Patent Application
20130180265
The invention provides for methods for the use of both liquefied natural gas and liquid nitrogen in the operation of a vehicle for transporting refrigerated goods.
Large semitrailers or tractor trailers are used to transport frozen goods, such as food to consolidate fuel and labor costs associated with the transport. Often times this transportation is over long distances such as from a manufacturing plant for prepared meats and foods to restaurants or fast food chains. Alternatively, this transportation of frozen goods may require a series of stops to unload the frozen cargo which requires the opening and closing of the trailer's doors for considerable periods of time, all over the length of the delivery route. This can ultimately have a deleterious effect on the frozen cargo, particularly as to those items that are last to be unloaded.
Natural gas is seeing increasing use as a fuel alternative to combustion fuels such as gasoline and diesel and avoids certain drawbacks such as production cost and combustion emissions that the other fuels possess. Natural gas is relatively inexpensive compared to conventional motor vehicle fuels. Natural gas burns cleaner than gasoline or diesel and will rise up in the air and dissipate adding to its safety, thus making it attractive in relation to federal emission and pollution laws.
LNG is stored on vehicles in tanks that must account for it being a cryogenic fluid and having a boiling point below −160° C. Double walled and insulated tanks are the norm but during periods of non-use, heat flows to the LNG which will cause it to vaporize and build pressure in the storage tank. This problem with boil-off and necessary venting is exacerbated by losses suffered during fueling and onboard storage resulting in economic loss and environmental concerns. These are undesirable conditions due to the potential environmental harms as well as the obvious economic losses.
Bulk liquid nitrogen and liquefied natural gas storage tanks are provided at a fueling facility. During storage and refueling, a portion of the liquid nitrogen at the fueling facility is used to prevent liquefied natural gas from venting. Typically a reliquefaction heat exchanger is employed to inhibit liquefied natural gas venting; however, one of ordinary skill in the art could employ other means to inhibit liquefied natural gas venting.
Onboard the vehicle that supplies refrigeration, there are storage tanks for the liquefied natural gas and the liquid nitrogen. The liquefied natural gas is the fuel for the refrigeration vehicle and the amount stored and used onboard is determined by the fuel requirements of the vehicle's engine. The LNG is a cryogenic fluid having a normal boiling point of about −160° C. and is able to provide a significant amount of refrigeration. The LNG used by the vehicle is first vaporized and warmed through heat exchange in the refrigeration space. The amount of refrigeration that is provided by the LNG relative to the demands of the refrigeration space will depend on the usage pattern of LNG and refrigeration requirements. Typically about 50 to 100% of the refrigeration can be supplied by LNG with the remainder being provided by LIN.
LNG storage onboard the refrigeration vehicle can also be subject to boil-off and venting, particularly during periods when the vehicle's engine is not operating. Similar to the fueling station, the onboard LIN is available to inhibit the LNG venting through the use of a reliquefaction heat exchanger.
The invention addresses the concerns of using liquid nitrogen as a refrigerant in a vehicle and using liquefied natural gas as the fuel for said vehicle.
The invention is a method for fueling and operating a vehicle that provides refrigeration to goods requiring such wherein the vehicle is fuelled by liquefied natural gas and uses liquid nitrogen as the primary refrigerant.
In one embodiment there is disclosed a method for operating a vehicle that provides refrigeration and is powered by an engine burning liquefied natural gas comprising feeding liquefied natural gas from a storage tank to the engine; periodically contacting natural gas from the liquefied natural gas storage tank with liquid nitrogen and periodically feeding liquid nitrogen to the vehicle thereby providing refrigeration.
The liquid nitrogen and liquefied natural gas are both stored in separate on-board storage tanks that are in thermal communication with each. This thermal communication is typically a line that connects the vapor space of the liquefied natural gas storage tank with the liquid space of the liquid nitrogen storage tank.
The liquid nitrogen will provide cooling to the natural gas which will liquefy as such and return as liquefied natural gas to the on-board liquefied natural gas storage tank. A temperature probe will measure the temperature of the natural gas present in the vapor portion of the on-board liquefied natural gas storage tank and send this data to a programmable logic control (PLC). Based on this data a valve can be manipulated which will allow the warmer natural gas to flow from the liquefied natural gas storage tank to the liquid nitrogen storage tank where it will contact the liquid nitrogen, be cooled and return to the liquefied natural gas storage tank where it can be used as the fuel for the vehicle.
Nitrogen will be periodically vented from the on-board liquid nitrogen storage tank after the liquid nitrogen has provided its refrigerant functionality to the refrigeration container that forms part of the vehicle.
Alternatively, there is provided a method for providing refrigeration to a vehicle powered by a liquefied natural gas engine comprising periodically feeding liquid nitrogen to a storage area of the vehicle and periodically contacting the liquefied nitrogen with natural gas whereby heat from the natural gas is transferred into the liquid nitrogen.
In another embodiment, there is disclosed a method for fueling a vehicle comprising feeding liquefied natural gas to an on-board storage tank; feeding liquid nitrogen to an on-board storage tank, wherein the liquefied natural gas storage tank and the liquid nitrogen storage tank are in thermal communication with each other whereby natural gas from the liquefied natural gas storage tank periodically contact the liquid nitrogen, and periodically feeding the liquid natural gas to an engine of the vehicle.
The figure is a schematic showing the fueling of a refrigerated vehicle and the onboard liquefaction system according to the invention.
Turning to the figure, a fueling facility and refrigerant vehicle are shown. Two storage tanks for liquid nitrogen A and for liquefied natural gas B are shown for filling the storage tanks on vehicle C. A nitrogen vent line 1 exits the bottom of the liquid nitrogen storage tank A and passes through the vapor region of the liquefied natural gas storage tank B where it will cool some of the vaporized natural gas before exiting the liquefied natural gas storage tank B. The cooled natural gas will blend with the liquefied natural gas in the tank and this lessens the problems associated with pressure build up and boil off of the liquefied natural gas.
Line 2 exits the liquid nitrogen storage tank and carries the liquid nitrogen to LIN tank E onboard the vehicle C. Line 3 exits the liquefied natural gas tank B and connects to the LNG tank D aboard the vehicle C. The amount of each fed to their respective onboard storage tanks is the amount necessary to refuel the vehicle C for its next journey, be it as engine fuel in the case of the liquefied natural gas or as a refrigerant for the liquid nitrogen.
The vehicle C has onboard storage tanks for LNG D and LIN E mounted in convenient locations for fueling the engine and refrigerating the goods that the vehicle typically carries. In this representation, the vehicle is a semitrailer or tractor trailer for transporting refrigerated goods and employing an engine that can use LNG as a fuel.
Once on-board tanks D and E have been filled from storage tanks A and B, the cooling properties of the LIN will be employed to keep refrigerated the contents of the vehicle C for example frozen foods, pharmaceuticals or fine chemicals. While at rest, the LIN from tank E provides cooling to the interior of vehicle C where the items that are being transported and in need of refrigeration are stored. Some of the liquid nitrogen that vaporizes inside tank E is fed through line 6 and a heat exchanger and will vent from the interior of the vehicle C through line 6.
The LNG used to fuel vehicle C is fed from tank D through line 5 to the engine, and this tank will be gradually depleted as the vehicle C travels and its engine consumes the LNG as fuel.
Line 4 thermally connects LNG tank D with LIN tank E. When the vehicle C is at rest for example when some of the cargo is being unloaded, the LNG in tank D is not being steadily withdrawn as a fuel. Some of the LNG will volatilize into natural gas and this can cause a pressure build up in tank D which can present a dangerous situation if this pressure is not relieved. Typically some form of venting is employed but in the invention, valve V1 is opened and the natural gas is withdrawn from the header space of LNG tank D through line 4 where it will pass through the LIN in tank E and condense back to LNG where it will return to the liquid portion of the LNG tank D. These same phenomena may occur during operation of the vehicle as well and the same operation will be performed then.
While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the invention.
