Spray Combustion and Particulate Matter Emissions of a Wood Derived Fast Pyrolysis Liquid-Ethanol Blend in a Pilot Stabilized Swirl Burner

Abstract

Biomass fast pyrolysis liquid (or bio-oil) is a cellulose based alternative fuel with the potential to displace fossil fuels in stationary heat and power applications. To better understand the combustion behavior and emissions of bio-oil, a 10 kW spray burner was designed and constructed. The effect of swirl, atomization quality, ignition source energy, air/fuel preheat, and equivalence ratio on the particulate matter emissions of bio-oil spray flames was investigated. A blend of 80% pyrolysis liquid and 20% ethanol by volume was used during the tests. Increasing the residence time of spray droplets in the hot combustion zone by increasing the swirl number promotes the burnout of solid residues. Decreasing the mean diameter of fuel droplets by increasing the atomizing air flow rate has a similar effect. Ignition source energy, air/liquid fuel preheat, and equivalence ratio have either a weak or ambiguous effect on the measured particulate emissions. The residual material collected from the exhaust is composed of both carbonaceous matter and fly ash. However, the majority of particulate matter consists of ash, even at relatively poor combustion conditions. These results suggest that it is possible to provide enough oxygen availability and residence time for droplets to undergo nearly complete burnout during combustion. Under such conditions, the total particulate matter emissions could be further mitigated by reducing the inherent ash content in the fuel.

Mathematical Modeling of Fast Biomass Pyrolysis and Bio-Oil Formation. Note II: Secondary Gas-Phase Reactions and Bio-Oil Formation

“…Pyrolysis bio-oil is a dark-brown acidic liquid (pH 2−3) with high water and solid content, and has a heating value that is less than half of hydrocarbon fuels. 72,73 It is possible to increase the heating value only through expensive deoxygenation processes. 74 Upgrading of Pyrolysis Bio-Oil.…”

“…The low liquid yields, the high capital expenses, together with further technical problems, make these catalytic methods less attractive. 73 The second and more suitable approach to increase the oil quality are based on biomass pretreatment 3,79,80 and physical upgrading. These methods include hot gas filtration, liquid filtration, distillation, and solvent addition.…”

“…Conventional soot mechanisms contribute only partially to the total particulate emissions. 73 It is therefore necessary to develop models able to predict not only the complex evaporation of a bio-oil droplets but also its combustion kinetics, including pollutant formation, as well as char formation and particle burnout. From a kinetic modeling perspective, the description of the combustion of bio-oil is a very complex task at least for three different reasons.…”

“…As clearly summarized by Lindfors et al., the properties of fast pyrolysis bio-oils differ significantly from those of fossil fuels. Pyrolysis bio-oil is a dark-brown acidic liquid (pH 2–3) with high water and solid content, and has a heating value that is less than half of hydrocarbon fuels. , It is possible to increase the heating value only through expensive deoxygenation processes …”

Fuel and Chemical Properties of Waste Tire Pyrolysis Oil Derived from a Continuous Twin-Auger Reactor

“…Assuming similar atomization quality, a fuel with low volatility tends to form localized regions in the reaction zone, with a lower equivalence ratio than the nominal value. The net result is a reduced rate of heat release that promotes the onset of flame extinction and blow-out at higher overall equivalence ratios than more volatile fuels [77].…”