EP1070224B1 - Method and device for regulating burning ring furnaces - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to the field of furnaces with so-called rotating fire chambers ("ring furnace"). in English) for cooking carbonaceous blocks and more particularly a process and a device for regulating such ovens.

STATE OF THE ART

We already know methods of regulating this type of oven, as in French applications FR 2 600 152 and FR 2 614 093 in the name of the plaintiff, and in international application WO 91/19147.

This type of oven, also called "open chamber", includes, as described in these documents cited, in the long sense, a plurality of preheating, cooking chambers and cooling, each chamber being formed, in the transverse direction, by the alternating juxtaposition of hollow heating partitions in which the combustion gases, and cells in which the carbon blocks to be cooked are stacked, the blocks being drowned in carbonaceous dust.

This type of oven has two spans, the total length of which can reach more than one hundred meters. Each bay has a succession of rooms separated by transverse walls and open at the top, to allow loading raw blocks and unloading of the cooked cooked blocks. Each room has, arranged parallel to the long direction of the furnace, i.e. to the long axis of the furnace, a set of hollow partitions, with thin walls, in which the gases will circulate hot or combustion fumes ensuring the cooking, alternating, in the cross direction of the oven, with cells in which the baking blocks are stacked.

The hollow partitions are provided, at their upper part, with closable openings called "Workmen". They also have baffles to lengthen and distribute more uniformly the path of combustion gases or fumes.

The oven is heated by burner burners with a length equal to the width of the chambers, the injectors of these burners being introduced, via the ports, in the hollow partitions of the rooms concerned. Upstream of the burners (compared in the direction of advance of the fire), there are nozzles for blowing combustion air mounted on a blowing ramp fitted with fans, these blowing nozzles being connected, via the ports, to the said partitions. Downstream of the burners, there are combustion smoke suction nozzles, mounted on a suction ramp supplying smoke capture centers, and fitted with shutters to shut off said suction nozzles at the desired level. Heating is provided by both the combustion of the fuel injected into the cooking chambers, and by that of the vapors of pitch emitted by the blocks during cooking in the preheating chambers, vapors which, taking into account the vacuum in the preheating chambers, leave the alveoli through the hollow partition and burn with the oxygen remaining in the combustion fumes circulating in the hollow partitions of these chambers.

Typically, around ten rooms are “active” simultaneously: four in the cooling zone, three in the heating zone, and three in the heating zone preheating.

As the cooking takes place, we advance by one room, for example every 24 hours, the whole "blowing nozzles - burners - nozzles suction ”, each chamber thus successively ensuring, upstream of the zone of preheating, a loading function for the raw carbon blocks, then, in the preheating, a natural preheating function by combustion fumes and combustion of pitch vapors, then in the cooking zone, a heating function blocks at 1100-1200 ° C, and finally, in the cooling zone, a function of cooling of the blocks with cold air and, correspondingly, preheating of the air constituting the oxidizer of the furnace, the cooling zone being followed, downstream, by a unloading area for cooled carbon blocks.

The most common method of regulating this type of oven is to regulate temperature and / or pressure a certain number of furnace chambers. Typically, on 10 simultaneously active chambers, 4 have temperature measurements and 2 have pressure measurements. On the one hand, the three burner banks are regulated according to the temperature of the combustion fumes, the fuel injection being adjusted to follow a temperature rise curve, typically the temperature of the combustion, but possibly that of carbonaceous blocks. On the other hand, the speed of blower manifold fans are typically regulated based on pressure static measured upstream of the burners, but it can also be left constant. Finally, the flaps of the suction ramp are regulated according to a measured vacuum in a chamber located between the burners and the suction nozzles. But, the most often, especially in the most recent ovens, said depression is itself controlled by a temperature setpoint, typically the temperature of the flue gases combustion, so that said flaps are controlled by a temperature measurement and its comparison to a set value.

• dans la demande française FR 2 600 152 est décrit en outre un dispositif pour optimiser la combustion dans la zone de cuisson permettant de mesurer l'opacité des fumées dans les piquages d'aspiration et de réguler cette aspiration en conséquence ;
• dans la demande française FR 2 614 093 est décrite en outre une méthode pour optimiser la combustion dans le four en injectant, en permanence, la quantité d'air nécessaire et suffisante pour obtenir la combustion complète à la fois des matières volatiles dégagées au cours de la cuisson des blocs carbonés et du combustible injecté dans les brûleurs ;
• dans la demande WO 91/19147, en outre on contrôle le rapport oxygène/carburant dans le four en mesurant la teneur en oxygène dans le four.

The regulation of the oven can also call on other complementary means:

• in the French application FR 2 600 152 is further described a device for optimizing combustion in the cooking zone making it possible to measure the opacity of the fumes in the suction nozzles and to regulate this suction accordingly;
• in French application FR 2 614 093 a method is further described for optimizing combustion in the furnace by continuously injecting the quantity of air necessary and sufficient to obtain complete combustion of both the volatile materials released during cooking the carbon blocks and the fuel injected into the burners;
• in application WO 91/19147, in addition, the oxygen / fuel ratio in the oven is checked by measuring the oxygen content in the oven.

PROBLEM

The regulatory methods used to date are mainly based on temperature and pressure measurements, in a large number of rooms, and in different partitions of the same room. Complementary measures, as indicated in the cited state of the art, can complement these measures of based.

In addition, the temperature and pressure setpoint values are known. each room, to be respected in order to obtain carbon blocks of the required quality and for obtain correct operation of the oven, in particular in the preheating zone. Indeed, it is during the preheating of the carbon blocks to be cooked that the volatile matter contained in the pitch. It is important that these gases or vapors are sucked towards hollow partitions and burn immediately in the presence of residual oxygen present in combustion fumes. Otherwise, these pitch vapors can foul the nozzles, the suction ramp and the pipes leading to the collection. These deposit may ignite on contact with incandescent dust particles. These lights damage the pipes and their hot fumes burn the filters and collection center fans. Faced with these risks, safety margins are taken by increasing the flow rates of the suction combustion films, flow rates which generate in turn overconsumption of fuel and lower energy performance from the oven.

In addition, we observe that the current regulation of the ovens leads to instabilities, and generates sudden random variations in the flow rates of the exhausted combustion fumes and fuel flows, so that the furnace does not have a stable transfer rate thermal, which is detrimental to the efficiency of the heat exchange or transfer between the combustion fumes and said carbon blocks.

Finally, this dispersion of the different flow rates results in a dispersion of the levels of cooking which requires overcooking part of the carbon blocks or anodes to ensure the minimum quality of all the anodes, which ipso facto leads to degradation energy performance of the oven.

Ultimately, the current operation and regulation of ovens is characterized, on the one hand, by a considerable increase in the number of measurement sensors, and on the other hand, by the adoption of large safety margins with regard to each of the three parameters main ones that operate the oven: the air blowing upstream of the cooling, injecting fuel into the cooking chambers, and extracting combustion fumes downstream of the preheating chambers.

• d'une part, l'ensemble des moyens de mesure et de régulation intervient pour une part non négligeable dans le coût de l'investissement et de fonctionnement du four, beaucoup de capteurs, compte tenu des conditions particulièrement difficiles de température et d'environnement, ayant une faible durée de vie et pouvant de ce fait être considérés comme une matière consommable,
• d'autre part, comme cet ensemble de moyens de mesure et de régulation ne permet pas de stabiliser le fonctionnement du four, il en résulte une consommation énergétique variable, avec une consommation moyenne assez éloignée de l'optimum compte tenu des marges de sécurité qui sont prises pour garantir la qualité des blocs de carbone fabriqués et pour garantir l'intégrité et la longévité du four.

It follows from this fact that:

• on the one hand, all of the measurement and regulation means account for a non-negligible part of the cost of the investment and operation of the oven, many sensors, taking into account the particularly difficult conditions of temperature and environment , having a short lifespan and which can therefore be considered as consumable material,
• on the other hand, as this set of measurement and regulation means does not allow the operation of the oven to be stabilized, this results in variable energy consumption, with an average consumption quite far from the optimum taking into account the safety margins which are taken to guarantee the quality of the carbon blocks produced and to guarantee the integrity and longevity of the furnace.

The present invention aims to solve this double problem and to ensure the conduct automated and optimized oven while reducing both the investment cost and of operating control and regulation equipment, and consumption energy of the oven.

DESCRIPTION OF THE INVENTION

A first object of the invention is a method of regulating a rotary fire oven for cooking carbonaceous blocks comprising a succession of chambers C _i active simultaneously but in a differentiated manner, namely, from upstream to downstream and in the direction longitudinal, cooling chambers, the first of which, at the head, is supplied with atmospheric air using blowing nozzles S _j , cooking chambers equipped with at least one ramp of injector burners I _j supplied with fuel , and preheating chambers, the last of which, at the end, is fitted with suction nozzles A _j of combustion fumes, and comprising, in the cross direction and alternately, a succession of hollow heating partitions Cl _ij and d ' cells Al _ij in which the carbonaceous blocks to be baked are stacked, said partitions Cl _ij of a given chamber Ci provided with openings intended to receive said blowing nozzles S _j and / or said injectors I _j and / or said suction nozzles A _j and / or measuring means communicating with the hollow partitions Cl _i-1j and Cl _i-1j of the chambers preceding C _i-1 and following C _i-1 so as to ensure the upstream circulation downstream of a gas flow comprising atmospheric air and / or combustion films, characterized in that the mass flow rate DG _j of each of the combustion smoke flows G _j passing through said suction tapping A _j tail of the preheating chambers, is regulated by measuring the mass flow DG _j and the temperature T _j of each of the combustion smoke flows G _j , by calculating the corresponding enthalgic energy flows E _j , typically by the product R equal to DG _j . (T _j -T _a ) .C _g , T _j and T _a being respectively the temperature of the combustion fumes G _j and that of the ambient air, and C _g being the specific mass heat of the combustion fumes at the temperature T _j , so as to maintain, for each of the smoke flows d e combustion G _j , said enthalgic energy flow E _j at a predetermined set value Eo _j .

This setpoint value Eo _j can be either a constant or a function of the predetermined time f (t). Typically every 24 hours, the mobile equipment of the furnace (burner ramps, blow-off nozzle ramp, suction nozzle ramp, etc.) advances by one chamber. Therefore, the set values which are a function of time are defined over this period T, as may be the case for Eo _j . It may be advantageous to have, during the residence time T of the fire in a given chamber, a set value Eo _j which includes either a ramp, that is to say a regular variation of the set value Eo _j during the residence time, either specific set values at the start or end of the residence time T.

The essential means of the invention therefore resides in the fact of controlling the energy flow E _j of the combustion fumes sucked in by each suction nozzle A _j to control the actuators of the oven, whereas according to the prior art, the suction nozzles, like the burners, are controlled according to a temperature curve, which itself is generally a function of time over period T.

The energy flow E _j of each flow of combustion fumes is in fact an enthalpy flow whose value of R (= DG _j . (T _j - Ta). C _g ) constitutes a good approximation. A more precise value can be obtained by replacing "(Tj - Ta). C _g ”by the value of the integral ∫ C _g (T) .dT for T between Ta and T _j , or by any approximate polynomial expression of this integral.

• un fonctionnement du four stabilisé, au lieu d'un fonctionnement avec de brusques variations des paramètres,
• un fonctionnement économique en ce qui concerne la consommation de carburant,
• une simplification des équipements et dispositifs de contrôle et régulation.

Surprisingly, the Applicant has found that this essential means according to the invention, although much simpler than the control means used in the prior art, constituted the solution to the problem posed. Indeed, it was able to verify that this means in particular allowed:

• stabilized oven operation, instead of operation with sudden variations in parameters,
• economical operation with regard to fuel consumption,
• a simplification of control and regulation equipment and devices.

Overall, this results in the production of baked carbon blocks of more constant quality and at a better cost. The reasons why the means according to the invention leads to these surprising results are not clearly established. However, according to an assumption of the applicant, the outside air flows which enter the preheating chambers in vacuum in an open chamber oven, could interfere with the operation of the oven and constitute a disturbing element contributing to accentuate the variations in oven settings.

Based on its hypothesis, the Applicant had the idea of choosing as the parameter of regulation, a parameter independent of the greater or lesser supply of outside air. For this, it found that a parameter such as the parameter R, equivalent to a flow of energy compared to room temperature, was therefore completely independent of the more or less large amount of air having entered the oven and could allow this effectively controls the oven with a stable and economical oven line.

According to the invention, said setpoint, denoted Eo _j , of the energy flows E _j of the combustion fumes G _j is chosen, typically experimentally, at a lowest possible value which is compatible with the usual quality requirements of carbonaceous blocks produced and operating the furnace.

According to the invention, it is also possible to regulate not all the energy flows E _j but only a limited number of flows, for example one in two. In this case, the unregulated flow E _k is assigned the mean of the neighboring regulated flow values E _k-1 and E _k-1 .

DESCRIPTION OF THE FIGURES

Figures 1, 1a, 1b, 2, 3, 3a, 6 and 7, relating to the invention, are explained in the example according to the invention or in the description. Figures 4 and 5 illustrate elements already known from the ovens according to the invention.

Figure 1 is a top view of the "active" part of a rotary fire cooking oven (1) according to the invention. Figure la corresponds to Figure 1 and shows a sectional view of the oven (1), in the vertical plane and in the long direction, and in particular the succession of hollow heating partitions, from Cl _1j to Cl _10j , ensuring circulation different gas flows. FIG. 1b is the curve of air pressure (34) and / or combustion smoke (35) in the various heating partitions. FIG. 1c schematically represents the computer control and regulation means (5) associated with the preceding figures.

Figure 2 is a partially exploded perspective view of an oven (1) comprising means according to the invention.

Figure 3 shows in longitudinal section a flow sensor. FIG. 3a shows a variant of the invention in which the temperature T _j is measured in the suction connection (210), preferably downstream from the flow sensor (214).

Figure 4 is a sectional view in the XZ plane of a heating partition (3) of a chamber C _i (2) according to the state of the art ensuring the circulation of gas flows (34,35). Each chamber C _i comprises baffles (31) increasing the path of the gas flows (34,35) and is separated from the previous C _i-1 and the following C _{i + 1} by a transverse wall (32). The partition (3) comprises openings (30) provided with covers (36) to the right of which is a well (39), that is to say a vertical space comprising neither baffle (31) nor spacer (33) , so as to be able to descend into said partition the mobile devices necessary for the operation of the oven, in particular said suction nozzles (210) and said blowing nozzles (230).

Figure 5 is a sectional view in the XY plane of a preheating chamber C _i according to the prior art, showing the alternation of partitions (3) and cells (4). Each cell (4) contains the carbonaceous cooking blocks (40) covered with a carbon powder (42), each cell Al _ij (4) being heated by virtue of the two heating partitions Cl _ij and Cl _{ij + 1} adjacent. The pitch vapors (41), released by the heating of the carbonaceous blocks, spread in the partitions (3) under vacuum and ignite in the presence of the oxygen remaining from the combustion fumes (35) or that of the flow d 'air (38).

FIG. 6 represents a plot of points, each point corresponding to a reading of experimental measurements carried out by the applicant on state-regulated ovens of technique. The graph shows on the ordinate the energy consumed Ec (fuel) in MJ per tonne of carbon blocks produced, and on the abscissa, the energy dissipated Eg in the combustion fumes in MJ per tonne produced.

Figure 7 is a schematic representation of the regulation according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention originates from the applicant's idea of studying the operation of state-of-the-art regulated ovens, in terms of energy comparison consumed and energy lost, as shown in the graph in Figure 6. It This graph shows that the energy consumed varies considerably, between the extreme straight lines (61, 62), from 2200 to 2900 MJ / t. The plaintiff observed a strong correlation between the values of Ec and Eg, which results in a regression line (6).

With the regulation method according to the invention, one chooses to operate the oven with a predetermined value of Eg, the lowest possible, determined value experimentally, and with a value of Ec equal to or close to the value of correlation of this value of Eg on the portion (63) of the regression line (6).

The values of Eg-Ec, expressed in MJ / t, correspond to proportional values of Eo-DCo having the dimension of an energy per unit of time, so that the regression line portion (63) also allows, once experimentally defined the set values Eo for the overall energy of the combustion films or Eo _j for the energy of the combustion fumes at each suction connection A _j , to determine the corresponding set value for the fuel flow rates DCo for all the burners, or the flow rates DCo _j or DCo _ij corresponding to the partitions Cl _j or Cl _ij depending on whether there are one or more burner burners.

Preferably, the fuel flow DC _j supplying said burners I _j is therefore fixed at a predetermined level DCo _j as illustrated in FIGS. 1 and 1c, and in FIG. 7.

Thus, the invention allows an absence of measurement of the temperature of the combustion fumes for regulating the fuel flow DC _j , it being understood that this fuel flow, generally distributed between several burner banks, typically three to four burner banks, positioned on successive chambers, from C _i to C _{i + 2} or to C _{i + 3,} is fixed at a predetermined value DCo _j , possibly as a function of time, established in particular during the oven start-up tests, and as a function of the energy level Eo _j , as has already been mentioned in connection with FIGS. 6 and 7, this setpoint DCo _j being correlated, according to the portion (63) of the line of experimental regression of FIG. 6, with the predetermined level of said product R, corresponding to the energy flow Eo or Eo _j of the combustion fumes.

This is a means which goes completely against the teaching of the state of the technique where, in a traditional way, the flow of fuel is typically regulated by the temperature of the combustion gases in the cooking chambers.

However, said predetermined level of fuel flow rate DCo _j can be chosen, for a given hollow partition Cl _ij (3) of a given cooking chamber C _i (22) of a given oven, so that the temperature measured combustion fumes (35) in said hollow partition Cl _ij (3) has a predetermined value, typically between 1000 ° and 1300 ° C.

It goes without saying that, during the development phase of an oven or the restarting of an oven, it is advisable to check that the temperatures aimed in each room are well which is to be distinguished from the actual regulation of an operating oven Routine.

In the context of the invention, said air flow DA _{j of} said blowing nozzles S _j (230) at the head of the cooling chambers (23) can be regulated, either so that the pressure in the hollow partitions Cl _{ij of} said cooking chambers C _i (22) is less than atmospheric pressure and is within a predetermined pressure range, the static pressure P _j at the tail of the cooling chambers (23) being substantially equal to atmospheric pressure, or so that the speed of the air flow (34), or that of the fan setting in motion this air flow, at the inlet of said cooking chambers is constant, and at a predetermined value, as illustrated in FIGS. 1, 1a, 1b and 1c.

However, according to the invention, the air flow DA _j is preferably fixed at a predetermined value so that the static pressure at the top of the cooking chambers (22) is less than atmospheric pressure. In this case, the pressure measurement P _j can optionally be used to check, at regular time intervals, for example once a day or once a week, the absence of process drift.

According to the invention, the set values, in particular Eo corresponding to the energy flow of the combustion fumes aspirated outside the furnace, and the corresponding value of DCo corresponding to the fuel consumption in the burners, are defined for each partitions Cl _ij of the furnace, and are identified in the transverse direction of the furnace by the index “j”, and over the entire length of the furnace by the index “i”, so as to have a map of the set values which take account of the side effects both on the sides of said oven and at its ends when moving the light. Indeed, it is advantageous, in order to obtain consistency in the quality of the products produced and at the lowest possible cost, to take account of side effects, that is to say to define according to the indices "i" and “j”, for any partition Cl _ij , the optimum setpoint values, which can be done once and for all at the time of starting the oven, setpoint corrections can then be made during the life of the oven taking into account for example aging of materials and possible alterations in the tightness of the oven. The set value DCo _j can be corrected, during cooking, so as to maintain it at an optimal value. In particular, it has been found advantageous to correct DCo _j using a measurement of the carbon monoxide content contained in the flue gases at the outlet of the oven. For this, the measurement of the carbon monoxide content can be carried out on the suction ramp or at the entrance to the film processing center.

Preferably, computer means (5.50), known in themselves, are used to store set values or ranges of said set values of different parameters for each partition Cl _ij over the entire oven, in particular Eo _ij , to compare these values with the measured values of these parameters, after calculation if necessary, as well as actuators, controlled by said computer means, for possibly correcting said regulation parameters, in particular by modifying the air flow DA _ij , so that that the measured values are equal to the set values or fall within the set value ranges.

• des moyens de mesure des débits DG_j des flux de fumées de combustion G_j,
• des moyens informatiques (5,50) pour stocker des valeurs de consigne ou plages de valeurs de consigne des flux d'énergie Eo_j, pour comparer ces valeurs, après calcul de la valeur de R en fonction notamment du débit DG_j et de la température T_j des fumées de combustion, avec les valeurs de flux d'énergie mesurées E_j,
• et des actionneurs (213), commandés par lesdits moyens informatiques, pour corriger éventuellement la valeur du flux d'énergie mesurée E_j en modifiant le débit DG_j du flux de filmées de combustion, de façon à ce que les valeurs de mesure E_j soient égales aux valeurs de consigne Eo_j ou rentrent dans les plages de valeurs de consigne.

Another object of the invention consists of an oven control device for implementing the control method according to the invention, device comprising:

• means for measuring the flow rates DG _j of the combustion smoke flows G _j ,
• computer means (5.50) for storing reference values or ranges of reference values of the energy flows Eo _j , for comparing these values, after calculation of the value of R as a function in particular of the flow rate DG _j and the temperature T _j of the combustion fumes, with the measured energy flow values E _j ,
• and actuators (213), controlled by said computer means, for possibly correcting the value of the measured energy flow E _j by modifying the flow rate DG _j of the stream of combustion films, so that the measurement values E _j are equal to the setpoints Eo _j or fall within the ranges of setpoints.

This device can also comprise the storage of the correlation function (63) between the set values of the energy flows Eo or Eo _j and the set values of the fuel flows DCo or DCo _j and the corresponding regulation of said flows at from any variation of Eo or Eo _j .

It may optionally include computer means (5) for storing reference values or ranges of reference values of the pressure Po _j , to compare this value with the pressure value P _j measured, as well as actuators, controlled by said means computer, to possibly correct said regulation parameters by modifying the air flow DA _j , so that the measurement values are equal to the set values or fall within the ranges of set values. However, preferably, as already indicated, the air flows DA _j are maintained at a predetermined constant value.

It has been found advantageous to choose, as a means for measuring the flow rates DG _j of the combustion gases G _j, a Venturi tube (214) placed in each of said suction nozzles A _j (210). Preferably, the Venturi tubes used are of small size, so that they can be placed inside said suction nozzles A _j and only capture a determined fraction of the gas flow G _j , typically 1/5 th to 1/20 th of this flow, in fact the plaintiff observed that. the use of such tubes had great advantages compared to the use of a Venturi tube through which the entire gas flow would pass, namely, low cost, low pressure drop, low fouling, low size, and above all very good accuracy of the flow measurement.

In the device according to the invention, the air flows DA _j and the flows DG _j of combustion smoke (35) drawn in can be modulated by adjusting shutters, denoted respectively VA _j (232) and VG _j ( 212) and placed respectively on each of the blow-off nozzles S _j (230) connected to an air supply ramp (231) and on each of the suction nozzles A _j (210) connected to a suction ramp (211 ).

EXAMPLE OF IMPLEMENTATION

Figures 1, 1a, 1b, 1c, 2, 3, 3a, 6 and 7 illustrate the invention.

FIG. 1, according to the invention, is a top view of the “active” part of a rotary baking oven (1), “active” part comprising, in the long direction, 10 chambers C _i (2 ) with i = 1 to 10 and, from left to right, a succession of 3 preheating chambers (21) (C ₁ to C ₃ ), 3 cooking chambers (22) (C ₄ to C ₆ ), and 4 chambers cooling (23) (C ₇ to C ₁₀ ), and, in the cross direction, and alternately, a succession of hollow heating partitions Cl _ij (3) and Al _ij cells (4) in which the blocks are stacked carbonaceous to be cooked (40), with i = 1 to 10, and j = 0 to 6 for Cl _ij and 1 to 6 for Al _ij .

• une rampe de soufflage d'air (231) placée transversalement à l'extrémité amont de la chambre C₁₀ de refroidissement, munie de piquages de soufflage d'air S_j (230), chaque piquage de soufflage d'air S_j insufflant dans la cloison chauffante correspondante Cl_10j un débit d'air DA_j régulé grâce à un volet d'obturation VA_j (232) et à un actionneur (233) de ce volet,
• trois rampes de brûleurs (220) placées transversalement sur les chambres de cuisson C₄ à C₆, chaque rampe comprenant deux rangées de brûleurs (221) avec injecteurs de carburant I_ij (222) avec i = 4 à 6, et j = 0 à 6, chaque injecteur de carburant I_ij assurant un débit de carburant DC_ij.
• une rampe d'aspiration (211) placée transversalement à l'extrémité aval de la chambre C₁ de préchauffage, munie de piquages d'aspiration A_j (210), chaque piquage aspirant dans ladite cloison chauffante Cl_1j un flux de filmées de combustion G_j de débit massique DG_j pouvant varier grâce à un volet d'obturation VG_j (212) et à un actionneur (213) de ce volet.

The heating partitions Cl _ij (3) are provided with openings (30) making it possible to introduce into said partitions the necessary mobile devices, with, from right to left, ie from upstream to downstream in the direction of circulation gas flows (34, 35):

• an air blowing ramp (231) placed transversely at the upstream end of the cooling chamber C ₁₀ , provided with air blowing nozzles S _j (230), each air blowing nozzle S _j blowing into the corresponding heating partition Cl _10j an air flow DA _j regulated by a shutter VA _j (232) and an actuator (233) of this shutter,
• three burner burners (220) placed transversely on the cooking chambers C ₄ to C ₆ , each burner comprising two rows of burners (221) with fuel injectors I _ij (222) with i = 4 to 6, and j = 0 at 6, each fuel injector I _ij ensuring a fuel flow DC _ij .
• a suction ramp (211) placed transversely at the downstream end of the preheating chamber C ₁ , provided with suction nozzles A _j (210), each nozzle sucking in said heating partition Cl _1j a stream of combustion films G _j of mass flow DG _{j which} can vary thanks to a shutter VG _v (212) and to an actuator (213) of this shutter.

With a view to regulating according to the invention, each suction connection A _j is provided with a device (214) for measuring the mass flow rate DG _j of the flow of combustion smoke, of the "Venturi tube" type as described in Figures 3 and 3a, a device for measuring the temperature T _j of this flow, another device measuring the temperature Ta of the ambient air. These devices are not in themselves shown in FIG. 1. Said temperature measurement device comprises a gas temperature sensor (215), which measures the temperature Tj of the gases flowing in the suction nozzles Aj (210 ), preferably downstream of the device (214) for measuring the mass flow. The temperature measurement is typically carried out using thermocouples.

A ramp of deployable shutters (217), positioned on the chamber C ₀ , obstructs the hollow partitions Cl _ij downstream of the suction ramp (211) positioned on the chamber C ₁ , so that the flow of smoke combustion is diluted by an air supply from the chambers located downstream of the fire.

A pressure sensor ramp (234) is placed on the chamber C ₇ to measure the pressure P _j and thus verify that the first combustion chamber C ₆ is indeed at a pressure slightly lower than atmospheric pressure.

Figure la corresponds to Figure 1 and shows a sectional view of the oven (1), in the vertical plane and in the long direction, and in particular the succession of hollow heating partitions, from Cl _1j to Cl _10j , ensuring circulation different gas flows, air flow (34) in the cooling chambers C ₇ to C ₁₀ , combustion smoke flow (35) in the combustion chambers C ₄ to C ₆ and in the preheating chambers C ₁ to C ₃ . The chambers C ₇ to C ₁₀ being in overpressure, an air flow (37) escapes from these chambers, while an air flow (38) enters the chambers C ₁ to C ₆ which are in depression , as shown in Figure 1b.

FIG. 1b is the air pressure (34) or combustion smoke (35) pressure curve in the different heating partitions: the chamber C ₇ upstream of the combustion chambers is at atmospheric pressure Pa, while the pressure in upstream of the chamber C ₁₀ is equal Pa + p with p = 50 to 60 Pa, while the pressure downstream of the chamber C ₁ is equal to Pa-p ', with p' = 100 to 200 Pa.

• en amont, de préférence, la fixation à une valeur prédéterminée du débit d'air DA_j soufflé dans les cloisons chauffantes creuses Cl_10j, ou éventuellement, la régulation du débit d'air DA_j, grâce au volet d'obturation VA_j (232) et à son actionneur (233), de manière à ce que la pression P_j mesurée juste en amont des chambres de combustion soit maintenue constante et comprise dans une plage de valeur de consigne sous la forme Po_j ± po,
• au niveau des chambres de combustion, la fixation des débits de carburant des trois rampes d'injecteurs I_4j, I_5j et I_6j, le débit DC_ij d'un injecteur I_ij devant être égal à une valeur de consigne DCo_ij,
• en aval, le régulation des flux des fumées de combustion (35) aspirés, en mesurant les valeurs de chaque débit gazeux DG_j, de sa température T_j, de la température ambiante Ta, en calculant la valeur du produit R, c'est à dire la valeur de l'énergie E_j = DG_j . Cg . (T_j - Ta) contenue dans le flux G_j de fumées aspirées, et en régulant chaque débit DG_j de manière à ce que E_j soit égal à une valeur de consigne Eo_j.

FIG. 1c shows, schematically, the computer control and regulation means (5) allowing:

• upstream, preferably, the fixing at a predetermined value of the air flow DA _j blown into the hollow heating partitions Cl _10j , or possibly, the regulation of the air flow DA _j , thanks to the shutter VA _j ( 232) and to its actuator (233), so that the pressure P _j measured just upstream of the combustion chambers is kept constant and included in a set value range in the form Po _j ± po,
• at the combustion chambers of setting fuel flow rates of the three ramps of injectors I _{4j, 5j} I and I _6j, flow DC _ij I _ij of an injector to be equal to a set value DCo _ij,
• downstream, regulating the flow of combustion smoke (35) drawn in, by measuring the values of each gas flow DG _j , its temperature T _j , the ambient temperature Ta, by calculating the value of the product R, that is to say the value of the energy E _j = DG _j . Cg. (T _j - Ta) contained in the flow G _j of aspirated smoke, and regulating each flow DG _j so that E _j is equal to a set value Eo _j .

Figure 2 is a perspective view, partially exploded, of an oven (1) according to the prior art comprising means according to the invention. It shows in particular, in the transverse direction noted Y-Y ', the succession of hollow heating partitions (3) provided with openings (30) and baffles (31), and cells (4) containing the stacks of carbonaceous blocks (40) to be cooked. It shows, in the long direction denoted X-X ', a first chamber (chamber C ₂ ) in exploded form, and a second chamber (chamber C ₁ ) equipped with suction nozzles (210) connected to a suction ramp (211), each connection comprising a flow sensor (214), a shutter (212) and an actuator (213) of this shutter.

FIGS. 3 and 3a represent in longitudinal section a flow sensor according to the invention, constituted by a “Venturi” type tube placed inside each suction connection A _j (210) measuring a static pressure Ps and a differential pressure Pd, allowing the calculation of the mass flow DG _j. This flow rate is equal to K. (Ps.Pd / T) ^1/2 , K being a constant taking account in particular of geometric factors, only a fraction of the flow of combustion fumes (35) passing through the Venturi tube.

FIG. 7 is a schematic representation of the regulation according to the invention: each suction connection (210), connected to the suction ramp (211), comprises a flow sensor (214) of Venturi type, a shutter d shutter (212) driven by an actuator (213). Regulation and control means (50) of the DG _j flow rates of the combustion fumes make it possible, in particular from the pressure measurements supplied by the flow sensor (214), to calculate the mass flow DG _j of the combustion smoke flow (35), then to calculate the value of R, that is to say of the corresponding energy E _j , taking into account either the temperature measurements Ta and T _j required, or other data entered in memory, such as the specific specific heat of the fumes C _g as a function of their temperature and of their pressure, of comparing it with a set value Eo _j or with a range of set values, and actuating the shutter shutter (212) of so as to vary DG _j in the desired direction and thus correct the value of R or E _j .

FIG. 7 also shows the burners (221) with a predetermined flow rate DCo. A dotted line (630) connects the values of DCo or DCo _j to those of Eo or Eo _j , the relationship between the two being constituted by the correlation between Ec and Eg illustrated by the portion (63) of the regression line ( 6) of figure 6.

ADVANTAGES OF THE INVENTION

• d'une part de simplifier la régulation des fours de cuisson à feu tournant, et ainsi de diminuer le coût d'investissement ou de remplacement des dispositifs de mesure, ce qui correspond à des gains importants, compte tenu du fait que la régulation d'un four compte environ pour 10% de l'investissement total. Avec une régulation selon l'invention dans laquelle les brûleurs notamment sont pilotés par une consigne de puissance (flux d'énergie Eo - Eoj) et non plus de température comme selon l'état de la technique, et ainsi, ce sont 50 à 100 thermocouples par four ayant une durée de vie de trois mois qui sont économisés,
• d'autre part de diminuer la consommation énergétique des fours d'au moins 10%, en la faisant passer d'une moyenne de 2450 MJ/t à moins de 2200 MJ/t,
• d'assurer une constance de qualité des blocs carbonés cuits, compte tenu de la disparition de variations brusques de la température dans les fours,
• de s'adapter aux fours existants et ainsi d'améliorer le fonctionnement de ces fours sans investissement important.

The invention has very significant advantages. It allows:

• on the one hand to simplify the regulation of baking ovens with rotating fire, and thus to reduce the cost of investment or replacement of the measuring devices, which corresponds to significant gains, taking into account that the regulation of an oven accounts for around 10% of the total investment. With a regulation according to the invention in which the burners in particular are controlled by a power setpoint (energy flow Eo - Eoj) and no longer of temperature as according to the state of the art, and thus, these are 50 to 100 thermocouples by oven having a lifespan of three months which are saved,
• on the other hand to reduce the energy consumption of the ovens by at least 10%, by reducing it from an average of 2450 MJ / t to less than 2200 MJ / t,
• to ensure consistency in the quality of the cooked carbonaceous blocks, taking account of the disappearance of sudden variations in temperature in the ovens,
• adapt to existing ovens and thus improve the operation of these ovens without significant investment.

Claims (19)

1. Process for regulation of a ring furnace (1) for baking carbonaceous blocks (40), including a sequence of sections C_i (2, 21, 22, 23) that are active simultaneously but in a different manner, namely working along the longitudinal direction from upstream to downstream, cooling sections (23) the first of which at the head is supplied with atmospheric air (34) through blowing openings S_j (230), baking sections (22) equipped with at least one burner ramp (220) with injectors I_j (221) supplied with fuel, and preheating sections (21) the last of which at the tail is equipped with openings A_j (210) through which combustion exhaust gases (35) are drawn in, and in the transverse direction comprising a sequence of flue walls Cl_ij (3) alternating with pits Al_ij (4) in which carbonaceous blocks to be baked (40) are stacked, the said flue walls Cl_ij (3) in a given section C_i (2, 21, 22, 23) being fitted with peep holes (30) through which the said blowing openings S_j (230) and/or the said injectors I_j (221) and/or the said exhaust openings A_j (210) and/or measurement means (214, 215, 234) communicating with flue walls Cl_i-1j and Cl_i+1j in the previous section C_i-1 and the next section C_i+1 will be fitted, to control circulation of a gas stream from the upstream side towards the downstream side, the gas including atmospheric air (34) and/or combustion exhaust gases (35), characterized in that the mass flow DG_j of each of the combustion exhaust gas streams G_j (35) passing through the said exhaust openings A_j (210) at the tail of the preheating sections (21), is regulated by measuring the mass flow DG_j and the temperature T_j of each of the streams of combustion exhaust gas G_j, by calculating the corresponding enthalpic energy fluxes E_j, so as to maintain the said enthalpic energy flux E_j equal to a predetermined set value Eo_j for each of the combustion exhaust gas streams G_j.
2. Process according to claim 1, in which the energy fluxes E_j are calculated by the product R = DG_j. (T_j-T_a).C_g, where T_j and T_a are the temperatures of the combustion exhaust gases G_j and of the ambient air respectively, and C_g is the specific heat of combustion exhaust gases at temperature T_j.
3. Process according to claim 1 or 2, in which the said set value Eo_j is either a predetermined constant, or a predetermined function of time f(t).
4. Process according to any one of claims 1 to 3, in which the fuel flow DC_j into the said burners I_j (221) is fixed at a predetermined level DCo_j.
5. Process according to claim 4, in which the said predetermined level DCo_j of the said fuel flow DC_j is determined from a set value Eo_j for the said energy flux E_j and an experimental correlation curve (63) between the said energy flux E_j and the said fuel flow DC_j into the said burners.
6. Process according to any one of claims 4 to 5, in which the said predetermined fuel flow is chosen for a given flue wall Cl_ij (3) in a given baking section C₁ (22) in a given furnace, such that the measured temperature of the combustion exhaust gases (35) in the said flue wall Cl_ij (3) is a predetermined value, typically between 1000° and 1300°C.
7. Process according to any one of claims 1 to 6, in which the said air flow DA_j through the said blowing openings S_j (230) at the head of the cooling sections (23) is regulated, either such that the pressure in the said flue walls Cl_ij in the said baking sections C_i (22) is below atmospheric pressure and is within a predetermined pressure range, the static pressure P_j at the tail of the cooling sections (23) being approximately equal to atmospheric pressure, or such that the speed of the air stream (34), or the speed of the fan used to apply movement to this air stream, at the inlet to the said baking sections is constant and equal to a predetermined value.
8. Process according to any one of claims 1 to 6, in which the air flow DA_j through the said blowing openings S_j (230) at the head of the cooling sections (23) is preferably fixed at a predetermined value such that the static pressure at the head of the baking sections (22) is below atmospheric pressure.
9. Process according to any one of claims 1 to 3 in which the set values, and particularly Eo_j, are defined for each flue wall Cl_ij in the furnace, not only along the transverse direction of the furnace identified by subscript j, but also along the longitudinal direction of the furnace identified by subscript i, in order to produce a map of set values, e.g. Eo_ij, that takes account of boundary effects both on the sides of the said furnace and at its ends as combustion moves forwards.
10. Process according to any one of claims 4 to 8 in which the set values, and particularly Eo_j and the corresponding value of DCo_j, are defined for each flue wall Cl_ij in the furnace, not only along the transverse direction of the furnace identified by subscript j, but also along the longitudinal direction of the furnace identified by subscript i, in order to produce a map of set values, e.g. Eo_ij, that takes account of boundary effects both on the sides of the said furnace and at its ends as combustion moves forwards.
11. Process according to any one of claims 4 to 8 or 10, in which DCo_j is corrected during baking by means of measurements of the carbon monoxide content in exhaust gases at the furnace outlet.
12. Process according to any one of claims 1 to 11 in which computer means (5) are used to store set values or ranges of the said set values of the different parameters for each flue wall in the entire furnace, and particularly Eo_ij, to compare these values with measured values of these parameters possibly after calculation, and actuators controlled by the said computer means to correct the said regulation parameters if necessary, particularly by modifying air flows DA_ij such that measured values are equal to set values or are within set value ranges.
13. Process according to any one of claims 1 to 12, in which the temperature T_j is measured in the exhaust openings A_j (210).
14. Furnace regulation device to implement the regulation process according to claim 1, including:

    means of measuring flows DG_j of streams of combustion gases G_j,

    computer means (5, 50) for storing set values or ranges of set values of energy fluxes Eo_j, for comparing these values, with the values of the measured enthalpic energy flux E_j,

    and actuators (213) controlled by the said computer means, to correct the value of the measured enthalpic energy flux E_j if necessary by modifying the flow DG_j of combustion exhaust gases G_j such that measured values E_j are equal to the set values Eo_j or are within ranges of set values.
15. Furnace regulation device to implement the regulation process according to any one of claims 2 to 13, including:

    means of measuring flows DG_j of streams of combustion gases G_j,

    computer means (5, 50) for storing set values or ranges of set values of energy fluxes Eo_j, for comparing these values after calculating the value of R depending particularly on the flow DG_j and temperature T_j of combustion exhaust gases, with the values of the measured enthalpic energy flux E_j,

    and actuators (213) controlled by the said computer means, to correct the value of the measured enthalpic energy flux E_j if necessary by modifying the flow DG_j of combustion exhaust gases G_j such that measured values E_j are equal to the set values Eo_j or are within ranges of set values.
16. Device according to claims 14 or 15, also including storage of the correlation function (63) between the set values of energy fluxes Eo_j and the corresponding set values of fuel flows DCo_j and providing the corresponding regulation of the said flows starting from any variation of Eo_j.
17. Regulation device according to any one of claims 14 to 16, in which the said means of measuring the flows DG_j of the stream of combustion exhaust gases G_j comprise a Venturi tube (214) placed in each of the exhaust openings A_j (210), so as to capture only a determined fraction of the gas flow G_j.
18. Regulation device according to any one of claims 14 to 17, in which the blown air flows DA_j or the flows DG_j of the stream of drawn in combustion exhaust gases (35) are fixed or modulated by adjusting dampers, denoted VA_j (232) and VG_j (212) respectively, and placed on each of the blowing openings S_j (230) connected to an air blowing ramp (231) and onto each of the exhaust openings A_j (210) connected to an exhaust ramp (211), respectively.
19. Regulation device according to any one of claims 14 to 18 in which a gas temperature sensor (215) measures the temperature T_j of gases circulating in the exhaust openings A_j (210).

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