Load temperature control system

Abstract

To provide a load temperature control system capable of precisely controlling a secondary side outlet temperature even when a flow rate of a secondary side fluid of a heat exchanger largely varies over a relatively short period of time.SOLUTION: A load temperature control system includes a control valve that controls a flow rate of a primary side fluid which is supplied to a heat exchanger, a controller that controls an opening degree of the control valve, a secondary side outlet temperature meter that measures a secondary side outlet temperature, and a secondary side outlet flowmeter that measures a secondary side outlet flow rate. The control valve includes at least one master control valve and one slave control valve whose rated flow rate is smaller than the rated flow rate of the master control valve., where the master control valve and the slave control valve are arranged in parallel. The controller controls, on a feedforward basis, the opening degree of the master control valve according to the secondary side outlet flow rate, and controls, on a feedback basis, the opening degree of the slave control valve according to the secondary side outlet temperature.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a load temperature control system that controls the temperature of a load. [Background technology]

[0002] There are systems that control a load, such as a production device installed in a factory, at a predetermined temperature. For example, one such system supplies a secondary fluid that has undergone heat exchange with a primary fluid in a heat exchanger to the load. In this system, the flow rate of the primary fluid supplied from a heat source to the heat exchanger is controlled by a flow control valve to control the temperature of the secondary fluid supplied to the load at a predetermined temperature. The system disclosed in Patent Document 1 below feedback-controls the opening of a flow control valve provided on the primary side of the heat exchanger based on the secondary outlet temperature of the heat exchanger. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-148686 Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the load, the flow rate of the secondary fluid (load flow rate) may fluctuate significantly in a relatively short period of time during startup or temperature control (for example, the flow rate of the secondary fluid may fluctuate by more than 50% of the maximum flow rate). In this case, the flow rate of the primary fluid must also be fluctuated significantly, which means that the opening of the flow control valve must be changed significantly to the point where it falls outside the effective opening range for flow control. In this case, the flow rate fluctuations cannot be absorbed by controlling the opening of the flow control valve, and the flow rate of the primary fluid fluctuates significantly as the opening of the flow control valve changes. As a result, the secondary outlet temperature repeatedly hunts, leading to a decrease in temperature controllability for the load.

[0005] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a load temperature control system that can accurately control the secondary-side outlet temperature, and therefore the load temperature, even when the flow rate of the secondary-side fluid in a heat exchanger fluctuates significantly in a relatively short period of time. [Means for solving the problem]

[0006] To solve the above-mentioned problems, a first aspect of the present disclosure relates to a load temperature control system that supplies a load with a secondary fluid that has undergone heat exchange in a heat exchanger. The load temperature control system includes a control valve that controls the flow rate of the primary fluid supplied to the heat exchanger and a control device that controls the aperture of the control valve. The load temperature control system further includes a secondary outlet thermometer that measures a secondary outlet temperature, which is the temperature of the secondary fluid at a secondary outlet of the heat exchanger, and a secondary outlet flow meter that measures a secondary outlet flow rate, which is the flow rate of the secondary fluid at the secondary outlet. The control valve includes at least one parent control valve and one child control valve that has a rated flow rate smaller than the rated flow rate of the parent control valve, which are arranged in parallel. The control device feedforward controls the aperture of the parent control valve based on the secondary outlet flow rate, and feedback controls the aperture of the child control valve based on the secondary outlet temperature.

[0007] The second aspect has the following characteristics in addition to the first aspect: The load temperature control system further includes a secondary inlet thermometer that measures a secondary inlet temperature, which is the temperature of the secondary fluid at the secondary inlet of the heat exchanger. The control device feedback-controls the opening of the sub-control valve based on the heat quantity calculated from the secondary outlet flow rate and the temperature difference obtained by subtracting the secondary inlet temperature from the secondary outlet temperature.

[0008] The third aspect has the following feature in addition to the first or second aspect: Two or more parent control valves are provided. As a result, even if the flow rate of the secondary fluid in the heat exchanger fluctuates significantly in a relatively short period of time, the opening of the parent control valves is more likely to remain within an opening range in which flow rate control is effective, compared to when one parent control valve is provided. Furthermore, when the opening of a leading parent control valve reaches a predetermined upper limit opening and the control device starts controlling the opening of a trailing parent control valve, the control device maintains the opening of the leading parent control valve at the upper limit opening, thereby suppressing disturbances in the flow rate of the primary fluid. [Effects of the Invention]

[0009] According to the present disclosure, the aperture of the parent control valve is feedforward controlled based on the secondary outlet flow rate, and any flow rate shortfall caused by the parent control valve aperture control is compensated for by feedback control of the child control valve aperture based on the secondary outlet temperature. This allows the parent control valve to absorb any significant fluctuations in the flow rate of the secondary fluid in the heat exchanger over a relatively short period of time, thereby enabling the child control valve to operate within an aperture range where flow rate control is effective. This allows for accurate control of the secondary outlet temperature and, ultimately, the temperature of the load. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a configuration of a load temperature control system according to an embodiment. [Figure 2] FIG. 4 is a diagram showing the opening degrees of a parent control valve and a child control valve. [Figure 3] (a) is a diagram showing the change in supply volume when the required load increases, (b) is a diagram showing the change in the opening degree of the leading parent control valve, (c) is a diagram showing the change in the opening degree of the trailing parent control valve, and (d) is a diagram showing the change in the opening degree of the child control valve. [Figure 4] (a) is a diagram showing the disturbance in supply volume due to the start of control of the trailing parent control valve, (b) is a diagram showing the change in the opening degree of the leading parent control valve, and (c) is a diagram showing the change in the opening degree of the trailing parent control valve. [Figure 5]FIG. 10 is a schematic diagram showing the configuration of a load temperature control system according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Common or corresponding elements in each drawing are designated by the same reference numerals, and descriptions thereof will be simplified or omitted. In each drawing, illustration of some components may be omitted for convenience of drawing.

[0012] FIG. 1 is a schematic diagram showing the configuration of a load temperature control system 1 according to an embodiment. The load temperature control system 1 is a system that controls the temperature of a load 10 to a predetermined temperature. The load 10 is, for example, a production device or a measurement device installed in a factory (not shown). The load 10 is not limited to these production devices, and may be any device that requires temperature control.

[0013] The load temperature control system 1 includes a heat exchanger 2, a heat source 3, a primary line 4, flow control valves (hereinafter referred to as "control valves") AV1 to AV3, a secondary line 5, a secondary outlet flow meter 6, a secondary outlet thermometer 7, and a pump PU.

[0014] The heat exchanger 2 is configured to be able to exchange heat between a primary fluid flowing through a primary line 4 and a secondary fluid flowing through a secondary line 5. A known heat exchanger can be used as the heat exchanger 2, and a detailed description thereof will be omitted here. The heat source 3 is, for example, a boiler that generates steam. In this embodiment, the primary fluid is steam, the secondary fluid is hot water (water), and the secondary fluid at a predetermined temperature (for example, 95°C to 98°C) is supplied to the load 10. In this case, the temperature of the secondary fluid flowing through a secondary return pipe 52 (described later) is expected to be, for example, 70°C to 80°C.

[0015] The primary line 4 connects the heat exchanger 2 and the heat source 3 and includes a primary-side forward piping 41 and a primary-side return piping 42. The primary-side return piping 42 is provided with at least one (two in this embodiment) control valve (hereinafter referred to as "parent control valve") AV1, AV2 having a relatively large rated flow rate, and one control valve (hereinafter referred to as "child control valve") AV3 having a rated flow rate smaller than the rated flow rates of the parent control valves AV1, AV2, in parallel. The parent control valves AV1, AV2 can be selected, for example, at 60% of the primary-side rated flow rate. The child control valve AV3 can be selected, for example, at 30% of the primary-side rated flow rate. In other words, the child control valve AV3 can be smaller than the parent control valves AV1, AV2. The parent control valves AV1, AV2 and the child control valve AV3 can be, for example, globe valves of different sizes and rated flow rates. Known globe valves can be used, and detailed description thereof will be omitted here. The number of parent control valves AV1, AV2 can be set appropriately according to the primary-side rated flow rate flowing through the primary-side line 4. A bypass valve BV is installed in parallel with the control valves AV1, AV2, AV3 in a bypass pipe 43 branching off from the primary-side return pipe 42, so that the primary-side fluid can be bypassed in the event of a failure of the control valves AV1, AV2, AV3. Note that the bypass pipe 43 and bypass valve BV can be omitted in consideration of the failure rate of the multiple control valves AV1, AV2, AV3.

[0016] The secondary-side line 5 connects the heat exchanger 2 and the load 10 and includes a secondary-side forward piping 51 and a secondary-side return piping 52. The secondary-side forward piping 51 is provided with a secondary-side outlet flow meter 6 and a secondary-side outlet thermometer 7. The secondary-side outlet flow meter 6 is a flow meter that measures the flow rate FM of the secondary-side fluid at the secondary-side outlet of the heat exchanger 2 (hereinafter referred to as the "secondary-side outlet flow rate" or "load flow rate"). The secondary-side outlet thermometer 7 is a thermometer that measures the temperature TE1 of the secondary-side fluid at the secondary-side outlet of the heat exchanger 2 (hereinafter referred to as the "secondary-side outlet temperature"). As will be described later, the secondary-side outlet flow rate FM is used for feedforward control of the parent control valves AV1 and AV2, and the secondary-side outlet temperature TE1 is used for feedback control of the child control valve AV3. In addition, a pump PU is provided in the secondary-side return piping 52 to circulate the secondary-side fluid. As the secondary side outlet flow meter 6, the secondary side outlet thermometer 7 and the pump PU, known ones can be used, and therefore detailed description thereof will be omitted here.

[0017] The load temperature control system 1 includes a control device 11. The control device 11 includes a processor 111 and a memory 112. The memory 112 stores programs for causing the load temperature control system 1 to function, and also temporarily stores measured and calculated values ​​of the secondary outlet flow meter 6, the secondary outlet thermometer 7, and the secondary inlet thermometer 8 described below. The processor 111 performs overall control of the load temperature control system 1, including control of the opening degrees of the parent control valves AV1 and AV2 and the child control valve AV3, in accordance with the programs stored in the memory 112.

[0018] However, when the control valve on the primary side of the heat exchanger is feedback-controlled based on the secondary outlet temperature of the heat exchanger as in the above-mentioned conventional example, if the secondary outlet flow rate (load flow rate) fluctuates significantly, the flow rate of the primary fluid (required flow rate) required to control the load 10 to a predetermined temperature also fluctuates significantly. As a result, the opening of the control valve changes significantly, and accordingly, the secondary outlet temperature repeatedly hunts against the set temperature.

[0019] Therefore, in this embodiment, the control valves are divided into parent control valves AV1, AV2 and a child control valve AV3, and as described below, the parent control valves AV1, AV2 are feedforward controlled and the child control valve AV3 is feedback controlled. Figure 2 shows the apertures of the parent control valves AV1, AV2 and the child control valve AV3. Figure 3(a) shows the change in supply amount when the required load increases, Figure 3(b) shows the change in aperture of the leading parent control valve AV1, Figure 3(c) shows the change in aperture of the trailing parent control valve AV2, and Figure 3(d) shows the change in aperture of the child control valve AV3.

[0020] First, the apertures of the parent control valves AV1 and AV2 are feedforward controlled based on the secondary outlet flow rate FM measured by the secondary outlet flow meter 6. The relationship between the secondary outlet flow rate FM and the apertures of the parent control valves AV1 and AV2, as shown in FIG. 2, is stored in the memory 112 as a mathematical formula or map. As shown in FIG. 3(a), the feedforward control portion of the parent control valves AV1 and AV2 is responsible for the base flow rate, which accounts for the majority of the flow rate of the primary fluid required to control the load 10 to a predetermined temperature (hereinafter referred to as the "required flow rate"). Here, the base flow rate is set so that the remainder after subtracting the base flow rate from the required flow rate (i.e., the shortfall in flow rate made up by the child control valve AV3) can be effectively flow-controlled by controlling the aperture of the child control valve AV3.

[0021] Then, small fluctuations in the shortage flow rate, which is the required flow rate minus the base flow rate, are handled by the feedback control of the secondary control valve AV3 (see FIG. 3(a)). The opening of the secondary control valve AV3 is feedback controlled based on the secondary outlet temperature TE1 measured by the secondary outlet thermometer 7. The relationship between the secondary outlet temperature TE1, shown in a box in FIG. 2, and the opening of the secondary control valve AV3 is stored in the memory 112 as a formula or map.

[0022] Next, we will explain the opening control of each control valve AV1, AV2, AV3 when the required flow rate increases with an increase in the load flow rate. When the required flow rate increases at time t0 (see Figure 3(a)), control of the parent control valves AV1 and AV2 is not initiated until time t1 when the required flow rate reaches the reference amount, i.e., while the required flow rate is relatively low, and only control of the child control valve AV3 is performed, as shown in Figure 3(d). The opening of the child control valve AV3 is feedback-controlled based on the secondary-side outlet temperature TE1. The reference amount can be set appropriately according to the rated flow rates of the parent control valves AV1 and AV2.

[0023] Subsequently, at time t1, when the required flow rate reaches the reference amount as shown in FIG. 3(a), control of the leading parent control valve AV1 begins as shown in FIG. 3(b). That is, the opening of the parent control valve AV1 is feedforward controlled based on the secondary outlet flow rate FM (see FIG. 2). Simultaneously, feedback control of the child control valve AV3 based on the secondary outlet temperature TE1 continues. As a result, the majority of the required flow rate is handled by the feedforward control of the parent control valve AV1, and the remaining shortfall is compensated for by the feedback control of the child control valve AV3. Even if the load flow rate and the required flow rate fluctuate significantly, the feedforward control of the parent control valve AV1 absorbs the fluctuations, allowing the child control valve AV3 to operate within the opening range in which flow control is effective. Note that control of the trailing parent control valve AV2 does not begin until the opening of the leading parent control valve AV1 reaches a preset upper limit (e.g., 100% VOmax shown in FIG. 3(b)). The upper limit VOmax is not limited to 100% and can be set taking into account the opening range in which flow control is effective. For example, if the upper limit value of the opening range is set as the upper limit opening VOmax, the controllability of the supply amount handled by the master control valve AV1 can be improved, which is advantageous.

[0024] At time t2, when the opening of parent control valve AV1 reaches the upper limit opening VOmax (100%) as shown in Figure 3(b), control of the following parent control valve AV2 begins as shown in Figure 3(c). That is, the opening of parent control valve AV2 is feedforward controlled based on the secondary outlet flow rate FM (see Figure 2). At the same time, feedback control of child control valve AV3 based on the secondary outlet temperature TE1 continues. Similarly, even if the load flow rate and required flow rate fluctuate greatly, these fluctuations can be absorbed by the feedforward control of parent control valves AV1 and AV2, allowing child control valve AV3 to operate within the opening range in which flow rate control is effective.

[0025] Here, at time t2, as shown in FIG. 4(c), when the opening control of the trailing parent control valve AV2 is started, if the openings of the two parent control valves AV1 and AV2 are controlled to be the same, the opening of the leading parent control valve AV1 decreases as shown in FIG. 4(b). At the same time, the opening of the trailing parent control valve AV2 rapidly increases as shown in FIG. 4(c). In this way, when the trailing parent control valve AV2 is rapidly opened, the flow rate of the primary fluid (hereinafter also referred to as the "supply rate") supplied to the heat exchanger 2 becomes excessive (excessive) relative to the required flow rate. Starting from this, a large fluctuation (hunting) in the supply rate relative to the required flow rate occurs, as shown by the dashed-dotted line in FIG. 4(a).

[0026] In contrast, in this embodiment, after time t2 when control of the trailing parent control valve AV2 begins, the opening of the leading parent control valve AV1 is maintained at a preset upper limit opening VOmax (100%). That is, after the leading parent control valve AV1 stops at the upper limit opening VOmax (100%), the trailing parent control valve AV2 is sequentially operated. At this time, because the opening of the leading parent control valve AV1 does not decrease, the opening of the trailing parent control valve AV2 gradually increases after time t2. This makes it possible to suppress fluctuations in the supply amount after time t2 compared to when the openings of the parent control valves AV1 and AV2 are controlled to be the same (see FIG. 3(a)).

[0027] Furthermore, after time t1, feedback control of the opening of the child control valve AV3 is also continuously executed. By making the child control valve AV3, whose opening is constantly changed by feedback control, smaller than the parent control valves AV1 and AV2, the controllability of the supply amount can be improved.

[0028] As described above, according to this embodiment, the apertures of the parent control valves AV1 and AV2 are feedforward controlled based on the secondary outlet flow rate FM, and any flow rate shortfall caused by the aperture control of the parent control valves AV1 and AV2 is compensated for by feedback control of the aperture of the child control valve AV3 based on the secondary outlet temperature TE1. As a result, even if the flow rate of the secondary fluid in the heat exchanger 2 fluctuates significantly over a relatively short period of time, the fluctuations can be absorbed by the feedforward control of the parent control valves AV1 and AV2, and the child control valve AV3 can be constantly operated within the aperture range in which flow rate control is effective. This makes it possible to accurately control the secondary outlet temperature, and ultimately the temperature of the load 10.

[0029] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments and can be implemented in various modifications without departing from the spirit of the present disclosure. In the above embodiments, the case where globe valves are used as the control valves AV1 to AV3 has been described as an example, but the present disclosure is not limited to this and valves that can control the flow rate depending on the opening degree, such as butterfly valves, can also be used.

[0030] In the above embodiment, two parent control valves AV1 and AV2 are used. However, it is also possible to use a single parent control valve. In this case, a large-diameter control valve is used as the parent control valve. Therefore, when the flow rate (required flow rate) handled by the parent control valve is low, the parent control valve opens only slightly, which may reduce the controllability of the supply rate handled by the parent control valve. In contrast, by using two or more parent control valves AV1 and AV2 as in the above embodiment, the opening of each parent control valve AV1 and AV2 is larger than when a single parent control valve is used, even when the flow rate handled by each parent control valve AV1 and AV2 is small. This reduces the possibility of a reduction in the controllability of the supply rate handled by each parent control valve AV1 and AV2. Furthermore, by sequentially operating (stopping) two or more parent control valves AV1 and AV2, it is possible to suppress disturbances in the flow rate of the primary fluid, as in the above embodiment.

[0031] In the above embodiment, the case where the secondary fluid is heated by heat exchange in the heat exchanger 2 has been described as an example, but the present disclosure can also be applied to a case where the secondary fluid is cooled by heat exchange. Also, in the above embodiment, the case where the required flow rate increases as the load flow rate increases has been described as an example, but the present disclosure can also be applied to a case where the required flow rate decreases as the load flow rate decreases.

[0032] In the above embodiment, the same main control valves AV1 and AV2 are used, but different main control valves may also be used.

[0033] Depending on the load 10, the return temperature of the secondary-side fluid flowing from the secondary-side return pipe 52 into the secondary-side inlet of the heat exchanger 2 (hereinafter referred to as the "secondary-side inlet temperature") may become higher than expected. In this case, the temperature difference between the secondary-side outlet temperature TE1 and the secondary-side inlet temperature TE2 may become smaller than expected, and a situation may arise in which the primary-side fluid (steam) is supplied to the primary side of the heat exchanger 2 at an excessive flow rate. This situation is likely to occur when the load 10 is started up.

[0034] FIG. 5 is a schematic diagram showing the configuration of a load temperature control system 1 according to a modified example. The load temperature control system 1 shown in FIG. 5 further includes a secondary-side inlet thermometer 8. The secondary-side inlet thermometer 8 is a thermometer that measures the temperature TE2 of the secondary-side fluid at the secondary-side inlet of the heat exchanger 2 (hereinafter referred to as the "secondary-side inlet temperature"). The control device 11 calculates the heat quantity by multiplying the secondary-side outlet flow rate FM by the temperature difference (TE2-TE1) obtained by subtracting the secondary-side inlet temperature TE2 from the secondary-side outlet temperature TE1. Based on the calculated heat quantity, the control device 11 feedback-controls the aperture of the secondary control valve AV3. In this case, the relationship between the heat quantity and the aperture of the secondary control valve AV3 may be stored in the memory 112. According to this modified example, feedback-controlling the aperture of the secondary control valve AV3 based on the heat quantity can prevent the primary-side fluid (steam) from being supplied to the primary side of the heat exchanger 2 at an excessive flow rate, even when the temperature difference between the secondary-side outlet temperature TE1 and the secondary-side inlet temperature TE2 is smaller than expected. [Explanation of symbols]

[0035] 1...Load temperature control system, 2...Heat exchanger, 3...Heat source, 4...Primary side line, 41...Primary side forward piping, 42...Primary side return piping, 5...Secondary side line, 51...Secondary side forward piping, 52...Secondary side return piping, 6...Secondary side outlet flow meter, 7...Secondary side outlet thermometer, 8...Secondary side inlet thermometer, 10...Load, 11...Control device, AV1, AV2...Parent control valve (control valve), AV3...Child control valve (control valve), FM...Secondary side outlet flow rate, PU...Pump, TE1...Secondary side outlet temperature, TE2...Secondary side inlet temperature, VOmax...Upper limit opening

Claims

1. A load temperature control system that controls the temperature of a load by supplying a secondary fluid that has been heat exchanged in a heat exchanger to the load, a control valve for controlling the flow rate of a primary fluid supplied to the heat exchanger; and a control device for controlling the opening degree of the control valve, a secondary-side outlet thermometer that measures a secondary-side outlet temperature, which is the temperature of the secondary-side fluid at the secondary-side outlet of the heat exchanger; a secondary-side outlet flow meter that measures a secondary-side outlet flow rate, which is a flow rate of the secondary-side fluid at the secondary-side outlet; The control valves include at least one parent control valve and one child control valve arranged in parallel, the child control valve having a rated flow rate less than the rated flow rate of the parent control valve; A load temperature control system in which the control device feedforward controls the opening of the parent control valve based on the secondary outlet flow rate, and feedback controls the opening of the child control valve based on the secondary outlet temperature.

2. a secondary-side inlet thermometer for measuring a secondary-side inlet temperature, which is the temperature of the secondary-side fluid at the secondary-side inlet of the heat exchanger; 2. The load temperature control system of claim 1, wherein the control device feedback controls the opening of the sub-control valve based on the heat quantity calculated from the secondary outlet flow rate and the temperature difference obtained by subtracting the secondary inlet temperature from the secondary outlet temperature.

3. 3. The load temperature control system according to claim 1, Two or more parent control valves are provided; A load temperature control system in which the control device maintains the opening of the preceding parent control valve at a predetermined upper limit opening when the opening of the preceding parent control valve reaches the predetermined upper limit opening and starts controlling the opening of the following parent control valve.

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