Thermodynamic and economic analyses of sewage sludge resource utilization systems integrating Drying, Incineration, and power generation processes

In an effort to beneficially utilize sewage sludge as a resource, a process system integrating sewage sludge drying, incineration, and power generation are proposed and subjected to thermodynamic and economic analysis. The proposed system comprises wet sewage sludge drying using a low pressure steam, dry sewage sludge incineration in a boiler to raise steam for power generation in a steam turbine whose exhaust facilitates the drying of the wet sewage sludge. Three alternative schemes are considered. Scheme 1 features higher temperature and pressure of the turbine exhaust for drying without auxiliary fuel; Scheme 2 includes an external steam input while Scheme 3 incorporates firing of coal as auxiliary fuel. The results indicate that the energy efficiency of Schemes 2 and 3 can reach up to 49.93 % and 48.69 %, respectively. The economic analysis suggests that Scheme 2 outperform Schemes 1 and 3. The cost of electricity for Schemes 2 and 3 are as low as 0.037 and 0.039 USD/kWh, respectively, with corresponding dynamic payback period being 13.63 and 13.70 years. The net present value attains 48.67 million and 48.62 million USD, respectively. Therefore, the proposed schemes 2 and 3 are suitable and promising for sewage sludge resource utilization from the viewpoint of thermodynamics and economics. Moreover, a conceptual proposal for renewable energy dispatch is presented and analyzed, which would provide a reference for practical engineering application.