JPS5993114A - Combustion air feed method for disolving furnace - Google Patents

Abstract

PURPOSE:To prevent the occurrence of mutual interference between burners, by a method wherein an air pressure control loop consists of a damper device, a damper control device, an air pressure or an air amount detector, and an individual air pressure or an air amount regulator. CONSTITUTION:Control for the number of revolutions of a blower 11 is effected in combination with control for the opening degree of a damper 15 at a burner inlet, and an air pressure control loop consisting of a damper device 15, a damper control device 16, an air pressure or an air amount detector 17, and an individual air pressure or an air amount regulator 19 is mounted to each burner 18. Further, in response to an air pressure or an air amount signal from each burner 18, a pressure loss between the blower 11 and each burner 18 is automatically compensated to obtain an instruction for the number of revolutions to the blower 11. This prevents the occurrence of interference between the burners, and enables arbitrary regulation of a heating power and the high-efficient supply of the air for combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for supplying combustion air to a metal melting furnace.

In a metal melting furnace that has multiple combustion burners where combustion air is supplied by a single blower, it is necessary to appropriately and arbitrarily adjust the amount of air in each burner depending on the operating state of the furnace. .

Conventionally, the amount of air has been adjusted by operating a blower at a constant rotation speed and changing the opening degree of a damper installed at the inlet of each burner either manually or automatically using an automatic control device such as an air-fuel ratio controller. It was

Therefore, although the blower is installed with the capacity to supply the maximum wind pressure and air volume under the various operating conditions of the furnace, in general, in average furnace operation, the capacity of the blower is set to its maximum capacity. It is used less frequently,
Since the damper was used with a reduced pressure, the drive power of the blower was not significantly reduced, resulting in an uneconomical operating situation.

In addition, in the latest furnaces, heat exchangers such as air preheaters are often installed to increase thermal efficiency, and in this case, the air ducts etc. become long and the pressure loss from the blower to each burner becomes large enough to not be ignored. However, when the air volume of one burner was changed, the air volume of other burners also changed, causing mutual interference in which the thermal power fluctuated.

On the other hand, the amount of air in the burner can be adjusted by controlling the rotation speed of the blower and changing the discharge pressure, without relying on the pressure loss effect of the damper.This method reduces the mechanical efficiency of the blower and reduces the drive power. Proportional to approximately the third power of the number,
This is a widely applied method for burner threads that have a decreasing characteristic and can therefore be considered single in the case of a single burner or even in the case of multiple burners.

In addition, to prevent mutual interference between burners, a tamper is installed at the air intake inlet to detect the wind pressure at the air duct branch point of each burner, and the opening of the suction damper is adjusted to keep the wind pressure at the branch point constant. A method has been adopted that automatically adjusts and automatically compensates for pressure drop fluctuations in the air duct.

However, it has multiple burners that cannot be considered as a single burner,
In addition, in a furnace where it is necessary to arbitrarily adjust the thermal power without mutual interference between the two, a method for supplying combustion air that can achieve high efficiency operation by controlling the rotation speed of the blower has not been realized.

FIG. 1 is a flow sheet showing the conventional combustion air supply method described above, in which 1 is a blower driven by a motor 2, 3 is a suction damper, 4 is a heat exchanger, and 5 is a burner. are the drive device 7 of the inlet damper 6, respectively.
is operated manually or automatically using a thermal power setting device 8 to change the opening degree of the damper 6 to send an arbitrarily adjusted air volume. 9 is a constant fuel ratio control device; 10
is the melting furnace.

This invention was discovered as a result of studies in view of the drawbacks of the conventional combustion air supply method described above, and its purpose is to combine the rotational speed control of the blower and the opening degree control of the burner inlet damper. By providing a wind pressure or air volume control loop for each burner, and furthermore, by providing a device that automatically controls pressure loss from the blower to each burner based on the wind pressure or air volume setting signal of each burner, and obtains a rotation speed command to the blower. The present invention aims to provide a method for supplying combustion air that prevents mutual interference between burners, allows arbitrary adjustment of thermal power, and is highly efficient.

The combustion air supply method of the present invention will be explained below with reference to the flow sheet of FIG. 2.

In addition, in this invention, both air volume control and wind pressure control are used as a means to adjust the burner thermal power (heat amount), but based on the relationship of air volume ∝■, they are considered to be essentially the same, so we will take wind pressure control as an example. This will be explained below.

(1) First, for each burner 18 (or for each group of burners that can be considered as a single burner due to having the same characteristics, etc.), the damper device 15, damper opening/closing device 16, wind pressure or air volume detector 17, individual wind pressure or A wind pressure control loop consisting of an air volume regulator 19 is installed respectively.

(2) A wind pressure setting command is supplied to each burner wind pressure control loop by the burner thermal power setting device 14, and wind pressure control is performed for each burner.

(3) A blower variable speed drive and control device 12 is connected to the blower 11, and a maximum value selection and pressure loss compensation calculator 1
The rotation speed of the blower 11 is accurately controlled by the rotation speed command from No. 3 to obtain a predetermined wind pressure.

(4) Input the wind pressure set value for each burner 18 from the burner thermal power setting device 14 into the maximum value selection and pressure loss compensation calculator 13, and according to the principle described next, the wind pressure at the inlet of the damper device 15 is determined as the wind pressure or air volume. The number of revolutions of the blower 11 required to be slightly higher than the wind pressure value required by the detector 17 by the amount of pressure loss between the damper devices 15 and 17 or the air volume detector is determined and sent to the computing unit 13. Output as rotation speed command.

In other words, the rotation speed N of the blower 11 and the required discharge pressure H are N
=K1■ (however, K1 is a proportionality constant) and H=MaxSP
+Σ△P However, MaxSP is the maximum value of the wind pressure set for each burner Σ△P must supply the total pressure loss of the air duct, and the total pressure loss Σ△P is Σ△
P=K2(ΣQ)2 =K2(QA+QB+QC)2 =K2(KA■+KB■+KC■) However, K2... proportionality constant determined by the shape of the air duct ΣQ... total air volume of the air duct QA, QB, QC...Air volume of each burner SPA, SPB
, SPC... Setting wind pressure of each burner KA, KB, KC.
...It is a proportionality constant determined by the shape of the burner.

Therefore, the blower rotation speed N is N=K1■ It can be found by

However, if the pressure loss in the air duct is small or negligible, or if it is roughly adjusted, the pressure loss may be kept at a constant value.

As described above, if a device that performs the control operations described in items (1) to (4) above is installed, unless the set values of each burner are extremely different during average operation of the furnace, it will be possible to The blower only needs to supply the minimum wind pressure required by each burner, and each damper has a maximum wind pressure set. , fully open, and the others are changed from the maximum value to the operation that is reduced by the difference between each set value. Therefore, this method, coupled with the operation of the pressure control loop of each burner, can be operated arbitrarily without mutual interference between burners. This makes it possible to provide an excellent method of supplying combustion air that allows the air volume to be adjusted and achieves high efficiency operation by controlling the rotational speed of the blower.

In the flow sheet of FIG. 2, 20 is an air-fuel ratio control device, 21 is a heat exchanger, 22 is a melting furnace, and SPA,
SPB and SPC are the set wind pressures of each burner, ΣQ is the total air volume value, and QA, QB, and QC are the air volume values of each burner.

The combustion air supply method of the present invention explained above includes (1)
The total air volume flowing through the air duct is calculated and determined individually according to the characteristics of each burner using the wind pressure or air volume setting signal of each burner, and the pressure loss value is determined based on the value of the total air volume according to the air duct characteristics.

(2) Each burner is provided with a damper device and a wind pressure or air volume detector, and a pressure control loop is configured for each burner.

(3) The pressure loss value of the air duct obtained in (1) and the wind pressure setting value of each burner. In the case of air volume setting, find the wind pressure setting value according to the burner characteristics, and calculate the maximum setting value and pressure loss value. This function calculates the minimum required operating discharge pressure of the blower, and automatically compensates for the pressure loss in the air duct even if the set air volume of the burner changes, preventing mutual interference in conjunction with the pressure control loop in item (2). do.

This method has the following characteristics: (1) Since it is a method of obtaining the minimum necessary wind pressure by changing the rotation speed of the blower, the average driving power of the blower can be significantly reduced when obtaining the same air volume.

(2) To automatically compensate for pressure loss fluctuations in air ducts,
To be able to reduce interference between burners even if the air volume of the burners is changed.

(3) Since a pressure control loop is provided for each burner,
The degree of freedom in adjusting the burner air volume is not hindered.

The effect of such things is entrusted to

Thus, in an actual steel melting furnace, a blower with a 400KW drive motor was driven by a 12-phase variable voltage variable frequency control device, and the operation was performed for 200 hours. In this case, we were able to significantly reduce the driving power to an average power of 51KW.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet for explaining a conventional combustion air supply method, and FIG. 2 is a flow sheet for explaining a combustion air supply method according to the present invention. DESCRIPTION OF SYMBOLS 11... Blower, 12... Blower variable speed drive and control device, 13... Maximum value selection and pressure loss compensation calculator, 14... Burner thermal power setting device, 15... Damper device, 16. ... Damper opening/closing device 17... Wind pressure or air volume detector, 18... Burner 19... Individual wind pressure or air volume regulator, 20... Air-fuel ratio control device, 21.
... Heat exchanger patent applicant Patent attorney Kazu 1) Showa 1 Figure 2

Claims (1)

[Claims] In the method of supplying combustion air to multiple burners through a common air duct by one blower, the maximum value is selected by the blower variable speed drive control device attached to the blower, and the blower rotation speed is determined by the pressure loss compensation calculator. Combustion air for a melting furnace characterized by controlling commands and controlling the driving rotation speed of a blower by receiving preset wind pressure or air volume signals of a plurality of burners from an air volume control device attached to each burner. Supply method.