JP7772015B2 - Ferrule for heat transfer tube of heat exchanger and method for assembling the same - Google Patents

Description

The present invention relates to a ferrule for a heat transfer tube that is assembled to the fluid inlet of a heat exchanger heat transfer tube, and a method for assembling the ferrule.

Shell-and-tube heat exchangers are widely known as heat exchangers used in boilers and other equipment. They have multiple heat transfer tubes fixed and supported by a tube plate near the fluid inlet and outlet, and exchange heat between the inside and outside of these heat transfer tubes.

The inlet of a heat transfer tube is susceptible to damage due to turbulence that occurs when fluid flows into the tube, so a ferrule (short tube) is often installed in this area to protect the tube.

As prior art in this regard, for example, Patent Document 1 discloses a protective tube with a flange protruding from the outer periphery of the end and an inner diameter approximately equal to the inner diameter of the main body of the heat transfer tube.

Patent Document 2 also discloses a structure in which the ceramic layer covering the tube plate on the gas inlet side is made up of multiple rectangular prism-shaped sockets arranged adjacent to each other and abutting each other along their outer edges, with each socket having a conical opening that tapers toward the tube portion, and the tube portion being inserted into each tube in the tube bundle of the heat exchanger.

In addition to damage caused by turbulence that occurs when fluid flows into the heat exchanger tubes, solids in the fluid flowing through the tubes, or solids produced by chemical reactions between components in the fluid, can adhere to the inner surface of the tubes and block the flow path of the tubes, causing an increase in the differential pressure in the heat exchanger and making stable operation difficult.

In this case, the technologies disclosed in Patent Documents 1 and 2 above cannot be used to deal with the problem, so the equipment operation must be stopped as soon as a rise in differential pressure is observed and the blockage removed, or the blockage must be removed periodically before the differential pressure rises in order to avoid a rise in differential pressure.

Patent Document 2, cited above, lists the issue of protecting the gas inlet side from high-temperature corrosion and erosion, and claims that the shape of the socket interior narrows toward the entrance of the heat transfer tube, accelerating the fluid (gas) and preventing solid particles from accumulating at the fluid inlet section of the socket. However, because the fluid flow rate within the heat transfer tube is the same whether or not a socket is present, under conditions where blockages occur within the heat transfer tube, increasing the flow rate by installing a socket cannot prevent such blockages.

Japanese Patent Application Publication No. 9-292195 Japanese Patent Application Publication No. 5-306893

The object of the present invention is to propose a ferrule for heat exchanger heat transfer tubes and an assembly method therefor that can effectively suppress the adhesion of solid particles to the heat transfer tubes and the resulting blockage of the heat transfer tubes, thereby extending the interval between equipment shutdowns.

The inventors conducted a detailed investigation into the causes of heat transfer tube clogging. As a result, they discovered that the main cause is that the heat-resistant porcelain generally used for ferrules has a porous structure and an uneven surface, making it easy for fine particulate solid matter contained in the gas to penetrate into and adhere to the interior or uneven surface, leading to adhesion and growth on the inner surface of the heat transfer tube.

We therefore investigated the possibility of suppressing the adhesion of solid substances by applying a glaze to the ferrule and firing it to form a dense glassy coating on its surface. As a result, we discovered that for a ferrule with a flange portion that is not inserted into the heat transfer tube and a short tube portion that is inserted into the heat transfer tube, applying a glaze to the inner surface of the entry side of the short tube portion to form a glass layer can effectively suppress the adhesion of solid substances and blockage of the heat transfer tube, leading to the completion of this invention.

That is, the present invention relates to a ferrule for a heat exchanger heat transfer tube that is fitted to the fluid inlet of a heat transfer tube for circulating a fluid. The ferrule has a short tube portion that is inserted into the heat transfer tube and a flange portion provided at the end of the short tube portion, and the short tube portion has a vitrified glaze layer on at least the inner surface of the inlet side.

The present invention also relates to a ferrule for a heat exchanger tube that is fitted to the fluid inlet of a heat transfer tube for circulating a fluid. The ferrule has a short tube portion that is inserted into the heat transfer tube and a flange portion provided at the end of the short tube portion, and the short tube portion has a coating layer of glaze that can be vitrified by heating on at least the inner surface of the inlet side.

The above-mentioned heat exchanger is preferably a heat exchanger in which combustion exhaust gas produced by burning a substance containing sulfur flows as a fluid through the heat transfer tube.

The present invention also relates to a method for assembling a ferrule for a heat transfer tube of a heat exchanger, which comprises forming a glaze coating layer on at least the inner surface of the inlet side of the short tube section when assembling the ferrule to the fluid inlet section of the heat transfer tube, then assembling the ferrule to the fluid inlet section of the heat transfer tube, and then heating the ferrule to convert the coating layer into a vitrified glaze layer; and further, after assembling the short tube section of the ferrule to the fluid inlet section of the heat transfer tube, forming a glaze coating layer on at least the inner surface of the inlet side of the short tube section, and then heating the ferrule to convert the coating layer into a vitrified glaze layer.

According to the present invention, at least the inner surface of the entry side of the short tube section inserted into the heat transfer tube is covered with a vitrified glaze layer, which makes it possible to suppress the adhesion of solid substances and enable the equipment to operate for long periods of time. It also achieves a longer life for the ferrule itself.

FIG. 1 is a schematic diagram of a heat exchanger combined with a combustion furnace. FIG. 2 is a view showing the AA end face of FIG. FIG. 3 is a view showing a part of the cross section taken along the line BB in FIG. 2. 1 is a graph showing the relationship between the number of operating days of a heat exchanger and the differential pressure.

The present invention will be described in more detail below with reference to the drawings.
Fig. 1 is a schematic diagram of a heat exchanger combined with a combustion furnace, Fig. 2 is a diagram showing the A-A end face of Fig. 1 (the dashed line in the figure shows the heat transfer tubes omitted), and Fig. 3 is a diagram showing the B-B cross section of Fig. 2.

The ferrule according to the present invention is attached to the fluid inlet of a heat transfer tube of a heat exchanger such as that shown in Figure 1 above.

In Figures 1 to 3, reference numeral 1 denotes a combustion furnace, 2 denotes a heat exchanger connected to the combustion furnace 1, 3 denotes a tube plate attached to the heat exchanger 2, 4 denotes refractory material attached to the surface of the tube plate 3, and 5 denotes a heat transfer tube. The heat transfer tube 5 has a fluid inlet and a fluid outlet fixedly supported by the tube plate 3. Reference numeral 6 in Figures 1 to 3 denotes a ferrule attached to the fluid inlet of the heat transfer tube 5. The heat exchanger 2 may be a heat exchanger that circulates flue gas produced by burning a sulfur-containing substance as a fluid through the heat transfer tube 5, but the fluid is not limited to flue gas produced by burning a sulfur-containing substance.

The ferrule 6 can be made of ceramics primarily composed of alumina, and is composed of a short tube section 6a that is inserted into the heat transfer tube 5, and a flange section 6b that is attached to the end of the short tube section 6a and used to secure the short tube section 6a to the tube sheet 3 or the like. 7 is a vitrified glaze layer that is attached to at least the entry side of the inner surface of the short tube section 6a.

The heat exchanger 2 configured as described above is provided with a path 8 for circulating a secondary fluid, such as water, and when the high-temperature fluid (gas) supplied from the combustion furnace 1 passes through the heat transfer tubes 5, the heat of the fluid is transferred to the secondary fluid via the heat transfer tubes 5, thereby performing heat exchange.

The vitrified glaze layer 7 can be made by firing the applied glaze layer to turn it into a glassy substance; for example, a material containing sodium borosilicate is used. It is also preferable to use a glaze that can be applied to ceramics or metals directly or in liquid form, with the solid suspended in water.

The ferrule 6 according to the present invention is made by applying a glaze to the surface of a bisque-fired ceramic substrate to form a coating layer, which is then fired to form a vitrified glaze layer 7, and then assembling it into the fluid inlet of the heat transfer tube 5 of the heat exchanger 2.

In addition, in a heat exchanger 2 in which a high-temperature fluid sufficient to bake the glaze flows through the heat transfer tubes 5, a glaze coating layer can be formed in advance on at least the inlet side of the inner surface of the short tube section 6a, and after installing the ferrule 6 at the fluid inlet of the heat transfer tube 5, or after installing the ferrule 6 at the fluid inlet of the heat transfer tube 4, a glaze coating layer can be formed at least on the inlet side of the short tube section 6a. By flowing a high-temperature fluid through the heat transfer tubes 5 of the heat exchanger 2, the heat from the fluid firing the glaze coating layer can be used to form a vitrified glaze layer 7.

By forming the vitrified glaze layer 7 using the procedure described above, the firing of the glaze and the assembly of the ferrule 6 can be performed simultaneously, enabling the ferrule 6 to be efficiently assembled into the heat exchanger 2.

It is effective to apply the glaze within a range of at least 10 mm from the entry side of the short tube section 6a, and it is even more effective to apply it within a range of 20 mm to 50 mm from the entry side.

The reason for this is that precipitates such as particulate solid matter contained in the fluid flowing through the heat transfer tube 5 are most likely to precipitate at the entry side of the short tube portion 6a of the ferrule 6, with the greatest amount tending to precipitate within a range of 50 mm from the entry side.

It is possible to extend the glaze application range further, but even if the application range extends more than 50 mm from the entry side of the ferrule 6, the effect of preventing blockage at the entry side of the heat transfer tube 5 will saturate, so application more than 50 mm from the entry side is optional.

The glaze can also be applied to the surface of the flange portion 6b, which is preferable because it can prevent deposits from forming on the surface of the flange portion 6b. However, to prevent blockage of the heat transfer tube 5, it is more important to cover the inlet side of the short tube portion 6a with glass than the surface of the flange portion 6b, so the formation of a vitrified glaze layer 7 on the flange portion 6b is not essential.

The glaze is preferably applied so that the thickness of the vitrified glaze layer 7 is 0.1 mm or more and 3 mm or less. If the thickness of the vitrified glaze layer 7 is less than 0.1 mm, unevenness is likely to occur when the glaze is applied, and if it exceeds 3 mm, the flow of fluid (gas) will be disturbed at the tip of the glaze layer 7. Furthermore, by making the thickness of the vitrified glaze layer 7 thicker at the entrance side of the short tube portion 6a of the ferrule 6, for example, and thinner further back, it is possible to suppress disturbances in the fluid flow.

The vitrified glaze layer 7 seals the small pores and irregularities on the surface of the ferrule 6, creating a smooth surface. This makes it difficult for particulate matter contained in the fluid to adhere, thereby preventing clogging of the heat transfer tubes 5 and enabling long-term operation of the heat exchanger 2.

A heat exchanger such as that shown in Figure 1 above was installed in a facility that produces sulfuric acid by burning a sulfur-containing slurry recovered from carbonization gas generated in a coke manufacturing plant. Ferrules according to the present invention were attached to the heat transfer tubes of the heat exchanger, and combustion exhaust gas at a temperature of approximately 1050°C discharged from a combustion furnace was passed through the heat transfer tube to bake the glaze coating on the ferrules. The differential pressure between the inlet and outlet of the heat exchanger was measured, and the relationship between the number of days since operation began and the differential pressure was investigated. The results are shown in Figure 4, along with those for heat exchangers in which ferrules without a glaze coating were attached to the heat transfer tubes (Comparative Examples 1 and 2).

The combustion furnace used in this example is a furnace that injects sulfur-containing slurry, coke oven gas, combustion air, steam, etc., and burns the coke oven gas and sulfur to produce high-temperature gas (primary fluid).

In addition, the heat exchanger (boiler) used in this example had the following specifications: main body (shell) inner diameter: 2700 mm, number of heat transfer tubes: 313, length of heat transfer tube: approximately 6000 mm, treated air volume: 23000 Nm ³ /h, gas temperature at the inlet of the heat transfer tube: 1050°C, gas temperature at the outlet: 440°C or less, operating pressure: gauge pressure approximately 1 kPa, combustion exhaust gas: containing CO ₂ , H ₂ O, N ₂ , O _2, etc. in addition to SO ₂ generated by the combustion of sulfur, and secondary fluid: water.

The ferrule was made of a bisque-fired ceramic primarily composed of alumina, with a short tube length of approximately 160 mm, an inner diameter of approximately 50 mm, a wall thickness of approximately 4 mm, a flange diameter of approximately 70-80 mm, and a flange thickness of approximately 10 mm. A glaze primarily composed of sodium borosilicate was applied to the flange surface (the surface in contact with the gas) over a length of 50 mm from the entry side, to a thickness of approximately 1 mm, to form a glaze coating layer.

Figure 4 shows that in Comparative Examples 1 and 2, the pressure difference reached 1 kPa between approximately 60 and 100 days, and clogging of the heat transfer tubes became noticeable. In contrast, in the heat exchanger equipped with the ferrule according to the present invention, the pressure difference reached 1 kPa 165 days after the start of operation, confirming that providing a vitrified glaze layer on the ferrule can significantly extend the period until clogging of the heat transfer tubes becomes noticeable. We also conducted a study in which the glaze application range was extended to within 10 mm from the inlet end of the short tube portion of the ferrule. Even in this case, it took approximately 140 days for the pressure difference between the inlet and outlet ends of the heat exchanger to reach 1 kPa, demonstrating that sufficient effects can be expected.

The present invention provides a ferrule for heat exchanger heat transfer tubes and an assembly method thereof that effectively suppresses adhesion of solid particles to heat transfer tubes and the resulting blockage of the heat transfer tubes, thereby extending the interval between equipment shutdowns.

REFERENCE SIGNS LIST 1 Combustion furnace 2 Heat exchanger 3 Tube plate 4 Refractory material 5 Heat transfer tube 6 Ferrule 6a Short tube portion 6b Flange portion 7 Vitrified glaze layer 8 Path

Claims (5)

A ferrule to be assembled to a fluid inlet portion of a heat transfer tube of a heat exchanger having a heat transfer tube through which a fluid flows, comprising:
the ferrule has a short pipe portion inserted into the heat transfer tube and a flange portion provided at an end of the short pipe portion,
the short tube portion has a vitrified glaze layer on at least the inner surface of the inlet side portion,
10. A ferrule for a heat transfer tube of a heat exchanger, wherein the glaze layer is provided within a range of 10 mm to 50 mm from the inlet side of the short tube portion . A ferrule to be assembled to a fluid inlet portion of a heat transfer tube of a heat exchanger having a heat transfer tube through which a fluid flows, comprising:
the ferrule has a short pipe portion inserted into the heat transfer tube and a flange portion provided at an end of the short pipe portion,
the short tube portion has a coating layer of a glaze that can be vitrified by heating on at least the inner surface of the inlet side portion,
10. A ferrule for a heat transfer tube of a heat exchanger, wherein the glaze coating layer is provided within a range of 10 mm to 50 mm from the inlet side of the short tube portion . A ferrule for a heat transfer tube of a heat exchanger according to claim 1 or 2, characterized in that the heat exchanger is a heat exchanger in which combustion exhaust gas produced by burning a substance containing sulfur flows as a fluid through the heat transfer tube. When the ferrule according to claim 2 is assembled to a fluid inlet of a heat transfer tube of a heat exchanger,
A method for assembling a ferrule for a heat transfer tube of a heat exchanger, comprising: forming a glaze coating layer on the inner surface of at least the inlet side of a short tube section; assembling the ferrule to the fluid inlet section of the heat transfer tube; and then heating the ferrule to convert the coating layer into a vitrified glaze layer. When the ferrule according to claim 2 is assembled to a fluid inlet of a heat transfer tube of a heat exchanger,
a method for assembling a ferrule for a heat transfer tube of a heat exchanger, comprising: assembling the short tube portion of the ferrule to the fluid inlet portion of the heat transfer tube; forming a coating layer of glaze on at least the inner surface of the inlet portion of the short tube; and then heating the ferrule to convert the coating layer into a vitrified glaze layer.