Producing single phase fast pyrolysis oils from straw by staged condensation

Bio-oil produced from straw by means of ablative fast pyrolysis will separate into two phases due to high amount of water. This paper investigates the influence of staged condensation temperature on the water content of the condensates, with the aim of finding the minimum temperature at which the resulting bio-oil in the first stage will be a single phase liquid. The pyrolysis vapours were fractioned using a two-stage condensation system, each stage consisting of a cooler and an electrostatic precipitator (ESP) connected in series. The cooling medium temperature of the first stage was varied between 60 °C and 80 °C, whereas the temperature of the second stage was kept constant at 4 °C. The minimum vapour temperature at which the 1st stage condensate is a single-phase liquid was found to be 65.8 °C. The investigation showed that staged condensation is a possible way of producing single-phase bio-oils with a reduced water content and total acid number (TAN). Compared to the tarry phase of total condensates, the 1st stage condensates had an increased yield of organics.