JP3483598B2 - Method and apparatus for cleaning finned heat transfer tubes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for cleaning a finned heat transfer tube used in an exhaust heat recovery system such as an exhaust heat recovery boiler, and more particularly to nitrogen oxidation by injecting ammonia into exhaust gas. Provided in an exhaust heat recovery system having a denitration catalyst layer for reducing substances (NOx) to harmless nitrogen (N ₂ ),
The present invention relates to a method for cleaning a finned heat transfer tube, which is suitable for removing ammonium sulfate-based compounds such as acidic ammonium sulfate salt and dust deposited on the surface of the finned heat transfer tube, and an apparatus for carrying out the method.

[0002]

2. Description of the Related Art As a heat transfer tube used in a conventional exhaust heat recovery system such as an exhaust heat recovery boiler, a finned heat transfer tube having a large heat transfer area is used in order to improve heat exchange efficiency. Then, in order to convert nitrogen oxides (NOx) contained in the exhaust gas into harmless nitrogen, an exhaust heat recovery boiler or the like is provided with a denitration catalyst layer for injecting ammonia and performing catalytic reduction in the presence of a catalyst. There is. In addition, since the exhaust gas also contains sulfur oxides (SOx), unreacted ammonia that has not reacted with NOx has a denitration catalyst layer (exhaust gas temperature of 30
Exhaust gas temperature of 15
The surface of the heat transfer tube with fins provided in the range of 0 to 300 ° C., particularly ammonium sulfate-based compounds such as ammonium ammonium sulfate adhere between the fins, and the heat transfer tube with fins by the adhered ammonium sulfate-based compound Corrosion of aluminum, and decrease in heat transfer efficiency and increase in draft loss (pressure loss) due to deposits formed by mixing and depositing ammonium sulfate compounds and dust contained in exhaust gas.
For example, there is a problem such as a reduction in output of a gas turbine or the like in a combined cycle power plant. In order to solve this problem, the conventional fin heat transfer tube cleaning method is
For example, as shown in FIG. 4 and FIG. 5 or FIG. 6 and FIG. 7, the finned heat transfer tube group 11 is provided with a plurality of cleaning water spray pipes 5, 5a, 5b, and the finned heat transfer tube tube (heat transfer tube ) 2 at a right angle to the fins 3 and in a direction parallel to the fins 3 in order to wash away and remove the deposits accumulated between the fins, or further to the finned heat transfer tube group 11
In order to wash the whole of the washing water spray pipe 5a,
The cleaning water spray pipe 5 having a structure capable of moving or rotating 5b was provided. 5 is a view taken along the line AA of FIG. 4, and FIG. 7 is a view taken along the line BB of FIG. This conventional fin-equipped heat transfer tube cleaning device requires a drive device (not shown) for moving or rotating the cleaning water spray pipes 5, 5a, 5b. It is supplied from the provided pipe assembling part and introduced into the washing water spray pipe 5 via the connecting pipes 7a and 7b or directly, and becomes the washing spray 6 and is parallel to the fins 3 of the finned heat transfer pipe group 11. Then, it was sprayed in a direction perpendicular to the tube 2 to wash and remove deposits such as ammonium sulfate-based compounds and dust adhered and deposited on the heat transfer surface between the fins. However, when the heat exchanger constituted by the finned heat transfer tube group 11 becomes large, the wash water spray pipes 5, 5a, 5b become long, and the back pressure in the upper spray part and the lower spray part is reduced due to the pressure loss. If the spray hole diameter is the same, the amount of the lower water-washing spray 6 will be extremely large. Now, the back pressure required by the washing spray 6 is 0.5k.
and g / cm ^2, 0.5kg / c the back pressure of the upper spray
According to m ² , the back pressure of the lower spray becomes about 1.5 kg / cm ² when the length of the cleaning water spray pipes 5, 5a, 5b is 10 m in the spray system shown in FIG. The amount is about 1.7 times. As a solution to this problem, there is a method in which the hole diameter of the nozzle of the water washing spray 6 is made smaller toward the bottom, or a method of dividing the washing water spray pipes 5a and 5b into upper and lower halves as shown in FIG. When the heat transfer tube is composed of only the tube 2 and the fins 3 are not attached, the washing spray 6 is sprayed from the upper part of the tube 2 and the washing water is simply washed down (down) on the surface of the tube 2. However, in the case of the heat transfer tube with fins, the cleaning method in which the water spray 6 is sprayed so as to hit the gap between the fins 3 is used as described above. As a conventional technique, for example, Japanese Patent Laid-Open No. 4-161702 can be cited.

[0003]

As described above, in the prior art, since a drive device for moving or rotating the wash water spray pipe is required, it becomes necessary to perform maintenance and inspection of them. Due to the washing pipe, the drive unit and the wiring cable for the washing pipe, there were great restrictions on the arrangement of the washing water spray pipe, which was a great obstacle to maintenance and inspection. Further, the above driving device requires a wiring cable and a power supply facility, and there is a problem that it becomes an extremely expensive facility in combination with a restriction on arrangement.

An object of the present invention is to solve the above problems in the prior art, and to dissolve ammonium sulfate-based compounds such as acidic ammonium sulfate salts which reduce heat transfer efficiency due to corrosive properties accumulated between fins of a finned heat transfer tube. It is an object of the present invention to provide a method for cleaning a heat transfer tube with fins and an apparatus for the same, which is capable of removing dust and the like by an effective and inexpensive method.

[0005]

In order to achieve the above-mentioned object of the present invention, a denitration catalyst layer for injecting ammonia into exhaust gas and reducing it to harmless nitrogen is provided, and headers are provided above and below. In the exhaust heat recovery system of the structure supporting a plurality of finned heat transfer tube groups arranged vertically by the cleaning method in which the ammonium sulfate compound and dust deposited between the fins of the finned heat transfer tube are washed and removed. Water is dropped vertically to the heat transfer tube with fins and at right angles to the fins, and the cleaning water propagates on the surface of the fins, and the surface tension of the cleaning water causes the cleaning water toward the gap between the fins. It utilizes the phenomenon of flowing down while traveling, and a means for adjusting the flow of washing water flowing down toward the gap between the fins, so-called surface flow, is provided. Kicking those. FIG. 3 (a),
(B) shows the principle of the cleaning method of the present invention. Figure 3 (a)
Shows the flow of cleaning water when there is no deposit of ammonium sulfate compound or dust between the fins of the finned heat transfer tube, and FIG. 3 (b) shows the ammonium sulfate compound. This figure shows the flow of cleaning water when deposits such as dust and dirt are attached. If the above deposits are adhered between the fins, the cleaning water will flow into the gap between the fins. It was found that the phenomenon of flowing down, washing and removing while becoming more prominent became even more prominent. The specific configuration of the finned heat transfer pipe cleaning device of the present invention is an exhaust heat recovery device having a denitration catalyst layer for injecting ammonia into exhaust gas and reducing it to harmless nitrogen. A plurality of finned heat transfer tubes, which are supported by upper and lower pipe bundles that bundle a plurality of finned heat transfer tubes, and are located at the upper position of the finned heat transfer tube group or at the upper part of the finned heat transfer tube group. , A washing water spray pipe for horizontally washing and removing the ammonium sulfate compound and dust adhered and deposited between the fins of the finned heat transfer tubes arranged vertically at a position lower than the upper pipe drawer was sprayed. Means is provided for adjusting the surface of the fin heat transfer tube so that the cleaning water flows down toward the gap between the fins on the surface of the fin heat transfer tube.

[0006]

For example, in a spiral heat transfer tube with fins, when cleaning water is sprayed on the upper part of the finned heat transfer tube group, a part of the cleaning water is scattered from the tip of the fin, but most of it is Since it flows down from the fin tip to the fin tip, it has been conventionally considered that there is no cleaning effect for deposits such as ammonium sulfate-based compounds and dust accumulated between the fins. However, according to a detailed observation of the flow state of the washing water on the fin surface of the finned heat transfer tube installed vertically, one side of the water film of the washing water flowing down the tip of the fin is a metal (fin and tube). Since the other surface of the water film becomes a free surface, most of the flow of the water film is directed inward between the fins due to the surface tension, and a part of the flow of the water film is part of the inside of the fins. It was found to flow down the surface. It has been found that the tendency of the flow of the washing water is more remarkable as the deposits are present in the gaps between the fins. On the other hand, most of the deposits adhering between the fins are ammonium sulfate-based compounds such as acidic ammonium sulfate and have some water solubility, so in addition to the above-mentioned cleaning removal action by the kinetic energy of the flow of cleaning water, It is considered that a part of the soluble ammonium sulfate compound in the substance is dissolved and the deposit such as dust adhering thereto is simultaneously fluidized and removed. Further, it has been found that the above effect is further enhanced in the case of a heat transfer tube with serrated (saw tooth) fins.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 shows a configuration of an upper header portion of the finned heat transfer tube cleaning device of the present invention, and FIG.
(A), (b) shows the CC arrow line view of FIG. In the figure, a cleaning water spray pipe 5 is horizontally installed near the lower parts of the upper headers 1, 1a, 1b of the finned heat transfer tube group 11 including the tube 2 and the spiral fins 3, and a plurality of cleaning sprays 6 are provided. , Heat transfer tube group with fin 1
Water is sprinkled on top of 1. The sprinkled washing water is a spiral fin even if it is not sprinkled all around the fins 3 at the upper end of the finned heat transfer tube.
By flowing down to a certain extent, a liquid film of cleaning water spreads over the entire peripheral surface of the fin 3, and it becomes possible to remove deposits such as ammonium sulfate compounds and dust between the fins while dissolving. The washing water sprinkled on the upper part of the finned heat transfer tube group 11 flows down while dissolving and removing the deposits between the fins by the above phenomenon, and is guided to the drainage system provided at the lower part of the finned heat transfer tube group, It is discharged outside. The washing water spray pipe 5 is installed on the upper part of the upper header 1, and the washing spray 6 is sprinkled from the upper part of the upper header 1 of the heat transfer tube group with fins to the entire heat transfer tube group, and then propagates through the heat transfer tube 2 with each fin. Although it is possible to clean the heat transfer tubes, in order to clean the heat transfer tubes as soon as possible after the plant operation is stopped and to shorten the cleaning stop period, the high temperature upper header 1 In addition, direct water sprinkling causes a problem in terms of thermal stress. Therefore, it is better to sprinkle water on the finned heat transfer tube which is designed to withstand thermal deformation relatively easily. Therefore, it is desirable that the cleaning water spray pipe 5 is installed at the side level of the upper header 1 or below the upper header 1. When there are a plurality of finned heat transfer tube groups, for example, as shown in FIG.
As shown in (b), one cleaning water spray pipe 5
It is also possible to use a structure in which a plurality of pipe groups are sprinkled with water for cleaning.

[0008]

As described in detail above, according to the method for cleaning a finned heat transfer tube of the present invention, a drive device for moving and rotating the cleaning water spray pipe is not required, and the cleaning water spray pipe can be vertically moved. It is placed horizontally above the array of heat transfer tubes, spraying an appropriate amount of cleaning water, and forming a liquid film flow that flows between the fins of the heat transfer tube with fins. In addition to being able to dissolve and remove ammonium sulfate compounds, it is also possible to fluidize and remove deposits such as dust at the same time, so that corrosion of finned heat transfer tubes can be prevented and heat exchange efficiency can be improved. You can In addition, a heat exchanger consisting of heat transfer tubes with fins arranged vertically can be freely planned, and an economical design can be achieved, which eliminates the need for a conventional drive device for moving or rotating the cleaning water spray pipe, maintenance, and inspection. Therefore, it is possible to realize a simple and inexpensive cleaning device for heat transfer tubes with fins, which has a large cleaning ability.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a fin-equipped heat transfer tube cleaning device exemplified in an embodiment of the present invention.

FIG. 2 is a schematic view showing an arrangement configuration of a wash water spray pipe, which is a view taken along the line CC of FIG.

FIG. 3 is an explanatory view showing the principle of cleaning the finned heat transfer tube exemplified in the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a conventional fin-equipped heat transfer tube cleaning device.

5 is a view on arrow AA of FIG. 4. FIG.

FIG. 6 is a schematic diagram showing another configuration of a conventional finned heat transfer tube cleaning device.

FIG. 7 is a view on arrow BB in FIG.

[Explanation of symbols]

1, 1a, 1b ... upper header 2, 2a, 2b ... Tube (heat transfer tube) 3, 3a, 3b ... fin 4 ... Lower header 5, 5a, 5b ... Wash water spray pipe 6… Washing spray 7a, 7b ... Connecting pipe 8… Radial flow of washing water (downstream) 9 ... Surface flow of wash water 10 ... Adhered matter (deposit) 11 ... Heat transfer tube group with fins

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-324002 (JP, A) JP-A-4-161702 (JP, A) JP-A 61-27402 (JP, A) JP-A 62- 41595 (JP, A) Actually developed 62-93505 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F22B 37/48 F22B 37/52 F22B 1/18 F28G 1/16 F28G 9/00

Claims (2)

(57) [Claims] 1. An exhaust heat recovery system having a denitration catalyst layer for injecting ammonia into exhaust gas to reduce it to harmless nitrogen and supporting a plurality of finned heat transfer tubes arranged vertically by upper and lower headers. In the cleaning method of washing and removing the ammonium sulfate-based compound and dust adhered and deposited between the fins of the finned heat transfer tube, a cleaning water spray pipe is horizontally provided above the vertically arranged finned heat transfer tube group. Arrange the cleaning water so that it drips vertically to the heat transfer tubes with fins and at right angles to the fins. A method of cleaning a heat transfer tube with fins, characterized in that a surface flow is formed to flow down toward the gap of the fin to remove deposits between the fins. 2. An exhaust heat recovery apparatus having a denitration catalyst layer for injecting ammonia into exhaust gas to reduce it to harmless nitrogen,
In the exhaust heat recovery device, a plurality of finned heat transfer tube groups having a structure of supporting a plurality of vertically arranged finned heat transfer tubes by bundling vertically are provided, and an upper part of the finned heat transfer tube group, Alternatively, at the upper part of the finned heat transfer tube group, at a position lower than the upper heat sink, horizontally install a spray pipe for removing ammonium sulfate compounds and dust deposited between the fins of the vertically arranged finned heat transfer tubes. A heat transfer tube with fins, which is provided with a means for adjusting the surface of the fin heat transfer tube so that the sprayed cleaning water flows down toward the fins on the surface of the fin heat transfer tube. Cleaning equipment.