Discharging device for electrolyzer, electrolyzer system and method for operating the same

Abstract

The invention relates to a discharging device for an electrolysis system (2), comprising a control unit (1), two contact elements (DC+, DC-), one contact element being provided for connection to a direct current pole of the electrolysis system (2) and the other contact element being provided for connection to the other direct current pole of the electrolysis system (2), wherein a discharge resistor (R1), a switch (S1) which can be activated by the control unit (1) and a voltage measuring unit (V) which is configured for measuring the voltage between one and the other direct current pole of the electrolysis system (2) are arranged between the two contact elements. The control device (1) is configured to close the switch (S1) in response to a discharge signal as long as the voltage measured by the voltage measuring unit (V) is greater than a first threshold value, and to open the switch (S1) when the measured voltage is less than the first threshold value.

Description

[0001] Discharging device for electrolyzer, electrolyzer system and method for operating the same

[0002] Description

[0003] The invention relates to a discharging device for an electrolyzer, an electrolyzer system with such a discharging device and a method for operating the same.

[0004] Problem definition

[0005] If an electrolyzer is switched off during operation (safety shutdown, shutdown for maintenance and servicing, stopping hydrogen production), the DC voltage between the poles of the electrolyzer drops very quickly to the open-circuit voltage of the electrolyzer. Depending on the electrolyzer type and manufacturer, this can be between 300V and 1000V.

[0006] If the open-circuit voltage of the electrolyzer is set, an effect occurs in which the highly capacitive behavior of the electrolyzer takes effect. This capacitive behavior results in the voltage reducing very slowly. The values measured in the field are around 1V / min. As a result, maintenance work can often only be carried out the next day after the electrolyzer has been switched off.

[0007] State-of-the-art solutions accelerate the discharge of the residual voltage at the electrolyzer by creating an isolated grid using the residual voltage at the poles of the electrolyzer. In this case, the residual voltage is discharged via losses of a converter that creates an island network. However, this process can only be carried out up to a certain voltage, for example 50V. Once 50V is reached, the discharge process is stopped.

[0008] Subsequently, the capacitive effect of the electrolyzer again leads to an increase in the residual voltage, whereby this time the discharge via an isolated network and the losses of the corresponding converter do not work.

[0009] The task is therefore to safely and quickly reduce a residual voltage of an electrolyzer to a voltage which allows safe maintenance.

[0010] This task is solved by the unloading device according to the main claim. Aspects and further embodiments according to the invention are the subject of the subclaims and the other independent claim.

[0011] The discharging device according to the main claim has a control unit and two contact elements, one contact element being provided for connection to a direct current pole of an electrolysis system and the other contact element being provided for connection to the other direct current pole of an electrolysis system. Furthermore, a discharge resistor, a switch that can be controlled by the control unit and a voltage measuring unit, which is configured to measure the voltage between one and the other direct current pole of an electrolysis system, are arranged between the two contact elements. The control unit is configured to close the switch in response to a discharge signal as long as the voltage measured by the voltage measuring unit is greater than a first threshold value, and to open the switch when the measured voltage is less than the first threshold value.

[0012] The discharging device according to the invention can ensure that the residual voltage of the electrolyzer is low. For this purpose, the first threshold value can be set to a non-damaging voltage, such as 30V. If the control unit detects a residual voltage that is greater than the first threshold value and the discharge of the electrolyzer is ordered by a discharge signal, the control unit controls the switch so that it is closed. The poles of the electrolyzer are now connected via a resistor and are discharged. If the voltage falls below the first threshold value, the switch is opened again. In this way, the residual voltage on the electrolyzer can be safely brought below a threshold value.

[0013] According to one embodiment of the discharging device, the control unit is also configured to close the switch again if, after a predetermined time has elapsed after the voltage falls below the first threshold value, the measured voltage exceeds a second threshold value which is higher than the first threshold value.

[0014] As already described, the capacitive properties of the electrolyzer can cause the residual voltage of the electrolyzer to increase again after discharging below a first threshold value. For this reason, a second threshold value is defined in this embodiment, which is higher than the first threshold value and is so high that the voltage at the second threshold value is harmless.

[0015] If the residual voltage now rises again to a value that is potentially harmful to a maintenance employee, the discharge process is restarted by closing the switch.

[0016] According to one embodiment of the discharging device, the control unit is also configured to close the switch again when a third threshold value, which is lower than the first threshold value, is exceeded after falling below the first threshold value.

[0017] In this embodiment, a third threshold value is defined, which is lower than the first threshold value. To increase the safety of discharging, a third threshold value can be defined, up to which the residual voltage is reduced before the discharging process is completed and maintenance of the electrolyzer can begin. According to one embodiment of the discharging device, the control unit is also configured to open the switch again when the measured voltage falls below the third threshold value.

[0018] In this embodiment, the end of the temporary discharge is defined such that the switch is opened when the measured voltage falls below the third threshold value.

[0019] One aspect of the invention is an electrolysis system with a discharging device which is configured as described in the above embodiments.

[0020] The electrolysis system with such a discharging device can be safely discharged and maintained, as the existing residual voltage is permanently reduced to a low level by the discharging device.

[0021] Another aspect of the invention relates to a method for operating the discharging device of one of the preceding embodiments or in an electrolysis plant of claim 5 by carrying out the steps of measuring a voltage between poles of an electrolyzer via a voltage measuring unit, if the measured voltage is greater or equal to a first threshold value, closing a switch, to discharge the voltage between the poles of the electrolyzer via a discharge resistor, if then the measured voltage is smaller than the first threshold value, opening the switch.

[0022] The method for operating a discharging device according to the invention can ensure that the residual voltage of the electrolyzer is low. For this purpose, the first threshold value can be set to a non-damaging voltage, such as 30V. If the control unit detects a residual voltage that is greater than the first threshold value and the discharge of the electrolyzer is ordered by a discharge signal, the control unit controls the switch so that it is closed. The poles of the electrolyzer are now connected via a resistor and are discharged. If the voltage falls below the first threshold value, the switch is opened again. In this way, the residual voltage on the electrolyzer can be safely brought below a threshold value.

[0023] In an embodiment of the aspect above the method further comprises the step, after a predetermined time has elapsed after the voltage falls below the first threshold value and the measured voltage exceeds a second threshold value which is higher than the first threshold value, closing the switch.

[0024] As already described, the capacitive properties of the electrolyzer can cause the residual voltage of the electrolyzer to increase again after discharging below a first threshold value. For this reason, a second threshold value is defined in this embodiment, which is higher than the first threshold value and is so high that the voltage at the second threshold value is harmless. If the residual voltage now rises again to a value that is potentially harmful to a maintenance employee, the discharge process is restarted by closing the switch. In an embodiment of the aspect above the method further comprises the step of closing the switch, after the first threshold value has been undershot, a third threshold value, which is lower than the first threshold value, is exceeded.

[0025] In this embodiment, a third threshold value is defined, which is lower than the first threshold value. To increase the safety of discharging, a third threshold value can be defined, up to which the residual voltage is reduced before the discharging process is completed and maintenance of the electrolyzer can begin.

[0026] In an embodiment of the aspect above the method further comprises the step of opening the switch when the measured voltage falls below the third threshold value.

[0027] In this embodiment, the end of the temporary discharge is defined such that the switch is opened when the measured voltage falls below the third threshold value.

[0028] The invention is illustrated below with the aid of the figures, where

[0029] Fig. 1 shows an electrolysis system with a discharging device according to the invention and

[0030] Fig. 2 shows a flowchart of the method according to an aspect of the invention.

[0031] The figures are explained in detail below.

[0032] Fig. 1 shows an electrolyzer 2 with a discharging device according to the invention. The discharging device comprises a control unit 1, a voltage measuring unit V, a discharging resistor R1 and a switch S1.

[0033] In the flowchart of Fig. 2, the method starts with S10, in which the residual voltage between the poles of the electrolyzer is measured. In the following Step S20 it is decided whether the residual voltage exceeds a first threshold value. If the residual voltage exceeds the first threshold value, the method proceeds via S20:-, closes a switch S1 and goes back to S10. If the residual voltage is smaller than the first threshold value, the method proceeds via S20:+, opens the switch S1 and executes S30. In S30 the residual voltage is measured again. In S40, if the residual voltage rises higher than a second threshold value larger than the first threshold value, the switch S1 is closed again via S40:- and the method returns to S10. If the residual voltage is smaller than the first threshold value but bigger than a third threshold value being smaller than the first threshold value, the switch S1 is closed again via S40:+.

[0034] Lastly, if the residual voltage is smaller than the third threshold value in S50, the method returns to S10. List of reference symbols

[0035] 1 Control unit

[0036] 2 Electrolyzer

[0037] V Voltage measuring unit

[0038] S1 Switches

[0039] R1 Discharge resistor

[0040] DC+, DC- Contact elements

[0041] S10-S50 Steps

Claims

Claims:

1. Discharging device for an electrolysis system (2), comprising a control unit (1), two contact elements (DC+, DC-), one contact element being provided for connection to a direct current pole of the electrolysis system (2) and the other contact element being provided for connection to the other direct current pole of the electrolysis system (2), wherein a discharge resistor (R1), a switch (S1) which can be activated by the control unit (1) and a voltage measuring unit (V) which is configured for measuring the voltage between one and the other direct current pole of the electrolysis system (2) are arranged between the two contact elements, wherein the control device (1) is configured to close the switch (S1) in response to a discharge signal as long as the voltage measured by the voltage measuring unit (V) is greater than a first threshold value, and to open the switch (S1) when the measured voltage is less than the first threshold value.

2. Discharging device for an electrolysis plant according to claim 1, wherein the control device (1) is also configured to close the switch (S1) again if, after a predetermined time has elapsed after the voltage falls below the first threshold value, the measured voltage exceeds a second threshold value which is higher than the first threshold value.

3. Discharging device for an electrolysis plant according to claim 2, wherein the control device (1) is also configured to close the switch (S1) again if, after the first threshold value has been undershot, a third threshold value, which is lower than the first threshold value, is exceeded.

4. Discharging device for an electrolysis plant according to claim 3, wherein the control device (1) is also configured to open the switch (S1) again when the measured voltage falls below the third threshold value.

5. Electrolysis system with a discharging device which is configured as described in claims 1 to 4.

6. Method for operating the discharging device of one of claims 1 to 4 or in an electrolysis system of claim 5 by carrying out the steps of measuring (S10) a voltage between poles of an electrolyzer via a voltage measuring unit (V), if the measured voltage is greater or equal to a first threshold value, closing (S20:-) a switch (S1), to discharge the voltage between the poles of the electrolyzer via a discharge resistor (R1), if then the measured voltage is smaller than the first threshold value, opening (S20:+) the switch (S1).

7. Method according to claim 6, wherein the method further comprising the step, after a predetermined time has elapsed after the voltage falls below the first threshold value and the measured voltage exceeds a second threshold value which is higher than the first threshold value, closing (S40:-) the switch (S1).

8. Method according to claim 6 or 7, wherein the method further comprising the step closing (S40:+) the switch (S1), after the first threshold value has been undershot, a third threshold value, which is lower than the first threshold value, is exceeded.

9. Method according to claim 8, wherein the method further comprising the step opening (S50) the switch (S1) when the measured voltage falls below the third threshold value.

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