Brazilian mining company Samarco has developed a new, more efficient and economical technology to verify the percentage of coating of iron ore pellets used in the manufacture of steel. Pellets are sinter feed made from iron ore (iron oxide or hematite – Fe2O3), with diameters ranging from 6.3 to 16 millimeters. They are produced by transforming low ore content minerals into a product with high added value. The challenge is to minimize the tendency for this product to stick together in the reactors of Samarco’s clients during the reduction process. During this process, the pellets must be transformed into metallic iron (Fe) by removing oxygen, in a chemical process called reduction, which is the opposite of oxidation.
Pellets are the Company’s main product, and are exported to more than twenty countries as raw material in the steelmaking process. The reduction process is done at reactors that operate at high temperatures, which can reach 950°C in some regions of the furnaces. Samarco process technician Heidy de Oliveira Simões explains that temperature and pressure are directly related to the productivity of the reactors. “But there is a limit, because higher temperatures favor the formation of a phenomenon in which the pellets stick to each other, called clustering, which reduces permeability of the base and has a negative impact on productivity.”
The ore travels a long way to reach this phase. The process begins with extraction at the Germano and Alegria open pit mine complex in the municipalities of Mariana and Ouro Preto in the state of Minas Gerais, where Samarco has approximately three billion metric tons of reserves of this product. All the ore production and waste material removal are done using large- scale moveable equipment. “Next, the ore is transported to the concentrators by a system of belts that eliminates the need to use trucks, thus reducing dust and noise.”
At these concentrators, located at two industrial plants at the Germano unit, the ore from the mine is crushed and ground. Impurities are then removed by reverse flotation, a process pioneered by Samarco in which the contaminant is floated, instead of the product. After this beneficiation, the material, which previously had an iron content of 46%, now stands at 67.5%, and also now has the chemical and physical specifications necessary for the subsequent phases. Water is added to this fine-grain and concentrated ore, transforming it into slurry with a consistency similar to that of mud. Composed of 70% iron ore and 30% water, this slurry is transferred to storage tanks, which are then transported to the pelletizing plants at the Ubu unit in Espírito Santo. Three pipelines, each around 400 kilometers long, make this transportation possible. These are actually large pipes buried underground at a depth of around 1.5 meter, though which the iron ore slurry is transported.
Pumped over the mountains
The first pipeline, with pipe sections with diameters of 18, 20 and 22 inches, was laid in 1977 and has the capacity to transport 15.3 million metric tons a year. The second, with diameters ranging from 14 to 16 inches, began operations in 2008 and can carry up to 8.5 million metric tons annually. The newest pipeline has been in operation since April 2014, with diameters of 20 and 22 inches and the capacity to transport 20 million metric tons a year. The slurry is pumped through the pipelines by a system of pumping stations located along the way from Mariana to Matipó (MG). “In this latter city, Samarco has pumping stations that push the slurry up the Caparaó mountain range,” explains Vitor Quites, Samarco pipeline manager. “In the cities of Guaçuí and Alegre (state of Espírito Santo), we have valve stations, which control the downhill flow from the mountains, on the Espírito Santo side. After these cities, the slurry continues until it reaches the Ubu unit.” In its three-day trip along the pipeline, the ore travels through 25 cities, from Minas Gerais to Espírito Santo.
The pipelines are made of highly resistant steel to prevent any abrasion that could be caused as the ore passes through it, according to Quites. In addition to being a more economical means of transport, they do not cause relevant impacts on the environment or on the communities they pass through. “The pipelines consume little energy, do not make noise, do not emit carbon dioxide (CO2) and do not disperse particulates (ore dust),” Quites affirms. “Also, since they are underground, they do not interfere with highways, railways or bridges, not even in the urban areas of the municipalities. Another important point is the degree of safety associated with this type of transportation, which is an even more relevant factor when compared to highway and railway transportation.”
After it reaches the Ubu unit, the slurry is filtered to remove some of the water and for production of the pellets. Inputs are then added (coal, limestone and agglomerating agent) and the agglomeration process begins to produce the green pellets. Finally, they undergo a hardening process (burning) and are then screened to remove material with improper grain size. After this stage, the pellets receive a refractory oxide spray in an aqueous solution (in other words, the product is mixed with water). This is done in the transfer towers before the pellets are piled in the stockyards or sent to the companies purchasing them.
The spray forms a layer of refractory oxide coating on the surface of the pellets (which is resistant to high temperatures), called a coating agent or non-sticking agent. The purpose of this application is to minimize the tendency of the pellets to stick together during the reduction process, by acting as a physical barrier between them. “In order to increase the competitiveness of our product, it is necessary to quantify the coating; that is, to know how much of the surface of each pellet is coated with the refractory oxide,” Simões explains. “Reducing clustering is essential for Samarco’s strategy on the direct reduction market.”
According to Simões, before Samarco’s innovation, the test to verify the pellet coating could only be done using standardized analysis (ISO 11256), a test conducted at a temperature of 850ºC, simulating the reduction process. “The problem was the time it took to conduct the test, which was twelve hours to conclude a single result,” she says. “This meant that a ship that carries 45,000 metric tons was loaded even before the analysis to determine the sticking rate was released.” The new technology analyzes the coating of the pellets using a piece of equipment that is basically composed of a camera, which takes pictures of the pellets, and an algorithm (computer program), which calculates the coating rate of the pellets. The result shows the percentage of the pellet surface coated with this refractory oxide product. The main advantage is that the test for each sample takes no more than an hour and a half.
In numerical terms, this new methodology reduced response time for determining the tendency for the pellets to stick together during the reduction process by 88%. This led to annual savings of R$193,300 for Samarco, which did not have to conduct partial shipment tests (the results declared on the shipping certificate relative to the representative composition of the entire shipment continue to be conducted, based on the ISO 11256 standard, for contractual purposes). For this same reason, the Company’s innovation also led to environmental gains: 300 kilos of carbon dioxide (CO2) are prevented from being released each year due to the reduction in the number of tests conducted based on the ISO 11256 standard. “The results obtained by this new methodology enable us to make strategic decisions while ships are being loaded, guaranteeing high performance of the product in our clients’ reactors,” says Simões.
According to the head of Samarco’s Process Engineering Department, Thiago Marchezi Doellinger, this equipment is considered to be cutting edge, and the Company is studying whether to file for a patent at the National Industrial Property Institute (INPI). “This is a tool that will help us to work pro-actively in an ever more competitive and demanding market,” he says. “The relevance of the direct reduction market for Samarco is clearly proven, and tools like these will enable us to stand out in the commodities market as a preferential supplier for our clients. For the Company, rapid response is essential. Besides being more efficient, the new method is economical, safe and environmentally friendly. For these reasons, its adoption into our routine represents a major gain for the Company and the entire chain of production.”
Founded in 1977, Samarco is a privately held Brazilian company, equally controlled by two shareholders, Vale and BHP Billiton Brasil, the latter an Anglo-Australian company. It is one of the most important Brazilian mining companies and the second largest on the global iron ore pellet market, as well as being one of the largest exporters in Brazil. “With clients in over twenty countries, the Company currently has annual nominal production capacity of 30.5 million metric tons of pellets, generating approximately 3,000 direct and 3,400 indirect jobs,” Quites says. “With headquarters in Belo Horizonte, the Company has two industrial units in the states of Minas Gerais and Espírito Santo, its own maritime terminal located at Ubu (ES) and three sales offices located in Amsterdam, the Netherlands, Hong Kong, in China, and Vitória (ES).Republish