JPS61253327A - Method for decreasing dew point of heating furnace - Google Patents

Abstract

PURPOSE:To reduce the time required for decreasing the dew point of a heating furnace and to improve the operating efficiency thereof by heating the inside of the furnace while injecting an inert gas or reducing gas of a low dew point into the spacing between the outside wall of the furnace body and refractories of the heating furnace. CONSTITUTION:The inside of the heating furnace A for heating treatment of a material C to be heated conveyed by means of rollers B is heated up while the inert gas or reducing gas of <=-40 deg.C dew point is introduced from a gas feed main pipe 4 through a branch pipe 5 and a gas feed hole 6 into the spacing 3 between the outside wall 2 of the body of the furnace A and the retractories 1 lined on the inside thereof and is discharged from a discharge hole 9 to a discharge pipe 11 prior to the operation of the above-mentioned furnace. The gaseous N2 having -78 deg.C dew point is suitable as the above-mentioned inert gas and the gaseous Ax (N2+H2) or the like having -70 deg.C dew point is adequate as the reducing gas. The gas is preferably preheated to about 250-300 deg.C to maintain the pressure in the spacing 3 slightly higher than the pressure in the furnace. The moisture of the refractories 1 is thereby absorbed and the decrease of the dew point in the furnace is accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for lowering the dew point of a heating furnace prior to its operation.

(Prior Art) Various heating furnaces (including heat treatment furnaces) are installed in continuous rolling processes, continuous plating processes, etc. depending on the purpose. For example, in a continuous hot-dip galvanizing process, it is essential that the material be subjected to heat treatment for annealing and cleaning purposes before plating. In such heating furnaces, when the furnace is newly built or renovated, the refractories contain a large amount of moisture, and the refractories also absorb moisture when the furnace is stopped for a long period of time for repairs or the like. Furnaces in such conditions have a high dew point, which can cause deterioration of plating adhesion in continuous plating processes, so be sure to lower the dew point to a predetermined value or less before starting furnace operation. drying work must be carried out.

(Problem to be solved by the invention) The above drying work involves injecting Nu gas or HJ gas with a low dew point into the furnace while heating it from the inside to dry the refractories containing moisture. However, in the case of a continuous hot-dip galvanizing process, the stable dew point during operation is -40℃~
It is assumed that the dew point is -50°C, and it often takes 5 days or more to lower the dew point to this extent. Therefore, we normally start operations when the dew point reaches around 115 degrees Celsius, and until the dew point reaches a stable dew point, we operate by reducing the twin speed to ensure plating adhesion, but even then - 15℃
It takes an average of 40 hours or more to reach the dew point of .

An object of the present invention is to provide a dew point lowering method that shortens the time required for lowering the dew point, advances the start of furnace operation, and greatly improves operational efficiency.

(Means and actions for solving the problem) By the way, when we look at the structure of the heating furnace, we can see that there is a gap between the outer wall of the furnace body and the refractory inside it due to the difference in thermal expansion between the two. . Although this gap varies depending on the scale and type of furnace, it is usually a value of about 10 mm. The present inventor focused on this existing gap, and if Nu gas, HJ gas, etc. with a low dew point is simultaneously introduced into this part during dew point lowering work, the time required for dew point lowering work can be shortened. I thought,
Various field tests were conducted. As a result, it was found that the time required for lowering the dew point can be reduced to approximately % of the conventional time by using gas flow to the 4-mm gap.

The present invention was made based on this knowledge, and the inside of the heating furnace is heated while injecting an inert gas or reducing gas with a dew point of 140°C or less into the gap between the outer wall of the furnace body and the refractory. The gist is a method for lowering the dew point of a heating furnace, which is characterized by heating.

Hereinafter, the method of the present invention will be explained in more detail with reference to the drawings. In Figure 1, (3) is the heating furnace, and the outer wall of the short body (1
) (iron shell) with a gap (3) inside the refractory (21
The structure is lined with (brick). (2) is a roller installed inside the heating furnace (2) for conveying the object to be heated (Q).

On the outside of the heating furnace (4), there are two air supply main pipes (4) parallel to the furnace.
) are provided. A plurality of air supply branch pipes (5) branched from this main pipe (4) are connected to the lower part of the outer wall (1) at appropriate intervals, and communicate with the gap (3) through air supply holes (6). are doing. Each air supply branch pipe is provided with a valve (7) and a pressure gauge (8). On the other hand, one or more exhaust holes (9) are provided in the outer wall (1) at the top of the furnace, and an exhaust pipe αυ is connected to this through a valve QQ. (A) is a pressure gauge for measuring the gas pressure in the gap (3), and one or more pressure gauges are installed as necessary.

An inert gas or reducing gas with a dew point of 140 degrees Celsius or less is supplied to the air supply main pipe (4). As a reducing gas, for example, Ax gas (N+H)
(dew point -70°C), etc.

In order to carry out the method of lowering the dew point of the present invention in the heating furnace equipment described above, it is necessary to heat the inside of the heating furnace (8) while passing conventional cine active gas or reducing gas into the heating furnace (8), and at the same time The dew point supplied via the air supply branch pipe (5) -
Pulp (
7) is opened and introduced into the gap (3) of the furnace through the intake hole (6).

At this time, the opening degree of the valve (7) is adjusted while measuring the pressure gauge 02 so that the gas pressure in the gap (3) is higher than the pressure inside and outside the furnace. This is to prevent outside air from entering and to enhance the purging effect. Further, in order to promote the effect of lowering the dew point, the introduced gas is preferably heated to about 250°C to 800°C.

The gas injected into the gap (3) as described above becomes a so-called carrier gas and reversely absorbs the moisture absorbed by the refractory brick (1), and then passes through the exhaust hole (9) to the exhaust pipe 01. ), which, together with the heating of the kettle itself, promotes a lowering of the dew point inside the furnace.

The amount of inert gas or reducing gas to be fed varies depending on the scale of the heating furnace, but is preferably 100 Nn1/Hr or more.

(Example) In a heating furnace for continuous hot-dip galvanizing whose specifications are shown in Table 1 below, after regular repairs, the inside of the furnace was heated to 800°C while Co gas (flow rate 30ON → RIr) was passed through the furnace. At the same time, the dew point in the gap between the furnace wall and the refractory reaches 17.
Dry Ax C ammonia decomposition gas (NJ+H) at 8℃
) i Heated to 260°C, +8011 mAq pressure, 1
A flow rate of 2ONtrI/Hr was continuously fed. The dew point at the start of feeding (startup) was +10°C to 20°C.

Figure 2 shows the change in furnace dew point over time as a solid line. For comparison, the results obtained when only in-furnace heating and in-furnace gas feeding were performed in a heating furnace of the same type and size are shown by a broken line in the figure as a conventional method.

As is clear from Table 1 and Figure 2, the conventional method required 40 hours to lower the furnace temperature to -15°C, but the method of the present invention reduced the time to 80 hours.

In addition, the total amount of gas used to lower the temperature to -15°C is 120 N"/HrX 40 Hr -48 in the conventional method.
0ONn? However, although the method of the present invention requires extra gas during the working period, the working period is greatly shortened, resulting in a total of 4,600 NINII, which is a reduction of 4.2%.
achieved a reduction in As a result, the total amount of energy used (the sum of furnace heating energy, gas heating energy, and gas feeding energy) decreased from 96 million Kcat to 770,075.
We were able to achieve a 19.8% reduction in Kcal.

(Effects of the Invention) As is clear from the above description, the present invention not only accelerates the dew point reduction rate of the heating furnace and brings the furnace into operation earlier, and has a great effect on improving operational efficiency, but also It is possible to save the energy required for lowering, and furthermore, since the existing void is used, it is easy to implement and has a significant economic effect.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a heating furnace for carrying out the dew point lowering method according to the present invention, and Fig. 2 is a diagram comparing and contrasting the change in the furnace dew point over time between the conventional technology and the method of the present invention. It is. 1: Furnace outer wall (iron shell), 2: Refractory (brick), 3: Gap, 4: Air supply main pipe, 5: Air supply branch pipe, 6: Air intake hole, 7,
lO: Pulp, 8.12: Pressure gauge, 9: Exhaust hole, 11:
Exhaust pipe

Claims (1)

[Claims] (1) The dew point of a heating furnace characterized by heating the inside of the furnace while injecting an inert gas or reducing gas with a dew point of -40% or less into the gap between the outer wall of the furnace body and the refractory. How to lower.