AU2009224502B2

AU2009224502B2 - Method for detecting an at least partially clogged partition in a chamber oven

Info

Publication number: AU2009224502B2
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: 2014-10-23
Anticipated expiration: 2029-02-19
Also published as: EP2257753A2; CN102007359A; RU2010139874A; WO2009112734A9; FR2928206B1; ZA201005877B; CN102007359B; AU2009224502A1; WO2009112734A3; EP2257753B1; FR2928206A1; CA2716761A1; WO2009112734A2

Abstract

The invention relates to a method that comprises defining a variable R

Description

PCT/FR2009/050269 1 Title METHOD FOR DETECTING AN AT LEAST PARTIALLY CLOGGED PARTITION 5 IN A CHAMBER OVEN Throughout this specification, unless the context requires otherwise, the word "comprise" and variations such as "comprises", "comprising" and "comprised" are to be understood to imply the presence of a stated integer or group of integers but not the exclusion of any other integer or 0 group of integers. Throughout this specification, unless the context requires otherwise, the word "include" and variations such as "includes", "including" and "included" are to be understood to imply the presence of a stated integer or group of integers but not the exclusion of any other integer or 5 group of integers. Technical Field This invention relates to the field of what are called multiple-chamber "ring" furnaces, for 0 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. Background Art 25 Any discussion of background art, any reference to a document and any reference to information that is known, which is contained in this specification, is provided only for the purpose of facilitating an understanding of the background art to the present invention, and is not an acknowledgement or admission that any of that material forms part of the common general 30 knowledge in Australia or any other country as at the priority date of the application in relation to which this specification has been filed.

PCT/FR2009/050269 2 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 5 schematic view of the structure of a ring furnace with open chambers, with two fires in this 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. 0 The furnace 1 comprises two parallel casings or bays la and 1b, extending the length of 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, 5 and pits 4 open in their upper part to allowing loading the green carbon blocks to be baked and 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 la or lb, and these hollow partitions 6 communicate with one another by means 0 of ports 7 in the upper part of their longitudinal walls, which face longitudinal passages arranged in the transverse walls 3, such that the hollow partitions 6 form lines of longitudinal partitions 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 25 more uniformly distribute the path of the combustion gases or fumes, and said hollow partitions 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 30 by crossover flues 10, which transfer gases from one end of each row of hollow partitions 6 of a PCT/FR2009/050269 3 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 5 furnaces, consists of advancing a flame front from one chamber 2 to an adjacent one during a 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 0 represented in figure 1, in a position in which one extends across thirteen chambers 2 of bay la and the other across thirteen chambers 2 of bay 1b) 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 1b, 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 5 cyclical advancement from chamber to chamber: A) A preheating zone comprising, if one refers to the fire in bay la 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 0 which this exhaust manifold extends, a system for measuring and adjusting the flow rate of the combustion gases and fumes per row of hollow partitions 6, said system being able to comprise, in each suction pipe 11 a which has one end secured to the exhaust manifold 11 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 25 sealing flap pivoted by a flap actuator, for adjusting the flow rate, as well as a flowmeter 12, slightly upstream in the corresponding pipe 11 a, 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) 30 and pressure sensors; PCT/FR2009/050269 4 B) A heating zone comprising: - several identical heating lines 16, two or preferably three as represented in figure 1; each equipped with burners and fuel injectors (liquid or gas fuel) and temperature sensors (thermocouples), each of the lines 16 extending above one of the respective 5 chambers of a corresponding number of adjacent chambers 2, such that the injectors 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 0 immediately upstream from the one under the heating line 16 furthest upstream, and 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 5 flow rate of ambient air blown into each of the hollow partitions 6 of a chamber 2 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; 0 D) a forced cooling zone, which extends across three chambers 2 upstream from the blowing line 18, and which in this example comprises two parallel cooling lines 19, each 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 25 and unpacking of anodes 6, as well as chamber 2 maintenance. 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 30 combustion gases and fumes circulate in the rows of hollow partitions 6), the blowing line 18 PCT/FR2009/050269 5 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", 5 which circulate in the rows of hollow partitions 6. 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) 0 from the pitch released by the anodes 5 in the pits 4 of the chambers 2 in the preheating and 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. 5 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 0 C and D, because of the cooling lines 19 and especially the blowing line 18, is preheated in the 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 25 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 30 partitions 6, because of the negative pressure in the hollow partitions 6 of the chambers 2 in the PCT/FR2009/050269 6 preheating zone A, then, in the heating or baking zone B, for the function of baking the blocks 5 at about 1 100'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 5 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 0 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). 5 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 0 the first and the second level. The second level comprises a central system of computers with 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. 25 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 30 in an exhaust duct 20, for example a cylindrical duct partially represented in figure 2, with an PCT/FR2009/050269 7 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. 5 The invention, as will be further described herein, 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: 0 - 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, - 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 5 thermal gradients, or - a combination of several of the above situations. 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 0 partitions 6 of the heating zone B although there is not enough combustion air because of the clogging. This situation can result in explosions. 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 25 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. 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 11 a of the 30 exhaust manifold 11, or by a flow rate measurement, for example by means of a Venturi tube, PCT/FR2009/050269 8 Pitot tube, diaphragm, cone, etc. placed in the suction pipe 11 a of the exhaust manifold 11. The 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 5 these two variables. Measurement of the flow rate, using a flowmeter 12 in the corresponding suction pipe lla, 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 0 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 suction pipe lla, 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 lla, and the flow rate of the gases which are 5 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 experimentally that solely measuring the flow rate of diluted gases as measured in the pipe 11 a is not sufficient to detect reliably a situation of an at least partially clogged partition 6. 0 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 advantageously be used by a system with real-time analysis of measurements made in the preheating zone A, and which allows definite identification of partition clogging situations without requiring additional equipment or instrumentation, and yet without generating false 25 alarms which could needlessly interfere with the operation of the furnace. 30 PCT/FR2009/050269 9 Summary of Invention In accordance with an aspect of the present invention there is provided a method for detecting an at least partial clogging of at least one hollow partition of a multi-chamber furnace, 5 referred to as a "ring" furnace, comprising at least the steps 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, - defining a confidence interval for the population of variables R of at least several partitions of rank 1 to n of said chamber while excluding Rx, based on a mean m and 0 a standard deviation a for said variables R, - checking at successive moments whether the variable Rx 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 partition of the row of partitions to which belongs said partition of rank x relative to 5 the other partitions, and/or ordering at least one modification to the operating settings of the furnace wherein the variable Rx representative of the flow rate of the gases for the rank x partition is defined as a combination of three measurements made in the preheating zone A of the furnace, and which are the flow rate Qx and temperature Tx of the gases and the negative static pressure 0 Px for said rank x partition, and the said variable Rx is defined by the formula: Rx= Qax * Tx / PYX, where a, 3, and x are weighting factors for the measurements. Preferably, checking at successive moments comprises checking continuously. In practice, it is preferable that the weighting factors a, 3, X are chosen by comparing the statistically significant differences for a clog with the respective measurement scales for the flow 25 rate Q, temperature T, and negative static pressure P. Preferably, based on data obtained from several furnaces, the weighting factors a, 3, and X are chosen within the following ranges: a from 0.3 to 0.5, 0 from 1 to 1.5, and x from 0.3 to 0.5. Preferably, to be representative of a situation of an at least partial clogging of the 30 partition 6, the method of the invention further comprises a step of defining, as a condition of an PCT/FR2009/050269 10 at least partial clogging of the rank x partition of said chamber, the condition in which the value Cx is negative, where Cx = Rx - [k*m(Ri.. .Rx.

1 , Rx41... R.) - p*a(Ri ... Rx 1 , Rx4 1 ... R)], where k is a 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 5 standard deviations from the mean m, p being a natural whole number chosen to be greater than or equal to 3. More preferably, p is a natural whole number chosen to be greater than or equal to 3 and less than or equal to 6. By this condition, one can also verify that the variable Rx of the rank x partition is outside the confidence interval of the population of variables R of partitions of rank 1 to n excluding Rx, 0 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 method of the invention can order modifications to the operating settings of the furnace, 5 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, for example, 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 injection by said heating line is stopped or limited, and/or by setting the exhaust 0 manifold in the preheating zone A of the furnace 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 of the different lines of the furnace aimed at reducing the risk of an explosion related 25 to a clogged partition situation. 30 PCT/FR2009/050269 11 Brief Description of Drawings 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 5 drawings, in which: - 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, 0 - 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 Cx and the flow rate Q for the gases, for 5 five of the eight hollow partitions of a same chamber of the furnace, under the exhaust manifold 11 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. 0 Description of Embodiments 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 25 population is found within an interval [m-3a, m+3a] and that 99.99% of this population is within another interval [m-6a, m+6a], where m represents a mean and a a standard deviation. 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 30 method that is both effective and reliable. Over a confidential observation period of 3 months at PCT/FR2009/050269 12 a pilot industrial site, the method was able to detect all situations established as a complete or 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 furnace 1, 5 comprises a step consisting of defining a confidence interval for a variable Rx, itself defined as representative of the flow rate of gases in a partition 6 of rank x among the partitions of rank 1 to n of a same chamber 2 of the furnace 1, which is the chamber 2 situated under the exhaust 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 Rx 0 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 1 to n while excluding Rx, this interval being defined using a mean m and a standard deviation a 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 5 (thermocouple) 13 placed in each of the suction pipes 11 a respectively connecting the exhaust manifold 11 to one of the hollow partitions 6 of this chamber 2 through the opening or peephole 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. 0 If there is clogging of a partition 6 of the chamber 2, in communication with the exhaust manifold 11 of a fire, or clogging of at least one partition in a row of partitions to which said 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. 25 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: Rx = Qax * Tox / PYX, where a, 3, and x are 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 PCT/FR2009/050269 13 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 Cx being defined by the following formula: Cx = Rx - [k*m(RI...Rx.1, Rx41 ...R.) - p*a(Ri ... Rx1, Rx4I...R.)], where 5 - Rx 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, - n is the total number of partitions 6 of the chamber 2 of the furnace 1, - m is the mean of the representative variables R excluding Rx, 0 - 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. By this condition, it is verified that the variable Rx 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 5 the partitions 6 of rank 1 to n of this chamber 2 excluding Rx, 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 clogging of at least one hollow partition 6 of the row of partitions which comprises this rank x partition 6. 0 The choice of weighting factors a, 3, 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. Thus, based on data from several different furnaces of this same type, ranges for the weighting factors were determined such that a varies from 0.3 to 0.5, 0 from 1 to 1.5, and x from 25 0.3 to 0.5. The method of the invention can be implemented using a statistical data analysis, in particular of the variable Rx, which in addition has the advantage of being done over time, and thus does not require maintaining a data history. Due to this fact, the statistical calculations to be performed for implementing the method 30 of the invention are accessible to the control system of the furnace 1, and in particular to its PCT/FR2009/050269 14 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 operation. In addition, as the data analysis implementing the method of the invention is done by 5 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. 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. 0 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 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 5 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 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 0 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 Cx and the 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 furnace 1. This partial representation of the results for only five 25 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 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 30 8, but is not sufficiently different from the flow rate Q3 of the rank 3 partition to allow clear and PCT/FR2009/050269 15 definite identification of an abnormal clogged partition situation. On the other hand, calculating the variable Cx 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 C1, C3, C4 and C8 calculated by the method of the invention for the four partitions of ranks 1, 3, 4 5 and 8 are very positive and grouped more or less together, which unmistakably indicates an abnormal situation for the rank 5 partition. The calculations and data processing necessary for determining the Cx 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, 0 and which control corresponding actuators such as flow rate adjustment flaps, as mentioned above. Whilst preferred embodiments of the present invention have been herein before described, the scope of the present invention is not limited to those specific embodiments, and may be embodied in other ways, as will be apparent to a skilled addressee. 5 Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. Reference numbers and letters appearing between parentheses in the claims, identifying features described in the embodiment(s) and/or example(s) and/or illustrated in the accompanying drawings, are provided as an aid to the reader as an exemplification of the matter 0 claimed. The inclusion of such reference numbers and letters is not to be interpreted as placing any limitations on the scope of the claims. 25

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, comprising at least the steps 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 0 partitions (6) of rank 1 to n of said chamber (2) while excluding Rx, based on a mean m and a standard deviation a for said variables R, - checking at successive moments whether the variable Rx 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 5 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), wherein the variable Rx representative of the flow rate of the gases for the rank x partition (6) is defined as a combination of three measurements made in the preheating 0 zone (A) of the furnace (1), and which are the flow rate Qx and temperature Tx of the gases and the negative static pressure Px for said rank x partition (6), and the said variable Rx is defined by the formula: Rx= Qax * Tox / PIX, where a, 3, and x are weighting factors for the measurements.

2. A method according to claim 1, wherein checking at successive moments comprises 25 checking continuously.

3. A method according to claim 1 or 2, wherein the weighting factors a, 3, x are chosen made 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. PCT/FR2009/050269 17

4. A method according to claim 3, wherein the weighting factors a, 3, x are chosen within the following ranges: a from 0.3 to 0.5, 0 from I to 1.5, and X from 0.3 to 0.5.

5. A method according to any of claims 1 to 4, further comprising a step of defining, as a 5 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 Cx = Rx - [k*m(Ri... Rx 1 , Rx41... R.) p*a(RI ... Rx 1 , Rx4 ... 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 0 from the mean m, p being a natural whole number chosen to be greater than or equal to 3.

6. A method according to claim 5, wherein p is a natural whole number chosen to be greater than or equal to 3 and less than or equal to 6. 5

7. A method according to any one of claims 1 to 6, wherein 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 the furnace (1) is ordered by setting at least one heating line (16) in the heating zone (B) of 0 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 1 to 7, wherein if an at least partial clogging is detected of at least one partition (6) of the row of partitions (6) comprising the rank x 25 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.

9. A method according to any one of claims 1 to 8, wherein if an at least partial clogging is 30 detected of at least one partition (6) of the row of partitions (6) comprising the rank x PCT/FR2009/050269 18 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 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 5 blowing (18) lines.

10. A method for detecting an at least partial clogging of at least one hollow partition of a multi-chamber furnace substantially as herein before described with reference to the accompanying drawings. 0