Particulates

Подпись: 3.6.2Particulate levels may be high from char and ash carry-over. Separation of solids and liquids is poorly understood with reliance placed on primary separation in the vapour phase downstream of the reactor before condensation. Efficient separation inevitably causes some condensation or precipitation and carefuf design is essential. Solid separation in the liquid phase is not believed to have been studied, but is very likely to be troublesome. However, it is clear that a fairly high level of charcoal can be assimilated in the liquid product, for example Alten reported up to 15% (126) although some lumpiness was evident in the bio-oil. Both char particle size and proportions will influence the liquid product quality. This is why research into char-oil mixtures could prove valuable.

3.6.3 Oxygen content

The oxygen content of the pyrolysis liquid is very high, at up to 40% wt. When produced from dry or low moisture content feeds it typically has a heating value a little below that of the biomass feed in the range 16-20 MJ/kg depending on moisture content (around 22-23 MJ/kg on a dry basis). The oxygen content arises from the wide range of oxygenated compounds including phenols and polyphenols, which are one of the chemical products that can be recovered as a valuable fraction (119).