Waste toilet paper to electricity - A techno-economic feasibility study

Abstract

The goal of this research was to assess the techno-economic feasibility of a waste toilet paper (WTP) to electricity plant. This concept uses new technologies to create local electricity out of a waste source. The specific case was to convert WTP from the wastewater treatment plant from Waternet in Amsterdam-West to electricity at the site of the waste incineration company AEB that lies directly next to it. Input would be 25.000 tonne WTP per year with 60% moisture and an energy content of about 5MWth, delivered at the gate of the AEB. The system set up would include a gasification reactor and a high temperature fuel cell. The method for assessing the system had six steps. First, the elemental composition and energy content of the fuel were determined. The second step was to design a system for conversion of WTP to electricity. A gasification model was created in excel to determine the product gas composition. Third, the electricity yield and energy efficiency of the system were calculated. Fourth, an economic analysis was performed to calculate the Net Present Value (NPV), Internal Rate of Return (IRR), discounted Pay Back Period (PBP) and Levelized Cost of Electricity (LCOE). In the fifth step learning effects on the gasifier and fuel cell system were assessed. Finally, an uncertainty analysis was conducted which included both a sensitivity analysis and a pedigree analysis. The results section starts with the elemental composition of WTP followed by the product gas composition after gasification. It continues with a system design that includes (among other components) the indirect MILENA gasifier from ECN and a solid oxide fuel cell (SOFC). Further, the energy analysis reveals an electricity production of 2.8 MW at 57.2% electrical efficiency and total efficiency of 69.7%. Next, the economic results show that the system is (currently) not economically feasible; NPV is -38.2 Meuro, IRR -24.2% and LCOE 23.05 eurocent/kWh. The payback period could not be calculated. Subsidy could reduce the LCOE to 12.67 eurocent/kWh, while learning effects of the SOFC system could reduce the LCOE to 15 eurocent/kWh. Finally, the uncertainty analysis showed that priorities for future research are the SOFC investment cost and the water content and amount of WTP. Although the system is currently unfeasible, it shows that a waste source can be converted to electricity at high efficiency. The main recommendations are to invest in SOFC development and scale up the project.