CN110173994A - A kind of porous radiation Blackbody element of cavity - Google Patents

Abstract

The invention discloses a radiation black body element with porous cavity, which is installed on the furnace wall. The whole is cylindrical and hollow inside. There is an end cover, and there are through holes on the end cover; the through holes are circular, the number is 7 to 10, one is arranged on the axis, and the others are evenly distributed on the concentric circle; the total area of the through holes accounts for the area of the bottom surface of the black body element 20-28% of that. The invention can improve the blackness of the blackbody element to the greatest extent, increase the contact area between the furnace gas and the furnace wall, effectively improve the utilization rate of the heat energy of the furnace, and has low cost, simple structure, easy mass production and no need to change The original kiln structure can be widely used in various heating furnaces, and it is basically not aging, and it is safer in engineering applications.

Description

A cavity porous radiation blackbody element

technical field

The invention relates to a heat transfer element of an industrial furnace, in particular to a radiation blackbody element with a porous cavity.

Background technique

There are two ways to improve the thermal efficiency of the heating furnace: one is to strengthen the heat transfer in the furnace, and the other is to strengthen the waste heat recovery. Because the temperature of the heating furnace is usually high when it is working, the heat transfer in the furnace is dominated by radiation, accounting for more than 90% of the total heat transfer. Radiation heat flow is a fourth power function of temperature. Slightly increasing the average radiation temperature and pressure can effectively increase the heat transfer. Compared with most waste heat recovery technologies that rely on convective heat transfer, the enhanced heat transfer in the furnace has great advantages.

In the prior art, in order to enhance the heat transfer in the furnace, many energy-saving technologies are adopted in actual industrial furnaces. For example: use light furnace building materials to reduce heat loss, use high-temperature coatings to increase the blackness of the furnace wall, change the structure of the furnace wall (reduce the height of the furnace wall, add a partition wall inside the furnace), etc. to strengthen the heat transfer in the furnace. Although these measures can improve the thermal efficiency of the furnace wall in theory, their energy-saving effect is limited in practical application.

There are also some industrial furnaces using black body technology. Black body technology is based on the black body theory of infrared physics, and technicalizes the concept of "absolute black body", and develops an industrial standard black body, which is called a black body element. Enlarging the heat transfer area and increasing the emissivity of the furnace can more effectively control the heat rays in the furnace, control them from a diffuse disordered state to an orderly one, and direct them to the heated material to increase the heat rays. In place rate, enhanced radiation heat transfer, achieved significant production increase and energy saving effects. This technique somewhat improves the emissivity and directional radiation issues within the cavity. But there is still a lot of room for improvement in the emissivity in the furnace, and the internal space of the black body element has not been fully utilized.

Contents of the invention

Aiming at the disadvantages in the prior art that the internal space of the blackbody element in the industrial furnace is not fully utilized, the problem to be solved by the present invention is to provide a porous radiating blackbody element which can improve the energy-saving effect.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

The invention is a radiating black body element with porous cavity, which is installed on the furnace wall. The whole is cylindrical and hollow inside. The end cover is provided with a through hole.

The through holes are circular, the number is 7-10, one is arranged at the axis, and the others are evenly distributed on the circumference of the concentric circle.

The total area of the through holes accounts for 20-28% of the area of the bottom surface of the blackbody element.

The ratio of length to base diameter of each blackbody element is 5:4.

The blackbody element is made of magnesia-alumina bricks with high refractoriness and strong oxidation resistance; the high-temperature radiation blackbody element is pre-set on the refractory bricks used to build the furnace wall, or is set simultaneously during the process of building the furnace wall.

The present invention has the following beneficial effects and advantages:

1. The invention can maximize the blackness of the black body element, increase the contact area between the furnace gas and the furnace wall, effectively improve the utilization rate of the furnace heat energy, and the cost is low.

2. The present invention has a simple structure, is easy to manufacture in batches, and has the basis of mechanized assembly line operation. When in use, it does not need to change the original kiln structure, and can be widely used in various heating furnaces, and it is basically not aging. More security in the application.

Description of drawings

Fig. 1 is the schematic diagram of the installation of the cavity porous blackbody element of the present invention in the heating furnace kiln;

Fig. 2 is the schematic sectional view of the front view of the cavity porous blackbody element of the present invention;

Fig. 3 is a top view of the cavity porous blackbody element of the present invention.

Among them, 1 is a black body element, 2 is a furnace, 3 is a furnace wall, 4 is a heating workpiece, 5 is a cavity, and 6 is a through hole.

Detailed ways

The present invention will be further elaborated below in conjunction with the accompanying drawings of the description.

As shown in Figures 1 to 2, a radiating blackbody element with a porous cavity in the present invention is installed on the furnace wall 3. Facing the material, an end cover is provided at the end facing the material, and a through hole 6 is provided on the end cover.

As shown in FIG. 3 , the through holes 6 are circular, and the number is 7 to 10. One is arranged at the axis of the cylinder, and the others are evenly distributed on the concentric circumference of the cylinder.

The total area of the through holes accounts for 20-28% of the area of the bottom surface of the blackbody element 1 , and the ratio of the length of each blackbody element 1 to the diameter of the bottom surface is 5:4.

The blackbody element 1 is made of magnesia-aluminum bricks, and its molding methods include sintering molding and fusion casting molding. The high-temperature radiation blackbody element can be set on the refractory bricks for building the furnace wall first, or can be set at the same time during the process of building the furnace wall. The axis of the high temperature black body element 1 always points to the heating material in the kiln.

Compared with other refractory bricks, magnesia-alumina bricks have higher refractoriness, which can reach more than 2000°C, have higher load softening temperature, greater high-temperature mechanical strength, and good resistance to iron oxide and calcium oxide. The chemical erosion performance of alkaline slag can well adapt to the high temperature environment in the furnace.

In this embodiment, the black body element 1 is a cylinder as a whole, with a cavity 5 inside, and an end cap is provided at one end, and seven through holes are arranged on the end cap, as shown in Figure 3. Holes, and others are evenly distributed on the circumference of the concentric circle in a symmetrical manner; the other end is straight and installed on the furnace wall 3. The small hole is set on the end cover under the black body element 1 because after the radiant energy enters the cavity 5 through the small hole, it will undergo multiple absorption and reflection in the cavity 5, and each time after one absorption, the radiant energy will The share of the absorption rate of the inner wall is weakened once, and finally the energy leaving the small hole is negligible, which can be considered to be completely absorbed in the cavity 5 . Therefore, in terms of radiation characteristics, the pinhole has the same properties as the surface of a black body. In principle, the absorptivity of the material used to manufacture the black body element has no effect on the blackness of the small holes. The smaller the proportion of the small hole area and the total area of the inner wall of the cavity, the higher the absorption ratio of the small hole and the greater the blackness.

Let the absorption ratio in the cavity be α, S _hole /S _cavity =f, the S _hole is the total area of the through hole, and the S _cavity is the cavity cross-sectional area of the blackbody element. Radiant energy Q enters the cavity from the outside through the small hole. The energy change after each reflection is as follows:

Energy absorbed by the inner wall of the cavity:

Q _wall = αQ+α(1-f)(1-α)Q+...+α(1-f) ^n-1 (1-α) ^n-1 Q (1)

Simplified: |

Similarly, the energy reflected through the small hole:

Absorption rate of the pores:

Generally, the absorptivity α of the surface of the blackbody element 1 is 0.8. In the black body element 1 of the present invention, the area S _hole of the small hole is 2.2×10 ^-3 m ² , the area S _cavity of the black body cavity 5 is 0.043 m ² , then f=0.05, α _hole =0.987. Because the furnace wall and steel billet of the industrial furnace can be regarded as a gray surface, the blackness of the small hole can be obtained ε _hole = 0.987. Compared with the surface without small holes, the blackness at the small holes is increased by 23%. According to the Stefan-Boltzmann law, the increase of blackness increases the reflected heat flow, and the heating efficiency of the billet will also increase. has seen an increase.

Simultaneously, after installing the blackbody element 1 of the present invention, the area of the inner surface of the furnace wall 3 is also greatly increased. In a fuel furnace, when the temperature difference between the high-temperature furnace gas and the inner surface of the furnace wall 3 is not large, the heat flux of the radiation heat exchange between the high-temperature furnace gas and the inner surface of the furnace wall 3 is:

In the formula: ε _G is the blackness of the furnace gas at T _G , ε _W is the blackness of the inner surface of the furnace wall, T _G is the temperature of the furnace gas, T _w is the temperature of the furnace wall, and F _W is the area of the inner surface of the furnace.

For fuel furnaces, the high-temperature furnace gas is in contact with the furnace wall and materials during the process of continuous flow and circulation, and the furnace gas continuously radiates energy, so the high-temperature furnace gas is provided to the furnace in two heat transfer forms: convection and radiation. heat. It can be seen from the above formula that the addition of the black body element 1 of the present invention increases the area F _W of the furnace wall 3, strengthens the radiation heat exchange between the high-temperature furnace gas and the inner surface of the furnace wall 3, and makes the temperature of the inner surface of the furnace 2 rise, so The heat exchange Q on the surface of the billet is also enhanced, the heating time of the billet is greatly shortened, the temperature of the exhaust gas from the furnace is lowered, and the fuel consumption is reduced. Moreover, because the black body element 1 of the present invention is a hollow structure, compared with the traditional black body element, not only the manufacturing cost is reduced, but the economic benefit is improved, and the contact area between the high temperature furnace gas and the black body element 1 is nearly doubled.

In the present invention, numerous blackbody elements 1 are installed at proper positions of the furnace wall 3, which not only increases the heat transfer area, but also increases the emissivity of the furnace 2. At the same time, punching through holes 6 at appropriate positions of the blackbody element 1 can effectively increase the blackness of the blackbody element 1 itself, and maximize the thermal efficiency in the furnace. The performance of the black body element 1 is stable, and it will not age basically. It can effectively control the heat rays of the furnace, so that they can be adjusted from a diffuse disordered state to an orderly state, and directly radiate to the heated object to improve the rate of heat rays. Enhanced radiation heat transfer, achieving significant energy-saving effects.

The invention has a simple structure and is easy to implement, and can be widely used in various heating furnaces without changing the structure of the original kiln, and the engineering implementation scheme has strong safety.

Claims (5)

1. A radiation black body element with porous cavity, characterized in that: it is installed on the furnace wall, the whole is a cylinder, and the interior is hollow, one end is the installation end, fixed on the furnace wall, the other end faces the material, and the other end faces the material. An end cover is provided at one end, and a through hole is provided on the end cover. 2. The cavity porous radiating black body element according to claim 1, characterized in that: the through holes are circular, the number is 7-10, one is arranged on the axis, and the others are evenly distributed on the circumference of the concentric circle. 3. The cavity porous radiating black body element according to claim 1, characterized in that: the total area of the through holes accounts for 20-28% of the bottom surface area of the black body element. 4. The cavity porous radiating black body element according to claim 1, characterized in that: the ratio of the length of each black body element to the diameter of the bottom surface is 5:4. 5. The cavity porous radiation blackbody element according to claim 1, characterized in that: the blackbody element is made of magnesia-aluminum bricks with high refractoriness and strong oxidation resistance; the high temperature radiation blackbody element is pre-set in the construction furnace On the refractory bricks of the wall, or at the same time during the construction of the furnace wall.