JPS6335681B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for controlling heating and combustion in a reducing atmosphere heat treatment furnace, and particularly to a method for controlling heating and combustion that can effectively utilize reducing atmosphere gas. In order to use metal powder such as atomized iron powder, reduced iron powder, etc. for powder metallurgy, a reduction process in a continuous heat treatment furnace with a reducing atmosphere is essential to remove the oxygen, carbon, nitrogen, etc. contained in the metal powder. . The present invention is utilized in a reducing atmosphere heat treatment furnace used for heat treatment of such metal powder. [Prior Art] An example of a reducing atmosphere heat treatment furnace for finishing reduction of atomized iron powder and reduced iron powder for powder metallurgy will be explained with reference to FIG. The reducing atmosphere heat treatment furnace 2 is composed of a heating and soaking zone 4, a slow cooling zone 6, and a cooling zone 8.
0 is supplied from the raw material charging port 12 onto an endless steel conveyor 14 and moves within the furnace. A radiant tube 16 is arranged in the heating and soaking zone 4,
It is heated by burning fuel such as coke oven gas, converter gas, and blast furnace gas. On the other hand, reducing gases such as hydrogen gas, ammonia decomposition gas, and carbon monoxide gas are supplied into the furnace from a reducing gas pipe 18, and the reducing gases are controlled by a furnace pressure regulator 20 and a furnace pressure control valve 22. The reducing gas is discharged through the reducing gas discharge pipe 24. The iron powder 10 on the steel conveyor 14 is moved through a heating and soaking zone 4, an annealing zone 6, and a cooling zone 8 in a reducing atmosphere at a temperature as shown in FIG. The waste is discharged and crushed and classified in a subsequent process to produce products with a predetermined particle size. Conventionally, these reducing gases were exhausted from the furnace through the reducing gas exhaust pipe 24 after a reduction reaction in the furnace, and were burned and released at the tip. This exhaust amount is as large as 130Nm ³ /H in a 1.9T/H furnace, and when ammonia decomposition gas is used as the reducing gas, H ₂ in the exhaust gas reaches 65%, and its calorific value is 174× 10 ³ Kcal/H was also hot. This amount of heat was equivalent to 25% of the amount of heat of the fuel for the radiant tube in the heat treatment furnace 2. The technology to recover the reducing gas supplied and discharged into the furnace and effectively use it as fuel for the atmosphere heating furnace was developed in 1983.
-5830 publication is known. However, this technique has the following problems because the reducing gas is directly exposed to the radiant tube that serves as heating fuel from the ceiling of the furnace. That is, (a) Since the recovered gas is directly introduced into the radiant tube as heating fuel, the pressure inside the furnace becomes unstable and there is a risk of explosion due to the intrusion of outside air. (b) Since the amount of recovered gas is unknown, it is difficult to maintain an appropriate air/fuel ratio for combustion, and it is also impossible to control the temperature inside the furnace, resulting in unstable furnace operation. Therefore, there is a problem that safe and stable operation cannot be expected.
Furthermore, this technique has the drawback that almost the entire amount of reducing gas cannot be used effectively. [Problems to be Solved by the Invention] The purpose of the present invention is to safely and efficiently control the furnace internal pressure to an appropriate level by using the combustible heat in the reducing gas exhaust as the heat for the radiant tube, which is the problem with the prior art described above. It is an object of the present invention to provide a heating combustion control method that can be used effectively while ensuring stable operation. [Means and effects for solving the problems] The gist of the present invention is as follows.
That is, in a heating combustion control method for a reducing atmosphere heat treatment furnace in which a large number of radiant tubes are arranged to indirectly heat metal powder, etc., and to supply reducing gas into the furnace to continuously heat-treat metal powder, etc., the radiant tube is divided into the first group, which collects and reuses the reducing gas discharged into the furnace while controlling the furnace internal pressure, and the second group, which uses coke oven gas etc. as fuel. Reducing atmosphere heat treatment characterized by burning the recovered gas while controlling the ratio of the amount of recovered gas and the amount of gas from a coke oven or the like so as to preferentially burn the recovered gas based on a temperature detection signal and supplement it with the coke oven gas or the like. This is a heating and combustion control method for a furnace. First, the combustion control system according to the present invention will be explained with reference to FIG. The reducing gas exhaust pipe 24A is provided with a gas cooler 26, a blower 28, a furnace pressure control valve 22, a furnace pressure regulator 20, and a reducing exhaust gas adjustment valve 3.
0, reducing exhaust gas flow rate indicator controller 31, release valve 3
There is a first radiant tube group in which a radiant tube burner (for reducing exhaust gas) 34 is provided at the final end. Also, as in the past, a second radiant is provided with a coke oven gas pipe 36 for burning coke oven gas, a coke oven gas control valve 38, a radiant tube burner (for coke oven gas) 40, and a coke oven gas flow rate indicator controller 42. There is a tube group. Also, a gas ratio controller 44, a thermometer 46, and a temperature regulator 48 for adjusting the amount of reducing exhaust gas and coke oven gas.
is provided. Each combustion gas system includes an air pipe 50, an air control valve 52, and a ratio setter 5.
4. An air flow rate indicator controller 56 is provided. Next, a heating combustion control method of the present invention using the combustion control system as described above will be explained. After the reducing gas supplied to the heat treatment furnace 2 is used for reduction etc.
Almost the same amount as the supply amount is sucked by the blower 28 through the reducing gas exhaust pipe 24A. If the amount of suction is greater than the amount of supply, the pressure inside the furnace will become negative and there is a risk of explosion due to intruding air, so the amount of suction is controlled by the furnace pressure regulator 20 so that the inside of the furnace is at a predetermined positive pressure. The exhaust gas sucked from the reducing gas exhaust pipe 24A is approximately
Since the temperature is as high as 900° C., it is cooled to a predetermined temperature by a gas cooler 26 in consideration of the heat resistance of the blower 28 and the like. The reducing gas pressurized by the blower 28 is mixed with air and burned in a radiant tube burner (for reducing exhaust gas) 34. In addition,
Heating by the radiant tube 16 is performed by a radiant tube burner 34 for reducing exhaust gas and a radiant tube burner 40 for coke oven gas.
There are two systems, which are arranged alternately along the length of the furnace in order to maintain uniformity of temperature inside the furnace. The furnace temperature necessary for heat treatment is detected by a furnace thermometer 46. During normal operation, the temperature inside the furnace required for heat treatment is the radiant tube 34 for reducing exhaust gas.
Since the combustion heat alone is not sufficient to obtain the required temperature, the deficiency is compensated for by combustion in the radiant tube burner 40 for coke oven gas. The use of coke oven gas is determined by gas ratio controller 44. That is, during low-load operation, the amount of heat required to achieve the same furnace temperature is small, so the gas ratio controller 44 directs the coke oven gas flow rate to the radiant tube burner 40 for coke oven gas. It is throttled through the controller 42 and the coke oven gas control valve 38. The gas ratio controller 44 is set so that the coke oven gas flow rate indicator 42 outputs an output when the output of the reducing gas flow rate indicator 31 is 100%. Even if the coke oven gas amount is reduced to zero, if the furnace temperature is still too high, the reducing exhaust gas amount is throttled by the reducing exhaust gas regulating valve 30 to appropriately adjust the combustion amount. In this case, in order not to reduce the amount of gas sucked from the reducing exhaust gas exhaust pipe 24A, the release valve 32 is opened and a portion of the reduced exhaust gas is combusted and released as in the conventional manner, thereby maintaining the furnace internal pressure constant. Note that the diffusion valve 32 receives the output from the furnace pressure regulator 20 and performs diffusion only when the furnace pressure control valve 22 is fully open. Further, combustion air is supplied in an amount necessary to completely burn each combustion gas through a ratio setter 54, an air flow rate indicating controller 56, and an air control valve 52. As described above, in the method of the present invention, almost all of the reducing exhaust gas can be effectively utilized for heating the heat treatment furnace under safe and stable operating conditions, and the amount of coke oven gas used can be reduced. [Example] Iron powder was reduced by the method of the present invention shown in FIG. 1 and the conventional method shown in FIG. 2 in a reducing atmosphere heat treatment furnace. The total length of the furnace is 40m, and the throughput of iron powder is 2T/
H, iron powder was heated from 40℃ to 900℃, ammonia decomposition gas 130Nm ³ /H was used as the atmospheric gas,
Under the same conditions, in the method of the present invention, exhaust gas after reduction of ammonia decomposition gas, which is a reducing gas, was burned in a radiant tube, and coke oven gas was used to compensate for the lack of heat. On the other hand, in the conventional method, the reducing exhaust gas was combusted and dissipated, and heating by the radiant tube depended only on the coke oven gas. Table 1 shows a comparison of the calorific value of the coke oven gas used for heating, and the method of the present invention was able to reduce the calorific value by 17% compared to the conventional method. This reduction in the calorific value of coke oven gas is compensated for by the combustion of the recovered reducing gas, which is equivalent to 95% of the amount of recovered reducing gas, and almost all of the recovered gas is effectively used as heating fuel for the radiant tube. It shows that

〔Effect of the invention〕

As is clear from the above embodiments, the present invention effectively utilizes the exhaust gas of the reducing gas by recovering the reducing gas for the furnace atmosphere and burning it as fuel in the radiant tube. We were able to achieve the effect of reducing heating fuel.

[Brief explanation of the drawing]

Fig. 1 is a combustion control system diagram showing combustion in the present invention, Fig. 2 is a sectional view showing a conventional reducing atmosphere heat treatment furnace, and Fig. 3 is a diagram showing temperature changes of iron powder in a reducing atmosphere heat treatment furnace. It is. 2... Reducing atmosphere heat treatment furnace, 16... Radiant tube, 24, 24A... Reducing gas exhaust pipe, 34... Radiant tube burner (for reducing exhaust gas), 40... Radiant tube burner (for coke oven gas) ).

Claims (1)

[Claims] 1. In a heating combustion control method for a reducing atmosphere heat treatment furnace in which a large number of radiant tubes are arranged to indirectly heat and supply reducing gas into the furnace to continuously heat treat metal powder, etc., the radiant tubes are The reducing gas supplied to the furnace and discharged while controlling the furnace pressure is recovered and reused as fuel; the second group uses coke oven gas, etc. as fuel, and the furnace temperature is controlled. A reducing atmosphere heat treatment furnace characterized in that the recovered gas is burnt preferentially based on a detection signal and the recovered gas is combusted while controlling the ratio of the amount of gas in a coke oven or the like so as to be supplemented with the coke oven gas or the like. heating combustion control method.