Patent Application
20130008558
The present invention relates generally to fuel storage and distribution and, more particularly, to a system, apparatus and method for the cold-weather storage and distribution of gaseous fuels.
As gasoline prices have soared and concerns over harmful emissions have mounted in recent years, vehicles that run on alternative fuel sources are becoming increasingly important. For example, the use of compressed natural gas (“CNG”) as an alternative fuel for motor vehicles is becoming increasingly popular throughout the world because it is relatively inexpensive, burns cleanly, is relatively abundant and is adaptable to existing technologies.
Natural-gas vehicles use the same basic principles as gasoline-powered vehicles. In other words, the fuel (natural gas) is mixed with air in the cylinder of, e.g., a four-stroke engine, and then ignited by a spark plug to move a piston up and down. Although there are some differences between natural gas and gasoline in terms of flammability and ignition temperatures, natural-gas vehicles themselves operate on the same fundamental concepts as gasoline-powered vehicles. Accordingly, existing gasoline-powered vehicles may be converted to run on CNG, thereby easing the transition between gasoline and CNG in markets where gasoline-powered vehicles are dominant. In addition, an increasing number of vehicles worldwide are being originally manufactured to run on CNG.
Advantageously, CNG-fueled vehicles have lower maintenance costs when compared with other fuel-powered vehicles. In addition, CNG emits significantly fewer pollutants such as carbon dioxide, hydrocarbons, carbon monoxide, nitrogen oxides, sulfur oxides and particulate matter compared to petrol.
Despite the advantages of compressed natural gas as a motive fuel, the use of natural gas vehicles faces several logistical concerns, including fuel storage and infrastructure available for delivery and distribution at fueling stations. Natural gas suitable for vehicle use is customarily stored in small capacity tank, at 3,600 psi at 70° F., and is distributed from storage tanks to an on-vehicle receiving tank by “cascade filling.” Cascade filling is accomplished by starting out with the storage tank at a higher pressure than the receiving tank and then allowing this pressure to force the gas (or liquid) into the receiving tank. In so doing, natural gas is transferred, and the pressure in the storage tank drops to the point where the pressures of the two tanks become equal and nothing more is transferred.
The storage and distribution of CNG is severely affected, however, at low temperatures, and particularly when the temperature drops below 40° F. At low temperatures, the pressure in the storage tank drops, thereby resulting in less of a difference in pressure between the receiving tank and the storage tank, ultimately resulting in inefficiencies in gaseous fuel transfer (i.e., less gaseous fuel being transferred to the receiving tank on board the compatible vehicle, and longer filling times).
Moreover, the storage of CNG in large capacity tanks at high pressures is also problematic. In particular, storing CNG in tanks at 3,000-3,600 psi requires that the tank's walls be cast from thick steel or other suitable metal in order to withstand the enormous stresses caused by the compressed gas. As will be readily appreciated, large capacity CNG storage tanks would therefore be undesirably heavy and inefficient and expensive to manufacture and transport. As a result, transportation and storage of CNG is customarily effectuated by using numerous smaller, tube-shaped cylinders, which themselves are extremely heavy.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide a system and method for the cold-weather storage and distribution of gaseous fuels, which utilizes large capacity tanks that are insulative and have a reduced weight.
With the forgoing concerns and needs in mind, it is a general object of the present invention to provide a system and method for the cold-weather storage and distribution of gaseous fuels.
It is another object of the present invention to provide a system and method for the cold-weather storage and distribution of compressed natural gas.
It is another object of the present invention to provide a system and method for the cold-weather storage and distribution of gaseous fuels that compresses the fuels to a predetermined storage pressure.
It is another object of the present invention to provide a system and method for the cold-weather storage and distribution of gaseous fuels that maintains the gaseous fuel at a desired storage temperature.
It is another object of the present invention to provide a system and method for the cold-weather storage and distribution of gaseous fuels having a tank that has a greater storage capacity and is lighter than existing storage tanks.
These and other objectives of the present invention, and their preferred embodiments, shall become clear by consideration of the specification, claims and drawings taken as a whole.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:
An embodiment of the system of the present invention is indicated in general at 10 in
As described in greater detail below, gaseous fuel, e.g., natural gas, is transferred from a low-pressure source to the slow fill compressor 12. As used herein, “low pressure” is intended to mean the pressure at which the particular gas is originally introduced to the system 10. In the preferred embodiment, the low-pressure source is a low pressure gas line 22 extending from a gas main, wherein the low pressure is the line pressure of the gas main. Alternatively, however, the low-pressure source may be a low-pressure gas tank 24 that is fluidly connected to the slow fill compressor 12 by a pipeline 26. In this embodiment, the natural gas may be delivered by a tanker truck, unloaded from the truck via a loading pipeline 28, and stored in the low-pressure gas tank 24 for use on demand. In any event, the low pressure gas line 22 and/or the low pressure gas tank 24 provide an on-demand supply of gaseous fuel for compression, storage and distribution by the system 10, as described in detail hereinafter.
Returning to
As alluded to above, gaseous fuel storage and distribution and, in particular CNG storage and distribution are greatly affected when temperatures drop below 40° F. It is therefore crucial for efficient storage and distribution that the CNG in the storage tanks is maintained at roughly 70° F. at 3,600 psi, as is standard in the industry. Importantly, the system 10 further includes a means of maintaining the temperature of the gaseous fuel in the storage tanks at a desired level, even when ambient air temperature drops, as discussed below.
In cold weather, especially below 40° F., the temperature of the gaseous fuel in the storage tanks begins to drop, as does the pressure within the storage tanks. As gaseous fuel stored in the tanks 16 is distributed to compatible vehicles, the slow fill compressor 12 is actuated to intake and compress source gas to replenish the gaseous fuel and pressure in the tanks 16. As the low-pressure source gas is compressed by the slow fill compressor 12, its temperature, as well as pressure, rises. This heated, compressed gas is then routed along the direct fill pipeline 32 to the storage tanks 16 for storage. The warmer compressed gas enters the tanks 16 so as to allow the incoming, warmer compressed gas to mix with the gaseous fuel already present in the tanks 16 so as to raise its temperature to a desired and optimum point, namely, approximately 70° F.
In this manner, compression of low-pressure source gas generates heat, which is then transferred to the gaseous fuel inside the storage tanks 16 to maintain the temperature thereof. As will be readily appreciated, fuel distribution to compatible vehicles triggers an almost continuous, slow pumping and compression of source gas, thereby providing the storage tanks 16 with an almost continuous supply of heat. As a result, cost savings can be realized because stand-alone heaters do not need to be utilized to maintain the temperature of the gaseous fuel within the tanks.
As further shown in
In the event that the tanks 16 are full, for instance when no dispensing is occurring, no compression is taking place and thus no heat from the compression of source gas is available to maintain the temperature of the gaseous fuel inside the storage tanks 16. Accordingly, in order to maintain the temperature of the gaseous fuel in cold weather during times of little or no replenishing of the tanks (i.e., when fuel dispensing is low), the storage tanks 16 are additionally provided with an auxiliary electric heater 42 located in the main body of each of the tanks, discussed in more detail below. In the preferred embodiment, the power supply 30 that powers the slow fill compressor 12 also powers each electric heater 42, although a separate power supply may also be used without departing from the broader aspects of the present invention.
Importantly, as discussed above, the temperature sensor 34 positioned within each storage tank 16 monitors a temperature of the gaseous fuel within each tank 16. As shown in
Preferably, the electric heater 42 is envisioned as a “blanket” which surrounds at least a portion of the tanks 16, although other configurations and positioning of the electric heater 42 are also contemplated in the present invention.
As further shown in
Check valves 54 are positioned downstream from the solenoid valve along the direct fill line 32 and downstream the heat exchange apparatus 14 along the heat exchange loop 40. The check valves 54 desirably control the direction of flow through the heat exchange loop 40 and the direct fill line 32 toward the storage tanks 16, and prevent undesirable flow reversals that might otherwise occur due to unexpected pressure changes, leaks, equipment failures, or the like. Check valves 56 are also positioned along the output pipelines to control the direction of flow therethrough and to prevent similar flow reversals.
Importantly, the system 10 of the present invention is, broadly speaking, applicable to CNG storage tank assemblies of any size, both small and large capacity. The large capacity tank concept complements this system in the preferred embodiment, but it is not required.
In connection with the above, the configuration of the gaseous fuel storage tanks 16 is another important aspect of the present invention. In the preferred embodiment, each tank 16 is a large capacity tank, capable of storing a large quantity of gaseous fuel, in contrast to known small-volume tanks. Where the gaseous fuel is compressed natural gas, stored at approximately 70° F. and 3,600 psi, each tank 16 has a storage capacity large enough fill 500-700 compatible vehicles with CNG. Moreover, each storage tank is specially designed to withstand the pressures of the gaseous fuel inside the tank 16 and to insulate the gaseous fuel inside the tank from outside, ambient air, while having a lower weight profile than has heretofore been known.
As further shown therein, a polymer based resin 66 fills the remainder of the annular space 64. Importantly, this resin 66 functions as an insulation layer to insulate the interior of the tank from the outside, ambient air (and potential low temperature thereof), as well as functioning as a mechanical reinforcement layer that effectively bonds the inner wall 60 to the outer wall 62, and as a shock absorber for absorbing stress on the walls of the inner wall 60. In this manner, the inner wall 60 and outer wall 62 are essentially joined together as a single unit. As will be readily appreciated, this increases the ability of the tank 16 to withstand the high pressures of gaseous fuel stored therein, as discussed below. In addition, the use of two walls bonded together with a polymer resin 66 decreases the weight of the tank 16 as compared to a single-walled tank of equal volume.
In the preferred embodiment, each wall is manufactured from steel, although other metals or materials known in the art may also be used without departing from the broader aspects of the present invention. Preferably, the walls of each wall 60,62 are approximately 1″ thick in embodiments where steel is utilized. In contrast to the present invention, known single-wall storage tanks not having the structure of the tanks 16 shown in
Through testing, it has been shown that the greatest stresses in cylindrical storage tanks oriented in the horizontal direction are concentrated along the top of the tank. Advantageously, as discussed above, the polymer based resin 66 disposed in the annular space 64 functions as a shock absorber to absorb the stresses upon the inner wall 60 of the tank, such that the outer wall 62 is subject to little stress, thereby allowing the walls 60,62 to be manufactured from steel or other metals of a lesser thickness. As compared to a single-walled storage tank having the same capacity and suitable to withstand gaseous fuel at a pressure of 3,600 psi at 70° F., the tank 16 of the present invention provides for an approximately 50% reduction in weight. In addition, significant weight savings are also realized in comparison to utilizing a large number of smaller storage tanks to store the same volume of gas, as more tanks equate more weight.
Referring now to
In contrast, finite element analysis of a single walled tank having a 44″ diameter and a 1″ thick wall has shown that the tank would yield to internal pressures prior to reaching the optimum internal pressure of 3,600 psi. As shown in
It is therefore another important aspect of the present invention that the gaseous fuel storage tank 16 of the system of the present invention is capable of withstanding much higher pressures than known single-walled tanks of similar wall thickness. As a result, significant savings in weight, materials, cost, and ease of manufacture are realized, as discussed above. In view of the above, the present invention therefore provides a much lighter tank with the added ability to more precisely control the temperature of pressurized gaseous fuel stored within the tank. Indeed, by utilizing the compression of source gas to maintain the temperature within the storage tanks, significantly less energy is expended than would be the case if a stand-alone heater were utilized. Importantly, the temperature sensor and thermostat allow the temperature within the tanks to be more precisely controlled. Moreover, when the tanks are full and no compression is needed to fill the tanks, the temperature sensor and thermostat are arranged so as to control the auxiliary electric heater located in the main body of the tank to further maintain an optimum temperature of the CNG stored therein.
As discussed in detail above, the system 10 of the present invention utilizes the heat generated by gaseous compression of the fuel as a way to maintain the proper temperature and pressure regiment within the CNG storage tanks. In addition, the present invention provides a novel construction for large capacity CNG storage tanks that can be manufactured economically and at a much reduced weight profile. It will therefore be readily appreciated that a combination of the system 10 shown in
Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of this disclosure.
