EP-4736575-A1 - HEATING PANEL, PROCESS GAS HEATER COMPRISING SAID PANEL AND METHOD FOR MONITORING THE CONDITIONS OF SAID PANEL

Abstract

The present invention relates to a heating panel which allows to easily monitor the status of each heating element so as to quickly identify a malfunction and act by replacing the panel inside a heating module. The heating panel is highly reliable and easy to maintain. The heating panel (P) comprises at least one heating element (T) formed by a triplet of resistors (R1, R2, R3) mutually connected in a star pattern, in which each free end of each resistor (R1, R2, R3) of said triplet receives power from a different phase of a three-phase system and is connected, by at least one controlled switch (SCR, 4), to a first busbar (3). A first control switch (2A) is interposed between the controlled switches (SCR, 4) and said first busbar (3). Furthermore, the first busbar (3) is connected to at least one transformer (1 ) by at least one second control switch (2B). The star center (CS) of the triplet (R1, R2, R3) is in turn connected to a second busbar (8). Furthermore, a current measuring device (6) is provided, positioned between the star center (CS) of the triplet (R1, R2, R3) and the second busbar (8) or along said second busbar (8), so as to detect the extent of the possible current passing through the star center (CS) of the triplet, and in which a control unit (PLC) is provided which is adapted to receive measurement data coming from said current measuring device (6) in order to monitor the conditions of the heating panel (P).

Inventors

• RICCI, Matteo Giacomo
• COZZAROLO, Giacomo
• CODUTTI, ANDREA

Assignees

• Danieli & C. Officine Meccaniche S.p.A.

Dates

Publication Date

20260506

Application Date

20240628

Claims (1)

1. CLAIMS 1 ) A heating panel (P) comprising at least one heating element (T) formed by a triplet of resistors (R1 , R2, R3) mutually connected in a star pattern, wherein each free end of each resistor (R1 , R2, R3) of said triplet receives power from a different phase of a three-phase system and is connected, by at least one controlled switch (SCR, 4), to a first busbar (3), and wherein at least one first control switch (2A) is interposed between the outputs of the controlled switches (SCR, 4) and said first busbar (3), wherein said first busbar (3) is connected to at least one transformer (1 ) by at least one second control switch (2B), wherein the star center (CS) of the triplet (R1 , R2, R3) is in turn connected to a second busbar (8), wherein a current measuring device (6) is provided, positioned between the star center (CS) of the triplet (R1 , R2, R3) and the second busbar (8) or along said second busbar (8), so as to detect the extent of the possible current passing through the star center (CS) of the triplet, and wherein a control unit (PLC) is provided which is adapted to receive measurement data coming from said current measuring device (6) to monitor the conditions of the heating panel (P). 2) The heating panel according to claim 1 , wherein said at least one controlled switch (SCR, 4) is a thyristor, in particular a 3P zero-crossing thyristor. 3) The heating panel according to claim 1 or claim 2, wherein said heating panel comprises a plurality of heating elements (T), each formed by a triplet of resistors (R1 , R2, R3) mutually connected in a star pattern, and wherein said at least one controlled switch (SCR, 4) simultaneously controls said plurality of heating elements (T). 4) The heating panel according to one of the preceding claims, wherein said first busbar (3) is a three-phase busway or cable line and the second busbar (8) is the neutral busway or cable line. 5) The heating panel according to one of the preceding claims, wherein said current measuring device (6) is a current transducer (6). 6) The heating panel according to one of the preceding claims, wherein said resistors (R1 , R2, R3) are selected from the following types: metal resistors, made as wires or plates or other geometric types with Iron-Chrome-Aluminum or Nickel-Chrome alloys, made with sintered powders and drawn or rolled; resistors made of ceramic materials, e.g., Silicon Carbide, SiC; or resistors made of ceramic metal (cermet), e.g., Molybdenum Disilicide, MoSi2. 7) The heating panel according to one of the preceding claims, wherein said heating panel (P) comprises a remote input/output unit (RIO) for receiving said measurement data detected by the current measuring device (6) and sending them towards a network (NET) for the remote monitoring of the conditions of the heating panel (P). 8) The heating panel according to one of the preceding claims, wherein said control unit (PLC) is adapted to control the measurement data detected by said current measuring device (6) and, in the case where a measurement data exceeds an alarm threshold, said control unit (PLC) is adapted to generate a request for replacing the panel (P). 9) The heating panel according to one of the preceding claims, wherein said current measuring device (6) connected to the star center (CS) is an amperometric transformer which integrates the phase measurement function, and wherein a connection (9) of said current measuring device (6) with one of the controlled switches (4) serving as the reference phase is provided. 10) The heating panel according to one of claims 1 to 8, wherein for a current measuring device (6) connected to the star center (CS) without phase measurement, a phase measuring device (10) is added, connected to the star center (CS), and a device (11 ) adapted to calculate the phase difference between a controlled switch (4) and the star center (CS), connected to said phase measuring device (10) by means of a connection (9). 11 ) A heating wall (W) comprising at least one heating panel (P) according to any one of the preceding claims 1 to 7. 12) A heating module (M) comprising at least one heating wall (W) according to claim 11 . 13) A process gas heater, adapted to heat the process gas before using it in an industrial process, wherein said heater is crossed by at least one pipe to convey the process gas and comprises at least one heating module (M) according to claim 12. 14) A method for monitoring the conditions of a heating panel according to one of claims 1 to 10, said method comprising the following steps: - detecting a current variation in the star center (CS) of the triplet of resistors (R1 , R2, R3) of said at least one heating element (T) by means of the current measuring device (6), and - monitoring the conditions of the heating panel (P) by means of the control unit (PLC) which receives the measurement data coming from said current measuring device (6) and processes them to detect possible malfunctions of said at least one heating element (T). 15) The method according to claim 14, wherein said control unit (PLC) identifies a current flow variation trend between the star center (CS) of the triplet (R1 , R2, R3) and the second busbar (8) or along said second busbar (8), and in the event that said current flow exceeds an alarm threshold, said control unit (PLC) generates a request for replacing the heating panel (P).

Description

HEATING PANEL, PROCESS GAS HEATER COMPRISING SAID PANEL AND METHOD FOR MONITORING THE CONDITIONS OF SAID PANEL * * * * * FIELD OF THE INVENTION The present invention relates to the field of electric heaters. In particular, the present invention relates to a heating panel, to a process gas heater comprising at least one heating panel and to a method for monitoring the conditions of said heating panel, preferably all applied to steel plants. Nonetheless, it may be applied to any panel that electrically heats any industrial process. BACKGROUND ART In the prior art, for example in plants for heating steel products, such as, for example, tunnel furnaces, or in ladle and tundish preheating units, or in Process Gas Heaters (PGH) used in direct reduction, the use of gas heating systems to reach the thermal targets useful for the process and bring the elements which need to be heated to the desired temperature is known. Many of these gas heating systems use burners, resulting in emissions of CO2 and other pollutants due to gas combustion. Furthermore, such known solutions also have a low performance. Solutions have already been proposed in the prior art in which the concept of electric heating of steel products, components of a steel plant, or a process gas is introduced. However, such known solutions have a low reliability. In fact, the resistors used undergo deterioration over time, which depends both on the maximum temperatures reached as well as on the number, amplitude and gradients of the cycles of temperature itself, to which they are subjected. The most commonly used configurations for the electrical connection of the resistors are those that provide electric power supply with a three-phase alternating current, in which each resistor (where the term "resistor" may also mean a group of electrical resistors connected to one another in series or in parallel), is connected and is a phase of the three-phase system. If the three phases, and therefore the resistors which compose them, are identical, then the electrical load is defined as "balanced" and the currents passing through the three phases are identical, producing, due to the Joule effect, the same thermal power. Such three-phase resistor systems may be connected in parallel to a single three-phase power line, in which the electric current is controlled by switches, for example solid state switches, called thyristors. Line electric currents, in relation to the thermal powers required by the process, may easily reach a few thousand amperes. When more than one of such systems are connected in this manner it becomes difficult, if not impossible, to monitor the status of one of the phases of the system in the event of malfunction of one of said resistors, since the extent of the resulting unbalance of the three-phase currents may be insufficient to be detected by the instrumental systems. This is even more true as the line currents and the number of three-phase groups connected in parallel increase. In other words, the status of the resistors is not adequately monitored, therefore it is difficult, if not impossible, to predict and/or identify a possible malfunction of one of the resistors in a time useful to reduce the risks of low quality production or of a downtime of the production itself. Therefore, the need arose for a solution which allows to have a plant which is highly reliable and with low emissions. SUMMARY OF THE INVENTION It is the object of the present invention to create a heating panel which allows to easily monitor the status of each heating element so as to quickly identify a malfunction and act by replacing the panel inside a heating module. It is a further object of the present invention to create a heating panel which is highly reliable and easy to maintain. It is another object of the present invention to provide an efficient method for monitoring the conditions of said heating panel. The objects of the invention have been achieved by a heating panel as defined in claim 1 . One of the two schemes most frequently used for this purpose is the one with the resistors connected in a “star pattern", since, in this manner, the line currents are lower than the corresponding currents with a "delta" configuration, given the same power delivered. A second advantage consists in the fact that the star center, to which the three phases, and therefore the three resistors, converge, is accessible and, therefore, the status of the electrical potential thereof may be monitored. In the event that the three phases, and therefore the three resistors which form them, are not identical, or undergo variations in resistivity and/or size over time, or, even, a phase is interrupted, the load becomes "unbalanced" and, consequently, the potential of the star center increases and a current flow is generated through the neutral line, connected from the star center of the three-phase system to the earth potential. The heating panel according to the present invention