Techno-economic analysis and case study of combined heat and power systems in a wastewater treatment plant

Combined heat and power systems can reduce the energy and carbon footprints of wastewater treatment plants by reducing their electricity demand and direct methane emissions. However, large capital costs can be a deterrent for installation of such systems. Therefore, this work sizes a combined heat and power system based on annual and hourly biogas production data, thermal demand data, and electrical demand data of a wastewater treatment plant located in the Southwestern U.S. The annual analysis sizes a combined heat and power system to satisfy 60% of the facility's thermal demand and yields 13.94 million USD in savings over a 20 year analysis. Conversely, the hourly analysis sizes a combined heat and power system to satisfy 75% of the facility's thermal demand and results in 8.92 million USD in savings over a 20 year analysis. This discrepancy between the annual and hourly analyses is partially due to the biogas and natural gas consumptions. This paper shows that an annual analysis cannot accurately estimate combined heat and power sizing and savings for a wastewater treatment plant due to high variability in biogas production and time of use demand costs.