JPH0159517B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the amount of exhaust gas flowing through the bypass duct in an apparatus in which a bypass duct is provided in the exhaust gas duct of a furnace such as an arc furnace, and scrap is preheated by the exhaust gas flowing through the bypass duct.

The amount of exhaust gas generated from an arc furnace varies depending on the operating conditions of the furnace, such as during the melting period and scouring period. For this reason, the amount of exhaust gas to be discharged through the exhaust gas duct is controlled by controlling the rotation speed of the exhaust blower or the opening degree of the damper in the exhaust gas duct using a flow rate command signal programmed in advance in the main controller, so that the pressure inside the furnace does not fluctuate greatly. It is configured as follows.

By the way, since the above exhaust gas has a high temperature, it has been conventionally done to save energy by utilizing the heat to preheat the scrap to be melted in an arc furnace. That is, a bypass duct is connected to the exhaust gas duct, and the scrap to be charged as a raw material to the arc furnace is charged into a scrap preheating device installed in the bypass duct, and the high temperature exhaust gas flows through the scrap to generate heat. The process involves preheating the scrap by sending and receiving energy. However, since the shape and loading conditions of the scraps fed into the scrap preheating device vary each time they are fed, the ventilation resistance of the exhaust gas varies greatly. As a result, in some cases, not only the desired preheating effect could not be achieved, but also the amount of exhaust gas discharged could not match the flow rate command, causing large fluctuations in the pressure inside the furnace, which could lead to an accident.

The present invention aims to solve the above-mentioned drawbacks, and is intended to programmatically control the amount of exhaust gas to be discharged through an exhaust gas duct in accordance with the operational status of the furnace. A preheating device and a blower are interposed in series, the pressure difference between the inlet side and the outlet side of the scrap preheating device is detected, and the blower is adjusted so that the detected differential pressure value becomes a predetermined differential pressure setting value. When automatically controlling the rotation speed, the differential pressure setting value is based on the ventilation resistance coefficient of the scrap carried into the scrap preheating device and the target flow rate of exhaust gas to be discharged through the bypass duct as instructed by the program control. This is a method for controlling the air volume of a scrap preheating device, in which the air volume is determined by calculation using as a variable.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is an arc furnace, 2 is its exhaust gas duct, 3 is an exhaust blower, 4 is a damper, 5 is a bypass duct formed by connecting a scrap preheating device 6 and a blower 7 in series, and 8 and 9 are the bypass ducts. This is an on-off valve provided at both ends of the duct. Pressure transmitters 10 and 1 on the inlet and outlet sides of the scrap preheating device 6 measure the atmospheric pressure in the duct and convert it into an electrical signal.
1, and receives signals from each pressure transmitter to calculate the differential pressure between the input side and the output side.
2 will be provided. That is, if the pressure on the inlet side is P1 and the pressure on the outlet side is P2, the calculator 12 calculates ΔP=P1-P.
2 and outputs the detected differential pressure value to the control device 13. The amount of exhaust gas to be discharged is programmed in the main controller 14 in advance according to the operating status of the arc furnace 1, and the damper 4 is programmed in accordance with that order.
Issues a flow rate command signal to control the opening of the valve. Reference numeral 15 measures the exhaust gas temperature with a thermometer provided on the outlet side of the blower 7, converts it into an electrical signal, and inputs it to the control device 13. Reference numeral 16 denotes a drive motor that rotationally drives the blower 7, and 17 denotes a control motor that controls rotational transmission from the drive motor to the blower 7 and controls the rotational speed of the blower 7. However, the control device 1
3 sends a control signal to the control motor 17 so that the differential pressure detection value ΔP obtained from the calculator 12 becomes a predetermined differential pressure setting value PS while the scrap for preheating is loaded into the scrap preheating device 6 and the scrap is in operation. The output MV is output and the rotation speed of the blower 7 is automatically controlled by PID control. That is, as is well known, PID control uses the proportional term, integral term, and differential term of the detected differential pressure value as adjustment elements, and MV=K _P (e+1/T ₁ ∫edt+T _D・de/dt) ...(1) However, the control signal output MV is calculated and controlled using MV; control signal output K _P ; proportional constant T ₁ ; integral constant T _D ; differential constant e; deviation (PS - ΔP).

However, in the present invention, the differential pressure setting value PS is
The ventilation resistance coefficient K _D of the input scrap and the target flow rate Q of the exhaust gas to be discharged through the bypass duct 5, which is commanded by the program control of the main controller 14, are used as variables and are determined by the following equation.

PS=273+T/273・Q ² /K _D ² ...(2) Where T: Exhaust gas temperature (℃) The ventilation resistance coefficient K _D in formula (2) is: K _D = Q _O /√ΔP _O ...( 3).

Here, for ΔP _O , the differential pressure detected value P1-P2 at that time when the blower 7 is rotated at a constant speed before carrying the scrap into the preheating device 6 and starting preheating is substituted. Further, Q _O is determined from ΔP _O using the performance curve of the blower 7 shown in FIG. That is, to explain one example, if the constant rotation speed of the blower 7 is set to 750 rpm and ΔP _O now shows 400 mmAq,
From this performance curve, as shown by the broken line in Figure 2,
Since it is known that Q _O =550m ³ /min, substitute that value into equation (3) to calculate K _D =550/√400. Note that this calculation of K _D is performed every time new scrap is brought into the preheating device 6.

The target flow rate Q in equation (2) is the main controller 14
specified by the programming of Therefore, the differential pressure setting value PS can be calculated using equation (2).

In this way, in the present invention, the differential pressure set value PS is calculated from the ventilation resistance coefficient K _D , which varies depending on the scrap shape, loading situation, etc., and the target flow rate Q, which is commanded by program control. Since the rotation speed of the bypass duct blower is automatically controlled so that the detected differential pressure value ΔP during operation is added to the differential pressure set value PS, the shape of the scrap and the loading condition are changed each time it is brought in. Even if the flow rate of the exhaust gas flowing through the bypass duct is different, the flow rate of the exhaust gas flowing through the bypass duct can be reliably controlled to the desired flow rate according to the program control command from the main controller. Therefore, a sufficient preheating effect can be achieved, and there are other beneficial effects such as being able to keep the pressure inside the furnace at an appropriate level.

[Brief explanation of drawings]

FIG. 1 is a control system diagram according to an embodiment of the present invention, and FIG. 2 is a diagram showing a performance curve of a blower. DESCRIPTION OF SYMBOLS 1... Arc furnace, 2... Exhaust gas duct, 5... Bypass duct, 6... Scrap preheating device, 7... Blower, 10, 11... Pressure transmitter, 12... Arithmetic unit, 1
3...Control device, 14...Main controller.

Claims (1)

[Claims] 1. In a device that programmatically controls the amount of exhaust gas to be discharged through an exhaust gas duct according to the operational status of the furnace, a bypass duct is provided in the exhaust gas duct, a scrap preheating device and a blower are interposed in series in the bypass duct, and the When detecting the differential pressure between the inlet side and outlet side of the scrap preheating device, and automatically controlling the rotation speed of the blower so that the detected differential pressure value becomes a predetermined differential pressure setting value, the differential pressure The set value is calculated by using as variables the ventilation resistance coefficient of the scrap carried into the scrap preheating device and the target flow rate of the exhaust gas to be discharged through the bypass duct, which is commanded by the advance program control. An air volume control method for a scrap preheating device, characterized in that: