Reduction of Water Content in Sewage Sludge Pyrolysis Liquid by Selective Online Condensation of the Vapors

A selective online condensation system, including a scrubber and an electrostatic precipitator, has been tested in a lab-scale fluidized bed pyrolysis plant with the aim of reducing the water content of the pyrolysis liquid obtained from sewage sludge. Water and triethylene glycol at different temperatures were tested as washing liquids in the scrubber. The pyrolysis liquids collected with this liquid recovery system showed lower water contents (13-30 wt %) than those collected with a previous system (48 wt %) consisting of two condensers and an electrostatic precipitator. In spite of these significant reductions in the water contents, the liquids obtained still separated into three phases (light organic, heavy organic, and aqueous). The properties and yields of these phases were also affected by the operational conditions used in the scrubber. The aqueous phase was the most affected because the compounds present in this phase are those with greater affinity for the polar washing liquid used in the scrubber. The properties of the organic phases were less affected by the condensation system, although it is of interest that when using triethylene glycol at 80 C as washing liquid, the yield to the light organic phase was increased by about 41% compared to the previous system without affecting its good properties as fuel.