Superheating device and control method for superheated steam temperature by superheating device

Abstract

To provide a superheating device that can prevent high-temperature corrosion of superheating pipes, and a control method for a superheated steam temperature by the superheating device.SOLUTION: A superheating device according to an embodiment of the present invention comprises a first heat exchanger for superheating superheated steam in a superheating pipe in a first region in an exhaust gas flow passage, a second heat exchanger for superheating the superheated steam in a superheating pipe in a second region upstream of the first region in an exhaust gas flow direction in the exhaust gas flow passage, an inlet temperature decreasing device for decreasing an inlet steam temperature in an introducing pipe for introducing the superheated steam into the superheating pipe of the first heat exchanger, an outlet temperature measuring part for measuring an outlet steam temperature after superheating by the second heat exchanger, and a control unit for controlling the inlet steam temperature at a saturated temperature or higher at an inlet pressure of the first heat exchanger on the basis of the outlet steam temperature, and controlling the outlet steam temperature at a superheated steam temperature below 600°C. The superheating pipe of the second heat exchanger has higher corrosion resistance than that of the superheating pipe of the first heat exchanger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a superheating device for superheating steam and a method for controlling the temperature of superheated steam by the superheating device.

Background Art

[0002] Conventionally, a boiler installed in a furnace such as a waste treatment furnace (incinerator) for incinerating garbage and industrial waste is provided with a superheating device that superheats the steam generated by the boiler using the heat of the exhaust gas discharged from the furnace. Generally, the superheating device includes a plurality of superheaters composed of superheating tubes for superheating the steam generated by the boiler, and superheats the steam in the superheating tubes to a high temperature in multiple stages through heat exchange with the exhaust gas discharged from the furnace. The steam (superheated steam) superheated by the superheating device is supplied from the superheating device to an external device such as a steam turbine via a pipe and consumed as driving energy for the external device.

[0003] For example, as the plurality of superheaters, Patent Documents 1 and 2 disclose a primary superheater (first superheater) that superheats the steam from the boiler to generate superheated steam, a secondary superheater (second superheater) that further superheats the superheated steam after being superheated by the primary superheater, and a tertiary superheater (third superheater) that further superheats the superheated steam after being superheated by the secondary superheater and sends it to an external device. These primary superheater, secondary superheater, and tertiary superheater are in a state where the respective superheating tubes are connected in series, and are arranged inside an exhaust gas flow path such as a flue through which the exhaust gas from the furnace flows. Specifically, as disclosed in Patent Document 1, these three superheaters are arranged in the order of tertiary superheater, secondary superheater, and primary superheater from the upstream side (high temperature side) to the downstream side (low temperature side) in the flow direction of the exhaust gas. Alternatively, as disclosed in Patent Document 2, the secondary superheater is arranged on the upstream side in the flow direction of the exhaust gas, the primary superheater is arranged on the downstream side, and the tertiary superheater is arranged between these two superheaters.

[0004] In the above three superheaters, each superheater tube of the secondary superheater and the tertiary superheater is located in an environment (high-temperature environment) where it comes into contact with flue gas at a higher temperature than the superheater tubes of the primary superheater arranged on the downstream side in the flue gas flow direction. In addition to this, superheated steam at a higher temperature than the superheater tubes of the primary superheater flows through each superheater tube of the secondary superheater and the tertiary superheater. Therefore, the surface temperature of each superheater tube of these secondary superheater and tertiary superheater becomes higher than the surface temperature of the superheater tubes of the primary superheater. Such superheater tubes in a high-temperature state may be corroded (high-temperature corrosion) by contact with corrosive gases contained in the flue gas from the furnace.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to prevent the high-temperature corrosion of the superheater tubes described above, for example, it is effective to employ a build-up tube formed by build-up welding a corrosion-resistant material on the outer periphery of the superheater tube, thereby improving the corrosion resistance of the superheater tube in a high-temperature environment. As the superheater tube, it is also conceivable to employ a metal tube with lower corrosion resistance than the build-up tube, but in this case, since it is necessary to control the surface temperature of the superheater tube to be lower, it becomes difficult to prevent the high-temperature corrosion of the superheater tube.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a superheating device capable of preventing high-temperature corrosion of a superheater tube and a method for controlling the superheated steam temperature by the superheating device.

Means for Solving the Problems

[0008] In order to solve the above-described problems and achieve the object, a superheater according to the present invention is provided in a boiler that generates steam using the heat of exhaust gas discharged from a furnace, and is a superheater that superheats the steam by heat exchange with the exhaust gas. The superheater has superheater tubes in a first region in an exhaust gas flow path through which the exhaust gas flows, and a first heat exchanger that superheats superheated steam in the superheater tubes in the first region by heat exchange with the exhaust gas. The superheater has superheater tubes in a second region that is in the exhaust gas flow path and is an upstream region in the flow direction of the exhaust gas with respect to the first region, and a second heat exchanger that superheats superheated steam in the superheater tubes in the second region by heat exchange with the exhaust gas. An inlet desuperheater that supplies cooling water into an introduction pipe that introduces superheated steam into the superheater tubes of the first heat exchanger to lower the inlet steam temperature, which is the temperature of the superheated steam in the introduction pipe. An outlet temperature measuring unit that measures the outlet steam temperature, which is the temperature of the superheated steam superheated by the second heat exchanger and sent from the superheater tubes of the second heat exchanger to an outlet pipe. A control unit that controls the supply amount of the cooling water by the inlet desuperheater based on the outlet steam temperature, controls the inlet steam temperature to be equal to or higher than the saturation temperature at the inlet pressure of the first heat exchanger, and controls the outlet steam temperature to be a superheated steam temperature of less than 600°C. The superheater tubes of the second heat exchanger are characterized by having higher corrosion resistance than the superheater tubes of the first heat exchanger.

[0009] Further, the superheater according to the present invention is, in the above invention, characterized in that the superheater tubes of the second heat exchanger are tubes including at least one of a stainless steel tube and a cladding tube having a corrosion-resistant cladding layer on the outer wall surface of the steel tube.

[0010] Further, the superheater according to the present invention is, in the above invention, characterized in that the superheater tubes of the first heat exchanger are tubes including at least one of a carbon steel tube and a stainless steel tube.

[0011] Further, in the superheating device according to the present invention, in the above invention, a superheating tube is provided in a downstream region within the exhaust gas flow path, which is a region downstream of the first region in the flow direction of the exhaust gas, and a superheater that superheats the steam in the superheating tube in the downstream region by heat exchange with the exhaust gas to generate superheated steam is further provided.

[0012] Further, in the superheating device according to the present invention, in the above invention, the introduction pipe is a communication pipe that communicates the outlet of the superheating tube of the primary superheater and the inlet of the superheating tube of the first heat exchanger.

[0013] Further, in the superheating device according to the present invention, in the above invention, a communication pipe that communicates the outlet of the superheating tube of the first heat exchanger and the inlet of the superheating tube of the second heat exchanger is further provided.

[0014] Further, in the superheating device according to the present invention, in the above invention, a superheating tube is provided in an intermediate region within the exhaust gas flow path between the first region and the second region, an intermediate superheater that superheats the superheated steam in the superheating tube in the intermediate region by heat exchange with the exhaust gas, a first communication pipe that communicates the outlet of the superheating tube of the first heat exchanger and the inlet of the superheating tube of the intermediate superheater, and a second communication pipe that communicates the outlet of the superheating tube of the intermediate superheater and the inlet of the superheating tube of the second heat exchanger are further provided.

[0015] Further, in the superheating device according to the present invention, in the above invention, a superheating tube is provided in a third region within the exhaust gas flow path, which is a region upstream of the second region in the flow direction of the exhaust gas, a third heat exchanger that superheats the superheated steam in the superheating tube in the third region by heat exchange with the exhaust gas, a desuperheater that supplies cooling water to the superheated steam flowing into the superheating tube of the third heat exchanger to lower the temperature of the flowing superheated steam, and a communication pipe that communicates the outlet of the superheating tube of the third heat exchanger and the inlet of the superheating tube of the first heat exchanger are further provided.

[0016] Moreover, the method for controlling the superheated steam temperature by the superheating device according to the present invention includes a first heat exchanger that superheats superheated steam in a superheating tube disposed in a first region within an exhaust gas flow path through which exhaust gas discharged from a furnace flows, by heat exchange with the exhaust gas, and a second heat exchanger that superheats superheated steam in a superheating tube disposed in a second region within the exhaust gas flow path, which is a region upstream of the first region in the flow direction of the exhaust gas, by heat exchange with the exhaust gas. In the method for controlling the superheated steam temperature by the superheating device, a temperature measurement step of measuring an outlet steam temperature, which is the temperature of the superheated steam superheated by the second heat exchanger and sent from the superheating tube of the second heat exchanger to an outlet tube, a water supply amount control step of controlling the supply amount of cooling water into an introduction tube that introduces superheated steam into the superheating tube of the first heat exchanger based on the outlet steam temperature, and a temperature control step of controlling the inlet steam temperature, which is the temperature of the superheated steam in the introduction tube, to be equal to or higher than the saturation temperature at the inlet pressure of the first heat exchanger by supplying the cooling water with the supply amount, and controlling the outlet steam temperature to a superheated steam temperature of less than 600°C. The superheating tube of the second heat exchanger is characterized by having higher corrosion resistance than the superheating tube of the first heat exchanger.

Advantages of the Invention

[0017] According to the present invention, there is an effect that high-temperature corrosion of the superheating tube can be prevented.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

[0019] Hereinafter, with reference to the accompanying drawings, preferred embodiments of the superheater and the method for controlling the superheated steam temperature by the superheater according to the present invention will be described in detail. Note that the present invention is not limited by the present embodiment. Also, the drawings are schematic, and it should be noted that the dimensional relationships between elements, the ratios of the elements, etc. may be different from the actual ones. There may also be portions where the dimensional relationships and ratios are different between the drawings. In each drawing, the same reference numerals are assigned to the same components.

[0020] (Embodiment 1) First, the superheater according to Embodiment 1 of the present invention will be described in detail. FIG. 1 is a block diagram showing a configuration example of the superheater according to Embodiment 1 of the present invention. The superheater 10 according to Embodiment 1 of the present invention is provided, for example, in a boiler (not shown), and is a device that superheats the steam generated by the boiler by heat exchange with the exhaust gas discharged from a furnace (not shown). Specifically, as shown in FIG. 1, the superheater 10 includes a primary superheater 1, a secondary superheater 2, a tertiary superheater 3, an inlet desuperheater 11, an outlet temperature measuring unit 12, and a control unit 15. The superheater 10 also includes a steam pipe 100, communication pipes 101 and 102, and an outlet pipe 104 as pipes through which the steam to be superheated or the superheated steam flows.

[0021] In the present specification, the boiler is, for example, a heat recovery type boiler that is arranged beside a furnace and generates steam using the heat of the exhaust gas discharged from the furnace. Examples of the furnace include a waste treatment furnace (incinerator) that incinerates garbage and industrial waste, a combustion furnace that burns fuel, and the like. Hereinafter, unless otherwise specified, the term "steam" means steam generated by the boiler, and the term "exhaust gas" means exhaust gas discharged from the furnace.

[0022] The primary superheater 1, the secondary superheater 2, and the tertiary superheater 3 are examples of a plurality of superheaters that superheat steam in multiple stages by heat exchange with exhaust gas. For example, as shown in FIG. 1, the primary superheater 1, the secondary superheater 2, and the tertiary superheater 3 are arranged inside the exhaust gas flow path 200 so as to be aligned in the flow direction of the exhaust gas (the direction of the thick arrow shown in FIG. 1). The exhaust gas flow path 200 is a flow path through which exhaust gas flows, such as a flue provided in a furnace or a boiler.

[0023] In the first embodiment, as shown in FIG. 1, the internal region of the exhaust gas flow path 200 is divided into an upstream region 201, an intermediate region 202, and a downstream region 203 in the flow direction of the exhaust gas. The upstream region 201 is a region inside the exhaust gas flow path 200 that is upstream of the intermediate region 202 and the downstream region 203 in the flow direction of the exhaust gas. The downstream region 203 is a region inside the exhaust gas flow path 200 that is downstream of the upstream region 201 and the intermediate region 202 in the flow direction of the exhaust gas. The intermediate region 202 is a region inside the exhaust gas flow path 200 that is downstream of the upstream region 201 in the flow direction of the exhaust gas and upstream of the downstream region 203 in the flow direction of the exhaust gas.

[0024] As shown in FIG. 1, the primary superheater 1 is disposed in the exhaust gas flow path 200 such that the superheater tubes 1a are located in the downstream region 203 within the exhaust gas flow path 200. The superheater tubes 1a are formed of, for example, carbon steel tubes such as STB, and have a tube shape that reciprocates multiple times between the opposing inner walls of the exhaust gas flow path 200, and are disposed in the downstream region 203 within the exhaust gas flow path 200. As shown in FIG. 1, a steam pipe 100 is connected to the inlet of the superheater tubes 1a. The steam pipe 100 is a pipe that communicates with a boiler drum (not shown) that accumulates steam generated by the boiler. The superheater tubes 1a communicate with the boiler drum via the steam pipe 100. Further, as shown in FIG. 1, a communication pipe 101 is connected to the outlet of the superheater tubes 1a. The communication pipe 101 is an example of an introduction pipe that introduces superheated steam into the superheater tubes of the first heat exchanger of the present invention. In the first embodiment, the communication pipe 101 is a pipe that introduces the superheated steam 111 to be superheated into the superheater tubes 2a of the secondary superheater 2, which is the first heat exchanger, and as shown in FIG. 1, it connects the outlet of the superheater tubes 1a of the primary superheater 1 and the inlet of the superheater tubes 2a of the secondary superheater 2.

[0025] The primary superheater 1 having such a configuration superheats steam by heat exchange with the exhaust gas to generate superheated steam. Specifically, the primary superheater 1 receives the steam 110 generated by the boiler from the boiler drum through the steam pipe 100 into the inside of the superheater tubes 1a. The primary superheater 1 circulates the received steam 110 from the inlet side to the outlet side of the superheater tubes 1a, and superheats the steam 110 in the superheater tubes 1a by heat exchange with the exhaust gas 212 in the downstream region 203. Thereby, the primary superheater 1 generates superheated steam 111 that is at a higher temperature than the steam 110. The primary superheater 1 sends out the generated superheated steam 111 from the outlet of the superheater tubes 1a into the inside of the communication pipe 101. Although not particularly shown, the exhaust gas 213 used for heat exchange with the steam 110 in the superheater tubes 1a becomes cooler than the exhaust gas 212 before being used for this heat exchange, and is discharged to the outside of the boiler from the exhaust gas flow path 200 via a chimney or the like, for example.

[0026] The secondary superheater 2 has superheater tubes in the first region within the exhaust gas flow path 200, and is an example of a first heat exchanger (also referred to as the first heat exchanger of the present invention) that superheats the superheated steam in the superheater tubes in the first region by heat exchange with the exhaust gas. In Embodiment 1, the first region is the intermediate region 202 within the exhaust gas flow path 200. That is, as shown in FIG. 1, the secondary superheater 2 is disposed within the exhaust gas flow path 200 such that it has superheater tubes 2a in the intermediate region 202 within the exhaust gas flow path 200.

[0027] Specifically, the superheater tubes 2a have the same tube shape as the superheater tubes 1a of the primary superheater 1 described above, and are disposed in the intermediate region 202 within the exhaust gas flow path 200 as shown in FIG. 1. At the inlet of the superheater tubes 2a, as shown in FIG. 1, the above-described communication pipe 101 is connected. The superheater tubes 2a communicate with the superheater tubes 1a of the primary superheater 1 via the communication pipe 101. Further, at the outlet of the superheater tubes 2a, as shown in FIG. 1, a communication pipe 102 is connected. The communication pipe 102 is a pipe that communicates the outlet of the superheater tubes 1a of the secondary superheater 2 and the inlet of the superheater tubes 3a of the tertiary superheater 3.

[0028] The metal tubes constituting such superheater tubes 2a are selected so as to prevent high-temperature corrosion of the superheater tubes 2a in a temperature environment considering both the temperature of the superheated steam flowing through the superheater tubes 2a and the temperature of the exhaust gas in the intermediate region 202 that contacts the outer wall surface of the superheater tubes 2a. For example, the superheater tubes 2a are preferably tubes including at least one of a carbon steel tube and a stainless steel tube (SUS tube). That is, the superheater tubes 2a having a tube shape that reciprocates a plurality of times between the opposing inner walls of the exhaust gas flow path 200 may be constituted only by carbon steel tubes, may be constituted only by stainless steel tubes, or may be constituted by combining a carbon steel tube and a stainless steel tube (for example, joining the two steel tubes in series, etc.). Among these, from the viewpoint of corrosion resistance, the superheater tubes 2a are particularly preferably stainless steel tubes having higher corrosion resistance than the superheater tubes 1a of the primary superheater 1 described above.

[0029] The secondary superheater 2 having the above-described configuration further superheats the superheated steam through heat exchange with the exhaust gas. Specifically, the secondary superheater 2 receives the superheated steam 111 generated by the primary superheater 1 from the primary superheater 1 through the communication pipe 101 into the interior of the superheater tube 2a. While causing the received superheated steam 111 to flow from the inlet side to the outlet side of the superheater tube 2a, the secondary superheater 2 further superheats the superheated steam 111 in the superheater tube 2a by heat exchange with the exhaust gas 211 in the intermediate region 202. Thereby, the secondary superheater 2 generates superheated steam 112 at a temperature higher than that of the superheated steam 111. Note that the exhaust gas 211 in the intermediate region 202 is a gas at a higher temperature than the exhaust gas 212 (i.e., the exhaust gas used for heat exchange with the superheated steam 111 in the superheater tube 2a) in the downstream region 203 described above. The secondary superheater 2 sends out the generated superheated steam 112 from the outlet of the superheater tube 2a into the interior of the communication pipe 102.

[0030] The tertiary superheater 3 is an example of a second heat exchanger (also referred to as the second heat exchanger of the present invention) that has a superheater tube in a second region which is a region upstream of the first region in the exhaust gas flow path 200 in the exhaust gas flow direction, and superheats the superheated steam in the superheater tube in the second region by heat exchange with the exhaust gas. In the first embodiment, the second region is the upstream region 201 in the exhaust gas flow path 200. Note that the first region is the intermediate region 202 in the exhaust gas flow path 200 as described above. That is, as shown in FIG. 1, the tertiary superheater 3 is arranged in the exhaust gas flow path 200 so as to have a superheater tube 3a in the upstream region 201 in the exhaust gas flow path 200.

[0031] Specifically, the superheater tube 3a has the same tube shape as the superheater tube 1a of the primary superheater 1 or the superheater tube 2a of the secondary superheater 2 described above, and as shown in FIG. 1, is disposed in the upstream region 201 within the exhaust gas flow path 200. As shown in FIG. 1, the communication pipe 102 described above is connected to the inlet of the superheater tube 3a. The superheater tube 3a communicates with the superheater tube 2a of the secondary superheater 2 via the communication pipe 102. Further, as shown in FIG. 1, an outlet pipe 104 is connected to the outlet of the superheater tube 3a. The outlet pipe 104 is a pipe for sending the superheated steam superheated by the second heat exchanger (the tertiary superheater 3 in the first embodiment of the present invention) to the outside of the superheating device 10. For example, the outlet end of the outlet pipe 104 communicates with an external device (not shown) via a steam drum (not shown) of the boiler or the like. The external device is a device that is driven using superheated steam as driving energy, such as a turbine of a generator.

[0032] The metal pipe constituting such a superheater tube 3a is selected so as to be able to prevent high-temperature corrosion of the superheater tube 3a in a temperature environment considering both the temperature of the superheated steam flowing through the superheater tube 3a and the temperature of the exhaust gas in the upstream region 201 contacting the outer wall surface of the superheater tube 3a. That is, the superheater tube 3a of the tertiary superheater 3 is composed of a metal tube having higher corrosion resistance than the superheater tube 2a of the secondary superheater 2 described above. For example, the superheater tube 3a is preferably a tube including at least one of a stainless steel tube and a cladded tube. That is, the superheater tube 3a having a tube shape that reciprocates a plurality of times between the opposing inner walls of the exhaust gas flow path 200 may be composed only of a stainless steel tube, may be composed only of a cladded tube, or may be composed by combining a stainless steel tube and a cladded tube (for example, joining the two steel tubes in series). The cladded tube is a tube having a corrosion-resistant cladding layer on the outer wall surface of the steel tube and has higher corrosion resistance than a carbon steel tube and a stainless steel tube. For example, the corrosion-resistant cladding layer can be formed by cladding welding a corrosion-resistant metal material on the outer wall surface (outer peripheral surface) of a steel tube such as a carbon steel tube. Examples of the corrosion-resistant metal material include chromium, alloys containing chromium, and the like. From the viewpoint of improving corrosion resistance, the superheater tube 3a is preferably a cladded tube. Further, when the superheater tube 3a is a cladded tube, the thickness of the steel tube constituting the cladded tube (thickness excluding the cladding layer) is preferably 2 mm or more, and the nickel content in the metal material (cladding material) of the cladding layer is more preferably 50% or more.

[0033] The tertiary superheater 3 having the above-described configuration further superheats the superheated steam to a higher temperature by heat exchange with the exhaust gas. Specifically, the tertiary superheater 3 receives the superheated steam 112 after being superheated by the secondary superheater 2 from the secondary superheater 2 into the interior of the superheater tube 3a via the communication pipe 102. While causing the received superheated steam 112 to flow from the inlet side to the outlet side of the superheater tube 3a, the tertiary superheater 3 further superheats the superheated steam 112 in the superheater tube 3a by heat exchange with the exhaust gas 210 in the upstream region 201. Thereby, the tertiary superheater 3 generates superheated steam 114 at a higher temperature than the superheated steam 112. Note that the exhaust gas 210 in the upstream region 201 is a gas at a higher temperature than the exhaust gas 211 (i.e., the exhaust gas used for heat exchange with the superheated steam 112 in the superheater tube 3a) in the above-described intermediate region 202. The tertiary superheater 3 sends out the generated superheated steam 114 from the superheater tube 3a into the interior of the outlet pipe 104. The high-temperature superheated steam 114 superheated by the tertiary superheater 3 in this way is supplied from the outlet pipe 104 to an external device via a steam drum of the boiler or the like, and is consumed as driving energy for the external device.

[0034] Note that each of the superheater tubes 1a, 2a, and 3a of the primary superheater 1, the secondary superheater 2, and the tertiary superheater 3 described above is piped such that the flow of steam or superheated steam from the superheater inlet to the superheater outlet is a countercurrent with respect to the flow direction of the exhaust gas, as shown in FIG. 1, for example. However, in the present invention, each of the superheater tubes 1a, 2a, and 3a may be piped such that the flow of the above-described steam or superheated steam is a parallel flow with respect to the flow direction of the exhaust gas. Alternatively, each of the superheater tubes 1a, 2a, and 3a may include a superheater tube piped to be the countercurrent and a superheater tube piped to be the parallel flow.

[0035] The inlet desuperheater 11 is an example of a desuperheater that supplies cooling water into an introduction pipe that introduces superheated steam into the superheater tube of the first heat exchanger of the present invention to lower the inlet steam temperature T1, which is the temperature of the superheated steam in the introduction pipe. In the first embodiment, as described above, the first heat exchanger is the secondary superheater 2, and the introduction pipe is the communication pipe 101. That is, as shown in FIG. 1, the inlet desuperheater 11 supplies cooling water into the communication pipe 101 to lower the inlet steam temperature T1.

[0036] Specifically, the inlet desuperheater 11 is composed of a water supply pipe for supplying cooling water and a water supply mechanism (not shown) such as a pump, and an adjustment valve (not shown) for adjusting the supply amount of the cooling water. As shown in FIG. 1, it is provided in the middle of the communication pipe 101. Based on the control by the control unit 15, the inlet desuperheater 11 supplies cooling water into the communication pipe 101, thereby reducing the inlet steam temperature T1, which is the temperature of the superheated steam 111 in the communication pipe 101. The supply amount of the cooling water into the communication pipe 101 increases by increasing the opening degree of the adjustment valve of the inlet desuperheater 11 and decreases by decreasing the opening degree. The superheated steam 111 after desuperheating by the inlet desuperheater 11 flows from the communication pipe 101 into the superheating pipe 2a of the secondary superheater 2.

[0037] The outlet temperature measuring unit 12 is an example of a temperature measuring unit that measures the temperature of the superheated steam after superheating by the second heat exchanger of the present invention, that is, the outlet steam temperature T2, which is the temperature of the superheated steam sent from the superheating pipe of the second heat exchanger to the outlet pipe. In the first embodiment, the second heat exchanger is the tertiary superheater 3 as described above. That is, as shown in FIG. 1, the outlet temperature measuring unit 12 measures the outlet steam temperature T2 in the outlet pipe 104 that communicates with the outlet of the superheating pipe 3a of the tertiary superheater 3.

[0038] Specifically, as shown in FIG. 1, the outlet temperature measuring unit 12 is provided in the middle of the outlet pipe 104. As described above, the superheated steam 114 after superheating by the tertiary superheater 3 is sent from the superheating pipe 3a into the outlet pipe 104. The outlet temperature measuring unit 12 measures the outlet steam temperature T2, which is the temperature of the superheated steam 114 flowing through the outlet pipe 104. Each time, the outlet temperature measuring unit 12 transmits an electric signal indicating the obtained outlet steam temperature T2 to the control unit 15. Note that the outlet temperature measuring unit 12 may continuously measure the outlet steam temperature T2 along the time series, may intermittently measure it at a predetermined time interval, or may measure it based on a measurement command from the control unit 15.

[0039] The control unit 15 controls the above-described inlet steam temperature T1 and outlet steam temperature T2. Specifically, the control unit 15 is composed of a CPU, a memory, etc. for executing various programs. In the first embodiment 1, the control unit 15 controls the supply amount of the cooling water by the inlet desuperheater 11 based on the outlet steam temperature T2 measured by the outlet temperature measuring unit 12. Thereby, the control unit 15 controls the inlet steam temperature T1 of the superheated steam 111 flowing into the superheating tube 2a of the secondary superheater 2 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2. And the control unit 15 controls the outlet steam temperature T2 of the superheated steam 114 in the outlet pipe 104 to a superheated steam temperature of less than 600 °C (that is, equal to or higher than the saturation temperature of the superheated steam 114 and less than 600 °C). In the first embodiment 1, the saturation temperature of the superheated steam 114 is the saturation temperature at the outlet pressure of the tertiary superheater 3.

[0040] From the viewpoint of preventing the drainage (water droplet formation) of the superheated steam 111, the lower limit value of the inlet steam temperature T1 controlled by the control unit 15 is preferably equal to or higher than the temperature (Ta + Tm) obtained by adding a predetermined margin temperature Tm to the saturation temperature Ta of the superheated steam 111.

[0041] Also, from the viewpoint of ensuring the driving energy (energy of the superheated steam) required for an external device such as a turbine, the lower limit value of the outlet steam temperature T2 controlled by the control unit 15 is preferably equal to or higher than the temperature of the superheated steam 112 after superheating by the secondary superheater 2, for example, preferably higher than 300 °C. The upper limit value of the outlet steam temperature T2 is preferably 500 °C or lower from the viewpoint of facilitating the prevention of high-temperature corrosion of the superheating tube 3a of the tertiary superheater 3.

[0042] Next, a method for controlling the superheated steam temperature by the superheating device according to Embodiment 1 of the present invention will be described. FIG. 2 is a flowchart showing an example of a method for controlling the superheated steam temperature by the superheating device according to Embodiment 1 of the present invention. The above-described superheating device 10 (see FIG. 1) controls the temperature of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 (inlet steam temperature T1) and the temperature of the superheated steam 114 sent from the superheating tube 3a of the tertiary superheater 3 into the outlet pipe 104 (outlet steam temperature T2) by executing each process of steps S101 to S103 shown in FIG. 2.

[0043] Specifically, as shown in FIG. 2, the superheating device 10 measures the temperature of the superheated steam after superheating by the second heat exchanger of the present invention (step S101). In step S101, the outlet temperature measuring unit 12 measures the temperature of the superheated steam 114 after superheating by the tertiary superheater 3, that is, the outlet steam temperature T2 in the outlet pipe 104. The outlet temperature measuring unit 12 transmits an electric signal indicating the measured outlet steam temperature T2 to the control unit 15.

[0044] After executing the temperature measurement process of step S101, the superheating device 10 controls the supply amount of cooling water for reducing the temperature of the superheated steam introduced into the superheating tube of the first heat exchanger of the present invention (step S102). In step S102, the control unit 15 controls the supply amount of cooling water into the communication pipe 101 through which the superheated steam 111 is introduced into the superheating tube 2a of the secondary superheater 2 based on the outlet steam temperature T2 obtained in step S101.

[0045] In the present Embodiment 1, a reference outlet steam temperature T2s, which is the above-described reference value of the outlet steam temperature T2, is preset in the control unit 15. For example, the reference outlet steam temperature T2s has the outlet steam temperature T2 when the above-described inlet steam temperature T1 becomes the same temperature as the saturation temperature Ta at the inlet pressure of the secondary superheater 2 as the lower limit temperature, and is set within a temperature range of 600°C or less above the lower limit temperature.

[0046] Based on the electrical signal received from the outlet temperature measuring unit 12, the control unit 15 obtains the outlet steam temperature T2 in step S101. The control unit 15 calculates the steam temperature difference ΔT2, which is the difference between the obtained outlet steam temperature T2 and the reference outlet steam temperature T2s. Next, the control unit 15 calculates the supply amount of the cooling water to be supplied into the communication pipe 101 to eliminate the steam temperature difference ΔT2 (make ΔT2 = 0), and calculates the opening degree of the regulating valve of the inlet desuperheater 11 necessary to supply the cooling water of this supply amount into the communication pipe 101. Thereafter, the control unit 15 transmits a control signal instructing the calculated opening degree as the opening degree of the regulating valve to the inlet desuperheater 11. Thereby, the control unit 15 controls the opening degree of the regulating valve, and controls the supply amount of the cooling water through the control of the opening degree.

[0047] After executing the feed water control process in step S102, the superheater 10 controls the temperature of the superheated steam introduced into the superheating pipe of the first heat exchanger of the present invention and the temperature of the superheated steam after superheating by the second heat exchanger of the present invention (step S103), and ends this process. In step S103, based on the control signal from the control unit 15, the inlet desuperheater 11 obtains the instructed opening degree, and adjusts the opening degree of the regulating valve to the obtained opening degree. Subsequently, the inlet desuperheater 11 supplies (injects) the cooling water of the supply amount corresponding to the adjusted opening degree into the communication pipe 101. Thereby, the inlet desuperheater 11 reduces the temperature of the superheated steam 111 introduced from the communication pipe 101 into the superheating pipe 2a of the secondary superheater 2, that is, the inlet steam temperature T1.

[0048] With the decrease in this inlet steam temperature T1, the temperature of the superheated steam 112 after superheating by the secondary superheater 2 decreases, and accordingly, the temperature of the superheated steam 114 after superheating by the tertiary superheater 3 (that is, the outlet steam temperature T2) decreases. In this way, the control unit 15 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C.

[0049] After executing the temperature control process of step S103, the superheater 10 repeatedly executes each process of steps S101 to S103 as necessary. Thereby, the superheater 10 sequentially controls the inlet steam temperature T1 and the outlet steam temperature T2 over time.

[0050] As described above, in the superheater 10 according to Embodiment 1 of the present invention, the temperature of the superheated steam 114 after superheating by the tertiary superheater 3 (second heat exchanger), that is, the outlet steam temperature T2 in the outlet pipe 104, is measured, and the supply amount of cooling water into the communication pipe 101 that introduces the superheated steam 111 into the superheating pipe 2a of the secondary superheater 2 (first heat exchanger) is controlled based on the measured outlet steam temperature T2. By supplying the cooling water of the supply amount into the communication pipe 101, the inlet steam temperature T1 in the communication pipe 101 is controlled to be equal to or higher than the saturation temperature at the inlet pressure of the secondary superheater 2, and the outlet steam temperature T2 in the outlet pipe 104 is controlled to a superheated steam temperature of less than 600°C. Further, in the superheater 10, the superheating pipe 3a of the tertiary superheater 3 is configured to have higher corrosion resistance than the superheating pipe 2a of the secondary superheater 2.

[0051] Therefore, the temperature of the superheated steam 114 supplied from the superheating pipe 3a of the tertiary superheater 3 to an external device such as a turbine via the outlet pipe 104 or the like can be controlled to a temperature sufficient to ensure the driving energy required for the external device, and the temperature of the superheated steam 111 introduced into the superheating pipe 2a of the secondary superheater 2 that contacts the relatively high-temperature exhaust gas can be reduced as much as possible with the saturation temperature at the inlet pressure of the secondary superheater 2 as the lower limit. As a result, the degree of freedom in selecting a metal pipe that can be used for the superheating pipe 2a of the secondary superheater 2 increases, so that a metal pipe having corrosion resistance and being less expensive than the superheating pipe 3a of the tertiary superheater 3 can be easily selected as the superheating pipe 2a. As a result, high-temperature corrosion of the superheating pipes 2a and 3a can be prevented.

[0052] (Embodiment 2) Next, the superheating device according to Embodiment 2 of the present invention will be described in detail. FIG. 3 is a block diagram showing a configuration example of the superheating device according to Embodiment 2 of the present invention. As shown in FIG. 3, the superheating device 20 according to Embodiment 2 further includes a temperature measuring unit 13 that measures the inlet steam temperature T1 in addition to the outlet temperature measuring unit 12 of the superheating device 10 according to Embodiment 1 described above, and includes a control unit 25 instead of the control unit 15 described above. Other configurations are the same as those in Embodiment 1, and the same reference numerals are given to the same components.

[0053] The temperature measuring unit 13 is an example of a temperature measuring unit that measures the temperature of superheated steam (that is, the inlet steam temperature T1) in the introduction pipe that introduces superheated steam into the superheating pipe of the first heat exchanger of the present invention. In Embodiment 2, as in Embodiment 1 described above, the first heat exchanger is the secondary superheater 2, and the introduction pipe is the communication pipe 101. That is, as shown in FIG. 3, the temperature measuring unit 13 measures the temperature of the superheated steam 111 introduced from the communication pipe 101 into the superheating pipe 2a of the secondary superheater 2.

[0054] Specifically, as shown in FIG. 3, the temperature measuring unit 13 is provided in the middle of the communication pipe 101 between the superheating pipe 2a of the secondary superheater 2 and the inlet desuperheater 11. The superheated steam 111 in the communication pipe 101 flows from the primary superheater 1 side to the secondary superheater 2 side as in Embodiment 1 described above, is desuperheated by the inlet desuperheater 11, and then is introduced into the superheating pipe 2a of the secondary superheater 2. The temperature measuring unit 13 measures the temperature of the superheated steam 111 introduced from the communication pipe 101 into the superheating pipe 2a of the secondary superheater 2 after being desuperheated by the inlet desuperheater 11, that is, the inlet steam temperature T1 in the communication pipe 101. Each time, the temperature measuring unit 13 transmits an electrical signal indicating the obtained inlet steam temperature T1 to the control unit 25. Note that the temperature measuring unit 13 may continuously measure the inlet steam temperature T1 along the time series, may intermittently measure it at a predetermined time interval, or may measure it based on a measurement command from the control unit 25.

[0055] The control unit 25 is composed of a CPU, a memory, etc. for executing various programs, and controls the above-described inlet steam temperature T1 and outlet steam temperature T2. Specifically, in the second embodiment, the control unit 25 sets a reference value of the inlet steam temperature T1 based on the outlet steam temperature T2 measured by the outlet temperature measuring unit 12, and eliminates the difference between the set reference value of the inlet steam temperature T1 and the measured value of the inlet steam temperature T1 by the temperature measuring unit 13. Thus, the control unit 25 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2 and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C, in the same manner as in the first embodiment described above. Note that the upper and lower limit values of each of the inlet steam temperature T1 and the outlet steam temperature T2 controlled by the control unit 25 are the same as those in the first embodiment described above.

[0056] Next, a method for controlling the superheated steam temperature by the superheating device according to the second embodiment of the present invention will be described. The superheating device 20 (see FIG. 3) according to the second embodiment executes each process substantially the same as the steps S101 to S103 (see FIG. 2) of the first embodiment described above, thereby controlling the temperature of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 (inlet steam temperature T1) and the temperature of the superheated steam 114 sent from the superheating tube 3a of the tertiary superheater 3 into the outlet pipe 104 (outlet steam temperature T2).

[0057] That is, in the superheating device 20 according to the second embodiment, in step S101, the outlet temperature measuring unit 12 measures the outlet steam temperature T2 in the outlet pipe 104 in the same manner as in the first embodiment described above, and transmits an electric signal indicating the measured outlet steam temperature T2 to the control unit 25. Further, the temperature measuring unit 13 measures the temperature of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 after being cooled by the inlet desuperheater 11, that is, the inlet steam temperature T1 in the communication pipe 101. The temperature measuring unit 13 transmits an electric signal indicating the measured inlet steam temperature T1 to the control unit 25.

[0058] Also, in the superheating device 20 according to the second embodiment, in step S102, the control unit 25 controls the supply amount of cooling water into the communication pipe 101 that introduces the superheated steam 111 into the superheating pipe 2a of the secondary superheater 2 based on the inlet steam temperature T1 and the outlet steam temperature T2 obtained in the above step S101.

[0059] Specifically, in the second embodiment, the control unit 25 is preset with the initial inlet steam temperature T1d which is the initial value of the above-mentioned inlet steam temperature T1, and the reference value (reference outlet steam temperature T2s) of the above-mentioned outlet steam temperature T2. For example, the initial inlet steam temperature T1d has the saturation temperature Ta of the superheated steam 111 at the inlet pressure of the secondary superheater 2 as the lower limit temperature, and the inlet steam temperature T1 when the above-mentioned outlet steam temperature T2 reaches its upper limit temperature (less than 600°C) as the upper limit temperature, and is set within the temperature range of not less than the lower limit temperature and not more than the upper limit temperature. Note that the reference outlet steam temperature T2s in the second embodiment is the same as that in the first embodiment described above.

[0060] In step S102 of the second embodiment, the control unit 25 obtains the outlet steam temperature T2 obtained in the above step S101 based on the electrical signal received from the outlet temperature measurement unit 12, and obtains the inlet steam temperature T1 obtained in the above step S101 based on the electrical signal received from the temperature measurement unit 13. The control unit 25 calculates the difference (steam temperature difference ΔT2) between the obtained outlet steam temperature T2 and the reference outlet steam temperature T2s, and sets the reference inlet steam temperature T1s which is the reference value of the inlet steam temperature T1 based on the steam temperature difference ΔT2.

[0061] For example, when the steam temperature difference ΔT2 is a value calculated by ΔT2 = T2 - T2s, the control unit 25 subtracts a predetermined value from the initial inlet steam temperature T1d according to the steam temperature difference ΔT2, and sets the value obtained thereby as the reference inlet steam temperature T1s. Or, when the steam temperature difference ΔT2 is a value calculated by ΔT2 = T2s - T2, the control unit 25 adds a predetermined value to the initial inlet steam temperature T1d according to the steam temperature difference ΔT2, and sets the value obtained thereby as the reference inlet steam temperature T1s. That is, as the outlet steam temperature T2 rises to a temperature higher than the reference outlet steam temperature T2s, the control unit 25 sets the reference inlet steam temperature T1s as low as possible within the limit of the lower limit temperature of the inlet steam temperature T1. Also, as the outlet steam temperature T2 drops to a temperature lower than the reference outlet steam temperature T2s, the control unit 25 sets the reference inlet steam temperature T1s as high as possible within the limit of the upper limit temperature of the inlet steam temperature T1. Note that when the outlet steam temperature T2 is the same value as the reference outlet steam temperature T2s, the control unit 25 may set the initial inlet steam temperature T1d as the reference inlet steam temperature T1s.

[0062] Next, the control unit 25 calculates the steam temperature difference ΔT1, which is the difference between the above-described inlet steam temperature T1 and the reference inlet steam temperature T1s, and calculates the supply amount of the cooling water to be supplied into the communication pipe 101 in order to eliminate the steam temperature difference ΔT1 (make ΔT1 = 0). Thereafter, the control unit 25 calculates the opening degree of the regulating valve of the inlet desuperheater 11 based on the calculated supply amount of the cooling water, and transmits a control signal instructing the calculated opening degree to the inlet desuperheater 11, in the same manner as in the above-described Embodiment 1, thereby adjusting the opening degree of the regulating valve to control the supply amount of the cooling water.

[0063] Note that in the second embodiment, the process of step S103 is the same as that in the above-described first embodiment. Thereby, the control unit 25 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature lower than 600°C. Also, after executing the process of step S103, the superheating device 20 repeatedly executes the processes of steps S101 to S103 as necessary. Thereby, the superheating device 20 sequentially controls the inlet steam temperature T1 and the outlet steam temperature T2 in time series.

[0064] As described above, in the superheating device 20 according to the second embodiment of the present invention, based on the difference between the measured value of the outlet steam temperature T2 in the outlet pipe 104 and the reference value, the reference value (reference inlet steam temperature T1s) of the inlet steam temperature T1 in the communication pipe 101 is set, and the supply amount of the cooling water into the communication pipe 101 is controlled so that the difference between the inlet steam temperature T1 measured by the temperature measuring unit 13 and the reference inlet steam temperature T1s disappears, thereby controlling the inlet steam temperature T1 and the outlet steam temperature T2. The rest is the same as in the first embodiment. Therefore, the same operational effects as those of the above-described first embodiment are enjoyed, and the reference inlet steam temperature T1s can be set to be changeable according to the increase or decrease of the outlet steam temperature T2 in the outlet pipe 104, and the supply amount of the cooling water into the communication pipe 101 can be controlled so that the difference between the reference inlet steam temperature T1s and the inlet steam temperature T1 disappears. As a result, the inlet steam temperature T1 and the outlet steam temperature T2 can be easily controlled to desired temperatures.

[0065] (Embodiment 3) Next, the superheating device according to the third embodiment of the present invention will be described in detail. FIG. 4 is a block diagram showing a configuration example of the superheating device according to the third embodiment of the present invention. As shown in FIG. 4, the superheating device 30 according to the third embodiment includes a first desuperheater 16 and a second desuperheater 17 instead of the inlet desuperheater 11 of the superheating device 20 according to the second embodiment described above, and includes a control unit 35 instead of the control unit 25. Other configurations are the same as those in the second embodiment, and the same reference numerals are given to the same components.

[0066] The first desuperheater 16 is a desuperheater having the same configuration and function as the inlet desuperheater 11 (see FIG. 3) of the second embodiment described above. That is, as shown in FIG. 4, the first desuperheater 16 is provided in the middle of the communication pipe 101, and supplies cooling water into the communication pipe 101 based on the control by the control unit 35. Thereby, the first desuperheater 16, like the inlet desuperheater 11, reduces the temperature (inlet steam temperature T1) of the superheated steam 111 in the communication pipe 101. The superheated steam 111 after being desuperheated by the first desuperheater 16 flows from the communication pipe 101 into the superheating pipe 2a of the secondary superheater 2.

[0067] The second desuperheater 17 is an example of a desuperheater that supplies cooling water into a second introduction pipe that introduces superheated steam into the superheated tubes of the second heat exchanger of the present invention, thereby reducing the temperature of the superheated steam in the second introduction pipe (hereinafter referred to as the intermediate steam temperature T3). In Embodiment 3, the second heat exchanger is the tertiary superheater 3 as in Embodiments 1 and 2 described above. As shown in FIG. 4, the second introduction pipe is a communication pipe 102 that introduces the superheated steam 112 after being superheated by the secondary superheater 2 into the superheated tubes 3a of the tertiary superheater 3. That is, the second desuperheater 17 supplies cooling water into the communication pipe 102 to reduce the intermediate steam temperature T3.

[0068] Specifically, the second desuperheater 17 is composed of a water supply pipe for supplying cooling water and a water supply mechanism (not shown) such as a pump, and an adjustment valve (not shown) for adjusting the supply amount of the cooling water. As shown in FIG. 4, it is provided in the middle of the communication pipe 102. Based on the control by the control unit 35, the second desuperheater 17 supplies cooling water into the communication pipe 102, thereby reducing the intermediate steam temperature T3, which is the temperature of the superheated steam 112 in the communication pipe 102. The supply amount of the cooling water into the communication pipe 102 increases by increasing the opening degree of the adjustment valve of the second desuperheater 17 and decreases by decreasing the opening degree. The superheated steam 112 after being desuperheated by the second desuperheater 17 flows from the communication pipe 102 into the superheated tubes 3a of the tertiary superheater 3.

[0069] The control unit 35 is composed of a CPU, a memory, etc. for executing various programs, and controls the above-described inlet steam temperature T1 and outlet steam temperature T2. Specifically, in the third embodiment, the control unit 35 sets a reference value of the inlet steam temperature T1 based on the measured value of the outlet steam temperature T2, similar to the case of the inlet desuperheater 11 in the second embodiment described above, and controls the supply amount of the cooling water by the first desuperheater 16 so as to eliminate the difference between the reference value and the measured value of the inlet steam temperature T1. Further, the control unit 35 controls the supply amount of the cooling water by the second desuperheater 17 so as to eliminate the difference between the reference value and the measured value of the outlet steam temperature T2. By controlling the first desuperheater 16 and the second desuperheater 17, the control unit 35 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature lower than 600°C. Note that the upper limit values and the lower limit values of the inlet steam temperature T1 and the outlet steam temperature T2 controlled by the control unit 35 are the same as those in the first and second embodiments described above.

[0070] Next, a method for controlling the superheated steam temperature by the superheating device according to the third embodiment of the present invention will be described. The superheating device 30 (see FIG. 4) according to the third embodiment executes each process substantially similar to steps S101 to S103 of the second embodiment described above, thereby controlling the temperature (inlet steam temperature T1) of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 and the temperature (outlet steam temperature T2) of the superheated steam 114 sent from the superheating tube 3a of the tertiary superheater 3 into the outlet pipe 104.

[0071] That is, in the superheating device 30 according to the third embodiment, after the process of step S101 is executed in the same manner as in the second embodiment described above, in step S102, the control unit 35 controls the supply amount of the cooling water into the communication pipe 101 for introducing the superheated steam 111 into the superheating tube 2a of the secondary superheater 2 and the supply amount of the cooling water into the communication pipe 102 for introducing the superheated steam 112 into the superheating tube 3a of the tertiary superheater 3 based on the inlet steam temperature T1 and the outlet steam temperature T2 obtained in step S101.

[0072] Specifically, in the third embodiment, the control unit 35 has the initial inlet steam temperature T1d and the reference outlet steam temperature T2s preset in the same manner as in the second embodiment described above. The control unit 35 calculates the difference (steam temperature difference ΔT2) between the outlet steam temperature T2 and the reference outlet steam temperature T2s in step S101 in the same manner as in the second embodiment described above, and sets the reference inlet steam temperature T1s based on the steam temperature difference ΔT2.

[0073] Next, the control unit 35 calculates the supply amount of the cooling water to be supplied into the communication pipe 101 in order to eliminate the difference (steam temperature difference ΔT1) between the inlet steam temperature T1 and the reference inlet steam temperature T1s in the same manner as in the second embodiment described above. The control unit 35 calculates the opening degree of the regulating valve of the first desuperheater 16 based on the calculated supply amount of the cooling water, and transmits a control signal instructing the calculated opening degree to the first desuperheater 16, thereby controlling the opening degree of the regulating valve to control the supply amount of the cooling water.

[0074] Furthermore, the control unit 35 calculates the supply amount of the cooling water to be supplied into the communication pipe 102 in order to eliminate the difference (steam temperature difference ΔT2) between the outlet steam temperature T2 and the reference outlet steam temperature T2s described above (make ΔT2 = 0). The control unit 35 calculates the opening degree of the regulating valve of the second desuperheater 17 required to supply the calculated amount of the cooling water into the communication pipe 102, and transmits a control signal instructing the calculated opening degree as the opening degree of the regulating valve to the second desuperheater 17. Thereby, the control unit 35 controls the opening degree of the regulating valve, and through this control of the opening degree, controls the supply amount of the cooling water by the second desuperheater 17.

[0075] Further, in the superheating device 30 according to the third embodiment, in step S103, the first desuperheater 16 adjusts the opening degree of the regulating valve based on the control signal from the control unit 35, in the same manner as in the case of the inlet desuperheater 11 described above, and supplies the cooling water with a supply amount corresponding to the adjusted opening degree into the communication pipe 101. Thereby, the first desuperheater 16 reduces the inlet steam temperature T1. Further, the second desuperheater 17 obtains the indicated opening degree based on the control signal from the control unit 35, and adjusts the opening degree of the regulating valve to the obtained opening degree. Subsequently, the second desuperheater 17 supplies (injects) the cooling water with a supply amount corresponding to the adjusted opening degree into the communication pipe 102. Thereby, the second desuperheater 17 reduces the temperature of the superheated steam 112 introduced from the communication pipe 102 into the superheating pipe 3a of the tertiary superheater 3, that is, the intermediate steam temperature T3. As the intermediate steam temperature T3 decreases, the temperature of the superheated steam 114 after superheating by the tertiary superheater 3 (that is, the outlet steam temperature T2) decreases. As described above, the control unit 35 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C.

[0076] Note that, in the third embodiment, after executing the process of step S103, the superheating device 30 repeatedly executes the processes of steps S101 to S103 as necessary. Thereby, the superheating device 30 sequentially controls the inlet steam temperature T1 and the outlet steam temperature T2 in time series.

[0077] As described above, in the superheating device 30 according to the third embodiment of the present invention, the supply amount of the cooling water by the first desuperheater 16 is controlled so that the difference between the measured value of the inlet steam temperature T1 and the reference value disappears, thereby controlling the inlet steam temperature T1. At the same time, the supply amount of the cooling water by the second desuperheater 17 is controlled so that the difference between the measured value of the outlet steam temperature T2 and the reference value disappears, thereby controlling the outlet steam temperature T2. The rest is the same as in the second embodiment. For this reason, the same operational effects as those of the above-described second embodiment are enjoyed, and the temperature of the superheated steam 114 sent from the superheating device 30 as the driving energy of the external device can be reduced as much as possible with the temperature required by the external device as the lower limit by cooling the superheated steam 112 by the second desuperheater 17. As a result, the degree of freedom in selecting the metal tube that can be employed for the superheating tube 3a of the tertiary superheater 3 increases, so that it is possible to ensure prevention of high-temperature corrosion of the superheating tube 3a.

[0078] (Embodiment 4) Next, the superheating device according to the fourth embodiment of the present invention will be described in detail. FIG. 5 is a block diagram showing a configuration example of the superheating device according to the fourth embodiment of the present invention. As shown in FIG. 5, the superheating device 40 according to the fourth embodiment further includes a quaternary superheater 4 in addition to the primary superheater 1, the secondary superheater 2, and the tertiary superheater 3 of the superheating device 30 according to the above-described third embodiment. The tertiary superheater 3 is used as the first heat exchanger of the present invention, and the quaternary superheater 4 is used as the second heat exchanger of the present invention. Further, the superheating device 40 includes a control unit 45 instead of the control unit 35 of the third embodiment described above. The other configurations are the same as those of the third embodiment, and the same reference numerals are given to the same components.

[0079] The primary superheater 1, the secondary superheater 2, the tertiary superheater 3, and the quaternary superheater 4 are examples of a plurality of superheaters that superheat steam in multiple stages by heat exchange with exhaust gas. For example, as shown in FIG. 5, the primary superheater 1, the secondary superheater 2, the tertiary superheater 3, and the quaternary superheater 4 are arranged inside the exhaust gas flow path 200 so as to be aligned in the exhaust gas flow direction.

[0080] In Embodiment 4, as shown in FIG. 5, the internal region of the exhaust gas flow path 200 is divided into an upstream region 201, intermediate regions 202A and 202B, and a downstream region 203 in the flow direction of the exhaust gas. The upstream region 201 is a region in the exhaust gas flow path 200 that is upstream of the intermediate regions 202A and 202B and the downstream region 203 in the flow direction of the exhaust gas. The downstream region 203 is a region in the exhaust gas flow path 200 that is downstream of the upstream region 201 and the intermediate regions 202A and 202B in the flow direction of the exhaust gas. The intermediate regions 202A and 202B are regions between the upstream region 201 and the downstream region 203 in the exhaust gas flow path 200. The intermediate region 202A is a region in the exhaust gas flow path 200 that is downstream of the upstream region 201 in the flow direction of the exhaust gas and upstream of one of the intermediate regions 202B in the flow direction of the exhaust gas. The intermediate region 202B is a region in the exhaust gas flow path 200 that is downstream of the intermediate region 202A in the flow direction of the exhaust gas and upstream of the downstream region 203 in the flow direction of the exhaust gas.

[0081] The primary superheater 1 of Embodiment 4 is the same as the primary superheater 1 of the above-described Embodiments 1 to 3, except that it is disposed in the downstream region 203 which is downstream of the intermediate region 202B in the exhaust gas flow path 200. That is, in Embodiment 4, the primary superheater 1 circulates the steam 110 received into the interior of the superheater tube 1a from the boiler drum via the steam pipe 100 from the inlet side to the outlet side of the superheater tube 1a, in the same manner as in the above-described Embodiments 1 to 3, and is superheated by heat exchange with the exhaust gas 213 in the downstream region 203. As a result, the primary superheater 1 generates superheated steam 111 that is hotter than the steam 110, and sends the generated superheated steam 111 from the outlet of the superheater tube 1a into the interior of the communication pipe 101. Although not particularly shown, the exhaust gas 214 used for heat exchange with the steam 110 in the superheater tube 1a becomes cooler than the exhaust gas 213 before being used for heat exchange, and is discharged, for example, outside the boiler from the exhaust gas flow path 200 via a chimney or the like.

[0082] Unlike the secondary superheater 2 in the above-described Embodiments 1 to 3, the secondary superheater 2 of the present Embodiment 4 is not the first heat exchanger of the present invention. As shown in FIG. 5, it is disposed in an intermediate region 202B downstream of the intermediate region 202A in the exhaust gas flow path 200. Except for these, the secondary superheater 2 of the present Embodiment 4 is the same as the secondary superheater 2 in the above-described Embodiments 1 to 3. That is, in the present Embodiment 4, the secondary superheater 2 causes the superheated steam 111 received into the inside of the superheater tube 2a from the primary superheater 1 via the communication pipe 101 to flow from the inlet side to the outlet side of the superheater tube 2a, and is further superheated by heat exchange with the exhaust gas 212 in the intermediate region 202B. Thereby, the secondary superheater 2 generates superheated steam 112 at a temperature higher than that of the superheated steam 111, and sends the generated superheated steam 112 from the outlet of the superheater tube 2a into the inside of the communication pipe 102. Note that the exhaust gas 212 in the intermediate region 202B is a gas at a temperature higher than that of the exhaust gas 213 in the downstream region 203 described above (that is, the exhaust gas used for heat exchange with the superheated steam 111 in the superheater tube 2a).

[0083] Further, in the present Embodiment 4, the metal tube constituting the superheater tube 2a is selected so as to prevent high-temperature corrosion of the superheater tube 2a in a temperature environment considering both the temperature of the superheated steam flowing through the inside of the superheater tube 2a and the temperature of the exhaust gas in the intermediate region 202B that contacts the outer wall surface of the superheater tube 2a. Examples of such a superheater tube 2a include a carbon steel pipe, a stainless steel pipe, or a pipe in which a carbon steel pipe and a stainless steel pipe are combined by series joining or the like. Among these, a carbon steel pipe is preferable as the superheater tube 2a.

[0084] Unlike the tertiary superheater 3 in the above-described Embodiments 1 to 3, the tertiary superheater 3 of the present Embodiment 4 is an example of the first heat exchanger rather than the second heat exchanger of the present invention. As described above, the first heat exchanger has a superheater tube in the first region in the exhaust gas flow path 200, and superheats the superheated steam in the superheater tube in the first region by heat exchange with the exhaust gas. In the present Embodiment 4, the first region is the intermediate region 202A in the exhaust gas flow path 200. That is, as shown in FIG. 5, the tertiary superheater 3 is disposed in the exhaust gas flow path 200 so as to have a superheater tube 3a in the intermediate region 202A in the exhaust gas flow path 200.

[0085] Specifically, in the fourth embodiment, as shown in FIG. 5, the superheater tube 3a is disposed in the intermediate region 202A within the exhaust gas flow path 200. Note that the shape of the superheater tube 3a is the same as that in the above-described first to third embodiments. As shown in FIG. 5, a communication pipe 102 is connected to the inlet of the superheater tube 3a. The communication pipe 102 in the fourth embodiment is an example of an introduction pipe that introduces superheated steam into the superheater tube of the first heat exchanger of the present invention. That is, in the fourth embodiment, unlike the above-described first to third embodiments, the communication pipe 101 shown in FIG. 5 (a pipe that connects the outlet of the superheater tube 1a of the primary superheater 1 and the inlet of the superheater tube 2a of the secondary superheater 2) is not the introduction pipe. The communication pipe 102 in the fourth embodiment is a pipe that introduces the superheated steam 112 to be superheated into the superheater tube 3a of the tertiary superheater 3, which is the first heat exchanger, and as shown in FIG. 5, connects the outlet of the superheater tube 2a of the secondary superheater 2 and the inlet of the superheater tube 3a of the tertiary superheater 3. Further, as shown in FIG. 5, a communication pipe 103 is connected to the outlet of the superheater tube 3a. The communication pipe 103 is a pipe that connects the outlet of the superheater tube 3a of the tertiary superheater 3 and the inlet of the superheater tube 4a of the quaternary superheater 4.

[0086] Also, in the fourth embodiment, the metal tube constituting the superheater tube 3a is selected so as to prevent high-temperature corrosion of the superheater tube 3a in a temperature environment considering both the temperature of the superheated steam flowing through the superheater tube 3a and the temperature of the exhaust gas in the intermediate region 202A that contacts the outer wall surface of the superheater tube 3a. For example, this superheater tube 3a is preferably a tube including at least one of a carbon steel tube and a stainless steel tube. That is, the superheater tube 3a having a tube shape that reciprocates a plurality of times between the opposing inner walls of the exhaust gas flow path 200 may be constituted only by a carbon steel tube, may be constituted only by a stainless steel tube, or may be constituted by combining a carbon steel tube and a stainless steel tube (for example, joining the two steel tubes in series). Among these, from the viewpoint of corrosion resistance, this superheater tube 3a is particularly preferably a stainless steel tube having higher corrosion resistance than the superheater tube 1a of the primary superheater 1 or the superheater tube 2a of the secondary superheater 2 described above.

[0087] The tertiary superheater 3 of Embodiment 4 having the above-described configuration further superheats the superheated steam by heat exchange with the exhaust gas. Specifically, in Embodiment 4, the tertiary superheater 3 receives the superheated steam 112 superheated by the secondary superheater 2 from the secondary superheater 2 into the interior of the superheater tube 3a via the communication pipe 102. While causing the received superheated steam 112 to flow from the inlet side to the outlet side of the superheater tube 3a, the tertiary superheater 3 further superheats the superheated steam 112 in the superheater tube 3a by heat exchange with the exhaust gas 211 in the intermediate region 202A. Thereby, the tertiary superheater 3 generates superheated steam 113 at a temperature higher than that of the superheated steam 112. Note that the exhaust gas 211 in the intermediate region 202A is a gas at a temperature higher than that of the exhaust gas 212 (i.e., the exhaust gas used for heat exchange with the superheated steam 112 in the superheater tube 3a) in the downstream intermediate region 202B described above. The tertiary superheater 3 sends out the generated superheated steam 113 from the outlet of the superheater tube 3a into the interior of the communication pipe 103.

[0088] The quaternary superheater 4 is an example of a second heat exchanger that has a superheater tube in a second region that is in the exhaust gas flow path 200 and upstream of the first region in the flow direction of the exhaust gas, and superheats the superheated steam in the superheater tube in the second region by heat exchange with the exhaust gas. In Embodiment 4, the second region is the upstream region 201 in the exhaust gas flow path 200. Note that the first region is the intermediate region 202A in the exhaust gas flow path 200 as described above. That is, as shown in FIG. 5, the quaternary superheater 4 is disposed in the exhaust gas flow path 200 such that it has a superheater tube 4a in the upstream region 201 in the exhaust gas flow path 200.

[0089] Specifically, the superheater tube 4a has the same tube shape as any of the above-described superheater tubes 1a, 2a, and 3a, and is disposed in the upstream region 201 within the exhaust gas flow path 200 as shown in FIG. 5. Such a superheater tube 4a is composed of a metal tube having higher corrosion resistance than the superheater tube 3a of the tertiary superheater 3 of the fourth embodiment. For example, examples of the superheater tube 4a include the same metal tubes as the superheater tube 3a of the first to third embodiments described above, such as a stainless steel tube and a cladded tube. Further, as shown in FIG. 5, the communication pipe 103 described above is connected to the inlet of the superheater tube 4a. The superheater tube 4a communicates with the superheater tube 3a of the tertiary superheater 3 via the communication pipe 103. An outlet pipe 104 is connected to the outlet of the superheater tube 4a. The outlet pipe 104 is a pipe for sending the superheated steam superheated by the second heat exchanger (the quaternary superheater 4 in the fourth embodiment) of the present invention to the outside of the superheating device 40. The outlet pipe 104 of the fourth embodiment is the same as the outlet pipe 104 of the first to third embodiments described above, except that it is connected to the outlet of the superheater tube 4a of the quaternary superheater 4.

[0090] The quaternary superheater 4 having the above-described configuration further superheats the superheated steam to a higher temperature by heat exchange with the exhaust gas. Specifically, the quaternary superheater 4 receives the superheated steam 113 after being superheated by the tertiary superheater 3 from the tertiary superheater 3 into the inside of the superheater tube 4a via the communication pipe 103. The quaternary superheater 4 further superheats the superheated steam 113 in the superheater tube 4a by heat exchange with the exhaust gas 210 in the upstream region 201 while allowing the received superheated steam 113 to flow from the inlet side to the outlet side of the superheater tube 4a. As a result, the quaternary superheater 4 generates superheated steam 114 at a temperature higher than that of the superheated steam 113. The exhaust gas 210 in the upstream region 201 is a gas at a higher temperature than the exhaust gas 211 (i.e., the exhaust gas used for heat exchange with the superheated steam 113 in the superheater tube 4a) in the above-described intermediate region 202A. The quaternary superheater 4 sends the generated superheated steam 114 from the superheater tube 4a into the inside of the outlet pipe 104. The high-temperature superheated steam 114 superheated by the quaternary superheater 4 in this way is supplied to an external device via the outlet pipe 104 or the like and consumed as driving energy for the external device, in the same manner as in the first to third embodiments described above.

[0091] In addition, as shown in, for example, FIG. 5, each of the superheater tubes 1a, 2a, 3a, and 4a of the primary superheater 1, secondary superheater 2, tertiary superheater 3, and quaternary superheater 4 described above is piped such that the flow of steam or superheated steam from the superheater tube inlet to the superheater tube outlet is a countercurrent flow with respect to the flow direction of the exhaust gas. However, in the present invention, each of the superheater tubes 1a, 2a, 3a, and 4a may be piped such that the above-described flow of steam or superheated steam is a parallel flow with respect to the flow direction of the exhaust gas. Alternatively, each of the superheater tubes 1a, 2a, 3a, and 4a may include a superheater tube piped to be the countercurrent flow and a superheater tube piped to be the parallel flow.

[0092] Further, the outlet temperature measuring unit 12 of the fourth embodiment is the same as the outlet temperature measuring unit 12 of the third embodiment described above, except that it is connected to the outlet of the superheater tube 4a of the quaternary superheater 4 as shown in FIG. 5. That is, the outlet temperature measuring unit 12 of the fourth embodiment measures the temperature of the superheated steam 114 in the outlet pipe 104 as the outlet steam temperature T2. Further, the temperature measuring unit 13 of the fourth embodiment is the same as the temperature measuring unit 13 of the third embodiment described above, except that it is provided in the middle of the communication pipe 102 that connects the secondary superheater 2 and the tertiary superheater 3 as shown in FIG. 5. That is, the temperature measuring unit 13 of the fourth embodiment measures the temperature of the superheated steam 112 that has been cooled by the first desuperheater 16 in the communication pipe 102 as the inlet steam temperature T1.

[0093] In addition, the first desuperheater 16 of the fourth embodiment is the same as the first desuperheater 16 of the third embodiment described above, except that it is provided in the middle of the communication pipe 102 as shown in FIG. 5. That is, the first desuperheater 16 of the fourth embodiment reduces the temperature (inlet steam temperature T1) of the superheated steam 112 in the communication pipe 102 by supplying cooling water into the communication pipe 102 based on the control by the control unit 45. The second desuperheater 17 of the fourth embodiment is the same as the second desuperheater 17 of the third embodiment described above, except that it is provided in the middle of the communication pipe 103 as shown in FIG. 5. That is, the second desuperheater 17 of the fourth embodiment reduces the temperature (intermediate steam temperature T3) of the superheated steam 113 in the communication pipe 103 by supplying cooling water into the communication pipe 103 based on the control by the control unit 45.

[0094] The control unit 45 is composed of a CPU, a memory, etc. for executing various programs, and controls the above-described inlet steam temperature T1 and outlet steam temperature T2. The control of the supply amount of each cooling water to the first desuperheater 16 and the second desuperheater 17 of the control unit 45 is the same as that of the control unit 35 in the above-described Embodiment 3. By controlling these first desuperheater 16 and second desuperheater 17, the control unit 45 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the tertiary superheater 3, and controls the outlet steam temperature T2 to a superheated steam temperature of less than 600°C. Note that the upper limit values and lower limit values of the inlet steam temperature T1 and the outlet steam temperature T2 controlled by the control unit 45 are the same as those in the above-described Embodiment 3.

[0095] Next, a method for controlling the superheated steam temperature by the superheating device according to Embodiment 4 of the present invention will be described. The superheating device 40 (see FIG. 5) according to Embodiment 4 of the present invention controls the temperature (inlet steam temperature T1) of the superheated steam 112 introduced into the superheating tubes 3a of the tertiary superheater 3 and the temperature (outlet steam temperature T2) of the superheated steam 114 sent from the superheating tubes 4a of the quaternary superheater 4 into the outlet pipe 104 by executing processes substantially the same as those in Steps S101 to S103 of the above-described Embodiment 3.

[0096] That is, in the superheating device 40 according to Embodiment 4 of the present invention, in Step S101, the outlet temperature measuring unit 12 measures the outlet steam temperature T2 in the outlet pipe 104 communicating with the outlet of the superheating tube 4a of the quaternary superheater 4, and transmits an electric signal indicating the measured outlet steam temperature T2 to the control unit 45. Further, the temperature measuring unit 13 measures the temperature of the superheated steam 112 introduced into the superheating tube 3a of the tertiary superheater 3 after being cooled by the first desuperheater 16, that is, the inlet steam temperature T1 in the communication pipe 102. The temperature measuring unit 13 transmits an electric signal indicating the measured inlet steam temperature T1 to the control unit 45.

[0097] Also, in the superheating device 40 according to the fourth embodiment, in step S102, the control unit 45 controls the supply amount of cooling water into the communication pipe 102 that introduces the superheated steam 112 into the superheating pipe 3a of the tertiary superheater 3 and the supply amount of cooling water into the communication pipe 103 that introduces the superheated steam 113 into the superheating pipe 4a of the quaternary superheater 4 based on the inlet steam temperature T1 and the outlet steam temperature T2 obtained in step S101. The control unit 45 controls the supply amount of cooling water into the communication pipe 102 by the first desuperheater 16 in the same manner as the control unit 35 in the above-described third embodiment. Further, the control unit 45 controls the supply amount of cooling water into the communication pipe 103 by the second desuperheater 17 in the same manner as the control unit 35 in the above-described third embodiment.

[0098] Also, in the superheating device 40 according to the fourth embodiment, in step S103, the first desuperheater 16 adjusts the opening degree of the regulating valve in the same manner as in the above-described third embodiment based on the control signal from the control unit 45, and supplies the cooling water with the supply amount corresponding to the adjusted opening degree into the communication pipe 102. Thereby, the first desuperheater 16 reduces the inlet steam temperature T1 in the communication pipe 102. Further, the second desuperheater 17 adjusts the opening degree of the regulating valve in the same manner as in the above-described third embodiment based on the control signal from the control unit 45, and supplies the cooling water with the supply amount corresponding to the adjusted opening degree into the communication pipe 103. Thereby, the second desuperheater 17 reduces the intermediate steam temperature T3 in the communication pipe 103. In the fourth embodiment, as the intermediate steam temperature T3 decreases, the temperature of the superheated steam 114 after superheating by the quaternary superheater 4 (i.e., the outlet steam temperature T2) decreases. As described above, the control unit 45 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the tertiary superheater 3, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C.

[0099] Note that in the fourth embodiment, after executing the process of step S103, the superheating device 40 repeatedly executes the processes of steps S101 to S103 as necessary. Thereby, the superheating device 40 sequentially controls the inlet steam temperature T1 and the outlet steam temperature T2 in time series.

[0100] As described above, in the superheater 40 according to the fourth embodiment of the present invention, among the plurality of superheaters (primary superheater 1, secondary superheater 2, tertiary superheater 3, and quaternary superheater 4) that superheat steam in multiple stages by heat exchange with exhaust gas, the temperature (inlet steam temperature T1) of the superheated steam 112 introduced into the superheater tubes 3a of the tertiary superheater 3 disposed in the intermediate region 202A on the upstream side in the exhaust gas flow path 200 is controlled by supplying cooling water to the superheated steam 112. Further, the temperature (outlet steam temperature T2) of the superheated steam 114 sent from the superheater tubes 4a of the quaternary superheater 4 disposed in the upstream region 201 in the exhaust gas flow path 200 into the outlet pipe 104 is controlled by supplying cooling water to the superheated steam 114, and the rest is the same as in the third embodiment. Therefore, even when the number of superheaters for superheating steam in multiple stages by heat exchange with exhaust gas is increased, the same operational effects as those of the third embodiment described above can be achieved.

[0101] (Embodiment 5) Next, the superheater according to the fifth embodiment of the present invention will be described in detail. FIG. 6 is a block diagram showing a configuration example of the superheater according to the fifth embodiment of the present invention. As shown in FIG. 6, the superheater 50 according to the fifth embodiment uses the secondary superheater 2 as the first heat exchanger of the present invention instead of the tertiary superheater 3 of the superheater 30 according to the third embodiment described above, and includes a temperature measuring unit 13 and a first desuperheater 16 in the middle of the communication pipe 101 instead of the communication pipe 102 described above, and includes a control unit 55 instead of the control unit 45 described above. Other configurations are the same as those in the fourth embodiment, and the same reference numerals are given to the same components.

[0102] In Embodiment 5, among the primary superheater 1, secondary superheater 2, tertiary superheater 3, and quaternary superheater 4 shown in FIG. 6, the secondary superheater 2 rather than the tertiary superheater 3 is an example of the first heat exchanger of the present invention. As described above, the first heat exchanger has superheater tubes in the first region within the exhaust gas flow path 200 and superheats the superheated steam in the superheater tubes in the first region by heat exchange with the exhaust gas. As shown in FIG. 6, the secondary superheater 2 is disposed within the exhaust gas flow path 200 such that it has superheater tubes 2a in the intermediate region 202B on the downstream side within the exhaust gas flow path 200. That is, in Embodiment 5, the first region is the intermediate region 202B within the exhaust gas flow path 200. Note that the secondary superheater 2 of Embodiment 5 is the same as the secondary superheater 2 of Embodiment 4 described above, except that it is the first heat exchanger of the present invention.

[0103] Also, as shown in FIG. 6, a communication pipe 101 is connected to the inlet of the superheater tubes 2a of the secondary superheater 2. In Embodiment 5, the communication pipe 101 is an example of an introduction pipe that introduces superheated steam into the superheater tubes 2a of the secondary superheater 2, which is the first heat exchanger of the present invention, and connects the outlet of the superheater tubes 1a of the primary superheater 1 and the inlet of the superheater tubes 2a of the secondary superheater 2. That is, in Embodiment 5, unlike in Embodiment 4 described above, the communication pipe 102 shown in FIG. 6 (the pipe that connects the outlet of the superheater tubes 2a of the secondary superheater 2 and the inlet of the superheater tubes 3a of the tertiary superheater 3) is not the introduction pipe.

[0104] The tertiary superheater 3 of the fifth embodiment is an example of an intermediate superheater that has superheater tubes in the intermediate region between the first region and the second region within the exhaust gas flow path 200 and superheats the superheated steam in the superheater tubes of the intermediate region by heat exchange with the exhaust gas. In the fifth embodiment, the first region is the intermediate region 202B on the downstream side within the exhaust gas flow path 200 where the secondary superheater 2, which is the first heat exchanger of the present invention, is disposed. The second region is the upstream region 201 within the exhaust gas flow path 200 where the quaternary superheater 4, which is the second heat exchanger of the present invention, is disposed. That is, in the fifth embodiment, the intermediate region between the first region and the second region is the upstream intermediate region 202A within the exhaust gas flow path 200 as shown in FIG. 6. Note that the tertiary superheater 3 of the fifth embodiment is the same as the tertiary superheater 3 of the fourth embodiment described above, except that it is an intermediate superheater rather than the first heat exchanger of the present invention.

[0105] Also, as shown in FIG. 6, a communication pipe 102 is connected to the inlet of the superheater tube 3a of the tertiary superheater 3. In the fifth embodiment, the communication pipe 102 is an example of a first communication pipe that connects the outlet of the superheater tube 2a of the secondary superheater 2, which is the first heat exchanger of the present invention, and the inlet of the superheater tube 3a of the tertiary superheater 3, which is the intermediate superheater of the present invention. A communication pipe 103 is connected to the outlet of the superheater tube 3a of the tertiary superheater 3. In the fifth embodiment, the communication pipe 103 is an example of a second communication pipe that connects the outlet of the superheater tube 3a of the tertiary superheater 3, which is the intermediate superheater of the present invention, and the inlet of the superheater tube 4a of the quaternary superheater 4, which is the second heat exchanger of the present invention.

[0106] Note that the primary superheater 1 and the quaternary superheater 4 of the fifth embodiment are the same as the primary superheater 1 and the quaternary superheater 4 of the fourth embodiment described above, respectively. That is, the quaternary superheater 4 of the fifth embodiment is an example of the second heat exchanger of the present invention, similar to the fourth embodiment described above.

[0107] Further, the temperature measuring unit 13 of the fifth embodiment is the same as the temperature measuring unit 13 of the fourth embodiment described above, except that it is provided in the middle of the communication pipe 101 that connects the primary superheater 1 and the secondary superheater 2 as shown in FIG. 6. That is, the temperature measuring unit 13 of the fifth embodiment measures the temperature of the superheated steam 111 after being cooled by the first desuperheater 16 in the communication pipe 101 as the inlet steam temperature T1.

[0108] Further, the first desuperheater 16 of the fifth embodiment is the same as the first desuperheater 16 of the fourth embodiment described above, except that it is provided in the middle of the communication pipe 101 as shown in FIG. 6. That is, the first desuperheater 16 of the fifth embodiment reduces the temperature (inlet steam temperature T1) of the superheated steam 111 in the communication pipe 101 by supplying cooling water into the communication pipe 101 based on the control by the control unit 55.

[0109] The control unit 55 is composed of a CPU, a memory, etc. for executing various programs, and controls the above-described inlet steam temperature T1 and outlet steam temperature T2. The control of the supply amount of each cooling water to the first desuperheater 16 and the second desuperheater 17 of the control unit 55 is the same as that of the control unit 45 of the fourth embodiment described above. By controlling these first desuperheater 16 and second desuperheater 17, the control unit 55 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C. Note that the upper and lower limit values of the inlet steam temperature T1 and the outlet steam temperature T2 controlled by the control unit 55 are the same as those of the fourth embodiment described above.

[0110] Next, a method for controlling the superheated steam temperature by the superheating device according to the fifth embodiment of the present invention will be described. The superheating device 50 (see FIG. 6) according to the fifth embodiment executes each process substantially the same as steps S101 to S103 of the fourth embodiment described above, thereby controlling the temperature of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 (inlet steam temperature T1) and the temperature of the superheated steam 114 sent from the superheating tube 4a of the fourth superheater 4 into the outlet pipe 104 (outlet steam temperature T2).

[0111] That is, in the superheating device 50 according to the fifth embodiment, in step S101, the outlet temperature measurement unit 12 measures the outlet steam temperature T2 in the same manner as in the fourth embodiment described above, and transmits an electrical signal indicating the measured outlet steam temperature T2 to the control unit 55. Further, the temperature measurement unit 13 measures the temperature of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 after being cooled by the first desuperheater 16, that is, the inlet steam temperature T1 in the communication pipe 101. The temperature measurement unit 13 transmits an electrical signal indicating the measured inlet steam temperature T1 to the control unit 55.

[0112] Also, in the superheating device 50 according to the fifth embodiment, in step S102, the control unit 55 controls the supply amount of cooling water into the communication pipe 101 for introducing the superheated steam 111 into the superheating tube 2a of the secondary superheater 2 and the supply amount of cooling water into the communication pipe 103 for introducing the superheated steam 113 into the superheating tube 4a of the fourth superheater 4 based on the inlet steam temperature T1 and the outlet steam temperature T2 obtained in step S101. The control unit 55 controls the supply amount of cooling water into the communication pipe 101 by the first desuperheater 16 in the same manner as the control unit 45 in the fourth embodiment described above. Further, the control unit 55 controls the supply amount of cooling water into the communication pipe 103 by the second desuperheater 17 in the same manner as the control unit 45 in the fourth embodiment described above.

[0113] Also, in the superheater 50 according to the fifth embodiment, in step S103, the first desuperheater 16 adjusts the opening degree of the regulating valve based on the control signal from the control unit 55, and supplies the cooling water with a supply amount corresponding to the adjusted opening degree into the communication pipe 101, in the same manner as in the fourth embodiment described above. Thereby, the first desuperheater 16 reduces the inlet steam temperature T1 in the communication pipe 101. Further, the second desuperheater 17 adjusts the opening degree of the regulating valve based on the control signal from the control unit 55, and supplies the cooling water with a supply amount corresponding to the adjusted opening degree into the communication pipe 103, in the same manner as in the fourth embodiment described above. Thereby, the second desuperheater 17 reduces the intermediate steam temperature T3 in the communication pipe 103. In the fifth embodiment, as the intermediate steam temperature T3 decreases, the temperature of the superheated steam 114 after superheating by the fourth superheater 4 (i.e., the outlet steam temperature T2) decreases. As described above, the control unit 55 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C.

[0114] In the fifth embodiment, after executing the process of step S103, the superheater 50 repeatedly executes the processes of steps S101 to S103 as necessary. Thereby, the superheater 50 sequentially controls the inlet steam temperature T1 and the outlet steam temperature T2 over time.

[0115] As described above, in the superheater 50 according to Embodiment 5 of the present invention, among a plurality of superheaters (primary superheater 1, secondary superheater 2, tertiary superheater 3, and quaternary superheater 4) that superheat steam in multiple stages by heat exchange with exhaust gas, the secondary superheater 2 is used as the first heat exchanger of the present invention, the quaternary superheater 4 is used as the second heat exchanger of the present invention, and with the tertiary superheater 3, which is the intermediate superheater of the present invention, interposed between the first heat exchanger and the second heat exchanger, the temperature (inlet steam temperature T1) of the superheated steam 111 introduced into the superheat tubes 2a of the secondary superheater 2 is controlled by supplying cooling water to the superheated steam 111. Further, the temperature (outlet steam temperature T2) of the superheated steam 114 sent from the superheat tubes 4a of the quaternary superheater 4 into the outlet pipe 104 is controlled by supplying cooling water to the superheated steam 114, and the rest is the same as in Embodiment 4. For this reason, even when there is an intervening tertiary superheater 3 that further superheats the superheated steam after superheating by the secondary superheater 2 and sends it toward the quaternary superheater 4 in a state where the superheated steam is further superheated, between the secondary superheater 2 that superheats the superheated steam 111 with the inlet steam temperature T1 as the control target and the quaternary superheater 4 that generates the superheated steam 114 with the outlet steam temperature T2 as the control target, the same operational effects as those of Embodiment 4 described above can be achieved.

[0116] (Embodiment 6) Next, the superheater according to Embodiment 6 of the present invention will be described in detail. FIG. 7 is a block diagram showing a configuration example of the superheater according to Embodiment 6 of the present invention. As shown in FIG. 7, the superheater 60 according to Embodiment 6 includes the secondary superheater 2 of the superheater 40 according to Embodiment 4 described above on the upstream side of the flow direction of the exhaust gas from the tertiary superheater 3 (the first heat exchanger of the present invention) and the quaternary superheater 4 (the second heat exchanger of the present invention), a temperature measuring unit 14 that measures the temperature of the superheated steam introduced into the superheat tubes 2a of the secondary superheater 2, and a third desuperheater 18 that reduces the temperature of the superheated steam. Further, the superheater 60 includes a control unit 65 in place of the control unit 45 of Embodiment 4 described above. The other configurations are the same as those in Embodiment 4, and the same reference numerals are given to the same components.

[0117] In Embodiment 6, unlike the arrangement in Embodiment 4 described above, the primary superheater 1, the secondary superheater 2, the tertiary superheater 3, and the quaternary superheater 4 are arranged inside the exhaust gas flow path 200 in the order of the secondary superheater 2, the quaternary superheater 4, the tertiary superheater 3, and the primary superheater 1 from the upstream side to the downstream side in the exhaust gas flow direction. That is, as shown in FIG. 7, the secondary superheater 2 is arranged in the upstream region 201 in the exhaust gas flow path 200, and the quaternary superheater 4 is arranged in the intermediate region 202A on the upstream side in the exhaust gas flow path 200. The tertiary superheater 3 is arranged in the intermediate region 202B on the downstream side in the exhaust gas flow path 200, and the primary superheater 1 is arranged in the downstream region 203 in the exhaust gas flow path 200.

[0118] Note that the functions of the primary superheater 1, the secondary superheater 2, the tertiary superheater 3, and the quaternary superheater 4 in Embodiment 6 are the same as those in Embodiment 4 described above. In particular, in Embodiment 6, similar to Embodiment 4 described above, the tertiary superheater 3 is the first heat exchanger of the present invention, and the quaternary superheater 4 is the second heat exchanger of the present invention.

[0119] Also, in Embodiment 6, among the primary superheater 1, the secondary superheater 2, the tertiary superheater 3, and the quaternary superheater 4 arranged as described above, the secondary superheater 2 is an example of the third heat exchanger of the present invention. The third heat exchanger has superheating tubes in a third region which is a region on the upstream side in the exhaust gas flow direction than a second region where the second heat exchanger of the present invention is arranged within the exhaust gas flow path 200, and superheats the superheated steam in the superheating tubes in the third region by heat exchange with the exhaust gas. In Embodiment 6, the second region is the intermediate region 202A on the upstream side in the exhaust gas flow path 200, and the third region is the upstream region 201 in the exhaust gas flow path 200.

[0120] Thus, the superheater tubes 2a of the secondary superheater 2 arranged in the upstream region 201 are preferably made of a metal tube having higher corrosion resistance than the superheater tubes 4a of the quadruple superheater 4 arranged in the intermediate region 202A on the upstream side. For example, as the superheater tubes 2a in the sixth embodiment, the same metal tubes as the superheater tubes 3a in the first to third embodiments described above, such as stainless steel tubes and clad tubes, can be mentioned. That is, in the sixth embodiment, the superheater tubes 4a of the quadruple superheater 4 may be composed of only the above-described clad tubes, may be composed of only stainless steel tubes, or may be composed by combining stainless steel tubes and clad tubes (for example, joining both steel tubes in series). The superheater tubes 4a are preferably tubes containing at least one of carbon steel tubes and stainless steel tubes, similar to the superheater tubes 2a of the secondary superheater 2 in the first to third embodiments described above. Among these, from the viewpoint of corrosion resistance, a stainless steel tube is particularly preferable. Further, in the sixth embodiment, the superheater tubes 3a of the tertiary superheater 3 arranged in the intermediate region 202B on the downstream side are preferably tubes containing at least one of carbon steel tubes and stainless steel tubes, similar to the superheater tubes 2a of the secondary superheater 2 in the fourth embodiment described above. Among these, a carbon steel tube is more preferable.

[0121] Further, in the sixth embodiment, as shown in FIG. 7, the communication pipe 101 communicates the outlet of the superheater tube 1a of the primary superheater 1 arranged in the downstream region 203 and the inlet of the superheater tube 2a of the secondary superheater 2 arranged in the upstream region 201. The communication pipe 102 communicates the outlet of the superheater tube 2a of the secondary superheater 2 and the inlet of the superheater tube 3a of the tertiary superheater 3 arranged in the intermediate region 202B on the downstream side. The communication pipe 103 communicates the outlet of the superheater tube 3a of the tertiary superheater 3 and the outlet of the superheater tube 4a of the quadruple superheater 4 arranged in the intermediate region 202A on the upstream side. Further, as shown in FIG. 7, an outlet pipe 104 is connected to the outlet of the superheater tube 4a of the quadruple superheater 4, similar to the fourth embodiment described above. A steam pipe 100 is connected to the inlet of the superheater tube 1a of the primary superheater 1, similar to the fourth embodiment described above.

[0122] Note that each of the superheater tubes 1a, 3a, and 4a of the primary superheater 1, the tertiary superheater 3, and the quaternary superheater 4 described above is piped such that the flow of steam or superheated steam from the superheater tube inlet to the superheater tube outlet is a countercurrent flow with respect to the flow direction of the exhaust gas, as shown in FIG. 7, for example. Also, the superheater tubes 2a of the secondary superheater 2 are piped such that the flow of superheated steam from the superheater tube inlet to the superheater tube outlet is a parallel flow with respect to the flow direction of the exhaust gas. However, in the present invention, each of the superheater tubes 1a, 2a, 3a, and 4a may be piped such that the above-described flow of steam or superheated steam is a parallel flow with respect to the flow direction of the exhaust gas, or may be piped such that it is a countercurrent flow. Alternatively, each of the superheater tubes 1a, 2a, 3a, and 4a may include one or more superheater tubes piped to be the above-described countercurrent flow and one or more superheater tubes piped to be the above-described parallel flow, respectively, in a combination other than that shown in FIG. 7.

[0123] The temperature measuring unit 14 measures the temperature of the superheated steam flowing into the superheater tubes of the third heat exchanger of the present invention. In the sixth embodiment, the third heat exchanger is the secondary superheater 2 as described above. As shown in FIG. 7, the temperature measuring unit 14 is provided in the middle of the communication pipe 101 that communicates with the inlet of the superheater tubes 2a of the secondary superheater 2, between the superheater tubes 2a of the secondary superheater 2 and the third desuperheater 18. The superheated steam 111 in the communication pipe 101 flows from the primary superheater 1 side in the downstream region 203 to the secondary superheater 2 side in the upstream region 201, while being desuperheated by the third desuperheater 18, and then flows into the superheater tubes 2a of the secondary superheater 2. The temperature measuring unit 14 measures the temperature of the superheated steam 111 (hereinafter referred to as the desuperheated steam temperature T4) that flows from the communication pipe 101 into the superheater tubes 2a of the secondary superheater 2 after being desuperheated by the third desuperheater 18. Each time, the temperature measuring unit 14 transmits an electrical signal indicating the measured desuperheated steam temperature T4 to the control unit 65. Note that the temperature measuring unit 14 may continuously measure the desuperheated steam temperature T4 along the time series, may intermittently measure it at a predetermined time interval, or may measure it based on a measurement command from the control unit 65.

[0124] The third desuperheater 18 is an example of a desuperheater that supplies cooling water to the superheated steam flowing into the superheater tubes of the third heat exchanger of the present invention to lower the temperature of the flowing superheated steam. In Embodiment 6, the third heat exchanger is the secondary superheater 2 as described above, and the superheated steam flowing into the superheater tubes of the third heat exchanger is the superheated steam 111 in the communication pipe 101.

[0125] Specifically, the third desuperheater 18 is configured in the same manner as the first desuperheater 16 and the second desuperheater 17 described above, and is provided in the middle of the communication pipe 101 as shown in FIG. 7. The third desuperheater 18 supplies cooling water to the inside of the communication pipe 101 based on the control by the control unit 65, thereby lowering the temperature of the superheated steam 111 in the communication pipe 101 (desuperheated steam temperature T4). For example, the supply amount of the cooling water into the communication pipe 101 increases by increasing the opening degree of the regulating valve of the third desuperheater 18, and decreases by decreasing the opening degree. The superheated steam 111 after being desuperheated by the third desuperheater 18 flows from the communication pipe 101 into the superheater tubes 2a of the secondary superheater 2.

[0126] The control unit 65 is composed of a CPU, a memory, etc. for executing various programs, and controls the above-described inlet steam temperature T1 and outlet steam temperature T2. The control of the supply amount of each cooling water to the first desuperheater 16 and the second desuperheater 17 of the control unit 65 is the same as that of the control unit 45 in Embodiment 4 described above. By controlling these first desuperheater 16 and second desuperheater 17, the control unit 65 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the tertiary superheater 3, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C. Note that the upper limit values and lower limit values of the inlet steam temperature T1 and the outlet steam temperature T2 controlled by the control unit 65 are the same as those in Embodiment 3 described above.

[0127] Further, the control unit 65 controls the desuperheated steam temperature T4 described above. For example, a reference value of the desuperheated steam temperature T4 after desuperheating by the third desuperheater 18 (hereinafter referred to as the reference desuperheated steam temperature T4s) is preset in the control unit 65. The control unit 65 controls the water supply amount to the superheated steam 111 by the third desuperheater 18 so that the difference between the desuperheated steam temperature T4 measured by the temperature measuring unit 14 and the reference desuperheated steam temperature T4S disappears, and controls the desuperheated steam temperature T4 through the control of the water supply amount. The reference desuperheated steam temperature T4s is set, for example, within a range equal to or higher than the saturation temperature of the superheated steam 112 in the communication pipe 102 leading to the inlet of the superheating pipe 3a of the tertiary superheater 3 (saturation temperature at the inlet pressure of the superheating pipe 3a) as the lower limit temperature and equal to or lower than the upper limit value of the heat-resistant temperature of the communication pipe 101 as the upper limit temperature.

[0128] Next, a method for controlling the superheated steam temperature by the superheating device according to Embodiment 6 of the present invention will be described. The superheating device 60 (see FIG. 7) according to Embodiment 6 executes each process substantially the same as steps S101 to S103 of Embodiment 4 described above, so that the temperature of the superheated steam 111 introduced into the superheating pipe 2a of the secondary superheater 2 (desuperheated steam temperature T4), the temperature of the superheated steam 112 introduced into the superheating pipe 3a of the tertiary superheater 3 (inlet steam temperature T1), and the temperature of the superheated steam 114 sent from the superheating pipe 4a of the quaternary superheater 4 into the outlet pipe 104 (outlet steam temperature T2) are controlled.

[0129] That is, in the superheating device 60 according to Embodiment 6, in step S101, the outlet temperature measuring unit 12 measures the outlet steam temperature T2 in the outlet pipe 104 in the same manner as in Embodiment 4 described above, and transmits an electric signal indicating the measured outlet steam temperature T2 to the control unit 65. The temperature measuring unit 13 measures the inlet steam temperature T1 in the communication pipe 102 in the same manner as in Embodiment 4 described above, and transmits an electric signal indicating the measured inlet steam temperature T1 to the control unit 65. Further, the temperature measuring unit 14 measures the temperature of the superheated steam 111 flowing into the superheating pipe 2a of the secondary superheater 2 after desuperheating by the third desuperheater 18, that is, the desuperheated steam temperature T4 in the communication pipe 101. The temperature measuring unit 14 transmits an electric signal indicating the measured desuperheated steam temperature T4 to the control unit 65.

[0130] Also, in the superheater 60 according to the sixth embodiment, in step S102, the control unit 65 controls the supply amount of cooling water into the communication pipe 101 that introduces the superheated steam 111 into the superheater pipe 2a of the secondary superheater 2, the supply amount of cooling water into the communication pipe 102 that introduces the superheated steam 112 into the superheater pipe 3a of the tertiary superheater 3, and the supply amount of cooling water into the communication pipe 103 that introduces the superheated steam 113 into the superheater pipe 4a of the quaternary superheater 4, based on each measured temperature obtained in step S101.

[0131] Specifically, the control unit 65 obtains the desuperheated steam temperature T4 obtained in step S101 based on the electrical signal received from the temperature measuring unit 14, and calculates the difference (steam temperature difference ΔT4) between the obtained desuperheated steam temperature T4 and the reference desuperheated steam temperature T4s. The control unit 65 calculates the supply amount of cooling water to be supplied into the communication pipe 101 in order to eliminate the calculated steam temperature difference ΔT4 (make ΔT4 = 0). Next, the control unit 65 calculates the opening degree of the regulating valve of the third desuperheater 18 necessary to supply the calculated amount of cooling water into the communication pipe 101. After that, the control unit 65 transmits a control signal instructing the calculated opening degree as the opening degree of the regulating valve to the third desuperheater 18. Thereby, the control unit 65 controls the opening degree of the regulating valve, and controls the supply amount of the cooling water through the control of the opening degree. Also, the control unit 65 controls the supply amount of cooling water into the communication pipe 102 by the first desuperheater 16 and the supply amount of cooling water into the communication pipe 103 by the second desuperheater 17 in the same manner as in the fourth embodiment described above.

[0132] Also, in the superheater 60 according to the sixth embodiment, in step S103, the third desuperheater 18 obtains the indicated opening based on the control signal from the control unit 65, and adjusts the opening of the regulating valve to the obtained opening. Subsequently, the third desuperheater 18 supplies (injects) the cooling water with the supply amount corresponding to the adjusted opening into the communication pipe 101. Thereby, the third desuperheater 18 reduces the temperature of the superheated steam 111 introduced from the communication pipe 101 into the superheater tubes 2a of the secondary superheater 2, that is, the desuperheated steam temperature T4. Also, the first desuperheater 16 adjusts the opening of the regulating valve based on the control signal from the control unit 65 in the same manner as in the case of the fourth embodiment described above, and supplies the cooling water with the supply amount corresponding to the adjusted opening into the communication pipe 102. Thereby, the first desuperheater 16 reduces the inlet steam temperature T1 in the communication pipe 102. The second desuperheater 17 adjusts the opening of the regulating valve based on the control signal from the control unit 65 in the same manner as in the case of the fourth embodiment described above, and supplies the cooling water with the supply amount corresponding to the adjusted opening into the communication pipe 103. Thereby, the second desuperheater 17 reduces the intermediate steam temperature T3 in the communication pipe 103. As described above, the control unit 65 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the tertiary superheater 3, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C.

[0133] Note that in the sixth embodiment, after executing the process of step S103, the superheater 60 repeatedly executes the processes of steps S101 to S103 as necessary. Thereby, the superheater 60 sequentially controls the inlet steam temperature T1, the outlet steam temperature T2, and the desuperheated steam temperature T4 in time series.

[0134] As described above, in the superheater 60 according to Embodiment 6 of the present invention, among the plurality of superheaters (primary superheater 1, secondary superheater 2, tertiary superheater 3, and quaternary superheater 4) that superheat steam in multiple stages by heat exchange with exhaust gas, the secondary superheater 2 is arranged upstream of the tertiary superheater 3 and the quaternary superheater 4 in the flow direction of the exhaust gas. Along with the temperature of the superheated steam 111 (desuperheated steam temperature T4) introduced into the superheater tubes 2a of the secondary superheater 2, the temperature of the superheated steam 112 (inlet steam temperature T1) introduced into the superheater tubes 3a of the tertiary superheater 3 and the temperature of the superheated steam 114 (outlet steam temperature T2) sent from the superheater tubes 4a of the quaternary superheater 4 into the outlet pipe 104 are controlled, and the rest is the same as in Embodiment 4.

[0135] Therefore, while enjoying the same operational effects as those of Embodiment 4 described above, after the heat exchange between the superheated steam 111 in the superheater tubes 2a of the secondary superheater 2 and the exhaust gas, the exhaust gas cooled by this heat exchange can be brought into contact with the superheater tubes 4a of the quaternary superheater 4 on the downstream side of the secondary superheater 2. Thereby, while maintaining the above-described outlet steam temperature T2 within the required temperature range of the external device, the temperature of the exhaust gas that exchanges heat with the quaternary superheater 4, which is difficult to lower the superheated steam temperature in the superheater tubes 4a to ensure the outlet steam temperature T2 within the required temperature range, can be appropriately lowered. As a result, high-temperature corrosion of the superheater tubes 4a can be prevented.

[0136] (Embodiment 7) Next, the superheater according to Embodiment 7 of the present invention will be described in detail. FIG. 8 is a block diagram showing a configuration example of the superheater according to Embodiment 7 of the present invention. As shown in FIG. 8, the superheater 70 according to the present Embodiment 7 includes exhaust gas temperature measurement units 19a, 19b, and 19c instead of the temperature measurement unit 13 of the superheater 30 according to Embodiment 3 described above, and includes a control unit 75 instead of the control unit 35 described above. Other configurations are the same as those in Embodiment 3, and the same reference numerals are given to the same components.

[0137] The exhaust gas temperature measurement units 19a, 19b, and 19c measure the temperature of the exhaust gas that exchanges heat with each of the first heat exchanger and the second heat exchanger of the present invention. Specifically, as shown in FIG. 8, the exhaust gas temperature measurement unit 19a is provided in the exhaust gas flow path 200 such that it has a temperature detection unit in the upstream region 201 within the exhaust gas flow path 200. Within the upstream region 201, the exhaust gas 210 flows toward the tertiary superheater 3, which is the second heat exchanger of the present invention. The exhaust gas temperature measurement unit 19a measures the temperature of the exhaust gas 210 within the upstream region 201, that is, the temperature of the exhaust gas 210 before it exchanges heat with the superheated steam 112 within the superheater tube 3a. Each time, the exhaust gas temperature measurement unit 19a transmits an electrical signal indicating the obtained temperature of the exhaust gas 210 to the control unit 75.

[0138] Also, as shown in FIG. 8, the exhaust gas temperature measurement unit 19b is provided in the exhaust gas flow path 200 such that it has a temperature detection unit in the intermediate region 202 within the exhaust gas flow path 200. Within the intermediate region 202, the exhaust gas 211 flows from the above-described tertiary superheater 3 toward the secondary superheater 2, which is the first heat exchanger of the present invention. The exhaust gas 211 is the exhaust gas after it exchanges heat with the superheated steam 112 within the superheater tube 3a of the tertiary superheater 3 and is also the exhaust gas before it exchanges heat with the superheated steam 111 within the superheater tube 2a of the secondary superheater 2. That is, the temperature of the exhaust gas 211 is lower than the temperature of the exhaust gas 210 in the upstream region 201 by the amount of heat used for heat exchange with the superheated steam 112 within the superheater tube 3a. The exhaust gas temperature measurement unit 19b measures the temperature of the exhaust gas 211 within such an intermediate region 202. Each time, the exhaust gas temperature measurement unit 19b transmits an electrical signal indicating the obtained temperature of the exhaust gas 211 to the control unit 75.

[0139] Also, as shown in FIG. 8, the exhaust gas temperature measuring unit 19c is provided in the exhaust gas flow path 200 such that it has a temperature detection unit in the downstream region 203 within the exhaust gas flow path 200. In the downstream region 203, the exhaust gas 212 flows from the above-described secondary superheater 2 toward the primary superheater 1. The exhaust gas 212 is the exhaust gas after heat exchange with the superheated steam 111 in the superheater tube 2a of the secondary superheater 2 and is the exhaust gas before heat exchange with the steam 110 in the superheater tube 1a of the primary superheater 1. That is, the temperature of the exhaust gas 212 is lower than the temperature of the exhaust gas 211 in the intermediate region 202 by the amount of heat used for heat exchange with the superheated steam 111 in the superheater tube 2a. The exhaust gas temperature measuring unit 19c measures the temperature of the exhaust gas 212 in such a downstream region 203. Each time, the exhaust gas temperature measuring unit 19c transmits an electrical signal indicating the obtained temperature of the exhaust gas 212 to the control unit 75.

[0140] Note that each of the above-described exhaust gas temperature measuring units 19a, 19b, and 19c may continuously measure the exhaust gas temperature along the time series, may intermittently measure the exhaust gas temperature at a predetermined time interval, or may measure the exhaust gas temperature based on a measurement command from the control unit 75.

[0141] The control unit 75 is composed of a CPU, a memory, etc. for executing various programs, and controls the above-described inlet steam temperature T1 and outlet steam temperature T2. Specifically, in the seventh embodiment, the control unit 75 sets the reference inlet steam temperature T1s in the same manner as in the third embodiment described above, based on the outlet steam temperature T2 measured by the outlet temperature measurement unit 12. Further, the control unit 75 calculates the inlet steam temperature T1 based on the temperatures of the respective exhaust gases 210 to 212 measured by the exhaust gas temperature measurement units 19a, 19b, and 19c. The control unit 75 controls the supply amount of the cooling water by the first desuperheater 16 so as to eliminate the steam temperature difference ΔT1, which is the difference between the calculated inlet steam temperature T1 and the set reference inlet steam temperature T1s. Also, the control unit 75 controls the supply amount of the cooling water by the second desuperheater 17 so as to eliminate the difference (steam temperature difference ΔT2) between the outlet steam temperature T2 measured by the outlet temperature measurement unit 12 and the preset reference outlet steam temperature T2s, in the same manner as in the third embodiment described above. Thereby, the control unit 75 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C, in the same manner as in the third embodiment described above. Note that the upper and lower limit values of each of the inlet steam temperature T1 and the outlet steam temperature T2 controlled by the control unit 75 are the same as those in the third embodiment described above.

[0142] Next, a method for controlling the superheated steam temperature by the superheating device according to the seventh embodiment of the present invention will be described. FIG. 9 is a flowchart showing an example of a method for controlling the superheated steam temperature by the superheating device according to the seventh embodiment of the present invention. The above-described superheating device 70 (see FIG. 8) controls the temperature of the superheated steam 111 introduced into the superheating tube 2a of the secondary superheater 2 (inlet steam temperature T1) and the temperature of the superheated steam 114 sent from the superheating tube 3a of the tertiary superheater 3 into the outlet pipe 104 (outlet steam temperature T2) by executing each process of steps S201 to S203 shown in FIG. 9.

[0143] Specifically, as shown in FIG. 9, the superheating device 70 measures the temperature of the superheated steam after superheating by the second heat exchanger of the present invention and the temperature of the exhaust gas that exchanges heat with each of the first heat exchanger and the second heat exchanger of the present invention (step S201).

[0144] In step S201, the outlet temperature measurement unit 12 measures the outlet steam temperature T2 in the outlet pipe 104 in the same manner as in the above-described Embodiment 3, and transmits an electric signal indicating the measured outlet steam temperature T2 to the control unit 75. Further, the exhaust gas temperature measurement unit 19a measures the temperature of the exhaust gas 210 before heat exchange with the superheated steam 112 in the superheater tube 3a of the tertiary superheater 3, and transmits an electric signal indicating the measured temperature to the control unit 75. The exhaust gas temperature measurement unit 19b measures the temperature of the exhaust gas 211 after heat exchange with the superheated steam 112 in the superheater tube 3a of the tertiary superheater 3 and before heat exchange with the superheated steam 111 in the superheater tube 2a of the secondary superheater 2, and transmits an electric signal indicating the measured temperature to the control unit 75. The exhaust gas temperature measurement unit 19c measures the temperature of the exhaust gas 212 after heat exchange with the superheated steam 111 in the superheater tube 2a of the secondary superheater 2, and transmits an electric signal indicating the measured temperature to the control unit 75.

[0145] After executing the temperature measurement process in step S201, the superheating device 70 controls the supply amount of cooling water for lowering the temperature of the superheated steam introduced into the superheater tube of the first heat exchanger of the present invention and the supply amount of cooling water for lowering the temperature of the superheated steam introduced into the superheater tube of the second heat exchanger of the present invention (step S202).

[0146] In step S202, based on the electrical signal received from the outlet temperature measurement unit 12, the control unit 75 obtains the outlet steam temperature T2 in step S101. Further, based on each electrical signal received from each of the exhaust gas temperature measurement units 19a, 19b, and 19c, the control unit 75 obtains the temperatures of the respective exhaust gases 210 to 212 in step S101. Next, based on the difference between the temperature of the exhaust gas 210 and the temperature of the exhaust gas 211 obtained above, the control unit 75 calculates the rising temperature of the superheated steam 112 and 114 before and after superheating by the tertiary superheater 3. The control unit 75 calculates the temperature of the superheated steam 112 before superheating by the tertiary superheater 3 by subtracting the rising temperature of the superheated steam 112 and 114 calculated above from the obtained outlet steam temperature T2. Subsequently, based on the difference between the temperature of the exhaust gas 211 and the temperature of the exhaust gas 212 obtained above, the control unit 75 calculates the rising temperature of the superheated steam 111 and 112 before and after superheating by the secondary superheater 2. The control unit 75 calculates the temperature of the superheated steam 111 before superheating by the secondary superheater 2, that is, the inlet steam temperature T1, by subtracting the rising temperature of the superheated steam 111 and 112 calculated above from the calculated temperature of the superheated steam 112.

[0147] Next, the control unit 75 sets the reference inlet steam temperature T1s based on the difference (steam temperature difference ΔT2) between the obtained outlet steam temperature T2 and the reference outlet steam temperature T2s in the same manner as in the above-described Embodiment 3, and calculates the steam temperature difference ΔT1, which is the difference between the calculated inlet steam temperature T1 and the set reference inlet steam temperature T1s. Thereafter, the control unit 75 controls the supply amount of the cooling water by the first desuperheater 16 so as to eliminate the calculated steam temperature difference ΔT1 in the same manner as in the above-described Embodiment 3. Further, the control unit 75 controls the supply amount of the cooling water by the second desuperheater 17 so as to eliminate the above-described steam temperature difference ΔT2 in the same manner as in the above-described Embodiment 3.

[0148] After executing the feed water amount control process in step S202, the superheating device 70 controls the temperature of the superheated steam introduced into the superheating tubes of the first heat exchanger of the present invention and the temperature of the superheated steam after superheating by the second heat exchanger of the present invention (step S203), and ends this process.

[0149] In step S203, the first desuperheater 16 adjusts the opening degree of the regulating valve based on the control signal from the control unit 75, and supplies the cooling water with a supply amount corresponding to the adjusted opening degree into the communication pipe 101, in the same manner as in the above-described Embodiment 3. Thereby, the first desuperheater 16 reduces the inlet steam temperature T1. Further, the second desuperheater 17 adjusts the opening degree of the regulating valve based on the control signal from the control unit 75, and supplies the cooling water with a supply amount corresponding to the adjusted opening degree into the communication pipe 102, in the same manner as in the above-described Embodiment 3. Thereby, the second desuperheater 17 reduces the intermediate steam temperature T3 in the same manner as in the above-described Embodiment 3. The above-described outlet steam temperature T2 decreases in the same manner as in the above-described Embodiment 3 as the intermediate steam temperature T3 decreases. As described above, the control unit 75 controls the inlet steam temperature T1 to be equal to or higher than the saturation temperature Ta at the inlet pressure of the secondary superheater 2, and controls the outlet steam temperature T2 to be a superheated steam temperature of less than 600°C.

[0150] After executing the temperature control process of step S203, the superheating device 70 repeatedly executes each process of steps S201 to S203 as necessary. Thereby, the superheating device 70 sequentially controls the inlet steam temperature T1 and the outlet steam temperature T2 in time series.

[0151] As described above, in the superheating device 70 according to Embodiment 7 of the present invention, the exhaust gas temperature before and after heat exchange with the secondary superheater 2, which is the first heat exchanger of the present invention, and the exhaust gas temperature before and after heat exchange with the tertiary superheater 3, which is the second heat exchanger of the present invention, are measured, the inlet steam temperature T1 is calculated based on each of these measured exhaust gas temperatures and the outlet steam temperature T2, and the supply amount of the cooling water by the first desuperheater 16 is controlled so as to eliminate the difference between the calculated inlet steam temperature T1 and the reference inlet steam temperature T1s, and the rest is the same as in Embodiment 3. Therefore, even when measuring the exhaust gas temperature instead of the inlet steam temperature T1, the same operational effects as those of the above-described Embodiment 3 can be enjoyed.

[0152] In the above-described Embodiments 1 to 7, a plurality of superheaters (for example, primary superheater 1, secondary superheater 2, tertiary superheater 3, and quaternary superheater 4) that superheat steam in multiple stages by heat exchange with exhaust gas were arranged inside the exhaust gas flow path 200 so as to be adjacent to each other in the exhaust gas flow direction. However, the present invention is not limited to this. For example, at least one of the upstream side and the downstream side in the exhaust gas flow direction with respect to these plurality of superheaters may have a heat exchanger with a piping system different from that of these plurality of superheaters arranged therein, or the heat exchanger may be interposed between these plurality of superheaters. Further, the heat exchanger may be a horizontal evaporation tube for generating steam from water by heat exchange with exhaust gas, or a reheater for reheating the superheated steam after being used to drive an external device such as a turbine again by heat exchange with exhaust gas, or may be other heat exchangers.

[0153] Also, in the above-described Embodiments 1 to 7, three or four superheaters were exemplified as a plurality of superheaters that superheat steam in multiple stages by heat exchange with exhaust gas. However, the present invention is not limited to this. For example, these plurality of superheaters may consist of two superheaters, or may consist of five or more superheaters.

[0154] Also, in the above-described Embodiments 2 to 6, a measurement unit for measuring the temperature of the superheated steam (inlet steam temperature T1) was provided in the middle of the introduction pipe (for example, communication pipe 101 or communication pipe 102) for introducing superheated steam into the superheating pipe of the first heat exchanger (for example, secondary superheater 2 or tertiary superheater 3) of the present invention. However, the present invention is not limited to this. For example, instead of providing a temperature measurement unit in the middle of the introduction pipe, a measurement unit for measuring the temperature of the superheated steam after superheating by the first heat exchanger may be provided in the middle of the communication pipe communicating with the outlet of the superheating pipe of the first heat exchanger of the present invention, or temperature measurement units may be provided in both the introduction pipe and the communication pipe.

[0155] Further, in the above-described Embodiments 2 to 6, a measuring unit for measuring the temperature of the superheated steam in the introduction pipe that introduces the superheated steam into the superheated pipe of the first heat exchanger of the present invention (inlet steam temperature T1) is provided downstream (on the downstream side in the flow direction of the superheated steam) of the inlet desuperheater (first desuperheater) that reduces the temperature. However, the present invention is not limited to this. For example, the temperature measuring unit may be provided upstream (on the upstream side in the flow direction of the superheated steam) of the inlet desuperheater, or may be provided on both the upstream and downstream sides of the inlet desuperheater.

[0156] Further, in the above-described Embodiment 7, the temperatures of the respective exhaust gases before and after heat exchange with each of the first heat exchanger and the second heat exchanger of the present invention are measured by three exhaust gas temperature measuring units 19a, 19b, and 19c, and the above-described inlet steam temperature T1 is calculated using the measured temperatures obtained thereby. However, the present invention is not limited to this. For example, the temperatures of the respective exhaust gases before and after heat exchange with the second heat exchanger of the present invention may be measured by two exhaust gas temperature measuring units 19a and 19b, and the temperature of the superheated steam after superheating by the first heat exchanger of the present invention may be calculated using the measured temperatures obtained thereby.

[0157] Also, the present invention is not limited by the above-described Embodiments 1 to 7, and those configured by appropriately combining the above-described respective components are also included in the present invention. In addition, all other embodiments, examples, operation techniques, etc. made by those skilled in the art based on the above-described Embodiments 1 to 7 are included in the scope of the present invention.

Explanation of Reference Numerals

[0158] 1 Primary superheater 1a Superheated pipe 2 Secondary superheater 2a Superheated pipe 3 Tertiary superheater 3a Superheated pipe 4 Quaternary superheater 4a Superheated pipe 10, 20, 30, 40, 50, 60, 70 Superheating device 11 Inlet desuperheater 12 Outlet temperature measuring unit 13, 14 Temperature measuring unit Control units 15, 25, 35, 45, 55, 65, 75 16 First desuperheater 17 Second desuperheater 18 Third desuperheater 19a, 19b, 19c Exhaust gas temperature measurement parts 100 Steam pipe 101 - 103 Communication pipes 104 Outlet pipe 110 Steam 111 - 114 Superheated steam 200 Exhaust gas flow path 201 Upstream region 202, 202A, 202B Intermediate regions 203 Downstream region 210 - 214 Exhaust gas

Claims

1. An overheating device provided in a boiler that generates steam using the heat of exhaust gas discharged from a furnace, and overheats the steam by heat exchange with the exhaust gas, having superheating tubes in a first region in an exhaust gas flow path through which the exhaust gas flows, and a first heat exchanger that overheats superheated steam in the superheating tubes in the first region by heat exchange with the exhaust gas; having superheating tubes in a second region in the exhaust gas flow path that is an upstream region in the flow direction of the exhaust gas from the first region, and a second heat exchanger that overheats superheated steam in the superheating tubes in the second region by heat exchange with the exhaust gas; an inlet desuperheater that supplies cooling water into an introduction pipe that introduces superheated steam into the superheating tubes of the first heat exchanger, and reduces the inlet steam temperature, which is the temperature of the superheated steam in the introduction pipe; an outlet temperature measuring unit that measures the outlet steam temperature, which is the temperature of the superheated steam that has been superheated by the second heat exchanger and sent from the superheating tubes of the second heat exchanger to an outlet pipe; a control unit that controls the supply amount of the cooling water by the inlet desuperheater based on the outlet steam temperature, controls the inlet steam temperature to be equal to or higher than the saturation temperature at the inlet pressure of the first heat exchanger, and controls the outlet steam temperature to a superheated steam temperature of less than 600°C; comprising The superheating tubes of the second heat exchanger are characterized in that they have higher corrosion resistance than the superheating tubes of the first heat exchanger. An overheating device.

2. The superheating tubes of the second heat exchanger are tubes including at least one of a stainless steel tube and a build-up tube having a corrosion-resistant build-up layer on the outer wall surface of the steel tube, The overheating device according to claim 1, characterized in that.

3. The superheating tubes of the first heat exchanger are tubes including at least one of a carbon steel tube and a stainless steel tube, The overheating device according to claim 1, characterized in that.

4. Further comprising a superheater having superheating tubes in a downstream region in the exhaust gas flow path that is a downstream region in the flow direction of the exhaust gas from the first region, and overheating the steam in the superheating tubes in the downstream region by heat exchange with the exhaust gas to generate superheated steam, The overheating device according to claim 1, characterized in that.

5. The introduction pipe is a communication pipe that communicates the outlet of the superheating tubes of the primary superheater and the inlet of the superheating tubes of the first heat exchanger, The overheating device according to claim 4, characterized in that.

6. Further comprising a communication pipe that communicates the outlet of the superheating tubes of the first heat exchanger and the inlet of the superheating tubes of the second heat exchanger, The superheating device according to any one of claims 1 to 5, characterized in that...

7. An intermediate superheater having a superheating tube in an intermediate region within the exhaust gas flow path between the first region and the second region, and superheating superheated steam in the superheating tube of the intermediate region by heat exchange with the exhaust gas; A first communication pipe communicating the outlet of the superheating tube of the first heat exchanger with the inlet of the superheating tube of the intermediate superheater; A second communication pipe communicating the outlet of the superheating tube of the intermediate superheater with the inlet of the superheating tube of the second heat exchanger; The superheating device according to any one of claims 1 to 4, further comprising...

8. A third heat exchanger having a superheating tube in a third region within the exhaust gas flow path, which is a region upstream of the second region in the flow direction of the exhaust gas, and superheating superheated steam in the superheating tube of the third region by heat exchange with the exhaust gas; A desuperheater that supplies cooling water to the superheated steam flowing into the superheating tube of the third heat exchanger to lower the temperature of the flowing-in superheated steam; A communication pipe communicating the outlet of the superheating tube of the third heat exchanger with the inlet of the superheating tube of the first heat exchanger; The superheating device according to any one of claims 1 to 4, further comprising...

9. A first heat exchanger that superheats superheated steam in a superheating tube disposed in a first region within an exhaust gas flow path through which exhaust gas discharged from a furnace flows, by heat exchange with the exhaust gas, and a second heat exchanger that superheats superheated steam in a superheating tube disposed in a second region within the exhaust gas flow path, which is a region upstream of the first region in the flow direction of the exhaust gas, by heat exchange with the exhaust gas. In a method for controlling the temperature of superheated steam by a superheating device comprising... A temperature measurement step of measuring an outlet steam temperature, which is the temperature of the superheated steam superheated by the second heat exchanger and sent from the superheating tube of the second heat exchanger to an outlet pipe; A water supply amount control step of controlling the supply amount of cooling water into an introduction pipe that introduces superheated steam into the superheating tube of the first heat exchanger, based on the outlet steam temperature; A temperature control step of controlling the inlet steam temperature, which is the temperature of the superheated steam in the introduction pipe, to be equal to or higher than the saturation temperature at the inlet pressure of the first heat exchanger by supplying the cooling water with the supply amount, and controlling the outlet steam temperature to a superheated steam temperature of less than 600°C; Including A method for controlling the temperature of superheated steam by a superheating device, characterized in that the superheating tube of the second heat exchanger has higher corrosion resistance than the superheating tube of the first heat exchanger.

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