When China’s stainless steel industry began to develop rapidly, it caused extreme concern in the Western world and a sudden increase in the price of metallic nickel. Thanks to the rise and rapid development of the ferronickel smelting industry from laterite nickel mines, my country’s stainless steel industry has achieved leapfrog development. The technology of producing ferronickel from self-baking electrodes roasted by electrode paste in submerged arc furnace is inseparable from raw material conditions and process routes. The production practice shows that the long-term stable operation of the electric furnace is related to the fact that the electrode paste self-baking electrode rarely breaks the paste accident and the molten iron does not pass through the furnace at the bottom of the furnace. Many users of ferronickel electric furnaces reported that the special sealed electrode paste produced by Gongyi Rongxin Carbon Products Co., Ltd. has high strength and good resistance to rapid cold and heat. It can effectively prevent the electrode from soft and hard breaking, less accidents, and iron consumption per ton. The amount of paste used is about 10 kg. The magnesia knotted furnace bottom technology solves the problem of iron running at the bottom of the furnace. This paper focuses on the related technologies for the successful use of special sealed electrode pastes in ferronickel electric furnaces.
2. Self-baking electrode and electrode paste
2.1 The requirements for the use of the electrode of the mine thermoelectric furnace
The process technology to produce deoxidizers and alloying agents required by the iron and steel industry with electric energy as the main heat source is the production of ferroalloys in submerged arc furnaces. The high temperature and thermal energy required for the production of ferroalloys are usually converted by sending electrical energy into the furnace through self-baking electrodes. Self-baking electrode is the basic condition and premise of submerged arc furnace smelting ferroalloy production technology.
In view of the need for continuous high-temperature production, the submerged arc furnace usually operates uninterruptedly for several years. For this reason, the self-baking electrode of the electric furnace is required to be able to continuously transmit electricity. The quality, performance, firing technology and conditions of the electrode paste should meet the requirements of the production technology.
2.2 Preparation process of self-baking electrode (electrode paste)
The self-baking electrode is made of anthracite, pitch and residual materials, mixed in a certain proportion, mixed uniformly, stirred and kneaded at an appropriate temperature, then pressed into shape, and cooled to make a paste. When in use, the small pieces of electrode paste are loaded into the electrode shell of the submerged arc furnace, and during the production process, it relies on the Joule heat generated when the current passes through and the conduction heat in the furnace to self-sinter and coke. The electrode can be used in continuous forming and used while being connected and sintered, and different diameters can be configured according to the capacity of the electric furnace. Self-baking electrodes are widely used in ferroalloy production due to their simple process and low cost.
2.3 Raw materials for preparing electrode paste
The raw material for making electrode paste is composed of solid carbon material and binding material. The quality of the electrode paste is related to the raw material formula and preparation process. Solid materials include calcined anthracite, metallurgical coke, petroleum coke and graphite electrode scraps. Anthracite is dense and has a high carbon content, which can improve the thermal stability, conductivity and mechanical strength of the electrode; the binder of the electrode paste includes pitch and tar, and tar is added to adjust the softening point. The binder is decomposed during the sintering process of the electrode paste, and after removing the volatiles, it is transformed into coke to cause coking, so that the electrode is formed into a hard whole. The formula of electrode paste should consider the proportion of various solid materials, particle size composition, softening point of the binder and the added amount.
2.4 Classification and performance of electrode paste
Electrode pastes are divided into standard pastes and sealed pastes due to their different uses. The former is mostly used in semi-closed submerged arc furnaces; the latter is often used in closed electric furnaces and large-capacity semi-closed electric furnaces due to its low roasting temperature and easy sintering. The solid material of the standard paste is mostly anthracite and metallurgical coke, while the solid material in the closed paste is mixed with graphite and petroleum coke in large quantities. The binder in the standard paste is mostly medium temperature pitch, and the binder in the closed paste uses a lot of tar while also using more graphite chips. The special sealed electrode paste favored by ferronickel smelting enterprises in submerged arc furnaces has significantly increased the amount of tar and graphite scraps. The high prices of crushed graphite and tar are the main reasons for the high prices of airtight pastes, especially the high prices of super dense pastes.