Electrothermal Fluidized Bed
One of the main advantages of the high-temperature chemistry technological processes implementation (iron oxides direct reduction, carbides production, carbon materials enrichment, coal gasification and activation, etc.) in fluidized bed units is the heat and mass transfer intensification possibility and highly productive continuous technology creation. High-temperature processes occur in the temperature range of 1000-3000°C. Such processes require a constant supply of heat energy, which compensates for heat losses and maintains the required temperature. The source of heat energy can be:
hot gaseous coolant, which is fed into the furnace as a fluidizing agent;
burning fuel (solid or gaseous) directly in the bed;
electric heating.
General concept of the Electrothermal Fluidized Bed Technology
The supply of hot combustion products to the bed and combustion of the fuel directly in the bed ensure the operation of the furnaces at temperatures up to 900-1200°C. Based on this knowledge, the main method of high-temperature processing in a fluidized bed is the use of electric heating, which includes several areas:
induction heating of electrically conductive particles of the fluidized bed;
plasma heating, indirect heating by electric heaters;
heating by passing a current through the fluidized bed (electrothermal fluidized bed).
The electrothermal fluidized bed technology ensures the operation of furnaces at bed temperatures in the range of 1000-3000°C. The material processing time is unlimited and allows you to organise a continuous production process.
The basic principle of creating an electrothermal fluidized bed is the presence of three necessary components:
the presence of at least two electrodes;
fluidized bed with electrically conductive material;
current source.
The choice of the fluidized bed implementation is determined by the process temperature level, which determines the using refractory materials possibility for the furnace working chamber manufacture. In this regard, all technological processes and furnace designs are divided for:
'low temperature' - layer temperature 1000-1600°C;
'high temperature' - layer temperature 1600-3000°C.
Options for the implementation of electrothermal fluidized bed
Various refractory materials are used for the production of "low-temperature" furnaces”[5, 6]: chamotte, corundum, magnesia, dinas. But, only graphite is used for “high-temperature” furnaces, which determines the furnace design and technological process formation.
In most designs of continuous furnaces, unloading is carried out through a channel in the gas distribution grate, where material moves in a dense layer due to gravity. After unloading the treated material from the furnace working chamber, it is sent to the refrigerator. A dense layer of material is formed, which is the hydraulic resistance (gate) that impedes the movement of gases from the working space to the refrigerator (Fig. 20). In [25], a distribution chamber is provided in which the material is averaged, distributed between refrigerators, and exposed at high temperatures, providing additional particles treatment. The movement of the material in the refrigerator is determined either by feeders (Fig. 10) or by various types of (Fig. 20) [9]. The material moves in the refrigerator with the help of conveyors (Fig.11) or various types of valves (Fig.21) [9].