The North River Wastewater Treatment Plant (WWTP) currently implements cogeneration (i.e. combined heat and power) through 10 direct drive engine driven pumps and blowers. These 10 engines have reached the end of their useful life and a Cogeneration Feasibility Study was undertaken to develop and evaluate options to repair or replace them considering: reliability, cost, operational complexity, energy and reducing Title V air permitting.
Investment Grade Feasibility Study for Cogeneration
In order for cogeneration to be successful at North River a balance between the electrical, thermal, and digester gas production profiles of the plant had to be established. Savin Engineers performed a comprehensive hour by hour analysis of the entire plant’s energy profile, looking at the consumption of digester gas, natural gas, diesel fuel and electricity in relation to sewage flow and seasonal temperature variations in order to create a complete computerized model of the existing plant. With this model, Savin was able to accurately estimate future energy consumption with the implementation of various forms of cogeneration. Savin’s Feasibility Report resulted in the recommendation to implement a 10 MW electric generating cogeneration system for the following principal reasons:
• Decouples engine operation from process equipment to allow flexibility for cost-effective plant operation.
• Dramatically increases reliability for two of the most critical processes at the North River site – raw sewage pumping and aeration.
• Eliminates the use of fuel oil, which significantly reduces Green House Gas emissions and removes a combustible liquid from the site.
• Reduces energy costs up to $3.8 million per year.
Savin subsequently specified the cogeneration units and created the bid documents used to pre-select the cogeneration units. Savin designed the major mechanical systems associated with the installation of the new cogeneration units, including new digester gas compressors, pre-combustion natural gas compressors, heat recovery heat exchangers, hot water pumps and gas and water piping.
Savin also designed an upgrade of the existing solids handling facility’s mixers, grinders and sludge pumps under a separate contract at North River WWTP, which will ultimately help increase digester gas production and therefore produce more free fuel to support the new cogeneration system.
