Desenvolvimento de caldeira de leito fluidizado borbulhante operando com gás natural

Abstract

The increase of energy demand, concomitantly with population growth, has induced researches and developments of new technologies to harness the energy potential of both fossil and renewable fuels, seeking to mitigate environmental impacts. In this context, fluidized bed combustion emerges as a technological alternative for the use of solid and gaseous fuels, efficiently and with lower pollutant emission indices, compared to conventional methods. In line with this proposal, the present dissertation deals with the development of a fluidized bed boiler applied to solid and gaseous fuels, focusing on natural gas as reference fuel and using silica as the constituent medium of the porous bed. For this reason, this research was divided into the following steps: i) Study fluid dynamic phenomena and parameters in preliminary prototypes; ii) Basic and constructive designs of a fluidized bed combustion reactor in laboratory-scale; iii) Manufacture, assembly, and instrumentation; iv) Experimental tests of fluidization and combustion of vehicular natural gas (VNG) and operation analysis of the built laboratory prototype. The experimental setup for preliminary prototype studies consisted of 3 acrylic tubes of different internal diameters (DI) (44, 65 and 90 mm) with a height of 1000 mm and a reactor coated internally of refractory concrete with a diameter of 53 mm and height 550 mm. The experimental apparatus, built for this research, consisted of a carbon steel reactor with a height of 935 mm and an internal diameter of 110 mm, internally covered by a refractory material. In addition, the laboratory prototype has a preheated air distribution system for combustion, a startup system of the kind flamethrower and an exhaust system, among others. To this end, the basic and constructive designs were performed, aiming manufacture and assembly of the prototype, including the provision of process monitoring instruments. Lastly, through experimental testing, fluidization and combustion processes were investigated, focusing on stability and startup of the prototype in operation, evaluating its performance with VNG for broad equivalence ratio ranges (0.61 <RE <1.27) and fluidization velocity. Along the tests, average operating temperatures were observed between 711 °C and 956 °C, obtaining NOx and CO emissions about 4 ppm and 0.205% by volume, respectively.