JPH0631687B2 - Furnace pressure control method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a furnace pressure control method in an industrial furnace equipped with an exhaust gas fan.

(Prior art) In order to control the furnace pressure of an industrial furnace in which the exhaust gas fan sucks and exhausts the gas in the furnace to a constant level, a furnace pressure control damper is installed in the exhaust gas line, and the opening of the furnace pressure control damper is set. It is common to change it according to the sensor signal. However, when the exhaust gas is at a high temperature, the furnace pressure control damper, which prioritizes heat resistance over sealability, is used, so the rangeability of the furnace pressure control damper should be set in a furnace where the load fluctuation of the furnace reaches 1:10 or more. It has been exceeded and it has been difficult to control the furnace pressure accurately. In addition, in the furnace pressure control method using only the furnace pressure control damper, there may be points where hunting is amplified due to disturbance and control becomes impossible.In this case, the response must be sacrificed and control parameters must be selected. There was a problem such as not becoming.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and a furnace pressure control method capable of accurately controlling the furnace pressure even in a wide load variation of the furnace. It was completed for the purpose of.

(Means for Solving Problems) According to the present invention, the number of revolutions of an exhaust gas fan, which controls the exhaust capacity of a furnace, is gradually increased or decreased in accordance with the amount of fuel used or the amount of combustion air in the furnace so that the number of revolutions is constant. About the section, it is a furnace pressure control method that controls the exhaust capacity by the furnace pressure control damper, and when the fuel usage amount or combustion air amount of the furnace is increased or decreased, the set value to transition to the next rotation speed is set. It is characterized by different things.

Next, the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows an example of a furnace for carrying out the present invention. (1)
Is a furnace such as a steel plate heat treatment furnace, (2) is a recuperator for recovering heat from the exhaust gas, (3) is a furnace pressure control damper installed in the exhaust gas line, and (4) is the exhaust capacity of the furnace. The dominant exhaust gas fan, (5) is the chimney. Further, (6) is a blower for supplying air to the recuperator (2), (7) is a burner provided in the furnace (1), and each burner (7) is heated by the recuperator (2). In addition to the exchanged preheated air, fuel is supplied from the fuel supply line (8). A furnace pressure sensor (9) is attached to the furnace (1) to input a furnace pressure signal to the pressure controller (10), and the pressure controller (10) controls the opening of the furnace pressure control damper (3). . The actual load of the furnace is detected by the fuel consumption measured using the orifice (11) and input to the rotation speed selector (12) such as a sequencer, but the actual load of the furnace is detected by the combustion air amount. It is also possible.

Note that (13) is a rotation speed controller such as an inverter, and (14) is a dilution air introduction valve.

(Operation) Next, the furnace pressure control method of the present invention will be specifically described with reference to FIGS. 2 and 3.

In these graphs, the horizontal axis shows the amount of fuel used (actual load of the furnace) and the vertical axis shows the rotation speed of the exhaust gas fan (4). Assuming that the fuel consumption is at point A in Fig. 2, the exhaust gas fan (4) rotation speed is Y ₂ at this time, and the opening of the furnace pressure control damper (3) at this time is about 50. %. As the fuel consumption increases from point A, the opening of the furnace pressure control damper (3) increases to about 80% at point B and about 90% at point C. Is controlled to be constant. However, when the amount of fuel used further increases beyond point C, the rotation speed of the exhaust gas fan (4) is changed from Y ₂ to Y ₃ and the opening of the furnace pressure control damper (3) is increased to about 20%. squeeze. If the fuel consumption further increases toward point F, the rotation speed is changed to Y ₃
Then, open the furnace pressure control damper (3) again.

On the contrary, when the fuel consumption gradually decreases from the state of the point F, even if the opening of the furnace pressure control damper (3) reaches the point D of about 20%, the exhaust gas fan (4 The rotation speed of) is not immediately decreased from Y ₃ to Y ₂ , and the rotation speed is transitioned to Y ₂ only after reaching the point E where the opening is about 10%.
At the same time, the opening of the furnace pressure control damper (3) is about 8
It is set to 0%, and the state of point B is reached.

As described above, in the present invention, when the amount of fuel used or the amount of combustion air in the furnace is increased, the path of A → B → C → D → F is drawn to represent the rotation speed of the exhaust gas fan (3) and the furnace pressure control damper. The opening of (4) changes, and when the amount of fuel used in the furnace or the amount of combustion air decreases, it changes along the path of F → D → E → B → A. In other words, when the fuel usage amount or combustion air amount of the furnace is increased, the rotation speed transition is performed at the point of X ₅ , and when it is decreased, X ₄ is the set point of the rotation speed transition.

In FIG. 3, the set point at which the rotational speed is changed is X ₄ when the fuel consumption or combustion air amount of the furnace is increased, and X ₄ when it is decreased.
An example changed to ₅ is shown. Therefore, in the case of FIG. 3, a path of A → B → E → D → F is drawn when the actual load is increased, and a path of F → D → C → B → A is drawn when the actual load is decreased. It will be.

In the present invention, as described above, the furnace pressure control is not performed solely by the furnace pressure control damper (3), but the furnace pressure control is performed in combination with the stepwise change in the number of revolutions of the exhaust gas fan (4). Therefore, it is possible to avoid the portion near the limit of the rangeability of the furnace pressure control damper (3), and it is possible to accurately control the furnace pressure even in a furnace having a wide range of load fluctuations. Further, in the present invention, since the set value of the rotational speed transition is different when the fuel usage amount or combustion air amount of the furnace is increased and decreased, even when the actual load of the furnace is finely changed due to disturbance Correspondingly, a rotation speed transition is not triggered. Therefore, according to the present invention, there is no possibility of hunting due to disturbance as in the conventional case,
There is no need to change the control parameters at the expense of responsiveness to prevent hunting.

When controlling the reactor pressure by the method shown in FIG. 3, the fuel usage amount is increased so that the fuel usage amount becomes X ₄₅ corresponding to G between E and D corresponding to the fuel usage amounts X ₄ and X _5. At some point, the amount of fuel used cannot be immediately reduced from G to B. That is, the exhaust gas fan rotation speed cannot be immediately reduced from Y ₃ to Y ₂ . Therefore, once the fuel consumption is
It is necessary to increase from C to B and then to C → B.

It should be noted that the method shown in FIG. 2 is more preferable than the method shown in FIG. 3 because there is no such fear.

(Effects of the Invention) As is apparent from the above description, the present invention gradually increases or decreases the number of revolutions of the exhaust gas fan in accordance with the change in the amount of fuel used in the furnace or the amount of combustion air, and the amount of fuel used in the furnace Alternatively, since the set value for transition to the next rotation speed is different when the combustion air amount is increasing and when it is decreasing, it has the following advantages.

It can follow a wide range of load fluctuations and can control the furnace pressure with high accuracy.

The furnace pressure control damper does not require a wide range ability. For this reason, relatively inexpensive and highly accurate control becomes possible.

In the case where the furnace pressure control damper is used alone, there is a point that the furnace pressure cannot be controlled under certain operating conditions depending on the operating conditions, but the instability can be avoided by selecting the rotation speed of the exhaust gas fan.

The amount of electric power (running cost) can be reduced by controlling the rotation speed of the exhaust gas fan according to the amount of fuel used in the furnace or the amount of combustion air.

As described above, the present invention is extremely large in that it contributes to industrial development as a furnace pressure control method that eliminates the conventional problems.

[Brief description of drawings]

FIG. 1 is a piping diagram showing an example of a furnace whose furnace pressure is controlled according to the present invention, and FIGS. 2 and 3 are graphs showing the relationship between the number of revolutions of an exhaust gas fan and the amount of fuel used. (1): Furnace, (3): Furnace pressure control damper, (4): Exhaust gas fan.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Nakajima 5-1 Higashisayagaya-cho, Tobata-ku, Kitakyushu-shi, Fukuoka (56) Reference JP-A-48-78022 (JP, A)

Claims (1)

[Claims] 1. The number of revolutions of an exhaust gas fan, which controls the exhaust capacity of the furnace, is increased and decreased in stages according to the amount of fuel used in the furnace or the amount of combustion air, and exhaust is carried out by a furnace pressure control damper for sections where the number of revolutions is constant. A furnace pressure control method for controlling capacity, characterized in that the set value for transition to the next rotation speed is different when the fuel usage amount or combustion air amount of the furnace increases and when it decreases. Pressure control method.