Experimental Study of the Pulverized Biomass Flames in a pilot-scale reactor using OH* Chemiluminescence Imaging and In-flame Probe Measurements
Session chaired by Pr. Epaminondas Mastorakos
Abstract submitted to the “Low Carbon Combustion” days Joint meeting of the French and British sections of the Combustion Institute, 6th-7th May 2020, Lille Experimental Study of the Pulverized Biomass Flames in a pilot-scale reactor using OH* Chemiluminescence Imaging and In-flame Probe Measurements Hassan Mohannaa,b,c, Carole Gobinb, David Honoréb, Benoit Taupina, Patrick Levya, Jean-Michel Commandréc, Bruno Piriouc a Veolia Recherche et Innovation (VeRI), 78520 Limay, France b Normandie Univ, INSA Rouen, UNIROUEN, CNRS, CORIA, 76000 Rouen, France c CIRAD UPR BioWooEB, 34398 Montpellier, France Corresponding author: hassan.mohanna@veolia.com The world efforts to reduce the dangerous levels of pollution present biomass as an attractive fuel for the industrial power plants. In many ways, biomass is regarded as an economical solution of energy production and waste management. Its abundance and sustainability and its resemblance to coal, makes it a potential candidate of incorporating it with coal in the existing infrastructure. An experimental study is performed on a pilot-scale combustion facility to evaluate the structure and characteristics of pulverized biomass flames. The design of the 20kW bluff-body burner and the 4m-length vertical combustion chamber is made in a way to allow analyzing the different involved phenomena using chemiluminescence and in-flame probe measurements of temperature and gas concentrations (O2, CO, CO2, NO). Pine (82% volatiles) was grinded (< 500 µm) and thermally treated into two degrees to produce a moderately torrefied pine (72% volatiles) and a pyrolyzed one (44% volatiles). The chemiluminescence signal of OH* excited radicals marks the zone of the volatiles reactions. The intensity of the signal is strongly dependent on the fuel volatile content. However, the position and structure of the reaction zone is rather affected by the particle size distribution in the first order than by the biomass thermal treatment. Despite having low volatile content, pyrolyzed pine flames show earlier OH* chemiluminescence radiation than pine flames thanks to the finer granulometry. The wide granulometry of pine produces a first close-to-burner reaction zone, which is penetrated by the large particles that devolatilize further in the reactor forming a second reaction zone. This decreases the reaction zone intensity near the burner and explains why the finer moderately torrefied pine has a more intense reaction closer to the burner despite lower volatile content and less devolatilisation reactivity observed at particle level. The probing results validate these conclusions where the two-stage devolatilisation of pine has the advantage of reducing the NOx fraction in the second devolatilisation region. Moreover, higher and earlier devolatilisation, oxygen consumption and temperature rise are detected on the jet axis for the treated pine compared to their raw counterpart. The confined jet aerodynamics creates in the combustion chamber a large recirculation zone around the main central jet where hot combustion products are entrained upstream. The earlier release of volatiles reduces the particle density and prepares them to follow the air streams to undergo their char conversion in this outer recirculation zone.
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