Tecnologia para abatimento de óxidos de nitrogênio em escala industrial

Abstract

The industrial development presents a close relationship to continuous advancement searching for innovations in the most varied sectors. However, these advances brought negative implications, such as the considerable increase in the emission of harmful gases in the Earth's atmosphere, such as CO2, NOx and SOx. The emission of these gases has become the main environmental risk factor on a global scale and, therefore, controlled by the legislation of each country, due to environmental damage, human health and ecosystems. Among these gases, nitrogen oxides (NOx) stand out due to their origin from fossil fuels in production processes, thermoelectric plants and motor vehicles. In the chemical pickling process, these gases are released into the atmosphere by the action of evaporation and chemical transformations of nitric acid (HNO3) at high temperatures. The methods for washing and purifying these gases, although well established, are relatively complex and may impose economic limitations. From this, more accessible and efficient alternatives for reducing pollutant gas emissions, as well as for their purification and reuse of generated waste, can result in significant economic and socio-environmental gains. The solution proposed for the metallurgical industry that performs chemical pickling from nitric acid is based on a gas absorption system in urea solution to reduce the concentration of nitrogen oxides (NOx) emitted into the atmosphere. The processes were monitored in a preliminary way, analyzing the concentrations in the work tank (without treatment) and in the chimney (after treatment), pH, conductivity, and the visual aspect. The results obtained by applying the urea washing solution with sodium chlorite additive (NaClO2) at concentrations defined in this work for four days in the gas washing system of the metallurgical company showed an average daily removal of 85.5% of oxides of nitrogen, as well as the saturation of the solution and, consequently, the need to change it on the fourth day from the conductivity data. It was also verified that the pH is outside the ideal range according to the literature (pH 5-9), presenting itself in the range of 3, but that it is necessary to carry out an economic feasibility study including the fine control of the pH, to optimize the cost-benefit ratio. The results demonstrated the potential of the proposed solution for the abatement of NOx and that the test carried out on an industrial scale reached the standards imposed by the current legislation on the emission of NOx.