Patent Application
20150001101
The invention relates generally to transportation vehicles or other devices fueled by natural gas or other natural gas stored at low pressure. More particularly, the invention relates to such vehicles or devices having fuel storage apparatus employing high-surface-area adsorptive materials and also to refueling apparatus for such vehicles.
Over the years, concerns have developed over the availability of conventional fuels (such as gasoline or diesel fuel) for internal combustion engine vehicles, the operating costs and fuel efficiencies of such vehicles, and the potentially adverse effects of vehicle emissions on the environment. Because of such concern, much emphasis has been placed on the development of alternatives to such conventional vehicle fuels. One area of such emphasis has been the development of vehicles fueled by natural gas or other methane-type natural gas, either as the sole fuel or as one fuel in a dual-fuel system. As a result, vehicles using such fuels have been produced and are currently in use both domestically and abroad.
In order to provide such natural gased vehicles with a reasonable range of travel between refuelings, it has previously been necessary to store the on-board natural gas at very high pressures, generally in the range of approximately 2000 psig (13.9 MPa) to 3000 psig (20.7 MPa). Without such high-pressure on-board storage, the practical storage capacity of such vehicles was limited because of space and weight factors to the energy equivalent of approximately one to five gallons (3.7 to 19 liters) of conventional gasoline. Thus, by compressing the natural gas to such high pressures, the on-board storage capacities of such vehicles were increased.
One disadvantage of the compressed natural gas systems discussed above is that they require complex and comparatively expensive and refueling apparatus in order to compress the fuel to such high pressures. Such refueling apparatus has been found to effectively preclude refueling the vehicle from a user's residential natural gas supply system as being commercially impractical on an individual ownership basis. Furthermore, such high pressure apparatus is frequently perceived by the public as being more dangerous than low pressure apparatus. For example, the public is already accustomed to refrigerant pressures in the area of approximately 200 psig (1380 KPa) in home refrigeration units and does not find such low pressures objectionable.
Another disadvantage of high pressure on-board natural gas storage systems is that heavy walled containers must typically be used, thereby increasing the cost and weight of the system. Additionally, as the cylinders are discharged during the operation of the vehicle, significant condensation on the cylinders and associated piping can occur as a result of the magnitude of the decrease in the pressure inside the cylinder.
Another alternative to the above discussed fuel storage and vehicle range problems, has been to store the on-board fuel in a liquid state generally at or near atmospheric pressure in order to allow sufficient quantities of fuel to be carried on board the vehicles to provide reasonable travel ranges between refuelings. Such liquefied gas storage may be disadvantageous if it involves complex and comparatively expensive cryogenic equipment, both on board the vehicle and in the refueling station, in order to establish and maintain the necessary low gas temperatures.
In U.S. Pat. Nos. 4,522,159 and 4,523,548 there is disclosed a utilization system for gaseous hydrocarbon fuel powered vehicles which stores the fuel on-board at relatively low pressures up to approximately 500 psig using sorptive storage means. The disclosed vehicle utilization system comprises means for on-board storage of a self-contained supply of the gaseous hydrocarbon fuel, a prime mover, means for conveying the gaseous hydrocarbon fuel to and from the on-board storing means and means for controlling the pressure of the gaseous hydrocarbon fuel from the on-board storing means to the prime mover. The on-board storing means is said to include one or more vessels or cylinders, containing a predetermined sorbent material for allowing a given amount of the gaseous hydrocarbon fuel to be stored at such lower pressure. The prime mover such as an internal combustion engine includes means for combining the gaseous hydrocarbon fuel with air to produce the mechanical energy therefrom necessary to move the vehicle. The conveying means is reported to be adapted so as to convey the gaseous hydrocarbon fuel to the on-board storing means from a stationary refueling apparatus, and also to convey the gaseous hydrocarbon fuel from the on-board storing means to the combining means of the prime mover during operation of the vehicle. In the preferred embodiment, the maximum pressure at which the gaseous hydrocarbon fuel is stored in the on-board storing means is the range of approximately 100 psig to approximately 400 psig.
As described in the above-mentioned patents, the power plant includes a fuel port, a storage vessel, and interposed between the fuel port and the storage vessel is a sorptive filter, which forms an important part of the invention. The sorptive filter is comprised of a vessel, which contains a predetermined sorbent material for filtering the flow of the gaseous hydrocarbon fuel to the storage vessel. The sorptive filter vessel may be any shape or construction, which is capable of withstanding the maximum pressure at which the power plant is intended to operate. However, it is generally preferred that the size of the filter vessel be related to the size of the storage vessel. Specifically, it has been found advantageous to provide at least 0.0052 cubic feet of filter capacity to each cubic feet of storage capacity. With regard to the sorbent material, it is preferred that this sorbent material be comprised of activated carbon. In this regard, both the sorbent material contained in the sorptive filter and the sorbent material contained in the storage vessel may both be comprised of activated carbon.
It should be noted that the sorptive filter is associated with the conveying means of the power plant such that the gaseous hydrocarbon fuel supplied by a stationary source thereof must first pass through the sorptive filter before being stored in the storage vessel. Likewise, before the stored gaseous hydrocarbon fuel can be conveyed to a carburetor of the power plant, this fuel must again pass through the sorptive filter. During the charging of the stored vessel, the sorptive filter adsorptively and/or absorptively removes predetermined constituents of the gaseous hydrocarbon fuel, as well as any odorent previously introduced to the fuel, before the gaseous hydrocarbon fuel is conveyed to the storage vessel. These predetermined constituents include, for example, oil, water vapor, and so-called “heavy end” constituents of the fuel. Generally speaking, such heavy end constituents include propane and other constituents that are heavier than methane. The purpose of removing such heavy end constituents is to maximize the capability of the storage vessel to sorptively store the lighter hydrocarbons, such as methane for example. It is also important to note that the sorptive filter also operates to prevent the accummulation over time of any unwanted fuel constituents in the storage vessel.
When the engine for the power plant is energized and enabled to consume the gaseous hydrocarbon fuel stored in the storage vessel, the sorptive filter operates to desorptively re-introduce the removed constituents and odorent to the flow of the gaseous hydrocarbon fuel from the storage vessel to the carburetor of the engine. Accordingly, it should be appreciated that the sorptive filter is self-cleaning during each charge and discharge cycle of the storage system.
In order to assist the desorption of the undesirable constituents from the sorbent material contained in the filter, means for increasing the temperature of the sorptive filter may also be provided in the appropriate application. Preferably, this temperature increasing means is associated with the engine of the power plant so that the heat generated by the operation of the engine is utilized by the temperature increasing means. One form of a suitable temperature increasing means is a conduit, which is wrapped around the sorptive filter. This conduit could be connected, for example, to either the engine cooling system or to the engine exhaust system in order to utilize at least a portion of the waste heat generated by the engine. Additionally, it may be advantageous in some applications to simply locate the sorptive filter in relatively close proximity to the engine in order to utilize the heat radiated by the engine.
Unfortunately, since the mid-1980's, researchers have not been able to substantially increase the capacity of the adsorbent storage vessels. Even with the use of guard beds, such as described in the above-mentioned patents as sorptive filters, substantial increases in the storage capacity of the sorbent vessels have not increased sufficiently to achieve commercial use of adsorptive natural storage. The prior art has not recognized the sorptive properties of the constituents in the natural gas stream supply to effectively manipulate the pressurization (fueling) and depressurization (throttling) of the power plant to substantially improve the storage capacity of the adsorbent in the storage vessel to allow such means to be used in commercial vehicles. While the afore-mentioned patents describe a manual shut-off valve between the adsorbent storage vessel and the sorptive filter, the patents do not otherwise teach or recognize a manipulation of the system to allow significant decrease in the size of the sorptive filter, and at the same time, vastly increase the capacity of the adsorptive storage vessel.
In accordance with the present invention, a natural gas-powered vehicle is provided, which has substantially increased methane storage utilizing a storage vessel which contains a methane adsorbent. In this invention, a sorbent-containing guard bed is provided, along with the primary adsorptive storage vessel. The guard bed is substantially smaller than the primary adsorptive storage vessel, yet the proposed system greatly increases the adsorptive capacity of the primary adsorptive storage vessel by the addition of a valve between the guard bed and the primary storage vessel, to allow optimal pressurization between the two vessels during fueling of the system and depressurization during operation of the engine. Heating of the guard bed during depressurization improves desorption of C3+ hydrocarbons and improves adsorptive capacity during refueling.
Storage systems for gaseous hydrocarbon fuel powered vehicles are known, wherein the natural gas fuel is stored on-board at relatively low pressures up to approximately 500 psig using sorptive storage means. Such systems are disclosed, for example, in U.S. Pat. Nos. 4,522,159 and 4,523,548, discussed previously.
In general, the natural gas storage system comprises means for on-board storage of a self-contained supply of the gaseous hydrocarbon fuel, a prime mover, means for conveying the gaseous hydrocarbon fuel to and from the on-board storing means and means for controlling the pressure of the gaseous hydrocarbon fuel from the on-board storing means to the prime mover. The on-board storing means is said to include one or more vessels or cylinders, containing a predetermined sorbent material for allowing a given amount of the gaseous hydrocarbon fuel to be stored at such lower pressure. The prime mover such as an internal combustion engine includes means for combining the gaseous hydrocarbon fuel with air to produce the mechanical energy therefrom necessary to move the vehicle. The conveying means is reported to be adapted so as to convey the gaseous hydrocarbon fuel to the on-board storing means from a stationary refueling apparatus, and also to convey the gaseous hydrocarbon fuel from the on-board storing means to the combining means of the prime mover during operation of the vehicle. In the preferred embodiment, the maximum pressure at which the gaseous hydrocarbon fuel is stored in the on-board storing means is the range of approximately 100 psig to approximately 600 psig.
The specifics of the prime mover, and connections between the prime mover and the natural gas storage vessel or vessels, as well as the specific fueling supply connections are not part of the present invention and are believed to be known, again, as described in the above-mentioned U.S. patents. The storage system, which forms the basis of the present invention includes a fuel port, a primary storage vessel, and interposed between the fuel port and the primary storage vessel is a sorptive filter or guard bed, which forms an important part of the invention.
Each of the primary storage vessels contain a predetermined sorbent material for reducing the pressure at which the gaseous hydrocarbon fuel is stored within the cylinders. As referred to herein, the terms “sorbent” or “sorptive” are intended to refer to “adsorbents”, “absorbents” or both. The absorbent material may comprise any of a number of adsorbents or molecular sieves, such as activated carbon, zeolite compounds, various clays, silica gels, or metal organic framework (MOF) materials, for example. Such adsorbent materials may be in the form of pellets, spheres, granulated particles, or other suitable forms whereby the surface area of the adsorbent material is optimized in order to maximize the amount of natural gas adsorbed on the surface thereof. The present invention also contemplates the use of liquid absorbents, such as a liquid coating on an adsorbent material.
The guard bed is comprised of a vessel, which contains a predetermined sorbent material for filtering the flow of the gaseous hydrocarbon fuel to the primary storage vessel or vessels. The guard bed may be any shape or construction, which is capable of withstanding the maximum pressure at which the power plant is intended to operate. However, it is generally preferred that the size of the filter vessel be substantially smaller than the size of the primary storage vessel. Specifically, it has been found advantageous to provide the guard bed with at most 60% of the storage capacity of the primary storage vessel, preferably at most 45% of the capacity of the primary storage vessel, more preferably at most 30% of the capacity of the primary storage vessel. By the further application of heat to the guard bed, storage capacity can be at most about 15%, of the storage capacity of the primary storage vessel, can be at most about 13%, of the storage capacity of the primary storage vessel, and can be even further reduced to 5% or less than the storage capacity of the primary storage vessel. With regard to the sorbent material, it is preferred that this sorbent material is comprised of a material having the ability to absorb C3+ hydrocarbons. In this regard, both the sorbent material contained in the guard bed and the sorbent material contained in the primary storage vessel may both be comprised of the same or different adsorbent. Examples of adsorbent include, but are not limited to activated carbon, zeolites, silica, metal organic frameworks (MoFs), etc.
It should be noted that the guard bed is associated with the conveying means of the power plant such that the gaseous hydrocarbon fuel supplied by a stationary source thereof must first pass through the guard bed before being stored in the primary storage vessel. Likewise, before the stored gaseous hydrocarbon fuel can be conveyed to a carburetor of the power plant, this fuel must again pass through the guard bed. During the charging of the primary storage vessel, the guard bed adsorptively and/or absorptively removes predetermined constituents of the gaseous hydrocarbon fuel, as well as any odorent previously introduced to the fuel, before the gaseous hydrocarbon fuel is conveyed to the primary storage vessel. These predetermined constituents include, for example, oil, water vapor, and so-called “heavy end”, i.e. C3+ hydrocarbon constituents of the fuel. Generally speaking, such heavy end constituents include propane and other constituents that are heavier than methane. The purpose of removing such heavy end constituents is to maximize the capability of the primary storage vessel to sorptively store the lighter hydrocarbons, such as methane for example. It is also important to note that the guard bed also operates to prevent the accumulation over time of any unwanted fuel constituents in the primary storage vessel.
When the engine for the power plant is energized and enabled to consume the gaseous hydrocarbon fuel stored in the storage vessel, the guard bed operates to desorptively re-introduce the removed constituents and odorant to the flow of the gaseous hydrocarbon fuel from the storage vessel to the carburetor of the engine. Accordingly, it should be appreciated that the guard bed is self-cleaning during each charge and discharge cycle of the storage system. Previous to this invention, it was not recognized that the pressurization of the guard bed and the primary storage vessel could be manipulated, so as to optimize the adsorption of the heavier hydrocarbon components in the guard bed, thus, allowing increased methane adsorption capacity in the primary storage vessel. The present inventors recognize that the heavier hydrocarbon components are best adsorbed at higher pressures, and most favorably desorbed at lower pressures. In accordance with this invention, a valve is provided between the guard bed and the primary storage vessel, so as to optimize adsorption of the heavy hydrocarbons during the fueling of the vehicle, and optimize desorption of the heavy hydrocarbons from the guard bed during depressurization and throttling of the engine. The manipulation of the valve between the guard bed and primary storage vessel to provide this optimization during pressurization and depressurization will be described below with respect to
In order to assist the desorption of the undesirable constituents from the sorbent material contained in the guard bed, means for increasing the temperature of the guard bed are provided in the appropriate application. Preferably, this temperature increasing means is associated with the engine of the power plant so that the heat generated by the operation of the engine is utilized by the temperature increasing means. One form of a suitable temperature increasing means is a conduit, which is wrapped around the guard bed. This conduit could be connected, for example, to either the engine cooling system or to the engine exhaust system in order to utilize at least a portion of the waste heat generated by the engine. Additionally, it may be advantageous in some applications to simply locate the guard bed in relatively close proximity to the engine in order to utilize the heat radiated by the engine. Alternatively, heat can be provided to the guard bed by heat exchange with gas entering the guard bed during depressurization.
The natural gas storage system of the present invention can now best be explained by referring to the figures. As shown in
In
The storage system 10 shown in
The operation of the natural gas storage system of this invention can best be described by referring to
The operation of the methane storage system 10 as shown in
Two natural gas storage systems as shown in
For the first system, a supply of natural gas was sent to an opened connection 18 at a pressure of 600 psia to a guard bed 14 to pressurize the guard bed 14 from 60 to about 515 psia. During the pressurization of the guard bed 14, valve 16 was closed to retain primary storage tank 12 at 60 psia. As the pressure within guard bed 14 reached 515 psia, valve 16 was opened to pressurize primary storage vessel 12 to about 515 psia to store filtered natural gas from guard bed 14. During the engine acceleration process, connection 18 was opened to depressurize guard bed 14 from 515 psia to the same pressure as the engine, about 60 psia. During the depressurization, valve 16 was closed to maintain primary storage vessel at about 500 psia. As guard bed 14 reached about 60 psia, valve 16 was opened to depressurize primary storage tank 12, allowing filtered natural gas to flow toward and to purge guard bed 14.
The above-mentioned process was repeated as 30 cycles, and during the last accelerating cycle, amounts of C4, C5 and C6 hydrocarbons were collected from the filtered gas exiting storage tank 12. The amounts of hydrocarbons were compared with the amounts of C4, C5 and C6 hydrocarbons gathered in the initial fueling of the first cycle from connection 18.
As shown in
Two natural gas storage systems as shown in
A supply of natural gas was sent to an opened connection 18 at 600 psia to a guard bed 14 to pressurize the guard bed 14 from 60 to about 515 psia. During the pressurization of guard bed 14, valve 16 was closed to retain primary storage tank 12 at 60 psia. As the pressure within guard bed 14 reached 515 psia, valve 16 was opened to pressurize primary storage vessel 12 to about 515 psia to store filtered natural gas from guard bed 14. During the engine acceleration process, connection 18 was opened to depressurize guard bed 14 from 515 psia to the same pressure as the engine, about 60 psia. During the depressurization, valve 16 was closed to maintain primary storage vessel at about 500 psia. As guard bed 14 reached about 60 psia, a heating mechanism 20 heated guard bed 14 to about 80° C., then valve 16 was opened to depressurize primary storage tank 12, allowing filtered natural gas to flow toward and to purge guard bed 14.
The above-mentioned process was repeated as 30 cycles, and during the last accelerating cycle, amounts of C4, C5 and C6 hydrocarbons were collected from the filtered gas exiting storage tank 12. The amounts of hydrocarbons were compared with the amounts of C4, C5 and C6 hydrocarbons gathered in the initial fueling of the first cycle from connection 18.
As shown in
| Number | Date | Country | |
|---|---|---|---|
| 61840114 | Jun 2013 | US |
