AU2009224502A1

AU2009224502A1 - Method for detecting an at least partially clogged partition in a chamber oven

Info

Publication number: AU2009224502A1
Application number: AU2009224502A
Authority: AU
Inventors: Pierre Mahieu; Andre Pinoncely
Original assignee: Solios Carbone SA
Current assignee: Solios Carbone SA
Priority date: 2008-02-29
Filing date: 2009-02-19
Publication date: 2009-09-17
Anticipated expiration: 2029-02-19
Also published as: CA2716761A1; CN102007359B; AU2009224502B2; WO2009112734A9; WO2009112734A2; FR2928206A1; FR2928206B1; ZA201005877B; EP2257753A2; CN102007359A; RU2010139874A; WO2009112734A3; EP2257753B1

Description

PCT/FR2009/050269 METHOD FOR DETECTING AN AT LEAST PARTIALLY CLOGGED PARTITION IN A CHAMBER OVEN 5 This invention relates to the field of what are called multiple-chamber "ring" furnaces, for the baking of carbon blocks and more particularly of carbon anodes and cathodes intended for the production of aluminum by electrolysis. The invention more particularly relates to a method for detecting an at least partially clogged partition in a multiple-chamber furnace. 10 Ring furnaces for baking 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 may be referred to for further information. Their structure and operation will be partially reviewed here, however, with reference to figures 1, 2 and 3 below. Figure 1 represents a schematic view of the structure of a ring furnace with open chambers, with two fires in this 15 example, while figure 2 shows a partial perspective and transverse cross-sectional view with a cutaway section representing the internal structure of such a furnace, and figure 3 shows a longitudinal cross-sectional view of a conventional hollow partition of such a furnace. The furnace 1 comprises two parallel casings or bays la and Ib, extending the length of 20 the furnace along a longitudinal axis XX and each comprising a succession of transverse chambers 2 (perpendicular to the axis XX), separated from each other by transverse walls 3. The length of each chamber 2, meaning in the transverse direction of the furnace 1, is constituted of alternating hollow heating partitions 6 with thin walls, generally braced by transverse spacers 6a, and pits 4 open in their upper part to allowing loading the green carbon blocks to be baked and 25 unloading the cooled baked blocks, and in which are stacked the green carbon blocks 5 packed in carbon powder. The hollow partitions 6 of one 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 in the same bay 1 a or 1 b, and these hollow partitions 6 communicate with one another by means of ports 7 in the upper part of their longitudinal walls, which face longitudinal passages arranged 30 in the transverse walls 3, such that the hollow partitions 6 form lines of longitudinal partitions PCT/FR2009/050269 2 parallel to the major axis XX of the furnace and within which gases will circulate (combustion air, combustible gases, and combustion gases and fumes) to ensure the anodes 5 are preheated and baked, then cooled. The hollow partitions 6 additionally comprise baffles 8, to prolong and more uniformly distribute the path of the combustion gases or fumes, and said hollow partitions 5 6 also have, in their upper part, openings 9 called peepholes which can be sealed off with removable covers, arranged in a crowning block 9a of the furnace 1. The two bays la and lb of the furnace 1 are in communication at their longitudinal ends by crossover flues 10, which transfer gases from one end of each row of hollow partitions 6 of a 10 bay la or lb to the end of the corresponding row of hollow partitions 6 in the other bay lb or la, forming substantially rectangular loops of rows of hollow partitions 6. The operating principle of ring furnaces, which could also be called fire-advance furnaces, consists of advancing a flame front from one chamber 2 to an adjacent one during a 15 cycle, each chamber 2 successively undergoing the stages of preheating, forced heating, full fire, then cooling (natural then forced). The anodes 5 are baked by one or more fires or fire groups (two fire groups are represented in figure 1, in a position in which one extends across thirteen chambers 2 of bay la 20 and the other across thirteen chambers 2 of bay Ib) which cyclically advance from chamber 2 to chamber 2. Each fire or fire group is composed of five successive zones A to E, which are, as is represented in figure 1 for the fire for bay I b, from downstream to upstream relative to the direction the gases flow in the rows of hollow partitions 6, and in the opposite direction to the cyclical advancement from chamber to chamber: 25 A) A preheating zone comprising, if one refers to the fire in bay I a and considers the direction the fires rotate as indicated by the arrow next to the crossover flue 10 at the end of the furnace at the top of figure 1: - an exhaust manifold 11 equipped, for each hollow partition 6 of the chamber 2 above which this exhaust manifold extends, a system for measuring and adjusting the flow 30 rate of the combustion gases and fumes per row of hollow partitions 6, said system PCT/FR2009/050269 3 being able to comprise, in each suction pipe 1 la which has one end secured to the exhaust manifold I1 and emptying into it while the other end is engaged in the opening 9 of one of the respective hollow partitions 6 of this chamber 2, an adjustable sealing flap pivoted by a flap actuator, for adjusting the flow rate, as well as a 5 flowmeter 12, slightly upstream in the corresponding pipe 1 la, a temperature sensor (thermocouple) 13 for measuring the temperature of the combustion gases being suctioned, a preheating line 15, substantially parallel to the exhaust manifold 11 above the same chamber 2, and equipped with temperature sensors (thermocouples) and pressure sensors; 10 B) A heating zone comprising: - several identical heating lines 16, two or preferably three as represented in figure 1; each equipped with buyers and fuel injectors (liquid or gas fuel) and temperature sensors (thermocouples), each of the lines 16 extending above one of the respective chambers of a corresponding number of adjacent chambers 2, such that the injectors 15 of each heating line 16 are engaged in the openings 9 of the hollow partitions 6 in order to inject the fuel; C) A blowing or natural cooling zone comprising: - a line referred to as the "zero point" line 17, extending above the chamber 2 immediately upstream from the one under the heating line 16 furthest upstream, and 20 equipped with pressure sensors for measuring the pressure prevailing in each of the hollow partitions 6 of this chamber 2, in order to be able to adjust this pressure as indicated below, and - a blowing line 18, equipped with electric fans that have a means for adjusting the flow rate of ambient air blown into each of the hollow partitions 6 of a chamber 2 25 upstream from the one situated under the zero point line 17, such that the flow rates for the ambient air blown into these hollow partitions 6 can be regulated to obtain a desired pressure (slightly negative or slightly positive pressure) at the zero point line 17; D) a forced cooling zone, which extends across three chambers 2 upstream from the 30 blowing line 18, and which in this example comprises two parallel cooling lines 19, each PCT/FR2009/050269 4 equipped with electric fans and pipes blowing ambient air into the hollow partitions 6 of the corresponding chamber 2; and E) a work area, extending upstream from the cooling lines 19 and allowing the packing and unpacking of anodes 6, as well as chamber 2 maintenance. 5 The furnace 1 is heated by the heating lines 16, whose burner injectors are introduced, via the openings 9, into the hollow partitions 6 of the chambers 2 concerned. Upstream from the heating ramps 16 (relative to the direction of the fire advancement and to the direction the air and combustion gases and fumes circulate in the rows of hollow partitions 6), the blowing line 18 10 and the cooling line or lines 19 comprise pipes that blow combustion air supplied by the electric fans, these pipes being connected, via the openings 9, to the hollow partitions 6 of the chambers 2 concerned. Downstream from the heating lines 16 is the exhaust manifold 11 for extracting the combustion gases and fumes, designated in general below by the term "combustion gases", which circulate in the rows of hollow partitions 6. 15 The heating and baking of the anodes 5 occurs both by the combustion of fuel (gas or liquid) which is injected in a controlled manner by the heating lines 16, and to a substantially equal measure by the combustion of volatile matter (such as polycyclic aromatic hydrocarbons) from the pitch released by the anodes 5 in the pits 4 of the chambers 2 in the preheating and 20 heating zones, as said volatile matter that is released in the pits 4, which is mostly combustible, is able to flow into the two adjacent hollow partitions 6 through passages arranged in these partitions, and can burn in these two partitions because of the residual combustion air present in the combustion gases in these hollow partitions 6. 25 Thus, the circulation of air and combustion gases occurs along the rows of hollow partitions 6, and a negative pressure, imposed downstream from the heating zone B by the exhaust manifold 11 at the downstream end of the preheating zone A, allows controlling the flow rate of the combustion gases within the hollow partitions 6, while the air from the cooling zones C and D, because of the cooling lines 19 and especially the blowing line 18, is preheated in the PCT/FR2009/050269 5 hollow enclosures 6 as it cools the baked anodes 5 in the adjacent pits 4 along its path and serves as a combustion agent when it reaches the heating zone B. As the anodes 5 bake, the set of lines and manifold 11 to 19 and the associated equipment 5 and devices for measurement and recording are advanced cyclically (for example every 24 hours or so) by one chamber 2. Each chamber 2 is thus successively used, upstream from the preheating zone A, for the function of loading green carbon blocks 5, then, in the preheating zone A, for the natural preheating function by the combustion gases resulting from the combustion of the fuel and pitch vapors, which leave the pits 4 and penetrate the hollow 10 partitions 6, because of the negative pressure in the hollow partitions 6 of the chambers 2 in the preheating zone A, then, in the heating or baking zone B, for the function of baking the blocks 5 at about I 100"C, and lastly, in the cooling zones C and D, for the function of cooling the baked blocks 5 with ambient air and correspondingly preheating this air which constitutes the combustion agent for the furnace 1, the forced cooling zone D being followed, in the direction 15 opposite the direction of the fire advancement and the circulation of combustion gases, by a zone E for unloading cooled carbon blocks 5, then possibly loading green carbon blocks into the pits 4. The furnace 1 regulation process essentially comprises regulating the temperature and/or 20 pressure of the preheating A, heating B, and blowing or natural cooling C zones of the furnace 1, as well as the steps of monitoring and adjusting the combustion by adjusting the fuel injection by the heating lines 16, as well as the amount of air necessary, or even the continual optimization of these parameters, for example based on the CO content or the opacity of the combustion gases, as measured in the exhaust manifold 11 (see figure 2). 25 To ensure the operation and monitoring of the furnace 1, the furnace control system can comprise two levels. The first can extend to all the lines and manifold 11 to 19, which are equipped with sensors and actuators controlled by programmable logic controllers (PLC), as well as a local shop network for communication between the PLCs and for exchanging data between 30 the first and the second level. The second level comprises a central system of computers with PCTIFR2009/050269 6 their peripheral equipment for communicating with the first level, monitoring all the fires, centrally regulating the furnace 1, entering set point rules, managing baking data histories, event handling, and storing and printing out reports at baking completion. 5 Each fire is regulated per row of hollow partitions 6 from the blowing line 18 to the exhaust manifold 11, and for each row of hollow partitions 6, the regulation is done for example by a PID (Proportional-Integral-Derivative) controller. The combustion gases extracted from the fires by the exhaust manifolds 11 are collected in an exhaust duct 20, for example a cylindrical duct partially represented in figure 2, with an 10 exhaust flue 21 which can have a U shape in a plan view (see dotted lines in figure 1) or can extend around the furnace, with an outlet 22 directing the suctioned and collected combustion gases towards a fume treatment center (FTC) which is not represented as it is not a part of the invention. 15 The invention concerns a method for detecting an at least partial clogging of a hollow partition such as 6. The clogging of at least one partition 6 or a major obstruction of the gas flow in one or more partitions 6 of a row of partitions can occur primarily in the following situations: - the infiltration, from a pit 4 to an adjacent partition 6, and subsequent deposit in this partition 6 of carbon powder in which the anodes 6 are packed in said pit 4, 20 - one or more broken spacers 6a in a partition 6, which interfere with the flow of gases passing through this partition 6, - a partition wall 6 that is deformed and/or compressed due to the effect of successive thermal gradients, or - a combination of several of the above situations. 25 The risks related to an at least partial clogging of a partition 6 are significant to the extent that, when not detected, the temperature regulation system continues to inject fuel into the partitions 6 of the heating zone B although there is not enough combustion air because of the clogging. This situation can result in explosions. 30 PCT/FR2009/050269 7 An at least partial clogging of a partition 6 can also be harmful to the baking quality of the anodes 5 present not only in a pit 4 adjacent to the clogged partition 6, but also in the pits 4 upstream and downstream but included in the fire, due to poor circulation of gases and therefore a degraded heat exchange between the gases and the partition or partitions 6. 5 The flow rate in a partition 6 is monitored either by measuring the negative static pressure in the lower portion of a peephole 9 and/or in the corresponding suction pipe 1 la of the exhaust manifold 11, or by a flow rate measurement, for example by means of a Venturi tube, Pitot tube, diaphragm, cone, etc. placed in the suction pipe I1 a of the exhaust manifold 1 1. The 10 negative static pressure measurement is representative of the flow rate when the flow is stable. In a situation where there is an at least partial clogging of a partition 6, the flow rate of the gases tends to decrease but the negative static pressure increases, reversing the natural correlation of these two variables. 15 Measurement of the flow rate, using a flowmeter 12 in the corresponding suction pipe 1 la, allows quantifying the flow of gases coming from each partition 6. In a situation where there is an at least partial clogging of a partition 6, there is a significant amount of air infiltration due to the increase in the negative static pressure, said infiltration originating in particular from the top of the furnace 1 and/or the first section upstream from the fire and/or the corresponding 20 suction pipe I1 a, partially compensating for the decrease in the flow rate of the gases passing through the partition 6 and thus generating a difference between the flow rate of the gases diluted by this air infiltration as measured in the pipe I Ia, and the flow rate of the gases which are actually passing through the partition 6. This difference can be significant in certain cases and mask a large drop in the flow rate within the partition 6. For this reason, it has been established 25 experimentally that solely measuring the flow rate of diluted gases as measured in the pipe 1 Ia is not sufficient to detect reliably a situation of an at least partially clogged partition 6. The problem which led to the invention was the need for a solution to the above disadvantages, using a process which detects an at least partial clogging of a partition, which can 30 advantageously be used by a system with real-time analysis of measurements made in the PCTIFR2009/050269 8 preheating zone A, and which allows definite identification of partition clogging situations without requiring additional equipment or instrumentation, and yet without generating false alarms which could needlessly interfere with the operation of the furnace. 5 The invention therefore proposes a method for detecting an at least partial clogging of at least one hollow partition of a multi-chamber furnace referred to as a "ring" furnace, which is characterized in that it comprises at least the steps consisting of: - defining a variable R, representative of the flow rate of the gases in a hollow partition of rank x among the partitions of a chamber of the furnace, 10 - defining a confidence interval for the population of variables R of at least several partitions of rank I to n of said chamber while excluding R,, based on a mean m and a standard deviation a for said variables R, - checking at successive moments, and preferably continuously, whether the variable R, is outside said confidence interval by a lower value, and if so, 15 - issuing an alarm signal indicating an at least partial clogging of at least one hollow partition of the mw of partitions to which belongs said partition of rank x relative to the other partitions, and/or ordering at least one modification to the operating settings of the furnace. In the invention, the variable R, representative of the flow rate of the gases for the rank x 20 partition of a furnace chamber is advantageously defined as a combination of three measurements made in the preheating zone A of the furnace, which are the flow rate Q. and Temperature T, of the gases and the negative static pressure P., for said rank x partition. In particular, the variable R, is advantageously defined, according to the invention, by the formula: R.= Q'X * TOX / Px, where a, 3, and X are weighting factors for the measurements. 25 In practice, the weighting factors a, p, X can be chosen by comparing the statistically significant differences for a clog with the respective measurement scales for the flow rate Q, temperature T, and negative static pressure P. Thus, based on data obtained from several furnaces, the weighting factors a, p, and X can advantageously be chosen within the following ranges: a from 0.3 to 0.5, P from I to 1.5, and x 30 from 0.3 to 0.5.

PCTIFR2009/050269 9 To be representative of a situation of an at least partial clogging of the partition 6, the method of the invention comprises a step consisting of defining, as a condition of an at least partial clogging of the rank x partition of said chamber, the condition in which the value Cx is negative, where C,, = R, - [k*m(Ri...Rx.1, Rx+i... R,) - p*o(Ri...Rx.i, Rx+...Rn)], where k is a 5 detection adjustment coefficient of a value selected between 0.8 to 1, m is the mean of the variables R excluding Rx, n is the total number of partitions of a chamber, and p is the number of standard deviations from the mean m, p being a natural whole number chosen to be greater than or equal to 3, and preferably less than or equal to 6. By this condition, one can also verify that the variable Rx of the rank x partition is outside 10 the confidence interval of the population of variables R of partitions of rank I to n excluding Rx, and moreover, by a value which is exclusively below said interval, which reveals an abnormal situation in the rank x partition compared to the population of other partitions. If such is detected, and alternatively or concurrently when an alarm signal to the furnace operators is issued, a system for analyzing the data resulting from the implementation of the 15 method of the invention can order modifications to the operating settings of the furnace, according to the severity of the clogging detected, and until maintenance operations take place in the partition or partitions concerned by the clogging detected. In the invention, such modifications to the operating settings of the furnace can consist of setting at least one heating line in the heating zone B of the furnace into a mode in which the fuel 20 injection by said heating line is stopped or limited, and/or by setting the exhaust manifold in the preheating zone A of the furmace into a mode of maximum draw by said exhaust manifold, and/or by setting at least one cooling line in the forced cooling zone D of the furnace and/or the blowing line in the natural cooling zone C of the furnace into a maximum blowing mode in at least one of said cooling and blowing lines, and/or any other action or arrangement in at least one 25 of the different lines of the furnace aimed at reducing the risk of an explosion related to a clogged partition situation. Other features and advantages of the invention will become apparent from the following non-limiting description of an exemplary embodiment, described with reference to the attached drawings, in which: PCT/FR2009/050269 10 - figure 1 is a schematic plan view of the structure of a ring furnace with open chambers, having two fires in this example, - figure 2 is a partial perspective and transverse cross-sectional view with a cutaway section, representing the internal structure of such a furnace, 5 - figure 3 is a longitudinal cross-sectional view of a conventional hollow partition of such a furnace, these figures 1 to 3 having already been described above, and - figures 4 and 5 are characteristic curves over time (expressed in hours) in the baking cycle, respectively representing the value C,, and the flow rate Q for the gases, for 10 five of the eight hollow partitions of a same chamber of the furnace, under the exhaust manifold II in the preheating zone A of the furnace, and of rank 1, 3, 4, 5 and 8, for which the characteristics curves are labeled Cl, C3, C4, C5 and C8 for figure 4, and Q1, Q3, Q4, Q5, and Q8 for figure 5. 15 The detection method of the invention is implemented in a furnace as represented in figures 1 to 3, described above, and with the aid of a data analysis system based on the statistical theory of normal (Gaussian) distribution. For such a distribution, it is known that 99.73% of a population is found within an interval [m-3a, m+3u] and that 99.99% of this population is within another interval [m-6a, m+6o], where m represents a mean and a a standard deviation. 20 Although the distribution of operative data for all partitions of rank 1 to n has no particular reason to obey a normal (Gaussian) law, it has been demonstrated experimentally that the use of this statistical model as described below results in a partition clogging detection method that is both effective and reliable. Over a confidential observation period of 3 months at a pilot industrial site, the method was able to detect all situations established as a complete or 25 partial clogging of a partition but did not generate a single false alarm. Based on such a Gaussian distribution, the method of the invention, for detecting an at least partial clogging of at least one hollow partition 6 of a multi-chamber 2 ring fumace 1, comprises a step consisting of defining a confidence interval for a variable R,, itself defined as representative of the flow rate of gases in a partition 6 of rank x among the partitions of rank I to 30 n of a same chamber 2 of the furnace 1, which is the chamber 2 situated under the exhaust PCT/FR2009/050269 11 manifold 11 in the preheating zone A of at least one fire, and preferably of each fire of the furnace 1, to allow identifying a clogging situation in at least one partition 6, if the variable R, representative of the flow rate of the gases for this rank x partition 6 is outside the confidence interval for the population of variables R of partitions 6 of rank I to n while excluding R', this 5 interval being defined using a mean m and a standard deviation or for said variables. In the invention, the representative variable R is a combination of three measurements made in the preheating zone A, for example using the flowmeter 12 and the temperature sensor (thermocouple) 13 placed in each of the suction pipes 1 1 a respectively connecting the exhaust manifold 11 to one of the hollow partitions 6 of this chamber 2 through the opening or peephole 10 9 furthest downstream, in the direction the gases are circulating, for each of these hollow partitions 6. These three measurements are the flow rate Q and temperature T of the gases, as well as the negative static pressure P in the partition 6 considered. If there is clogging of a partition 6 of the chamber 2, in communication with the exhaust manifold I1 of a fire, or clogging of at least one partition in a row of partitions to which said 15 partition of the chamber 2 belongs, it is observed that the flow rate Q and temperature T of the gases tend to decrease, while the negative static pressure P tends to increase, as has already been explained above. For this reason, by defining the variable Rx, representative of the flow rate of gases for the rank x partition 6, by the following formula: R, = Q'X * T% / P'x, where a, P, and X are 20 weighting factors for the measurements which are positive, it is understood that the variable Rx of a rank x partition 6 which is clogged is very clearly decreased compared to the variables R representative of the flow rate of the gases in other partitions 6 of the same chamber 2. In the invention, a condition representative of an abnormal situation in the rank x partition 6 is the fact that the variable Cx is negative, this variable C, being defined by the following formula: 25 Cx = Rx - [k*m(Ri...Rx., Rx+ 1 ... R,) - p*o-(Ri...Rx.i, Rx,1...R,)], where - R. is the variable representative of the flow rate of gases for the rank x partition 6 of the chamber 2 connected to the exhaust manifold 11, - k is an adjustment factor for the detection test, and can vary from 0.8 to 1, 30 - n is the total number of partitions 6 of the chamber 2 of the furnace 1, PCT/FR2009/050269 12 - m is the mean of the representative variables R excluding Rx, - a is the standard deviation, - p is a natural whole number of standard deviations from the mean m and is greater than or equal to 3, and preferably less than or equal to 6. 5 By this condition, it is verified that the variable R, representative of the flow rate of gases for the rank x partition 6 is outside the confidence interval for the population of variables R for the partitions 6 of rank 1 to n of this chamber 2 excluding R,, and more importantly, by a value which is exclusively lower, thus exposing an abnormal situation in the rank x partition 6 relative to the population of other partitions 6 of the same chamber 2, which indicates an at least partial 10 clogging of at least one hollow partition 6 of the row of partitions which comprises this rank x partition 6. The choice of weighting factors a, P, and x for the respective measurements of Q, T, and P can be done empirically, by comparing the statistically significant differences for a clogged partition 6 with the respective measurement scales for each of the variables Q, T and P. 15 Thus, based on data from several different furmaces of this same type, ranges for the weighting factors were determined such that a varies from 0.3 to 0.5, P from 1 to 1.5, and x from 0.3 to 0.5. The method of the invention can be implemented using a statistical data analysis, in particular of the variable R,, which in addition has the advantage of being done over time, and 20 thus does not require maintaining a data history. Due to this fact, the statistical calculations to be performed for implementing the method of the invention are accessible to the control system of the furnace 1, and in particular to its automation system that is part of the equipment of the furnace 1, without requiring an interface with another level of monitoring or data processing, thus guaranteeing intrinsically reliable 25 operation. In addition, as the data analysis implementing the method of the invention is done by comparing variables R, to each other at a given moment, the proposed detection method is independent of adjustments to the furnace 1 baking process and of evolutions in baking variables during the baking cycle.

PCT/FR2009/050269 13 If clogging of a partition 6 is detected, the control system of the furnace 1 can issue an alarm signal, advantageously in the form of an alarm message notifying the furnace operators. Alternatively or concurrently, and depending on the severity of the clogging detected, the furnace control system may order modifications to the baking process settings, and more 5 generally to the furnace operation, until maintenance or repair operations can be done on the partition or partitions 6 concerned by the clogging. Such modifications may concern setting the heating lines 16 in the heating zone B into a mode in which fuel injection by these lines 16 is limited or cut off, and/or setting the exhaust manifold 11 in the preheating zone A into a mode of maximum drawing (or suction) of gases by 10 this exhaust manifold 11, and/or setting the cooling lines 19 in the forced cooling zone D and/or the blowing line 18 in the natural cooling zone C of the furnace, into a mode of maximum blowing for at least one of these lines 19 and 18, and/or any other action or arrangement aimed at reducing the risk of an explosion in the furnace 1 related to a clogged partition 6 situation. Figures 4 and 5 respectively represent characteristic curves of the variable C., and the 15 flow rate of the gases Q expressed in Nm 3 per hour, as a function of time expressed in hours, during a baking cycle of about 27 hours, for only five hollow partitions 6 of the eight hollow partitions per chamber 2 of the furmace 1. This partial representation of the results for only five partitions out of eight in figures 4 and 5 is solely for clarity in the example provided; all eight partitions per chamber 2 of the furnace 1 were taken into account during the confidential 20 clogging detection testing in the rank 5 partition. The flow rate curves in figure 5 show that the flow rate Q5 of the partially clogged partition is substantially less than the flow rates Q1, Q4 and Q8 for the partitions of rank 1, 4 and 8, but is not sufficiently different from the flow rate Q3 of the rank 3 partition to allow clear and definite identification of an abnormal clogged partition situation. On the other hand, calculating 25 the variable C., for the rank 5 partition by applying the method of the invention, yields the curve C5 in figure 4, which remains negative over almost the entire baking cycle, while the values Cl, C3, C4 and C8 calculated by the method of the invention for the four partitions of ranks 1, 3, 4 and 8 are very positive and grouped more or less together, which unmistakably indicates an abnormal situation for the rank 5 partition.

PCT/FR2009/050269 14 The calculations and data processing necessary for determining the C" values are done by programs which can be loaded into some of the programmable logic controllers connected to the temperature sensors, flowmeters, and pressure sensors of the exhaust manifold 11 in particular, and which control corresponding actuators such as flow rate adjustment flaps, as mentioned 5 above. 10

Claims

1. A method for detecting an at least partial clogging of at least one hollow partition (6) of a 5 multi-chamber (2) furnace (1) referred to as a "ring" furnace, characterized in that it comprises at least the steps consisting of: - defining a variable R, representative of the flow rate of the gases in a hollow partition (6) of rank x among the partitions (6) of a chamber (2) of the furnace (1), - defining a confidence interval for the population of variables R of at least several 10 partitions (6) of rank 1 to n of said chamber (2) while excluding R., based on a mean m and a standard deviation a for said variables R, - checking at successive moments, and preferably continuously, whether the variable R, is outside said confidence interval by a lower value, and if so, - issuing an alarm signal indicating an at least partial clogging of at least one hollow 15 partition (6) of the row of partitions (6) to which belongs said partition (6) of rank x relative to the other partitions (6), and/or ordering at least one modification to the operating settings of the furnace (1).

2. A method according to claim 1, characterized in that the variable R, representative of the 20 flow rate of the gases for the rank x partition (6) is defined as a combination of three measurements made in the preheating zone (A) of the furnace (1), and which are the flow rate Qx and temperature T. of the gases and the negative static pressure P., for said rank x partition (6). 25

3. A method according to claim 2, characterized in that said variable R" is defined by the formula: Rx= Q'X * To, / Pl, where a, 1, and X are weighting factors for the measurements.

4. A method according to claim 3, characterized in that the weighting factors a, P, X are 30 chosen made by comparing the statistically significant differences for a clog with the PCT/FR2009/050269 16 respective measurement scales for the flow rate Q, temperature T, and negative static pressure P.

5. A method according to claim 4, characterized in that the weighting factors a, P, X are chosen within the following ranges: a from 0.3 to 0.5, P from I to 1.5, and x from 0.3 to 5 0.5.

6. A method according to any of claims 3 to 5, characterized in that it comprises a step consisting of defining, as a condition of an at least partial clogging of the rank x partition (6) of said chamber (2), the condition in which the value Cx is negative, where C, = Rx 10 [k*m(RI.. .R.I, R.+i... R.) - p*o(Ri ... R. 1 , R±,. ... R,)], where k is a detection adjustment coefficient of a value selected between 0.8 and 1, m is the mean of the variables R excluding Rx, n is the total number of partitions (6) of a chamber (2), and p is the number of standard deviations from the mean m, p being a natural whole number chosen to be greater than or equal to 3, and preferably less than or equal to 6. 15

7. A method according to any one of claims 1 to 6, characterized in that if an at least partial clogging is detected of at least one partition (6) of the row of partitions (6) comprising the rank x partition of the chamber (2), extending into the preheating zone (A) of the furnace (1) under an exhaust manifold (11), at least one modification to the operating settings of 20 the furnace (1) is ordered by setting at least one heating line (16) in the heating zone (B) of the furnace (1) into a mode in which the fuel injection by said heating line (16) is stopped or limited.

8. A method according to any one of claims I to 7, characterized in that if an at least partial 25 clogging is detected of at least one partition (6) of the row of partitions (6) comprising the rank x partition of the chamber (2), extending into the preheating zone (A) of the furnace (1) under an exhaust manifold (11), a setting of the exhaust manifold (11) into maximum drawing mode by said manifold is ordered. PCTIFR2009/050269 17

9. A method according to any one of claims 1 to 8, characterized in that if an at least partial clogging is detected of at least one partition (6) of the row of partitions (6) comprising the rank x partition of the chamber (2), extending into the preheating zone (A) of the furnace (1) under an exhaust manifold (11), at least one of the cooling lines (19) in the forced 5 cooling zone (D) and/or the blowing line (18) in the natural cooling zone (C) of the furnace (1), is ordered into a mode of maximum blowing by at least one of said cooling (19) and blowing (18) lines.