An electric calcining furnace is a relatively simple vertical resistance furnace. Electrodes mounted at both ends of the furnace drum utilize the inherent electrical resistance of the material to form a path, converting electrical energy into heat, heating the carbon raw material to a high temperature (1300-1400°C), and achieving calcination.
Electric calcining furnaces can be divided into single-phase and three-phase types depending on the power supply method. A single-phase furnace has a cylindrical furnace chamber lined with refractory bricks, with an asbestos insulation layer between the outer shell and the refractory bricks. Carbon blocks (or rammed with paste) serve as the other conductive electrode at the bottom of the furnace chamber, and a discharge pipe with a cooling water jacket is located at the bottom of the furnace.
Single-phase electric calcining furnaces are powered by a low-voltage, high-current single-phase transformer. The transformer capacity depends on the furnace chamber size and is determined based on operational experience. The maximum current density across the furnace chamber cross section is 0.18-0.25A/cm². The maximum voltage of the transformer depends on the furnace height and the resistivity of the material; it is generally 30-35V per meter (from the electrode end to the furnace bottom).
The furnace body of a three-phase electric calciner is similar to that of a single-phase electric calciner, but the conductive electrodes are built directly into the furnace body. To ensure a more uniform temperature within the furnace, three graphite electrodes, each with a cross-section of 350mm x 350mm, are built into the upper and middle sections of the furnace body. These three pairs of electrodes are laid in parallel at 120° intervals on the same horizontal line and connected to the power transformer via busbars.