Fuel recovery system

A fuel recovery system for a machine is disclosed. The fuel recovery system may have a tank configured to store a liquid fuel. The fuel recovery system may also have an accumulator fluidly connected to the tank and configured to receive gaseous fuel formed in the tank. The fuel recovery system may further have a compressor fluidly connected to the accumulator and configured to compress the gaseous fuel. In addition, the fuel recovery system may have a separator fluidly connected to the compressor and the tank. The separator may be configured to receive the compressed gaseous fuel, and separate the compressed gaseous fuel into a first flow of gaseous fuel at a first temperature and a second flow of gaseous fuel at a second temperature. In addition, the separator may be configured to direct the second flow to the tank.

TECHNICAL FIELD

The present disclosure relates generally to a fuel recovery system and, more particularly, to a gaseous fuel recovery system.

BACKGROUND

Natural gas has received much attention as a plentiful and viable alternative to traditional fuels such as diesel. Natural gas, however, has a lower energy density than traditional fuels such as diesel and gasoline. As a result, mobile machines generally use liquefied natural gas (“LNG”) as fuel. To maintain natural gas in liquid form at atmospheric pressure, its temperature must remain below about −160° C. Mobile machines utilizing LNG as a fuel, therefore, typically store LNG in insulated tanks. Some heat can still enter the tank because of imperfect insulation, causing some of the LNG to change its state to a gaseous form.

The gaseous fuel (“boil-off”) accumulates near the upper portions of the tank. Moreover, as the amount of gaseous fuel produced in the tank increases, the pressure within the tank also increases. The increasing pressure, if left unchecked, can damage the tank and can even cause the tank to explode. Traditional LNG systems, therefore, vent the gaseous fuel (composed mostly of methane) directly to the atmosphere. Government regulations, however, no longer permit direct venting of gaseous fuel to the atmosphere because it contributes to greenhouse gas (GHG) emissions. To get around this problem, some LNG systems ignite the gaseous fuel as it vents to atmosphere, thus reducing the amount of methane leaving the tank. Although effective, this process results in an inefficient waste of potential fuel energy.

One attempt to address the problems described above is disclosed in Japanese Patent No. JP 2009216078 of Masataka et al. that issued on Sep. 24, 2009 (“the '078 patent”). In particular, the '078 patent discloses a canister containing an adsorbent material to adsorb fuel vapors generated in a fuel tank. The '078 patent further discloses a vortex tube, which receives a supply of compressed air at an inlet and separates the compressed air into a hot stream of air and a cold stream of air. The system of the '078 patent directs the cold air stream towards the fuel tank, cooling the fuel tank, and reducing the amount of fuel vapor produced in the tank. Simultaneously, the system of the '078 patent directs the hot air stream towards the canister to help segregate the adsorbed fuel from the adsorbent material and introduces the segregated fuel into the suction passage of an engine. The '078 patent also discloses that at least a portion of the gaseous fuel formed in the fuel tank is discharged to the atmosphere.

Although the '078 patent discloses a method for partial recovery of fuel vapor generated in a fuel tank, the system of the '078 patent requires an adsorbent material to adsorb and release the fuel vapor generated in the fuel tank. Moreover, the '078 patent requires an external source of compressed air to generate the required hot and cold streams of air. The adsorbent material and external source of compressed air add complexity and make the system of the '078 patent more expensive. Further, although the system of the '078 patent consumes some of the fuel vapor by using it in the engine, the system of the '078 patent also discharges some fuel vapor into the atmosphere contributing to GHG emissions.

The fuel recovery system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.

SUMMARY

In one aspect, the present disclosure is directed to a fuel recovery system for a machine. The fuel recovery system may include a tank configured to store a liquid fuel. The fuel recovery system may also include an accumulator fluidly connected to the tank. The accumulator may be configured to receive gaseous fuel formed in the tank. The fuel recovery system may further include a compressor fluidly connected to the accumulator. The compressor may be configured to compress the gaseous fuel. In addition, the fuel recovery system may include a separator fluidly connected to the compressor and the tank. The separator may be configured to receive the compressed gaseous fuel. The separator may also be configured to separate the compressed gaseous fuel into a first flow of gaseous fuel at a first temperature and a second flow of gaseous fuel at a second temperature. In addition, the separator may be configured to direct the second flow to the tank.

In another aspect, the present disclosure is directed to a method of recovering gaseous fuel from a tank containing liquid fuel. The method may include collecting the gaseous fuel from the tank in an accumulator. The method may also include compressing the gaseous fuel. The method may further include separating the compressed gaseous fuel into a first flow of gaseous fuel at a first temperature and a second flow of gaseous fuel at a second temperature. In addition, the method may include returning the second flow to the tank.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary embodiment of a machine10. Machine10may be a mobile machine that performs some type of operation associated with an industry such as railroad, marine, mining, construction, farming, power generation, or another industry known in the art. For example, machine10may be a locomotive designed to pull rolling stock. Machine10may have a plurality of wheels12configured to engage a track14and a first base platform16supported by wheels12. Machine10may also have an engine18mounted to first base platform16and configured to drive wheels12. Any number of additional engines may be included within machine10and operated to produce power that may be transferred to one or more traction motors (not shown) used to drive wheels12. In an exemplary embodiment as shown inFIG. 1, engine18may be lengthwise aligned on first base platform16along a travel direction of machine10. One skilled in the art will recognize, however, that engine18may be located in tandem, transversally, or in any other orientation on first base platform16.

Machine10may also include a tender20. Tender20may include a tank22configured to store a liquid fuel for combustion within engine18. Tank22may be an insulated, single or multi-walled tank configured to store a liquid fuel at low temperatures. In one exemplary embodiment, tank22may be configured to store a liquid fuel at a temperature below about −160° C. In another exemplary embodiment, the liquid fuel stored in tank22may be liquid natural gas. Tank22may be mounted to a second base platform24of tender20configured to be moved by machine10. Tank22may also be connected to engine18to supply fuel to engine18. Second base platform24may be supported by wheels12. Although machine10has been illustrated as having tank22mounted on tender20, alternatively, tank22may be mounted to first base platform16, if desired. Similarly, engine18may be mounted to second base platform24instead of being mounted to first base platform16, if desired.

FIG. 2illustrates a schematic diagram of a fuel recovery system40that may be used in conjunction with machine10shown inFIG. 1. Fuel recovery system40may include components that cooperate to maintain a first pressure in tank22below a safety threshold. In one exemplary embodiment, the safety threshold may be selected as a fraction of the pressure at which tank22may structurally fail or explode. In another exemplary embodiment, the safety threshold may be about 6 to 7 atmospheres.

Fuel recovery system40may include tank22, accumulator42, heat exchanger44, compressor46, separator48, engine18, and controller50. Fuel recovery system40may also include first control valve52, second control valve54, third control valve56, and fourth control valve58. In addition, fuel recovery system40may include first pressure sensor60and second pressure sensor62. Fuel recovery system40may also include a refrigeration system70and temperature sensors (not shown) to monitor the temperature in various portions of the system.

As shown inFIG. 2, accumulator42may be fluidly connected to tank22. Gaseous fuel may be directed from tank22to accumulator42through passageway82. First pressure sensor60may be mounted on tank22to measure a first pressure within tank22. First control valve52may be mounted on passageway82to selectively direct gaseous fuel from tank22to accumulator42when the first pressure measured by first pressure sensor60exceeds a first pressure threshold. In one exemplary embodiment, the first pressure threshold may be about 1.5 atmospheres.

Compressor46may be fluidly connected to accumulator42. Gaseous fuel from accumulator42may be directed to compressor46through passageway84. Second pressure sensor62may be mounted on accumulator42to measure a second pressure within accumulator42. Second control valve54may be mounted on passageway84to selectively direct gaseous fuel to compressor46when the second pressure in accumulator42exceeds a second pressure threshold. In one exemplary embodiment, the second pressure threshold may be about 1.5 atmospheres. Compressor46may compress the gaseous fuel and direct the compressed gaseous fuel through passageway86to separator48, which may be fluidly connected to compressor46.

A heat exchanger44may be disposed on passageways84,86, between accumulator42and separator48, such that gaseous fuel flowing from accumulator42to compressor46in passageway84may exchange heat with the compressed gaseous fuel passing from compressor46to separator48through passageway86. Specifically, heat from the compressed gaseous fuel in passageway86may flow to the gaseous fuel in passageway84, thereby cooling the compressed gaseous fuel after it leaves compressor46.

Separator48may separate the compressed gaseous fuel received from compressor46into a first flow of gaseous fuel and a second flow of gaseous fuel. The first flow of gaseous fuel from separator48may be directed via passageway88to engine18. Third control valve56may be mounted on passageway88to control an amount of the first flow transferred to engine18. The first flow may be combusted in engine18to generate power which may be used to drive compressor46. It is contemplated, however, that power generated by engine18may be used for functions of machine10other than driving compressor46. For example, the power generated by engine18may be used to drive refrigeration system70, which may be used to cool the liquid fuel in tank22. The second flow of gaseous fuel from separator48may be directed to flow through passageway90back to tank22. Fourth control valve58may be mounted on passageway90to control an amount of the second flow transferred to tank22from separator48.

The first flow of gaseous fuel may have a first temperature as it exits separator48. Similarly, the second flow of gaseous fuel may have a second temperature as it exits separator48. In one exemplary embodiment, the second temperature may be lower than the first temperature. In another exemplary embodiment, the second temperature may be lower than a condensation temperature of the liquid fuel at atmospheric pressure. In yet another exemplary embodiment, the liquid fuel in tank22may be LNG and the second temperature may be about −160° C. The second flow of gaseous fuel may be bubbled through the liquid fuel stored in tank22and may condense in tank22. Thus, by combusting the first flow of gaseous fuel in engine18and condensing the second flow of gaseous fuel in tank22, the first pressure in tank22may be maintained below the safety threshold without discharging any gaseous fuel into the atmosphere.

Accumulator42may be a floating piston type accumulator. For example, as illustrated inFIG. 2, accumulator42may include a piston110, which separates a first chamber112of accumulator42from a second chamber114. Gaseous fuel from tank22may enter first chamber112of accumulator42. As gaseous fuel flows into first chamber112, piston110may move from first end116of accumulator42towards second end118, compressing gas trapped in second chamber114. It is contemplated that the gas in second chamber114may include air or alternatively may include gaseous fuel from tank22. As gaseous fuel continues to flow into first chamber112, compressed gas in second chamber114may resist movement of piston110towards second end118. As a result pressure in first chamber112may increase. Moreover, when gaseous fuel is permitted to exit accumulator42through second control valve54, the compressed gas in second chamber114may push piston110from second end118towards first end116thereby expelling the gaseous fuel from first chamber112. Although accumulator42has been described above as a piston type accumulator, it is contemplated that accumulator42may take other forms. For example, accumulator42may be a bladder type accumulator made of a material that can expand as gaseous fuel fills accumulator42. Alternatively, accumulator42may be a pressure vessel.

Heat exchanger44may be a gas-to-gas heat exchanger. For example, heat exchanger44may embody a flat-plate heat exchanger or a shell-and-tube heat exchanger. As the compressed gaseous fuel passes through heat exchanger44, the compressed gaseous fuel may conduct heat through internal walls of heat exchanger44to gaseous fuel also passing through heat exchanger44. It is contemplated that the gaseous flows in heat exchanger44may be parallel flows, opposite flows, or cross flows, as desired. Although only one heat exchanger44is shown inFIG. 2, one skilled in the art would recognize that more than one heat exchanger44may be included in fuel recovery system40.

Compressor46may be a single-stage or multi-stage compressor and may be mechanically or electrically driven by engine18or by any other power source known in the art. Compressor46may be configured to pressurize gaseous fuel, for example, natural gas, propane, or methane, that is directed to compressor46from accumulator42through passageway84. It is contemplated that fuel recovery system40may include more than one compressor46, which may be used to compress the gaseous fuel from the accumulator.

Separator48may be a Hilsch vortex generator. For example, the compressed gaseous flow from passageway86may be injected into a swirl chamber (not shown) of separator48and accelerated to a high rate of rotation about an axis100. Separator48may include a nozzle102, at one end which may allow only an outer shell of the compressed gaseous fuel to escape as the first flow from nozzle102. The remainder of the compressed gaseous fuel may be forced to exit from outlet104in a vortex of reduced diameter. Although a Hilsch vortex generator is described above, one skilled in the art would recognize that separator48may take other forms. For example, separator48may be a membrane based separator, an adsorption type separator, an absorption type separator, a distillation type separator or any other type of gas-gas separator known in the art.

First control valve52may be a two position or proportional type valve having a valve element movable to regulate a flow of gaseous fuel through passageway82. The valve element in first control valve52may be solenoid-operable to move between a flow-passing position and a flow-blocking position. In the flow-passing position, first control valve52may permit fluid to flow through passageway82substantially unrestricted by first control valve52. In contrast, in the flow-blocking position, first control valve52may completely block fluid from flowing through passageway82. Second, third, and fourth control valves54,56,58may have structures and methods of operation similar to those of first control valve54.

Refrigeration system70may include a compressor driven by engine18, a condenser, and an evaporator that are coupled to each other via a closed-circuit. The compressor may be configured to compress a refrigerant, for example R-134, propane, nitrogen, helium, or any other appropriate refrigerant known in the art. As the refrigerant is pressurized, it is vaporized and moves into the condenser as a high-pressure gas. Within the condenser, the refrigerant cools and condenses back into liquid form at a lower energy state than when initially within the compressor. The lower-energy liquid then passes into the evaporator, where it is expanded, causing a rapid drop in temperature. Liquid fuel from tank22may be circulated around the evaporator of refrigeration system70to transfer heat to the evaporator thereby chilling the liquid fuel and warming the refrigerant in preparation for another cycle. Alternatively the evaporator of refrigeration system70may be immersed in the liquid fuel in tank22, if desired.

Controller50may be configured to control the operation of fuel recovery system40. Controller50may embody a single or multiple microprocessors, digital signal processors (DSPs), etc. that include means for controlling an operation of fuel recovery system40and engine18. Numerous commercially available microprocessors can be configured to perform the functions of controller50. It should be appreciated that controller50could readily embody a microprocessor separate from that controlling other machine-related functions, or that controller50could be integral with a machine microprocessor and be capable of controlling numerous machine functions and modes of operation. If separate from the general machine microprocessor, controller50may communicate with the general machine microprocessor via datalinks or other methods. Various other known circuits may be associated with controller50, including power supply circuitry, signal-conditioning circuitry, actuator driver circuitry (i.e., circuitry powering solenoids, motors, or piezo actuators), and communication circuitry.

Controller50may also be configured to regulate operation of first, second, third, and fourth control valves52,54,56,58. For example, controller50may cause first control valve52to direct some or all gaseous fuel from tank22to accumulator42based on the signals received from first pressure sensor60in tank22. Similarly, controller50may cause second control valve54to direct some or all gaseous fuel from accumulator42to compressor46based on the signals received from the second pressure sensor62in accumulator42. Controller may adjust flows of gaseous fuel through third and fourth control valves56,58to ensure that the first and second pressures in tank22and accumulator42, respectively, remain below the first and second pressure thresholds.

FIG. 3illustrates an exemplary operation performed by controller50during fuel recovery operations.FIG. 3will be discussed in more detail in the following section to further illustrate the disclosed concepts.

INDUSTRIAL APPLICABILITY

The disclosed fuel recovery system may be used in any machine or power system application where it is beneficial to recover vaporized liquid fuel from a liquid fuel tank. The disclosed fuel recovery system may find particular applicability with mobile machines such as locomotives that can be exposed to extreme environmental conditions, including extremely hot ambient temperatures. The disclosed fuel recovery system may provide an improved method for recovering gaseous fuel by drawing some or all of the gaseous fuel from the fuel tank, using a portion of the gaseous fuel to generate power in an engine, and condensing and returning the remaining portion of the gaseous fuel to the fuel tank. Operation of fuel recovery system40will now be described.

During operation of machine10, liquid fuel in tank22may vaporize and accumulate in an upper portion of tank22. As gaseous fuel accumulates in tank22, pressure within tank22may rise and exceed a first pressure threshold. Controller50may continuously monitor the first and second pressure sensors in tank22and accumulator42, respectively (Step130). Controller50may ascertain based on these signals whether the first pressure “PT” in tank22has exceeded the first pressure threshold “TPTH” (Step132). When controller50determines that the first pressure “PT” has not exceeded the first pressure threshold “TPTH” (Step132, NO), controller50may return to step130and continue to monitor the first and second pressure sensors in tank22and accumulator42, respectively. When controller50determines, however, that the first pressure “PT” in tank22has exceeded the first pressure threshold “TPTH” (Step132, YES), controller50may open first control valve52to direct gaseous fuel from tank22to flow to accumulator42(Step134).

Controller50may ascertain whether pressure “PA” in accumulator42has exceeded the second pressure threshold “APTH” (Step136). When controller50determines that the second pressure “PA” has not exceeded the second pressure threshold “APTH” (Step136, NO), controller50may return to step130and continue to monitor the first and second pressure sensors in tank22and accumulator42, respectively. When controller50determines, however, that the second pressure “PA” in accumulator42has exceeded the second pressure threshold “APTH” (Step136, YES), controller50may open second control valve54to direct gaseous fuel from accumulator42to flow to compressor46(Step138).

Compressor46may compress the gaseous fuel received from accumulator42and direct the compressed gaseous fuel to separator48(Step140). Separator48may separate the compressed gaseous fuel into a first flow of gaseous fuel and a second flow of gaseous fuel (Step142). Controller50may control third control valve56to direct the first flow of gaseous fuel to engine18and fourth control valve58to direct the second flow of gaseous fuel to tank22(Step144). At this point controller may return to step130to continue monitoring the first and second pressure sensors60,62. The disclosed fuel recovery system may help eliminate GHG emissions by maintaining the pressure within fuel tank below the safety threshold without discharging gaseous fuel into the atmosphere. The disclosed fuel recovery system may also provide a less complex and more economical system by using an accumulator to collect and recover the gaseous fuel.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed fuel recovery system without departing from the scope of the disclosure. Other embodiments of the fuel recovery system will be apparent to those skilled in the art from consideration of the specification and practice of the fuel recovery 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.