DE102007023821B4 - Method for filling a cryogenic hydrogen storage container, in particular a motor vehicle - Google Patents

Abstract

A method for filling a for a cryogenic storage medium, in particular cryogenic hydrogen, provided storage container, in particular a cryogenic pressure tank (7) of a motor vehicle, wherein prior to filling with new from a large reservoir (1) in the liquid state removed cryogenic storage medium (3) at least a subset of the storage medium still contained as residual gas (4a) in the storage tank / cryogenic pressure tank (7) is removed from the storage tank (7), which is further cooled using the refrigeration potential of the large storage tank (1) and thus preconditioned for refilling, characterized in that the residual gas for preconditioning of the storage container (7) as long as in a cycle from the storage container (7) and by a the refrigeration potential of the large reservoir (1) using the heat exchanger (27) into a buffer tank (28) and out of this by means of a cryogenic pump (32) comp tet and back into the storage container (7) is performed until this storage container (7) is sufficiently cooled in terms of refilling with storage medium from the large reservoir (1).

Description

The invention relates to a method for filling a for a cryogenic storage medium, in particular cryogenic hydrogen, provided storage container, in particular a cryogenic pressure tank of a motor vehicle, wherein prior to filling with new taken from a large reservoir in the liquid state cryogenic storage medium at least a subset of still as Residual gas contained in the storage tank / cryogenic pressure tank storage medium is discharged from the storage tank, which is further cooled using the refrigeration potential of the large reservoir and thus preconditioned for refilling. In addition to the currently used refueling technology, which, for example, is applied to the vehicle "Hydrogen 7" by the applicant of the present patent application and explained in the following paragraph, the prior art is directed to the non-prepublished published patent application DE 10 2007 011 530 A1 referred to the applicant.

State of the art in the mentioned vehicle "Hydrogen 7", which is equipped with a so-called. Cryo-tank for storing cryogenic hydrogen (to supply the running as an internal combustion engine Fzg. Drive unit) is a "subcritical" storage tank (as a cryogenic tank ), which consists of a metallic inner tank, a metallic outer tank and an intermediate vacuum superinsulation to reduce the heat input into the inner tank. The typical operating pressure of this storage tank is between 1 bar absolute and 10 bar absolute, and the operating temperatures in the so-called "cold regular operation" are between 20 K (Kelvin) and about 30 K, d. H. the cryogenic hydrogen contained in the storage tank or in the inner tank thereof has these physical values mentioned, which are in the pressure-density diagram of the hydrogen in the so-called subcritical range. The refueling of the cryogenic tank according to this prior art is carried out with cryogenic liquid hydrogen at pressures between 1 bar and 6 bar and corresponding saturation temperatures of the cryogenic hydrogen or with slight supercooling thereof. The currently maximum representable supercooling is in the order of 6 Kelvin as the difference of the saturation temperature at a pressure of 6 bar absolute and the saturation temperature at a pressure of 1 bar absolute. The so-called subcritical refueling takes place in a two-fold process. The flow liquid saturated or under use of a gas station cryogenic pump supercooled hydrogen from the LH2 tank (= liquid hydrogen tank) of the gas station, which is referred to herein as a large reservoir in the vehicle storage tank adds a return gas line from the vehicle storage tank in the large Reservoir of the gas station. Since liquid hydrogen remains in the storage tank (= cryogenic tank) only when complete cooling of the Fzg. Storage tank and all supplying lines using the refrigeration potential of the large reservoir, is usually a significant amount of liquid hydrogen to use it, the Fzg. -Storage container and the lines to cool at the beginning of the refueling process, d. H. precondition. The resulting return gas mass flow is currently either not yet used on the gas station side and discharged to the environment, or further used via a secondary consumer system (for example a fuel cell or a pressure tank). The feedback of the hydrogen return gas in the gas station side large reservoir (= LH2 tank) is another way of using return gas, but is subject to the withdrawal of potentially contaminated fuel.

In the non-prepublished published patent application mentioned above DE 10 2007 011 530 A1 a method for filling a for a cryogenic storage medium, in particular hydrogen, provided pressure accumulator is described. Basically, the filling of a cryogenic pressure tank - to this tank technology is in addition to the aforementioned non-prepublished patent application, for example. Reference is made to US 6,708,502 B1 - done with subcritical liquid hydrogen analogous to the above paragraph described subcritical liquid hydrogen refueling, with the difference in that for preconditioning, ie for cooling the lines and the cryogenic pressure tank, a considerable additional effort is necessary and thus a larger amount of residual gas (or return gas, which can also be referred to as flushing medium) has to be fed back into the large reservoir of the filling station.

An alternative concept for the supercritical refueling of a cryogenic accumulator is disclosed in the non-prepublished published patent application DE 10 2007 011 530 A1 described. This is based essentially also on the return of the residual gas (or return gas or so-called flushing medium, which is also storage medium) during pressure equalization and cooling (and thus the so-called. Preconditioning) of the storage tank or cryogenic pressure tank in the large reservoir of the gas station with liquid subcritical hydrogen (with generally low subcritical pressure of about 1 bar absolute to 4 bar absolute). Subsequently, however, takes place the removal of liquid subcritical hydrogen from the large reservoir of the gas station with subsequent compression in a gas station installed cryogenic pump and filling (= refueling) of the vehicle Kryodendruckanks with cryogenic hydrogen at supercritical pressure level.

Since the present invention has its focus in the filling of a cryogenic pressure tank with cryogenic hydrogen at supercritical pressure level, the following some vulnerabilities of the non-prepublished published patent DE 10 2007 011 530 A1 called method described. However, it should be expressly understood that the method described with the present invention can also be used in the refueling or filling of a subcritical cryogenic tank, ie a simple storage container provided for a cryogenic storage medium.

A weak point of the above-described method for filling a cryogenic pressure tank is that a return of the before the filling still in the cryogenic pressure tank (or generally in the storage tank) residual gas in terms of pressure equalization and during cooling of the lines and the storage container (= Cryo-pressure tanks) takes place in the gas station side large reservoir. In this case, possibly contaminated hydrogen (or generally contaminated storage medium) in the large reservoir, from which later other users or customers are supplied, get. In the case of hydrogen as a storage medium, the residual gas fed back into the large storage tank of the filling station usually contains a high proportion of ortho-hydrogen which, when returned to the tank-side large storage container, results in a lower heat absorption capacity and therefore in an accelerated pressure build-up (in the large storage tank). and thus lead to increased boil-off quantities (of the large reservoir).

The regulation of the optimal residence time of the cryogenic hydrogen in the storage container of the motor vehicle during its Durchkühlung or preconditioning is complex and leads because of the fixed pressure in the large reservoir of the gas station and the resulting pressure boundary conditions in the entire filling process (the storage container in general or. Cryogenic pressure tanks in particular) in the refueling cycle to increased refueling times and / or residual gas quantities. Furthermore, the resulting by the residual gas recirculation and the associated heat input into the large reservoir of the gas station resulting release of hydrogen (generally cryogenic storage medium) from the large reservoir of the gas station for pressure maintenance (as a boil-off) is not yet included in the refueling process , Utilization of the filling station-side boil-off gas can only be achieved outside the tank or filling system for a cryogenic storage medium.

An improved method according to the preamble of claim 1 is therefore an object of the present invention.

The solution to this problem is characterized in that the residual gas for preconditioning of the storage tank as long as in a cycle from the storage tank and passed through a cold storage potential of the large storage tank heat exchanger into a buffer tank and compressed out of this by means of a cryogenic pump and back into the Storage tank is performed until this storage tank is sufficiently cooled in terms of refilling with storage medium from the large reservoir.

Advantageous developments are content of the dependent claims. In particular, a tank system for motor vehicles is claimed, which is equipped with the necessary elements for carrying out the method proposed here. These include, in addition to a suitable heat exchanger, a cryopump including suitably laid or interconnected lines and valves as well as an associated electronic control unit.

To meet the disadvantages of the prior art described (be it the supercritical filling of a cryogenic accumulator or the conventional filling of a provided for a cryogenic storage medium storage container such as in the said vehicle "Hydrogen 7), a filling or refueling principle is proposed in which a Return of residual gas in the gas station side large reservoir is not required. Nevertheless, its cooling potential can be used for the preconditioning of the storage container to be filled, in particular cryogenic pressure tanks. According to the invention, the residual hydrogen (or generally the storage medium or residual gas still contained in it) is passed through a heat exchanger which is connected to the large gas tank-side storage tank or with it before it starts refilling the cryogenic pressure tank or storage tank is stored in this stored hydrogen or storage medium in a suitable manner in heat transfer connection and thus can use its cooling potential. (In a preferred embodiment, this heat exchanger is located inside the large reservoir). With this passage through the said heat exchanger is located in the cryogenic pressure tank at the beginning of filling (= refueling start) under usually higher pressure and higher temperature (namely up to 350 bar and about 340 K) than after the filling process Hydrogen essentially to the temperature of the hydrogen in the large reservoir (namely, about 20 K to 25 K) cooled. (In the case of a simple cryogenic storage container, not as so-called. Cryo-pressure tank is formed, the pressure and temperature values of the withdrawn from the storage tank residual gas are of course considerably lower).

According to the invention, the residual gas, which has thus been cooled back, is passed into a buffer vessel and thereby expanded; Preferably, this buffer tank is sufficiently large (= voluminous) dimensioned to completely absorb the discharged from the cryogenic pressure tank (or generally the cryogenic storage tank) residual gas, relax and under a pressure which is below a pressure, with the following - what in following paragraph - a cryogenic pump promotes this residual gas in the cryopressure tank. In this way, the cryogenic pressure tank (the motor vehicle or general cryogenic storage tank) is emptied and relaxed.

For further cooling of the cryopressure tank (no further reference is made to the general, further relevant case of a simple cryogenic storage tank), the cryogenic hydrogen (or gas) in the buffer tank (or the gas) is / are stored via a cryopump. gen. Cryogenic storage medium) from this buffer tank as so-called. Rinsing medium pumped back into the cryopressure tank. This is thereby cooled, wherein the flushing medium is heated and increases its pressure, so that this in turn is removed as residual gas from the cryogenic pressure tank, again through said heat exchanger in said buffer tank. It is thus a circular process, which is carried out until the cryogenic pressure tank to be filled has cooled sufficiently. The residual gas is thus circulated as long or as often in the circle until a sufficient cooling of the cryopressure tank is detected, d. H. until it is sufficiently preconditioned. At this point in time or state, a so-called. Return gas valve of the cryopressure tank is closed and said cycle thus subsequently, then via the or a gas station side cryogenic pump cryogenic hydrogen (generally cryogenic fresh storage medium) from the large reservoir of the gas station in the cryo Pressure tank can be introduced until its filling pressure is reached and the cryogenic pressure tank is thus completely filled.

By the heat input or the heat input from said heat exchanger in the large reservoir of the gas station develops in this naturally a slight overpressure, which - even today in the known state of the art - typically degraded by blowing off gaseous hydrogen from the gas layer of the large reservoir becomes. This known as boil-off gas cold gas loss can be used in terms of an advantageous development of the invention for cooling the discharged from the cryogenic pressure tank residual gas or recirculated according to the method proposed here residual gas ("flushing medium"), d. H. This Boil-off gas of the large reservoir is provided as a cooling potential medium by the medium or through another heat exchanger through which the residual gas or recirculated residual gas is passed as a second medium to be cooled.

In terms of an advantageous development, the withdrawn from the buffer tank and compressed by a cryogenic pump recirculated residual gas, which now acts as a flushing medium and is also referred to as such, before being introduced into the storage tank by another the cooling potential of the large reservoir heat exchanger used be released to the developed or absorbed by the compression in the cryogenic pump heat again and thus for the cryogenic pressure tank to be conditioned, a higher refrigeration potential and for the last run of the said cycle, with which the withdrawn from the buffer tank residual gas substantially remains in the cryogenic pressure tank to have residual gas with higher density available. Moreover, the flushing medium (= recirculated residual gas) still present in the buffer container after completion of the said cyclic process and thus after completion of the preconditioning of the storage container can be fed to a secondary consumer, for example a fuel cell for immediate use or a duck tank for storage for later use.

In the following, the proposed method is further explained with reference to a preferred embodiment, wherein the accompanying single figure shows schematically an apparatus for performing this method.

With the reference number 1 is a large reservoir located at a gas station, in which cryogenic liquid hydrogen 3 Usually stored at ambient pressure (= 1 bara) and corresponding saturation temperature of 20.24 K. For this big reservoir 1 should be in its entirety with the reference number 7 marked cryogenic pressure tank of a motor vehicle to be fueled, ie the latter is intended with cryogenic liquid hydrogen from the large Vorhaltsbehälter 1 be filled. For this purpose, a cryo-pressure tank 7 , as usual, from a hydrogen at cryogenic to above ambient temperatures storing inner tank 6 and a vacuum-tight outer tank enclosing it under vacuum superinsulation 8th exists, associated filler pipe 18 ultimately with the large reservoir 1 connected.

After docking a dual-flow refueling intake 21a in or on the filler pipe 18 of the vehicle cryogenic pressure tank 7 to one of these assigned filling station refueling coupling 21b Both are a return gas valve 19 in the insulated filler pipe 18 , as well as the cryogenic pressure tank 7 associated extraction valve 14 opened, leaving residual hydrogen 4a from the inner tank 6 of the cryopressure tank 7 as residual gas through one in the inner tank 6 in the upper half of the tank opening sampling line 9 is removed to ultimately be delivered to the gas station and thus the cryogenic pressure tank 7 both to relax and to initiate its cooling (so-called "preconditioning"). This is what happens in the cryopressure tank 7 withdrawn and returned to the gas station residual gas via an insulated (preferably flexible) refueling line 22 to a gas station side isolated so-called conditioning unit 5 guided. In this - optionally - the residual gas (preferably as a function of which by means of a temperature sensor 23 measured temperature) in a heat exchanger 24 pre-cooled, which with cold boil-off gas, which is used to equalize the pressure of the large reservoir 1 via a boil-off line 37 from the gas layer 4 of the big storage tank 1 is removed, is flowed through.

Subsequently, the recycled residual gas via a valve 25 in one with the big reservoir 1 or with the liquid hydrogen contained therein 3 in a suitable heat-transferring connection standing heat exchanger 27 introduced and in this up to or near the temperature of the liquid hydrogen 3 in the storage container 1 cooled. (Alternatively, the recirculated residual gas without precooling in the heat exchanger 24 directly via a valve 26 in the heat exchanger 27 led and cooled there). That in the heat exchanger 27 , which is here in liquid hydrogen 3 of the storage container 1 is, cooled and thus contracted residual gas, which is also hydrogen, is then in a buffer tank 28 collected, for what downstream of which provided valves 31 and 38 are closed. This buffer tank 28 is preferably sufficiently large to ensure adequate relaxation of the entire cryogenic pressure tank 7 to enable.

Moreover, all or the said lines are 9 . 18 . 22a and the heat exchanger 27 Sufficiently large enough to allow quick relaxation in the cryogenic pressure tank 7 (or in its inner tank 6 ) and by the rapid relaxation of the still remaining residual hydrogen 4a resulting expansion cold for pre-cooling the inner tank 6 to use and thus accelerate the filling or refueling process.

After sufficient relaxation of the inner tank 6 or the remaining hydrogen contained therein 4a passing through the pressure sensors 11 and 30 is quantifiable, is the said valve 31 opened so that the residual gas, more precisely, from the cold lower part of the buffer tank 28 removed hydrogen from the buffer tank 28 dissipated and this by means of a cryogenic pump 32 can be compressed. The resulting heat of compression in the residual gas / hydrogen can be opened by opening a valve 35 in a further heat exchange in one with the liquid hydrogen 3 of the big storage tank 1 related further heat exchanger 34 be compensated; Alternatively, this can be done by means of the cryogenic pump 32 compressed residual gas directly (and thus without detour via the heat exchanger 34 in slightly warmed condition) to the vehicle cryogenic pressure tank 7 be recycled as so-called. Rinsing medium. This flushing medium (= recirculated residual gas) passes through a valve 33 and a refueling line 22b to the already mentioned refueling coupling 21b the gas station. From there, the cold hydrogen as said flushing medium with sufficient pressure through a refueling valve 20 in the filler pipe 18 and a filling valve 15 in the filling line 10 of the cryopressure tank 7 in its inner tank 6 expanded. Ideally, in this are the openings of the filling line 10 and the already mentioned sampling line 9 spaced sufficiently far apart to the residence time of the flushing medium in the inner tank 6 during the cooling process / preconditioning process of the same.

This described cycle of removal of residual gas / residual hydrogen 4a from the cryopressure tank 7 or the inner tank 6 the same, followed by cooling and subsequent return of the residual gas as flushing medium is before refilling the inner tank 6 with liquid hydrogen 3 from the big storage tank 1 carried out or repeated until sufficient cooling of the inner tank 6 it is determined which, for example, via a temperature sensor 23 (in the pipe 22a ) can be quantified. If there is sufficient cooling of the inner tank 6 then the valves 14 . 25 respectively. 26 closed and after sufficient emptying of the buffer tank 28 , the content of which advantageously at least partially back into the cryopressure tank 7 and thus can be used again, also the valve 31 , For refilling the inner tank 6 of the cryo-pressure-tan 7 then becomes cold liquid hydrogen 3 from the big storage tank 1 via a sampling line 36 taken and advantageously via the same already mentioned cryogenic pump 32 on the way already described in the cryo-pressure tank 7 introduced into its inner tank 6 the final filling pressure (eg. In the order of 13 bar to about 350 bar or even higher) is reached.

What the buffer tank 28 If necessary, this or its residual content, which may still be present after completion of said cycle, may be supplied by the cryogenic pump 32 could not be dissipated and has heated up in the meantime possibly under pressure, before filling the cryogenic pressure tank 7 but also at another appropriate time to prepare for another refueling operation (another cryogenic pressure tank of another motor vehicle) via a valve 38 and a bypass valve 40 be completely relaxed. The case from the buffer tank 38 delivered amount of hydrogen can be via an outlet 41 delivered to a secondary consumer (eg. A fuel cell) and used there.

As already described, this can be achieved by the introduction of heat into the large reservoir 1 and the consequent need for relaxation resulting boil-off gas via a boil-off pipe 37 and a valve 39 for pre-cooling the from the inner tank 6 of the cryopressure tank 7 recycled hydrogen or residual gas can be used during the cooling process. Subsequently, the so-preheated boil-off gas via an output 41 at one. secondary consumer, which may be, for example, a conditioning unit for a high pressure refueling system or a fuel cell delivered. Alternatively, such a pre-cooling of the cryopressure tank 7 removed residual gas and it will be the boil-off gas of the large reservoir 1 via a valve 40 directly in cold condition to the mentioned exit 41 (to the secondary consumer).

Advantageously, with the proposed method, substantially complete reintroduction of the start of refueling (ie, prior to preconditioning) in the cryopressure tank occurs 7 hydrogen in the same, so that, with the exception of a minor, with completion of said cycle for preconditioning still in the buffer tank 28 remaining amount of residual gas practically no fuel losses. Advantageously, no direct introduction of the recirculated residual gas or residual hydrogen takes place 4a from the cryopressure tank 7 in the big storage tank 1 the gas station. There is thus no risk of contamination or weakening of the heat capacity of the large reservoir 1 by recycling (higher-energy) ortho-hydrogen from the cryopressure tank 7 , The so-called two-parting of the filling process, namely the said preconditioning using the residual gas in the cryogenic pressure tank in said cycle (= Kreiszyklierung during cooling) with subsequent refilling of the cryogenic pressure tank with this residual gas or flushing medium, and the subsequent practical Lossless filling of the cryogenic pressure tank 7 with new fresh storage medium from the large storage tank 1 thus creates a possibility for lossless pre-cooling of the cryopressure tank 7 (or generally storage container). Advantageously, it is possible to cycle at higher pressures as well as the cryopressure tank 7 to fill, so that despite the Vorkühlphase (= preconditioning), a relatively fast refueling process can be realized.

Finally, there is the option of optional use of the heat input in the large reservoir 1 emerging boil-off gas for precooling the cryo-pressure tank to be filled 7 (or storage container). By refueling, for example, one or two cryogenic pressure tanks 7 in the order of magnitude, for example, a corresponding motor vehicle (for example, by means of a fuel cell) can be operated from the large storage tank (with appropriate use of the boil-off gas produced during the preconditioning). 1 ) a loss-free operation of the gas station are made possible. For refueling a vehicle cryogenic pressure tank ( 7 ) at a gas station for liquid hydrogen would be without the heat input from the described refueling namely other energy for pressure maintenance in the large reservoir ( 1 ) of the gas station necessary, wherein it should be noted that quite a variety of details may differ from the above explanations designed without departing from the content of the claims.

Claims (7)

Method for filling a storage container provided for a cryogenic storage medium, in particular cryogenic hydrogen, in particular a cryogenic pressure tank ( 7 ) of a motor vehicle, wherein prior to filling with new from a large reservoir ( 1 ) in the liquid state removed cryogenic storage medium ( 3 ) at least a portion of the still as residual gas ( 4a ) in the storage tank / cryogenic pressure tank ( 7 ) contained storage medium from the storage container ( 7 ) is discharged, which further using the refrigeration potential of the large reservoir ( 1 ) is cooled and thus preconditioned for refilling, characterized in that the residual gas for preconditioning of the storage container ( 7 ) in a cycle from the storage tank ( 7 ) and by a the cold potential of the large reservoir ( 1 ) using heat exchanger ( 27 ) into a buffer container ( 28 ) and out of this by means of a cryogenic pump ( 32 ) and back into the storage container ( 7 ) is guided until this Storage container ( 7 ) with a view to refilling with storage medium from the large reservoir ( 1 ) is sufficiently cooled. A method according to claim 1, characterized in that the from the storage container ( 7 ) discharged residual gas ( 4a ) or recirculated residual gas to use the refrigeration potential of the large reservoir ( 1 ) by a arranged in this heat exchanger ( 27 ) to be led. A method according to claim 1 or 2, characterized in that the discharged from the storage tank residual gas or recirculated residual gas to use the refrigeration potential of the large reservoir by one with the boil-off gas of the large reservoir ( 1 ) acted upon heat exchanger ( 24 ) to be led. Method according to one of the preceding claims, characterized in that the discharged from the storage tank residual gas or recirculated residual gas after passing through the heat exchanger ( 27 ) in a sufficiently large buffer container ( 28 ) is relaxed and collected. Method according to one of the preceding claims, characterized in that the from the buffer container ( 28 ) and by means of a cryogenic pump ( 32 ) compressed recirculated residual gas, which now acts as flushing medium and is also referred to as such, prior to introduction into the storage container ( 7 ) by a the cold potential of the large reservoir ( 1 ) using heat exchanger ( 34 ) to be led. Method according to one of the preceding claims, characterized in that after completion of the preconditioning of the storage container ( 7 ) still in the buffer tank ( 28 ) located flushing medium is supplied to a secondary consumer. Tank system for motor vehicles, which has a large reservoir and lines, valves and at least one heat exchanger for carrying out the method according to any one of the preceding claims.

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