Evaporation of biomass pyrolysis oil as single droplets.

摘要

Biomass pyrolysis oil is an organic liquid produced by the pyrolysis of biomass materials. The fuel is known as a clean, cost-effective, renewable resource and a potential replacement for petroleum fuels in boiler, gas turbine, and diesel engine applications. The fuel oils are usually introduced into the burner as sprays of droplets; therefore, the evaporation behaviour of individual fuel droplet has an important role in understanding of the combustion characteristics of the droplets in spray combustion and in the burner performance. Single droplet evaporation/combustion experiments have been performed by several researchers in the past years with different kind of fuels by using two main techniques: Suspended droplet/moving furnace technique and freely falling droplet technique. In this research, the suspended droplet technique has been preferred because of its advantages that the droplet is stationary and easily observed.; The mathematical model presented in this thesis is based on a model developed by Hallett and Clark (2006) to describe the evaporation of a pyrolysis oil droplet and its pyrolysis to gas and char. A well-mixed liquid phase is assumed in the previous model, which is reasonable owing to the vigorous bubbling during much of the evaporation process. However, this assumption is questionable during the pre-bubbling period. In order to gain some insight into this period, and into the onset and the location of bubbling, a diffusion-limited model, developed by Law and Law (1981) and extended by Hallett (2000) to a continuous mixture form, is used with some modifications to extend the earlier model. The results are compared to the experimental results, and conclusions for evaporation modelling are drawn.