Sequential cycle engineering reverse osmosis desalination unit

Abstract

The present application relates to a sequential cycle engineering reverse osmosis desalination device, more particularly, to a sequential cycle engineering reverse osmosis desalination device which basically ensures high recovery rate using closed circuit reverse osmosis technology, and sequentially applies reverse reverse osmosis technology to reduce fouling, and can perform efficient water treatment without a separate energy recovery device.

Description

Technical Field

[0001] This invention relates to a sequential-cycle reverse osmosis desalination device, and more specifically, to a sequential-cycle reverse osmosis desalination device that employs closed-loop reverse osmosis technology to ensure a high recovery rate, and sequentially applies reverse reverse osmosis technology to reduce fouling, while also performing high-efficiency water treatment without the need for a separate energy recovery device. Background Technology

[0002] Water scarcity means that it is difficult to obtain freshwater sources due to resource depletion, and the global water shortage is becoming increasingly severe due to factors such as high industrial development and abnormal climate phenomena.

[0003] However, as water is an essential element in human life and various industrial sectors, the demand for it continues to increase. As one of the effective methods to meet this demand, a method called seawater desalination has been proposed, which involves desalinating large amounts of seawater.

[0004] Seawater desalination refers to a series of water treatment processes that remove dissolved substances containing salt from seawater that is difficult to use directly for domestic or industrial purposes, in order to obtain high-purity drinking water, domestic water, and industrial water.

[0005] Currently, seawater desalination equipment uses either the Multiple-Stage Flash Distillation process (MSF) or the Reverse Osmosis process. The Reverse Osmosis process is a process that applies pressure above the osmotic pressure to raw water or brine to make pure water, which does not contain solutes such as ions or organic molecules, move through a semi-permeable membrane to produce fresh water.

[0006] On the other hand, unlike the general reverse osmosis process, in order to achieve the target recovery rate, there is also a closed-circuit reverse osmosis (CCRO) seawater desalination method. The operation involves mixing the concentrated water discharged from the reverse osmosis equipment with the raw water or brine and then injecting it back into the reverse osmosis equipment. After the target concentration is reached, the concentrated water is discharged.

[0007] Relatedly, Korean Patent No. 10-1052662 discloses a device for continuous batch sequential desalination of brine in a closed loop via reverse osmosis, which consists of multiple closed-loop desalination devices (closed-loop reverse osmosis, CCRO) connected in parallel.

[0008] However, a problem with conventional closed-loop reverse osmosis (CCRO) desalination units is that the time it takes for the pressure of the concentrated water discharged from the reverse osmosis unit to increase is shortened as the process continues, thus shortening the cleaning or replacement cycle of the reverse osmosis unit. Summary of the Invention

[0009] The technical problem to be solved by the present invention

[0010] The present invention is proposed to solve the aforementioned problems and aims to provide a sequential circulation reverse osmosis (Circle-SEQ RO) desalination device, which uses closed-loop reverse osmosis technology to basically ensure a high recovery rate, and sequentially applies reverse reverse osmosis technology to reduce fouling. On the other hand, it can perform high-efficiency water treatment without the need for a separate energy recovery device.

[0011] Other objects of the present invention will become more apparent from the following embodiments.

[0012] Technical solution

[0013] To address the aforementioned problem, this invention, as an embodiment, proposes a sequential circulation reverse osmosis desalination device, which connects each of a plurality of forward reverse osmosis modules and at least one backward reverse osmosis module in parallel, wherein concentrated water discharged from the forward reverse osmosis modules flows into the reverse reverse osmosis modules, and concentrated water discharged from the reverse reverse osmosis modules flows into each of the forward reverse osmosis modules.

[0014] In a reverse osmosis desalination apparatus according to an embodiment of the present invention, it includes: a feed pump for supplying raw water; and a first pump (1 st pump), connected to the output end of the feed pump; second pump (2 nd The third pump (3) is connected to the output end of the forward and reverse osmosis module. rd pump), connected to the output of the first pump; and controller, in the first operation step (1 st In step (2), the feed pump and the first pump are controlled to allow raw water to enter the multiple forward and reverse osmosis modules. nd In step (3), the second pump is controlled to allow concentrated water discharged from the forward reverse osmosis module to enter the reverse reverse osmosis module. In the third operating step (3)... rdIn step), the concentrated water discharged from the reverse osmosis module by the third pump is combined with the raw water and then enters the forward reverse osmosis module.

[0015] High-pressure pumps can be used as the first and second pumps, and jet pumps that use the flow of concentrated water to accelerate the raw water in the third operation step can be used as the third pump.

[0016] Furthermore, three-way control valves are respectively configured at the input and output ends of the plurality of forward reverse osmosis modules and the reverse reverse osmosis module, and the controller can be configured to: in the fourth operation step (4 th In step), the three-way control valve is controlled so that when the preset first condition is met, the reverse osmosis module is converted into a forward reverse osmosis module, and raw water is continuously supplied to the input end of all reverse osmosis modules and the concentrated water at the output end of all reverse osmosis modules is discharged to the outside until the preset second condition is met.

[0017] In addition, the following can be used as the first condition: the measurement value of at least one of the concentration sensor, flow sensor, and pressure sensor configured on the movement path of the concentrated water reaches a preset reference value, or a preset time has elapsed after the third operation step.

[0018] In addition, the following can be used as the second condition: the concentration of the concentrated water reaches the preset initial concentration.

[0019] The controller can be configured to execute a fifth operation step (5) after completing one batch process from the first operation step to the fourth operation step. th In the fifth operating step, the three-way control valve is controlled to convert at least one of the plurality of forward reverse osmosis modules into a reverse reverse osmosis module and to convert an existing reverse reverse osmosis module into a forward reverse osmosis module.

[0020] Furthermore, the controller can execute the fifth operation step after executing multiple batches of the aforementioned processes.

[0021] Beneficial effects

[0022] According to an embodiment of the present invention, before the closed-loop reverse osmosis (CCRO) process of mixing concentrated water and raw water, the concentrated water discharged from the forward reverse osmosis module flows into the backward reverse osmosis module for circulation in a state of additional concentration, thereby significantly reducing energy consumption and chemical usage compared to conventional multi-stage reverse osmosis processes.

[0023] Furthermore, according to embodiments of the present invention, by periodically applying the opposite direction of raw water injection, the formation rate of biofouling and scale in the reverse osmosis module can be slowed down, and some scale can be removed, thereby shortening the reduction in the pressure increase time of the concentrate and thus extending the Clean in Place (CIP) cycle.

[0024] The effects of the present invention are not limited to those mentioned above, and those skilled in the art can clearly understand other effects not mentioned from the following description. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a sequential circulation reverse osmosis desalination device according to an embodiment of the present invention.

[0026] Figure 2 This is a block diagram illustrating the configuration of a sequential circulation reverse osmosis desalination apparatus according to an embodiment of the present invention.

[0027] Figure 3 This is a flowchart illustrating the operation steps of a sequential circulation reverse osmosis desalination device according to an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram illustrating the fourth operating step of a sequential circulation reverse osmosis desalination apparatus according to an embodiment of the present invention.

[0029] Figure 5 This is a schematic diagram illustrating the fifth operating step of a sequential circulation reverse osmosis desalination apparatus according to an embodiment of the present invention.

[0030] Figure 6 This is a graph showing the reduction in the time of pressure increase during one batch process of a reverse osmosis desalination apparatus for each repeated sequential cycle according to an embodiment of the present invention, from the first operating step to the fourth operating step. Detailed Implementation

[0031] This invention can be subject to various modifications and has multiple embodiments. Specific embodiments are illustrated in the accompanying drawings and described in detail in the accompanying description. However, it should be understood that this is not limited to the specific implementation, but rather includes all variations, equivalents, or substitutions contained within the spirit and scope of the invention.

[0032] When describing the present invention, if it is determined that a detailed description of relevant prior art would obscure the essence of the present invention, such detailed description will be omitted.

[0033] The terminology used in this application is for illustrative purposes only and is not intended to limit the invention. Unless the context clearly specifies otherwise, singular expressions include plural expressions. Terms such as "comprising" or "having" in this application are used to specify the presence of features, numbers, steps, actions, constituent elements, components, or combinations thereof described in the specification, and do not preclude the presence or additional possibilities of more than one other feature, number, step, action, constituent element, component, or combination thereof.

[0034] Unless otherwise defined, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art. Terms as defined in commonly used dictionaries shall be interpreted as having a meaning consistent with the context of the relevant art, and shall not be interpreted as having an ideal or overly formal meaning unless expressly defined in this application.

[0035] The term "module" as used in this specification can refer to a unit that performs a specific function or action, and can refer to hardware or software or a combination of hardware and software.

[0036] While terms such as "first" and "second" can be used to describe various constituent elements, the constituent elements are not limited to these terms. These terms are used only to distinguish one constituent element from others.

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. When describing the invention with reference to the drawings, the same or corresponding constituent elements will be given the same reference numerals regardless of the reference numerals, and repeated descriptions thereof will be omitted.

[0038] Hereinafter, the sequential circulation reverse osmosis desalination apparatus 1 according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0039] Hereinafter, in describing the sequential circulation reverse osmosis desalination apparatus 1 according to an embodiment of the present invention, the meaning of "connection" should be interpreted as including all ways of connection, such as direct connection to the reverse osmosis module or connection via pumps, valves, controllers, etc.

[0040] Figure 1 This is a schematic diagram of a sequential circulation reverse osmosis desalination device according to an embodiment of the present invention. Figure 2 This is a block diagram illustrating the configuration of a sequential circulation reverse osmosis desalination apparatus according to an embodiment of the present invention. Figure 3 This is a flowchart illustrating the operation steps of a sequential circulation reverse osmosis desalination device according to an embodiment of the present invention.

[0041] like Figure 1 and Figure 2 As shown, according to one embodiment, the sequential circulation reverse osmosis desalination device 1 includes multiple reverse osmosis modules 10, 20, 30 (RO modules), a feed pump FP, and a first pump P1 (1 st pump), second pump P2(2) nd pump), third pump P3 (3 rd The system includes a pump, multiple 3-way valves, a concentrate drain valve (DV), and a controller (C).

[0042] The reverse osmosis modules 10, 20, and 30 include multiple forward RO modules 10 and 20 and at least one backward RO module 30.

[0043] This specification illustrates an embodiment consisting of two forward reverse osmosis modules and one reverse reverse osmosis module, but it is not limited to this. Depending on the amount of brine to be treated, the reverse osmosis module may consist of two or more modules. As a specific example, it may consist of one forward reverse osmosis module and one reverse reverse osmosis module, three forward reverse osmosis modules and one reverse reverse osmosis module, or three forward reverse osmosis modules and two reverse reverse osmosis modules.

[0044] For ease of explanation, the multiple reverse osmosis modules 10, 20, and 30 (Ro modules) will be referred to as the first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30, respectively.

[0045] The first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30 are connected in parallel. The concentrated water B (Brine) discharged from the first reverse osmosis module 10 and the second reverse osmosis module 20 flows into the third reverse osmosis module 30, and the concentrated water B discharged from the third reverse osmosis module 30 flows back into the first reverse osmosis module 10 and the second reverse osmosis module 20 respectively, thus forming a circulation circuit.

[0046] The feed pump FP is designed to supply raw water R to the reverse osmosis module, for example, it can deliver raw water R at a pressure of about 3 bar (g).

[0047] The first pump P1 is connected to the output of the feed pump FP and starts to drive when the flow rate of raw water R supplied from the feed pump FP exceeds a preset benchmark.

[0048] The second pump P2 is connected to the output terminals of the first reverse osmosis module 10 and the second reverse osmosis module 20, and moves the concentrated water B discharged from the first reverse osmosis module 10 and the second reverse osmosis module 20 to the input terminal of the third reverse osmosis module 30.

[0049] A high-pressure pump can be used as the first pump P1 and the second pump P2.

[0050] The concentrated water B2 discharged from the third reverse osmosis module 30 merges with the raw water R supplied by the feed pump FP and flows into the third pump P3. The third pump P3 delivers the merged water to the input terminals of the first reverse osmosis module 10 and the second reverse osmosis module 20.

[0051] A jet pump can be used as the third pump P3, which utilizes the principle of accelerating the flow of raw water R by the flow of concentrated water B.

[0052] That is, since the pressure of concentrated water B is higher than that of raw water R, a pressure drop is required for the smooth mixing and transfer of raw water R and concentrated water B, but this also requires bearing the corresponding energy loss. Therefore, by using a jet pump as a third pump P3, the flow of concentrated water B can be used to accelerate raw water R without the need for a separate pressure drop.

[0053] Three-way control valves V11, V12, V21, V22, V31, and V32 (collectively referred to as V) are respectively configured at the input and output ends of the first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30, and open and close along the horizontal or vertical flow direction according to the control of the controller C.

[0054] The concentrated water drain valve DV is located on the pipe where the output ends of the first reverse osmosis module 10, the second reverse osmosis module 20 and the third reverse osmosis module 30 converge. When the discharged water B meets the specified conditions, the drain valve DV opens and closes under the control of the controller C.

[0055] The controller C will control the start-up and operation level of each pump FP, P1, P2 for each operation step (S10 to S50) described later, and control the opening and closing of the three-way control valve V and the concentrate discharge valve DV.

[0056] The operation steps controlled by controller C include: the first operation step (1) st Step 1): Supply raw water R(S10); Second operation step (2) nd Step 1): Supply concentrated water B (S20); Third operating step (3) rd Step 1): Circulate concentrated water B (S30); Fourth operating step (4) th Step 1): Drain concentrated water B (S40); and the fifth operating step (5) th Step), change the operating direction of each reverse osmosis module (S50).

[0057] Here, it is assumed that the first reverse osmosis module 10 and the second reverse osmosis module 20 are set to forward, and the third reverse osmosis module 30 is set to reverse, and each operation step is described in detail.

[0058] In the first operation step (S10), the controller C controls the three-way control valves V11, V12, V21, and V22, which are respectively configured at the input and output ends of the first reverse osmosis module 10 and the second reverse osmosis module 20, to open in the horizontal flow direction, and controls the three-way control valves V31 and V32, which are configured at the input and output ends of the third reverse osmosis module 30, to open in the vertical flow direction.

[0059] Furthermore, in the first operation step (S10), the controller C controls the feed pump FP and the first pump P1 to allow raw water R to enter the first reverse osmosis module 10 and the second reverse osmosis module 20. Specifically, the controller C supplies raw water by driving the feed pump FP, and starts driving the first pump P1 when the flow rate of raw water R supplied from the feed pump FP exceeds a preset reference value. At this time, the controller C controls the operation of the first pump P1 based on the signal from a flow sensor (not shown) configured on the supply line of the raw water R.

[0060] In the second operation step (S20), the controller C controls the second pump P2 to allow the concentrated water B discharged from the first reverse osmosis module 10 and the second reverse osmosis module 20 to flow into the third reverse osmosis module 30. Specifically, when the flow rate of the concentrated water B exceeds a preset reference, the controller C starts the second pump P2 and controls the operation of the second pump P2 based on the signal from a flow sensor (not shown) configured on the supply line of the concentrated water B. On the other hand, the fresh water filtered (permeated) as it flows through the first reverse osmosis module 10 and the second reverse osmosis module 20 is discharged through a pipe.

[0061] In the third operating step (S30), the concentrated water B discharged from the third reverse osmosis module 30 flows through the three-way control valve V31 located at the output end of the third reverse osmosis module 30 and into the third pump P3. Additionally, the raw water R supplied by the feed pump FP and the first pump P1 also flows into the third pump P3, merging with the flowing concentrated water B. On the other hand, the fresh water filtered (permeated) during its flow through the third reverse osmosis module 10 is also discharged through a pipe.

[0062] The first operation step (S10) to the third operation step (S30) described above are repeated until any one of the concentration, pressure, flow rate, or scale amount of concentrated water B detected by the specified sensor S exceeds a preset threshold. Therefore, the specified sensor S can be any one of a concentration sensor, flow sensor, pressure sensor, or scale sensor, and at least one of these sensors is arranged along the movement path of the concentrated water B.

[0063] When any of the concentration, pressure, flow rate, or scale content of concentrated water B exceeds a preset threshold, the fourth operation step (S40) is executed. Figure 4 This is a schematic diagram illustrating the fourth operating step of a sequential circulation reverse osmosis desalination apparatus according to one embodiment.

[0064] In the fourth operation step (S40), when the preset first condition is met, the controller C controls the three-way control valves V31 and V32 to convert the third reverse osmosis module 30 into a forward reverse osmosis module, and continuously supplies raw water R to the input terminals of all reverse osmosis modules 10, 20, and 30 and discharges the concentrated water B from the output terminals of all reverse osmosis modules 10, 20, and 30 to the outside until the preset second condition is met.

[0065] Specifically, when the measured value of sensor S reaches a preset threshold, controller C will open all three-way control valves (V11 to V32) configured at the input and output ends of all reverse osmosis modules 10, 20, and 30 in the horizontal flow direction, and open the closed concentrate discharge valve DV. At this time, the operation of the second pump P2 can be stopped, or operated at the minimum Hz, or reversed and operated.

[0066] In the fourth operation step (S40), the first condition means that the measurement value of the sensor S configured on the movement path of the concentrated water B reaches a preset benchmark (e.g., a threshold of at least one of concentration, salinity, flow rate, pressure, and scale amount) or a preset time has elapsed after the third operation step (S30).

[0067] Furthermore, in the fourth operation step (S40), the second condition refers to the concentration of concentrated water B reaching a preset initial concentration.

[0068] The concentrated water discharge valve DV is in a shielded state during the first operation step (S10) to the third operation step (S30), and then opens in the fourth operation step (S40) to discharge concentrated water B when the first condition is met. After that, it switches back to the shielded state when the second condition is met.

[0069] The first operation step (S10) to the fourth operation step (S40) described above can be defined as a batch process, and will be simply referred to as "one batch".

[0070] In one embodiment of a sequential cycle reverse osmosis desalination apparatus, the running direction of the reverse osmosis module is reset each time a batch is completed.

[0071] For example, in the first batch, if the first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30 operate in the forward, forward, and reverse directions respectively, then in the second batch, the first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30 operate in the forward, reverse, and forward directions respectively; in the third batch, the first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30 operate in the reverse, forward, and forward directions respectively; and in the fourth batch, the first reverse osmosis module 10, the second reverse osmosis module 20, and the third reverse osmosis module 30 can operate in the same way as in the first batch, in the forward, forward, and reverse directions respectively.

[0072] However, this is just one example, and the number of forward and reverse directions can vary depending on the number of reverse osmosis modules, and the reset order of the running directions can also be modified in various ways.

[0073] That is, the controller C can determine the object of reverse operation in real time based on the measurement values ​​of the sensors S of each reverse osmosis module, and determine the operating direction of each reverse osmosis module according to the judgment result.

[0074] For example, if the pressure of the concentrate B in each reverse osmosis module is measured, and it is found that the pressure of a particular reverse osmosis module is high due to unpredictable reasons, then that particular reverse osmosis module needs to be reversed to intentionally remove dirt or scale. Therefore, even if it is time to reverse other reverse osmosis modules according to the preset schedule, the schedule can be changed to reverse the specific reverse osmosis module.

[0075] Fifth operating step (5) thStep 4 is the process of resetting the operating direction of the reverse osmosis module after a batch of operations from the first operation step (S10) to the fourth operation step (S40) is completed. Figure 5 This is a schematic diagram showing a sequential cycle reverse osmosis desalination unit performing the fifth operation step.

[0076] In the fifth operating step (S50), the controller C controls the relevant three-way control valves (at least four of V11 to V32) to convert either the first reverse osmosis module 10 or the second reverse osmosis module 20, which is operating in the forward direction, into a reverse reverse osmosis module, and to convert the previously reverse-operating third reverse osmosis module 30 into a forward reverse osmosis module.

[0077] When raw water R is injected into the reverse osmosis module, its concentration increases towards the downstream end, thus increasing the probability of scale formation. Furthermore, as scale accumulates, the total flux decreases, leading to performance degradation. Therefore, periodically reversing the injection direction of raw water R can eliminate some of the scale through injection pressure, while simultaneously reducing the formation rate of both biofouling and scale within the reverse osmosis module.

[0078] On the other hand, controller C can execute the fifth operation step (S50) immediately after completing a batch of processes, or it can execute the fifth operation step (S50) only when preset conditions are met after repeating multiple batches of processes.

[0079] Figure 6 This is a graph showing the reduction in the time of pressure increase during one batch process of a reverse osmosis desalination apparatus for each repeated sequential cycle according to an embodiment of the present invention, from the first operating step to the fourth operating step.

[0080] refer to Figure 6In a typical closed-circuit reverse osmosis (CCRO) process, when the reverse osmosis module is continuously circulated through a batch process, the time for the pressure of the discharged concentrate B to increase decreases with each batch repetition. However, in this invention, before the CCRO process of mixing concentrate B and raw water R, the concentrate B discharged from the forward reverse osmosis module flows into the backward reverse osmosis module to periodically reverse the injection direction of the raw water. This slows down the formation rate of biofouling and scale in the reverse osmosis module and removes some of the scale, thereby shortening the reduction in the pressure increase time of the concentrate and extending the Clean in Place (CIP) cycle.

[0081] The above description refers to several embodiments of the present invention. However, those skilled in the art will understand that various modifications and alterations can be made to the present invention without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A sequential circulation reverse osmosis desalination device, characterized in that, Each of a plurality of forward reverse osmosis modules is connected in parallel with at least one reverse reverse osmosis module, and the concentrated water discharged from the forward reverse osmosis module flows into the reverse reverse osmosis module, and the concentrated water discharged from the reverse reverse osmosis module flows into each of the forward reverse osmosis modules. The sequential circulation reverse osmosis desalination unit includes: Feed pump, supplies raw water. The first pump is connected to the output end of the feed pump. The second pump is connected to the output terminal of the forward and reverse osmosis module. The third pump is connected to the output terminal of the first pump. Three-way control valves are respectively configured at the input and output ends of the multiple forward reverse osmosis modules and the reverse reverse osmosis module, and The controller, in a first operating step, controls the feed pump and the first pump to allow raw water to enter the plurality of the forward and reverse osmosis modules, and in a second operating step, controls the second pump to allow concentrated water discharged from the forward and reverse osmosis modules to enter the reverse osmosis modules; In the third operating step, when the concentrated water discharged from the reverse osmosis module merges with the raw water and enters the forward reverse osmosis module, the third pump is activated without additional control. The controller is configured to: In the fourth operation step, when the preset first condition is met, the three-way control valve is controlled to convert the reverse osmosis module into a forward reverse osmosis module, and raw water is continuously supplied to the input end of all reverse osmosis modules and the concentrated water at the output end of all reverse osmosis modules is discharged to the outside until the preset second condition is met.

2. The sequential circulation reverse osmosis desalination device according to claim 1, characterized in that, The first and second pumps are high-pressure pumps, and the third pump is a jet pump that uses the flow of concentrated water to accelerate the raw water in the third operation step.

3. The sequential circulation reverse osmosis desalination device according to claim 1, characterized in that, The following condition shall be used as the first condition: The measurement value of at least one of the concentration sensor, flow sensor, and pressure sensor configured on the movement path of the concentrated water reaches a preset reference value, or a preset time has elapsed after the third operation step.

4. The sequential circulation reverse osmosis desalination device according to claim 3, characterized in that, The following conditions shall be used as the second condition: The concentration of the concentrated water reaches the preset initial concentration.

5. The sequential circulation reverse osmosis desalination device according to claim 3, characterized in that, The controller is configured to: After completing a batch of processes from the first operation step to the fourth operation step, a fifth operation step is performed, in which the three-way control valve is controlled to convert at least one of the plurality of forward reverse osmosis modules into a reverse reverse osmosis module and to convert an existing reverse reverse osmosis module into a forward reverse osmosis module.

6. The sequential circulation reverse osmosis desalination device according to claim 5, characterized in that, After executing multiple batches of the aforementioned processes, the controller executes the fifth operation step.

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