JP7740123B2 - Boilers and boiler protection methods - Google Patents

Description

The present invention relates to a boiler and a method for protecting a boiler.

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

Examples of inventions for removing dust adhering to boiler heat transfer tubes are those disclosed in Patent Documents 1 and 2. The invention disclosed in Patent Document 1 mixes fuel gas and oxidant gas under high pressure, causing explosive combustion, and removes dust adhering to the heat transfer tubes using the pressure waves generated by the explosive combustion. The invention disclosed in Patent Document 2 removes ash adhering to the water tube banks of the boiler by dropping ash balls formed from ash lumps smaller than a specified size, and ash lumps larger than a specified size, onto the water tube banks.

JP 2017-181008 A Japanese Patent Application Laid-Open No. 2019-184151

The invention disclosed in Patent Document 1 requires high running costs because it consumes fuel gas and oxidant gas to generate pressure waves. Furthermore, the invention disclosed in Patent Document 1 can only be operated intermittently due to explosive combustion, and strong impacts are generated, so the safety of workers must be ensured. The invention disclosed in Patent Document 2 requires the processes of sorting ash lumps, drying ash balls, and transporting ash lumps and ash balls, which incur costs for the equipment required for these processes 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.

The present invention was made in consideration of the above, and aims to prevent dust from adhering inside the boiler and protect the boiler.

One aspect of the present invention relates to a boiler that includes 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 through heat exchange between the exhaust gas and the heat transfer tube. The boiler also includes a plasma actuator on the circumferential surface of the heat transfer tube that generates an airflow when an AC voltage is applied.

Furthermore, 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.

The boiler protection method of the present invention involves applying an AC voltage to a plasma actuator attached to the circumferential surface of the heat transfer tube in a boiler equipped with 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 through heat exchange between the exhaust gas and the heat transfer tube, thereby inducing an airflow along the circumferential surface.

This invention has the effect of preventing dust from adhering to the inside of the boiler and protecting the boiler.

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

Embodiments of the present invention are described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments described below. It should also be noted that the drawings are schematic, and the dimensional relationships between elements may differ from the actual situation.

[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, for example, an incinerator that incinerates waste. A boiler 2 is connected to the incinerator 1, 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 a first radiant chamber 11, a second radiant chamber 12, and a convective heat transfer chamber 13 in the boiler 2, from the upstream side of the exhaust gas flow path. Note that 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.

Figure 2 shows the interior of the boiler 2. In the second radiation chamber 12, heat transfer tubes 40 are arranged as radiation heat transfer surfaces, receiving radiant heat from the exhaust gas to generate steam. 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 also be provided in the convection heat transfer chamber 13, if necessary.

The secondary superheater 34, tertiary superheater 36, and primary superheater 38 each include a heat transfer tube group consisting of multiple heat transfer tubes 40 arranged horizontally in multiple vertical stages. This heat transfer tube group forms a convection heat transfer surface and further superheats the steam generated in the heat transfer tubes 40 in the second radiation chamber 12 through 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 the dust components contained in the exhaust gas, separating them as dust from the exhaust gas. An economizer (not shown) is connected to the convection heat transfer chamber 13, and the exhaust gas that passes through the primary superheater 38 flows through the economizer.

In an embodiment of the present invention, a plasma actuator 100 is provided on the outer circumferential surface 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 the flow of ambient gas.

Figure 3 is a perspective view of the plasma actuator, and Figure 4 is a cross-sectional view taken along line A-A in Figure 3. The plasma actuator 100 has 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, from a dielectric ceramic and has a rectangular shape. The first electrode 101 and the second electrode 102 are formed, for example, from titanium electrodes made by coating titanium with platinum and have a rectangular shape. 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 when viewed from above. 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 from an insulator and covers the back surface of the dielectric layer 103 and the second electrode 102.

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

Figure 5 shows an example of the arrangement of the plasma actuator 100. Figure 5 shows a cross section of a heat transfer tube 40. The plasma actuator 100 is arranged, for example, as shown in Figure 5, so that the insulating layer 104 contacts the outer surface of the heat transfer tube 40 at the lower end of the outer surface of the heat transfer tube 40.

The plasma actuator 100 on the left side shown in Figure 5 is positioned so that an airflow occurs 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 an airflow occurs 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, exhaust gas flows from below to above, 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.

Here, dust contained in the exhaust gas also flows along the airflow generated by the plasma actuator 100, preventing the dust contained in the exhaust gas from adhering to the heat transfer tube 40. Furthermore, preventing dust from adhering to the heat transfer tube 40 prevents corrosion of the heat transfer tube 40 due to dust. Furthermore, preventing dust from adhering to the heat transfer tube 40 prevents a decrease in heat transfer efficiency. 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 existing boilers after removing dust 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 are kept low and maintenance is easy. Furthermore, because the plasma actuator 100 can prevent dust from adhering to the heat transfer tube 40 by simply supplying power, running costs are kept low.

[Modification]
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.

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.

In the above-described embodiment, the plasma actuator 100 is configured to include 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 arranged 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 arranged at a predetermined distance on the back surface of the dielectric layer 103. The second electrode 102 arranged 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 in a vertical direction. The first electrode 101 arranged on the back surface of the dielectric layer 103 is positioned so as not to overlap the second electrode 102 on the front surface in a vertical direction. The two first electrodes 101 are connected to an AC power source 200. In addition, the two second electrodes 102 are connected to the AC power supply 200 and ground GND.

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

Figure 8 is a cross-sectional view of a modified plasma actuator 100B. In plasma actuator 100B, a first electrode 101 and a third electrode 105 are arranged at a predetermined distance on the upper surface of dielectric layer 103. In plasma actuator 100B, a second electrode 102 is arranged on the back surface of dielectric layer 103. Third electrode 105 is a titanium electrode, for example, titanium coated with platinum, and is formed in a rectangular shape. The first electrode 101 of plasma actuator 100B is connected to AC power supply 200. The second electrode 102 of plasma actuator 100B is connected to AC power supply 200 and ground GND. The 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 Figure 8. By placing plasma actuator 100B 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 location where plasma actuator 100, plasma actuator 100A, or plasma actuator 100B is arranged is not limited to the heat transfer tube 40. Plasma actuator 100, plasma actuator 100A, or plasma actuator 100B may also be arranged on the inner wall 11a of the first radiation chamber 11, the inner wall 12a of the second radiation chamber 12, the inner wall 13a of the convection heat transfer chamber 13, and the heat transfer tube 40 arranged in the second radiation chamber 12, as shown in FIG. 2.

REFERENCE SIGNS LIST 1 incinerator 2 boiler 11 first radiation chamber 11a inner wall 12 second radiation chamber 12a inner wall 13 convection heat transfer chamber 13a inner wall 21, 22 bent portion 32 screen tube 34 secondary superheater 36 tertiary superheater 38 primary superheater 40 heat transfer tube 100, 100A, 100B plasma actuator 101 first electrode 102 second electrode 103 dielectric layer 104 insulating layer 105 third electrode 200 AC power supply 201 DC power supply

Claims (3)

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,
A boiler comprising a plasma actuator disposed on a circumferential surface of the heat transfer tube, the plasma actuator generating an airflow along the circumferential surface of the heat transfer tube when an AC voltage is applied thereto. The boiler according to claim 1 , wherein the plasma actuators are provided on the inner walls of the radiation chamber and the convection heat transfer chamber. 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,
A boiler protection method comprising applying an AC voltage to a plasma actuator provided on a circumferential surface of the heat transfer tube to induce an airflow along the circumferential surface.