Patent Grant
7155918
The present embodiments relate to a system for processing and transporting compressed natural gas.
The current art teaches three known methods of transporting natural gas across bodies of water. A first method is by way of subsea pipeline. A second method is by way of ship transport as liquefied natural gas (LNG). A third method is by way of barge, or above deck on a ship, as compressed natural gas (CNG). Each method has inherent advantages and disadvantages.
Subsea pipeline technology is well known for water depths of less than 1000 feet. The cost of deep water subsea pipelines is very high and methods of repairing and maintaining deep water subsea pipelines are just being pioneered. Transport by subsea pipeline is often not a viable option when crossing bodies of water exceeding 1000 feet in depth. A further disadvantage of subsea pipelines is that, once laid, it is impractical to relocate.
Liquefied natural gas systems, or LNG systems, require natural gas to be liquefied. This process greatly increases the fuel's density, thereby allowing relatively few numbers of ships to transport large volumes of natural gas over long distances. An LNG system requires a large investment for liquefaction facilities at the shipping point and for re-gasification facilities at the delivery point. In many cases, the capital cost of constructing LNG facilities is too high to make LNG a viable option. In other instances, the political risk at the delivery and/or supply point may make expensive LNG facilities unacceptable. A further disadvantage of LNG is that even on short routes, where only one or two LNG ships are required, and the transportation economics are still burdened by the high cost of full shore facilities. The shortcoming of a LNG transport system is the high cost of the shore facilities that, on short distance routes, becomes an overwhelming portion of the capital cost.
Natural gas prices are currently increasing rapidly due to an inability to meet demand. Unfortunately, the LNG import terminals existing in the United States are presently operating at capacity. New import terminals of the type currently used in the United States cost hundreds of millions of dollars to build. Moreover, it is very difficult and expensive to find and acquire permissible sites for such facilities. Besides the space needed for the import tanks, pumps, vaporizers, etc., large impoundment safety areas must also be provided around all above-ground LNG storage and handling vessels and equipment. LNG import facilities also consume large amounts of fuel gas and/or electrical energy for pumping the LNG from storage and vaporizing the material for delivery to gas distribution systems.
Compressed natural gas, or CNG, can be transported by way of barge or above deck on a ship. For the method to work, the CNG is cooled to a temperature around −75 degrees Fahrenheit at a pressure of around 1150 psi. The CNG is placed into pressure vessels contained within an insulated cargo hold of a ship. Cargo refrigeration facilities are not usually provided aboard the ship. A disadvantage of this system is the requirement for connecting and disconnecting the barges into the shuttles that takes time and reduces efficiency. Further disadvantages include the limited seaworthiness of the multi-barge shuttles and the complicated mating systems that adversely affect reliability and increase costs. In addition, barge systems are unreliable in heavy seas. Finally, current CNG systems have the problem of dealing with the inevitable expansion of gas in a safe manner as the gas warms during transport.
The amount of equipment and the complexity of the inter-connection of the manifolding and valving system in the barge gas transportation system bears a direct relation to the number of individual cylinders carried onboard the barge. Accordingly, a significant expense is associated with the manifolding and valving connecting the gas cylinders. Thus, the need has arisen to find a storage system for compressed gas that can both contain larger quantities of compressed gas and simplify the system of complex manifolds and valves.
A need exists to transfer compressed natural gas across heavy seas to locations greater than 500 nautical miles.
A need exists for a system that can solve the concerns of the inevitable expansion of gas experienced as CNG warms during transport.
A system for processing and transporting compressed natural gas includes a separator for separating the pressurized high-energy content gas into saturated gas, natural gas liquid, and a condensate. The system includes a decontamination unit for removing impurities from the saturated gas to create a decontaminated saturated gas and a dehydration unit for dehydrating the decontaminated saturated gas to remove water forming a dry pressurized gas. The system has a chiller for cooling the dry pressurized gas cooled from ambient temperature to a temperature ranging from −80 degrees Fahrenheit to −120 degrees Fahrenheit. The system has one or more storage modules located on a floating vessel for receiving the vapor gas, the natural gas liquid, and the condensate. The modules maintain a pressure ranging from about 800 psi and about 1200 psi. The floating vessel transports the storage modules a distance ranging from 500 nautical miles to 2500 nautical miles and utilizes the vapor phase during transit to power the floating vessel.
The present embodiments will be explained in greater detail with reference to the appended Figures, in which:
a depicts a perspective view of one rack and two stanchions of the storage module.
a depicts the spherical shape embodiment of the storage element.
The present embodiments are detailed below with reference to the listed Figures.
Before explaining the present embodiments in detail, it is to be understood that the embodiments are not limited to the particular embodiments herein and it can be practiced or carried out in various ways.
Embodied herein is a system for processing and transporting compressed natural gas.
With reference to the figures,
The system involves a decontamination unit (30) connected to the separator (20) for receiving the saturated gas (22). The decontamination unit (30) removes impurities (34) from the saturated gas (22) to form decontaminated saturated gas (32). The types of impurities removed from the saturated gas (22) are CO2, mercury, H2S, and combinations thereof. Examples of decontamination units include an amine contactor, a catalytic bed, a scrubber vessel, or combinations thereof.
As shown in
The system then includes a chiller (50) connected to the dehydration unit (40). The chiller receives the dry pressurized gas (42) and cools the dry pressurized gas (42) from ambient temperature to a temperature ranging from −80 degrees Fahrenheit to −120 degrees Fahrenheit forming a two-phase gas having a vapor phase (52) and a liquid phase (54). Examples of chillers (50) are a single-stage mixed refrigerant process and a two-stage cascade system. The chiller (50) is also used to sub-cool the dry pressurized gas (42) to delay the formation of the vapor phase (52).
Continuing in
The system finally includes a floating vessel (10). The floating vessel (10) is adapted to transport the at least one storage module (200) at a distance of ranging from 500 nautical miles to 2500 nautical miles. The vapor phase (52a) that is formed due to the warming of the two phase gas during transport is used to power the floating vessel (10). Using the vapor phase from the two-phase gas to power the floating vessel both alleviates the environmental concerns of the gas being vented to the atmosphere and also lowers the cost.
As shown in
Each storage module holds one or more storage elements (100). The storage elements have a first end (135) and a second end (140). An individual storage element (100) is shown in
Returning to
The storage module supports between three and fifteen storage elements. The weight of the storage module when loaded with at least one empty storage element ranges from 5000 short tons to 8000 short tons.
The structural frames (210 and 220) can support up to five racks between the stanchions. The structural frames (210 and 220) can be located on a floating vessel (10) with a hull wherein the structural frames (210 and 220) extend beyond the hull and are supportable on at least two jetties.
The first and second racks can support up to five storage elements. The rack can further include a plate supported by a plurality of ridges for removably holding the storage element. The rack has an anchor for fixing the storage element at the first end. The second end, or unanchored end, is adapted to travel to accommodate thermal strain.
The storage element's empty weight ranges from 350 short tons to 700 short tons when loaded. Each storage element can have a length up to about 350 feet.
Returning to
The construction material for the inner wall (105) is a high-strength steel alloy, such as a nickel-steel alloy. The construction material for the inner wall could be a basalt-based fiber pipe.
The shape of the storage element can either be cylindrical or spherical. The cylindrical shape, as shown in
For the spherical shape, the inner wall has a diameter ranging from 30 feet to 40 feet. The outer wall has a diameter that is up to three feet larger in diameter than the inner wall.
The insulating layer is either perlite or a vacuum.
While these embodiments have been described with emphasis on the preferred embodiments, it should be understood that within the scope of the appended claims the embodiments might be practiced or carried out in various ways other than as specifically described herein.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/485,984 filed on Jul. 10, 2003 now abandoned.
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