JPH0555765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to combustion control technology, and particularly to combustion control technology for combustion devices such as heating furnaces that utilize surplus oxygen in steel plants and the like.

(Prior Art) Generally, a steelworks has equipment for producing oxygen for refining to convert molten iron into steel. This equipment was originally designed to leave a certain amount of surplus capacity for the scale of steel production, and as a result of the decrease in steel production in recent years and the improvement in the oxygen consumption rate during steel production due to technological innovations associated with this, a large amount of Now able to generate surplus oxygen. In addition, the recovery of by-product rare gases associated with oxygen production, such as argon and neon, and the increased demand for these gases are creating an even greater abundance of surplus oxygen within steelworks.

As a result, attempts have been made to increase combustion efficiency by mixing this surplus oxygen into combustion air in combustion devices such as heating furnaces. This makes it possible to use inexpensive fuel in equipment that conventionally required expensive fuel gas.

For example, JP-A No. 59-157420 proposes a method of obtaining a constant combustion temperature from the relationship of fuel calorific value in controlling oxygen-enriched combustion, and JP-A No. 59-131821
No. 2 presents a means to recover excess high pressure associated with oxygen enrichment.

All of these disclose techniques for enriching oxygen in combustion air to raise combustion temperature, thereby improving combustion efficiency.

Furthermore, JP-A No. 60-4724 discloses that in controlling oxygen-enriched combustion, the oxygen concentration in combustion air enriched with oxygen is measured in advance, and an appropriate air-fuel ratio is achieved based on the measured value. This figure shows how to control the amount of combustion air.

(Problems to be Solved by the Invention) In all conventional oxygen-enriched combustion technologies, countermeasures against an increase in nitrogen oxides accompanying an increase in combustion temperature are insufficient. This is a limiting factor in the adoption of oxygen-enriched combustion methods, especially now that the concentration of nitrogen oxides in exhaust gases has become strictly regulated as a result of pollution problems.

In this respect, the Japanese Patent Application Laid-Open No. 1989-1997, which was previously exemplified as a prior art,
-4724's combustion control method is no exception. This method is thought to have been adopted for convenience due to the reliability of the measuring instruments used and the accuracy of control equipment such as flow control valves, but this method, which uses control based on a predetermined air-fuel ratio table, Unable to respond to changes in conditions such as fuel composition and fluid pressure. It is also stated that the increase in the concentration of nitrogen oxides in exhaust gas can be ignored when the oxygen concentration in oxygen-enriched air is 35% or less, but this cannot be said with certainty due to the regulatory concentration of nitrogen oxides in exhaust gas, etc. Conceivable.

(Means and effects for solving the problems) The present invention solves the problems of the above-mentioned conventional technology, and enables oxygen-enriched combustion within pollution regulation values without requiring modification of pure oxygen burners, etc. This was done to establish a control technology that would

Here, the present invention provides a method for controlling combustion of fuel and oxygen-enriched air in a combustion device, including controlling the oxygen concentration in the oxygen-enriched air based on the nitrogen oxide concentration in the exhaust gas of the combustion. , further controlling the mixing ratio of the fuel and the oxygen-enriched air based on the oxygen concentration in the combustion exhaust and the oxygen concentration in the oxygen-enriched air, and controlling the nitrogen oxide concentration in the combustion exhaust at a plurality of levels. This oxygen-enriched combustion control method is characterized in that the oxygen concentration in the oxygen-enriched air is divided into value ranges and the oxygen concentration in the oxygen-enriched air is controlled according to a different method for each value range.

Furthermore, from another aspect, the present invention provides a nitrogen oxide concentration meter that measures the nitrogen oxide concentration in the exhaust gas of the combustion in a control device for combustion of fuel and oxygen-enriched air in a combustion device; an oxygen concentration meter that measures the oxygen concentration in the exhaust gas; a computing device that computes a target oxygen concentration value in oxygen-enriched air based on the measured value of the nitrogen oxide concentration meter; and an oxygen concentration target computed by the computing device. an oxygen concentration controller that controls the oxygen concentration in the oxygen-enriched air; and an air-fuel ratio controller that controls the mixing ratio of oxygen-enriched air,
The combustion control device is characterized in that the computing unit includes means for switching the computing method according to the range classification of the measured value of nitrogen oxide concentration.

Therefore, according to the present invention, in oxygen-enriched combustion control, the concentration of nitrogen oxides in the exhaust gas is measured,
Based on this measured concentration, the oxygen concentration in the oxygen-enriched air for combustion is determined and controlled. This is because the concentration of nitrogen oxides in the exhaust gas depends on the combustion temperature, and the combustion temperature is directly related to the oxygen concentration of the combustion air. Furthermore, the mixture ratio of oxygen-enriched combustion air and fuel is controlled based on the oxygen concentration in the combustion air determined in this way and the oxygen concentration in the exhaust gas measured separately, and an appropriate air-fuel ratio is always maintained. do.

(Operation) Next, the present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is a block diagram when the present invention is applied to combustion control of a steel billet heating furnace as a combustion device.

The steel billet 1a in the heating furnace 1 is heated by burning coke oven gas led from a coke oven 2 constituting a fuel gas source in a burner 1b. At this time, the coke oven gas is mixed in advance with air sent from the air pump 3 and oxygen gas generated in the oxygen plant 4, and then guided to the burner 1b.
The oxygen plant 4 is normally a facility that generates oxygen for hot metal refining in a steelworks, and the heating furnace 1 utilizes surplus oxygen generated by the facility.

As mentioned above, three types of fluids, namely coke oven gas from the coke oven 2, atmospheric air from the air pump 3, and pure oxygen from the oxygen plant 4, are sent to the burner 1b for combustion. Therefore, burner 1b
Combustion is controlled by controlling the supply amount and mixing ratio of these three types of fluids to appropriate values. This control not only maintains the temperature inside the heating furnace 1 at a predetermined value and maintains an appropriate air-fuel ratio, but also suppresses the concentration of nitrogen oxides in the exhaust gas within a predetermined range while increasing combustion efficiency as much as possible. This is done with the aim of improving the performance of the students.

This control system will be explained below.

The fuel gas flow rate controller 5 controls the coke oven gas flow rate based on the furnace temperature detected by the furnace temperature detector 1c. That is, the temperature sensor 1 c detects the temperature inside the heating furnace 1 and outputs the detected value to the fuel gas flow rate controller 5 . Further, the fuel gas flow meter 2a measures the coke oven gas flow rate sent from the coke oven 2 to the burner 1b, and outputs the measured value to the controller 5. Based on these detected values and measured values, the controller 5 calculates the supply amount of coke oven gas necessary to maintain the temperature inside the heating furnace 1 at an appropriate value, and controls the valve 2b according to the calculated value. Adjust the coke oven gas flow rate to burner 1b.

On the other hand, the oxygen concentration in the oxygen-enriched combustion air sent to the burner 1b is controlled based on the nitrogen oxide concentration in the exhaust gas as follows. included in exhaust
The concentration of nitrogen oxides such as NO and NO ₂ is detected by a nitrogen oxide concentration meter (hereinafter abbreviated as NOx meter) 1d and sent to a computing unit 7 in the oxygen concentration control system 6.
The computing unit 7 computes a target oxygen concentration value in the combustion air based on the nitrogen oxide concentration detected by the NOx meter 1d, and outputs this to the oxygen concentration controller 8 and the air-fuel ratio controller 9. This takes into account that the nitrogen oxide concentration in the exhaust gas is directly dependent on the oxygen concentration in the combustion air, and calculates the oxygen concentration target value based on the nitrogen oxide concentration. It controls the oxygen concentration in the combustion air. Arithmetic unit 7
The details of the operation will be described later.

Next, control of the oxygen concentration based on the above target value will be described. The oxygen flow rate sent from the oxygen plant 4 is measured by an oxygen flow meter 4a. Further, the oxygen concentration in the oxygen-enriched combustion air obtained by mixing atmospheric air from the air pump 3 and oxygen from the oxygen plant 4 is detected by an oxygen concentration meter 3a. Based on these two values, the oxygen concentration controller 8 calculates the oxygen concentration in the oxygen-enriched combustion air using the calculator 7.
The valve 4b is controlled to adjust the amount of oxygen supplied from the oxygen plant 4 so as to maintain the calculated target value. Note that the main part of the oxygen concentration control system 6 may be configured by a single microcomputer.

On the other hand, the air-fuel ratio controller 9 adjusts the amount of combustion air supplied to maintain the air-fuel ratio at an appropriate value. That is, based on the oxygen concentration in the exhaust gas detected by the exhaust oxygen concentration meter 1e, the oxygen concentration in the combustion air output from the computing unit 7, and the coke gas supply amount output from the fuel gas flow rate controller 5, the flow meter 3b The amount of combustion air is controlled via the valve 3c. At this time, an appropriate air-fuel ratio is achieved by maintaining the oxygen concentration in the exhaust gas at a constant value.

Next, the configuration and operation of the computing unit 7 of the oxygen concentration control system 6 will be explained in more detail with reference to FIG.

That is, in FIG. 2, the detected value signal output from the NOx meter 1d is sent to a filter 7a, noise components are removed, and the signal is sent to an arithmetic method switching controller 7b and a calculator 7c. The calculator 7c normally performs a proportional-integral operation (PI operation) and calculates a target oxygen concentration value in the combustion air based on the nitrogen oxide detection value sent from the filter 7a. At this time, the calculator 7c changes the proportional sensitivity and integration time in the proportional-integral operation based on the switching signal output from the switching controller 7b, and changes the control method from the proportional-integral operation to another operation. The calculated value outputted from the calculator 7c in this way is sent to the comparator 7d and compared with the preset upper and lower limits of the air oxygen concentration, and if it is within the range of these two values, then The oxygen concentration target value is directly output from the comparator 7d to the controllers 8 and 9, respectively. When the calculated value output by the calculator 7c exceeds the upper and lower limits, the upper limit or the lower limit is output as a target value to the controllers 8 and 9, depending on whether it exceeds the upper limit or falls below the lower limit. Any value higher than the atmospheric oxygen concentration can be selected as the lower limit, but in the case of the present invention, it may be set to 23%, for example. Further, the upper limit value should be determined by the flame combustion temperature of the burner 1b, but since it is difficult to directly measure this, it is determined based on the coke oven gas and the amount of combustion air supplied.

Next, switching of the calculation method by the switching controller 7b and the calculator 7c will be specifically explained.

In order to suppress pollution, the concentration of nitrogen oxides in exhaust gas has been set at a legal limit as its upper limit. In a preferred embodiment of the present invention, taking this into consideration, the nitrogen oxide concentration is divided into three control ranges. That is, the concentration is set in an emergency control range exceeding the upper limit set slightly lower than the legal regulation value, a normal control range from a preset normal lower value to the upper limit, and a control range below the normal lower value. It is divided into three control areas, and the calculation method is switched depending on which control area the detected nitrogen oxide concentration belongs to. Therefore, the switching controller 7b compares the detected value inputted from the filter 7a with the above-mentioned upper limit value and the normal lower value, and determines to which of the above-mentioned three control ranges the detected value belongs. The calculator 7c, which receives the result of this judgment, switches the calculation method according to the result.

When the switching controller 7b determines that the detected value is lower than the normal lower value, the calculator 7c sets the proportional sensitivity in the proportional-integral operation to a small value and the integration time to a large value, so that stability is preferred over responsiveness. Control combustion safely by gradually increasing the oxygen concentration in the combustion air while focusing on On the other hand, if the nitrogen oxide detection value is within the above normal control range, control is performed that emphasizes responsiveness rather than stability by increasing the proportional sensitivity in the proportional-integral operation and setting the integral time to be small. The goal is to always keep the oxide concentration within this range. Furthermore, when the detected value exceeds the upper limit and enters the emergency control region, the calculator 7c calculates the oxygen concentration from the current oxygen concentration detected by the oxygen concentration meter 3a, for example, the oxygen concentration lower limit, without using the proportional integral operation. Calculate and output the value by subtracting 1/2 of the difference between the value (23%) and the current value. That is,
Cuts off 50% of the portion where the current oxygen concentration exceeds the lower limit, thereby rapidly reducing the nitrogen oxide concentration. After a certain period of time has passed, if the detected value of nitrogen oxide concentration still exceeds the upper limit, this 50% cut is repeated.

As described above, the calculator 7c switches its calculation method depending on the detected value detected by the NOx meter 1d, thereby improving the combustion efficiency while suppressing the concentration of nitrogen oxides in the exhaust gas.

(Example) Using the method shown in Figures 1 and 2, a test of oxygen-enriched combustion control was carried out in a continuous steel slab heating furnace in a rolling mill with a processing capacity of 300 tons per hour, in accordance with the present invention. I went there.

Conventionally, the maximum emissions of nitrogen oxides were about 75% of the legal regulation value of 160 ppm, but as a result of oxygen-enriched combustion control according to the present invention, the oxygen concentration in the combustion air has been reduced to the average converted value. We were able to increase it by 24%. The maximum concentration of nitrogen oxides in exhaust gas is
It was 150ppm. As a result, we succeeded in reducing the fuel consumption rate, that is, the input fuel heat required to heat one ton of steel billet, by 5%.

(Effects of the Invention) As detailed above, according to the oxygen-enriched combustion control method according to the present invention, combustion efficiency can be improved while suppressing the concentration of nitrogen oxides in exhaust gas to a predetermined value or less, It has become possible to economically control heating furnaces under pollution regulations, and the economic effects are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an oxygen-enriched combustion control device when the present invention is applied to a billet heating furnace; and FIG. 2 is a block diagram showing the structure of an oxygen concentration calculator of the device shown in FIG. be. 1: Heating furnace, 2: Coke oven, 3: Air pump, 4: Oxygen plant, 5: Fuel gas flow rate controller, 7: Arithmetic unit, 8: Oxygen concentration controller, 9: Air-fuel ratio controller.

Claims (1)

[Claims] 1. A method for controlling combustion of fuel and oxygen-enriched air in a combustion device, comprising controlling the oxygen concentration in the oxygen-enriched air based on the concentration of nitrogen oxides in the exhaust gas of the combustion. , further controlling the mixing ratio of the fuel and the oxygen-enriched air based on the oxygen concentration in the combustion exhaust and the oxygen concentration in the oxygen-enriched air, and controlling the nitrogen oxide concentration in the combustion exhaust at a plurality of levels. A method for controlling oxygen-enriched combustion, characterized in that the oxygen concentration in oxygen-enriched air is divided into value ranges and the oxygen concentration in oxygen-enriched air is controlled according to a different method for each value range. 2. The oxygen-enriched combustion control method according to claim 1, wherein the amount of fuel supplied is controlled by the temperature within the combustion device. 3. In a control device for combustion of fuel and oxygen-enriched air in a combustion device, a nitrogen oxide concentration meter that measures the nitrogen oxide concentration in the exhaust gas from the combustion, and an oxygen concentration meter that measures the oxygen concentration in the exhaust gas. a computing unit that computes a target oxygen concentration value in the oxygen-enriched air based on the measured value of the nitrogen oxide concentration meter; A mixing ratio of the fuel and oxygen-enriched air is controlled based on an oxygen concentration controller to be controlled, a measured value of the oxygen concentration in the exhaust gas measured by the oxygen concentration meter, and a target oxygen concentration value calculated by the calculator. An air-fuel ratio controller, wherein the computing unit includes means for switching a computing method according to a range classification of a measured value of nitrogen oxide concentration. 4. The combustion control device according to claim 3, wherein the arithmetic unit and the oxygen concentration controller are constituted by a microcomputer. 5 a thermometer that measures the temperature inside the combustion device;
5. The combustion control device according to claim 3, further comprising a fuel amount controller that controls the amount of fuel supplied based on the measured value of the thermometer.