Diagram of a resistive Acheson graphitization furnace for producing electrode rods formed from powdered coke mixed with silica clay. a - Mixture of Coke and Sand, b - Bricks, c - Carbon Electrodes, d - Refractory Material, e - Rods to Graphitize, f - Granulated Coke
The Acheson furnace consists of the furnace body, the transformer of the power supply system, and a short network connecting the two parts.
► What is acheson graphitization furnace?
A graphitization furnace named after the inventor E.G.Acheson. The Acheson furnace was invented in 1895 and first patented in the United States. Its embryonic form is: a long furnace body constructed of refractory materials, filled with carbon blanks and granular materials to form a conductive furnace core, around the furnace core It is a thermal insulation material. Conductive electrodes are arranged on the two upper end walls of the furnace head, which are connected with the power source to form an energized loop (see figure). When the circuit is connected, the furnace core heats up due to the resistance, so that the carbon blank is converted into artificial graphite by high-temperature heat treatment at a temperature of 2200-2300°C.
The development of Acheson graphitization furnaces has a long history. At present, Acheson furnaces are generally used in the artificial graphite industry. This kind of furnace is simple in structure, sturdy and durable, and easy to maintain. It has always been the most used graphitization equipment in the carbon industry.
Acheson graphitization furnace is classified as a direct heating furnace according to the heating method. The so-called direct heating means that the product itself is a conductor, and the product is heated by resistance to complete graphitization. The early Acheson graphitization furnace used alternating current, but the alternating current has the disadvantages of low power, low current density, low power factor, and long power transmission time. After the 1960s, with the rapid development of rectifier equipment, Acheson graphitization furnace began to use DC power supply, which greatly reduced energy consumption.
► Advantages of Acheson graphitization furnace
1) Other heating methods are the main methods. The conductive furnace core is composed of carbon blanks as products and carbon pellets as resistance materials. Although the product is both a heating resistor and an object to be heated, the resistance of the resistive material is much larger in comparison, so the heat required for the graphitization of the product mainly depends on the heat transfer of the resistive material. The heating of the product starts from the surface and then gradually penetrates into the interior. This external heating method causes uneven temperature distribution and thermal stress. Generally, the thermal conductivity of carbon products is relatively poor. When the furnace temperature rises quickly, it will There may be obvious external heat and internal cooling, and cracked waste products. In actual production, "start power" and "up power" are used to limit the amount of electricity sent into the furnace to achieve the purpose of controlling the furnace temperature. The transmission power of the product is limited, and the power-on time cannot be shortened too short, so the production capacity is small, the power consumption is high, and the product quality is poor due to uneven temperature.
2) The Acheson furnace is operated intermittently and periodically. Generally, 5 to 7 furnaces are a production unit. Only one furnace in the furnace group is powered, and the other furnaces are loaded, cooled, unloaded, and cleaned. , Repair furnace and other operations. For each furnace, heating and power transmission only takes 3 to 5 days, while a production cycle takes 12 to 15 days. Because of the long production cycle, the unit production capacity is low, and because a large amount of resistive materials and insulation are used in production Insulation materials, a large amount of heat is consumed in the heating and heat storage of these materials, so the thermal efficiency of the Acheson furnace is relatively low, only 30% to 35%. If more than 20% of the electricity loss is calculated, the energy use The total efficiency is only 23%-28%.
3) Because a large amount of resistance materials and thermal insulation materials are used in the production, and it is an intermittent operation, the work load of the furnace is very large, and there is a large amount of dust. During the operation of the furnace, there is a large amount of harmful gases, such as CO. , SO2, etc., the operating environment is poor.
4) The method of graphitization with Acheson furnace is simple, easy to realize, reliable in production, and has few failures. This is also the reason why Acheson furnaces have been quickly promoted and widely used.
The Acheson furnace has been developing rapidly in countries all over the world since its inception. For a long period of time, almost all the Acheson furnaces used in graphitization production, people have been used to equate it with the graphitization furnace, although it is only a furnace type of the graphitization furnace. The Acheson furnace is divided into two stages in its development process, namely the initial AC graphitization furnace and the DC graphitization furnace developed after the 1960s. Although the two adopt the same furnace shape, the direct current furnace is superior to the AC furnace in various technical indicators due to the different types of currents. Therefore, the direct current furnace gradually replaces the AC furnace. In addition to AC furnaces and DC furnaces according to the current type, Acheson furnaces also have removable graphitization furnaces placed on the furnace carts, chemical purification furnaces for special purposes, and furnace cores arranged in the shape of "П". Shaped furnace, etc. After the appearance of tandem graphitization furnace in the 1980s, its advanced technology attracted the attention of all countries in the world. Its rise broke the situation that almost all Acheson furnaces were used in graphitization production. Although the Acheson furnace still occupies a considerable proportion, the rapid development of the series furnace will gradually replace the Acheson furnace. However, the series furnace is only suitable for the production of a single large-size product, and the technology is relatively complex, so The Acheson furnace will not be completely replaced, but will still occupy a certain position in graphitization production, especially in small and medium-sized carbon plants.