The document summarizes the technology of storing liquefied petroleum gas (LPG) in underground caverns below sea level. Mined caverns are created using mining techniques in hard rock selected based on geological criteria. LPG is contained in the caverns using the hydraulic containment principle where the water pressure in the surrounding rock is higher than the gas pressure, preventing leakage. Key components of the caverns include access shafts, a water curtain gallery surrounding the storage area, and safety systems like gas detection, firefighting, and corrosion monitoring to ensure safe operation. Underground storage has advantages over above-ground storage like greater safety, less environmental impact, and lower land usage.

1. SUB - SEA LEVEL UNDER WATER
LPG CAVERNS
V.SRIJANA
B.A.SREYA MANJU
M.ANUSHA
DEPARTMENT OF CHEMICAL ENGINEERING
ANDHRA UNIVERSITY COLLEGE OF ENGINEERING (A)

2. INTRODUCTION
The technology of storing LPG (liquefied petroleum gas) in a
subsea level, under water cavern is much safer method as
compared to above-ground methods like pressurized sphere or
refrigerating tanks method. These caverns are extremely safe
from wars , sabotages, terrorist attacks and natural calamities
like storms, earth quakes etc., and are also leak proof .This
cavern is environment friendly and occupies a very little surface
area.
The technique involved in underwater LPG caverns is
“mined cavern”.

3. MINED CAVERN
• A typical mined cavern consists of one or more galleries excavated in
rock.
• Rock must be hard enough for the cavern to be stable, so the sites
are selected essentially based on geological criteria.
• This cavern is created in the rock using mining techniques.

4. HYDRAULIC CONTAINMENT PRINCIPLE
• In a simplified way, the principle is that for the cavern to be
leak tight (meaning to ensure containment of the stored
product), the pressure in the cavern (due to the product
stored) has to be lower at any point of the cavern wall than
the pressure of water in rock mass at the corresponding
point.
• the caverns are located at such a depth that the water
naturally present in the surrounding rock creates a counter
pressure higher than the pressure of the stored product,
preventing it from migrating.
• Typical cavern depths vary from 70 to 200 m.
The underground storage of liquid and gaseous hydrocarbons is based on
the principle of natural hydraulic containment.

5. Two other factors should be added to the Product Vapour
Pressure i.e., Safety Factor and Shape Factor when determining
the maximum possible pressure in the Cavern.
 SAFETY FACTOR
It is the extra pressure needed depending on the cavern
dimension, cavern shape and storage arrangements etc.
 SHAPE FACTOR
It refers to a designed safety margin.

6. HYDRAULIC CONTAINMENT PRINCIPLE

7. FUNCTIONING takes place in following steps:
1.Injecting gas through gas – inlet into the cavern
2. Allowing free flow of water into the vessel
3.Compressing the gas in the vessel
4. Hydraulic sealing of cavern by water curtain
5.Clearing of seepage water
6. Water flooding will isolate the LPG safely in emergency
7. Principle of containment to avoid leakage or
contamination.
8. In depth storage of LPG is fully isolated.

8. PROCESS FLOW DIAGRAM OF A TYPICAL LPG
CAVERN

9. CAVERN OPERATIONS consists of :
• Cavern filling
• Cavern unloading
• Seepage water treatment
CAVERN FILLING:
Generally LPG would be unloaded at a combined flow rate
ranging from 500 m3 to 2,000 m3. the product temperature
would be –45oC for propane and –5oC for butane.

10. CAVERN UNLOADING:
Cavern unloading would be done through an ejector, which
allows for sucking and condensing the gas taken from the
cavern. This process overcomes any pressure build up in the
cavern when unloading at full flow . The outlet temperature at
the exit of the ejector would be approximately 30C to 70C.
SEEPAGE WATER TREATMENT:
Water is expected to seep continuously from the rock mass into
the cavern. This is a requirement to ensure hydraulic
containment of the storage. The water, therefore, needs to be
removed from the cavern on a regular basis. Water pumped out
of the Cavern would be stripped off any hydrocarbons through
the use of a counter current packed column, which would use
air for stripping.

11. Isometric view of the cavern

12. The general components of the CAVERN are
described below :
• Operating Shaft:
The shaft is designed for access to the cavern and house the
steel supporting structures and most of the casings and tubings
for operating the underground storage.
• Access Shaft:
The shaft is used during construction for access to the cavern.
Once excavated, it was equipped to enable muck hoisting and
personnel and equipment transportation to underground.
Ventilation ducts and utilities necessary for cavern construction
will pass through this shaft. After completion of the underground
construction, steel support structures and two casings, one for
receipt of LPG and one for level measurement were installed in
this shaft.

13. ACCESS SHAFT:

14. • Water Curtain:
The water curtain consists of a gallery and Horizontal
boreholes should be drilled from the water curtain gallery at
specific intervals. During construction, these boreholes are
connected to a water feeding line and during operation they
are left open and in connection with the water-filled water
curtain gallery.

15. WATER CURTAIN GALLERY

16. • Storage Cavern:
The Cavern consists Horizontal columns with intermediate
connections shaped as such that the layout ensures proper
mixing of the LPG in the Cavern.
Cavern under construction:

17. Concrete Plugs:
The Cavern is isolated from the surface by two plugs, one in the
operation shaft and the other in the access shaft. This concrete plug
will be topped by a clay plug.

18. SAFTEY PROVISIONS
Gas Detection :
LPG leakage during operations such
as filling, emptying, and ship loading /
unloading will be monitored. Gas
detectors should be permanently
installed to monitor the presence of
LPG vapours at various critical locations
throughout the plant. The detectors
should be connected to a monitoring
unit, which dispatches information to
the control system and ESD system.

19. Fire fighting / detection:
The fire fighting / detection equipment should be capable of:
• providing water to spraying system for pressure vessels cooling.
• diluting LPG clouds with water curtains or sprinklers.
• filling the Cavern sump.
• The fire network should be supplied with water from dedicated
fire water tanks and diesel engine driven fire pumps.
• fighting a fire in the electrical room or control room, detecting
fire through melting fuses at different points around surface
facilities.

20.  Vent system:
This will comprise of a knock out drum and a vent stack. Outlet
from various points in the Cavern & the various above ground
facilities will be routed to the Knock out drum and then to a vent
stack for safely venting the gases.
Corrosion Control and Monitoring:
As storage caverns are connected to the aboveground facilities
by vertical casings, their corrosion control is a fundamental
safety issue. Cathodic protection system includes protection of:

21. • seepage water pumps, internal surface of casings and external
surface of tubing are protected by sacrificial anodes.
• buried pipelines are protected by impressed current.
• seawater pumps and associated equipment by sacrificial
anodes.
Nitrogen System :
Nitrogen will be used for:
• inerting of loading arms before disconnection
• fill-line control valve command.
• Specific maintenance operations

22. Advantages of SUB-SEA LEVEL LPG
CAVERN :
• Underground storage is safe from warfare, sabotage and natural
calamities like earthquakes.
• There is no risk of leakage and hence, the threat to environment is
minimal.
• In case of leakage also no combustion takes place as there is no
direct contact with atmosphere.
• They need much less land area than surface storage facilities.
• The natural landscape and scenic beauty of the project area is not
affected as the major installations are located under ground as
compared to above ground storage facilities.
• They can be used as buffer/ strategic storage for the country.
• For large quantity storage, underground cavern storage is cheaper
as compared to above ground storage. Underground storage also
needs little maintenance.
• Underground storage has a longer life as compared to surface tanks.

23. ANY QUESTIONS……..????