JPH0619218B2 - Combustion air preheater for radiant tubes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention uses combustion exhaust gas heat of the radiant tube as combustion air supplied to a radiant tube burner that is attached to a radiant tube in heat treatment equipment, chemical industry equipment, etc. The present invention relates to a combustion air preheating device for a radiant tube which is preheated.

<Prior Art> Conventionally, in a radiant tube such as a continuous annealing furnace, a device for preheating combustion air supplied to a radiant tube burner has a heat exchanger at the exhaust pipe end of the radiant tube 11, as shown in FIG. (Recuperator) 12 is installed, the combustion air is fed from the air supply pipe 13 into the heat exchanger 12, and the heat is exchanged with the hot combustion exhaust gas flowing in the radiant tube 11. Preheat.
In the figure, 12a is a fin provided on the inner peripheral surface of the heat exchanger 12, 14 is a lining, and the arrow indicates the flow direction of the combustion air.

<Problems to be Solved by the Invention> However, the above-described conventional combustion air preheating device for a radiant tube has the following problems.

(1) A large amount of heat is dissipated from the radiant tube 11, so that not only the energy loss is large, but also the skin temperature of the lining 14 rises and the working environment is deteriorated. That is,
This is because the radiant tube 11 of the mounting part of the heat exchanger 12
This is a problem caused by the extremely high temperature of 600 ° C or higher. The exhaust gas temperature immediately before the heat exchanger 12 is 600 ° C., but immediately after that it is 400 ° C. or higher, and the heat radiation loss is large.
On the other hand, in order to reduce heat dissipation, the lining of that part 14
However, if so, the burner bangs become large and maintenance becomes difficult. Further, if the flange portion is lined, the bolt cannot be retightened, so that a gap is apt to occur and there is a risk of sucking air from there. Not only the combustion air temperature sucked air is reduced, and the amount of O ₂ is changed O ₂ control becomes impossible.

(2) The heat transfer surface is small and the heating capacity of air is limited.
Although the heat transfer surface can be expanded by lengthening the heat exchanger 12, if the length is too long, the tube temperature at the front surface of the slip, which is the object to be heated, will drop. Therefore, the length cannot be increased indefinitely. In the conventional type, the preheated air temperature after heat exchange is 300 for the exhaust gas temperature of 600 ° C.
The limit was ℃ to 450 ℃.

The present invention solves such conventional problems, and an object of the present invention is to provide a combustion air preheating device for a radiant tube, which reduces energy loss and enhances the combustion air heating capacity.

<Means for Solving Problems> The configuration of the combustion air preheating device for a radiant tube according to the present invention for achieving this object is to use the combustion exhaust gas heat of the radiant tube for the combustion air supplied to the radiant tube burner. In a combustion air preheating device for radiant tubes that is preheated by means of a flat plate portion that faces the outer skin around the through portion of the lining through which the radiant tube passes with a predetermined gap, and is integrally connected to the flat plate portion. The radiant tube has a cylindrical portion that covers the outer periphery of the protruding portion from the lining, and the combustion air is fed through the gap between the flat plate portion and the outer cover and the gap between the cylindrical portion and the radiant tube. And a primary heat exchanger that is provided inside the radiant tube and communicates with the primary heat exchanger. A secondary heat exchanger to which the combustion air, which is preheated by the heat exchanger, is fed.

<Operation> Combustion air is first sent to the primary heat exchanger where it is preheated. That is, in the gap between the flat plate portion and the outer skin of the lining, it is heated by the heat of the outer skin of this lining,
Then, in the gap between the cylindrical part and the radiant tube,
By heating the outside of this radiant tube with heat, it is primarily preheated and then sent to a secondary heat exchanger where it is further heated by the heat of combustion exhaust gas inside the radiant tube and then sent to the burner. To be

<Example> Hereinafter, one example of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a sectional view of a combustion air preheating device for a radiant tube according to an embodiment of the present invention, and FIG. 2 is a II-II of FIG.
FIG. As shown in FIGS. 1 and 2, a primary heat exchanger 15 is provided outside the outer furnace of the radiant tube 11. The primary heat exchanger 15 includes a disc portion 15a that faces the outer skin 14a of the lining 14 with a slight gap, and the lining 14a.
It is composed of a cylindrical portion 15b that projects from the outer periphery of the radiant tube 11 and a central portion of the disk portion 15a that passes from the inlet 16 provided at the outer edge of the disk portion 15a through the disk portion 15a and the lining skin 14a. There is formed a flow path from there to the outlet 17 through between the cylindrical portion 15b and the radiant tube 11. On the other hand, a secondary heat exchanger 18 is arranged inside the radiant tube 11. The secondary heat exchanger 18 has the same structure as the conventional heat exchanger 12 described above, and includes an outer cylinder 19 inserted into the radiant tube 11 and an inner cylinder 20 inserted into the outer cylinder 19. From the inlet 21 of the inner cylinder 20 to the inner cylinder 20
It goes through the inside to the tip of the inner cylinder 20 and folds back from there to the inner cylinder.
A flow path is formed between the outer cylinder 19 and the outer cylinder 19 to reach the outlet 22. On the inner peripheral surface of the outer cylinder 19 facing the inner cylinder 20, a plurality of fins 20a are provided in a protruding manner. Outlet of these primary heat exchangers 15
17 and the inlet 21 of the secondary heat exchanger 18 are connected by a connecting pipe 23.

In such a configuration, the combustion air first flows into the primary heat exchanger.
It enters from the inlet 16 of 15 and is pre-heated by the heat of the outer peripheral surface of the lining skin 14a and the radiant tube 11 while passing through the flow passage there. Next, the combustion air discharged from the outlet 17 of the primary heat exchanger 15 passes through the connecting pipe 23 and the secondary heat exchanger.
18, while being passed through the flow path there, is heated to a higher temperature by the heat of the exhaust gas inside the radiant tube 11.
After that, it exits from the outlet 22 and is sent to a burner (not shown) for combustion of fuel.

Here, generally, the heat transfer amount Q in convective heat transfer is given by the following equation, where α is the heat transfer coefficient, A is the heat transfer area, and Δt is the temperature difference.

Q = α × A × Δt Therefore, the heat transfer area A as a whole by providing the primary heat exchanger 15
It is understood that the heat transfer amount Q can be easily increased to a very large value by enlarging.

Now, as an example, use a 7-inch radiant tube with 12
When a burner of 0,000 kcal / h is attached and burned, the temperature of the combustion air supplied to the burner is about 400 ° C when using a conventional preheating device, but according to the device of the present invention, the temperature is about 5 ° C.
It can be preheated to 00 ℃. This means a reduction in fuel consumption of about 3%, which leads to significant energy savings.

<Effects of the Invention> As described above specifically with reference to the embodiment, according to the present invention, not only the heat exchange with the combustion exhaust gas flowing through the radiant tube but also the lining is performed outside the radiant tube. Since the primary heat exchanger capable of heat exchange is provided, the heat exchange rate can be increased, and the temperature of the combustion air supplied to the burner can be raised to save energy. Further, the heat of the outside of the radiant tube and the heat of the outer skin of the lining are effectively used for heating the combustion air, so that the temperature rise in that portion can be suppressed and the deterioration of the working environment can be prevented. Moreover, 2
Since the secondary heat exchanger is provided inside the radiant tube, the primary heat exchanger can be provided on the outer circumference of the protruding portion from the lining of the radiant tube, and therefore the bulk of the apparatus is not increased. .

[Brief description of drawings]

FIG. 1 is a sectional view of a combustion air preheating device for a radiant tube according to an embodiment of the present invention, FIG. 2 is a II-II sectional view of FIG. 1, and FIG. 3 is a combustion air preheating for a radiant tube according to a conventional example. It is sectional drawing of an apparatus. In the drawing, 11 is a radiant tube, 15 is a primary heat exchanger, and 18 is a secondary heat exchanger.

Claims (1)

[Claims] 1. A combustion air preheating device for a radiant tube, which preheats combustion air supplied to a radiant tube burner by utilizing the heat of combustion exhaust gas of the radiant tube, with respect to an outer skin around a penetrating portion of a lining through which the radiant tube penetrates. And a flat plate portion facing each other with a predetermined gap therebetween, and a cylindrical portion integrally connected to the flat plate portion and covering the outer periphery of the protruding portion of the radiant tube from the lining, the flat plate portion and the outer cover. A primary heat exchanger to which combustion air is fed through a gap between the primary heat exchanger and a gap between the cylindrical portion and the radiant tube, the primary heat exchanger being provided inside the radiant tube and communicating with the primary heat exchanger. A radiant chew comprising: a secondary heat exchanger to which combustion air, which is preheated by the heat exchanger, is fed. Use combustion air preheating device.