CA2245322C - Procedure for process management in an anode furnace - Google Patents
Procedure for process management in an anode furnace Download PDFInfo
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- CA2245322C CA2245322C CA 2245322 CA2245322A CA2245322C CA 2245322 C CA2245322 C CA 2245322C CA 2245322 CA2245322 CA 2245322 CA 2245322 A CA2245322 A CA 2245322A CA 2245322 C CA2245322 C CA 2245322C
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
- C04B35/528—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components
- C04B35/532—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components containing a carbonisable binder
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B13/00—Furnaces with both stationary charge and progression of heating, e.g. of ring type, of type in which segmental kiln moves over stationary charge
- F27B13/06—Details, accessories, or equipment peculiar to furnaces of this type
- F27B13/14—Arrangement of controlling, monitoring, alarm or like devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D19/00—Arrangements of controlling devices
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- Manufacture And Refinement Of Metals (AREA)
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Abstract
The present invention is directed to a procedure for process management in an anode furnace, from which an adjustable flow of flue gas is directed into at least one combustion space: The procedure involves the measuring the flue gas temperature in each combustion space as the actual temperature, registering the oxygen or hydrocarbon content, setting the power of the burners in accordance with the fire duct temperature and/or the available oxygen content in the fire duct, comparing the actual temperature in the combustion space with a specified set point temperature, determining a time integral of the temperature deviation and, controlling the actual temperature during the process management as a function of the determined time integral in such a way that the time integral is reduced to zero at the end of the process management.
Description
Procedure for Process Management in an Anode Furnace The present invention relates to a procedure for process management in an anode furnace, from which an adjustable flow of flue gas is directed into at least one combustion space.
In anode furnaces of this type, the gas flow is directed through a fire duct past anodes held under the exclusion of air and is thereby heated by the combusted anodes. In the form of pre-heated combustion air, the flow of gas is then directed through the fire zone and heats up the cold anodes as flue gas. In accordance with the annular furnace principle, the fire zone moves around the furnace which is made up of chambers arranged in a ring structure, whereas the anodes are held stationary. As such, the furnace may consist of individual large chambers for the anodes and have a single flow of flue gas, or it may be made up of a range of adjacent anode and fire ducts.
Such furnaces are used for the purpose of burning large quantities of carbon anodes which are used in the electrolysis process for manufacturing aluminium through the reduction of alumina.
The carbon anodes consist of petroleum coke and pitch which are subjected to a heat-treatment process in the furnace under the exclusion of oxygen. The procedure involved in the heat treatment process is such that the anode is initially heated up to about 1000 °C with a defined temperature/time gradient and then cooled down according to the sintering process.
The heat treatment process is undertaken in open or covered annular furnaces which consists of anode combustion spaces into which the uncombusted anodes are loaded and sealed against the ingress of oxygen by means of anthracite. The heat treatment process for the anodes must take place in a defined sequence in order to make it possible to determine the quality of the combusted anodes in advance. To this end, moving "fires" are arranged on the furnace, these fires consisting of mobile flue gas extraction, measurement, burner and cooling ramps.
In anode furnaces of this type, the gas flow is directed through a fire duct past anodes held under the exclusion of air and is thereby heated by the combusted anodes. In the form of pre-heated combustion air, the flow of gas is then directed through the fire zone and heats up the cold anodes as flue gas. In accordance with the annular furnace principle, the fire zone moves around the furnace which is made up of chambers arranged in a ring structure, whereas the anodes are held stationary. As such, the furnace may consist of individual large chambers for the anodes and have a single flow of flue gas, or it may be made up of a range of adjacent anode and fire ducts.
Such furnaces are used for the purpose of burning large quantities of carbon anodes which are used in the electrolysis process for manufacturing aluminium through the reduction of alumina.
The carbon anodes consist of petroleum coke and pitch which are subjected to a heat-treatment process in the furnace under the exclusion of oxygen. The procedure involved in the heat treatment process is such that the anode is initially heated up to about 1000 °C with a defined temperature/time gradient and then cooled down according to the sintering process.
The heat treatment process is undertaken in open or covered annular furnaces which consists of anode combustion spaces into which the uncombusted anodes are loaded and sealed against the ingress of oxygen by means of anthracite. The heat treatment process for the anodes must take place in a defined sequence in order to make it possible to determine the quality of the combusted anodes in advance. To this end, moving "fires" are arranged on the furnace, these fires consisting of mobile flue gas extraction, measurement, burner and cooling ramps.
A predefined, time-dependent set point characteristic on the burner ramps and the flue gas extraction ramps is used for achieving a specified temperature/time characteristic in the anode ducts arranged between the fire ducts. Whilst the heat thereby created is directed over the anodes at differing points, a specified temperature/time characteristic is established in the fire ducts arranged between the anode ducts.
The temperature/time characteristic is set during the heating-up period by means of a controlled flow of flue gas drawn out of the fire zone. At the same time, the temperature/time characteristic can be set in the fire zone by controlling the supply of fuel.
The temperature/time characteristic is regulated in the cooling zone by blowing in cold air.
Starting from the temperature prevailing at the anode during the combustion process, the quality of the anode is determined by the temperature/time area in the sintering range, which is also referred to as the combustion index. A specific temperature/time characteristic is required in the fire ducts in order to achieve a defined combustion index. In the plants which are in service, a temperature program of this type is specified as a set point and the plant controllers follow this program as the set point as precisely as possible.
Heating of the anode causes the pitch which was used as a binding agent to escape in the form of a combustible gas. The consistency for the anodes is limited by having the same quantity of flue gas flowing through several anode ducts arranged in the flue gas flow direction during the heating-up phase. The gas evolution speed depends on the temperature at the anode and takes place over quite a large temperature interval. This means several chambers in a row are involved in the gas evolution. However, in certain cases this can lead to uncontrollable temperature fluctuations in the fire ducts, or alternatively if the temperature is below the ignition temperature, it can be expected that uncombusted hydrocarbons will be emitted.
Furthermore, the status of the individual fire ducts worsens continuously over time due to the thermal stress, in other words the continuous heating up and cooling down.
This invariably leads to an increase in flow resistance in the fire ducts, so the proportion of infiltrated air flowing in increases. This additional amount of air also influences the anode temperatures which have to be achieved, with the result that the desired temperature characteristic is not attained.
In addition, the burner bridges are switched off for a greater or lesser amount of time during the conversion, or situations arise in which not enough oxygen is present in the fire duct so the fuel is not completely combusted and consequently the set point temperatures are not achieved.
All these disruptions to the combustion process have the effect of making it impossible to prevent fluctuations in the combustion index, resulting in different levels of quality in individual anodes.
For anodes of the same composition, the quality of the combusted anode is largely dependent on the combustion temperature and combustion duration which were achieved. The higher the temperature and the longer the period during which it is maintained, the better the quality.
However, a high combustion temperature and a long duration lead to increased combustion costs and the service life of the fire ducts is reduced as a result of the higher thermal stresses.
Furthermore, during the manufacture of anodes, it is also necessary to bear in mind that the electrolysis process for obtaining aluminium is dependent on which anode displays the shortest service life during the electrolysis, because the shortest service life of an anode determines the service life of the electrolysis cells. Consequently, during the manufacture of anodes, care must be taken to ensure that all anodes which are to be used in an electrolysis process should have as even a level of quality as possible. This is why the most similar possible combustion indices should be achieved during different combustion processes.
The purpose of the present invention is to provide a procedure for combustion process management which guarantees an optimum combustion process to the extent that the combusted anodes display as consistently even a level of quality as possible in order to minimise the combustion costs and the costs of electrolysis by having the same anode quality.
Beyond the scope of state-of the-art measurements of flue gas temperatures and setting the burner and flue gas volumes in accordance with the required temperature/time characteristic, this problem is solved by means of the following process steps:
~ measuring the flue gas temperature in each combustion space as the ACTUAL
temperature, ~ registering the oxygen content or the hydrocarbons, ~ setting the power of the burners in accordance with the fire duct temperature and/or the available oxygen content in the fire duct, ~ comparing the ACTUAL temperature in the combustion space with a specified set point temperature and/or ~ determining the amount of oxygen available in the fire duct by direct measurement or by means of an empirical model involving the supplied quantity of fuel and the equivalent quantity of fuel from the pitch gas evolution as well as the flow of flue gas, ~ determining a deviation index as a time integral of the temperature deviation, ~ continuously modifying the set point characteristic in order to zero the deviation integral at the end of the process management and/or ~ determining a combustion index or a deviation integral in each anode duct and ~ controlling the ACTUAL temperature in order to zero the deviation integral at the end of the process management.
Further advantageous configurations of the invention derive from the subordinate claims.
The procedure in accordance with the present invention specifies two stages with which the consistency of the anodes and thereby the combustion index can be improved and the energy consumption for the combustion process can be reduced.
In the first stage of the procedure, it is assumed that the combustion index is directly dependent on the fluctuations in the fire duct temperature. The important factor here is not a specific temperature characteristic, but rather the equivalent temperature characteristic, namely the one which guarantees the flow of heat to the anodes. As a first degree of approximation, it is possible to assume that the conduction of heat remains approximately constant during a limited temperature interval. This means it is possible to accept a deviation from the rated curve, in other words away from the set point temperature characteristic, provided the time integral of the deviation is returned to zero at the end of the combustion process by an opposing temperature deviation of corresponding duration and magnitude away from the set point.
This method provides a means of measuring the lack of or surplus heat flow to the anode within the combustion space, so a deviation from the set point temperature can be deliberately allowed to arise. For example, if an attempt is made to maintain a specified temperature characteristic during the heating-up phase, the volumetric flow of the flue gas must be reduced when the evolved pitch gas is combusted. This combustion situation leads to a lack of oxygen in the fire duct, resulting in an inadequate combustion temperature and the liberation of uncombusted hydrocarbons.
In accordance with the present invention, this undesirable situation is avoided by increasing the flow of flue gas before this state of affairs arises, thereby achieving the ignition temperature and thus providing enough oxygen for combustion. It has also proved advantageous to permit the excess temperature during the heating-up phase and not to regulate it, thereby allowing the temperature to set itself to an appropriate value independently. This ensures that combustion is complete and there are no harmful emissions of uncombusted hydrocarbons.
As part of this procedure, the deviation index from the known set point temperature is to be measured and compensated for during the continuation of the process management in order to guarantee an even consistency in all combusted anodes. The fire duct temperature is reduced by supplying smaller quantities of flue gas and/or fuel during the continuation of the combustion process.
A further combustion situation arises if there is insufficient oxygen in a fire duct because the burners do not have their own air supply. Instead, the air required for combustion which is supplied to the burners is the pre-heated air from the cooling zone which is drawn into the fire zone. However, this means more fuel has to be used in this combustion situation in order to achieve the set point temperature. Nevertheless, it is also possible that this set point is not achieved despite the fact that the burner is operated at full power. Instead, the fuel leaves the fire duct without being combusted, thereby leading to the liberation of harmful hydrocarbons.
Assuming an adequate supply of oxygen, a specific quantity of fuel is required within a specific temperature interval in order to achieve a specified temperature gradient, and consequently it is possible to draw conclusions about the efficiency of combustion by comparing these measurable values, in particular with regard to the necessary burner power.
If a burner then falls below a lower limit of efficiency, the procedure in accordance with the present invention dictates that the quantity of fuel is reduced until the available oxygen is completely combusted at that burner power level, thereby preventing the lower efficiency threshold of the combustion process from being violated. Attainment of the set point temperature is thus consciously dispensed with since this combustion situation only arises in the heating-up phase and can be corrected during the continuation of the combustion process in accordance with the present invention.
The measurements of oxygen content and/or hydrocarbons as volatile constituents of the flow of flue gas demand a considerable complexity of apparatus, so consequently these values are estimated in the procedure in accordance with the present invention without additional measuring sensors being required.
To this end, the burner power levels and the position of the flue gas slide valves are defined as manipulated variables in the control system. In addition to these, the low pressure level in the combustion channel must be measured, with the result that these values permit a simple and easy method of registering parameters which can be used for estimating the total fuel quantity and the volumetric flow of the flue gas with the required degree of accuracy.
The parameters obtained in this manner must be brought into relationship with one another so that these normalised values permit conclusions to be drawn relating to the fuel load in the fire duct as a measure of the free oxygen content.
In order to estimate the volatile constituents in the flow of flue gas, it is necessary to include the combustible constituents of the anode, since these constituents lead to an increase in temperature in the gas evolution zone, the gradient of which represents a measure of the fuel quantity. The volatile constituents present in the form of a quantity of fuel in the fire duct are thus made up of hydrocarbons, sulphur gases and the combustible constituents of the anode.
This empirical data makes it possible to calculate a quantity of fuel which is equivalent to the quantity of fuel actually supplied to the burners. Thus, without requiring additional measuring instruments, it is possible to determine the quality of fuel present in the entire fire duct, and consequently the available oxygen as well.
The conventional furnace management system involves a rise in temperature followed by a period during which this temperature is maintained. The thermal inertia of the anode ducts means the anode duct wall only reaches the fire duct temperature after a considerable time lag.
The present invention makes beneficial use of this thermal inertia to the extent that it is possible to achieve a dynamic optimisation of the temperature characteristic, because the temperature of the first holding phase is raised above the set point temperature without leading to overheating and thus irreparable damage to the anode duct wall. The temperature can then be gradually lowered in the second and following holding phases or it can be maintained in the region of the set point temperature, with the effect that the deviation integral of the fire duct temperature or the anode temperature between the actual temperature and the set point temperature is reduced to zero during the management of the process.
Consequently, given that the heat transfer is the same, this first stage of the procedure guarantees that the heat flow to the anode is the same at the end of each combustion process, even if each combustion process was subject to different interim deviations.
Although the aforementioned steps in the procedure improve the consistency of the anodes and therefore their quality as well, there is nevertheless no guarantee that the correct combustion index is actually achieved on each anode.
The temperature at the anode is registered by means of the second stage of the procedure in accordance with the present invention, because the heat transfer alters as a function of the wear on the flameproof material during the combustion process.
In order to keep the wear on anode thermocouples as low as possible, the second stage of the procedure can be supplemented to the effect that a dynamic adaptive model of the thermal behaviour is created. For this purpose, the basic structure is assumed to be that obtained from the identification of the combustion process, namely by means of measuring the temperatures in the two fire ducts between which the anode duct is arranged, as well as by measuring the anode temperature. The parameters are automatically adapted by the fact that all anode ducts are equipped with thermocouples up to a temperature of approx. 500 °C.
This time interval is sufFcient to adapt the basic model to the specific dynamics of heat transfer in an anode duct by means of the measured temperatures. The anode thermocouples can be removed following identification at low temperature. The further anode temperatures are then obtained from a model calculation.
Once these values have been obtained, it is possible to calculate a combustion index and/or the deviation index for each anode duct. Once the dynamic adaptive model for heat transfer to the anode is available, it is possible to modify the set point characteristic of the fire duct temperature so as to achieve the optimum combustion index at the end of the combustion process.
Since the fire and anode ducts are arranged in an alternating succession, each anode duct is located between two fire ducts which means it is heated from two sides.
Equally, each fire duct is also supplied by two anode ducts. Consequently, an iterative optimisation method must be employed in order to find the specific temperature for each fire duct which guarantees the lowest maximum temperature. Since both outer fire ducts only supply one anode duct each, it is possible to solve the optimisation problem.
The present invention has been described with regard to preferred embodiments.
However, it will be obvious to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.
The temperature/time characteristic is set during the heating-up period by means of a controlled flow of flue gas drawn out of the fire zone. At the same time, the temperature/time characteristic can be set in the fire zone by controlling the supply of fuel.
The temperature/time characteristic is regulated in the cooling zone by blowing in cold air.
Starting from the temperature prevailing at the anode during the combustion process, the quality of the anode is determined by the temperature/time area in the sintering range, which is also referred to as the combustion index. A specific temperature/time characteristic is required in the fire ducts in order to achieve a defined combustion index. In the plants which are in service, a temperature program of this type is specified as a set point and the plant controllers follow this program as the set point as precisely as possible.
Heating of the anode causes the pitch which was used as a binding agent to escape in the form of a combustible gas. The consistency for the anodes is limited by having the same quantity of flue gas flowing through several anode ducts arranged in the flue gas flow direction during the heating-up phase. The gas evolution speed depends on the temperature at the anode and takes place over quite a large temperature interval. This means several chambers in a row are involved in the gas evolution. However, in certain cases this can lead to uncontrollable temperature fluctuations in the fire ducts, or alternatively if the temperature is below the ignition temperature, it can be expected that uncombusted hydrocarbons will be emitted.
Furthermore, the status of the individual fire ducts worsens continuously over time due to the thermal stress, in other words the continuous heating up and cooling down.
This invariably leads to an increase in flow resistance in the fire ducts, so the proportion of infiltrated air flowing in increases. This additional amount of air also influences the anode temperatures which have to be achieved, with the result that the desired temperature characteristic is not attained.
In addition, the burner bridges are switched off for a greater or lesser amount of time during the conversion, or situations arise in which not enough oxygen is present in the fire duct so the fuel is not completely combusted and consequently the set point temperatures are not achieved.
All these disruptions to the combustion process have the effect of making it impossible to prevent fluctuations in the combustion index, resulting in different levels of quality in individual anodes.
For anodes of the same composition, the quality of the combusted anode is largely dependent on the combustion temperature and combustion duration which were achieved. The higher the temperature and the longer the period during which it is maintained, the better the quality.
However, a high combustion temperature and a long duration lead to increased combustion costs and the service life of the fire ducts is reduced as a result of the higher thermal stresses.
Furthermore, during the manufacture of anodes, it is also necessary to bear in mind that the electrolysis process for obtaining aluminium is dependent on which anode displays the shortest service life during the electrolysis, because the shortest service life of an anode determines the service life of the electrolysis cells. Consequently, during the manufacture of anodes, care must be taken to ensure that all anodes which are to be used in an electrolysis process should have as even a level of quality as possible. This is why the most similar possible combustion indices should be achieved during different combustion processes.
The purpose of the present invention is to provide a procedure for combustion process management which guarantees an optimum combustion process to the extent that the combusted anodes display as consistently even a level of quality as possible in order to minimise the combustion costs and the costs of electrolysis by having the same anode quality.
Beyond the scope of state-of the-art measurements of flue gas temperatures and setting the burner and flue gas volumes in accordance with the required temperature/time characteristic, this problem is solved by means of the following process steps:
~ measuring the flue gas temperature in each combustion space as the ACTUAL
temperature, ~ registering the oxygen content or the hydrocarbons, ~ setting the power of the burners in accordance with the fire duct temperature and/or the available oxygen content in the fire duct, ~ comparing the ACTUAL temperature in the combustion space with a specified set point temperature and/or ~ determining the amount of oxygen available in the fire duct by direct measurement or by means of an empirical model involving the supplied quantity of fuel and the equivalent quantity of fuel from the pitch gas evolution as well as the flow of flue gas, ~ determining a deviation index as a time integral of the temperature deviation, ~ continuously modifying the set point characteristic in order to zero the deviation integral at the end of the process management and/or ~ determining a combustion index or a deviation integral in each anode duct and ~ controlling the ACTUAL temperature in order to zero the deviation integral at the end of the process management.
Further advantageous configurations of the invention derive from the subordinate claims.
The procedure in accordance with the present invention specifies two stages with which the consistency of the anodes and thereby the combustion index can be improved and the energy consumption for the combustion process can be reduced.
In the first stage of the procedure, it is assumed that the combustion index is directly dependent on the fluctuations in the fire duct temperature. The important factor here is not a specific temperature characteristic, but rather the equivalent temperature characteristic, namely the one which guarantees the flow of heat to the anodes. As a first degree of approximation, it is possible to assume that the conduction of heat remains approximately constant during a limited temperature interval. This means it is possible to accept a deviation from the rated curve, in other words away from the set point temperature characteristic, provided the time integral of the deviation is returned to zero at the end of the combustion process by an opposing temperature deviation of corresponding duration and magnitude away from the set point.
This method provides a means of measuring the lack of or surplus heat flow to the anode within the combustion space, so a deviation from the set point temperature can be deliberately allowed to arise. For example, if an attempt is made to maintain a specified temperature characteristic during the heating-up phase, the volumetric flow of the flue gas must be reduced when the evolved pitch gas is combusted. This combustion situation leads to a lack of oxygen in the fire duct, resulting in an inadequate combustion temperature and the liberation of uncombusted hydrocarbons.
In accordance with the present invention, this undesirable situation is avoided by increasing the flow of flue gas before this state of affairs arises, thereby achieving the ignition temperature and thus providing enough oxygen for combustion. It has also proved advantageous to permit the excess temperature during the heating-up phase and not to regulate it, thereby allowing the temperature to set itself to an appropriate value independently. This ensures that combustion is complete and there are no harmful emissions of uncombusted hydrocarbons.
As part of this procedure, the deviation index from the known set point temperature is to be measured and compensated for during the continuation of the process management in order to guarantee an even consistency in all combusted anodes. The fire duct temperature is reduced by supplying smaller quantities of flue gas and/or fuel during the continuation of the combustion process.
A further combustion situation arises if there is insufficient oxygen in a fire duct because the burners do not have their own air supply. Instead, the air required for combustion which is supplied to the burners is the pre-heated air from the cooling zone which is drawn into the fire zone. However, this means more fuel has to be used in this combustion situation in order to achieve the set point temperature. Nevertheless, it is also possible that this set point is not achieved despite the fact that the burner is operated at full power. Instead, the fuel leaves the fire duct without being combusted, thereby leading to the liberation of harmful hydrocarbons.
Assuming an adequate supply of oxygen, a specific quantity of fuel is required within a specific temperature interval in order to achieve a specified temperature gradient, and consequently it is possible to draw conclusions about the efficiency of combustion by comparing these measurable values, in particular with regard to the necessary burner power.
If a burner then falls below a lower limit of efficiency, the procedure in accordance with the present invention dictates that the quantity of fuel is reduced until the available oxygen is completely combusted at that burner power level, thereby preventing the lower efficiency threshold of the combustion process from being violated. Attainment of the set point temperature is thus consciously dispensed with since this combustion situation only arises in the heating-up phase and can be corrected during the continuation of the combustion process in accordance with the present invention.
The measurements of oxygen content and/or hydrocarbons as volatile constituents of the flow of flue gas demand a considerable complexity of apparatus, so consequently these values are estimated in the procedure in accordance with the present invention without additional measuring sensors being required.
To this end, the burner power levels and the position of the flue gas slide valves are defined as manipulated variables in the control system. In addition to these, the low pressure level in the combustion channel must be measured, with the result that these values permit a simple and easy method of registering parameters which can be used for estimating the total fuel quantity and the volumetric flow of the flue gas with the required degree of accuracy.
The parameters obtained in this manner must be brought into relationship with one another so that these normalised values permit conclusions to be drawn relating to the fuel load in the fire duct as a measure of the free oxygen content.
In order to estimate the volatile constituents in the flow of flue gas, it is necessary to include the combustible constituents of the anode, since these constituents lead to an increase in temperature in the gas evolution zone, the gradient of which represents a measure of the fuel quantity. The volatile constituents present in the form of a quantity of fuel in the fire duct are thus made up of hydrocarbons, sulphur gases and the combustible constituents of the anode.
This empirical data makes it possible to calculate a quantity of fuel which is equivalent to the quantity of fuel actually supplied to the burners. Thus, without requiring additional measuring instruments, it is possible to determine the quality of fuel present in the entire fire duct, and consequently the available oxygen as well.
The conventional furnace management system involves a rise in temperature followed by a period during which this temperature is maintained. The thermal inertia of the anode ducts means the anode duct wall only reaches the fire duct temperature after a considerable time lag.
The present invention makes beneficial use of this thermal inertia to the extent that it is possible to achieve a dynamic optimisation of the temperature characteristic, because the temperature of the first holding phase is raised above the set point temperature without leading to overheating and thus irreparable damage to the anode duct wall. The temperature can then be gradually lowered in the second and following holding phases or it can be maintained in the region of the set point temperature, with the effect that the deviation integral of the fire duct temperature or the anode temperature between the actual temperature and the set point temperature is reduced to zero during the management of the process.
Consequently, given that the heat transfer is the same, this first stage of the procedure guarantees that the heat flow to the anode is the same at the end of each combustion process, even if each combustion process was subject to different interim deviations.
Although the aforementioned steps in the procedure improve the consistency of the anodes and therefore their quality as well, there is nevertheless no guarantee that the correct combustion index is actually achieved on each anode.
The temperature at the anode is registered by means of the second stage of the procedure in accordance with the present invention, because the heat transfer alters as a function of the wear on the flameproof material during the combustion process.
In order to keep the wear on anode thermocouples as low as possible, the second stage of the procedure can be supplemented to the effect that a dynamic adaptive model of the thermal behaviour is created. For this purpose, the basic structure is assumed to be that obtained from the identification of the combustion process, namely by means of measuring the temperatures in the two fire ducts between which the anode duct is arranged, as well as by measuring the anode temperature. The parameters are automatically adapted by the fact that all anode ducts are equipped with thermocouples up to a temperature of approx. 500 °C.
This time interval is sufFcient to adapt the basic model to the specific dynamics of heat transfer in an anode duct by means of the measured temperatures. The anode thermocouples can be removed following identification at low temperature. The further anode temperatures are then obtained from a model calculation.
Once these values have been obtained, it is possible to calculate a combustion index and/or the deviation index for each anode duct. Once the dynamic adaptive model for heat transfer to the anode is available, it is possible to modify the set point characteristic of the fire duct temperature so as to achieve the optimum combustion index at the end of the combustion process.
Since the fire and anode ducts are arranged in an alternating succession, each anode duct is located between two fire ducts which means it is heated from two sides.
Equally, each fire duct is also supplied by two anode ducts. Consequently, an iterative optimisation method must be employed in order to find the specific temperature for each fire duct which guarantees the lowest maximum temperature. Since both outer fire ducts only supply one anode duct each, it is possible to solve the optimisation problem.
The present invention has been described with regard to preferred embodiments.
However, it will be obvious to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.
Claims (12)
1. Procedure for process management in an anode furnace, from which an adjustable flow of flue gas is directed into at least one combustion space, characterised by the process steps of:
i) measuring the flue gas temperature in each combustion space as the ACTUAL
temperature, ii) registering the oxygen content or the hydrocarbons, iii) setting the power of burners in accordance with a fire duct temperature and/or the available oxygen content in a fire duct, iv) comparing the ACTUAL temperature in the combustion space with a specified set point temperature, v) determining a time integral of the temperature deviation and vi) controlling the ACTUAL temperature during the process management as a function of the determined time integral in such a way that the time integral is reduced to zero at the end of the process management.
i) measuring the flue gas temperature in each combustion space as the ACTUAL
temperature, ii) registering the oxygen content or the hydrocarbons, iii) setting the power of burners in accordance with a fire duct temperature and/or the available oxygen content in a fire duct, iv) comparing the ACTUAL temperature in the combustion space with a specified set point temperature, v) determining a time integral of the temperature deviation and vi) controlling the ACTUAL temperature during the process management as a function of the determined time integral in such a way that the time integral is reduced to zero at the end of the process management.
2. Procedure in accordance with Claim 1, characterised in that the flow of flue gas is increased prior to the start of evolution of volatile constituents, in such a way that there is a sufficiently high ACTUAL temperature for igniting sulphur gases and there is adequate oxygen available in the combustion space.
3. Procedure in accordance with Claim 1, characterised in that:
i) the power of the burners is reduced to an adjustable minimum firing system efficiency by reducing the supply of fuel if there is too little oxygen in the combustion space and, ii) during the continuation of the process management, the power of the burner is increased as a function of the quantity of oxygen available, in such a way as to compensate for the temperature loss during the low-oxygen phase.
i) the power of the burners is reduced to an adjustable minimum firing system efficiency by reducing the supply of fuel if there is too little oxygen in the combustion space and, ii) during the continuation of the process management, the power of the burner is increased as a function of the quantity of oxygen available, in such a way as to compensate for the temperature loss during the low-oxygen phase.
4. Procedure in accordance with Claim 1, characterised in that the free oxygen content in the fire duct is registered by calculating the total burner power and the volatile constituents in relation to the flue gas volume.
5. Procedure in accordance with Claim 1, characterised in that the temperature gradient in the gas evolution zone is determined in order to estimate the volatile constituents.
6. Procedure in accordance with Claim 1, characterised in that the ACTUAL
temperature generated by the burners is raised above a sintering temperature in a first phase and reduced below a set point temperature in a second phase in such a manner that a deviation index is reduced to zero over the period of the process management.
temperature generated by the burners is raised above a sintering temperature in a first phase and reduced below a set point temperature in a second phase in such a manner that a deviation index is reduced to zero over the period of the process management.
7. Procedure for process management in an anode furnace, characterised by the process steps of;
i) determining a combustion index at each anode by means of temperature sensors in. an anode duct for calculating a temperature/time integral during sintering and/or, ii) determining a deviation integral from a specified temperature characteristic of the anode.
i) determining a combustion index at each anode by means of temperature sensors in. an anode duct for calculating a temperature/time integral during sintering and/or, ii) determining a deviation integral from a specified temperature characteristic of the anode.
8. Procedure in accordance with Claim 7, characterised in that measured values are used for establishing a dynamic adaptive process model of the temperature/time behaviour during a first heating-up phase in the anode duct, which can be used during the process management as a reference parameter for the actual anode temperature characteristic without the use of temperature sensors on the anode and/or in the anode duct.
9. Procedure in accordance with one of Claims 7 or 8, characterised in a the set point temperature characteristic in the fire duct is modified in such a way that a specified combustion index is achieved at the end of the process management.
10. Procedure in accordance with Claim 9, characterised in that a low maximum temperature is achieved in the combustion spaces by means of the adaptive process model.
11. Procedure in accordance with any one of claims 1 to 10 characterised in that the process steps can be combined in any way.
12. Procedure in accordance with one of any one of claims 1 to 11, characterised in that individual temperature corrections to set point characteristics are optimised in such a way that the maximum temperature in all fire ducts is as low as possible.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19736950 | 1997-08-25 | ||
| DE19736950.2 | 1997-08-25 | ||
| DE19827361A DE19827361A1 (en) | 1997-08-25 | 1998-06-19 | Process for controlling an anode furnace |
| DE19827361.4 | 1998-06-19 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2245322A1 CA2245322A1 (en) | 1999-02-25 |
| CA2245322C true CA2245322C (en) | 2004-04-13 |
Family
ID=26039450
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2245322 Expired - Lifetime CA2245322C (en) | 1997-08-25 | 1998-08-19 | Procedure for process management in an anode furnace |
Country Status (2)
| Country | Link |
|---|---|
| EP (1) | EP0899250B1 (en) |
| CA (1) | CA2245322C (en) |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4859175A (en) * | 1986-06-17 | 1989-08-22 | Aluminium Pechiney | Apparatus and process for optimizing combustion in chamber-type furnaces for baking carbonaceous blocks |
| DD280377A1 (en) * | 1989-03-03 | 1990-07-04 | Elektrokohle Lichtenberg Veb | METHOD FOR TEMPERATURE CONTROL OF A UNDERFLURRING CHAMBER OVEN |
| WO1991019147A1 (en) * | 1990-05-29 | 1991-12-12 | Alcoa Of Australia Limited | Method and apparatus for control of carbon baking furnaces |
-
1998
- 1998-07-17 EP EP19980113341 patent/EP0899250B1/en not_active Expired - Lifetime
- 1998-08-19 CA CA 2245322 patent/CA2245322C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2245322A1 (en) | 1999-02-25 |
| EP0899250A3 (en) | 2001-09-12 |
| EP0899250B1 (en) | 2004-08-04 |
| EP0899250A2 (en) | 1999-03-03 |
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| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20180820 |