WO2011131880A1

WO2011131880A1 - Fuel-fired furnace and method for controlling combustion in a fuel-fired furnace

Info

Publication number: WO2011131880A1
Application number: PCT/FR2011/050703
Authority: WO
Inventors: Philippe Beaudoin; Benoit Loiselet
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2010-04-23
Filing date: 2011-03-30
Publication date: 2011-10-27
Also published as: BR112012027190A2; CN102859307B; FR2959298A1; US20130115560A1; CA2797168A1; TR201809425T4; EP2561295B1; PL2561295T3; JP2013530366A; CN102859307A; CA2797168C; BR112012027190B1; ES2675910T3; RU2012149939A; EP2561295A1; FR2959298B1

Abstract

Fuel-fired furnace and a method for operating it, in which method: a main oxidizing agent is injected at a controlled flow rate into the combustion chamber (2) of the furnace; the combustible material is burnt in the combustion chamber (2) with the main oxidizing agent, producing thermal energy and flue gases (6) at a temperature higher than 600^oC; the flue gases (6) are removed via an exhaust duct (13), said removed flue gases (6) possibly containing residual materials that could be oxidized, the exhaust duct (13) being equipped with an inlet (14) for a diluting oxidizing agent downstream of the combustion chamber (2); the residual materials that could be oxidized are burnt with the diluting oxidizing agent by means of a flame (12) at the inlet (14) for the diluting oxidizing agent; the flame intensity inside the exhaust duct (12) is detected; and the flow rate at which the main oxidizing agent is injected into the combustion chamber (2) is controlled according to the detected flame intensity.

Description

The present invention relates to the regulation of combustion in flame furnaces.

Flame kilns are commonly used in industry for thermal energy generation and for high temperature processing of materials.

The term "flame oven" refers to an oven, such as a melting furnace or incinerator, wherein at least a portion of the thermal energy is produced in the furnace combustion chamber by combustion of a fuel with an oxidant present in the oxidant. Thus, the term "flame oven" also covers furnaces in which at least a portion of the thermal energy is produced by a combustion without a visible flame, often called "flameless combustion" (in English: "flameless combustion").

The fumes generated by the combustion, generally containing CO ₂ , CO and PH ₂ O, are removed from the combustion chamber of the flame furnace at a temperature above 600 ° C by an exhaust duct.

In theory, a maximum of thermal energy is generated by combustion when it is stoichiometric, that is to say when the oxidant is injected into the combustion zone in an amount corresponding to the amount of oxidant necessary for the total combustion of the fuel present in the combustion zone. In this case, the carbon present in the fuel is entirely oxidized to CO ₂ , the hydrogen generally present in the fuel is entirely oxidized to H ₂ O, etc. In industrial practice, however, it is found that a slight excess of oxidant is necessary to arrive at a total combustion of the fuel.

Inadequate injection of oxidant results in a decrease in furnace efficiency due to non-combustion or partial combustion of the fuel. Too much excess of oxidant also leads to a decrease in the efficiency of the furnace (for example: greater loss of thermal energy by the fumes discharged and, in the case of oxy-combustion, the evacuation with the fumes of the part of the furnace. oxygen has not participated in the combustion, oxygen having a non-negligible cost).

Among the other drawbacks of an excessively large flow rate of oxidant, it is possible in particular to point out a higher oxidation rate of the feedstock in the case of a oxidizable filler, as is the case in an oxidizable metal melting furnace, such as aluminum, and some reheating furnaces (in English "reheating furnace"). It is in particular known to operate flame furnaces under over- or under-stoichiometry, to avoid or limit harmful reduction or oxidation of the charge by the atmosphere in the combustion zone. Thus, for some applications, optimal combustion differs from stoichiometric combustion.

Optimized operation of a flame furnace is generally possible in flame furnaces in which fuel and oxidant inputs and compositions thereof are fully controlled.

However, in a large number of industrial applications of flame furnaces, the amount and / or composition of the combustible material available in the combustion zone are poorly or poorly controlled.

This is for example the case:

- in flame furnaces, the charge of which contains a variable quantity and / or quality of combustible materials, such as waste incinerators and secondary melting furnaces for the recycling of metals,

- in flame-melting furnaces in which the filler contains inherent and / or added fuels, and in which the filler releases uncontrolled fuels to the combustion zone generally above the filler, such as for example, secondary melting furnaces for the recycling of metals,

- In flame furnaces for post-combustion fumes from furnaces as described above, for example afterburner chambers of arc furnaces for the secondary melting of steel.

From JP-A-1314809 and JP-A-2001004116, it is known to equip an incinerator with a camera directed towards the interior of the combustion chamber and to regulate the afterburner inside the combustion chamber. above the main combustion according to the image obtained from the combustion inside the chamber.

From WO-A-2005/024398, it is known to measure the quantity of chemical species contained in a gas resulting from a metal treatment furnace, such as an electric arc furnace or a converter, by sampling of a portion of the gas to be analyzed, cooling it to less than 300 ° C and measuring the amount of CO and / or CO ₂ present in the gas using the coherent light signal emitted by a laser diode, said method allowing a measuring said quantities with a response time of less than 10 seconds and a control of the oven in real time.

WO-A-03/056044 discloses an aluminum smelting process in which solid aluminum is introduced into an oven, the aluminum is melted to form an aluminum bath, the variations in concentration of carbon monoxide (CO) and the temperature in the flue gases leaving the furnace, the formation of aluminum oxides on the surface of the aluminum bath is deduced and the melting process is regulated according to the formation of aluminum oxides.

The measurement of the concentration of certain species in the flue gas fumes, however, is made difficult by the nature and amounts of pollutants, such as soot, in said fumes.

WO-A-2004/083469 discloses an aluminum melting process in which the fuel / oxidant ratio injected by a burner into the flame furnace is regulated as a function of the temperature of the flue gases in the flue gas discharge duct. an air inlet called "dilution air".

In such a method, the dilution air flow rate can vary according to different parameters (size of the openings, speed of the extraction of fumes, state of the flue gas ducts, flow of the other flue gases collected by the same extractor) . This variable flow can have an influence on the temperature of the fumes in the exhaust duct and thus have an impact on the setting of the oven. Daily (day and night) and seasonal (summer and winter) variations in the dilution air temperature, which is usually ambient air, can also affect the flue gas temperature in the flue .

The present invention aims to provide a control of the combustion in a flame oven that does not have the disadvantages of known methods described above.

The present invention thus relates to a method of operating an improved flame oven. According to this method, an oxidant, called "main oxidant", is injected at a regulated flow rate into a combustion chamber of the flame oven. Combustible material is burned in the combustion chamber with the main oxidant thus injected, producing thermal energy and fumes having a temperature above 600 ° C. in the combustion chamber. The fumes thus produced are evacuated from the combustion chamber by an exhaust duct. This exhaust duct is provided with an inlet of an oxidant called "dilution oxidizer", typically, but not necessarily, ambient air, downstream of the combustion chamber, so that the oxidant dilution comes into contact with fumes at 600 ° C or more. When the fumes still contain oxidizable materials, that is to say when the combustion of combustible material in the combustion chamber is not complete, a flame is obtained at the inlet of the dilution oxidation agent. inside the exhaust duct. Indeed, the contact between the dilution oxidant and the oxidizable materials in the fumes at high temperature generate a self-combustion of said oxidizable materials, such as CO and / or H ₂ present in the fumes evacuated. According to the invention, the intensity of the flame is detected inside the evacuation pipe, and therefore downstream of the combustion chamber, and the main oxidant injection flow rate is regulated in the combustion chamber. depending on the flame intensity detected.

The combustible material may in particular be introduced into the combustion chamber in a controlled manner, for example by injecting a fuel jet into the combustion chamber by means of a lance or a burner. The combustible material may be present in the charge and thus be introduced into the combustion chamber with the charge. The combustible material may also be introduced into the combustion chamber by a combination of controlled introduction and introduction with the charge into the combustion chamber.

Advantageously, the main oxidant injection flow rate injected into the combustion chamber is reduced when the flame intensity thus detected is lower than a predetermined lower limit and the main oxidant flow rate injected into the combustion chamber is increased when the flame intensity thus detected is greater than a predetermined upper limit.

The presence of oxidizable materials, such as CO, in the fumes is thus detected by the intensity of their combustion with the dilution oxidant using a flame detector which returns a signal indicative of the intensity of the the combustion / flame inside the exhaust duct: (a) a strong intensity is indicative of a significant presence of oxidizable materials in the exhaust fumes, and (b) a low intensity is a sign of a low presence of oxidizable materials in the evacuated fumes.

The invention thus makes it possible to determine the level of the presence of oxidizable materials in the fumes and to apply in real time a correction to the control of the combustion in the combustion zone.

The predetermined lower and upper limits are set depending on the nature of the combustion process in the combustion chamber, as discussed above. When the combustion process aims at a complete combustion of the material fuel in the combustion chamber, the predetermined lower limit is very low, but greater than zero. In this way, it is ensured that the main oxidant injection rate is neither excessive nor too low for the combustion process in the combustion chamber.

The invention makes it possible in particular to compensate for imperfect knowledge of the fuel content of the furnace charge (a typical case for recycling furnaces), the quality of the combustible material and / or its release into the combustion chamber by real-time adaptation of the control of the main oxidant flow and, as explained below, possibly also the fuel flow injected into the combustion chamber.

Another advantage of the invention is that it can be achieved with an inexpensive and simple flame intensity detector implementation.

In some combustion processes, the content of oxidizable materials in the evacuated fumes may vary frequently, but often of short duration. According to one embodiment, the flame intensity inside the exhaust duct is detected for predetermined periods Δίΐ and At2. The main oxidant injection rate in the combustion chamber is reduced when the detected flame intensity has remained below the lower limit for the predetermined time Δίΐ. Similarly, the main oxidant injection rate in the combustion chamber is increased when the detected flame intensity has remained above the upper limit for the predetermined time Δί2. Thus, excessive fluctuations in the combustion process are avoided. Another possibility is (a) to reduce the main oxidant injection rate in the combustion chamber when the average value of the flame intensity detected during the predetermined time Δίΐ is lower than the lower limit, and (b) to increase the main oxidant injection rate in the combustion chamber when the average value of the flame intensity detected during the predetermined duration Δί2 is greater than the upper limit. In practice, the predetermined durations Δίΐ and Δί2 are typically identical.

According to one embodiment, the main oxidant and the combustible material are injected into the combustion chamber at controlled flow rates, the combustible material is burned with the main oxidant in the combustion chamber, producing thermal energy. and fumes at a temperature above 600 ° C in the combustion chamber, and exhaust fumes thus produced from the combustion chamber through a discharge conduit. As mentioned above, the exhaust fumes may contain residual oxidizable materials. The exhaust duct is provided with a diluent oxidizer inlet downstream of the combustion chamber. The residual oxidizable materials of the flue gases are burned with the dilution oxidant to obtain a flame inside the exhaust duct at the dilution oxidizer inlet. According to the invention, the flame intensity is detected inside the evacuation pipe and the main oxidant injection rate in the combustion zone is regulated as a function of the flame intensity detected.

It is also possible to regulate the main oxidant injection rate and the fuel injection rate in the combustion chamber as a function of the detected flame intensity.

Advantageously, the ratio between the main oxidant injection flow rate and the injection rate of combustible material in the combustion chamber is reduced when the flame intensity detected inside the exhaust duct is less than at a predetermined lower limit and the ratio of the main oxidant injection rate to the fuel injection rate in the combustion chamber is increased when the intensity of the detected flame is greater than a predetermined upper limit.

In particular, it is possible to (a) reduce the ratio of the main oxidant injection rate to the fuel injection rate in the combustion chamber when the detected flame intensity is below the lower limit during a period of time. predetermined duration Atl, and (b) increasing the ratio of the main oxidant injection rate to the fuel injection rate in the combustion chamber when the flame intensity detected inside the conduit discharge is greater than the upper limit for a predetermined time Δί2. It is also possible (a) to reduce the ratio between the main oxidant injection rate and the fuel injection rate in the combustion chamber when the average value of the flame intensity detected inside the conduit during the predetermined time Δίΐ is less than the lower limit, and (b) increasing the ratio of the main oxidant injection rate to the fuel injection rate in the combustion chamber when the average value of the flame intensity detected during the predetermined time Δί2 is greater than the upper limit.

The ratio of the main oxidant injection rate to the fuel injection rate in the combustion chamber can be modified by changing the main oxidant injection rate with respect to the material injection flow rate. predetermined fuel, or by changing (a) the main oxidant injection rate and (b) the fuel injection rate. It should be noted, however, that the injection rate of combustible material into the combustion chamber is often regulated according to the need for thermal energy in the combustion chamber.

According to one embodiment, the combustion chamber is equipped with at least one lance for injecting a regulated flow rate of main oxidant. The combustion chamber may also be equipped with at least one burner for the injection of a regulated flow rate of main oxidant and a regulated flow rate of combustible material. The combustion chamber may also comprise at least one such lance and at least one such burner.

The process may be a batch process, a semi-batch process or a continuous feed process.

The combustion chamber may be the combustion chamber of an arc furnace, a rotary kiln, a fixed melting furnace, a heating furnace, a boiler, an afterburner chamber. gaseous effluents, etc.

The process may be a melting or vitrification process, and in particular a secondary melting process for recovered metals, a method for burning solid, liquid or gaseous waste, a method for post-combustion of gaseous effluents, a method of reheating, such as reheating of metallurgical products, etc.

The dilution oxidant inlet is typically an ambient air inlet in the exhaust duct (in English: "air gap"), but may also be an oxidant injector, such as an air injector enriched with oxygen or oxygen.

The flame detector is advantageously an optical detector and in particular an optical detector chosen from ultraviolet detectors, infrared detectors and visible radiation detectors. The detector is preferably an infrared detector or an ultraviolet detector.

To avoid interference by combustion, called main combustion, which takes place inside the combustion chamber, the flame is detected inside the exhaust duct preferably in a place protected from combustion main.

To better separate the detection zone inside the exhaust duct of the main chamber, the exhaust duct may be provided with a bend. The flame detection is then preferably carried out downstream of this bend. The dilution oxidant inlet is advantageously immediately upstream, in or downstream of the elbow, so as to that the flame generated by the combustion of the oxidizable materials in the fumes with the diluting oxidant develops at least mainly downstream of the elbow.

When the furnace has a geometry preventing interference between the main combustion and the flame detector or if the furnace has elements forming a screen between the main combustion and the flame detector, such a bend is not necessary.

The present invention also relates to a flame oven adapted for carrying out the method described above.

Thus, the invention more particularly relates to a flame oven comprising a combustion chamber, means for the injection of main oxidant at a controlled flow rate into this combustion chamber and a conduit for the evacuation of fumes from said chamber of combustion. combustion. The exhaust duct has a diluent oxidizer inlet downstream of the combustion chamber. The flame oven of the invention also includes a detector for detecting a flame intensity within the exhaust conduit at the dilution oxygen inlet. The detector is positioned and oriented to prevent the main combustion from distorting the detected flame intensity.

The exhaust duct may in particular comprise a bend as mentioned above. As regards the process according to the invention, the flame detector is preferably positioned downstream of this bend. Advantageously, the dilution oxidant inlet is positioned immediately upstream, in or downstream of the elbow of the exhaust duct.

The oven advantageously comprises a control unit connected to the detector and the means for the main oxidant injection. This control unit is programmed:

to compare the flame intensity detected by the detector within the exhaust duct with a predetermined lower limit and a predetermined upper limit,

to reduce the main oxidant injection rate in the combustion chamber by the main oxidant injection means when the detected flame intensity is below the predetermined lower limit, and

to increase the main oxidant injection rate in the combustion chamber by the main oxidant injection means when the detected flame intensity is greater than a predetermined upper limit.

The control unit can more particularly be programmed:

to reduce the main oxidant injection rate in the combustion chamber when the detected flame intensity is lower than the lower limit for a predetermined period Δίΐ and / or when the average value of the flame intensity detected during a predetermined period Δίΐ is less than the lower limit during the predetermined period Δίΐ, and

- to increase the main oxidant injection rate in the combustion chamber when the intensity of the detected flame is greater than the upper limit for a predetermined period Δί2 and / or when the average value of the flame intensity detected during the predetermined period Δί2 is greater than the upper limit for a predetermined period Δί2.

The furnace according to the invention may also comprise means for injecting combustible material at a controlled rate into the combustion chamber.

In this case, the flame furnace preferably comprises a control unit linked (a) to the detector, (b) the means for injecting the main oxidant into the combustion chamber, and (c) the means for the injection of combustible material into the combustion chamber. This control unit is programmed (i) to compare the flame intensity detected by the detector within the exhaust duct with a predetermined lower limit and a predetermined upper limit, (ii) to reduce the ratio of the flow rate. of main oxidant injection and the injection rate of combustible material into the combustion chamber when the detected flame intensity is lower than the predetermined lower limit, and (iii) to increase the ratio between the injection rate of main oxidant and the rate of injection of combustible material into the combustion chamber when the detected flame intensity is greater than a predetermined upper limit.

According to a preferred embodiment, the control unit is more particularly programmed:

to reduce the ratio of the main oxidant injection rate to the fuel injection rate in the combustion chamber when the flame intensity detected inside the conduit discharge is below the lower limit for a predetermined period Δίΐ and / or when the average value of the flame intensity detected during the predetermined time Δίΐ is lower than the lower limit, and

- to increase the ratio between the main oxidant injection rate and the fuel injection rate in the combustion chamber when the detected flame intensity is greater than the upper limit for a predetermined period At2 and / or when the average value of the flame intensity detected during the predetermined duration At2 is greater than the upper limit.

In order to vary the ratio between the main oxidant injection flow rate and the fuel injection rate in the combustion chamber, the control unit will advantageously vary the main oxidant injection rate as a function of the injection rate of the combustible material. However, it is also possible for the control unit to vary the ratio between the main oxidant injection rate and the fuel injection rate by regulating the injection rate of the main oxidant and the flow rate. injecting the combustible material. In this case, the control unit may, for example, in the case of a flame intensity lower than the predetermined lower limit, reduce the ratio between the main oxidant injection flow rate and the injection rate of the combustible material by increasing the injection rate of combustible material at an unchanged main oxidant injection rate.

The main oxidant injection means of the furnace may include one or more lances for the main oxidant injection into the combustion chamber.

The furnace fuel injection means may comprise one or more lances for the injection of combustible material into the combustion chamber.

The oven may also include one or more burners for injecting combustible materials and main oxidant into the combustion chamber. Such a burner is therefore on the one hand, part of the means for the injection of the main oxidant and on the other hand, the means for injecting combustible material from the furnace.

The oven according to the invention may be an oven for a batch process, for a semi-batch process or for a continuous process.

The oven may especially be an arc furnace, a rotary kiln, a fixed melting furnace, a reheating furnace, such as a reheating furnace for metallurgical products, a boiler, a post-combustion chamber for gaseous effluents, etc. The furnace may be a melting or vitrification furnace, and in particular a secondary melting furnace for recovered metals, an incinerator for solid, liquid or gaseous waste, etc.

The dilution oxidant inlet is typically an ambient air inlet in the exhaust duct (in English: "air gap"), but may also be an oxidant injector, such as an air injector enriched with oxygen or an oxygen injector.

The flame detector is preferably an optical detector and in particular an optical detector selected from ultraviolet detectors, infrared detectors and visible radiation detectors.

The combustible material injected into the combustion chamber may be a gaseous, liquid or solid fuel (for example: natural gas, liquid fuel, propane, bio-fuel, pulverized coal) or a combination of several fuels. This combustible material may be injected in addition to combustible material introduced into the combustion chamber with the charge, which may be mixed with the charge before its introduction into the combustion chamber and / or may be an intrinsic part of the charge.

The main oxidant may be air, oxygen-enriched air, pure oxygen (having by definition an oxygen content of 88% to 100% vol) or a mixture of oxygen with recycled fumes . In the latter cases (air enriched with oxygen and in particular pure oxygen or oxygen mixture with recycled fumes), one benefits from a volume of fumes and a reduced fuel consumption.

The invention is particularly useful for flame furnaces used for secondary melting of metals. Second fusion refers to the melting of recycled or primary metallurgical materials (for example: cast iron from a blast furnace).

The metals considered are for example: cast iron, lead, aluminum, copper, or any other metal that can be melted in a flame oven.

The metal charge can also be loaded into the oven in mixture with combustible materials composed of a high proportion of carbon (plastic, coke, ...). These combustible materials may be present in the metallic filler (for example in the case of aluminum recycling) and / or intentionally added to the filler for the purpose of the melting process (for example in the case of the deoxidation reaction for recycling of lead). The present invention and its advantages appear more clearly in the illustrative example below, reference being made to Figure 1 which shows schematically a flame melting furnace according to the invention.

The oven is more particularly a rotary kiln for the secondary melting of lead with a combustion chamber 2 with a capacity of 15t.

The oven is equipped with a natural gas / oxygen burner 24 which generates the flame 11 in the combustion chamber 2. The burner power 24 and the oxygen / natural gas ratio are controlled by the automatic control of the furnace (control device 20). connected to the oxygen flow regulator 15 and the natural gas flow controller 17) as a function of the progress of the heating cycle, as described below.

The load 30 consists of lead waste from automobile battery crushing. A large part of this lead is in the form of a "paste" of oxide (PbO, Pb0 ₂ ...) and lead sulphate (PbS0 ₄ ...). To this metallic charge are added materials necessary for the reduction of oxides partly made of coke (having a high carbon content), also called "reagents".

The lead recycling process consists in heating the charge 30, and then keeping the hot charge in contact with the reagents to obtain liquid lead 4 and a slag which fixes the impurities and the sulfur present in the lead sulfate.

The oven is discontinuous. The combustion chamber 2 is charged at the beginning of each cycle. The burner 24 is then ignited and its power modulated by the control device 20 so that the temperature of the load follows a heating cycle which has been determined empirically.

During the heating step, a substantial portion of the carbon present in the solid feed reacts with the atmosphere of the rotary combustion chamber 2 consisting essentially of the hot smoke produced by the burner 24.

This reaction produces CO and PH ₂ by the following reaction between part of the smoke and part of the carbon of the feed, the mechanisms of which can be schematically presented as follows:

C0 ₂ + C -> 2.CO

H ₂ O + C -> H ₂ + CO.

To limit the formation of CO in the atmosphere of the chamber 2, it is possible to preset the burner 24 in order to inject an excess of oxygen into the chamber 2. However, the reaction rate of the carbon present in the solid charge With the furnace atmosphere varies according to the different parameters of the process, such as in particular the composition of the load, which varies according to the source of the batches to be recycled.

For a load of 15t, the power of the burner 24 will for example be set between 1 and 1.5 MW depending on the progress of the heating cycle. In the middle of the cycle, the burner is for example tuned for a power of 1.3 MW with the following flow rates:

- natural gas 130 Nm3 / h

- pure oxygen 270 Nm3 / h.

An analysis of the fumes 6 leaving Chamber 2 reveals the following composition:

- C0 ₂ : 56% / CO: 25% / H ₂ : 4% remains N ₂ .

The CO and the H ₂ of the fumes burn with dilution air in the flame 12 inside the chimney 13 which has a bend downstream and close to the chamber 2. The dilution air is ambient air entering the chimney 13 through the opening 14 provided for this purpose downstream of the elbow. This dilution air allows the combustion of CO ₂ in C0 ₂ and the cooling of the fumes before filtration (not shown) which precedes the evacuation of fumes. A level of CO too important in the fumes 6 has several disadvantages:

an incomplete combustion of the CO in the chimney 13, and thus a residual CO emission at the chimney 13,

a very significant increase in the temperature of the flue gases in the chimney 13 not allowing a passage of fumes in the downstream filter

(Not shown), hence the forced reduction of the power of the burner 24, or even the shutdown of the burner 24 on temperature safety, to allow filtration and compliance with environmental standards, and

- an overconsumption of fuel and therefore a reduction in energy efficiency in the furnace, because the reactions C0 ₂ + C -> 2.CO and H ₂ 0 + C ->

H ₂ + CO are endothermic.

The detection according to the invention by means of the UV detector 10 of the D-LX100 range marketed by the Durag company of the intensity of the combustion flame 12 of the CO + H ₂ mixture with the dilution air just after the exit 5 of the oven makes it possible to correct the setting of the burner 24 by acting on the "Oxygen / Natural Gas" ratio. For this purpose, the detector 10 transmits to the control device 20 a signal corresponding to the detected flame intensity. The elbow of the chimney 13 and the positioning of the detector UV10 with respect to said elbow ensures that the detector UV10 detects only the intensity of the flame 12 inside the chimney 13 without interfering with the UV radiation of the combustion inside. of the combustion chamber 2.

The invention allows, for example, the control device 20, especially when the intensity of this combustion in the chimney 13 exceeds an experimentally predetermined upper limit:

to increase, by means of the oxygen flow regulator 15, the flow of oxygen at 340 Nm3 / h and to keep the flow rate of natural gas unchanged at 130 Nm3 / h,

to reduce by means of the fuel flow regulator 17 the fuel flow rate to 95 Nm3 / h and to keep the oxygen flow rate unchanged at 270 Nm3 / h, and

to modulate the two flow rates by increasing the oxygen flow rate to 300 Nm3 / h by means of the regulator 15 and by decreasing the flow of natural gas to 110

Nm3 / h using the regulator 17.

In all three cases, the burner 24 injects an excess of 70 Nm 3 / h of oxygen, relative to the initial setting. This excess of oxygen is then available for the combustion inside the furnace 2 of the combustible materials released by the charge.

As soon as the rate of release of combustible material by the charge decreases, following the evolution of the cycle, the intensity of the combustion of CO and H ₂ in the chimney 13 decreases and the intensity of the flame 12 detected by the detector 10 therefore also decreases.

It is then possible to progressively reduce the oxygen and natural gas flow rates of the burner 24 to the predetermined initial or base flow rates and thus reduce the oxygen / natural gas ratio.

This adjustment of the oxygen / natural gas ratio is dynamic according to the intensity of the post combustion of the smoke in the chimney 13 (intensity of the flame 12 detected).

The energy efficiency of the furnace 2 is significantly improved and effective treatment of fumes, including their filtering, is ensured.

Claims

claims

1) A method of operating a flame oven comprising a combustion chamber (2),

process in which

a main oxidant is injected at a regulated flow rate into the combustion chamber (2),

- Combustible material is burned in the combustion chamber (2) with the main oxidant producing thermal energy and fumes (6) at a temperature above 600 ° C in the combustion chamber,

the fumes (6) thus produced are evacuated from the combustion chamber (2) via an evacuation pipe (13), said evacuated fumes (6) possibly containing residual oxidizable materials, the evacuation pipe (13) being provided with a diluent oxidizer inlet (14) downstream of the combustion chamber (2),

the residual oxidizable materials are burned with the dilution oxidant by means of a flame (12) inside the evacuation pipe (13) at the dilution oxidizer inlet (14),

the method being characterized in that:

the flame intensity of said flame is detected inside the evacuation duct (12),

the main oxidant injection flow rate in the combustion chamber (2) is regulated as a function of the flame intensity detected.

2) The process of claim 1, wherein:

reducing the main oxidant injection rate in the combustion chamber (2) when the detected flame intensity is below a predetermined lower limit and

the flow rate of main oxidant injected into the combustion chamber (2) is increased when the flame intensity thus detected is greater than a predetermined upper limit.

3) The process of claim 1, wherein:

the main oxidant injection flow rate in the combustion chamber (2) is reduced when the detected flame intensity is lower than the lower limit for a predetermined time Atl or when the average value of the flame intensity detected during the predetermined time Δίΐ is lower than the lower limit, and

the main oxidant injection flow rate in the combustion chamber (2) is increased when the detected flame intensity is greater than the upper limit for a predetermined duration Δί2 or when the average value of the detected flame intensity during the predetermined period Δί2 is greater than the upper limit.

4) A method of operating a flame oven comprising a combustion chamber (2),

process in which

a main oxidant and combustible material are injected at regulated flow rates into the combustion chamber (2),

- the combustible material is burned with the main oxidant in the combustion chamber (2) producing thermal energy and fumes (6) at a temperature above 600 ° C in the combustion chamber (2),

the flue gases (6) produced in this way from the combustion chamber (2) are evacuated via an evacuation pipe (13), said evacuated flue gases (6) possibly containing residual oxidizable materials, said evacuation duct (13) being provided with a diluent oxidizer inlet (14) downstream of the combustion chamber (2),

the residual oxidizable materials are burned with the dilution oxidant by means of a flame (12) at the dilution oxidizer inlet (14) in the discharge pipe (13),

the method being characterized in that:

the flame intensity is detected inside the evacuation duct (13),

the main oxidant injection flow rate, and optionally the injection rate of combustible material, is regulated in the combustion chamber (2) as a function of the detected flame intensity.

The process of claim 4 wherein:

the ratio of the main oxidant injection flow rate and the injection rate of combustible material in the combustion chamber (2) is reduced when the detected flame intensity is lower than a predetermined lower limit, and the ratio of the main oxidant injection flow rate and the injection rate of combustible material in the combustion chamber (2) is increased when the intensity of the detected flame is greater than a predetermined upper limit. The process of claim 5, wherein:

reducing the ratio between the main oxidizing injection flow rate and the fuel injection rate in the combustion chamber (2) when the detected flame intensity is lower than the lower limit for a predetermined time Atl or when the average value of the flame intensity detected during the predetermined time Δίΐ is lower than the lower limit, and

the ratio of the main oxidant injection flow rate and the fuel material injection flow rate in the combustion chamber (2) is increased when the detected flame intensity is greater than the upper limit for a predetermined duration Δί2 or when the average value of the flame intensity detected during the predetermined time Δί2 is greater than the upper limit.

7) Process according to any one of claims 5 and 6, wherein the fuel injection rate is varied in the combustion chamber (2) according to the need for thermal energy in the combustion chamber (2) .

Process according to any one of the preceding claims, wherein the flame intensity is determined by means of an optical detector, preferably by means of an optical detector selected from ultraviolet detectors, infrared detectors and detectors. of visible radiation.

9) Furnace with flame

a combustion chamber (2),

means (15, 24) for injecting main oxidant at a controlled rate into the combustion chamber (2), and

a duct (13) for evacuation of flue gases (6) from said combustion chamber (2), said duct (13) comprising a dilution oxidizer inlet (14) downstream of the combustion chamber (2) ,

the oven being characterized in that it also comprises: a detector (10) for detecting a flame intensity at the dilution oxygen inlet (14) within the exhaust duct (13); 10) a flame furnace according to claim 9, also comprising a control unit (20) connected to (a) the detector (10) and (b) the means for the main oxidant injection (15, 24), the control unit (20) being programmed:

to compare the flame intensity detected by the detector (10) with a predetermined lower limit and a predetermined upper limit,

- to reduce the main oxidant injection rate in the combustion chamber (2) by the main oxidant injection means (15, 24) when the detected flame intensity is lower than the predetermined lower limit, and

- To increase the main oxidant injection rate in the combustion chamber (2) by the main oxidant injection means (15, 24) when the detected flame intensity is greater than a predetermined upper limit.

Flame kiln according to claim 10, wherein the control unit (20) is programmed:

- to reduce the main oxidant injection rate in the combustion chamber (2) when the detected flame intensity is lower than the lower limit for a predetermined period Δίΐ or when the average value of the detected flame intensity during the predetermined time Δίΐ is less than the lower limit, and

- to increase the main oxidant injection rate in the combustion chamber (2) when the detected flame intensity is greater than the upper limit for a predetermined period Δί2 or when the average value of the detected flame intensity during the predetermined period Δί2 is greater than the upper limit.

12) A flame furnace according to claim 9, further comprising means (17, 24) for the injection of combustible material at a controlled rate into the combustion chamber (2). 13) A flame furnace according to claim 12, further comprising a control unit (20) connected (a) to the detector (10), (b) means for the main oxidant injection (15, 24) and (c) ) means for injecting combustible material (17, 24), the control unit (20) being programmed:

to reduce the ratio between the main oxidant injection flow rate and the fuel injection rate in the combustion chamber (2) when the detected flame intensity is lower than the predetermined lower limit, and

- to increase the ratio between the main oxidant injection rate and the fuel injection rate in the combustion chamber (2) when the detected flame intensity is greater than a predetermined upper limit.

The flame furnace according to claim 13, wherein the control unit (20) is programmed:

- to reduce the ratio between the main oxidant injection flow rate and the fuel injection rate in the combustion chamber (2) when the detected flame intensity is lower than the lower limit for a predetermined period Δίΐ or when the average value of the flame intensity detected during the predetermined time Δίΐ is lower than the lower limit, and

to increase the ratio between the main oxidant injection rate and the fuel injection rate in the combustion chamber (2) when the intensity of the detected flame is greater than the upper limit for a predetermined period Δί2 or when the average value of the flame intensity detected during the predetermined duration Δί2 is greater than the upper limit.

15) A furnace according to any one of claims 9 to 14 wherein the flame detector (10) is selected from optical detectors, preferably ultraviolet detectors, infrared detectors and visible radiation detectors.