Patent Description:
The invention in particular concerns a method for managing the power that is transmitted to the electric furnace and/or to the charge material of the furnace, to guarantee improved functioning by optimizing the delivery of power by a combination of sources, for example, but not only, electrical and chemical sources, necessary to carry out a melting process.

Melting plants are known which comprise an electric furnace, for example an electric arc furnace, used for melting a metal charge by means of an operating cycle which normally provides the following main steps:.

The operations of charging, generating the electric arc and perforating the material can be repeated several times during a single melting cycle. For example, after a first charge of metal material into the furnace and the melting of this charge, it is possible to provide the introduction of a further charge of metal material, and the subsequent melting, before proceeding with the refining and then with the tapping.

In the case of a melting process with a continuous charge, the melting cycle described above generally provides to load a first basket into the furnace and the subsequent melting of the discharged material in order to generate a liquid pool; then, it provides the continuous introduction of the charge material to be melted in order to obtain a desired quantity to be tapped.

The melting process determines on the whole very high energy consumption and is characterized by a melting profile which must be optimized for the furnace to reach the required levels of productivity and performance.

By melting profile we substantially mean the quantity of energy, electrical and chemical, which is required so that the operational cycle can take place successfully; this profile is normally characterized by a plurality of variables such as the voltage of the power supply grid, the current, the flame delivery rate of the burners, the type of steel to be produced, the mixture of scrap used and other factors.

The melting profile is also predefined based on the size of the furnace and the electrical and chemical power installed.

Normally, an electric arc furnace is powered by an electric transformer which can vary the output voltage in a discrete manner.

The melting profiles, in general, adapt to the constraints provided by the transformer, so currently it is almost never possible to exactly meet the theoretical process requirements desired in the entire melting cycle.

This can cause a decrease in the productivity of the furnace, due to the need to adapt the available energy to all the other parameters involved, or it can cause the failure to achieve quality objectives on the casting, or also excessive production costs.

Furthermore, currently, the controlled variables for electrical and chemical energy are guided only by using a parameter that is representative of the melting state of the scrap and cannot be dynamically adapted to other process variables, nor are they adjusted on the basis of a historic record of the results obtained in the past.

It is also known that the energy available for the melting process also depends very much on the type of infrastructure for supplying the electrical and chemical energy, present in the place of installation of the melting plant. It is therefore evident that the method for managing the furnace must necessarily take this aspect into account.

Document <CIT> describes a method for controlling a melting process in which an optimization occurs at discrete intervals (<NUM>-<NUM> seconds) and not in a continuous and dynamic manner, with enormous limits on the control of the process, the parameters of which vary continuously. Furthermore, this method does not take into account the historic record of the results obtained in previous melting operations.

Document <CIT>, on the other hand, describes a method for controlling the consistency of the slag in a metal melting plant, but does not explain how to optimize the delivery of both electric and chemical power, which is necessary to carry out a melting process.

There is therefore a need to perfect a melting plant and corresponding apparatus and management method, for example of an electric arc furnace, which can overcome at least one of the disadvantages of the state of the art.

One purpose of the present invention is to provide a melting plant which comprises a management apparatus able to optimize the delivery of electrical and chemical energy available at that moment.

Another purpose of the present invention is to perfect a method for managing the power supply of an electric arc furnace that allows to optimize the delivery profile of the electrical and chemical energy available at that moment.

Another purpose of the present invention is to provide a management method in which the melting profile adapts dynamically to the energy available.

Another purpose of the present invention is to provide a management method that allows, in a substantially continuous way, to optimize the overall performance of the furnace and to improve the efficiency of the melting process.

In accordance with the invention, a melting plant comprises an electric furnace, provided with one or more electrodes, at least chemical substances introduction means, and a management apparatus comprising at least one decoupling unit disposed between an electricity grid and the electric furnace.

The management apparatus comprises a control unit having:.

In accordance with the invention, a method for managing a melting plant is therefore provided which provides to control the electric power supply and chemical supply of an electric furnace, by means of a decoupling unit between the electric furnace and the power supply grid and by means of chemical substances introduction means.

The method provides that during a melting cycle:.

These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-limiting example with reference to the attached drawings wherein:.

The embodiments described here concern a melting plant <NUM> comprising an electric arc furnace <NUM> and an apparatus <NUM> for managing the power supply of the electric furnace <NUM>.

The electric furnace <NUM> comprises one or more electrodes <NUM> which can be electrically powered to supply an electric power necessary to melt a mass of metal material R. For example, there can be two, three, or more than three electrodes <NUM>.

The apparatus <NUM> is connected to an electricity grid <NUM> supplying alternating voltage and current which can be, for example, three-phase.

The electricity grid <NUM>, as a function of the site of installation of the plant <NUM>, is characterized by its own mains electric quantities such as a mains current Ii and a mains voltage Ui, which are suitably supplied to the electrodes <NUM>, by means of the apparatus <NUM>, at a mains frequency Fi.

The apparatus <NUM> comprises a decoupling unit <NUM> operatively disposed between the electricity grid <NUM> and the electric furnace <NUM>. The decoupling unit <NUM> is configured to decouple the mains electric quantities (Ii, Ui, Fi) from electric power supply quantities of the electrodes <NUM>, which are an arc current Ia and an arc voltage Ua, both supplied at an arc supply frequency Fa.

The decoupling unit <NUM> allows to perform the regulation of at least one mains electric quantity (Ii, Ui, Fi) in order to obtain a desired electric power supply quantity (Ia, Ua, Fa).

The decoupling unit <NUM> comprises a modular converter device configured to convert the mains current Ii and the mains voltage Ui to values of the arc current Ia and arc voltage Ua for powering the electrodes <NUM>.

The modular converter device comprises a plurality of modules, each provided at least with rectifying circuits, intermediate circuits and inverter circuits as described, for example, in the Applicant's patent <CIT>.

The decoupling unit <NUM> allows to control the arc current Ia, the arc voltage Ua and the arc power supply frequency Fa independently and continuously with respect to the mains current Ii, the mains voltage Ui and the mains frequency Fi. The possibility of continuously controlling these electric power supply quantities allows to have a more precise control of the melting process at any time.

The electric power delivered by the electrodes <NUM> is adjusted by acting on the arc current Ia, on the arc voltage Ua and on the arc supply frequency Fa. Preferably, the regulating action occurs by acting on the frequency parameter.

In possible embodiments, the decoupling unit <NUM> can comprise a multi-tap transformer provided with a plurality of transformation ratios which can be selectively set in relation to a desired electric melting profile. In this case, the arc current Ia and the arc voltage Ua are controlled discreetly. In the case of a multi-tap transformer, it is not possible to act on the frequency parameter.

The electric furnace <NUM> comprises chemical substances introduction means, indicated as a whole with the reference number <NUM>, configured to deliver, during use and according to the specific step of the melting cycle, a desired chemical power necessary to reach the raw chemistry desired for the production of a particular steel.

The chemical substances introduction means <NUM> can be, for example, burners, lances, injectors of oxygen, coal and other additives to be loaded inside the electric furnace <NUM>.

The chemical substances introduction means <NUM> are characterized by chemical supply quantities which comprise at least one oxygen stream QO2, one fuel stream Qfuel, one carbon stream Qc and one lime stream Qlime. Other chemical supply quantities are possible and essentially depend on the chemical reactions that have to take place inside the electric furnace <NUM>.

The management apparatus <NUM> comprises a control unit <NUM> operatively associated with the decoupling unit <NUM> and the chemical substances introduction means <NUM> to respectively manage the delivery of the electric power and the chemical power required.

The electric and chemical supply to the electric furnace <NUM> is managed on the basis of a melting profile MP which is characterized by the sum of the electric power and the chemical power required during the steps of the melting cycle.

The melting profile MP depends on the process and construction parameters A of the electric furnace <NUM>. For example, the parameters A can comprise dimensional characteristics of the electric furnace <NUM> - for example shape, containing capacity - and chemical composition of the mix of metal material R introduced to produce a desired type of steel. The melting profile MP can also depend on the type and size of the pieces of the metal material R used, on its shape and on the modalities, continuous or discontinuous, with which it is introduced into the electric furnace <NUM>. The melting profile MP can also depend on the typology of chemical substances introduction means <NUM>.

The melting profile MP can be represented as a curve that varies as a function of the process time or of the steps of the melting process. For example, in a charging step or in a refining step, the melting profile MP could be characterized solely by the electric power or solely by the chemical power, while in a melting step it could be characterized by a combination of electric power and chemical power. For this reason, the melting profile MP can be defined, instant by instant, by the sum of an electric melting profile and a chemical melting profile.

The electric power supply quantities that can be controlled during the process in order to follow a desired electric melting profile are the arc current Ia, the arc voltage Ua and the electric power supply frequency Fa.

Some of the chemical supply quantities that can be controlled during the process in order to follow a desired chemical melting profile are an oxygen stream QO2, a fuel stream Qfuel, a carbon stream Qc and a lime stream Qlime.

The window to control these quantities depends on existing electrical and chemical constraints, as well as on the availability and mode of delivery of the electrical energy and chemical energy, respectively.

The electrical constraints can be, for example, a nominal power, a maximum output voltage and a maximum output current of the modular converter device, an electric arc resistance or other.

The chemical constraints can be, for example, a nominal power or a nominal flow rate of fuel injected, a limit ratio of injected oxygen/carbon, a limit ratio of injected oxygen/fuel.

According to some embodiments, the control unit <NUM> comprises a storage module <NUM> which has a database in which a plurality of melting profiles MP of the electric furnace <NUM> are stored.

In fact, at each melting operation it is possible to record the data at least of the melting profile MP and of the type of steel produced. Advantageously, the data of the corresponding electric power supply quantities and of the chemical supply quantities which define the melting profile MP are also recorded.

The storage module <NUM> therefore offers a history of melting profiles MP of the electric furnace <NUM>.

According to one possible embodiment, the control unit <NUM> is connected to a cloud storage device <NUM> on which a plurality of melting profiles MP of other electric furnaces <NUM>, which are part of other melting plants distinct from the melting plant <NUM>, are stored.

The control unit <NUM> also comprises a calculation module <NUM> configured to perform a comparison between the parameters A relating to a determinate melting condition to be achieved in the electric furnace <NUM> and corresponding operating parameters which have occurred in previous meltings, in the same electric furnace <NUM> or in other electric furnaces <NUM>, so as to select one or more optimal melting profiles MP which can possibly be combined to obtain a base melting profile MP.

The base melting profile MP is used, at least initially, as a guide for the melting to be achieved. By monitoring, step by step, the variation of the different controlled parameters A, it is possible to verify whether the current melting profile MP is being adhered to or not and, in the latter case, realign it with appropriate modifications.

In the event that the base melting profile MP relates to one of the other electric furnaces <NUM>, it is necessary that these have similar characteristics in terms of sizes, mixture of scrap R and chemical substances introduction means.

The greater the number of acquired/monitored meltings, the more data there will be to feed algorithms based on this data able to define the base melting profile MP. The greater the amount of data, the greater the effectiveness and performance of the electric furnace <NUM>.

According to some embodiments, the calculation module <NUM> is programmed to implement an optimization function APG which automatically generates a melting profile MP that is dynamic, in its electrical and chemical component, and minimizes a cost function CF of the electrical and chemical energy. The optimization function APG is configured to select, by analyzing the signal of the electric quantities, the "best" current and frequency combinations in each melting step of the process, that is, the current and frequency combinations that guarantee the greatest stability of the arc (for example, minimum standard deviation, minimum total harmonic deviation) and therefore minimize the so-called Power On Time "PON". Minimizing the PON means minimizing thermal losses.

It is therefore possible to impose current and active power targets on the secondary of the decoupling unit <NUM> such that the optimization function APG selects the best current and frequency combination, for example to minimize PON or losses.

Furthermore, in the event that there is a reduced power available from the electricity grid <NUM>, for example in certain time slots, it is possible to integrate the missing electric power by delivering, through the chemical substances introduction means <NUM>, the necessary chemical power, deriving from a suitable active monitoring.

The cost function CF can be defined on the basis of different parameters that can be chosen through machine learning techniques that are able to reduce the dimensionality of the problem to a limited number of variables.

The parameters that define the cost function can be different depending on the step in which the ongoing process is, therefore the cost function will take, on each occasion, a different form.

The cost function CF to be minimized is defined as a function of the electric power supply and chemical supply quantities involved in the process.

For example, the cost function CF can be defined in relation to the electric power supply quantities and the chemical supply quantities according to the relation: <MAT>.

For example, by minimizing the cost function CF it is possible to implement one of the following management strategies, or a combination thereof:.

The optimization function APG is configured to generate the melting profile MP which minimizes the cost function CF taking into account the constraints of the electrical components of the plant <NUM> and the constraints of the chemical components of the plant <NUM>. The techniques that can be used to optimize the cost function are, for example, genetic algorithms or dual optimization methods, taking into account the type of constraints.

According to some embodiments, the control unit <NUM> comprises a management module <NUM> configured to receive the melting profile MP, in its electrical and chemical components, from the calculation module <NUM> and to translate them into operating signals to be sent respectively to the decoupling unit <NUM> and to the chemical substances introduction means <NUM> so that they deliver the optimized quantity of energy.

The management module <NUM> is also configured to receive the data relating to the current melting profile MP and to record them on the storage module <NUM> in order to continuously update the database.

The management apparatus <NUM> described heretofore is used to put into practice a method for managing a melting plant <NUM> in which at least the following steps occur:.

The charging, melting and refining steps are characterized both in terms of time, for example the average duration of each step, and also in terms of quantities, for example the power required to complete each step within the timeframe and with the same result necessary to consider their completion suitable, from an optimal melting profile MP.

The optimal melting profiles MP are those which, with the same initial conditions, for example parameters A, and aimed at achieving a precise result, for example a particular steel grade, require less consumption and time and therefore lower costs. On the contrary, the least suitable melting profiles MP are those that exceed timeframes, costs or do not reach the desired target.

Once the melting program has been established, before the charging step of each melting cycle it is provided that the calculation module <NUM> of the control unit <NUM> compares the process parameters A of the melting to be carried out with the process parameters of previous meltings which are loaded into the database within the storage module <NUM>.

Possibly, the database present in the storage unit <NUM> can be updated or have access to the cloud storage device <NUM> which contains information on meltings of other furnaces <NUM>.

Once the most similar previous meltings have been defined, the calculation module <NUM> extracts the corresponding melting profiles MP and possibly combines them in order to obtain a melting profile MP which, in its electrical and chemical component, is a base that will be followed, at least at the beginning, to implement the melting process.

Once the melting profile MP has been determined, the calculation module <NUM> dynamically adjusts the current melting profile MP, in its electrical and chemical components, on the basis of the optimization function APG, with the aim of maximizing the overall efficiency of the melting process, that is, minimizing the cost function CF.

The function APG is used to continuously optimize and generate both the electric melting profile and also the chemical melting profile.

The method provides to vary the electric and chemical melting profile MP in an optimized way according to the specific step of the process.

It is clear that modifications may be made to the method for managing an electric arc furnace as described heretofore, without departing from the field and scope of the present invention as defined by the claims.

Claim 1:
Melting plant (<NUM>) comprising an electric furnace (<NUM>), provided with one or more electrodes (<NUM>) and chemical substances introduction means (<NUM>), and a management apparatus (<NUM>) comprising a decoupling unit (<NUM>) disposed between an electricity grid (<NUM>) and said electric furnace (<NUM>), wherein said management apparatus (<NUM>) comprises a control unit (<NUM>) that has:
- a calculation module (<NUM>) programmed to implement an optimization function that automatically generates a current melting profile that minimizes a cost function of electrical and chemical energy, and
- a management module (<NUM>) configured to receive from said calculation module (<NUM>) the data relating to said melting profile and to translate them into operating signals to be sent respectively to said decoupling unit (<NUM>) and to said chemical substances introduction means (<NUM>),
characterized in that said control unit (<NUM>) that has a storage module (<NUM>) which has a database in which a plurality of melting profiles are stored, wherein said calculation module (<NUM>) is configured to perform a comparison between parameters relating to a determinate melting condition to be achieved in said electric furnace (<NUM>) and corresponding operating parameters which have occurred in previous meltings, so as to select one or more base melting profiles from the database of said storage module (<NUM>).