Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
ANALYSIS OF POLLUTANT EMISSIONS FROM THE BURNING OF BIOMASS PELLETS AND AIR FOR DIFFERENT OPERATING CONDITIONS
Submission Author:
Milena de Morais Farenzena , SC
Co-Authors:
Milena de Morais Farenzena, Norton Trennepohl, Roberto Wolf Francisco Jr.
Presenter: Milena de Morais Farenzena
doi://10.26678/ABCM.ENCIT2022.CIT22-0579
Abstract
Biomass combustion is a promising option for combustion processes with low emissions of pollutants, despite causing carbon dioxide emissions, these emissions are equivalent to the amount of carbon dioxide that was captured by the biomass in its photosynthesis. Thus representing a neutral balance, less harmful to the environment than fossil fuels. In this context, the objective of the present work is to investigate the emissions of pollutants from the combustion of biomass and air using a fixed bed burner. This study will be carried out numerically and experimentally, using biomass from pine reforestation, free from the addition of chemical products. The wood bark is removed, cut, dried, ground and compressed into its final form, pellets, with a diameter between 6 and 8 mm. Pellets are fed automatically from the top of the burner. The burner has a grate at the base to support the fuel. Combustion takes place in two stages, in the first, primary air is supplied, passing through the fuel and ensuring its pyrolysis and the combustion of fixed carbon. In the second, it is where the combustion of volatiles and suspended particles takes place. The burner was instrumented with temperature and pollutant concentration meters. Air flow was measured using a Pitot tube, while fuel flow was determined using the weighing method. Pollutant emissions were determined experimentally for different operating conditions (air and fuel flows). Numerically, the concentrations of volatiles were estimated for different reaction temperatures and the products of combustion were determined, assuming chemical equilibrium for the same conditions of temperature and equivalence ratio. The estimated volatiles are constituted by H2, C2H4, C3H8, C2H6, CO, CO2, CH4 and N2. The main combustion products considered are CO, CO2, H2, N2, H2O and O2. For an equivalence ratio equal to 0.8, it was numerically observed that the increase in the reaction temperature from 650 to 850 °C resulted in a variation in the composition of volatiles, increasing the molar concentration of CO present in the combustion products and, reducing the concentration of CO2, due to its dissociation. For this equivalence ratio the molar fraction of H2 is negligible. The molar fractions of CO and H2 become more significant for equivalence ratios greater than the stoichiometric one. All analyzes were performed at atmospheric pressure and assuming standard dry air. In general, the numerical results for pollutant emissions for different equivalence ratios and reaction temperatures showed excellent agreement with the literature.
Keywords
Biomass combustion, pyrolysis, wood pellets, fixed bed burner
