Some of the main components in the production of pellets are the processes:
            a. transporting raw pellets with uniform distribution on a roller screen;
            b. screening with separation of substandard classes -8mm and +16mm;
            c. loading in an even layer along the height and width of the trolley;
       One of the most important technological operations is the transportation of raw pellets from pelletizers to the firing section and their uniform loading onto the firing machine. Due to the low static strength of pellets and their susceptibility to deformation, it is necessary to ensure careful transportation, minimum height overloads and, finally, their careful and uniform stacking onto firing trolleys. Transportation of raw pellets after pelletizing to the firing machine is carried out by conveyor transport. As indicated above, when transporting raw pellets, it is necessary to minimize the number of handling units and the height of the pellet fall at each of the overloads. To evenly distribute the load on the roller screen, pendulum devices or reciprocating loading trolleys are installed. The most acceptable and effective way to distribute raw pellets on a roller screen is with reciprocating trolleys on a hydraulic or chain drive, allowing to distribute the load uniformly over a given stacking amplitude (without gaps and distortions in layer height) onto a wide intermediate conveyor and then over the entire area of the roller screen. Uniformity of pellet stacking on the firing trolleys is ensured by three interconnected control loops: the speed control loop of the collecting conveyor drum, the speed of the collecting conveyor belt, and the speed control loop of the wide intermediate conveyor. Such distribution allows to effectively use the entire area of the roller screen in order to increase the efficiency of screening by size classes, to give a rounded shape to the pellets, and to eliminate a number of minor defects (small internal cracks formed along the pellet transportation path) by rolling and strengthening.

          At pelletizing plants built in the 60-90s of the last century, raw pellets after disc pelletizers were fed to a single-deck roller screen, where only the fine fraction of -8 mm was screened. The large fraction of +16mm was not removed from the raw pellets and was placed together with the conditioned pellets of the fraction of 8-16mm on the incinerator. Drum pelletizers worked in tandem with three-product screens, where separation into three fractions of -8mm, +16mm and the conditioned class of 8-16mm was performed. Also, before placing on the incinerator, the fraction of -8mm was additionally removed on a single-deck roller screen. This solution allowed not to screen the fired pellets by small class, since the content of class -6.3mm in the finished product was no more than 3.0mm, which was acceptable for consumers of blast furnace pellets. When delivering products for metallization plants, screening of fired pellets was carried out, which made it possible to obtain a commercial product at the output with a content of class - 6.3mm of no more than 1.0%. Drum pelletizers in conjunction with a three-product screen were installed where there were significant fluctuations in the properties of the feedstock materials fed for pelletizing and additional requirements were required for the quality of the raw pellets fed to the firing machine or the grate-tube furnace-ring cooler system. Recirculation on drum pelletizers is allowed up to 300%. Modern or reconstructed factories are equipped with three-product screens after disc pelletizers, or they are installed directly before loading raw pellets onto the firing machine. The technology of raw pellet production is constantly being improved in two directions - one of them is a set of solutions allowing to obtain high-quality raw pellets with the maximum yield of the suitable class, the second is to more effectively screen raw pellets placed on the firing trolleys. The installation of two-deck screens using rollers with a diameter of 89mm or less allowed to increase the screening area by 30% compared to previously used designs. Industrial samples of three-deck, four product roller screens have been created, which allow sifting out small and large fractions, and divide the conditioned fraction placed on the firing machine into two fractions 8-12.5mm is placed at the bottom of the pellet layer, and the fraction 12.5-16mm in the upper part of the pellet layer.

           This type of laying of green pellets allows reducing the compaction of the layer and improve the firing of pellets along the layer height, due to the formation of a two-level layer of pellets with better permeability than a standard layer. During the firing process, the descending hot gas flow processes large pellets in the upper part of the layer, which are difficult to fire at low temperatures at the bottom of the layer, the gas flow with a lower temperature then fires small pellets, which are fired more easily and this does not lead to their over-firing in the upper part of the layer, as with standard loading. This segregation concept can also be used with a two-level roller stacker, if the pelletizing department already has an optimal screening system with large-class screening of +16mm. These solutions allow improving the quality of the product or increase the productivity of the firing machine, while simultaneously reducing energy costs due to better gas permeability of the layer and better heat exchange between the pellets and the coolant passing through the layer. The founder of this concept is the Canadian company Metal7. The efficiency of screening (sifting) depends on the following factors:
             Characteristics of the screen
             a. number of rollers – the greater the number of rollers, the higher the screening efficiency;
            b. roller diameter – the smaller the diameter of the rollers, the higher the screening e  fficiency and removal of fine                               fraction;
             c. roller length – the greater the length of the rollers, the higher the screening efficiency;
            Characteristics of the state during operation
             a. wear of rollers – reduces screening efficiency;
             b. uniformity of gap opening – uniformity of space between rollers over the entire area of the screen – increases                                    screening efficiency;
             c. straightness of rollers – increases screening efficiency;
             d. angle of inclination – set during commissioning;
             e. rotation speed – set during commissioning (increasing speed promotes the efficiency of removing small class, but also                    leads to a decrease in the efficiency of preserving granules of the conditioned class);
             f. transport capacity of rollers – excessive roller roughness of more than 50 microns reduces the screening efficiency due                    to material sticking, a smoother surface of less than 30 microns – reduces the efficiency of transporting and screening                     due to the creation of a "cigarette" effect with deformation of the pellet shape;
             g. distribution of material on the roller screen – the more uniformly the material is distributed, the higher the screening                     efficiency;
             Characteristics of the material fed to the screen
            a. granulometric composition – the percentage content of each range in the product exiting the pelletizers (the higher                       the content of the required size range, the higher the screening efficiency);
          After screening of raw pellets, fractions of -8mm and +16mm are removed as a recirculation load to the pelletizers. This load is especially critical for disc pelletizers, since its optimal amount should not exceed 25% of the mass of the material fed to the pelletizers. Lower humidity of the recirculation load, usually 0.25-0.35% lower than the humidity of the batch fed for pelletizing, leads to the appearance of many small conglomerates in the mixture with a humidity different from the humidity of the batch. An imbalance in moisture in the volume of the batch and uneven distribution of capillary forces between the particles occurs, which leads to the formation of small and less durable raw pellets or large substandard pellets. The greater the recirculation load, the greater its influence on the granulometry composition of the pellets. The volume of recirculation load often contains large, half-destroyed pieces of raw pellets of class +16mm, which, when entering the pelletizer, are sources of formation of large, substandard pellets of 50-100mm in size, having a layered structure. To destroy these pellets, devices of various configurations, called "hedgehogs", are used. Some of them (a conveyor roller with welded rods) are installed on cables and lowered into the zone of formation of large balls, others (a metal ball with welded rods) are thrown directly into the bowl itself in the same zone. Some Chinese companies are conducting industrial tests of robotic devices (like an arm) for removing large pellets from the pelletizer, eliminating human intervention in this process.

        One of the problematic issues is the destruction of the large class +16mm formed after screening on the upper deck of a two-level screen. There are many types of equipment for crushing this class with varying degrees of efficiency, one of which is installed on top of the outgoing conveyor from under the roller stacker and is based on the principle of crushing large pellets (car wheels, rollers of various configurations), the other (crusher) is installed in the transfer unit of the large-class conveyor and is based on the principle of impact load (a fast-rotating shaft with stiffening ribs). Recently, a device has found its application consisting of a rotating roller, which is installed on the upper deck of the roller screen at the end of the working rollers of the screen, in front of the largeclass conveyor and operates in automatic mode. Periodically, this roller is lowered to the main roller of the upper deck with a gap of 8mm to crush large pellets before entering the large-class conveyor. The most acceptable option, taking into account the efficiency and ease of maintenance, is the installation of a fast-rotating shaft with stiffening ribs in the transfer unit of the discharge conveyor from under the roller screen. The laying of raw pellets after the roller screen is carried out on the calcination trolleys using a sliding board or direct layer-by-layer laying.   

         In general, the control system of the raw pelletizing section should ensure stabilization of the quality of raw pellets, their efficient transportation and uniform stacking, thereby contributing to the stabilization of the high-temperature pellet processing mode on the firing machine.