JPH037892A - Heat transmission pipe for heat exchanger - Google Patents

Abstract

PURPOSE:To provide a heat transmission pipe which has a high thermal conductivity, is well suited to be joined with other metallic parts and presents a long service life while assuring corrosion resistance, heat resistance, shock resistance and hermetic property by impregnating metal at a certain ratio in a tubular refractory porous object or ceramic porous object. CONSTITUTION:A tubular fire-resistance porous object or ceramic object is impregnated with metal at a rate of 1 to 90weight%. In this instance, the ends of the tube desirably contain metal at a rate larger than the other part does, and the other side of the tube desirably contain metal at a rate larger than the inner side does. For the refractory porous object which is impregnated with metal, any ceramics based on silicon nitride, silicon carbide, sialon, zircon or alumina may be used. For metal to be impregnated, iron, stainless steel, lead, tin, aluminium, copper, chrome, nickel or a mixture of them may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger tube for a heat exchanger used as a heat exchanger tube of a shell-and-tube heat exchanger.

[Prior Art] In recent years, shell-and-tube heat exchangers having ceramic tubes have been put into practical use in order to effectively utilize the thermal energy of waste gas. Ceramic tubes have better corrosion resistance than metal tubes, and can recover sensible heat from high-temperature corrosive gases, which was previously considered impossible, and can also recover heat from high-temperature gases without air dilution. Become. Such ceramic tubes are attracting attention because they satisfy various performances as heat transfer tubes, such as corrosion resistance, heat resistance, thermal shock resistance, and airtightness. By using ceramic tubes for heat exchanger tubes, the range of heat recovery targets is further expanded, and the range of heat recovery targets is further expanded, including waste gas containing highly corrosive solid phase dust and
It becomes possible to recover heat even from high-temperature waste gas of 500°C.

Ceramic tubes as conventional heat transfer tubes are made of silicon nitride, silicon carbide, or cordierite.

[Problems to be Solved by the Invention] However, conventional ceramic heat exchanger tubes have lower thermal conductivity and lower thermal efficiency than metal heat exchanger tubes. Additionally, special bonding techniques are required when bonding with other metal members. Furthermore, heat exchanger tubes made of silicon nitride and silicon carbide are easily deteriorated by oxidizing gases such as chlorine gas, sulfur dioxide gas, and carbon oxide gas, and have a short lifespan, especially in an oxidizing atmosphere.

This invention was made in view of the above circumstances, and
A long-life heat exchanger conductor that maintains corrosion resistance, heat resistance, thermal shock resistance, and airtightness, has high thermal conductivity, has good bonding properties with other metal parts, is difficult to be attacked by oxidizing gas, and has a long life. The purpose is to provide heat tubes.

[Means for Solving the Problems] The heat exchanger tube according to the present invention is characterized in that the tubular refractory porous body or ceramic porous body is impregnated with metal at a ratio of 1 to 90% by weight. shall be.

In this case, it is preferable that both ends of the tube have a larger amount of metal impregnation than other parts. Furthermore, it is preferable that the amount of metal impregnated on the outside of the tube is larger than that on the inside of the tube. can also be used.

The metal to be impregnated may be any metal, such as iron, stainless steel, lead, tin, aluminum, copper, chromium, etc.
Examples include nickel. Moreover, a mixture of these metals may be used.

The amount of metal impregnated is selected within the range of 1 to 90% by weight based on the weight of the refractory so as to obtain the desired effect.

The reason for limiting this range is that refractories generally have pores of 3% by volume or more, and the amount of impregnation required to fill the pores is 1% by weight or more, and Maximum amount of metal that can be impregnated while maintaining strength is 90% by weight
That's why.

Although the method for impregnating the refractory porous body with metal is not particularly limited, for example, the following method can be used.

First, the refractory is preheated to about 1000 to 1300°C and degassed. Thereafter, it is immersed in a hot metal bath containing molten metal and pressurized. By this method, the refractory porous body can be impregnated with metal.

For example, the porosity of a refractory having a porosity of 5 to 90% can be reduced to about 2% or less by the method described above.

[Function] In the heat exchanger tube for a heat exchanger according to the present invention, the refractory porous body is impregnated with metal at a ratio of 1 to 90% by weight.

In such a metal-impregnated refractory body, the pores of the refractory porous body are filled with metal, so that corrosive gas hardly enters the pores of the refractory, and oxidation of the refractory by the gas is prevented.

In addition, by impregnating the refractory with metal, the thermal conductivity of the refractory is improved, the heat dispersibility is improved, and a temperature difference between the inside and outside of the heat exchanger tube is less likely to occur, and the heat recovery rate is improved.

Furthermore, by increasing the amount of metal impregnated at both ends or the outer portion of the heat exchanger tube than in other portions, the bondability with other metal members is improved and airtight bonding is facilitated.

[Example] Hereinafter, an example of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a longitudinal cross-sectional view schematically showing a heat recovery part of a waste gas treatment apparatus using a heat exchanger tube according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the heat exchanger tube.

A dust catcher is provided in the flue of the incinerator, and a heat exchanger is provided in the flue further downstream of the dust catcher to recover the sensible heat of the waste gas. The heat exchanger is a channel type multi-tube heat exchanger composed of multiple units, and is provided so as to surround the flue. That is, the heat exchanger units 11 to 18 are arranged in a staggered manner in this order from the upstream side to the downstream side of the flue 10, and the heat exchanger tubes 20 of each unit are provided at a predetermined pitch so as to cross the flue 10. ing. The downstream unit 18 is provided with a heat medium inlet 19, while the upstream unit 11 is provided with a heat medium outlet 12. Entrance 1
9 and outlet 12 are each a heating medium supply source (not shown).
The heat exchanger is in communication with the heat exchanger so that the heat medium circulates between the heat medium supply source and the heat exchanger. In this case, for example, air is used as the heating medium. The heat exchanger tube 20 of each unit has an inlet 19
and the outlet 12 communicate vertically with each other.

As shown in FIG. 2, the heat exchanger tube 20 has a passage 21, a heat medium flows through the passage 21, and waste gas flows outside the heat exchanger tube 20 perpendicularly to the tube axis. The heat exchanger tube 20 is made of a porous ceramic tinib impregnated with a predetermined amount of stainless steel.

Note that both ends of the heat exchanger tube 20 have a higher metal impregnation amount than other parts. The tube ends are fixed within the unit body and are seal welded to prevent leakage.

Next, a method for manufacturing the heat exchanger tube will be explained.

A method for producing heat exchanger tubes as a refractory raw material! 120i 98% by weight alumina powder was used. The average particle size of the powder was adjusted to 01.3 microns. In order to control the porosity of the fired body, approximately 4 micron organic fibers were blended into the raw material powder. mix both,
When the fibers are sufficiently dispersed in the raw material powder, a binder agent is added thereto and further stirred and mixed. This mixture is poured into a cylindrical groove and molded under pressure. The molded body is fired at a predetermined temperature to obtain a tubular silicon nitride porous body. The obtained porous tube has an average pore diameter of 4 microns and a porosity of 45.
%.

The porous tube is impregnated with metallic nickel.

Note that this metal impregnation process is divided into two stages; in the first step, the entire porous tube is impregnated with metal under low pressure, and in the second step, only both ends of the porous tube are impregnated with metal under high pressure. As a result, the amount of metal impregnated at the end of the tube is approximately 27% by weight.
, the amount of metal impregnated in parts other than the tube ends is about 31% by weight.

In addition, in order to increase the amount of metal impregnated on the outside of the heat exchanger tube than on the inside, fill the portion of the heat exchanger tube corresponding to the gas passage 21 so that the metal penetrates into the refractory only from the outside of the tube. . Another method is to create a difference in pressure between the inside and outside of the pipe during metal impregnation.

Hereinafter, the results of actually manufacturing and testing a metal-impregnated ceramic tube that can be used as the heat transfer tube will be described in detail.

Thermal Shock Resistance The above samples were heated from 0 to 1600°C and then cooled with water. We investigated how the strength of the sample was affected by the temperature difference (ie, thermal shock) caused by this rapid heating and cooling.

FIG. 3 is a graph showing the thermal shock resistance of metal-impregnated large-sized materials, with the horizontal axis representing the quenching temperature difference and the vertical axis representing the strength index of the refractory. In this case, the strength index of the refractory is the strength of the specimen after quenching, expressed as an index, with the strength of the refractory without quenching being 100. In the figure, white circles, white squares, and black angles of view are respectively 10% by weight and 20% by weight of silicon nitride tubes.
This shows the results of impregnating 40% by weight of nickel. Note that the black circles indicate the results of a silicon nitride tube not impregnated with metal as a comparative example. As is clear from the figure, it was found that by impregnating the refractory with metal, it could withstand considerably more thermal shock than when it was not impregnated with metal. It was also confirmed that the greater the amount of metal impregnated, the less the decrease in the strength index and the better the heat-resistant spalling.

Oxidation Resistance Figure 4 shows the oxidation resistance of silicon nitride tubes impregnated with metal, with the amount of metal impregnated on the horizontal axis and the erosion index of metal-impregnated bulky materials by CO2 gas on the vertical axis. It is a graph diagram. In this case, the erosion index is an index representing the amount of oxidative erosion of the specimen relative to the amount of oxidative erosion caused by CO2 gas of the silicon nitride tube not impregnated with metal as 100. As is clear from the figure, the desired effect cannot be obtained if the amount of metal impregnation is too small or too large, and when the amount of metal impregnation is in the range of 20 to 70% by weight, the erosion index is less than 30. It was found to reduce

The combinations of thermally conductive refractories and impregnated metals were variously changed, three types of heat exchanger tube samples with different compositions were created, and the thermal conductivity of each was measured. AI 20 as the first sample
A, Q20i60 as the second sample, impregnated with iron at a ratio of 20% by weight to s 80' gl%.
A third sample was impregnated with nickel at a ratio of 40% by weight to Ag2O, and a third sample was impregnated with 30% by weight of iron and 20% by weight of nickel to 50% by weight of Ag2O. Using. In addition, AfI20,99
Heat exchanger tube weighing 96 (Comparative Example 1), 120380% by weight -
A heat exchanger tube containing 20% by weight of 5iOz (Comparative Example 2) was used as a comparative example.

The thermal conductivity measurement results show that the first sample has 12 Kcal
I-hr・℃, the second sample is 40 Kcal/m-hr
・'C.

The third sample was 33. It was Kcal/m-hr·°C.

These results show that 4 Kcal/g-hr of Comparative Example 1
・"C and Comparative Example 2 5 Kcal/a+-hr・℃
It was found that the metal-impregnated tube has high thermal conductivity.

As described above, it has been confirmed that the heat exchanger tube of the present invention has superior heat resistance and oxidation resistance compared to conventional ceramic tubes.

In addition, although the above-mentioned example explained the case where heat exchanger tubes were used in a channel type heat exchanger constituted by a plurality of units, the present invention is not limited to this.
It can also be applied to heat exchanger tubes for tower type heat exchangers.

Further, in the above embodiment, the case of a heat exchanger used in an incinerator was explained, but the case is not limited to this, and it can be used in a soaking furnace, a forging furnace, a heat treatment furnace, a melting furnace, a continuous heating furnace for steel, etc. It can also be applied to heat exchangers used for heat recovery in various furnaces.

[Effects of the Invention] According to the present invention, it is possible to provide a heat exchanger tube for a heat exchanger that has excellent corrosion resistance, heat resistance, thermal shock resistance, and airtightness and has a long life.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view schematically showing a heat recovery part of a waste gas treatment equipment using a heat exchanger tube according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the heat exchanger tube, and FIG. FIG. 4 and FIG. 4 are graphs for explaining the effects of the embodiment, respectively.

Claims (3)

[Claims] (1) A heat exchanger tube for a heat exchanger, characterized in that the tubular refractory porous body or ceramic porous body is impregnated with metal at a ratio of 1 to 90% by weight. (2) A heat exchanger tube for a heat exchanger, characterized in that both ends of the tube have a larger amount of metal impregnated than other parts. (3) A heat exchanger tube for a heat exchanger, characterized in that the outside of the tube has a larger amount of metal impregnated than the inside of the tube.