Reduction of Moisture of the Ore
Researchers at Vale Institute of Technology in Ouro Preto (MG) test technologies for the moderate reduction of moisture in iron ore sinter feed, by injecting hot and dry air via a transfer chute. This technology may reduce an impact that, for years, has fallen upon the all-in cost of the company’s main product:Vale’s iron ore that leaves a port currently contains, on average, 9.5% of moisture. That is, taking as an example a Valemax, the largest iron ore ship in the world with capacity to carry 400,000 tons, this represents 36,000 tons of water that leaves Brazil and goes to the company’s main clients on the other side of the world.
The origin of the water in iron ore is twofold. On one hand, moisture is related to the physical composition of the mineral itself. On the other, the processing is executed in a wet form, which still occurs in many Vale mines. Processes such as flotation used to increase the iron content of the ore, use water. In addition to the visible cost – transport and the discount for the sale of dry iron ore at the destination port – water represents a greater expense in insurance for the cargo transported on the ship and also, in some cases, can provoke the interruption of loading at a port.
For more than a decade, Vale has studied how to reduce moisture, but all solutions were shown to be economically unfeasible. By the conventional method, it is possible to use industrial driers, but, due to the great volumes of iron ore moved by the company, the investment (CapEx) and operation (OpEx) costs of this equipment are prohibitive. Then, a solution that ITV has been working on for the past two years appeared. The objective is to reduce the moisture in iron ore between 1% and 1.8%.
Instead of using industrial driers, the solution was to adapt the iron ore transfer chute as a drying chamber. The chutes are closed equipment where the change in direction of the conveyor belts is made, which take the iron ore from the yard to the ship. The idea is to inject hot and dry air within the transfer chute in countercurrent – that is, bottom-up – when the ore is passing through, in order to remove a moderate amount of water. The proposed equipment uses dehumidifiers and heaters for the treatment of atmospheric air, which is injected into the transfer chute. The proposal is to use a gas driven system, which can be either Liquefied Petroleum Gas (LPG) or natural gas.
The solution developed by ITV-MI was submitted to an industrial scale proof of concept, where the results showed that it is possible to reduce the moisture content of the iron ore within the project range, with OpEx costs of cents per processed ton.