Proceedings of COBEM 2005 18th International Congress of Mechanical Engineering Copyright © 2005 by ABCM November 6-11, 2005, Ouro Preto, MG Still Furnace Optimization Pacifico, Antonio Luiz Inst. Pesq. Tec. Est. S. Paulo S/A – IPT Av. Prof. Almeida Prado, 532 São Paulo, SP, Brazil pacifico@ipt.br de Sousa, Francisco D. A. Inst. Pesq. Tec. Est. S. Paulo S/A – IPT Av. Prof. Almeida Prado, 532 São Paulo, SP, Brazil fdasousa@ipt.br Serfaty, Ricardo Cenpes – Petrobras Av. 1, Quadra 7, 2118 Ilha do Fundão, Rio de Janeiro, RJ, Brazil rserfaty@cenpes.petrobras.com.br Abstract. Aiming better uniformity of the heat transfer fluxes inside still furnaces, an experimental work was carried out in a pilot scale furnace. The methodology used was based in the modification of the mixture processes between fuel and air in order to smoother the reaction rates along the flame and, therefore, the gas temperature profiles and the heat transfer fluxes on the wall. The mixture process was altered changing the angle between the nozzle sprays` and making the use of three concentric air streams (primary, secondary and tertiary). Also, measurements of the CO, NOx and particulate material were carried out searching for a good compromise among the better solutions for heat transfer fluxes which would result in acceptable levels of emissions for these pollutants. The reference for comparisons was an atmospheric industrial burner commonly used in still furnaces that was tested in the same furnace. The better results in terms of heat transfer fluxes revealed that the lower possible amount of air must be supplied to the secondary air flow. The amounts of primary and tertiary air flows must be carefully divided so the primary air flow rate does not reach the blow out limit. The addition of swirl always resulted prejudicial for the main objective. Finally, the angle between nozzle spray’s must be reduced to the minor possible value that do not yield a significant coalescence of the spray’s drops Keywords: optimization, still furnaces, heat transfer fluxes 1. Introduction Nowadays in Brazil there are several situations where the still furnaces work on their limit, constituting bottle necks for refinery throughputs. In general, these operational limits do not come from limitations in the mass flow rates of air and fuel, neither from the exhaust systems capability. In fact the limits referred in this article are related with the non-uniformity of the heat transfer fluxes to the coils inside which the process fluids are flowing (liquid or gaseous) to be heated. These coils are disposed uniformly over or between the internal walls in combustion chamber of the furnaces, constituting the so called “furnace radiation zones”. The flames, generally vertical, produced by the burners, have inevitably non-uniformity properties distribution (like temperature, chemical species concentrations, local emission and absorption radiation coefficients). As a result some peaks in the heat transfer fluxes over the coils will exist, as a consequence of the mainly heat transfer mechanism inside these furnaces being the radiation one. These peaks generate two undesirable facts: (1) high skin temperatures, what are a risk for the integrity of the tubes; and (2) over-heating of the fluid flowing inside them; these phenomena generating a progressively coke formation over the internal wall of the tubes, increasing the pressure loss of the fluid flow. In the limit condition, a significant reduction of the mass flow rate of the process fluid will occur. In summary, for remotion of the bottle neck to increase the production of these furnaces will consist in the attainment of the more uniformity heat transfer fluxes distribution over the coils. After words it will be possible to increase the power of the burners. In order to obtain a greater uniformity of the heat transfer fluxes over the coils, the solution proposed in this work was the modification in the mixing process between fuel and air to soften the reaction rate along the flame. To achieve this objective, a new air distribution box for the burner was developed in order to have not only two air streams (the common arrangement of the present still furnace burners), but three air streams. Also a spray angle of the nozzles was explored combined with these air streams configurations. Finally, it is important to notice that the solutions obtained were confronted with pollutant emissions they produced. The better solutions must be those in which a compromise can be established.