Method and device 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 invention relates to a device according to the preamble of claim 1 and to a method according to the preamble of claim 5.

[0002] The present invention relates to the production of hydrogen and the poor efficiency of hydrogen electrolysis and the heat produced thereby. [Background technology]

[0003] Carbon-neutral and timely supply of 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 growth), heat pumps require a waste heat source with a constant heat flow as input heat flow.

[0004] The input heat stream can be waste heat generated during hydrogen production. Typically, hydrogen is produced by electrolysis, for example by proton exchange electrolysis or membrane electrolysis. In this case, electrolysis is carried out at temperatures ranging from 30°C to 80°C, and approximately 50% to 80% of the electrical energy used is converted into hydrogen. The heat released from the water during the electrical separation of hydrogen and oxygen must be extracted and cooled. The subsequent compression of the hydrogen to the required operating pressure also generates waste heat. Therefore, hydrogen production is generally less than 50% efficient. The majority of the energy used is therefore converted into heat.

[0005] Patent document 1 already describes an energy system with an electrolyzer for water electrolysis and a heat pump that can increase the waste heat from the electrolyzer and provide it to a heating network.

[0006] However, using a heat pump to utilize waste heat from hydrogen production presents several challenges. For one, electrolyzers age, decreasing their efficiency over time and increasing the amount of waste heat generated. For an electrolyzer with a power of 17 MW, the waste heat could increase over time from 5 MW to 8.5 MW. Therefore, a relatively small heat pump is sufficient for a new electrolyzer, whereas a relatively large one is required for an older electrolyzer. Furthermore, the economic operation of hydrogen production is influenced by energy prices. This requires flexible operation of the electrolyzer with a continuous supply of hydrogen, oxygen, and heat, which requires complex control and operating modes for the various components (electrolyzer, heat pump, heat storage, compressors for oxygen and hydrogen). Furthermore, coupling an electrolyzer with a heat pump presents the problem of combining two components with different operating modes and ramp-up curves. While an electrolyzer, as a chemical-electrical process, responds quickly to control measures, a heat pump, together with the compressor, responds rather slowly due to the inertia of the rotating masses. If the individual components are not used according to their start-up and shutdown curves, total failure of the system will result or dynamic operation cannot be achieved. Dynamic operation must take into account fluctuations in energy prices to operate the system, and fluctuations in the removal of hydrogen, oxygen, and heat. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Patent Application Publication No. 102019202439A1 Summary of the Invention [Problem to be solved by the invention]

[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 above-mentioned problems. [Means for solving the problem]

[0009] This problem is solved by a device having the features of independent claim 1 and by a method having the features of independent claim 5. Advantageous configurations and developments of the invention are set out in the dependent claims.

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

[0011] The method according to the present invention relates to the operation of an energy system in which hydrogen is produced by water electrolysis using an electrolyzer, the heat generated during hydrogen production is transferred to the heat source side of a heat pump, the temperature level is raised by the heat pump, and the heat is discharged into a district heating circuit or a commercial heating circuit. According to the present invention, a heat storage device is incorporated into the district heating circuit or the commercial heating circuit, the return line of the heat storage device is connected after the heat exchanger, and the feed line of the heat storage device is connected before the heat exchanger of the heat pump, so that the heat from the heat storage device is used to raise the temperature of the return line of the district heating circuit or the commercial heating circuit.

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

[0013] Furthermore, the present invention recognizes that in order for a heat pump to be able to operate under full load and therefore at optimum efficiency, it is necessary to adapt the fluctuating amount of heat energy generated to the continuous demand of the heat pump. This adaptation is surprisingly achieved by a heat reservoir whose return line is connected after the heat exchanger and whose feed line is connected before the heat exchanger of the heat pump.

[0014] The heat storage arrangement according to the invention makes it possible to compensate for both slowly changing heat inputs, such as those caused by the aging of the electrolyzer, and rapidly changing heat inputs, such as those caused by the different operating behavior and ramp-up curves of the electrolyzer and the heat pump. The heat exchanger according to the invention, on the one hand, directly cools the hydrogen production unit, separating heat production from heat utilization. The heat pump can therefore be oversized for the waste heat stored by the hydrogen production unit, so that it has sufficient reserves in case of an increase in waste heat due to aging. This compensation may be achieved via a control procedure that, in the event of an increase in waste heat on the heat pump's source side, correspondingly reduces the proportional heat flow output from the heat storage to the district or commercial heating circuit, so that the heat pump can continue to operate under full load.

[0015] With the present invention, waste heat utilization from the electrolyzer and other components can be increased from 75% to over 90% energy efficiency. Compared to configurations without a heat pump, it is possible to save on additional chillers or other equipment for cooling the electrolyzer.

[0016] In addition to the electrolyzer, further components of the hydrogen production unit can be integrated into the cooling water circuit and waste heat can be extracted and utilized, such as the hydrogen compressor, oxygen compressor or other heat source of the unit.

[0017] To further increase the flexibility in setting the heat pump capacity, an advantageous development of the invention further provides a low-temperature storage tank integrated into the cooling water circuit. This low-temperature storage tank is provided in addition to any pre-cooling tanks that may be present and serves to directly cool the hydrogen generation unit. The low-temperature storage tank allows the hydrogen generation unit to be directly cooled on the one hand, while heat generation is decoupled from the heat pump. The heat pump can thus reduce the amount of waste heat stored by the hydrogen generation unit or compensate for the increase in waste heat due to aging.

[0018] Here, the cold storage may be part of a control system in which the heat storage and the cold storage are both controlled variables. Thus, via a 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 cold storage to the heat source side of the heat pump can be increased to keep the heat pump running under full load.

[0019] Depending on the size of the cold storage tank, waste heat can also be generated simply by filling the cold storage tank. This can be advantageous, for example, during start-up of the energy system or in the event of a heat pump failure. For this purpose, in an advantageous further development of the invention, the feed line of the cold storage tank is connected to the heat source side of the heat pump so that the cold storage tank can be discharged via the heat pump. This operating mode is advantageous in the event of a failure of the hydrogen production unit, for example, when waste heat can no longer be accumulated. This further development forms a closed circuit between the cooling water storage tank and the heat pump, which can increase the flexibility of the system during operation.

[0020] The present invention is suitable for high temperature heat pumps, characterized by achieving feedline temperatures of 100 to 150 degrees Celsius. [Brief explanation of the drawings]

[0021] In the following, the invention and advantageous developments are explained in more detail with reference to the drawings.

[0022] [Figure 1] 1 shows an energy system according to the invention with a heat storage device. [Figure 2] 1 shows a development of the energy system according to the invention with a cold storage. [Figure 3] 1 shows a particular development of an energy system for the discharge of a cryogenic reservoir. DETAILED DESCRIPTION OF THE INVENTION

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

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

[0025] Hydrogen is produced in the electrolyzer 2 by water electrolysis. For an electrolyzer with a 70 MW output, 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 circuit 4. The heat pump 5 thus directly cools the hydrogen production unit 2. The temperature level of the heat is raised via the heat pump 5 and discharged via a heat exchanger 8 to a district or commercial heating circuit 10. A feature of the present invention is that a heat storage device 9 is incorporated into the district or commercial heating 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 return line temperature of the district or commercial heating circuit 10 can be raised using the heat from the heat storage device 9.

[0026] In this configuration, when the electrolyzer 3 starts up, the heat pump capacity is greater than the waste heat generated. The heat pump 5 is therefore oversized. Nevertheless, the heat pump can be operated at full load and therefore with an optimum coefficient of performance, since the temperature difference is compensated for by the heat store 9. The necessary time-dependent adaptation to the aging of the electrolyzer 3 is compensated for accordingly by the control means. During control, the amount of waste heat increases on the heat source side 6 of the heat pump 5, so that the heat flow output from the heat store 9 to the district or commercial heating circuit is reduced accordingly.

[0027] 2 shows a further development of the invention with an additional cold store 14 integrated into the cooling water circuit. Fig. 2 further shows that in addition to the electrolyzer 3, the hydrogen production unit 2 may comprise further components, such as a hydrogen compressor unit 15, an oxygen compressor unit 16, and other waste heat sources. The cold store 14 is integrated into the cooling water circuit 4. The cold store 14 allows for further flexibility in configuring the heat pump capacity. On the one hand, the cold store 14 directly cools the hydrogen production unit 2, and the heat production can be decoupled from the heat pump 5.

[0028] In this configuration, the heat pump capacity at start-up of the electrolyzer 3 is less than the waste heat generated. The heat pump 5 is therefore below setpoint already at start-up of the electrolyzer 3 or after ageing. The heat pump 5 can therefore be relatively small. Nevertheless, the temperature difference is compensated for by the cold store 14, so the heat pump can operate under full load and therefore with optimum efficiency. The necessary adaptation to the aging of the electrolyzer 3 is controlled accordingly.

[0029] 3 shows a further development with a particular interconnection of the energy system 1 for the discharge of the cold store 14. The feed line 12 of the cold store 14 is connected to the heat source side 6 of the heat pump 5 via a branch line 18. The cold store can then be discharged via the heat pump. With this further development, a closed circuit can be formed between the cold store 14 and the heat pump 5. This can be advantageous, for example, during start-up 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 electrolyzer (3) for water electrolysis thermally coupled to a cooling water circulation circuit (4); a heat pump (5) whose heat source side is thermally coupled to the cooling water circulation circuit (4) and whose heat sink side (7) is coupled to a district or commercial heating circulation circuit (10) via a heat exchanger (8); An energy system (1) comprising: A heat storage device (9) is connected to a district or commercial heating circuit (10), The return line (11) of the heat reservoir is connected after the heat exchanger (8) of the heat pump (5), and the feed line (12) of the heat reservoir (9) is connected before the heat exchanger (8) of the heat pump (5), Heat from the heat reservoir (9) increases the return line temperature of the district or commercial heating circuit (10); Energy System (1).

2. 2. The energy system (1) according to claim 1, wherein the cooling water circuit (4) further comprises a cold reservoir (14).

3. The feed line (12) of the cold storage (14) is connected to the heat source side (6) of the heat pump (5); The heat pump (5) allows the cold reservoir (14) to be discharged. 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 an electrolysis device (2), The heat generated during hydrogen production is transferred to the heat source side (7) of the heat pump (5) via a cooling water circulation circuit (4), The temperature level is increased by the heat pump (5), Discharged via the heat exchanger (8) into a district or commercial heating circuit (10), A method for operating an energy system, comprising: a heat storage device (9) incorporated into the district or commercial heating circuit (10); The return line (11) of the heat storage (9) is connected after the heat exchanger (8) of the heat pump (5), and the feed line of the heat storage (9) is connected before the heat exchanger (8) of the heat pump (5); Heat from the heat reservoir (9) increases the return line temperature of the district or commercial heating circuit (10); How energy systems operate.

6. 6. The method for operating an energy system (1) according to claim 5, further comprising incorporating a cold reservoir (14) in the cooling water circuit.

7. a feed line (12) of the cold storage (14) connected to the heat source side (6) of the heat pump (5); The cold reservoir (14) is discharged via the heat pump (5), A method for operating an energy system (1) according to claim 6.

8. 8. A method for operating an 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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