WO2011064752A1

WO2011064752A1 - Method for correcting the combustion settings of a set of combustion chambers and apparatus implementing the method

Info

Publication number: WO2011064752A1
Application number: PCT/IB2010/055454
Authority: WO
Inventors: Patrick Giraud
Original assignee: Fives Stein
Priority date: 2009-11-30
Filing date: 2010-11-26
Publication date: 2011-06-03
Also published as: FR2953280B1; BR112012013060A2; KR20120106965A; EP2507551B1; CN102686946B; FR2953280A1; US20120291679A1; CN102686946A; EP2507551A1

Abstract

The invention relates to a method for real-time, continuous adjustment of a set of thermal combustion chambers (2, 2i) having similar characteristics supplied by the same combustive agent (8) and fuel (9) networks, according to which one of the chambers (2i) is used as a reference chamber, combustion parameters are measured (7) in the fumes output from the reference chamber, and the control parameters of all the chambers (2) are adjusted according to the combustion parameters measured at the output of the reference chamber (2i), in particular according to the ratio of combustive agent to fuel and/or the composition of the combustive agent and/or fuel.

Description

METHOD FOR CORRECTING THE COMBUSTION SETTINGS OF A COMBUSTION CHAMBER ASSEMBLY AND INSTALLATION USING THE METHOD

The present invention relates to a method of adjusting the supply devices of a combustion chamber assembly supplied with an oxidant and a fuel whose properties are variable. It makes it possible to take into account the possible fluctuations of these properties so as to maintain the desired combustion quality.

Many industrial heating equipment consists of a set of separate combustion chambers fed by a common oxidizer and fuel supply device. For example, in the iron and steel industry, this is the case of furnaces for continuous lines for treating metal strips, equipped with radiant tubes.

In many cases, the oxidants or fuels used have variable properties over time. For example, when using enriched air or depleted air, or when using locally produced fuels such as coke oven gas, steelmaking gas, a gas mixture, or still alternative fuels such as bio gas or a generator gas. There are many methods of correcting the regulation of an oven according to the properties of the fuel. These methods make it possible to correct the fluctuation of one of the main parameters of the fuel, for example the heating value PCI, the comburivore power, the combustion index or the Wobbe index.

These methods do not allow the properties of the fuel and the oxidant to be fully accounted for because, in most cases, the sampling modifies the properties of the fuel and the oxidant. These methods also have the disadvantage of having a relatively long response time and require the installation of measuring devices in protected places.

A particular method is provided by FR2712961. According to this method, a burner is adjusted by taking a given flow rate of fuel. burns this fuel in a dedicated chamber with an air flow such that it leads to combustion in excess of air, and a total quantity reflecting the stoichiometric difference is measured in the complete combustion fumes of the fuel. This quantity is then used to determine the representative value of the combustion air flow rate regulator of the burner. This comburimeter device consists of a combustion tunnel, a burner and appropriate measuring means.

This system has the disadvantage of implementing a specially constructed mini oven in which one burns an air / fuel mixture to proportions set to have an excess of air. This mini oven consumes fuel and must operate in excess of air. Combustion is carried out in this mini-oven on an operating point which may be remote from that of the installation to be regulated, for example as regards the power of the burner, the air / gas ratio, the temperature of the oven, and the containment of the flame. The exploitation of the results thus requires the use of mathematical correction formulas.

This system also has the disadvantage of being dedicated exclusively to taking into account variations in fuel properties. It does not take into account the variations in oxidant properties or the combustion parameters specific to the controlled installation, namely the unburnt rate or the emission rate of NOx nitrogen oxides. The object of the invention is, above all, to improve the control of the combustion of a set of combustion chambers participating in a manufacturing process; in particular, the invention aims to improve the adjustment of a set of radiant tubes of a line of continuous treatment of metal strips. These combustion chambers are of the same nature. The power of each of them can be variable but the technologies implemented are similar. The differences between these combustion chambers have no influence on the combustion parameters that we want to control. In order to control the combustion of all the radiant tubes, one of these tubes is used in the furnace laboratory as a reference tube. It participates in heating the band as all other tubes. This radiant tube is of a construction similar to that of the others tubes and is solicited in a manner representative of the operation of the other tubes which participate in the heating.

The combustion products at the outlet of the radiant tube cooled by participating in the furnace heating process. At the outlet of this reference tube, a measuring apparatus is installed which provides information on the state of the combustion products after the tube. It is usually a gas analyzer allowing in particular to know for example the excess air and / or unburnt.

Thus, according to the invention, the method of real-time and continuous adjustment of a set of combustion combustion chambers having similar characteristics supplied by the same oxidant and fuel networks, is characterized in that:

one of the speakers is used as a reference speaker,

combustion parameters are measured in the fumes at the outlet of the reference chamber,

- the regulation parameters of all the speakers are adjusted according to the combustion parameters measured at the outlet of the reference chamber, in particular according to the proportion between the oxidant and the fuel and / or the composition of the oxidizer and / or fuel.

The combustion parameters measured in the fumes at the outlet of the reference chamber may consist of at least the oxygen concentration, and / or the carbon dioxide concentration, and / or the hydrogen concentration, and / or the concentration of nitrogen oxides and / or the rate of unburnt. The excess air can be determined according to the concentration of oxygen or carbon dioxide in the flue gases leaving the reference chamber. The air defect can be determined by the concentration of carbon monoxide, or hydrogen, or unburned, in the flue gas leaving the reference chamber.

Advantageously, the control parameters of all the enclosures are adjusted so as to obtain the excess air and / or the rate of unburnt targeted. We can adjust the regulation parameters of all the speakers so as to obtain the air defect, and / or the target unburnt rate.

The concentration of nitrogen oxides can be regulated by adjusting the composition of the oxidant and / or the fuel, in particular by dilution with products of combustion.

The thermal chambers may consist of radiant tubes supplied with gas proportions different from those of the reference tube.

The invention also relates to an installation for implementing a method as defined above, comprising a set of combustion combustion chambers having similar characteristics, fed by the same oxidant and fuel networks, characterized in that what:

one of the speakers is used as a reference speaker,

means for measuring combustion parameters are installed on the output of the reference chamber for measuring these combustion parameters in the flue gases at the outlet,

adjustment means are provided for adjusting the regulation parameters of all the speakers as a function of the measurements made at the outlet of the reference chamber, in particular as a function of the proportion between the oxidant and the fuel and / or the composition of the oxidant and / or the fuel. The thermal chambers may consist of radiant tubes, and a reference tube may be fed in a common manner with the other tubes, the regulating members being placed on supply circuits common to all the tubes. According to another possibility, the radiant tubes are supplied in a manner distinct from the reference tube and have regulating means different from those of the reference tube, on different supply circuits, the regulating members of the tubes being controlled so that these tubes are fed with the same proportions of gas as the reference tube. According to another possibility, the regulating members of the radiant tubes can be controlled so that these tubes are fed with proportions of gases different from those of the reference tube, in particular with a different excess of air. Compared to the equipment used according to the state of the art, according to the invention is used as combustion chamber standard equipment similar to the others, which participates in the process and whose setting is perfectly representative of the operation of all equipment. It allows, in particular, to control parameters that depend on the operating mode of the entire installation.

Generally, the master parameter is the excess air measured by the oxygen concentration. However, it may be necessary to control other parameters, for example, the unburnt when the oven is cold, or the NOx emissions that can be regulated, for example according to the changes in the properties of the oxidant and / or fuel. The method according to the invention also makes it possible to regulate equipment operating in lack of air. In this case, the controlled parameter may be a compound representing one of the gases representative of this mode of combustion, present in large proportion in the fumes. It can be for example CO carbon monoxide.

The reference tube is fed by fuel and fuel supply circuits equipped with regulating devices to adjust their proportion. It can also be powered by additional circuits, for example combustion fumes or oxygen.

The analyzes carried out on the products of combustion at the outlet of the reference tube are taken into account to control the regulating elements of the supply circuits so as to reach the desired combustion quality. When the reference tube is fed in a common way with the other tubes, that is to say when the regulating members are placed on supply circuits common to all the tubes, including the reference tube the other tubes benefit from this same setting. When radiant tubes are supplied in a manner distinct from the reference tube, that is to say that they have regulating members on different supply circuits, these regulating members are controlled so that these tubes are fed with the same proportions of gas as the reference tube, or with a different proportion.

If the two sets of radiant tubes are designed to have identical regulated parameters, for example an identical supply pressure, for a different operating power while maintaining the same proportion of gas, the regulated parameters of the reference tube are reproduced for the members of the supply circuits of the second set of tubes.

If the two sets of radiant tubes are designed to have different regulated parameters, for example a different supply pressure, while maintaining the same proportion of gas, the regulated parameters of the reference tube are corrected for the circuit elements of feeding the second set of tubes. This correction depends on the physical law of the measured value, for example the variation of the flow as a function of the square variation of the differential pressure.

According to the invention, when radiant tubes are fed in a manner distinct from the reference tube, their regulating members can be controlled so that these tubes are fed with proportions of gas different from those of the reference tube, for example with a different air excess.

The regulation of the heat demand of the reference tube can be carried out in terms of rate modulation or modulation of duration. It may be associated with that of other radiant tubes or it may be distinct.

The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed hereinafter with regard to exemplary embodiments, described with reference to the accompanying drawings, but which do not are in no way limiting. On these drawings:

- Fig. 1 is a schematic view of a line of continuous treatment of metal strips,

- Fig. 2 is a schematic view of a radiant tube,

- Fig. 3 represents an example of feeding a pair of radiant tubes,

and FIG. 4 is a second example of feeding a set of radiant tubes. Referring to FIG. 1 of the drawings, we can see, schematically represented, a furnace 1 equipped with radiant tubes 2 for heating a metal strip 3, scrolling on unrepresented rollers. The heating is carried out under a protective atmosphere generally composed of a mixture of nitrogen and hydrogen. In each radiant tube, combustion is provided in a confined combustion chamber, separated from the laboratory oven by the tube. We then have indirect heating. Referring to FIG. 2 of the drawings, one can see, schematically shown, a U-shaped radiant tube 2. The radiant tubes may have other shapes, for example I, P, double P or W. A burner 4 is located at one end of the tube 2. The flame 5 propagates in the tube and releases its energy towards the walls of the tube which heats the laboratory and the band. As they travel through the tube, the fumes heat up on the walls of the tube. At the end of the tube opposite the burner is generally located a heat recovery unit, not shown, for preheating the combustion air. At the outlet of the tube, the fumes in spent parts are discharged to a manifold 6, connected to a chimney. An analyzer 7, implanted after the exit of the tube, allows the analysis of the products of combustion.

Referring to FIG. 3 of the drawings, we can see, schematically represented, an embodiment of the fuel supply circuit and fuel of a set of U-shaped radiant tubes, including a reference tube 2r. The burners 4 are fed by an oxidizer supply system 8, with an FCVc control valve, and a fuel supply system 9, with an FCVf control valve. The automatic adjustment of the valves can be provided by a controller (not shown) which receives as input the information on the combustion parameters measured by the analyzer 7 at the output of the reference tube 2r. The controller provides, on outputs connected to the valve controls, setting instructions determined according to the input data. In this embodiment, the furnace zone is equipped with radiant tubes 2 whose burners 4 are supplied in parallel by common oxidant and fuel networks. The variation in heat demand is managed by the operating times of the burners, that is to say for each burner the proportion of the opening time of its FCVc oxidizer valve and its FCVf fuel valve for a given time.

Each of the burners was previously set during commissioning for a known operating point by means of manual flow rate limiters 10. For a given operating point, for example at 100% of the power, each of the burners was previously regulated by a singular device of limitation of flow. Under these conditions, for a given general operation of the furnace zone, the operation of a tube chosen as a reference tube is the overall image of the operation of all the burners connected to the same supply systems. By modifying the settings of the supply system of the reference tube, that is to say FCVc and FCVf valves, to take into account a change in the characteristics of the fuel or the oxidant, the setting of the set of radiant tubes.

The setting of the FCVc and FCVf valves causes a variation in the pressure of the oxidant Pc or the fuel pressure Pf making it possible to adjust the proportion of gases to the same for all the tubes. The measurements made by the analyzer 7 placed at the outlet of the reference tube may for example be limited to two parameters: the oxygen content, which represents the excess of oxidant, and the proportion of unburnt, the quantity of which may lead to Excess air corrections, especially at low temperatures.

Referring to FIG. 4 of the drawings, one can see, schematically represented, an oven equipped with U-shaped radiant tubes.

On this installation, a set of four radiant tubes 2 is fed by oxidizing networks 8 and fuels 9 common to all four tubes by means of control valves FCVc and FCVf. In this installation, a reference radiant tube 2i is fed separately with its own oxidizer supply system 8i regulated by a valve FCVci, and fuel 9i regulated by a valve FCVfi.

According to a preferred embodiment of the invention, the transmitters used on the reference tube 2i and the group of tubes 2 to be regulated exploit the same physical laws. For example, a differential pressure transmitter can be used to measure a flow rate.

For a given operating point, for example at 100% of the power, each of the burners, including that of the reference tube, was previously set for commissioning by a singular device for limiting the flow rate, in particular manual adjustment, so as to obtain the same oxidizer / fuel ratio on each burner. This adjustment is made under the same conditions for all the tubes, that is to say with the same quality of oxidant and fuel.

It should be noted that each of the tubes may have a nominal power and / or different dimensions. The tubes may also be of different shapes, for example in U or W.

In control mode, the oxidant and fuel flow rates of the reference tube are adjusted to have the correct oxygen level in the flue gas according to the changes in the properties of the fuel and / or the oxidant. The analyzer 7 makes it possible to adjust the FCVci and FCVfi valves so as to obtain the targeted combustion quality in the reference tube. The corresponding operating point, measured by the pressures Pci and Pfi, defines the setpoints Pc and Pf used to set the valves FCVc and FCVf.

Since the settings of the reference tube 2i are representative of the desired combustion on all the tubes, the values measured on its feed system serve to govern the regulation of the entire group of tubes 2.

For example, the fuel valve FCVf will be adjusted according to the heat demand and the oxidizer valve FCVc will be set so that the value Iva of the signal of the representative flow rate measurement of the oxidant on the group to be regulated, is defined according to the following relation:

Iva / lvf = K x Ivai / Ivfi

In this relation, K is a constant, Ivai expresses the signal of the representative measurement of the oxidant on the reference tube 2i, Ivfi expresses the signal of the measurement representative of the fuel on the reference tube 2i, and Ivf expresses the signal of the representative measurement of the fuel on the group of tubes 2 to be regulated.

The advantage of this system is that it makes it easy to make corrections to the regulation of a heating system. The response time is then very low and the settings parameters are perfectly representative of what we want to adjust.

An extension of this application is to control an installation whose composition of the oxidant is variable. This variation can be unintended, for example the composition of the air is dependent on the moisture content.

This variation can be voluntary, for example by changing the oxygen content of the oxidizer. Thus, an oxygen enrichment can be achieved to increase the production of an oven, reduce fuel consumption or reduce CO2 emissions. Oxygen depletion can be achieved in order to modify the heat transfer, for example by lengthening the flame, or to reduce NOx emissions. In this application, a measurement of NOx in the flue gases of the reference tube will be used to regulate the dilution ratio of the oxidant.

The invention makes it possible to adjust settings that may be different from that of the reference burner. According to the invention the flame develops in a reference chamber similar to other speakers, and not in the open air.

The combustion in an enclosure is strongly influenced by the geometry of it. This conditions the flame confinement, the nature of the gas flows, the recirculation of a part of the fumes and the temperature mapping in the enclosure. All these parameters affect the combustion, especially the flame temperature.

The combustion results measured at the outlet of the reference chamber are thus directly representative of the combustion as it occurs in the other enclosures.

Claims

1. A method of real-time and continuous adjustment of a set of combustion combustion chambers (2, 2r, 2i) having similar characteristics supplied by the same oxidant (8) and fuel (9) networks, characterized in that than :

one of the enclosures (2, 2r, 2i) is used as a reference enclosure, combustion parameters are measured in the flue gases at the outlet of the reference chamber,

2. Method according to claim 1, characterized in that the combustion parameters measured in the fumes at the outlet of the reference chamber consist of at least the oxygen concentration, and / or the concentration of carbon dioxide, and or the concentration of carbon monoxide, and / or the hydrogen concentration, and / or the level of unburnt, and / or the concentration of nitrogen oxides.

3. Method according to claim 2, characterized in that the excess air is determined according to the concentration of oxygen or carbon dioxide in the flue gas leaving the reference chamber.

4. Method according to claim 2, characterized in that the air defect is determined by the concentration of carbon monoxide, or hydrogen, or unburned, in the fumes at the outlet of the reference chamber.

5. Method according to any one of claims 1 to 3, characterized in that one adjusts the regulation parameters of all the speakers so as to obtain the excess air and / or the rate of unburnt target.

6. Method according to claim 4, characterized in that one adjusts the regulation parameters of all the enclosures so as to obtain the target air defect.

7. Process according to claim 2, characterized in that the concentration of nitrogen oxides is regulated by adjusting the composition of the oxidant and / or the fuel, in particular by dilution with combustion products.

8. Method according to any one of the preceding claims, characterized in that the thermal chambers consist of radiant tubes, one of the radiant tubes constitutes a reference tube, and the other radiant tubes are fed with proportions of gas different from those of the reference tube.

9. Installation for the implementation of a method according to any one of the preceding claims, comprising a set of combustion combustion chambers (2, 2r, 2i) having similar characteristics fed by the same networks of oxidizer (8). ) and fuel (9), characterized in that:

one of the enclosures (2, 2r, 2i) is used as a reference chamber, - combustion parameter measurement means (7) are installed on the output of the reference chamber for measuring these combustion parameters in the flue gases. the exit,

adjustment means (FCVc, FCVf) are provided for adjusting the regulation parameters of the set of speakers as a function of the measurements made at the outlet of the reference chamber, in particular as a function of the proportion between the oxidizer and the fuel and / or the composition of the oxidant and / or the fuel.

10. Installation according to claim 9, wherein the thermal chambers consist of radiant tubes, characterized in that a reference tube (2r) is fed in a common manner with the other tubes, the regulating members (FCVc, FCVf) being placed on supply circuits (8,9) common to all the tubes.

1 1. Installation according to claim 9, in which the thermal chambers consist of radiant tubes, characterized in that one of the radiant tubes constitutes a reference tube (2i), and that the other radiant tubes are fed separately from the reference tube (2i) and have regulating members (FCVc, FCVf) different from those (FCVci, FCVfi) ) of the reference tube (2i), on different supply circuits (8, 9, 8i, 9i), the control members (FCVc, FCVf) of the tubes (2) being controlled so that these tubes (2) are fed with the same proportions of gas as the reference tube (2i).

12. Installation according to claim 1 1, characterized in that the regulating members (FCVc, FCVf) of the radiant tubes (2) are controlled so that these tubes are fed with proportions of gas different from those of the reference tube ( 2i), especially with a different excess of air.