Method and apparatus for integrating heat into a district heating network

Abstract

The present invention relates to an energy system (1) and a method for operating the energy system (1), which comprises a hydrogen production unit (2) with at least one electrolyzer (3) for water electrolysis thermally coupled to a cooling water circuit (4), and a heat pump (5) whose heat source side (6) is thermally coupled to the cooling water circuit (4) and whose heat sink side (7) is connected to a district or commercial heating circuit (10) via a heat exchanger (8). According to the invention, a heat storage device (9) is provided in the district or commercial heating circuit (10), whose return line (11) is connected after the heat exchanger (8) and whose feed line (12) is connected before the heat exchanger (8) of the heat pump (5), so that the return temperature of the district or commercial heating circuit (10) is increased by heat from the heat storage device (9).

Description

Technical Field

[0001] The present invention relates to an apparatus described in the generic concept of claim 1 and a method described in the generic concept of claim 5.

[0002] The present invention relates to the production of hydrogen, and the poor efficiency of hydrogen electrolysis, and the heat generated thereby.

Background Art

[0003] A carbon-neutral and timely supply to heating networks such as district heating and industrial processes is increasingly expected to be based on heat pumps. To achieve a high efficiency COP (Coefficient of Performance), a heat pump requires a waste heat source with a constant heat flow as an input heat flow.

[0004] As the input heat flow, the waste heat generated during hydrogen production can be utilized. Typically, hydrogen production is carried out by electrolysis, for example, proton exchange electrolysis or membrane electrolysis. In this case, electrolysis is carried out at a temperature in the range of 30°C to 80°C, and about 50% to 80% of the electrical energy used is converted into hydrogen. The heat released from water during the electrical separation of hydrogen and oxygen must be removed and cooled. Similarly, waste heat is generated during the subsequent compression of hydrogen to the required operating pressure. Therefore, the production of hydrogen as a whole has an efficiency of less than 50 percent. Most of the energy used is thus converted into heat.

[0005] Patent Document 1 already describes an energy system having an electrolytic cell for water electrolysis and a heat pump capable of increasing the waste heat from the electrolytic cell and providing it to a heating network.

[0006] However, using a heat pump to utilize waste heat from hydrogen production presents several problems. Firstly, electrolytic equipment deteriorates over time, leading to decreased efficiency and increased waste heat generation. For an electrolytic cell with 17 MW of power, waste heat could increase from 5 MW to 8.5 MW over time. Therefore, a relatively small heat pump is sufficient for a new electrolytic cell, while a larger one is needed for an aging one. Furthermore, the economic operation of hydrogen production is dependent on energy prices. This requires flexible operation of the electrolytic cell along with a continuous supply of hydrogen, oxygen, and heat, which necessitates complex control and operating modes for various components (electrolytic cell, heat pump, heat reservoir, and compressors for oxygen and hydrogen). Additionally, the combination of the electrolytic cell and heat pump presents the problem of two components with different operating modes and ramp-up curves. The electrolytic cell, as a chemical-electrical process, responds rapidly to control means, while the heat pump, along with the compressor, responds rather slowly due to the inertia of the rotating mass. If individual components are not used according to their start-up and shutdown curves, it can lead to a complete system failure or prevent dynamic operation from being achieved. Dynamic operation must take into account fluctuations in the energy price required to operate the system, as well as fluctuations in the removal of hydrogen, oxygen, and heat. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] German Patent Application Publication No. 102019202439A1 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The object of the present invention is to improve the utilization of heat from water electrolysis as a heat source for a heat pump and to solve the aforementioned problem. [Means for solving the problem]

[0009] This problem is solved by an apparatus having the features of independent claim 1 and a method having the features of independent claim 5. Advantageous configurations and variations of the present invention are described in the dependent claims.

[0010] The present invention relates to an energy system comprising a hydrogen generation unit having at least one electrolytic cell for water electrolysis thermally coupled to a cooling water circulation circuit, and a heat pump whose heat source side is thermally coupled to the cooling water circulation circuit and whose heat sink side is coupled to a local or commercial heating circulation circuit via a heat exchanger. According to the present invention, a heat storage unit is connected to a local or commercial heating circulation circuit, the return line of the heat storage unit is connected after the heat exchanger of the heat pump, and the feed line of the heat storage unit is connected before the heat exchanger of the heat pump, so that the heat from the heat storage unit can raise the return line temperature of the local or commercial heating circulation circuit.

[0011] The present invention relates to the operation of an energy system that generates hydrogen by water electrolysis using an electrolysis apparatus, transfers the heat generated during hydrogen generation to the heat source side of a heat pump, raises the temperature level by the heat pump, and discharges it to a district heating circuit or commercial heating circulation circuit. According to the present invention, a heat storage unit is incorporated into the district or commercial heating circulation circuit, the return line of the heat storage unit is connected after the heat exchanger, and the feed line of the heat storage unit is connected before the heat exchanger of the heat pump, so that the heat from the heat storage unit is used to raise the return line temperature of the district or commercial heating circulation circuit.

[0012] This invention begins with the consideration that hydrogen electrolysis is advantageous for supplying this thermal energy to district heating networks or for use in industrial processes, either due to its low energy efficiency or, on the one hand, the large amount of thermal energy it generates, or on the other hand, due to its high temperature of approximately 40°C. For a heating network with a feedline temperature of 110°C, the Carnot coefficient of a heat pump for electrolysis waste heat at 40°C is typically 5.5 for electrolysis waste heat and 3.8 for waste heat from river water at 10°C. The waste heat from the hydrogen production unit can be raised by a heat pump to the temperature level of a district or commercial heating circulation circuit and thus can be effectively utilized.

[0013] Furthermore, the present invention recognizes that in order for the heat pump to operate under full load and therefore with optimal efficiency, it is necessary to adapt the fluctuations in the generated thermal energy to the continuous demand of the heat pump. Surprisingly, this adaptation is achieved by a heat reservoir in which the return line is connected after the heat exchanger and the feed line is connected before the heat exchanger of the heat pump.

[0014] The arrangement of the heat storage device according to the present invention makes it possible to compensate for both slowly changing heat quantities, such as those caused by the aging of the electrolytic cell, and rapidly changing heat quantities, such as those caused by the different operating behaviors and ramp-up curves of the electrolytic cell and the heat pump. With the heat exchanger according to the present invention, the hydrogen production unit is directly cooled on the one hand, and heat production is separated from heat utilization. Therefore, the heat pump can be made oversized to accommodate the waste heat stored by the hydrogen production unit, and as a result the heat pump has sufficient reserves in case waste heat increases due to aging. This compensation may also be achieved through a control procedure that reduces the proportional heat flow output from the heat storage device to the regional or commercial heating circulation circuit accordingly when waste heat increases on the heat source side of the heat pump, so that the heat pump can continue to operate under full load.

[0015] This invention allows for increased energy efficiency of over 75% to 90% in the utilization of waste heat from the electrolytic cell and other components. Compared to configurations without a heat pump, it is possible to save on additional coolers or other equipment for cooling the electrolytic cell.

[0016] In addition to the electrolytic cell, further components of the hydrogen production unit can be incorporated into the cooling water circulation circuit, allowing for the discharge and utilization of waste heat, such as the unit's hydrogen compressor, oxygen compressor, or other heat sources.

[0017] To further enhance flexibility in setting the heat pump capacity, an advantageous development of the present invention further includes a cryogenic storage unit incorporated into the cooling water circuit. This cryogenic storage unit may be provided in addition to any existing pre-coolers to help directly cool the hydrogen production unit. The cryogenic storage unit directly cools the hydrogen production unit while separating the heat generation from the heat pump. Thus, the heat pump can reduce the amount of waste heat accumulated by the hydrogen production unit or compensate for the increase in waste heat over time.

[0018] Here, the cryogenic storage unit may be part of a control system in which both the heat storage unit and the cryogenic storage unit are control variables. Therefore, through the corresponding control procedure, if there is a reduced amount of waste heat on the heat source side of the heat pump, the proportional heat flow output from the cryogenic storage unit to the heat source side of the heat pump can be increased, allowing the heat pump to continue operating at full load.

[0019] Depending on the size of the cryogenic storage, waste heat can also be generated simply by filling the cryogenic storage. This can be advantageous, for example, during the startup of an energy system or in case of a heat pump failure. For this purpose, in an advantageous further development of the invention, the feed line of the cryogenic storage is connected to the heat source side of the heat pump, and the cryogenic storage is made to be able to be discharged via the heat pump. This operating mode is advantageous when the hydrogen production unit fails, for example, when waste heat no longer accumulates. This further development forms a closed circuit between the cooling water storage and the heat pump, and can increase the flexibility during the operation of the system.

[0020] The present invention is suitable for high-temperature heat pumps. The high-temperature heat pump is characterized by achieving a feed line temperature from 100 degrees Celsius to 150 degrees Celsius.

Brief Description of the Drawings

[0021] The present invention and advantageous developments will be described in more detail below with reference to the drawings.

[0022] [Figure 1] An energy system according to the present invention having a heat storage is shown. [Figure 2] A development form of an energy system according to the present invention having a cryogenic storage is shown. [Figure 3] A specific development form of an energy system for discharging a cryogenic storage is shown.

Modes for Carrying Out the Invention

[0023] FIG. 1 shows an energy system 1 according to the present invention having a heat storage 9 with a feed line 12 and a return line 11.

[0024] Furthermore, a hydrogen production unit 2 having at least one electrolyzer 3 for water electrolysis, a cooling water circulation circuit 4, a heat pump 5 having a heat source side 6 and a heat sink side 7, a heat exchanger 8, and a regional or commercial heating circulation circuit 10 which is part of a district heating network are shown.

[0025] Hydrogen is produced in the electrolytic cell 2 by water electrolysis. In the case of an electrolytic cell with an output of 70 MW, this may correspond to 15 MW of waste heat. This heat is transferred to the heat source side 7 of the heat pump 5 via the cooling water circulation circuit 4. Thus, the heat pump 5 directly cools the hydrogen production unit 2. The temperature level of the heat is raised via the heat pump 5 and discharged to the regional or commercial heating circulation circuit 10 via the heat exchanger 8. A feature of the present invention is that a heat reservoir 9 is incorporated into the regional or commercial heating circulation circuit 10, with its return line 11 connected after the heat exchanger 8 of the heat pump 5 and its feed line 12 connected before the heat exchanger 8 of the heat pump 5. As a result, the heat from the heat reservoir 9 can raise the return line temperature of the regional or commercial heating circulation circuit 10.

[0026] In this configuration, when the electrolytic cell 3 is started, the heat pump capacity is greater than the waste heat generated. Therefore, the heat pump 5 is over-engineered. Nevertheless, the heat pump can operate at full load and thus with an optimal coefficient of performance because the temperature difference is compensated for by the heat reservoir 9. The necessary time-dependent adaptation to the aging degradation of the electrolytic cell 3 is adequately compensated for by the control means. During control, the amount of waste heat increases on the heat source side 6 of the heat pump 5, so the heat flow output from the heat reservoir 9 to the regional or commercial heating circulation circuit is reduced accordingly.

[0027] figure Figure 2 shows a further development of the present invention having an additional cold storage unit 14 incorporated into the cooling water circulation circuit. In Figure 2, in addition to the electrolytic cell 3, the hydrogen generation unit 2 includes further components, such as a hydrogen compressor unit 15, an oxygen compressor unit 16, and other waste heat sources. 17 It has been further shown that the following may be provided: The cold storage unit 14 is incorporated into the cooling water circulation circuit 4. The cold storage unit 14 can further increase the flexibility in configuring the heat pump capacity. The cold storage unit 14 can, on the one hand, directly cool the hydrogen generation unit 2, and heat generation can be separated from the heat pump 5.

[0028] In this configuration, the heat pump capacity at startup of the electrolytic cell 3 is less than or equal to the waste heat generated. Therefore, the heat pump 5 is already below the set level at startup of the electrolytic cell 3 or after aging. Thus, the heat pump 5 can be relatively small. Nevertheless, since the temperature difference is compensated by the cold storage unit 14, the heat pump can operate under full load and therefore at optimal efficiency. Accordingly, the necessary adaptation to the changes in the electrolytic cell 3 over time is controlled.

[0029] Figure 3 shows a further developmental form having a specific interconnection of the energy system 1 for the discharge of the cold storage unit 14. The feed line 12 of the cold storage unit 14 is connected to the heat source side 6 of the heat pump 5 via a branch line 18. As a result, the cold storage unit can be discharged via the heat pump. This further development allows for the formation of a closed circuit between the cold storage unit 14 and the heat pump 5. This may be advantageous, for example, during the startup of the energy system 1 or in the event of a failure of the hydrogen production unit 2.

Claims

1. A hydrogen generation unit (2) having at least one electrolytic cell (3) for water electrolysis thermally coupled to a cooling water circulation circuit (4), A heat pump (5) whose heat source side (6) is thermally coupled to the cooling water circulation circuit (4), and whose heat sink side (7) is coupled to a regional or commercial heating circulation circuit (10) via a heat exchanger (8), An energy system (1) comprising, The heat storage unit (9) is connected to the local or commercial heating circulation circuit (10), The return line (11) of the heat storage unit (9) is connected after the heat exchanger (8) of the heat pump (5), and the feed line (12) of the heat storage unit (9) is connected before the heat exchanger (8) of the heat pump (5). The heat from the heat storage device (9) causes the return line temperature of the regional or commercial heating circulation circuit (10) to rise. Energy systems (1).

2. The energy system (1) according to claim 1, wherein a cold storage unit (14) is further incorporated into the cooling water circulation circuit (4).

3. The feed line (12) of the cold storage unit (14) is connected to the heat source side (6) of the heat pump (5). The hydrogen generation unit (2) is directly cooled by the cold storage unit (14), and heat generation is separated from the heat pump (5). The energy system (1) according to claim 2.

4. The energy system (1) according to any one of claims 1 to 3, wherein the heat pump (5) is a high-temperature heat pump.

5. Hydrogen is produced by water electrolysis using the electrolytic device (2). The heat generated during hydrogen production is transferred to the heat source side (6) of the heat pump (5) via the cooling water circulation circuit (4). The temperature level rises due to the heat pump (5), The heat is released through the heat exchanger (8) into the local or commercial heating circulation circuit (10). A method for operating an energy system (1), A heat storage device (9) is incorporated into the aforementioned regional or commercial heating circulation circuit (10). The return line (11) of the heat storage unit (9) is connected after the heat exchanger (8) of the heat pump (5), and the feed line of the heat storage unit (9) is connected before the heat exchanger (8) of the heat pump (5). The heat from the heat storage device (9) causes the return line temperature of the regional or commercial heating circulation circuit (10) to rise. Operating method for energy system (1).

6. A method for operating the energy system (1) according to claim 5, wherein a cold storage unit (14) is further incorporated into the cooling water circulation circuit.

7. The feed line (12) of the cold storage unit (14) is connected to the heat source side (6) of the heat pump (5). The electrolytic device (2) is directly cooled by the cold storage unit (14), and heat generation is separated from the heat pump (5). A method for operating the energy system (1) according to claim 6.

8. A method for operating the energy system (1) according to any one of claims 5 to 7, wherein the heat pump (5) is a high-temperature heat pump.

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