The embodiments described herein relate to the collection of natural gas for transportation from remote reserves and, more particularly, to systems and methods that utilize modularized storage and process equipment configured for floating service vessels, platforms, and transport vessels to yield a total solution to the specific needs of a supply chain, enabling rapid economic development of remote reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems, in particular reserves of a size deemed “stranded” or “remote” by the natural gas industry.
Natural gas is primarily moved by pipelines on land. Where it is impractical or prohibitively expensive to move the product by pipeline, LNG shipping systems have provided a solution above a certain threshold of reserve size. With the increasingly expensive implementation of LNG systems being answered by economies of scale of larger and larger facilities, the industry has moved away from a capability to service the smaller and most abundant reserves. Many of these reserves are remotely located and have not been economic to exploit using LNG systems. A backlash of land based environmental and safety issues in recent years has also led to counter innovations in floating LNG (FLNG) production facilities, and on board deepwater re-gasification and offloading processing trains and storage being fitted to some vessels—all at additional capital cost. Finding savings from simplification of the LNG transportation/processing cycle by turning to related pressurized LNG (PLNG) technology also has yet to materialize in the industry.
For LNG systems 40 as shown in
The LNG carriers 44 are specially constructed cryogenic gas carriers that transport 17 the liquid natural gas product at a density of 600 times that of natural gas at atmospheric conditions. A fleet shuttle service of LNG carriers 44 is run to LNG receiving and processing terminals 46 at the market end of the sea route, which typically require cryogenic temperature storage facilities 45. These terminals 46 receive the LNG, store and reheat it to atmospheric temperatures prior to compressing and cooling 47 it to the entry pressure of the transmission pipelines 26 and then injecting 48 the natural gas into the transmission pipelines 26 that deliver natural gas to market.
Recent work by the industry seeks to improve delivery capabilities by introducing floating LNG liquefaction plants and storage at the gas field and installing on board regasification equipment on LNG carriers for offloading gas offshore to nearby market locations that have opposed land based LNG receiving and processing terminals. To further reduce energy consumption by simplification of process needs, the use of pressurized LNG (PLNG) is once again under review by the industry for improvement of economics in an era of steeply rising costs for the LNG industry as a whole.
The advent of CNG transportation systems, to cater to the needs of a world market of increasing demand, has led to many proposals in the past decade. However, during this same time period there has only been one small system placed into full commercial service on a meaningful scale. CNG systems inherently battle design codes that regulate wall thicknesses of their containment systems with respect to operating pressures. The higher the pressure, the better the density of the stored gas with diminishing returns—however, the limitations of “mass of gas-to-mass of containment material” have forced the industry to look in other directions for economic improvements on the capital tied up in CNG containment and process equipment.
Work discussed in U.S. Pat. No. 6,655,155 (Bishop) is an example of the direction sought to improve cargo (gas) mass-to-containment mass ratio. In Bishop, increasing pressure is recognized as having limitations and the concepts of decreasing temperature and moving the gas into a dense phase state (as described in prior art by others) while avoiding the liquid phase of the gas is suggested by Bishop to be beneficial.
For CNG systems 50, as shown in
During marine transportation 17 of the CNG, the CNG containment tanks aboard the CNG transport vessel 54 typically operate at temperatures as low as −30 F and at pressures from 1400 psig to 3600 psig. (Packaging of small amounts of natural gas for vehicle fuel resorts to pressures in the region of 10,000 psig to attain practical storage volumes). In general, designs proposed for commercial bulk transport are intended to carry the product at densities from 200 to 250 times the densities of the gas at atmospheric conditions. Under conditions of low temperature and high pressure a density approaching 300 times the atmospheric value is possible with accompanying higher energy requirements for compression and cooling, along with the requirement of even thicker walls for the containment vessels.
Unloading the CNG at receiving terminals requires a variety of solutions to ensure the product is completely evacuated or transferred from the containment vessels. These evacuation solutions range from the elegant use of displacement fluids 57, with or without pigging, to equilibrium blow-down 56, and to using energy consuming suction compressors 55 for final evacuation. Heat (along with NGL extraction 58 if required) has to be added to compensate for initial expansion cooling of the natural gas, and compression cooling 59 is then provided for injection 24 into the transmission pipelines 26 or storage vessels 25 if required.
Yet, the improved cargo density of CNG returns described in Bishop still do not meet those attainable with the combination of lower process energy for a liquid state storage method as outlined in U.S. Published Patent Application No. 2006/0042273 for a methodology to both create and store a liquid phase mix of natural gas and light hydrocarbon solvent, which is incorporated herein by reference. The liquid phase mix of natural gas and light hydrocarbon solvent is referred to hereafter as compressed gas liquid (CGL) product.
However, current solutions or services for natural gas production and transmission to market tend to be one size fits all and tend not to afford economic development of remote or stranded gas reserves. Accordingly, it is desirable to provide systems and methods that facilitate economic development of remote or stranded reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems.
Provided herein are exemplary embodiments directed to systems and methods that utilize modularized storage and process equipment scalably configurable for floating service vessels, platforms, and transport vessels to yield a total solution to the specific needs of a supply chain, enabling rapid economic development of remote reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems, in particular reserves of a size deemed “stranded” or “remote” by the natural gas industry. The systems and methods described herein provide a full value chain to the reserve owner with one business model that covers the raw production gas processing, conditioning, transporting and delivering to market pipeline quality gas or fractionated products—unlike that of LNG and CNG. Moreover, the systems and methods described herein enable raw production gas to be loaded, processed, conditioned, transported (in liquid form) and delivered as pipeline quality natural gas or fractionated products at the market as well as providing complimentary natural gas service to sources presently linked to LNG (liquid natural gas) systems. It can also service on demand the needs of the industry to transport NGLs.
The disclosed embodiments provide a scalable means of receiving raw production or semi-conditioned gas, conditioning, CGL production and transporting this CGL product to a market where pipeline quality gas or fractionated products are delivered in a manner utilizing less energy than either CNG or LNG systems and giving a better ratio of cargo-mass to containment-mass for the natural gas component than that offered by CNG systems.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description.
The details of the invention, including fabrication, structure and operation, may be gleaned in part by study of the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely.
The embodiments provided in the following descriptions are directed to a total delivery system built around CGL production and containment and, more particularly, to systems and methods that utilize modularized storage and process equipment scalably configurable for floating service vessels, platforms, and transport vessels to yield a total solution to the specific needs of a supply chain, enabling rapid economic development of remote reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems, in particular reserves of a size deemed “stranded” or “remote” by the natural gas industry. The systems and methods described herein provide a full value chain to the reserve owner with one business model that covers the raw production gas processing, conditioning, transporting and delivering to market pipeline quality gas or fractionated products—unlike that of LNG and CNG.
Moreover, the special processes and equipment needed for CNG and LNG systems are not needed for a CGL based system. The operation specifications and construction layout of the containment system also advantageously enables the storage of pure ethane and NGL products in sectioned zones or holds of a vessel on occasions warranting mixed transport.
In accordance with a preferred embodiment, as depicted in
To contain the CGL cargo, the containment system preferably comprises a carbon steel, pipeline-specification, tubular network nested in place within a chilled environment carried on the vessel. The pipe essentially forms a continuous series of parallel serpentine loops, sectioned by valves and manifolds.
The vessel layout is typically divided into one or more insulated and covered cargo holds, containing modular racked frames, each carrying bundles of nested storage pipe that are connected end-to-end to form a single continuous pipeline. Enclosing the containment system located in the cargo hold allows the circulation of a chilled nitrogen stream or blanket to maintain the cargo at its desired storage temperature throughout the voyage. This nitrogen also provides an inert buffer zone which can be monitored for CGL product leaks from the containment system. In the event of a leak, the manifold connections are arranged such that any leaking pipe string or bundle can be sectioned, isolated and vented to emergency flare and subsequently purged with nitrogen without blowing down the complete hold.
At the delivery point or market location, the CGL product is completely unloaded from the containment system using a displacement fluid, which unlike LNG and most CNG systems does not leave a “heel” or “boot” quantity of gas behind. The unloaded CGL product is then reduced in pressure outside of the containment system in low temperature process equipment where the start of the fractionation of the natural gas constituents begins. The process of separation of the light hydrocarbon liquid is accomplished using a standard fractionation train, with the rectifier and stripper sections split into two lower profile vessels in consideration of marine stability.
Compact modular membrane separators can also be used in the extraction of solvent from the CGL. This separation process frees the natural gas and enables it to be conditioned to market specifications while recovering the solvent fluid.
Trim control of minor light hydrocarbon components, such as ethane, propane and butane for BTU and Wobbe Index requirements, yields a market specification natural gas mixture for direct offloading to a buoy connected with shore storage and transmission facilities.
The hydrocarbon solvent is returned to vessel storage and any excess C2, C3, C4 and C5+ components following market tuning of the natural gas can be offloaded separately as fractionated products or value added feedstock supply credited to the account of the shipper.
For ethane and NGL transportation, or partial load transportation, sectioning of the containment piping also allows a portion of the cargo space to be utilized for dedicated NGL transport or to be isolated for partial loading of containment system or ballast loading. Critical temperatures and properties of ethane, propane and butane permit liquid phase loading, storage and unloading of these products utilizing allocated CGL containment components. Vessels, barges and buoys can be readily customized with interconnected common or specific modular process equipment to meet this purpose. The availability of de-propanizer and de-butanizer modules on board vessels, or offloading facilities permits delivery with a process option if market specifications demand upgraded product.
As depicted in
The barges 14 equipped for production and storage and the barges 20 equipped for separation can conveniently be relocated to different natural gas sources and gas market destinations as determined by contract, market and field conditions. The barge and vessel 14 and 20 configuration, having a modular assembly, can accordingly be outfitted as required to suit route, field, market or contract conditions.
In an alternative embodiment, as depicted in
The CGL product 105 is loaded into the containment piping 106 against the back pressure of a displacement fluid 107 to retain the CGL product 105 in its liquid state. The back pressure of the displacement fluid 107 is controlled by a pressure control valve 108 interposing the containment piping 106 and a displacement fluid storage tank 109. As CGL product 105 is loaded into the containment piping 106, it displaces the displacement fluid 107 causing it to flow toward the storage tank 109
As illustrated in Table 1 below, the natural gas cargo density and containment mass ratios achievable in a CGL system surpass those achievable in a CNG system. Table 1 provides comparable performance values for storage of natural gas applicable to the embodiments described herein and the CNG system typified by the work of Bishop for qualified gas mixes.
The specific gravity (SG) value for the mixes shown in Table 1 is not a restrictive value for CGL product mixes. It is given here as a realistic comparative level to relate natural gas storage densities for CGL based systems performance to that of the best large commercial scale natural gas storage densities attained by the patented CNG technology described in Bishop's work.
The CNG 1 values, along with those for CGL 1 and CGL 2 are also shown as “net” values for the 0.6 SG natural gas component contained within the 0.7 SG mixtures to compare operational performances with that of a pure CNG case illustrated as CNG 2. The 0.7 SG mixes shown in Table 1 contain an equivalent propane constituent of 14.5 mol percent. The likelihood of finding this 0.7 SG mixture in nature is infrequent for the CNG 1 transport system and would therefore require that the natural gas mix be spiked with a heavier light hydrocarbon to obtain the dense phase mixture used for CNG as proposed by Bishop. The CGL process, on the other hand and without restriction, deliberately produces a product used in this illustration of 0.7 SG range for transport containment.
The cargo mass-to-containment mass ratio values shown for CGL 1, CGL 2, and CNG 2 system are all values for market specification natural gas carried by each system. For purposes of comparison of the containment mass ratio of all technologies delivering market specification natural gas component gas, the “net” component of the CNG 1 stored mixture is derived. It is clear that the CNG systems, limited to the gaseous phase and associated pressure vessel design codes, are not able to attain the cargo mass-to-containment mass ratio (natural gas to steel) performance levels that the embodiments described herein achieve using CGL product (liquid phase) to deliver market specification natural gas.
Table 2 below illustrates containment conditions of CGL product where a variation in solvent ratio for select storage pressures and temperatures yields an improvement of storage densities. Through the use of more moderate pressures at lower temperatures than previously discussed, and applying the applicable design codes, reduced values of wall thickness from those shown in Table 1 can be obtained. Attainable values for the mass ratio of gas-to-steel for CGL product of over 3.5 times the values quoted earlier for CNG are thereby achievable.
Turning to
As the CGL product 105 flows F into the containment system 106 it displaces displacement fluid 107 causing it to flow through an isolation valve 124 positioned in a line returning to a displacement fluid tank 109 and set to open. A pressure control valve 127 in the return line maintains the displacement fluid 107 at sufficient back pressure to ensure the CGL product 105 is maintained in a liquid state in the containment system 106. During the loading process, an isolation valve 125 in a displacement fluid inlet line is set to closed.
Upon reaching its destination, the CGL vessel or carrier unloads the CGL product 105 from the containment system through an unloading process 132 that utilizes a pump 126 to reverse the flow F of the displacement fluid 107 from the storage tank 109 through an open isolation valve 125 to containment pipe bundles 106 to push the lighter CGL product 105 into a process header towards fractionating equipment of a CGL separation process train 129. The displaced CGL product 105 is removed from the containment system 106 against the back pressure of control valve 123 in the process header as isolation valve 122 is set to open. The CGL product 105 is held in the liquid state until this point, and only flashes to a gaseous/liquid process feed after passing through the pressure control valve 123. During this process, isolation valves 121 and 124 are set to close.
The displacement fluid 107 is reused in the filling/emptying of each successive pipe bundle 106 in the further interests of the limited storage space on board a marine vessel. The pipeline containment 106, in turn, is purged with a nitrogen blanket gas 128 to leave the “empty” pipe bundles 106 in an inert state while evacuating the pipe bundles 106 of displacement fluid 107.
U.S. Pat. No. 7,219,682, which illustrates one such displacement fluid method adaptable to the embodiments described herein, is incorporated herein by reference.
Turning to
As shown in
As shown in
Turning to
As noted above, the carrier vessel 300 advantageously includes modularized processing equipment including, for example, a modular gas loading and CGL production system 302 having a refrigeration heat exchanger module 304, a refrigerator compressor module 306, and vent scrubber modules 308, and a modular CGL gasification offloading system 310 having a power generation module 312, a heat medium module 314, a nitrogen generation module 316, and a methanol recovery module 318. Other modules on the vessel include, for example, a metering module 320, a gas compressor module 322, gas scrubber modules 324, a fluid displacement pump module 330, a CGL circulation module 332, natural gas recovery tower modules 334, and solvent recovery tower modules 336. The vessel also preferably includes a special duty module space 326 and gas loading and offloading connections 328.
The loading barge 400 preferably includes CGL product storage modules 402 and modularized processing equipment including, for example, a gas metering module 408, a mol sieve module 410, gas compression modules 412 and 416, a gas scrubber module 414, power generation modules 418, a fuel treatment module 420, a cooling module 424, refrigeration modules 428 and 432, refrigeration heat exchanger modules 430, and vent module 434. In addition, the loading barge preferably includes a special duty module space 436, a loading boom 404 with a line 405 to receive solvent from a carrier and a line 406 to transmit CGL product to a carrier, a gas receiving line 422, and a helipad and control center 426.
The flexibility to deliver to any number of ports according to changes in market demand and the pricing of a spot market for natural gas supplies and NGLs would require that the individual vessel be configured to be self contained for offloading natural gas from its CGL cargo, and recycling the hydrocarbon solvent to onboard storage in preparation for use on the next voyage. Such a vessel now has the flexibility to deliver interchangeable gas mixtures to meet the individual market specifications of the selected ports.
At the rear of the vessel 500, deck space is provided for the modular placement of necessary process equipment in a more compact area than would be available on board a converted vessel. The modularized processing equipment includes, for example, displacement fluid pump modules 510, refrigeration condenser modules 512, a refrigeration scrubber and economizer module 514, a fuel process module 516, refrigeration compressor modules 520, nitrogen generator modules 522, a CGL product circulation module 524, a water treatment module 526, and a reverse osmosis water module 528. As shown, the containment fittings for the CGL product containment system 506 are preferably above the water line. The containment modules 508A, 508B and 508C of the containment system 506, which could include one or more modules, are positioned in the one or more containment holds 532 and enclosed in a nitrogen hood or cover 507.
Turning to
The disclosed embodiments advantageously make a larger portion of the gas produced in the field available to the market place, due to low process energy demand associated with the embodiments. Assuming all the process energy can be measured against a unit BTU content of the natural gas produced in the field, a measure to depict percentage breakout of the requirements of each of the LNG, CNG and CGL process systems can be tabulated as shown below in Table 3.
Each system starts with a High Heat Value (HHV) of 1085 BTU/ft3. The LNG process reduces HHV to 1015 BTU/ft3 for transportation through extraction of NGLs. Make-up BTU spiking and crediting the energy content of NGLs is included for LNG case to level the playing field. A heat rate of 9750 BTU per kWhr is used in all cases.
76%
97%
With credit for NGL's, the LNG process will sum up to 85% total value for Market delivery of BTUs—a quantity still less than the deliverable of this invention. Results are typical for individual technologies. The data provided in Table 3 was sourced as follows: LNG—third party report by Zeus Energy Consulting Group 2007; CNG—reverse engineering Bishop U.S. Pat. No. 6,655,155; and CGL—internal study by SeaOne Corp.
Overall the disclosed embodiments provide a more practical and rapid deployment of equipment for access to remote, as well as developed natural gas reserves, than has hitherto been provided by either LNG or CNG systems in all of their various configurations. Materials required are of a non-exotic nature, and are able to be readily supplied from standard oilfield sources and fabricated in a large number of industry yards worldwide.
Turning to
However, gas with high content condensates from fields such as the South Pars fields could be handled by providing additional separator capacity to the separator equipment 812. For natural gas mixes with undesirable levels of acid gasses such CO2 and H2S, Chlorides, Mercury and Nitrogen the bypass valves 803, 811 and 819 at modular connection points 801, 809 and 817 can be closed as needed and the gas stream routed through process modules 820, 822 and 824 attached to the associated branch piping and isolation valves 805, 807, 813, 815, 821 and 823 shown at each by pass station 801, 809 and 817. For example, raw gas from the Malaysian deepwater fields of Sabah and Sarawak containing unacceptable levels of acid gas could be routed around a closed by-pass valve 803 and through open isolation valves 805 and 807 and an attached module 820 where amine absorption and iron sponge systems extract the CO2, H2S, and sulfur compounds. A process systems module for the removal of mercury and chlorides is best positioned downstream of dehydration unit 814. This module 822 takes the gas stream routed around a closed by pass valve 811 through open isolation valves 813 and 815, and comprises a vitrification process, molecular sieves or activated carbon filters. For raw gas with high levels of nitrogen as found in the raw gas from some areas of the Gulf of Mexico, the a gas stream is routed around a closed by-pass valve 819 and through open isolation valves 821 and 823, passing the natural gas stream through a scale selected process module 824 to remove nitrogen from the gas stream. Available process types include membrane separation technology, absorptive/adsorptive tower and a cryogenic process attached to the vessels nitrogen purge system and storage pre chilling units.
The extraction process describes above can also provide a first stage to the NGL module 816, assisting the additional capacity required to deal with high liquids mixes such as those found in the East Qatar field.
In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions shown in the process flow diagrams described herein is merely illustrative, unless otherwise stated, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. As another example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Features and processes known to those of ordinary skill may similarly be incorporated as desired. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.
This application is a continuation of U.S. patent application Ser. No. 12/486,627, filed Jun. 17, 2009, which claims the benefit of U.S. Provisional Appl. No. 61/074,505, filed Jun. 20, 2008, both of which are fully incorporated herein by reference.
Number | Date | Country | |
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61074502 | Jun 2008 | US |
Number | Date | Country | |
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Parent | 12486627 | Jun 2009 | US |
Child | 16998556 | US |