JP3108493B2 - Heat exchanger components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger member, and more particularly to a member such as a heat storage element used in a high-temperature heat exchanger in which heat exchange between gases is performed via a heat storage element.

[0002]

2. Description of the Related Art In recent years, effective use of heat energy (recovery of waste heat, etc.) has been emphasized in consideration of resource saving and reduction of environmental load. Role is growing. Conventionally, in heat exchangers used under relatively low temperature conditions, there are few restrictions on performance such as heat resistance, so various materials have been widely used, and heat exchangers themselves have been widely used. ing.

However, in a high-temperature heat exchanger for the purpose of recovering heat from a high-temperature gas, the development of practical equipment has been delayed due to great restrictions on materials, and the development of new materials has been eagerly desired. ing. For example, in a known high-temperature heat exchanger in which heat exchange between a high-temperature gas of 1000 ° C. or more is performed through a heat storage material, a ceramic heat storage material (such as a rod or a pebble) is used. Under the above operating conditions, an alumina-based material is used. However, when alumina is used as a heat storage element of a heat exchanger used at a high temperature exceeding 1800 ° C., melting or fusing may occur, which is a problem.

[0004]

SUMMARY OF THE INVENTION The present invention relates to
A main object of the present invention is to provide a heat exchanger member having excellent heat resistance and durability that can be used at the above-mentioned high temperature, and in some cases, at a high temperature of 2000 ° C. or more.

[0005]

[Means for Solving the Problems] A member such as a heat storage element of a heat exchanger used at a high temperature of 2000 ° C. or more must have the following high performance.

(A) Since it is in direct contact with a high-temperature gas of 2000 ° C. or more, not only does it not melt at the operating temperature, but also the heat storage bodies do not fuse with each other to lower the gas permeability. (B) Do not evaporate harmful components by contact with high-temperature gas.

(C) The vapor component from the member does not contaminate the gas.

(D) It has excellent thermal shock resistance and does not break down during use.

(E) It has excellent durability such that it does not substantially deteriorate even after long-term use.

The present inventor has conducted research while paying attention to the current state of the art as described above. As a result, among the extremely large number of heat-resistant oxide ceramics, a zirconia-based ceramic sintered body, particularly Y ₂ O ₃ , has been used. It has been found that a stabilized zirconia-based ceramic sintered body in which the crystal phase, crystal grain size, impurity concentration, and the like are controlled exhibits excellent performance as a heat exchanger member used at high temperatures.

That is, the present invention provides the following heat exchanger member; A heat exchanger member having the following constitutional requirements: (1) a zirconia sintered body containing 4.5 to 8 mol% of Y ₂ O ₃ , (2) a main crystal phase of the sintered body is cubic (3) the content of SiO ₂ is 0.5% by weight or less and the content of Al ₂ O ₃ is 1% by weight or less,
(4) The average crystal grain size of the sintered body is 5 μm or more.

2. 1 of the content of Y ₂ O ₃ (as Y)
Item 2. The heat exchanger member according to Item 1, wherein up to / 2 is replaced by at least one of Mg, Ca, and a lanthanoid.

The heat exchanger member according to the present invention is characterized by the following properties (1) to (4).

(1) A zirconia sintered body containing 4.5 to 8 mol% of Y ₂ O ₃ .

The pure zirconia sintered body has a temperature of about 1100 ° C.
The crystal phase changes from monoclinic to tetragonal in
Transform to cubic at 400 ° C. Since this transition is a reversible transition, the transition from a tetragonal system to a monoclinic system involves expansion as much as 4%, and the sintered body is destroyed.
In order to reduce this amount of transition, the zirconia sintered body is
It is used in a cubic or metastable tetragonal form in which an oxide such as Y ₂ O ₃ , MgO, CaO or a lanthanoid element is dissolved as a stabilizer in a zirconia sintered body.

In the present invention, in particular, Y is used as a stabilizer.
The ₂ O ₃ using a zirconia sintered body containing 4.5 to 8 mol%. A zirconia sintered body using an oxide other than Y ₂ O ₃ as a stabilizer cannot be used because cracks and the like occur under high temperature conditions of 18000 ° C. or higher. When the content of Y ₂ O ₃ in the zirconia-based sintered body is less than 4.5 mol%, a monoclinic crystal is formed and cracks are generated when used under a high temperature condition. If it exceeds mol%, no crystal phase transition occurs, but the thermal shock resistance is reduced and cracks or fractures are more likely to occur. The content of Y ₂ O ₃ is 5 to
More preferably, it is 7 mol%.

In the present invention, up to 1/2 (amount as Y) of Y ₂ O ₃ in the zirconia sintered body is changed to Mg.
O, CaO and lanthanoid elements ( ₅₇ La to ₇₁ Lu)
Up to 15 types of oxides (meaning the respective internal metal elements). Also in this case, an effect substantially the same as when using only Y ₂ O ₃ is obtained.

(2) The main crystal phase of the sintered body is cubic.

It is essential that the crystal phase of the zirconia sintered body used in the present invention is mainly composed of cubic crystals. When a large amount of monoclinic crystal is contained, as described above, the sintered body is broken by the transition to another crystal phase. If the amount of monoclinic is small, it absorbs thermal stress during the transition,
Since the thermal shock resistance is improved, the presence of up to about 5% by volume is permissible. The presence of a tetragonal system is preferable from the viewpoint of improvement in mechanical strength and thermal shock resistance, however, it changes to a monoclinic system by repeated use and causes a fracture of a sintered body. I do.

(3) When the content of SiO _{2 in} the sintered body is 0.
5% by weight or less and the content of Al ₂ O ₃ is 1% by weight or less.

The zirconia sintered body naturally contains SiO ₂ and Al ₂ O ₃ derived from sintering aids or raw material impurities.

Since SiO ₂ reacts with ZrO ₂ and Y ₂ O ₃ at a high temperature to form a liquid phase, if it is present in a large amount, it may cause fusion between the members or may cause the high-temperature durability of the members. Or decrease. Therefore, its content is at most 0.5% by weight, more preferably 0.2% by weight or less, most preferably 0.1% by weight or less. Al ₂ O ₃ does not adversely affect the zirconia sintered body as much as SiO ₂ , but is still agglomerated at the ZrO ₂ grain boundaries at high temperatures, causing an increase in thermal strain due to the difference in expansion coefficient,
At a higher temperature, it reacts with ZrO ₂ to form a liquid phase, so that fusion occurs between members. Therefore, its content is
It is at most 1% by weight, more preferably 0.5% by weight or less, and most preferably 0.2% by weight or less.

Further, impurities such as Fe ₂ O ₃ (HfO ₂
) Should be at most 1% by weight or less, more preferably 0.5% by weight or less, and most preferably 0.2% by weight or less.

(4) The average crystal grain size of the sintered body is 5 μm or more.

The mechanical properties of the zirconia sintered body are better as the crystal grain size is smaller, but the thermal shock resistance, corrosion resistance, fusion resistance and the like are reduced. Therefore, in the present invention, which emphasizes thermal shock resistance, corrosion resistance, fusion resistance, etc., the average crystal grain size of the zirconia sintered body is 5 μm.
m or more, preferably 10 μm or more, more preferably 15 to 500 μm.

The heat exchanger member of the present invention can be manufactured, for example, as follows. First, a zirconia powder and a stabilizer powder are mixed at a predetermined ratio, or both materials are mixed in a solution state and then solidified by coprecipitation or the like, and then calcined to prepare a raw material powder. . Next, this powder is pulverized and formed into a predetermined shape by a known method such as mechanical press molding, CIP, or casting, and then 1500.
By baking at a temperature of 1900 ° C., a desired heat exchanger member is obtained.

When manufacturing the heat exchanger member of the present invention, the selection of the raw materials and the manufacturing process are performed so that the content of impurities such as SiO ₂ and Fe ₂ O ₃ in the product is kept within a specified range. Need to be managed. In addition, it is necessary to carefully select the type, state, compounding ratio, and the like of the raw materials and to control the manufacturing process so that the crystal phase and the crystal grain size in the sintered body are as specified. Such selection or management can be easily performed by those skilled in the art.

[0028] The zirconia sintered body thus obtained usually has a bulk density of 4.8 g / mm ³ or more, and can balance thermal shock resistance and mechanical strength as required. For example, a certain amount of pores are present in the sintered body, the bulk density is adjusted to 4.8 to 5.7 g / mm ³ to improve the thermal shock resistance, or the pores of the sintered body are reduced,
When the bulk density is 5.7 g / mm ³ or more, the mechanical strength is 15
kgf / mm ² or more. These physical properties may be appropriately selected according to the type of parts, use conditions, and the like.

The heat exchanger member made of the zirconia sintered body according to the present invention has a high degree of heat resistance and durability that can be used even under a high temperature condition exceeding 2000 ° C. Therefore, it is useful as a heat storage body (pebble, rod-like body, etc.) and wall material of a heat exchanger for high temperature, and also useful as a crucible, a tundish nozzle, a high temperature furnace wall material and the like. Further, since the zirconia sintered body has conductivity at a high temperature, it is also suitable as a heating element.

[0030]

According to the present invention, a heat exchanger member made of a zirconia sintered body according to the present invention can be melted even under a high temperature condition of 1800 ° C. or more, and even 2000 ° C. or more when used as a heat storage body. They do not fuse with each other and do not hinder the flow of gas. Moreover, it does not break even when used at a high temperature, and does not deteriorate even after repeated use over a long period of time. Furthermore, since the zirconia sintered body of the present invention is extremely stable chemically, it does not evaporate harmful components and does not pollute gas.

[0031]

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention.

Example 1 ZrO ₂ and Y ₂ O ₃ powders having a purity of 99.98% or more were blended so as to have a ZrO ₂ content shown in Table 1 and uniformly mixed by a wet method in the presence of water. When mixing
In order to prevent impurities from being mixed, a container and a member made of zirconia were used. The dried powder is then added to 130
Heat treatment was performed at 0 ° C. for 3 hours to obtain a raw material powder.

Al ₂ O ₃ and / or SiO ₂ were added to the obtained synthetic powder (however, only sample Nos. 1-g to 1-i), and the finally obtained sintered body had the composition shown in Table 1. A raw material powder was prepared so as to have In Table 1,
The Y ₂ O ₃ content is given in mol%, the SiO ₂ content and the Al ₂ O ₃ content in wt%.

Table 1 Sample No. Y ₂ O ₃ content SiO ₂ content Al ₂ O ₃ content (%) (%) (%) 1-a 4.2 0.01 0.01 1-b 4.6 0.01 0.01 1-c 5.0 0.01 0.01 1-d 6.0 0.01 0.01 1- e 6.0 0.01 0.01 1-f 7.0 0.01 0.01 1 1-g 7.0 0.35 0.5 1-h 7.0 0.6 0.01 1-i 7 0.0 0.01 1.2 1-j 7.0 0.5 1.2 1-k 8.1 0.01 0.01 Next, the above-mentioned raw material powder was prepared using a zirconia ball mill and a ball. After wet pulverization for 24 hours and addition of an acrylic resin-based molding binder, a molding powder having a granule diameter of 60 μm was prepared using a spray dryer. After CIP molding this powder into a sphere having a diameter of 18 mm at a molding pressure of 1 ton / cm ² ,
Baking in air at the temperature shown in Table 2 for 3 hours
mm sintered body balls were obtained. The characteristics are also shown in Table 2.

Table 2 Sample No. Firing temperature Cubic content Crystal grain size (℃) (%) (M) 1-a 1600 80 5.5 1-b 1600 92 7.0 1-c 1600 95 10.5 1-d 1600 100 20 1-e 1450 98 4.0 1-f 1650 100 35 1-g 1650 98 30 1-h 1600 95 30 1-i 1650 95 25 1-j 1600 93 20 1-k 1650 100 45 Next, a sintered ball having the characteristics shown in Table 2 was obtained with an inner diameter of 10 cm and a height of 1 mm. Fill into a 30 cm cylinder, send combustion gas (temperature about 2050 ° C) from the lower part, raise the temperature at a rate of 800 ° C / hour until the upper part reaches 1900 ° C, and raise the temperature until the upper part reaches 1900 ° C. After the temperature was maintained for a period of time (the highest temperature portion reached about 2000 ° C.), the supply of the combustion gas was stopped, and hot air was supplied to cool to 500 ° C. Such an operation was repeated three times.

Thereafter, the sintered balls were taken out of the cylinder and the state of the change was examined.

The results are shown in Table 3 below. The third
In the table, each symbol indicates the following state.

…: Extremely good ○: Good ×: Poor--Not judged Table 3 Sample No. Reduction in weight of fused crack cracking 1-a ◎ × ×-1-b ◎ ○ ◎ ◎ 1-c ◎ ○ ◎ ◎ 1-d ◎ ◎ ◎ ◎ 1-e × ○ ◎ ◎ 1-f ◎ ◎ ◎ ◎ 1-g ○ ○ ◎ ○ 1-h × × ○ × 1-i × ○ ◎ ○ 1-j × × × -1 From the results shown in Table 3, the sintered body according to the present invention (sample No.
It is clear that 1-b, 1-c, 1-d, 1-f and 1-g) have excellent properties as members for high-temperature heat exchangers.

Example 2 ZrO ₂ powder and Y ₂ O ₃ powder having a purity of 99.98% or more, and CaCO ₃ and MgCO 2 as a second stabilizer
₃ , CeO ₂ , Yb ₂ O ₃ or Nd ₂ O ₃ were blended so as to have the composition shown in Table 4, and a sintered ball having a diameter of 15 mm was obtained in the same manner as in Example 1. The characteristics are shown in Table 5.

[0040] Note that in Table 4, Y ₂ O ₃ content and the second stabilizer content indicated by mol%, SiO ₂
The content and Al ₂ O ₃ content are indicated by weight%.

Table 4 Sample No. Y ₂ O ₃ Second stabilizer SiO ₂ Al ₂ O ₃ Content (%) Content (%) Content (%) Content (%) 2-a 2.0 CaO: 4.0 0.01 0.01 2-b 2.5 MgO: 6.0 0.0. 01 0.01 2-c 3.5 CaO: 3.0 0.01 0.01 2-d 5.0 MgO: 2.0 0.01 0.01 2-e 5.0 CeO ₂ : 1.0 0.01 0.01 2-f 5.0 Nd ₂ O ₃ : 1.5 0.01 0.01 2-g 5.0 Yb ₂ O ₃ : 1.0 0.01 0.01 0.01 2-h 6 5.0 CaO: 5.0 0.01 0.01 2-i 5.0 MgO: 2.0 0.1 0.2 2-j 5.0 MgO: 2.0 0.6 0.2 2-k _{5.0 Yb 2 O 3: 1.0 0.2} 0.2 2-l 3.5 CaO: 3.0 0.01 1.2 table 5 sample No. firing temperature cubic content grain size (℃) (%) (M) 2-a 1600 90 15 2-b 1650 9525 2-c 1600 95 20 2-d 1600 100 20 2-e 1650 100 35 2-f 1650 100 35 2-g 1650 100 35 2- h 1650 100 45 2-i 1600 98 30 2-j 1600 92 30 2-k 1650 100 35 2-l 1600 85 20 The obtained sintered body ball was evaluated by the same heat resistance test method as in Example 1. The results were as shown in Table 6.

Table 6 Sample No. Reduction in weight of fused crack cracks 2-a ○ × × − 2-b ◎ × × − 2-c ○ ○ ◎ ◎ 2-d ◎ ◎ ◎ ○ 2-e ◎ ◎ ◎ ◎ 2-f ◎ ◎ ◎ ◎ 2-g ◎ ◎ ◎ ◎ 2-h ○ × × ○ 2-i ◎ ○ ◎ ○ 2-j × × × − 2-k ○ ◎ ◎ ◎ 2-l ○ × ○ ◎ From the results shown in Table 6, the sintered body according to the present invention (sample No.
It is apparent that 2-c, 2-d, 2-e, 2-f, 2-g, 2-i and 2-k) have excellent properties as members for a high-temperature heat exchanger.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-252963 (JP, A) U.S. Pat. Zirkonoxid- SauerstoffmeBsonde n nach dem Einsatz in Regenerativkam mern von Flachglas wannen "Glastechnis che Berichte (1986), Vol. 59, No. 8, pp. 211-218 (58) investigated the field (Int.Cl. ^7, DB name) C04B 35/48 F28F 21/04 CA (STN) REGISTRY (STN) JICST file (J IS)

Claims (2)

(57) [Claims] 1. A heat exchanger member having the following components: (1) a zirconia sintered body containing 4.5 to 8 mol% of Y ₂ O ₃ ; (2) a main sintered body (3) The content of SiO ₂ is 0.5% by weight or less and the crystal phase is cubic.
The content of ₂ O ₃ is 1% by weight or less. (4) The average crystal grain size of the sintered body is 5 μm or more. 2. The heat exchanger member according to claim 1, wherein up to 1/2 of the content of Y ₂ O ₃ (as Y) is replaced by at least one of Mg, Ca and lanthanoids.