Avaliação do uso de biodiesel como alternativa para redução de emissões de poluentes gasosos em processos industriais.

Abstract

The last stage of production of alumina during the Bayer Process consists of the elimination of the crystallization water from the hydrate (AI2O1.3H2O). To reach so, the hydrate is calcined at a temperature of about 1000 °C in ovens called "calcinadores" using diesel and BPF oil as fuels. The diesel oil is used in the stage of heating-up the oven ("calcinador") and the BPF to calcine alumina. The BPF Oil used in the process contains in average about I to 2 % of sulphur. This element is undesirable due to corrosive action of its composites and causes the formation of toxic gases as SO2 (sulphur dioxide) and SOi (sulphur trioxide) during its combustion. ALUMAR produces about 1,5 million ton alumina per year what consumes a significant amount of BPF oil. The burning of all this oil, in turn, produces a great load of pollutants in the form of sulphur emissions that is released to the atmosphere. Aiming to mitigate the environment impact, the company has been searched alternative to reduce such gaseous emissions. Among the alternatives stands the use of other type of fuel with lesser sulphur content. Following this line, an option would be the use of biodíesel or also called green combustible. It is produced from renewable raw materials as vegetable oils, animal fats and waste vegetable oils. It is a clean burning fuel virtually free of sulphur. This fuel has been used pure or blended with diesel in different percentages in diesel cycle engines. In view of the environmental benefits of the biodíesel use in diesel engines, we choose to test it as an alternative fuel in the calcination process. Firstly it was measured the physical-chemical properties of the neat biodíesel and its mixtures with BPF oil. The properties were evaluated regarding the quality control parameters used in the ALUMAR calcination process. The physical-chemical properties studied were the heat power, sulphur content, viscosity, density and vanadium content. The results showed that the benefits in the quality of the fuel in terms of sulphur content and viscosity reduction compensate the loss in its heat content and density. Nevertheless, the biodíesel actual cost is still high what restrict its utilization as an alternative fuel in the process. This situation reflects the fact that Brazil still don't have a biodíesel production capacity to replace, at least partially, the heavy oil (BPF) utilized in industrial processes and nowadays the government effort is focused in the diesel replacement. Another issue that must be regarded during the evaluation of the economic balance is the carbon credits. Biodiesel is a renewable fuel and in spite of/Brazil is not inserted in the annex 1 of Kioto Protocol, Alcoa have many other branches around the word that can take the benefits of those credits