System and process for starting up an electrolytic cell
It is disclosed a system and process for starting up an electrolytic cell. The system and process are particularly adapted for preheating an electrolytic cell or pot having cathodes before installing preheated anodes in the cell, for the production of a metal (e.g. aluminum). The system comprises one or more electrical heaters installed in the cell in place of the anode assemblies and can be used with a dry bath or a liquid melted bath (e.g. cryolite). The cell is preferably preheated by as many cell preheaters as there are anode assemblies. The cell preheater is preferably powered by current available in the pot's busbar. The invention is environmentally friendly as being preferably adapted for preheating a cell working with inert or oxygen-evolving anodes. Furthermore, the starting up process allows optimizing/reducing the time necessary for starting up the electrolytic cell, while securing the materials located inside the cell.
1 . A preheating system for preheating an electrolytic cell and for maintaining the preheated electrolytic cell in temperature, wherein the electrolytic cell comprises at least one cathode assembly located at a bottom section of the electrolytic cell and having a plurality of vertical cathodes, and wherein the electrolytic cell is configured for receiving at least one anode assembly, each of said at least one anode assembly comprising a plurality of vertical anodes extending downwardly towards the vertical cathodes once the anode assembly is installed in the electrolytic cell, the vertical anodes being inert or oxygen-evolving anodes extending from a top section of the electrolytic cell toward the cathodes, the at least one anode assembly configured for being preheated outside the electrolytic cell before being moved and placed in the electrolytic cell, the electrolytic cell being further configured to receive an electrolytic bath for the electrolytic production of a metal, wherein the preheating system comprises:
at least one electrical heater, each of the at least one electrical heater being configured to be installed in the electrolytic cell in place of one of the at least one anode assembly and configured for preheating the electrolytic cell before installing said one of the at least one anode assembly into the electrolytic cell;
wherein the electrolytic cell is configured for receiving a number N AA of the at least one anode assembly, with N AA ≥1, the preheating system further comprising:
a number N CH of the at least one electrical heater, with N CH ≥1, each of the at least one electrical heater being configured to be installed in the electrolytic cell in place of the at least one anode assembly, with N CH =N AA ; and
a power module operatively connected to each of the at least one electrical heater and configured for powering the at least one electrical heater with a current for preheating the electrolytic cell,
wherein the power module is configured to connect a main busbar of the electrolytic cell to each of the at least one electrical heater for providing the current available in the main busbar; and
wherein the preheating system is configured to impose a power P by the current amperage A and the resistance R CH of the number N CH of the at least one electrical heater, with P=(R CH /N CH )*A 2 , and with the power P being then higher than a power required to heat up the electrolytic cell and configured to create a surplus of energy, the electrolytic cell being then configured to evacuate the surplus of energy.
2 . The preheating system according to claim 1 , wherein the at least one electrical heater is configured for providing a resistance R CH equivalent to a resistance R AA of the at least one anode assembly once installed in the electrolytic bath, so that electrical and heat distribution of the electrolytic cell remain balanced during the replacement of the at least one electrical heater by the at least one anode assembly.
3 . The preheating system according to claim 1 , wherein the at least one electrical heater is configured for providing a variable resistance R CH which is configured to be tuned to be equivalent to a resistance R AA of the at least one anode assembly once installed in the electrolytic bath, so that electrical and heat distribution of the electrolytic cell remain balanced during the replacement of the at least one electrical heater by the at least one anode assembly.
4 . The preheating system according to claim 1 , further comprising at least one resistance located on a top section of the preheating system to evacuate said surplus of energy.
5 . The preheating system according to claim 1 , wherein at least one resistance is located above at least one heating element of the at least one electrical heater.
6 . The preheating system of claim 1 , further comprising an evacuation mechanism located above at least one heating element of the at least one electrical heater, wherein the evacuation mechanism is configured to evacuate the surplus of energy.
7 . The preheating system of claim 1 , further comprising a gas evacuation system of the electrolytic cell located on a top section of the electrolytic cell and configured for evacuating the surplus of energy from the cell.
8 . The preheating system of claim 1 , wherein the power module is configured to directly connect a main busbar of the electrolytic cell to each of the at least one electrical heater for providing the current available in the main busbar.