Patent Application
20130305744
The field of the invention relates generally to natural gas distribution, and specifically to a natural gas dispensing system for a vehicle.
Motor vehicles that operate on gaseous fuels such as natural gas and hydrogen are refueled at stations that dispense gas at high pressure. While commercial refueling stations are capable of refueling a motor vehicle in minutes, residential refueling stations typically refuel motor vehicles over a period of several hours. Typical residential refueling stations use compressors to pressurize the gas to the required delivery pressure. These known compression systems are typically slow, generate vibrations and noise pollution, and may be expensive to operate due to high power consumption. Known residential refueling stations also typically include adsorption-based moisture removal systems. Such known adsorption-based removal systems can be inefficient, costly and present additional components that require maintenance and further complicate the system.
In one embodiment, a fuel gas delivery system is provided. The fuel gas delivery system includes a feed line configured to provide a natural gas stream and a cryocooler fluidly coupled to the feed line. The cryocooler is configured to condense the natural gas to provide a liquefied natural gas (LNG) stream and to freeze impurities contained in the natural gas stream. The frozen impurities are separated from said LNG stream. A first heat exchanger is fluidly coupled to the cryocooler and the first heat exchanger is configured to vaporize at least a portion of the LNG stream to provide compressed natural gas. A delivery line is configured to supply the compressed natural gas to an end user and a removal line is configured to remove the impurities from the fuel gas delivery system.
In another embodiment, a fuel gas delivery system is provided. The fuel gas delivery system includes a feed line configured to provide a natural gas stream and a cryocooler fluidly coupled to the feed line. The cryocooler is configured to cool the natural gas below the freezing point of impurities contained in the natural gas stream to separate the frozen impurities from a cooled and densified natural gas stream. A first heat exchanger is fluidly coupled to the cryocooler and the first heat exchanger is configured to vaporize at least a portion of the cooled and densified stream to provide compressed natural gas. A delivery line is configured to supply the compressed natural gas to an end user and a removal line is configured to remove the impurities from the fuel delivery system.
In yet another embodiment, a method of supplying purified compressed fuel gas is provided. The method includes supplying a natural gas stream to a cryocooler of a compressed natural gas delivery system, freezing impurities contained in the natural gas stream and condensing the natural gas to provide an LNG stream. The method further includes separating the frozen impurities from the LNG stream, vaporizing the LNG stream to provide a compressed natural gas stream at a predetermined pressure, and supplying the compressed natural gas to a delivery line.
In yet another embodiment, a method of delivering a high purity compressed fuel gas is provided. The method includes supplying a natural gas stream to a cryocooler of a compressed fuel gas delivery system, cooling the natural gas in the cryocooler to a temperature below the freezing point of impurities contained in the natural gas stream, and separating the frozen impurities from the condensed natural gas to provide a cooled and densified natural gas stream. The method further includes vaporizing the cooled and densified stream to provide a compressed natural gas stream at a predetermined pressure, and delivering the compressed natural gas to a delivery line.
In yet another embodiment, a method of removing impurities from a fuel gas stream in a fuel gas delivery system is provided. The method includes supplying a natural gas stream to a cryocooler of the fuel delivery system. The cryocooler is configured to condense the natural gas to an LNG stream, freeze impurities contained in the natural gas, and separate the impurities from the LNG stream. The method further includes selectively supplying the LNG stream to one of a first storage tank and a second storage tank, and selectively precooling the natural gas stream against LNG in the first storage tank when the first storage tank is filled with a predetermined amount of LNG. The LNG is vaporized into compressed natural gas. The method further includes selectively precooling the natural gas stream against the LNG in the second storage tank when the second storage tank is filled with a predetermined amount of LNG. The LNG is vaporized into compressed natural gas. The method further includes opening a first valve when the compressed natural gas in the first tank is at a predetermined pressure to supply the compressed natural gas to a delivery line, and opening a second valve when the compressed natural gas in the second tank is at the predetermined pressure to supply the compressed natural gas to the delivery line. The LNG is vaporized in the first tank while the second tank is being filled with LNG from the cryocooler and LNG is vaporized in the second tank while the first tank is being filled with LNG from the cryocooler to provide a steady supply of compressed natural gas to the delivery line.
Known gaseous fuel delivery systems utilize adsorption-based removal systems to remove impurities from gaseous fuel and compressors to provide fuel at high pressure. In contrast, the present system utilizes a cryocooler based system to remove impurities and provide fuel at high pressure, without the need for a compressor or an adsorption-based removal system.
In the exemplary embodiment, feed line 12 is fluidly coupled to cryocooler 16 and is configured to supply natural gas thereto. Feed line 12 is fluidly connected to a source (not shown) of natural gas such as, for example, a residential natural gas line. Cryocooler 16 includes a cold head 20 that is capable of producing extremely low temperatures at cold head 20, for example below 2 K. Cryocooler 16 may be any type of known cryocooler that enables delivery system 10 to function as described herein such as, for example, a GM, Stirling, or pulse tube cryocooler.
In the exemplary embodiment, cryocooler 16 cools and condenses natural gas from feed line 12 to provide a liquefied natural gas (LNG) stream to delivery line 18. Because of the extremely low temperatures required to liquefy the natural gas, impurities having a higher freezing point than natural gas are frozen and thus separated from the LNG stream. The frozen impurities, for example water, hydrocarbons, and hydrogen sulfide, adhere to cold head 20 and/or surrounding structure of feed line 12, cryocooler 16, and delivery line 18. The frozen impurities are later removed from the system via removal line 28, as will be described below.
In the exemplary embodiment, the LNG stream passes from cryocooler 16 to pump 22 where it is raised in pressure to a suitable delivery pressure. The high-pressure LNG stream then passes to regenerator 14 where it is warmed in indirect heat exchange with natural gas in feed line 12 to precool the natural gas. Precooling the natural gas stream in feed line 12 against the LNG stream in delivery line 18 increases system efficiency by reducing the cooling and power consumption required of cryocooler 16 to condense the natural gas stream. The high-pressure LNG stream may be at least partially vaporized and pressurized in regenerator 14 to produce a high-pressure compressed natural gas (CNG) stream that is supplied through delivery line 18 to storage and/or a vehicle (not shown). A heat exchanger 24 may be thermally coupled to delivery line 18 to provide additional heating to completely vaporize the high-pressure LNG stream. Heat exchanger 24 may be, for example, an electrical heater or an ambient air heat exchanger. A cooler 26 may also be provided in delivery line 18 to remove excess heat before the CNG stream is dispensed to an end user.
In the exemplary embodiment, fuel gas delivery system 10 may optionally include an intermediate buffer tank 30 coupled to delivery line 18. Buffer tank 30 is filled with CNG and is configured to store CNG at a pressure higher than a vehicle fuel tank dispensing pressure. Fuel gas delivery system 10 is configured to fill buffer tank 30 over the course of several hours to a whole day, resulting in a considerably reduced size requirement and operational cost for fuel delivery system 10. When required, buffer tank 30 dispenses the stored CNG at the dispensing pressure to an end user, for example a vehicle fuel tank (not shown). Thus, buffer tank 30 is configured to provide a relatively large supply of CNG for quickly refueling a vehicle.
In operation, natural gas is supplied through feed line 12 and is precooled in regenerator 14. The precooled natural gas stream is further cooled and at least partially condensed by cryocooler cold head 20 and/or surrounding cooled components. During cooling in regenerator 14 and/or against cold head 20 and surrounding components, impurities contained within the natural gas stream are frozen and separated from the condensed LNG stream. The frozen impurities adhere to surfaces within delivery system 10 and/or are captured by a separate capturing device (not shown). The LNG stream is supplied through the delivery line 18, pumped to a delivery pressure in pump 22, and warmed and/or vaporized in regenerator 14 and heat exchanger 24. The resulting CNG stream is cooled in cooler 26 and is dispensed to an end user or stored for later use, such as in intermediate buffer tank 30.
In the exemplary embodiment, once CNG delivery through delivery line 18 is complete, fuel delivery system 10 may be operated in a regeneration mode. During regeneration mode, fuel delivery system 10 is disconnected from the natural gas supply and is depressurized and warmed to near ambient temperature. As a result, the frozen impurities separated and captured in the dispensing mode are warmed and become gas and/or liquid. A valve 29 in removal line 28 is opened and the captured impurities are removed from system 10. Fuel gas delivery system 10 may then return to a dispensing mode and repeat the above process.
In the exemplary embodiment, feed line 12 is fluidly coupled to cryocooler 16 and is configured to supply natural gas thereto. Natural gas condensed by cryocooler 16 and/or surrounding components is supplied as an LNG stream to LNG line 40. Frozen impurities are separated and removed from the natural gas stream, as described above. Storage tank 42 is fluidly coupled to LNG line 40 and receives the LNG stream from cryocooler 16. In the exemplary embodiment, a heater 44 is thermally coupled to storage tank 42 to vaporize LNG stored therein to provide CNG. Alternatively, feed line 12 may be thermally coupled to storage tank 42 to provide indirect heat exchange between the natural gas stream and LNG stored in storage tank 42 to vaporize the stored LNG. Delivery line 18 is fluidly coupled to storage tank 42 to receive the CNG and deliver a CNG stream to a buffer tank 30 and/or an end user. Fuel delivery system 100 also includes a valve 46 operatively associated with feed line 12 to control flow of the natural gas stream to cryocooler 16, and a valve 48 operatively associated with delivery line 18 to control flow of CNG from storage tank 42.
In operation, valve 46 is in an open state and natural gas in feed line 12 is supplied to cryocooler 16 for condensing and separation of impurities, as described above. Valve 48 is in a closed state and prevents fluid from entering delivery line 18 from storage tank 42. LNG is supplied from cryocooler 16 to storage tank 42 via LNG line 40 until storage tank 42 reaches a predetermined level of LNG. Upon reaching the predetermined level of LNG, valve 46 is closed to prevent further filling of storage tank 42. Heater 44 then begins to vaporize and pressurize the stored LNG until the resulting CNG reaches a predetermined pressure at which point valve 48 is opened to supply CNG through delivery line 18 to buffer tank 30 and/or an end user. Additionally, a pump (not shown) may be provided in delivery line 18 to pump the CNG to a desired pressure.
Once the CNG stream is delivered, fuel delivery system 100 may enter a regeneration mode. Valve 46 is opened and fuel delivery system 100 is disconnected from the natural gas supply and is depressurized and warmed to near ambient temperature. As a result, the frozen impurities separated and captured in the dispensing mode are warmed and extracted via removal line 28, as described above. Fuel delivery system 100 may then return to a dispensing mode and repeat the above operations.
In the exemplary embodiment, feed line 12 is fluidly coupled to cryocooler 16 and is configured to supply natural gas thereto. Natural gas is chilled and densified by cryocooler 16 and/or surrounding components and is supplied as a cooled and densified natural gas stream to chilled natural gas line 41. Alternatively, cryocooler 16 may simply be any cooler or chiller capable of lowering the temperature of the natural gas stream below the freezing point of the impurities desired to be separated. Frozen impurities are separated and removed from the natural gas stream, as described above. In addition, some impurities may only be condensed and are removed by, for example, a trap, a knockout device, or the like. Storage tank 42 is fluidly coupled to chilled natural gas line 41 and receives the chilled stream from cryocooler 16.
In the exemplary embodiment, storage tank 42 includes adsorbent material 32 to adsorb the chilled and densified natural gas. Adsorbent material 32 may be any material enabling fuel gas to be adsorbed as described herein such as, for example, a carbon adsorbent and/or metal organic frameworks. Typically, impurities impede gas adsorption; however the removal of impurities upstream of storage tank 42 improves adsorption of the densified gas and thereby reduces the volumetric requirement of storage tank 42. Thus, storage tank 42 may be smaller, resulting in reduced space requirements for fuel delivery system 200.
In the exemplary embodiment, a heater 44 is thermally coupled to storage tank 42 to desorb and pressurize the densified natural gas stored in adsorbent material 32 to provide CNG. Alternatively, feed line 12 may be thermally coupled to storage tank 42 to provide indirect heat exchange between the natural gas stream and gas adsorbed in storage tank 42 to desorb the stored natural gas. Delivery line 18 is fluidly coupled to storage tank 42 to receive the CNG and supply a CNG stream to a buffer tank 30 and/or an end user. Fuel delivery system 200 also includes a valve 46 operatively associated with chilled natural gas line 41 to control flow of the natural gas stream to storage tank 42, and a valve 48 operatively associated with delivery line 18 to control flow of CNG from storage tank 42. Alternatively, valve 46 may be upstream of cryocooler 16.
In operation, valve 46 is in an open state and natural gas in feed line 12 is supplied to cryocooler 16 for chilling and separation of impurities, as described above. Valve 48 is in a closed state and prevents fluid from entering delivery line 18 from storage tank 42. Chilled and densified natural gas is supplied from cryocooler 16 to storage tank 42 via chilled natural gas line 41 until adsorbent material 32 adsorbs a predetermined level or volume of densified natural gas. Upon reaching the predetermined level of adsorption, valve 46 is closed to prevent further filling of storage tank 42. Heater 44 then begins to desorb and pressurize the stored natural gas until the resulting CNG reaches a predetermined pressure at which point valve 48 is opened to deliver CNG through delivery line 18 to buffer tank 30 and/or an end user. Additionally, a pump (not shown) may be provided in delivery line 18 to pump the CNG to a desired pressure.
Once the CNG stream is delivered, fuel delivery system 200 may enter a regeneration mode. Valve 46 is opened and fuel delivery system 100 is disconnected from the natural gas supply and is depressurized and warmed to near ambient temperature. As a result, the frozen and/or condensed impurities separated and captured in the dispensing mode are warmed and extracted via removal line 28, as described above. Fuel delivery system 200 may then return to a dispensing mode and repeat the above operations.
In the exemplary embodiment, feed line 12 is split at a switching valve 52 into split feed lines 54 and 56. Split feed lines 54 and 56 are fluidly coupled to cryocooler 16 and are configured to supply natural gas thereto. Switching valve 52 selectively supplies natural gas to either of split feed lines 54 and 56. Natural gas condensed by cryocooler 16 and/or surrounding components is supplied as an LNG stream to LNG line 40. Frozen impurities separated and removed from the natural gas stream, as described above. LNG line 40 is split at a switching valve 58 into split LNG lines 60 and 62. Switching valve 58 selectively supplies LNG to either of split LNG lines 60 and 62.
In the exemplary embodiment, storage tank 42 is fluidly coupled to split LNG line 60 and storage tank 50 is fluidly coupled to split LNG line 62 to receive LNG from cryocooler 16. In the exemplary embodiment, split feed line 54 is thermally coupled to storage tank 42 to provide indirect heat exchange between natural gas in line 54 and LNG stored in storage tank 42. Similarly, split feed line 56 is thermally coupled to storage tank 50 to provide indirect heat exchange between natural gas in line 56 and LNG stored in storage tank. In this arrangement, natural gas in split lines 54 and 56 is precooled against vaporizing LNG stored in respective storage tanks 42 and 50. Alternatively, or in addition, a heater (not shown) may be thermally coupled to storage tank 42 and/or 50 to vaporize LNG stored therein to provide CNG.
In the exemplary embodiment, delivery line 18 is fluidly coupled to storage tanks 42 and 50 to receive CNG therefrom and supply a CNG stream to a buffer tank 30 and/or an end user. A valve 48 is operatively associated with delivery line 18 to control flow of CNG from storage tank 42 and a valve 64 is operatively associated with delivery line 18 to control flow of CNG from storage tank 50.
In general, during operation, fuel delivery system 300 fills one of storage tanks 42 and 50 while the other already filled tank undergoes vaporization and pressurization of LNG stored therein. Once the CNG in the filled tank reaches a predetermined pressure, the CNG is supplied to delivery line 18 and vaporization and pressurization of the other now filled tank begins while filling of the now evacuated tank begins. The process is repeated and thus, fuel delivery system 300 is configured to provide a steady flow of CNG.
In more detail, during operation, switching valve 52 supplies gas from feed line 12 through split feed line 54 where it is precooled against LNG stored in storage tank 42. The precooled natural gas is then supplied to cryocooler 16 for condensing and separation of impurities, as described above. Valve 48 is in a closed state and prevents fluid from entering delivery line 18 while LNG is vaporized and pressurized in storage tank 42 until the CNG reaches a predetermined pressure. Switching valve 58 supplies LNG from cryocooler 16 to evacuated storage tank 50 via split LNG line 62 until storage tank 50 reaches a predetermined level of LNG. Once the CNG in storage tank 42 reaches the predetermined pressure, valve 48 is opened and CNG is supplied to delivery line 18 to buffer tank 30 and/or an end user.
Once storage tank 42 is evacuated, switching valve 52 directs the supply of natural gas into split feed line 56 to precool the natural gas and commence vaporization and pressurization of LNG in filled storage tank 50. Alternatively, vaporization and pressurization of storage tank 50 may occur during evacuation of storage tank 42. Valve 64 is in a closed state and prevents fluid from entering delivery line 18 while LNG is vaporized and pressurized in storage tank 50 until the resulting CNG reaches the predetermined pressure. The natural gas precooled in line 56 is then supplied to cryocooler 16 for condensing and separation of impurities. Switching valve 58 supplies LNG from cryocooler 16 to now evacuated storage tank 42 until storage tank 42 reaches the predetermined level of LNG. Once the CNG in storage tank 50 reaches the predetermined pressure, valve 64 is opened and CNG is supplied to delivery line 18 to buffer tank 30 and/or an end user. Additionally, a pump (not shown) may be provided in delivery line 18 to pump the CNG to a desired pressure. The operation may be repeated to alternate storage tanks 42 and 50 between a filling mode and a vaporization, pressurization and evacuation mode.
At a predetermined time, fuel delivery system 300 may enter a regeneration mode. Valves 48 and 64 may be closed and fuel delivery system 300 is disconnected from the natural gas supply and is depressurized and warmed to near ambient temperature. As a result, the frozen impurities separated and captured in the dispensing mode are warmed and extracted via removal line 28, as described above. Fuel delivery system 300 may then return to a dispensing mode and repeat the above operations.
As described above, the gaseous fuel systems of the present invention provide removal of impurities from a gaseous fuel by lowering the temperature of the gaseous fuel below the freezing point of the impurities desired to be removed, thus not requiring an adsorption based removal system. Further, the gaseous fuel systems of the present invention vaporize and pressurize gas to provide a compressed gas without requiring a compressor, thereby reducing vibrations and power consumption. The gaseous fuel systems of the present invention also provide quick refueling of vehicles. For example, 5 kg of CNG can be dispensed in less than an hour. Moreover, the systems may utilize heat exchange between various fuel streams in the system to improve thermal efficiency and energy usage. Thus, the gaseous fuel systems described above provide quiet, compact and efficient systems to remove impurities and provide compressed fuel to storage, a vehicle, or the like.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
| Number | Date | Country | |
|---|---|---|---|
| 61649672 | May 2012 | US |
