Abstrict Hydrocarbon liquid, such as propylene, is charged (dry) from manufacture
by way of a bed of desiccant into a salt (brine-containing) cavern
for wet storage, thusly regenerating the wet desiccant having been
used to dry wet hydrocarbon yielded from the cavern as product.
Claims I claim:
1. A hydrocarbon fluid storage system comprising in operable conjunction:
a cavern formed within an underground salt strata below a ground
surface, said cavern comprises a lower liquid volume of saturated
sodium chloride storage brine and an upper fluid volume of wet hydrocarbon
storage fluid,
surface fluid handling means;
conduit connecting said lower storage brine and upper storage hydrocarbon
fluid with said surface fluid handling means, of fluid transfer
means enabling transfer of brine and hydrocarbon fluid from said
surface to said cavern and from said cavern to said surface, such
that brine can be added to or withdrawn from said lower brine volume
and hydrocarbon fluids can be added to or withdrawn from said upper
hydrocarbon fluid volume, and
at least one desiccant drier means positioned at the surface in
operable association with said surface fluid handling means whereby
said wet hydrocarbon fluid upon withdrawal from said cavern passes
through said desiccant drier means and thereby becomes dry, and
dry hydrocarbon fluid intended for storage passes through said desiccant
drier prior to entering said storage cavern and thereby becomes
wet.
2. The storage system according to claim 1 wherein said desiccant
drier means comprises desiccant selected from the group consisting
of molecular sieves, silica gel, and calcium sulfate.
3. The storage system according to claim 2 wherein said desiccant
is a said molecular sieve and has a pore size of about 3 .ANG. or
4 .ANG..
4. The storage system according to claim 3 wherein said hydrocarbon
fluid is LPG.
5. The storage system according to claim 3 wherein said hydrocarbon
fluid is propylene.
6. A hydrocarbon storage facility comprising in operable relationship:
a surface,
a cavity formed in an underground salt strata and having an upper
volume and a lower volume,
connecting means between said surface and said upper volume suitable
for fluid flow,
connecting means between said surface and said lower volume suitable
for fluid flow,
a first fluid in said lower volume comprising salt brine,
a second fluid in some upper volume comprising a moisture wet hydrocarbon
fluid,
first fluid transfer means positioned at the surface and adapted
to withdraw said first fluid from said lower volume or replenish
said first fluid in said lower volume,
first fluid transfer connecting means between said first fluid
transfer means and said receiving means adapted
receiving means positioned at the surface and, adapted to receive
dry second fluid,
second fluid transfer means adapted to withdraw said wet second
fluid from said upper volume or replenish said wet second fluid
in said upper volume,
dehydrating means at said surface,
second fluid transfer connecting means between said second fluid
transfer means and said dehydrating means,
whereby said dry second fluid passes through said dehydrating means
prior to passage to said upper volume, thereby becoming wet second
fluid and returning moisture contained therein to said cavity, and
whereby said wet second fluid passes through said dehydrating means
upon withdrawal from said upper volume, thereby becoming dry second
fluid.
7. The storage system according to claim 5 wherein said dehydrating
means comprises a desiccant drier means containing desiccant selected
from the group consisting of molecular sieves, silica gel, and calcium
sulfate.
8. The storage system according to claim 7 wherein said desiccant
is a said molecular sieve having a pore size of about 3 .ANG. to
4 .ANG..
9. The storage system according to claim 8 wherein said hydrocarbon
fluid is LPG.
10. The storage system according to claim 8 wherein said hydrocarbon
fluid is propylene.
11. A method for moisturizing a relatively dry hydrocarbon fluid
entering stream prior to storage in a salt cavern storage facility,
which comprises:
(a) passing said relatively dry hydrocarbon fluid through at least
one moisture wet desiccant bed, said relatively dry hydrocarbon
fluid substantially stripping said moisture from said moisture wet
desiccant bed thereby becoming an at least partically moisture wet
hydrocarbon fluid and said moisture wet desiccant bed becoming a
relatively dry desiccant bed,
passing said now at least partially moisture wet hydrocarbon fluid
into said storage cavern;
thereafter, (b) withdrawing at least a portion of said moisture
wet hydrocarbon fluid through said now dry desiccant bed, thereby
becoming a dry exiting hydrocarbon fluid stream, and said desiccant
bed becoming a moisture wet desiccant; and
(c) continuing alterating said steps (a) and (b).
12. The method according to claim 11 wherein said desiccant bed
is selected from the group consisting of molecular sieves, silica
gel and calcium sulfate.
13. The method according to claim 12 wherein said desiccant is
said molecular sieves.
14. The method according to claim 13 wherein said hydrocarbon fluid
is LPG.
15. The method according to claim 13 wherein said hydrocarbon fluid
is propylene.
Description FIELD OF THE INVENTION
The invention pertains to methods for storage of hydrocarbons in
salt caverns. In one aspect, the invention pertains to methods to
provide a relatively dry hydrocarbon from wet storage over brine
to use purposes. In a further aspect, the invention pertains to
underground storage caverns in which a hydrocarbon fluid being stored
displaces brine upon being received into the cavern, and in turn
is displaced by brine upon removing the hydrocarbon fluid from the
storage cavern. In another aspect, the invention pertains to a cavern
with drying apparatus.
BACKGROUND OF THE INVENTION
Expanding production and uses of hydrocarbon fluids both as fuel
gases and as raw materials for various purposes create a definite
problem in providing large storage facilities for these fluids.
Sometimes long storage of some hydrocarbons, such as propylene,
is required to provide capacity for variable demands.
Salt storage caverns have provided a convenient answer, easily
handling the frequently several hundred pound per square inch storage
pressures required, and providing relatively economical large storage
capacities to provide response to seasonal peak load demands and
requirements, and corresponding storage during seasonal slack periods.
In a cavern formed in a salt strata, a pool of brine generally
occupies the lower portion of the cavern volume, and the stored
hydrocarbon fluid occupies the upper portion. Thus, the cavern always
is maintained full. An access bore is provided, relatively small
in diameter, with dual fluid passages so that fluid handling means
at the surface provide capability for brine to be pumped in or out
of the lower area of the cavern, and hydrocarbon fluid then can
be taken from the upper area. Hydrocarbon product is added to storage
by pumping into the cavern under sufficient pressure to displace
brine therein back to the surface. Displaced brine is maintained
at ground level in a brine pit or reservoir, and then is returned
to the salt cavern to replenish the brine volume as hydrocarbon
fluid is retrieved. Precautions are taken to assure that the brine
in and out is always salt-saturated to avoid enlarging the brine
cavern and/or to avoid salt dropout at the surface due to changes
in temperature.
However, with a "wet" stored hydrocarbon, other problems
exist. The hydrocarbons from pipeline or production for storage
normally is dry. It becomes wet in the cavern. Upon retrieval, it
must be re-dried. Moisture in transmission pipelines is undesirable.
Re-drying is a relatively expensive procedure requiring desiccant
beds to dry the retrieved wet hydrocarbon, periodic regeneration
with hot gases which is an energy-consuming step, and so on. However,
this is and has been the current practice.
Needed is a method and apparatus to wet store hydrocarbon fluids,
and yet retrieve the hydrocarbon fluids relatively dry, in an energy
efficient manner.
BRIEF DESCRIPTION OF THE INVENTION
I have discovered a method of and an apparatus for introducing
wet hydrocarbon to storage, and retrieving dry hydrocarbon from
storage, essentially energy free. If further drying is required,
this can be handled by the hot gas generating driers in conventional
manner, but the operation of such becomes much simpler and cheaper.
According to my method and apparatus, a desiccant drier bed is
installed such that all hydrocarbon product flows through the dessicant
drier bed whether entering or leaving the cavern storage. The normally
dry hydrocarbon product directed to storage passes through the dessicant
bed, thus in effect regenerating the bed and carrying moisture back
to the cavern, which helps maintain appropriate moisture relationship
in the cavern. Thus the entering dry product retrieves and carries
with it moisture from the desiccant bed which has been previously
removed and retained by the bed from previously stored removed hydrocarbon
product. Upon retrieval of the now wet hydrocarbon fluid, from storage,
the wet hydrocarbon then passes back through the desiccant bed in
reverse flow, and therein becomes substantially dry before taken
to normal usage. If further drying is necessary by the usual energy-intensive
methods, then the requirements of such in the way of regeneration
heat become much reduced due to much reduced frequency of conventional
regeneration procedures.
It is an object of my invention to provide dry retrieval of wet
stored hydrocarbons, in an energy efficient method using an energy
efficient apparatus.
BRIEF DESCRIPTION OF THE DRAWING
A cavern 1 is shown in irregular outline within a salt strata 2
positioned above bed rock 3 and below surface strata 4. Contained
in the salt cavern 1 is a lower layer or volume of aqueous brine
5 and above the brine is a layer or volume of hydrocarbon fluid
6 which can be liquid or gas, fitting the remaining volume of cavern
1. Preforating the surface of the ground 7 and connecting with cavern
1 is a stringer assembly 8 comprising connecting piping 9 for hydrocarbon
input and removal and providing connection to and fluid access with
the upper volume 6 of the cavern; and a brine input-output tubing
11 which then connects with and provides fluid access with the lower
or brine volume 5 of the cavern. As hydrocarbon fluid flows or is
pumped in 12 to storage 6 brine 5 is removed out of storage via
11 13 to surface storage 14. As hydrocrbon fluid 6 is drawn out
15 from storage, brine 14 then is added back 16 11 to lower volume
5 of the cavern. The interface 16' between the lower brine 5 and
the hydrocarbon fluid 6 raises or lowers as hydrocarbon 15 is withdrawn
15 or added back 12 to cavern storage.
In accordance with my invention, at least one drier, shown in the
drawing as here a pair of driers 21 and 21a, is added to the hydrocarbon
fluid line 22. The hydrocarbon fluid received 22 flows 23 23a through
one or both driers 21 or 21a, and enters 24 24a the hydrocarbon
inlet line 25 in a moist condition for pumping 12 into hydrocarbon
storage 6. Upon withdrawal 15 of hydrocarbon fluid 6 from storage,
the hydrocarbon fluid being withdrawn flows through line 25 into
26 or 26a to the respective drier 21 or 21a, exits dry or substantially
dry 27 or 27a for return 28 for transport to such usages as may
be required as fuel, chemical conversion, polymerization, or the
like, depending on the hydrocarbon involved.
If supplementary drying for removal of any residual traces of moisture
should be required for a particular end use, then conventional desiccation
means can be employed with conventional heated gas regeneration
of the desiccant. Such dehydration (desiccation) means are regenerated
by temperature cycle employing a flow of heated gas, such as hot
air, or combustion gases, or combination, to drive off absorbed
moisture, followed by cool-down of the desiccant, and finally return
to service. However, such operations are time-consuming, and energy-intensive.
By my invention, the need for conventional drying means is greatly
eliminated and in many instances can be eliminated. Clearly, the
frequency between regenerations of the conventional units is greatly
stretched out, saving time and fuel.
Hydrocarbon fluids delivered from the pipeline are received dry,
are put through drier 21 or 21a, regenerate same by removing moisture
therefrom, and then flow to storage. Hydrocarbon fluids in storage
become moisture saturated, are withdrawn from storage, wet, the
wet (moist) hydrocarbon fluids pass back through the driers, leave
the moisture, and exit dry for return to the pipeline. Thus, hydrocarbon
fluid to or from a salt storage cavern is passed via the same desiccant
bed. Moisture removed from exiting hydrocarbon fluid to yield dry
hydrocarbon fluid is in turn picked back up by dry hydrocarbon fluid
entering the desiccant bed for storage in the cavern.
Storage caverns which are used in only one flow direction, that
is, either in or out, need only one economizer drier bed, through
more than one in sequence or tandem can be employed. Such bed or
beds should be sized in accordance with maximum flow rates in or
out. Dual beds, as shown in the drawing, can be employed, if desired,
or other multiple beds depending on convenience for maintenance,
need for alternation of flows, and the like.
Some storage caverns are used in an unusual fashion of both ingoing
hydrocarbon fluid flow and outgoing hydrocarbon fluid flow at the
same time, such as propylene storage. In this situation, for example,
propylene being stored may be percolated through the brine for maximum
residence time. Thus, propylene leaving the storage can be passed
through a drier bed for drying to usage, while an alternate bed
previously wetted by exiting propylene can be dried by dry propylene
being piped into the cavern. When one bed becomes saturated and
the other dry, then the flow through each can be rotated or alternated.
For such operation a second conduit (not shown) between 1 and 21/21a
will be required.
My cyclic process for regenerating saturated desiccant beds is
effective, provides dry outflowing fluid, while drying and thus
regenerating wetted desiccant beds as hydrocarbon fluid is returned
or brought into the storage facility. If desired, conventional regeneration
equipment could be used to augment the regeneration by incoming
dry hydrocarbon.
HYDROCARBON FLUIDS
The hydrocarbon fluid can be normally liquid or gaseous, and under
storage temperatures and pressures can be gaseous, compressed gaseous,
or liquefied gaseous. The hydrocarbon can be saturated or unsaturated.
For example, liquefied petroleum gas (LPG) is a frequently stored
material. Liquefied propylene is a material frequently stored prior
to use in polymerization or dimerization facilities.
DESICCANTS
Any of the normally solid desiccants which are not destroyed or
changed in physical condition by moisture or hydrocarbon fluids
or by exposure to traces of brines can be employed.
Among the suitable desiccants are such as calcium sulfate, silica
gel, and preferably the molecular sieves, generally those of about
3 .ANG., 4 .ANG., or the like. Such molecular sieves and desiccants
are well known in the art and require no particular further description.
Suitable particle sizes are well known, and drier containers are
well known in the art. |