Energetic comparison of sewage sludge mono-incineration and hydrothermal carbonisation coupled with hydrochar incineration

This works aimed to compare the energetic implications of a sewage sludge mono-incineration to a system, consisting of a Hydrothermal Carbonisation (HTC) and subsequent mono-incineration. Both scenario were modelled using Aspen Plus and energetically evaluated. The impact of different HTC parameters was evaluated. The Hydrochar show a similar carbon content and calorific, but significantly lower ash content the dewatered sewage sludge. The heat demand of the HTC can be covered by up to 98% by an efficient heat recovery system. The steam cycle, following the incineration, delivered electric power with an efficiency, based on the fuel input, of 0.7 and 14.7% without and with HTC, respectively. The truck fuel consumption for transport of dewatered matter to the incineration plant is reduced by 63%, if the HTC is applied. In conclusion, HTC can contribute to a highly energy efficient thermal treatment of sewage sludge, if a proper heat integration is implemented.