Boiler Replacement, Digester Gas Utilization and Solar Energy Study

Lafayette Renew and the City of Lafayette understands that while a portion of digester gas is currently used for digester and building heating, there are opportunities to further optimize digester and natural gas utilization by improving solids and waste handling processes. Additionally, the plant has long envisioned the installation of a solar field to accomplish their long-term goal of energy and carbon neutrality. Greeley and Hansen studied different scenarios and technologies to help Lafayette Renew accomplish their immediate and future goals. 

Electricity and natural gas consumption for the last two years as well as current rate structure were analyzed to determine the feasibility of a CHP installation. A spark spread calculation indicated that a CHP installation was favorable due to lower natural gas rates at the anticipated future gas demand. Due to a maximum on-site power generation cap of 1 MW established by the local electrical utility company, several arrangements of CHP systems and solar field capacities were analyzed to determine the most optimal electrical and thermal output for the operation of the plant. Both internal combustion engines and micro-turbines ranging from 65kW to 1 MW were included in the analysis for the CHP systems. 

Greeley and Hansen performed a thorough study of the electric rate structure and collaborated closely with Lafayette Renew to find the perfect, personalized financial, social, and environmental balance. After developing a triple-bottom-line analysis and calculating individual system payback, it was determined that an installation of 166 kW of solar power and 833 kW of CHP will be the most beneficial for the plant. The CHP system considered an internal combustion engine capable of providing 3,800 MBH of thermal output. This thermal capacity will be sufficient to account for the future average digesters heating demand which is likely to occur in the summer months. In the winter, the existing boiler will work in tandem with the CHP system to meet the heating demand. It was also recommended that a 7,500 MBH dual-fuel boiler be installed for back-up and low-demand periods. Utilizing a smaller boiler with automatic fuel control will improve operational flexibility at different outdoor temperatures and will increase the overall heating plant efficiency while optimizing digester and natural gas utilization. 

Project Highlights: 

• The project included long-term planning for energy and carbon neutrality. 

• The wastewater treatment plant enhancements included digester gas utilization. 

• Our team performed a feasibility study of solar energy. 

• The Lafayette Wastewater Treatment Plant has been recognized as a Utility of the Future.