KR20120106965A - Method for correcting the combustion settings of a set of combustion chambers and apparatus implementing the method - Google Patents

Abstract

To a method for real-time continuous adjustment of a set of heated combustion chambers 2, 2i with similar features supplied by the same combustor 8 and fuel 9 network, one of the combustion chambers 2i Is used as the reference chamber, the combustion variables are measured at the fumes output from the reference chamber (7), and the control variables of all the chambers 2 are determined according to the combustion variables measured at the output of the reference chamber 2i. In particular according to the combustion of the combustor and / or fuel and / or the ratio of the combustor to the fuel.

Description

METHOD FOR CORRECTING THE COMBUSTION SETTINGS OF A SET OF COMBUSTION CHAMBERS AND APPARATUS IMPLEMENTING THE METHOD}

The present invention is directed to a method for the adjustment of devices for supplying a set of combustion chambers that are supplied with a combustor and fuel whose properties can vary. The present invention makes it possible to take account of possible variations in these properties to maintain combustion of the desired quality.

Many industrial heating devices consist of a set of individual combustion chambers supplied by a general device for supplying a combustor and fuel. In the steel industry, for example, these devices are furnaces for continuous processing lines for metal strips with radiant tubes.

In many cases, the combustors or fuels used have properties that can vary over time. Fuel produced together, for example, when using rich air or depleted air, or even on-site, such as coke oven gas, steel furnace gas, mixtures of gases Field or other fuels such as biogas or generator gas.

There are a number of ways to adjust the regulation of the furnace depending on the characteristics of the fuel. The methods make it possible to adjust the fluctuations of one of the main variables of fuel, eg calorific power PCI, combustion power, combustion index or Webbe index.

The methods do, in most cases, do not allow the properties of the combustor and fuel to be properly considered when the sampling process changes the properties of the combustor and fuel. The methods also have the disadvantage of having a relatively long response time and requiring the measuring devices to be put in place in the protected areas.

One particular method is proposed in FR2712961. According to this method, a burner is controlled by removing a predetermined amount of fuel, and the fuel is combusted in a predetermined amount of air and a designated chamber to be burned with excess air, and a variable reflecting a deviation from the stoichiometry of the fuel Measured from soot from complete combustion. This variable is then used to determine representative values of the coefficients for adjusting the amount of combustion air from the combustor. The combustion measuring device is composed of a combustion tunnel, a combustor and suitable measuring means.

The system has the disadvantage of using a specially configured mini-furnace in which the air / fuel mixture is combusted at a controlled rate to provide excess levels of air. The small furnace consumes fuel and must be operated at an excess level. This combustion is carried out in the small-furnace at an operating point which can be very different from that of the device to be controlled, for example with respect to the combustor output, air-fuel ratio, furnace temperature and flame containment. Therefore, the processing of these results requires the use of mathematical correction formulas.

The system also has the disadvantage that it is designated exclusively to take into account deviations in the properties of the fuel. It does not take into account deviations in the properties of the combustor or combustion parameters suitable for the monitored device, ie the proportion of unburned residues or even the proportion of nitrous oxide NOx emissions.

It is an object of the present invention to improve the control of the combustion of a set of combustion chambers, mainly related to the manufacturing process; In particular, the present invention seeks to improve the control of a set of radiation tubes for a continuous machining line for metal pieces.

The combustion chambers are of the same type. The output of each of the combustion chambers may be different but the techniques implemented are similar. Potential differences between the combustion chambers do not affect the combustion parameters that are desired to be monitored.

In order to ensure control of the combustion of a set of radiant tubes, one of the tubes installed in the furnace shell is used as reference tube. The reference tube, like all the other tubes, participates in the heating of the metal piece. The radiation tube has a structure similar to that of other tubes and acts in a way that represents the operation of the other tubes participating in the heating process.

At the outlet of the radiation tube the combustion products are cooled by participating in a process of heating the furnace. A measuring device is installed at the outlet of the reference tube, which provides information about the state of combustion products downstream of the tube. In general, the device is a gas analyzer that allows information, in particular regarding unburned residues to be obtained and / or excess air, for example.

Therefore, according to the invention, a method for real-time and continuous control of a set of combustion chambers with similar features, supplied by the same combustor and fuel networks, is:

One of the chambers is used as a reference chamber,

Combustion parameters are measured at the soot at the outlet of the reference chamber,

The control parameters of all the chambers are adjusted in particular according to the combustion parameters measured at the outlet of the reference chamber, in particular depending on the ratio of the combustion agent to fuel and / or the composition of the combustion agent and / or fuel.

The combustion parameters measured at the soot at the outlet of the reference chamber may consist of at least the proportion of unburned residues and / or the concentration of nitrates and / or the concentration of hydrogen and / or the concentration of carbon dioxide and / or the concentration of oxygen.

The level of excess air can be determined by the concentration of oxygen or carbon dioxide at the soot at the outlet of the reference chamber. The lack of air can be determined by the concentration of carbon monoxide or hydrogen or unburned residues at the soot at the outlet of the reference chamber.

Advantageously, the control parameters for all chambers are adjusted to obtain the desired level of excess air and / or unburned residues. The control parameters for all chambers can be adjusted to obtain the ratio of unburned residues and / or the desired air shortage.

The concentration of nitric oxide can be adjusted, in particular, by dilution with combustion products, by adjusting the composition of the combustor and / or fuel.

Thermal chambers may consist of radiant tubes fed with gases in different proportions than that of the reference tube.

In addition, the present invention is:

An apparatus for carrying out the method described above comprising a set of combustion chambers having similar features, supplied by the same combustor and fuel networks, the apparatus:

One of the chambers is used as reference chamber,

Means for measuring combustion variables is installed at the outlet of the reference chamber to measure the combustion variables at soot at the outlet,

Control means are provided for adjusting the control parameters of the set of chambers in accordance with the measurements made at the outlet of the reference chamber, in particular in accordance with the ratio of the burner to fuel and / or the composition of the burner and / or fuel. It features.

The thermal chambers may consist of radiation tubes, the reference tube may be supplied with the other tubes, and the control members are provided in supply circuits common for all the tubes.

According to another possibility, the radiation tubes are supplied separately from the reference tube and have different control members than those of the reference tube in different supply circuits, and the control members of the tubes control such that the tubes are supplied with the same ratio of gas as the reference tube. do. According to a further possibility, the control members of the radiation tubes can be controlled such that the tubes are supplied with different proportions of gas, in particular with different levels of excess air.

Compared to the equipment used in the prior art, a standard device is used according to the invention as a combustion chamber, the device being similar to others and used in the method and its control is wholly representative of the operation of all devices. In particular, this allows variables that depend on the mode of operation of the overall device to be controlled.

In general, the main variable is the level of excess air measured by the concentration of oxygen. However, depending on other variables, for example unburned residues or variations in the properties of the burner and / or fuel when the furnace is cold, it may be necessary to monitor the nitrous oxide exhaust gas which can be adjusted. have.

The method according to the invention allows the device to function even in the absence of air to be regulated. In this case, the monitored variable may be a component representing one of the gases representing this combustion mode, which is present at a high rate in soot. This gas can be, for example, carbon monoxide (CO).

The reference tube is supplied by circuits for supplying fuel and a combustor having control members allowing the ratio to be adjusted. The reference tube may for example be supplied by additional circuits for combustion fumes or oxygen.

Analyzes carried out on the combustion products at the outlet of the reference tube considered controlling the control members of the supply circuits to obtain the desired quality combustion.

When the reference tube is fed together with the other tubes, that is, when the control members are placed in supply circuits common to all the tubes including the reference tube, the other tubes benefit from this same control.

When the radiation tubes are fed separately from the reference tube, ie when they have control members in different supply circuits, the control members are controlled such that the tubes are fed in the same proportions of gas as the reference tube, or at different rates. .

If the two sets of radiant tubes are designed to have the same control variables, for example the same supply pressure for different operating outputs, while maintaining the same proportion of gas, then the control variables of the reference tube are the supply circuits of the second set of tubes. Is duplicated for the absence of these.

If the two sets of radiant tubes are designed to have different control variables, for example different supply pressures, while maintaining the same proportion of gas, then the control variables of the reference tube are relative to the members of the supply circuits of the second set of tubes. Adjusted. The adjustment depends on the change in flow rate with the change using the physical law of the measured value, for example the square of the pressure difference.

According to the invention, when the radiating tubes are supplied separately from the reference tube, the control members can be controlled such that the tubes are supplied with different proportions of gas than, for example, different levels of excess air. .

Control of the exothermic requirements of the reference tube can be effected by varying the duration or the flow rate. The control may be associated with or separate from that of other reference tubes.

Apart from the combination of devices presented above, the present invention is disclosed with reference to the accompanying drawings, but is not limited in any way, but consists of a number of other devices described in more detail below with reference to embodiments. do.

1 is a schematic representation of a continuous processing line of metal pieces.
2 is a schematic view of a radiation tube.
3 shows a first example of supplying a pair of radiation tubes;
4 shows a second example of supplying a set of radiation tubes.

With reference to FIG. 1 of the drawings, one can see a furnace 1, shown schematically, with radiation tubes 2 providing heating of a piece of metal 3, passing along rollers not shown. This heating is usually carried out in a protective atmosphere, consisting of a mixture of nitric oxide and hydrogen. In each radiation tube, combustion is ensured in a limited combustion chamber spaced from the furnace shell by the tube. Indirect heating is therefore achieved.

Referring to FIG. 2 of the drawings, as schematically shown, a U-shaped radiation tube 2 can be seen. The radiation tubes can have other shapes, for example they can be I-shaped, P-shaped, double P-shaped, or W-shaped. The combustor 4 is located at one end of the tube 2. Flame 5 propagates in the tube and releases its energy towards the walls of the tube, which heats the perimeter and the metal pieces. As they pass through the tube, soot thermally radiates the walls of the tube. A heat recovery system (not shown) allows the combustion air to be preheated and is generally located at the end of the tube opposite the combustor. At the outlet of the tube, the partially emitted soot is discharged towards the collector 6 which is connected to the flue. An analyzer 7 located downstream of the outlet of the tube allows analysis of the combustion products.

Referring to FIG. 3 of the drawings, one embodiment of a circuit for supplying a burner and fuel to a set of U-shaped radiant tubes, including a reference tube 2r, is shown schematically. The combustors 4 are supplied by a system for supplying fuel 9 to control valve FCVf and a system for supplying combustor 8 to control valve FCVc. Automatic control of the valves can be ensured by an automated system (not shown), which receives information at the inlet about the combustion parameters measured by the analyzer 7 at the outlet of the reference tube 2r. The automation system provides specific commands for control as a function of input data at the outlets connected to the controls of the valves.

In this embodiment, the furnace area is provided with radiation tubes 2, the combustors 4 being fed in parallel by common combustion and fuel networks. The change in the exothermic requirement is controlled by the operating time of the combustors, ie the ratio of the open duration of the fuel valve FCVf and the combustor valve FCVc for a predetermined time for each combustor.

Each combustor was previously controlled during commissioning to a known operating point by manual flow limiters 10. For a given operating point, for example, at 100% power, each combustor was previously controlled by a separate flow limiter device. In these conditions, for some general operation of the furnace area, the operation of the tube selected as the reference tube generally shows the operation of a set of combustors connected to the same supply system. The control of all radiation tubes is adjusted by adjusting the settings of the system supplying the reference tube, ie the valves FCVc, FCVf, to take into account changes in the properties of the combustor or fuel.

The control of the valves FCVc, FCVf can cause a change in the pressure Pf of the fuel or the pressure Pc of the combustor, such that the proportion of gases is adjusted to be equal to all the tubes.

The measurements carried out by the analyzer 7 arranged at the outlet of the reference tube can be limited, for example, to two variables: oxygen content indicating the proportion of unburned residues and the level of excess combustion agent, especially at low temperatures. , The amount of unburned residue adjusted to the level of excess air.

Referring to FIG. 4 of the drawings, a furnace with U-shaped radiation tubes, shown schematically, can be seen.

In this apparatus, a set of four radiation tubes 2 are supplied by control valves FCVc, FCVf by the combustor 8 and fuel 9 networks common to the four tubes of this set. . In this arrangement, the reference radiation tube 2i is supplied separately by its own system which supplies fuel 9i regulated by valve FCVfi and combustor 8i regulated by valve FCVci.

According to a preferred embodiment of the present invention, the transmitters used for the set of tubes 2 and the reference tube 2i to be adjusted use the same physical laws. For example, a pressure differential transmitter can be used to measure the flow rate.

At certain operating points, for example, at 100% power, each combustor comprising a combustor of a reference tube previously separates, in particular by manual control, so as to obtain the same ratio of combustor / fuel in each combustor It was controlled during the test run by the flow control device 10 of. This control was carried out under the same conditions for all the tubes, ie with the same quality of combustion and fuel.

It should be appreciated that each tube may have a nominal power and / or a different dimension. The tubes can be of different shapes, for example they can be U-shaped or W-shaped.

In the control mode, the flow of combustor and fuel from the reference tube is adjusted to have the correct oxygen ratio in the soot as the fuel and / or the properties of the combustor change. The analyzer 7 allows the valves FCVci and FCVfi to be controlled to obtain the desired combustion quality in the reference tube. The corresponding operating point, measured in pressures Pci, Pfi, defines the control variables Pc, Pf used to control the valves FCVc, FCVf.

Since the setting of the reference tube 2i represents the desired combustion in all the tubes, the values measured in the supply system are used to govern the regulation of the set of tubes 2.

For example, the combustor valve FCVc is controlled so that the value Iva of the measured signal indicative of the flow of the combustor in the set of tubes to be regulated is defined according to the relationship Is controlled according to:

In this relationship, K is a constant value, Ivai represents a measurement signal representing a combustion agent in the reference tube 2i, Ivfi represents a measurement signal representing fuel in the reference tube 2i, and Ivf represents a tube to be regulated. Represent the measurement signal representing the fuel in the set of (2).

The advantage of this system is that adjustments can be easily made to the control of the heating system. Therefore the response time is very short and the control variables fully represent the desired control.

An extension of this application is the control of devices in which the composition of the burner can change. This change may not be intended, for example, the composition of the air depends on the humidity content.

Such a change can be intended, for example, by adjusting the oxygen ratio of the combustor. Therefore, oxygen enrichment can be carried out to increase the output of the furnace, to reduce fuel consumption or to reduce CO 2 emissions. Oxygen depletion can be carried out to reduce NOx emissions or to adjust heat transfer, for example by expanding the flame. In this application, the measurement of NOx in the soot of the reference tube acts to control the dilution rate of the burner.

The invention makes it possible to adjust settings which may differ from that of the reference combustor. According to the invention, the flame is formed in the reference chamber, similar to other chambers but not in open air.

Combustion in the chamber is greatly affected by its geometry. The geometry governs the confinement of the flame, the nature of the gas flow, the recycling of some of the soot and the temperature mapping in the chamber. All of these variables affect the combustion, in particular the temperature of the flame.

Therefore the combustion results measured at the outlet of the reference chamber directly represent the same combustion as is produced in the other chambers.

1: furnace 2: replica tube
3: metal piece 4: combustor
5: flame 6: picker
7: Analyzer 8: Combustion
9: fuel 10: limiter

Claims (12)

In a method for real-time and continuous control of a set of heated combustion chambers 2, 2r, 2i with similar features, supplied by the same combustor 8 and fuel 9 networks,
One of the combustion chambers 2, 2r, 2i is used as a reference chamber,
Combustion parameters are measured at the soot at the outlet of the reference chamber (7),
Combustion chamber control, characterized in that the control parameters of all the chambers are adjusted in accordance with the combustion parameters measured at the outlet of the reference chamber, in particular in accordance with the ratio of the combustion agent to fuel and / or the composition of the combustion agent and / or fuel. Way. The method of claim 1,
The combustion parameters measured at the soot at the outlet of the reference chamber are at least the proportion of unburned residues and / or the concentration of nitrates and / or the concentration of hydrogen and / or the concentration of carbon monoxide and / or the concentration of carbon dioxide and / or oxygen Combustion chamber control method, characterized in that consisting of. The method of claim 2,
The level of excess air is determined by the concentration of oxygen or carbon dioxide at the soot at the outlet of the reference chamber. The method of claim 2,
The lack of air is determined by the concentration of carbon monoxide or hydrogen or unburned residues in the soot at the outlet of the reference chamber. The method according to any one of claims 1 to 3,
Control parameters of all chambers are adjusted to obtain the desired level of excess air and / or unburned residues. The method of claim 4, wherein
A control method for a combustion chamber, characterized in that the control parameters of all the chambers are adjusted to obtain the desired lack of air. The method of claim 2,
The concentration of nitrates is in particular diluted with combustion products, so as to be adjusted by adjusting the composition of the combustion agent and / or fuel. The method according to any one of claims 1 to 7,
And wherein the thermal chambers are comprised of radiant tubes in which one of the radiant tubes constitutes a reference tube and the other radiant tubes are supplied with a gas at a different rate than that of the reference tube. The apparatus according to any one of claims 1 to 8, comprising a set of heated combustion chambers 2, 2r, 2i with similar features, supplied by the same combustor 8 and fuel 9 networks. An apparatus for carrying out the method according to the present invention,
One of the combustion chambers 2, 2r, 2i is used as reference chamber,
Means for measuring combustion parameters (7) are installed at the outlet of the reference chamber to measure the combustion parameters of the soot at the outlet,
Control means FCVc to adjust the control parameters of the set of chambers in accordance with the measurements made at the outlet of the reference chamber, in particular in accordance with the ratio of the burner to fuel and / or the composition of the burner and / or fuel; FCVf) is provided. The method of claim 9,
The thermal chambers are composed of radiation tubes, the reference tube 2r is supplied with the other tubes, and the control members FCVc and FCVf are arranged in the supply circuits 8 and 9 common to all the tubes. Characterized in that the device. The method of claim 9,
The thermal chambers are composed of radiation tubes, one of the radiation tubes constitutes a reference tube 2i, the other radiation tubes are supplied separately from the reference tube 2i and are supplied with different supply circuits 8, 9, In 8i, 9i, the control members FCVc and FCVf are different from the members FCVci and FCVfi of the reference tube 2i, and the control members FCVc and FCVf of the tubes 2 are the tube 2. Device is controlled to receive gas at the same rate as the reference tube (2i). The method of claim 11,
The control members (FCVc, FCVf) of the radiation tubes (2) are characterized in that the tubes are controlled to be supplied with different rates of gas, in particular at different levels of excess air than that of the reference tube (2i).

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