EP2475948B1 - Method for characterizing the combustion in lines of partitions of a furnace having rotary firing chamber(s) - Google Patents

Description

The invention relates to the field of so-called "rotating fire" chamber furnaces for the firing of carbonaceous blocks, more particularly carbon anodes and cathodes intended for the electrolytic production of aluminum. and the invention more particularly relates to a method for characterizing combustion in partition lines of such a chamber furnace.

Fire burners (x) turning to bake anodes are described in particular in the following patent documents: US 4,859,175 , WO 91/19147 , US 6,339,729 , US 6,436,335 and CA 2550880 , which will be referred to for more details about them. However, their structure and functioning are partially recalled, with reference to figures 1 and 2 hereinafter, respectively showing a schematic plan view of the structure of a furnace (x) rotating (s) and open chambers, two lights in this example, for the figure 1 , and a partial perspective view and cutaway cross section showing the internal structure of such an oven, for the figure 2 .

The baking oven (FAC) 1 comprises two parallel casings or bays 1a and 1b, extending along the longitudinal axis XX along the length of the oven 1 and each comprising (e) a succession of transverse chambers 2 (perpendicular to the axis XX), separated from each other by transverse walls 3. Each chamber 2 is constituted, in its length, that is to say in the transverse direction of the furnace 1, by the juxtaposition, alternately, of 4 cells, open at their upper part, to allow the loading of the carbonaceous blocks to be cooked and the unloading of the cooled cooked blocks, and in which are stacked the carbonaceous blocks 5 to be embedded in a carbonaceous dust, and hollow-walled hollow heating partitions 6, generally kept spaced apart by transverse spacers 6a. The hollow partitions 6 of a chamber 2 are in the longitudinal extension (parallel to the major axis XX of the furnace 1) of the hollow partitions 6 of the other chambers 2 of the same span 1a or 1b, and the hollow partitions 6 are in communication with each other through skylights 7 at the upper part of their longitudinal walls, facing longitudinal passages formed at this level in the transverse walls 3, so that the hollow partitions 6 form rows of longitudinal partitions, arranged parallel to the XX axis of the furnace and in which will circulate gaseous fluids (combustion air, combustible gases and gases and combustion fumes) for preheating and cooking the anodes 5, and then cooling. The hollow partitions 6 further include baffles 8, to elongate and distribute more uniformly the path of the combustion gases or fumes, and these hollow partitions 6 are provided at their upper part with openings 9, called "openings", closable by removable covers and arranged in an oven crown block 1.

The two bays 1a and 1b of the furnace 1 are placed in communication at their longitudinal ends by turning flues 10, which make it possible to transfer the gaseous fluids from one end of each line of hollow partitions 6 of a span 1a or 1b at the end of the line of corresponding hollow partitions 6 on the other bay 1b or 1a, so as to form substantially rectangular loops of hollow partition lines 6.

The principle of operation of rotating fire furnaces (x), also called "fire advance (x)" furnaces, consists in causing a flame front to move from one chamber 2 to another which is adjacent during a cycle, each chamber 2 undergoing successively stages of preheating, forced heating, fire, then cooling (natural then forced).

1. A) Une zone de préchauffage comportant, en se reportant au feu de la travée 1a, et en tenant compte du sens de rotation des feux indiqué par la flèche au niveau du carneau de virage 10 à l'extrémité du four 1 en haut sur la figure 1 :
   • une rampe d'aspiration 11 équipée, pour chaque cloison creuse 6 de la chambre 2 au-dessus de laquelle cette rampe d'aspiration s'étend, d'un système de mesure et de réglage du débit des gaz et fumées de combustion par ligne de cloisons creuses 6, ce système pouvant comprendre, dans chaque pipe d'aspiration 11 a qui est solidaire de la rampe d'aspiration 11 et débouchant dans cette dernière, d'une part, et, d'autre part, engagée dans l'ouverture 9 de l'une respectivement des cloisons creuses 6 de cette chambre 2, un volet d'obturation réglable pivoté par un actionneur de volet, pour le réglage du débit, ainsi qu'un débitmètre 12, légèrement en amont, dans la pipe 11a correspondante, d'un capteur de température (thermocouple) 13 de mesure de la température des fumées de combustion à l'aspiration, et
   • une rampe de mesure de préchauffage 15, sensiblement parallèle à la rampe d'aspiration 11 en amont de cette dernière, généralement, au-dessus de la même chambre 2, et équipée de capteurs de température (thermocouples) et de capteurs de pression pour préparer la dépression statique et la température régnant dans chacune des cloisons creuses 6 de cette chambre 2 afin de pouvoir afficher et régler cette dépression et cette température de la zone de préchauffage;
2. B) Une zone de chauffage comportant :
   • plusieurs rampes de chauffage identiques 16, deux ou, de préférence, trois, comme représenté sur la figure 1 ; chacune équipée de brûleurs ou d'injecteurs de combustible (liquide ou gazeux) et de capteurs de température (thermocouples), chacune des rampes 16 s'étendant au-dessus de l'une des chambres respectivement d'un nombre correspondant de chambres 2 adjacentes, de sorte que les injecteurs de chaque rampe de chauffage 16 sont engagés dans les ouvertures 9 des cloisons creuses 6 pour y injecter le combustible ;
3. C) Une zone de soufflage ou de refroidissement naturel comportant :
   • une rampe dite de « point zéro » 17, s'étendant au-dessus de la chambre 2 immédiatement en amont de celle en dessous de la rampe de chauffage 16 la plus en amont, et équipée de capteurs de pression pour mesurer la pression régnant dans chacune des cloisons creuses 6 de cette chambre 2, afin de pouvoir régler cette pression comme indiqué ci-après, et
   • une rampe de soufflage 18, équipée de moto ventilateurs munis d'un dispositif permettant le réglage du débit d'air ambiant insufflé dans chacune des cloisons creuses 6 d'une chambre 2 en amont de celle située sous la rampe de point zéro 17, de sorte que les débits d'air ambiant insufflés dans ces cloisons creuses 6 peuvent être régulées de sorte à obtenir une pression voulue (légère surpression ou légère dépression) au niveau de la rampe de point zéro 17 ;
4. D) Une zone de refroidissement forcé, qui s'étend sur trois chambres 2 en amont de la rampe de soufflage 18, et qui comporte, dans cet exemple, deux rampes de refroidissement 19 parallèles, chacune équipée de moto ventilateurs et de pipes de soufflage insufflant de l'air ambiant dans les cloisons creuses 6 de la chambre 2 correspondante ; et
5. E) Une zone de travail, s'étendant en amont des rampes de refroidissement 19 et permettant l'enfournement et le détournement des anodes 5, et l'entretien des chambres 2.

The cooking of the anodes 5 is carried out by one or more fires or groups of fires (two groups of fires being represented on the figure 1 in a position in which one extends, in this example, on thirteen chambers 2 of span 1a and the other on thirteen chambers 2 of span 1b) which move cyclically from chamber 2 to chamber 2 Each light or group of lights is composed of five successive zones A to E, which are, as shown on the figure 1 for the fire of the span 1b, and downstream upstream with respect to the flow direction of the gaseous fluids in the hollow partition lines 6, and in the opposite direction to the cyclic displacements from chamber to chamber:

1. A) A preheating zone comprising, referring to the light of the span 1a, and taking into account the direction of rotation of the lights indicated by the arrow at the turning flue 10 at the end of the furnace 1 at the top of the figure 1 :
   • a suction ramp 11 equipped, for each hollow partition 6 of the chamber 2 above which this suction ramp extends, a system for measuring and regulating the flow of gases and combustion fumes by line of hollow partitions 6, this system may comprise, in each suction pipe 11 a which is integral with the suction ramp 11 and opening into the latter, on the one hand, and, on the other hand, engaged in the opening 9 of one respectively of the hollow partitions 6 of this chamber 2, an adjustable shutter pivoted by a shutter actuator, for adjusting the flow, and a flowmeter 12, slightly upstream, in the pipe 11a corresponding, of a temperature sensor (thermocouple) 13 for measuring the temperature of the exhaust combustion fumes, and
   • a preheating measurement ramp 15, substantially parallel to the suction ramp 11 upstream of the latter, generally above the same chamber 2, and equipped with temperature sensors (thermocouples) and pressure sensors for preparing the static depression and the temperature prevailing in each of the hollow partitions 6 of this chamber 2 in order to be able to display and adjust this depression and this temperature of the preheating zone;
2. B) A heating zone comprising:
   • several identical heating ramps 16, two or, preferably, three, as shown in FIG. figure 1 ; each equipped with burners or fuel injectors (liquid or gaseous) and temperature sensors (thermocouples), each of the ramps 16 extending above one of the chambers respectively of a corresponding number of adjacent chambers 2 , so that the injectors of each heating ramp 16 are engaged in the openings 9 of the hollow partitions 6 to inject the fuel therein;
3. C) A natural blowing or cooling zone comprising:
   • a ramp called "zero point" 17, extending above the chamber 2 immediately upstream of that below the heating ramp 16 the most upstream, and equipped with pressure sensors to measure the pressure prevailing in each of the hollow partitions 6 of this chamber 2, in order to adjust this pressure as indicated below, and
   • a blowing ramp 18, equipped with motorcycle fans provided with a device for adjusting the flow rate of ambient air blown into each of the hollow partitions 6 of a chamber 2 upstream of that located under the zero point ramp 17, of so that the ambient air flows insufflated in these hollow partitions 6 can be regulated so as to obtain a desired pressure (slight overpressure or slight depression) at the zero point ramp 17;
4. D) A forced cooling zone, which extends over three chambers 2 upstream of the blast ramp 18, and which comprises, in this example, two parallel cooling ramps 19, each equipped with motor fans and blow pipes injecting ambient air into the hollow partitions 6 of the corresponding chamber 2; and
5. E) A working zone, extending upstream of the cooling ramps 19 and allowing the charging and diversion of the anodes 5, and the maintenance of the rooms 2.

The heating of the oven 1 is thus provided by the heating ramps 16, the injectors of the burners are introduced through the openings 9 in the hollow walls 6 of the chambers 2 concerned. Upstream of the heating ramps 16 (with respect to the direction of fire and the flow direction of the air and combustion gases and fumes in the hollow partition lines 6), the blowing ramp 18 and the the cooling ramp (s) 19 comprise combustion air insufflation pipes supplied by motorcycle fans, these pipes being connected, via the openings 9, to the hollow partitions 6 of the chambers 2 concerned. Downstream of the heating ramps 16, the suction ramp 11 is available to extract the combustion gases and fumes, referred to collectively as "combustion fumes", which circulate in hollow partition lines 6.

The heating and cooking of the anodes 5 are ensured both by the combustion of the fuel (gaseous or liquid) injected, in a controlled manner, by the heating ramps 16, and, to a substantially equal extent, by the combustion of volatile materials. (such as polycyclic aromatic hydrocarbons) pitch diffused by the anodes 5 in the cells 4 of the chambers 2 in preheating and heating zones, these volatile materials, largely combustible, diffused into the cells 4 can flow in both adjacent hollow partitions 6 by passages formed in these partitions, to ignite in these two partitions, thanks to the residual combustion air present at this level, among the combustion fumes in these hollow partitions 6.

Thus, the flow of air and combustion fumes takes place along the lines of hollow partitions 6, and a negative pressure, imposed downstream of the heating zone B by the suction ramp 11 at the downstream end. of the preheating zone A, makes it possible to control the flow rate of the combustion fumes inside the hollow partitions 6, whereas the air coming from the cooling zones C and D, thanks to the cooling ramps 19 and especially to the ramp 18, is preheated in the hollow partitions 6, cooling the anodes 5 cooked in the adjacent cells 4, during its journey and serves as an oxidizer when it reaches the heating zone B.

As the firing of the anodes 5 occurs, cyclically (e.g. every 24 hours or so) of a chamber 2, all of the ramps 11 to 19 are advanced and the measuring equipment and equipment associated register, each chamber 2 thus ensuring, successively, upstream of the zone of preheating A, a loading function of the green carbonaceous blocks 5, then, in the preheating zone A, a natural preheating function by the fuel combustion fumes and pitch vapors leaving the cells 4 by penetrating into the hollow partitions 6, taking into account the depression in the hollow partitions 6 of the chambers 2 in the preheating zone A, then, in the heating zone B or cooking zone, a heating function of the blocks 5 at about 1100 ° C., and finally, in the cooling zones C and D, a cooling function of the blocks baked by the ambient air and, correspondingly, of preheating this air constituting the oxidizer of the oven 1, the forced cooling zone D being followed, in the opposite direction in the direction of advancement of the fire and flue gas circulation, a zone E of unloading cooled carbonaceous blocks 5, then possibly loading green carbonaceous blocks in the cells 4.

The control method of the FAC 1 essentially comprises the temperature and / or pressure regulation of the preheating zones A, heating B and natural blowing or cooling C of the oven 1 according to predefined setpoint laws.

The combustion fumes extracted from the fires by the suction ramps 11 are collected in a flue gas duct 20, for example a cylindrical duct partially shown on the figure 2 , with a smoke flue 21 that can have a U-shaped shape (see dotted line on the figure 1 ) or which can circumnavigate the furnace, and whose outlet 22 directs the combustion fumes sucked and collected to a smoke treatment center (CTF) not shown because not forming part of the invention.

In order to give the anodes (carbon blocks) their optimal characteristics, and therefore mainly to guarantee the obtaining of a final cooking temperature, the current conduct of ovens of this type favors the fuel supply (liquid or gaseous fuel) of the heating ramps 16 regardless of draft depression conditions and aeraulic conditions in the partitions 6, where it This can result in incomplete combustion in a significant number, even high, of the partition lines 6. This, in turn, results in high operating costs of the furnace, not only because of the overconsumption of fuel, but also Because of the clogging of ducts and suction ducts that lead to the capture by unburnt deposits, deposits which also represent a potential risk of ignition and drift of the cooking process.

The problem underlying the invention is, in general, to improve the continuous optimization of the operation of such ovens, in order to reduce operating costs and prevent the risk of fire and drift of the cooking process, and for this purpose, the invention proposes a method or a method for characterizing the combustion in the partition lines of a chamber furnace called "fire (s) turning (s)" for the firing carbon blocks, by analyzing the value of at least one image parameter of the overall content of unburned in the combustion gases and residual air from said partition lines and collected in a suction ramp of said oven, said furnace comprising a succession of preheating chambers, heating, natural cooling and forced cooling, arranged in series along the longitudinal axis of the furnace, each chamber being formed by the juxtaposition, transversely to said longitudinal axis; nal and alternately, cells in which are arranged carbon blocks to cook and hollow heating partitions, in communication and aligned with the partitions of the other rooms, parallel to the longitudinal axis of the furnace, in lines of partitions in which circulate cooling and combustion air and combustion gases, said suction ramp being connected to each of the partitions the first chamber preheating by one respectively of suction pipes, the necessary combustion air being partially injected by a blowing ramp of the natural cooling zone, connected to at least one fan, and partly infiltrated by depression through the partition lines, and the fuel required for cooking the carbonaceous blocks being partially injected by at least two heating ramps each extending over one respectively of at least two adjacent chambers of the heating zone and capable of injecting each of the fuel into each of the partitions of the corresponding respective chamber of the heating zone, the regulation of the combustion of the furnace essentially comprising a temperature and / or pressure regulation of the zones of preheating, heating and natural cooling , per line of partitions, according to predefined temperature and / or pressure setpoint laws, and said method of characterization of the combustion is characterized in that it comprises at least one step of successive tests for total fuel injection stoppage, line of partitions per line of partitions, of a duration sufficient for the measurement of said image parameter of the overall content of unburned in the combustion gases stabilizes, and without controlling action on the walls of lines other than that in total injection stop test during the duration of this test, the characterization of the combustion being based on the calculation of the variation between the measurements of said image parameter taken before and after the total injection stoppage in each of the lines of partitions tested, in order to identify one or more partition lines in an incomplete combustion situation, if said variation is greater than x% of the value of said image parameter at the beginning of said total injection stop test, x% being preferably of the order of 5% to 10%, the value of x depending on t the number of partitions per chamber, detection threshold values and the measurement accuracy of at least one detector of said image parameter.

Thus, by a total fuel injection stop test in a line of partitions only for a time sufficient to stabilize the measurement of the image parameter, and without changing anything on the other lines of partitions, it is possible, thanks to the method of the invention, identify a line of partitions operating in an incomplete combustion situation, on which later measurements of combustion optimization can be taken.

In order to limit the number of injection stop tests and to enable the system to identify more quickly the partition (s) in an incomplete combustion situation, the method according to the invention further comprises at least one previous step, so-called preselection of the partition lines likely to be in an incomplete combustion situation, and making it possible to limit the number of injection stop tests, in said step of successive tests of total fuel injection stoppage, to only lines of preselected partitions, and consisting in calculating, for each line of partitions of rank n, a combustion ratio, equal to the ratio of the quantity of combustion air available to the quantity of fuel injected into said line of partitions of rank n , to define empirically a so-called stoichiometric limit ratio from measurements of said image parameter of the unburned content in the combustion gases collected at the output of a line of standard partitions, representative of the best state of the oven partition lines, and so that this stoichiometric ratio corresponds to a measured threshold of said image parameter below which the combustion is considered incomplete, to compare the combustion ratio of all the lines of partitions with a stoichiometric ratio, and to consider as incomplete the combustion in any line of partitions of rank n for which the corresponding ratio of combustion is lower than the stoichiometric ratio.

Thus, the identification of the partition lines in an incomplete combustion situation, thanks to the total injection stop test, is advantageously preceded by a pre-selection of the partition lines likely to be in this incomplete combustion situation, thanks to the calculations, on the one hand, of the combustion ratio for each of the oven partition lines, and, on the other hand, of said stoichiometric ratio, empirically defined from measurements of the image parameter in a standard partition line, chosen as being representative of the best state of the partition lines and finally by comparing each combustion ratio with the stoichiometric ratio, to deduce which (s) is or are the line or lines of combustion, in which or which combustion may be considered incomplete.

In an advantageous embodiment of the combustion characterization method according to the present application, in said step of preselecting the incomplete combustion partition lines, it is possible to calculate the combustion ratio (RCcn) in a line of partition walls. row n being proportional to the square root of the static draw depression measured in the preheating zone for said line of partitions considered, and inversely proportional to the sum of the fuel injection power of the injectors of the heating ramps operating on the same line of partitions of rank n.

où P₁ et P₇ sont les pressions mesurées dans les cloisons de rang n des chambres en communication respectivement avec la rampe d'aspiration et la rampe dite de « point zéro » dans la zone de refroidissement naturel, N est le nombre de rampes de chauffage, en général égal à 2 ou 3, et InjHRi est la puissance d'injection totale dans la cloison de rang n des injecteurs de la rampe de chauffage de rang i, où i varie de 1 à N.In particular, during this preselection step, the combustion ratio of the row of partitions of rank n can be easily calculated by applying the following formula: $${\mathrm{RC}}_{\mathrm{cln}}=10x\sqrt{\left|P_1-P_7\right|}x\left(\frac{\mathrm{NOT}}{{\displaystyle \underset{i=1}{\overset{\mathrm{NOT}}{\Sigma }}}\mathit{InjHRi}}\right)$$

where P ₁ and P ₇ are the pressures measured in the n-row partitions of the chambers in communication with the suction ramp and the so-called "zero point" ramp respectively in the natural cooling zone, N is the number of ramps of heating, generally equal to 2 or 3, and InjHRi is the total injection power in the row n partition of the injectors of the heating ramp of rank i, where i varies from 1 to N.

Advantageously, moreover, in the characterization method according to the present application, the step of preselecting the incomplete combustion partition lines may also comprise a step consisting in classifying the incomplete combustion partition lines in the order of that where the combustion is the most incomplete to the one where the combustion is least incomplete, by applying a system of notation of the partition lines according to which any line of partitions of rank n is assigned a classification note NC _cln given by the following formula : $${\mathrm{NC}}_{\mathrm{cln}}=20-10\left(\frac{{\mathit{RC}}_{\mathrm{vs}\ln }}{\mathit{RS}}\right)\mathrm{.}$$

In addition, in order to quickly obtain an easy-to-use preselection information, it is possible to perform the step of classifying the partition lines by advantageously considering that, for a line of walls of rank n in good condition, the combustion is complete. if NC _cln <10, the combustion is incomplete if 10 <NC _cln <12, and the combustion is very incomplete, and therefore critical, if NC _cln > 12.

To ensure an implementation of this method of characterization which is advantageous in terms of the simplicity of the detection means and the processing of the signals provided by these means, the overall content of the unburned content in the combustion gases is chosen as an image parameter. , the carbon monoxide (CO) content, which is measured, to determine said stoichiometric ratio, in the suction pipe of said suction ramp which is connected to the partition wall of the standard partition line in the first chamber of preheating, said threshold of this image parameter which corresponds to the stoichiometric ratio being about 500 ppm CO measured at said suction pipe, which corresponds, under the standard operating conditions of this type of oven, to a level of 1000 ppm of CO at the point of combustion.

Thus, since a carbon monoxide detector can already be present in such furnaces of the state of the art, in the manifolds of the suction manifold, the process of the invention can be carried out without it is necessary to implement a specific detection and / or measurement apparatus, but only by using measurement data already available, because provided by sensors of a detection instrumentation already installed on such furnaces, the implementation the method of the invention being carried out only through a software module that can simply and easily be integrated into the current programs for driving such ovens.

Furthermore, the method according to the present application can be completed by the fact that after the characterization steps for identifying and selecting the partition lines in incomplete combustion, it is possible to implement at least one subsequent step called combustion optimization.

Advantageously, such an optimization of the combustion can consist in automatically modifying control parameters in the zones of preheating, heating and / or natural cooling of the oven, in order to balance the stoichiometric ratio RS combustion air on fuel, in order to recover a complete combustion situation, which can be defined simply by passing the value of said image parameter under a parameterizable threshold.

But, whether this optimization step is carried out as specified in the preceding paragraph, or in any other way, the method of the present application can be advantageously such that, following said optimization step, at least one complementary step of characterization of the combustion as defined above, in the lines of non-preselected partitions, as also indicated above, among the partition lines assumed to be incomplete combustion, is activated if at least one step of optimizing the combustion as mentioned above did not recover a complete combustion situation.

• les figures 1 et 2, déjà décrites ci-dessus, sont respectivement une vue schématisée en plan de la structure d'un four à deux feux tournants et chambres ouvertes, et une vue partielle en perspective et coupe transversale avec arrachement représentant la structure interne d'un tel four,
• la figure 3 est un graphique double représentant l'évolution, d'une part, du CO mesuré (en ppm) et, d'autre part, du pourcentage d'oxygène résiduel dans les fumées collectées à la pipe d'aspiration d'une même ligne de cloisons, en fonction de la puissance d'injection totale, dans la ligne de cloisons, exprimée en pourcentage de la puissance maximum installée, selon trois valeurs différentes de la dépression statique de tirage mesurées au niveau de la rampe de mesure de préchauffage associée à la première chambre de préchauffage du four ;

• la figure 4 est une courbe de caractérisation de la combustion dans une ligne de cloisons de rang n, indiquant la teneur en CO mesurée (en ppm) par ligne de cloisons en fonction du rapport de combustion RC_cln ;
• la figure 5 est un diagramme représentant, en abscisse, la notation de la combustion dans une ligne de cloisons de rang n par la note NC_cln, résultant de la mise en oeuvre du système de classification de la combustion selon la présente demande, alors que la teneur en CO mesurée (en ppm) par ligne de cloisons dans la pipe d'aspiration correspondante est représentée en ordonnées, et
• la figure 6 est un diagramme correspondant à un exemple de test d'arrêt total d'injection de combustible successivement dans trois lignes de cloisons α, β, et γ, et représentant, en ordonnées, la valeur de la teneur en CO globale mesurée (en ppm) dans la rampe d'aspiration en fonction du temps (exprimé en minute), et faisant apparaitre, pour la première ligne de cloisons α testée, une réduction de la teneur en CO globale mesurée, due au test, supérieure à un seuil indicatif d'un état de combustion incomplète dans cette ligne de cloisons α.

Other features and advantages of the invention will emerge from the description given below, without limitation, with reference to the accompanying drawings in which:

• the figures 1 and 2 , already described above, are respectively a schematic plan view of the structure of a furnace with two rotating lights and open chambers, and a partial perspective view and cutaway cross-section showing the internal structure of such an oven,
• the figure 3 is a double graph showing the evolution, on the one hand, of the measured CO (in ppm) and, on the other hand, the percentage of residual oxygen in the fumes collected at the suction pipe of the same line of partitions, according to the total injection power, in the partition line, expressed as a percentage of the maximum installed power, according to three values different from the static draft depression measured at the preheating measurement ramp associated with the first preheating chamber of the oven;

• the figure 4 is a combustion characterization curve in a n-row partition line, indicating the measured CO content (in ppm) per partition line as a function of the combustion ratio RC _cln ;
• the figure 5 is a diagram showing, on the abscissa, the notation of the combustion in a line of partitions of rank n by the note NC _cln , resulting from the implementation of the classification system of the combustion according to the present application, while the content of Measured CO (in ppm) per line of partitions in the corresponding suction pipe is plotted on the ordinate, and
• the figure 6 is a diagram corresponding to an example of a total fuel injection stop test successively in three rows of partitions α, β, and γ, and representing, on the ordinate, the value of the total measured CO content (in ppm) in the suction ramp as a function of time (expressed in minutes), and showing, for the first line of partitions tested α, a reduction in the overall measured CO content, due to the test, above a threshold indicative of an incomplete combustion state in this line of partitions α.

The method of the invention relates to a combustion characterization loop in the partition lines 6 of the furnace 1 by analysis of the total content of carbon monoxide (CO), or any other image parameter of the unburned content, in the fumes collected at the suction ramp 11 of a furnace fire 1, where this total CO content is measured by the CO-analyzer-detector 14 in the manifold of the suction ramp 11 (see figure 2 ), and the method of characterizing the combustion in the partition lines 6 comprises a first step of estimating the quality of combustion in each of the rows of partitions 6 and preselection of partition lines estimated in incomplete combustion state, then classifying the partition lines using a rating system, for selecting partition lines considered to be incomplete combustion, and defined according to the ratio of the combustion air to the fuel available in each line of partitions 6 and a ratio stoichiometric RS empirically defined by measurements in a line of standard partitions 6, representative of the best state of the walls of the walls of the furnace.

This first step of the combustion characterization method makes it possible to preselect lines of partitions 6 which are estimated to be incomplete combustion if their so-called combustion ratio RC, which is the ratio of the combustion air to the fuel available for each line of partitions. 6 considered, is lower than the stoichiometric ratio RS presented above.

This step of preselecting the partition lines estimated in incomplete combustion is immediately followed by a step of selecting the rows of partitions 6 considered incomplete combustion by classification, according to a rating system of the combustion quality in the partition lines which is based, as already said, on the principle of the stoichiometry of the ratio of the amount of combustion air to the amount of fuel available in each line of partitions.

Indeed, the maximum amount of fuel that can be injected at a given moment in a line of partitions 6 depends on the air flow in this line of partitions, or the level of static depression measured in this line partitions at the same time. Below the stoichiometric ratio, the combustion is incomplete, and some of the fuels present in the line of partitions no longer burn completely, giving rise to the formation of carbon monoxide (CO).

This threshold phenomenon is better perceived by the consideration of figure 3 , representing, by 3 continuous curves, the CO content measured in ppm by a CO analyzer 14 in the suction pipe 11a (see figure 2 ) of a line of partitions considered, as a function of the quantity of fuel injected, expressed as total injection power in the said line of partitions considered, and evaluated as a percentage of the maximum installed power, the three continuous curves of measurements of CO each being established for one respectively of three different static pulling depressions in the partition line considered and respectively corresponding to three phantom curves indicative of the percentage of residual oxygen in the flue gases collected in the suction pipe of 11a of the suction ramp 11 considered, these three different static depressions being measured by the preheating ramp 15, at the first chamber 2 preheating.

Thus, the curves 23, 24 and 25 of the CO content measured (in ppm) at said suction pipe 11a by varying the total injection power from 10% to about 30% of the maximum installed power, with static vacuum draw respectively of -140 Pa, - 120 Pa and -70 Pa respectively correspond to the curves in phantom 26, 27 and 28 indicating the corresponding variation (in continuous reduction) of the percentage of residual oxygen, as indicated on the y axis of the right of the figure 3 , respectively for the same drawdown depressions.

Note that, for a total injection power in a line of partitions 6 between 10% and 15% of the maximum installed power, the curves of CO measured 23, 24 and 25 to the suction pipe 11a of the said line of partitions 6 are little different from each other, and indicate low levels of CO (substantially less than 500 ppm), corresponding to a combustion considered complete, while for values of the total injection power greater than 15% of the maximum installed power, the three CO 23, 24 and 25 measuring curves diverge from one another with slopes that are initially increasing and then substantially constant, but as important as the draft depression is small in absolute value. Moreover, for a total injection power per line of partitions greater than about 25% of the maximum installed power, the three measurement curves of CO 23, 24 and 25 give results greater than 1000 ppm, which corresponds to a combustion even more incomplete as the draft depression is low in absolute value. Simultaneously, the curves 26, 27 and 28 indicating the variation of the percentage of residual oxygen are decreasing with a negative slope substantially constant and little different from one curve to another.

On the basis of this observation, for each row of partitions 6 of rank n, a combustion ratio RC _{cln is defined} which gives the ratio of the quantity of fuel injected in said line of partitions of rank n to the quantity of air oxidant available in this same line of partitions of rank n. The amount of combustion air available in the line of partitions of rank n corresponds to the air flow in this line of partitions of rank n, which can be estimated by the calculation of the square root of the static draft depression in this line. of partitions of rank n, measured in the preheating zone A by the preheating measurement ramp 15 (see figure 1 ).

The quantity of fuel injected into the same line of partitions of rank n can be directly obtained by summing the powers of the injectors that operate on the same line of partitions.

où P1 et P7 sont les pressions mesurées dans la ligne de cloisons de rang n au niveau des chambres 2 en communication respectivement avec la rampe d'aspiration 11 pour P1, dans la zone de préchauffage A, et avec la rampe de « point 0 » 17 dans la zone de refroidissement naturel C, et où N est le nombre de rampes de chauffage 16, en général égal à 2 ou 3, et InjHRi est la somme des puissances d'injection des injecteurs de la rampe de chauffage 16 de rang i où i varie de 1 à N (2 ou 3) dans la ligne de cloison de rang n. On note de plus que chaque rampe de chauffage 16 comporte généralement deux injecteurs par cloison 6 de la même chambre 2 correspondante, de sorte que si N = 3, comme dans l'exemple de la figure 1 (avec trois rampes de chauffage 16), une ligne de cloisons de rang n est alimentée en combustible par six injecteurs. Ainsi, le rapport de combustion RCcln dans une ligne de cloisons de rang n est proportionnel à la racine carrée de la dépression statique de tirage mesurée dans la zone de préchauffage A pour cette ligne de cloisons 6 considérée et inversement proportionnel à la somme des puissances d'injection de combustible des injecteurs des rampes de chauffage 16 opérant sur cette même ligne de cloisons 6 de rang n.Thus, the formula (1) expressing the ratio or combustion ratio of this row of partitions of rank n, namely RCcln, may be the following: $${\mathrm{RC}}_{\mathrm{cln}}=10x\sqrt{\left|P_1-P_7\right|}x\left(\frac{\mathrm{NOT}}{{\displaystyle \underset{i=1}{\overset{\mathrm{NOT}}{\Sigma }}}\mathit{InjHRi}}\right);$$

where P1 and P7 are the pressures measured in the line of partitions of rank n at the chambers 2 in communication respectively with the suction ramp 11 for P1, in the preheating zone A, and with the "point 0" ramp 17 in the natural cooling zone C, and where N is the number of heating ramps 16, generally equal at 2 or 3, and InjHRi is the sum of the injection power of the injectors of the heating ramp 16 of rank i where i varies from 1 to N (2 or 3) in the partition line of rank n. It is further noted that each heating ramp 16 generally comprises two injectors per partition 6 of the same chamber 2 corresponding, so that if N = 3, as in the example of the figure 1 (With three heating ramps 16), a line of partitions n rank is fueled by six injectors. Thus, the combustion ratio RCc1n in a line of partitions of rank n is proportional to the square root of the static draft depression measured in the preheating zone A for this line of partitions 6 considered and inversely proportional to the sum of the powers of the injecting fuel injector heating ramps 16 operating on the same line of partitions 6 of rank n.

The figure 4 represents, for this line of partitions 6 of rank n, a shaded and curved zone 29, which corresponds to the envelope of the different measurement points of the CO measured in ppm to the corresponding suction pipe 11 a as a function of the variation of the corresponding combustion ratio RCcln. The threshold value of RC below which the combustion is estimated to be incomplete, that is to say the value of said stoichiometric ratio RS, is defined empirically by observation of the value of CO in a line of partitions representative of the best state oven partitions.

Above a value of 1000 ppm undiluted CO, which corresponds approximately to a value of 500 ppm measured at the CO detector 14 in the suction pipe 11a ( figure 2 ) given the dilution in kiln 1, combustion is considered incomplete.

On the figure 4 , the incomplete combustion threshold is therefore indicated at 500 ppm measured CO, which corresponds to a value of the stoichiometric ratio RS of about 6, at the intersection of the shaded area 29 of the envelope of the measuring points of the CO measured and the incomplete combustion threshold of 500 ppm.

Thus, a pre-selection of the rows of partitions 6 likely to be in an incomplete combustion situation, is further specified that the CO content, chosen in this embodiment as an image parameter of the overall content of unburned in the combustion gases , is measured, to determine the stoichiometric ratio RS, in that of the suction pipes 11a of the suction ramp 11 which is connected to that of the partitions 6 which is at the intersection of the line of standard partitions and the first chamber 2 of preheating, the threshold of the CO content corresponding to the stoichiometric ratio RS being about 500 ppm CO measured at this suction pipe 11a, which corresponds, under standard operating conditions of this type of oven 1, at a level of 1000 ppm CO at the point of combustion.

From calculation of the combustion ratio RCc1n, it is also deduced, at least for the rows of partitions 6 estimated in incomplete combustion by comparison of their combustion ratio RCc1 with the stoichiometric ratio RS, but preferably for all the rows of partitions 6 of the furnace 1, a note for classifying the partition lines in descending order from the one with the most incomplete combustion to the one with the least incomplete combustion, or even the most complete if all the partition lines are noted, for example by a system of notation from 0 to 20, defined such that beyond the value 10, the stoichiometric limit is exceeded and combustion is considered incomplete in the corresponding line of partitions.

où RCcln et RS sont les rapports précédemment définis, à savoir respectivement le rapport de combustion dans la cloison de rang n et le rapport stoechiométrique.By way of example, a classification of the pre-selected partition lines as being in incomplete combustion in the manner described above, consists in classifying these partition lines in the order from that in which combustion is most incomplete to that in which combustion is the less incomplete by applying the system of scoring partition lines according to which is assigned to any line of partitions 6 of rank n a classification note NCcln given by the following formula (2): $${\mathrm{NC}}_{\mathrm{cln}}=20-10\left(\frac{{\mathit{RC}}_{\mathrm{vs}\ln }}{\mathit{RS}}\right),$$

where RCc1 and RS are the previously defined ratios, namely respectively the combustion ratio in the n-rank partition and the stoichiometric ratio.

The partition lines having been rated from 0 to 20, depending on their ratio RCcnl / RS, it is considered that if the combustion rating NCcln is less than 10, the combustion is complete, whereas if this combustion note NCcln is between 10 and 12, the combustion is incomplete, this combustion is even very incomplete, and therefore critical, if the note NCcln is greater than 12.

The result of such a notation is represented, for example, on the figure 5 , on which the notes NCc1n are indicated by round dots on a continuous curve which crosses three hatched rectangular zones, one of which extends between 0 and 10 on the abscissa and between 0 and the incomplete combustion threshold of 500 measured ppm of CO, for complete combustion partition lines, of which a second zone 31 extends on the abscissa between the notes 10 and 12 and on the ordinate between the values of 500 and 1000 ppm of CO measured, for one or more lines (s) partitions in incomplete combustion, and finally whose third zone 32 extends for grades greater than 12 on the abscissa and a measured CO greater than 1000 ppm on the ordinate, for any line of partitions in combustion very incomplete and therefore critical .

By such a notation, the lines of closions considered in incomplete combustion are thus selected as having a grade greater than 10, which are then each subjected to a step of identification of the incomplete combustion partition lines, using a complete fuel injection stop test for a specified period and in succession on the fuel lines selected partitions, starting with the one with the highest rating and performing the test successively on the partition lines whose burn scores are in descending order.

The figure 6 schematically represents the unfolding of the fuel injection total stop test successively on three rows of partitions of rank α, β and γ, whose NC combustion ratings are progressively decreasing. On the figure 6 , the ordinate shows the total CO content measured in ppm in the collector of the suction manifold 11 by the CO detector 14 (see FIG. figure 2 ), and, on the x-axis, the time in minutes has been indicated. Curve 33 represents the evolution over time of the total CO content measured in the manifold of the suction ramp 11. At time t1, the row of partitions 6 of rank α is controlled by the total stopping of the supply of fuel to the injectors of the heating ramps 16 operating on this line of partitions α, by an almost instantaneous break, starting from from an initial value (for the total stop test) of fuel injection rate to a zero flow rate, which corresponds to the left side with downward arrow of the rectangle "α", symbolizing the fuel supply control fuel injectors of this line of partitions α during this total injection stop test. The injection is stopped for a time interval t1 t2 sufficient for the measurement of the CO content to stabilize before the time t2 of the end of the total injection cutoff. The curve 33 of the CO content shows a drop to a stabilized value of, for example, 500 ppm during the interval t1 t2, so that it is possible to measure the value ΔCO corresponding to the difference between the initial value at time t1 and the final value at time t2 of the CO content due to this interruption of supply. Then, at time t2, the fuel supply of this line of partitions α is restored to its initial value, as symbolized on the right side of the rectangle "α" of the figure 6 , by the rising arrow. Then a time interval t2 t3 elapses, of a duration slightly greater than or substantially equal to the interval t1 t2, itself of the order of 2 minutes, to start at time t3, the same test total stop of fuel injection on the line of partitions of rank β, knowing that, during the execution of a test of total stop on a line of particular partitions, no modification is controlled on the course of the cooking process in all the other lines of partitions. The duration of the second test, on the line of partitions β, corresponding to the interval t3 t4, is the same as the duration t1 t2, and the curve 33 of the CO content, which is returned, after the end of the test on the line of partitions α, at a normal level, marks, as a result of the test on the line of partitions β, a limited decrease in the CO content measured following the total injection stop in the line of partitions β during the interval t3 t4. It is the same for the third total injection stop test, conducted on the line of partitions γ during the time interval t5 t6, of the same duration of about 2 min as the durations of the other tests t1 t2 and t3 t4, so that each time the measurement of the CO content during each test can stabilize after this fuel injection cut, and that it can again stabilize following the end of the shutdown of the fuel supply, during the interval of time separating two successive tests.

For each test, the resulting CO reduction, ΔCO, is compared to a percentage X of the initial value of the CO content at the beginning of this test, COi, and, as is the case for the line of partitions α, if ΔCO is greater than X% of COi, the line of partitions α is identified as being in incomplete combustion, which is not the case of the partition lines β and γ, if we consider the curve 33 of the figure 6 .

The total fuel injection stop test is therefore conducted, line of partitions per line of partitions, on the partition lines previously selected by their NC combustion rating. It is essential that no action be commanded on the lines of partitions 6 other than the one in total injection stop test, during the complete duration of this test, so as not to disturb the characterization of the combustion. This characterization indeed depends on the calculation of the variation of the measured CO content between the initial moment of the test and the final moment, while noting that the measurements of CO content always remain global. The sudden downward inflection then the rise of curve 33 on the figure 6 therefore reflect the impact of the total fuel injection shutdown in the line of partitions α on the CO content in the collector of the intake manifold 11, which therefore takes into account the flue gases extracted from all the walls of the oven walls.

With regard to the X% threshold of the value of the COi content at the beginning of each total injection stop test, this value of X depends in particular on the number of partitions 6 per chamber 2 of the oven, as well as the accuracy of measurement and detection threshold values of the CO detector 14, in particular. In general, X% is selected in a range of 5% to 10%. Typically, for an oven 1 to 9 partitions 6 per chamber 2, the characterization system implementing the method of the invention must be able to detect at least one partition of rank n among 9 partitions 6 where the combustion tends to become incomplete. If it is considered that the flows flowing in each line of partitions, and therefore in each partition, are equivalent, the decrease in the CO content following the stopping of the injection of fuel into the partition of rank n will be at least equal to ΔCOn = 500 ppm / 9 = 56 ppm, due to the dilution, ie approximately X = 10% of the CO content measured at the manifold of the suction ramp 11, where this content is equal to less than 500 ppm.

After having thus selected the partition lines considered in incomplete combustion, using the stoichiometric ratio RS, RC combustion ratios of the partition lines, the comparison of the combustion ratios with the stoichiometric ratio, and the assignment of notes. of combustion NC to the partition lines, then after the identification of incomplete combustion partition lines by the total fuel injection stop test, at least one subsequent step, called combustion optimization, can be carried out implemented.

Such a step may consist in modifying, preferably automatically, control parameters in at least one of the natural cooling zones C, heating B and preheating A, in order, as far as possible, to balance the combustion ratios on the stoichiometric ratio of combustion air on fuel, to recover a complete combustion situation in as large a number as possible of the partition lines, this transition to a complete combustion situation that can be defined by the passage of the measured value of the CO content, or by passing the value of at least one other image parameter of the overall unburned content in the combustion gases, below a parameterizable threshold.

But, if the combustion optimization step (s), as presented in a general way above, did not or did not make it possible to recover a complete combustion situation for all the partition lines. of the furnace 1, then the method according to the present application proposes at least one additional stage of characterization of the combustion, which is carried out by applying the total injection stop test to those of the partition lines which do not have have been preselected, according to the demand method, from the partition lines assumed to be incomplete combustion, simply because their RC combustion ratio has been calculated lower than the stoichiometric RS ratio. In addition, this additional characterization step makes it possible to identify partitions whose stoichiometric conditions are satisfactory, having an NC combustion rating of less than 10, in the example of the notation system previously described, but whose physical conditions generate problems. of combustion, because partitions are deformed, pinched or plugged more or less completely.

Claims (10)

1. Method for characterizing the combustion in lines of partitions of a chamber-type ring furnace for baking carbon blocks (5), by analyzing the value of at least one parameter indicative of the total content of unburnt material in the combustion gases and residual air issuing from said lines of partitions (6) and collected in an exhaust manifold (11) of said furnace (1), said furnace (1) comprising a succession of chambers (2) for preheating, heating, natural cooling, and forced cooling, arranged serially along the longitudinal axis (XX) of the furnace (1), each chamber (2) consisting of pits (4) in which are arranged the carbon blocks (5) to be baked, adjacent to and alternating with, transversely to said longitudinal axis (XX), hollow heating partitions (6), in communication with and aligned with the partitions (6) of other chambers (2), parallel to the longitudinal axis (XX) of the furnace (1), in lines of partitions (6) in which circulate cooling and combustion air and combustion gases, said exhaust manifold (11) being connected to each of the partitions (6) of the first preheating chamber (2) by one of respective exhaust pipes (11 a), the necessary combustion air being partially injected by a blowing ramp (18) of the natural cooling zone (C), connected to at least one fan, and partially infiltrating through the lines of partitions (6) due to the negative pressure, and the fuel necessary for baking the carbon blocks (5) being partially injected by at least two burner (B) ramps (16) each respectively extending over one of at least two adjacent chambers (2) of the heating zone, and each able to inject fuel into each of the partitions (6) of the corresponding chamber (2) of the heating zone (B), the regulation of the furnace (1) combustion essentially comprising a regulation of the temperature and/or pressure of the preheating (A), heating (B), and natural cooling (C) zones, per line of partitions (6), as a function of predefined temperature and/or pressure setpoint rules, said method for characterizing the combustion being characterized in that it comprises at least one step of successive tests of totally stopping the fuel injection, one line of partitions (6) after another , for a sufficient period to allow the measurement of said parameter indicative of the total content of unburnt material in the combustion gases to stabilize, and without ordering any action in the lines of partitions (6) other than for the one concerned by the totally stopped injection test for the duration of this test, the characterization of the combustion being based on calculating the variation between the measurements of said indicative parameter made before and after totally stopping injection in each of the tested lines of partitions (6), in order to identify one or more lines of partitions (6) in a situation of incomplete combustion, if said variation is greater than x% of the value of said indicative parameter at the start of said totally stopped injection test, x% being preferably between about 5% to 10%, the value of x depending in particular on the number of partitions (6) per chamber (2), the detection threshold values, and the accuracy of the measurement of said indicative parameter by at least one detector.
2. Method according to claim 1, characterized in that it additionally comprises at least one prior step, called the step of preselecting the lines of partitions (6) likely to be in a situation of incomplete combustion, which allows limiting the number of stopped injection tests, in said step of successive totally stopped fuel injection tests, to only the preselected lines of partitions (6), and consisting of: calculating, for each line of partitions (6) of row n, a combustion ratio (RC_cln) which is equal to the ratio of the amount of combustion air available to the amount of fuel injected into said line of partitions (6) of row n; empirically defining a limit ratio called the stoichiometric ratio (RS) based on measurements of said parameter indicative of the content of unburnt material in the combustion gases collected at the outlet from a benchmark line of partitions (6), representative of the best state of the lines of partitions (6) of the furnace, and such that this stoichiometric ratio (RS) corresponds to a measured threshold for said indicative parameter below which the combustion is considered to be incomplete; comparing the combustion ratio (RC_cln) of all the lines of partitions (6) to the stoichiometric ratio (RS); and considering the combustion as incomplete in any line of partitions (6) of row n for which the corresponding combustion ratio (RC_cln) is less than the stoichiometric ratio (RS).
3. Method according to claim 2, characterized in that, in said step of preselecting the lines of partitions (6) in a state of incomplete combustion, the combustion ratio (RC_cln) in a line of partitions (6) of row n is calculated as being proportional to the square root of the static negative suction pressure measured in the preheating zone (A) for said line of partitions (6), and inversely proportional to the sum of the fuel injection capacities from the injectors of the burner ramps (16) operating on the same line of partitions (6) of row n.
4. Method according to claim 3, characterized in that, during said preselection step, the combustion ratio for the line of partitions (6) of row n is calculated by applying the following formula: $${\mathrm{RC}}_{\mathrm{cln}}=10x\sqrt{\left|P_1-P_7\right|}x\left(\frac{N}{{\displaystyle \sum _{i=1}^N}\mathit{InjHRi}}\right),$$

   

   
   where P₁ and P₇ are the pressures measured in the partitions (6) of row n of the chambers (2) respectively in communication with the exhaust manifold (11) and a "zero point" ramp (17) in the natural cooling zone (C), N is the number of burner ramps (16), generally equal to 2 or 3, and InjHRi is the total injection capacity in the partition of row n for the injectors of the burner ramp (16) of row i, where i varies from 1 to N.
5. Method according to any one of claims 2 to 4, characterized in that said step of preselecting the lines of partitions (6) in a state of incomplete combustion also comprises a step which consists of classifying the lines of partitions (6) in a state of incomplete combustion, ordered from the one in which combustion is the most incomplete to the one in which combustion is the least incomplete, by applying a scoring system to the lines of partitions (6) in which each line of partitions (6) of row n is assigned a classification score NC_cln given by the following formula: $${\mathrm{NC}}_{\mathrm{cln}}=20-10\left(\frac{{\mathit{RC}}_{c\ln }}{\mathit{RS}}\right)\mathrm{.}$$

   
6. Method according to claim 5, characterized in that the step of classifying the lines of partitions (6) is carried out by considering that, for a line of partitions (6) of row n in a good state, the combustion is complete if NC_cln<10, the combustion is incomplete if 10<NC_cln<12, and the combustion is very incomplete and therefore critical if NC_cln> 12.
7. Method according to any one of claims 1 to 6, characterized in that the carbon monoxide (CO) content is chosen as the parameter indicative of the total content of unburnt material in the combustion gases, said CO content being measured, for determining said stoichiometric ratio, in the exhaust pipe (11 a) of said exhaust manifold (11) which is connected to the partition (6) of the benchmark line of partitions (6) in the first preheating chamber (2), said threshold for this indicative parameter to which the stoichiometric ratio (RS) corresponds being approximately 500 ppm of CO measured in said exhaust pipe (11 a), which corresponds, in the standard operating conditions for this type of furnace, to a level of 1000 ppm of CO at the point of combustion.
8. Method according to any one of claims 1 to 7, characterized in that, after the characterization steps which allow identifying and selecting the lines of partitions (6) in a state of incomplete combustion, at least one later combustion optimization step is applied.
9. Method according to claim 8, characterized in that the combustion optimization consists of automatically modifying regulation parameters in the preheating (A), heating (B), and/or natural cooling (C) zones of the furnace (1), in order to balance the stoichiometric ratio (RS) of combustion air to fuel, for the purpose of restoring a situation of complete combustion, defined as the value of said indicative parameter falling below a configurable threshold.
10. Method according to either of claims 8 or 9, characterized in that, after said optimization step, at least one additional step of characterizing the combustion according to claim 1, in the lines of partitions (6) not pre-selected according to claim 2 from among the lines of partitions (6) thought to be in a state of incomplete combustion, is activated if the combustion optimization step according to claim 8 or 9 did not restore a situation of complete combustion.

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