 9% nickel inner tank an outer tank made of either prestressed concrete or reinforced concrete. Type of LNG storage tanks in Arun, Indonesia, is double containment tank.
The outer concrete wall increases the cost of the tank, but less space is required because no need for containment dike. If the inner tank fail, the liquid will be contained and vapor will escape through the annular gap which is the space between the two tanks or tanks and the concrete wall.
Full Containment Tank
Full containment tank is double containment tank in which the annular gap between outer and inner tank is sealed. Typical feature of full containment tank is primary liquid containment open-top inner tank and a concrete outer tank. The outer tank provides primary vapor containment and secondary liquid containment. In the event of leak, the outer tank contains the liquid and provides controlled release of the vapor. Majority of LNG storage tanks built in the last 10 years worldwide have been designed as full containment tanks.
In-Ground Storage Tank
The advantages of in-ground storage tanks is required less space area and reduced seismic loading but are very expensive and required longer time to build – about 4 to 5 years compared to 3 years for a tank built above ground.