Liquid conditioning for cryogen vessel fill station

Abstract

A method for conditioning a liquid cryogen in a tank includes reducing a pressure of the liquid cryogen in the tank for reducing a temperature of the liquid cryogen and condensing any vapor boil-off in the tank for reclaiming the liquid cryogen in the tank. The liquid cryogen may be selected from the group consisting of liquid nitrogen (LIN), liquid oxygen (LOX), and liquid argon (LAR).

Claims

1. A method for conditioning a liquid cryogen in a tank, comprising: reducing a pressure of the liquid cryogen in the tank by venting vapor in the tank to atmosphere external to the tank to cool the liquid cryogen in the tank, wherein the pressure of the tank is reduced from 50 psig to 10 psig, withdrawing the liquid cryogen from the tank to a vaporizer, vaporizing the liquid cryogen with the vaporizer for providing vapor boil-off, and introducing the vapor boil-off from the vaporizer into the tank for re-pressurizing the tank with the vapor boil-off, wherein the reducing, the withdrawing, and the introducing steps condition the liquid cryogen in the tank to a new level lower than a liquid level of the liquid cryogen that existed in the tank before the reducing the pressure of the liquid cryogen in the tank.

2. The method of claim 1, wherein the liquid cryogen is selected from the group consisting of liquid nitrogen (LIN), liquid oxygen (LOX), and liquid argon (LAR).

3. The method of claim 1, wherein the re-pressurizing the tank is resumed to 50 psig.

4. The method of claim 1, wherein after the re-pressurizing a temperature of the liquid cryogen is uniform throughout the tank.

5. The method of claim 1, wherein the reducing the pressure and the re-pressurizing the liquid cryogen in the tank occurs automatically.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention, reference may be had to the following description of exemplary embodiments considered in connection with the accompanying drawing Figures, of which:

(2) FIGS. 1A and 1B show side plan schematic views of a known conditioning system for use with known liquid cryogen tanks;

(3) FIGS. 2 and 3 show side plan schematic views of apparatus embodiments for implementing method embodiments according to the present invention and which can be used with the tanks of FIGS. 1A and 1B; and

(4) FIG. 4 shows a side plan schematic view of connections for the tanks of FIGS. 2 and 3.

DETAILED DESCRIPTION OF THE INVENTION

(5) Before explaining the inventive embodiments in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, if any, since the invention is capable of other embodiments and being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

(6) In the following description, terms such as a horizontal, upright, vertical, above, below, beneath and the like, are to be used solely for the purpose of clarity illustrating the invention and should not be taken as words of limitation. The drawings are for the purpose of illustrating the invention and are not intended to be to scale.

(7) The predictive and computational abilities of the apparatus and method embodiments of the present invention provide for an automated and/or remote ability to re-condition a cryogenic liquid, such as LIN, at for example a customer station.

(8) Embodiments of the present invention are illustrated in FIGS. 2-4. Advantages of the present method embodiments include: a more consistent liquid quality at point of use; the ability to operate the liquid storage tank to a lower level of liquid in same, and to deliver more fully loaded trucks of LIN (rather than partial loads to the bulk storage LIN tank); a reduction in two-phase flow from the storage tank to the downstream process, and a related increase in cost savings; reliably more consistent chill times for batch type processes; and a potential reduction in pipe size and less capital spend on same for a commensurate amount of liquid movement.

(9) Referring to FIG. 2, a cryogen (such as LIN) storage tank shown generally at 10 is at a head pressure of for example 50 psig to push or exert a force upon LIN 12 in the tank from proximate a bottom 14 of the tank into a pipe 16 for delivery to a subsequent user or customer process or equipment (not shown). The LIN 12 can be at a temperature of for example −312° F. (−191° C.), and the tank 10 may contain a volume of the LIN in a range of from, for example, 6,000-15,000 gallons (22,712-56,781 litres). This volume may of course be smaller or larger depending upon the particular application process being employed. Initially, a temperature of the LIN 12 is uniform throughout a height and volume of the tank 10. That is, the cooled temperature of the LIN 12 in the tank 10 is essentially uniform throughout its volume, such as when the tank is recently filled with fresh LIN to a position approaching a top 18 of the tank. In FIG. 2, the LIN 12 is shown filled to a level 20 within the tank 10. A head or ullage space 22 at the top 18 of the tank 10 above the LIN 12 is provided to receive fresh or recirculated LIN, and as a volume into which pressure for the tank can be introduced.

(10) As the LIN 12 is drained from or forced out of the tank 10 under pressure over a period of time, which may be for example 3-7 days depending upon the volume of usage of the LIN, heat leak occurs at the tank and in the LIN, resulting in temperature stratification occurring throughout a volume of the tank, as shown in FIG. 2. For example, the temperature of the LIN 12 proximate the bottom 14 remains for the most part at or very close to −312° F. (coldest liquid), but the temperature progressively increases through the volume of the LIN closer to the top 18 of the tank as the temperature of the LIN warms to approach for example −293° F. (−181° C.) at a warmed upper level 24 (warmest liquid) of the LIN in the tank.

(11) Still referring to FIG. 2, the LIN 12 in the tank 10 has warmed during use due to heat leak effecting same and therefore, temperature stratification of the LIN similar to that which occurred with respect to the LIN b in the tank a (FIG. 1A). However, instead of providing fresh LIN to the tank 10 to replenish same, the operator de-pressurizes the tank from 50 psig down to for example 10 psig. This reduction in pressure will result in a decrease in the LIN temperature. Accordingly, boil-off vapour shown generally at 26 of the LIN 12 occurs due to the de-pressurization of same and therefore, the temperature of the LIN will also be reduced to recondition the LIN as shown in FIG. 3 for subsequent use without having to resort to an immediate refilling of the tank 10 with fresh LIN. The amount of time that elapses from the condition of the tank 10 in FIG. 2 until the tank condition in FIG. 3 can be for example 15 minutes to a few hours, depending upon the pressure differential. However, due to heat leak and the fact that not all of the vaporized LIN will be reclaimed after re-pressurization, there is a new level 28 (a re-conditioned level) of the LIN 12 in the tank 10, and the new level is lower than the level 24 before additional LIN is added to the tank, as shown in FIG. 3.

(12) FIG. 4 shows the tank 10 with the LIN 12 therein, and piping connections for filling, emptying and pressurizing the tank for an end user, such as for example a customer filling station.

(13) The tank 10 as described above with respect to FIGS. 2-3 includes the pipe 16 for withdrawing the LIN from the bottom 14 of the tank to a customer process or other equipment (not shown). A valve 30 is interposed in the pipe 16 for controlling a flow of the LIN through the pipe to the process. The pipe 16 may be connected, by way of example only, to food processing equipment for chilling and freezing applications with the LIN.

(14) A fill connection pipe 31 may be used by a driver of a bulk delivery trailer (not shown) to fill the tank 10 being used as a customer storage tank for the LIN. The fill connection pipe 31 is branched or split at 32 into two separate lines, i.e. a top fill line 34 having an end 36 terminating in and in fluid communication with the head space 22 to provide the LIN to the top of the tank, and a bottom fill line 38 having an end 40 terminating in and in fluid communication with the LIN 12 in the tank near the bottom 14 to provide the LIN to the tank, or to fill the tank from the bottom up. The fill connection pipe 31 can have a standard coupling (not shown) constructed to releasably engage a corresponding coupling of a driver's tanker truck (not shown) delivering the LIN. The top fill line 34 is provided with a valve 42, and the bottom fill line 38 is provided with a valve 44. The valves 42,44 permit an operator of the tank 10 to determine into which volume of the LIN 12 in the tank 10 that the fresh, replenishing LIN is to be received. Top filling of the tank 10 may reduce the vapor pressure in same, and controls the tank storage pressure during the filling process.

(15) A pressure-vent line 46 has an end 48 terminating in and in fluid communication with the head space 22 of the tank 10. An opposite end of the line 46 includes a valve 50, such as for example a solenoid valve, for controlling pressure at the head space 22 and therefore, in the tank 10 by being constructed to vent pressure in the tank in excess of what is needed in same. The valve 50 vents to atmosphere external to the tank 10 to prevent uncontrollable pressure increases in the tank, and to maintain pressure in the tank within a range of from +/−15 psig of the bulk tank set pressure, but set as close as possible to minimize the pressure differential.

(16) A pressure line 52 includes a first end 54 terminating in and in fluid communication with the LIN 12 at the bottom 14 of the tank 10, and a second end 56 terminating in and in fluid communication with the head space 22 of the tank. A valve 58 is interposed in the line 52 to control pressure in the tank when such pressure gets too low. The pressure line 52 passes through and is in contact with a vaporizer 60. When pressure in the tank 10 drops to a lower, unacceptable level, the valve 58 is opened to draw the LIN 12 from the bottom 14 of the tank and causes the LIN to be vaporized when passing through the vaporizer 60 so that the vapour/gas is introduced into the top 18 of the tank through the second end 56 to be distributed into the head space 22 to increase pressure in the tank.

(17) Struts 62 or legs support the tank 10 off an underlying surface (not shown), such as for example a floor, pad, skid, etc. The struts 62 may each be adjustable to accommodate any irregularities of the underlying surface.

(18) By adding the remote control feature with respect to a flow disruption resulting from the quality of the liquid in the storage tank, the operator has the ability to remotely (online or at a remote delivery scheduling center) activate a re-conditioning cycle or de-activate a cycle if a new delivery is enroute. The remote control method, at its most basic level, will analyse properties of the LIN in the tank by measuring temperature, head space pressure, liquid pressure and liquid level. With these measurements, thermodynamic equations of equilibrium can be applied to understand if the LIN in the tank exists in a saturated or subcooled state. This in turn is one metric for providing guidance to an operator and the system itself in determining if it is necessary to perform a reconditioning cycle for the LIN.

(19) The system through its processor can also “learn” about the customer usage rates and idle time of the tank 10. This is realized through monitoring the following variables over time: tank head space pressure, tank bottom pressure, LIN temperature, liquid level in tank, daily and weekly operating schedules of the customer, and weather conditions. Such can assist with predicting the next re-conditioning cycle of the LIN 12 by understanding the period of time necessary for a subcooled state of the LIN to last in the tank 10 before the LIN needs to be re-conditioned.

(20) It will be understood that the embodiments described herein are merely exemplary, and that a person skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as provided in the appended claims. It should be understood that the embodiments described above are not only in the alternative, but can be combined.