METHOD FOR ON-DEMAND CLOSED-LOOP CONTROL OF AN ELECTROCHEMICAL PLANT

Abstract

Demand-based closed-loop control is used in an electrochemical plant that has modules and a control unit, with each module being individually controlled by the control unit and supplied with a module-specific electric operating current. For each module to generate a separate product flow, product flows of the individual modules, connected in parallel, are merged to form a total product flow. When a start condition occurs, the control unit records a current total product flow demand, records a current efficiency of the modules based on a ratio of respective operating current and product flow, determines operationally ready modules, determines module-specific target operating currents for the operationally ready modules to cover the demand from a range of permissible module-specific target operating currents based on the efficiency of the modules and the demand, and sets the operating currents of the operationally ready modules to the determined module-specific target operating currents.

Claims

1.-19. (canceled)

20. A method for demand-based closed-loop control of an electrochemical plant that comprises modules and a control unit, each module being individually controlled by the control unit and supplied with a module-specific electric operating current, wherein for each of the modules to generate a separate product flow, the product flows of the individual modules, which are connected in parallel with regard to their product flows, are merged to form a total product flow of the plant, wherein the following steps are performed by the control unit when a start condition is satisfied: recording a current total product flow demand; recording a current efficiency of the modules depending on a ratio of the respective operating current and product flow; determining operationally ready modules; determining module-specific target operating currents for the operationally ready modules to cover the current total product flow demand from a range of permissible module-specific target operating currents as a function of the efficiency of the modules and the current total product flow demand, wherein to determine the module-specific target operating currents, the respective modules are sorted according to a module-specific life-cycle parameter and are raised or lowered according to that order until the current total product flow demand is met; and setting the operating currents of the operationally ready modules to the module-specific target operating currents that have been determined, wherein the life-cycle parameter is calculated from the current efficiency of the modules and a correction term that accounts for maintenance costs of the electrochemical plant, wherein the correction term generates a deviation from a currently most efficient operating point of the plant, which allows non-uniform aging of the modules in terms of their efficiency.

21. The method of claim 20 comprising determining the correction term based on a total charge quantity that flowed through the respective module during a previous life cycle, based on an age of the respective module, and/or based on a position of the module in the electrochemical plant.

22. The method of claim 20 comprising determining iteratively the module-specific target operating currents for the operationally ready modules to meet the total product flow demand using a predictive calculation of the efficiency achievable for each individual module and assuming a stepwise change of the respective module-specific operating current.

23. The method of claim 22 wherein the iteration is based on a greedy algorithm.

24. The method of claim 22 wherein the iteration is performed with an adaptive step size that is selected depending on a current deviation of the total product flow from the total product flow demand.

25. The method of claim 20 wherein the efficiency of the modules when determining the module-specific target operating currents is weighted with a weighting factor that depends on a ratio of the module-specific operating current and a sum of the module-specific operating currents of all of the modules.

26. The method of claim 20 comprising assigning all of the modules a minimum operating current corresponding to a basic load by the control unit.

27. The method of claim 20 wherein the control unit is a plant monitoring unit.

28. The method of claim 20 wherein a predefinable amount of deviation of the currently generated product flow from the total product flow demand is used as the start condition.

29. The method of claim 20 wherein the commissioning or decommissioning of individual modules is used as the start condition.

30. The method of claim 20 wherein exceeding or undershooting a temperature of the modules, determined by the control unit, by a predefinable maximum amount is used as the start condition.

31. The method of claim 20 wherein the electrochemical plant is a water electrolysis plant.

32. The method of claim 20 wherein the efficiency of the individual modules is determined based on a current-voltage characteristic.

33. The method of claim 20 wherein the efficiency of the individual modules in the control unit is stored as documentation of module aging.

Description

[0041] In the following, the invention is described in greater detail based on exemplary embodiments and with reference to the attached figures. In the drawings:

[0042] FIG. 1: shows an illustration of the method steps of the method according to the invention,

[0043] FIG. 2: shows an illustration of the method steps of the method according to the invention in accordance with a preferred refinement, in which the modules are sorted according to their current efficiency and are raised or lowered according to that order and

[0044] FIG. 3: shows an illustration of the method steps of the method according to the invention according to an alternative preferred refinement, in which the determined module-specific target operating current is modified by multiplication with a weighting factor and

[0045] FIG. 4: shows a schematic illustration of the method according to the invention based on a water-electrolysis plant, which comprises a control unit and a plurality of modules connected in parallel, the modules being formed from electrolysis cells connected in series.

[0046] In the various figures, identical parts are always labeled with the same reference signs and are therefore usually named or mentioned only once in each case.

[0047] The method according to the invention for the demand-based closed-loop control of an electrochemical plant can be applied to plants that comprise modules and a control unit. Each module is individually controlled by the control unit and supplied with a module-specific electrical operating current. A product flow is generated by supplying the modules with an electric operating current. Such a product flow may contain, for example, chlorine and caustic soda in the case of chlorine-alkali electrolysis, or hydrogen in the case of water electrolysis. If the plant is in the form of a battery, the product flow is simply an electric current. In either case, the product flows generated by the individual modules are combined to form a total flow.

[0048] In FIG. 1, the essential method steps performed by the control unit are visualized schematically. If a start condition is satisfied, these include:

[0049] recording a current total product flow demand (1). The current total product flow demand can vary greatly. Extremely large fluctuations in the total product flow demand are possible, particularly in batteries.

[0050] As soon as the total product flow demand is recorded, the efficiency of the modules of the electrochemical plant is recorded (2). The efficiency depends on the ratio of the respective operating current and the product flow.

[0051] In a further step, the modules are identified (3), in particular which modules are actually available. Optionally, the operationally ready modules can also be identified: modules that are not operationally ready are, for example, those that are defective or taken out of service for maintenance purposes. Non-operational modules can also be assigned a fixed operating current of essentially zero, for example, for the duration of the fault or the maintenance activities.

[0052] The following method step according to the invention relates to the determination of module-specific target operating currents for the modules to meet the current total product flow demand. The module-specific target operating currents are determined from a range of permissible module-specific target operating currents, which, for example, can prevent damage being caused to the module by selecting an excessively high operating current. Instead, the module-specific target operating currents are determined as a function of the efficiency of the modules and the current total product flow demand (4). The consideration of the efficiency of the modules is an essential step of the method according to the invention, since this enables the operation of the chemical plant close to the minimized total power consumption point.

[0053] After the module-specific target operating currents have been determined, the operating currents of the modules are set to the determined module-specific target operating currents (5).

[0054] A preferred refinement of the method according to the invention is shown schematically in FIG. 2. This refinement is characterized in that, to determine the module-specific target operating currents the respective modules are sorted according to their current efficiency and are raised or lowered according to that order until the current total product flow demand is met (3a). In this way, the power consumption of the plant can be reduced in the event of an increasing or decreasing total product flow demand by assigning a higher or lower operating current to efficient or inefficient modules respectively. The sorting of the modules in terms of efficiency is necessary in order to be able to raise or lower them according to that order, subsequently. Since this sorting can involve a considerable amount of computing effort or time, a refinement of the method according to the invention provides that to sort the n modules with regard to their efficiency, an algorithm is used which scales with n*log(n), thus ensuring a manageable computing time even for large plants with large numbers of modules. This can be the Quicksort algorithm, for example.

[0055] Alternatively—also shown in the method diagram according to FIG. 2—to determine the module-specific target operating currents in step (3a) the respective modules can be sorted according to a module-specific life-cycle parameter and are raised or lowered according to that order until the current total product flow demand is met. The life-cycle parameter is calculated from the current efficiency of the modules (M) and a correction term that takes into account maintenance costs of the electrochemical plant. The correction term is preferably determined depending on a total charge quantity that flowed through the respective module during the previous life-cycle and/or depending on the age of the respective module and/or depending on the position of the module in the electrochemical plant.

[0056] The module-specific target operating currents (I.sub.m) for the operationally ready modules (M) for meeting the total product flow demand (B) in the above-described methods are preferably determined iteratively, using a predictive calculation of the efficiency achievable for each individual module (M) and assuming a gradual change of the respective module-specific operating current. Greedy algorithms are particularly preferably used for the iteration. The iteration is preferably carried out with an adaptive step size, which is selected as a function of a current deviation of the total product flow from the total product flow demand (B).

[0057] When determining the module-specific target operating currents (I.sub.m), the efficiency of the modules (M) is preferably weighted with a weighting factor that depends on the ratio of the module-specific operating current and the sum of the module-specific operating currents of all modules (M). This means that the effect of the efficiency change of the individual module on the overall efficiency is already taken into account when determining the module-specific target operating currents (I.sub.m).

[0058] A preferred alternative refinement of the method according to the invention is shown in FIG. 3. In this case, the determined module-specific target operating current is modified by multiplication by a weighting factor which depends on the ratio of the module-specific operating current and the sum of the module-specific operating currents of all modules (4a). This brings the operating point of the plant even closer to its optimum energy efficiency.

[0059] FIG. 4 illustrates a schematic representation of the method according to the invention based on a water-electrolysis plant (E), which comprises a control unit (C) and a plurality of modules (M) connected in parallel, which modules (M) are formed from electrolysis cells connected in series for producing hydrogen. The control unit (C) records the total product flow demand (B) and records the efficiency of the individual modules (M), sorts them according to their efficiency and determines the operational readiness of the modules (M) (indicated by a tick or a cross). The target operating currents of the modules (I.sub.m) are then determined, multiplied by a weighting factor, so that the weighted target operating currents of the modules (I.sub.m,g) are obtained in order to bring the entire plant closer to its most energy-efficient operating point. After setting the operating currents to the weighted target operating currents (I.sub.m,g), the control unit can monitor the system for the presence of a new start condition.

LIST OF REFERENCE SIGNS

[0060] 1 Recording the current total product flow demand [0061] 2 Recording the module efficiency [0062] 3 Identifying the modules [0063] 3a Sorting and variation according to efficiency/life-cycle parameters [0064] 4a Multiplication of the module-specific target operating currents with weighting factor [0065] 4 Determining the module-specific target operating currents [0066] 5 Setting the module-specific target operating currents [0067] B Total product flow demand [0068] C Control unit [0069] E Water electrolysis plant [0070] M Module [0071] I.sub.m Target operating current of a module [0072] I.sub.m,g Target operating current of a module after weighting