Boilers and boiler protection methods

Abstract

To prevent dust from adhering to the interior of a boiler to protect the boiler.SOLUTION: A boiler includes: a heat radiation chamber having a heat transfer pipe which receives radiant heat of an exhaust gas circulating from a waste incinerator to generate steam, and a convective heat transfer chamber which overheats steam through heat exchange between the exhaust gas and the heat transfer pipe. The boiler has a plasma actuator, which generates airflow by an AC voltage being applied thereto, on a peripheral surface of the heat transfer pipe. Dust contained in the exhaust gas flows along the airflow generated by the plasma actuator. Thus, the structure can inhibit the dust contained in the exhaust gas from adhering to the heat transfer pipe and inhibit corrosion of the heat transfer pipe from being caused by the dust.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a boiler and a method for protecting a boiler. [Background technology]

[0002] Power generation in waste incinerators is achieved by recovering heat in a boiler from the high-temperature exhaust gas obtained from the combustion of waste in the incinerator, generating steam at a specified temperature and pressure, and introducing it into a turbine generator. The exhaust gas generated during waste incineration contains small particle size dust containing chlorine, sulfur, heavy metals, etc., and when this dust adheres to the boiler's heat transfer tubes, the adhered dust acts as an insulator, reducing heat transfer efficiency.

[0003] Inventions for removing dust adhering to boiler heat transfer tubes are disclosed in, for example, Patent Documents 1 and 2. The invention disclosed in Patent Document 1 mixes fuel gas and oxidant gas under high pressure, causes explosive combustion, and removes dust adhering to the heat transfer tubes using the pressure wave generated by the explosive combustion. The invention disclosed in Patent Document 2 removes ash adhering to the water tube group of the boiler by dropping ash balls formed from ash lumps smaller than a specified size and ash lumps larger than the specified size onto the water tube group. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-181008 [Patent Document 2] Japanese Patent Application Publication No. 2019-184151 Summary of the Invention [Problem to be solved by the invention]

[0005] The invention disclosed in Patent Document 1 consumes fuel gas and oxidant gas to generate pressure waves, resulting in high running costs. Furthermore, the invention disclosed in Patent Document 1 can only be operated intermittently due to explosive combustion, and strong impacts are generated, making it necessary to ensure the safety of workers. The invention disclosed in Patent Document 2 requires the steps of sorting ash lumps, drying ash balls, and transporting the ash lumps and ash balls, which incur costs for the equipment required for these steps and for operation. Furthermore, with the invention disclosed in Patent Document 2, there is a risk that the impact of the ash balls on impact may damage parts.

[0006] The present invention has been made in view of the above, and has an object to prevent dust from adhering to the inside of a boiler and protect the boiler. [Means for solving the problem]

[0007] A boiler according to one aspect of the present invention is a boiler comprising a radiation chamber equipped with a heat transfer tube that generates steam by receiving radiant heat from exhaust gas circulating from a waste incinerator, and a convection heat transfer chamber that superheats the steam by heat exchange between the exhaust gas and the heat transfer tube, and has a plasma actuator on the circumferential surface of the heat transfer tube that generates an airflow when an alternating current voltage is applied.

[0008] In the boiler according to the present invention, the plasma actuator may be provided on the inner walls of the radiation chamber and the convection heat transfer chamber.

[0009] The boiler protection method of the present invention is for a boiler having a radiation chamber equipped with a heat transfer tube that generates steam by receiving radiant heat from exhaust gas circulating from a waste incinerator, and a convection heat transfer chamber that superheats the steam by heat exchange between the exhaust gas and the heat transfer tube, by applying an AC voltage to a plasma actuator provided on the circumferential surface of the heat transfer tube to induce an airflow along the circumferential surface. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent dust from adhering to the inside of the boiler, thereby protecting the boiler. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the configuration of an incinerator and a boiler according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the inside of the boiler according to the embodiment. [Figure 3] FIG. 3 is a perspective view of the plasma actuator according to the embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along line AA in FIG. [Figure 5] FIG. 5 is a diagram showing an example of the arrangement of plasma actuators. [Figure 6] FIG. 6 is a diagram showing an example of the arrangement of plasma actuators. [Figure 7] FIG. 7 is a diagram showing a modified example of the plasma actuator. [Figure 8] FIG. 8 is a diagram showing a modified example of the plasma actuator. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. It should be noted that the drawings are schematic and that the dimensional relationships between elements may differ from the actual ones.

[0013] [Embodiment] FIG. 1 is a diagram showing the configuration of an incinerator 1 and a boiler 2 according to an embodiment of the present invention. The incinerator 1 is an incinerator that incinerates, for example, waste. The incinerator 1 is connected to a boiler 2, and exhaust gas generated in the incinerator 1 flows into the boiler 2. The boiler 2 is provided with bent portions 21 and 22 that bend the flow of the exhaust gas. The bent portions 21 and 22 form, from the upstream side of the exhaust gas flow path, a first radiant chamber 11, a second radiant chamber 12, and a convective heat transfer chamber 13. The exhaust gas discharged after burning waste in the incinerator 1 flows from bottom to top through the first radiant chamber 11, from top to bottom through the second radiant chamber 12, and from bottom to top through the convective heat transfer chamber 13.

[0014] 2 is a diagram showing the inside of the boiler 2. In the second radiation chamber 12, heat transfer tubes 40 that receive radiant heat from the exhaust gas and generate steam are arranged as radiation heat transfer surfaces. In the convection heat transfer chamber 13, from the upstream side of the exhaust gas flow path, a screen tube 32, a secondary superheater 34, a tertiary superheater 36, and a primary superheater 38 are provided. Note that an economizer may be provided in the convection heat transfer chamber 13 as needed.

[0015] The secondary superheater 34, the tertiary superheater 36, and the primary superheater 38 each include a heat transfer tube group consisting of a plurality of heat transfer tubes 40 arranged horizontally in multiple stages in the vertical direction. This heat transfer tube group forms a convection heat transfer surface and is configured to further superheat the steam generated in the heat transfer tubes 40 in the second radiation chamber 12 by heat exchange with the exhaust gas. The heat transfer tubes 40 are provided on the screen tube 32. The screen tube 32 cools the exhaust gas introduced into the convection heat transfer chamber 13 and solidifies dust components contained in the exhaust gas, which are then separated from the exhaust gas as dust. An economizer (not shown) is connected to the convection heat transfer chamber 13, and the exhaust gas that has passed through the primary superheater 38 flows through the economizer.

[0016] In this embodiment of the present invention, a plasma actuator 100 is provided on the outer circumferential surfaces of the heat transfer tubes 40 of the screen tube 32, secondary superheater 34, tertiary superheater 36, and primary superheater 38. The plasma actuator 100 is a device that uses a dielectric barrier discharge to induce and control a flow of atmospheric gas.

[0017] FIG. 3 is a perspective view of the plasma actuator, and FIG. 4 is a cross-sectional view taken along line AA in FIG. 3. The plasma actuator 100 includes a first electrode 101, a second electrode 102, a dielectric layer 103, and an insulating layer 104. The dielectric layer 103 is formed, for example, into a rectangular shape from a dielectric ceramic. The first electrode 101 and the second electrode 102 are formed, for example, into a rectangular shape from titanium electrodes formed by coating titanium with platinum. The first electrode 101 is disposed on the surface of the dielectric layer 103, and the second electrode 102 is disposed on the back surface of the dielectric layer 103 so as not to overlap the first electrode 101 in the vertical direction. The first electrode 101 is connected to an AC power supply 200 that outputs an AC voltage. The second electrode 102 is connected to the AC power supply 200 and ground GND. The insulating layer 104 is formed of an insulator and covers the back surface of the dielectric layer 103 and the second electrode 102.

[0018] When an AC voltage is applied from AC power supply 200 to first electrode 101 and second electrode 102, a discharge occurs in the area sandwiched between first electrode 101 and dielectric layer 103, inducing a gas flow in the direction of the arrow shown in Fig. 4. The voltage applied from AC power supply 200 to first electrode 101 and second electrode 102 is several kV and several kHz.

[0019] Fig. 5 is a diagram showing an example of the arrangement of plasma actuator 100. Fig. 5 shows a cross section of heat transfer tube 40. Plasma actuator 100 is arranged, for example, as shown in Fig. 5, at the lower end side of the outer circumferential surface of heat transfer tube 40 so that insulating layer 104 comes into contact with the outer circumferential surface of heat transfer tube 40.

[0020] The plasma actuator 100 on the left side shown in Figure 5 is positioned so that it generates an airflow along the circumferential surface of the heat transfer tube 40 in the opposite direction to the plasma actuator 100 on the right side, and the plasma actuator 100 on the right side shown in Figure 5 is positioned so that it generates an airflow along the circumferential surface of the heat transfer tube 40 in the opposite direction to the plasma actuator 100 on the left side. In the convection heat transfer chamber 13, the exhaust gas flows from below to above the heat transfer tube 40, so the exhaust gas flows from below the heat transfer tube 40 in the direction of the thick arrow shown in Figure 5. The exhaust gas that reaches the heat transfer tube 40 flows along the circumferential surface of the heat transfer tube 40 in the direction of the thin arrow shown in Figure 5 due to the airflow generated by the plasma actuator 100.

[0021] Here, dust contained in the exhaust gas also flows along the airflow generated by the plasma actuator 100, so the dust contained in the exhaust gas can be prevented from adhering to the heat transfer tube 40. Furthermore, because dust can be prevented from adhering to the heat transfer tube 40, corrosion of the heat transfer tube 40 due to dust can be prevented. Furthermore, because dust can be prevented from adhering to the heat transfer tube 40, a decrease in heat transfer efficiency can be prevented. Furthermore, because the plasma actuator 100 is installed on the surface of the heat transfer tube 40, the plasma actuator 100 can be easily retrofitted to an existing boiler after dust has been removed from the heat transfer tube 40. Furthermore, because the plasma actuator 100 has no mechanically moving components and a small number of parts, introduction costs can be kept low and maintenance can be easily performed. Furthermore, because the plasma actuator 100 can prevent dust from adhering to the heat transfer tube 40 by simply supplying power, running costs can be kept low.

[0022] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0023] In the embodiment described above, two plasma actuators 100 are arranged on the lower end side of the heat transfer tube 40, but the number of plasma actuators 100 arranged on the heat transfer tube 40 is not limited to two. For example, as shown in Fig. 6, plasma actuators 100 may be arranged on the circumferential surface of the heat transfer tube 40 between the upper and lower ends and also on the upper end side.

[0024] In the above-described embodiment, the plasma actuator 100 includes one first electrode 101 and one second electrode 102. However, the number of first electrodes 101 and second electrodes 102 is not limited to one. FIG. 7 is a cross-sectional view of a plasma actuator 100A according to a modified example. In the plasma actuator 100A, the first electrode 101 and the second electrode 102 are disposed at a predetermined distance on the upper surface of the dielectric layer 103. In the plasma actuator 100A, the first electrode 101 and the second electrode 102 are disposed at a predetermined distance on the back surface of the dielectric layer 103. The second electrode 102 disposed on the back surface of the dielectric layer 103 is positioned so as not to overlap the first electrode 101 and the second electrode 102 on the front surface when viewed in the vertical direction. The first electrode 101 disposed on the back surface of the dielectric layer 103 is positioned so as not to overlap the second electrode 102 on the front surface when viewed in the vertical direction. The two first electrodes 101 are connected to an AC power source 200. The two second electrodes 102 are connected to an AC power supply 200 and the ground GND.

[0025] With plasma actuator 100A, when AC voltage is applied from AC power supply 200 to first electrode 101 and second electrode 102, a gas flow is induced in the direction of the arrows shown in FIG. 7 by first electrode 101 on the front surface and second electrode 102 on the back surface, and by second electrode 102 on the front surface and first electrode 101 on the back surface. By disposing plasma actuator 100A on heat transfer tube 40, an air flow is generated around heat transfer tube 40, preventing dust from adhering to heat transfer tube 40. The AC voltage applied to plasma actuator 100A may have a DC component superimposed thereon. The voltage applied to plasma actuator 100A may also be a pulse voltage.

[0026] FIG. 8 is a cross-sectional view of a plasma actuator 100B according to a modified example. In plasma actuator 100B, first electrode 101 and third electrode 105 are arranged at a predetermined distance on the upper surface of dielectric layer 103. In plasma actuator 100B, second electrode 102 is arranged on the back surface of dielectric layer 103. Third electrode 105 is a rectangular titanium electrode, for example, titanium coated with platinum. First electrode 101 of plasma actuator 100B is connected to AC power supply 200. Second electrode 102 of plasma actuator 100B is connected to AC power supply 200 and ground GND. Third electrode 105 is connected to the positive electrode of DC power supply 201, which applies a DC voltage. The negative electrode of DC power supply 201 is connected to ground GND. With plasma actuator 100B, when AC voltage is applied from AC power supply 200 to first electrode 101 and second electrode 102, and DC voltage is applied to third electrode 105, a gas flow is induced in the direction of the arrow shown in Fig. 8. By placing plasma actuator 100B on heat transfer tube 40, an air flow is generated around heat transfer tube 40, making it possible to prevent dust from adhering to heat transfer tube 40.

[0027] The position where plasma actuator 100, plasma actuator 100A, or plasma actuator 100B is arranged is not limited to heat transfer tube 40. Plasma actuator 100, plasma actuator 100A, or plasma actuator 100B may also be arranged on inner wall 11a of first radiation chamber 11, inner wall 12a of second radiation chamber 12, inner wall 13a of convection heat transfer chamber 13, and heat transfer tube 40 arranged in second radiation chamber 12, as shown in FIG. [Explanation of symbols]

[0028] 1. Incinerator 2 boilers 11 1st radiation room 11a Inner wall 12 Second radiation room 12a Inner wall 13 Convection heat transfer chamber 13a Inner wall 21, 22 Bend 32 Screen tube 34 Secondary superheater 36 Tertiary superheater 38 Primary superheater 40 Heat transfer tube 100, 100A, 100B Plasma Actuator 101 1st electrode 102 2nd electrode 103 Dielectric layer 104 Insulating layer 105 3rd electrode 200 AC power supply 201 DC power supply

Claims

1. A boiler comprising: a radiation chamber equipped with a heat transfer tube that generates steam by receiving radiant heat from exhaust gas flowing from a waste incinerator; and a convection heat transfer chamber that superheats the steam by heat exchange between the exhaust gas and the heat transfer tube, The heat transfer tube has a plasma actuator on its circumferential surface that generates an airflow along the circumferential surface of the heat transfer tube when an AC voltage is applied to it. Boiler.

2. The plasma actuator is provided on the inner walls of the radiation chamber and the convection heat transfer chamber. The boiler of claim 1.

3. A boiler having a radiation chamber equipped with a heat transfer tube that generates steam by receiving radiant heat from exhaust gas flowing from a waste incinerator, and a convection heat transfer chamber that superheats the steam by heat exchange between the exhaust gas and the heat transfer tube, An AC voltage is applied to a plasma actuator provided on the circumferential surface of the heat transfer tube to induce an airflow along the circumferential surface. How to protect your boiler.

Images