- NextGen pelletizing technology
- Development of new technologies (sponge iron production without reformers)*
- Basic engineering (drafting of technical documentation)
- Balance studies of the production cycle phases and ramp up of the pelletizing plants
- Engineering solutions on the costs reduction, improvement of quality and increase of production rate
NextGen pelletizing technology
Cutting-edge technology has been successfully incorporated at one of the TOREX landmark facility in Russia - Mikhailovsky GOK, with an energy efficient indurating machine MOK-1-592M as the core product of technology.
Contemporary indurating machines are equipped with developed gas-duct systems consisting of collecting manifolds, gas ducts, gas cleaning and induced-draft fans, which provide temperature-filtration modes for heat treatment of a pellet bed in various technological zones of the machine. In the furnaces of high-temperature heating and firing zones, burners are installed to ensure and control the temperature mode. Between the technological zones, the recirculation of hot gases heated during firing and cooling of the pellet bed is carried out in order to reuse the heat of flue gases leaving the bed or coolant, as well as to reduce the amount of flue gas discharges into the atmosphere. Transportation of technological gases in indurating machines is performed using draft fans and a direct recuperator (a fanless method), connecting the first section of the cooling zone with the technological furnace zones of drying, heating, and firing. Using modern machines, the cleaning results in gases from the drying and heating zones, with a low temperature (usually below 100°C) and high moisture content, being discharged in the atmosphere.
The most significant technological stage of the heat treatment process is the drying of the raw pellet bed to ensure high technical, economic, and heat energy operation indicators of the thermal unit and the formation of optimal structural characteristics of the layer and the specified quality parameters and metallurgical properties of the fired pellets. In most of the indurating machines currently in operation, the technology of the two-section layer drying of pellets with drying agent reversal according to the “blow-through-coolant transfer” scheme was implemented. In this case, hot air or flue gases transported through the gas duct system from other technological zones of the indurating machine are used as a heat carrier. The disadvantages of this scheme include the limited possibilities of heat intensification and mass transfer drying processes due to the moisture zone formation during layer drying, which can lead to the decomposition and softening of raw pellets of different layer horizons, as well as a noticeable decrease in the gas permeability of the pellet bed both in the drying zone and in subsequent high-temperature zones of heating and firing. In the new generation’s energy-efficient indurating machine by TOREX, the above-mentioned disadvantages are eliminated due to the fact that the straight grate machine for the production of heat-strengthened pellets, which contains loading and unloading units and a movable grate for forming a raw pellet bed and transporting it through the technological zone, is equipped with the following: a three-section reversible drying zone, high-temperature heating, firing, and after-firing zones, a four-section pellet cooling zone, and a recuperation system for fanless transport and selective distribution of hot air from the cooling zone within the technological zones.
Generally, the TOREX approach to the design of an indurating machine is to tailor the furnace and its thermal circuit to the specific Customer requirements and the properties and features of a particular feed material, and is based on the following principles:
1) Strict proportioning of the indurating machine zones:
Heat treatment of iron ore pellets is carried out in 5 process zones: Drying, Preheating, Firing, After-firing and Cooling. The dimensions of each zone is calculated according to the required heating/cooling rate of the pellet bed. This principle is based on the fact that low heating rate decreases the capacity of the machine and swift heating deteriorates the quality of fired pellets. Therefore, the lenght of each the zone and its share among other zones should be estimated precisely by numerical simulation.
2) Drying section with 3 subsections
Drying section is a bottleneck in the pellet induration process.
To increase the efficiency of drying zone TOREX created a drying zone with 3 sub compartments to tackle the bottleneck. The mentioned design has been introduced in the indurating machines OK-306 of Lebedinskiy GOK (Russia), OK-306 of Severniy GOK (Ukraine), OK-520 of Mikhailovskiy GOK, OK-536 of Kostomukshskiy GOK (Russia). Three sectional design allowed for intensification of the pellet drying process and increase of the machine output.
3) Optimal distribution of the gas flows by temperature and volume.
Such distribution allows for consistent supplying of the heat medium to a zone, with required temperature and the utilization of the temperature potential. A process fan is considered for each process zone of the machine.
4) Aerodynamic shape of gas ducts and manifolds for gas transit.
Gas velocity stabilizes by smooth change of direct recuperator diameter from section to section. Jointing of the downcoming pipes with direct recuperator is implemented under 45° degree. The pipes of windboxes are evenly jointed with conical manifolds.
This results in lower aerodynamic resistance and less power is consumed for gas transfer.
5) The recuperation system consisting of three conical recuperation mains:
Central and two lateral. Heat carrier medium is fed to drying and preheating zones through the central direct recuperator, and to the firing zone - through lateral lines. Due to such arrangement of the gas recycling (recuperation) system, injection burners for fuel combustion can be installed only in the firing zone (consuming less fuel, producing less emissions). The heat of the fired pellets and gas is utilized to the greatest possible extent. Only the low temperature moist gas from the Drying zone is being discharged through the stack. In this respect, it is feasible to decrease harmful emissions up to 1200 – 1300 m3/t of product pellets. Fuel heat consumption can reach 300 Mj/ton (8.4 m3/t), and electricity — less than 20 kilowatt hours per ton.
The key state-of-the-art solutions applicable to the brand-new designed indurating machine:
MOK-1-592 is an indurating machine of the new generation, with a very high degree of automation of the various process operations and heat treatment allowing for lowering considerably the power & utilities consumption and harmful emissions to the ambience, this machine is second to none at this point.
The basic features of a flexible thermal scheme of the new indurating machine:
- Thermal scheme can be adjusted to produce the pellets of different type (magnetite or hematite) and designation (BF or DRI pellets).
- Flexible scheme of the drying zone comprises the three sections with various length and temperature of the heat carrier.
- It becomes more common to prepare the special requirements for relatively small batches of the fired pellets.
- Fan-less gas recycling mains (2 collecting mains/manifolds)
- Improved gas ducts and collecting mains/manifolds ensuring minimum
- No dedusting of gases in recycled gas ducts
- Rational proportioning of loads on process fans (maximum
- Flexibility of in-furnace thermal and gas flow mode
The energy-efficient thermal scheme of the indurating machine was developed based on computational model studies, which resulted in a method for intensifying the magnetite oxidation in an unheated heating zone. This method transferred highly heated air with maximal oxygen potential from the first section of the cooling zone directly into the heating zone through a separate central transfer manifold without using any flow booster. In this case, air from the second section of the cooling zone is also fanlessly transferred to the injection burners of the firing zone through the lateral transfer manifolds (recuperators).
Computational studies were performed using a numerical simulation model developed at the NPVP TOREX in 2002–2012. These studies showed that, while maintaining the required pellet quality, the proposed method for providing a heating zone with high-temperature air with increased oxygen potential reduces the specific fuel consumption by 8–15% and increases the machine efficiency by 10–17% depending on the initial pellet properties.
TOREX is always striving to create the new technologies and developments and improve the existing ones. A spectaclurar example is the new import-substituting technology of metallization. The DRI technology of iron ore raw materials with the conversion of the hydrocarbons in the shaft furnace has the certain advantages over the other wide-spread methods of DRI. This is due to a significant reduction of capital and operating costs. The mentioned technology allows skipping the expensive conversion units (reformer units with catalyzers) due to the application of natural gas oxygen conversion. This also envisages in-furnace conversion of a surplus amount of the hydrocarbons on the freshly reduced iron (sponge iron - active catalyzer) in order to ensure recovery of a sponge iron with the specified quality. There is an additional advantage of the new DRI technology as follows: we have proposed to divide the shaft furnace by two process zones (by height) with a various sources of gas - as a heat carrier and reducer according to features and requirements in those zones. This method ensures a reduction of energy costs and facilitates the production of high quality metallized product.
Originally developed know-how on grinding, milling, sizing and dedusting of different materials
TOREX has developed the technologies to recover a polydisperse and fractioned powders of materials, such as bentonite clay, limestone, lime, coal powder etc. In this case, an efficient combination of drying, grinding and sizing of materials is considered in a single unit. The developed technologies are distinctive by a low
power consumption, high metal intensity and environment friendly approach.