Pellet growth is controlled by the small amount of water sprayed in the disc and the adjustment in the disc rotational speed. Additionally, it is a natural material with variable composition depending on its origin. The iron ore pellets are shown in Fig 1.The typical properties of the iron ore pellets are given in Tab 1There are four stages involved in the production of iron ore pellets. Beberapa pelajaran apabiala kalian bisa tampil dalam satu situs poker online yang terbaik 2019 ini banyak loh, salah satunya kamu bisa menyimpan banyak peluang untuk mendapatkan keuntungan yang akan didapatkan dalam situs itu dengan cepat biala anda padahal pada tempat keberuntungan dikau, beberapa seperti bonus, hadiah berupa uang asli ayang bias di cairkan nayata, chip gratis untuk permainan judi selanjutnya, dan ditemui beberapa lainnya keuntungan –keuntungan yang bisa kalian miliki. With the continuous addition of binder and feedstock, particles continue to pick up more fines, rolling and growing in similar fashion to a snowball.
Source: Prepared by the authors with data from Tuck and Virta [2].The iron ore pelletizing process consists of three main steps:Pelletizing feed preparation and mixing: the raw material (iron ore concentrate, additives—anthracite, dolomite—and binders are prepared in terms of particle size and chemical specifications, dosed, and mixed together to feed the pelletizing process;Balling process: the green pellet is the rolled pellet without any thermal process. Midrex® process. These reactions can include the oxidation of magnetite and dehydration of earthy hematite. In general, three primary phases occur in iron ore pelletizing:The mixing step sets the stage for the remainder of the process, creating a homogeneous mixture that will allow for a uniform product to be created. When the solid particles come in contact with water, the ore surface is wetted and coated with water film. FEECO is a leader in feasibility testing, custom disc pelletizers and balling drums, and aftermarket services for the iron ore balling/pelletizing industry. The resulting heated air is used in the upstream steps of firing and drying.Induration processes were initially developed for ores composed of magnetite, since they are oxidized, producing hematite, and generating heat (−482.4 kJ/mol of FeThe most widely used industrial processes for pellet induration are the straight grate and the grate-kiln.The straight grate process is composed of a single furnace where an endless line of pallet cars moves. Formation of oxides and slag bonds is decisive of this stage.Bonding of mineral grains developed during induration of pellets is affected by the three factors consisting of (i) solid oxide bonding, (ii) re-crystallization of iron oxide, and (iii) slag bonding. All formed pellets are discharged, regardless of particle size, which is different from the disc where only balls larger than a certain size are discharged. The Process Development Behind Iron Ore Pelletizing . In the second drying stage, hot air from the firing zone is blown on the top of the car. As the added ore aggregates unto the surface of the pellets, they increase in size and the coefficient of friction is reduced causing the pellets to acquire a centrifugal force that carries them out of the nucleation zone. Once induration is complete, pellets are ready for the blast furnace.The Process Development Behind Iron Ore Pelletizing As there can be significant variation in process requirements and sources of iron ore fines, testing is often an essential part of the development of a successful iron ore pelletizing operation. During pre-heating stage (temperature range of 500 deg C to 1,100 deg C), decomposition of carbonates and hydrates takes place. Source: Elaborated by the authors from Metso [9] and Vale [10].The balling equipment that can be either a disc or a drum produces green pellets in a variable size distribution.Schematic diagram of laboratory balling disc. Ore fines are lifted upwards until the friction is overcome by gravity and the material rolls down to the bottom of the disc. Source: Modified by the authors with data from Ball [1].The main bonding mechanisms of size enlargement are described as being [solid bridges between agglomerating particles, which may occur by sintering, partial melting, chemical reaction, hardening binders, recrystallization of dissolved substances, and deposition of colloidal particles;interfacial forces and capillary pressure in movable liquid surfaces (liquid bridges);adhesional and cohesional forces in bonding bridges, which are not freely movable (highly viscous binder), adsorption layers <3 nm thickness);attraction between solid particles: molecular forces (Van der Walls forces, free chemical bonds—valence forces—associations—nonvalence—and hydrogen bridges), electric forces (electrostatic, electrical double layers, excess charges), and magnetic forces;interlocking, depending on the shape of particles, for example, fibers, threads, or lamellae.The agglomerated growth mechanism was defined by Sastry and Fuerstenau [Details of the mechanisms proposed by Sastry and Fuerstenau [14]. The binder causes the particles to become tacky, picking up more fines as they roll in the drum or disc – a layering phenomenon known as accretion. In order to increase its mechanical strength, green pellets are thermally treated in the induration process.Pellets undergo drying, firing, and cooling steps. As such, it’s important to note that the process described here is a generalized approach subject to many variations.