JPH0120357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preheating raw materials for steelmaking, particularly scrap.

[Conventional technology]

When manufacturing steel using steelmaking furnaces such as electric furnaces or converters, it is necessary to preheat the scrap charged into these steelmaking furnaces in order to effectively utilize the heat generated by the steelmaking furnace or to improve steelmaking efficiency. Various studies have been conducted and many preheating means and preheating devices have been developed, such as Utility Model Publication No. 56-23677 and Japanese Patent Publication No. 56-26684.
No. 59-66687, or Japanese Patent Application Laid-open No. 59-66687.

In the publication of these gazettes, for example,
In Japanese Patent Publication No. 23677, a preheating device was proposed that circulated and used part of the exhaust gas from the preheating container when scrap was preheated in the preheating container. A method for preheating raw material for charging iron into a converter using high-temperature non-oxidizing gas generated in an electric furnace has been proposed, and in Japanese Patent Application Laid-open No. 1983-66687, a method for heating clean gas such as air using high-temperature gas discharged from an electric furnace has been proposed. It has been proposed to preheat the scrap in the skip with heated gas heated in an exchanger and optionally supplemented with heat in a combustor.

According to these known scrap preheating means,
The heat of high-temperature gas discharged from electric furnaces, etc. can be used effectively to a certain extent, but heating of scrap depends on the operating conditions of the furnace and is unstable, as well as being affected by the effects of contained dust, etc. There are problems and insufficient thermal efficiency can be obtained when the scrap heating is done by a separate heat source.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a scrap preheating method that solves the above-mentioned problems and can obtain excellent thermal efficiency and stable scrap preheating.

[Means for Solving the Problems] The method for preheating scrap according to the present invention is to connect a hot gas inlet pipe and an exhaust gas pipe having an air preheater using passing gas in parallel via an on-off valve. A plurality of scrap preheating furnaces connected to the furnace are used as a primary preheating furnace, a secondary preheating furnace, and a finishing preheating furnace, and hot gas is introduced into the finishing preheating furnace to heat the scrap in the furnace to a finishing temperature, The exhaust gas is distributed and passed through the primary preheating furnace and the secondary preheating furnace to preheat the scrap in the furnace, and then the hot scrap in the finishing preheating furnace is replaced with cold scrap, which is used as the primary preheating furnace. Change the previous primary preheating furnace to the secondary preheating furnace, 2
It is characterized in that hot gas is introduced in order to use the secondary preheating furnace as a final preheating furnace.

〔Example〕

The following description will be made with reference to the accompanying drawings.

FIG. 1 is a schematic structural explanatory diagram showing an example of a preheating plant for implementing the scrap preheating method according to the present invention.

In FIG. 1, reference numeral 1 denotes a scrap preheating furnace, which may have any structure such as a preheating furnace with a shell structure whose inner surface is made of a heat insulating material.

In the present invention, it is necessary to arrange two or more preheating furnaces 1, preferably three or more in parallel. In FIG. 1, the preheating furnace 1 consists of three preheating furnaces 1a, 1b, and 1c, and thus the preheating furnace 1
A, 1b and 1c are respectively provided with high temperature gas inlet holes 2a, 2b and 2c and waste gas discharge holes 3a, 3b and 3c at one end of the furnace.

Further, the other ends of the preheating furnaces 1a, 1b, 1c are connected by a connecting pipe 4 via branch pipes 5a, 5b, 5c.

Further, the high temperature gas inlet holes 2a, 2b, 2c are connected to the combustion device 6. In addition, in the present invention,
Although the combustion gas generated by the combustion device 6 is introduced into the high-temperature gas inlet holes 2a, 2b, and 2c of the preheating furnace 1 through an introduction pipe, it is also possible to directly connect a burner and introduce the combustion gas directly. It can also be injected into the furnace.

Furthermore, the exhaust gas exhaust holes 3a, 3b, and 3c are connected to the exhaust gas exhaust pipe 8 via valves 7a, 7b, and 7c.

The waste gas discharge pipe 8 is further connected to a stripping tower 10 via a heat exchanger 9.

In the heat exchanger 9, combustion air to be introduced into the combustion device 6 is introduced, and the air is preheated by heat exchange with the waste gas. 11 is its preheated air conduit.

In the present invention, when combustible gas from combustible materials adhering to the scrap preheated in the preheating furnace 1 is mixed into the waste gas, a combustion device (not shown) is connected to the waste gas discharge pipe 8 in front of the heat exchanger 9. ), and the combustion heat can also be effectively utilized in the heat exchanger. 12 is a fuel gas pipe,
The combustion device 6 is connected to supply fuel gas from an arbitrary fuel source (not shown) to the combustion device 6.

11a, 11b, 11c and 12a, 12b,
12c is a valve provided in a connecting pipe between the preheating air conduit 11, the fuel gas pipe 12, and each of the preheating furnaces 1a, 1b, and 1c.

In the above preheating plant, containers (not shown) containing scrap to be preheated, such as scrap skips or scrap shoots, are charged into the respective preheating furnaces 1a, 1b, and 1c. Thus, for example, when the preheating furnace 1a is the finishing preheating furnace, 1b is the secondary preheating furnace, and 1c is the primary preheating furnace, the combustion device 6 is set to the preheating furnace 1a, and for introducing combustion gas and preheating air. Conduit settings, i.e. valve 11
a, 12a, and open valves 11b, 11c and 1.
2b and 12c are closed, and fuel and combustion air are supplied to the combustion device 6.

On the other hand, the valve 7 of the connecting pipe to the waste gas discharge pipe 8
In a, 7b and 7c, the valve 7a attached to the finishing preheating furnace 1a is closed, and the secondary preheating furnace 1b and the primary preheating furnace 1 are closed.
Both valves 7b and 7c of c are opened.

Further, the valves of the connecting branch pipes 5a, 5b, 5c at the other ends of the preheating furnaces 1a, 1b, 1c are open.

After that, the combustion high temperature gas is introduced from the combustion device 6 into the finishing preheating furnace 1a through the high temperature gas inlet 2a,
The scraps are heated to a predetermined preheating temperature, for example 300-500°C.

However, although the exhaust gas discharged from the finishing preheating furnace 1a imparts its sensible heat to the scrap in the furnace, it has a considerably high heat of around 800°C, for example, so it is passed through the connecting pipe 4. It is divided into a secondary preheating furnace 1b and a primary preheating furnace 1c, and preheats the scraps stored in each.

The scraps stored in the primary preheating furnace 1c and the secondary preheating furnace 1b are heated to 80°C, for example.
Preheat to 180℃ and lower the temperature, e.g. 260℃, 450℃
The gas that has reached a temperature of After preheating to ℃, it is discharged from the stripping tower 10.

In the above preheating work, when the scrap in the finishing preheating furnace 1a reaches a preheating temperature predetermined according to the operating conditions of the electric furnace or converter, etc., the preheating work is completed, and then the scrap in the finishing preheating furnace 1a The preheating scrap is taken out, a new cold scrap is charged, and this is used as the primary preheating furnace for the next preheating operation.The valve 7a to the waste gas discharge pipe 8 is opened, and the combustion device 6 is turned into the high temperature gas of the secondary preheating furnace 1b. A valve 7b connected to the inlet hole 2b and connected to the waste gas discharge pipe 8
At the same time, the valves 11b and 12b are opened to operate the combustion device 6a.

Further, the primary preheating furnace 1c is upgraded to a secondary preheating furnace.

In addition, when replacing the scrap, the preheating furnaces 1b, 1
In order to prevent cooling of the pipes c, valves of the connecting branch pipes 5b and 5c and valves 7b and 7c to the waste gas discharge pipe 8 are installed.
It is preferable to keep it closed.

Thus, the same scrap preheating operation as last time is performed, and the scrap in the finishing preheating furnace 1b in this preheating operation is brought to a predetermined preheating temperature.

At this time, the scraps in the primary preheating furnace 1a and the secondary preheating furnace 1c can each obtain the same preheating temperature as the previous time.

After the current preheating work is completed, the preheating furnaces will be switched sequentially in the same way as the previous time, and a new preheating work will be performed.

The combustion device 6 for generating high-temperature gas that is passed through the finishing preheating furnace is not limited to the movable type as described above, but may be of a fixed type in each furnace.

In the present invention, when combustible components are present in the exhaust gas due to vaporization of combustible substances such as oils and fats that adhere to the scrap, a combustion device is installed in front of the heat exchanger 9 as necessary to incinerate the waste. The heat of combustion can also be used to preheat the combustion air.

The preheating method using the preheating plant shown in FIG. 1 above is as follows.

At the start of the preheating work, scrap is charged into each of the three preheating furnaces 1a, 1b, 1c installed in parallel, and each of the preheating furnaces 1a, 1
b, 1c are arbitrarily determined. In this example, the second
As shown in Figure A, first, 1a is designated as a finishing preheating furnace, 1b is a secondary preheating furnace, and 1c is a primary preheating furnace.The combustion device 6 is set and operated in the finishing preheating furnace 1a, and the valve 7a is closed. On the other hand, a valve 7b to the waste gas discharge pipe 8 of the secondary preheating furnace 1b and the primary preheating furnace 1c,
7c is opened to perform preheating work.

The hot gas from the combustion device 6 is passed into the finishing preheating furnace 1a at a temperature of 1200°C to heat the charging scrap. During this heating, the exhaust gas from the finishing preheating furnace 1a still has a high temperature of 850°C, and passes through the connecting pipe 4 as shown by the arrow 13 to the secondary preheating furnace 1b.
and the primary preheating furnace 1c in an even distribution.

The distribution amount at that time does not necessarily have to be equal and can be determined arbitrarily.

The respective waste gases are then mixed in a common waste gas discharge pipe 8 and passed into a heat exchanger 9 in the direction of arrow 14 at a temperature of 450°C.

On the other hand, combustion air is introduced into the heat exchanger 9,
There was mutual heat exchange and the combustion air was preheated to 250°C. On the other hand, it exited the heat exchanger 9 and was discharged from the stripping tower 10 at a temperature of 300°C.

In the above preheating operation, the scrap in the finishing preheating furnace 1a was preheated to 400°C, the scrap in the secondary preheating furnace 1b was preheated to 180°C, and the scrap in the primary preheating furnace 1c was preheated to 80°C.

At this time, the temperature of the waste gas from each furnace was 470°C and 430°C, respectively, and was mixed in the waste gas discharge pipe 8, and the temperature at the inlet of the heat exchanger 9 was 400°C.

After the scrap in the finishing preheating furnace 1a reaches a predetermined preheating temperature, the preheating operation is interrupted, the scrap in the finishing preheating furnace is taken out, and a new cold scrap is charged, and this is used as the primary preheating furnace. The secondary preheating furnace was used as a finishing preheating furnace, and the previous primary preheating furnace was used as a secondary preheating furnace, as shown in FIG. 2B, and scrap preheating was performed by gas flow.

〔Effect of the invention〕

Since the scrap preheating method of the present invention is as described above, it is possible to prevent the temperature inside the furnace from decreasing and use the heat retained in the heating medium extremely effectively, and it is also possible to efficiently heat irregularly shaped objects such as scrap. heating can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic structural explanatory diagram showing an example of a preheating plant for carrying out the preheating method of the present invention, and FIG. 2 is a gas flow diagram during preheating. In the figure, 1a, 1b, 1c: preheating furnace, 4: connecting pipe, 6: combustion device, 8: waste gas discharge pipe, 9: heat exchanger.

Claims (1)

[Claims] 1 A plurality of scrap preheating furnaces are connected in parallel via on-off valves to a hot gas inlet pipe and an exhaust gas pipe having an air preheater using passing gas, which are connected via branch pipes, and a primary preheating furnace, 2 A secondary preheating furnace and a finishing preheating furnace are used. Hot gas is introduced into the finishing preheating furnace to heat the scrap in the furnace to the finishing temperature, and the exhaust gas is distributed to the primary preheating furnace and the secondary preheating furnace. preheat the scrap in the furnace, then replace the hot scrap in the finishing preheating furnace with cold scrap, and
In addition to using the secondary preheating furnace, the previous primary preheating furnace is used as the second preheating furnace.
A method for preheating scrap characterized by introducing hot gas into the secondary preheating furnace and the secondary preheating furnace to serve as a finishing preheating furnace.