U.S. patent application number 11/452538 was filed with the patent office on 2006-12-21 for enhanced floating power generation system.
Invention is credited to Leendert Poldervaart, Leon D. Rosen, Bram Van Cann, Hein Wille.
Application Number | 20060283590 11/452538 |
Document ID | / |
Family ID | 37572212 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060283590 |
Kind Code |
A1 |
Poldervaart; Leendert ; et
al. |
December 21, 2006 |
Enhanced floating power generation system
Abstract
A system is provided for more efficiently using offshore
produced hydrocarbons, where the produced hydrocarbons contain
considerable amounts of liquid hydrocarbons and both heavy gaseous
hydrocarbons (at least two carbon atoms per molecule) and light
hydrocarbons (with two or less carbon atoms per molecule). The
produced hydrocarbons are separated into liquid hydrocarbons which
are stored in a tank structure (183) for later offloading to a
tanker (56), and into heavy gaseous hydrocarbons and light
hydrocarbons. The heavy gaseous hydrocarbons are liquefied and
stored in a tank (212) for fueling an electricity generator unit
(192) when needed, and the light hydrocarbons are immediately used
to fuel the electricity generator unit (192).
Inventors: |
Poldervaart; Leendert;
(US) ; Van Cann; Bram; (Nice, FR) ; Wille;
Hein; (Eze, FR) ; Rosen; Leon D.; (Los
Angeles, CA) |
Correspondence
Address: |
LEON D. ROSEN;FREILICH, HORNBAKER & ROSEN
Suite 1220
10960 Wilshire Blvd.
Los Angeles
CA
90024
US
|
Family ID: |
37572212 |
Appl. No.: |
11/452538 |
Filed: |
June 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60692304 |
Jun 20, 2005 |
|
|
|
Current U.S.
Class: |
166/265 |
Current CPC
Class: |
B63B 35/44 20130101;
E21B 43/34 20130101; E21B 41/005 20130101 |
Class at
Publication: |
166/265 |
International
Class: |
E21B 43/00 20060101
E21B043/00 |
Claims
1. A method for the production and transport of hydrocarbons using
a floating structure that floats at the sea surface, that has
electrically powered equipment, and that is connected by a riser to
a subsea reservoir that produces hydrocarbons that include both
gaseous and liquid hydrocarbons comprising: separating the produced
hydrocarbons into gaseous hydrocarbons and liquid hydrocarbons;
storing the liquid hydrocarbons in a tank structure, and offloading
the liquid hydrocarbons to a tanker at intervals; using at least
some of the gaseous hydrocarbons to fuel an energized electrical
generator unit to produce electricity, and using at least some of
said electricity to power at least said electrically powered
equipment on the floating structure.
2. The method described in claim 1 including: separating the
gaseous hydrocarbons into heavier gaseous hydrocarbons that have a
number of carbon atoms per molecule that is at least two, and light
gaseous hydrocarbons that have a number of carbon atoms per
molecule that is less than three; storing said heavier gaseous
hydrocarbons in a tank on the floating structure.
3. The method described in claim 2 including: using said light
gaseous hydrocarbons to fuel said energized generator unit to
produce electricity to the extent that said light gaseous
hydrocarbons are available to provide fuel required for said
generator unit, and using said heavier gaseous hydrocarbons that
have been stored to fuel said generator unit when sufficient light
gaseous hydrocarbons are not available.
4. The method described in claim 3 including: when the tank that
stores heavier gaseous hydrocarbons is full, transporting some of
said heavier gaseous hydrocarbons by ship away from said floating
structure.
5. The method described in claim 1 including: carrying electricity
from said electric generator unit through an undersea electric
cable to a shore facility that is located on shore; said step of
carrying electricity including carrying direct current electricity
through said undersea cable, and converting said direct current
electricity to alternating current electricity at said shore
facility.
6. The method described in claim 1 including: separating said
gaseous hydrocarbons and delivering primarily methane to said
electrical generator unit, and storing at least propane in a
tank.
7. A hydrocarbon production system which includes a floating
structure that floats at the sea surface, that carries electrically
powered equipment, and that is connected through a riser to an
undersea reservoir that produces liquid hydrocarbons and natural
gas, comprising: a processor connected to said riser that separates
liquid hydrocarbons from components of natural gas; a liquid tank
structure connected to said processor to store liquid hydrocarbons
received from said processor; an electricity generator unit; a
conduit structure that carries natural gas from said processor to
said generator unit to fuel said generator unit with natural
gas.
8. The system described in claim 7 wherein: said processor
separates light gases that include methane, from heavy gases that
include butane; said conduit structure carries said light gases
from said separator to said generator unit to fuel it; and
including a heavy gas tank that stores said heavy gases, said heavy
gas tank being coupled to said generator unit to supply fuel when
there are insufficient of said light gases.
Description
CROSS REFERENCE
[0001] Applicant claims priority from U.S. Provisional patent
application Ser. No. 60/692,304 filed Jun. 20, 2005.
BACKGROUND OF THE INVENTION
[0002] Hydrocarbons can be produced from undersea reservoirs that
lie in the vicinity (e.g. within 50 kilometers) of a consumer such
as a community that could use electricity. Some of the produced
hydrocarbons can be used to generate electricity that can be
delivered to such community. However, there may be much more
produced hydrocarbons than are needed to supply the demand for
electricity in the vicinity. Where the produced hydrocarbons
include considerably quantities of liquid and gas, and the gaseous
hydrocarbons include a variety of different molecules with
different numbers of carbon atoms per molecule, it would be
desirable to use the hydrocarbons so the greatest economic value
can be derived from the production.
[0003] Liquid hydrocarbons are usually the most valuable, in part
because they are economical to store and transport since they
remain liquid over a wide range of environmental temperatures.
Gaseous hydrocarbons, which are gaseous at environmental
temperatures such as 10.degree. C. and at temperatures often
encountered in a sun-heated tank such as 40.degree. C., are less
valuable because they are more difficult to store and transport.
For example, methane, which is often the most common gaseous
hydrocarbon, must be cooled to -162.degree. C. to liquify it and
transport it economically over a long distance. The most economical
use of gaseous hydrocarbons from an undersea reservoir is highly
desirable.
SUMMARY OF THE INVENTION
[0004] In accordance with one embodiment of the present invention,
applicant provides a method and system that economically uses a
variety of hydrocarbons that are produced from an undersea
reservoir that lies in the vicinity of a consumer such as a
community while supplying electricity to the consumer. Hydrocarbons
that are produced from a floating structure are separated into
liquid and gaseous hydrocarbons, and the gaseous hydrocarbons are
separated into heavy and light gaseous hydrocarbons. The liquid
hydrocarbons are stored for offloading to a tanker. The light
gaseous hydrocarbons are immediately used to fuel an electricity
generator unit. The heavy gaseous hydrocarbons are stored
preferably after they are liquefied, and are used to fuel the
electricity generator unit only when sufficient light gaseous
hydrocarbons are not available. If excess heavy gaseous
hydrocarbons are available, they are shipped to a distant
consumer.
[0005] The novel features of the invention are set forth with
particularity in the appended claims. The invention will be best
understood from the following description when read in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is an isometric view of a system for the production
of hydrocarbons and the generation of electricity, of one
embodiment of the present invention.
[0007] FIG. 2 is a sectional side view of another system which is
similar to that of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0008] FIG. 1 illustrates a system 10 which includes a floating
structure in the form of a vessel 12 with a hull 16 that floats at
the sea surface and with a turret 20 that is moored by a mooring
system that includes catenary lines 32 that extend to the sea floor
and along it. Risers 34 extend from a fluid swivel 36 on the turret
to a sea floor platform 40, and from there extend to a subsea
hydrocarbon reservoir 64. The turret allows the vessel to
weathervane, that is to head in different directions with changing
winds and waves, while the catenary lines allow the vessel to drift
but only a limited distance, from a location 44 over the sea floor
platform. Other mooring systems that can be used include spread
mooring systems, disconnectable buoy-turret systems, etc.
[0009] The vessel carries an electricity generating unit 42 that
uses hydrocarbons as a fuel to generate electricity. A preferred
unit is a turbine-generator set wherein the turbine is powered, or
fueled, by hydrocarbons and the turbine spins a rotor of an
electric generator. Such turbine-generator set is of light weight
in proportion to the electrical power it generates. The system
includes a power cable 50 that extends from the vessel and that has
a major portion 56 that extends along the sea floor to an onshore
distribution facility 52. The facility distributes electricity to
consumers such as residential, factory and office structures.
[0010] Hydrocarbons produced from the subsea reservoir 64 commonly
includes liquid hydrocarbons, which have at least five to eight
carbon atoms per hydrocarbon molecule, and gaseous hydrocarbons,
which have one to four, or one to seven carbon atoms per molecule.
Gaseous molecules are in a gaseous state at temperatures commonly
reached during storage and transport. There is an overlap (of
molecules with five to seven carbon atoms per molecule) between
liquid and gaseous hydrocarbons. At the production system, liquid
hydrocarbons are more valuable than gaseous hydrocarbons. This is
largely due to the fact that liquid hydrocarbons are much more
easily transported long distances because they do not have to be
cooled to liquify them and do not later have to be heated to regas
them.
[0011] Where substantial amounts of gas and liquid hydrocarbons are
produced from the reservoir 64, applicant uses the gas to fuel the
electricity generator unit 42. Gas is less valuable if it is to be
stored or transported, but it produces less polluting gasses and is
easier to use in turbines. Applicant stores all liquid hydrocarbons
that are not needed to produce electricity, which may be all of the
produced liquid hydrocarbons. The stored liquid hydrocarbons are
offloaded to a tanker 56, such as at predetermined intervals when
it is expected that the liquid hydrocarbon tanks will be largely
full. In FIG. 1, the tanker is shown moored through a capstan 66 to
the vessel 12 during unloading, with the liquid hydrocarbons
transferred though a transfer conduit 68.
[0012] It would be possible to use all of the natural gas produced
from the undersea reservoir to fuel the electricity generator unit
42. However, applicant uses the produced hydrocarbons more
economically by separating, by processor 60, the produced gaseous
hydrocarbons into light gaseous hydrocarbons, which are gaseous
hydrocarbons with a minimum number of carbon atoms per molecule,
and heavy gaseous hydrocarbons, which have a greater number of
carbon atoms per molecule. Light gaseous hydrocarbons include
methane (CH.sub.4). Heavy gaseous hydrocarbons include propane
(C.sub.3H.sub.8) and butane (C.sub.4H.sub.10). Ethane
(C.sub.2H.sub.6) can be placed in either category. Applicant first
uses light gaseous hydrocarbons to fuel the electricity generator
unit, and stores the heavy gaseous hydrocarbons. Only when there is
an insufficient supply of light gaseous hydrocarbons to provide the
amount of required fuel, does applicant use the stored heavy
gaseous hydrocarbons (often referred to as LPG, or liquid petroleum
gas).
[0013] FIG. 2 illustrates a system 170 with a floating structure
172 in the form of a vessel similar to that of FIG. 1 but with the
vessel being spread moored. The vessel carries an
electrically-energized processor 182 that receives effluent from a
reservoir 174. The effluent passes along a riser 176 and pipe 180
to the processor which removes sand, stones, etc. The processor
includes a separator that separates liquid hydrocarbons from
gaseous hydrocarbons. The liquid hydrocarbons are stored in a
liquid oil tank structure 183 that includes several tanks 184. The
processor also separates light gaseous hydrocarbons (e.g. methane)
from heavy gaseous hydrocarbons (e.g. including propane and butane,
and possibly also ethane, pentane and hexane). The light gaseous
hydrocarbons, or light gas (which includes at least methane),
passes into an accumulator 190 that holds the gas under a variable
pressure to thereby store a limited amount of the light gas. The
light gas is delivered to a gas turbine-generator unit 192 that
uses gas to generate electricity.
[0014] Heavy gaseous hydrocarbon, or heavy gas (which includes at
least propane and butane), passes to a storage tank 212. The tank
212 usually is cooled by an electrically-energized refrigerator
unit 213 to liquify the heavy gases for more efficient storage.
About 200 times more gas can be stored in a given volume as cold
liquified gas than in a gaseous state at atmospheric pressure.
Since the amount of light gas stored in accumulator 190 is small,
there is a possibility that the supply of light gas to the
generator unit 192 will not be sufficient to meet requirements.
This can occur if there is an interruption in the flow of effluent
from the reservoir, or if the reservoir effluent temporarily
contains less light gas than usual, or if the demand for
electricity temporarily increases beyond the capacity of the
processor to supply light gas. In any of these cases, liquified
heavy gas from the storage tank 212 is heated by a heating station
215 to regas it, and the gaseous heavy hydrocarbons are delivered
through a conduit structure 214 that also carries light gasses, to
the electricity generator unit 192. In a situation where the heavy
gas storage tank is repeatedly full so additional heavy gas would
have to be flared, the liquified heavy gas can be offloaded to a
refrigerated tank 217 (FIG. 1) that is provided on the tanker.
[0015] The different gaseous hydrocarbons have widely different
boiling, or vaporization temperatures. Methane (CH.sub.4) has a
boiling point temperature of -162.degree. C., and considerable
refrigeration is required to liquify it for storage. Ethane
(C.sub.2H.sub.6) has a boiling point temperature of -89.degree. C.
which is moderately difficult to liquify. Propane (C.sub.3H.sub.6)
and butane (C.sub.4H.sub.10) have boiling point temperatures of
-42.degree. C. and -0.5.degree. C., respectively, which are much
easier to achieve. By using only the light gas (primarily methane)
to fuel the electricity generator unit when sufficient light gas is
available, while efficiently storing the heavy gas as cooled
liquified gas to be used only when there is insufficient light gas,
applicant provides a more reliable source of fuel in an economical
manner. Excess light gas can be flared (burned) or released in an
unburned condition into the atmosphere if there are winds to widely
disperse it.
[0016] Some of the electricity produced by the electricity
generator unit 192 (FIG. 2) is used to energize
electrically-energized equipment on the vessel, such as the
processor 182. Most of the produced electricity is delivered though
a cable 194 that extends in the sea 200 to an onshore distribution
facility 202. The output of the generator is AC (alternating
current). An AC-DC converter 204 is on the vessel, and a DC-AC
converter 206 is at the onshore facility. This allows electricity
to be sent though the in-sea cable 194 at e.g. 150 kV (kilovolts)
for smaller losses. If AC current were sent though the same cable,
it would have to have an equivalent voltage of 106 RMS to assure
the peak voltages were no more than 150 kV, resulting in 30%
greater current and therefore 30% greater losses at the same power
levels.
[0017] Waste heat from the gas powered electricity turbine unit 192
is delivered to a steam generator 196 where the steam output drives
a steam turbine-generator set 198. In one example, eight gas
turbine generator units 192 are provided that each has an output of
40 megawatts, while three steam turbine generator units are
provided that each has an output of 35 megawatts. Not all units are
operating at one time, and the generating capacity is 400
megawatts. Steam from the steam turbine generator units pass into
condensers 201 after passing though the turbines. Applicant locates
the condensers below the water line 202. This reduces the static
head to a minimum to improve efficiency. Water for cooling the
condensers is preferably drawn though free hanging, deep suction
hoses 205 that carry cold water.
[0018] Thus, the invention provides a system for producing
hydrocarbons from a subsea reservoir and using some of the produced
hydrocarbons to generate electricity for local consumption. The
produced hydrocarbons are efficiently used by separating the liquid
hydrocarbons from the gaseous ones, with the liquid hydrocarbons
usually stored and transported to a market. The gaseous
hydrocarbons are separated into light gas which includes methane
and possibly ethane, and into heavy gasses which include propane
and butane and possibly ethane. The light gases are immediately
used, with only short term storage of light gas in gaseous form, to
fuel an electricity generator unit. The heavy gases are usually
refrigerated to liquify them for storage, and kept in reserve for
fueling the electricity generator in the event there is temporarily
insufficient light gases. If excess heavy gases are accumulated,
they also can be shipped to a market.
[0019] Although particular embodiments of the invention have been
described and illustrated herein, it is recognized that
modifications and variations may readily occur to those skilled in
the art, and consequently, it is intended that the claims be
interpreted to cover such modifications and equivalents.
* * * * *