METHOD FOR FILLING A CAVERNA STORAGE TANK WITH LIQUID HYDROGEN

Description

[0001] The invention relates to a method for filling a cavern storage facility with liquid hydrogen (H 2 ).

[0002] To fill a cavern storage facility with natural gas (CH4), it is common practice to pump gaseous natural gas (CH4), i.e. methane with natural foreign gas admixtures, directly into the cavern using existing pipeline pressure and subsequent compression. The temperature increase of the compressed natural gas (CH4) caused by the heat of compression is compensated for by the release of heat in the cavern storage facility to the rock and / or to an existing ground brine in the cavern. It can be observed that temperature equilibration takes place in the cavern, so that the gas temperature in a cavern can be between 20°C and 30°C. Depending on the depth of the cavern, the prevailing temperature of the geothermal energy there can heat the natural gas (CH4) in the cavern or cool the natural gas (CH4) in the cavern using the heat of compression that is lost in the large gas volume in the cavern.

[0003] During a filling operation with LNG (liquefied natural gas), it was determined that the immediate filling of a cavern with LNG at a temperature of approximately 110 K causes the temperature inside the cavern to drop so low that a minimum pressure cannot be maintained. The pressure drop associated with the temperature drop can cause damage to the cavern and, in extreme cases, lead to rock collapse, which constitutes a serious disaster.

[0004] Typical caverns are located at depths between 800 m and 2,000 m, have heights between 100 m and 300 m, and a diameter between 30 m and 80 m. Significantly larger caverns also exist. However, caverns of the type described above are predominant in Germany. At these sizes, the caverns prevalent in Germany have nominal volumes ranging from 100 million standard cubic meters to 300 million standard cubic meters. If such a cavern is filled with a typical overseas ship's cargo of LNG without first undergoing energy-intensive gasification, a cavern collapse as described above is possible and likely. In order to unload a ship's LNG cargo as quickly as possible, it would therefore be necessary to gasify the LNG in special plants with a correspondingly high capacity in order to feed the gasified LNG into a pipeline system, where the gasified natural gas would be pumped into the cavern using conventional means.Currently, there is no LNG terminal in Germany capable of gasifying typical shiploads of LNG within a timeframe that would still be economically viable for lightering a ship. Document US6932121B1 discloses the storage of LNG in caverns.

[0005] A nearly identical situation arises for ship cargoes of liquid hydrogen (H 2 ). Despite the extremely low temperature of hydrogen (H 2 ) and the transport loss due to so-called boil-off gas during overseas transport, it is being considered to import liquid hydrogen (H 2 ) from overseas by ship and store it in Germany in caverns that were originally designed for the storage of natural gas (CH 4 ). Liquid hydrogen (H 2 ) differs from LNG in that it has a temperature of 20 K, compared to approximately 110 K for LNG. Hydrogen (H 2 ) also has a noticeably high specific heat capacity. Hydrogen (H 2 ) can also be stored in caverns by mixing natural gas (CH 4 ) with hydrogen (H 2 ), for example by feeding hydrogen (H 2 ) into caverns filled with natural gas (CH 4 ). This creates a mixed gas, which is then passed on to the consumer from the cavern.Concepts are also being implemented to fill cavern storage facilities exclusively with hydrogen (H2) to make the hydrogen (H2) usable for vehicles and / or fuel cells. Here, too, there is a need to find a process to unload a ship loaded with liquid hydrogen (H2) as quickly as possible and to fill the hydrogen (H2) into a cavern. The regasification problem is even more pronounced with liquid hydrogen (H2) than with LNG.

[0006] The object underlying the invention is achieved by the sequence of steps in claim 1. Further advantageous embodiments are specified in the subclaims to claim 1.

[0007] According to the concept of the invention, it is provided that liquid hydrogen (H 2 ) is introduced directly into the cavern, contrary to the expectation that the temperature in the cavern could fall below a critical point with an associated pressure drop. In order to avoid the expected consequences of the pressure drop, according to the concept of the invention, it is provided that the liquid hydrogen (H 2 ) is fed into the cavern through a heat exchanger coil or a pipe ('coil tubing'). The heat exchanger coil or pipe is present in the cased borehole that leads to the cavern head. When the liquid hydrogen (H 2 ) is introduced into the heat exchanger coil or pipe, the liquid hydrogen (H 2 ) absorbs heat from the rock and / or the counterflowing hydrogen (H 2 ), natural gas (CH 4 ) or mixed gas above the cavern.However, this amount of heat is not sufficient to completely gasify the introduced liquid hydrogen (H2), even if the depth and thus the length of the heat exchanger coil or pipe can be 800 m to 2 km. Liquid hydrogen (H2) still arrives at the cavern head. This liquid hydrogen (H2) is spread out by a baffle plate at the end of the heat exchanger coil or pipe. As a result, the liquid hydrogen (H2) gasifies during free fall in the cavern over a distance of up to 300 m.

[0008] In order to prevent the temperature and pressure drops in the cavern that occur during gasification from becoming too great, a typical truckload of between 10 m³ and 50 m³ of liquid hydrogen (H²) can be introduced into the cavern. The resulting temperature drop, although noticeable, does not lead to such a pressure drop that the stability of the cavern is endangered. The existing gas in the cavern is heated up again by the earth's heat, and the pressure therefore rises. Only when the pressure has risen again to between 70% and 120% of the original pressure is another truckload of liquid hydrogen (H²) between 10 m³ and 50 m³ injected into the cavern. Cavern storage facilities usually comprise several adjacent caverns. To fill the cavern storage facility, which comprises several adjacent caverns, the neighboring caverns can be filled in turn with truckloads.With four or more caverns, the first cavern can be refilled as soon as the last of four caverns has been refueled. This allows a ship to be unloaded with a larger number of tankers, and the tankers travel from the port to the cavern site, which can be up to several hundred kilometers away, for example, from Wilhelmshaven, Bremerhaven, or Brunsbüttel to Halle / Saale in the Salzland district, where cavern storage facilities are located.

[0009] It has proven advantageous if, during refueling with liquid hydrogen (H 2 ), gaseous hydrogen (H 2 ), natural gas (CH 4 ) or a mixed gas flows from outside along the heat exchanger coil or the line. For this purpose, gaseous hydrogen (H 2 ), natural gas (CH 4 ) or a mixed gas can be taken from the cavern. It is even more advantageous if, while the liquid hydrogen (H 2 ) is being introduced, additional gaseous gas, i.e. hydrogen (H 2 ), natural gas (CH 4 ) or a mixed gas, is pumped into the caverns. The hydrogen gas (CH 4 ), natural gas (CH 4 ) or a mixed gas heated by compression thus heats the heat exchanger coil or the line and helps to gasify the liquid hydrogen (H 2 ). Contrary to the expectation that the introduction of liquid hydrogen (H 2 ) would further reduce the cavern pressure, the opposite is observed.The hydrogen gas (H2), natural gas (CH4) or mixed gas flowing against or alongside the liquid hydrogen (H2) in the heat exchanger coil or pipe gives off heat to the liquid hydrogen (H2) and cools itself down in the process. If hydrogen (H2), natural gas (CH4) or mixed gas is taken out of the cavern, this gas must undergo a heating process during expansion in order to adapt its temperature to the local gas network. In this case, the expanded and thereby cooled gas would have to be heated by atmospheric or heated heat exchangers or absorb more atmospheric heat during the expansion process or absorb heat from the combustion of hydrogen (H2), natural gas (CH4) or mixed gas.To prevent the temperature of the hydrogen (H2) extracted during refueling from being reduced too much, the extracted hydrogen (H2) can be mixed with hydrogen (H2), natural gas (CH4), or a mixed gas taken from other, adjacent caverns of the same cavern storage facility. However, if the cavern is simultaneously filled with gaseous hydrogen (H2), natural gas (CH4), or a mixed gas, cooling the hydrogen (H2), natural gas (CH4), or mixed gas heated by compression is actually advantageous.

[0010] The invention is explained in more detail with reference to the following figures.

[0011] It shows: Fig. 1a refueling process of a cavern storage facility

[0012] In Figure 1A cavern 100 is sketched, which is arranged at a depth assumed here of 800 m to 2,000 m. This cavern 100 is connected to the earth's surface via a cased borehole 120, through which gaseous hydrogen gas (CH 4 ), natural gas (CH 4 ) or mixed gas 310 can be withdrawn from the cavern 100. To introduce liquid hydrogen (H 2 ) 300, it is necessary to pump the liquid hydrogen (H 2 ) 300 into the cavern against the cavern pressure using a cryogenic high-pressure pump 105. According to the concept of the invention, it is provided that a heat exchanger coil 110 or a line is introduced into the cased borehole 120, but at least a line that is present in the gas extraction piping. This heat exchanger coil 110 or line leads to the cavern head 130, where the liquid hydrogen (H 2 ) 300 emerging from the outlet 111 falls onto a baffle plate 112 and is thereby widely spread.The fanning out creates the cone of liquid hydrogen (H 2 ) 300 shown here, in which the fanned-out liquid hydrogen (H 2 ) 300 falls freely over a wide diameter within the cavern 100, which can have a height of between 100 m and 300 m, down to a residual level at the bottom. The liquid hydrogen (H 2 ) 300 evaporates into gaseous hydrogen (H 2 ) and absorbs the heat from the hydrogen gas (CH 4 ), natural gas (CH 4 ) or mixed gas in the cavern 100. The cavern 100 is then reheated using geothermal energy available at depths of 800 m to 2,000 m. In order to accelerate the gasification of the liquid hydrogen (H 2 ) 300, it can be provided that during the refueling of a cavern 100 with a nominal volume of 100 million standard cubic metres to 300 million standard cubic metres, gaseous hydrogen gas (CH 4 ), natural gas (CH 4 ) or mixed gas is withdrawn from the cavern 100.This creates a countercurrent heat exchanger effect between the gaseous hydrogen (H 2 ), natural gas (CH 4 ), or mixed gas 310 flowing out of the cavern 100 and the countercurrent liquid hydrogen (H 2 ) 300. The cooled gaseous hydrogen (H 2 ), natural gas (CH 4 ), or mixed gas 310 can then be reheated via an atmospheric or heated heat exchanger 400. Alternatively, it is possible to fill the cavern with gaseous hydrogen (H 2 ), natural gas (CH 4 ), or mixed gas in parallel with the filling with liquid hydrogen (H 2 ). The heat generated by the compression helps to gasify the introduced liquid hydrogen (H 2 ).

[0013] In order to prevent the temperature in the cavern 100 from falling below a critical point which would lead to an excessive pressure drop, it can be provided in an embodiment of the method according to the invention that various adjacent caverns 100 are refueled in turn with liquid hydrogen (H 2 ) 300 according to the method according to the invention.

[0014] Detail A shows the outlet of the heat exchanger coil 110 or the line, which has a baffle plate 112 at its outlet 111, which widely spreads the outflowing liquid hydrogen (H 2 ) 300. LIST OF REFERENCE SYMBOLS

[0015] 100 Cavern storage 300 liquid hydrogen 105 Cryogenic high-pressure pump 310 Hydrogen (H 2 ), natural gas (CH 4 ) or mixed gas 110 Heat exchanger coil 111 Exit 400 Heat exchanger device 112 baffle plate A detail 120 borehole 130 Cavern head

Claims

1. Method for filling a cavern (100) of a cavern storage facility (101) with liquid hydrogen, characterized by - introducing a heat exchanger coil (110) or a tube (coil tubing) into a cased bore hole (120), which leads from the ground surface (200) to the cavern head (130) all the way up to the cavern head (130), - sealing an outlet (111) of the heat exchanger coil (110) or the line with a baffle plate (112), - introducing 10 m3 to 50m3 of liquid hydrogen (H2) (300) into the heat exchanger coil (110) or into the tube, - waiting until the pressure in the cavern of the cavern storage facility (100) has risen again to 70% to 120% of the original pressure, - re-introducing 10 m3 to 50 m3 of liquid hydrogen (H2) (300) into the heat exchanger coil (110) or into the tube, - wherein the waiting and re-introducing are repeated until a pre-selected filling quantity of the cavern storage facility (100) has been reached.

2. The method according to Claim 1, characterized by a standard volume of the cavern storage facility being filled (100) between 100 million m3 and 300 million m3.

3. Method according to Claim 1 or 2, characterized by introducing 10m3 to 50 m3 of liquid hydrogen (H2) for each individual refuelling operation.

4. The method according to any one of the Claims 1 to 3, characterized in that the cavern storage facility (100) consists of a plurality of adjacent individual caverns that are filled in turn.

5. Method according to one of the Claims 1 to 4, characterized by simultaneous extraction of gaseous hydrogen (H2), natural gas (CH4) or mixed gas (310) during filling.

6. The method according to Claim 5, characterized by decompressing the extracted natural gas (310) and heating the natural gas (310) by at least one atmospheric or heated heat exchanger device (400).

7. The method according to Claim 5, characterized by mixing hydrogen (H2), natural gas (CH4) or mixed gas (310) from the currently filled cavern (100) with hydrogen (H2), natural gas (CH4) or mixed gas from an adjacent cavern before decompressing the hydrogen (H2), natural gas (CH4) or mixed gas (310) from the currently filled cavern (100).

8. The method according to any one of the Claims 1 to 4, characterized by simultaneously introducing gaseous hydrogen (H2), natural gas (CH4) or mixed gas (310) during filling.