AU2012306185A1 - Device and method for optimising combustion in partition lines of a chamber kiln for firing carbon blocks - Google Patents

Abstract

The invention relates to a method for optimising combustion in partition lines of a so-called rotary-burner chamber kiln for firing carbon blocks, said kiln comprising heating chambers, the fuel required for firing the carbon blocks being partially injected by at least two heating manifolds (16) directly controlled by a master controller (42a, 42b), which controls the inputs/outputs of said manifolds (16), the method including the automatic identification, by the master controller (42a, 42b), of the relative position of one manifold relative to the others when said manifold is connected to the grid, and the operation of the injectors of the heating manifolds (16) being organised by distributing the operating sequences of the injectors individually over time.

Description

1 METHOD AND DEVICE FOR OPTIMIZING COMBUSTION IN LINES OF PARTITIONS OF A RING FURNACE FOR BAKING CARBONACEOUS BLOCKS 5 The invention relates to ring furnaces for baking carbonaceous blocks, particularly carbonaceous anodes and cathodes intended for aluminum production by electrolysis. It more particularly relates to a method and a device for optimizing combustion in the lines of partitions of such a multi-chamber furnace. 10 Ring furnaces for baking anodes are described in particular in patent application W0201127042, which should be referred to for more information. Their structure and operation will be partially reviewed here, however, with reference to figures 1 and 2. A schematic plan view of the structure of a ring furnace with open chambers is represented with two fire groups in the example 15 in figure 1, and a partial perspective cross-sectional view with a cutaway section showing the internal structure of such a furnace is represented in figure 2. The baking furnace (BF) 1 comprises two parallel shells or section la and lb extending the length of the furnace 1 along the longitudinal axis XX, each comprising a succession of transverse chambers 2 (perpendicular to the axis 20 XX), separated from each other by transverse walls 3. Each chamber 2 consists, in the direction transverse to the furnace 1, of open-top pits 4 alternating with hollow heating partitions 6 also referred to as flues. The pits 4 allow loading the green carbonaceous blocks and unloading the cooled baked blocks; the green carbonaceous blocks are stacked inside them and packed in 25 carbonaceous powder. The hollow heating partitions 6 have thin walls generally held apart from each other by transverse spacers 6a. 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 section 1 a or 1 b, and these hollow partitions 6 interconnect by means of ports 7 30 in the upper part of their longitudinal walls, facing longitudinal passages in the transverse walls 3, so that the hollow partitions 6 form longitudinal lines of compartments parallel to the major axis XX of the furnace. Gases (combustion 2 air, combustible gases, and combustion gases and fumes) circulate in these compartments to preheat and bake the anodes 5, then cool them. The hollow partitions 6 additionally comprise baffles 8 to prolong and more uniformly distribute the path of the combustion gases or fumes, and these hollow 5 partitions 6 have openings 9 at the top called "peepholes", which can be closed with removable covers and are arranged in a block crowning the furnace 1. The two sections 1 a and 1 b of the furnace 1 are interconnected at their longitudinal ends by crossovers 10, which transfer the gases from one end of each line of hollow partitions 6 in a section 1a or 1b to the end of the corresponding line of 10 hollow partitions 6 in the other section 1b or 1a, so as to form substantially rectangular loops of lines of hollow partitions 6. The operating principle of ring furnaces, also known as advancing fire furnaces, consists of advancing a flame front from one chamber 2 to an adjacent one during a cycle, with each chamber 2 successively undergoing the phases of 15 preheating, forced heating, full firing, 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, with one extending in this example across thirteen chambers 2 of section 1a and the other across thirteen chambers 2 of section 1 b) which move cyclically from chamber 2 to chamber 2. 20 Each fire or fire group consists of five successive zones A to E, which are, as represented in figure 1 for the fire for section 1 b, from downstream to upstream relative to the direction of the gas flow in the lines of hollow partitions 6, and in the direction opposite to the cyclic displacements from chamber to chamber: A) A preheating zone comprising, if referring to the fire for section la, and 25 taking into account the direction of rotation of the fires indicated by the arrow at the crossover 10 at the end of the furnace 1 at the top in figure 1: - an exhaust manifold 11 which is equipped, for each hollow partition 6 of the chamber 2 above which this exhaust manifold extends, with a system for measuring and adjusting the flow rate of the combustion gases and fumes per 30 line of hollow partitions 6, this system possibly comprising, in each exhaust pipe 11 a which has one end solidly attached to the exhaust manifold 11 and opening into said exhaust manifold while the other end is engaged in the opening 9 of 3 one of the respective hollow partitions 6 of this chamber 2, an adjustable shutter pivoted by a shutter actuator, for adjusting the flow rate, as well as a flow meter 12 slightly upstream in the corresponding pipe 11a, a temperature sensor (thermocouple) 13 for measuring the temperature of the combustion gases 5 being suctioned, and - a preheating measurement ramp 15, substantially parallel to the exhaust manifold 11 and upstream from the latter, generally, above the same chamber 2, and equipped with temperature sensors (thermocouples) and pressure sensors for preparing the static negative pressure and the temperature that will 10 prevail in each of the hollow partitions 6 of this chamber 2, to enable displaying and regulating this negative pressure and this temperature in the preheating zone; B) A heating zone comprising: - several identical heating ramps 16, two or preferably three as represented in 15 figure 1, or more depending on the duration of the cycle; each equipped with fuel injectors or burners (liquid or gas fuel) and temperature sensors (thermocouples), each of the ramps 16 extending above one of the respective chambers of a corresponding number of adjacent chambers 2, such that the injectors of each heating ramp 16 engage with the openings 9 of the hollow 20 partitions 6 in order to inject the fuel; C) A blowing or natural cooling zone comprising: - a so-called "zero point" ramp 17, extending above the chamber 2 immediately upstream from the one below the heating ramp 16 furthest upstream, and equipped with pressure sensors to measure the pressure prevailing in each of 25 the hollow partitions 6 of this chamber 2, in order to be able to adjust this pressure, and - a blowing manifold 18, equipped with electric fans having a means for adjusting the flow of ambient air blown into each of the hollow partitions 6 of a chamber 2 upstream from the one located under the zero point ramp 17, such 30 that the flow of ambient air blown into these hollow partitions 6 can be regulated to obtain a desired pressure (slight negative or positive pressure) at the zero point ramp 17; 4 D) A forced cooling zone, which extends across three chambers 2 upstream from the blowing manifold 18, and which in this example comprises two parallel cooling manifolds 19, each equipped with electric fans and pipes for blowing ambient air into the hollow partitions 6 of the corresponding chamber 2; and 5 E) A work area, extending upstream from the cooling manifolds 19, for packing and unpacking the anodes 5 in the furnace, as well as for chamber 2 maintenance. Upstream from the heating ramps 16, the blowing manifold 18 and the forced cooling manifold(s) 19 comprise pipes for blowing combustion air supplied by 10 electric fans; these pipes are connected to the hollow partitions 6 of the chambers 2 concerned via the openings 9. The exhaust manifold 11 is placed downstream from the heating ramps 16, for extracting the combustion gases and fumes (designated in general below by the term "combustion gases") circulating in the lines of hollow partitions 6. 15 The anodes 5 are heated and baked by the combustion of the fuel (gas 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) from pitch released by the anodes 5 in the pits 4 of the chambers 2 in the preheating and heating zones. As these volatile 20 materials released in the pits 4 are for the most part combustible, and are able to flow into the two adjacent hollow partitions 6 through passages arranged in these partitions, they catch fire in these two partitions because of the residual combustion air present among the combustion gases in the hollow partitions 6. Thus the combustion air and gases circulate through the lines of hollow 25 partitions 6, and a negative pressure created 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 combustion gases inside the hollow partitions 6; the air coming from the cooling zones C and D due to the cooling manifolds 19 and the blowing manifold 18 in particular, is preheated in the 30 hollow partitions 6, cooling the anodes 5 baked in the adjacent pits 4 as it travels and serving as combustion air when it reaches the heating zone B.

5 As the anodes 5 bake, the assembly of ramps and manifolds 11 to 19 with the associated measurement and recording equipment and devices are advanced cyclically (for example every 24 hours or so). Each chamber 2 thus successively ensures the function of loading green carbonaceous blocks 5 upstream from the 5 preheating zone A, then, in the preheating zone A, the function of natural preheating by the fuel combustion gases and pitch fumes which leave the pits 4 and enter the hollow 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 zone B or baking zone, the function of baking blocks 5 at about 1100 C, and 10 lastly, in the cooling zones C and D, the function of cooling the baked blocks 5 with ambient air and correlatively preheating this air which acts as combustion air for the furnace 1. The forced cooling zone D is followed, in the direction opposite the direction the fire advances and the combustion gases circulate, by a zone E where the cooled carbonaceous blocks 5 are unloaded and then 15 green carbonaceous blocks may possibly be reloaded into the pits 4. The method for regulating the furnace BF 1 essentially comprises regulating the temperature and/or pressure of the preheating A, heating B, and blowing or natural cooling C zones of the furnace 1 according to predefined setpoints. The combustion gases extracted from the fires by the exhaust manifolds 11 are 20 collected in a duct 20, for example a cylindrical duct partially represented in figure 2, with a flue main 21 that may appear U-shaped in a plan view (see dotted lines in figure 1) or may extend around the furnace, its outlet 22 conveying the exhausted and collected combustion gases to a flue gas treatment center (GTC) which is not represented because it is not a part of the 25 invention. In order for the anodes (carbonaceous blocks) to achieve their optimum characteristics, and therefore to guarantee that a final baking temperature is reached, the current preference for furnaces of this type is to supply the heating ramps 16 with fuel independently of the pressure differential and air flow 30 conditions in the partitions 6. Incomplete combustion may result within a significant or high number of the lines of partitions 6. This in turn may result in high operating costs for the furnace, not only because of the excess 6 consumption of fuel, but also because of fouling in the exhaust pipes and ducts which leads to the retention of unburnt material, representing an increased potential risk of fire and an impacted baking process. The injectors of a heating ramp are arranged in pairs, providing two injectors 5 per hollow partition. The number of injectors per manifold is equal to twice the number of hollow partitions, for example fourteen injectors for seven partitions. For a heating zone having three heating ramps, a total of six injectors inject fuel into the same hollow partition. The gas or liquid fuel supply system on a heating ramp 16 is adapted to the 10 type of fuel, particularly if it is a gas such as natural gas or a liquid such as fuel oil. To simplify the following description of the invention, the fuel is considered to be a gas. Figure 3 schematically represents an example of a known heating ramp 16 for gas fuel. Four of the pairs of injectors 23 are represented in this figure, bearing 15 in mind that a ramp 16 is generally equipped with 7 to 10 pairs. The injectors 23 are connected to the same fuel line carried on the heating ramp 16 and connected to the plant's supply system via a hose 26 and a quick release coupling 25. Each injector 23 is preceded by an on/off solenoid valve 37 providing individual control for each injector 23. The fuel line for the manifold 20 comprises a quick release coupling 25, a hose 26, a filter 27, a general safety solenoid valve 28, a bypass circuit for this general safety solenoid valve comprising a needle valve 29 and a solenoid valve 30 for verifying the fluid tightness of the line, a flow measurement device 31 (optional), a pressure regulator 32 (optional), a pressure switch 33 triggered by a minimum pressure 25 threshold, a pressure switch 34 triggered by a maximum pressure threshold, and a pressure sensor 35. This main circuit supplies all the injectors 23, which are each preceded by a manual valve 36, a solenoid valve 37, and a hose 38. Figure 4 schematically represents an example of a vertical cross-section of a known furnace along the longitudinal axis XX through the middle of a hollow 30 partition 6. This example comprises three successive heating ramps 16a, 16b and 16c. The blowing manifold 18 ensures the circulation of fresh air to cool baked anodes and provide oxygen for combustion of the fuel injected by the 7 heating ramps 16a, 16b, 16c. The flow of air, then of combustion gases, in the hollow partition 6 is indicated by the dotted line. The openings 9 in the chambers 2 located between the blowing manifold 18 and the heating ramps 16a, 16b, 16c are closed to limit the escape of the forced air. Upstream from the 5 first heating ramp 16c is the "zero point" ramp 17. Represented for this partition 6 and these three heating ramps 16a, 16b, 16c are the pairs of injectors 23a1, 23a2, 23b1, 23b2, 23c1, 23c2 and the thermocouples 24a, 24b and 24c for measuring the temperature in the partition. For each heating ramp 16a, 16b, 16c, the corresponding injectors are placed in two openings 9 separated by an 10 opening 9 that remains unused and closed off by a cover. The thermocouples 24 are downstream from the injectors in the direction of the gas flow. The exhaust manifold 11 is located at the end of the fire group, preceded by the preheating measurement ramp 15. On the average, a heating ramp 16 operates at about 30% of its total capacity. 15 To limit the cost, dimensions, and weight of the ramp 16, its fuel line is sized for a nominal flow rate of fuel equivalent to 30% of the flow necessary to supply all injectors 23 of this ramp 16 simultaneously at their nominal capacity. If a large number of injectors 23 are open at the same time, the flow capacity of the ramp 16 is exceeded and the gas pressure drops in an uncontrolled manner. This 20 drop in pressure has the effect of reducing the flame length, and can result in degraded combustion quality. This phenomenon is particularly noticeable with gas fuel, because with liquid fuel it can be compensated for by a pump on the ramp 16 which maintains the pressure and continuously circulates from 3 to 5 times the volume of injected liquid fuel in the fuel line. 25 The fuel is injected in pulses. The amount injected is generally adjusted by varying the length of time the automatic valves 37 of the injectors 23 are closed. It can also be adjusted by varying the length of time the valves 37 are open. When an injector 23 is open, it injects 100% of its capacity and consumes its maximum flow. For example, for natural gas, the injection durations generally 30 vary from 0.5 to 4s, while the injection durations generally vary from 30 to 150ms for fuel oil.

8 As a variant, adjusting the injection capacity can also be achieved by varying the fuel supply pressure to the injectors 23, for example by means of a pressure regulator 32 placed on the fuel line for each ramp 16. This solution has the effect of modifying the flame length according to the pressure level, as a low 5 pressure results in a shorter flame than when operating at nominal capacity. It therefore has an impact on heat distribution in the hollow partitions 6 and the temperature profile along the height of each partition 6. The gross injection capacity is calculated by a P.I.D. unit for each pair of injectors for each ramp 16, meaning per partition 6. Depending on the 10 difference between the temperature measured by the thermocouple 24 for the ramp 16 of the partition 6 concerned and the setpoint configured by the operator, the PID unit calculates a gross total control variation. This variation added to the previous gross control gives a total gross control of between 0 and 100%. This control is then restricted by upper and lower limits not to be 15 exceeded that are entered by the operator for the ramp 16. The distribution of this capacity over the two injectors, such as 23a1 and 23a2 for ramp 16a, occurs for example based on a ratio parameter which is entered by the operator. The ratio is always respected, with the upper and lower limits possible for the ramp 16 being calculated to allow this. The system then adjusts 20 this total capacity to comply with the maximum capacity limit that has been set for the partition 6. The maximum limit is set either by the operator or by a module that monitors combustion. The finalized total capacity is then sent to a PLC (programmable logic controller) for the ramp 16, with the ratio and pulse duration. The PLC then 25 calculates a closure time for the upstream injector (such as 23a2) and the downstream injector (such as 23a1) so that the injected amount complies with the ratio and total capacity. The pulses calculated in this manner are sent to the injectors 23. In existing embodiments, there is no specific timing established with the other 30 pairs of injectors 23 for the other ramps 16 placed over the same partition 6. As the combustion air comes primarily from upstream (blown by the blowing manifold 18), it contains less and less oxygen as it travels from the first heating 9 ramp (such as 16c) to the last one (such as 16a). Depending on the injection sequence between the injectors 23 placed over the same partition 6, there are situations where injectors 23 inject into the same air volume as their predecessors. This volume would then be short of oxygen, resulting either in a 5 lag in combustion relative to the injection location, or incomplete combustion of the injected fuel and the production of unburned material. The phenomenon is more pronounced with gas fuel than with liquid fuel, due to the longer injection durations. To limit variations in fuel pressure in a heating ramp 16, in the best case an 10 initial lag is created when starting up the different pairs of injectors 23 on the same ramp 16 but this is not maintained. Limitations arise from the fact that the injectors 23 are often controlled by an independent device, such as an electronic board specifically developed for this application, which generates the pulses as a function of a frequency value sent 15 by the PLC for the ramp 16, which does not allow carefully timing the relative rhythms between pairs. The injectors 23 are sometimes controlled directly by the PLC for the ramp 16. It is then possible to fine-tune the timing for the ramp 16, but the processing capacity and the relatively slow refresh of outputs from the PLCs limits the feasibility of accurate timing. The relatively slow 20 communication between PLCs and the scattered distribution of the control devices does not allow maintaining a precise timing between different heating ramps 16. Figure 5 schematically represents a control/command system for a fire group of the current art. Control is ensured by two redundant central computers CCS-A 25 42a & CCS-B 42b which send the commands to be applied to the PLCs 45 located on each ramp or manifold 11, 15, 16, 17 and 18. These PLCs 45 control the actuators directly, particularly the shutters on the manifold 11, the injectors 23 on the heating ramps 16, and the fans on the manifold 18. Communication between the various controllers is assured by a communication network which 30 may be wired or, for example, WiFi. The central computers calculate the commands for each actuator according to the setpoints configured by the operators and the measurements coming from the PLCs 45 for the ramps and 10 manifolds. These commands are then sent to each PLC 45 for execution. The level 1 communication network between the central computers 42a & 42b and the PLCs 45 for the ramps and manifolds consists of Ethernet switches 40 and WiFi access points 43 distributed in the furnace building. Each PLC 45 is 5 connected to the WiFi network via a client (44); an Ethernet internal to the ramp or manifold allows exchanging information by means of an Ethernet switch 46 between the Wi-Fi client 44, the local screen 47, and the speed regulators 48 in the case of the blowing manifold 18. An auxiliary PLC 43 (situated for example in an electrical room) captures information from elements related to the furnace 10 such as the flue gas treatment center. A DMS computer 41 is used to archive data from the method, and is connected to the central computers 42a & 42b through a switch 40 which forms the Level 2 Ethernet. This network can be connected to the plant network for data extraction and processing by Level 3 systems. 15 The process is monitored via control screens 39 which may be remote, for example in a control room, over a dedicated network if necessary (KVM network). These screens 39 display the real time data coming from the central computers 42a & 42b but also the archived data from the DMS computer 41. To remedy these disadvantages, a first aspect of the invention consists 20 primarily of a method for optimizing combustion in the lines of partitions of a ring furnace for baking carbonaceous blocks. The furnace comprises a succession of chambers for preheating, heating, natural cooling, and forced cooling, arranged in a series along the longitudinal axis XX of the furnace. Each chamber consists, in the direction transverse to said longitudinal axis XX, of pits 25 alternating with hollow heating partitions. Carbonaceous blocks are arranged inside the pits. The hollow heating partitions interconnect with and are aligned with the partitions of other chambers, parallel to the longitudinal axis XX of the furnace, to form lines of hollow partitions in which air for cooling and combustion and combustion gases circulate. An exhaust manifold is connected to each of 30 the partitions of the first chamber during preheating by one of the respective exhaust pipes. The combustion air required is partly injected by a blowing manifold of the natural cooling zone, connected to at least one fan, and is partly 11 infiltrated through the lines of partitions due to negative pressure. The fuel necessary for baking the carbonaceous blocks is partly injected by at least two heating ramps which each extend over a respective one of at least two adjacent chambers of the heating zone, and are each able to inject each fuel into each of 5 the hollow partitions of the corresponding respective chamber of the heating zone. A master controller directly controls at least the heating ramps, controlling the inputs/outputs for said ramps. The method then comprises the automatic identification by the master controller of the relative position of each heating ramp relative to the others when said ramp or manifold is connected to the 10 network, and the sequencing of the operation of the heating ramp injectors is done by distributing over time the individual operating sequences of the injectors. The technology for the real time kernel and real time network provide timing control, because the real time kernel has a clock cycle time that is accurately 15 defined and of constant duration. The master controller calculates the commands by reading the data directly from the inputs and it sets the outputs connected to the actuators. The heating ramps at least no longer carry PLCs. In each cycle, the master controller collects all the inputs before beginning its 20 calculations and then sets all the outputs before starting a new cycle. Therefore all the outputs that control the injectors on the various heating ramps are controlled by a single controller, rapidly and with precise and reliable timing made possible by the kernel and the real time network. The resulting choices of actions and output settings are made based on task 25 priorities. The real time network is fundamental to this, because it ensures that all inputs are read and all outputs are written at each cycle. In one example of an embodiment of the invention, the control/command functions for the ramps and manifolds are programmed in a software PLC. 30 In one example of an embodiment of the invention, the master controller is a

PC.

12 The real time network connecting the master controller and the inputs/outputs of the ramps and manifolds is, for example, an Ethernet. In another example of an embodiment of the invention, a Twincat real time kernel is associated with an Ethercat real time network. 5 In addition, the operating sequences of the injectors in the method of the invention are distributed over time such that an injector only operates when the volume of gas under said injector contains sufficient oxygen to ensure combustion of the injected fuel. Therefore, the operating sequences of the injectors in the method of the 10 invention are distributed over time so as to limit the formation of unburnt materials, particularly CO. A general algorithm allows optimizing the injection timing to optimize the air available in the hollow partitions while also maintaining a controlled flow rate in the fuel piping for each heating ramp, in order to retain uniform injection 15 characteristics. The operating sequences of the injectors are therefore distributed over time so as to limit variations in the fuel flow rate for each ramp. In addition, the time distribution is done by limiting the number of injectors operating simultaneously to a maximum number, where said maximum number is the one which results in the nominal flow rate of fuel for said ramp. 20 In one aspect of the invention, the method also proposes optimizing the combustion of fuel injectors over a length of time denoted D, for a furnace comprising a number N of injectors distributed among the hollow partitions and heating ramps of the furnace. The injectors operate in full-on and full-off pulses with adjustment of the duration. An operating duration Ai that is less than or 25 equal to the duration D is assigned to each of the N injectors, the operating durations Ai being determined from the energy requirements of the furnace and provided by the furnace control/command system. From that point, in the method: - the operating duration Ai of an injector is divided into a series of pulses, with 30 the sum of the pulse durations being equal to the operating duration Ai of said injector; 13 - a sequencing is defined by distributing the pulses over time for each of the N injectors individually and coded as a binary temporal function pi which is equal to 1 when the injector of order i is emitting a pulse at time s and equal to 0 if not; - the sequencing is calculated at computation time T, taking into account the 5 desired operating durations Ai for the injectors, with the pulses of an injector occurring no earlier than an initial time ti later than computation time T, and no later than time ti+D, - the initial times ti for each injector depend on the relative position of the injectors of the same partition and the flow rate Vk of the combustion gases in 10 this partition. Advantageously, the sequencing is calculated as follows: /a/ any initial sequencing is chosen, /b/ an order number i of 1 to N is associated with each injector, /c/ for the injector having an order number i equal to 1, one looks for the 15 distribution of operating pulses of this injector which allow maximizing a function Uk representative of the oxygen content in the combustion gases after the last injector of the same partition over an interval of time between times tk and tk+D, where tk is the time associated with the last injector of the same partition, the pulses of the other injectors maintaining the positions in the initial sequencing, 20 and a resulting sequencing is obtained with the optimum distribution of the pulses for the injector having an order number i equal to 1, /d/ step /c/ is repeated using the sequencing resulting from step /c/ and successively considering the injectors of order number i greater than 1 until the injector of order number N is reached. 25 The method may comprise the following additional steps: /e/ using the sequencing obtained from step /d/ as the initial sequencing, a new order number i from 1 to N is associated with each injector and steps /c/ and /d/ are repeated, /f/ the sequencing obtained is compared to the initial sequencing and the better 30 of the two is retained as the sequencing.

14 /g/ steps /e/ and /f/ are repeated a number of times compatible with the computation time available between computation time T and the first of the initial times ti for injectors of the same partition. With these additional steps, one determines the better sequencing of the two 5 from step /f/, in which the total fuel flow rate for each ramp resulting from the distribution of operating pulses of the injectors of a ramp does not exceed the maximum possible fuel flow rate for said ramp. Depending on the temperature settings entered by the operator and the temperatures read for each partition, combined with related measurements 10 such as CO or air flow in the partitions, an injection matrix is calculated using the processing power of the master controller. This is then sent to the remote outputs on each of the heating ramps to control the injectors. In a second aspect, the invention also relates to a device for optimizing combustion in lines of flues. 15 Apart from the arrangements described above, the invention consists of a certain number of other arrangements which will be described below in more detail using exemplary embodiments and referring to the attached drawings. These examples are not to be considered limiting. The first five figures have already been described concerning the current art: 20 - Fig. 1 is a plan view schematic of the structure of a ring furnace with two fire groups and open chambers; - Fig. 2 is a partial perspective and transverse cross-sectional view with cutaway of a diagram representing the internal structure of the furnace of Fig. 1; 25 - Fig. 3 is a fluid flow diagram illustrating an example of a heating ramp; - Fig. 4 is a partial longitudinal cross-sectional diagram illustrating the position of the ramps and manifolds over a line of partitions; - Fig. 5 is a schematic representation of a control/command system of the current art; 15 - Fig. 6 is a schematic representation of a control/command system of the invention; and - Fig.7 is a timing chart illustrating the operation of an injector over a given period of time. 5 As represented in Fig. 6, a control/command system of the invention comprises for example a DMS computer for archiving data 41 and at least one master controller, for example two controllers CCS 42a & 42b. These machines are connected by an Ethernet switch 40 which constitutes the Level 2 Ethernet. The controllers 42a and 42b each have an embedded real time PLC which controls, 10 via the real-time Level 1 Ethernet, the remote input/output units 52 for the ramps and manifolds 11, 15, 16, 17 and 18, as well as the auxiliary PLC 43. The ramps and manifolds 11, 15, 16, 17 and 18 are connected to the real time network by a cable which is connected to junction boxes 51 positioned facing each chamber 2 of the furnace 1. 15 Process monitoring occurs via control screens 39 which can be used remotely over a dedicated network if necessary (KVM Network). These screens 39 display the real-time data coming from the controllers 42a & 42b but also the archived data originating from the DMS 41. Additional screens 50 are placed in the furnace building for monitoring the process. These screens 50 display the 20 real-time data from the controllers 42a & 42b. They are connected to the real time network by using a group of dedicated inputs/outputs 52. The master controller 42a, 42b automatically identifies the relative position of a ramp or manifold compared to the others, when said ramp or manifold is connected to the network. 25 In one embodiment, at system startup, the theoretical duration of the baking cycle, the initial position of the fire group, and the theoretical configuration of each fire group are entered into the system for this purpose. "Theoretical configuration of each fire group" is understood to mean the relative position of the ramps and manifolds for the same fire group. 30 From the theoretical duration of the cycle, the initial position, the theoretical configuration of the fire group, and the current date and time, the master 16 controller 42a, 42b continuously calculates the theoretical positions for each fire group, recognized for example by a number indicating a section in the furnace 1, for the different types of ramps and manifolds 11, 15, 16, 17, 18 required to control the baking process related to the fire group. 5 For equipment, each ramp or manifold 11, 15, 16, 17, 18 comprises a head end, identified by a unique number, and inputs/outputs. The master controller 42a, 42b uses a lookup table which allows it to identify the ramp or manifold as well as its type (exhaust manifold, heating ramp, etc.) based on this number. The wired network around the furnace 1 consists of a succession of network 10 switches. Each section of the furnace 1 is equipped with a single network jack to which the ramp placed in that section is connected. This jack is connected at installation to an input, identified by number, of one of the switches forming the field network. The pair formed by the section number and switch input number 15 is unique, and at field network setup will be specified in a lookup table for use by the master controller 42a, 42b. The master controller 42a, 42b continuously monitors the various inputs from the switches to detect any changes such as connecting or disconnecting a ramp/manifold 11, 15, 16, 17, 18. When it detects such a connection, the 20 master controller 42a, 42b retrieves the number from the head end for the ramp/manifold in question, which it combines with the switch input number to allow it to associate a section number with the ramp/manifold. Thus the position of each ramp/manifold in the furnace 1, relative to each other, is identified by the master controller 42a, 42b at connection. 25 Based on the identified position for each ramp/manifold 11, 15, 16, 17, 18, the master controller 42a, 42b can then compare the actual position with the calculated theoretical position and decide whether or not to approve the ramp/manifold connection and therefore control it. In the invention, the six injectors 23 placed over the same line of partitions 6 are 30 controlled as a function of each other but also as a function of the injectors 23 placed over the other lines of partitions 6. Sequencing the opening of the 17 injectors 23 and choosing the pulse durations allows in particular optimizing the operation of each heating ramp 16 and of the fire group. More specifically, in order to optimize the combustion of the fuel injectors 23, an optimization duration period D is considered for the furnace 1 equipped with 5 injectors 23. The parameters relative to the injector 23 of order number i will be assigned an index i, where i is between 1 and N and N is the total number of injectors 23 of the furnace, distributed over a number R of heating ramps 16 and a number M of partitions 6 of the furnace 1. For example, in the case where the furnace 1 comprises two sections 1a and 1b, with three heating ramps 16 10 per section and each ramp comprising four pairs of injectors 23 and therefore each heating ramp 16 being associated to four partitions 6 per section, as is illustrated in figures 2 and 3, the total number N of injectors in the furnace 1 will be equal to forty eight. In the following description, the terms "first" and "last" will be relative to the 15 direction the fire advances, it being understood that a first injector for a given hollow partition is the one which first receives the air blown in by the blowing manifold 18. The injectors 23 operate in full-on full-off pulses, with adjustments to the duration. 20 An operating duration Ai that is less than or equal to the optimization duration D is assigned to injector 23 of order number i. The operating duration Ai of each injector 23 is deduced from the energy requirements of the furnace 1. It is provided by the control/command system 42a, 42b of the furnace 1. The operating duration Ai of the injector 23 of order number i is divided into a 25 series of a number of pulses denoted Ki, such that the sum of the duration of the Ki pulses is equal to the operating duration Ai. The sequencing is then defined by a temporal distribution of the Ki pulses for each injector 23 individually, and is coded as a binary temporal function pi(s), where s is the time, which is equal to 1 if the injector 23 of order number i is 30 emitting and is equal to 0 if not. The function pi(s) is illustrated in figure 7.

18 The sequencing is calculated at computation time T, taking into account the desired operating durations Ai for the injectors 23. The Ki pulses of the injector 23 of order number i occur no earlier than an initial time ti later than computation time T, and no later than time ti+D. In other words, 5 the first pulse of the injector 23 of order number i begins no earlier than the initial time ti, and the last pulse ends no later than time ti+D. The initial times ti for each injector 23 depend on the relative position of the injectors 23 of a same partition 6 and on the flow speed, denoted Vk, of the combustion gases in the partition 6 concerned. Below, the index k indicates that 10 this is a parameter related to a partition 6 of order number k, where k is between 1 and M. From this point, the sequencing of injectors 23 for a given partition 6 of order number k is calculated according to the following successive steps: /a/ any initial sequencing of injectors 23 in the partition 6 of order number 15 kis chosen, /b/ an order number i of 1 to N is associated with each injector 23, assigned for example according to the relative position of the injectors 23 in the direction of the fires in the partition 6 of order k concerned, /c/ for a first injector of assigned order number 1, one looks for the 20 distribution of the K1 operating pulses of this injector 23 which maximizes a function Uk(s) representative of the oxygen content in the combustion gases after the last injector of partition 6 of order number k over an interval of time between times tk and tk+D, where tk is the time of the first pulse of the last injector of partition 6 of order number k, the pulses of the 25 other injectors of order number i greater than 1 maintaining the positions in the initial sequencing, and a resulting sequencing is obtained with the optimum distribution of the pulses for the injector of order number 1, /d/ step /c/ is repeated using the sequencing resulting from step (c) and successively considering the injectors of higher order numbers until 30 injector 23 of order number N is reached.

19 Advantageously, the method for optimizing combustion comprises the following additional steps: /e/ using as the initial sequencing the sequencing obtained from step /d/, a new order number of 1 to N is associated with each injector 23 and 5 steps (c) and (d) are repeated, /f/ the sequencing obtained is compared to the initial sequencing and the better of the two is retained as the sequencing, /g/ steps /e/ and /f/ are repeated a number of times compatible with the computation time available between computation time T and the first of 10 the initial times ti for the first pulse of the injectors 23. In an additional characteristic of the invention, for the better sequencing of the two from step /f/, ones ensures that the total flow rate of fuel for each of the R ramps 16 resulting from the distribution of operating pulses for the injectors 23 of the ramp 16 does not exceed the maximum possible flow rate of fuel for said 15 ramp 16. In effect, the above sequencing calculations for the partitions 6 generally result in the injectors 23 of the same ramp 16 not having the same pulse distribution, so that it is necessary to verify that sequencing calculations based on optimization according to oxygen content per partition 6 also conform with the 20 optimum operation of each ramp 16. Thus the sequencing calculation allows optimizing the temporal distribution of pulses of injectors 23 per partition 6 and per heating ramp 16, for the entire furnace 1. The time 6ti necessary for the combustion gas to travel at velocity Vk over the 25 distance di between an injector 23 of order number i of the partition 6 of order number k and the last injector 23 of this partition 6 of order number k, is: 6ti = di/Vk In the invention, the difference between the time ti associated with an injector 23 of order number i of a partition 6 of order number k and the time tk 30 associated with the last injector of the same partition 6 of order number k is 20 equal to the time necessary for the combustion gas to travel the distance between two injectors 23, which is: ti = tk - 6ti Advantageously, the durations between the sequencing computation time T and 5 the times ti of the first injectors 23 of each partition 6 are less than one second. In the invention, the function Uk(s), representative of the oxygen content in a reference volume T at time s after the last injector of partition k, is equal to the oxygen content Ck available in the reference volume T before the first injector 23 of partition 6 of order number k, reduced by the sum of the oxygen content qi 10 necessary to obtain complete combustion by an injector 23 of order number i operating when the reference volume T passes under the injector 23 of order number i at time s - 6ti: Uk(s) = Ck - Eick qi x pi(s - 6ti) In other words, this ensures that the reference volume T contains a sufficient 15 amount of oxygen relative to the amount of fuel injected by an injector 23 of order number i of the partition 6 of order number k when this reference volume T passes under this injector 23 of order number i. In effect, the oxygen will have been consumed by combustion under the injectors 23 of order number less than i of the partition 6 of order number k. Thus when the reference volume T passes 20 under the last injector 23 of the partition 6 of order number k, the oxygen content in the reference volume T must be sufficient for the combustion reaction to take place, therefore limiting the formation of unburnt material. In one example of an embodiment of the invention, maximizing the function Uk for an injector i consists of maximizing the total period during which the function 25 Uk(s) is positive for times s in the interval [tk, tk+D]. In another example of an embodiment of the invention, maximizing the function Uk for an injector of order number i consists of maximizing a sum Sk over the interval[tk, tk+Djof positive values of Uk(s): Sk = Ese[tk, tk+D] (IUk(s)I+Uk(s))/2.

21 As an example, the duration of the pulses of the injectors 23 is between second and 5 seconds and the time between two successive pulses of the same injector 23 is between second and 5 seconds. We will now refer to figure 7 which represents the function pi(s), illustrating the 5 distribution over time of the pulses of an injector 23 of order number i in full-on or full-off operation. For each injector 23 of order number i, the function pi(s) is defined for times s in the time interval between times ti and ti+D. One exemplary embodiment consists of defining the binary function pi as being 10 a pulse train having pulses of identical durations a and inter-pulse durations b, the pulses occurring between times ti+c and ti+D-c. The inter-pulse duration b may be one of the following ten values: { 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, 5s }. The durations a, b and c are related by the following relations: 15 Ki * a = Ai and Ki * a + (Ki - 1) * b + 2 * c = D The function pi is completely defined by the operating duration Ai and by the choice of inter-pulse duration b. 20 For an operating duration Ai, depending on the choice for b and considering that the total pulse duration is equal to Ai, the number of pulses Ki is equal to the integer part of (Ai + D)/b increased by 1: Ki = [ (Ai + D) / b] + 1 The values of c and a are determined directly: 25 a = Ai / Ki and c = * (D - Ai - (Ki - 1) * b) 22 The choice of value for b is only acceptable if the resulting duration a is between 0.5s and 5s. By choosing an acceptable value for b, as the operating duration Ai is set by the equipment, the function pi(s) is completely defined. The function Uk(s) is thus 5 determined and the sequencing calculation can be performed.

Claims (10)

1. Method for optimizing combustion in lines of partitions of a multi-chamber ring furnace (1) for baking carbonaceous blocks (5), said furnace (1) comprising a 5 succession of chambers (2) for preheating, heating, natural cooling, and forced cooling, arranged in a series along the longitudinal axis (XX) of the furnace (1), each chamber (2) consisting, in the direction transverse to said longitudinal axis (XX), of pits (4) alternating with hollow heating partitions (6), carbonaceous blocks (5) being arranged within said pits (4) and said hollow heating partitions 10 (6) interconnecting with and aligning with the partitions (6) of other chambers (2), parallel to the longitudinal axis (XX) of the furnace (1), to form lines of hollow partitions (6) in which air for cooling and combustion and combustion gases circulate, an exhaust manifold (11) being connected to each of the partitions (6) of the first chamber (2) during preheating by one of the respective 15 exhaust pipes (11a), the combustion air required being partly injected by a blowing ramp (18) of the natural cooling zone (C), connected to at least one fan, and partly infiltrating through the lines of partitions (6) due to negative pressure, and the fuel necessary for baking the carbonaceous blocks (5) being partly injected by at least two heating ramps (16) each extending over a respective 20 one of at least two adjacent chambers (2) of the heating zone, and each able to inject fuel into each of the hollow partitions (6) of the corresponding respective chamber (2) of the heating zone (B), with a master controller (42a, 42b) directly controlling at least the heating ramps (16) by controlling the inputs/outputs of said heating ramps (16), said method being characterized in that it comprises 25 the automatic identification by the master controller (42a, 42b) of the relative position of each heating ramp relative to the others when said ramp is connected to the network, and the sequencing of the operation of the injectors (23) of the heating ramp (16) being done by distributing over time the individual operating sequences of the injectors (23). 30

2. Method for optimizing combustion according to claim 1, wherein the operating sequences of the injectors (23) are distributed over time such that an injector 24 (23) only operates when the volume of gas under said injector (23) contains sufficient oxygen to ensure combustion of the injected fuel.

3. Method for optimizing combustion according to claim 1 or claim 2, wherein the operating sequences of the injectors (23) are distributed over time so as to 5 limit the formation of unburnt material, particularly CO.

4. Method for optimizing combustion according to any one of claims 1 to 3, wherein the operating sequences of the injectors (23) are distributed over time so as to limit the number of injectors (23) of a heating ramp (16) operating simultaneously to a maximum number, said maximum number being the one 10 which results in the nominal flow rate of fuel for said ramp (16).

5. Method for optimizing combustion according to any one of claims 1 to 3, wherein the operating sequences of the injectors (23) are distributed over time so as to limit variations in the fuel flow rate for each heating ramp (16).

6. Method for optimizing the combustion of fuel injectors (23) according to any 15 one of the above claims, over a length of time denoted D, for a furnace (1) comprising a number N of injectors (23) distributed among the hollow partitions (6) and heating ramps (16) of the furnace (1), said injectors (23) operating in full-on and full-off pulses with adjustment of the duration, an operating duration (Ai), less than or equal to the duration D being assigned to each of the N 20 injectors (23), the operating durations (Ai) being determined from the energy requirements of the furnace (1) and provided by the control/command system (42a, 42b) of the furnace (1), characterized in that: - the operating duration (Ai) of an injector (23) is divided into a series of pulses where the sum of the pulse durations is equal to the operating duration (Ai) of 25 said injector (23); - a sequencing is defined by distributing the pulses over time for each of the N injectors (23) individually and coded as a binary temporal function (pi) which is equal to 1 when the injector (23) of order number i is emitting a pulse at time s and is equal to 0 if not; 25 - the sequencing is calculated at computation time (T), taking into account the desired operating durations (Ai) for the injectors (23), with the pulses of an injector (23) occurring no earlier than an initial time (ti) later than computation time (T), and no later than time ti+D, 5 - the initial times (ti) for each injector (23) depend on the relative position of the injectors (23) of a same partition (6) and on the flow rate (Vk) of the combustion gases in this partition (6).

7. Method for optimizing combustion according to claim 6, wherein the sequencing is calculated as follows: 10 /a/ any initial sequencing is chosen, /b/ an order number (i) of 1 to N is associated with each injector (23), /c/ for the injector of order number (i) equal to 1, one looks for a distribution of the operating pulses of this injector (23) that maximizes a function (Uk) representative of the oxygen content in the combustion gases after the last 15 injector of the same partition (6) over an interval of time between times tk and tk+D, where tk is the time associated with the last injector (23) of the same partition (6), the pulses of the other injectors (23) maintaining their positions of the initial sequencing, and a resulting sequencing is obtained with the optimum distribution of the pulses for the injector (23) of order number (i) equal to 1, 20 /d/ step /c/ is repeated, based on the sequencing resulting from step /c/ and successively considering the injectors (23) of order number (i) greater than 1 until the injector of order number N is reached.

8. Method for optimizing combustion according to claim 7, wherein it comprises the following additional steps: 25 /e/ using as the initial sequencing the sequencing retained in step /d/, a new order number (i) of 1 to N is associated with each injector (23) and steps /c/ and /d/ are repeated, /f/ the sequencing obtained is compared to the initial sequencing and the better of the two is retained as the sequencing, 26 /g/ steps /e/ and /f/ are repeated a number of times compatible with the computation time available between computation time (T) and the first of the initial times (ti) of the injectors (23) of the same partition (6).

9. Method for optimizing combustion according to claim 8, wherein for the better 5 of the two sequencings from step /f/ it is ensured that the total fuel flow rate for each heating ramp (16) resulting from the distribution of operating pulses of the injectors (23) of a heating ramp (16) does not exceed the maximum possible fuel flow rate for said ramp (16).

10. Device for optimizing combustion in lines of flues of a multi-chamber ring 10 furnace for baking carbonaceous blocks (5), said furnace (1) comprising a succession of chambers (2) for preheating, heating, natural cooling, and forced cooling, arranged in a series along the longitudinal axis (XX) of the furnace (1), each chamber (2) consisting, in the direction transverse to said longitudinal axis (XX), of pits (4) alternating with hollow heating partitions (6), carbonaceous 15 blocks (5) being arranged in said pits (4) and said hollow partitions (6) interconnecting with and aligning with the partitions (6) of other chambers (2), parallel to the longitudinal axis (XX) of the furnace (1), to form lines of hollow partitions (6) in which air for cooling and combustion and combustion gases circulate, an exhaust manifold (11) being connected to each of the partitions (6) 20 of the first chamber (2) during preheating by one of the respective exhaust pipes (11 a), the combustion air required being partly injected by a blowing ramp (18) of the natural cooling zone (C), connected to at least one fan, and partly infiltrating through the lines of partitions (6) due to negative pressure, and the fuel necessary for baking the carbonaceous blocks (5) being partly injected by 25 at least two heating ramps (16) each extending over a respective one of at least two adjacent chambers (2) of the heating zone, and each able to inject fuel into each of the hollow partitions (6) of the corresponding respective chamber (2) of the heating zone (B), with a master controller (42a, 42b) directly controlling at least the heating ramps (16) by controlling the inputs/outputs of said heating 30 ramps (16), said device being characterized by the relative position of each heating ramp relative to the others being identified automatically by the master controller (42a, 42b) at the time said heating ramp is connected to the network 27 so as to ensure that this relative position is appropriate for the safe operation of the furnace (1).