DE10021681C2 - Energy storage system, in particular system for storing hydrogen - Google Patents

Description

The invention relates to an energy storage system with a first storage, the with a feed line for a liquid energy carrier, in particular for liquid Hydrogen, as well as with an extraction line for transporting the Providing energy to a consumer and with a second storage for storing energy vapor evaporated in the first store is connected to the flow.

Such energy storage systems are known and are found, for example, in the Use of fuel cell technology. Fuel cell drives are increasingly as a serious alternative to conventional drives for Seen vehicles. The fuel cell needs one as a reactant chemical energy sources, usually hydrogen, and oxygen. During oxygen, similar to the combustion engine, mostly from the Air taken from the environment is used for the hydrogen Storage systems needed. The hydrogen either becomes immediate or as part of another substance, such as methanol or natural gas, saved.

The storage of hydrogen in the form of methanol requires a relatively complex and expensive system for harnessing hydrogen energy. On the other hand, systems that store the hydrogen directly, ie in the form of liquid or gaseous hydrogen, are simpler in construction and use. The storage of hydrogen in liquid form appears particularly expedient, since a high energy density is achieved with liquid hydrogen. Vehicles that are equipped with a liquid hydrogen storage have ranges per storage filling that are comparable to those of conventional diesel or gasoline vehicles. The use of this storage technology in motor vehicles is described, for example, in the company magazine "gas aktuell" 36, p. 17 ( 1991 ).

The disadvantage of conventional liquid hydrogen storage, however, is that that even with the best thermal insulation of the hydrogen tank, for example with the help of super insulation, a small residual heat flow remains inside the tank, which leads to a slow rise in pressure in the tank. As long as regularly Hydrogen is taken from a consumer, this is irrelevant because in this case by removing the pressure inside the tank again is lowered. However, if none over a long period of time Removal takes place, the pressure can reach the opening pressure of the overflow valve rise, resulting in a continuous blow-off flow the tank comes. The residual heat flow is the evaporation of the compensated for liquid hydrogen in the tank. In practice, the blow-off lies amount of a liquid hydrogen tank for vehicles currently around 1 to 5% the maximum tank filling per day.

EP 0 473 555 A2 proposes that it be in a first memory derive evaporating gas in a second storage, which by means of a Pressure relief valve is fluidly connected to the first memory. exceeds the gas pressure in the second container that of the first container, so can over corresponding distribution valve can be achieved that to supply a Consumer gas is removed from the second store.

A disadvantage of this known system is that the capacity of the second Storage is quickly exhausted. At the latest after the pressure equalization of both Containers are obtained without gas withdrawal by a consumer Need to vent excess gas into the environment.

The object of the present invention is to provide an energy storage system develop in which the loss of evaporation of the energy source used is minimized even with longer idle times.

This task is solved with an energy storage system at the beginning mentioned type in that the second memory comprises a pressure tank, which is preceded by a fluid-pressure increasing device.  

In the energy storage system according to the invention, the due to the Residual heat input evaporating in the first store and not from Consumers' share of the stored energy source in the second Memory collected and is therefore available for later use Available. So it does not escape into the environment like this conventional systems is the case where the energy source is only stored in liquid form. The second memory includes thereby a pressure tank, the fluidically a device for Pressure increase is connected upstream. This will increase the storage capacity of the second memory particularly high. With this technology the Share of energy loss when storing is drastically reduced. Across from a pure gas storage has the form of the invention Energy storage has the advantage that when stored in liquid form a higher energy storage density can be achieved, resulting in a lower Space is required. Furthermore, when filling the first store uses a lower filling pressure with liquid energy and the Filling can be done much faster, so far with conventional fuels comparable, done. The invention is particularly expedient Technology when using hydrogen as an energy source, but it is not limited to this.

Suitable pressure tanks are, for example, conventional compressed gas cylinders for Pressures between 0 and 300 bar, but are particularly advantageous High-pressure composite container for pressures up to 1000 bar and more.

The device for increasing the pressure is preferably one Compressor.

In an advantageous development, the device for increasing the pressure is included a pressure control system, by means of which the compression of the Energy carrier in the pressure tank depending on the pressure of the energy carrier in the first memory can be regulated.  

For example, the pressure regulator can be set such that shortly before Reaching a limit pressure, which is a pressure relief valve in the first store opens, the device for increasing the pressure is put into operation and more gaseous Energy is pressed from the first storage into the pressure tank.

A particularly simple pressure control can then be implemented in particular be when the removal of the gaseous energy source always from the Pressure tank and not directly from the first store. there the pressure control includes a bypass line, which is the pressure side connects the device for increasing the pressure to the first store. A part the gas is thus at the outlet of the device for increasing the pressure in the Liquid phase of the energy source returned in the first memory.

To extract the gaseous energy source from the second store To enable, this is preferably provided with a derivative. To one  To produce any necessary pressure compensation, this derivation is preferred wise equipped with a pressure reducer.

The extraction line is expediently each separate from the first and the second memory can be fluidly connected. With this configuration is an alternate withdrawal of energy from the first or the second memory possible.

A further development of the latter embodiment of the invention provides to provide the sampling line with a pressure-controlled fitting, which the removal of energy from the two stores depending on is able to control the pressure prevailing in the respective store.

A heat exchanger is preferably integrated in the extraction line by means of whose the gaseous energy source from the first storage before reaching of the consumer is warmed up. This is how hydrogen is used Energy carriers in the first tank at a temperature in the range of Boiling point of the hydrogen is. The use of such a cryogenic Gases can cause problems for consumers, such as icing u. the like. These problems are solved by installing a Heat exchange in the extraction line is at least mitigated, if not eliminated.

A further development of the invention provides that the first memory has a cryogenic pressure tank, especially a high pressure tank comprises, which flows with the pressure tank of the second reservoir connection stands. Such a low-temperature pressure tank can with liquid hydrogen can be filled at low pressure. Will the tank shut off immediately after filling, the pressure in the tank rises very much quickly because the tank jacket, unlike the low-temperature tank, does not has a special insulation effect. A pressure equalization can be done via a Heat exchanger with the pressure tank of the second store, the must be designed for at least the same maximum pressure.  

Alternatively or in addition to the aforementioned low-temperature suitability Pressure tank the first store includes a low temperature tank that is preferably provided with super insulation. Due to the thermal Isolation of such tanks can be the evaporation losses of the Minimize the amount of liquid hydrogen used.

Especially when using hydrogen as an energy source chemical storage of the hydrogen in the second storage makes sense Alternative or addition to the aforementioned pressure tank. So at Metal hydride technology that chemically hydrogenates certain metals bound. This creates metal hydrides, which depend on the pressure in one small volumes can absorb relatively large amounts of hydrogen. Typical working pressures for metal hydride storage are between 0 and 35 bar.

A particularly advantageous embodiment of the invention provides the use of Energy storage system for fuel cell drives, especially for the Use in vehicles.

Exemplary embodiments of the invention are to be described below with reference to the drawing are explained in more detail.

Schematic views show:

Fig. 1 is a usable for storing hydrogen according to the invention energy storage system in a first embodiment;

Fig. 2 is a usable for storing hydrogen according to the invention energy storage system in a second embodiment, and

Fig. 3 shows a typical temporal pressure curve of the hydrogen in the first storage when operating a hydrogen storage system according to the invention.

The hydrogen storage system 1 shown in Fig. 1 comprises a first memory in the form of a cryogenic tank 2 and a second memory in the form of a high-pressure tank 3.

A high-pressure tank 3 can be, for example, a hybrid accumulator which is suitable for pressures between 0 and 35 bar, a pressurized gas bottle for pressures from 0 to 300 bar or a high-pressure composite container for pressures from 0 to 1000 bar.

The low-temperature tank 2 , which is intended for the absorption of liquid hydrogen at a temperature of approximately 20 K, is provided with thermal insulation 5 . In order to produce the thermal insulation 5 , the low-temperature tank 2 comprises an inner container 6 which is intended to hold the hydrogen and which is surrounded by an outer container 7 at a distance of, for example, 40 mm. The space between the inner container 6 and the outer container 7 is evacuated and can be provided with appropriate radiation shields to protect against radiation losses. A typical structure for such thermal insulation is described, for example, in the company magazine "gas aktuell" No. 36, p. 17 ( 1991 ). Of course, any insulation known from low-temperature technology and suitable for the present purpose can be used.

The inner container 6 can be at least partially filled with liquid hydrogen by means of a filling line 9 . Despite the good insulation, there is a residual heat input in such low-temperature tanks, which leads to the evaporation of part of the filled hydrogen, usually of about 1 to 5% per day. The inner container therefore has a safety valve 10 which opens when a certain minimum pressure, for example 5 bar, is reached and allows gaseous hydrogen to escape into the environment.

The gas phase 11 formed in the inner container 6 by evaporation of the filled hydrogen is in flow connection with a consumer 13 via a removal line 12 . A heat exchanger 14 for heating the cryogenic gas and a shut-off valve 15 are integrated in the extraction line 12 .

A compressor 17 is arranged between the low-temperature tank 2 and the high-pressure tank 3 , the low-pressure side 18 of which is flow-connected to the gas phase 11 of the hydrogen via a branch 19 on the extraction line 12 and the high-pressure side 21 of which is connected to the high-pressure tank 3 . The compressor 17 is designed such that when a certain pressure is reached in the inner container 6 of the low-temperature tank 2 , the value of which lies below the opening pressure of the safety valve 10 , hydrogen is removed from the gas phase 11 and is supplied to the high-pressure container 3 in the compressed state. The pressure control takes place, for example, by measuring the pressure in the inner container 6 , and a corresponding control which starts the compressor when the corresponding pressure value is reached by means of a suitable control.

The high-pressure tank 3 is also fluidly connected to the consumer via an extraction line 23 . In order to adapt the pressure of the hydrogen removed to the requirements of the consumer 13 , a pressure reducer 24 is integrated in the extraction line 23 .

In the hydrogen storage system 1 , gaseous hydrogen can either be taken from the gas phase 11 in the inner container 6 of the low-temperature tank 2 or from the high-pressure tank 3 . This is particularly expedient if, for example immediately after refueling the low-temperature tank 2 , there is only a little gaseous hydrogen in the inner container 6 of the low-temperature tank 2 . In this case, the gaseous hydrogen can be removed from the high pressure container. When a certain pressure value is reached, the low-temperature tank 2 can be switched on , for example by means of a suitable pressure-controlled automatic system 25 in the shut-off valve 15 . In this case, if necessary, the extraction line 23 of the high-pressure tank 3 can be blocked at the same time via a further pressure-controlled automatic system (not shown here ) . In order to permanently ensure a minimum supply pressure in the low-temperature tank 2 , a heater - also not shown here - can be provided in the inner container 6 in a known manner.

If the gaseous hydrogen is taken exclusively from the high-pressure tank 3 , and the low-temperature tank 2 thus serves only as an energy store and not at the same time as a supply tank, there is no need for complex pressure control of the compressor 17 . In this case, pressure control can take place by means of an appropriately dimensioned bypass line 26 , through which a small partial flow of the already significantly heated hydrogen gas is passed into the liquid phase of the hydrogen in the inner container 6 of the low-temperature tank 2 and causes a pressure increase in the inner container 6 .

An alternative embodiment of an energy storage system is presented in FIG. 2. The hydrogen storage system 30 shown there also comprises a high-pressure tank 33 , which is fluidly connected to a tank 32 for holding hydrogen in liquid form via a connecting line 31 . In contrast to the low-temperature tank 2 of the hydrogen storage system 1 , the tank 32 is not a super-insulated low-temperature tank, but a high-pressure tank suitable for holding cryogenic liquids, which is not equipped with a thermal insulation comparable to the thermal insulation 5 . If the tank 32 is filled with liquid hydrogen (at low pressure, about 1-4 bar) via the filling line 34 and shut off with a shut-off element (not shown here), part of the hydrogen evaporates immediately and the pressure in the tank 32 rises very sharply on. The pressure equalization with the high-pressure tank 33 takes place after opening a shut-off valve 35 via the connecting line 31 into which a heat exchanger 36 , for. B. an air-heated coil is integrated. It goes without saying that in this exemplary embodiment the tank 32 and the high-pressure tank 33 should be designed for the same maximum pressure. A compressor between tank 32 and high-pressure tank 33 can be dispensed with in this exemplary embodiment. The removal for a consumer 37 takes place exclusively via an extraction line 38 of the high-pressure tank 33 , which is equipped with a suitable pressure reducer 39 for connecting the consumer 37 .

Fig. 3 shows an example, but the typical pressure variation in the inner container 6 of the cryogenic tank 2 during operation.

When hydrogen is removed by a consumer 13 directly from the low-temperature tank 2 , the pressure in the inner container 6 drops to the supply pressure p _{1, which is} constantly maintained, for example by means of a heater (operating state B1). At time t ₁ , the removal of hydrogen is stopped. If hydrogen is not withdrawn, the pressure in the inner container 6 rises slowly as long as the compressor 17 is not yet switched on (operating state B2). At time t ₂ , the response pressure p _{2 of} the compressor 17 is reached and the compressor 17 is started. Gaseous hydrogen is now removed from the inner container 6 of the low-temperature tank 2 and fed to the high-pressure container 3 in compressed form (operating state B3). As a result, the pressure in the inner container 6 drops again. When the supply pressure p _{1 is reached} , at time t ₃ , the compressor 17 switches off. As a result, the pressure in the inner container rises again until it reaches the response pressure p ₂ at time t ₄ . The compressor switches on again, the pressure in the inner container drops and reaches the supply pressure p ₁ again at time t ₅ , and then gradually increases again after the compressor 17 has been switched off. When the consumer removes hydrogen again (from time t ₆ ), the pressure drops again into the range of the supply pressure p ₁ . The pressure thus always remains below the response pressure p _{3 of} the safety valve 10 . This reliably prevents hydrogen from escaping into the environment.

For vehicles in vehicle fleets that are operated regularly without long parking times, the capacity of the high-pressure tank 3 can be selected to be smaller than that of the low-temperature tank 2 , since usually only a few evaporation losses occur in the case of their use profile. In these vehicles, the high-pressure tank 3 primarily has the function of a “cold start storage”, since gaseous hydrogen is always present in this tank, at least in a small amount, but sufficient for a cold start. This hydrogen can be withdrawn immediately without having to evaporate part of the liquid hydrogen in a time-consuming manner before starting the vehicle, as is required in conventional vehicles with only one liquid hydrogen tank.

In vehicles that are used as private vehicles, for example, and which are sometimes parked over a longer period of time, the high-pressure tank 3 should have a capacity comparable to the low-temperature tank 2 , in order to be able to use the tank at z. B. a four-week period of time after the last refueling can be saved.

LIST OF REFERENCE NUMBERS

1

Hydrogen storage system

2

Cryogenic tank

3

High pressure tank

4

-

5

thermal insulation

6

inner container

7

outer container

8th

-

9

Fill line

10

safety valve

11

gas phase

12

withdrawal line

13

consumer

14

heat exchangers

15

shut-off valve

16

-

17

compressor

18

Low pressure side

19

diversion

20

-

21

High pressure side

22

-

23

withdrawal line

24

-

25

pressure controlled automatic

26

Bypass line

27

-

28

-

29

-

30

Hydrogen storage system

31

connecting line

32

tank

33

High pressure tank

34

A filler pipe

35

shut-off valve

36

heat exchangers

37

consumer

38

withdrawal line

39

pressure reducer
p ₁

supply pressure
p ₂

Response pressure compressor
p ₃

Response pressure safety valve
t ₁

-t ₆

timings
B1 operating status
B2 operating status
B3 operating status

Claims (13)

1. Energy storage system with a first memory ( 2 , 32 ) with a feed line ( 9 , 34 ) for a liquid energy carrier, in particular for liquid hydrogen, and with a removal line ( 12 , 23 , 38 ) for transporting the energy carrier to a consumer ( 13 , 37 ) and which is flow-connected to a second store ( 3 , 33 ) for storing energy vapor evaporated in the first store ( 2 , 32 ), characterized in that the second store comprises a pressure tank ( 3 , 33 ), which a device for increasing the pressure ( 17 ) is connected upstream in terms of flow technology. 2. Energy storage system according to claim 1, characterized in that a compressor ( 17 ) is provided as a device for increasing the pressure. 3. Energy storage system according to one of claims 1 or 2, characterized in that a high-pressure composite container is provided as the pressure tank ( 3 , 33 ). 4. Energy storage system according to one of the preceding claims, characterized in that the device for increasing the pressure is operatively connected to a pressure control which regulates the compression of the energy carrier in the pressure tank ( 3 , 33 ) depending on the pressure of the energy carrier in the first memory ( 2 ). 5. Energy storage system according to claim 4, characterized in that the pressure control comprises a bypass line ( 26 ) which connects the pressure side of the device for increasing the pressure with the first memory ( 2 ). 6. Energy storage system according to one of the preceding claims, characterized in that the second store ( 3 , 33 ) is flow-connected with a discharge line ( 23 , 38 ) for gaseous energy carriers, soft discharge line ( 23 , 38 ) preferably with a pressure reducer ( 24 , 39 ) is equipped. 7. Energy storage system according to one of the preceding claims, characterized in that the extraction line ( 12 ) is in each case separately flow-connectable to the first store ( 2 ) and to the second store ( 3 ). 8. Energy storage system according to claim 7, characterized in that the removal line ( 12 ) is provided with a pressure-controlled fitting ( 15 ), by means of which the removal of the energy source from the stores ( 2 , 3 ) corresponding to that in the stores ( 2 , 3 ) prevailing pressures can be controlled. 9. Energy storage system according to one of the preceding claims, characterized in that a heat exchanger ( 14 , 36 ) is integrated in the extraction line ( 12 ). 10. Energy storage system according to one of the preceding claims, characterized in that the first storage comprises a low-temperature suitable pressure tank ( 32 ). 11. Energy storage system according to one of the preceding claims, characterized in that the first storage comprises a - preferably super-insulated - low-temperature tank ( 2 ). 12. Energy storage system according to one of the preceding claims, that the second memory ( 3 , 33 ) has means for temporarily chemical bonding of hydrogen, such as a metal hydride tank. 13. Energy storage system according to one of the preceding claims, characterized by the use as an energy storage system, preferably a hydrogen storage system ( 1 , 30 ) for a fuel cell drive.