Patent Application
20140116396
The present disclosure relates generally to a fuel system, and more particularly, to a cryogenic fuel system having a priming circuit.
A motor vehicle, such as a mining truck, can be equipped with a liquefied natural gas (LNG) pump that fuels an engine of the truck. When the truck is in use, and the pump is active, the pump pushes LNG from an associated tank into the engine. During periods of nonuse, LNG is no longer drawn through the pump.
LNG is a fuel that has been cooled to about −160° C. Therefore, a pump that has been inactive for an extended period of time is devoid of this cold fuel and warms to ambient temperatures. The pump is then required to be primed, and thereby cooled, before the engine may be started. Priming an LNG pump traditionally involves flooding the pump with LNG or a separate coolant to cool the pump. However, introducing LNG to a warm pump can cause the LNG to boil during the priming process. This boiling releases an unwanted gaseous build-up at the pump inlet or in the pump itself, causing it to be “vapor locked.” The pump then requires additional cooling time to liquify the vapor before the pump is ready to perform. Introducing a separate coolant involves the extra step of removing the coolant from the system and disposing of it before the LNG can be pumped from the tank.
One attempt to avoid gaseous build-up in an LNG pump during priming is to connect the pump to a vapor dome collector that sits above the pump. In this configuration, any gaseous release naturally flows up and into the vapor dome collector, allowing only LNG to flow down and into the pump. The gas vapor may then be directed back into the tank, securely away from the pump. One such system is described in U.S. Pat. No. 5,431,546 (the '546 patent) by Rhoades, issued on Jul. 11, 1995.
Although the '546 patent may allow the pump to be primed without risk of vapor lock, the system may be wasteful, expensive, and incapable of safely venting. In particular, when using the system disclosed in the '546 patent, an amount of LNG may be boiled and converted into gas, which is of no use when priming a pump. Additionally, LNG may be expensive for use as a coolant, especially when LNG is boiled and therefore wasted. LNG released into the atmosphere, from the vapor dome collector and/or tank, may constitute an environmental and safety hazard. LNG may evaporate and form a flammable vapor cloud that can explode. Therefore, a user may not want to vent LNG into the atmosphere, especially when working in a shop or other closed enviroment.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.
In one aspect, the present disclosure is directed to a fuel priming system that includes a tank configured to hold a cryogenic fuel, a pump, a first passage connecting the tank and the pump, and a second passage configured to hold a cooling fluid and located to cool the first passage.
In another aspect, the present disclosure is directed to a method of cooling a pump. The method includes releasing fuel from a tank into a warmed passage, allowing the fuel to expand within the warmed passage, directing the expanding fuel from the warmed passage toward the pump, and directing cooling fluid into a second passage to cool the warmed passage.
The fuel system 30 may form a fuel priming system including a priming circuit 20 connecting a tank 40 with a pump 60 and a vapor dome collector 50 by way of a first conduit 80 and a second conduit 95. The fuel system 30 may be located within the machine 10 and connected to an engine 70 of the machine 10 to supply the engine 70 with cryogenic fuel. As shown in
The vapor dome collector 50 may be located between the tank 40 and the pump 60. The vapor dome collector 50 may be of sufficient size and material to collect gaseous boil off from priming circuit 20 formed within the first conduit 80. Specifically, the vapor dome collector 50 may include a large interior configured to collect vapor gas in an upper portion and liquid fuel in a bottom portion. The exterior may be insulated to safely hold the liquid fuel. Several sensors and valves (not shown) may be located within the vapor dome collector 50, including a liquid level sensor, a pressure sensor, a vapor check valve, and a liquid check valve to regulate the amount of vapor gas and fuel in the vapor dome collector 50.
The first conduit 80, which may connect the tank 40 to the pump 60, may include an upstream portion 83 and a downstream portion 87, relative to the vapor dome collector 50. A vertical section 90 of the upstream portion 83 may extend a sufficient distance from the tank 40 to allow fluid within the tank 40 to be drawn by gravity downward at a desired rate, when vent 110 is open. Vent 110 connects the first conduit 80 to the tank 40 and selectively opens and closes. In one exemplary embodiment, the vent 110 is positioned on a bottom surface of the tank 40.
At a location A, the upstream portion 83 of the first conduit 80 may transition from the vertical section 90 to an inclined section 100. Therefore, location A may form an outlet for the vertical section 90. Location A may be a distinct point, as shown in
The second end 130 of the upstream portion 83 of the first conduit 80 may connect to the vapor dome collector 50 and to pump 60 in parallel via downstream portion 87, allowing the first conduit 80 to be in fluid communication with each of the tank 40, vapor dome collector 50, and pump 60. As also shown in
The first and second passages 150, 160 may be in fluid communication with the tank 40, vapor dome collector 50, pump 60, vent 110, and valve 140. Vent 110 may be of any vent configuration known in the art, and moveable between at least two distinct positions. When in the first position, the vent 110 connects the second passage 160 to the atmosphere, and when in the second position, the vent 110 connects the second passage 160 to tank 40. Vent 110 may be selectively moveable between the first and second positions during a priming event based on the type of cooling fluid passing through the second passage 160.
Valve 140 may be of any configuration know in the art, and may be connected to the first and second passages 150, 160 at the pump 60. In one exemplary embodiment, valve 140 may include a solenoid valve, and in another embodiment it may include a manual valve. The valve 140 may further be selectively moveable between at least two distinct positions. When in the first position, the valve 140 may direct cooling fluid, from an optional coolant supply 145, into the second passage 160, and when in the second position it may redirect fuel from the first passage 150 into the second passage 160. Specifically, valve 140 may be configured to selectively connect a cooling fluid, for example liquid nitrogen or another cooling fluid, with the second passage 160 so that the cooling fluid in the second passage 160 cools the first passage 150. Additionally, the valve 140 may be configured to selectively re-circulate fuel so that the fuel in the second passage 160 cools the first passage 150. The optional coolant supply 145 may forcibly or passively transport the cooling fluid through valve 140 into the second passage 160.
The disclosed fuel system may provide at least two ways to prime and cool a fuel pump of a machine. The first option may allow for cooling fluid to be introduced into the system and vented, and the second option may allow for where fuel is re-circulated within the system. In an exemplary embodiment, a user of the machine may selectively switch between the first and second methods. Operation of the fuel system will now be described in detail.
As illustrated in
Vapor gas that is produced from the expanding fuel within the first conduit 80, may be collected within the vapor dome collector 50. Second end 130 of the inclined section 100, being gravitationally higher than the first end 120, may allow the vapor gas to easily rise into the vapor dome collector 50. Furthermore, vapor gas within the downstream portion 87 may rise into the vapor dome collector 50 via branches B and C. The vapor gas may flow from the vapor dome collector 50, through the second conduit 95, and back into the tank 40 as shown in
While the fuel flows toward pump 60, a cooling fluid may be selectively introduced into the second passage 160 via valve 140. Specifically, the cooling fluid may be directed into an end of the second passage 160, at pump 60, through valve 140. The cooling fluid may alternatively be introduced before or after the fuel flows into the warmed fuel system 30. This cooling fluid may flow through the second passage 160 of the first conduit 80 from valve 140 toward vent 110. Such flowing of the cooling fluid may cool the first passage 150 and reduce any production of vapor gas.
In one exemplary embodiment, the cooling fluid is liquid nitrogen. The valve 140 may direct the liquid nitrogen into the second passage 160, from the optional coolant supply 145. The liquid nitrogen may be colder than the LNG flowing within the first passage 150 to cool the first passage 150 rapidly. Once a sufficient amount of liquid nitrogen passes through the first conduit 80, the fuel system 30 should be cooled to a degree sufficient that boiling no longer occurs, or occurs below an acceptable level, and the pump 60 is primed. Vent 110 is moveable to selectively vent and release the liquid nitrogen from the second passage 160 into the atmosphere. Liquid nitrogen is nonhazardous so that it may be released into the atmosphere.
After sufficient cooling has taken place, LNG may be released from the tank 40, through vent 110, to flow to pump 60 via the first passage 150. Alternatively, the liquid nitrogen may cool the system in the second passage 160 at the same time that the LNG flows within the first passage 150. In this latter situation, both the liquid nitrogen and LNG together may cool the first conduit 80.
In a second exemplary embodiment, the LNG from the first passage 150 may be selectively re-circulated to act as the cooling fluid within the second passage 160. Specifically, LNG flowing within the warmed first conduit 80 may be directed down branch C and into valve 140. The LNG may then be directed, by valve 140, through the second passage 160 of branch B. This re-circulated LNG may then flow within the second passage 160, toward vent 110, to cool the fuel system 30 and prime the pump 60, and then back into the tank 40. Although the LNG may boil and produce vapor gas during this cooling process, the vapor gas may enter the tank 40 through the second conduit 95, and migrate to the top of the tank 40. Alternatively, both the LNG flowing within the warmed first passage 150 and the re-circulated LNG flowing within the second passage 160 may cool the warmed first conduit 80 simultaneously. Once a sufficient amount of LNG has been re-circulated within the first conduit 80, the system should be cooled and the pump 60 primed. Vent 110 may be moveable to selectively release and vent the re-circulated LNG back into the tank 40.
In a third exemplary embodiment, a user may switch between use of liquid nitrogen and LNG as the cooling fluid. In particular, the user may move valve 140 between the first and second positions depending on which fluid the user desires to cool the first passage 150 with. Such switching of the system may, for example, permit a user to utilize liquid nitrogen while in a mechanic's shop, where liquid nitrogen is readily available, and change to LNG when in the field working, where liquid nitrogen may not be as accessible.
The present disclosure aims to provide a fuel system with at least two ways to prime and cool a fuel pump of a machine. The fuel system may help to reduce waste and expense associated with priming an inactive pump. Specifically, a user may cool the system with a cooling fluid and thereby reduce the amount of fuel wasted and boiled into vapor gas. Providing the option to use either liquid nitrogen or LNG as the cooling fluid may decrease the expense of priming a pump, as liquid nitrogen is cheaper than LNG.
The present disclosure may provide a system that is capable of safely venting to the atmosphere and thereby reduces emissions. Liquid nitrogen may be safely released into the atmosphere, but is not always available. Therefore, the present disclosure may allow a user to utilize LNG, when it is the only cooling fluid available, but switch to liquid nitrogen, a more environmentally favored coolant, when the user is not so limited.
It will be apparent to those skilled in the art that various modifications and variations can be made to the system of the present disclosure. Other embodiments of the system will be apparent to those skilled in the art from consideration of the specification and practice of the method and system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.
