Pyrolysis of residual biomass via thermo-catalytic reforming - experimental investigation of sewage sludge

Producing energy from residue and waste biomass is essential for a sustainable bioenergy supply. An organic waste with certain problematic issues is municipal sewage sludge, which is mainly disposed of by landfill and landspreading, and occasionally by incineration depending on local regulations. Besides incineration, several other thermal processes have been introduced to replace the landfilling and produce bioenergy. However, due to high water content, low heating value, high ash content, and low ash melting point, sewage sludge is still not often utilized for bioenergy applications.The aim of the presented work was to test and characterize the Thermo-Catalytic Reforming (TCR®) process and its variable parameters, for the feedstock sewage sludge and its products for bioenergy applications. TCR® is an intermediate pyrolysis and reforming process for the energetic utilization of underutilized waste biomass. For the presented work, the parameters of the TCR® plant were varied, focusing on the gaseous and liquid product quality. Pre-dried sewage sludge was tested in the reactor and the products were analyzed by different methods. Blends of bio-oil with biodiesel and syngas were utilized in a dual fuel engine. The bio-oil produced revealed a very high thermal stability during distillation at 350 °C by forming a low viscosity distillate and a high viscosity residue which could be easily liquefied again by heating up. Furthermore, by hydrotreatment and distillation of the crude TCR® bio-oil, renewable gasoline and renewable diesel can be produced which meet the European standards EN 228 and EN 590. Overall sewage sludge showed high potential as a feedstock for high quality products like renewable fuel, phosphate recovery, and combined heat and power applications.