JPS6354972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for preheating scrap raw material in a melting furnace to which scrap is supplied as raw material.

When supplying scrap as raw material to the melting furnace,
It is being considered to save energy in melting furnace operation by preheating scrap using the exhaust gas from the melting furnace.

However, with conventional scrap preheating equipment, the exhaust gas from the melting furnace is simply vented to the scrap once and then discarded, so the scrap is not preheated effectively and it is difficult to preheat the scrap to a sufficient temperature. This has the problem of requiring a long time. In addition, since the preheated gas is simply discarded, the exhaust gas whose temperature has been lowered by preheating contains flammable components such as oil mixed in the scrap, and odor components from the decomposition of plastics, etc. These substances are emitted into the atmosphere without being burned or decomposed by high-temperature heating, resulting in a problem that significantly deteriorates the environment.

The present invention can solve the above-mentioned problems, and includes a combustion furnace for combusting exhaust gas from a melting furnace, a plurality of preheaters for preheating scrap with gas from the combustion furnace, and a heat exchanger that raises the temperature of the gas after primary preheating from the heat exchanger; a decomposition furnace that burns combustible components and decomposes odor components contained in the gas from the heat exchanger; a pilot burner provided in the cracking furnace to branch and guide gas to form a high-temperature spark; a flow path for guiding and discharging the gas in the cracking furnace to each of the preheaters;
The heat exchanger is characterized in that the preheater includes opening/closing dampers provided on the inlet and outlet sides of the primary and secondary gases in each of the preheaters, and the heat exchanger is disposed in the secondary gas flow path. This relates to a scrap preheating device.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flow sheet showing the principle of the present invention in an easy-to-understand manner. Exhaust gas (usually about 830 to 850° C.) from a melting furnace, for example, an electric furnace 1, is introduced into a combustion furnace 3 via an elbow 2. Combustion furnace 3 collects CO in exhaust gas.
It is designed to completely burn the gas and eliminate the risk of explosion, and it also has sufficient functions as a pre-duster. The combustion furnace 3
The preheating gas 4 combusted in the scrap is led to the preheater 5 to preheat the scrap, and the primary preheating lowers the temperature (about 300 to 500°C) and increases the temperature due to the oil and plastic contained in the scrap. Gas 6 after primary preheating containing generated combustible components and odor components
is introduced into the cracking furnace 8 via the heat exchanger 7.

The cracking furnace 8 is equipped with a pilot burner 9 at its upper part, which acts as a fire source. The pilot burner 9 includes a fuel introduction section 10 that supplies kerosene and oxygen, a combustion air introduction section 12 that includes an air preheater 11 and supplies preheated air, and a part of the preheating gas 4 that is branched and supplied. A high-temperature gas introduction part 13 is provided to form a columnar flame in the decomposition furnace 8, and the primary preheated gas 6 from the preheater 5 is brought into direct contact with the gas 6, and the temperature inside the decomposition furnace 8 is raised to about 750°C or higher. I'm trying to keep it.

The gas heated in the cracking furnace 8 is introduced into the preheater 5' as a secondary preheating gas through the pipe 14 to perform secondary preheating of the scrap, and the gas 15 after the secondary preheating is transferred to the heat exchanger. 7 to exchange heat with the primary preheated gas 6, and then pass through the chimney 2 in order through a suga cooler 16 for dust collector protection, a dust collector 17, a control damper 18, and an exhaust fan 19.
0 to the atmosphere.

With the above configuration, the preheating gas 4 is discharged from the electric furnace 1 via the elbow 2 and burned in the combustion furnace 3.
is introduced into the preheater 5 to preheat the scrap in the preheater 5. Gas 6 after primary preheating by the above preheating
The scrap is heated in a heat exchanger 7 and guided to a decomposition furnace 8 while being at a low temperature and containing combustible components such as oil and odor components such as plastics mixed in the scrap. The gas introduced into the cracking furnace 8 removes the combustible components it contains.
It is effectively combusted by direct contact with the high-temperature columnar flame that is formed inside, and odor-causing components such as methyl sulfide, methylamine, ammonia, and acetaldehyde are kept at a temperature of about 750℃ or higher. Due to the temperature inside the decomposition furnace 8, the substance is heated and decomposed at a high temperature and converted into an odorless substance. At this time, in order to complete the function of the decomposition furnace 8 in a short time, it is preferable that the temperature inside the decomposition furnace 8 is 800° C. or higher.

The gas that has been burned and decomposed in the cracking furnace 8 is led to the preheater 5' through the pipe 14, and the scrap that has been primarily preheated in the preheater 5 is subjected to secondary preheating, and its temperature is further raised. Close. The gas 15 after secondary preheating (about 700℃ or higher) is led to the heat exchanger 7, and the gas 6 after primary preheating at a low temperature (about 300 to 500℃) is guided to the heat exchanger 7.
heating. At this time, since the secondary preheated gas 15 has a sufficiently higher temperature and a larger flow rate than the primary preheated gas 6, heat recovery in the heat exchanger 7 can be easily performed. Furthermore, by recovering heat from the secondary preheating gas 15 to raise the temperature of the primary preheating gas 6 and increasing the temperature inside the cracking furnace 8, the fuel supplied from the fuel introduction section 10 is It is possible to improve the combustion and decomposition functions by reducing the amount of combustion air, reducing the size of the air preheater 11 and the blower (not shown), and increasing the temperature inside the decomposition furnace 8. Further, by branching a part of the preheating gas 4 and guiding it to the pilot burner 9, it is possible to form a high-temperature spark in the pilot burner 9, thereby effectively burning and increasing the temperature in the cracking furnace 8. be able to. In addition, the pilot burner 9
The amount of high-temperature gas introduced through the high-temperature gas introduction part 13 is generated in excess of the amount required for the preheating gas 4 to preheat the scrap, so this surplus is used.

After the heat has been recovered by the heat exchanger 7, the gas is cooled by the gas cooler 16 to a temperature that does not cause any trouble to the dust collector 17, and then collected by the dust collector 17. While the suction force is adjusted by the damper 18, it is sucked in by the exhaust fan 19, and is discharged to the atmosphere from the chimney 20.

The scrap, which has undergone primary preheating in the preheater 5 and secondary preheating in the preheater 5', is supplied to the electric furnace 1 as a raw material. Incidentally, FIG. 1 shows the principle of the present invention, and since preheating must be stopped when discharging and charging scrap in the preheaters 5 and 5', an embodiment to solve this problem is shown. will be explained with reference to FIG.

FIG. 2 shows a case where three preheaters 5a, 5b, and 5c are provided, and the parts in the figure with the same reference numerals as in FIG. 1 indicate the same parts. The preheating gas 4 from the combustion furnace 3 is transferred to the preheaters 5a, 5b, 5c.
Opening/closing dampers 21a, 21b, 21c are provided in the middle of each branch pipe, and the primary preheated gas 6 from the preheaters 5a, 5b, 5c is introduced into the heat exchanger 7. Opening/closing dampers 22a, 22b, 22c are installed in the middle of each pipe to
will be established. Further, the gas led out from the cracking furnace 8 through the pipe 14 is branched and guided to the preheaters 5a, 5b, 5c, and opening/closing dampers 23a, 23b, 23c are provided in the middle of each branch pipe, and each preheater An opening/closing damper 24a, 2 is provided in the middle of each pipe of the secondary preheated gas 15 led out from 5a, 5b, 5c.
4b and 24c are provided.

To explain the case where the preheater 5a performs primary preheating and the preheater 5b performs secondary preheating, among the opening/closing dampers 21a, 22a, 23b, and 24b are opened and the other opening/closing dampers are closed. Then, the preheating gas 4 from the combustion furnace 3 hits the opening/closing damper 21a.
The gas 6 after the primary preheating is led to the preheater 5a via the opening/closing damper 22a, passing through the heat exchanger 7 and the decomposition furnace 8 to raise its temperature, and then passing through the piping 14 and the opening/closing damper. 23
The scrap is guided to a preheater 5b via a pipe 5b for secondary preheating of the scrap. The secondary preheated gas 15 is guided to the heat exchanger 7 via the opening/closing damper 24b, where its heat is recovered and then discharged. At this time, the preheater 5c discharges the preheated scraps into the bucket and charges the scraps for the next preheating.

After preheating for a predetermined time in the above state, switching is performed so that only the opening/closing dampers 21c, 22c, 23a, and 24a are opened and the other opening/closing dampers are closed.
Then, the preheater 5c where the new scrap was brought in
The primary preheating is performed in the preheater 5a, and the secondary preheating is performed in the preheater 5a where the primary preheating was performed. Charging takes place.

Next, the opening/closing dampers 21b, 22b, 23c, 2
Switch so that only 4c is open and the other opening/closing dampers are closed. Then, the preheater 5b performs primary preheating, 5c
Secondary preheating is performed at 5a, and scrap is discharged and charged at 5a.

In this way, the primary and secondary preheating of scrap can be performed continuously by opening and closing each opening/closing damper, and the scrap is discharged and charged using the preheater that is not in use. , the exhaust gas from the electric furnace 1 can be continuously and effectively used for preheating the scrap.

In addition, because the suction by the exhaust fan 19 has traditionally been increased by approximately 100% of the amount of exhaust gas from the electric furnace, unnecessary excess air is drawn into the electric furnace 1, resulting in excessive energy consumption. In addition, air suction from the elbow 2 lowers the exhaust gas temperature, making it difficult to utilize the exhaust heat. Therefore, in carrying out the present invention, by increasing the temperature of the preheating gas 4 while suppressing the amount of leaked air to less than half of the conventional amount, the gas temperature of the entire preheating circuit can be increased. Therefore, the temperature of the scrap can be raised easily and in a short time, and the function of the cracking furnace 8 can be improved, and the overall heat recovery effect can be enhanced.

It should be noted that the present invention can be applied to various devices for preheating scrap, and can also be applied to cases equipped with a cracking furnace of a type other than that shown in the figure. However, it is also possible to first perform heat exchange with the gas from the cracking furnace and then perform secondary preheating, and by installing two or more preheaters and performing primary and secondary preheating, it is possible to Scrap preheating can be performed, and in the case of scrap that has almost no deposits and does not generate odor components, it is also possible to preheat to a higher temperature by simply using two preheaters in parallel and extending the preheating time. It goes without saying that the opening and closing operations of each opening and closing damper can be performed under automatic control, and that various other changes can be made without departing from the gist of the present invention.

According to the above-mentioned scrap preheating device of the present invention, the following excellent effects are exhibited.

(i) After the primary preheating of the scrap, the gas is heated in the cracking furnace, and that gas is used to perform the secondary preheating, making it easy to heat the scrap to a high temperature. As a result, the energy required for melting in the melting furnace can be reduced, and the melting and smelting time can be shortened, thereby improving productivity.

(ii) Since a plurality of preheaters are provided to switch the gas flow, the scrap can be preheated continuously, and thus the heat of the exhaust gas can be effectively recovered.

(iii) By preheating the scrap, the combustion of combustible components and the decomposition of odor components generated in the gas can be effectively carried out in the decomposition furnace. Expanding the scope of use can contribute to waste treatment and resource conservation.

(iv) Since the combustible components contained in the scrap are burned in the cracking furnace, it is possible to utilize the thermal energy of the combustible components.

(v) Since the gas after primary preheating is heated by the gas after secondary preheating, the temperature inside the cracking furnace is increased to improve the function of the cracking furnace and to increase the temperature of the gas for secondary preheating. can be achieved.

(vi) By introducing high-temperature gas from the combustion furnace into the cracking furnace, the temperature inside the cracking furnace can be easily raised, improving the cracking furnace function and increasing the temperature of the gas for secondary preheating.

(vii) It can be easily applied and implemented in similar technical fields, whether new or existing.

(viii) By adjusting the amount of suction by the exhaust fan to maintain the preheating gas at a high temperature, scrap preheating and processing of the gas after primary preheating can be performed even better.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet for explaining the principle of the present invention, and FIG. 2 is a flow sheet showing an embodiment of the present invention. 1 is an electric furnace, 2 is an elbow, 3 is a combustion furnace, 4 is a preheating gas, 5, 5', 5a, 5b, 5c are a preheater,
6 is a gas after primary preheating, 7 is a heat exchanger, 8 is a decomposition furnace, 9 is a pilot burner, 13 is a high temperature gas introduction section, 15 is a gas after secondary preheating, and 19 is an exhaust fan.

Claims (1)

[Claims] 1. A combustion furnace that burns the exhaust gas from the melting furnace, a plurality of preheaters that preheat the scrap with the gas from the combustion furnace, and a temperature rise of the gas after primary preheating from the preheater. A heat exchanger, a decomposition furnace that burns combustible components and decomposes odor components contained in the gas from the heat exchanger, and branches and guides the gas from the combustion furnace to form a high-temperature spark. A pilot burner provided in the cracking furnace, a flow path for guiding gas from the cracking furnace to each of the preheaters and discharging it, and an inlet and an outlet of the primary and secondary gas in each of the preheaters, respectively. 1. A scrap preheating device, comprising: an opening/closing damper provided therein, and the heat exchanger is disposed within a secondary gas flow path.