JPS63291670A - Manufacture of heat transfer tube for heat exchanger - Google Patents

Abstract

PURPOSE:To form an enamel layer with uniform coat thickness on the surface of steel pipe by coating the pipe with enamel while steel pipe is suspended in an alternately upside down fashion. CONSTITUTION:Steel pipe 2 suspended vertically is coated with an enamel layer on the internal and/or external surface. Next, the steel pipe is suspended upside down, and further coated with another layer on the above enamel layer. By virtue of this economical method, an enamel layer of uniform coat thickness can be formed on the surface of the steel pipe. Thus it is possible to manufacture the heat transfer tube for a heat exchanger that is capable of heat recovery at close to an acid dew point or even at upto room temperature level, depending on the temperature conditions of cold rusty fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a method of manufacturing a heat exchanger tube for a heat exchanger by coating the surface of a steel tube with an enamel layer.

[Conventional technology] With the recent increase in energy conservation, the demand for heat recovery from exhaust gas and other waste heat sources is increasing, and the recovery temperature level will inevitably shift to heat recovery from lower temperature ranges. This trend is expected to continue in the future.

However, when recovering heat from exhaust gas containing SOx, such as boiler #gas that burns heavy oil, coal, etc., when operating below the acid dew point (usually around 120 to 150 degrees Celsius), some of the As a result, the temperature range for heat recovery has traditionally been limited to 140 to 150 degrees Celsius (140 to 150 degrees Celsius) at most.
It was a dead end.

Therefore, despite the increasing demand for heat recovery from lower temperature ranges as mentioned above, low-temperature corrosion is a barrier and it is difficult to recover heat from combustion exhaust in the temperature range below the acid dew point. A corrosion-resistant heat exchanger has not yet appeared.

Traditionally, enamel-coated steel has been produced as an "enamel" product with excellent heat resistance, corrosion resistance, and a beautiful luster, and has been widely used not only in arts and crafts and building materials, but also industrially as corrosion-resistant heat transfer plates for air preheaters. It has been well proven that it has excellent corrosion resistance.

[Problem to be Solved by the Invention 1] The main reason why the above enamel coating was not adopted for heat exchanger tubes is that a coating removal technique was established to form an enamel layer with a uniform thickness on the surface of the tube. The problem was that it was not done.

The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to coat the surface of a heat exchanger tube with enamel to a uniform thickness by a quick and economical method, and to The object of the present invention is to provide a method for producing a heat transfer tube for a heat exchanger that can recover heat not only near the dew point but also down to room temperature depending on the temperature conditions of the low-temperature rust fluid.

[a! Means for Solving Problem I 1 The method of manufacturing a heat exchanger tube for a heat exchanger of the present invention involves coating the inner and/or outer surface of the steel tube with an enamel layer while vertically hanging the tube, and then vertically suspending the steel tube. On the contrary, it is characterized in that it is hung in reverse and a further layer of enamel is applied on top of the enamel layer.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

First, we avoided complicated shapes by selecting bare steel pipes for the shape of the heat exchanger tubes, and minimized the two-pronged parts and some corners. This minimizes the defects of the enamel heat transfer surface, prevents dust from adhering to it, and makes it easy to remove dust, making it possible to apply it to highly dust-containing gases (dirty gases).

As a result of repeated experiments, we found the most effective and economical method to coat the surface of this steel pipe with an enamel layer and produce a heat transfer tube with a uniform film thickness.
We have found that the best method is to hook the glaze and leave it in a glaze bath, or to apply it to the surface of the tube with a spray gun, hang it vertically, send it to a firing furnace on a conveyor, and then bake it.

Suspending the tube vertically makes it possible to form a uniform film thickness in the circumferential direction of the tube, and is also economical since it is possible to suspend a large number of tubes at a time per unit volume in the furnace.

However, if the glaze is coated only once, there will be relatively many defects such as pinholes, and the glaze will flow down the tube surface due to gravity before the firing process, so the film will be thicker at the bottom of the tube than at the top. tends to become thicker.

To solve this problem, we hung the coated enameled tube upside down and coated it a second time, creating a perfect surface with no pinholes and a uniform surface along the vertical direction of the tube. The film thickness can be formed.

Of course, it is possible to increase the number of coatings to three or more times to achieve a more perfect surface, but this increases production costs and
If the film thickness becomes too thick, the heat transfer resistance will increase, which is not a good idea.

FIG. 1 shows the most common suspension example in which the inner and outer surfaces of a steel pipe are coated simultaneously.

In this suspension example, the suspension hole 1 is located near the end of the steel pipe 2 with two holes above and below.
The first time was through hole 1 at one end, and the second time, it was hung upside down using hole 1 at the other end, and after being immersed in a glaze bath, it was fired. Two enamel layers are formed on the inner and outer surfaces of the steel pipe 2 at the same time.

Figure 2 shows when the pipe opening is closed with plug 4 and immersed in the glaze tank.
A suspension example is shown in which no glaze adheres to the inside of the steel pipe 2, and only the outer surface of the pipe is coated with an enamel layer.

FIG. 3 shows a suspension example in which the outer surface is covered with a cover 5, hollow sockets 6 are inserted into both ends of the steel pipe 2, and only the inner surface of the steel pipe 2 is coated with an enamel layer.

Table 1 shows the thickness of the outer surface of the enamel layer measured with a thickness meter when the inner and outer surfaces of the steel pipe 2 are coated with the enamel layer twice by the suspension method shown in FIG.

According to the measurement results, it can be confirmed that a uniform film thickness of about 0.3 + ui was obtained.

Table 1 Film thickness of enamel layer [Effect of the invention 1 Since the enamel coating treatment is performed while the steel pipes are hung upside down alternately, it is possible to form an enamel layer with a uniform thickness on the surface of the steel pipes. can.

[Brief explanation of the drawing]

FIGS. 1 to 3 are cross-sectional views each showing an example of suspending a steel pipe for enamel coating. 1... Hanging hole, 2... Steel pipe, 3... Hook, 4...
...Plug, 5...Cover, 6...Hollow socket.

Claims (1)

[Claims] While the steel pipe is hung vertically, an enamel layer is coated on its inner and/or outer surface, and then the steel pipe is hung upside down and another enamel layer is coated on top of the enamel layer. A method for manufacturing a heat exchanger tube for a heat exchanger, characterized in that: