DEVICE AND METHOD FOR FILLING CRYOGENIC TANKS

Abstract

A body structure includes an inlet port (15) that receives fluid from a supply device, a first outlet port (12) that connects to a filling line at the top in communication with a cryogenic tank, a second outlet port (13) that connects to a filling line at the bottom in communication with a cryogenic tank, and a sliding tube cylinder (19). A cylinder housing (22) is connected to the body structure and has a pressure comparator cylinder with an upper volume (23) and a lower volume (27), the latter being in fluid communication with a cryogenic tank. A piston (21) slides within the pressure comparator cylinder, and a piston rod is connected to the piston. A pressure regulator (24) is in fluid communication with the upper volume of the pressure comparator cylinder and the sliding tube cylinder.A sliding tube (29) is connected to the piston shaft and slides inside the sliding tube cylinder. The sliding tube cylinder directs fluid to a top fill line through the first outlet port when the pressure in the lower volume exceeds a pressure setpoint, and directs fluid to a bottom fill line through the second outlet port when the pressure in the lower volume falls below a pressure setpoint.

Description

The present description refers in general to devices and methods for filling a cryogenic tank and, more particularly, to a device and method that fill a cryogenic tank with a cryogenic fluid while automatically maintaining a predetermined reference pressure in the cryogenic tank. Background of the Invention Cryogenic fluids, meaning fluids with a boiling point generally below -150 °C at atmospheric pressure, are used in a variety of applications, such as mobile and industrial applications. Cryogenic fluids are stored in insulated cryogenic tanks due to the low temperature requirements (-160 °C) and, typically, lower pressures. Regulating the temperature and pressure of cryogenic fluids in these tanks is extremely important. Cryogenic tanks are typically filled from a mobile supply unit that connects to the cryogenic tank. Figure 1 illustrates a typical example of the above art of a system for filling a cryogenic tank. In the illustrated embodiment, the supply unit connects to a cryogenic tank with a single nciccnn / eznz / B / YiAi Ref. 345588 Connection point for filling. The cryogenic tank system, generally indicated in 11, includes a cryogenic tank 1 with an inner cover 14 and an outer cover 17. Tank 1 contains a portion of cryogenic liquid 3 and an upper space for vapor 2. Cryogenic tank 1 is in communication with a supply device by means of supply line 4 at supply inlet 5. Supply line 4 branches at intersection / junction 6 into two separate lines 7 and 8 in communication with cryogenic tank 1. The first line 7 includes a route for filling the tank from the top, and the second line 8 includes a route for filling the tank from the bottom. Each route contains at least one valve, which can be regulated to allow the desired amount of flow through each route. The first line 7 is shown with valve 9, and the second line 8 is shown with valve 10.Valves 9 and 10 are typically globe valves. Cryogenic tank 1 is filled by introducing cryogenic fluid from a supply device at inlet 5 through supply line 4. Valves 9 and 10 on tank lines 7 and 8 are manually adjusted to supply the fluid to the tank via the desired route. The cryogenic tank can be filled from the top (i.e., the incoming fluid is sprayed into the vapor space 2 of the tank) through line 7 by opening valve 9. The tank can also be filled from the bottom through line 8 by opening valve 10. The cryogenic fluid transferred from the mobile supply unit is generally subcooled to some extent. That is, the pressure of the fluid as it flows through the transfer lines is greater than the fluid's saturation pressure.When the fluid is transferred in this subcooled manner, it does not boil in the lines and is therefore transferred efficiently. The purpose of having one route for filling the tank from the top and another for filling it from the bottom is to equalize pressure. Filling from the top cools the tank's vapor space 2 and reduces the tank pressure, allowing the tank to be filled without venting. On the other hand, filling the tank from the bottom (i.e., the incoming fluid being pushed into the liquid space by means of a dip tube or bottom nozzle) causes the liquid level to rise, acting like a piston and increasing the tank pressure. The system described above requires manual adjustment of the filling valves and monitoring during the filling process to maintain the desired cryogenic tank pressure. Therefore, maintaining the desired cryogenic tank pressure during filling requires operators with a high level of skill, training, and experience. Summary of the Invention There are several aspects of the subject matter herein that may be incorporated separately or jointly into the methods, devices, and systems described and claimed herein. These aspects may be used alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the appended claims herein. In one aspect, a device for filling a cryogenic tank includes a body structure, a pressure comparator cylinder, a piston, a pressure regulator, and a sliding tube. The body structure includes an inlet port for receiving fluid from a supply tank, a first outlet port configured to connect to a top-loading filling line in communication with a cryogenic tank, a second outlet port configured to connect to a bottom-loading filling line in communication with a cryogenic tank, and a sliding tube cylinder. The cylinder housing is connected to the body structure and defines a pressure comparator cylinder having an upper volume and a lower volume. The lower volume is in fluid communication with a cryogenic tank.The piston slides into the pressure comparator cylinder, and a piston rod connects the piston to the slide tube. The pressure regulator is in fluid communication with the upper volume of the pressure comparator cylinder and the slide tube cylinder. The slide tube slides into the slide tube cylinder. The slide tube cylinder is configured to direct fluid to the fill line from the top through the first outlet port when the pressure in the lower volume exceeds the reference pressure, and to direct fluid to the fill line from the bottom through the second outlet port when the pressure in the lower volume is below the reference pressure. In another aspect, a method for filling a cryogenic tank includes the steps of providing a fluid flow stream from a supply tank to an inlet port of a filling device; comparing a cryogenic tank pressure with a reference pressure using the filling device; diverting fluid from the fluid flow stream to a top filling line in communication with the cryogenic tank when the cryogenic tank pressure exceeds the reference pressure; and diverting fluid from the fluid flow stream to a bottom filling line in communication with the cryogenic tank when the cryogenic tank pressure is below the reference pressure. Brief Description of the Figures Figure 1 is a schematic illustration of a system for filling a prior art cryogenic tank. Figure 2 is a schematic illustration of one modality of the description filling device. Figure 3 is a schematic illustration of one modality of the filling device described incorporated into a cryogenic tank system. Figure 4 is a schematic illustration of an alternative modality of the description filling device. Figure 5 is a schematic illustration of another alternative modality of the description filling device. Detailed Description of the Invention One embodiment of the filling device described provides a piston that compares a target reference pressure with the pressure of the tank being filled with cryogenic fluid and selectively diverts a flow stream to a top filling path and / or a bottom filling path, or flow portions to each path, based on the comparison, thereby reducing or eliminating the need to manually monitor and divert the flow stream while operating the filling device to supply cryogenic fluid to the tank. Figure 2 illustrates one embodiment of the filling device 16 of the current description. The filling device 16 supplies cryogenic fluid to a cryogenic tank. The filling device includes a body structure 18, a cylinder housing 22, a piston 21, a pressure regulator 24, and a sliding tube 29. By way of example only, the body structure 18 may be in the form of a tube. The body structure includes an inlet port 15 for receiving fluid from a supply tank (such as the tank of a mobile supply unit) or an alternative supply device or system. The body structure also includes a first outlet port 12 to a top-fill line in communication with a cryogenic tank being filled and a second outlet port 13 to a bottom-fill line in communication with the cryogenic tank. The body structure 18 defines a slip tube cylinder 19 that slides into a slip tube 29. The slip tube 29 has the ability to slide freely up and down within the slip tube cylinder 19. Although specific details are not shown in the figures, both the inlet and outlet ports may feature a variety of specific fittings. For example, each port may include a removable and reusable seal. Each port may also include a valve or a vent hole. Inlet port 15 is connected to a supply tank or other supply device during filling, for example, by means of a flexible hose or insulated pipe. The cylinder housing 22 defines a pressure comparator cylinder that slides into the piston 21. The piston can slide freely up and down within the pressure comparator cylinder. The pressure comparator cylinder includes two separate volume cavities: an upper volume 23 and a lower volume 27. The upper volume 23 is maintained at a predetermined reference pressure by the pressure regulator 24, as explained below. The lower volume 27 is in fluid communication with the upper space of the cryogenic tank being filled through port 28 and is therefore maintained at the cryogenic tank pressure.The piston 21 preferably includes a seal between the piston 21 and the inner surface of the wall of the comparator cylinder of nQccnn / eznz / e / YiAi the pressure defined by the cylinder housing 22, which eliminates any type of communication or gas exchange between the upper volume 23 and the lower volume 27. A piston shaft 30 is connected to the piston head 21 and the sliding tube 29. The piston shaft 30 also preferably includes a seal that prevents fluid exchange between the pressure comparator cylinder defined by the cylinder housing 22 and the cylinder 19 of the sliding tube of the body structure 18. As noted above, the pressure regulator 24, which is preferably a pressure relief regulator, is used to maintain the pressure in the upper volume 23 of the cylinder housing 22 at a generally constant reference pressure. Suitable pressure regulators are well known in the art and may include at least one valve that opens based on the pressure setting or setpoint to allow fluid to either enter the upper volume 23 (if the pressure inside the upper volume is below the setpoint) or exit the upper volume (if the pressure inside the upper volume is above the setpoint). The pressure regulator 24 is connected to the upper volume 23 of the pressure comparator cylinder and to the cylinder 19 of the slide tube via communication lines 25 and 26, respectively. nciccnn / eznz / B / YiAi Piston 21 will move downward when the cryogenic tank pressure (which is equal to the pressure inside the lower volume 27) falls below the reference pressure of regulator 24, and it will move upward when the cryogenic tank pressure exceeds the reference pressure of regulator 24. In the latter case, the excess pressure caused by the upward movement of piston 21 is vented from the upper volume 23 to the atmosphere by means of the pressure regulator 24 (through line 25), generally maintaining the upper volume 23 at a constant reference pressure. When the pressure inside the lower volume 27 (i.e., the cryogenic tank pressure) of the pressure comparator cylinder drops below the reference pressure and, consequently, below the pressure inside the upper volume 23, piston 21 will move downward.When this occurs, regulator 24 opens, and the pressurized fluid from the upper portion of the slide tube cylinder 19 travels through lines 26 and 25 into the upper volume 23 to maintain the setpoint pressure. When the setpoint pressure is reached within the upper volume 23 and the downward movement of piston 21 stops, regulator 24 closes. The sliding tube cylinder 29 is configured to direct a larger portion of the fluid from a flow stream entering the inlet port 15 of the device nciccnn / eznz / B / YiAi to a fill line at the top of the cryogenic tank through the first outlet port 12 (to decrease the pressure of the cryogenic tank) when the pressure in the lower volume 27 of the pressure comparison cylinder exceeds a pressure reference point and to direct the fluid to a fill line at the bottom of the cryogenic tank through the second outlet port 13 (to increase the pressure of the cryogenic tank) when the pressure in the lower volume 27 is below a pressure reference point.The sliding tube 29 has slots, holes, or other openings 20a, 20b that direct the flow of cryogenic fluid from the inlet 15 to the outlet 12 of the fill line at the top and / or the outlet 13 of the fill line at the bottom, depending on the position of the sliding tube 29. Although one slot is shown on each side of the sliding tube, the sliding tube may include more than two slots / holes. The holes or slots 20a, 20b may be of any shape. They may be circular, rectangular, or any other known shape. In one embodiment, the slots are teardrop-shaped to provide a variable flow rate based on the position of the sliding tube 29 within the cylinder 19 of the sliding tube. A design element that can be exploited is the fact that the filling pressure (the pressure of the fluid entering through the inlet port 15) always exceeds the tank pressure, which is the ratio of the cross-sectional area of ​​the piston shaft 30 to the weight of the piston-shaft-sliding tube assembly. If the pressure drop from the body structure 18 to the cryogenic tank during normal filling operations is known, the weight of the piston-shaft-sliding tube assembly can be selected to match the excess upward force on the piston 21. Ideally, there is no net force on the piston-shaft-sliding tube assembly when the cryogenic tank pressure is exactly equal to the reference pressure (the pressures in the lower chamber 27 and the upper chamber 23, respectively).The downward force on piston 21 = the force of gravity on the piston-shaft-sliding tube assembly + (the pressure in the upper volume 21 x the cross-sectional area of ​​the pressure comparison cylinder). The upward force on piston 21 = the pressure in the lower volume 27 x (the cross-sectional area of ​​the pressure comparison cylinder - the cross-sectional area of ​​the piston shaft 30) + (the pressure in the body structure 18 x the cross-sectional area of ​​the piston shaft 30). The weight of the piston-shaft-sliding tube assembly is ideally equal to the pressure reduction from the body structure 18 to the cryogenic tank nciccnn / eznz / B / YiAi multiplied by the cross-sectional area of ​​the shaft 30. However, it is not necessary (or possible) to have this set exactly because the pressure reduction from the body structure 18 to the tank depends on the filling rate, which can vary slightly from one mobile supply vehicle to another depending on the vehicle's capabilities. The filling device 16 in Figure 2 may be included in a cryogenic fluid delivery system, which includes a volumetric cryogenic fluid tank (in fluid communication with the inlet port 15 in Figure 2), or a cryogenic tank system. An example of the latter is shown in general at 102 in Figure 3. The system 102 includes a cryogenic tank 101 having an inner cover 114 and an outer cover 132, wherein the inner cover defines an interior of the tank. The cryogenic liquid 136 is stored within the interior of the inner cover 114, with an upper space occupied by the cryogenic vapor 134. As illustrated in Figure 3, the cryogenic tank 101 is connected to the filling device 116 by a series of lines. The filling device 116 operates in the same manner as the filling device 16 shown in Figure 2 and described above. The pressure sensing line 128 connects the upper space of the cryogenic tank. 101 to the filling device 116. More specifically, the pressure sensing line 128 connects the lower volume 127 of the cylinder housing at port 128a of the filling device to the upper space of the inner cover 114 of the cryogenic tank at port 128b. The pressure sensing line 128 allows communication between the upper space of the tank and the filling device so that the lower volume 127 of the filling device and the cryogenic tank are maintained at the same pressure. The filling device 116 is also connected to the cryogenic tank 101 by means of the filling transfer lines 112 and 113. The top filling line 112 connects the body structure 118 of the filling device 116 at port 112a to the vapor space 134 of the inner cover 114 of the cryogenic tank at port 112b.The bottom filling line 113 connects the body structure 118 of the filling device 116 at port 113a to the cryogenic liquid 136 of the inner cover 114 of the cryogenic tank at port 113b. Although the filling lines 112 and 113 are shown connected to the inner cover 114 at the top and bottom respectively, the filling lines can also be connected to the vapor space and the cryogenic liquid portion along either side of the inner cover. Continuing with reference to Figure 3, the cryogenic tank 101 is filled by means of the filling device 116 in the manner described above for the filling device 16 in Figure 2. Cryogenic fluid is supplied from a supply tank or other filling system to the filling device through the inlet port 115. The filling device diverts at least a portion of the cryogenic fluid stream entering through port 115 to the top filling line 112 when the pressure inside the cryogenic tank 101 exceeds a pressure setpoint, and diverts at least a portion of the cryogenic fluid stream entering through port 115 to the bottom filling line 113 when the pressure inside the cryogenic tank 101 falls below the setpoint pressure. As described above, the process is performed automatically by the filling device 116.The pressure regulator 124 in Figure 3 generally provides a constant reference pressure in the upper volume 123 and the piston 121 moves the sliding tube 129 based on the pressure inside the lower volume 127 (cryogenic tank pressure 101) so that there is little or no change in pressure inside the cryogenic tank 101 during filling. As described with reference to Figure 2, the use of the pressure release regulator 24 allows any excess pressure in the upper volume 23 of the filling device 16 to be vented to the atmosphere. Other modalities that accomplish the same task without venting to the atmosphere are illustrated in Figures 4 and 5. The coordinating components in Figures 4 and 5 are numbered similarly to the device components in Figure 2 and function in the same manner. In the device of Figure 4, generally indicated as 216, the upper volume 223 of the pressure comparison cylinder expands. The functionality of device 216 is otherwise identical to that of device 16 in Figure 2. The combined volume of the upper volume 223 and the communication line 225 in Figure 4 is designed to be much larger than the displacement volume of the piston head 221, so that the pressure change is minimal along the piston stroke. However, a disadvantage of this method is that daily or annual temperature cycles can still cause the pressure within the upper volume 223 to increase relative to the gas temperature. In the device of Figure 5, generally indicated as 316, a backpressure control device 340 (such as a backpressure regulator or a relief valve) has been added to the communication line 325 with a reference point slightly above the reference point of a pressure regulator (without relief) 324. The functionality of device 316 is otherwise identical to that of device 16 in Figure 2. Although the preferred modalities of the description have been shown and described, it will be evident to those skilled in the art that changes and modifications can be made without departing from the spirit of the description, the scope of which is defined by the following claims. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A device for filling a cryogenic tank, characterized in that it comprises: a body structure including: an inlet port for receiving fluid from a supply device; a first outlet port configured to connect to a filling line at the top in communication with a cryogenic tank; a second outlet port configured to connect to a filling line at the bottom in communication with a cryogenic tank; a sliding tube cylinder; a cylinder housing connected to the body structure defining a pressure comparison cylinder having an upper volume and a lower volume, the lower volume being in fluid communication with a cryogenic tank; a piston slidably positioned in the pressure comparison cylinder; a piston rod connected to the piston;a pressure regulator in fluid communication with the upper volume of the noccnn / cznz / B / YiAi pressure comparator cylinder and the slide tube cylinder; a slide tube connected to the piston shaft and slidably positioned within the slide tube cylinder, the slide tube cylinder being configured to direct fluid to a filling line from the top through the first outlet port when a pressure in the lower volume exceeds a pressure reference point and to direct fluid to a filling line from the bottom through the second outlet port when the pressure in the lower volume is below a pressure reference point.

2. The filling device according to claim 1, characterized in that the sliding tube has at least two openings for directing the fluid.

3. The filling device according to claim 2, characterized in that the openings are teardrop-shaped.

4. The filling device according to claim 1, characterized in that the pressure regulator is a pressure release regulator.

5. The filling device according to claim 1, characterized in that the weight of the piston, shaft and sliding tube is approximately equal to the pressure reduction from the body structure to the tank while filling the cryogenic tank, multiplied by the cross-sectional area of ​​the piston shaft.

6. The filling device according to claim 1, characterized in that the upper volume of the cylinder housing is greater than the lower volume of the cylinder housing.

7. The filling device according to claim 1, characterized in that it further comprises a second pressure regulator in the fluid circuit between the upper volume and the pressure regulator.

8. The filling device according to claim 1, characterized in that it further comprises a seal between the piston and the pressure comparison cylinder.

9. The filling device according to claim 1, characterized in that it further comprises a seal around the piston axis configured to prevent fluid from flowing between the pressure comparator cylinder and the body structure.

10. A method for filling a cryogenic tank, characterized in that it comprises the steps of: providing a fluid flow stream from a supply device to an inlet port of a filling device; comparing a cryogenic tank pressure with a reference pressure using the filling device; diverting fluid from the fluid flow stream to a top filling line in communication with the cryogenic tank when the cryogenic tank pressure exceeds the reference pressure and diverting fluid from the fluid flow stream to a bottom filling line in communication with the cryogenic tank when the cryogenic tank pressure is below the reference pressure.

11. The method according to claim 10, characterized in that the pressure comparison step is performed using a piston with the cryogenic tank pressure on a first side of the piston and the reference pressure on a second side of the piston.

12. The method according to claim 11, characterized in that the sliding tube is moved by the piston by means of a piston shaft.

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