Particulate emissions measurements by laser-based techniques in a boiler fueled by wood pellets

Abstract

This paper describes mainly laser-based techniques applied to a boiler fueled by wood pellets which is a real complicated combustion system. To our knowledge, laser-induced incandescence (LII) and extinction are used to characterize particulate emission at the exhaust for the first time because laser diagnostics are generally applied to laboratory flames, automotive engines and aeroengines. The 30-kW boiler was first characterized by temperature mapping in the combustion chamber and particle diameter analysis by scanning mobility particle sizer at the exhaust and inside the first combustion chamber for a better understanding of the running of this complex combustion system. Non-intrusive laser-based diagnostics including broadband LII, two-color LII and laser extinction excited at 1064 nm have been employed to study the particulate emissions at the exhaust of the boiler during the start-up and the steady-state phases of the boiler. The cross analysis of the experimental results obtained with the different diagnostics shows that particle size distributions, particles volume fractions and the temperature distribution are strongly dependent on the boiler cycle linked to the pellets loading. Laser extinction and LII-based methods provided complementary information about the particulate emissions. The LII technique probes incandescent soot particles formed during the combustion of pellets, while laser extinction detects both soot and non-incandescent particles (such as dust, fly ashes).